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Pen shell community patterns and assemblage: interpretation of local and regional dynamics.
Munguia, Pablo*,1,2, 1 Dept. Biological Science, Tallahassee, FL2 Instituto de Biología, Ecología y Conservación, AC, Guadalajara, Mexico
ABSTRACT- The interaction between local and regional diversity patterns has been a major focal point in ecology. Theory predicts one of two outcomes: (1) diversity at the local scale is a constant proportion of diversity at a regional scale. (2) Local diversity saturates at higher regional richness. The second outcome has been difficult to observe in nature due to three main reasons: problems in delimiting a species pool, pseudoreplication, and assuming that communities are at some equilibrium . Here I incorporate the relative abundance of species and assembly time to show how the relationship between local and regional diversity develops during different colonization times. At St. Joe Bay, Florida, the pen shell (Atrina sp.) is one of the few sources of hard substrate, serving as a habitat for sessile and mobile invertebrates and fish. During the summer of 2001 I placed empty pen shells spread among different plots within the bay and removed them at different time intervals. The results showed that with time, species richness increases significantly while evenness indices saturate. Initially a local-regional plot of species richness shows that few species are present at the local scale, regardless of the species pool size. With time the slope between local and regional richness increases, presenting unsaturated communities. Rarefying the number of species at the local scale and comparing them to the regional species pool shows a different pattern. With rarefied richness there is a positive linear relationship between local and regional richness initially, but at subsequent times the curve saturates. These results suggest two things: (1) the degree of species saturation will depend on the colonization stage of a community. (2) Incorporating species abundances (i.e. through rarefaction or other techniques) demonstrates the role of species commonness or rarity in determining patterns of community diversity at different scales.
KEY WORDS: local-regional diversity, benthic communities, rarefaction, assembly time