Obligate versus rich patch opportunism: evolution and endocrine mechanisms.

Opportunistic breeding has been hypothesized to evolve in response to rare or unpredictable resource pulses. In this traditional view of opportunism, individuals invest heavily in reproduction whenever conditions are permissive for breeding, perhaps at the expense of investment in survival. We term this strategy 'obligate opportunism' (OBO). We also present an additional strategy that could account for the evolution of opportunism. High mobility may allow individuals to move between rich patches of resources that are spatially or temporally unpredictable, reducing exposure to food scarcity and taking advantage of breeding opportunities. This strategy, which we term 'rich patch exploiter' (RPE), predicts that investment in survival-enhancing processes may occur at the expense of reproduction despite high resource availability. We review examples to determine which opportunists better match predictions from the OBO strategy or the RPE strategy and then review endocrine profiles in the context of the two strategies.