Coexistence of two newt species in a transition zone of range overlap

Abstract Theory suggests that spatial segregation of similar, co-occurring species may be driven by alternative innate life history and dispersal strategies, it operates through catastrophic events. An inventory the evolutionary closely related small-bodied newts Lissotriton helveticus L. vulgaris in northwest France demonstrated species’ partitioning, with dominating two pond-rich historically disturbed coastal areas prevailing inland where ponds are sparser. Population numbers were followed over several decades (1975–2021) a pond within narrow (ca. 2000 m wide) transition zone. Early temporal survey (1986) massive die-off was observed two-third breeding population from late frost event. Yet, contribution to newt assemblage more or less stable around 60%, even though total size fluctuated an order magnitude. third species, Ichthyosaura alpestris , made up ca. 30% 10% till 1993, after which date their relative contributions reversed. These data suggest state shift have occurred among latter assumed two-species dynamics underlying study has been oversimplification. The local decline is paralleled loss well-vegetated wider agricultural terrain affects this than I. alpestris.