Effects of climate change on terrestrial animals

Habitat fragmentation

During the Carboniferous Rainforest Collapse, the vast and lush rainforests of Euramerica were destroyed, fragmenting into small 'islands' in a much less diverse landscape. This event decimated amphibian populations and spurred on the evolution of reptiles.

Increased temperatures

“Average Temperature changes do not in themselves provide simple predictions about evological consequences. Average temperatures have changed more in high latitudes than in the tropics, but tropic species are likely more sensitive to temperature changes than temperate ones (IPCC 2008).” Q₁₀ is the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10 °C.

Phenology

Phenology is the life cycles of animals or plants due to seasonal or other variable climate changes. These responses by animals due to climate change may or may not be genetic

Researchers are exploring ways to breed livestock like chickens, turkeys, and pigs to better withstand the heat.

Range shifts

Range shifts are a natural response to climate change. Species with sufficient levels of mobility may respond quickly to environmental change, with species capable of undertaking long migratory movements likely to shift ranges first (Lundy et al., 2010). Migration is not limited to animal populations - plants can migrate via passive seed dispersal, establishing new individuals where conditions allow.

“The range of plants and animals are moving in response to recent changes in climate (Loarie 2009).” As Temperature increases, ecosystems are particularly threatened when their niche has, essentially no were else to move to. This hindrance is particularly prevalent in mountain ranges for example. The speed at which climate is changing is derived from ratio of temporal and spatial gradients of mean annual near-surface temperature.

“Mountainous biomes require the slowest velocities to keep pace with climate change. In contrast, flatter biomes, such as flooded grasslands, mangroves and deserts require much greater velocities. Overall, there is a strong correlation between topographic slope and velocity from temperature change (Loarie 2009).”

Temperatures are expected to rise more than average in higher latitudes and at higher elevations. Animals living at lower elevations could migrate to higher elevations in response to climate change as temperatures rises. Whereas animals in higher elevations will eventually ‘run out of mountain’. “Results confirmed that protected large-scale elevation gradients retain diversity by allowing species to migrate in response to climate and vegetation change. The long-recognized importance of protecting landscapes has never been greater"(Moritz 2008).

Over the past 40 years, species have been extending their ranges toward the poles and populations have been migrating, developing, or reproducing earlier in the spring than previously (Huntley 2007).

Adaptation

The 2007, IPCC's report stated that “adaptation will be necessary to address impacts resulting from the warming which is already unavoidable due to past emissions.” (IPCC 2007)

Changes in phenology

As mentioned earlier, phenology is the changing in timing of an animal’s behavior due to climatic circumstances. It may or may not be genetic. The genetic changes in animal populations have involved adaptation to the timing of seasonal events or to season length. For example, the Canadian red squirrels are reproducing earlier in the spring, thereby capitalizing on earlier spruce cone production (Huntley 2007).

Because of the increasing evidence that humans have had a significant impact on global climate over the previous centuries, many scientists wonder how species—and the ecosystems they live in—will adapt to these changes, or if they even can.

Usually the first and most easily detectable response is a change in the species’ phenotype, or its physical features. But there is a debate among scientists over whether or not these changes reflect an adaptive genetic evolution or simply phenotypic plasticity.

A recently published study by Franks et al. sought to demonstrate that a shift in the annual flowering time of the Bassica Rapa plant in response to a multi-annual drought is southern California is in fact an adaptive evolutionary response. Based on the study, they concluded that post-drought genotypes appeared to be better adapted to shorter growing seasons than the pre-drought genotypes, and that this was a result of adaptive evolution.

Huntley counters the findings of Franks et al. (Huntley 2007) with a study by Wu, et al. (Wu L 1975) which provided evidence that not only different species but also different populations of the same species exhibited markedly different potentials for the selection of heavy metal tolerant genotypes. This lead Bradshaw and McNeilly to conclude that different populations of the same species can adapt their phenology to survive in the short term and at local sites, but genetic variation across an entire species in response to rapid climate change is not possible (Bradshaw 1991).

Huntley concludes that while some evolution is likely to occur in some species in relation to global climate change, it is unlikely to be sufficient to mitigate the effects of said changes, especially if they occur as rapidly as has happened in the past.

In refuting the findings of Franks, et al., Huntley concludes: “Although the demonstration of an evolutionary basis for a phenotypic response may be interesting, it is insufficient to overturn the conclusions of Bradshaw and McNeilly (Bradshaw 1991). Evolutionary adaptation is unlikely to be of major importance in the response of species to the climatic changes expected this century. Furthermore, even its limited potential is likely to be severely reduced as a consequence of habitat and population fragmentation, and of the rapidity and magnitude of the expected climatic changes, that together are likely to lead to rapid genetic impoverishment of many populations. A more likely outcome is that, rather as in the grasslands developed on heavy metal contaminated soils, a small number of species that happen to have the necessary genetic variance will come to dominate many plant communities, with potentially far-reaching consequences for biodiversity, ecosystem function and the ecosystem services upon which mankind depends (Huntley 2007).”

There are many ways that an animal can alter its behavior. The timing of their Reproduction, Mating, and migration, or the changes in abundance-changes in timing of feeding, etc.,

Evolutionary

Adaptive shifts in the timing of seasonal events should precede adaptive shifts of thermal optima or increased heat tolerance over evolutionary time, and that is the pattern that is emerging (Bradshaw 1991).

It has been hypothesized that as temperature increases, body size would decrease. Smaller body size would dissipate heat more efficiently, so in an increased temperature environment one would expect an animal to be smaller. The opposite also holds true, when temperature decreases, studies have shown with great correlation that body size increases. This was shown.

Climate change has been associated with changes in plant as well as animal size.

Factors contributing to adaption

Short generational times as for many microbial disease organisms, small insects, common fisheries species and annual plants are thought to be highly more adaptive.

Wide dispersal areas allow animals to migrate and move to an environment better suitable in an effort to handle climate change.

Broad climatic tolerance is essentially the ability an animal has to withstand a large range of conditions. For example, the kangaroo has a very broad climatic tolerance.

Generalists are non-habitat species in that they are not restricted to a very specific location, environment, food source, etc. The American Coyote is an example of a generalist.

Opportunistic species feed and adapt to many changes.

Factors hindering adaption

Long generation times limit the rate at which a species can become more varied.

Poorly dispersed animals are unable to migrate and essentially escape and survive the climate change.

Narrow climatic tolerance in animals inhibits animals to adapt because their basic survival needs cannot range in location, temperature or resources.

Population confined to one geographic location does not have a simple option of migration- such as animals that live in cold regions at the tops of low-lying mountains. These animals are in habitats that will run out as climate change increases and global warming becomes more impacted.

Extinction or extirpation

According to Stuart L. Pimm and his coauthors, human actions have raised species extinction or extirpation rates to three orders of magnitude above their natural, background rates. Pimm says that "[Scientists] predict that 400 to 500 of the worlds 8500 landbird species will go extinct by 2100 with a warming estimate of 2.8 degrees Celsius. A further 2150 species will be at risk of extinction" (Pimm 2009).

Given that species have limits to where they can exist, if conditions are unfavorable, mortality will be high and a species will be absent or rare in those areas. The corresponding graph representing this statement can be seen. The graph represents an experiment conducted using sand shrimp and their relative mortality rates based on salinity and temperature in a controlled environment. If climate change prompted the particular animal’s environment to become more or less salty, or too hot or too cold, and the organism was unable to move or to adapt, it would instead become extinct.

In Australia, the Grey-headed Robin is restricted to rainforests of the Wet Tropics region; and another population in the New Guinea highlands. Although in some places it can be locally common, this bird's range is very restricted; it is found only in the north east of Queensland, and there only in the higher altitude rainforest. This is a projection of its range as climate change continues. This animal could be considered in danger of extinction.

A similar but more dramatic prediction is cast for the Lemuroid Ringtail Possum. As one can see, with a high enough temperature (climate) shift, this animal will become extinct.

Global warming as caused by humans is confirmed by the IPCC fourth Assessment to be “very likely”. This being the case, a tipping point may be reached for many species, leading ultimately to extinction (Pimm 2009).

Sometimes a species may react in one of the other two ways, by moving or by adapting, and yet find that its efforts do not save it from extinction. While not yet extinct, the Pied Flycatcher, a small insectivorous bird that migrates to Western Europe from Africa each spring, has declined to 10% of its former population. This has occurred at the same time as a main food source for the young flycatchers, caterpillars, have begun to peak much earlier. Although the birds have also begun to arrive earlier, they have not yet caught up to the peaking of the caterpillars. This individual species may or may not go extinct, but it goes to demonstrate that a species can sometimes begin to move or adapt and yet find itself dying nevertheless (Pimm 2009).