Models predict large impact of climate change on amphibians

This summer one of the most powerful men alive today, president Obama, spoke out very clearly his opinion on climate change and the human role in it: “The planet is warming. Human activity is contributing to it”. He added to that, pointing his arrows at the climate change skeptics, “we don’t have time for a meeting of the Flat Earth society”. Such a clear statement from the political leader of the USA is good news, because much time has been wasted on the question whether climate change is real and less time has therefore remained for solving the issue. The USA is one of the biggest CO₂-contributors and is home to the most fanatic climate change skeptics. At least Obama’s words suggest that the political powers that be in the USA are acknowledging the problem of CO₂-pollution and subsequent global warming. Moreover, they are willing to put their words into actions since they have launched an energy policy plan in which significant cuts on CO₂-emissions are proposed. Needless to say, that this isn’t a done deal, because Obama still has to overcome the resistance from the Republican party and the lobby from the energy sector. For here it suffices to say that Obama’s intention to change the status quo is already a positive step forward. How much imminent action is needed, became clear at the end of September, when the IPCC presented a new report on climate change. U.S. Secretary of State, John Kerry  summed up the conclusions of the report: “Boil down the IPCC report and here’s what you find: climate change is real, it’s happening now, human beings are the cause of this transformation, and only action by human beings can save the world from its worst impacts”. Not much to  add here.

 

 

 

 

 

 

 

 

 

I have linked this news to an article by Foden et al, that was published earlier this year and that reports on a comprehensive study of the world’s amphibians, birds and corals and their sensitivity to climate change. The study has received a considerable amount of attention from mainstream media, mainly because of its implications for conservation of these taxons and the fact that studies on the effects of climate change receive much attention these days. My focus in this post is on the results for the amphibians. Studying the impact of climate change on biodiversity in general is not something new, but the approach that was chosen in this study, certainly is. Previous studies have used bioclimatic envelope models to predict this impact. The variables that make up such a model are the current distribution of a species, the climatic variation within their range/distribution and the projected climatic change. Combining these variables gives an estimate of the area of the range that remains as suitable habitat due to climate change, the ‘climate envelope’.

The article of Thomas et al. (2004) is a much-cited example of such as study and predicted that 15–37% of species could be ‘committed to extinction’ due to climate change by 2050. Besides the variables mentioned above that are used to develop a bioclimatic envelope model, these researchers also took into account a biological parameter, namely whether a species was able to migrate into the future ‘climate envelope’. They used an all or nothing approach to this dispersal matter: or a species experienced no limits to dispersal or a species was unable to disperse at all. This depended on the dispersal abilities of the species and/or its isolation.

Foden et al. mention in their article that previous studies “ largely ignore biological differences” and to improve the predictive capacity of their models they used more biological parameters. The need to include these parameters has been shown by a number of studies that conclude that climate change-induced-stresses are mediated by species’ biological traits. Therefore they used a framework with three dimensions of vulnerability to climate change, that includes various biological traits: sensitivity, the tolerance of a species in situ; exposure, meaning the change in environment, and adaptive capacity, referring to dispersal ability or micro-evolutionary capacity.

 

 

 

 

 

The parameters are made up by species-specific traits like micro-evolutionary capacity, tolerance of a species or dispersal adaptability that are not easily quantified. Therefore they pose a methodological problem of how to come to numbers that can be put into a model. They have used an approach in which they tried to unlock all the information there is on these traits by using expert knowledge, workshops and a survey of existing literature. To give an indication of the amount of work involved: more than 90 biological, ecological, physiological and environmental were identified that likely influence climate change sensitivity and adaptive capacity. Then these had to be elaborated for each species, with a staggering total of 6204 species. These traits were brought together into five trait sets for the sensitivity dimension and two traits sets for adaptive capacity. With all this information put together they could identify the species most vulnerable to climate change, the ones that qualify as highly sensitive, highly exposed and of lowest adaptive capacity. The researchers also ascribed species to three other categories; ‘ potential adapters’, i.e. species that are highly exposed and sensitive but have the ability to adapt to these changing circumstances; ‘ potential persisters’, species that have low adaptive capacity and are highly exposed but might survive in situ because they are not so sensitive to climate change and species of ‘high latent risk’, the ones that are not exposed to climate change now, but because of low adaptive capacity and high sensitivity would be vulnerable if climate change would ever come to their doorstep as well.

The results indicate that 1,368–2,740 amphibian species (22–44%) can be ascribed to the category ‘most vulnerable to climate change’. As can be expected, not all trait data were available for each species. The upper and lower boundaries of the estimate are determined by the optimistic or pessimistic assumptions for missing trait data. A subsequent analysis was done to point out the regions on the globe where a high concentration of these highly vulnerable species occurs.  The Amazon emerges as a region of high climate change vulnerability for amphibians, also characterized by large overall number of species. In addition to the Amazon, high proportions of highly climate change vulnerable species were found to occur in Mesoamerica, the northern Andes, North Africa, eastern Russia to Mongolia, the Himalayas and the western Arabian Peninsula.

Species with relatively low sensitivity and/or higher adaptive capacity, which may help them to avoid or adjust to climate change impacts, and that are indicated as ‘potential adapters’ and/or ‘potential persisters’, are mainly found in southern Asia, western North America and parts of Europe. They account for 23-59% of total amphibian species, in absolute numbers 822–1,988 species. The ‘high latent risk species’, that should be monitored carefully since they could rapidly become in danger if climate change would worsen beyond the current predictions, are primarily found in the Congo basin, eastern North and South America, southern Africa and Australia.

To see how many of those amphibian species are already under threat, because of mainly other agents of decline, the IUCN Red List was used.  The number of species that are both highly climate change vulnerable and already listed as ‘threatened’ added up to 670–933 (11–15%). Species that are both highly climate change vulnerable and threatened and the regions in which they are concentrated deserve particular conservation attention. His attention should be directed at both mitigating current threats and planning for future climate change adaptation interventions. High concentration areas for highly climate change vulnerable and threatened amphibians include parts of the northern Andes and Mesoamerica.

Species that are highly climate change vulnerable but are not currently threatened potentially represent new priorities for conservation. These include 698–1,807 (11–29%) amphibian species and represent 51–66% of all highly climate change vulnerable amphibians. Those species are concentrated in the Amazon basin, Eurasia, southern North America to Mesoamerica.

These results provide the first global maps of climate change vulnerability for the entire taxonomic group of the amphibians. And in comparison to previous studies, the input for the models include significant amounts of biological and environmental information that leads, probably, to a better predictive ability of the models. This information is seen by the authors “as vital for large-scale conservation planning exercises, and highlights where more detailed assessment is needed. The approach we describe, as well as the priorities identified through this study, will strengthen global strategies to reduce climate change impacts”.

At least one person doesn’t agree with the remarks by the authors that this information is vital for conservation planning. Around the time of the appearance of this article the Guardian posted an opinion letter by Dr. James Watson, adjunct professor at the University of Queensland and involved in several climate change specialist groups. He responds in his letter to the growing amount of literature that investigates how and where climatic change will make species more vulnerable. He points to a fundamental problem with these studies, namely that the conservation scientists carrying out these studies, have been asking the wrong questions.  Watson claims that “understanding the ecology of species and their likely responses to climate change is helpful, but understanding how humans are going to be affected by climate and what this impact will be on those species is far more important”. And that it would be better for scientists to focus on understanding how human modifications will affect other species, because the impact of these human actions will be larger than the impact of climate change alone.

I am not quite sure how I feel about this: on the one hand it seems very valuable that better models are being developed to ensure a more accurate prediction of climate change on different species. The more we learn about the precise effects that climate change can have, the more we might be able to counteract those effects.  On the other hand, Watson concludes with a remark that I can sympathize with as well, namely that “failure to predict likely human adaptations to climate change commits us to a future of reactive, emergency responses likely to be wholly inadequate to the demands of the coming century”. Especially the part about ‘reactive, emergency responses’ seems to be fitting, because I feel that a lot of time has already passed by before we could even find the connection between climate change and amphibian declines and we might not have too much time left to figure out how they exactly will respond to climate change. Then it might be better to take a very pragmatic approach and look at the dominant force in nature conservation and that is human behavior.