Stenotypy and Eurytopy - Distribution Models as a Tool for Estimating Niche Overlap in two Spider species, Trochosa terricola and Eresus kollari (Araneae: Lycosidae/Eresidae)

Distribution models are a standard tool of contemporary ecology and conservation biology, but literature on distribution modelling for spiders is sparse. The ecological niches of the eurytopic species Trochosa terricola Thorell 1856 (Lycosidae) and the endangered stenotopic species Eresus kollari Rossi 1846 (Eresidae) have been studied by means of comparing their ecological niche overlap. Both species share the same habitat allowing for environmental data to be gathered by pitfall trapping during the locomotive period of E kollari. Two methodological approaches were used to analyse the data: GLM (general linear model) and PCA (principle component analysis). Significant overlap of the two niches was found with the E kollari niche almost forming a subset within that of T terricola which spanned a much wider niche. Statistic modelling indicated that both species follow the 'co-existence principle' rather than the 'competitive exclusion principle'. Moreover, the high number of capture rates revealed that T terricola wanders widely as opposed to following the sit-and-wait hunting strategy. It is recommended that a heathland management strategy should be developed that aims to keep the landscape continuously semi-open. As E kollari may serve as a target species or even an umbrella species, it can be assumed that both species will benefit from management measures aimed at maintaining a semi-open landscape.