Bird Community Changes in Response to Single and Repeated Fires in a Lowland Tropical Rainforest of Eastern Borneo

Our current understanding of bird community responses to tropical forest fires is limited and strongly geographically biased towards South America. Here we used the circular plot method to carry out complete bird inventories in undisturbed, once burned (1998) and twice burned forests (1983 and 1998) in East Kalimantan (Indonesia). Additionally, environmental variables were measured within a 25 m radius of each plot. Three years after fire the number of birds and bird species were similar for undisturbed and burned forests, but species diversity and turnover were significantly lower in the burned forests. The bird species composition also differed significantly between undisturbed and burned forests, with a strong decline of closed forest preferring bird species accompanied by a strong increase in degraded forest preferring species in burned forests. These differences were strongly related to differences in environmental conditions such as shifts in vegetation cover and layering and differences in ground and understorey vegetation structure. We also found significant shifts in body mass distribution, foraging height and feeding guilds between the bird communities in unburned and burned forests. Surprisingly, repeated burning did not lead to increasing impoverishment of the avifauna, and both once and twice burned forests still contained most of the bird species that were also present in undisturbed forest, even though their densities were considerably lowered.     

The functional importance of rare and dominant species in a Neotropical forest bird community

Bird communities in Tropical forests have high rate of rare species, but only recently some studies suggested their disproportional role for the overall functional diversity. We investigated data from bird communities monitored annually using point counts over ten years in Iguassu National Park, that is a large and protected area in the southern portion of the Atlantic Forest in Brazil. We aimed (1) to determine the rare and dominant species in the community based on their abundance over time; (2) to evaluate the impact of each class of rarity on the overall functional volume of the community; (3) to investigate the pattern of occupancy of the trait space filled by each dominance class, and (4) to assess the disparity in functional trait composition between classes of rarity. We defined dominant, intermediate, and rare species in communities using cluster analysis and data of relative abundance of species in five sections of 1-km in the forest interior. The number of clusters was defined in accordance with the silhouette criterion measures of cohesion and separation that range from −1 to 1, with values > 0.5 indicating high-quality clusters. Among total 138 bird species recorded, 107 were rare, 26 intermediates, and 5 dominants. Our data corroborate a functional disproportional importance of rare bird species in the community considering the functional space (FRic), but functional dispersion (FDis) was not significantly different between the rare and intermediate species. In fact, there is a large overlap of the functional volume occupied by rare in relation to dominant/intermediate species. The niche space occupied by rare species covers most of the space occupied by intermediate and dominant species. The low representativeness of functional turnover indicates that few functions are unique to the classes of higher dominance. Our data suggest the importance of rare bird species to the overall functional diversity but also highlights the potential use of dominants/intermediates species as indicators to select important forests areas for conservation, as certain forest fragments. Through these most abundant species it would be possible to assess which functions are heaviest in abundance, becoming core functions, in the context of each independent forest fragment.     

Functional traits reveal the expansion and packing of ecological niche space underlying an elevational diversity gradient in passerine birds

Variation in species richness across environmental gradients may be associated with an expanded volume or increased packing of ecological niche space. However, the relative importance of these alternative scenarios remains unknown, largely because standardized information on functional traits and their ecological relevance is lacking for major diversity gradients. Here, we combine data on morphological and ecological traits for 523 species of passerine birds distributed across an Andes-to-Amazon elevation gradient. We show that morphological traits capture substantial variation in species dietary (75%) and foraging niches (60%) when multiple independent trait dimensions are considered. Having established these relationships, we show that the 14-fold increase in species richness towards the lowlands is associated with both an increased volume and density of functional trait space. However, we find that increases in volume contribute little to changes in richness, with most (78%) lowland species occurring within the range of trait space occupied at high elevations. Taken together, our results suggest that high species richness is mainly associated with a denser occupation of functional trait space, implying an increased specialization or overlap of ecological niches, and supporting the view that niche packing is the dominant trend underlying gradients of increasing biodiversity towards the lowland tropics.     

Functional diversity of avian communities increases with canopy height: From individual behavior to continental‐scale patterns

Vegetation complexity is an important predictor of animal species diversity. Specifically, taller vegetation should provide more potential ecological niches and thus harbor communities with higher species richness and functional diversity (FD). Resource use behavior is an especially important functional trait because it links species to their resource base with direct relevance to niche partitioning. However, it is unclear how exactly the diversity of resource use behavior changes with vegetation complexity. To address this question, we studied avian FD in relation to vegetation complexity along a continental‐scale vegetation gradient. We quantified foraging behavior of passerine birds in terms of foraging method and substrate use at 21 sites (63 transects) spanning 3,000 km of woodlands and forests in Australia. We also quantified vegetation structure on 630 sampling points at the same sites. Additionally, we measured morphological traits for all 111 observed species in museum collections. We calculated individual‐based, abundance‐weighted FD in morphology and foraging behavior and related it to species richness and vegetation complexity (indexed by canopy height) using structural equation modeling, rarefaction analyses, and distance‐based metrics. FD of morphology and foraging methods was best predicted by species richness. However, FD of substrate use was best predicted by canopy height (ranging 10–30 m), but only when substrates were categorized with fine resolution (17 categories), not when categorized coarsely (8 categories). These results suggest that, first, FD might increase with vegetation complexity independently of species richness, but whether it does so depends on the studied functional trait. Second, patterns found might be shaped by how finely we categorize functional traits. More complex vegetation provided larger "ecological space" with more resources, allowing the coexistence of more species with disproportionately more diverse foraging substrate use. We suggest that the latter pattern was driven by nonrandom accumulation of functionally distinct species with increasing canopy height.     

Spatio-temporal organization of the bird communities in two Mediterranean montane forests

Seasonal changes of bird communities and use of foraging substrates by the birds were studied in two forests with contrasting vegetation structure in montane and subalpine levels of central Spanish mountains throughout complete annual cycles. Common factors contributing most to foraging segregation among species were found to be the foraging on the ground vs that on vegetation and use of proximal vs distal tree parts. A complete dissimilarity exists between the composition of the respective foliage-gleaning guilds, the converse being true for the trunk-searchers.
Temporal distribution of bird species is to a great extent determined by their use of space, thus existing a gradient of seasonality with maxima for ground-searchers, minima for trunk-gleaners and intermediate positions for foliage-gleaners. A close relationship among temporal variability, mean annual density and niche breadth is found for the subalpine pinewood community, but not for that from the montane oakwood, this being related with their contrasting migratory patterns and the structural stability of vegetation in each wood. The pattern of covariation in community parameters mirrors the summed response of individual bird species to the changing environmental conditions. Increases in community richness, density and diversity are related to temporal invasion by ground and foliage-gleaners of these highly seasonal Mediterranean habitats.     

The Effects of Cropping Systems on Avian Communities in Cacao and Banana Agro‐Forestry Systems of Talamanca,Costa Rica

Multispecies agro‐forestry is generally lauded for providing ecosystem services, especially in tropical environments. Avian communities contribute to services such as biodiversity and pest management. Characterizing and evaluating avian community composition in similar cropping systems will help optimize management for ecosystem services. We examined the relationship between cropping system vegetation and avian communities in four shaded agro‐forestry systems common to the Limón province of Costa Rica: abandoned and managed systems of cacao, cacao with banana, and banana. During two field seasons, we detected 2605 birds from 106 species and identified 2791 trees and shrubs from 62 morphospecies. We compared vegetation and avian species richness across systems with mixed‐effects linear models. Canopy, understory, and groundcover vegetation differed among agro‐forestry systems. More ground‐ and understory‐foraging forest species were detected in agro‐forestry systems lacking banana, whereas richness of agricultural generalist species was highest in systems with banana. Richness of understory‐ and ground‐foraging species correlated with understory tree species richness and leaf litter. Our results indicate that shaded cacao and banana systems can have similar canopy‐foraging species richness that includes both agricultural and woodland generalist species, but that interspersing banana with cacao can adversely influence understory forest bird community composition. Agro‐forests with diverse understory vegetation support more understory‐foraging bird species that have proven valuable in pest management. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Bat and bird diversity along independent gradients of latitude and tree composition in European forests

Species assemblages are shaped by local and continental-scale processes that are seldom investigated together, due to the lack of surveys along independent gradients of latitude and habitat types. Our study investigated changes in the effects of forest composition and structure on bat and bird diversity across Europe. We compared the taxonomic and functional diversity of bat and bird assemblages in 209 mature forest plots spread along gradients of forest composition and vertical structure, replicated in 6 regions spanning from the Mediterranean to the boreal biomes. Species richness and functional evenness of both bat and bird communities were affected by the interactions between latitude and forest composition and structure. Bat and bird species richness increased with broadleaved tree cover in temperate and especially in boreal regions but not in the Mediterranean where they increased with conifer abundance. Bat species richness was lower in forests with smaller trees and denser understorey only in northern regions. Bird species richness was not affected by forest structure. Bird functional evenness increased in younger and denser forests. Bat functional evenness was also influenced by interactions between latitude and understorey structure, increasing in temperate forests but decreasing in the Mediterranean. Covariation between bat and bird abundances also shifted across Europe, from negative in southern forests to positive in northern forests. Our results suggest that community assembly processes in bats and birds of European forests are predominantly driven by abundance and accessibility of feeding resources, i.e., insect prey, and their changes across both forest types and latitudes.     

A functional trait-based approach to understand community assembly and diversity–productivity relationships over 7 years in experimental grasslands

Several multi-year biodiversity experiments have shown positive species richness–productivity relationships which strengthen over time, but the mechanisms which control productivity are not well understood. We used experimental grasslands (Jena Experiment) with mixtures containing different numbers of species (4, 8, 16 and 60) and plant functional groups (1–4; grasses, legumes, small herbs, tall herbs) to explore patterns of variation in functional trait composition as well as climatic variables as predictors for community biomass production across several years (from 2003 to 2009). Over this time span, high community mean trait values shifted from the dominance of trait values associated with fast growth to trait values suggesting a conservation of growth-related resources and successful reproduction. Increasing between-community convergence in means of several productivity-related traits indicated that environmental filtering and exclusion of competitively weaker species played a role during community assembly. A general trend for increasing functional trait diversity within and convergence among communities suggested niche differentiation through limiting similarity in the longer term and that similar mechanisms operated in communities sown with different diversity. Community biomass production was primarily explained by a few key mean traits (tall growth, large seed mass and leaf nitrogen concentration) and to a smaller extent by functional diversity in nitrogen acquisition strategies, functional richness in multiple traits and functional evenness in light-acquisition traits. Increasing species richness, presence of an exceptionally productive legume species (Onobrychis viciifolia) and climatic variables explained an additional proportion of variation in community biomass. In general, community biomass production decreased through time, but communities with higher functional richness in multiple traits had high productivities over several years. Our results suggest that assembly processes within communities with an artificially maintained species composition maximize functional diversity through niche differentiation and exclusion of weaker competitors, thereby maintaining their potential for high productivity.     

The evolution of morphological diversity in continental assemblages of passerine birds

Understanding geographic variation in the species richness and lineage composition of regional biotas is a long‐standing goal in ecology. Why do some evolutionary lineages proliferate while others do not, and how do new colonists fit into an established fauna? Here, we analyze the morphological structure of assemblages of passerine birds in four biogeographic regions to examine the relative influence of colonization history and niche‐based processes on continental communities of passerine birds. Using morphological traits related to habitat choice, foraging technique, and movement, we quantify the morphological spaces occupied by different groups of passerine birds. We further quantify morphological overlap between groups by multivariate discriminant analysis and null model analyses of trait dispersion. Finally, we use subclade disparity through time to assess the temporal component of morphological evolution. We find mixed support for the prediction, based on priority, that first colonizers constrain subsequent colonizers. Indeed, our results show that the assembly of continental communities is idiosyncratic with regards to the diversification of new clades and the filling of morphospace.     

Natural Windbreaks Sustain Bird Diversity in a Tea-Dominated Landscape

Windbreaks often form networks of forest habitats that improve connectivity and thus conserve biodiversity, but little is known of such effects in the tropics. We determined bird species richness and community composition in windbreaks composed of remnant native vegetation amongst tea plantations (natural windbreaks), and compared it with the surrounding primary forests. Fifty-one, ten-minute point counts were conducted in each habitat type over three days. Despite the limited sampling period, our bird inventories in both natural windbreaks and primary forests were nearly complete, as indicated by bootstrap true richness estimator. Bird species richness and abundance between primary forests and windbreaks were similar, however a difference in bird community composition was observed. Abundances of important functional groups such as frugivores and insectivores did not vary between habitat types but nectarivores were more abundant in windbreaks, potentially as a result of the use of windbreaks as traveling routes, foraging and nesting sites. This preliminary study suggests that natural windbreaks may be important habitats for the persistence of bird species in a production landscape. However, a better understanding of the required physical and compositional characteristics for windbreaks to sustain bird communities is needed for effective conservation management.     

Forest edges have high conservation value for bird communities in mosaic landscapes

A major conservation challenge in mosaic landscapes is to understand how trait‐specific responses to habitat edges affect bird communities, including potential cascading effects on bird functions providing ecosystem services to forests, such as pest control. Here, we examined how bird species richness, abundance and community composition varied from interior forest habitats and their edges into adjacent open habitats, within a multi‐regional sampling scheme. We further analyzed variations in Conservation Value Index (CVI), Community Specialization Index (CSI) and functional traits across the forest‐edge‐open habitat gradient. Bird species richness, total abundance and CVI were significantly higher at forest edges while CSI peaked at interior open habitats, i.e., furthest from forest edge. In addition, there were important variations in trait‐ and species‐specific responses to forest edges among bird communities. Positive responses to forest edges were found for several forest bird species with unfavorable conservation status. These species were in general insectivores, understorey gleaners, cavity nesters and long‐distance migrants, all traits that displayed higher abundance at forest edges than in forest interiors or adjacent open habitats. Furthermore, consistently with predictions, negative edge effects were recorded in some forest specialist birds and in most open‐habitat birds, showing increasing densities from edges to interior habitats. We thus suggest that increasing landscape‐scale habitat complexity would be beneficial to declining species living in mosaic landscapes combining small woodlands and open habitats. Edge effects between forests and adjacent open habitats may also favor bird functional guilds providing valuable ecosystem services to forests in longstanding fragmented landscapes.     

Grassland versus non-grassland bird abundance and diversity in managed grasslands: local,landscape and regional scale effects

Declines of West European farmland birds have been associated with intensive agricultural practices, while in Central and Eastern European countries grasslands still harbour a diverse and unique bird community. However, in these countries comparative studies on the effects of agricultural intensity on biodiversity are virtually missing. We compared bird communities of paired extensively and intensively grazed cattle pastures in three different regions of the Hungarian Great Plain. The influence of grazing intensity, landscape and regional effects were tested on the abundance and species richness of two ecological groups of bird species (grassland and non-grassland birds), as well as on the abundance of the three commonest grassland bird species (Skylark, Yellow wagtail, Corn bunting) in linear mixed models. We found significant effects of grazing intensity on the abundance of grassland birds, which were more abundant on the extensive sites, whereas no effects were found on non-grassland birds. This could be explained by a closer dependence of grassland birds on grasslands for nesting and foraging, whereas non-grassland birds only used grasslands opportunistically for foraging. Landscape effect was shown on grassland bird abundance, but not on non-grassland birds. The regions did affect only the species richness of grassland birds. At species level, the effect of management was significant for the three commonest grassland species, which were more abundant on the extensive fields in all regions. Additionally, on Skylark abundance landscape and regional effects were also shown. These findings suggest that conservation of biodiversity in agricultural systems requires the consideration of landscape perspective to apply the most adequate management.     

Faunal diversity and vegetation structure of some deciduous forests in South Sweden

The relationships of faunal diversity and vegetation structure were studied in twenty deciduous forest plots in South Sweden, all of them managed. Following animal groups were censused: shrews (Soricidae), bats (Chiroptera), voles (Cricetidae), fieldmice (Muridae), birds (Aves), groundliving beetles (Coleoptera), spiders (Araneida), and harvestmen (Opilionidae). The analysis of the 22 vegetation variables was made by means of repeated and rotated PCA. Rarefaction was used to ordinate the bird species richness of the different forest plots.
The multivariate vegetational analysis resulted in three distinct and readily interpretable components: horizontal and vertical spatial heterogeneity, and mean basal area. The number of small mammal species (except bats) was greatest in forests with great amount of understory while the number of bat species increased with increasing mean basal area. The number of bird species in a fixed number of territories was also highly correlated with the mean basal area. Hence, maximum bird species richness was obtained in mature forests but not in those with greatest vertical heterogeneity. The invertebrate communities showed very few distinct relationships to the vegetation structure.
Dominance decreased as vegetation complexity increased. Dominance also decreased with increasing species richness in all faunal communities studied.     

Habitat quality is more important than matrix quality for bird communities in protected areas

Protected areas are meant to preserve native local communities within their boundaries, but they are not independent from their surroundings. Impoverished habitat quality in the matrix might influence the species composition within the protected areas through biotic homogenization. The aim of this study was to determine the impacts of matrix quality on species richness and trait composition of bird communities from the Finnish reserve area network and whether the communities are being subject of biotic homogenization due to the lowered quality of the landscape matrix. We used joint species distribution modeling to study how characteristics of the Finnish forest reserves and the quality of their surrounding matrix alter species and trait compositions of forest birds. The proportion of old forest within the reserves was the main factor in explaining the bird community composition, and the bird communities within the reserves did not strongly depend on the quality of the matrix. Yet, in line with the homogenization theory, the beta‐diversity within reserves embedded in low‐quality matrix was lower than that in high‐quality matrix, and the average abundance of regionally abundant species was higher. Influence of habitat quality on bird community composition was largely explained by the species' functional traits. Most importantly, the community specialization index was low, and average body size was high in areas with low proportion of old forest. We conclude that for conserving local bird communities in northern Finnish protected forests, it is currently more important to improve or maintain habitat quality within the reserves than in the surrounding matrix. Nevertheless, we found signals of bird community homogenization, and thus, activities that decrease the quality of the matrix are a threat for bird communities.     

Effect of forest landscapes composition and configuration on bird community and its functional traits in a hotspot of biodiversity of Chile

Understanding the effect of landscape configuration on the bird species richness and their functional traits (dietary preferences) is important to link the conservation and restoration plans to the production of the crops. Our aims were: 1) to study the influence of forest types (native, mixed and plantations) on the bird species richness in two agroforestry landscapes (heterogeneous/homogeneous); 2) to assess the effect of size/density of forest patches in the birds’ functional traits; 3) to evaluate the effect of isolated trees on them, and 4) to discuss conservation and restoration measures for the birds’ functional traits in agroforestry landscapes. We used hierarchical occupancy models to evaluate the effect of different landscape metrics and detectability measures on bird communities. We recorded a total of 64 bird species. The estimated species richness was considerable higher in homogeneous landscape (31.7 ± 2.7) than heterogeneous (27.3 ± 2.5). Our results showed the bird assemblage had a positive trend with native forests, negative with mixed forests and neutral trend for plantations. The granivores and insectivore’s species showed significant preferences for homogeneous landscape, while omnivores had significant preferences for heterogeneous landscape. Carnivores/Piscivores and herbivores/frugivores species did not show preferences by any landscape type. The response of functional traits depended on different forests attributes. The isolated trees had a significant effect on the birds’ functional traits. In conclusion, it is necessary a deep knowledge about the relationship between the landscape configuration and the bird species richness/functional traits. These findings could help in the future with the conservation, restoration, and rewilding policies in this important hotspot of biodiversity, avoiding alterations in the ecosystem services.     

Avian richness and abundance in temperate Danish forests: tree variables important to birds and their conservation

Many studies on avian diversity and forest structure have focused onfiner scale forest variables such as foliage height diversity, foliagediversity, foliage density, vertical distribution of vegetation and horizontalvegetation density. From a conservation and forestry operational point of viewit would be of great interest if tree variables influenced directly by forestrymanagement decisions also had significant influence on avian richness andabundance. The species, age and size of a tree are examples of such treevariables. A great number of studies also have focused on avian diversityindices to reveal relationships with vegetation variables. However, it may bemore appropriate for foresters and conservation officers to operate withrichness and abundance measures directly, because indices complicateinterpretations on the relative importance of the two variables (richness andabundance) constituting the index. Fourteen managed temperate forests in Denmarkwere investigated for avian species richness and abundance and related tomeasures on different tree variables influenced directly by forestry managementdecisions. A rapid assessment method of avian richness and abundance wasemployed. It consisted of point-counts of bird richness and abundance within 1km² of forest. General linear models were tested byanalyses of variance statistics to reveal the tree variables most important toavian richness and abundance. It was found that more old trees, more treespecies and more tree size-classes correlated with more bird species andindividuals. However, some variation in bird richness and abundance was alsorelated to site quality and/or chance colonization. Moreover, it was shown thatthe guild of cavity-nesting birds correlated positively to age of tree stand.The potential number of bird species in Danish forest is similar to that innearly pristine forest in Poland, and much larger than that recorded in any ofthe forests investigated. Together with the results above, this indicates a highpotential for squeezing in more avian species in a higher quality forest from abiodiversity point of view. Modern Danish forestry affects tree variablesinfluenced directly by forestry management decisions. Such tree variables havegreat influence on avian richness and abundance, but simple measures in forestrypractices can be taken to enhance the conservation of bird richness andabundance.     

Winter bird communities in the northern Negev: species dispersal patterns, habitat use and implications for habitat conservation

Bird habitat conservation may require different management strategies for different seasonal bird assemblages. We studied habitat use by winter birds in forest and scrubland habitat patches in the northern Negev, Israel. Our goal was to assess whether differences in responses to landscape and habitat structure between breeding and non-breeding seasons require changes in future conservation plans that have been suggested for the Negev breeding bird community. We evaluated habitat and area effects on bird abundance and distribution and tested whether species habitat use during winter involves niche shifts. Compared with breeding birds, a larger proportion of winter bird species occupied both scrubland and forest. As in summer, forest bird species responded to habitat structure, whereas scrubland species were associated with both habitat structure and area. Resident birds disperse into habitats in which they were not present during summer. Consequently, for several species, the correlation between bird densities and environmental factors showed a better fit at the landscape rather than at the habitat scale. In addition, rather than niche shift, birds actually extended their niche breadth. Nest site selection may constrain bird distribution into a realized niche, smaller than their fundamental niche. Despite the scale differences in habitat use, the similar species diversity patterns between seasons suggest that both winter and summer birds would benefit from conservation of scrub patches larger than 50 ha, and enrichment of foliage layers within the planted forests.     

The formation of “mega‐flocks” depends on vegetation structure in montane coniferous forests of Taiwan

A mixed‐species bird flock is a social assemblage where two or more bird species are moving together while foraging and might benefit from increased foraging efficiency and antipredator vigilance. A “mega‐flock,” which includes flocking species from different vegetation strata, often exhibits high species diversity. Mechanisms for the formation of mega‐flocks have not yet been explored. In this study, we evaluated the influence of vegetation structure and bird species diversity in driving the occurrence of mega‐flocks. We investigated the composition of mixed‐species flocks, local bird communities, and vegetation structure in five vegetation types of two high‐elevation sites in central Taiwan. Mega‐flocks occurred more frequently in pine woodland than later successional stages of coniferous forests. However, species richness/diversity of local bird communities increased along successional stages. Therefore, vegetation variables exhibit more influence on the occurrence of mega‐flocks than local bird communities. Besides foliage height diversity, understory coverage also showed positive effects on flock size of mixed‐species flocks. Our results indicated that pine woodlands with more evenly distributed vegetation layers could facilitate the interactions of canopy and understory flocks and increase the formation of mega‐flocks and thus the complexity of mixed‐species flocks.     

Trait variation and functional diversity maintenance of understory herbaceous species coexisting along an elevational gradient in Yulong Mountain,Southwest China

Characterizing trait variation across different ecological scales in plant communities has been viewed as a way to gain insights into the mechanisms driving species coexistence. However, little is known about how changes in intraspecific and interspecific traits across sites influence species richness and community assembly, especially in understory herbaceous communities. Here we partitioned the variance of four functional traits (maximum height, leaf thickness, leaf area and specific leaf area) across four nested biological scales: individual, species, plot, and elevation to quantify the scale-dependent distributions of understory herbaceous trait variance. We also integrated the comparison of the trait variance ratios to null models to investigate the effects of different ecological processes on community assembly and functional diversity along a 1200-m elevational gradient in Yulong Mountain. We found interspecific trait variation was the main trait variation component for leaf traits, although intraspecific trait variation ranged from 10% to 28% of total variation. In particular, maximum height exhibited high plasticity, and intraspecific variation accounted for 44% of the total variation. Despite the fact that species composition varied across elevation and species richness decreased dramatically along the elevational gradient, there was little variance at our largest (elevation) scale in leaf traits and functional diversity remained constant along the elevational gradient, indicating that traits responded to smaller scale influences. External filtering was only observed at high elevations. However, strong internal filtering was detected along the entire elevational gradient in understory herbaceous communities, possibly due to competition. Our results provide evidence that species coexistence in understory herbaceous communities might be structured by differential niche-assembled processes. This approach--integrating different biological scales of trait variation--may provide a better understanding of the mechanisms involved in the structure of communities.     

Frugivoría por Aves en un Paisaje Fragmentado: Consecuencias en la Dispersión de Semillas1

Few data exist on seed dispersal by frugivorous birds in fragmented landscapes, originating from tropical dry forests, in contrast to more abundant data from tropical rain forests. In this study, we assessed the effect of frugivorous birds in a fragmented landscape of Veracruz, Mexico, now occupied by remnant fragments of tropical semi‐deciduous forest and dry deciduous forest, grassland, and shrubby patches on sand dunes. We determined four characteristics related to seed dispersal by birds: the interacting species of plants and birds, the characteristics of these species, spatio‐temporal variation in the dispersal system, and the outcome of the process. During one year, we recorded 54 frugivorous bird species and 33 ornithochorous plant species, which engaged in 176 different bird‐plant species interactions. Similarity (Sorensen index) of frugivorous bird communities using different vegetation types was high (>70%), suggesting that many bird species used all of the vegetation types. In contrast, the similarity of ornithochorous plant communities among vegetation types commonly was low (<37%), suggesting that most plant species were restricted to particular sites in this landscape. At the landscape level, as well as for tropical deciduous forest, we detected a significant positive relationship (Spearman's correlation of rank coefficient >0.65, P <0.05) among richness per month of frugivorous birds and plant species bearing fleshy fruits. Seeds of many plant species previously detected in studies of seed rain at the site were eaten by birds during this study. Most seeds of zoochorous species, which are deposited in the dry and decidous tropical forests patches, are produced within these vegetation types (i.e., they are autochthonous species), whereas bird‐dispersed seeds arriving in grassland and shrubby patches are produced outside (i.e., allochthonous) and are mostly woody species. Birds are important seed dispersers among vegetation types in this landscape but they have different effects in each one. The four characteristics studied, as well as the landscape approach of this research, allowed us to detect spatial and temporal patterns that otherwise would have remained undetected.