Climate change: Why tropical species are most threatened

The agreements ratified in Glasgow during COP26 will not be enough to limit global warming to less than 2°C, climatologist Benjamin Sultan recently told Franceinfo. Knowing that the effects of climate change have already been felt for several years: from heat waves to fires of an unprecedented scale in certain regions, including floods in other areas.

Species are not immune to these disturbances: this is what ecological researchers around the world point out in the IPBES documentation, IPCC equivalent for ecologists. Of dramatic staff reductions, especially in insects, have been observed all over the world, even in apparently unspoiled regions.

The projections for the future are not more reassuring: the studies to predict the effects of climate change suggest that there will be winners and losers, but above all losers, not to mention the disturbances that the proliferation of these "winners" could represent.

While the idea of ​​containing global warming to 2 ° C is gaining ground, this limitation remains insufficient, as a study highlighted in May 2019. published in the reference journal Climate Change.

Stronger effect in the tropics

As you can see, climate change risks costing us dearly, even in our regions where the climate is temperate. Nonetheless, more and more studies have shown a gradient in the intensity of these effects on species. The closer you get to the equator, the more these effects are accentuated. It's the case in birds in Europe, whose populations more southerly decline more than those living further north.

The same phenomenon is observed in the American mountains, where the birds come to seek freshness at altitude, but especially in the tropics.

This gradient was also observed on the body size of French passerines. A study that I carried out with the National Museum of Natural History and Publiée dance Global Ecology and Biogeography, showed that juveniles grew less well in unusually warm years, but only from the south of France.

I have also summarized this research, along with Benjamin Freeman (University of British Columbia), in this rap clip ...

“Species, climate change and latitude: Hot, humid and dark” (Scientific Rap Sessions, October 6, 2021).

Species closer to the tolerance threshold

How to explain such a phenomenon ? Could the southernmost species and populations be adapted to warmer climates? Of course yes. However, heat and drought remain the main constraints in these regions. A warming, for example in the Mediterranean region, will result in an increase in aridity, itself reducing the growth of plants, which constitute the base of the food chain.

More heat, more aridity, fewer plants, fewer insects, less food for birds. Ok, but in the tropics, where the climate is still very humid? The species are adapted to these climates, of course. Except that their hot tolerance limit is not very different from those present in our regions.

Tropical species live permanently near this limit, so a slight warming could cause them. pushing outside their physiological comfort zone.

Alarming forecasts for the future

It is possible to anticipate the consequences of climate change by using predictive models. After having identified the favorable climatic conditions of a species, the researchers in ecology have recourse to projections elaborated by the climatologists for the future.

In a study, which I carried out in collaboration with the University of Porto and the Madagascan association Madagasikara Voakajy, these models predict a dramatic decline in climatic conditions by 2070 for two species.

Phelsuma inexpectata
, a species of gecko living on Reunion Island.

B. Navez / Wikimedia, CC BY-NC-SA 

These are two small vertebrates already highly threatened: a gecko (lizard whose fingers allow it to adhere to all surfaces) living on the island of Reunion; a brightly colored Madagascan frog. Both are confined to an extremely small region and attached to very specific climatic conditions. The study takes into account a variety of sources of uncertainty, in particular those related to the different scenarios or the methods used.

In any case, the climate will become unfavorable for these two species, not only in their current area of ​​occupation, but also in the rest of their respective island. Climate change is therefore added to the list of threats to their environment.

A glimmer of hope

These models suggest to us that the ideal climatic conditions for these species will no longer be found in the future. On the other hand, they ignore everything about the adaptability of species. Some may change their habits to avoid the hottest periods. Others also find climatic micro-refuges, in nature as well as near dwellings. It is also possible that these species are more resistant to heat than expected.

Actions have already been taken to save the species in Reunion Island. Association Nature Indian Ocean has organized programs to restore the natural habitat of the gecko.

This work already makes it possible to anticipate the risks associated with climate change, by favoring existing populations, which will considerably increase their chances of adapting.

But what good, you will say, if the climate is no longer favorable in the future? Precisely, the predictive study has made it possible to precisely identify the areas where the conditions will be the least detrimental to the species. These results will guide conservation practitioners in their specifications, and will contribute to maintaining or creating habitats that will constitute a welcoming land for this small lizard in danger of extinction.

This study was carried out on only two species, data lacking, but these grim predictions could very well come true for many tropical species. An additional alarm bell in an already overheating world ...

Nicolas dubos, Researcher in Ecology, National Museum of Natural History (MNHN)

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.

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