Biology subjects

Robey, A. J.

Publications and source records attributed to Robey, A. J..

6 recordsLinked to original sources

bioRxiv2026

Bridging physiological responses to population outcomes under variable thermal stress

Embedding thermal tolerance metrics into population dynamics offers a promising toolkit for understanding the impacts of stressful heat events, but the time-dependence of thermal stress rarely factors into such assessments. Within organisms, heat causes damage that alternatively accumulates under stressful temperatures and is repaired under permissive ones. While risk under exclusively stressful temperatures is well characterized by thermal death time models, resilience to fluctuating temperatures is less clear. Understanding how this damage accumulation within organisms scales up to affect population thermal tolerance is a necessary step for predicting population dynamics and extinction risk. We address this gap by embedding a model of organismal stress and recovery into population dynamics, yielding time-dependent thermal performance curves of population growth rates. By parameterizing this novel framework with existing data from Drosophila melanogaster, we explore how integrating thermal stress across biological scales shapes the consequences of organismal stress on population outcomes under realistic thermal fluctuations.

ecology↗

bioRxiv2026

Temperature-dependent performance scales with maximum heat tolerance across ectotherms

Projecting species responses to changing temperatures remains a major challenge in ecology. Central to this effort is harnessing our understanding of species thermal physiological traits, which underlie ectotherm fitness. These traits are typically characterized by describing performance across temperatures (thermal performance curve, TPC), and/or tolerance limits, which capture endpoints of biological failure. Despite their importance, we still lack an understanding of the functional relationship between these traits, limiting our ability to integrate them into comprehensive vulnerability assessments. Using a synthesized dataset of >100 ectotherms, we tested how heat tolerance (CTmax) relates to key TPC traits: thermal optima, thermal maxima, and the supra-optimal range of temperatures where performance is positive. Across taxa, TPC traits were positively related to CTmax, demonstrating a link between heat tolerance and temperature-dependent performance at sub-critical temperatures. While acute locomotor performance scaled proportionally with CTmax, metabolic processes and sustained locomotion scaled sub-proportionally, suggesting decoupling of CTmax and performance among high-CTmax species. This suggests that using CTmax as a comparative metric may overestimate thermal safety margins for metabolic processes critical to growth. Our results indicate that while CTmax and TPCs reflect shared underlying constraints--particularly in acute neuro-muscular traits--their relationship is dependent on timescale and the TPC response trait. Our findings connect our understanding of the processes that maintain performance over thermal gradients with those that cause performance to fail, improving our ability to project species persistence in a warming world. SignificanceClimate warming is increasingly reshaping the thermal environments that govern species persistence worldwide. Predicting vulnerability requires integrating multiple aspects of thermal biology, yet relationships among widely used thermal traits remain poorly understood. By synthesizing data from more than 100 ectotherm species, we quantify links between acute heat tolerance and traits describing sustained biological function across temperatures. We show that performance at relatively benign temperatures and performance at thermal extremes are coupled, but this coupling is strongly process and timescale dependent, with close correspondence for short term locomotion but weaker coupling for metabolic processes. Our results link the processes that maintain performance across temperatures with those that cause failure, fundamentally advancing our projections of species performance in a warming world.

ecology↗

bioRxiv2026

Extreme Heat as the New Normal: A Methodological Roadmap for Behavior, Physiology, and Species Distributions

A defining feature of climate change is the increasing frequency, intensity, and severity of extreme weather events. Among them, extreme heat is recognized as a critical driver of ecological and evolutionary change. Intense heat episodes can exceed physiological limits, alter animal movement, restructure geographic ranges, and increase extinction risk more than gradual changes to mean temperatures. Yet links between extreme heat events and organismal biology remain limited, in part because definitions and metrics are not standardized, and user-friendly workflows and guides are lacking for many biologists. We present a methodological roadmap, with reproducible code, for integrating extreme heat into studies of behavior, physiology, biophysical ecology, species distribution models (SDMs), and population dynamics. First, we provide standardized computational approaches to define and quantify extreme heat. Second, we fit species distribution models for California quail (Callipepla californica) that include an extreme heat metric and showcase improved predictions of habitat suitability, particularly at range edges. Third, we compute biophysical simulations to quantify exposure to thermal stress in Sleepy lizards (Tiliqua rugosa) across distinct macro- and microclimates. Finally, accounting for temporal autocorrelation in temperature profiles in population simulation models, we show that clustered heat extremes--missed by averages--can increase the risk of population collapse. As extreme heat events become more common, incorporating their dynamics is essential for understanding ecological and evolutionary change, designing experiments across species geographic ranges, and supporting conservation in a rapidly warming world. Together, these case studies illustrate a reproducible, organism-informed roadmap to integrate extreme heat into predictions of ecological impacts and inference across levels of biological organization under ongoing climate change.

ecology↗

bioRxiv2025

Temporal autocorrelation increases temperature-driven extinction risk by clustering stressful conditions

Environments are becoming increasingly autocorrelated as global climate change progresses, leading to the intensification of deadly events like heatwaves and droughts. Theory shows that temporally-autocorrelated environments generate a higher risk of population extinction; however, little work has been done to incorporate temporal autocorrelation into thermal performance-based projections of extinction risk. Here, we pair stochastic simulation models of population dynamics with systematically generated temperature time series to determine when higher levels of autocorrelation generate greater extinction risk. We show that autocor-relation is a significant mediator of risk under stressful temperature regimes, with important ramifications for forecasting temperature-driven extinctions in ectothermic organisms. We validate our predictions with a factorial experiment in microcosms of the single-celled protist Paramecium caudatum. Taken together, these results provide the foundation for predicting which species and environments face the greatest risks under increasing autocorrelation.

ecology↗

bioRxiv2025

Forecasting Extinction Risk using Thermal Performance Curves and Population Dynamic Modeling

Thermal Performance Curves (TPCs) have become a popular tool for assessing the risks imposed by climate warming and variability on ectotherms. These assessments typically measure the match between an organism or populations TPC and the distribution of its current or future thermal environment as a proxy for extinction risk. However, extinction can occur even when the average thermal environment appears closely matched to a populations TPC because population dynamics can be very sensitive to thermal stress. Here, we develop a new metric for assessing extinction risk using a stochastic model of logistic growth as a foundation. We show that boundaries delimiting persistence and extinction regions of parameter space can be derived for the simple case where the intrinsic (Malthusian) growth rate r varies stochastically and that these boundaries continue to make reliable predictions when temperature T varies stochastically and the Malthusian growth rate is given by a thermal performance curve r (T). We accomplish this by combining theory with stochastic simulations of population dynamics and a laboratory experiment where populations of the single-celled protist Paramecium caudatum were cultured across different temporal means and variances of temperature. The measure of risk that we develop and validate is straightforward and easily applicable to any population for which the thermal performance of Malthusian fitness is known, allowing more rigorous identification of the risks imposed by warmer and more variable temperatures across the globe.

ecology↗

bioRxiv2024

Order matters: Autocorrelation of temperature dictates extinction risk in populations with nonlinear thermal performance

Forecasting the risks caused by climate change often relies upon combining species thermal performance curves with expected statistical distributions of experienced temperatures, without consideration for the order in which those temperatures occur. Such averaging approaches may obscure the disproportionate impacts that extreme events like heatwaves have on fitness and survival. In this study, we instead incorporate thermal performance curves with population dynamical modeling to elucidate the relationship between the sequence of temperature events - driven by temporal autocorrelation - and extinction risk. We show that the permutation of temperatures determines the extent of risk; as thermal regimes grow warmer, more variable, and more autocorrelated, the risk of extinction grows non-linearly and is driven by interactions among our three treatment variables. Given that the mean, variance, and autocorrelation of temperatures are changing in nuanced ways across the globe, understanding these interactions is paramount for forecasting risk. Using empirical data from a benchmarked set of thermal performance curves, we demonstrate how extinction risk is impacted by the change in mean, variance, and autocorrelation, while controlling for seasonal and diurnal cycling. Our results and modeling approach offer new tools for testing the robustness of thermal performance curves and emphasize the importance of looking beyond temporally-blind metrics, like mean population size or average thermal distributions, for forecasting impending extinction risks.

ecology↗