Diet Flexibility As an Indicator of Resilience in Lake Turkana, Kenya Fish Communities

Lake Turkana, Kenya, is the world’s largest desert lake and is fed primarily by the Omo River in Ethiopia.  Dam and irrigation development will alter the Omo River’s flow patterns over the coming decade, with implications for the lake’s ecological functioning.   Despite the importance of the lake’s fishes to the region’s wildlife and tribes, the ecosystem is remarkably understudied.  Our work aimed to predict how resilient Lake Turkana’s fish communities are to perturbation based on the incidence of diet flexibility.   We collected fish tissue samples from Lake Turkana (2008-2013) and analyzed them for δ­¹³C and δ¹⁵N.  We compared isotopic niche variables (e.g. SIBER, bootstrapped Layman’s Metrics) among 8 key species, chosen based on economic or ecological importance and to represent all trophic guilds in the ecosystem.  Among the 8 species studied, isotopic niche size varied by a factor of 2 and a priori factors (i.e. site, site, and year) explained approximately 50% of isotopic variability.  Measures of intra-species dispersion in isotopic signatures supported these findings, indicating higher trophic diversity among species with larger isotopic niches. Based on these data, we conclude that diet flexibility is most marked in Nile tilapia and least marked in characids and Tigerfish in this system.