Striving for population-level conservation: integrating physiology across the biological hierarchy

Abstract

The field of conservation physiology strives to achieve conservation goals by revealing physiological mechanisms that drive population declines in the face of human-induced rapid environmental change (HIREC) and has informed many successful conservation actions. However, many studies still struggle to explicitly link individual physiological measures to impacts across the biological hierarchy (to population and ecosystem levels) and instead rely on a 'black box' of assumptions to scale up results for conservation implications. Here, we highlight some examples of studies that were successful in scaling beyond the individual level, including two case studies of well-researched species, and using other studies we highlight challenges and future opportunities to increase the impact of research by scaling up the biological hierarchy. We first examine studies that use individual physiological measures to scale up to population-level impacts and discuss several emerging fields that have made significant steps toward addressing the gap between individual-based and demographic studies, such as macrophysiology and landscape physiology. Next, we examine how future studies can scale from population or species-level to community- and ecosystem-level impacts and discuss avenues of research that can lead to conservation implications at the ecosystem level, such as abiotic gradients and interspecific interactions. In the process, we review methods that researchers can use to make links across the biological hierarchy, including crossing disciplinary boundaries, collaboration and data sharing, spatial modelling and incorporating multiple markers (e.g. physiological, behavioural or demographic) into their research. We recommend future studies incorporating tools that consider the diversity of 'landscapes' experienced by animals at higher levels of the biological hierarchy, will make more effective contributions to conservation and management decisions.

Keywords: Biological Hierarchy; conservation; physiology; scaling up.

Figure 1

A conceptual diagram of the complexities of scaling up the biological hierarchy from individuals through ecosystems. A major aim of conservation physiology is to provide mechanistic links between physiological responses to human-induced environmental change (underlying green hexagon; key inset, bottom right) and population declines, and further to the ecosystem level response. Each biological level in the hierarchy (far left) occurs at increasingly broader spatial and temporal scales (blue boxes; Spatiotemporal Landscapes) and are linked to each other through various biological processes (examples given in grey arrows; Linking Processes). The green hexagon represents major human-induced environmental stressors that are known, or are expected, to influence these processes. For example, if habitat quality is degraded such that temperature extremes are common throughout the habitat, then individuals may shift patterns of behavioural thermoregulation by choosing new habitats that optimize their performance locally. Scaling up to the population level, though, requires information about the availability of preferred habitat and how that might be altered, for example by intraspecific interactions and how this affects reproductive output (i.e. fitness). As we strive to understand how individual-level responses to altered environments scale up to species, integration of not just how animals use the fine scale habitat but how they move throughout the entire landscape (e.g. movement ecology) is critical. Each step-up in the hierarchy results in a more complex abiotic and biotic landscape that influences the processes guiding interactions among individuals and species. For example, at the community level, the landscape represents layers of individual-level habitat choice that are dictated by physiological state, interactions among conspecifics and interspecific (e.g. predator-prey) dynamics. Finally, at the ecosystem level, we expect the entire suite of interactions to be reflected in the way that an ecosystem functions—or does not function—depending on the scope of environmental change. Finding these links and scaling up will require collaboration and integration across disciplines (examples given in italics, far right).