High niche overlap between two successfully coexisting pairs of Lake Malawi cichlid fishes

摘要

Many species in high-diversity assemblages appear to coexist in similar ecological niches. It has been proposed that interspecific resource partitioning in these assemblages may only occur during periods of resource scarcity. We tested this hypothesis by measuring resource abundance, dietary overlap, foraging rate, and territoriality in a Lake Malawi rock cichlid assemblage over a period of 1 year. Our study examined two pairs of morphologically similar species, with each pair comprising one native species and one invader species that has successfully established after being translocated from another region of the lake. All four species changed their diet and foraging rate in response to seasonal variation in resource abundance. However, dietary overlap within both species pairs remained high in all seasons and was not influenced by resource availability. Similarly, territoriality did not decline during periods of low resource availability, suggesting no decrease in the strength of interspecific competition. These data suggest that these species pairs are successfully coexisting despite substantial niche overlap during resource scarcity. Thus, the coexistence of species within this radiation may not depend on the evolution of divergent resource use patterns.