The effects of competition (intra–specific and inter–specific) and predation on the distribution and abundance of guppy fish (Poecilia reticulata)

Abstract

Competition and predation are among the major evolutionarily and ecological forces which play imperative role to determine the distribution, abundance, and population dynamics of species in a biotic community. The objective of this study was to test the effects of competition (i.e. intra–specific and interspecific) and predation on the distribution, abundance, and fitness of guppy fish. The data were collected in laboratory experiments where guppies were kept in homogenous aquarium with different densities in each partition under the influence of goldfish as competitors and predators. The experiment was conducted in three different stages: only guppies were kept in the aquarium, goldfish were used as competitors, and different densities of predatory fish (i.e. goldfish) were kept in both sides of the aquarium. Regression, isocline, and isodar methods were employed to analyze the data to measure the impacts of competition and predation on the distribution, abundance, and fitness of guppies and later to determine which factor is more influential over the other. The results revealed that both competition and predation were shown to be important evolutionarily and ecological forces to affect the distribution, abundance, and fitness of guppies. Competition coefficient was affected by the densities of both guppies and goldfish; however, predation coefficient was affected only by the density of goldfish. The results of the coefficients of competition and predation suggested that the effect was density–dependent. Generally, predation had the strongest effect on the distribution, abundance, and fitness of guppies followed by the effects of inter–specific and intra–specific competitions, respectively.