EVOLUTION OF RESISTANCE TO A MULTIPLE‐HERBIVORE COMMUNITY: GENETIC CORRELATIONS,DIFFUSE COEVOLUTION,AND CONSTRAINTS ON THE PLANT'S RESPONSE TO SELECTION

Although plants are generally attacked by a community of several species of herbivores, relatively little is known about the strength of natural selection for resistance in multiple‐herbivore communities—particularly how the strength of selection differs among herbivores that feed on different plant organs or how strongly genetic correlations in resistance affect the evolutionary responses of the plant. Here, we report on a field study measuring natural selection for resistance in a diverse community of herbivores of Solanum carolinense. Using linear phenotypic‐selection analyses, we found that directional selection acted to increase resistance to seven species. Selection was strongest to increase resistance to fruit feeders, followed by flower feeders, then leaf feeders. Selection favored a decrease in resistance to a stem borer. Bootstrapping analyses showed that the plant population contained significant genetic variation for each of 14 measured resistance traits and significant covariances in one‐third of the pairwise combinations of resistance traits. These genetic covariances reduced the plant's overall predicted evolutionary response for resistance against the herbivore community by about 60%. Diffuse (co)evolution was widespread in this community, and the diffuse interactions had an overwhelmingly constraining (rather than facilitative) effect on the plant's evolution of resistance.     

Reef fish community structure of the Fernando de Noronha Archipelago (Equatorial Western Atlantic): the influence of exposure and benthic composition

We studied the reef fish assemblage of eight reefs within the oceanic archipelago of Fernando de Noronha, off northeastern Brazil. In a total of 91 belt transects (20 × 2 m) we recorded 60 species from 28 families. The 25 most abundant species accounted for about 98% of all fish recorded in this study and most of these species are widely distributed in the Western Atlantic. The majority of fish counted were planktivores (37.0%), followed by mobile invertebrate feeders (28.5%), territorial herbivores (11.3%), roving herbivores (10.5%), omnivores (7.1%), macrocarnivores (6.5%) and sessile invertebrate feeders (0.03%). In terms of biomass, roving herbivores were the most representative (41.8%), followed by mobile invertebrate feeders (19.9%), macrocarnivores (14.3%), omnivores (14.0%), piscivores (8.3%), planktivores (1.4%), territorial herbivores (0.3%), and sessile invertebrate feeders (0.03%). Overall, density and biomass of fishes were positively correlated with coral cover and depth, and negatively correlated with wave exposure. These relationships are probably a response to the habitat complexity provided by the higher coral cover in deeper reefs (>10 m) of the archipelago or to the lower water turbulence below 10 m deep. Carnivores and mobile invertebrate feeders were mainly influenced by depth and non-consolidated substratum, planktivores and omnivores by wave exposure and herbivores by algal cover. Although our results suggest that habitat characteristics may play a role in determining the distribution of some fish species, we also found several habitat generalists, suggesting that the community is dominated by versatile species.     

Prevalence of Campylobacter jejuni,Campylobacter lari,and Campylobacter coli in different ecological guilds and taxa of migrating birds

A total of 1,794 migrating birds trapped at a coastal site in southern Sweden were sampled for detection of Campylobacter spp. All isolates phenotypically identified as Campylobacter jejuni and a subset of those identified as non-C. jejuni were identified to the species level by PCR-based techniques. C. jejuni was found in 5.0% of the birds, Campylobacter lari was found in 5.6%, and Campylobacter coli was found in 0.9%. An additional 10.7% of the tested birds were infected with hippurate hydrolysis-negative Campylobacter spp. that were not identified to the species level. The prevalence of Campylobacter spp. differed significantly between ecological guilds of birds. Shoreline-foraging birds feeding on invertebrates and opportunistic feeders were most commonly infected (76.8 and 50.0%, respectively). High prevalence was also shown in other ground-foraging guilds, i.e., ground-foraging invertebrate feeders (11.0%), ground-foraging insectivores (20.3%), and plant-eating species (18.8%). Almost no Campylobacter spp. were found in ground-foraging granivores (2.3%), arboreal insectivores (0.6%), aerial insectivores (0%), or reed- and herbaceous plant-foraging insectivores (3.5%). During the autumn migration, a high proportion of samples from juveniles were positive (7.1% in passerines, 55.0% in shorebirds), indicating transmission on the breeding grounds or during the early part of migration. Prevalence of Campylobacter spp. was associated with increasing body mass among passerine bird species. Furthermore, prevalence was higher in short-distance migrants wintering in Europe than in long-distance migrants wintering in Africa, the Middle East, or Asia. Among ground-foraging birds of the Muscicapidae, those of the subfamily Turdinae (i.e., Turdus spp.) showed a high prevalence of Campylobacter spp., while the organism was not isolated in any member of the subfamily Muscicapinae (i.e., Erithacus and Luscinia). The prevalence of Campylobacter infection in wild birds thus seems to be linked to various ecological and phylogenetic factors, with great variations in carriership between different taxa and guilds.     

Birds as marine–terrestrial linkages in sub-polar archipelagic systems: avian community composition, function and seasonal dynamics in the Cape Horn Biosphere Reserve (54–55°S), Chile

Marine environments are known to affect adjacent terrestrial biotic communities. In South America’s sub-Antarctic archipelago, birds are the most abundant and diverse terrestrial vertebrate assemblage. We hypothesized that birds would reflect a marine influence that would gradually decrease inland, expecting to find greater species richness, abundance, and biomass near the sea with decreases toward the island interior. We seasonally compared these parameters, with identified indicator species and assessed functional groups at 0, 150, and 300 m from the coast. Unexpectedly, we found a marked marine (0) and terrestrial (150–300) patterns for avian assemblages, rather than a gradient. In addition, seasonal patterns were warm (spring–summer) and cold (autumn–winter). The only parameter that displayed a true gradient was avian biomass in spring. During the cold season, higher values were observed in all variables for coastal assemblages, compared to inland sites. In the warm season, abundance and richness of coastal and terrestrial assemblages were similar, owing to migratory species. Milvago chimango was the only species abundant and frequent in both terrestrial and coastal systems, thereby indicating potential as a marine–terrestrial vector. Functionally, coastal assemblages were conformed of herbivores, carnivores, and scavengers, while terrestrial communities were made up of omnivores and insectivores. We conclude that the sea coast is a unique habitat in this archipelago, providing refuge for both marine and terrestrial sub-Antarctic birdlife particularly in the cold season. The relevance of the land/sea ecotone is poorly known, but important is given to high demand for the installation of salmon aquaculture facilities along the southern Chilean coastline.     

The ecology of mangrove forest birds in Peninsular Malaysia

The density, distribution and feeding ecology of birds of mangrove forests in Selangor on the west coast of Peninsular Malaysia were investigated between February and May 1989. Excluding aerial hunters and wading birds, 47 species were recorded from four mangrove forest sites in Selangor, though undoubtedly some rarer species were missed due to the brevity of the study. The estimated density of birds, using fixed-width transects, ranged from 15 to 26 birds per ha. One quarter of all birds counted belonged to just one species, the Ashy Tailorbird Orthotomus ruficeps. Excluding ground feeders (three species), four foraging guilds were recognized among 17 of the commonest bird species: obligate foliage-foraging insectivores (seven species), bark-foraging insectivores (four), facultative nectar-ivores (five) and aerial hawkers (one). Species within the first and third guilds apparently were partitioned by foraging technique and heights, while those of the second guild (woodpeckers) differed mainly in their selection of plant species. The horizontal distribution of several species corresponded to the zonation of mangroves. Avifaunal differences between sites reflected differences in forest floristics. The greatest number of species occurred at the dry landward edge site, which supported seven bird species not encountered elsewhere in Selangor. This habitat has almost completely disappeared from much of the peninsula owing to land reclamation. Four of the six resident mangrove-specialized bird species in Selangor were regularly recorded at two or more sites, another (Greater Gol-denback Woodpecker Chrysocolaptes lucidus) occurred at only one site and the last (Ruddy Kingfisher Halcyon coromanda) was never recorded. Two species of sunbirds probably play an important role in the pollination of several species of mangroves. The colonization of anthropogenic habitats by many mangrove-dwelling bird species is attributed partly to their generalized foraging niches, which may have evolved in response to regular fluctuations in food availability and the dynamic physiography of mangrove communities.     

Trophic structure of macrobenthos in the Tagus estuary and adjacent coastal shelf

The trophic structure of benthic communities in the Tagus estuary and adjacent coastal shelf was characterized according to a functional guild approach, based on sampling surveys conducted between 1987 and 2000. Macrobenthic organisms were assigned to seven distinct trophic groups (herbivorous, filter feeders, surface deposit feeders, subsurface deposit feeders, carnivores, filter feeders/detritivores, carnivores/detritivores) and the dominance of these groups was related to environmental variables using multivariate ordination techniques. Surface-deposit feeders were numerically dominant in the Tagus estuary, making up 52% of the benthic communities, while in the adjacent coastal shelf the assemblage was dominated by both surface-deposit feeders and filter feeders (37% and 33%, respectively). When biomass was considered, filter feeders and filter feeders/detritivores were the dominant groups in the estuary, while for the adjacent coastal shelf filter feeders represented 83% of the total biomass. Salinity, depth and sediment composition were the main factors structuring spatial distribution. Surface-deposit feeders were the most abundant macrobenthos of the upper estuary. Surface deposit feeders also dominated the middle and the lower estuary but the proportion of filter feeders as well as other trophic groups increased with salinity. Generally, a more even distribution of trophic structure was found at stations with high salinity. In the adjacent coastal shelf, the trophic diversity decreased with depth. The trophic structure revealed that filter feeders dominated in abundance and biomass in shallow sandy sediments (<25 m), while in deeper sandy mud and muddy habitats (>50 m to 260 m), deposit feeders and carnivores were the most important groups in abundance and biomass, respectively.     

Investigations of density interactions among breeding birds in ponderosa pine forests: correlative and experimental evidence

Summary We assessed the importance of interspecific competition among insectivorous birds breeding in northcentral Arizona's ponderosa pine forests. We examined density interactions among species using two analytic approaches; correlative and experimental. The correlative approach examined patterns of change in breeding densities over four years at the community level and within two foraging guilds; picker-gleaners and aerial feeders. The relationships between morphological and behavioral similarity with pairwise density interactions were also assessed. Our experimental approach involved placement of nest boxes on two treatment plots to increase breeding densities of secondary cavity nesting birds that were in foraging guilds with open nesting insectivores.We found little evidence of interspecific competition. Patterns of density fluctuations indicated large positive covariances among species at both the community level and within guilds. Pairwise density interactions were independent of morphological or behavioral similarity. Nest boxes significantly increased breeding densities of the secondary cavity nesters. However, these increases did not induce reprocal density changes in the open nesting species. Interspecific competition for food during the breeding season appears to be unimportant in ponderosa pine bird communities.     

THE BIRD SUCCESSION IN THE CONIFER PLANTATIONS ON MAT-GRASS LAND IN SLOVAKIA (CSR).

1. The species-composition, number of individuals and biomass per one-hectare are given. The three groups of areas studied were: (1) bare pastures, with an intermediate number of bird species, few individuals and high biomass of mainly carnivorous and insectivorous birds; (2) conifer plantations 1 to 5 years old, with the smallest number of bird species and the smallest biomass, but an intermediate number of individuals; (3) plantations six to twenty years old, with the highest number of both species and individuals of birds, but only intermediate biomass.
2. The change from pasture to forest occurs about six to ten years after planting. The last forest birds come in about 20 years after planting.
3. Birds have an important role in establishing the shrub layer and mixing some tree-species into the plantation, by dissemination.
4. Throughout the entire successional series the bird population seems to have a kernel of species, while other species come or go and/or change in density with the stages.     

Avian Density and Nest Survival on the San Pedro River: Importance of Vegetation Type and Hydrologic Regime

Abstract: Lowland riparian vegetation in the southwestern United States is critically important for maintaining a high richness and density of breeding birds. Further investigation is needed within riparian corridors, however, to evaluate the relative importance of vegetation type and hydrologic regime for avian density and nest survival as targets for regional conservation or restoration efforts. We estimated the densities of 40 bird species and for species grouped on the basis of nest height and dependence on surface water in gallery cottonwood–willow (Populus spp.–Salix spp.) forests, saltcedar (Tamarix spp.) shrub lands, and terrace vegetation types along a gradient in the hydrologic regime of the San Pedro River, Arizona, USA. We also assessed nest survival for shrub-nesting insectivores and herbivores. Canopy-nesting birds as a group and 14 individual bird species reached their greatest densities in cottonwood forests regardless of the hydrologic regime. Water-dependent birds as a group reached their highest density in both intermittent- and perennial-flow cottonwood stands, but certain species occurred almost exclusively in perennial-flow sites. Two shrub-nesting species and the brown-headed cowbird (Molothrus ater) were most abundant in saltcedar shrub lands, and the brown-headed cowbird was most abundant in saltcedar stands with intermittent flows. Mesquite (Prosopis spp.) and big sacaton (Sporobolus wrightii) grassland each maintained the highest densities of certain species within ≥1 hydrologic regime. Shrub-nesting insectivores had the greatest nest survival in cottonwood, including Arizona Bell's vireo (Vireo bellii arizonae), and also had lower proportions of nests parasitized and preyed upon, although 95% confidence intervals among vegetation types overlapped. Nest survival for both shrub-nesting insectivores and herbivores was lowest in intermittent-flow saltcedar, although, again, confidence intervals overlapped. Nest survival was lower in parasitized than nonparasitized nests in mesquite and across vegetation types for Arizona Bell's vireo and in cottonwood for Abert's towhee (Pipilo aberti). Riparian management that maintains heterogeneous riparian vegetation types, including floodplain vegetation comprising cottonwood–willow gallery riparian forests with some stretches of perennial flow, are important for maintaining the high diversity and abundance of breeding birds on the San Pedro River and probably across the region. Cottonwood stands also appear to maintain highest nest survival for some shrub-nesting birds.     

Long‐term effects of artificial nighttime lighting and trophic complexity on plant biomass and foliar carbon and nitrogen in a grassland community

The introduction of artificial nighttime lighting due to human settlements and transport networks is increasingly altering the timing, intensity, and spectra of natural light regimes worldwide. Much of the research on the impacts of nighttime light pollution on organisms has focused on animal species. Little is known about the impacts of daylength extension due to outdoor lighting technologies on wild plant communities, despite the fact that plant growth and development are under photoperiodic control. In a five‐year field experiment, artificial ecosystems (“mesocosms”) of grassland communities both alone or in combination with invertebrate herbivores and predators were exposed to light treatments that simulated street lighting technologies (low‐pressure sodium, and light‐emitting diode [LED]‐based white lighting), at ground‐level illuminance. Most of the plant species in the mesocosms did not exhibit changes in biomass accumulation after 5 years of exposure to the light treatments. However, the white LED treatment had a significant negative effect on biomass production in the herbaceous species Lotus pedunculatus. Likewise, the interaction between the white LED treatment and the presence of herbivores significantly reduced the mean shoot/root ratio of the grass species Holcus lanatus. Artificial nighttime lighting had no effect on the foliar carbon or nitrogen in most of the grassland species. Nevertheless, the white LED treatment significantly increased the leaf nitrogen content in Lotus corniculatus in the presence of herbivores. Long‐term exposure to artificial light at night had no general effects on plant biomass responses in experimental grassland communities. However, species‐specific and negative effects of cool white LED lighting at ground‐level illuminance on biomass production and allocation in mixed plant communities are suggested by our findings. Further studies on the impacts of light pollution on biomass accumulation in plant communities are required as these effects could be mediated by different factors, including herbivory, competition, and soil nutrient availability.     

Urban bird trends in a rapidly growing tropical city

Long-term studies of urban birds are relatively scarce, especially in Africa. We analysed trends in species richness and bird species occurrence over a 32-year period in Kampala, Uganda, in order to assess changes in the bird community in a period that has shown rapid expansion of the city's human population. Given that species may respond to urbanisation according to their diet, we also analysed bird community trends of species groups defined according to predominant diet. There was an overall decline in species richness that was largely driven by declines in insectivores and granivores. General declines were evident also when the trends in the most common individual species in these two groups were considered. The occurrence of the commonest predator and scavenger species tended to increase over the period considered. Insectivorous species are likely to be especially affected by increasing urbanisation due to air pollution. Predators and scavengers are likely to have benefitted from the inability of municipal waste management to keep pace with growth in the human population, hence providing more potential food resources. Both insectivores and predators/scavengers are therefore good candidates for the development of urban indicators.     

THE FORMATION, STRUCTURE AND FUNCTION OF MIXED-SPECIES INSECTIVOROUS BIRD FLOCKS IN WEST AFRICAN SAVANNA WOODLAND

Mixed-species flocks of birds were observed during the wet season (July to September 1975) in savanna woodland in Ghana. Thirty-four flocks contained birds of 56 species in 20 families, including insectivorous, granivorous, and nectarivorous species, using a wide range of foraging methods. Only two species occurred in more than half the flocks. There was no correlation between the number of flocks joined by a species and its abundance in the community. Among insectivores, but not granivores, the species which joined most flocks were those which habitually occurred in the largest single-species groups. All stages of breeding activity were represented by the various members. Some species joined flocks only while these were passing through their territories. Of the two species which were present most frequently, there were no differences between mixed and single-species flocks for Eremomela pusilla, but Parus leucomelas foraged and called on more occasions in mixed flocks than single-species flocks, though the rates of foraging and calling were related only to the number of P. leucomelas present. Groups of P. leucomelas appeared to initiate some flocks by attraction due to their conspicuous wing-bars, active movement, and loud calls. Black-and-white species joined them first, followed by birds of other plumage patterns. The advantages of mixed flocking are thought to be connected with finding patches of the food of bark- and foliage-searching insectivores, which were the only species regularly seen foraging in the flocks. Because of dry season burning which leaves small unburnt patches of savanna, these insect species may share a common, patchy distribution. Birds may also gain protection from predators, and some species probably gain no advantages. The species composition and behaviour of flocks previously recorded elsewhere in African savannas are similar to the Ghana flocks.     

Species-specific effects of woody litter on seedling emergence and growth of herbaceous plants

The effect of litter on seedling establishment can influence species richness in plant communities. The effect of litter depends on amount, and also on litter type, but relatively little is known about the species-specific effects of litter. We conducted a factorial greenhouse experiment to examine the effect of litter type, using two woody species that commonly co-occur in boreonemoral forest--evergreen spruce (Picea abies), deciduous hazel (Corylus avellana), and a mixture of the two species--and litter amount--shallow (4 mm), deep (12 mm) and leachate--on seedling emergence and biomass of three understorey species. The effect of litter amount on seedling emergence was highly dependent on litter type; while spruce needle litter had a significant negative effect that increased with depth, seedling emergence in the presence of hazel broadleaf litter did not differ from control pots containing no litter. Mixed litter of both species also had a negative effect on seedling emergence that was intermediate compared to the single-species treatments. Spruce litter had a marginally positive (shallow) or neutral effect (deep) on seedling biomass, while hazel and mixed litter treatments had significant positive effects on biomass that increased with depth. We found non-additive effects of litter mixtures on seedling biomass indicating that high quality hazel litter can reduce the negative effects of spruce. Hazel litter does not inhibit seedling emergence; it increases seedling growth, and creates better conditions for seedling growth in mixtures by reducing the suppressive effect of spruce litter, having a positive effect on understorey species richness.     

Influence of root herbivory on plant communities in heterogeneous nutrient environments

While plant species respond differently to nutrient patches, the forces that drive this variability have not been extensively examined. In particular, the role of herbivory in modifying plant-resource interactions has been largely overlooked. We conducted a glasshouse study in which nutrient heterogeneity and root herbivory were manipulated, and used differences in foraging among plant species to predict the influence of root herbivores on these species in competition. We also tracked the influence of neighborhood composition, heterogeneity, and herbivory on whole-pot plant biomass. When herbivores were added to mixed-species neighborhoods, Eupatorium compositifolium, the most precise forager, was the only plant species to display a reduction in shoot biomass. Neighborhood composition had the greatest influence on whole-pot biomass, followed by nutrient heterogeneity; root herbivory had the smallest influence. These results suggest that root herbivory is a potential cost of morphological foraging in roots. Root herbivores reduced standing biomass and influenced the relative growth of species in mixed communities, but their effect was not strong enough at the density examined to overwhelm the bottom-up effects of resource distribution.     

Body size changes in ground beetle assemblages – a reanalysis of Braun et al. (2004)'s data

Abstract.  1. Data in Braun et al .'s (2004) recent paper on size trends in ground beetles (Carabidae) are re-analysed, after re-classifying the species according to feeding categories.
2. When ground beetles are classified as predatory species, mixed feeders or herbivores, and evaluated separately, the size trends indicate group-specific differences. Most of these do not support the efficiency-specialisation hypothesis.
3. Taxonomic groups rarely fit into one ecological category and ecological analyses should explicitly consider this hurdle.     

Abundance,biomass and energy use of native and alien breeding birds in Britain

We quantify the contribution of alien species to the total breeding population numbers, biomass and energy use of an entire taxonomic assemblage at a large spatial scale, using data on British birds from 1997 and 2013. A total of 216 native and 16 alien bird species were recorded as breeding in Great Britain across the two census years. Only 2.8–3.7% of British breeding bird individuals were alien, but alien species co-opted 11.9–13.8% of the energy used by the assemblage, and contributed 19.1–21.1% of assemblage biomass. Neither the population sizes nor biomasses of native and alien species differed, on average, in either census, but alien species biomass is higher than native species biomass for a given population size. Species richness underestimates the potential effects of alien bird species in Britain, which have disproportionately high overall biomass and population energy use. The main driver of these effects is the ring-necked pheasant (Phasianus colchicus), which comprised 74–81% of alien biomass, yet the breeding population of this species is still only a small fraction of the estimated 35 million birds released in the UK in autumn. The biomass of this release exceeds that of the entire breeding avifauna, and suggests that the pheasant should have an important role in structuring the communities in which it is embedded.     

The influence of habitat homogenization on the trophic structure of fish fauna in tropical streams

Habitat homogenization is one of the most important drivers of change in riverine fauna. Therefore, the aim of this study was to determine whether habitat homogenization influences the trophic structure of fish assemblages in tropical streams. We sampled 78 streams located in pasture and crop lands to examine habitat variables and fish. Principal coordinates analysis, canonical analysis of principal coordinates, and a distance-based test for homogeneity of multivariate dispersions revealed two groups of streams, designated homogeneous and heterogeneous, based on the habitat variables. We determined trophic guilds according to the frequency and biovolume of food items. Seven guilds were identified: aquatic insectivores, terrestrial insectivores, detritivores, herbivores, omnivores, algivores, and detritivores–algivores. Homogeneous streams showed higher abundance and biomass of aquatic insectivores, detritivores, and algivores. Heterogeneous streams showed greater diversity of trophic guilds and higher abundance and biomass of terrestrial insectivores and herbivores than homogeneous streams. Our results demonstrate that trophic structure is influenced by habitat condition. Additionally, the riparian canopy and nearshore vegetation have a modulating role in the trophic structure of stream fishes due to their influence on resource supply and promotion of the physical heterogeneity of the channel.     

A comparison of bird communities in mixed fruit orchards and natural forest at Khao Luang, southern Thailand

The avifauna of a mixed fruit orchard and nearby isolated forest patch on the mountain of Khao Luang, southern Thailand, was compared with that in natural forest. The orchard was about 75% as rich in bird species as the forest and was dominated by smaller frugivores, nectarivores and widespread generalists. Sundaic birds contributed 26% of sightings in the orchard, and understorey insectivores were poorly represented. The avifauna of the 4.5-ha forest patch was similarly depauperate and bore greater resemblance to that in the orchard than to that in forest. These results have implications for management since increasing emphasis is being placed upon the rights of local communities to manage and exploit resources in protected areas. While agricultural diversification may assist in restoring modest levels of diversity in areas already degraded or committed to human use, it should not be seen as a substitute for conventional protection of forest and wildlife through exclusion of such use.     

Large-scale patterns of summer and winter bird distribution in relation to farmland type in England and Wales

Over the last 30 yr, the loss of traditional crop rotations and the polarisation of pastoral and arable farming have led to a marked reduction in mixed agriculture in Britain at both the individual farm and the landscape scale. We assess the potential impact of this change on lowland farmland birds by examining the extent to which distributions (as shown by national atlases of summer and winter birds) of different species are associated with arable, pastoral or mixed‐farming landscape types. Relatively few species appeared as either widespread generalists, equally associated across the three broad farmland types, or specialists associated only with one landscape type. Most were associated with two farmland types but distributions showed seasonal differences. During the breeding season there was an approximate ratio of 2:2:1 of species associated with arable, mixed and pastoral landscapes. However, in winter, most species were at highest abundance in mixed farming landscapes. This coincided with a reduction in the number of species associated with pastoral landscapes relative to the breeding season, whereas the number of species associated with arable landscapes remained relatively stable. These patterns are likely to be related to foraging requirements; granivorous birds tended to be associated with arable habitats, which tend to be more seed‐rich, and invertebrate‐feeding species tended to be associated with mixed or pastoral ones, which may be more invertebrate‐rich. The relative importance of mixed landscapes in winter was attributed to seasonal changes in the distribution of some invertebrate feeders, particularly small insectivores (pipits, chats and wagtails), and some of those species considered to be widespread in summer. The results have two important implications for future research. First, most research on farmland birds has, to date, focused on species associated with arable farming during the breeding season. More research is required on species associated with agricultural grasslands, reflecting its importance for farmland birds in Britain, and on the winter ecology of farmland birds in general. These results also emphasise the importance of mixed habitats for farmland birds, particularly in winter, and suggest that further changes in agricultural practices causing reduction in habitat diversity will be detrimental for the farmland bird community. However, widespread benefits may be derived from small scale measures that increase habitat diversity within farmland, for example field margin management options within agri‐environment schemes and support for traditional farming practices in some Environmentally Sensitive Areas.     

Distinct carbon sources indicate strong differentiation between tropical forest and farmland bird communities

The conversion of forest into farmland has resulted in mosaic landscapes in many parts of the tropics. From a conservation perspective, it is important to know whether tropical farmlands can buffer species loss caused by deforestation and how different functional groups of birds respond to land-use intensification. To test the degree of differentiation between farmland and forest bird communities across feeding guilds, we analyzed stable C and N isotopes in blood and claws of 101 bird species comprising four feeding guilds along a tropical forest-farmland gradient in Kenya. We additionally assessed the importance of farmland insectivores for pest control in C₄ crops by using allometric relationships, C stable isotope ratios and estimates of bird species abundance. Species composition differed strongly between forest and farmland bird communities. Across seasons, forest birds primarily relied on C₃ carbon sources, whereas many farmland birds also assimilated C₄ carbon. While C sources of frugivores and omnivores did not differ between forest and farmland communities, insectivores used more C₄ carbon in the farmland than in the forest. Granivores assimilated more C₄ carbon than all other guilds in the farmland. We estimated that insectivorous farmland birds consumed at least 1,000 kg pest invertebrates km^?2 year^?1. We conclude that tropical forest and farmland understory bird communities are strongly separated and that tropical farmlands cannot compensate forest loss for insectivorous forest understory birds. In tropical farmlands, insectivorous bird species provide a quantitatively important contribution to pest control.