Effects of climate change on terrestrial animals

"Average temperature changes do not in themselves provide simple predictions about ecological 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.

With rising global temperatures, terrestrial organisms will face greater hazards in the forms of increasingly frequent and more severe meteorological conditions such as droughts, snow storms, heat waves, hurricanes, and melting glaciers and sea ice.[3]

These harsher weather conditions will cause terrestrial wildlife many issues as their usual habitats will be significantly impacted, leading them to go extinct, migrate elsewhere or find ways to adapt to their new conditions. These ecological responses vary based on the situation. This was shown even in a 2018 study done at the University of Queensland, where over 350 observational studies were done on terrestrial animal populations (for over a year), with results showing a positive correlation between increased severe weather conditions in ecosystems and population declines or extinctions.[4]

Phenology is the study of 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.[5]

Researchers are exploring ways to breed livestock like chickens, turkeys, and pigs to better withstand the heat.[6]

The increasing global temperature has been devastating for the polar and equatorial regions, and the change in temperature in these already extreme regions has destroyed their fragile equilibrium. In the sub-Saharan regions, deserts are experiencing severe droughts that affect both water and agricultural resources, since crop production is harshly affected.[7]

Droughts, floods or changes in precipitation and warmth all influence the quality and amount of vegetation present in a region, in addition to the soil fertility and plant diversity. A region with vegetation or crops that have minimal tolerances and resilience to changes is at risk due to the uncertainty of the future effects of climate changes on crops and edible vegetation.[8]

This direct effect of climate change has an indirect effect on the health of terrestrial animals, since changes in their dietary availability will impact not only herbivores but all other terrestrial creatures in their food webs. Some of the negative impacts include:[9][10][11][12]

• Extinctions or declines in populations
• Increased competition for remaining resources
• increased foraging difficulty: for example, increased snowfall in northern latitude can make it harder for elk to find food
• Migration
• Changes in phenology
• Evolutionary favouring: species with less dietary restrictions will thrive in certain regions
• Reduced livestock production

Humans may be significantly impacted as terrestrial livestock will not be immune to the ravages of climactic changes. Temperature-related illness and death can be attributed to global warming, with homeothermic animals eating less feed and exerting more energy to maintain conditions to function normally. This heat stress on terrestrial mammals can weaken their immune systems leaving them vulnerable to a multitude of associated illnesses and diseases.[13]

Changes in climate and global warming have significant influences on the biology and distribution of vector-borne diseases, parasites and their associated illnesses. Regional changes resulting from changing weather conditions and patterns within temperate climates will stimulate the reproduction of certain insect species that are vectors for disease. Therefore, tropical diseases common to certain places and affecting only certain terrestrial species may probably migrate and become endemic in many other ecosystems.[14]

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 nowhere else to move to. This hindrance is particularly prevalent in mountain ranges, for example. The speed at which climate is changing is derived from the 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).

Similarly, dispersal and migration are crucial to preserving biodiversity as rapidly rising equatorial temperatures push an increasing number of species in poleward directions.[15]

As mentioned earlier, phenology is the changing of an animal's behavior because of 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 in 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) that 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 led 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, including the timing of its reproduction, mating, and migration.

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.[17]

Climate change has been associated with changes in plant size as well as animal size.[18]

Short generational times improve adaptability; e.g., many microbial disease organisms, small insects, common fishery species and annual plants are thought to be more highly 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 the ability of an animal to withstand a large range of conditions. For example, the kangaroo has a very broad climatic tolerance.[19]

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.

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

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

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

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