The How and Why of Climate-Mediated Extinction
Recent responses to climate change reveal the drivers of species extinction and survival (2020) Román-Palacios & Wiens, PNAS, https:/doi/10.1073/pnas.1913007117
We tend to think of climate change as bad, and despite the fact that some organisms will benefit from it, many others won’t. A big part of why we consider it bad is that species are predicted to be lost at an alarming rate, with some estimates as high as 54% of all organisms going extinct. An issue with these predictions is that they tend to assume that species will track their preferred temperature and precipitation conditions, but this eliminates any ability of organisms to adapt to their new normal over time.
Today’s authors wanted to use data from previous studies to estimate how species adapt (or don’t) to climate change. Although previous work has shown that climate change is detrimental for many species, this study aimed to learn if it was due to changes in the overall temperature, changes in the extremes (i.e. how hot the hottest day is), or was it the sheer speed of change that did organisms in.
What They Did
Using data from 10 different studies and focusing on terrestrial plants and animals on mountainous habitats, the authors analyzed species occurrence data from two different time periods. They compared species occurrence and climate conditions between the two time periods, allowing them to make inferences about the climate drivers of local extinctions.
In addition to the changes in climate, the authors also analyzed historical and contemporary data to understand how species may have dispersed due to climate change. One advantage with organisms in mountainous environment is the elevational gradient (see the Did You Know), so organisms can move a relatively short distance and experience a marked change in climatic conditions. After collecting data on both local extinctions and inferred dispersal the authors used predictive modelling to understand how organisms may be able to avoid extinction, either through changing their ability to tolerate temperature or via dispersal.
Did You Know: Elevational Gradients
In nature organisms tend to occur along environmental gradients. That could be a temperature, latitudinal, or depth gradient (among others). An elevational gradient, like the one studied here, is the gradient along a mountainside from the base to the summit. Since some of these gradients are quite steep, one can see a large difference in temperature, precipitation, and other environmental conditions by simply moving up or down the mountainside. Those changes are what allow montane species to disperse and track their preferred conditions.
What They Found
For all of the climate data analyzed, the change in maximum annual temperature was the most important predictor of local extinctions, when taking both the absolute change and the rate of said change into consideration. Changes in precipitation were also detrimental and decreased precipitation was associated with local extinctions, but to a lesser degree than temperature. Using the predicted upper limits of dispersal for the organisms in this study, a large percentage of the organisms (39%-60%) would not disperse quickly enough to avoid local extinctions.
In contrast, for the species that did not disperse or go locally extinct the authors found that the vast majority of them were able to tolerate large changes in their local climatic conditions, with only 9%-30% going locally extinct.
This study takes an elegant approach to understanding how climate change is causing local extinctions, using an enormous amount of climate data to predict patterns. However, despite evidence for changes in the maximum annual temperature driving local extinctions, not the mean, the authors did not incorporate changes in the temperature variance. That is to say, they did not analyze how varying temperatures over the year affected extinctions. They did have data on the annual temperature variation per site, but that was the average for the entire year and was likely too general to capture any patterns that may have occurred at smaller timescales.
By building models that account for changes in the organisms over time, be that in their preference for a given temperature or their physical location, we can more accurately predict how climate change will affect species loss. This has large implications for understanding species persistence in the face of climate change, because simply looking at changes in the precipitation and mean temperature may be misleading and overestimate the effects. I am not trying to say that climate change isn’t a real threat and that species can just “deal with it”, but in nature things are rarely simple and studies like this one do a great job at highlighting that complexity.
Adam Hasik is an evolutionary ecologist interested in the ecological and evolutionary dynamics of host-parasite interactions. You can read more about his research and his work at Ecology for the Masses here, or follow him on Twitter here.