The response of species to climate change

The climate crisis affects every aspect of biodiversity, but not every species responds in the same way to climate change. Some species can cope with climate change via adjustments and adaptation, or simply moving to new areas. Other species are unable to cope with climate change, they decline and eventually disappear.

The “adjust” response encompasses all changes that occur during an individual’s lifetime and that are typically not transmitted to offsprings. Species adjust in response to environmental pressures, including climate change, through shift in their development, morphology, physiology, and behavior. Species can also alter their phenology, the timing of cyclical biological events. Scientists found several examples of advancement of phenological events due to climate change, such as earlier flowering and breeding. However, changes in phenology can sometimes disrupt ecological interactions within an ecosystem, if a species’ phenology is no longer coordinated with key food or habitat resources its persistence might be compromised.

Adaptation is the process by which populations become better suited to new environmental conditions via heritable change over the course of generations. Heredity and natural variation are key requirements for adaptation and evolution via natural selection, which is defined as the differential survival or reproduction of organisms based in their fit to their environment. Adaptation is observed in response to many different selection pressures, such as climate change, and can lead to a wide variety of traits’ changes, from thermal tolerance to osmotic balance. One example of adaptation to changing climates is found in fruit fly Drosophila subobscura. At northern latitudes this species used to show a genetic mechanism which confers it an adaptation to colder climates, called chromosomal inversion. However, over the last 20 years, the frequency of this chromosomal inversion has decreased due to global warming. Mechanisms of evolutionary adaptations to climate change are also called “evolutionary rescue”.

Species can “move” to track spatial shift in their suitable climate. Species’ geographic range – the spatial extent of their distribution – are not stable through time, and environmental change (as determined by climate change and human pressure) has accelerated range shifts, which include contractions or expansions. For instance, the distribution of the emperor penguin (Aptenodytes forsteri) is projected to dramatically reduce because of the loss of polar sea ice due to global warming. However, climate change can also simultaneously induce contractions at one range margin of the range (eg south) and expansion at another margin (eg north). The most consistent patterns observed are distributional shifts towards poles, higher elevations, and deeper waters. Many mid-elevation species have shifted to higher altitudes, but high elevation species have nowhere to go, and their populations can become small, isolated, and more vulnerable to extinction.

When species vulnerable to climate change do not adjust, adapt, or move, they may be lost. While the loss of individuals of a species, and even the loss of an entire geographic population of such individuals, does not necessarily mean loss of the entire species, the risk of species extinction can dramatically increase from climate change. Reduced population size from climate change can increase vulnerability to other stressors and lead to further decreases in population size, in a self-sustaining feedback loop called “extinction vortex”. For instance, many amphibian species are now on the brink of extinction and climate change is having indirect and sublethal effects on their survival. Also, climate change is threatening corals’ survival, because rising temperatures disrupt the symbiosis between reef-building corals and their photosynthetic algae. The loss of symbionts and their associated pigments leads to corals bleaching and increases coral mortality.

Overall, the current extinction rates far exceed historical background extinction rates registered by the fossil record (they are ca. 100 times higher!). While most species decline in recent centuries depended on habitat degradation, hunting, invasive species, etc., climate change is rapidly becoming one of the main drivers of species decline and extinction.

External Resources

Carpenter, K. E., Abrar, M., Aeby, G., Aronson, R. B., Banks, S., Bruckner, A., … & Wood, E. (2008). One-third of reef-building corals face elevated extinction risk from climate change and local impacts. Science, 321(5888), 560-563.

Rezende, E. L., Balanyà, J., Rodríguez-Trelles, F., Rego, C., Fragata, I., Matos, M., … & Santos, M. (2010). Climate change and chromosomal inversions in Drosophila subobscura. Climate Research, 43(1-2), 103-114.

Wake, D. B., & Vredenburg, V. T. (2008). Are we in the midst of the sixth mass extinction? A view from the world of amphibians. Proceedings of the National Academy of Sciences, 105(supplement_1), 11466-11473.