Jennifer Sunday

Temperature fundamentally shapes ectotherm biology, from continuous changes in sublethal performance to acute functional failure at upper thermal limits. Sublethal performance is commonly characterized using thermal performance curves (TPCs), which describe continuous changes in performance across temperatures, whereas acute heat tolerance is often quantified by the critical thermal maximum (CT _max ), the temperature marking organism-level functional failure. Whether these dimensions of thermal physiology vary independently or covary as components of a coordinated warm-end thermal phenotype remains unclear. Synthesizing data from more than 100 ectotherm species, we tested how CT _max scales with two key warm-end TPC traits: the thermal optimum (T _opt ) and the upper limit of performance (TPC _max ). Across diverse taxa, both T _opt and TPC _max scaled approximately 1:1 with CT _max , and these relationships were broadly consistent across the biological, experimental, and environmental contexts represented in our dataset. Although both slopes were individually consistent with 1:1 scaling, when T _opt and TPC _max were compared directly, TPC _max increased more steeply with CT _max than did T _opt , such that the declining portion of the TPC widened as CT _max increased. Species with greater acute heat tolerance therefore tended to retain positive performance across a broader range of supra-optimal temperatures before reaching the upper performance limit. Together, these relationships show that sublethal warm-end performance and acute heat tolerance covary systematically across species, supporting their interpretation as broadly coordinated components of the thermal phenotype rather than independent axes of thermal biology. Significance: As climate warming pushes temperatures beyond the conditions species have previously experienced, predicting ectotherm vulnerability requires understanding how measures of thermal biology relate. Heat tolerance measures the maximum temperature organisms can survive, whereas temperature-dependent performance measures how they function across temperatures. Whether these measures capture related aspects of thermal biology has remained unclear. We synthesized thermal trait data from more than 100 ectotherm species to test how heat tolerance relates to temperature-dependent performance. We show that species with higher heat tolerance also reach peak performance and maintain function at higher temperatures, with these traits scaling approximately 1:1 across diverse contexts. This relationship links two major approaches to thermal biology and provides a quantitative basis for understanding ectotherm responses to warming.

Thermal performance curves are widely used to understand how ectotherms respond to anthropogenic climate change, yet comparable data remain fragmented for fishes despite their predicted sensitivity to warming. Here we introduce FishTherm, a compilation of 457 thermal responses from 107 wild fish species, spanning diverse performance metrics and temperatures. With this dataset, we estimated thermal optima, performance breadth, tolerance breadth, and activation energies, and tested how these thermal traits vary geographically, across latitude and habitat, and by type and functional context of performance. Thermal optima increase toward lower latitudes and warmer waters, consistent with established biogeographic patterns. We also found that responses measured at lower levels of biological organization exhibit higher thermal optima than population-level responses, supporting complexity constraints on thermal performance curves. Activation energies broadly matched predictions from the Metabolic Theory of Ecology, and we further found systematic variation of lower values in negatively-motivated responses, and associated with narrower thermal performance breadths, in line with theory. Our results provide supporting evidence for several unifying principles that advance our understanding of constraints and variation in thermal performance. FishTherm is a new resource for comparative thermal ecology and for improving our understanding of fish vulnerability under climate warming.

The latitudinal diversity gradient of increasing species richness toward the tropics is Earth's most ubiquitous and ancient macroecological pattern, but may not be immune to modern anthropogenic change. Urbanization represents a particularly severe and globally-distributed ecological change; while urbanization generally reduces local diversity, whether it affects large-scale diversity patterns is unclear. Analyzing global databases including >10,000 bird species on five continents, we show that the avian latitudinal diversity gradient is 3x weaker in urban than natural areas. Urbanization reduces diversity across latitudes, but tropical cities lose disproportionately more species, partly because tropical bird assemblages contain more specialists and specialists are particularly excluded by urbanization. Our results show that urbanization is disrupting macroecological patterns, and suggest that specialization mediates both latitudinal diversity gradients and urbanization impacts.

Open science skills are increasingly important for a career in ecology and evolutionary biology (EEB) as efforts to make data and analyses publicly available continue to become more commonplace. While learning core concepts in EEB, students are also expected to gain skills in conducting open science to prepare for future careers. Core open science skills like programming, data sharing, and practices that promote reproducibility can be taught to undergraduate students alongside core concepts in EEB. Yet, these skills are not always taught in biology undergraduate programs, and a major challenge in developing open science skills and learning EEB concepts simultaneously is the high cognitive load associated with learning multiple disparate concepts at the same time. One solution is to provide students with easily digestible, scaffolded, pre‐formatted code in the form of vignettes and interactive tutorials. Here, we present six open source teaching tutorials for undergraduate students in EEB. These tutorials teach fundamental ecological concepts, data literacy, programming (using R software), and analysis skills using publicly available datasets while introducing students to open science concepts and tools. Spanning a variety of EEB topics and skill levels, these tutorials serve as examples and resources for educators to integrate open science tools, programming, and data literacy into teaching EEB at the undergraduate level.

Ecological and evolutionary theories have proposed that species traits should be important in mediating species responses to contemporary climate change; yet, empirical evidence has so far provided mixed evidence for the role of behavioral, life history, or ecological characteristics in facilitating or hindering species range shifts. As such, the utility of trait‐based approaches to predict species redistribution under climate change has been called into question. We develop the perspective, supported by evidence, that trait variation, if used carefully can have high potential utility, but that past analyses have in many cases failed to identify an explanatory value for traits by not fully embracing the complexity of species range shifts. First, we discuss the relevant theory linking species traits to range shift processes at the leading (expansion) and trailing (contraction) edges of species distributions and highlight the need to clarify the mechanistic basis of trait‐based approaches. Second, we provide a brief overview of range shift–trait studies and identify new opportunities for trait integration that consider range‐specific processes and intraspecific variability. Third, we explore the circumstances under which environmental and biotic context dependencies are likely to affect our ability to identify the contribution of species traits to range shift processes. Finally, we propose that revealing the role of traits in shaping species redistribution may likely require accounting for methodological variation arising from the range shift estimation process as well as addressing existing functional, geographical, and phylogenetic biases. We provide a series of considerations for more effectively integrating traits as well as extrinsic and methodological factors into species redistribution research. Together, these analytical approaches promise stronger mechanistic and predictive understanding that can help society mitigate and adapt to the effects of climate change on biodiversity.

The effect of climate warming on community composition is expected to be contingent oncompetitiveoutcomes, yet approaches to projecting ecological outcomes often rely on measures of density‐independent performance across temperatures. Recent theory suggests that the temperature response of competitive ability differs in shape from that of population growth rate. Here, we test this hypothesis empirically and find thermal performance curves of competitive ability in aquatic microorganisms to be systematically left‐shifted and flatter compared to those of exponential growth rate. The minimum resource requirement for growth,R*—an inverse indicator of competitive ability—changes with temperature following a U‐shaped pattern in all four species tested, contrasting from their left‐skewed density‐independent growth rate thermal performance curves. Our results provide new evidence that exploitative competitive success is highest at temperatures that are sub‐optimal for growth, suggesting performance estimates of density‐independent variables might underpredict performance in cooler competitive environments.

Understanding how temperature determines the distribution of life is necessary to assess species’ sensitivities to contemporary climate change. Here, we test the importance of temperature in limiting the geographic ranges of ectotherms by comparing the temperatures and areas that species occupy to the temperatures and areas species could potentially occupy on the basis of their physiological thermal tolerances. We find that marine species across all latitudes and terrestrial species from the tropics occupy temperatures that closely match their thermal tolerances. However, terrestrial species from temperate and polar latitudes are absent from warm, thermally tolerable areas that they could potentially occupy beyond their equatorward range limits, indicating that extreme temperature is often not the factor limiting their distributions at lower latitudes. This matches predictions from the hypothesis that adaptation to cold environments that facilitates survival in temperate and polar regions is associated with a performance trade-off that reduces species’ abilities to contend in the tropics, possibly due to biotic exclusion. Our findings predict more direct responses to climate warming of marine ranges and cool range edges of terrestrial species.

Understanding how temperature determines the distribution of life is necessary to assess species’ sensitivities to contemporary climate change. Here we test the importance of temperature in limiting geographic ranges of ectotherms by comparing temperatures across occupied ranges to those species could potentially occupy based on their physiological thermal tolerances. Whereas marine and tropical terrestrial species occupy temperatures that closely match their thermal tolerances, high-latitude terrestrial species under-occupy warm temperatures and are absent from thermally tolerable areas towards the equator. This suggests that on land, temperature less often limits the equatorward range edge of temperate species, supporting the hypothesis that their historic expansion ‘out of the tropics’ was associated with tropical biotic exclusion. Our findings predict more direct responses to climate warming of marine ranges and cool range edges of terrestrial species.

A major challenge in ecology and evolution is to disentangle the mechanisms driving broad-scale variation in biological traits such as body size, colour, thermal physiology traits and behaviour. Climate has long been thought to drive trait evolution and abiotic filtering of trait variation in ectotherms because their thermal performance and fitness are closely related to environmental conditions. However, previous studies investigating climatic variables associated with trait variation have lacked a mechanistic description of the underpinning processes. Here, we use a mechanistic model to predict how climate affects thermal performance of ectotherms and thereby the direction and strength of the effect of selection on different functional traits. We show that climate drives macro-evolutionary patterns in body size, cold tolerance and preferred body temperatures among lizards, and that trait variation is more constrained in regions where selection is predicted to be stronger. These findings provide a mechanistic explanation for observations on how climate drives trait variation in ectotherms through its effect on thermal performance. By connecting physical, physiological and macro-evolutionary principles, the model and results provide an integrative, mechanistic framework for predicting organismal responses to present climates and climate change.

The California Current Marine Ecosystem is a highly productive system that exhibits strong natural variability and vulnerability to anthropogenic climate trends. Relating projections of ocean change to biological sensitivities requires detailed synthesis of experimental results. Here, we combine measured biological sensitivities with high‐resolution climate projections of key variables (temperature, oxygen, and pCO₂) to identify the direction, magnitude, and spatial distribution of organism‐scale vulnerabilities to multiple axes of projected ocean change. Among 12 selected species of cultural and economic importance, we find that all are sensitive to projected changes in ocean conditions through responses that affect individual performance or population processes. Response indices were largest in the northern region and inner shelf. While performance traits generally increased with projected changes, fitness traits generally decreased, indicating that concurrent stresses can lead to fitness loss. For two species, combining sensitivities to temperature and oxygen changes through the Metabolic Index shows how aerobic habitat availability could be compressed under future conditions. Our results suggest substantial and specific ecological susceptibility in the next 80 years, including potential regional loss of canopy‐forming kelp, changes in nearshore food webs caused by declining rates of survival among red urchins, Dungeness crab, and razor clams, and loss of aerobic habitat for anchovy and pink shrimp. We also highlight fillable gaps in knowledge, including specific physiological responses to stressors, variation in responses across life stages, and responses to multistressor combinations. These findings strengthen the case for filling information gaps with experiments focused on fitness‐related responses and those that can be used to parameterize integrative physiological models, and suggest that the CCME is susceptible to substantial changes to ecosystem structure and function within this century.