Thermal constraints to population growth of bacterial-feeding nematodes

Abstract

Bacterial-feeding nematodes are important participants in decomposition pathways and nutrient cycles in soils. The contribution of each species to component processes depends upon the physiology of individuals and the dynamics of populations. Having determined the effects of temperature on metabolic rates of several species of bacterial-feeding nematodes, we now present the effects of temperature on population growth rates and relate those data to observed field dynamics. Of nine species of bacterial-feeding nematodes screened for reproductive performance at 20°C, finite rates of population increase ranged from 4.833 d −1 for Caenorhabditis elegans Dougherty to 1.160 d −1 for Panagrolaimus detritophagus Fuchs. Species in the family Rhabditidae generally reproduced more rapidly than those in the Cephalobidae. From the nine species, finite rates of population increase and instantaneous population growth rates were measured at temperatures between 10 and 35°C for Acrobeloides bodenheimeri Thorne, A. buetschlii Steiner and Buhrer, Bursilla labiata Andrássy. Caenorhabditis elegans, Cephalobus persegnis Bastian, and Rhabditis cucumeris Andrássy. Caenorhabditis elegans at 20°C had the maximum finite rate of population increase while R. cucumeris at 35°C had the minimum rate (4.540 × 10 −25 d −1). We utilize the geometric mean of the finite rates of population increase (d −1) as an integral measure of the innate capacity of a species to maintain reproduction across temperatures. The geometric mean varied from 1.03 × 10 −4 for R. cucumeris to 1.45 for Cephalobus persegnis. In the field, temperatures exceeded the upper thermal threshold of R. cucumeris for a significant portion of the 1993 growing season. Population dynamics of this nematode closely matched predicted trajectories. Differences in population growth rates may partially explain the amount of N mineralized by each species.