Comparative Aspects of Food Dependence and Energetics of Freeliving Nematodes

Life history data, population parameter (r) and energetics obtained at a wide range of food supply are compared for two species of bacterivorous nematodes. Caenorhabditis briggsae (Cb) is representative for saprobic environments. Plectus palustris (Pp) and related species are known from heterogeneous habitats of higher predictability in food supply but lower bacterial biomass. In Cb the larval phase is short and maximal reproduction is attained immediately after maturation. Pp has a longer prereproductive period and a prolonged phase of egg production rates. Considerably higher rmax and production rates in Cb are linked to greater maintenance costs. Its food threshold is shifted to higher food densities compared to Pp. Differences in the functional response, thresholds and maximal performance of various parameters are contrasted with different qualities of food availability (overall density; heterogeneity; predictability) in the respective habitats of the two species. Short term, unpredictable conditions (i.e. saprobic environments) are exploited by species with high production performances and rmax. The high level of standard metabolism sets constraints at conditions of lower food availability. Heterogeneous environments of higher predictability in food supply call for homeostatic abilities: in Pp this is expressed in lower maintenance requirements, endurance of starvation and a prolonged reproductive phase.