Occurrence Of Interspecific Competition Research Articles

Interspecific competition among terrestrial slugs

ABSTRACT Interspecific competition among terrestrial gastropods has previously been considered to have little effect on population dynamics and local distribution. Recent studies, however, demonstrate several cases in which interspecific competition plays a major role in structuring terrestrial gastropod communities. To explore the general importance of interspecific competition for the ecology of slugs, we conducted a semi-systematic literature review, synthesizing available peer-reviewed literature relating interspecific interactions to the following: (1) mortality and reproduction; (2) activity, movement, feeding and growth; and (3) habitat use and geographical distribution of slugs. To support the literature on slugs, we also reviewed literature on terrestrial snails. The body of available literature is relatively limited, but the effect of interspecific competition on survival, reproduction, movement and activity has clearly been demonstrated in laboratory experiments for different slug species. The occurrence of interspecific competition seems, however, to be species specific, and no negative effects due to the presence of heterospecifics have been reported for many of the species combinations investigated to date. Most of the studies demonstrating interspecific effects between slug species involved interference from a few aggressive species (mainly Limax maximus as the aggressor). In addition, several correlative studies have indicated that in terrestrial gastropods, habitat use and geographical distribution might be mediated by interspecific competition. Further, well-designed experiments are needed to explore the general importance of interspecific competition among slugs, potentially with a focus on interactions between invasive and native species, where the lack of a shared evolutionary history and niche separation may increase the intensity of competition. Such experimental studies may produce information that has implications for the conservation of native species, as well as for management of invasive pests, because interspecific competition may result in local extinction of vulnerable species and influence the possibility of non-native species establishing invasive populations in new areas.

Avaliação experimental da ocorrência de competição contemporânea entre espécies endêmicas de lagartos das dunas do médio São Francisco, Bahia

The occurrence of interspecific competition is related to overlap in resources use by species and to the lowering of resources availability for a given species due to their use or anticipated appropriation by another one. Competitive interactions may produce a distinct pattern of resources use by the species, as that previously detected between Tropidurus psammonastes (Tropiduridae) and the species Eurolophosaurus divaricatus (Tropiduridae) and Cnemidophorus sp n (Teiidae), species of lizards endemic to the dunes of Ibiraba, Bahia. In order to test the hypotheses that the presence of T. psammonastes reduces the local density of the two other species (what would indicate occurrence of strong contemporary competition) and the pattern of use of microhabitat by them (what would indicate occurrence contemporary competition, although weak), I performed a field experiment lasting 76 days during a period of the year when the potential for competitive interactions is high (i.e., between the end of dry season and the beginning of the rainy season). I manipulated the density of T. psammonastes by removing its individuals from four experimental sampling unities, evaluating the effect on the other two species in comparison with four unaltered sampling unities. In the control situation, the detected pattern of microhabitat use was the same as described in a previous study performed between 1995 and 1996 in the same area. Control and experimental situations were compared through randomization procedures (MRPP) based on total data and on data form the second half of the experiment. I was not able to find significant difference of densities between the control and experimental sampling unities for any of the species, indicating that, if competition occurred, it was not strong enough to generate short-term effects. I did not find significant differences of the patterns of multivariate use of microhabitat by the species between control and experiment. As microhabitat availabil

INTERSPECIFIC COMPETITION AND COEXISTENCE IN A GUILD OF CORAL-DWELLING FISHES

We investigated the effects of interspecific competition on abundance, habitat partitioning, and coexistence of six closely related species of gobies (genus Gobiodon) that inhabit a range of coral species at Lizard Island, Great Barrier Reef, Australia. After documenting the extent of overlap in habitat use among pairs of species in the field, we used a combination of field and laboratory experiments to investigate the relationship between these patterns and the occurrence of interspecific competition. Experiments in aquaria tested the ability of five of the species to compete against Gobiodon histrio, the apparent competitive dominant, including the effects of body size and prior residency. A manipulative field experiment, in which abundance of G. histrio was reduced, tested whether competition with this species limits the abundance of the other five species. Two species competed for space with G. histrio in the field, yet overlap in habitat use with G. histrio was high for one of these species (G. axillaris) and low for the other (G. brochus). In aquaria, G. axillaris and G. histrio preferred the same species of coral and had equivalent, size-based, competitive abilities. The coexistence of G. axillaris and G. histrio at the scale of tens of meters on the reef can thus be explained by a competitive lottery model. However, differential distributions of these two species across the reef flat and reef crest suggest that resource partitioning or habitat selection at larger spatial scales may also be important to their coexistence. In aquaria, G. brochus was an inferior competitor to G. histrio and could only gain access to the preferred species of coral through an advantage in body size or prior residency. Low overlap in habitat use between G. brochus and G. histrio in the field appears to result from niche shifts by the subordinate competitor only. The field experiment indicated that the other three species did not compete for space with G. histrio. Experiments in aquaria demonstrated that G. rivulatus and G. histrio exhibited low overlap in habitat use and did not compete, because they preferred different species of coral. In contrast, G. unicolor and G. histrio exhibited high overlap in habitat use but did not compete, because they were able to cohabit the same coral colonies without affecting each other. In aquaria, G. quinquestrigatus and G. histrio preferred the same coral species; however, in a field recolonization experiment, coral colonies previously occupied by G. quinquestrigatus were rarely recolonized by G. histrio, indicating that these species coexist because they use different types of coral colonies in the field. The study demonstrates that there is no single relationship between overlap in resource use and the occurrence of interspecific competition and that species within a guild can coexist by a diversity of mechanisms.