Cataxia on the edge: range contraction of endemic montane mygalomorph spiders in a biodiversity hotspot
Karlene Bain, Sarah Comer, Mark S. Harvey, Michael G. Rix, Barbara York MainContext
Large shifts in species distributions are projected under future climate scenarios, yet long-term empirical evidence remains scarce, particularly for invertebrates.
Aims
We quantified changes in occupancy, abundance, and population structure over 22 years for four short-range endemic trapdoor spider species (Cataxia sandsorum, C. stirlingi, C. colesi, C. barrettae) and tested associations with microhabitat, environmental, and disturbance conditions.
Methods
Presence–absence surveys conducted in 2002 and 2024 across >250 km of replicated traverses were combined with burrow density and microhabitat assessments from 293 quadrats across 17 subpopulations. Species distribution models identified predictors of occupancy and burrow density.
Key results
All species showed severe contractions, with 49–67% reductions in area of occupancy and >98% declines in burrow abundance. Declines were greatest at lower elevations and in areas exposed to repeated intense fires. These areas also supported fewer juveniles and recruits. Remnant populations persist mostly in cool, moist, high-elevation gullies where orographic cloud, rocky substrates, and microhabitat complexity provide climate buffering and fire refuge. Occupancy and burrow density were strongly associated with topography and fine-scale microhabitat variables.
Conclusions
Despite historical persistence linked to longevity and deep-burrowing behaviour, these species have declined rapidly over the past two decades.
Implications
Narrow habitat requirements and limited dispersal capacity render these taxa highly vulnerable to escalating climate and fire pressures. Other co-habiting surface and shallow-burrowing relict taxa may face even greater risk. Urgent conservation action is required, including habitat protection and restoration, microhabitat enhancement, fire-regime management, assisted recolonisation, connectivity management, long-term monitoring, legislative integration, and stakeholder engagement.