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Although both interspecific competition and coexistence mechanisms are central to ecological and evolutionary theory, past empirical studies have generally focused on simple (two‐species) communities over short time periods. Experimental tests of these species interactions are challenging in complex study systems. Moreover, several studies of ‘imperfect generalists’, consistent with Liem's Paradox, raise questions about the ability of evolved species differences to partition niche space effectively when resources vary considerably across the annual cycle. Here we used a recently developed theoretical framework to combine past research on population‐level processes with observational data on resource use to test for ongoing interspecific competition and understand the nature of resource overlap. We compared species diet overlaps and differences in several distinctive communities centred on a focal species, the American RedstartSetophaga ruticillareplicated both spatially and seasonally, in combination with documentation of population regulation to assess the ability of similar species to partition dietary niche space and limit interspecific competition. Our results document high dietary overlap in most of the communities studied, with only subtle differentiation consistent with known species differences in foraging behaviour and morphology. These findings are largely consistent with species foraging as imperfect generalists. However, in contrast to past studies, the high diet overlaps observed here during times of inferred resource scarcity were driven by low‐value prey taxa (e.g. small ants) and did not involve truly ‘private’ resources. All of these factors increase the potential negative impacts of interspecific competition, and limit the ability of these birds to avoid competition if food availability deteriorates further than observed in our study, either seasonally or at longer intervals.
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Extensions and limitations of MacArthur (1958): A review of ecological and evolutionary approaches to competition and diet in the New World wood warblers (Parulidae)
Abstract The extent to which interspecific competition structures species interactions and coexistence within communities, and the relevant mechanisms, are still debated. We focus on New World wood warblers (Parulidae), beginning with Robert MacArthur’s iconic 1958 paper in which he shows how subtle foraging behaviors, purportedly linked to dietary differences, within spruce trees contribute to the coexistence of 5 spruce-woods warbler species. MacArthur coined the phrase “resource partitioning”, and profoundly impacted the field of Ecology for subsequent decades in diverse ways. To understand what MacArthur got right and what he missed, we reviewed both ecological and evolutionary approaches to questions of the origin and coexistence of competing species in the context of diet. We argue that an important, underappreciated, mechanism of competition among coexisting migratory warbler species, particularly in winter, is diffuse exploitation competition, based in part on our own studies of warbler diets in relation to foraging behavior, substrate use, bird morphology, and other traits. Our review and synthesis of interspecific competition and coexistence in warblers have important consequences, including our questioning of the importance and effectiveness of resource partitioning in birds. We also suggest a novel hypothesis for the success of warblers today in the Caribbean and other habitats, beginning with their relatively recent adaptive radiation and the ecological opportunity on Caribbean islands.
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- Award ID(s):
- 2147043
- PAR ID:
- 10406938
- Date Published:
- Journal Name:
- Ornithology
- Volume:
- 139
- Issue:
- 2
- ISSN:
- 0004-8038
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/ornithology/ukac010
