Competition as a Factor Regulating the Geographical Distribution of Fish Species in a Baltic Archipelago: A Neutral Model Analysis

Hansson, Sture

The geographical distribution of perch (Perca fluviatilis L.), roach (Rutilus rutilus (L.)), ruffe (Gymnocephalus cernua (L.)), fourhorn sculpin (Myoxocephalus quadricornis (L.)) and whitefish (Coregonus widegreni malmgren) in the archipelago of Lulea, northern Gulf of Bothnia, cannot be explained as resulting from abiotic factors (salinity and temperature) alone. This paper explores the possibility that interspecific competition can help to explain these distributions. Niche overlap between species is calculated using a two-dimensional niche overlap index, in which both diet compositions and geographical distributions are considered. Overlaps calculated from natural data are compared to overlaps calculates assuming the same diets of the species, but with simulated geographical distributions. Two different types of simulations are run, one in which certain of the natural geographical distribution structures are maintained, and another in which the species are assumed to be randomly distributed. The mean niche overlap calculated from observed distributions were statistically significantly lower than expected from both neutral models. In both simulations also the pairwise niche overlaps are statistically significantly more dispersed than under natural conditions. Competition is a plausible explanation of these differences between observed and expected niche overlaps, which suggests that competition determines the local distribution of the investigated species.

Competition as a Factor Regulating the Geographical Distribution of Fish Species in a Baltic Archipelago: A Neutral Model Analysis

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