Erosion of tropical bird diversity over a century is influenced by abundance, diet and subtle climatic tolerances

Species-level correlates of land-use responses and climate-change sensitivity in terrestrial vertebrates

Land-use and climate change are major pressures on terrestrial biodiversity. Species' extinction risk and responses to human pressures relate to ecological traits and other characteristics in some clades. However, large-scale comparative assessments of the associations between traits and responses to multiple human pressures across multiple clades are needed. We investigated whether a set of ecological characteristics that are commonly measured across terrestrial vertebrates (ecological traits and geographic range area) are associated with species' responses to different land-use types and species' likely sensitivity to climate change. We aimed to test whether generalizable patterns in response to these pressures arise across both pressures and across vertebrate clades, which could inform assessments of the global signature of human pressures on vertebrate biodiversity and guide conservation efforts. At the species level, we investigated associations between land-use responses and ecological characteristics with a space-for-time substitution approach, making use of the PREDICTS database. We investigated associations between ecological characteristics and expected climate-change sensitivity, estimated from properties of species realized climatic niches. Among the characteristics we considered, 3 were consistently associated with strong land-use responses and high climate-change sensitivity across terrestrial vertebrate classes: narrow geographic range, narrow habitat breadth, and specialization on natural habitats (which described whether a species occurs in artificial habitats or not). The associations of other traits with species' land-use responses and climate-change sensitivity often depended on species' class and land-use type, highlighting an important degree of context dependency. In all classes, invertebrate eaters and fruit and nectar eaters tended to be negatively affected in disturbed land-use types, whereas invertebrate-eating and plant- and seed-eating birds were estimated to be more sensitive to climate change, raising concerns about the continuation of ecological processes sustained by these species under global changes. Our results highlight a consistently higher sensitivity of narrowly distributed species and habitat specialists to land-use and climate change, which provides support for capturing such characteristics in large-scale vulnerability assessments.

Wet and dry extremes reduce arthropod biomass independently of leaf phenology in the wet tropics

Warming temperatures are increasing rainfall extremes, yet arthropod responses to climatic fluctuations remain poorly understood. Here, we used spatiotemporal variation in tropical montane climate as a natural experiment to compare the importance of biotic versus abiotic drivers in regulating arthropod biomass. We combined intensive field data on arthropods, leaf phenology and in situ weather across a 1700-3100 m elevation and rainfall gradient, along with desiccation-resistance experiments and multi-decadal modelling. We found limited support for biotic drivers with weak increases in some herbivorous taxa on shrubs with new leaves, but no landscape-scale effects of leaf phenology, which tracked light and cloud cover. Instead, rainfall explained extensive interannual variability with maximum biomass at intermediate rainfall (130 mm month^-1 ) as both 3 months of high and low rainfall reduced arthropods by half. Based on 50 years of regional rainfall, our dynamic arthropod model predicted shifts in the timing of biomass maxima within cloud forests before plant communities transition to seasonally deciduous dry forests (mean annual rainfall 1000-2500 mm vs. <800 mm). Rainfall magnitude was the primary driver, but during high solar insolation, the 'drying power of air' (VPD_max ) reduced biomass within days contributing to drought related to the El Niño-Southern Oscillation (ENSO). Highlighting risks from drought, experiments demonstrated community-wide susceptibility to desiccation except for some caterpillars in which melanin-based coloration appeared to reduce the effects of evaporative drying. Overall, we provide multiple lines of evidence that several months of heavy rain or drought reduce arthropod biomass independently of deep-rooted plants with the potential to destabilize insectivore food webs.

High sensitivity of tropical forest birds to deforestation at lower altitudes

Habitat conversion is a major driver of tropical biodiversity loss, but its effects are poorly understood in montane environments. While community-level responses to habitat loss display strong elevational dependencies, it is unclear whether these arise via elevational turnover in community composition and interspecific differences in sensitivity or elevational variation in environmental conditions and proximity to thermal thresholds. Here we assess the relative importance of inter- and intraspecific variation across the elevational gradient by quantifying how 243 forest-dependent bird species vary in sensitivity to landscape-scale forest loss across a 3000-m elevational gradient in the Colombian Andes. We find that species that live at lower elevations are strongly affected by loss of forest in the nearby landscape, while those at higher elevations appear relatively unperturbed, an effect that is independent of phylogeny. Conversely, we find limited evidence of intraspecific elevational gradients in sensitivity, with populations displaying similar sensitivities to forest loss, regardless of where they exist in a species' elevational range. Gradients in biodiversity response to habitat loss thus appear to arise via interspecific gradients in sensitivity rather than proximity to climatically limiting conditions.