Three-dimensional niche partitioning between two colonially nesting ardeid species in central China

Abstract

Background Interspecific competition is known to be strongest between those species that are both closely related and sympatric. Egrets are colonially nesting wetland birds that often overlap and can therefore be expected to compete in roosting and nesting habitat as well as in diet. According to the niche partitioning hypothesis, it is to be expected that these similar species would show differentiation in at least one of the main niche dimensions to reduce competition. We tested niche partitioning between the colonially nesting Little Egret (Egretta garzetta) and Cattle Egret (Bubulcus ibis) in temporal, spatial and trophic dimensions. Methods Field study was conducted in three mixed egret colonies in Yangxian County, southwest Shaanxi Province, central China. For each nest colony we recorded its spatial location, the height of nesting trees and of nests, the height of roosting trees and of roosting individuals within the trees. We determined the first egg-laying and first hatching dates of the two species. Craw dissection of storm-killed egret nestlings was used to measure the diet. Six transects were surveyed to study foraging habitat selection. Results We found that hatching time of Little Egrets peaked earlier (by about 1 month) than that of Cattle Egrets. Cattle Egrets nested and roosted higher than Little Egrets. The foraging habitats used by Little Egrets were dominated by river banks (73.49%), followed by paddy fields (13.25%) and reservoirs (10.84%), whereas Cattle Egret foraging sites were characterized by grasslands (44.44%), paddy fields (33.33%) and river banks (22.22%). Little Egrets consumed more fishes (65.66%) and Odonata larvae (13.69%) than Cattle Egrets, while Cattle Egrets were found feeding mainly on Coleoptera (29.69%) and Orthoptera (23.29%). Little Egrets preyed on larger mean biomasses of food items than Cattle Egrets. Conclusions Our results confirm the niche partitioning hypothesis as a mechanism for coexistence among ecologically similar species. In two coexisting egret species, niche partitioning is multidimensional, such that the two coexistent species occupy differing ecological space based on all three temporal, spatial and trophic niche dimensions.

Increased density of conspecifics caused niche contraction in a multispecific passerine assemblage

“…The small distances between centroids among most of the species and the variability in niche similarity suggest that there is room for present competition to operate within the community. The intensity of interspecific competition is determined by the similarity of competitor requirements, being more intense with the increase of morphological similarity (Chesson, 2000; Hardin, 1960), or when sharing ecological requirements related to feeding habits, breeding ecology, or nesting sites, among others (Chesson, 2000; Pianka, 1974; Ye et al, 2021). During the breeding season, our passerine birds inhabiting a low productive landscape share requirements like nesting exclusively on the ground, feeding their broods with insects or larvae (de Juana, 2005), and displaying territoriality and aggressive behavior.…”

Comparison of Reproductive Strategies between Two Sympatric Copsychus Passerines

“…According to niche theory, coexisting species are expected to mitigate interspecific competition by partitioning shared resources, a process that may simultaneously favor the development of phenotypic differences [14]. Ecological niche competition can manifest as direct competition for resources such as forage, habitats, or nesting sites [15][16][17]. It can also manifest as indirect competition, for instance, in the forms of varied temporal utilization of ecological niches or behavioral differences, to mitigate direct competitive pressures [18,19].…”

Spatiotemporal Niche Separation among Passeriformes in the Halla Mountain Wetland of Jeju, Republic of Korea: Insights from Camera Trap Data

“…Niche separation refers to the process where bird species evolve distinct behaviors, feeding times, or habitat preferences, reducing direct resource competition. This separation allows for diverse species to coexist in the same ecological space [ 13 ]. Conversely, niche overlap occurs when species share similar ecological roles or resources, leading to increased competition.…”