Patterns of resource partitioning by nesting herons and ibis: How are odonata exploited?

Abstract

Herons and ibis are colonially nesting waders which, owing to their number, mobility and trophic role as top predators, play a key role in aquatic ecosystems. They are also good biological models to investigate interspecific competition between sympatric species and predation; two processes which structure ecological communities. Odonata are also numerous, diverse, mobile and can play an important role in aquatic ecosystems by serving as prey for herons and ibis. A relationship between prey size and bird predator has been observed in Numidia wetlands (NE Algeria) after analyzing food boluses regurgitated by six species of birds (Purple Heron, Black-crowned Night Heron, Glossy Ibis, Little Egret, Squacco Heron and Cattle Egret) during the breeding period, which also shows a temporal gradient for the six species. Both the Levins index and preliminary multivariate analysis of the Odonata as prey fed to nestling herons and ibis, indicated a high degree of resource overlap. However, a distinction of prey based on taxonomy (suborder and family) and developmental stage (larvae or adults) reveals a clear size dichotomy with large-sized predators (Purple Heron, Black-crowned Night Heron and Glossy Ibis) preying on large preys like Aeshnids and Libellulids and small-sized predators feeding mainly on small prey like Zygoptera. Overall, the resource utilization suggests a pattern of resource segregation by coexisting nesting herons and ibis based on the timing of reproduction, prey types, prey size and foraging microhabitats.

Occupancy of yellow‐billed and Pacific loons: evidence for interspecific competition and habitat mediated co‐occurrence

“…A central theme in community ecology is that competition, particularly among sympatric but taxonomically similar species, plays a key role in species’ ecology (Korpimäki 1987, Samraoui et al 2012) and distributional patterns (Hutchinson 1957, Hardin 1960). Competition is, in fact, considered not only a primary driver of species’ ecology, but also an evolutionary force, leading sympatric species to use new resources and promoting phenotypic divergence and less competitive sympatry (Schluter 2000).…”

On the breeding of the Grey HeronArdea cinereain Algeria

“…A rather poor ichthyofauna, early drought and fast emerging vegetation combine to make local wetlands less attractive for breeding Grey Herons. In contrast, the region hosts a rich and diverse insect fauna (Riservato et al 2009;Annani, Alfarhan, and Samraoui 2012) and herpetofauna , which may favour species with a broad diet (Nedjah et al 2010;Samraoui, Nedjah et al 2012). Thus, contrasting abundance and prey availability at a critical stage of the life cycle of each species (Van Vessem and Draulans 1986) may explain the divergent population dynamics between the Purple Heron and the Grey Heron in North Africa and southern Europe.…”

“…Table 3. Comparative growth rates of heron and ibis chicks in North-East Algeria (Samraoui, Menaï, and Samraoui 2007;Boucheker et al 2009;Nedjah et al 2010;Samraoui, Nedjah et al 2012 …”

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

“…The reproductive period is a critical time in the annual life cycle, when a lot of energy is expended and trophic resources may be limited and must be geared to meet the specific needs of the developing chick (Fasola 1994;Samraoui et al 2012). By the time Cattle Egrets began nesting in Yangxian County, 92.6% of Little Egret chicks had already hatched.…”

“…Little Egrets foraged in shallow, open waters using river banks whereas Cattle Egrets foraged mainly in grasslands and paddy fields. The differential exploitation of food resources may be the result of foraging site selection (Samraoui et al 2012;Choi et al 2016).…”