Boom‐Bust Dynamics Drive Community‐Wide Dietary Structuring in Desert‐Dwelling Raptors

TL;DR

Desert raptors adjust their diets in response to boom-bust cycles of productivity, with broader diets during tough times helping them survive climate changes.

Contribution

First study to elucidate how boom-bust dynamics structurally influence diets in a diverse desert raptor community.

Findings

Boom periods feature diets rich in small mammals and birds, while bust periods emphasize reptiles.

Nomadic raptors show greater dietary specialization regardless of productivity, unlike sedentary species.

Dietary niche breadth increases during bust periods, suggesting adaptation to resource scarcity.

Abstract

Boom‐bust dynamics (pulses of productivity followed by extended periods of low productivity) characterise many dryland, arid environments. These dynamics drive diverse ecological functions, with populations and communities of biota responding strongly to temporal changes in productivity. These changes have flow‐on effects to dietary structuring for consumers, including top predators. Here, we aimed to assess the influence of rainfall‐triggered productivity changes on the diets of raptors using data from long‐term monitoring of a diverse (19‐species) raptor community in a central Australian desert subject to extreme boom‐bust conditions. We showed that boom‐bust dynamics influence dietary structure of the raptor community and that dietary responses are mediated by species‐specific prey preferences and movement ecology. Mean raptor dietary niche breadth increased in bust (0.012 ± 0.0007 [SE]) compared to boom (0.009 ± 0.0006) periods (model β = 0.350) whilst overlap between raptor diets increased in boom versus bust periods. Small mammals, mostly irruptive rodents, and birds featured more in the diets of raptors during boom periods whereas reptiles were prominent during busts. Sedentary, resident, raptors had more varied but consistent diets between boom and bust periods in comparison to locally nomadic and nomadic species. Our results provide the first elucidation of dietary structure and its interaction with boom‐bust dynamics in a highly diverse assemblage of desert raptors. Except for dietary specialists, we propose that predators generally focus on preferred prey when productivity peaks but expand their diets to include alternative prey when conditions are unfavourable. Dietary switching may aid the persistence of such raptor species as boom‐bust systems destabilise due to climate change, whereas dietary specialists, especially if sedentary, are likely to be at risk if preferred prey taxa decline for long periods under future climates.

We investigated how boom‐bust productivity dynamics affected dietary structuring within raptor communities of an arid bioregion. We found that higher productivity was associated with high dietary overlap, lower niche breadth and greater foraging on small mammals; however, raptors that were nomadic exhibited greater specialisation regardless of productivity. We suggest that as climate change alters rainfall‐driven productivity cycles and associated prey communities, raptors with broader diets will be more resilient whereas those with narrower diets, especially those that are nomadic, will be more threatened.

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