PARENT SESSION
Poster Session #31: Animal Population and Community Ecology I.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Relative importance of intra- and inter-specific variations on the body size-abundance distributions of benthic invertebrates.

Pinna, Maurizio^*,1, Basset, Alberto², Sangiorgio, Franca³, ¹ University of Lecce, 73100 - Lecce, ITALY² University of Lecce, 73100 - Lecce, ITALY³ University of Lecce, 73100 - Lecce, ITALY

ABSTRACT- Individual body size shows regular patterns within ecological communities, which are described by the body size-abundance and body size-area distributions. These patterns are likely to reflect species interactions and coexistence relationships. Therefore, the analysis of the mechanisms underlying such distributions could greatly increase our understanding of community organization. On the other hand, the ecological meaning of the body size-abundance distributions was proposed to be limited in guilds dominated by invertebrates, because of the high intra-specific variability of the individual body size, due to age, growth rate and sex differences. Here, we tested this criticism in guilds of benthic invertebrates. The study was carried out on detritus based guilds of freshwater and salt marsh ecosystems in Southern Italy, using the leaf pack technique to sample the benthic guilds. Globally we analyzed 561 guilds, which were then pooled into a smaller number of larger assemblages according to sampling sites, seasonal periods and ecosystem type. Data were analyzed using one way ANOVA. In 83% of the 561 guilds the body size abundance distributions were due to the inter-specific component. The intra-specific component was more relevant than the inter- specific one only in guilds with very low taxonomic richness or numeric abundance. The relevance of the inter- specific component was also highly significant at the other levels of data aggregation. It had a significant influence in 80-86% of freshwater sites and in 95-100% of salt marsh sites. Therefore, the results strongly support the relevance of body size abundance distributions as a community characteristic, even in guilds dominated by invertebrates.

KEY WORDS: body size-abundance distribution, body size ratio, benthic detritivores, aquatic ecosystems