Birds optimize fruit size consumed near their geographic range limits.

Animals can adjust their diet to maximize energy or nutritional intake. For example, birds often target fruits that match their beak size because those fruits can be consumed more efficiently. We hypothesized that pressure to optimize diet-measured as matching between fruit and beak size-increases under stressful environments, such as those that determine species' range edges. Using fruit-consumption and trait information for 97 frugivorous bird and 831 plant species across six continents, we demonstrate that birds feed more frequently on closely size-matched fruits near their geographic range limits. This pattern was particularly strong for highly frugivorous birds, whereas opportunistic frugivores showed no such tendency. These findings highlight how frugivore interactions might respond to stressful conditions and reveal that trait matching may not predict resource use consistently.

An ultrasound-absorbing inflorescence zone enhances echo-acoustic contrast of bat-pollinated cactus flowers.

Flowering plants have evolved an extraordinary variety of signalling traits to attract their pollinators. Most flowers rely on visual and chemical signals, but some bat-pollinated plants have evolved passive acoustic floral signals. All known acoustic flower signals rely on the same principle of increased sonar reflectivity. Here, we describe a novel mechanism that relies on increased absorption of the area surrounding the flower. In a bat-pollinated cactus (Espostoa frutescens) we found a hairy inflorescence zone, a so-called cephalium. Flowers solely emerge out of this zone. We measured the echoes of cephalia, flowers and unspecialized column surfaces and recorded echolocation calls of approaching bats. We found that the cephalium acts as a strong ultrasound absorber, attenuating the sound by -14 dB. The absorption was highest around the echolocation call frequencies of approaching bats. Our results indicate that, instead of making flowers more reflective, plants can also evolve structures to attenuate the background echo, thereby enhancing the acoustic contrast with the target.

Global and regional ecological boundaries explain abrupt spatial discontinuities in avian frugivory interactions.

Species interactions can propagate disturbances across space via direct and indirect effects, potentially connecting species at a global scale. However, ecological and biogeographic boundaries may mitigate this spread by demarcating the limits of ecological networks. We tested whether large-scale ecological boundaries (ecoregions and biomes) and human disturbance gradients increase dissimilarity among plant-frugivore networks, while accounting for background spatial and elevational gradients and differences in network sampling. We assessed network dissimilarity patterns over a broad spatial scale, using 196 quantitative avian frugivory networks (encompassing 1496 plant and 1004 bird species) distributed across 67 ecoregions, 11 biomes, and 6 continents. We show that dissimilarities in species and interaction composition, but not network structure, are greater across ecoregion and biome boundaries and along different levels of human disturbance. Our findings indicate that biogeographic boundaries delineate the world's biodiversity of interactions and likely contribute to mitigating the propagation of disturbances at large spatial scales.

Looking inside the Blackbox: Cuenca's water metabolism.

The socio-ecological metabolism of the water connects concepts that emerge out of the complexity of ecosystems, linking endosomatic processes that are indispensable for society while forming different hierarchic levels and relations among as well as aligning to their particularities. The consumptive uses of Cuenca city in their different categories and social metabolism both at rural and urban levels were assessed, inquiring about diverse typologies of the city's water. Water Metabolic Rates (WMR) were calculated for each one of the consumptives' uses gauged in liters per hour of human activity. Our results indicate that farming and industrial uses of water were highly inefficient. Linked to farms, both consumption of water and metabolic rates were higher in the rural areas. While paid work showed higher metabolic rates than households. Rural households evidenced a greater use of water and higher metabolic rates than urban households as water use combines human consumption and family farming. This research determined the water metabolism of the socio-ecological system in the canton of Cuenca, Ecuador through different dimensions of water metabolism. Formulating a system of flows and uses of water that were metabolized by different hierarchy levels of diverse consumptive uses within the aforementioned canton, as a tool to implement policies that guarantee water access and ecological metabolism, linking social dynamics within ecosystems.

Similar composition of functional roles in Andean seed-dispersal networks, despite high species and interaction turnover.

The species composition of local communities varies in space, and its similarity generally decreases with increasing geographic distance between communities, a phenomenon known as distance decay of similarity. It is, however, not known how changes in local species composition affect ecological processes, that is, whether they lead to differences in the local composition of species' functional roles. We studied eight seed-dispersal networks along the South American Andes and compared them with regard to their species composition and their composition of functional roles. We tested (1) if changes in bird species composition lead to changes in the composition of bird functional roles, and (2) if the similarity in species composition and functional-role composition decreased with increasing geographic distance between the networks. We also used cluster analysis to (3) identify bird species with similar roles across all networks based on the similarity in the plants they consume, (i) considering only the species identity of the plants and (ii) considering the functional traits of the plants. Despite strong changes in species composition, the networks along the Andes showed similar composition of functional roles. (1) Changes in species composition generally did not lead to changes in the composition of functional roles. (2) Similarity in species composition, but not functional-role composition, decreased with increasing geographic distance between the networks. (3) The cluster analysis considering the functional traits of plants identified bird species with similar functional roles across all networks. The similarity in functional roles despite the high species turnover suggests that the ecological process of seed dispersal is organized similarly along the Andes, with similar functional roles fulfilled locally by different sets of species. The high species turnover, relative to functional turnover, also indicates that a large number of bird species are needed to maintain the seed-dispersal process along the Andes.

Direct and plant-mediated effects of climate on bird diversity in tropical mountains.

AIM: Although patterns of biodiversity across the globe are well studied, there is still a controversial debate about the underlying mechanisms and their generality across biogeographic scales. In particular, it is unclear to what extent diversity patterns along environmental gradients are directly driven by abiotic factors, such as climate, or indirectly mediated through biotic factors, such as resource effects on consumers. LOCATION: Andes, Southern Ecuador; Mt. Kilimanjaro, Tanzania. METHODS: We studied the diversity of fleshy-fruited plants and avian frugivores at the taxonomic level, that is, species richness and abundance, as well as at the level of functional traits, that is, functional richness and functional dispersion. We compared two important biodiversity hotspots in mountain systems of the Neotropics and Afrotropics. We used field data of plant and bird communities, including trait measurements of 367 plant and bird species. Using structural equation modeling, we disentangled direct and indirect effects of climate and the diversity of plant communities on the diversity of bird communities. RESULTS: We found significant bottom-up effects of fruit diversity on frugivore diversity at the taxonomic level. In contrast, climate was more important for patterns of functional diversity, with plant communities being mostly related to precipitation, and bird communities being most strongly related to temperature. MAIN CONCLUSIONS: Our results illustrate the general importance of bottom-up mechanisms for the taxonomic diversity of consumers, suggesting the importance of active resource tracking. Our results also suggest that it might be difficult to identify signals of ecological fitting between functional plant and animal traits across biogeographic regions, since different species groups may respond to different climatic drivers. This decoupling between resource and consumer communities could increase under future climate change if plant and animal communities are consistently related to distinct climatic drivers.

Direct and indirect effects of plant and frugivore diversity on structural and functional components of fruit removal by birds.

Seed dispersal is an important ecosystem function, but it is contentious how structural and functional diversity of plant and bird communities are associated with seed-dispersal functions. We used structural equation models to test how structural (i.e., abundance, species richness) and functional diversity (i.e., functional dispersion and community-weighted means of functional traits) of fruiting plants and frugivorous birds directly and indirectly influence the respective components of fruit removal. We recorded plant and bird diversity in point counts and observed plant-frugivore interactions in a tropical mountain forest in Ecuador. We also recorded plant and bird morphological traits to calculate measures of functional diversity. We found that fruit abundance had a positive direct effect on bird abundance, which directly and indirectly mediated the abundance of removed fruits. Plant and bird species richness were only directly related to the richness of the removed fruits. Functional dispersion of the plant community was positively associated to that of the bird community and to that of the removed fruits. Consistently, we found positive associations between community-weighted means of plant and bird traits and between community-weighted means of plant traits and that of plants with removed fruits. In contrast, community-weighted means of the bird community were unrelated to that of the removed fruits. Overall, our results suggest that plant abundance directly and indirectly influences fruit removal, likely because of avian fruit tracking. However, we did not find strong links between the functional diversity of the frugivore community and removed fruits, suggesting that other factors in addition to plant-animal trait matching might be important for the functional diversity of removed fruits. Our findings highlight the importance of frugivore abundance for maintaining seed dispersal by animals in tropical forests.

Different responses of taxonomic and functional bird diversity to forest fragmentation across an elevational gradient.

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.

Spatio-temporal variation in bird assemblages is associated with fluctuations in temperature and precipitation along a tropical elevational gradient.

Understanding the spatial and temporal dynamics of species assemblages is a main challenge in ecology. The mechanisms that shape species assemblages and their temporal fluctuations along tropical elevational gradients are particularly poorly understood. Here, we examined the spatio-temporal dynamics of bird assemblages along an elevational gradient in Ecuador. We conducted bird point counts at three elevations (1000, 2000 and 3000 m) on 18 1-ha plots and repeated the sampling eight times over two years (216 hours in total). For each plot, we obtained data of monthly temperatures and precipitation and recorded the overall resource availability (i.e., the sum of flower, fruit, and invertebrate resources). As expected, bird richness decreased from low to high elevations. Moreover, we found a significant decrease in bird abundance and richness and an increase in evenness between the most and least humid season at each of the three elevations. Climatic factors were more closely related to these temporal fluctuations than local resource availability. While temperature had significant positive effects on the abundance of birds at mid and high elevations, precipitation negatively affected bird abundance at low and mid elevations. Our study highlights that bird assemblages along tropical elevational gradients can show pronounced seasonal fluctuations. In particular, low temperatures and high precipitation seem to impose important constraints on birds. We conclude that potential changes in climate, due to global warming, are likely to affect the spatio-temporal dynamics of bird assemblages along tropical elevational gradients.

Land use change has stronger effects on functional diversity than taxonomic diversity in tropical Andean hummingbirds.

Land use change modifies the environment at multiple spatial scales, and is a main driver of species declines and deterioration of ecosystem services. However, most of the research on the effects of land use change has focused on taxonomic diversity, while functional diversity, an important predictor of ecosystem services, is often neglected. We explored how local and landscape scale characteristics influence functional and taxonomic diversity of hummingbirds in the Andes Mountains in southern Ecuador. Data was collected in six landscapes along a land use gradient, from an almost intact landscape to one dominated by cattle pastures. We used point counts to sample hummingbirds from 2011 to 2012 to assessed how local factors (i.e., vegetation structure, flowering plants richness, nectar availability) and landscape factors (i.e., landscape heterogeneity, native vegetation cover) influenced taxonomic and functional diversity. Then, we analyzed environment - trait relationships (RLQ test) to explore how different hummingbird functional traits influenced species responses to these factors. Taxonomic and functional diversity of hummingbirds were positively associated with landscape heterogeneity but only functional diversity was positively related to native vegetation coverage. We found a weak response of taxonomic and functional diversity to land use change at the local scale. Environment-trait associations showed that body mass of hummingbirds likely influenced species sensitivity to land use change. In conclusion, landscape heterogeneity created by land use change can positively influence hummingbird taxonomic and functional diversity; however, a reduction of native vegetation cover could decrease functional diversity. Given that functional diversity can mediate ecosystem services, the conservation of native vegetation cover could play a key role in the maintenance of hummingbird pollination services in the tropical Andes. Moreover, there are particular functional traits, such as body mass, that increase a species sensitivity to land use change.