Generalist Bird Research Articles

Frugivory and seed dispersal effectiveness in twoMiconia(Melastomataceae) species from ferruginouscampo rupestre

AbstractSeed dispersal effectiveness (SDE) is a useful framework to explore the evolutionary and ecological consequences of seed dispersal to plant fitness. However, SDE is poorly studied in tropical open grasslands. Here, we studied both quantitative and qualitative components of SDE in two species ofMiconia(Melastomataceae) from ferruginouscampo rupestre, a vegetation highly threatened by mining activities. We determined fruit traits and fruit availability and found that fruits of both species are produced in times of resource scarcity at the study site. Based on the number of visits and the number of fruits removed per visit, we calculated the quantitative component of SDE for both species. Finally, we explored the qualitative component of SDE by means of a controlled experiment that simulated the effects of gut passage on seed germination. Bird species differed strongly in the quantitative component of SDE. Gut passage did not affect germination compared with hand-extracted seeds, except for a minor negative effect on germination time inM. pepericarpa.However, seeds within intact fruits showed lower germination percentages compared with hand-extracted seeds. Our data indicate thatMiconiaspecies from ferruginouscampo rupestreare visited by a diverse assemblage of generalist birds that differ in quantitative, but not qualitative, seed dispersal effectiveness. We argue that plantingMiconiaspecies can overcome seed limitation in degraded areas and thus assist ecological restoration after mining abandonment.

Metapopulation modelling of long-term urban habitat-loss scenarios

ContextIncreasing human populations in urban areas pose a threat to species’ persistence through habitat loss and fragmentation. It is therefore essential that we develop methods to investigate critical habitat loss thresholds and least detrimental landscape configurations.ObjectivesWe develop a framework to assess how the pattern of habitat loss impacts the ecological and social characteristics of a landscape and how this varies depending on the species and criteria by which it is judged.MethodsWe use a scenario-based approach to test six propositions in which habitat is lost preferentially based on patch characteristics. We use eight bird and two amphibian species as indicator species. To compare scenarios, we present a method combining the output from a metapopulation model with measures of social impacts of land-cover change in a multiple criteria decision analysis. We also determine whether a habitat loss threshold exists, below which small loss of habitat can lead to large loss of species’ occupancy.ResultsWe found that, of the scenarios presented, preferentially losing common habitats and smaller patches was least detrimental for both ecological and social factors. Threshold effects were found for all but the generalist bird species.ConclusionsWe have outlined a workflow which allows for transparent, repeatable comparison between landscapes. This workflow can be used to compare urban landscape plans, or to develop general understanding of the impacts of different forms of habitat loss. Reassuringly, the recommendations based on the scenarios presented are in keeping with received conservation wisdom: to prioritise larger and/or rarer patches.

Neophobia is negatively related to reversal learning ability in females of a generalist bird of prey, the Chimango Caracara, Milvago chimango.

In an ever-changing environment, the ability to adapt choices to new conditions is essential for daily living and ultimately, for survival. Behavioural flexibility allows animals to maximise survival and reproduction in novel settings by adjusting their behaviour based on specific information and feedback acquired in their current environments. However, a growing body of evidence indicates that an individual's personality type can limit the extent to which the individual might behave flexibly, by influencing the way an individual pays attention to novelty and how much information it collects and stores, which in turn affects the individual's decision-making and learning process. In this study, the behavioural flexibility of a generalist predator, the Chimango Caracara, Milvago chimango, was analysed using the reversal learning paradigm, focusing on the comparison between age classes, and the relation of learning flexibility with a personality trait, the level of neophobia. Due to the low number of male individuals captured, this study was carried out only with female birds. The results showed that age had no significant effect either on the acquisition of a stimulus-reward association, or on the capacity of reversing this previously learned association. Reversal of the response was a harder task for these birds in comparison with the initial acquisition process. The individual's performances in the learning tasks seemed to be uncorrelated with each other, suggesting that they involve different neural mechanisms. Contrary to the general pattern observed in the majority of previous work on personality and cognition in non-human animals, the level of neophobia did not correlate with the initial associative learning performance in both adults and juveniles, yet it showed a significant negative relationship with reversal learning ability, mainly in the regressive phase of this task, for the two age classes. Our results suggest that the predatory and generalist lifestyle of female individuals of M. chimango along with the selective pressures of the environment of the individuals studied might play a critical role in the degree and direction of the linkage between novelty response and learning flexibility observed in this study.

Effect of forest composition on bird species abundance in tropical dry deciduous forest: A case of Bhimbandh Wildlife Sanctuary, India

Abstract. Khan MS. 2017. Effect of forest composition on bird species abundance in tropical dry deciduous forest: A case of Bhimbandh Wildlife Sanctuary, India. Biodiversitas 18: 78-85. The tropical dry deciduous forest (TDDF) with 38.2% of total forest cover in India forms the largest forest type of India. TDDF have been managed for centuries in the Indian subcontinent. However, so far it is not clear how different forest compositions and structures influence the abundance and the distribution patterns of faunal species vice versa. To provide further insights in this respect, we analysed how different habitat variables influence the abundance and diversity of forest birds. The difference in relative species abundances and habitat separation between forest specialist and generalist birds was also investigated. Different classes of bird density were discriminated with habitat variables. In general, it was found that higher bird densities were concentrated in the lower tree and shrub densities and diversities, however, high grass density and diversity with low tree density and diversity favoured the overall high bird density. Results further indicate the positive association of relative density of specialist bird species with the high grass density and diversity and low tree density and diversity. Specialists occurred in the lower relative densities (0.75±0.68) than that of generalists (0.86±0.69) and were found restricted to dense, pristine woody forest patches with high tree diversity.
 Keywords: Bhimbandh Wildlife Sanctuary, birds, Forest Composition, India, Tropical Dry Deciduous Forest

The effect of infrastructure on the invasion of a generalist predator: Pied crows in southern Africa as a case-study

Corridors can favour range expansion of generalists. Specifically, roads have been suspected of facilitating invasion. In southern Africa, pied crows (Corvus alba) have either colonised or increased in abundance, perhaps because climate warming has shifted their available habitat, assisted by roads. We investigated the link between abundance of this generalist bird species and roadkill, taking into account whether road infrastructure, socio-economics and driving habits influence roadkill. We surveyed 1170km of principal roads in South Africa (SA), Botswana, and Zimbabwe. SA has the most complex economy incorporating good roads, fast vehicles and more human activity. The economy of Botswana is intermediate and Zimbabwe's is smallest. Crows were sighted nearly 10 times more often in SA than Zimbabwe, although crows were historically rare in 60% of the SA area we surveyed. They were five times more abundant in Botswana than Zimbabwe. Roadkill was 20 times more frequent in SA and eight times more frequent in Botswana, than Zimbabwe. The average number of vehicle occupants in Zimbabwean vehicles was 5.5 and 2.8 times that of SA and Botswana, respectively. That is, the number people transported per roadkill was 4.5 in South Africa, compared to 433 in Zimbabwe. There was an interaction between roadkill and country. SA had the greatest increase in crow numbers per roadkill, indicating that crow densities were greater in SA because roads are particularly important for crows compared to the surrounding environment, and/or that the regular supply of roadkill on South African roads builds a “reservoir” of crows. Increased crow abundance places additional predation pressure on mammals, reptiles, birds and insects in the surrounding scrub-vegetation. Telegraph poles contribute to the problem, providing nest sites in an environment that provides few other nests and perches. An approach to socioeconomic development that considers contributing factors can be expected to reduce the spread of opportunist species.

Vacant lots as a habitat resource: nesting success and body condition of songbirds

AbstractVacant lots are a common feature throughout many cities and may provide necessary habitat resources for urban bird populations. We evaluated the quality of vacant lots throughout Baltimore, Maryland, by determining how differences in vacant lot properties related to songbirds' nesting success and body condition. We observed 130 nests from American robins (Turdus migratorius), gray catbirds (Dumetella carolinensis), and northern cardinals (Cardinalis cardinalis) across the city and assessed body condition of 19 adult robins. Nesting success for all three species was greatest within areas of vacant lots with high shrub densities. The robins' body condition index did not vary extensively and was not related to any vacant lot site‐ or landscape‐level variables. Even so, we found vacant lots to be actively used by 60 bird species for a variety of resources, with those containing more shrubs to be the most beneficial for bird species' nesting attempts. Vacant lots should no longer be discarded and underestimated; instead, they should be valued for the opportunities they provide for generalist bird species through small‐effort habitat management practices.

Tiny terminological disagreements with far reaching consequences for global bird trends

Various combinations of data and expert opinion have been used to select species for indices of bird trends. Commonly these indices break species into groups based on their habitat preference such as woodland specialist, farmland specialist and generalist birds. It is unclear what influence differences in how species are allocated to these groups might have on trends in these indices. There is uncertainty surrounding reported trends in these bird groups with studies variously showing declines or increases in prevalence. This is usually attributed to ecological factors but if studies classify bird groups differently this variation may be due to inconsistency in classification. Disagreement about whether these bird groups are stable, increasing or declining has the potential to obscure important changes in bird prevalence and impede appropriate, timely conservation.We examined how consistently European and Australian researchers classified woodland, farmland and generalist birds, and whether this affected the trends in indices of these groups. Researchers from both regions classified species differently, and the population trends seen in these groups were strongly affected by differences in classification. While all classifications we studied suggest that populations are consistently declining for Australian woodland and European farmland birds and increasing for European woodland birds. European generalist and Australian farmland and generalist birds may be seen as increasing or decreasing in prevalence depending on classification.Our results question the current practice of idiosyncratically classifying indicators in scientific research and conservation. Current practice is making it more difficult to infer whether, when and how to preserve bird groups in Europe and Australia, potentially leading to sub-optimal biodiversity outcomes. We offer suggestions for building consensus on how to classify these bird groups in order to provide more reliable evidence to support conservation decisions.

A novel relay nucleus between the inferior colliculus and the optic tectum in the chicken (Gallus gallus).

Processing multimodal sensory information is vital for behaving animals in many contexts. The barn owl, an auditory specialist, is a classic model for studying multisensory integration. In the barn owl, spatial auditory information is conveyed to the optic tectum (TeO) by a direct projection from the external nucleus of the inferior colliculus (ICX). In contrast, evidence of an integration of visual and auditory information in auditory generalist avian species is completely lacking. In particular, it is not known whether in auditory generalist species the ICX projects to the TeO at all. Here we use various retrograde and anterograde tracing techniques both in vivo and in vitro, intracellular fillings of neurons in vitro, and whole-cell patch recordings to characterize the connectivity between ICX and TeO in the chicken. We found that there is a direct projection from ICX to the TeO in the chicken, although this is small and only to the deeper layers (layers 13-15) of the TeO. However, we found a relay area interposed among the IC, the TeO, and the isthmic complex that receives strong synaptic input from the ICX and projects broadly upon the intermediate and deep layers of the TeO. This area is an external portion of the formatio reticularis lateralis (FRLx). In addition to the projection to the TeO, cells in FRLx send, via collaterals, descending projections through tectopontine-tectoreticular pathways. This newly described connection from the inferior colliculus to the TeO provides a solid basis for visual-auditory integration in an auditory generalist bird. J. Comp. Neurol. 525:513-534, 2017. © 2016 Wiley Periodicals, Inc.

Generalist birds promote tropical forest regeneration and increase plant diversity via rare-biased seed dispersal.

Regenerated forests now compose over half of the world's tropical forest cover and are increasingly important as providers of ecosystem services, freshwater, and biodiversity conservation. Much of the value and functionality of regenerating forests depends on the plant diversity they contain. Tropical forest diversity is strongly shaped by mutualistic interactions between plants and fruit-eating animals (frugivores) that disperse seeds. Here we show how seed dispersal by birds can influence the speed and diversity of early successional forests in Puerto Rico. For two years, we monitored the monthly fruit production of bird-dispersed plants on a fragmented landscape, and measured seed dispersal activity of birds and plant establishment in experimental plots located in deforested areas. Two predominantly omnivorous bird species, the Northern Mockingbird (Mimus polyglottos) and the Gray Kingbird (Tyrannus dominicensis), proved critical for speeding up the establishment of woody plants and increasing the species richness and diversity of the seed rain in deforested areas. Seed dispersal by these generalists increased the odds for rare plant species to disperse and establish in experimental forest-regeneration plots. Results indicate that birds that mix fruit and insects in their diets and actively forage across open and forested habitats can play keystone roles in the regeneration of mutualistic plant-animal communities. Furthermore, our analyses reveal that rare-biased (antiapostatic) frugivory and seed dispersal is the mechanism responsible for increasing plant diversity in the early-regenerating community.

Host-parasitoid evolution in a metacommunity.

Patch size and isolation are predicted to alter both species diversity and evolution; yet, there are few empirical examples of eco-evolutionary feedback in metacommunities. We tested three hypotheses about eco-evolutionary feedback in a gall-forming fly, Eurosta solidaginis and two of its natural enemies that select for opposite traits: (i) specialization and poor dispersal ability constrain a subset of natural enemies from occupying small and isolated patches, (ii) this constraint alters selection on the gall fly, causing phenotypic shifts towards traits resistant to generalist and dispersive enemies in small and isolated patches, and (iii) reduced dispersal evolves in small, isolated populations. We sampled patches in a natural metacommunity and found support for all hypotheses; Eurosta's specialist wasp parasitoid attacked fewer galls in small and isolated patches, generating a selection gradient that favoured small galls resistant to predation by a dispersive and generalist bird predator. Phenotype distributions matched this selection gradient, and these phenotypic differences were maintained in a common garden experiment. Finally, we found lower dispersal abilities in small and isolated patches, a phenotypic shift that aids in the maintenance of local adaptation. We suggest that the trophic rank and the species traits of consumers are central to evolution in metacommunities.

Spatial metrics effect of forest fragmentation on forest bird abundance and site occupancy probability: the influence of patch size and isolation

The persistence of species taxa within fragmented habitats is dependent on the source–sink metapopulation processes, and forest patch size and isolation are key factors. Unveiling species–patch area and/or species–patch isolation relationships may help provide crucial information for species and landscape management. In this study, relationship between forest patch size and isolation with abundance and occupancy probability of forest-dependent birds was investigated. This study was based within a coastal landscape that faces deleterious human activities such as clearing for agriculture. The study aimed to answer the question of whether the size and extent of isolation of forest patches influence abundance and/or occupancy probability of forest-specialist and generalist birds. Two bird species, namely Tiny Greenbul Phyllastrephus debilis subsp. rabai and Yellow-bellied Greenbul Chlorocichla flaviventris, were used as models. Birds were surveyed using distance sampling methods, and spatial metrics were measured from satellite imagery. Focal forest size and distance between forest patches were the most influential metrics whereby abundance and occupancy probabilities increased with increasing patch size, but were negatively influenced by increasing gaps between patches. These findings provide evidence of the existence of patch size/ isolation–occupancy relationships characterised by higher occupancy rate of large patches and distance-dependent dispersal, which decreased with increasing gaps between patches. Controlling deleterious human activities that reduce forest size should be a priority for the long-term conservation of forest-dependent birds.

Conservation implications of cascading effects among groups of organisms: The alien tree Robinia pseudacacia in the Czech Republic as a case study

Invasions of non-native plants often result in impoverished local communities; however, their cascading effects along food chain remain unknown. Here we investigated how the alteration of food resources and habitat structure due to the invasion of an alien tree affects the species richness of habitat specialist and generalist birds. During 2014, we sampled forest stands of the invasive Robinia pseudacacia and control stands of native trees in the Czech Republic (central Europe). Specifically, we performed intensive breeding bird counts and assessed moth diversity as a key food resource for breeding birds and, described the habitat structure of sampled stands. Compared to native tree stands, stands of R. pseudacacia had a lower species richness of habitat specialist birds, a higher species richness of habitat generalist birds, a lower diversity of moths, a less continuous canopy and a more developed shrub layer. Then we related bird species richness to moth diversity and descriptors of habitat structure. Moth diversity was the only variable significantly related to the species richness of habitat specialist birds, while the species richness of habitat generalist birds was related solely to the local habitat structure. Specialists were thus limited by a less diverse food supply in the invaded stands, most likely due to the absence of some arthropod species. In contrast, generalists were ecologically more flexible and exploited new breeding opportunities created by a shrub layer in the invaded stands. Our study thus provides evidence that impacts of an invasive tree scale up across trophic levels.

Effects of agricultural fragmentation on the bird community in sagebrush shrubsteppe

Habitat fragmentation can change the community composition of species in remnant habitat patches. We studied the impacts of fragmentation by agriculture on the bird community in heavily fragmented areas of the sagebrush shrubsteppe in western North America. We examined whether bird communities in sagebrush habitat near orchards and vineyards were different from the community in interior sagebrush habitat, and evaluated whether observed differences could be explained by predator abundance, local vegetation, the presence of the habitat edge, or the proportion of land cover in the surrounding landscape. The bird community near agricultural edges differed from interior habitat: edge habitats had higher species diversity and were dominated by generalist bird species, while Vesper Sparrows, which are sagebrush-associated in this region, were strong indicators of interior habitat. The bird community also differed between orchard edge habitat and vineyard edge habitat, although the difference was small. Edge effects on species composition were associated with differences in the local vegetation, rather than the predator community or the proportion of urban, agricultural, and sagebrush cover on the surrounding landscape. We suggest that differences in the bird community within edge and interior habitat are the result of multiple mechanisms: avoidance of exotic grasses and attraction to high shrub cover in edge habitat, attraction to resources in adjacent habitats, and spill-over of generalist birds from the adjacent agriculture. The results of this study suggest that sagebrush bird conservation areas should be placed away from agricultural development.

Impact of multiple bird partners on the seed dispersal effectiveness of China's relic trees.

Frugivorous birds generally exhibit an unequal contribution to dispersal effectiveness of plant species as a function of their habitat adaptation and body size. In our study, we compared the effectiveness of multiple bird species that contribute to the dispersal of the endangered relic Chinese yew, Taxus chinensis. Seven bird species dispersed T. chinensis seeds, with Picus canus, Turdus hortulorum, and Urocissa erythrorhyncha being the main dispersers. The quantity part of dispersal effectiveness was strongly influenced by two inherent characteristics of disperser species: body size and habitat adaptation. However, the quality part of dispersal effectiveness was only influenced by disperser type. For instance, small generalist birds and large specialist birds removed more seeds than other type dispersers. Moreover, small birds and specialist birds contributed slightly more to the dispersal quality of T. chinensis than large birds and generalist birds respectively; however, these differences were not significant. Our results suggest that dispersal effectiveness is affected by variety in the body size and habitat adaptation of different dispersers. Therefore, such variation should be incorporated into spatial and temporal management actions of relic plant species in patchy, human-disturbed habitats.

Patterns and predictors of β-diversity in the fragmented Brazilian Atlantic forest: a multiscale analysis of forest specialist and generalist birds.

Biodiversity maintenance in human-altered landscapes (HALs) depends on the species turnover among localities, but the patterns and determinants of β-diversity in HALs are poorly known. In fact, declines, increases and neutral shifts in β-diversity have all been documented, depending on the landscape, ecological group and spatial scale of analysis. We shed some light on this controversy by assessing the patterns and predictors of bird β-diversity across multiple spatial scales considering forest specialist and habitat generalist bird assemblages. We surveyed birds from 144 point counts in 36 different forest sites across two landscapes with different amount of forest cover in the Brazilian Atlantic forest. We analysed β-diversity among points, among sites and between landscapes with multiplicative diversity partitioning of Hill numbers. We tested whether β-diversity among points was related to within-site variations in vegetation structure, and whether β-diversity among sites was related to site location and/or to differences among sites in vegetation structure and landscape composition (i.e. per cent forest and pasture cover surrounding each site). β-diversity between landscapes was lower than among sites and among points in both bird assemblages. In forest specialist birds, the landscape with less forest cover showed the highest β-diversity among sites (bird differentiation among sites), but generalist birds showed the opposite pattern. At the local scale, however, the less forested landscape showed the lowest β-diversity among points (bird homogenization within sites), independently of the bird assemblage. β-diversity among points was weakly related to vegetation structure, but higher β-diversity values were recorded among sites that were more isolated from each other, and among sites with higher differences in landscape composition, particularly in the less forested landscape. Our findings indicate that patterns of bird β-diversity vary across scales and are strongly related to landscape composition. Bird assemblages are shaped by both environmental filtering and dispersal limitation, particularly in less forested landscapes. Conservation and management strategies should therefore prevent deforestation in this biodiversity hotspot.

Habitats matter: the incidence of and response to fear screams in a habitat generalist, the vinous-throated parrotbill Paradoxornis webbianus

A fear scream is a specific vocalization produced by many animal taxa including humans when confronted with an immediate threat of death. We studied population variation in the incidence of fear screams and its correlation with habitat type using a habitat generalist bird species, the vinous-throated parrotbill (Paradoxornis webbianus). Playback experiments were also conducted to determine how conspecifics respond to scream calls in this species. Overall, about 21 % of parrotbills consistently produced fear screams while being handled. Neither morphological traits nor flock size was related to screaming tendency, but females tended to scream more than males. The propensity to scream also differed significantly between geographic groups, and, interestingly, this difference was closely related to habitat type; parrotbills in closed habitats such as reedbeds or mountain forests screamed more frequently than those in open habitats. Playback experiments showed that fear screams successfully elicited rapid vocal and behavioral responses from conspecifics. Consistent with the attraction hypothesis, our study suggests that fear screams may function to gather both conspecifics and other species around the caller, which may directly or indirectly disturb the predator, thus giving the caller a chance to escape. The benefits of screaming may be influenced by environmental (e.g., habitat type) and biological (e.g., body mass) factors, which may ultimately account for the variability in propensity for screaming within and between species.

The restoration of tropical seed dispersal networks

Human activities have led to the loss of habitats and biodiversity in the Atlantic Rain Forest in Brazil. Ecological restoration aims to rebuild this biome and should include not only the reinstatement of species but also the reestablishment of complex ecological interactions and the ecological functions that they provide. One such function is seed dispersal, which is provided by the interactions between animal frugivores and plants. We studied seed dispersal networks in 3 different tropical forest sites restored 15, 25, and 57 years ago; temporal scales rarely observed in restoration studies. We investigated changes in network structure (nestedness, modularity, and network specialization) in these communities over restoration time. Although network size and the number of interactions increased with time since restoration, the networks were composed of generalist birds, and the large frugivores remained absent. Contrary to our expectations though, species richness was highest in the 25‐year‐old site, maybe due to the higher number of species used in the planting. Nestedness values were low in all 3 networks, but the highest nestedness was observed in the intermediate‐aged site. However, the oldest network was significantly modular and showed higher complementary specialization. These results suggest that 57 years after restoration, the complexity of mutualistic interactions in seed dispersal networks has increased, this enhancing ecosystem function in the Atlantic forest.

Birds in Anthropogenic Landscapes: The Responses of Ecological Groups to Forest Loss in the Brazilian Atlantic Forest.

Habitat loss is the dominant threat to biodiversity and ecosystem functioning in terrestrial environments. In this study, we used an a priori classification of bird species based on their dependence on native forest habitats (forest-specialist and habitat generalists) and specific food resources (frugivores and insectivores) to evaluate their responses to forest cover reduction in landscapes in the Brazilian Atlantic Forest. From the patch-landscapes approach, we delimited 40 forest sites, and quantified the percentage of native forest within a 2 km radius around the center of each site (from 6 - 85%). At each site, we sampled birds using the point-count method. We used a null model, a generalized linear model and a four-parameter logistic model to evaluate the relationship between richness and abundance of the bird groups and the native forest amount. A piecewise model was then used to determine the threshold value for bird groups that showed nonlinear responses. The richness and abundance of the bird community as a whole were not affected by changes in forest cover in this region. However, a decrease in forest cover had a negative effect on diversity of forest-specialist, frugivorous and insectivorous birds, and a positive effect on generalist birds. The species richness and abundance of all ecological groups were nonlinearly related to forest reduction and showed similar threshold values, i.e., there were abrupt changes in individuals and species numbers when forest amount was less than approximately 50%. Forest sites within landscapes with forest cover that was less than 50% contained a different bird species composition than more extensively forested sites and had fewer forest-specialist species and higher beta-diversity. Our study demonstrated the pervasive effect of forest reduction on bird communities in one of the most important hotspots for bird conservation and shows that many vulnerable species require extensive forest cover to persist.

Impacts of urban sprawl on species richness of plants, butterflies, gastropods and birds: not only built-up area matters

Urban growth is a major factor of global environmental change and has important impacts on biodiversity, such as changes in species composition and biotic homogenization. Most previous studies have focused on effects of urban area as a general measure of urbanization, and on few or single taxa. Here, we analyzed the impacts of the different components of urban sprawl (i.e., scattered and widespread urban growth) on species richness of a variety of taxonomic groups covering mosses, vascular plants, gastropods, butterflies, and birds at the habitat and landscape scales. Besides urban area, we considered the average age, imperviousness, and dispersion degree of urban area, along with human population density, to disentangle the effects of the different components of urban sprawl on biodiversity. The study was carried out in the Swiss Plateau that has undergone substantial urban sprawl in recent decades. Vascular plants and birds showed the strongest responses to urban sprawl, especially at the landscape scale, with non-native and ruderal plants proliferating and common generalist birds increasing at the expense of specialist birds as urban sprawl grew. Overall, urban area had the greatest contribution on such impacts, but additional effects of urban dispersion (i.e., increase of non-native plants) and human population density (i.e., increases of ruderal plants and common generalist birds) were found. Our findings support the hypothesis that negative impacts of urban sprawl on biodiversity can be reduced by compacting urban growth while still avoiding the formation of very densely populated areas.

Impact of landscape composition and configuration on forest specialist and generalist bird species in the fragmented Lacandona rainforest, Mexico

With accelerated land-use change throughout the tropics, an increasing proportion of global biodiversity is located in human-modified landscapes. Understanding the relative effects of landscape composition and configuration on biodiversity is needed to design effective conservation strategies. Yet this topic is poorly understood because most studies have been performed at the patch scale, and do not assess the impact of landscape structure on species. Using a multi-model inference approach, we assessed the relative effect of landscape composition (i.e. percentage of forest cover and matrix composition) and landscape configuration (i.e. number of forest patches and forest edge density) on α- and β-diversity of birds in 17 forest fragments and three areas of continuous forest within the Lacandona rainforest, Mexico. We tested these impacts at two spatial scales (100 and 500ha) for forest specialist and generalist birds. In general, forest specialist birds showed stronger responses to landscape characteristics than generalist species, particularly to variations in landscape composition at the 100-ha scale. The loss of forest cover represented the main threat to forest specialist birds, with a negative impact on α-diversity that was consistent across the two spatial scales. In contrast, at the two spatial scales generalist birds seemed to be favored by forest loss, as α-diversity of these birds increased in landscapes with lower forest cover and higher number of forest patches. If current deforestation rates continue, several forest specialists are likely to disappear. Future conservation and management initiatives should therefore prevent deforestation in this biodiversity-rich but vanishing tropical forest ecosystem.