Effects Of Interference Competition Research Articles

The effect of interference competition in Asplanchna brightwelli on its predation capacity

The effect of interference competition in Asplanchna brightwelli on its predation capacity

Interference competition in a planktivorous fish (Rutilus rutilus) at different prey densities and temperatures

The effect of interference competition can be assessed by comparing the capture rate of a predator foraging alone with that of the predator within a group. Since such an effect could be prey density dependent, a constant density of prey must be maintained while assessing this effect, irrespective of the elimination of prey by predation. However, when studying a predator-harvester, such as a planktivorous fish, which collects zooplankton at a rate of up to 1 prey s−1, instantaneous replacement of each consumed prey item is not feasible. This problem was solved in short-lasting mesocosm experiments by minute-by-minute supplementation to replace eliminated Daphnia and maintain a constant average prey density. Such experiments were performed with different numbers of foraging roach (Rutilus rutilus) at three prey densities and in two ranges of ambient temperature. The number of Daphnia required at the start of each experiment to establish the initial prey density and the number that it was necessary to add per minute were determined in experiments conducted without prey supplementation and in preliminary experiments with prey supplementation. The results of this study revealed that fish foraging in a group eat less, due to both exploitation and non-aggressive competition for space. Moreover, the effect of interference competition was stronger at higher temperatures, irrespective of the prey density, indicating that natural populations of roach foraging in shoals may suffer more from competitive interactions in warmer waters.

Intraguild predation and interference competition on the endangered dragonfly Aeshna viridis.

We examined the effects of intraguild predation (IGP) and interference competition on an endangered dragonfly, Aeshna viridis Eversm. (Odonata: Anisoptera). A. viridis is rare in Europe due to the decrease in suitable habitats harboring the macrophyte Stratiotes aloides L. Stratiotes plants are the principal oviposition substrate for A. viridis females and protect the larvae of A. viridis from fish predation. In our study lakes A. viridis larvae are sympatric with larvae of Aeshna grandis and Aeshna juncea. The susceptibility of A. viridis larvae to IGP by similar-sized larvae of A. grandis and A. juncea was tested in a laboratory predation experiment. Microhabitat use of A. viridis and A. grandis was studied in the laboratory to determine the possible effects of interference competition on the spatial distribution of A. viridis larvae. Our results show that at least in laboratory conditions, A. viridis is susceptible to IGP and interference competition. In competition, A. grandis larvae dominated the middle and outer portion of S. aloides rosettes whereas A. viridis stayed in the inner parts. When A. grandis larvae were absent, A. viridis colonized the middle and outer parts of the rosettes. We conclude that asymmetric predation between odonate larvae of equal size can be intense, and that both IGP and interference competition affect A. viridis. Although natural habitat complexity diminishes their impact, these interactions may nevertheless influence the distribution of A. viridis in S. aloides waters and restrict its microhabitat use in S. aloides rosettes.

Effects of Interference Competition on the Foraging Activity of Tropical Roseate Terns

Although difficult to detect, interference competition among foraging birds may affect the fitness of an inferior competitor by lowering foraging success. We studied foraging flocks of Roseate Terns (Sterna dougallii) at Culebra, Puerto Rico, in 1990 to examine the effects of small and large monospecific and mixed-species flocks on the foraging success and behavior of this threatened species. Roseate Terns mostly foraged in small flocks with Brown Noddies (Anous stolidus). The frequency of foraging attempts in Roseate Terns decreased with increasing size of mixed-species flocks, primarily due to passive interference by Brown Noddies, which foraged just over the water surface and limited the area available to Roseate Terns. The size of monospecific Roseate Tern flocks had no effect on foraging attempt frequency. Roseate Terns also aborted more feeding dives and foraged more by dipping when in flocks with noddies, relative to flocks of only conspecifics. Proportionally fewer Roseate Terns than expected foraged in large, mixed-species flocks (>8 birds), suggesting that they preferentially avoid large flocks that result in lower foraging success. Although Brown Noddies caused a reduction in Roseate Tern foraging attempt frequencies and an increase in aborted dives, we were unable to detect a negative effect on adult survival or reproductive success of this population.

The effects of interference competition on stability, structure and invasion of a multi-species system.

An interference competition model for a many species system is presented, based on Lotka-Volterra equations in which some restrictions are imposed on the parameters. The competition coefficients of the Lotka-Volterra equations are assumed to be expressed as products of two factors: the intrinsic interference to other individuals and the defensive ability against such interference. All the equilibrium points of the model are obtained explicitly in terms of its parameters, and these equilibria are classified according to the concept of sector stability. Thus survival or extinction of species at a stable equilibrium point can be determined analytically. The result of the analysis is extended to the successional processes of a community. A criterion for invasion of a new species is obtained and it is also shown that there are some characteristic quantities which show directional changes as succession proceeds.