Abstract
Food resources can be a limiting factor and natural and anthropogenic influences that alter the abundance of food resources can affect population performance and persistence. Reproduction in mammals is energetically costly; therefore, understanding how food resources influence reproduction is essential, especially for species of conservation concern.The objectives of this study were to characterize Pacific marten (Martes caurina) diets during the denning period and determine whether diets differed by sex or by phase of the denning period.We used 943 scats to reconstruct sex‐specific diets of martens in the Sierra Nevada mountains during the denning period to evaluate sex‐specific hypotheses of predation patterns. During the lactation phase, females preyed primarily on large‐sized prey (62.5% metabolizeable energy) 5.7‐times more than males. This likely optimized both energy gain and minimized time spent away from dependent young. During the weaning phase, females preyed primarily on medium‐ (90–200 g) and large‐sized prey (87.7% metabolizeable energy). During the predispersal phase, females exhibited a 4.7‐fold increase in use of small‐sized (<50 g) prey during the time kits are learning to hunt.Male overall diet and predation patterns appear to fit an optimal foraging strategy that is influenced primarily by prey profitability and abundance, with males preying primarily on medium‐sized prey, closest to meeting their lower energetic needs. In contrast, females appear to fit the predictions for a central place forager that is also influenced by prey profitability, but also the increased energetic and maternal demands of denning, leading them to use larger prey than males over the phases of the denning period when kits are growing. We hypothesize that switching to smaller prey is related to females assisting their kits in developing hunting skills and experience that may increase their chances of survival once they disperse.
Highlights
The influence of biotic and abiotic factors on population dynamics have long been of fundamental interest to ecologists (Andrewartha & Birch, 1954; Gaillard et al, 2010)
Females appear to fit the predictions for a central place forager that is influenced by prey profitability, and the increased energetic and maternal demands of denning, leading them to use larger prey than males over the phases of the denning period when kits are growing
Differences in the diets of males and females were greatest when compared between each denning phase and least when aggregated across all phases of the denning season
Summary
The influence of biotic and abiotic factors on population dynamics have long been of fundamental interest to ecologists (Andrewartha & Birch, 1954; Gaillard et al, 2010). We investi‐ gated diet composition during the period of the year when female marten diet choices affect both survival and reproduction while male diet choice affects primarily survival While both males and females experience the high energetic costs of foraging (Gilbert et al, 2009), female's have the increased risks of reproductive failure from being away from the den to influence their prey selection. During May, when prey populations are least abundant we predicted that males should capture any prey of any size (exhibit low selectivity), consistent with the predictions of an optimal foraging model and females should capture primarily large‐bodied prey (exhibit high selectivity) due to the combination of higher ener‐ getic needs and the need to reduce overall time away from the den foraging, consistent with the predictions of a central place foraging model. During June and July, when new prey populations emerge, we predicted both males and females should switch to increasing the use of the most abundant, energetically profitable prey sizes (exhibit high selectivity), and proportionately reduce use of the least profitable prey sizes, consistent with the predictions for both optimal and central place foraging models, respectively
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