Physiological differences between coexisting congeneric species of snails in a subarctic lake

Abstract

Quantitative measures of feeding, respiration, growth and reproduction were brought together to achieve an overview of differences in physiology between 2 sympatric species of Anisus (Gastropoda, Planorbidae) in subarctic Lake Krivoye, northwestern Russia. This is a resource-limited lake with a short summer growing season where one might expect intense competition for resources among the numerous snails. Because coexistence is a multidimensional process, we have aimed to quantify bioenergetic variables related to several different major physiological functions. Using experiments that manipulated detritus and periphyton, we showed that both species consume detritus in combination with algae, but used different feeding strategies. Anisus contortus has a steeper growth allometry, greater specific growth rate and faster reproductive cycle. Anisus acronicus, however, has a faster absolute growth rate and longer life cycle, which results in its dominance in biomass and numbers. Although bioenergetics in general cannot be used to test directly for competition between closely related species, we have shown alternative growth and energy-metabolism strategies used by different species in a common habitat. Indicators of niche partitioning, maintained by balance calculations, included differences in preferences, quality and consumption rate of consumed food. We expect that these differences are not only important in proximal coexistence, but may also present alternatives for surviving long-term changes in the lake's productivity and habitat types. © Inter-Research 2009.