Effects of increasing aridity and chronic anthropogenic disturbance on seed dispersal by ants in Brazilian Caatinga.

Anthropogenic disturbance and climate change are the main drivers of biodiversity loss and ecological services around the globe. There is concern that climate change will exacerbate the impacts of disturbance and thereby promote biotic homogenization, but its consequences for ecological services are unknown. We investigated the individual and interactive effects of increasing chronic anthropogenic disturbance (CAD) and aridity on seed dispersal services provided by ants in Caatinga vegetation of north-eastern Brazil. The study was conducted in Catimbau National Park, Pernambuco, Brazil. Within an area of 214 km2 , we established nineteen 50 × 20 m plots that encompassed gradients of both CAD and aridity. We offered diaspores of six plant species, three myrmecochorous diaspores and three fleshy fruits that are secondarily dispersed by ants. We then quantified the number of interactions, seed removal rate and dispersal distances, and noted the identities of interacting ant species. Finally, we used pitfall trap data to quantify the abundances of ant disperser species in each plot. Our results show that overall composition of ant disperser species varied along the gradients of CAD and aridity, but the composition of high-quality dispersers varied only with aridity. The total number of interactions, rates of removal and mean distance of removal all declined with increasing aridity, but they were not related to CAD. These same patterns were found when considering only high-quality disperser species, driven by the responses of the dominant disperser Dinoponera quadriceps. We found little evidence of interactive effects of CAD and aridity on seed dispersal services by ants. Our study indicates that CAD and aridity act independently on ant-mediated seed dispersal services in Caatinga, such that the impacts of anthropogenic disturbance are unlikely to change under the forecast climate of increased aridity. However, our findings highlight the vulnerability of seed dispersal services provided by ants in Caatinga under an increasingly arid climate due to low functional redundancy in high-quality disperser species. Given the large number of plant species dependent on ants for seed dispersal, this has important implications for future plant recruitment and, consequently, for the composition of Caatinga plant communities.

Increased anthropogenic disturbance and aridity reduce phylogenetic and functional diversity of ant communities in Caatinga dry forest.

Anthropogenic disturbance and climate change are major threats to biodiversity. The Brazilian Caatinga is the world's largest and most diverse type of seasonally dry tropical forest. It is also one of the most threatened, but remains poorly studied. Here, we analyzed the individual and combined effects of anthropogenic disturbance (three types: livestock grazing, wood extraction, and miscellaneous use of forest resources) and increasing aridity on taxonomic, phylogenetic and functional ant diversity in the Caatinga. We found no aridity and disturbance effects on taxonomic diversity. In spite of this, functional diversity, and to a lesser extent phylogenetic diversity, decreased with increased levels of disturbance and aridity. These effects depended on disturbance type: livestock grazing and miscellaneous resource use, but not wood extraction, deterministically filtered both components of diversity. Interestingly, disturbance and aridity interacted to shape biodiversity responses. While aridity sometimes intensified the negative effects of disturbance, the greatest declines in biodiversity were in the wettest areas. Our results imply that anthropogenic disturbance and aridity interact in complex ways to endanger biodiversity in seasonally dry tropical forests. Given global climate change, neotropical semi-arid areas are habitats of concern, and our findings suggest Caatinga conservation policies must prioritize protection of the wettest areas, where biodiversity loss stands to be the greatest. Given the major ecological relevance of ants, declines in both ant phylogenetic and functional diversity might have downstream effects on ecosystem processes, insect populations, and plant populations.

BIOFRAG - a new database for analyzing BIOdiversity responses to forest FRAGmentation.

Habitat fragmentation studies have produced complex results that are challenging to synthesize. Inconsistencies among studies may result from variation in the choice of landscape metrics and response variables, which is often compounded by a lack of key statistical or methodological information. Collating primary datasets on biodiversity responses to fragmentation in a consistent and flexible database permits simple data retrieval for subsequent analyses. We present a relational database that links such field data to taxonomic nomenclature, spatial and temporal plot attributes, and environmental characteristics. Field assessments include measurements of the response(s) (e.g., presence, abundance, ground cover) of one or more species linked to plots in fragments within a partially forested landscape. The database currently holds 9830 unique species recorded in plots of 58 unique landscapes in six of eight realms: mammals 315, birds 1286, herptiles 460, insects 4521, spiders 204, other arthropods 85, gastropods 70, annelids 8, platyhelminthes 4, Onychophora 2, vascular plants 2112, nonvascular plants and lichens 320, and fungi 449. Three landscapes were sampled as long-term time series (>10 years). Seven hundred and eleven species are found in two or more landscapes. Consolidating the substantial amount of primary data available on biodiversity responses to fragmentation in the context of land-use change and natural disturbances is an essential part of understanding the effects of increasing anthropogenic pressures on land. The consistent format of this database facilitates testing of generalizations concerning biologic responses to fragmentation across diverse systems and taxa. It also allows the re-examination of existing datasets with alternative landscape metrics and robust statistical methods, for example, helping to address pseudo-replication problems. The database can thus help researchers in producing broad syntheses of the effects of land use. The database is dynamic and inclusive, and contributions from individual and large-scale data-collection efforts are welcome.