Changes in seasonal climate outpace compensatory density-dependence in eastern brook trout

Ronald D. Bassar, Benjamin H. Letcher, Keith H. Nislow, Andrew R. Whiteley

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Understanding how multiple extrinsic (density-independent) factors and intrinsic (density-dependent) mechanisms influence population dynamics has become increasingly urgent in the face of rapidly changing climates. It is particularly unclear how multiple extrinsic factors with contrasting effects among seasons are related to declines in population numbers and changes in mean body size and whether there is a strong role for density-dependence. The primary goal of this study was to identify the roles of seasonal variation in climate driven environmental direct effects (mean stream flow and temperature) vs. density-dependence on population size and mean body size in eastern brook trout (Salvelinus fontinalis). We use data from a 10-year capture-mark-recapture study of eastern brook trout in four streams in Western Massachusetts, USA to parameterize a discrete-time population projection model. The model integrates matrix modeling techniques used to characterize discrete population structures (age, habitat type, and season) with integral projection models (IPMs) that characterize demographic rates as continuous functions of organismal traits (in this case body size). Using both stochastic and deterministic analyses we show that decreases in population size are due to changes in stream flow and temperature and that these changes are larger than what can be compensated for through density-dependent responses. We also show that the declines are due mostly to increasing mean stream temperatures decreasing the survival of the youngest age class. In contrast, increases in mean body size over the same period are the result of indirect changes in density with a lesser direct role of climate-driven environmental change.

    Original languageEnglish
    Pages (from-to)577-593
    Number of pages17
    JournalGlobal Change Biology
    Volume22
    Issue number2
    DOIs
    StatePublished - Feb 1 2016

    Keywords

    • Climate change
    • Density-dependence
    • Integral projection models
    • Metapopulations
    • Salmonids
    • Size-structure

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