Significance of intraspecific variation for decomposition processes

Over the last decades, communities and ecosystems globally have undergone dramatic changes, accompanied by rapid declines and changes in biodiversity at all levels, from biotopes to species and genetic variation within species. Consequently, considerable effort has been invested in ecological research to understand the functional importance of biodiversity as a regulator of ecosystem processes, dynamics and functioning. However, intraspecific (phenotypic) variation has been considered rarely in this context. With the proposed project, we aim at studying how intraspecific variation in ecological and physiological traits affect ecosystem processes and, respectively, is affected by environmental extremes. We will study decomposition as a fundamental ecosystem process, being controlled by macro-detritivores, such as terrestrial isopods. We hypothesize that (I) populations with variable digestive phenotypes are more efficient in consuming and breaking down diverse litter mixtures, and the relevance of intraspecific variation increases with increasing litter diversity; (II) variable populations are more resistant and tolerant against environmental fluctuations and extremes; (III) extreme (weather) events select for phenotypes that are able to cope with such extreme conditions, and populations from naturally fluctuating environments exhibit higher variation, as well as higher resistance and tolerance against environmental extremes. To test these, we will (I) experimentally increase intraspecific variation of detritivores and study its significance for decomposition processes; (II) experimentally breed different levels of intraspecific variation within populations, expose them to different environmental conditions and study their contributions to decomposition processes; (III) expose populations from different habitats that differ in the extent of environmental fluctuations to extreme events.

Over the last decades, communities and ecosystems globally have undergone dramatic changes, accompanied by rapid declines and changes in biodiversity at all levels, from biotopes to species and genetic variation within species. Consequently, considerable effort has been invested in ecological research to understand the functional importance of biodiversity as a regulator of ecosystem processes, dynamics and functioning. However, intraspecific (phenotypic) diversity has been considered rarely in this context. One of the most fundamental ecosystem processes is decomposition, being driven by microbes in interaction with detritivores (e.g., isopods). We expect that intraspecific diversity in ecological and physiological traits of isopods affects ecosystem processes (decomposition) on hand and, on the other hand, is affected by environmental conditions and extremes. Using molecular genetic techniques, we show that isopod populations over their pan- European distribution range are more similar to each other than expected obviously, there is (or recently was) exchange among geographically distinct populations. Nonetheless, mixing isopods from different regions in experimental lab populations results in an increased intraspecific diversity, and these mixed populations exert higher consumption rates of leaf litter only, however, if only a single litter species is offered as food: increasing litter diversity masks any effect of intraspecific isopod diversity. Similarly surprising is the close genetic similarity of two populations of an isopod species in low versus high altitude at Untersberg (Salzburg). Genetic studies proved an active exchange over an altitudinal difference of 800 m. Accordingly, isopods from both sub- populations exhibited responses to stress (heat, frost, inundation) at the gene expression level, but contrary to our hypothesis the sub-populations did not differ from each other in this regard. Litter mass loss, as driven by feeding, was faster with isopod populations from higher altitude, probably because isopods from higher altitudes were smaller than those from lower altitude: Obviously, climatic and seasonal conditions at 1240 m a.s.l. warrant slower growth than those at 440 m a.s.l., and smaller isopods feed more relative to their size. Considering altitude along hill slopes a suitable proxy for changing climatic conditions, these findings may suggest that rising temperatures in montane regions will affect detritivores and the decomposition processes they drive in that the latter will be slowed down. This does, however, not yet take into account potential changes in the vegetation and the quality of detrital matter as food for detritivores (and microbes).