Meso‐habitat distribution patterns and ecological requirements of two Mediterranean vipers depict weak competition in a contact zone

Abstract

Disentangling the multiple factors that shape the ecological niche of a species is often difficult, especially when in contact with other similar and potentially competing species. Ecological niche models (ENMs), albeit originally developed for environmental factors only, can help in assessing competition by comparing the niches of ecologically similar species. Here, we use ENMs and niche overlap tests to compare the ecological niches of the Western Mediterranean vipers, Vipera aspis and V. latastei, in the secondary contact zone of the High Ebro (Northern Spain), partitioning the species occurrences in sympatric and allopatric subsets. We considered nine geomorphological and landcover variables, obtained from remote sensing, and gathered at the meso‐habitat scale (100 × 100 m). Our ENMs showed partial interspecific divergence in habitat requirements between these two closely related species, with V. aspis selecting more canopied areas and V. latastei preferring more open habitats. No intraspecific differences in ecological requirements were found when sympatric and allopatric subsets were compared, that is, the two species are not experiencing ecological shift when in contact, which suggests weak competition in habitat use. Our findings, therefore, suggest that species distributions in this contact zone are mainly determined by the environmental conditions, with almost no contribution of competitive pressure. Still, a localized competition might exist due to minor differences in the ecological niches and a marked and unequal reduction of suitable areas for the sympatric populations, which could be favouring V. aspis in small regions of the contact zone.