Effects of an increased temperature regime on the population dynamics and species interactions of marine nematodes

Although changes in average environmental conditions can have serious consequences, the main impacts of global climate change on populations and communities may well result from changes in short-term climate variability. Both an increased frequency and intensity of extremes and changing amplitudes of diurnal temperature fluctuations may affect the fitness of species and the interactions between them. Such changing temperature regimes may affect reproductive success, population dynamics, species interactions and community structure. The present study compares the effects of an increased temperature regime with diurnal fluctuations with those of a constant temperature regime on the fitness and population dynamics of free-living marine nematodes and on their interspecific interactions. Microcosm experiments were performed on two congeneric monhysterid nematode species, which co-occur in their natural habitat, under a constant vs. an increased fluctuating temperature regime. The latter affected population dynamics of single species and altered the outcome of the interspecific interaction from a symmetrical to an asymmetrical inhibitory effect of D. meyli over D. oschei. Changes in the amplitude of diurnal temperature fluctuations as well as in the frequency of extreme temperatures may be very important determinants of the effects of temperature change on species interactions, potentially affecting assemblage structure and ecosystem functioning.