RESUMO
Birds in mixed-species flocks benefit from greater foraging efficiency and reduced predation, but also face costs related to competition and activity matching. Because this cost-benefit trade-off is context-dependent (e.g. abiotic conditions and habitat quality), the structure of flocks is expected to vary along elevational, latitudinal and disturbance gradients. Specifically, we predicted that the connectivity and cohesion of flocking networks would (i) decline towards tropical latitudes and lower elevations, where competition and activity matching costs are higher, and (ii) increase with lower forest cover and greater human disturbance. We analysed the structure of 84 flock networks across the Andes and assessed the effect of elevation, latitude, forest cover and human disturbance on network characteristics. We found that Andean flocks are overall open-membership systems (unstructured), though the extent of network structure varied across gradients. Elevation was the main predictor of structure, with more connected and less modular flocks upslope. As expected, flocks in areas with higher forest cover were less cohesive, with better defined flock subtypes. Flocks also varied across latitude and disturbance gradients as predicted, but effect sizes were small. Our findings indicate that the unstructured nature of Andean flocks might arise as a strategy to cope with harsh environmental conditions. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.
Assuntos
Aves , Ecossistema , Animais , FlorestasRESUMO
Pollinator foraging fidelity (i.e., consistent and repeated visitation to a particular plant species or area) is poorly understood for most bee species, but is important information for both the conservation of plant and pollinator species and the ecosystem services they provide to humans. We used plant-pollinator surveys and mark-recapture of floral-visiting Hymenoptera to study the foraging fidelity and species interaction network properties of a plant-pollinator community in the tropical Andes of southern Ecuador. After marking 92 bees visiting six plant taxa along four 100-m transects between July 16th and July 31st of 2019, only honeybees were resighted at a recapture rate of 47.7% (41/86). During our surveys, we observed nine bee and two wasp taxa feeding from the flowers of 10 morphospecies of plants, and we found significantly low network nestedness and significantly high network-level specialization. Specialization (d') was also significant for honeybees and bumblebees and for three plant taxa. Overall, our findings indicated that feral, non-native honeybees in this region dominated the local plant-pollinator network, yet this species is acting as a specialist forager at the individual level. Our results suggest that honeybees may be replacing the pollination services of some native bees and wasps in the region, but more research is needed to determine the effectiveness of honeybee pollination for the local plants.
Assuntos
Ecossistema , Vespas , Animais , Abelhas , Equador , Flores , Humanos , Plantas , PolinizaçãoRESUMO
Many studies have investigated how habitat fragmentation affects the taxonomic and functional diversity of species assemblages. However, the joint effects of habitat fragmentation and environmental conditions on taxonomic and functional diversity, for instance across elevational gradients, have largely been neglected so far. In this study, we compare whether taxonomic and functional indicators show similar or distinct responses to forest fragmentation across an elevational gradient. We based our analysis on a comprehensive data set of species-rich bird assemblages from tropical montane forest in the Southern Andes of Ecuador. We monitored birds over 2 years in two habitat types (continuous and fragmented forest) at three elevations (i.e., 1000, 2000, and 3000 m a.s.l) and measured nine morphological traits for each bird species on museum specimens. Bird species richness and abundance were significantly higher in fragmented compared to continuous forests and decreased towards high elevations. In contrast, functional diversity was significantly reduced in fragmented compared to continuous forests at low elevations, but fragmentation effects on functional diversity tended to be reversed at high elevations. Our results demonstrate that taxonomic and functional indicators can show decoupled responses to forest fragmentation and that these effects are highly variable across elevations. Our findings reveal that functional homogenization in bird communities in response to fragmentation can be masked by apparent increases in taxonomic diversity, particularly in diverse communities at low elevations.