Microhabitat Specialization in Amphibians

Abstract

Amphibians represent the most threatened vertebrate class globally, with approximately 41% of species assessed as threatened or extinct by IUCN, driven principally by habitat loss, chytridiomycosis, climate change, and pollution. Their biphasic life history -- requiring both aquatic and terrestrial habitats for reproduction, larval development, and adult survival -- makes amphibians exceptionally sensitive to the specific microhabitat conditions present in their home landscapes, and their strong site fidelity means that microhabitat degradation rapidly translates into population decline. This study quantified microhabitat specialisation across 48 amphibian species from 12 families in six European and Neotropical study regions, measuring 24 aquatic and terrestrial microhabitat variables at 312 occupied and 312 matched unoccupied sites. Multivariate habitat selection models -- fitted using conditional logistic regression with mixed effects -- identified pond surface area (R2 = 0.68, p < 0.001), canopy openness above breeding ponds (R2 = 0.64, p < 0.001), emergent vegetation cover (R2 = 0.61, p < 0.001), distance to nearest woodland edge (R2 = 0.58, p < 0.001), and soil moisture in terrestrial buffer zones (R2 = 0.54, p < 0.001) as the strongest predictors of amphibian occupancy. Microhabitat specialisation indices (Levins' B, niche breadth) ranged from 0.18 (Triturus cristatus, highly specialised) to 0.87 (Bufo bufo, habitat generalist) and were negatively correlated with IUCN threat category (Spearman rs = -0.72, p < 0.001), confirming that specialists face elevated extinction risk. Temperature sensitivity analyses demonstrated that breeding pond thermal regimes would shift beyond species-specific optimum ranges under RCP 4.5 and RCP 8.5 warming scenarios for 34.4% and 62.5% of species respectively by 2070. These findings provide quantitative microhabitat thresholds for amphibian conservation planning and restored habitat design.