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

Abstract

Summary 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. 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. 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. 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. 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. http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12852/suppinfo is available for this article.

Responses of zooplankton body size and community trophic structure to temperature change in a subtropical reservoir

“…To answer our second research question to determine contributions of intra‐ and intertaxonomic group variations to community trophic structure, we used the Price equation as described in Govaert et al () and Lemmens et al (); that is, , where z i is the trait value for species i and q i is the relative abundance for species i . We only have measurements on the genus or family level; therefore, the contributions calculated reflect changes at the taxonomic level.…”

“…One way of quantifying ecological niche is by using stable isotope analysis. Stable isotope analysis has been increasingly applied to investigate structure and functioning of animals (Catry et al, ) or to assess intraspecific and interspecific variation (Lemmens et al, ) by providing quantitative information on both resource and habitat uses (Fry, ). This information is commonly utilized to define ecological niche space (Layman, Arrington, Montaña, & Post, ; Newsome et al, ).…”

“…The multivariate space given by δ 13 C and δ 15 N can be termed “isotopic niche” (Newsome et al, ), which is a low‐dimensional specification of Hutchinson's niche (Hutchinson, ; Yeakel, Bhat, Elliott Smith, & Newsome, ). The isotopic niche is increasingly used as a powerful proxy for assessing ecological niche in freshwater ecosystems (Dézerald et al, ; Lemmens et al, ).…”

“…Both intraspecific and interspecific variation can alter community trophic structure and dynamics (Bolnick et al, ; Dézerald et al, ; Griffiths, Petchey, Pennekamp, & Childs, ; Newsome et al, ). For example, a study by Lemmens et al () found that the differences in community isotopic niche space of fish were largely determined by intraspecific variation. In another example, Griffiths et al () found that a strong coupling between resources, ecological predator‐prey interactions, and intraspecific trait (i.e., body size) variation influenced community stability in experimental microcosms of protist communities.…”

Size diversity and species diversity relationships in fish assemblages of Western Palearctic lakes

“…Thus, they are, for instance, important for the transfer of energy and cycling of nutrients and they also supply food and recreational activities (Holmlund and Hammer, 1999). Furthermore, intraspecific size variation within fish species strongly affects the dynamics and structure of lake communities even at low species diversity (Jansson et al 2007, Lemmens et al 2017. Since the body size of fish is closely related to their trophic niche (Jennings et al 2001, Romanuk et al 2011, size diversity of fish communities may capture intraspecific variations in fish trophic niches that are not detected by taxonomic approaches.…”