Temperature niche difference and interspecific competition determine the parapatric distribution of two congeneric species in Diaphanosoma

Abstract Background Diaphanosoma excisum and D. dubium are parapatrically distributed in tropical and subtropical waters, and rarely coexist at local communities in the transition between tropics and subtropics. According to Janzen’s hypothesis and the modern coexistence theory, the specific thermal adaptation and strong interspecific competition between the two congeneric species are assumed to result in their range limits. To explore the mechanisms underlying such parapatric distribution, we modeled their current geographic distribution, and compared temperature niche difference and fitness inequality in interspecific competition with their representative clones.Results The species distribution modeling showed that the two Diaphanosoma species had significantly divergent climate niches. Their life history parameters in monocultures also demonstrated as stable temperature niche difference, while D. excisum had higher fitness than D. dubium in dimension of food niche. The competition experiments revealed a strong exploitative competition between the two species, and D. excisum was the superior competitor, and excluded D. dubium in all the competition experiments within overlapping temperature niche regardless of food conditions.Conclusions Our results suggest that stable temperature niche difference overcoming interspecific competition for food plays a critical role in shaping Diaphanosoma species range.