Urbanization as a major cause of biotic homogenization

When measured by extent and intensity, urbanization is one of the most homogenizing of all major human activities. Cities homogenize the physical environment because they are built to meet the relatively narrow needs of just one species, our own. Also, cities are maintained for centuries in a disequilibrium state from the local natural environment by the importation of vast resources of energy and materials. Consequently, as cities expand across the planet, biological homogenization increases because the same “urban-adaptable” species become increasingly widespread and locally abundant in cities across the planet. As urbanization often produces a local gradient of disturbance, one can also observe a gradient of homogenization. Synanthropic species adapted to intensely modified built habitats at the urban core are “global homogenizers”, found in cities worldwide. However, many suburban and urban fringe habitats are occupied by native species that become regionally widespread. These suburban adapters typically consist of early successional plants and “edge” animal species such as mesopredator mammals, and ground-foraging, omnivorous and frugivorous birds that can utilize gardens, forest fragments and many other habitats available in the suburbs. A basic conservation challenge is that urban biota is often quite diverse and very abundant. The intentional and unintentional importation of species adapted to urban habitats, combined with many food resources imported for human use, often produces local species diversity and abundance that is often equal to or greater than the surrounding landscape. With the important exception of low-income areas, urban human populations often inhabit richly cultivated suburban habitats with a relatively high local floral and faunal diversity and/or abundance without awareness of the global impoverishment caused by urbanization. Equally challenging is that, because so many urban species are immigrants adapting to city habitats, urbanites of all income levels become increasingly disconnected from local indigenous species and their natural ecosystems. Urban conservation should therefore focus on promoting preservation and restoration of local indigenous species.     

Urbanization and riparian forest woody communities: Diversity, composition, and structure within a metropolitan landscape

Understanding how urban land-use structure contributes to the abundance and diversity of riparian woody species can inform management and conservation efforts. Yet, previous studies have focused on broad-scale (e.g., urban to exurban) land-use types and have not examined more local-scale changes in land use (e.g., the variation within “urban”), which could be important in urban areas. In this paper we examine how local-scale characteristics or fine-scale urban heterogeneity affect(s) the diversity, composition, and structure of temperate woody riparian vegetation communities in the highly urbanized area of Cincinnati, Ohio, USA. We use an information-theoretic approach to compare vegetation models and canonical correspondence analyses to compare species responses to urban variables. We found that urban riparian areas can harbor a high diversity of native canopy and shrub species (38 and 41, respectively); however, native and exotic woody plant species responded differently to urbanization. Exotic canopy species increased with the level of urbanization while native canopy and understory species declined. Understory species diversity displayed a greater response to urbanization than did canopy diversity, suggesting temporal lags in canopy response to disturbances associated with present and recent land-use changes. Certain native and exotic woody species represent ecological indicators of different levels of urbanization. Native species characteristic of pre-European settlement conditions were restricted to the wide riparian forests with little urban encroachment. Several native early-successional species appear tolerant to urbanization. Two exotic species, the tree Ailanthus altissima and the shrub Lonicera maackii, were the most abundant and ubiquitous woody species and appear to exploit urban disturbances. These exotic species invasions have the potential to modify forest composition and ecological function of urban riparian systems. In addition, altered hydrology may be a contributing factor as canopy and understory stem density of high-moisture-requiring species decreased with an increase in impervious surface and grass cover and with proximity to roads and railroads. In the face of urbanization, maintaining wide riparian forests and limiting building, road and railroad development within these areas may help reduce the invasion of exotic species and benefit hydrological function in temperate riparian areas.     

Flora and lepidoptera fauna adversely affected by invasive Lupinus polyphyllus along road verges

An increasing number of invasive species are changing ecosystems around the world. Road verges have commonly become the first footholds of non-native species in the new environments. Regularly mown road verges also offer habitats for meadow flora and fauna, which in Europe have suffered from the radical decline of semi-natural biotopes due to the agricultural modernization. We studied impacts of an invasive plant Lupinus polyphyllus on the plant and Lepidoptera species composition along road verges. The plant species composition was studied on 15 sites (with 1 m² quadrats) and butterflies and diurnal moths along 15 transects (with weekly censuses) in SE Finland, each site and transect representing equally lupine invaded verge and an adjacent non-lupine verge. The species richness and diversity of flora and the cover and species richness of low growing (<20 cm) species, in particular, was lower in lupine verges compared to non-lupine verges. Also, the abundance of butterflies was lower in lupine verges. As the lupine cover approached 100%, fewer butterflies were observed in lupine transects compared to the adjacent non-lupine transects and a higher proportion of individuals were flying. Our results suggest that the changes in plant species assemblages and lower plant species richness in lupine invaded areas had “bottom-up” effects on higher trophic levels. Further studies on the control of lupine are urgently needed, but meanwhile we suggest regular mowing before the lupines have shed their seeds, together with the removal of the cuttings, to be the best management option.     

Recent declines in northern tall-grass prairies and effects of patch structure on community persistence

Tall-grass prairies are a critically endangered ecosystem in North America. Our objectives were to evaluate potential roles of prairie patch structure (defined in terms of prairie patch area, matrix type, and edge effects) in explaining changes in number, size, and quality of northern tall-grass prairies over time. In 2006, we evaluated changes in remnant tall-grass prairies at the most northern extent of the tall-grass prairie range, by resurveying plant communities in 65 remnant patches in Manitoba, Canada, that were previously surveyed in 1987 or 1988. In 2007 and 2008 we conducted more detailed surveys of vegetation structure and composition at 580, 0.2 × 0.5 m quadrats distributed within 24 remnant patches of northern tall-grass prairie. Our findings suggest remnant northern tall-grass prairies continue to suffer from serious threats: 37% of the patches surveyed in 1987 or 1988 had changed to other habitat types by 2006; patches smaller than 21 ha tended to decrease in size, while larger patches increased in size; and most patches, particularly smaller ones, declined in quality. Both native and alien species responded more strongly to distance to edge than to patch size or matrix type. Edge effects may explain why prairie quality is lower and more likely to decline in smaller remnants. Richness of native plants was negatively correlated with cover and richness of alien species, suggesting that alien species may displace native species. Few existing northern tall-grass prairies are likely to be self-sustaining, and immediate active management is required to prevent further loss of remnant northern tall-grass prairies.     

The decline of native Pacific island faunas: changes in status of the land snails of Samoa through the 20th century

The highly diverse and endemic Pacific island biota is disappearing and being replaced by a relatively small number of widespread alien species. The land snail fauna of Samoa (formerly Western Samoa) contains at least 72 species (58 native, 10 alien, four cryptogenic—of unknown origin). In 1992-1994 we surveyed the fauna in order to evaluate its status and, by comparison with previous surveys, to detect any trends. Twelve species have declined (eight native, two cryptogenic); 17 (15 native, two cryptogenic) show a “probable decline” or “possible decline”; five (four alien, one native) have increased or possibly increased. Some species showed no clear trend; others could not be evaluated, but some of them may be extinct. The fauna faces threats similar to those faced elsewhere, primarily habitat destruction and alien species impacts. Most notable is the introduction of a predatory flatworm, Platydemus manokwari, in attempts to control the giant African snail, Achatina fulica, which became established in Samoa in the 1990s. The flatworm may or may not be able to control A. fulica but poses a serious threat to the native snail fauna. Further introduction and distribution of alien predators should be strongly discouraged.     

Large-scale correlates of alien plant invasion in Catalonia (NE of Spain)

Identification of the main correlates of the invasion process is a fundamental step in alien species management at the regional scale. This paper explores the main climatic, territorial, and anthropic correlates of alien plant species richness and percentage in Catalonia (NE of Spain), by means of GIS techniques. We used floristic data collected in FLORACAT per UTM 10 km × 10 km to set up the number and the percentage of alien species. The association of these variables with climate, topography, landscape, human settlement, and geographic position was explored by means of stepwise regression models applied on the axes obtained from principal component analysis. The significance of the resulting correlates was tested using the modified t test of Dutilleul to remove the effects of spatial autocorrelation. PCA reduced the 22 variables to 12 principal components (PC) that explained 90% of the cumulative variance. Regression models were highly significant and captured a high proportion of total variance (adjusted r² = 0.70 for alien species richness and r² = 0.56 for alien species percentage). Both alien species richness and percentage were mainly correlated to PC summarising variables concerning climate, habitat and landscape heterogeneity, and potential anthropogenic disturbance. However, while these PC exhibited similar weights on alien species richness, species percentage was mainly determined by climate. Implications for conservation are discussed considering a future scenario of climate warming and increasing land use change in Mediterranean areas.     

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.     

A river runs through it: Land-use and the composition of vegetation along a riparian corridor in the Cape Floristic Region, South Africa

Riparian zones are important for the many ecosystem services they supply. In settled areas, the vegetation of such zones is shaped by human land-use; this often creates conditions under which alien plant species thrive. Alien plants have been shown to induce large-scale changes in riparian habitats, and they pose a major threat to the continued provision of key ecosystem services. We used direct gradient analysis to assess correlations between land-use and the composition of vegetation along a riparian river corridor in the highly transformed landscape surrounding Stellenbosch in South Africa’s Western Cape Province. Vegetation plots were sampled along the entire length of the river from headwaters to estuary (ca. 40 km). Plant community composition was analyzed in relation to land-use data collected in the field, and additional land-use variables computed from digital land-cover data. Patterns of plant community structure were found to be directly related to land-use, with measures of cover, richness, and diversity differing significantly among land-use types. Portions of the riparian zone adjacent to agricultural land had the greatest level of alien plant cover, while areas bordered by urban land maintained the highest alien species richness. Areas adjacent to grazing and natural lands showed intermediate and low levels of invasion, respectively. Several native species were found to persist in areas with high abundance and diversity of invasive alien plants, suggesting that they will be valuable focal species for future restoration attempts. Due to the level of human-mediated change in many areas of the riparian zone, restoration to historic conditions over most of the river is not considered feasible. These areas should be recognized as examples of novel ecosystems, and management efforts should focus on restoring or creating desirable ecosystem functions, rather than on achieving assemblages comprising only native species.     

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.     

Habitat specialists and generalists drive homogenization and differentiation of temperate forest plant communities at the regional scale

In European temperate forests, changes in the compositional similarity among local plant communities (beta diversity) have rarely been studied due to the lack of adequate baseline data. Several studies, however, report the spread of common, generalist species or a decline in specialized, rare species. Both processes may lead to increased similarity among communities, i.e., biotic homogenization.To quantify changes in beta diversity, we resampled the herb layer composition of ancient broadleaf forests at 175 semi-permanent plots distributed across the Weser-Elbe region in NW Germany 20 years after first sampling. We hypothesized that beta diversity would have decreased on average as a result of a spread of habitat generalists and a decline in habitat specialists.After two decades, the forest communities did not yet exhibit severe biotic impoverishment, although there was a broad trend towards homogenization. The actual magnitude of change depended on which beta diversity measure was applied. The downward trend was primarily the result of the spread of native species that are able to tolerate broad pH and moisture ranges. A distinction between forest specialists (closely tied to forest habitats) and generalists (also found in open habitats) did not help explain changes in beta diversity. The study shows that on the regional scale and in habitats not yet threatened by the invasion of alien species, shifts in native species can promote biotic homogenization.     

Biotic homogenization of the California flora in urban and urbanizing regions

Biotic homogenization, driven by native species losses and invasive species gains was investigated for the flora of California. Data from a variety of available databases were aggregated at the county level to examine patterns in county population density and growth in relation to floristic change. Based on population, California was divided into three zones: high (n = 9; 257-1320 people/km²), medium (n = 25; 28-177 people/km²), and low (n = 24; 1-24 people/km²) density counties. Examining patterns of rare plant occurrences among these counties revealed that high and medium density counties contained, on average, as many or more rare and endemic species than low density counties. The largest pool of these species, 48 percent of the 962 highly threatened taxa in California, is restricted to high and medium density counties. Thus, urban and urbanizing counties play a strategic role in maintaining a part of California’s flora that is both globally significant and threatened with extinction. Examining species losses and noxious weed additions across high density counties, reveals a consistent pattern of low similarity among species that have been extirpated from high density counties and a high similarity among noxious weeds that these counties now share. The consequence is that California’s urban county floras appear to be homogenizing. Examining homogenization using the entire flora for urban counties demonstrates that less similar counties become more similar. The effect of loss of rare species could outweigh the gain in exotics, under an assumption of strong extinction. Finally, a strong negative relationship between population density and the proportion of county land in public ownership suggests that high and medium density counties are in a poor position to protect rare plant populations on a localized basis.     

The roles of habitat features, disturbance, and distance from putative source populations in structuring alien plant invasions at the urban/wildland interface on the Cape Peninsula, South Africa

Natural areas are becoming increasingly fragmented and embedded in an urban matrix. Natural and semi-natural areas at the urban/wildland interface are threatened by a variety of ‘edge effects’, and are especially vulnerable to invasion by introduced plants, with suburban gardens acting as significant sources of alien propagules. Urban/wildland interfaces also provide access for humans, leading to various types of disturbance. Alien plant invasions are one of the biggest threats facing remaining natural areas on the Cape Peninsula, South Africa. The area provides an ideal opportunity to study the dynamics of invasions at the urban/wildland interface, since the largest natural area, the Table Mountain National Park (TMNP), is surrounded by the city of Cape Town. We explored invasion patterns in Newlands Forest (a small section of the TMNP) and detailed the roles of habitat features and distance from putative source populations in three main habitat types: natural Afromontane forest, riverine woodland habitats, and plantations of exotic pines (Pinus radiata and P. pinaster). We also examined the role of disturbance in driving invasions in two of these habitat types (Afromontane forest and pine plantations). We hypothesized that alien richness and alien stem density would decrease with distance from the urban/wildland interface, and that alien richness and alien stem density would increase with increasing levels of human disturbance.Distance from putative source populations and levels of anthropogenic disturbance influenced alien richness in Newlands Forest but not alien stem density. Alien richness decreased significantly with distance from presumed sources in the pine habitat, and increased significantly with disturbance in the forest habitat. Percentage overstorey cover and soil pH were important environmental variables associated with alien plant species. A socio-economic approach is discussed as being the most effective approach to the management and prevention of alien plant species in Newlands Forest.     

Patterns of invasion in temperate nature reserves

The extent of plant invasions was studied in 302 nature reserves located in the Czech Republic, central Europe. Lists of vascular plant species were obtained for each reserve, alien species were divided into archaeophytes and neophytes (introduced before and after 1500, respectively). The statistical analysis using general linear models made it possible to identify the effects of particular variables. Flora representation by neophytes decreased with altitude (explained 23.8% of variance) while, with archaeophytes, the effect of altitude depended on their interaction with native species in particular vegetation types. The proportion of neophytes increased with increasing density of human population. Both the number and proportion of aliens plants significantly increased with increasing number of native species in a reserve. This relationship was affected by altitude, and after filtering out this variable, the effect remained positive for neophytes but became negative for archaeophytes in humid grasslands. The positive relationship between neophytes and native species is not a mere side effect of species-area relationship of native flora, but indicates that the two groups do not directly compete. Vegetation type alone explained 14.2 and 55.5% of variation in proportion of aliens in regions of mesophilous and mountain flora, respectively. Humid grasslands were the least invaded vegetation type. Positioning the reserve within large protected sections of landscape significantly decreases probability of it being invaded by potentially invasive alien species. Within the context of SLOSS debate, a new model — several small inside single large (SSISL) — is suggested as an appropriate solution from the viewpoint of plant invasions to nature reserves.     

Relative contributions of domestic and foreign sourced ballast water to propagule pressure in Puget Sound, Washington, USA

The movement and release of non-indigenous species (NIS) in ship ballast water is a global threat to the conservation of native aquatic species and habitats. One key to successful NIS establishment in coastal waters is propagule pressure - the size and frequency of NIS inoculations. We estimated propagule pressure of high-risk coastal zooplankton delivered in ballast water to Puget Sound, Washington, USA, which receives 7.5 × 10⁶ m³ of ballast water annually. We weighed the relative propagule pressure from domestic and foreign ballast water, in terms of propagule size (number of individuals), frequency of NIS occurrences, and diversity (number of known NIS species). Ship discharge volume was not a good predictor of propagule pressure. Instead route type (domestic or foreign) and ballast water exchange status (exchanged in mid-ocean vs. unexchanged) were much better predictors of propagule supply. Overall, while the diversity of non-indigenous zooplankton was higher in trans-oceanic ballast, the annual discharge of coastal zooplankton propagules to Puget Sound was much greater for ships conducting domestic voyages. These results suggest that intra-coastal ballast water must be further scrutinized as a pathway for NIS introduction, and calls into question regional “common waters” agreements that allow vessels to move ballast without conducting ballast water treatment.     

Effects of habitat disturbance on mixed species bird flocks in a tropical sub-montane rainforest

Despite their vulnerability to forest disturbances in the Neotropics, the consequences of forest perturbation on mixed species flocks are poorly understood in the threatened Southeast Asian rainforests. We examined the effects of local-scale habitat disturbance on mixed species flocks along an escalating gradient of anthropogenic modification (i.e., forest interior, forest edge, and urban) in a sub-montane tropical rainforest in Peninsular Malaysia that is presently experiencing low intensity development. Mixed species flocks in the forest interior and forest edge habitats (9.3 ± 2.3 and 8.4 ± 2.3, respectively) had significantly higher number of species than those observed in the urban habitat (5.1 ± 1.7). Flock participation was influenced by environmental characteristics (e.g., canopy cover). Flocking species sensitive to habitat disturbance were likely to be from the Families Corvidae, Nectariniidae, and Sylviidae; had narrow to restricted altitudinal ranges; and were exclusively dependent on primary forest and understory microhabitats. We conclude that sub-montane mixed species flocks are affected by even small scale urbanization and that they, particularly with species richness as a parameter, can be used as effective ecological indicators. With the looming development pressure on the sub-montane/montane habitats in Peninsular Malaysia and the Southeast Asian region, urgent conservation actions are needed for the preservation of their biotas.     

Multiple effects of urbanization on the biodiversity of developing countries: The case of a fast-growing metropolitan area (Concepción, Chile)

Urbanization is increasingly homogenizing the biota of less developed countries. Even though urban sprawl is a worldwide problem, most studies on the effects of urbanization, and the conceptual models have focused on developed countries. South America has not escaped urbanization, and here we discuss the potential impacts of urban sprawl with respect to three ecosystems in the metropolitan area of Concepción, Chile. We consider this area a good model and fairly representative of other cities in developing countries which are also experiencing rapid and uncontrolled growth. We found that the impacts of urban sprawl on biodiversity in the metropolitan area of Concepción differ little from cities in other parts of the world: native ecosystems are replaced by pavements and buildings and what is left of the natural soil is covered with green areas dominated by non-native ornamental species. Wetlands and other peri-urban ecosystems are rapidly being destroyed, fragmented or invaded by non-native species. We found that from a study area of 32,000 ha, there was a net loss to urbanization of 1734 ha of wetlands (23% of the original) and 1417 ha (9%) of agricultural, forest and shrub land cover types between 1975 and 2000. From the total area urbanized (3151 ha), 55% corresponded to wetlands and 45% to agricultural, forest and shrub lands cover types. We see the lack of environmental awareness as a major cause of the increasing deterioration of biodiversity in urban areas of developing countries. More research is needed to fully understand the effects of urban sprawl on the biodiversity of developing countries to include these ecosystems in global conservation strategies.     

Plant communities and soil phytolith assemblages relationship in native grasslands from southeastern Buenos Aires province,Argentina

This study has compared the phytolith production and soil phytolith assemblages of two native grass communities typical in Argentina, namely the monospecific Paspalum quadrifarium community or “pajonal”, and the Stipa-Piptochaetium community or “flechillar”. Five sites – three of which had been unmanaged while other two had been submitted to fire and fire-grazing management activities – were selected for study. The results show that in these sites a) phytolith production of the plant communities differed due to their diverse floristic composition, b) it was possible to define the type of management or the type of community based on soil phytolith assemblages, c) there were differences between plant communities and soil phytolith assemblages. These results suggest that modern phytolith assemblages are composed not only of local and present vegetation but also of extralocal/regional and probably past vegetation. Hypotheses about the probable processes involved in phytolith incorporation to soil have emerged during the investigation.     

Buffelgrass (Pennisetum ciliare) land conversion and productivity in the plains of Sonora, Mexico

Bufflelgrass (Pennisetum ciliare syn. Cenchrus ciliaris) is an African grass that has been widely introduced in subtropical arid regions of the world to improve rangelands for cattle production. However, it can have a negative effect on the diversity of native plant communities. Buffelgrass was introduced to Sonora, Mexico in the 1970s as a means to bolster the cattle industry. “Desmonte,” the process by which native desert vegetation is removed in preparation for buffelgrass seeding, alters the land surface such that buffelgrass plots are easily detectable from aerial and Landsat satellite images. We estimated the extent of conversion to buffelgrass in a 1,850,000 ha area centered on Hermosillo, from MSS and TM images from 1973, 1983, 1990 and 2000. We then compared the relative above-ground productivity of buffelgrass to native vegetation using Normalized Difference Vegetation Index values (NDVI) from Landsat and Moderate Resolution Imaging Spectrometer (MODIS) satellite sensor systems. Buffelgrass pastures have increased from just 7700 ha in 1973 to over 140,000 ha in 2000. Buffelgrass pastures now cover 8% of the land surface in the study area. Buffelgrass pastures have lower net primary productivity, estimated by MODIS NDVI values, than unconverted desert land. The desmonte process removes trees and shrubs, while the buffelgrass plantings are often sparse, leading to an apparent net loss in net primary production from land conversion. We recommend that the desmonte process be discontinued until its efficacy and safety for native ecosystems can be established, and that a comprehensive plan for preserving biodiversity while accomodating economic development be established for this region of the Sonoran Desert in Mexico.     

The responses of leaf litter invertebrates to environmental gradients along road edges in subtropical island forests

Knowledge of how roads affect forest biodiversity can be improved by measuring the responses of indicator species to complex environmental gradients caused by these infrastructures. We studied litter invertebrate species responses to road edges in laurel and pine forests in Tenerife, Canary Islands. We sampled invertebrates from litter and assessed the environmental variation related to road proximity. We also assessed the effect of relevant environmental predictors on a diverse array of potential indicator species. We applied canonical ordination and non-parametric regression (Lowess) to classify invertebrate species responses to roads and their associated gradients. Three types of responses to road edge proximity were defined for the most common invertebrate taxa: edge-preferring or edge specialists, interior-preferring or edge-avoiders, and edge-indifferent or neutral species. Those species appearing most frequently and with higher population density between 1 and 20 m from the edge (commonly peaking at 10 m from the road) were categorized as edge-preferring. We classified taxa attaining peak population densities at or beyond 60 m from the edge (and most commonly 100 m) as interior species. Edge-neutral species were those without an evident pattern of stabilization in abundance along the gradient and with peaks in abundance at varying distance intervals. These edge litter communities contain a high native and endemic diversity but also a significant density of alien fauna. The specific patterns of penetration of road edge effects on invertebrate species should be seen as having a pervasive and cumulative impact considering the exceptionally large number of roads in these forests and the high population densities of alien invertebrates. Future management plans for forest conservation on the Canary Islands should include the highly altered but valuable litter communities along road edges.     

Effects of age and intensity of urbanization on farmland bird communities

Urban sprawl is now occurring worldwide and considered as a major large-scale perturbation on ecosystems. Consequently, urban territory is replacing other habitats such as agricultural areas. As farmland biotic communities are already reported to be declining, it seems necessary to assess the urbanization impact on them. We conducted a bird survey on 92 plots of 1 × 1 km chosen after stratification on the proportion of urban area and farmland habitat (either 0%, 25%, 50%, 75%), focusing on farmland habitat. Two aspects of urbanization were studied: its intensity and its age. We found that farmland bird species richness did not vary with increasing proportion of urbanized habitat. Non-farmland bird species richness increased from 0% to 25% classes and was constant for other classes. No effect of the urbanization age on farmland bird species richness was found, whereas a positive one was found on the non-farmland birds’ species richness. Abundance of the most specialized farmland birds decreases with urbanization intensity and age. We also found that, the more urbanized and the more recently urbanized the plots, the more similar bird communities. A strong difference in farmland bird’s communities’ compositions was found between 0% and 25% of urbanization, whereas no distinction was found between 50% and 75%. Altogether, our results suggest that to maintain for farmland birds, it is better to add new urban habitat in place where it already exist, rather than to spread it in small lots throughout the landscape.