The role of avian ‘seed predators’ as seed dispersers

Seed dispersal is a central process in plant ecology with consequences for species composition and habitat structure. Some bird species are known to disperse the seeds they ingest, whereas others, termed ‘seed predators’, digest them and apparently play no part in dispersal, but it is not clear if these are discrete strategies or simply the ends of a continuum. We assessed dispersal effectiveness by combining analysis of faecal samples and bird density. The droppings of seed dispersers contained more entire seeds than those of typical seed predators, but over a quarter of the droppings of seed predators contained whole seeds. This effect was further magnified when bird density was taken into account, and was driven largely by one frequent interaction: the Chaffinch Fringilla coelebs, a typical seed predator and the most abundant bird species in the area and dispersed seeds of Leycesteria formosa, a non‐native plant with berry‐like fruits. These results suggest the existence of a continuum between seed predators and seed dispersers.     

Species richness matters for the quality of ecosystem services: a test using seed dispersal by frugivorous birds

The positive link between biodiversity and ecosystem functioning is a current paradigm in ecological science. However, little is known of how different attributes of species assemblages condition the quality of many services in real ecosystems affected by human impact. We explore the links between the attributes of a frugivore assemblage and the quantitative and qualitative components of its derived ecosystem service, seed dispersal, along a landscape-scale gradient of anthropogenic forest loss. Both the number and the richness of seeds being dispersed were positively related to frugivore abundance and richness. Seed dispersal quality, determined by the fine-scale spatial patterns of seed deposition, mostly depended on frugivore richness. In fact, richness was the only attribute of the frugivore assemblage affecting the probability of seed dispersal into deforested areas of the landscape. The positive relationships between frugivore richness per se (i.e. independent of frugivore abundance and composition) and all components of seed dispersal suggest the existence of functional complementarity and/or facilitation between frugivores. These links also point to the whole assemblage of frugivores as a conservation target, if we aim to preserve a complete seed dispersal service and, hence, the potential for vegetation regeneration and recovery, in human-impacted landscapes.     

Diversity of seeds captured by interception exceeds diversity of seeds deposited in traps

Seed dispersal, a key process in terrestrial landscapes, is increasingly important in the face of habitat fragmentation and global climate change. Seed dispersal is also notoriously difficult to characterize, especially in species rich and spatially complex tropical forests. We contrasted assemblages of biotically dispersed seeds collected from four sites using two methods: deposition into seed traps and interception by the capture of frugivorous birds. We also compared seed deposition and interception with local fruit production. Species accumulation curves for seeds deposited in seed traps began to level off sooner than curves for seeds collected from birds captured in mist nets, and extrapolation showed significantly greater estimated species richness for seeds collected from birds than for those deposited in traps. Assemblages from birds and from traps at each site were quite different, with an abundance‐based similarity index of 0.64; this dissimilarity increases if bat‐dispersed seeds are included in the analysis. Common bird‐dispersed species were retrieved from both mist‐netted birds and from seed traps, but numerous locally fruiting understory species were recovered only from birds. We conclude that the sampling of seeds carried by birds provides a valuable complement to other methods of studying seed dispersal in species‐rich tropical forests by revealing relationships between specific dispersers and their seed plants and by creating a more complete account of species diversity of seeds being transported at a given site.     

Nested patterns of community assembly in the colonisation of artificial canopy habitats by oribatid mites

An observed species–area relationship (SAR) in assemblages of oribatid mites inhabiting natural canopy habitats (suspended soils) led to an experimental investigation of how patch size, height in canopy and moisture influence the species richness, abundance and community composition of arboreal oribatid mites. Colonisation by oribatid mites on 90 artificial canopy habitats (ACHs) of three sizes placed at each of three heights on the trunks of ten western redcedar trees was recorded over a 1‐year period. Fifty‐nine oribatid mite species colonised the ACHs, and richness increased with the moisture content and size of the habitat patch. Oribatid mite species richness and abundance, and ACH moisture content decreased with increasing ACH height in the canopy. Patterns in the species richness and community composition of ACHs were non‐random and demonstrated a significant nested pattern. Correlations of patch size, canopy height and moisture content with community nestedness suggest that species‐specific environmental tolerances combined with the differential dispersal abilities of species contributed to the non‐random patterns of composition in these habitats. In line with the prediction that niche‐selection filters out species from the regional pool that cannot tolerate environmental harshness, moisture‐stressed ACHs in the high canopy had lower community variability than ACHs in the lower canopy. Colonising source pools to ACHs were almost exclusively naturally‐occurring canopy sources, but low levels of colonisation from the forest floor were apparent at low heights within the ACH system. We conclude that stochastic dispersal dynamics within the canopy are crucial to understanding oribatid mite community structure in suspended soils, but that the relative importance of stochastic dispersal assembly may be dependent on a strong deterministic element to the environmental tolerances of individual species which drives non‐random patterns of community assembly.     

Fragmentation, habitat composition and the dispersal/predation balance in interactions between the Mediterranean myrtle and avian frugivores

Human‐induced fragmentation and disturbance of natural habitats can shift abundance and composition of frugivore assemblages, which may alter patterns of frugivory and seed dispersal. However, despite their relevance to the functioning of ecosystems, plant‐frugivore interactions in fragmented areas have been to date poorly studied. I investigated spatial variation of avian frugivore assemblages and fruit removal by dispersers and predators from Mediterranean myrtle shrubs (Myrtus communis) in relation to the degree of fragmentation and habitat features of nine woodland patches (72 plants). The study was conducted within the chronically fragmented landscape of the Guadalquivir Valley (SW Spain), characterized by ~1% of woodland cover. Results showed that the abundance and composition of the disperser guild was not affected by fragmentation, habitat features or geographical location. However, individual species and groups of resident/migrant birds responded differently: whereas resident dispersers were more abundant in large patches, wintering dispersers were more abundant in fruit‐rich patches. Predator abundances were similar between patches, although the guild composition shifted with fragmentation. The proportion of myrtle fruits consumed by dispersers and predators varied greatly between patches, but did not depend on bird abundances. The geographical location of patches determined the presence or absence of interactions between myrtles and seed predators (six predated and three non‐predated patches), a fact that greatly influenced fruit dispersal success. Moreover, predation rates were lower (and dispersal rates higher) in large patches with fruit‐poor heterospecific environments (i.e. dominated by myrtle). Predator satiation and a higher preference for heterospecific fruits by dispersers may explain these patterns. These results show that 1) the frugivore assemblage in warm Mediterranean lowlands is mostly composed of fragmentation‐tolerant species that respond differently to landscape changes; and 2) that the feeding behaviour of both dispersers and predators influenced by local fruit availability may be of great importance for interpreting patterns of frugivory throughout the study area.     

Frugivory by Small Vertebrates Within a Deforested, Dry Tropical Region of Central America

Small vertebrates were inventoried within three habitat types in a degraded dry forest region of Panama. Animals were classified as frugivorous if they were observed foraging on fruit or if fecal samples contained mostly or exclusively seeds. Overall, we found that eight bat species and 21 bird species consumed fruit. The greatest numbers of birds were observed within live fences and bird species richness was greatest within riparian forests. Bat assemblages were not significantly different between habitats. The implication is that ecosystem services such as seed dispersal may still be functional in this landscape.     

Variation in seed dispersal effectiveness: the redundancy of consequences in diversified tropical frugivore assemblages

Plant–frugivore mutualistic assemblages frequently combine multiple, complementary or not (i.e. redundant), distinct effects of animal species. To a large extent, the outcomes of these interactions crucially depend on the delayed consequences of frugivore effectiveness on plant recruitment. We evaluated seed dispersal effectiveness for three plant species in a Brazilian Atlantic forest with a marked habitat heterogeneity defined by bamboo and non‐bamboo patches. Twenty one, 23 and 14 bird species ate fruits of Euterpe edulis, Sloanea guianensis and Virola bicuhyba trees, respectively. For both Euterpe and Virola, visitation rate was the variable contributing for most variance across frugivore species in the quantitative component of effectiveness (QC, which depends on the combined effects of interaction frequency and per‐interaction effect), while the number of fruits manipulated/visit had the greatest contribution in Sloanea. By combining observational data and experimental seed addition for Euterpe we tested for consistent functional patterns among species in the frugivore assemblage, extending beyond the fruit removal stage. Rankings of QC across Euterpe frugivores remained consistent with their relative contributions to fruit removal and, importantly, with their contributions to seedling establishment. Yet, QC of effectiveness across Euterpe frugivores were more homogeneous at the fruit removal and dispersal stages (contribution to seed dispersal) than for the delayed, dissemination and post‐dispersal effects on recruitment. High complementarity of diversified frugivore assemblages may increase through added variance in their delayed effects related to qualitative components of effectiveness. Our results underscore the importance of assessing how dispersal services provided by mutualistic frugivores play complementary, rather than redundant, roles in seed dispersal within heterogeneous landscapes. Such ecological outcomes highlight the value of combining observational and experimental field designs to assess functional diversity patterns of tropical frugivore assemblages and delayed effects of their interactions with plants.     

Frugivory,Post‐feeding Flights of Frugivorous Birds and the Movement of Seeds in a Brazilian Fragmented Landscape

Habitat fragmentation can break down the movement processes of frugivorous animals, thus influencing the relationship between plants and their seed dispersers by altering the number and identity of seed dispersers, and their relative contribution to seed dispersal. We studied the assemblages of frugivorous birds, their composition, species richness, and visitation rates to fruiting plants growing in the different landscape elements (forest fragments, live fences, and trees isolated in pastures) embedded in a Brazilian fragmented, agricultural landscape. By following the post‐feeding movements of frugivorous birds, we inferred the direction of seed movement from and to each of these landscape elements. Fruiting trees growing at different landscape elements were visited by frugivorous birds at similar rates. Isolated trees attracted a greater and distinct bird assemblage than trees in forest fragments or live fences. Judging by the post‐feeding flights of birds, the seeds of isolated trees were the most likely to reach all the landscape elements considered, but the contribution of isolated trees to the seeds falling in forested habitats or pastures depended on their degree of isolation. A few bird species were able to move widely, visiting fruiting plants in all landscape elements, and promoting long‐distance dispersal for plants. These few birds are of special interest because they are mobile links that connect habitats in fragmented landscapes with their seed dispersal services. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Seed Dispersal by Avian Frugivores: Non‐random Heterogeneity at Fine Scales

Seed dispersal studies have primarily examined dispersal as a function of distance from the parent tree and/or heterogeneity in dispersal due to animal use of nesting, roosting and sleeping sites. However, non‐random heterogeneity in seed dispersal is also likely to result from the post‐foraging behavior and movement of frugivores which prefer certain trees. To characterize variation in seed rain at fine scales, we studied the dispersal curve of Prunus ceylanica, a primarily bird‐dispersed species. We compared seed rain at conspecifics, heterospecific fruiting trees with similar frugivore assemblages, emergent trees, and the landscape surrounding these trees. Seed rain of P. ceylanica was found to peak globally under the canopy of conspecifics but to peak locally under the canopy and immediate neighborhood of heterospecific fruiting trees. Our results demonstrate that seed rain is highly clumped even at fine spatial scales. A large proportion of seeds are dispersed in specific, localized regions. This variation can have important implications for plant population dynamics and might significantly alter the impact of post‐dispersal processes. Seed dispersal models may need to incorporate this heterogeneity to explain manifestations of spatially explicit dynamics like mixed species ‘orchards’.     

Community assembly in temperate forest birds: habitat filtering,interspecific interactions and priority effects

Recent attempts to understand the processes governing community assembly have increasingly focused on patterns of phylogenetic relatedness and functional similarity among co-existing species. Considerations of the species pool, the number and identity of functional traits and the metrics used to identify patterns have come under scrutiny as possible influences on the detection of non-random patterns. Most mechanistic explanations of community assembly based on functional and phylogenetic approaches rely on deterministic explanations, while ignoring the role of stochastic processes and historical contingency, despite the prominent historical role of both types of explanations of species coexistence. We evaluated the phylogenetic and functional structure of 20 temperate forest bird assemblages in northeastern North America. We compared three approaches for characterizing the functional structure of assemblages. Regardless of approach, assemblages were generally no different than expected by chance. In contrast, phylogenetic structures of bird assemblages were overdispersed, clumped or consistent with random assembly depending on the site. Nonetheless, we found little evidence for differences in phylogenetic structure arising as a consequence of the identity of the species pool. We identified a strong relationship between the proportion of residents and phylogenetic relatedness that was unrelated to the species richness of assemblages. Our results suggest that different assembly mechanisms may structure resident and migratory subsets of temperate breeding bird communities. Resident assemblages are likely structured by interspecific interactions and habitat filtering prior to arrival of migrants. In contrast, the composition of migrant assemblages may be a consequence of priority effects in which the presence and abundance of residents and earliest arriving species affect the ability of subsequent migrants to colonize sites. This phenomenon enhances the likelihood of multiple alternative community structures in similar environments.     

Markedly Divergent Tree Assemblage Responses to Tropical Forest Loss and Fragmentation across a Strong Seasonality Gradient

We examine the effects of forest fragmentation on the structure and composition of tree assemblages within three seasonal and aseasonal forest types of southern Brazil, including evergreen, Araucaria, and deciduous forests. We sampled three southernmost Atlantic Forest landscapes, including the largest continuous forest protected areas within each forest type. Tree assemblages in each forest type were sampled within 10 plots of 0.1 ha in both continuous forests and 10 adjacent forest fragments. All trees within each plot were assigned to trait categories describing their regeneration strategy, vertical stratification, seed-dispersal mode, seed size, and wood density. We detected differences among both forest types and landscape contexts in terms of overall tree species richness, and the density and species richness of different functional groups in terms of regeneration strategy, seed dispersal mode and woody density. Overall, evergreen forest fragments exhibited the largest deviations from continuous forest plots in assemblage structure. Evergreen, Araucaria and deciduous forests diverge in the functional composition of tree floras, particularly in relation to regeneration strategy and stress tolerance. By supporting a more diversified light-demanding and stress-tolerant flora with reduced richness and abundance of shade-tolerant, old-growth species, both deciduous and Araucaria forest tree assemblages are more intrinsically resilient to contemporary human-disturbances, including fragmentation-induced edge effects, in terms of species erosion and functional shifts. We suggest that these intrinsic differences in the direction and magnitude of responses to changes in landscape structure between forest types should guide a wide range of conservation strategies in restoring fragmented tropical forest landscapes worldwide.     

Functional and phylogenetic structure of forest and savanna bird assemblages across spatial scales

Ecological and evolutionary mechanisms that drive community assembly vary in space and time. However, little is known about how such mechanisms act in contrasting habitats. Here, we estimated the functional and phylogenetic structure of forest and savanna bird assemblages across different spatial scales to understand: 1) the mechanisms that govern the structure of assemblages in these habitats; 2) the relationship between phylogenetic and functional structure; and 3) the influence of species richness on the functional and phylogenetic structure of assemblages. We used a null model where forest and savanna bird species were allowed to occur in the same null assemblages and other where species were separated based on their habitats. According to the first null model, forest bird assemblages were functionally and phylogenetically clustered at all spatial scales, whereas savanna bird assemblages generally showed random functional and phylogenetic structure. These results can be explained by the low dispersal rate of forest species across of the patchy habitats and the widespread distribution of savanna species. However, in the second null model, both forest and savanna bird assemblages showed random functional and phylogenetic structure at regional and local scales. This suggests that trait‐based assembly might not play an important role in both habitats and across different spatial scales. In addition, the phylogenetic and functional structure of assemblages were not correlated, evidencing that caution is necessary when using phylogenetic relationships as a surrogate to functional distances among species. Finally, the relationships between species richness and functional and phylogenetic structure indicated that an increase in the number of species can promote both clustering and overdispersion, depending on the studied habitat and scale. Our study shows that integrating different types of habitat, spatial scales and biodiversity components in a single framework can shed light on the mechanisms that determine the community assembly.     

Seed dispersal of a fleshy-fruited invasive shrub is affected by changes in the frugivorous bird assemblage along an elevational gradient

Seed dispersal by birds constitutes an essential mechanism for ornithochorous exotic plants to successfully invade a new system. New biotic associations with native birds might facilitate the upward spread of exotic plants from the foothills into the high mountains. However, environmental changes associated with elevation are known to drive changes in bird assemblages, and it is not clear how elevation changes impact the seed dispersal service of ornithochorous invaders. We evaluated changes in frugivorous bird assemblages of one of the exotic shrubs (Cotoneaster franchetii, Rosaceae) with the broadest elevation range among woody invaders in the Córdoba Mountains (Argentina). We quantified frugivory interactions (including absolute and proportional fruit consumption by seed dispersers, pulp consumers, and seed predators) using 4-h observations of focal C. franchetii shrubs distributed across low-elevation, mid-elevation, and high-elevation sites (700, 1100, and 1800 m a.s.l., respectively; 15 individuals per elevational band and one site per elevation). Seed disperser richness was highest at the low- and mid-elevation sites (three species vs. one at the high-elevation site), but proportional and absolute fruit consumption of C. franchetii was highest at the high-elevation site (39.1%, 88 seeds at high-elevation and 7.7%, 20 seeds at low-elevation). The Chiguanco Thrush (Turdus chiguanco, Turdidae) was the only seed disperser species found at the highest elevation site. Fruit consumption by seed dispersers was positively related to their abundance and elevation. In a high mountain system, a single abundant generalist seed disperser, rather than a high richness of seed disperser species, can uphold an effective dispersal service for an invasive ornithochorous shrub. This pattern may facilitate the spread of such plants across higher elevational ranges, thereby promoting the invasion of other exotic ornithochorous plants into upper elevations.     

Functional importance of avian seed dispersers changes in response to human-induced forest edges in tropical seed-dispersal networks

Although seed-dispersal networks are increasingly used to infer the functioning of ecosystems, few studies have investigated the link between the properties of these networks and the ecosystem function of seed dispersal by animals. We investigate how frugivore communities and seed dispersal change with habitat disturbance and test whether relationships between morphological traits and functional roles of seed dispersers change in response to human-induced forest edges. We recorded interaction frequencies between fleshy fruited plants and frugivorous bird species in tropical montane forests in the Bolivian Andes and recorded functional bird traits (body mass, gape width and wing tip length) associated with quantitative (seed-removal rate) and qualitative (seed-deposition pattern) components of seed-dispersal effectiveness. We found that the abundance and richness of frugivorous birds were higher at forest edges. More fruits were removed and dispersed seeds were less clustered at edges than in the interior. Additionally, functional and interaction diversity were higher at edges than in the interior, but functional and interaction evenness did not differ. Interaction strength of bird species increased with body mass, gape width and wing tip length in the forest interior, but was not related to bird morphologies at forest edges. Our study suggests that increases in functional and interaction diversity and an even distribution of interaction strength across bird morphologies lead to enhanced quantity and tentatively enhanced quality of seed dispersal. It also suggests that the effects of species traits on ecosystem functions can vary along small-scale gradients of human disturbance.     

Broad-scale reciprocity in an avian seed dispersal mutualism

Aim Coevolved relationships between individual species of birds and plants rarely occur in seed dispersal mutualisms. This study evaluates whether reciprocal relationships may occur between assemblages of bird and plant species. Location Vancouver Island, British Columbia, Canada (48°50′‐N, 125°22′‐W). Methods The distribution and fruiting phenologies of seven shrub species were compared to seasonal changes in habitat selection and seed dispersal by six fruit‐eating bird species. Results Shrub species inhabiting forest understorey habitat had earlier fruiting phenologies than shrub species inhabiting forest edge habitat along lake and bog margins. Birds showed a parallel pattern in habitat selection, being more abundant in the forest understorey early in the fruiting season, and more abundant in the forest edge later in the season. Rates of seed deposition covaried with avian habitat selection, in such a way that birds directed seed dispersal into habitats preferred by shrubs. Conclusions These results depict a broad‐scale pattern in the abundance of birds and fruits indicative of reciprocal interactions. Seasonal changes in seed dispersal to each habitat appear to reinforce the relationship between shrub habitat affinities and fruiting phenologies. Phenological differences between habitats may also reinforce seasonal changes in avian habitat selection. Therefore, although reciprocal interactions between pairs of bird and plant species are rare, broad‐scale reciprocal relationships may occur between assemblages of bird and plant species.     

Plant–frugivore networks are less specialized and more robust at forest–farmland edges than in the interior of a tropical forest

Forest fragmentation and local disturbance are prevailing threats to tropical forest ecosystems and affect frugivore communities and animal seed dispersal in different ways. However, very little is known about the effects of anthropogenic forest edges and of local disturbance on the structure and robustness of plant–frugivore networks. We carried out focal tree observations to record the frugivore species feeding on eight canopy tree species in the forest interior and at forest–farmland edges in a little and a highly disturbed part of a Kenyan rain forest. For each frugivore species, we recorded its body mass and its forest dependence. We examined how forest edge and local disturbance affected the abundance, the richness and the composition of the frugivore community and tested whether forest edge and local disturbance affected plant frugivore networks. Abundance and species richness of frugivores were higher at edges than in the forest interior. Forest visitors and small‐bodied frugivores increased, while forest specialists decreased in abundance at forest edges. The changes in frugivore community composition resulted in plant–frugivore networks that were more connected, more nested and more robust against species extinctions at forest–farmland edges than in the forest interior. Network specialization was lower at forest edges than in the forest interior because at the edges plant specialization on frugivores was very low in small‐fruited species. In contrast, small‐fruited plants were more specialized than large‐fruited plants in the forest interior. Our findings suggest that forest‐visiting birds may stabilize seed‐dispersal services for small‐fruited plant species at rain forest margins, while seed‐dispersal services for large‐fruited plant species may be disrupted at forest edges due to the decrease of large‐bodied frugviores. To assess the ultimate consequences of bird movements from farmland to forest edges for ecosystem functioning, future studies are required to investigate the seed‐dispersal qualities provided by forest‐visiting bird species in the tropics.     

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.     

Response of ants to human‐altered habitats with reference to seed dispersal of the myrmecochore Corydalis giraldii Fedde (Papaveraceae)

Anthropogenic habitat disturbance has potential consequences for ant communities. However, there is limited information on the effects of ant responses on associated ecological processes such as seed dispersal. We investigated the effect of disturbance on the abundance, richness, and composition of ant communities and the resulting seed‐dispersal services for a herbaceous myrmecochore, Corydalis giraldii (Papaveraceae), in an undisturbed habitat (forest understory), moderately disturbed habitat (abandoned arable field), and highly disturbed habitat (road verge) on Qinling Mountains, China. In total, we recorded 13 ant species, and five out of these were observed to transport seeds. The community composition of dispersers was significantly different amongst habitats. The richness of the dispersers did not differ among the habitats, but their total abundance varied significantly across habitats and was 21% lower in the road verge than in the abandoned arable fields. The major seed‐dispersing ant species in both the forest understory and the abandoned arable field were large‐bodied (Myrmica sp. and Formica fusca, respectively), whereas the major seed‐dispersing ants found in the road verge were the small‐bodied Lasius alienus. This difference resulted in lower seed removal rates and dispersal distances in the road verge than in the other two habitats. The different dispersal patterns were attributed primarily to differences in dispersing ant abundance and identity, most likely in response to habitats with different degree of anthropogenic disturbance. The possible influence of disturbance on the ecological specialization of ant‐seed dispersal interaction is also discussed.     

The influence of changes in habitat structure on the species composition of bird assemblages in the southern Kalahari

Land use management practices often change habitat structure, which in turn influence diversity and the composition of floral and faunal assemblages. In the southern Kalahari, southern Africa, heavy grazing after above‐average rainfall has lead to bush thickening, and widespread use of arboricides and/or removal of large trees for firewood has also impacted habitat structure. At sites near Kimberley, in South Africa, we investigated the effects of these changes on bird species richness and which aspects of habitat structure most influenced bird assemblage diversity and composition. We also investigated correlations between bird life history traits and habitat characteristics using RLQ analysis. Bird species richness and abundance were both explained by vertical habitat heterogeneity and density of woody species between the heights of 0–2 m, with bird species richness also explained by the density of woody species at heights above 6 m. Large trees within bush‐thickened areas dampened the effects of bush thickening on bird assemblages by enabling certain species to persist, consistent with the idea that large trees are keystone structures. Smaller insectivorous gleaners, ball‐ and cup‐nesters, birds with parts of their range extending into arid areas and birds with long‐wavelength plumage (i.e. red, orange or yellow plumage) dominated bush‐thickened habitats. Seed‐eaters, burrow‐ and ground‐nesters, bark‐foragers, birds that perch and sally, or perch and swoop to the ground, were all negatively associated with bush thickening. Cavity‐nesters, bark‐foragers, hawkers, frugivores, birds that perch and sally and species with iridescent plumage were negatively affected by the loss of large trees. Of the common species analysed, nearly 40% of species had life history traits tied to large trees; and 68% had traits negatively associated with bush thickening and removal of large trees together, suggesting that where these changes in habitat occur simultaneously, bird diversity will be strongly affected.     

Increasing habitat connectivity in agricultural landscapes as a weed management strategy reconciling ecology and agronomy

While studies have explored how habitat amount drives weed assemblages in agroecosystems, knowledge remains limited of the effects of habitat connectivity. The response-effect trait framework provides insights into the mechanisms underpinning the relationship between landscape structure and the taxonomic diversity and abundance of weed assemblages. This study evaluated how habitat connectivity and habitat amount affect weed diversity and abundance in winter cereal fields, and whether these effects are driven by the functional composition of weed assemblages. We sampled weeds in 27 winter cereal fields. We measured habitat connectivity and habitat amount provided by wooded, grassland and cropland elements. We selected five traits related to the dispersal, establishment, and competitive abilities of weed species likely to respond to landscape structure: seed number per plant, type of reproduction, seed dry mass, plant vegetative height and seed germination rate. The functional composition of weed assemblages was assessed using community weighted mean trait values. Weed diversity and abundance were used as proxies of weed management. The taxonomic approach did not reveal any effect of landscape structure on weed diversity and abundance. Only the grassland elements that contributed to habitat connectivity, and to a lesser extent to habitat amount, drove the functional composition of weed assemblages. High habitat amount favoured species with many seeds, while high habitat connectivity favoured species with fewer seeds, a higher ability to reproduce vegetatively and higher seed germination rates. In turn, higher seed germination rates increased weed evenness and reduced weed abundance. Some of these relationships were influenced by the presence of rare species. Overall, high connectivity provided by grassland elements increases weed evenness and reduces weed abundance by shaping weed functional composition. Our study suggests that land-use planning policies that enhance the connectivity provided by grassland elements could be considered as a weed management strategy reconciling ecology and agronomy.