COS 20-8
What drives consumer trophic structure across high Andean soil chronosequences?
Nitrogen (N) and Phosphorus (P) are major cellular components in consumer organisms and, limitations in their availability and accessibility can strongly affect growth and development, as well as life history strategies and population dynamics of consumer species. In environments where periodic disturbances induce formation of soil age gradients, biogeochemical shifts during soil development often are accompanied by individual and community modifications in primary producers, which in turn propagate these effects to consumer trophic levels. For example, as long-term soil development proceeds, changes in soil nutrient availability induce modifications in plant strategies to increase efficiency of nutrient (e.g. N and P) use and retention; which in turn affects herbivores and detritivores arthropods, that are under strong stoichiometric control, because, feed on low nutrient quality plant tissues and litter. Here we studied the effects of pronounced variability in primary producer nutrient content (i.e. leaf and litter) upon trophic structure and ecological stoichiometry (body C, N and P content) of arthropods and vertebrates during soil development in three c.20.000-years chronosequences in the Andean Dry Puna, Bolivia. We hypothesized that herbivores and arthropods in detritus-based food web experience major stoichiometric control across biogeochemical gradients during soil development because the chronic soil N-limitation in this Andean environment.
Results/Conclusions
Our results indicate that soil and plant N-limitation have a strong effect on nutrient body content and trophic structure of consumer species. C:N and N:P body contents in herbivores and detritivores species changed during soil development and were associated to increases in N-content of leaf and litter. Further, extreme lower N-contents in young soils were associated to lower arthropods species richness and simplified detritus-based food webs. Accordingly, biomass of herbivores and detritivores increased during soil development. Vertebrate predators abundance increased during late stages of development and this was positively related to increases in arthropods biomass. Significant differences in herbivores and detritivores diversity and biomass along soil age gradient indicate that soil and plant heterogeneity drives arthropods community structure and function, meanwhile biogeochemical gradients and N-limitation determined nutrient body content in both functional groups. These findings indicate that from individual to trophic structure chronic N-limitation is a critical driver of Andean food webs.