Consequências geométricas de processos dependentes de densidade em mexilhões e sua influência na biodiversidade de costões rochosos tropicais
Fonseca, Daniel Gonçalves
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Rocky shore communities represent an important component of the biodiversity in coastal regions, but are subject to environmental impacts resulting from anthropogenic activities. Thus, understanding the mechanisms involved in regulating the populations of these organisms is necessary to predict responses to the various impacts to which these communities are subject. In the intertidal zone, mussels form bands that can harbor high diversity of associated organisms. Density increases in mussel populations, due to the intensity of intraspecific competition, can result in self-thinning processes (ST) that affect individual morphometry and, consequently, habitat availability for the associated fauna. This thesis consists of three chapters focused on incorporating the effects of the formation of individual layers in this cascade of effects (ST - individual morphometry - habitat availability). In the first chapter, we evaluated the relation of ST in two sympatric species of mussels with different environmental tolerances, using a tridimensional model with density measurements that incorporate the presence of layers. The tridimensional model better described the biometric responses to density increases in relation to the bidimensional models traditionally used to describe the ST relation, by incorporating the number of layers and a measurement of effective density. In the second chapter, the same measurements were used to evaluate the influence of density increase on the morphometric variation of the mussels. Again, density indicators derived from the tridimensional model were more effective in estimating intraspecific competition when there was overlap of individuals in the rocky shore. The layers can act as a mechanism of competitive relief and favor the growth of mussels. In the third chapter, we evaluated whether these new biometric indicators derived from the tridimensional ST model would be better descriptors of the structure of communities associated with mussel beds. We found that, even at a reduced scale (10 cm), the layers add physical structures that influence the distribution of the fauna and favor their abundance and richness. Therefore, the use of traditional density measures may result in the inability to detect effects of density-dependent processes in populations with spatial overlap of individuals. New models that better describe the packaging of individuals can contribute to a better understanding not only of population responses to increased density, but also provide a better description of the diversity of the associated fauna.