Do intraspecific or interspecific interactions determine responses to predators feeding on a shared size‐structured prey community?

Abstract

Summary 1.Coexistence of predators that share the same prey is common. This is still the case in sizestructured predator communities where predators consume prey species of different sizes (interspecific prey responses) or consume different size classes of the same species of prey (intraspecific prey responses). 2. A mechanism has recently been proposed to explain coexistence between predators that differ in size but share the same prey species, emergent facilitation, which is dependent on strong intraspecific responses from one or more prey species. Under emergent facilitation, predators can depend on each other for invasion, persistence or success in a size-structured prey community. 3. Experimental evidence for intraspecific size-structured responses in prey populations remains rare, and further questions remain about direct interactions between predators that could prevent or limit any positive effects between predators [e.g. intraguild predation (IGP)]. 4. Here, we provide a community-wide experiment on emergent facilitation including natural predators. We investigate both the direct interactions between two predators that differ in body size (fish vs. invertebrate predator), and the indirect interaction between them via their shared prey community (zooplankton). 5. Our evidence supports the most likely expectation of interactions between differently sized predators that IGP rates are high, and interspecific interactions in the shared prey community dominate the response to predation (i.e. predator-mediated competition). The question of whether emergent facilitation occurs frequently in nature requires more empirical and theoretical attention, specifically to address the likelihood that its pre-conditions may co-occur with high rates of IGP.

Trophic niche overlap between sympatric harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) at the southern limit of their European range (Eastern English Channel)

“…Sympatric species with similar functional traits, diets, foraging strategies, and feeding grounds typically present a trophic overlap, and consequently coexist or compete (e.g., Cupples et al, 2011;González-Solís et al, 1997;Jones & Barmuta, 1998). Since the niche of a species is conceptualized in n dimensions defining the resources used in time and space (Hutchinson, 1957), parameters other than diet alone could explain coexistence: foraging on the same prey but at different time periods, and/or at different locations, and/or on different prey sizes/life stages (e.g., Brink et al, 2015). Describing the trophic niches of species in multiple dimensions is therefore necessary to accurately assess potential interactions (Costa-Pereira et al, 2019;Friedemann et al, 2016).…”

Does the evolution of ontogenetic niche shifts favour species coexistence? An empirical test in Trinidadian streams

“…Ontogenetic changes in resource use occur in one of three ways. First, in taxa like amphibians and holometabolous insects, there are discrete phases of the life cycle between which individuals shift their resource use and, often, their habitat (ten Brink et al, 2015). Second, in some taxa without discrete phases of the life cycle, discrete changes in resource use occur when animals pass a threshold body size (Cipriani et al, 2017; Graham et al, 2007).…”

Temperature‐ and light‐dependent ratio of energy gain to metabolic costs explains spatial and temporal habitat use of zooplanktivorous fish

“…Animals may choose less profitable habitats to avoid predators, or take the risk of exposing themselves to predators if their energy need is large enough (Rennie et al., ; Vijayan, Morris, & McLaren, ). In size‐structured populations, for example fish, foraging capacities as well as predation risk vary with individual size (ten Brink, Mazumdar, Huddart, Persson, & Cameron, ; Byström & Garcia‐Berthou, ; Ohlberger et al., ). Predation vulnerability and foraging efficiencies are both size dependent and will affect how organisms chose between habitats (Diehl & Eklöv, ; Werner, Gilliam, Hall, & Mittelbach, ).…”