The many responses to climate change: How to predict when populations will be affected
From a conservation management perspective, population responses are the most relevant aspect of research into the ecological impacts of climate change on organisms. Yet, much of the research focuses on phenological or physiological responses, while assuming further impacts on demographic or population dynamics. More recently, studies have shown that although phenological and physiological responses result in population changes for some species, this is not always the case. A better understanding of how different responses relate to one another, and how they affect key measures of population health will be vital for predicting species sensitivities to climate change. In this talk, we develop a conceptual framework that can be used to better understand how these different climate responses are related.
We categorise responses into three levels: trait (e.g. phenology), demographic (e.g. survival), and population level (e.g. population size). We describe four possible mechanisms by which changes at the trait level might fail to impact the population level: 1) a change in trait has no impact on demography, 2) a change in demography has no impact on population dynamics, 3) multiple pathways counteract higher-level responses and, 4) multiple climate variables counteract higher level responses. We identified hypotheses based on life-history and ecological characteristics that might make a species more likely to experience any of these mechanisms. For example, a change in survival is less likely to result in an impact at the population level for short-lived species. The ability to generalise sensitivity to climate solely from life-history characteristics is particularly important for data-poor species. The production of testable hypotheses based on species characteristics will provide an important opportunity for future research to better understand in which species we can expect effects of climate on traits and demographic rates to have consequences for population dynamics.