Facing complexity in tropical conservation: how reduced impact logging and climatic extremes affect beta diversity in tropical amphibian assemblages

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver-response relationships to develop conceptual models across ecosystems

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed 'beta diversity') is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.

At the edge of extinction: a first herpetological assessment of the proposed Serra do Pingano Rainforest National Park in Uíge Province, northern Angola

We systematically assess the herpetofaunal diversity of the Serra do Pingano Forest Ecosystem (SPFE) and additional localities throughout the northern Angolan province of Uíge during four independent Rapid Assessment (RA) field campaigns held between 2013 and 2019. These assessments represent the first systematic surveys of amphibians and reptiles from the province, and thus we provide the first province-wide species list. We collected data on the status and current threats to amphibians and reptiles in the proposed Serra do Pingano Rainforest National Park and were able to document 33 species of reptiles from Uíge province. Of the 33 species recorded from the province, 10 species are exclusively found in the SPFE. Amphibian surveys yielded 47 amphibian species from the province. These include 14 new country records and additional records that may represent undescribed species. This raises the amphibian count for Angola to at least 133 species, which includes 18 species exclusively found within the SPFE. Species-richness estimators indicate that more species should be detected if survey efforts are intensified. The species composition in the SPFE is unique and consists of a high proportion of forest specialists with restricted ranges and species found nowhere else in the country. This emphasizes today’s paramount importance of the SPFE, which is threatened by increasing agricultural encroachment and uncontrolled timber extraction and charcoal production. These principal factors need to be controlled and/or abandoned in already impacted areas. Conservation strategies should particularly consider the strict protection of remaining intact forests and both lentic and lotic aquatic systems. They are not only crucial for safeguarding a significant number of species that depend on these habitats for reproduction; they also provide key ecosystem services to the local population. Angola, and Uíge province in particular, is at a crossroads concerning decisions and trade-offs among utilization, conservation, and preservation of its forests and, thus, substantial parts of the country’s biodiversity. The establishment of a National Protected Area in the Serra do Pingano Ecosystem is therefore a necessary and urgently needed first step towards protecting Angola’s national biodiversity heritage.

Agriculture erases climate-driven β-diversity in Neotropical bird communities

Earth is experiencing multiple global changes that will, together, determine the fate of many species. Yet, how biological communities respond to concurrent stressors at local-to-regional scales remains largely unknown. In particular, understanding how local habitat conversion interacts with regional climate change to shape patterns in β-diversity-differences among sites in their species compositions-is critical to forecast communities in the Anthropocene. Here, we study patterns in bird β-diversity across land-use and precipitation gradients in Costa Rica. We mapped forest cover, modeled regional precipitation, and collected data on bird community composition, vegetation structure, and tree diversity across 120 sites on 20 farms to answer three questions. First, do bird communities respond more strongly to changes in land use or climate in northwest Costa Rica? Second, does habitat conversion eliminate β-diversity across climate gradients? Third, does regional climate control how communities respond to habitat conversion and, if so, how? After correcting for imperfect detection, we found that local land-use determined community shifts along the climate gradient. In forests, bird communities were distinct between sites that differed in vegetation structure or precipitation. In agriculture, however, vegetation structure was more uniform, contributing to 7%-11% less bird turnover than in forests. In addition, bird responses to agriculture and climate were linked: agricultural communities across the precipitation gradient shared more species with dry than wet forest communities. These findings suggest that habitat conversion and anticipated climate drying will act together to exacerbate biotic homogenization.