Life history patterns of six sympatric species of Leptophlebiidae (Ephemeroptera) in a New Zealand stream and the role of interspecific competition in their evolution

Nymphal life histories of six sympatric species of Leptophlebiidae (Ephemeroptera) were studied in Waitakere River and its tributary, Cascade Stream, a kauri forest stream system in northern New Zealand. Species examined were Neozephlebia scita (Walker), Austroclima jollyae Towns & Peters, Deleatidium myzobranchia Phillips, D. lillii Eaton, Deleatidium sp. A and Deleatidium sp. C. A mixture of well and poorly synchronised life cycles occurred within the guild. Species of Deleatidium had life histories which ranged from univoltine (D. lillii and D. myzobranchia) to weakly bivoltine with overlapping generations and cohorts (Deleatidium sp. C). There was little evidence of temporal segregation, but instead a highdegree of habitat and life history overlap. This conflicts with models based on stream insects from temperate northern hemisphere streams and usually attributed to niche differentiation in response to interspecific competition. The possible role of interspecific competition in evolution of life histories of stream in vertebrates is assessed. It is noted that temporal segregation of life histories does not by itself demonstrate differential use of common resources by congenerics, and that there is little direct evidence to support the widespread assumption that competition is a major influence on the evolution and composition of lotic communities.