Abstract
The relative importance of environment and dispersal related processes for community assembly has attracted great interest over recent decades, but few empirical studies from the marine/estuarine realm have examined the possible effects of these two types of factors in the same system. Importance of these processes was investigated in a hypothetical metacommunity of benthic invertebrates in 16 micro-tidal estuaries connected to the same open sea area. The estuaries differed in size and connectivity to the open sea and represented a salinity gradient across the estuaries. The Elements of Metacommunity Structure (EMS) approach on estuary scale was complemented with a mechanistic variance partitioning approach on sample scale to disentangle effects of factors affecting assembly of three trait groups of species with different dispersivity. A quasi-Clementsian pattern was observed for all three traits, a likely response to some latent gradient. The primary axis in the pattern was most strongly related to gradients in estuary salinity and estuary entrance width and correlation with richness indicated nestedness only in the matrix of the most dispersive trait group. In the variance partitioning approach measures of turnover and nestedness between paired samples each from different estuaries were related to environmental distance in different gradients. Distance between estuaries was unimportant suggesting importance of factors characterizing the estuaries. While the high dispersive species mainly were sorted in the salinity gradient, apparently according to their tolerance ranges towards salinity, the two less dispersive traits were additionally affected by estuary entrance width and possibly also area. The results exemplify a mechanism of community assembly in the marine realm where the niche factor salinity in conjunction with differential dispersal structure invertebrates in a metacommunity of connected estuaries, and support the idea that dispersive species are more controlled by the environment than less dispersive species.
Highlights
Finding biological explanations of beta diversity, the change of diversity, is a way to identify the factors underlying biodiversity [1]
The estuaries have entrance widths differing over 3 orders of magnitude (Table 1), and since the entrance width was a main predictor of salt water flushing from the sea [31] with potential influence on transport of pelagic larvae, post-settling juveniles and even some adults, the estuary openings may represent a gradient in strength of connectivity between the estuaries and the sea
There were highly significant marginal effects (P
Summary
Finding biological explanations of beta diversity, the change of diversity, is a way to identify the factors underlying biodiversity [1]. Processes like turnover were not addressed in these studies and it was not clear how much of the different richness in the estuaries was due to dispersal from the adjacent sea and how much was due to environmental sorting of species inside the estuaries. In the present metacommunity the environmental gradient is represented by the different levels of the environmental factor in the areas of each local community, which are connected to each other via a large assumedly reasonably homogeneous open sea species pool. It assumed that the major dispersal regulating factor for these communities is the entrance width of the.
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