Persistence without prosperity at the upper range margin: Elevation, microhabitat buffering and biotic pressure in a range-expanding spider

 

Persistence without prosperity at the upper range margin: Elevation, microhabitat buffering and biotic pressure in a range-expanding spider

Abstract

1. The upper elevational range limits of thermophilic arthropods reflect constraints on population persistence rather than simple presence.
2. We examined how elevation structures affect the occurrence, abundance, reproductive behaviour and biotic pressure of the spider Cheiracanthium punctorium in Central Europe using a hypothesis-driven synthesis of site-level and cocoon-level data collected over 4 years.
3. Both occurrence and abundance decreased steeply with elevation, with a pronounced loss of occupancy above approximately 850 m a.s.l., indicating a well-defined upper range boundary. Reproductive behaviour shifted systematically along the gradient, as females placed egg cocoons lower on vegetation at higher elevations, independent of vegetation height, which is consistent with behavioural adjustment to increasingly unfavourable microclimatic conditions. Surface moisture reduced the occurrence and abundance across elevations, whereas coarse geomorphological variables contributed little to the model's explanatory power. Anthropogenic linear features increased the probability of site occupancy and colonization at higher elevations but did not increase local abundance once the populations were established. Biotic pressure changed directionally with elevation, with the prevalence and intensity of parasitoids declining strongly. In contrast, the frequency of damaged cocoons (breaches of adult female reproductive nests, consistent with increased external disturbance and likely predator access) increased with elevation. Integrated abundance models identified elevation as the dominant constraint on population size, with microhabitat moisture as a consistent secondary limitation.
4. Behavioural plasticity and favourable microhabitats therefore permit persistence near elevational range limits but do not overcome strong abiotic constraints on abundance. The range expansion of thermophilic arthropods is likely characterized by sparse, demographically constrained populations with a limited capacity to contribute to ecosystem functioning at upper range margins.

Vacek, Z., Korenko, S. & Heneberg, P. (2026) Persistence without prosperity at the upper range margin: Elevation, microhabitat buffering and biotic pressure in a range-expanding spider. Ecological Entomology, 1–18. Available from: https://doi.org/10.1111/een.70110