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 b-diversity-differences among sites in their species compositions-is critical to forecast communities in the Anthropocene. Here, we study patterns in bird b-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 b-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.
Many insects rely on chemical signals to transmit precise information on the location, identity, and quality of potential mates. Chemical signals are often broadcasted at sites with physical properties that maximize signal propagation and signal transmission. Male neotropical orchid bees (Euglossini) perch and display on vertical branches and tree trunks in the forest to expose volatile blends (perfumes) that they previously collected from their environment. Previous studies have shown that the chemical composition of perfume blends is highly differentiated even between closely related species. However, variation in behavioral components of perfume exposure and male display remain poorly understood. We conducted a four-year study on orchid bee display sites (8 species) in pacific Costa Rica, using field observations along with chemical analysis and cage experiments to assess display niche partitioning among sympatric species. We evaluated the influence of physical factors (terrain, wind, light) on the distribution of perch sites and on display behavior, and tested a prediction of the sex pheromone-analogue hypothesis, i.e., that displaying males have above-average quantities or qualities of acquired perfumes. Males of different species displayed in the same general area and sometimes in close proximity to each other, but partitioned the display niche by selecting different perch diameters, display heights, and by displaying at different times of the day. Most perch sites were located inside the forest on elevated ground, especially along ridges, where stronger winds may help disperse perfume signals. Furthermore, the angular position of displaying males on perches was narrowly determined by wind direction, with males being positioned on the downwind side of the perch, where they would be most conspicuous to conspecifics approaching on an odor trail. Although our results generally support the hypothesis that perfumes serve as pheromone analogues, we did not find differences in the perfume composition of males caught at display perches and males captured at chemical baits. This suggests that, while chemical communication is an integral part of orchid bee display, male display activity is not determined by the history of, and success in, volatile acquisition.
1. The outcome of the ongoing biodiversity crisis depends on the capacity of the Earth's wildlife to persist in working landscapes. Yet, the species that occupy working landscapes are often distinct from those in protected areas, with a large group of "sensitive species" thought to rarely venture into human-dominated landscapes. As governments have committed to restoring degraded lands world-wide, determining whether and how working landscapes can be restored to benefit sensitive species remains a major challenge.2. We surveyed Neotropical birds across Northwestern Costa Rica in protected areas, farms and forests embedded within working landscapes. We analysed community composition to understand how gradients of forest cover, fragmentation and regional precipitation determine how conserving (or restoring) tropical forests in working landscapes could safeguard entire communities, especially sensitive species with limited ranges.3. We found agricultural sites maintained relatively high bird diversity but hosted very distinct communities from those found in protected areas. The average range size of species found in agricultural communities was double the size of species in protected areas. However, high forest cover sites in working landscapes housed bird communities with small range sizes that were equivalent to those in nearby protected areas, despite being twice as fragmented and significantly more disturbed.4. The effect of local forest cover on bird composition was contingent on both landscape context and regional climate. When local forest cover increased in wetter regions and more forested landscapes, bird communities in working landscapes exhibited a stronger shift towards the assemblages found in protected areas.Specifically, we found that reforesting the wettest sites would increase similarity to protected areas fourfold compared to only a twofold increase in the driest sites. Synthesis and applications.Despite experiencing much more fragmentation and degradation than protected areas, forests in Costa Rican working landscapes can maintain bird communities that strongly resemble those found in protected areas. This suggests that conserving or restoring forests in working landscapes,
Aim Changes in climate and land use are modifying biodiversity worldwide. Yet it remains unclear how both drivers interact to structure communities and determine patterns in taxonomic, phylogenetic and functional diversity at local scales. We focused on bird diversity and asked: how do precipitation and forest cover gradients interactively structure these elements of avian diversity? Location Guanacaste, North‐western Costa Rica. Methods We quantified changes in the abundance and composition of bird communities along independent gradients of regional precipitation, local forest cover and landscape forest cover that serve as proxies for climate drying and habitat conversion. We conducted point counts at 150 sites and statistically accounted for imperfect detection to test how environmental variation shaped community‐wide diversity metrics. Results We found that the three dimensions of diversity diverged in their responses to environmental gradients. Specifically, species richness increased linearly with precipitation, reached maximum values with intermediate tree cover at local scales and peaked at high levels of landscape tree cover. While phylogenetic diversity did not vary strongly across any gradient, functional diversity increased monotonically with both local and landscape‐level tree cover. Maximum values of functional diversity only occurred in large patches of forest where the tree cover was >75% at both local and landscape scales. Contrary to our expectations, we did not detect significant interactions between precipitation and tree cover gradients on any metric of local bird diversity. Main conclusions Our findings suggest that taxonomic diversity was more sensitive to environmental gradients than functional and phylogenetic diversity. The lack of synergies between precipitation and forest cover gradients on alpha diversity, at least in this system, simplifies the prospects of predicting future biodiversity change at local scales as our results suggest that climate change and land use act independently of one another.
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