Optimizing speleological monitoring efforts: insights from long-term data for tropical iron caves

Do you have enough space? Habitat selection of insectivorous cave-dwelling bats in fragmented landscapes of Eastern Amazon

Individual movements of bats are triggered by their life requirements, limited by their recognition of the environment and risks of moving, and mediated by habitat selection. Mining adds fragmentation and heterogeneity to landscapes, with poorly understood consequences to the life activities of the bats. Cave dwelling bats spend most of their life cycles within caves, and as they constantly forage in external landscapes, their contribution in the input of organic matter to the caves is of paramount importance to the subterranean biodiversity. We investigated habitat selection by cave bats in a mosaic of Amazonian forests, iron-rich savannas and iron-caves, studying the movements of the aerial insect-catcher Furipterus horrens (Furipteridae) and of the foliage gleaning bat Lonchorhina aurita (Phyllostomidae), both cave-dependent in the area. We used radio telemetry to assess their use of habitats, under the prediction that these species prefer preserved habitats for their foraging bouts, avoiding human-modified habitats. We also anticipated larger areas and commuting distances for both species when foraging in disturbed landscapes. Thirty-one bats were monitored in conserved habitats, mining sites and pastures resulting in an average range of 415.1 ± 837.4 ha and average commuting distances of 2163 ± 2453 m (F. horrens) and 681.1 ± 1101 ha and 2781.5 ± 2333 m (L. aurita). Our results suggest that F. horrens are open space foragers, frequently recorded in cangas, and L. aurita are forest foragers that use all habitats proportionally to their availability in the landscape. We detected landscape-related effects mediated by seasonal variation in the maximum commuting distance performed by both species. These are the first radiotelemetry data available for F. horrens and L. aurita, delivering original baselines to understand their movement behaviors. This information sheds light into constraints related to the optimal and adjusted biological cycles of these two species and their range shifts under scenarios of disturbance and may subsidize programs for their conservation.

Caves as wildlife refuges in degraded landscapes in the Brazilian Amazon

Cross-habitat spillover may be the outcome of a process of habitat loss or degradation where the receiving habitat serves as a refuge for organisms. Once surface habitats are lost or degraded, animals can find underground refuge in caves. This paper is focused on testing whether taxonomic order richness inside caves is positively affected by the loss of the native vegetation cover surrounding caves; whether degradation of native vegetation cover predicts cave community composition; and whether there is a pattern of cave community clusters delimited by similarity in the effects of habitat degradation on animal communities. We gathered a comprehensive speleological dataset consisting of occurrence data of thousands of invertebrates and vertebrates sampled in 864 iron caves in the Amazon, to test the effects of both variables measured inside caves and surrounding landscapes on spatial variation in richness and composition of animal communities. We show that caves can work as refuges for the fauna in landscapes where the native vegetation cover surrounding them was degraded, which was evidenced by landcover change increasing the richness of cave communities and clustering caves by similarity in community composition. Therefore, habitat degradation on the surface should be a key variable when characterizing cave ecosystems for conservation prioritization and offset planning. Habitat degradation causing a cross-habitat spillover effect highlights the importance of maintaining the connection between caves by the surface, especially large caves. Our study can help guide industry and stakeholders working on the complex conciliation between land use and biodiversity conservation.

Towards evidence-based conservation of subterranean ecosystems

Subterranean ecosystems are among the most widespread environments on Earth, yet we still have poor knowledge of their biodiversity. To raise awareness of subterranean ecosystems, the essential services they provide, and their unique conservation challenges, 2021 and 2022 were designated International Years of Caves and Karst. As these ecosystems have traditionally been overlooked in global conservation agendas and multilateral agreements, a quantitative assessment of solution-based approaches to safeguard subterranean biota and associated habitats is timely. This assessment allows researchers and practitioners to understand the progress made and research needs in subterranean ecology and management. We conducted a systematic review of peer-reviewed and grey literature focused on subterranean ecosystems globally (terrestrial, freshwater, and saltwater systems), to quantify the available evidence-base for the effectiveness of conservation interventions. We selected 708 publications from the years 1964 to 2021 that discussed, recommended, or implemented 1,954 conservation interventions in subterranean ecosystems. We noted a steep increase in the number of studies from the 2000s while, surprisingly, the proportion of studies quantifying the impact of conservation interventions has steadily and significantly decreased in recent years. The effectiveness of 31% of conservation interventions has been tested statistically. We further highlight that 64% of the reported research occurred in the Palearctic and Nearctic biogeographic regions. Assessments of the effectiveness of conservation interventions were heavily biased towards indirect measures (monitoring and risk assessment), a limited sample of organisms (mostly arthropods and bats), and more accessible systems (terrestrial caves). Our results indicate that most conservation science in the field of subterranean biology does not apply a rigorous quantitative approach, resulting in sparse evidence for the effectiveness of interventions. This raises the important question of how to make conservation efforts more feasible to implement, cost-effective, and long-lasting. Although there is no single remedy, we propose a suite of potential solutions to focus our efforts better towards increasing statistical testing and stress the importance of standardising study reporting to facilitate meta-analytical exercises. We also provide a database summarising the available literature, which will help to build quantitative knowledge about interventions likely to yield the greatest impacts depending upon the subterranean species and habitats of interest. We view this as a starting point to shift away from the widespread tendency of recommending conservation interventions based on anecdotal and expert-based information rather than scientific evidence, without quantitatively testing their effectiveness.