Interspecific dominance and asymmetric competition with respect to nesting habitats between two snowfinch species in a high‐altitude extreme environment

Abstract

Interference competition over shared resources is expected to be intensive in harsh environments between phylogenetically and morphologically similar species. We document interspecific dominance and nest habitat selection by two pika-burrow nesting Montifringilla species, white-rumped snowfinches M. taczanowskii (WRS), and rufous-necked snowfinches M. ruficollis (RNS), which commonly inhabit alpine meadows in the northeastern Tibetan plateau. Relative to the critical point (<0.60) for coexistence, high overlaps (0.68-0.86) between the two species in egg-laying date, nest site distribution and nesting burrow attributes suggested strong interspecific competition over these niches. This is also predicted by the ratios of inter-species body mass (1.4) and linear dimensions (1.1-1.2) below the minimum value (2.0 and 1.3) for stable coexistence of closely related species. Larger-sized WRS was behaviorally dominant over pikas and over smallsized RNS. Being dominant, WRS established nesting territories in areas with moderately steep slopes from which they required most of the food resources during the breeding season; in contrast, RNS exhibited no territoriality and had to nest at margins between WRS's territories and fed at dispersed sites. For the same reason, WRS mainly used active, and RNS used inactive, pika burrows. The asymmetric competition over nesting habitats could contribute to the relatively high nesting success and breeding density of the superior species. We argue that there is a spectrum in interspecific competition strength, from stable coexistence to complete exclusion along a gradient of increased environmental harshness, and the guild of the two snowfinch species is at a mediate position of the spectrum.

Interference from long-tailed finches constrains reproduction in the endangered Gouldian finch

“…adaptively broadening their niche; Pimm & Pimm 1982;Moreno, Barluenga & Barbosa 2001;Palmer 2003). This effect has also been demonstrated in cavity-nesting birds (Aitken & Martin 2008;Zeng & Lu 2009). In terms of nest-site selection characteristics, however, Gouldian finches have a narrower (relative specialist) niche than long-tailed finches (relative generalist) Brazill-Boast, Pryke & Griffith 2010), which is further supported by long-tailed finches' greater readiness to utilize nest-boxes over natural cavities.…”

Bi‐parental vs. cooperative breeding in a passerine: fitness‐maximizing strategies of males in response to risk of extra‐pair paternity?

“…We used the first brood for analysis. Monitoring of 43 bi‐parental and 17 cooperative broods from day 1–5 after hatching until fledging provided no evidence of brood reduction, presumably because of the nature of burrow nesting and abundant local food recourses (Zeng & Lu 2009). For the 48 nests in which no blood samples were collected, most failed to hatch.…”

Avifaunal disarray due to a single despotic species

“…This mechanism has been identified in groups as diverse as Amazonian birds (Robinson & Terbourgh, 1995), Tibetan snowfinches Montifringilla spp. (Zeng & Lu, 2009), desert rodents (Brown & Munger, 1985) and coral reef fishes (Shulman, 1985), but usually has been explored for its role in determining spatial segregation of similar species. The potential for anthropogenic habitat alteration to interact with competitive despotism and affect the structure of entire assemblages has received little attention.…”