Untapped potential of physiology, behaviour and immune markers to predict range dynamics and marginality

Abstract

Linking environmental conditions to the modulators of individual fitness is necessary to predict long-term population dynamics, viability, and resilience. Functional physiological, behavioral, and reproductive markers can provide this mechanistic insight into how individuals perceive physiological, psychological, chemical, and physical environmental challenges through physiological and behavioral responses that are fitness proxies. We propose a Functional Marginality framework where relative changes in allostatic load, reproductive health, and behavior can be scaled up to evidence and establish causation of macroecological processes such as local extirpation, colonization, population dynamics, and range dynamics. To fully exploit functional traits, we need to move beyond single biomarker studies to develop an integrative approach that models the interactions between extrinsic challenges, physiological, and behavioral pathways and their modulators. In addition to providing mechanistic markers of range dynamics, this approach can also serve as a valuable conservation tool for evaluating individual- and population-level health, predicting responses to future environmental change and measuring the impact of interventions. We highlight specific studies that have used complementary biomarkers to link extrinsic challenges to population performance. These frameworks of integrated biomarkers have untapped potential to identify causes of decline, predict future changes, and mitigate against future biodiversity loss.

Keywords: conservation; endocrinology; glucocorticoids; gut health; macrophysiology; microbiome; social networks; thyroid hormone.

FIGURE 1

A conceptual diagram showing the different biomarkers available that can be integrated into studies using the footprints and pathway approach

FIGURE 2

Conceptual framework for testing alternative hypotheses for different stressors. +/− indicates potential direction of change. ++/−− indicators are expected to show large magnitude responses. N.C. indicates no consistent/predictable response

FIGURE 3

Conceptual diagram of the Functional Marginality Framework. (a) Viable populations are determined by good functional condition leading to sustainable growth rates, range limits are determined by an increased burden of negative functional traits relative to positive ones. (b) Range shifts will be associated with improving functional condition on the expanding edge and declining condition on the retreating edge. (c) Habitat degradation leads to a net decline in functional condition (balance of positive indicators and negative allostatic load) across occupied habitat resulting in more sink populations and fewer source populations. (d) Functional condition can be tracked over time by repeatedly measuring positive and negative functional traits, and will exhibit characteristic profiles during periods of threat and recovery