Evaluating biotic interactions in a hard and fragile ecosystem: xerophilous land snails and epilithic cryptogram communities in rocky outcrops

In biodiversity hotspots like rocky outcrops, species distribution is shaped by environmental factors at multiple scales, with microhabitat characteristics like substrate composition and shelter playing key roles. These fragile ecosystems host a rich diversity of species, including endemic and endangered taxa. However, they remain underexplored in conservation research, despite their crucial role in sustaining xerophilic biodiversity. This study investigates the environmental drivers of xerophilous communities, specifically on land snails and epilithic cryptograms, in a Mediterranean Natural Park. Specifically, we examine how substrate composition influences species assemblages and their biotic relationship. Our field data and statistical models reveal that substrate heterogeneity, comprising conglomerates, pebbles, and sand, creates microclimatic conditions that support diverse communities. Land snails are particularly associated with larger pebbles that provide shelter and moisture retention, while epilithic species thrive on conglomerates and finer materials that stabilize microhabitats. Minimal overlap in habitat preferences between snails and epilithic suggests niche partitioning and complex biotic interactions, highlighting the importance of substrate diversity in sustaining biodiversity. From a conservation perspective, we propose conservation strategies focussed on preserving substrate structural diversity within rocky outcrops to maintain vital habitat features for xerophilous species. Management policies should integrate microhabitat-scale considerations to enhance ecosystem resilience and mitigate disturbances from human and wildlife activities. This research not only advances our understanding of invertebrate ecology in extreme habitats but also offers valuable insights for the conservation of other biodiversity-rich ecosystems facing similar challenges. • Substrate heterogeneity drives xerophilous biodiversity in Mediterranean rocky outcrops. • Land snails and epilithic cryptogams exhibit niche partitioning linked to microhabitat features. • Pebbles provide shelter and moisture for snails, while conglomerates favor epilithic species. • Conservation strategies should preserve substrate structural diversity to sustain ecosystem resilience.