Linking environmental conditions to the modulators of individual fitness
is necessary to predict long-term population viability and resilience.
Behavioural and physiological biomarkers can provide this mechanistic
insight into how individuals perceive and respond to environmental
challenges through primary physiological responses, secondary downstream
responses and tertiary whole organism responses. To fully exploit
biomarkers, we need to move beyond single biomarker studies to develop
an integrative approach that models the interactions between extrinsic
challenges, physiological and behavioural pathways and their modulators.
Here we introduce two frameworks for using multiple integrated
biomarkers to establish changes in functional condition. The Functional
Marginality Hypotheses proposes that relative changes in allostatic
load, reproductive health and behaviour can evidence and establish
causation driving macroecological processes such as local extirpation,
colonisation, population dynamics and range change. The Functional
Recovery Hypothesis proposes that a similar approach can 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. This framework of integrated biomarkers has
untapped potential to identify causes of decline, predict future changes
and mitigate against future biodiversity loss.