Cross-ecosystem engineers: the dual role of fruit bats in cave nutrient dynamics and landscape seed dispersal.

Bats provide key ecosystem services, yet their dual role in subterranean habitats remains understudied. Frugivorous species such as Artibeus planirostris can act both as seed dispersers in surface environments and as sources of organic matter in caves through guano deposition. We investigated these functions in Toca do Morrinho Cave (Bahia, Brazil), combining captive experiments and field monitoring to assess guano production, diet, deposition patterns, and seed fate. Bats consumed fruits from 11 plant species and produced an average of 3.24 g of dry guano per day. Most feces (91.1%) were deposited outside the cave, corresponding to ~ 275 seeds per bat per day, underscoring their efficiency as seed dispersers. In contrast, only 8.9% of feces were dropped inside the cave, where seeds failed to germinate under aphotic conditions. Nevertheless, this deposition enriched the hypogean environment, providing organic matter and moisture that support invertebrate assemblages. Germination trials showed that gut passage generally preserved or enhanced seed viability, particularly for Ficus gomelleira. Our results highlight the multifunctionality of A. planirostris as both a driver of plant recruitment across landscapes and a contributor to subterranean nutrient dynamics. While seed dispersal is highly effective in epigean systems, deposition underground represents an antagonistic outcome for plants but a critical subsidy for cave communities. By linking above- and belowground ecosystems, A. planirostris functions as a cross-ecosystem engineer. Protecting its cave colonies is therefore vital not only for subterranean biodiversity but also for broader ecological processes that depend on bat-mediated connectivity.