Ground beetles (Carabidae) and edge effect in oak-hornbeam forest and grassland transects

We evaluated ground beetle diversity in relation to forest edge between an oak-hornbeam forest and adjacent herbaceous grassland. To test our hypothesis that the diversity of ground beetles was higher in the forest edge than the interior, pitfall trap samples were taken along two forest-grassland transects in northern Hungary. The diversity of ground beetles was significantly higher at the forest edge and in the grassland than in the forest interior. Ground beetle assemblages in the forest interior, forest edge and grassland could be separated from each other by ordination. Indicator species analysis detected five groups of species: habitat generalists, grassland-associated species, forest generalists, forest specialists, and edge-associated species. Rank correlation indicated leaf litter, herb, canopy cover, and prey abundance as the most important factors influencing carabid diversity. The high diversity of the forest edge resulted from the presence of edge-associated species and of species characteristic of adjacent habitats. Forest edges seem to play an important role in maintaining diversity. Serving as source habitats, edges also contribute to the recolonisation by ground beetles after habitat destruction or other disturbance in the adjacent habitats.     

The importance of gallery forests in the tropical lowlands of Costa Rica for understorey forest birds

Rivers and streams lined by narrow forest strips are common in the lowland countryside of south-western Costa Rica. We studied the importance of these gallery forests for understorey birds, especially forest species. Using mist-nets, we captured 1110 birds belonging to 90 species between June and September 2007 at 16 sites spread equally over four habitat types: forest interior, forest margin, gallery forest connected to closed forest, and isolated gallery forest. Though isolated gallery forests had the greatest number of expected species in total, they supported the lowest number of forest-specialist species, lower even than connected gallery forests. Granivorous birds showed an increase from forest to isolated gallery forest, all other feeding guilds however showed no change. The studied habitats differed from each other in their faunal composition. Assemblages of three species groups categorised by their habitat preferences (forest specialists, forest generalists, non-forest species) showed nested distribution patterns across the four habitats. There was no significant difference in the proportion of birds with brood patches or of recaptures across the studied habitat types, leading to the assumption that birds not only use gallery forests for movement and foraging but also for reproduction. Though of limited conservation value for most forest understorey birds, at least for a small fraction of forest species gallery forests constitute an important secondary habitat. More significantly, they can form corridors or stepping stones that allow movements within the matrix of human-dominated habitats, and represent an important landscape component benefiting total bird species richness in the Costa Rican countryside.     

Underground mining can contribute to freshwater biodiversity conservation: Allogenic succession forms suitable habitats for dragonflies

Human-induced changes negatively affect all components of freshwater ecosystems and comprise the major cause of global loss of diversity and the biotic homogenization of freshwater faunas. The high diversity of dragonflies in heavily industrialized areas is therefore paradoxical, to say the least. We compared diversity of dragonflies in three main freshwater habitat types (natural and human-made) occurring in Upper Silesia (Central Europe). We used multivariate methods and diversity indices for a general analysis, comprising both species richness and the species composition of assemblages. We recorded 50 species in mine subsidence pools from the total of 54 sampled species. These included a high proportion of habitat specialists (typically threatened species). We emphasize that secondary habitats (e.g. spontaneously originated mine subsidence pools) should not a priori be regarded as ecological traps, because these often are the available habitats with highest quality. These habitats significantly outweigh ponds in species richness and proportion of habitat specialists. The conservation potential of specific secondary habitats lies in the fact that these habitats can substitute for very rare natural wetlands often restricted to higher elevations. We assume that high diversity in this type of secondary habitats is not random, but rather that it depends on environmental heterogeneity caused by a specific allogenic succession process occurring as a direct consequence of mining.     

Biotic homogenization of Central European urban floras depends on residence time of alien species and habitat types

Spread of alien species may result in biotic homogenization, i.e. increasing similarity between biotas of different areas. We examined whether the flora of Central European cities is becoming homogenized because of the spread of alien species, whether the contribution of aliens to homogenization depends on residence time, and whether habitats under more intense human pressure are more homogenized. Using floristic composition data from a standardized sample of 1-ha plots located in seven habitat types in 32 cities in Central Europe, Belgium and the Netherlands, we compared homogenization effects of archaeophytes (pre-AD 1500 aliens) and neophytes (post-AD 1500 aliens) using rarefaction curves, Jaccard dissimilarity index, Mantel tests and homogenization index. We found that archaeophytes contributed to homogenization and neophytes to differentiation of floras among cities, but generally the spread of alien species caused differentiation. Differentiation was low in the most disturbed urban habitats, such as city squares, boulevards or early successional sites, but was strongest in moderately disturbed habitats, such as city parks and residential areas with an open building pattern. We conclude that biotic homogenization depends on alien plants’ residence time. Aliens introduced within the past five centuries are often rare, not yet having achieved their potential range; they therefore increase floristic differentiation. Conversely, species introduced more than five centuries ago have had sufficient time to disperse into most suitable habitats, and consequently contribute to homogenization. Although invasions may therefore initially increase biodiversity, they could ultimately lead to homogenization. These processes are faster and stronger in more disturbed habitats.     

Projecting the local impacts of climate change on a Central American montane avian community

Significant changes in the climates of Central America are expected over the next century. Lowland rainforests harbor high alpha diversity on local scales (<1 km²), yet montane landscapes often support higher beta diversity on 10-100 km² scales. Climate change will likely disrupt the altitudinal zonation of montane communities that produces such landscape diversity. Projections of biotic response to climate change have often used broad-scale modelling of geographical ranges, but understanding likely impacts on population viability is also necessary for anticipating local and global extinctions. We model species’ abundances and estimate range shifts for birds in the Tilarán Mountains of Costa Rica, asking whether projected changes in temperature and rainfall could be sufficient to imperil high-elevation endemics and whether these variables will likely impact communities similarly. We find that nearly half of 77 forest bird species can be expected to decline in the next century. Almost half of species projected to decline are endemic to Central America, and seven of eight species projected to become locally extinct are endemic to the highlands of Costa Rica and Panamá. Logistic-regression modelling of distributions and similarity in projections produced by temperature and rainfall models suggest that changes in both variables will be important. Although these projections are probably conservative because they do not explicitly incorporate biological or climate variable interactions, they provide a starting point for incorporating more realistic biological complexity into community-change models. Prudent conservation planning for tropical mountains should focus on regions with room for altitudinal reorganization of communities comprised of ecological specialists.     

Land use and conservation value for forest birds in Central Sulawesi (Indonesia)

Unprecedented deforestation is currently underway in Southeast Asia. Since this trend is likely to continue, it is critical to determine the value of human-modified habitats (e.g., mixed-rural habitat) for conserving the regional native forest avifauna. The impacts of ongoing deforestation on the highly endemic avifauna (33%) of Sulawesi (Indonesia) are poorly understood. We sampled birds in primary and secondary forests in the Lore Lindu National Park in central Sulawesi, as well as the surrounding plantation and mixed-rural habitats. Species richness, species density and population density of forest birds showed a consistent decreasing trend in the following order: primary forests > secondary forests > mixed-rural habitat > plantations. Although primary forests contained the highest proportion (85%) of a total of 34 forest species recorded from our point count surveys, 40-yr old secondary forests and the mixed-rural habitat showed high conservation potential, containing 82% and 76% of the forest species, respectively. Plantations recorded only 32% of the forest bird species. Fifteen forest species had the highest abundance in primary forests, while two species had higher abundance outside primary forests. Our simulations revealed that all forest birds that were sensitive to native tree cover could be found in areas with at least 20% continuous native tree cover. Our study shows that although primary forests have the highest conservation value for forest avifauna, the potential of degraded habitats, such as secondary forests and the mixed-rural habitat, for conserving forest species can be enhanced with appropriate land use and management decisions.     

Land use and habitat gradients determine bird community diversity and abundance in suburban, rural and reserve landscapes of Minnesota, USA

Bird species’ community responses to land use in the suburbanizing Twin Cities, Minnesota, USA, were contrasted among reserves, rural lands, and suburbs. For each land use type, bird composition, diversity, and abundance were recorded for 2 years in ≈99 plots in three sampling units (each ≈4500 ha). A habitat gradient defined by canopy structure (grasslands to savannas to forests) was influenced by land use, so ≈300 plots were used to characterize simultaneous variation in bird communities along land use and habitat gradients. At broad scales (aggregate of 33 plots covering ≈4500 ha) suburbs supported the lowest bird richness and diversity and rural landscapes the most, with reserves slightly below rural. Although reserves were like rural lands in diversity of bird communities, they supported more species of conservation concern, particularly of grasslands and savannas. Differences among land use types varied with habitat structure. Suburbs, rural lands, and reserves had similar forest bird communities, but differed in grassland and savanna bird communities. The extensive rural forests are important for the region’s forest birds. Suburban grasslands and savannas had low shrub abundance, low native bird richness and high non-native bird richness and abundance. However, total bird richness and diversity were as high in suburban as in rural and reserve plots because high native richness in suburban forests and high non-native species richness in suburban grasslands and savannas compensated for lower native richness in suburban grasslands and savannas. Bird conservation here and in the Midwest USA should protect rural forests, expand grasslands and savannas in reserves, and improve habitat quality overall.     

The effects of forest patch size and matrix type on changes in carabid beetle assemblages in an urbanized landscape

In this study we compared ground beetles (Carabidae) from a range of different forest fragments along an urbanization gradient in Brussels, Belgium. We address the following questions: (i) How does the degree of urbanization in the surrounding habitat affect forest beetles, and does it interact with the effects of patch size and distance to forest edge? (ii) Do these factors have a different effect at the level of individual species, habitat affinity groups or total community? During 2002 we sampled 13 forest plots in 10 forest patches, ranging in size from 5.27 to 4383 ha. The beetles were captured using transects of pitfall traps from the edge to a distance of 100 m into each woodland and identified to species level. Effects of urbanization, forest size and forest edge were evaluated on total species number, abundance and habitat affinity groups and ten abundant, widespread model carabid species. Overall, the effects of urbanization, forest size and edge effects slightly influenced total species richness and abundance but appeared to have a major effect on ground beetle assemblages through species specific responses. More urbanized sites had significantly fewer forest specialists and more generalist species. Large forest fragments were favoured by forest specialist species while generalist species and species frequently associated with forest (forest generalists) dominated the smaller forests. Forest edges mainly harboured generalist species while forest specialist species were more frequent into the forests if the forest patches were large enough, otherwise they disappeared due to the destruction or impoverishment of their habitat. Our results show the importance of differentiating between habitat affinity, especially habitat generalists versus specialists, the latter having a higher value in nature conservation, and merely the quantity of species represented in human-dominated areas.     

Effects of habitat degradation on the abundance, richness and diversity of raptors across Neotropical biomes

Population growth and human development result in biodiversity loss and biological homogenization not only in developed countries, but increasingly in the less developed countries as well. In those countries, where urbanization and agricultural intensification occur at a faster rate than in developed countries, habitat degradation appears to be the leading cause of wildlife loss. During the breeding seasons of 2002–2005 we conducted road surveys across five biomes of Argentina to detect variations in raptor community attributes as potential indicators of broad scale habitat degradation. Abundance of individuals, richness and diversity of species were calculated to assess the effects of habitat transformation and patch size on these community attributes. Raptor communities strongly varied in relation to habitat transformations, with lower abundance of individuals, richness and diversity of species in more transformed landscapes. Small patches of natural vegetation and locations in which natural and cultivated lands where interspersed showed lower richness and diversity of raptors than large patches. Fragmentation was the main cause of reductions in abundance of individuals. Although the relative contribution of our two estimates of habitat degradation to abundance, richness and diversity of raptors varied among biomes, these community attributes proved useful as predictors of habitat degradation. This was especially true in habitats where raptor communities are more complex although overall patterns remained constant across biomes, from forests to deserts. Taking into account current trends of habitat transformation (drastic increments in monocultures, urban areas, and habitat patchiness), the conservation of raptor communities in these biomes could be seriously compromised. In terms of species-specific responses of raptors to habitat degradation, a rapid process of homogenization can be expected, resulting in only a few winner species within a general scenario of losers.     

The future of tropical species in secondary forests: A quantitative review

Deforestation and degradation of tropical old-growth forests has the potential to cause catastrophic species extinctions. In this review, we assess whether regenerating secondary forests (SF) can support species typically found in old-growth forest (OG) and so prevent extinctions. We review 65 studies that compare faunal diversity in SF and corresponding OG, and compare the similarity of species composition both within and between these two forest types using the Sorensen, Morisita-Horn and Sorensen-Chao indices. Comparisons between traditional similarity indices and Sorensen-Chao, which minimizes sampling biases, indicated that limited sampling effort consistently reduced apparent similarity between SF and OG and that similarity between SF and OG is actually higher than previously appreciated. Similarity, which ranges from 0 to 1, varied from 0.49 to 0.92 between replicate OG sites and was correlated with similarity between SF and OG. This correlation might be an artefact of variation among studies in sampling effort, especially for vertebrates where small samples reduce apparent similarity across all comparisons, as well as a real effect of variation among studies in landscape heterogeneity and the presence of species with patchy distributions. Therefore, similarity between SF and OG cannot be interpreted without an understanding of background variation in OG. Similarity between different SF sites provided no evidence that disturbance specialists dominate SF. Similarity to OG increased rapidly with SF age; when SF was contiguous with OG; when SF was growing in small clearings; and after low intensity land uses including clearing only, shifting agriculture and tree plantations. This describes the most frequently observed tropical SF; isolated from roads and on hilly terrain unsuitable for mechanized agriculture. Thus, our analyses indicate that tropical SF can play an important role in biodiversity conservation particularly when OG forests are nearby. An important caveat remains, however. Abundance, geographic range and levels of habitat specialization are often related. Widespread, abundant, habitat generalists might dominate similarity analyses even when relatively rare OG specialists are present. Additional species-level analyses of habitat specialization will be needed before the conservation value of tropical SF is fully understood.     

Habitat structure and proximity to forest edge affect the abundance and distribution of forest-dependent birds in tropical coastal forests of southeastern Madagascar

Despite the fact that Madagascar is classified a biological `hotspot' due to having both high levels of species endemism and high forest loss, there has been no published research on how Madagascan bird species respond to the creation of a forest edge or to degradation of their habitat. In this study, we examined how forest bird communities and different foraging guilds were affected by patch habitat quality and landscape context (forest core, forest edge and matrix habitat) in the threatened littoral forests of coastal southeastern Madagascar. We quantified habitat use and community composition of birds by conducting 20 point counts in each landscape contextual element in October and November 2002. We found that littoral forest core habitats had significantly (p<0.01) more bird species than forest edge and matrix habitats. Thirty-one (68%) forest dependent species were found to be edge-sensitive. Forest edge sites had fewer species, and a higher representation of common species than forest interior sites. Twenty-nine species were found in the matrix habitat, and the majority of matrix-tolerant forest species had their greatest abundance within littoral forest edge habitats. Guild composition also changed with landscape context. Unlike other tropical studies with which we are familiar, we found that frugivorous species were edge-sensitive while sallying insectivores were edge-preferring. The majority of canopy insectivores (n=15, 88%), including all six endemic vanga species, were edge-sensitive. When habitat quality was assessed, the distributions of nine edge-sensitive species were significantly (p<0.01) affected by changes in habitat complexity and vegetation vertical structure in core or edge point counts. Therefore, we believe that changes in vegetation structure at the edge of littoral forest remnants may be a key indicator of mechanisms involved in edge sensitivity of forest dependent species in these forests. Our findings indicate that habitat fragmentation and degradation affect Madagascan bird communities and that these processes threaten many species. With continued deforestation and habitat degradation in Madagascar, we predict the further decline of many bird species.     

Evaluating hedgerow corridors for the conservation of native forest herb diversity

The maintenance of connecting habitats such as hedgerows in production landscapes could become increasingly critical as species migration is expected to accelerate with climate change. Species of particular conservation interest that could benefit from connecting habitats especially in agroecosystems are native forest herbs. It is still unclear, however, which hedgerow habitats have the best potential of supporting diverse forest herb communities, making it hard to target particular structures for conservation. Our objective was to identify the local and landscape characteristics of hedgerows that could help predict their potential at maximizing the richness, abundance, and diversity of native forest herbs of temperate deciduous forests of North-East America. We used multiple regression, Moran’I correlograms, and conditional autoregressive models to assess the effect of landscape and historical variables (hedgerow age, amount of adjacent forest cover, connection to forests and other hedgerows) and of local variables (hedgerow width, canopy cover, cover of other species) on the response variables. The results show an increase in forest herb diversity and abundance in hedgerows with time and with increasing nearby forest cover. Local factors such as greater width and reduced cover of other species also relate to a greater abundance and diversity of forest herbs in linear habitats. The fact that forest herb communities can reassemble in hedgerow corridors with time implies that there could be long-term benefits in maintaining and even creating linear habitats where there is a pool of dispersing forest herbs.     

区域景观中生境特异性对昆虫多样性的影响——以西双版纳为例

生境特异性(habitat-specific)在维持生物多样性上发挥着重要作用。本研究旨在了解在区域景观中,不同类型生境对不同类群昆虫多样性的贡献及群落结构差异,从大尺度上探讨昆虫多样性分布格局和维持机制。于2019年8—9月,在西双版纳地区利用样线调查法,调查了保护区、次生林、人工林和农田4种生境中蝴蝶、蝽和甲虫的物种数、特有物种数,分析了昆虫群落的生境特异性指数、群落结构相似性及物种丰富度与生态因子的关系。共采集昆虫2588头,其中蝴蝶94种(744头),蝽197种(1094头),甲虫129种(750头),保护区的昆虫物种数和特有物种数均高于其余类型生境。保护区昆虫群落的生境特异性指数实测值高于期望值,而其余类型生境昆虫群落的生境特异性指数实测值均低于期望值;不同类型生境间,3个类群的昆虫群落汇总的生境特异性指数不存在显著差异(F_(3,57)=2.054),甲虫生境特异性指数差异显著(F_(3,55)=3.478),蝴蝶(F_(3,38)=1.504)和蝽类(F_(3,53)=1.153)生境特异性指数差异不显著。群落结构相似性分析显示,保护区和农田的3个类群昆虫群落汇总的群落结构差异显著;次生林和人工林的蝴蝶群落结构差异显著,保护区和次生林的蝽类群落结构差异显著,甲虫昆虫群落结构差异不显著。本研究还发现,只有生境类型对昆虫群落的物种丰富度产生的影响极显著(P0.01),而其他生态因子的影响不显著。在大尺度区域景观中,保护区对昆虫群落的多样性影响最大,生境类型与昆虫群落的物种丰富度密切相关,保护较好的天然林是维持区域昆虫群落分布格局和多样性的重要机制。     

Linking forest structure and composition: avian diversity in successional forests of Chiloé Island, Chile

We show how Chilean forest bird species richness, abundance and guild structure changes as a function of structural properties of forest stands. We surveyed bird assemblages in two old-growth (>200 years), two mid-successional (30-60 years), and two early-successional forest stands (4-20 years), from November 1999 to September 2000, on Chiloé Island, southern Chile (42°S). Birds were grouped into four habitat-use guilds: large-tree users, vertical-profile generalists, understory species, and shrub-users that occasionally use forests. We recorded a total of 24 bird species: 21 in old-growth, 14 in mid-successional and 16 in early-successional stands. Large-tree users and understory birds were most abundant in old-growth stands, vertical-profile generalists were common in both old-growth and mid-successional stands, and shrub-users were only common in early-successional stands. For nine bird species we found significant relationships between their local abundance and forest structural elements. Higher bird densities in old-growth forests were associated with greater availability of canopy emergent trees, snags, logs and understory bamboo cover in this habitat. Accordingly, bird species diversity in forest stands can be predicted by the presence of these structural elements, and forests should be managed to conserve structural elements that create favorable habitat for bird species in order to prevent future species losses due to logging practices.     

Forest management and wildlife in forested wetlands of the southern Appalachians

The southern Appalachian region contains a variety of forested wetland types. Among the more prevalent types are riparian and bottomland hardwood forests. In this paper we discuss the temporal and spatial changes in wildlife diversity and abundance often associated with forest management practices within bottomland and riparian forests. Common silvicultural practices within the southern Appalachians are diameter-limit cutting, clearcutting, single-tree selection, and group selection. These practices alter forest composition, structure, and spatial hetereogeneity, thereby changing the composition, abundance, and diversity of wildlife communities. They also can impact special habitat features such as snags, den trees, and dead and down woody material. The value of wetland forests as habitat also is affected by characteristics of adjacent habitats. More research is needed to fully understand the impacts of forest management in wetlands of the southern Appalachians.     

Effects of anthropogenic land use on forest birds and butterflies in Subic Bay, Philippines

Despite the loss of 83% of native forests in the Philippines, little is known on the effects of this massive habitat loss and degradation on its forest biotas. This is a cause for concern because of the threat posed to the country’s large number of endemic taxa. To investigate the impacts of anthropogenic disturbance, forest birds and butterflies were surveyed in closed and open canopy forests, as well as suburban, rural and urban areas within the Subic Bay Watershed Reserve and Olongapo City in western Luzon. Measures of forest species richness and population densities for both taxa were similar in the two forest types, but showed different patterns in the other habitats. Indirect gradient analysis showed that forest bird species were positively correlated with vegetation variables (i.e., canopy cover, tree density, height to inversion and ground cover), while forest butterflies were not strongly correlated to any of the measured habitat variables. Community composition of birds in forests was distinct from those in modified habitats, while butterfly communities were more similar. A simulation showed that canopy cover of 60% or higher was required by 24 of the 26 bird species that were sensitive to canopy loss. Endemicity and nesting strata were the significant predictors of vulnerability to habitat disturbance for birds, while endemicity and larval hostplant specificity were significant for butterflies. Both taxa were negatively affected by anthropogenic disturbance but may respond to different components in the habitat (i.e., structure and resources), and thus cannot be used as surrogates of each other. Conservation of forests with contiguous canopy cover should be prioritized, and more ecological research is needed to improve the knowledge on the effects of disturbance on Philippine biodiversity.     

Avian assemblages along a gradient of urbanization in a highly fragmented landscape

Our goal was to evaluate how avian assemblages varied along a gradient of urbanization in the highly fragmented landscape of coastal southern California. We measured species richness and abundance of birds within continuous blocks of habitat, within urban habitat fragments that varied in landscape and local habitat variables, and within the urban matrix at different distances from the wildland interface. These comparisons allowed us to characterize patterns of avifaunal response to a gradient of urban fragmentation. At the fragment scale, we found that fragment area was a strong, positive predictor of the total number of breeding species detected per fragment; total bird abundance per point count also increased with fragment size. Tree cover was higher in small fragments, as was the abundance of birds that typically occupy wooded habitats. Comparisons between core, fragment, and urban transects revealed differing patterns of response of individual bird species to urbanization. In unfragmented habitat, we recorded a relatively high diversity of urbanization-sensitive birds. In urban transects, these species were rare, and a relatively few species of non-native and anthropophilic birds were common. These urbanization-enhanced birds were also recorded in previous urban gradient studies in northern California and Ohio. Bird communities along the urban gradient reached their highest richness and abundance in fragments. The marked difference in vegetation structure between urban and natural landscapes in this arid shrubland system likely contributed to this pattern; the presence of native shrubs and exotic trees in fragments enabled both shrub and arboreal nesters to co-occur. As is characteristic of biotic homogenization, urban fragmentation in coastal southern California may increase local diversity but decrease overall regional avifaunal diversity.     

Impact of human dwellings on the distribution of the exotic Argentine ant: a case study in the Doñana National Park, Spain

The invasive Argentine ant Linepithema humile was found in close perimeters to inhabited houses situated in various habitat types in Doñana National Park (Southern Spain). We suggest that the Argentine ant is found in these sites largely due to passive importation by man, but from there may have the potential to spread into surrounding favourable natural habitats. Ant species richness and diversity around houses was similar to that in natural habitats, except in the cases where the Argentine ant dominated, where a considerable lower ant species diversity and richness was observed. The species composition of ants in the immediate vicinity of houses was very different from that of the surrounding natural habitats, although the species composition between houses was very similar, regardless of the type of surrounding natural habitat. Ant species around houses were typically generalists, opportunists or open habitat specialists. Many of these species are considered dominant in that they are characterised by having large nests, aggressive behaviour and mass recruitment in response to attack. However, these species are displaced by the Argentine ant when introduced. Not all ant species show the same responses to invasions by the Argentine ant, and some species, such as Cardiocondyla batesii, Oxyopomyrmex saulcyi or Cataglyphis floricola, may be able to persist for a period following an invasion of the Argentine ant. These species are characterised by small nests and submissive behaviour, and may survive by avoiding conflict with the invasive species.     

High sensitivity of montane bird communities to habitat disturbance in Peninsular Malaysia

Over the past few decades, the montane forests of Peninsula Malaysia have been severely impacted by the cultivation of exotic crops and urban sprawl. To guide conservation initiatives, montane bird communities were studied to determine their response along a disturbance gradient with the aim of identifying key factors influencing their distribution. Habitat types surveyed included primary and secondary montane forests, a tea plantation, rural, and urban areas in Cameron Highlands and Fraser’s Hill. Response variables included species richness and density quantified via point counts and mistnet surveys. Explanatory variables measured were related to vegetation structure, food abundance and land-use cover. Estimated ‘true’ species richness was higher for pristine and minimally disturbed sites, lower in tea plantation and lowest in heavily developed town centres. Nonmetric multidimensional scaling revealed that both vegetation structure (e.g. canopy density) and land-use cover (e.g. proportion of forest cover) influence species distribution; certain invasive lowland birds were tolerant of extreme development and native montane birds, in general, endured only slight habitat disturbances. A simulation indicated that montane forest dependant species richness started to decline when more than 20% of the canopy cover was lost. Less than a third of the species richness remained when more than 40% of the canopy cover was cleared. The logistic regression model suggested that sensitive species nested lower, were restricted to montane habitats and foraged in mid or high canopy. The dominance of lowland invasives in highly developed urban sites reveals that homogenisation of bird communities can occur even at higher altitudes (>1400 m a.s.l.). The results indicated that native montane birds communities are sensitive to habitat loss and degradation. Thus, any development in the highlands must proceed with minimal disturbance to montane forests, of which, keeping the canopy cover intact should be a crucial consideration.     

Forecasting faunal and floral homogenization associated with human population geography in North America

Human population and urbanization is unprecedented in its rate of growth and geographic scope. With the help of humans, exotic species have piggybacked their way to distant lands, which in combination with the loss of endemic native species, has led to the convergence of biological communities toward common and ubiquitous forms. However, the extent to which this “biotic homogenization” varies along gradients of human population size and urbanization remains mostly unexplored, especially at broad spatial scales. The present paper combines a recent conceptual model of homogenization with estimates of species invasions and extinctions to provide the first estimates of homogenization for five major taxonomic groups - land birds, freshwater fish, terrestrial mammals, plants, and freshwater reptiles and amphibians - at the continental-scale of North America (exclusive of Mexico). On average, the greatest levels of biotic homogenization were predicted for plants (22%) and fishes (14%), followed by reptiles/amphibians (12%), mammals (9%) and birds (8%). Substantial spatial variation in predictions of community similarity exists and emphasize that the outcome of species invasions and extinctions may not only increase community similarity, but may also decrease it (i.e., differentiation). Homogenization is predicted to be greatest for fish in southwestern and northeastern US, highest in eastern North America for plants, greatest for birds and mammals along the west coast of North America, and peak in southern US for reptiles and amphibians. We show that predicted change in community similarity for all taxonomic groups is positively related to human population size and urbanization, thus providing the first quantitative linkage between human population geography and homogenization for a number of major taxonomic groups at the continental-scale of North America. Our study helps identify regional hotspots of biotic homogenization across North America, thus setting the stage for future studies where more directed investigations of biotic homogenization along urban gradients can be conducted.