A predictive timeline of wildlife population collapse

Abstract

Contemporary rates of biodiversity decline emphasize the need for reliable ecological forecasting, but current methods vary in their ability to predict the declines of real-world populations. Acknowledging that stressors effects start at the individual level, and that it is the sum of these individual-level effects that drives populations to collapse, shifts the focus of predictive ecology away from using predominantly abundance data. Doing so opens new opportunities to develop predictive frameworks that utilize increasingly available multi-dimensional data, which have previously been overlooked for ecological forecasting. Here, we propose that stressed populations will exhibit a predictable sequence of observable changes through time: changes in individuals' behaviour will occur as the first sign of increasing stress, followed by changes in fitness related morphological traits, shifts in the dynamics (e.g. birth rates) of populations, and finally abundance declines. We discuss how monitoring the sequential appearance of these signals may allow us to discern whether a population is increasingly at risk of collapse, or is adapting in the face of environmental change, providing a conceptual framework to develop new forecasting methods which combine multidimensional (e.g. behaviour, morphology, life history and abundance) data.

Range contractions and reduced body mass predicted for endemic skinks of the Cameroon Volcanic Line with future warming

“…Altogether, the loss of larger sizes introduces the risk of eroding intraspecific morphological, behavioural and physiological variation necessary for buffering against climatic anomalies (Anderson et al, 2022;Buckley et al, 2013;Cerini et al, 2023;Domínguez-Godoy et al, 2020;Muñoz et al, 2022). Therefore, while our results demonstrate lizard persistence in some areas following climatic warming, a smaller body mass might influence interactions with local environments and species.…”

“…Declines in body size or mass can indicate the failure of species responses in coping with changing environments for maintaining metabolic and reproductive functions (Cerini et al, 2023;Rubalcaba & Olalla-Tárraga, 2020). Despite their initial buffering against climatic warming, reduced body sizes may result in greater vulnerabilities to extreme weather events (Gardner et al, 2011).…”

“…In squamate reptiles, many tropical montane species are endemic to small geographical regions, with future environmental change potentially rendering them extinct (Sinervo et al, 2010; Wiens et al, 2019). Additionally, for montane lizards varying in phenotypic traits along elevational gradients, especially body size, impacts prior to species extirpation can include the erosion of such variation (Cerini et al, 2023; Gardner et al, 2011). Understanding the distribution extents and trait diversity of range‐limited montane reptiles, as well as how climate change could affect these, will be instrumental in informing conservation efforts (Muñoz et al, 2022; Pacifici et al, 2015; Wiens et al, 2019).…”

Anthropogenic change decouples a freshwater predator’s density feedback

“…However, harvesting more older individuals may now have little effect on the growth of younger individuals given that the density feedback no longer exists. Sudden shifts in the dynamics of key species can also be indicative of broader population- or ecosystem-level changes that may need to be incorporated into management efforts 59 , 60 . Continuing with Lake Erie as an example, the disappearance of the density feedback is itself indicative of broader changes in the environment and prey community, including potential changes in walleye movements and their impacts on the food web (e.g., feeding elsewhere and supplementing their diet with an invasive species).…”

Meta‐analysis reveals impacts of disturbance on reptile and amphibian body condition

“…Individual-scale responses are valuable because they can consider a species' ability to respond behaviourally, morphologically and physiologically to disturbance (Doherty et al, 2022;Gardner et al, 2007;Pirotta et al, 2018;Sergio et al, 2018;Sih et al, 2011). Conceptual frameworks have linked individual responses to subsequent changes in population dynamics and encourage the use of individual metrics to complement population and community metrics (Berger-Tal et al, 2011;Cerini et al, 2023;Frid & Dill, 2002). There has been research assessing broad trends of disturbance impacts for some individual metrics, including behavioural responses such as avoidance and vigilance, and physiological responses such as glucocorticoid concentrations, heart rate, call rate and reproductive rate (Bateman & Fleming, 2017;Coetzee & Chown, 2016;Duquette et al, 2021;Kaisin et al, 2021).…”