Invasion success depends on invader body size in a size‐structured mixed predation–competition community

Abstract

Summary1. The size of an individual is an important determinant of its trophic position and the type of interactions it engages in with other heterospecific and conspecific individuals. Consequently an individual's ecological role in a community changes with its body size over ontogeny, leading to that trophic interactions between individuals are a size-dependent and ontogenetically variable mixture of competition and predation. 2. Because differently sized individuals thus experience different biotic environments, invasion success may be determined by the body size of the invaders. Invasion outcome may also depend on the productivity of the system as productivity influences the biotic environment. 3. In a laboratory experiment with two poeciliid fishes the body size of the invading individuals and the daily amount of food supplied were manipulated. 4. Large invaders established persistent populations and drove the resident population to extinction in 10 out of 12 cases, while small invaders failed in 10 out of 12 trials. Stable coexistence was virtually absent. Invasion outcome was independent of productivity. 5. Further analyses suggest that small invaders experienced a competitive recruitment bottleneck imposed on them by the resident population. In contrast, large invaders preyed on the juveniles of the resident population. This predation allowed the large invaders to establish successfully by decreasing the resident population densities and thus breaking the bottleneck. 6. The results strongly suggest that the size distribution of invaders affects their ability to invade, an implication so far neglected in life-history omnivory systems. The findings are further in agreement with predictions of life-history omnivory theory, that size-structured interactions demote coexistence along a productivity gradient.

Body size and species coexistence in consumer–resource interactions: A comparison of two alternative theoretical frameworks

“…Under laboratory conditions, they found that a larger beetle (Coccinella septumpunctata) introduced into North America suffers 60% larval mortality compared to 27% suffered by a smaller native species (Coleomegilla maculata) when the two interact competitively. Similar results were found in an experimental setup with large and small poeciliid fishes (Schröder et al 2009), where the large-bodied species had higher invasion success due to alternative mechanisms such as intra-guild predation. Thus, invasion success of large competitors may not always be attributed to superiority in exploitative competition per se, but, to alternative strategies such as intra-guild predation and other interference behaviors as stressed by Persson (1985).…”

An invasive gull displaces native waterbirds to breeding habitats more exposed to native predators

“…In the absence of native predators, the invasive competitor, being much stronger than the native prey, excluded the latter from the habitat. Invasion success is however, dependent on the body size of the invader in comparison to the native predators (Schröder et al 2009). The Caspian gull is much larger than the native predators and the latter were less likely to affect the invader population.…”

“…We expect this decrease derives from two processes: predation and competition for nesting islets. We assume there will be a strong negative impact of this gull on native species as predation success and competitive abilities are directly linked to body size (Lindstrom 1988;Jonart et al 2007;Oro et al 2009;Schröder et al 2009) and the Caspian gull is much larger than most of the native waterbirds which are potential prey and competitors; (3) Assuming that the large body size of Caspian gull does correspond with its competitive ability, this species will also displace native waterbirds from safe islets located in the center of the reservoir to suboptimal islets located near the shore (i.e., exposed to the predatory activity of native corvids); (4) The increasing population of Caspian gull will lead to increased nest predation on islets visited by this gulls and consequently lower nesting success of native waterbirds at the invaded reservoir as compared with the control one; (5) Over time, the invasion of the Caspian gull will lead to a decline in the population size of small-bodied native predators, namely corvids, as an effect of scramble competition.…”

Deadly competition and life-saving predation: the potential for alternative stable states in a stage-structured predator–prey system

“…the cultivation effect: [9,14]). Thus competition-dominated versus predationdominated dynamics can lead to alternative stable states in LHIGP systems [4,8,11,14,15]. Alternative stable states are only possible in complete diet shift LHIGP systems when two specific conditions are met: (i) prey have to be able to competitively exclude juvenile predators through resource competition (i.e.…”

“…prevent recruitment to the adult stage) and (ii) a relative increase in adult predator density has to reduce prey density and increase predator recruitment [14,17]. While studies of fish communities have supported the basic premise that competitively dominant prey can reduce growth rates of juvenile predators [10,18,19], empirical evidence demonstrating a prey's ability to eliminate predator recruitment through resource competition is scant (but see [11,12]). Furthermore, the effects of changes in adult predator abundance, relative to the prey, in regulating juvenile competitive bottleneck dynamics (condition (ii)) have received little attention.…”