Community patterns in sandy beaches of Chile: richness, composition, distribution and abundance of species

Abstract

The search for patterns, i.e., statistical arrangement in the data, is a key step to understand the way in which natural systems change in space and time. In order to detect community patterns I analyzed in this study some community traits of forty-five local assemblages of sandy beach invertebrates of Chile. There were identified three main community patterns. (1) Species richness tended to decrease with beach slope (morphodynamic state index), fitting a power model. The variability non-explained by beach slope (about 50%) was independent of grain size and latitude, but a little fraction (9%) was explained by sampling effort. Beach length seemed also to be related with this unexplained variability, but in a non-linear way. (2) The species composition of the local assemblages tended to be a non-random nested subgroup of the species composition of the: richer assemblages, i.e., the species composition fitted a nested pattern. (3) The species abundance and distribution were positively correlated, which indicate that wide distributed species tended also to be locally abundant. This is the first time that the "nested species composition pattern" (N degrees 2) and the "interspecific abundance-distribution pattern" (N degrees 3) are documented for sandy beach fauna. These three patterns were statistically evident at both regional (similar to 2 x 10(2) km) and geographical (similar to 2 x 10(3) km) scales, suggesting that they are scale-independent along the evaluated range. Much work is still needed to explain how sandy beach communities are structured, in the present study only the first step has been taken, i.e., the detection of patterns, leaving open the question about the underline processes and mechanisms.

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