Coexistence of two newt species in a transition zone of range overlap release_7es57lcjfba6rb7nlvsmyfq6wm

Abstract

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