Abstract
AbstractBalancing energy budgets are thought to be challenging for birds living in arid ecosystems because food supplies are low and unpredictable, and climatic conditions extreme. Thus, to ensure they obtain sufficient energy to fuel daily energetic budgets, birds may need to adjust their diets and become less selective (generalist) as conditions become harsher. To test this hypothesis, we used DNA metabarcoding to characterize both the prey availability (from pitfall traps) and the dietary content (from fecal samples) of several conspecific populations of a semi‐ and arid‐endemic insectivorous bird, the Karoo scrub‐robin (Cercotrichas coryphaeus) across a climatic gradient. Our results showed that Coleoptera, Hymenoptera, Orthoptera, and Lepidoptera were the main prey. When accounting for their presence as available prey, Coleoptera and Hymenoptera were preferred in all regions, whereas robins avoided Orthoptera and Lepidoptera in all but the most arid region. Although the different populations live in regions that vary with regards to productivity and thermoregulatory demands, we found that the dietary niche breadth (Bs) of the three populations was intermediate to low, and did not differ significantly. As a whole, our findings show that regardless of environmental harshness these insectivores have similar dietary niches, suggesting that large dietary plasticity is fundamental for their survival in energy‐depauperated ecosystems.
Highlights
Food acquisition is a basic need of all animals: it provides the en‐ ergy and nutrients required to sustain life in any given environment
The different populations live in regions that vary with regards to productivity and ther‐ moregulatory demands, we found that the dietary niche breadth (Bs) of the three populations was intermediate to low, and did not differ significantly
Our findings show that regardless of environmental harshness these insectivores have similar dietary niches, suggesting that large dietary plasticity is fundamental for their survival in energy‐depauperated ecosystems
Summary
Food acquisition is a basic need of all animals: it provides the en‐ ergy and nutrients required to sustain life in any given environment. The classical Optimal Foraging Theory model (Levins & MacArthur, 1969; MacArthur & Pianka, 1966; Schoener, 1971) predicts that animals seek to maximize energy intake, so as to meet their daily energy costs Both prey availability in the environment and animal physiological status can affect diet variation (e.g., Burgar et al, 2014). In this study we molecularly characterized both the diet and available arthropod prey community (Bohmann et al, 2011; Pompanon et al, 2012) of conspecific populations of the Karoo scrub‐robin (Cercotrichas coryphaeus; hereafter: robin), a ground‐feeding insectivore (Roberts, Hockey, Dean, & Ryan, 2005) This southern African passerine provides a good system with which to explore the avian dietary strategy to ensure adequate energy in‐ take, because its range spans an environmental gradient of primary productivity variation (Figure 1a). In particu‐ lar, we hypothesized that populations resident in the area with the lowest productivity and highest metabolic expansibility (capacity to increase metabolism so as to deal with any energetic demand, for instance cold), should exhibit the most generalist feeding strategy, as their means for coping with the harshness of the arid‐conditions
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