Effects of temperature and precipitation on a flood plain isopod community: a field study

Effects of a changing climate at individual, population and community levels on biocoenoses will cause profound changes in ecosystem functioning. Considering detritivore communities, we expect severe impacts on the balance of nutrient input through annual leaf fall and nutrient cycling through leaf litter decomposition. Thus, fluctuations of detrifivore populations under changing climatic conditions will affect the degradation of detritus. Monitoring populations of four isopod species, that represent the most abundant detritivores in a floodplain forest near Cologne, Germany, revealed three distinct patterns of breeding phenology. Porcellio scaber and Philoscia muscorum breed early in the season (late spring to summer), while Oniscus asellus breeds during summer and early fall. Hyloniscus riparius appears to have a prolonged breeding season, ranging from spring to fall. Over 5 years, I observed effects of annual variations in temperature and precipitation on isopod populations and the composition of the community of these detritivores. With respect to the onset of breeding and to overall population size, as estimated from the number of captured individuals, summer and winter temperature proved to be particularly important, while temperature during fall and spring had little influence on isopod number or phenology. Considering precipitation, mostly summer and spring were of importance, whereas fall and winter precipitation only played a role in determining phenology but did not influence population densities. Predominant effects of climatic factors were low population densities of R scaber, P. muscorum and O. asellus after warm winters and moist springs and during dry summers, while moist springs increased numbers of H. riparius. After moist springs, in turn, P. scaber and O. asellus started breeding earlier than after dry springs. According to the present field data, isopods (and maybe other detritivores) will be affected by regional climate change in that numbers will be reduced in response to increasing winter temperature, more intense precipitation during spring and dry summers as predicted by current climate models. Thus, climate change will result in reduced faunal contributions to decomposition processes that, in turn, will lead to slowed-down microbial degradation of detritus and nutrient cycling. (C) 2005 Elsevier SAS. All rights reserved.