Data from: Intra- and interspecific niche variation as reconstructed from stable isotopes in two ecologically different Ethiopian Rift Valley lakes

1. The concept of species niches has enhanced our understanding of
community assembly and food web structure in a variety of ecosystem types.
Niche-based species sorting profoundly determines community composition
along strong environmental gradients, while interspecific interactions
tend to be more important within habitats at local spatial scales. The
role of intraspecific niche variation in community assembly and ecosystem
functioning has only recently been highlighted. 2. The present study
undertakes a quantitative comparison of the trophic structure of fish
communities in two iconic Ethiopian Rift Valley lakes, Lake Abaya and Lake
Chamo, which are biodiversity hotspots with high societal importance. The
lakes differ strongly in ecology: whereas Lake Abaya is turbid due to a
very high sediment loading, Lake Chamo is a clear-water lake, which in
recent years is, however, rapidly becoming more turbid. Using stable
isotopes, we compare the structure of the food web in both lakes, and
investigate the degree to which differences in trophic structure between
the two lakes are mediated by changes in species composition with fixed
within-species niches or rather by flexibility in food acquisition within
species. 3. Different food web compartments, including fish and the main
basal sources, were sampled in both lakes. We used Bayesian stable isotope
mixing models and Bayesian community-wide metrics for a quantitative
comparison of the food web structure between the two lakes. 4. We
demonstrate that the isotopic niche of the fish community in Lake Abaya is
larger and more diversified compared to that in Lake Chamo. Sediment
organic material seems to be a major energy source for fish in Abaya,
while zooplankton is a dominant source for fish in Chamo. This is
consistent with the different ecology of the two lakes, where high
turbidity impedes primary and secondary production in Abaya. Differences
in trophic structure between the two lakes resulted from intraspecific
isotopic niche variation rather than from compositional variation between
fish communities. 5. Our results point to the importance of intraspecific
variation in feeding ecology of fish communities inhabiting two large
Ethiopian Rift Valley Lakes with distinct environmental conditions. We
anticipate that the approach we used has strong potential to explore
large-scale patterns in food web organization in relation to niche
variation across different types of ecosystems.