My Study Materials and some useful and Helpful informations: March 2017

ECOLOGY NOTES UTSC BIOB50

FINAL EXAM NOTES

Community Change

A type of Algae, the Caulerpa was introduced in the Mediterranean Sea in the early 1980s because everyone had thought that it wouldn’t be able to withstand the cold temperatures as it is used to warmer waters of the California region. What they failed to recognize was there was a strain of the Caulerpa that was cold resistant and as a result was able to outcompete the native sea grass meadows Posidonia and it has been in decline. The Caulerpa acts as an ecosystem engineer, where it accumulates sediments around its roots more that the native species which has caused a change in the invertebrate species found around it on the seafloor. An ecosystem engineer causes changes in the abiotic conditions that can cause species replacement such as a beaver creating wetlands that attracts new species causing species to be replaced.

Another natural experiment in the Mountains of St. Helen was used as a case study. What was once a peaceful mountain erupted into one of the largest disasters known. Because of this disaster, it wiped out all of the species that were a part of that ecosystem within the range that was affected by the eruption and caused a whole new ecosystem to be built.

Communities are constantly changing, and as a result, the species diversity continues to change as well.

Agents of change act on communities across all temporal and spatial scales.

Looking at a coral reef community, we see the changes they have experienced over a large span of time. The agents of change have been both subtle and catastrophic. Normal species interactions causes different species to be dominated by other species, with competition, predation and disease causing gradual changes within the ecosystem over time. Changes in abiotic conditions such as sea level, water temperature can cause physiological stress and other affects that eventually cause mortality to increase. A catastrophic event like the volcano eruption or a tsunami can have a huge effect and cause mass injuries and deaths in the coral reef.

Another example, in the Boreal Forests of Canada, because of global warming which shifts the temperature even by 1 degree has a mass effect. Due to increased winter temperatures, these populations which had been kept in check because of weather, have now had an outbreak of dominant species like a beetle that causes the death and destruction many of the widespread tress and has a large impact on the community.

Agents of change can be biotic or abiotic. Biotic would be the negative interactions such as predation, competition, herbivory disease as we saw in the coral reef example. The abiotic change would be the Tsunami in the coral reef example as well.

Abiotic changes can be either Disturbance or Stress. The difference between the two is the impact on the community it has. A stress is less impactful and causes there to be gradual change by reducing reproductive abilities and growth of the individuals. A disturbance injures or kills some individuals to create opportunity for new individuals to colonize.

Succession is the process of change in species composition over time as a result of abiotic and biotic agents of change.

Within a spectrum of a disturbance, we observe that a high frequency disturbance that is low in intensity produces more little succession changes versus a low frequency but high intensity disturbance causes a huge primary succession. Middle frequency with middle intensity produces secondary succession.

Primary succession is the pioneering stage where species come to colonize as if it were a newfound ecosystem when a disturbance kills off all life. Secondary succession occurs after a disturbance simply alters the ecosystem where most but not all living individuals are killed off. Theoretically, these changes ultimately result in a climax stage that experiences little change and the species living there are able to thrive until another disturbance comes in to reset the cycle.

Henry Cowles, an ecologist was studying successional changes in a community. Whilst studying a portion of a dune near Lake Michigan, he inferred that the part nearest to the lake was where new sand was being deposited and thus was where the earliest stages of succession were dominant. As you move farther back, you see species of later successional changes. This inference is based on his Space for Time Substitution which is being used today. It assumes that time is the main factor which causes communities to change and that unique conditions n particular locations are inconsequential.

Clements, another ecologist, believed that plant communities were like “super-organisms” where they work together to meet a common end and that if they are left undisturbed they could thrive to reach a “climax community”.

In contrast, Gleason, another ecologist, thought that the ability for a community is not based on whether it is left undisturbed but rather a random product of fluctuating environmental conditions acting on individual species.

Other ecologists like Charles Elton used both Gleason and Clements theories to predict something that was more along the lines of a middle ground indicating that both the organism and the environment interact to shape the direction of succession.

In 1977, Connell and Slatyer proposed three models for succession.

The facilitation model states that the pioneer species work to modify their environments in a way that does not benefit incoming species but rather later long term species and this sequence leads to a climax community.

The tolerance model states that the pioneer species works to modify their environments in a way that has little or no effect on the long term species.

The inhibition model states that the pioneer species work to modify their environment in a way that has negative effect on later successional species.

Experimental work on succession shows its mechanisms to be diverse and context-dependent.

A great way to study succession is by looking at the current ice that is melting in Alaska. Ecologists have created permanent plots that are still being used today to study the species. Successional changes over the years show that generally, there has been an increase over the 200 years following glacial retreat in plant species richness.

In the rocky intertidal zone of Southern California, the disturbances are created mainly by waves which can tear organisms from the rocks during storms or by propelling objects into them. There are also stresses caused by abiotic factors such as temperature that either kills or makes the species lose their attachment to the rocks. Sousa noticed that the algae dominated species on the boulders experienced disturbances every time the boulders were overturned by waves. He also noticed that the rocks were first colonized by green Ulva algae species and then by red Gigartina algae. By not allowing the green to colonize first, it accelerated the red colonization which proposes that there is an inhibition model of succession along these rocks. The green algae was also fed on by the native crab species and thus allowed for mid-succession of other species of algae to colonize.

In contrast, the rocky intertidal zone of Oregon shows that the Balanus species protects the macro-algae by reducing limpet grazing and experiments show that the larger the barnacle species the better it protects it.

The mechanisms of succession show that in the early succession, facilitation is likely most important. As you get to mid succession, you see a mixture of positive and negative interactions. With late succession, we see bigger, longer lived species where competition is most important.

The way an ecosystem responds to a disturbance also varies and determines the ecosystem strength and stability. Resilience refers to the length of time for recovery to occur. Resistance is a measure of deviation from the normal range. The ecosystem is stable if it returns to the initial conditions.

Communities can follow different successional paths and display alternative states.

Up until this point we have determined that a lot of the ways that species succeed one another is very predictable. Now what if our predictions are not right and the exact opposite tends to happen? Ecologists refer to these alternative scenarios as alternative stable states.

Sutherland did experiments in fouling communities by suspending ceramic tiles and allowing invertebrates to colonize on them. Most tiles were dominated by Styela whereas tiles placed later in the summer were dominated by Schizoporella. Without predation, the tiles developed communities dominated by Styela however it died off in the winter. With predation however, the communities were dominated by Schizoporella year round.

This experiment shows how different factors can lead to alternative stable states in the ecosystem whereby different species dominate with different biotic or abiotic factors.

Modelling Alternative Stable States, we see that at first we see a there occurs stability in a community. A change, if impactful enough, can shift the community to a different state and can lead to hysteresis which is the community’s inability to shift back to the original stable state even when original conditions are restored.

Going back to our example of the volcano at Mount St. Helen, we see that even after years and years that have passed after the disturbance the species richness of amphibians increased slowly but never to the point where it had been prior to the eruption and we see species disappearing then reappearing as well.

Energy Flow and Food Webs

Ecosystems consist of diverse species and populations that coexist. What links all of these species together are Trophic interactions, which is the influence an organism has on the movement of energy and nutrients through an ecosystem determined by what they eat and what eats them.

Trophic levels describe the feeding positions of groups of organisms in ecosystems.

Each tropic level is characterized by the number of feeding steps by which it is removed from autotrophs or the primary producers. Organisms that feed at multiple trophic levels are omnivores and change their feeding habits as changes in species diversity occurs. Organisms that are not consumed by other organisms end up as detritus for the detritivores. Because of all this organic matter that is stored in the ground, we are not aware of how little of the biomass we use. In fact, in terrestrial ecosystems most of the energy flow passes through the detritus. A multitude of studies have shown that more than 50% of the NPP ends up as detritus. Similarly, a relatively smaller portion of the NPP is consumed by herbivores.

External energy inputs are referred to as allochthonous inputs such as plant leaves, stems, wood, and dissolved organic matter that fall in from adjacent terrestrial ecosystems to aquatic ecosystems. Energy produced by autotrophs within the system is known as autochthonous inputs.

Environments such as a headwater stream in New Hampshire receives over 99% of its energy as allochthonous inputs whereas a nearby Mirror Lake receives 80% of its energy through autochthonous input. It should be noted that allochthonous is lower in quality because of the chemical composition of the carbon and as such not an efficient energy source.

The amount of energy transferred from one trophic level to the next depends on food quality and consumer abundance and physiology.

To conceptualize trophic relationships in an ecosystems, ecologists use a trophic pyramid. It portrays the relative energy or biomass at each trophic level and are used to show how energy flows through the ecosystem. In terrestrial ecosystems, energy and biomass pyramids are usually similar and decrease with each trophic level. In aquatic species, we see an inverted biomass pyramid relative to the energy pyramids and are more common in nutrient-poor waters with low autotroph biomass. This inverted shape is seen as a result of a more rapid turnover of phytoplankton, which have higher growth rates and shorter life spans than phytoplankton of more nutrient-rich waters. Thus, they provide a greater energy supply per unit of time. We also see that the amount of autotroph biomass consumed increases with increasing NPP in both terrestrial and aquatic ecosystems and is higher in aquatic systems.

Ecologists have come up with several hypothesis for the lower autotroph biomass consumption.

Herbivore populations are constantly constrained and limited by predators thus they never reach their carrying capacity.

Autotrophs have defences against herbivory.

In terrestrial plants, there are a lot of nutrient-poor structural materials which are typically absent in aquatic autotrophs. These are just some of the many hypothesis which ecologists are still trying to determine.

Now, not all of the energy that a heterotroph consumes is used up by the higher trophic level and thus gives us a problem of how efficient it is. Trophic efficiency is defined as the amount of energy at one trophic level divided by the amount of energy at the trophic level immediately below it. The proportion of energy transferred between trophic levels depends on efficiencies of consumption, assimilation and production.

The consumption efficiency is the proportion of the available biomass that is ingested by consumers. As we saw this is higher for aquatic consumers than terrestrial consumers. The assimilation efficiency is the proportion of the ingested biomass that consumers assimilate by digestion. This depends mainly on the quality of food available and the consumer’s physiology such as the low nutrient quality in terrestrial plants than in aquatic plants. The production efficiency is the proportion of assimilated biomass used to produce new consumer biomass.

Looking into assimilation efficiency, we said how it is determined by the quality of the food and the physiology of the consumer. By this we mean that plants have much of their energy stored in complex compounds that many consumers cannot break down and low concentrations of nutrients such as N and P. In contrast, we see a high assimilation efficiency in Carnivores than Herbivores as the prey have a Carbon: Nutrient ratio similar to the predator and thus assimilated more readily. Herbivores have a 20-50% efficiency versus Carnivores with 80% efficiency.

Endotherms tend to digest food more readily than ectotherms and thus have higher assimilation efficiencies.

Some herbivores like ruminants have mutualistic bacteria inside of them to help digest the complex molecule cellulose of plants which is high in energy but cannot be broken down by most animal digestive enzymes thus giving them higher assimilation efficiencies.

The production efficiency is strongly related to the thermal physiology and the size of the consumer. Endotherms allocate a lot of energy for metabolic heat production and less for growth and reproduction than ectotherms and thus have lower production efficiencies than them.

The food quality plays a big role as well which we saw with Steller Sea Lion populations which were in great decline over a span of 25 years because they had switched to eating the Pollock which had half the fat content than Herring from their diet. In other words, the trophic efficiency was in decline simply because of the change in diet because of the cod and Pollock dominance at the time.

Changes in the abundances of organisms at one trophic level can influence energy flow at multiple trophic levels.

Ecologists have two methods to look at the control of energy flow through ecosystems. The “bottom-up” approach determines that greater availability of limiting resources increases NPP and that the resources that limit NPP determine energy flow. The “top-down” approach determines that energy flow is governed by rates of consumption by predators at the highest trophic levels.

A trophic cascade is a series of events through trophic interactions that result in a change in energy flow and species composition. Omnivores usually act as buffers for such effects.

An example is seen with a Piper plant species which is consumed by herbivores, which are consumed by ants which are consumed by beetles. By reducing the beetle population, we see an increase in the ant population. This increase in the ant population leads to a decrease in the herbivore population which in turn leads to an increase in the Piper population.

Through trophic cascades a number of trophic levels are affected. What determines the number of trophic levels in an ecosystem? The three basic interacting controls are as follows. First, dispersal ability may constrain the ability of top predators to enter an ecosystem. Second, the amount of energy entering an ecosystem through primary production. Finally, the frequency of disturbances or other agents of change can determine whether population of top predators can be sustained. No disturbances allows each trophic level to reach a carrying capacity within the ecosystem. Frequent disturbances keeps the trophic levels in check and does not allow other trophic levels like secondary carnivores to come in.

Food webs are conceptual models of the trophic interactions of organisms in an ecosystem.

Food webs are vital in showing the connections between organisms and the food they consume. They can be simple or complex depending on their purpose. Simpler is easier to read but addition of more participants adds more realism but also more complexity. Food webs are static however the actual trophic interactions change over time depending on species availability. The Interaction Strength is the measure of importance of an interaction to other species. By using this, we can cut out weaker interactions whilst keeping an accurate food web that depicts realism in it. Keystone species have greater effects on energy flow and community composition that their abundance or biomass would predict. The net effect of a predator on a target prey species includes all possible indirect effects of the predator on other species in the community that interact with the target prey species as well as the direct effect of consumption.

Now are more complex food webs with higher diversity more stable? If they are then stability is gauged by the magnitude of change in the population sizes of species in the food web over time. How an ecosystem responds to species loss or gain is strongly related to the stability of food webs.

Elton and Odum argued that less diverse food webs should be more easily perturbed but mathematic analyses by May showed that higher diversity populations are less stable than those with lower diversity. In May’s model, strong trophic interactions accentuated population fluctuations. The more interacting species there were, the more likely that population fluctuations would reinforce one another leading to extinction of one species more than lower diversity communities.

Lawler performed an experiment that showed that increasing the number of protozoan species in laboratory microcosms decreased the stability of food webs. Eric Berlow instead, suggests that weak interactions can stabilize trophic interactions.

Metapopulations & Metacommunities

Looking at landscapes through a satellite image, we see that the world is not just a continuous landscape but rather occurs in patches of suitable habitat. These patches are heterogeneous and not similar in competition. Ecology in this field is fairly new as it gives a more realistic look of how species interact within their communities whilst including immigration and emigration rates. A lot of the fragmentation we see today is a cause of the natural disturbances as well as the effects we as humans have had and thus it is important in conservation biology to study such communities.

Many species have a metapopulation structure in which sets of spatially isolated populations are linked by dispersal.

A metapopulation is defined as groups of interacting populations that are seemingly isolated populations that do affect one another’s dynamics because individuals (or gametes) occasionally disperse from one population to another and are characterized by repeated extinctions and colonisations.

One of the earliest and indirect studies of metapopulations was looking at Huffaker’s previous experiment of mites on oranges where mites would go extinct until he added Vaseline and toothpicks. By changing the landscape dynamic, Huffaker gave the mites an advantage that led to the cycling of prey predator population.

Ecologists have noted that some species in these patches are prone to extinction for two reasons. The patchiness of their habitat makes dispersal between populations difficult, so if the populations are small they have small population sizes and are more likely to go extinct. This is known as the demographic stochasticity. The environmental conditions often change in a rapid and unpredictable manner and this is known as the environmental stochasticity.

Having many patches of suitable habitats with small populations aids in the persistence of a certain species because even if one patch goes extinct, there are still other patches that keep the gametes of that species intact. Although the individual patches of the populations are prone to extinction the metapopulation as a whole persists because of new colonization of patches that are established.

Building on the idea of random extinctions and colonisations, Richard Levins represented the equation:

dp/dt= immigration rate – extinction rate

dp/dt= cp(1-p)-ep

This equation determines the proportion of habitat patches that are occupied at time t. C is the patch colonization rate and e is the patch extinction rate. To derive this equation, Levins made a number of assumptions. He assumed that there is a an infinite number of identical habitat patches, that all patches have an equal chance of receiving colonists (hence the spatial arrangement of the patches does not matter), that all patches have an equal chance of extinction and that once a path is colonized, its population increases to its carrying capacity much more rapidly than the rates at which extinction and colonization occur (this assumption allows population dynamics within patches to be ignored). To graph this relationship, we see the immigration rate gives us a parabola whereas the extinction rate stays as a linear relation.

ṗ=1-e/c

For a population to persist for a long time the e/c ration needs to be less than 1 and thus this equation gives us what proportion of habitat is actually occupied.

Levins’s ground-breaking approach focused attention on a number of key issues, such as how to estimate factors that influence patch colonization and extinction, the importance of the spatial arrangement of suitable patches, the extent to which the landscape between habitat patches affects dispersal and the vexing problem of how to determine whether empty patches are suitable habitats or not.

Sometimes, a metapopulation can go extinct even when suitable habitat remains. The effects humans have on large regions often convert those regions into sets of spatially isolated habitat fragments. This habitat fragmentation can cause a species to have a metapopulation structure where it did not have one before. Continued disturbances from humans can further fragment the landscape and decrease the colonization rate (c) because it becomes harder to disperse as it becomes more and more isolated and an increase in extinction rate (e).

The Northern Spotted Owl is found in the Pacific Northwest region of North America in old-growth forests where nesting pairs establish large territories. Lande, another ecologist added further variables on how these owls might search for vacant patches as logging increased and reduced the fraction of habitat patches that were suitable for these owls. This illustrated how a species can go extinct if its habitat dropped below a critical threshold (in the owl’s case 20% of habitats) and is now a reason for why the Northern Spotted Owls are listed as a threatened species in the United States.

Ecologists often see violations of Levins’ model in real metapopulations such as some patches often differ considerably in population size and in the ease with which they can be reached by dispersal. As a result, the extinction and colonization rates may vary among these patches greatly. The rates can also be influenced by non-random environmental factors. Thus more complex models are needed to address practical questions in the field.

The skipper butterfly had lost suitable environments throughout the 1950s because of grazer numbers being reduced. It did pick up for them in the 1980s when livestock was reintroduced and thus ecologists observed different patches and which ones the butterflies colonized. They saw that isolation by distance played a role. They saw that new patches that were farther from occupied patches were less likely to be occupied than nearby patches in terms of colonization of a patch. The patch size also played a role as they observed that many of these butterflies colonized in at least 0.1 hectare patches. They proposed that butterflies that had colonized in smaller patches went extinct and thus the patch area affects the extinction rate. The smallest patches had the highest chances of being extinct. High rates of immigration to protect a population from extinction is known as the rescue effect by reducing problems associated with a small population size.

dp/dt=cp(1-p)-ep(1-p)

This new model by Hanski takes into account the rescue effect whereby now the extinction rate is a parabola than a linear rate. What this means now is there is no equilibrium between the two and that:

If c>e, then p goes to 1.

If c<e, then p goes to 0.

This is in contrast to Levins’s model which did suggest an equilibrium when the ratio was less than 1.

Now metapopulations examine spatial effects on single species, yet patches contain multiple species that interact. Examining species interactions in patches is called metacommunity ecology.

Multiple species within a patch are likely to compete, thus the ability to move can be critical for coexistence. There are four metacommunity paradigms that try to explain why dispersal among patches is important for coexistence.

The neutral perspective has species competitively equal, and everybody has an equal chance at landing and colonizing. The patches are identical and there is limited dispersal.

The patch dynamics perspective has an interaction effect, where the species compete. There is still identical patches and limited dispersal so there is local extinctions. Species can coexist here by not competing with each other locally. A trade-of is required usually between competition and colonization abilities.

The species sorting perspective is not a homogeneous habitat where the species compete but patches differ. There is still low dispersal so there is competitive exclusion that is fast relative to dispersal where competes outcompete one another because of different patches and the species get sorted depending on habitat preferences.

The mass effects perspective is where the species compete, and patches differ but there is still higher dispersal rates such that individuals in certain species can somewhat persist in lower number because the dispersal rates are higher compared to the competitive exclusion rates.

In terms of the role of heterogeneity, we observe that all paradigms except for the Neutral predict coexistence at larger scales, even though a single species may exclude all others within a patch. For how this happens, patch heterogeneity is critical where heterogeneity is mass effects as opposed to homogeneity which is based on patch dynamics and trade-offs.

ME has highest heterogeneity and dispersal versus SS which has high heterogeneity and low dispersal and PD which has low heterogeneity and middle ground dispersal.

Defining diversity from a local to a regional scale is defined differently.

Gamma=Beta+Alpha(absolute)

Alpha is the average number of species found in a local community. Beta is the average number of species NOT found in a local community (between-community diversity). Gamma is the total number of species in all communities.

Ecologists, Mouquet & Loreau modeled mass effects in a metacommunity with 20 communities and 20 species. Each species was the best competitor in a single community. They observed that when dispersal was zero, the local (alpha) diversity was minimum with one species present, whereas between-community (beta) and regional (gamma) diversities were maximum. In each community a different species was the locally best competitor. As dispersal increased to an intermediate level or Amax, more species were maintained by immigrations above the extinction threshold, and local diversity increased.

Communities then became more similar in species composition, and the between-community diversity decreased. Because all of the species remained in the metacommunity, the regional diversity remained constant. When dispersal was greater than Amax, the local diversity decreased because the best competitor at the scale of the region dominated each community, and other species were progressively excluded. In this case, the species that were not excluded were present in all communities, between-community diversity was zero, and regional diversity was equal to local diversity and decreased. Finally, when dispersal was highest, the metacommunity functioned as a single large community, in which the regionally bets competitor excluded all other species and the local and regional diversity were minimum.

Landscape Ecology & Habitat Fragmentation

Another new field in ecology has emerged through powerful assemblage of tools that we can now use to get a broader perspective on landscapes from a different perspective. Taking a step back, we can expand the scope of our view from local diversity to a more global scale through the use of satellites and aerial photography.

Landscape ecology examines spatial patterns and their relationships to ecological processes and changes.

A sub-discipline of ecology, landscape ecology emphasizes the causes and consequences of spatial variation across a range of scales. Landscape ecologists’ document observed spatial patterns of different landscape elements including those that occur across broad geographic regions and study how those patterns affect and are affect by ecological processes. These elements can be biotic or abiotic.

For some definitions, a landscape is a heterogeneous area composing of a dynamic mosaic of interacting ecosystems. In a landscape at least one element is spatially heterogeneous, or displaying a varied composition or a mixture of elements with many difference across space and/or time. This is in contrast to homogenous elements that consist of elements that are similar or identical with few to no differences across space and/or time. Ecologists often refer to the composite patter of heterogeneous elements that make up a landscape as a mosaic.

An example of landscape heterogeneity comes from Michigan’s Upper Peninsula where we see an aerial view where we can see the lands and the grasslands, a map of the six different soil types in that same area, and a map of seven different landscape elements in the same area.

Remote sensing satellites now provide images of Earth that have vastly expanded the interpretation of large-scale ecological patterns. GIS, or the Geographic information systems have become standard for use in landscape planning, for conservation and urban development. GIS is a computer based system that allows the storage analysis and display of data pertaining to specific geographic areas that can turn a simple google maps view into a map of predicted distribution of a species in the region versus in protected areas.

The scale that landscape ecologists use to study a landscape determines the results obtained thus it is a vital part and needs some clarification. A scale is the spatial or temporal dimension of an object or process, characterized by grain and extent. Grain is the size of the smallest homogeneous unit of study (like a pixel) determining the resolution of the landscape and extent is the boundary of the area or time period encompassed by the study.

Increasing grain reduces the resolution of the image but has fewer pixels to store and analyze. Increasing the extent increases the regional boundaries and thus has more pixels to analyze with the same resolution.

The heterogeneity that we see in landscapes can be described in terms of composition and structure. Landscape composition consists of the kinds of elements or patches and how much of each kind is present. The Yellowstone National Park, for example, shows a landscape composed of five different age classes of forest which was mapped to show the complexity. In terms of landscape structure, it is the physical configuration of the landscape elements. It is characterized by things such as the size of the patches, whether the patches are aggregated or dispersed, the complexity of patch shape, degree of fragmentation etc.

Disturbances can shape landscape patterns and create landscape heterogeneity. An example of this is seen in the 1988 burning of 1/3 of Yellowstone forests. It resulted in a complex mosaic of burned and unburned patches where areas that appeared black were burned by intense crown fires and brown patches were burned by severe ground fires, both of which killed most or all of the vegetation. This disturbance will dictate the landscape composition for decades to centuries.

Human actions parallel disturbances that have occurred as some areas have been subjected to human affects more than others. Humans converted areas into agricultural use, logging and hunting are all ways that our activities have altered landscapes greatly and they continue to affect current biodiversity and ecosystem processes even after humans ceased to affect it. These are known as landscape legacies and we are just now understanding how they shape communities.

An example was seen in central France where the legacy of Roman farming settlements that had been abandoned for nearly two millennia is still reflected in plant species richness in the forest that replaced them. More plant species were found closer to the center of the settlement sites, including more species that prefer a higher soil pH. Soil pH and soil phosphorous were also higher closer to the settlement sites. This probably resulted from lime mortar used in Roman buildings and agriculture.

Habitat loss and fragmentation decreases habitat area, isolates populations, and alters conditions at habitat edges.

In 1986, a massive hydroelectric project in Venezuela created islands of tropical forest surrounded by water in what had been an intact forest. This change in landscape was studied by Terborgh who found that small and medium-sized islands were lacking the top predators found on the mainland, and as a result, herbivory was increased and predators of invertebrates were more abundant than in the intact forest. This had a dramatic effect on the vegetation of these islands as tree recruitment decreased and tree mortality increased.

This showed that habitat loss and fragmentation are among the most prevalent and important changes occurring in Earth’s landscapes and a lot of it is because of human activities that have been converting large blocks of landscape by flooding, clearing, urbanization etc. This reduces the habitat available for other species resulting in a decline of thousands of species. Fragmentation increases edge effects, which refer to the changes in population or community structures that occur at the boundary of two habitats. It also results in spatial isolation of populations making them more vulnerable to small population problems.

Beginning in 1620, vast regions of old-growth forests in the US were cut down to provide lumber and to make room for agriculture, housing and other forms of development. What resulted was a dramatic wipe-out of old-growth forests which at once covered almost half of the region of the US now barely cover 1 percent.

Historically intact habitats are gradually reduced with increased human presence. The process includes intact forests, then areas within the forest get cleared for grazing, then the forest becomes further fragmented overtime to a point where only a few remnant of the forest remain.

Fragmentation has many consequences such as local species extinction within fragments, inadequate food resources, shelter, or nesting, and a disruption in mutualism as the mutualistic partners are disappearing. However, some species flourish under these changed conditions.

In the Hudson River valley, forest fragments of less than 2 hectares had high populations of white-footed mice because they had little to no predation there. These mice are also the most important carriers of a bacterium that causes Lyme disease. Ticks are the vector of this disease. Tick nymphs collected in these small fragments were significantly more likely to carry the disease and occurred at high densities than in larger fragments. Thus fragmentation has an implication for human health as well.

Fragmentation mainly results in habitat loss but has other effects too such as large populations being subdivided increasing extinction risk, isolation making it difficult to find mutualistic partners and mates etc. Fragments have edges, which are the habitat boundary. Edges increase as fragmentation increase and as we discussed already the edge effect is when biotic and abiotic changes are associated with the boundary. The physical environment changes over a certain distance into the fragment, and thus biological interactions and ecological processes change as well.

The amount of edge is usually measured as the perimeter-to-area (p/a) ratio. A round habitat has the lowest p/a versus irregular shaped patches that have higher p/a. With fragmentation, you get a reduction in the area which can be seen when putting a power line through a rectangular forest, you get a 44% loss of land where it was 64 hectares before and 36 hectares after. In general we see the patter that the larger the patch and the closer together the patches, the better it is.

When an intact forest is first fragmented, abiotic conditions change near the edge of the patch of forest that remains, giving rise to biotic changes. In the Amazon rainforest fragments we see that increased air temperatures and other abiotic changes lead to biotic changes such as increased rates of tree mortality and the arrival of disturbance-adapted plants. After logging, air temperatures increase for 65 m into the remaining patch of forest as well. Edge effects documented here show the great diversity of the edge phenomena and other varying distances they penetrate into forest interiors.

The effects of abiotic changes at a forest edge are illustrated by a study of microclimates 10-15 years after the clear-cutting of an old-growth Douglas fir forest. We saw that the biotic consequences included higher rates of decomposition, more wind-thrown trees and woody debris, and differential tree seedling survival. Pacific fir seedlings survived better in the edges than Douglas fir and western hemlock.

Roads are a special type of edge that cause mortality from construction, have road kill, induce behavioural modifications in nearby species, alters the physical and chemical environment, introduces foreign species and increases human use within that region.

Most Amazonian understory birds respond negatively to roads and if it’s wide enough they will not cross and endangered panthers have auto collision as the main reason for their mortality. Small mammals in Ontario would not cross roads over 20m wide. In the Mojave, of 387 rodents recaptured, only one had crossed to the other side. Turtles are highly susceptible to roads. To reduce such effects, there has been some development in creating critter crossings, tunnels and fences with one-way gates.

Grasping the true size of the effects of fragmentation can be difficult because it’s hard to separate the effects of fragmentation vs the habitat loss. The habitat loss effects are much greater than the fragmentation effect. There are both positive and negative impacts of fragmentation per se. Conservation in fragmented landscapes protect, and expand the amount of habitat, enhances habitat quality by preventing invasive species and natural disturbance regimes, providing landscape connectivity by maintaining crucial ‘stepping stone’ habitats’ for migratory species and critter crossings, and provides long-term vision to prevent the dynamic process of fragmentation.

In Ethiopia, fragmentation form centuries of agriculture and harvesting has resulted in less than 4% of the original forest remaining only because of religious church importance. It provides ecosystem services such as freshwater, honey, shade, pollinators etc. with the main threats being livestock foraging and edge effects which are greater that soil compaction leading to decreased seed generation which is greater than no forest regeneration. By protecting the remaining patches and fencing them as well as re-planting local trees, it helps build conservation measures that have now slowly increased the forest area.

Biogeography

Patterns of species diversity and distribution vary at global, regional, and local special scales.

The study of the variation in species composition and diversity among geographic locations is known as Biogeography.

Forest biomes vary greatly in their species composition and species richness. Travelling around the different latitudes, we see the Amazon, the most species rich humid forests with the more area you cover, you see more tree species. The richness, heat and humidity is incredible Going more north to the Southern coast of California has Oak Woodland forests, a dry biome with small though sclerophyllous leaved flowering plants with many kinds of trees and shrubs with thick barks and high species diversity but not even close to the Tropical Rainforests. Going even more north, we see cooler and wetter forests in the Pacific Northwest region of North America dominated by large conifers with fern covered floors in these Lowland temperate evergreen forests still a fraction of the species from the above two examples. Going even more north, we go to the Boreal Forests of Canada with a cold landscape of identical spruce trees, with spruce boughs, low-lying berry bushes reminding that light does penetrate under the canopy. Now finally, visiting the Forests of the North and South Islands in New Zealand, they span a large latitudinal gradient and thus have different forest types. The forests of the South Island are dominated by beeches while the warmer North Islands have greater tree species diversity and a different species composition than those on the South Island. The Southern Beech Trees of the South have small leaves and the branches of divaricating shrubs have a zigzag appearance. The North has trees like the Kauris, one of the largest trees on earth, and like those of many other fern species, the fronds of the tree ferns emerge as “fiddleheads”. Almost 80% of the species in New Zealand are endemic, which means they cannot be found anywhere else in the world.

There are several patterns we observe throughout this virtual tour. Assuming that forest communities are good global representative, species richness and composition tend to vary with latitude such that lower tropical latitudes have many more and different species than the higher temperate and polar latitudes. We also see that species richness and composition vary from continent to continent, even where longitude or latitude is roughly similar. Finally, the same community type or biome can vary in species richness and composition depending on its location on Earth.

These patterns vary at a global, regional, and local spatial scales. The global scale includes the entire world with climate and because species have been isolated from one another by areas like continents and as such the differences between the speciation, extinction and migration rates help to determine differences in species diversity and composition at the global scale. The regional scale encompasses smaller geographic areas in which the climate is roughly uniform and to which species are restricted by dispersal limitations. All of the species contained within a region are known as the regional species pool, or sometimes called gamma diversity of the region.

Global patterns of species diversity and composition are influenced by geographic area and isolation, evolutionary history and global climate.

Biogeography was born with scientific exploration in the 19^th century with Alfred Russel Wallace being known as the founding father of the field. On his second expedition to the Philippines, he made observations where he notices the mammals of the Philippines were more similar to those in Africa, which was 5500km away, than the mammal in New Guinea, which was 750km away. Wallace was first to notice the clear demarcation between these two faunas which came to be known as Wallace’s line. What we know now to be continental drift, affects the distribution of organisms. Although it is now much closer to New Guinea, the Philippines region was connected by land to Africa for a long time but until recently, it was separated by tectonic plates. As a result, the mammal communities of the Philippines are more similar to those of African than of New Guinea.

Wallace’s biogeographic research culminated in the publication of The Geographical Distribution of Animals in 1876 where he overlaid species distributions on top of geographic regions and reveals two important global patterns. First, that Earth’s land mass can be divided into six recognizable biogeographic regions containing distinct biotas that differ markedly in species composition and diversity. Second, there is a gradient of species diversity with latitude, where species diversity is greatest in the tropics and decreases towards the poles. The six biogeographic regions identified by Wallace roughly correspond to Earth’s major tectonic plates. These plates are sections of Earth’s crust that move or drift by causing continental drift, through currents generated from deep within the molten rock mantle.

The position of continents and oceans have changed over Geologic time. 251 mya, in the Permian Period, all of Earth’s land massed made up one large continent called Pangaea. 100 mya, in the Cretaceous Period, Pangaea broke into two large continents Laurasia and Gondwana. In the early tertiary period 60 mya, Laurasia and Gondwana broke up in turn to form today’s continents. Most of these movements resulted in the separation of continents from one another, but some continents were brought together. For example, North America was part of Laurasia and South America of Gondwana so they had no contact until about 3-6 mya. Since then, there has been some movement of species from one continent to another. This is known as ‘The Great American Biotic Interchange’.

The legacy of continental movements can be found in a number of existing taxonomic groups as well as in the fossil record. The evolutionary separation of species due to barriers such as those formed by continental drift is known as Vicariance. The pattern of evolutionary relationships among the ratites correspond to the patterns of continental drift as Gondwana broke up. These large flightless birds share a common ancestor that once lived on Gondwana, but they evolved differently after their populations were isolated by continental drift. Over the millennia, we see the separation of the Rhea bird becoming isolated from the other ratities when South America separated from Africa. The Kiwi appears to have evolved in Australia and migrated to New Zealand later.

Global patterns of species richness should be controlled by three processes: Speciation, extinction and migration. If we assume migration rates are similar everywhere, then species richness should reflect a balance between extinction and speciation. However, species rates differ because it differs between the three regions and thus it is difficult to find a balance.

Ecologists ask is there an upper limit on the number of species? Some have suggested that the number of ecological niches is endless, and in the absence of major global disturbance (e.g., climate change, meteorite impacts, etc.), there is no reason why global species diversity could not continue to increase indefinitely.

To many researches, the tropics are either a cradle or museum. The idea that tropics serve as a cradle for diversity says that they have higher rates of speciation that temperate regions (cradle=birth of species). The idea that the tropics act as a museum for diversity says they have lower extinction rates than temperate regions (museum=preservation of species).

What ultimately controls the rates of speciation and extinction? There are many hypotheses.

The difficulty hypothesis states that multiple and confounding gradients in geographic area, evolutionary age, and climate that are correlated with species diversity gradients control it.

The temperature/area hypothesis states that the tropics stable temperature and their land areas lead to high speciation rates and low extinction rates. This is because land area in the tropics are larger than in the other climatic zones and their average annual temperature is stable between 25 degrees North and South of the equator with the temperature declining steadily at higher latitudes. The main basis of this theory was that increased population/range sizes decreases the chance of extinction, increased temporal stability decreases extinctions, and that species with large geographic ranges would also have greater chance of geographic isolation and speciation.

The evolutionary history hypothesis suggests that tropical regions have longer histories and thus have been climatically stable with more time for evolution to occur. At higher latitudes, severe climatic conditions such as ice ages would increase extinction rates and hinder speciation.

The production hypothesis states that for terrestrial systems, species diversity is higher in the tropics because productivity is higher. Higher productivity should promote larger population sizes which would lead to lower extinction rate.

Regional differences of species diversity are controlled by area and distance due to a balance between immigration and extinction rates.

The species-area relationship states that species richness increases with are sampled. This can be represented visually through a species-area curve that plots species richness (S) of a particular sample against the area (A) of that sample. The relationship between S and A is estimated by linear regression:

S=zA + c

Because species-area data are typically nonlinear, ecologists transform S and A into logarithmic values so that the data fall along a straight line and conform to a linear regression model. Looking at the species-area curves plotted for plant species on the Channel Islands in mainland France we see that the slope of a linear regression equation (z) is greater for the islands than for the mainland areas. The greater the z value, or the steeper the slope, the greater the difference in species richness among the sampling areas.

The species-area curves plotted for reptiles on Caribbean islands, mammals on mountaintops in the American Southwest, and fishes living in desert springs in Australia all show a positive relationship between area and species richness. These islands and island like habitats display the same basic patter of large islands having more species than small islands.

This example shows that islands more distant from source populations (mainland, un-fragmented habitat) have fewer species than islands of roughly the same size closer to source populations. To address this, MacArthur and Wilson plotted the relationship between bird species richness and island area for a group of islands in the Pacific Ocean off New Guinea. Here, the islands varied both in size and in degree of isolation from the mainland but some patters were evident. Islands of equal size had more species the closer they were to the source (New Guinea).

MacArthur and Wilson developed these observations into a theoretical model, the equilibrium theory of island biogeography which states that the number of species on an island depends on a balance between immigration rates and extinction rates. Based on the theory, small, isolated islands are predicted to have fewer species than larger islands closer to a source of colonists. The point at which the immigration and extinction curves intersect predicts the equilibrium number of species on the island (S).

To test the equilibrium theory, Simberloff and Wilson surveyed small mangrove islands located at different distances from larger mangrove stands. The islands were sprayed with insecticides to remove all insects and spiders. The islands closest to a source of colonists recovered pre-insecticide species richness in 140 days. The island farthest from the source colonists still had not recovered to its pre-insecticide richness after a year.

In 1979, habitat fragmentation spurred Thomas Lovejoy to initiate the longest running ecological experiment ever conducted: The Dynamics of Forest Fragments Project (BDFFP). They found that forest fragmentation had even worse consequences than was first thought of. The largest fragment that they surveyed, 100 hectares, lost 50% of their species diversity within 15 years. They calculated that 1000 hectares would be needed to maintain bird species richness until forest regeneration could “rescue” species within the fragments. If forest regeneration did not occur, the fragment would have to be 10000 hectares or more to maintain most of its bird species over more than 100 years of isolation and it still wouldn’t sustain them all. They also found that habitat fragmentation exposes the species within a fragment to a wide variety of potential hazards including harsh environmental conditions, fires, hunting, predators, diseases, and invasive species. The edge effects can act together with these other effects to increase local species extinction.

Research at the BDFFP has shown us that most forest fragments are too small to maintain all their original species.

Conservation will be most effective if we err on the side of larger, closer, and more numerous fragments.

Conservation Biology

Humans have had a huge impact on the species populations on Earth especially because they have lost habitats through destruction and indirect effects to many different ecosystems. In North Carolina, there is a Military Base which has shown to be beneficial for the ecosystem at hand and has saved many species such as the Red-Cockaded Woodpecker which is an endangered species. The way this works is that for the 90 years that these forests have been a military base, the destructive fires have been beneficial to the pine savannas which depend on fire to persist so that it doesn’t undergo succession to another species. A species, the Red-Cockaded Woodpecker’s habitat is these pine savannas and they like to colonize on newly burned parts of the forest. While some longleaf pine savannah has been preserved, this ecosystem has been reduced to 3% of the more than 35 million hectares it once covered. Rapid human population growth, land clearing for plantations, and decline of the ecosystem with decline in many plant insect and invertebrate species have all factored into this phenomena. The story of the red-cockaded woodpecker reflects that of thousands of other imperiled species around the world. Legal protection and extraordinary human effort have resulted in stabilization and very slow recovery.

An extreme example of this is the Devil’s Hole Pupfish who has a very small region of habitat which is actually just a few meters deep and wide that was discovered in the 1900s. It’s easy for ecologists to monitor and thus it has been preserved and tried to be conserved for a long time.

The most recent list of threatened species by the IUCN lists over 16000 species as threatened with extinction, about 1% of species worldwide. This number is underestimated as only the best-studied taxonomic groups have been assessed and there are many other species that are threatened.

A Pyrenean Ibex, named Celia was found dead in a mountain near France that was apparently killed by a falling tree.

Another species, the Passenger Pigeon which was once one of the most abundant birds in North America, was subject to massive hunts in the 19^th century and thus the last passenger pigeon died in a zoo in 1914. The ecological effects of its extinction on the eastern deciduous forest coincided with the loss of the American chestnut and probably other effects we have not assessed yet.

The American plains bison was massively hunted by many people and has now become extinct.

Ecologists have come to terms with the biological consequences of the changes taking place on the planet with the loss of these species a lot of which are because of human impact. Thus we have the field of conservation biology.

Conservation biology is an integrative discipline that applies the principles of ecology to the protection of biodiversity.

The preservation of longleaf pine savannah at the Fort Bragg military base and on other federal and state lands, coupled with legal protection and extraordinary human effort has led to stabilization and slow recovery of the numbers of red-cockaded woodpeckers. This recovery requires expertise from biological disciplines as well as areas outside of biology like law, political science and sociology. Working with farmers, landowners, US military and business community has helped to arrive at a successful management approach. This is characteristic of conservation biology which is the scientific study of phenomena that affects the maintenance, loss, and restoration of biodiversity.

Some of the major timelines in conservation biology are as such. In 1915, the Ecological Society of America was formed whereby there was a disagreement on whether it should exist only to support ecologists and publish research or should it also pursue an agenda to preserve natural areas. In 1917, from the activist wing within the Ecological Society, the Committee for the Preservation of Natural conditions was created. In 1946, the committee resolved to take “direct action” to save threatened natural areas and renamed itself ‘The Nature Conservancy’ in 1950. Conservation biology wasn’t a science of preservation of species and ecosystems until the early 1980s. It has been integrated within the larger social context of human values. There is emerging journals and scientific papers dedicated solely to conservation biology and it indicates the need to make this a specialized discipline.

Biodiversity is declining globally, and Earth’s biota is becoming increasingly homogenized.

A famous botanist, Alwyn Gentry has devoted his life to observing and mapping the immense diversity of plants in Central and South America and as a consequence became an eyewitness to many plant extinctions due to deforestation. Between 1958 and 1988, a growing human population and government policies that served to stimulate rapid economic development led to rapid deforestation in western Ecuador. The extensive loss of forest habitat in this region is estimated to have resulted in the loss of more than 1000 endemic (found nowhere else) species.

The primary threats to biodiversity are habitat loss and degradation, invasive species, and overexploitation.

Understanding the causes of biodiversity losses is the first step towards reversing them. For any given species, multiple factors are likely to contribute to their decline and extinction. Taking the Pyrenean ibex we looked at before, it was eventually killed by the tree but its number had gradually declined because of hunting, climate change, disease and competition with domesticated livestock.

The ecological footprint of humanity on Earth is large and rapidly increasing. 83% of the land surface has been modified in some way. Homo sapiens is now appropriating 10-50% of the Earth’s primary production and has appropriated 98% of the area where wheat, corn or rice can be grown.

Habitat degradation are changes that reduce quality of the habitat for many but not all species.

Habitat loss is the conversion of an ecosystem to another use.

We already looked at habitat fragmentation before as the breaking up of continuous habitat into habitat patches amid a human-dominated landscape. Another factor to gradual decline in species population are invasive species which are non-native introduced species that sustain growing populations and have large effects on communities. Of particular concern are invasive species that impact native endangered species and can eventually outcompete them to make them become extinct.

An example of this is the mussel population with the introduction of the Eurasian zebra mussels to North American waters which was once the center of diversity of freshwater mussels. Prior to the introduction, these freshwater mussels were already threatened as many of them are endemic and threatened by water quality and river channelization. The zebra mussels were able to outcompete them and have brought about steep declines in population of the native freshwater mussels (60-90%) including some regional extinctions.

In many ecosystems, habitat fragmentation is followed by habitat degradation, which increases vulnerability to invasive species. As an example, the tropical dry forest of Hawaii harbors more than 25% of Hawaii’s threatened plant species. The area of tropical dry forest has been reduced by 90% since human settlement and what’s worse is the arrival of an invasive fountain grass species has not only outcompeted and displaced local plants but it is also an excellent source of fuel for brush fires and thus fire frequency have increased.

Another example is the cichlids which once made up 80% of biomass for a lake, but now the introduced Nile Perch accounts for 80% of the biomass and as many as 200 cichlid species may have gone extinct.

These examples show that species introduction has become a growing problem. The number of non-native species that have become established in the US has increased about fivefold over the past century. This pattern is tree for plant pathogen increase, and terrestrial vertebrates, mollusks and fishes and plants and insects.

Overfishing in the oceans has led to declines in top predators, and other fish species. For every ton of fish caught by commercial trawlers, 1 to 4 tons of other marine life may be brought aboard called by-catch. The by-catch includes species of conservation concern including marine mammals, birds and turtles.

The collapse of cod fishery can be seen with the changes over the years with a huge increase in the tons of cod caught which led to a collapse in the late 1960s which led to the closure of the fishery in 1992. A portion of the fishery reopened in 1998k but closed indefinitely in 2003. Overharvesting has been a huge problem over the past centuries, we see that as the years go by the fish sizes are getting smaller and smaller and in commercial and recreational fisheries, the largest fish are often preferred.

The importance of the different threats varies among biomes. As an example, we can see that habitat loss is greater in the tropics than in the polar zones, but climate change is having more of an effect in the polar zones. As such we see patterns such as habitat loss a big threat in tropical and temperate grasslands as well as in many dry-lands and forests versus overexploitation in the savannas and grassland. We see habitat loss and pollution as two big threats in inland water and coastal waters and invasive species threatening island regions and overexploitation big in marine biomes.

Conservation biologists use many tools and work at multiple scales to manage declining populations.

Ecologists often debate on whether to put focus on species or habitat conservation. The U.S. Endangered species act mandates the identification and protection of critical habitats for species that are endangered.

An example of conservation can be seen in the California condor where the last birds were captured to be conserved in an ex situ facility to be bred. Now there are more than 200 of the species and some have been released into the wild but this example shows that it takes a tremendous effort and many threats to these bird species to still exist in the wild. Ex Situ conservation efforts involve multiple steps such as reducing inbreeding and increasing number of eggs hatched successfully, then with the baby condors being fed by a condor puppet so it avoids being attached to humans, with those that are released landing on scales that can be read by telescopes to weigh them, and finally releasing them. As beneficial as they are, they are expensive and have had limited success, so ecologists wonder if their time and money could be put to managing species in the wild or on securing land, or in situ efforts, and a lot of the times it can’t especially for critically small populations.

Ecologists often take two approaches to conservation planning. Fine-filter approach which is focusing on the genetic aspects of populations and species, versus the Coarse-filter approach which emphasises maintaining ecosystem processes and protecting many species at once.

Biodiversity can be sustained by large reserves connected across the landscape and buffered from areas of intense human use.

The principles of landscape ecology and conservation biology guide biologists in selecting the most important lands for conservation. Design of nature reserves focuses on core natural areas, where conservation of biodiversity and ecological integrity takes precedence over other uses. These core areas can serve as sources for degraded areas. In designing the masoala national park, there is a huge core natural area that is undisturbed by human activities with a border of sustainable harvesting of timbre permitted in that buffer zone but still providing some habitat value in the midst of already deforested zone.

Ideally, these core natural areas must be large and uncut by roads or even trails. Not all protected areas qualify, and do not fully serve the purpose of protecting the whole biota from human interference.

Some spatial designs are better than others for fostering biodiversity. Large, compact and connected reserves are ideal, but smaller or disconnected reserves may sometimes be more desirable (ex. Diseases would spread less quickly in isolated patches).

The best spatial configurations for a core natural area show that a bigger reserve size instead of a few smaller reserves, that are closer together, and connected in a circular shape with a buffer zone prove as the best configuration.

The primary objectives of reserve configurations are to maintain the largest possible population, have a habitat for species throughout the entire area of distribution with enough area to maintain natural disturbance regimes.

Prioritizing species helps maximize the biodiversity that can be protected with limited resources.

Having a measure of how threatened a species is, permits us to focus our efforts on those species that are most threatened: the rarest and most rapidly declining.

The World Conservation Union began assessments of conservation status in 1963 with red-listing process, which is an assessment protocol that takes into account population size, the total geographic area that the species occupies, the rate of its decline and its risk of extinction.

The compilation of NatureServe data on the conservation status of species in the US has permitted identification of the most critical areas to protect such as California, Hawaii, and southern Appalachian mountains.

Protecting habitat for one species, such as the red-cockaded woodpecker, can result in the protection of another species as well called the surrogate species. This can be a shortcut with a lack of information about many species in the area.

A flagship species is a charismatic organism that people will want to give protection to such as giant pandas endangered due to habitat loss from China.

An umbrella species are selected with the assumption that protection of its habitat will serve as an umbrella to protect many other species with similar habitat requirements. They usually have large ranges like the grizzly bear, or specialized habitats like the red-cockaded woodpecker, or are easy to count like butterflies.

Global Ecology

Elements move among geologic, atmospheric, oceanic and biological pools at a global scale.

There are four elements that are of utter global significance. Carbon, Nitrogen, Phosphorus and Sulfur. They are emphasized because of their importance to biological activity and their roles as pollutants in the global environment.

The cycles are discussed in terms of pools (reservoirs), or the amounts of elements within the components of the biosphere, and fluxes, or rates of movement between pools.

As an example, terrestrial vegetation constitutes a pool of carbon, while photosynthesis is a carbon flux.

The Global Carbon Cycle represents four major global pools of C: atmosphere, oceans, land surfaces (including soil and vegetation) and sediments of rocks. The largest of these pools is the combination of sediments and rock, which contain 99% of the global carbon. The Carbon in this pool is found primarily in the form of carbonate minerals and organic compounds and is the most stable pool taking up and releasing Carbon on geologic times scales. The oceanic pool consists of surface waters and deeper colder waters. Most of the oceanic carbon is in the deeper waters. The terrestrial pool is the largest pool of biologically active Carbon. The soil pool contains twice as much C as the vegetation pool and the terrestrial pool exchanges C with the atmospheric pool primarily through photosynthesis and respiration.

As a result of the rapid human population growth, over the past 160 years, there has been an increase in the release of Carbon to the atmosphere from the terrestrial pool mainly due to forest clearings and burning of fossil fuels. This anthropogenic, or human linked release of C is the result of land use change and we see in 1970 where was a 4.1 Pg/year carbon dioxide emission rate that increased to 10.4 in 2011 which is more than double in 40 years. Today, burning of fossil fuels accounts for ~ 90% of the anthropogenic C flux to the atmosphere, whereas the remaining 10% is associated with deforestation.

CH4, or methane is released in fires, and can have a large influence on global climates. It is 25 times more effective as a greenhouse gas per molecule than carbon dioxide and unfortunately, the methane emissions have more than doubled over the last two centuries with a lot of livestock and cattle producing hundreds of kg of emission per year.

Ecosystems response to elevated CO2 concentrations provides a change in photosynthetic rates. We might expect increases in rates of photosynthesis as anthropogenic CO2 emissions increase. However, it is difficult to manipulate atmospheric CO2 concentrations experimentally in an intact forest may not have same capacity to take up that extra CO2.

The atmospheric CO2 concentrations directly affect acidity by decreasing pH by more CO2 diffusing into sea water and more carbonic acid being produced with less carbonate being available in the waters. Ocean acidity has increased by ~30% during the last century. These have consequences on marine life such as dissolving the existing shells of marine organisms (coral) and lowering carbonate concentrations decreasing organism’s ability to synthesize shells.

As an example, we see the rates of calcification of corals on Australia’s Great Barrier Reef have a sharp decrease after 1980s which is consistent with the observed decrease in the pH of seawater in the same time period.

Changes in Atmospheric CO2 and CH4 have varied over past 400k years. High concentrations correspond to warm interglacial periods whereas low concentrations correspond to cool glacial periods. Since the mid-1800s, CO2 concentrations have increased at a rate faster than at any other time over the past 400k years reaching values of 395ppm in 2013

Nitrogen, plays a key role in biological processes and is one of the resources commonly limiting primary production. The global nitrogen cycle has its largest pool as atmospheric N2 gas which is stable but cannot be used by most organisms except for nitrogen fixing bacteria. Terrestrial N2 fixation by bacteria provides approximately 128 Tg of reactive N per year and supplies 12% of the annual biological demand. The remaining 88% is met by uptake of N from the soil in forms released by decomposition. Oceanic N fixation contributes another 120 Tg to the biosphere annually with the geologic pool containing a much smaller fraction of global N than global C.

Changes in anthropogenic fluxes in the Global Nitrogen Cycle see increases in anthropogenic nitrogen fixation and nitrogen emissions have tracked human population growth.

The Global Phosphorus Cycle, unlike C and N, has essentially no atmospheric pool. It is released from sedimentary rocks in biologically available forms by weathering. The largest flux occur in internal ecosystem cycles that form a tight recycling loop between biological uptake by plants and microorganisms and release by decomposition. Much of the P transported from terrestrial to marine ecosystems (90%) is lost when it’s deposited in deep ocean sediments. Anthropogenic effects are associated with agriculture fertilizers, discharge of sewage and increase in terrestrial surface erosion. P is a non-renewable resource subject to depleting.

The Global Sulfur Cycle has major pools in rocks, sediments and the ocean which contain dissolved sulfate. Fluxes of S among these pools occur in many forms. There is a net movement of S from the terrestrial pool to the oceanic pool, and volcanic eruptions emit substantial amounts of sulfur dioxide into the atmosphere but averaged out in time it’s not a lot as they are episodic events. Anthropogenic emissions of S to the atmosphere have quadrupled since the Industrial Revolution. Most are associated with burning of S-containing coal and oil.

Earth is warming due to anthropogenic emissions of greenhouse gases. Changes in climate, in particular changes in the frequency of extreme events have profound effects on ecological patterns and processes. Climate is the long-term description of weather including both average conditions and the full range of variation. Climate change is distinguished from climate variation by the presence of significant directional trends lasting at least three decades.

Average global annual temperature has been on a rise since the 1900s and is continuing to increase. The trends we have seen are as such. The first decade of the twenty-first century was the warmest decade of the previous 1000 years. 2010 was the warmest year in over a century. There has been a widespread retreat of mountain glaciers, thinning of the polar ice caps and thawing of permafrost, and a rise in sea level since 1900.

The warming of Earth by atmospheric absorption and re-radiation of infrared radiation emitted by Earth’s surface is known as the greenhouse effect. This phenomenon is associated with radiatively active gases, or greenhouse gases, that are in the temperature such as water vapour, CO2, CH4 and N2O. Substantial increases in greenhouse gas concentrations in the atmosphere due to anthropogenic activities such as burning of fossil fuels and land use changes.

We can see large increases that have occurred in all three gases in the late 19^th century due to anthropogenic influences.

What does 1.1-4.8 degrees Celsius change in average global temperature mean for biological communities? Taking the median value of 2.9, this could mean shifts in vegetation zone with an increase in elevations and latitude. Ecological consequences would result in decrease in ice in the arctic regions and tundra regions with more boreal forests taking over.

Overpeck and colleagues used pollen records to reconstruct large-scale vegetation changes since the most recent glacial maximum which was 18000 years ago in North America. He found that not only the community types had made latitudinal shifts as the climate warmed, but also the community types without modern analogs existed under climate regimes that were unique and no longer present and concluded that future vegetation will see similar trends.

This rapid rate of climate change makes it unlikely that evolutionary responses will be possible and thus dispersal may be the only way for them to avoid extinction. Their dispersal abilities (and anthropogenic barriers) will be important constraints on their responses to climate change. Plants have much slower dispersal rates whereas animals have habitat and food requirements that can limit their dispersal.

As an example, we see that plants are moving up the Alps. Grabherr et. Al compared historical records of vascular plant species richness on the summits of mountain in the European Alps and we see an increase in the species richness in higher altitudes which were attributed to climate warming and the resulting movement of plant species.

The changes in terrestrial NPP show an increase in NPP in tropical ecosystems that were associated with decreases in cloud cover and increases in solar radiation.

Anthropogenic emissions of sulfur and nitrogen cause acid deposition, alter soil chemistry, and affect the health of ecosystems.

Emissions of N and S into the atmosphere have resulted in two related environmental issues: acid precipitation and N deposition.

Sulfuric and Nitric acid are the main acidic compounds found in the atmosphere and have caused significant damage to forests and aquatic systems such as acidification of soils, leaching of Aluminum which is toxic to roots etc. Acid rain has caused masses of European forests to be damaged. Fortunately, damage due to acid rain is now reduced in several countries due to control of S and N emissions however it is still a problem in rapidly developing countries like India and China.

We see nitrogen deposition overall increasing and expected to double by 2050, and you would think it’s a good thing as it can increase photosynthetic rates and plant growth, but it has been associated with environmental degradation, loss of biodiversity and acidification if there is too much. When N inputs are exceeded it is known as nitrogen saturation and has a number of effects on ecosystems. Some of the effects include greater N available to enhance NPP and rates of N cycling processes but eventually, losses of calcium and magnesium and greater aluminum concentrations lead to lower plant growth and decrease in NPP. At high rates of N input, the ecosystem reaches the final stage of N saturation where the system cannot retain N from both inputs and mineralization, and leaching of N into groundwater occurs.

Negative relationships have been observed between N deposition and species richness in plant communities across Great Britain. N deposition explained the greatest amount of variation in species richness amount 20 possible factors and was backed up by other studies. The studies found the sites with highest N deposition rates had the lowest species richness.

Losses of ozone in the stratosphere and increases in ozone in the troposphere each pose risks to organisms.

The ozone in the stratosphere (10-50km altitude) acts as a shield to protect the Earth’s surface from high-energy UVB radiation. A hole was discovered in 1980 over Antarctica. The Ozone Hole is defined as an area with an ozone concentration of less than 220 Dobson units.

By 1986, the ozone hole was as large as the Antarctic continent. By 1994, the ozone hole was as large as North America. We also see springtime concentrations gradually decreasing and have decreased by 70% since the early 1980s.

Some causes for this hole are CFCs or chlorofluorocarbons that destroy O3 molecules. They are found in refrigeration units, spray cans etc.

Consequences of the ozone hole lead to increase in UVB radiation especially over Antarctica (increase in skin cancer). After Montreal protocol have banned use of CFCs, their levels have remained constant and even decreased in some areas. Full recovery of stratospheric ozone is expected by 2050.

Although the stratospheric ozone accounts for 90%, the other 10% of ozone is in the troposphere. The Tropospheric ozone is environmentally damaging for two main reasons. First, Ozone is highly reactive with other compounds and thus causes a variety of harmful damages to human respiratory systems, plant membranes and inhibits plant growth as well as increases susceptibility to plant stressors.

Measurements of atmospheric concentrations of ozone-killing chlorinated compounds at five monitoring locations across the globe show that several of them have declined since the initial signing of the Montreal Protocol in 1989.

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