Trait-modulated decline of carabid beetle occurrence along elevation gradients across the European Alps

Aim: To assess how species traits modulate the responses of carabids to
elevation gradients, and how consistent these relationships are across
different Alpine regions. Location: Italian Alps. Taxon: Coleoptera,
Carabidae (ground beetles) Methods: Carabid communities were sampled using
pitfall traps along elevation gradients (697-2840 m) in 416 study sites
comprising a range of habitat types. The probability of carabid occurrence
was modelled in relation to elevation and its interaction with two key
traits, body size and wing development, using a mixed-modelling framework.
The consistency of these associations was then assessed across three
geographically separated regions. Results: Carabid occurrence declined
with increasing elevation, although this relationship was modulated by
both body size and wing development. Smaller species were less likely to
occur than larger-bodied species at lower elevations. There was a steep
decline in occurrence of larger species from low to high elevation, but a
slight increase in smaller species, when considering all regions combined.
All wing development types declined with elevation, most notably for
brachypterous (reduced wings) species. However, these patterns also varied
regionally, especially for wing development, indicating that
trait-elevation interactions are not geographically consistent. Habitat
could not explain the differences between regions for body size, but was
likely an important driver of regional differences in the role of wing
development on carabid occurrence. Main conclusions: Species traits are
important in explaining the distribution of carabids along elevation
gradients in mountains, and they may help to identify the species that are
the most vulnerable, and the most resilient, to future environmental
change. Increased probability of occurrence of smaller species at higher
elevations suggests that they may be particularly vulnerable to
environmental change in the future. However, the difference in responses
to elevation between regions has important implications for modelling
species distributions, as it suggests low model transferability, i.e. a
trait-based model derived from one region cannot necessarily be used to
project relative elevational shifts in a wider area.