High resource overlap and small dietary differences are widespread in food‐limited warbler (Parulidae) communities

Abstract

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 Redstart Setophaga ruticilla replicated 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.

Stabilizing selection on a plumage-based foraging adaptation: hooded warblers with average-sized white tail spots live longer

“…In all individuals the inner vanes of the three outer tail feathers (rectrices 4–6) are broadly tipped with white (figure 1 a ). By continuously flicking open their tails while foraging, hooded warblers startle winged insects that constitute the major portion of their diet [8,14,15]. Field experimental evidence indicates that the white tail spots are likely to be a target of selection, as birds with temporarily darkened tail spots have significantly reduced prey capture rates relative to sham-darkened controls (figure 1 b ; [8]).…”