Intra- and interspecific variations in life strategies of Erpobdella octoculata and Erpobdella vilnensis in different habitats along the longitudinal gradient of stream

Our study examines intra and interspecific variations in life histories, reproduction parameters, secondary production and feeding biology of two erpobdellid leech species (Erpobdella octoculata and Erpobdella vilnensis) across longitudinal gradient of streams. These species frequently cohabit in streams of Central Europe and present a very high niche overlap in terms of spatial distribution and trophic resources. In both species, a shift from biennial to annual life cycle was noted, as well as from iteroparity to semelparity. In general, annual erpobdellid populations invested more in reproduction than the biennial populations and E. octoculata invested more in reproduction than any E. vilnensis. The absolute individual growths of studied species were described by the von Bertalanffy growth model with seasonal oscillations. The highest values of daily growths (6.1–8.6% of dry mass per day) were noted during the first month after hatching. Annual production ranged for E. vilnensis from 3.48 to 10.01 g formalin mass m−2 year−1 and for E. octoculata from 11.29 to 19.29 g formalin mass m−2 year−1. The prey diversity and overlap of prey composition and potential prey resources of leeches indicate that, compared to older leeches, the younger leeches are more selective feeders.