Why are tropical species most vulnerable to climate change?

According to climatologist Benjamin Sultan, the agreements ratified at COP26 in Glasgow will not be enough to limit global warming to less than 2°C. For several years, the effects of climate change have been felt, ranging from heat waves to massive fires in some areas and floods in others.

Ecological researchers from all over the world report that species are not immune to these disturbances in the documentation of IPBES, the ecologists’ equivalent of the IPCC. Drastic population declines, particularly of insects, have been observed all over the world, even in seemingly pristine areas.

Future projections are less reassuring: studies aimed at predicting the effects of climate change suggest that there will be winners and losers, but mostly losers, not to mention the disruption caused by the emergence of these “winners.”

Although the idea of limiting warming to 2 degrees Celsius is gaining traction, it is still insufficient, according to a study published in the journal Climate Change in May 2019.

As we can see, even in temperate regions like ours, climate change can be costly. However, an increasing number of studies show a gradient in the intensity of these effects on species. The stronger these effects are, the closer you are to the equator. This is true for birds in Europe, where the southernmost populations are declining faster than those further north.

The same phenomenon can be seen in the American mountains, where birds flock to seek cooler temperatures at higher elevations, but especially in the tropics.

This gradient has been observed in the body size of French passerines as well. A study I co-authored with the National Museum of Natural History and published in Global Ecology and Biogeography found that young birds grew slower in unusually warm years, but only in southern France.

In this rap video, I collaborated with Benjamin Freeman (University of British Columbia) to summarize this research….

How can this occurrence be explained? Wouldn’t the most southern species and populations be better adapted to warmer climates? They would, of course. However, heat and drought continue to be major constraints in these areas. Warming in the Mediterranean region, for example, will increase aridity, reducing plant growth, which is the foundation of the food chain.

More heat, more aridity, fewer plants, fewer insects, and fewer food sources for birds. But what about the tropics, where the climate is still hot and humid? Of course, species have adapted to these climates. Except that their heat tolerance limit is not significantly different from that of our regions.

Because tropical species are always close to this limit, even a slight warming could push them out of their physiological comfort zone.

Future forecasts are concerning.

The use of predictive models allows for the prediction of the effects of climate change. Ecological researchers use climatologist projections for the future after identifying favorable climatic conditions for a species.

These models predict a dramatic decline in climatic conditions for two species by 2070 in one study, which I conducted in collaboration with the University of Porto and the Malagasy association Madagasikara Voakajy.

A gecko (a lizard with toes that allow it to cling to any surface) living on the island of La Réunion and a colorful Madagascar frog are two small vertebrates that are already critically endangered. Both are restricted to a very small geographical area and are associated with very specific climatic conditions. The study considers various sources of uncertainty, such as those related to the various scenarios or methods used.

In all cases, the climate will become unfavorable for both species, not only in their current range, but also on the rest of their respective islands. As a result, climate change adds to the list of threats to their environment.

There is a glimmer of hope.

According to these models, the ideal climatic conditions for these species will no longer exist in the future. They don’t, however, tell us anything about the species’ ability to adapt. Some people may alter their habits to avoid the hottest times of the year. Others discover climatic micro-shelters in nature and in buildings. It is also possible that these species are more heat resistant than previously thought.

Reunion has already taken precautions to protect the species. The association Nature Océan Indien has organized programs to restore the gecko’s natural habitat.

This research is already allowing us to anticipate the risks associated with climate change by favoring existing populations, which increases their chances of adaptation significantly.

But, you may wonder, what is the point if the climate is no longer favorable in the future? Our predictive study, on the other hand, has allowed us to precisely identify the areas where conditions will be less harmful to the species. These findings will help conservationists maintain or create habitats for this critically endangered small lizard.

The study only included two species due to a lack of data, but these dire predictions could come true for many tropical species. Another red flag in an already hot world.


Article Author Gerluxe

Image: wikimedia