Evidence-base conservation of mammals needs a better understanding of responses to threats across the entire life cycle

The following is a post from Maria Paniw.

In order to provide robust assessments of the fate of natural populations under increasing human pressures, we need a good understanding of some key mechanisms that determine the state of a population at any given time and place. Undoubtedly, age- or stage-specific survival and reproduction and how these demographic rates respond to threats are the most important mechanisms responsible for observed and projected changes in the state of a population. But what do we know about demographic responses to global threats? And perhaps more importantly, do we need to understand the full spectrum of such responses to project population fates; or can we base our projections on presumed global-change impacts on single demographic rates such as survival?

Our recent study published in the Journal of Animal Ecology [https://doi.org/10.1111/1365-2656.13467] reviewed literature that investigated how various measures of climate affect different demographic rates across the life cycle of a species. We found that researchers have assessed (and reported) such context-dependency in climate effects for only 87 mammal species, < 1 % of all mammals; and worse yet, we know very little about climate effects on multiple demographic rates in the most climate-vulnerable regions of the globe. A better understanding of such effects is essential though, because our review revealed that context-dependent responses (where climate effects can be positive or negative depending on the life-cycle stage or the general ecologic context) rule most populations. Indeed, studies that scaled the demographic effects of climate to population-level processes (changes in abundance or growth rates) showed that the latter are determined by complex interactions of climate and demography.  It is worrisome then that most assessments of species vulnerability to climate change do not consider such complex climate-demography interactions, despite a potentially large impacts of these interactions on our inference of population changes.

Figure caption: Three of the very few mammal species for which we have a robust understanding of the demographic mechanisms driving population responses to climate change. Our recent review shows that for > 99 % of mammals, we do not understand these mechanisms. Photo credit: Arpat Ozgul.

We advocate for a prioritization of more holistic approaches and data collection (or integration) efforts to understand the mechanism that drive population persistence. This is critical for evidence-based conservation across many taxa, not just mammals. It is here where open-source repositories such as COMADRE are key because they allow researchers to store stage-structured demographic information from single studies in a comparable format that can be used to forecast global population responses to environmental change using underlying demographic mechanisms across a wide range of organisms.