The effect of landscape fragmentation and forest continuity on forest floor species in two regions of Denmark

Abstract. Forest species composition was recorded in 82 forests in the Himmerland and Hornsherred regions in Denmark and analysed with respect to isolation (distance to other forests and areas of forest), forest continuity (older or younger than 200 yr), soil pH, tree species composition and seed dispersal groups. Continuity and isolation measures were correlated with forest species richness in Hornsherred. Myrmecochorous, autochorous, anemoballistic and endozoochorous species were markedly fewer in recent than in ancient forests. In Himmerland, patterns were much weaker and few significant correlations were found between forest species richness or different seed dispersal groups and continuity or isolation of the forests. Differences between the two regions may result from less intensive land use, a more humid climate and a smaller species pool with less species with short distance dispersal in Himmerland. Landscape fragmentation therefore appears to limit forest species’recolonization more in Hornsherred than in Himmerland.     

Understorey plant species richness and composition in metropolitan forest archipelagos: effects of forest size, adjacent land use and distance to the edge

Aim To address the relative role of adjacent land use, distance to forest edge, forest size and their interactions on understorey plant species richness and composition in perimetropolitan forests. Location The metropolitan area of Barcelona, north‐eastern Spain. Methods Twenty sampling sites were distributed in two forest size‐categories: small forest patches (8–90 ha) and large forest areas (> 18,000 ha). For each forest‐size category, five sites were placed adjacent to crops and five sites adjacent to urban areas. Vascular plant species were recorded and human frequentation was scored visually in 210 10 × 10 m plots placed at 10, 50 and 100 m from the forest edge, and additionally at 500 m in large forest areas. Plant species were grouped according to their ecology and rarity categories. A nonmetric multidimensional scaling (NMS) ordination was carried out to detect patterns of variation in species assemblage, and to explore the relationships between these patterns and the richness of the species groups and the studied factors. Factorial anovas were used to test the significance of the studied factors on the richness of species groups. Relationships between human frequentation and the studied variables were assessed through contingency tables. Results Forest‐size category was the main factor affecting synanthropic species (i.e. those thriving in man‐made or man‐disturbed habitats). Synanthropic species richness decreased with increasing distance from the forest edge and, when forests were adjacent to crops, it was higher in small forest patches than in large forest areas. Richness of rare forest species was lower in small forest patches than in large forest areas when forests were adjacent to urban areas. Richness of common forest species and of all forest species together were higher close to the forest edge than far from it when forests were adjacent to urban areas. Forests adjacent to urban areas were more likely to experience high human frequentation, particularly in those plots nearest to the forest edge. Main conclusions Forest‐size category and adjacent land use were the most important factors determining species richness and composition. The preservation of large forests adjacent to crops in peri‐urban areas is recommended, because they are less frequented by humans, are better buffered against the percolation of nonforest species and could favour the persistence of rare forest species.     

Seed arrival, ecological filters, and plant species richness: a meta-analysis

Theoretical models predict that effects of dispersal on local biodiversity are influenced by the size and composition of the species pool, as well as ecological filters that limit local species membership. We tested these predictions by conducting a meta-analysis of 28 studies encompassing 62 experiments examining effects of propagule supply (seed arrival) on plant species richness under contrasting intensities of ecological filters (owing to disturbance and resource availability). Seed arrival increased local species richness in a wide range of communities (forest, grassland, montane, savanna, wetland), resulting in a positive mean effect size across experiments. Mean effect size was 70% higher in disturbed relative to undisturbed communities, suggesting that disturbance increases recruitment opportunities for immigrating species. In contrast, effect size was not significantly influenced by nutrient or water availability. Among seed-addition experiments, effect size was positively correlated with species and functional diversity within the pool of added seeds (species evenness and seed-size diversity), primarily in disturbed communities. Our analysis provides experimental support for the general hypothesis that species pools and local environmental heterogeneity interactively structure plant communities. We highlight empirical gaps that can be addressed by future experiments and discuss implications for community assembly, species coexistence, and the maintenance of biodiversity.     

Rethinking patch size and isolation effects: the habitat amount hypothesis

I challenge (1) the assumption that habitat patches are natural units of measurement for species richness, and (2) the assumption of distinct effects of habitat patch size and isolation on species richness. I propose a simpler view of the relationship between habitat distribution and species richness, the ‘habitat amount hypothesis’, and I suggest ways of testing it. The habitat amount hypothesis posits that, for habitat patches in a matrix of non‐habitat, the patch size effect and the patch isolation effect are driven mainly by a single underlying process, the sample area effect. The hypothesis predicts that species richness in equal‐sized sample sites should increase with the total amount of habitat in the ‘local landscape’ of the sample site, where the local landscape is the area within an appropriate distance of the sample site. It also predicts that species richness in a sample site is independent of the area of the particular patch in which the sample site is located (its ‘local patch’), except insofar as the area of that patch contributes to the amount of habitat in the local landscape of the sample site. The habitat amount hypothesis replaces two predictor variables, patch size and isolation, with a single predictor variable, habitat amount, when species richness is analysed for equal‐sized sample sites rather than for unequal‐sized habitat patches. Studies to test the hypothesis should ensure that ‘habitat’ is correctly defined, and the spatial extent of the local landscape is appropriate, for the species group under consideration. If supported, the habitat amount hypothesis would mean that to predict the relationship between habitat distribution and species richness: (1) distinguishing between patch‐scale and landscape‐scale habitat effects is unnecessary; (2) distinguishing between patch size effects and patch isolation effects is unnecessary; (3) considering habitat configuration independent of habitat amount is unnecessary; and (4) delineating discrete habitat patches is unnecessary.     

Cross-Scale Responses of Biodiversity to Hurricane and Anthropogenic Disturbance in a Tropical Forest

Abstract In studies of biodiversity, considerations of scale—the spatial or temporal domain to which data provide inference—are important because of the non-arithmetic manner in which species richness increases with area (and total abundance) and because fine-scale mechanisms (for example, recruitment, growth, and mortality of species) can interact with broad scale patterns (for example, habitat patch configuration) to influence dynamics in space and time. The key to understanding these dynamics is to consider patterns of environmental heterogeneity, including patterns produced by natural and anthropogenic disturbance. We studied how spatial variation in three aspects of biodiversity of terrestrial gastropods (species richness, species diversity, and nestedness) on the 16-ha Luquillo Forest Dynamics Plot (LFDP) in a tropical forest of Puerto Rico was affected by disturbance caused by Hurricanes Hugo and Georges, as well as by patterns of historic land use. Hurricane-induced changes in spatial organization of species richness differed from those for species diversity. The gamma components of species richness changed after the hurricanes and were significantly different between Hurricanes Hugo and Georges. Alpha and two beta components of species richness, one related to turnover among sites within areas of similar land use and one related to variation among areas of different land use, varied randomly over time after both hurricanes. In contrast, gamma components of species diversity decreased in indistinguishable manners after both hurricanes, whereas the rates of change in the alpha component of species diversity differed between hurricanes. Beta components of diversity related to turnover among sites declined after both hurricanes in a consistent fashion. Those related to turnover among areas with different historic land uses varied stochastically. The immediate effect of hurricanes was to reduce nestedness of gastropod assemblages. Thereafter, nestedness increased during post-hurricane secondary succession, and did so in the same way, regardless of patterns of historic land use. The rates of change in degree of nestedness during secondary succession were different after each hurricane as a result of differences in the severity and extent of the hurricane-induced damage. Our analyses quantified temporal changes in the spatial organization of biodiversity of gastropod assemblages during forest recovery from hurricane-induced damage in areas that had experienced different patterns of historic human land use, and documented the dependence of biodiversity on spatial scale. We hypothesize that cross-scale interactions, likely those between the local demographics of species at the fine scale and the landscape configuration of patches at the broad scale, play a dominant role in affecting critical transfer processes, such as dispersal, and its interrelationship with aspects of biodiversity. Cross-scale interactions have significant implications for the conservation of biodiversity, as the greatest threats to biodiversity arise from habitat modification and fragmentation associated with disturbance arising from human activities.     

The effects of city–suburb–exurb landscape context and distance to the edge on plant diversity of forests in Wuhan,China

Abstract

We analysed the relative role of landscape context (city, suburb and exurb) and distance to the edge (from forest edge to 45 m in interior) on plant diversity of natural forests in Wuhan city. The results indicated that landscape context had significant effects on plant diversity, and both landscape context and distance to the edge affect vegetation and disturbance characteristics. Landscape context was the main factor affecting richness of woods, herbs, indigenous species, forest generalists and insect or wind pollination species. These species tended to be higher in exurban forests while non-indigenous species were higher in the urban forests. The number of non-indigenous species, forest specialists, herbs and insect pollination species also depended on distance to the edge or on both interactions. Richness of non-indigenous species decreased with increasing distance to the edge in urban forest. Vegetation characteristics that shrub cover was lower and disturbance characteristics that disturbed cover and human activity were higher in the urban edge than in the suburb and exurb edge, which decreased from the edge to the interior. Therefore, we should prioritize the preservation of less disturbed and frequented forests (suburban and exurban) to buffer the invasion of non-indigenous species, and to reserve more indigenous species.     

Landscape structure effects on forest plant diversity at local scale: Exploring the role of spatial extent

Since landscape attributes show different patterns at different spatial extents, it is fundamental to identify how the relation between landscape structure and plant species diversity at local scale varies with scale. Then, it is fundamental to assess the appropriate extent at which landscape factors affect plant species richness at the local scale. To investigate this relation, data on plant species richness of forest communities at plot scale were extracted from a large data set and landscape metrics were calculated around the same plots for a range of extents (250–3000 m). Then, multiple regression models and variance partitioning techniques were applied to assess the amount of variance explained by the landscape metrics on plant species richness for a range of extents. In general, we found that increasing extent of the surrounding landscape analyzed, improved the strength of relationship between the landscape metrics and the properties of plant communities at plot scale. The medium-large extent was most informative as it combined a decent total variance explained with high variance explained by the pure fractions of complexity, fragmentation and disturbance and the minimum of collinearity. In conclusion, we found that it is possible and beneficial to identify a specific extent, where the redundancy in the predictor variables is minimized and the explanatory power of the pure fractions (or single groups) maximized, when examining landscape structure effects on local plant species richness.     

Ant communities on small tropical islands: effects of island size and isolation are obscured by habitat disturbance and ‘tramp’ ant species

Aim Comparisons among islands offer an opportunity to study the effects of biotic and abiotic factors on small, replicated biological communities. Smaller population sizes on islands accelerate some ecological processes, which may decrease the time needed for perturbations to affect community composition. We surveyed ants on 18 small tropical islands to determine the effects of island size, isolation from the mainland, and habitat disturbance on ant community composition. Location Thousand Islands Archipelago (Indonesian name: Kepulauan Seribu) off Jakarta, West Java, Indonesia. Methods Ants were sampled from the soil surface, leaf litter and vegetation in all habitat types on each island. Island size, isolation from the mainland, and land‐use patterns were quantified using GIS software. The presence of settlements and of boat docks were used as indicators of anthropogenic disturbance. The richness of ant communities and non‐tramp ant species on each island were analysed in relation to the islands’ physical characteristics and indicators of human disturbance. Results Forty‐eight ant species from 5 subfamilies and 28 genera were recorded from the archipelago, and approximately 20% of the ant species were well‐known human‐commensal ‘tramp’ species. Islands with boat docks or human settlements had significantly more tramp species than did islands lacking these indicators of anthropogenic disturbance, and the diversity of non‐tramp species decreased with habitat disturbance. Main conclusions Human disturbance on islands in the Thousand Islands Archipelago promotes the introduction and/or establishment of tramp species. Tramp species affect the composition of insular ant communities, and expected biogeographical patterns of ant richness are masked. The island with the greatest estimated species richness and the greatest number of unique ant species, Rambut Island, is a forested bird sanctuary, highlighting the importance of protected areas in preserving the diversity of species‐rich invertebrate faunas.     

How does forest landscape structure explain tree species richness in a Mediterranean context?

Although the strong relationship between vegetation and climatic factors is widely accepted, other landscape composition and configuration characteristics could be significantly related with vegetation diversity patterns at different scales. Variation partitioning was conducted in order to analyse to what degree forest landscape structure, compared to other spatial and environmental factors, explained forest tree species richness in 278 UTM 10 × 10 km cells in the Mediterranean region of Catalonia (NE Spain). Tree species richness variation was decomposed through linear regression into three groups of explanatory variables: forest landscape (composition and configuration), environmental (topography and climate) and spatial variables. Additionally, the forest landscape characteristics which significantly contributed to explain richness variation were identified through a multiple regression model. About 60% of tree species richness variation was explained by the whole set of variables, while their joint effects explained nearly 28%. Forest landscape variables were those with a greater pure explanatory power for tree species richness (about 15% of total variation), much larger than the pure effect of environmental or spatial variables (about 2% each). Forest canopy cover, forest area and land cover diversity were the most significant composition variables in the regression model. Landscape configuration metrics had a minor effect on forest tree species richness, with the exception of some shape complexity indices, as indicators of land use intensity and edge effects. Our results highlight the importance of considering the forest landscape structure in order to understand the distribution of vegetation diversity in strongly human-modified regions like the Mediterranean.     

Landscape structure and land use history influence changes in island plant composition after 100 years

Aim We investigated how current and historical land use and landscape structure affect species richness and the processes of extinction, immigration and species turnover. Location The northern part of the Stockholm archipelago, Baltic Sea, Sweden. We resurveyed 27 islands ranging from 0.3 to 33 ha in area. Methods We compared current plant survey data, cadastral maps and aerial photographs with records obtained from a survey in 1908, using databases and a digital elevation model to examine changes in plant community dynamics in space and time. We examined the effects of local and landscape structure and land use changes on plant species dynamics by using stepwise regression in relation to eight local and three landscape variables. The eight local variables were area, relative age, shape, soil heterogeneity, bedrock ratio, number of houses, forest cover change, and grazing 100 years ago. The three landscape variables were distance to mainland, distance to closest island with a farm 100 years ago, and structural connectivity. Hanski’s connectivity measure was modified to incorporate both connectivity and fragmentation. Results The investigated islands have undergone drastic changes, with increasing forest cover, habitation, and abandonment of grassland management. Although the total species richness increased by 31% and mean island area by 23%, we found no significant increase in species richness per unit area. Local variables explain past species richness (100 years ago), whereas both local and landscape variables explain current species richness, extinctions, immigrations and species turnover. Grazing that occurred 100 years ago still influences species richness, even though grazing management was abandoned several decades ago. The evidence clearly shows an increase in nitrophilous plant species, particularly among immigrant species. Main conclusions This study highlights the importance of including land use history when interpreting current patterns of species richness. Furthermore, local environment and landscape patterns affect important ecological processes such as immigration, extinction and species turnover, and hence should be included when assessing the impact of habitat fragmentation and land use change. We suggest that our modified structural connectivity measure can be applied to other types of landscapes to investigate the effects of fragmentation and habitat loss.     

The effects of urban or rural landscape context and distance from the edge on native woodland plant communities

The increasing rate of urban sprawl continues to fragment European landscapes threatening the persistence of native woodland plant communities. The dynamics of woodland edges depend on the characteristics of woodland patches and also on landscape context. Our aim was to assess the extent of edge influences on the understorey vegetation of small native woodlands in rural and urban landscapes. The study was carried out in two cities of north-western France. Ten comparable woodlands, each of about 1.5 ha, were surveyed; five were situated adjacent to crops and five adjacent to built-up land. Vascular plant species were recorded in 420 3 × 3 m plots placed at seven different distances from the edge (from 0 to about 45 m from the edge). Soil pH, light levels, level of disturbance and tree and shrub cover were also recorded. Plant species were first classified as non-indigenous or indigenous and then three groups of indigenous species were distinguished according to their affinity for forest habitat (forest specialists, forest generalists and non-forest species). We inferred certain ecological characteristics of understorey vegetation by using Ellenberg values. An inter-class correspondence analysis was carried out to detect patterns of variation in plant community composition. Linear mixed models were used to test the effects of adjacent land use, distance from the edge and their interactions on the species richness of the different groups and on the ecological characteristics of vegetation. Total species richness, richness of forest generalists and of non-forest species decreased from edge to interior in both urban and rural woodlands. The number of non-indigenous species depended mainly on urban–rural landscape context. Urban woodland edges were not as rich in forest specialists as rural edges. More surprisingly, the number of forest specialists was higher in rural edges than in rural interiors. Community composition was mainly affected by urban–rural context and to a lesser degree by the edge effect: the community composition of urban edges resembled that of urban interiors whereas in rural woodlands vegetation near edges (up to 10 m) strongly differed from interiors with a pool of species specific to edges. Urban woodland vegetation was more nitrophilous than rural vegetation in both edges and interiors. A major difference between urban and rural vegetation was the distribution of basiphilous species according to distance from the edge. Generally edge vegetation was more basiphilous than interior vegetation however the presence of basiphilous species fell off quickly with distance from the edge in rural woodlands (in the first 10–15 m) and more slowly (from 25 m onwards) in urban woodlands. This pattern was linked to variation in measured soil pH. As regards the conservation of flora in small native woodlands, it appeared that invasion of exotic and non-forest species was currently limited in both urban and rural landscape contexts but might pose problems in the future, especially in urban woodlands. Forest species were not negatively affected by the edge effect and indeed edges seemed to provide important habitats for this group. Hence conservationists should pay particular attention to the protection of edges in urban woodlands.     

Ancient Maya Agroforestry Echoing Through Spatial Relationships in the Extant Forest of NW Belize

Previous research has shown that ancient Maya ‘forest gardens’—tree‐dominated home gardens containing a diversity of tree species used for daily household needs—still resonate in the species composition of the modern forest. Centuries of positive interspecies interactions may enhance the reproductive and survival success of garden species selected and encouraged by experienced Maya forest gardeners. We hypothesized that such interaction may result in aggregated spatial patterns between 32 pre‐selected, commonly utilized forest garden species. In this paper, we developed a novel randomization (Monte Carlo) method designed to measure and test if the spatial relationships among pairs of Maya ‘forest garden’ trees species differ between areas that experienced high and low ancient settlement density in northwestern Belize. A total of 28 high ancient settlement density and 27 low ancient settlement density plots containing a total of 2772 and 3134 trees, respectively, were used for this study. The analysis revealed that 58 pairs of forest garden species tended to ‘cluster’ together significantly more often in the high settlement density areas than would be expected in a random distribution. In low settlement density plots, only 12 pairs of species exhibited a significant clustered spatial relationship. The effect was not species specific, suggesting that some synergistic relationships, mediated by third‐party agents such as dispersers, may occur at the community level. The impacts of ancient human land use, echoing across centuries of dispersal, colonization, disturbance, and biotic and abiotic interactions, can have important implications for understanding the current biodiversity patterns and processes.     

Large‐scale distribution patterns of mangrove nematodes: A global meta‐analysis

Mangroves harbor diverse invertebrate communities, suggesting that macroecological distribution patterns of habitat‐forming foundation species drive the associated faunal distribution. Whether these are driven by mangrove biogeography is still ambiguous. For small‐bodied taxa, local factors and landscape metrics might be as important as macroecology. We performed a meta‐analysis to address the following questions: (1) can richness of mangrove trees explain macroecological patterns of nematode richness? and (2) do local landscape attributes have equal or higher importance than biogeography in structuring nematode richness? Mangrove areas of Caribbean‐Southwest Atlantic, Western Indian, Central Indo‐Pacific, and Southwest Pacific biogeographic regions. We used random‐effects meta‐analyses based on natural logarithm of the response ratio (lnRR) to assess the importance of macroecology (i.e., biogeographic regions, latitude, longitude), local factors (i.e., aboveground mangrove biomass and tree richness), and landscape metrics (forest area and shape) in structuring nematode richness from 34 mangroves sites around the world. Latitude, mangrove forest area, and forest shape index explained 19% of the heterogeneity across studies. Richness was higher at low latitudes, closer to the equator. At local scales, richness increased slightly with landscape complexity and decreased with forest shape index. Our results contrast with biogeographic diversity patterns of mangrove‐associated taxa. Global‐scale nematode diversity may have evolved independently of mangrove tree richness, and diversity of small‐bodied metazoans is probably more closely driven by latitude and associated climates, rather than local, landscape, or global biogeographic patterns.     

Camera trapping surveys of forest mammal communities in the Eastern Arc Mountains reveal generalized habitat and human disturbance responses

Large-bodied mammals are a rich and diversified faunal group in tropical rainforests. However, knowledge on community size and composition, and on species’ distribution and ecology remains often scant and inadequate against their chronic status of threats. We used camera trapping to detect mammals in the forests of the Eastern Arc Mountains (EAM) of Tanzania, a world renowned region for biodiversity comprised by a series of distinct and ancient mountain ranges partially covered in moist montane forest. We conducted surveys from 2003 to 2011 in eight of the 12 mountain blocks in Tanzania, and, through an overall sampling effort of 11,500 camera days, we detected 43 species. We normalized species richness and species’ detection events by effort, and used these metrics to assess the effect of habitat and human disturbance variables. We found that rarefied richness is positively affected by forest area at the block level, and that richness at forest patch level is also affected by forest area as well as surrounding human density (negative effect). For a subset of 17 species, we found consistent patterns of avoidance or tolerance of human disturbance and forest edges, and increased occurrence in areas at higher elevation, matching the historical forest loss that in most mountains occurred at lower elevation. Our study provides ecological insights that are novel for most species and sites, and reveals a general trend of negative impact of human disturbance on both community size and species’ relative abundance. Increased protection of the EAM forests in Tanzania is of urgent importance for the persistence of diversified mammal communities.     

Differences in mammal communities between forest fragments and restoration areas in the Atlantic Forest

The persistence of larger mammals in fragmented forest landscapes depends not only on the protection of remaining habitats but also on ecological restoration sites. It is known that the landscape context is an important predictor of species persistence, abundance and distribution. Here we evaluate how landscape characteristics influence the recovery of larger mammals in ecological restoration sites. We assess the richness and composition of mammals in forest fragments and restoration sites using landscape metrics such as forest cover and connectivity. Forest fragments and restoration sites present the same richness (n = 26), but differ in species composition. Some seed-dispersing mammals were absent in restoration areas, such as Alouatta guariba (brown howler monkey) and Coendou spinosus (paraguayan hairy dwarf porcupine). The percentage of forest cover in the landscape was responsible for 29.09% of the variation in species composition between the evaluated forest formations, exerting a positive or negative influence depending on the species requirements. The results demonstrate the importance of considering not only landscape metrics in an ecological restoration plan, but also the historical landscape context, such as the fauna composition before the disturbance and how these species respond to environmental changes, thus improving the success of future ecological restoration measurements and policies.     

Bird community composition patterns in urban parks of Madrid: The role of age, size and isolation

This study intends to assess the influence of fragment age, size and isolation (from the regional species pool) on bird community composition patterns in urban parks in Madrid, and the role of local and regional factors on community structure. Park age was a good indicator of habitat complexity. Park age and area accounted for 62% of the variability in species richness, but two measures of isolation from the regional species pool were not included as significant factors. Species composition in urban parks showed a high degree of nestedness, which was associated with park age and area, but not with two measures of isolation from the regional species pool. The degree of nestedness increased with park age; the distribution of species varying from nested in old and mature parks to random in young parks. The incidence (% of species occurrence in parks) in young parks was correlated with regional densities, whereas in mature and old parks the incidence was correlated with local densities. In this urban landscape, species composition appears to be regulated by local factors (particularly in mature and old parks), such that species accumulate in an orderly (not random) fashion in relation to park age and area. Regional influences seem to be more pronounced only in young parks, which are mainly colonized by species from the regional species pool.     

Influence of landscape context on the abundance and diversity of bees in Mediterranean olive groves

The diversity and abundance of wild bees ensures the delivery of pollination services and the maintenance of ecosystem diversity. As previous studies carried out in Central Europe and the US have shown, bee diversity and abundance is influenced by the structure and the composition of the surrounding landscape. Comparable studies have so far not been carried out in the Mediterranean region. The present study examines the influence of Mediterranean landscape context on the diversity and abundance of wild bees. To do this, we sampled bees in 13 sites in olive groves on Lesvos Island, Greece. Bees were assigned to five categories consisting of three body size groups (small, medium and large bees), the single most abundant bee species (Lasioglossum marginatum) and all species combined. The influence of the landscape context on bee abundance and species richness was assessed at five radii (250, 500, 750, 1000 and 1250 m) from the centre of each site. We found that the abundance within bee groups was influenced differently by different landscape parameters and land covers, whereas species richness was unaffected. Generally, smaller bees' abundance was impacted by landscape parameters at smaller scales and larger bees at larger scales. The land cover that influenced bee abundance positively was olive grove, while phrygana, conifer forest, broad-leaved forest, cultivated land, rock, urban areas and sea had mostly negative or no impact. We stress the need for a holistic approach, including all land covers, when assessing the effects of landscape context on bee diversity and abundance in the Mediterranean.     

Ecological processes in urban landscapes: mechanisms influencing the distribution and activity of insectivorous bats

Urbanisation affects indigenous fauna in many ways; some species persist and even increase in urban areas, whereas others are lost. The causative mechanisms determining changes in distributions and community structure remain elusive. We investigated three hypothesized mechanisms, which influence success or failure of the insectivorous bat assemblage across the urban landscape of Sydney, Australia; landscape heterogeneity (diversity of land uses), productivity (as indexed by landscape geology) and trait diversity. We present data on species richness and activity (bat passes per night) collected systematically using ultrasonic bat detectors from randomly selected landscapes (each 25 km²). Landscapes were categorized into classes including ‘urban’, ‘suburban’ and ‘vegetated’, where suburban sites were additionally stratified based on geology, as a proxy for productivity. Four landscape elements were sampled within each landscape, including remnant bushland (>2 ha), riparian areas, open space/parkland and residential/built space. We found that there was significantly greater bat activity and more species of bat in areas on fertile shale geologies (p<0.05), supporting the productivity, rather than the heterogeneity hypothesis. Within landscapes, there was no significant effect of the landscape element sampled, although bushland and riparian sites recorded greater bat activity than open space or backyard sites. Using general linear mixed models we found bat activity and species richness were sensitive to landscape geology and increasing housing density at a landscape scale. Using an RLQ analysis a significant relationship was found between these variables and species traits in structuring the community present (p<0.01). Specifically, open‐adapted bats were associated with areas of greater housing density, while clutter‐adapted bats were uncommon in urban areas and more associated with greater amounts of bushland in the landscape. Overall we found greater support for the productivity and traits hypotheses, rather than the heterogeneity hypothesis. The degree of urbanisation and amount of bushland remaining, in combination with landscape geology, influenced bat activity and mediated the trait response. Our findings reflect global trends of species diversity and abundance in urban landscapes, suggesting that processes affecting bat species distribution in urban ecosystems may be predictable at a landscape scale.     

Land‐use history and fragmentation of traditionally managed grasslands in Scandinavia

Abstract. Plants associated with traditional agricultural landscapes in northern Europe and Scandinavia are subjected to drastic habitat fragmentation. In this paper we discuss species response to fragmentation, against a background of vegetation and land‐use history. Recent evidence suggests that grassland‐forest mosaics have been prevalent long before the onset of human agriculture. We suggest that the creation of infield meadows and outland grazing (during the Iron Age) increased the amount and spatial predictability of grasslands, resulting in plant communities with exceptionally high species densities. Thus, distribution of plant species in the present‐day landscape reflects historical land‐use. This holds also when traditional management has ceased, due to a slow response by many species to abandonment and fragmentation. The distribution patterns are thus not in equilibrium with the present habitat distribution. Fragmentation influences remaining semi‐natural grasslands such that species density is likely to decline as a result of local extinctions and invasion by habitat generalists. However, species that for a long time have been subjected to changing mosaic landscapes may be more resistant to fragmentation than is usually believed. Conservation should focus not only on ‘hot‐spots’ with high species richness, but also consider species dynamics in a landscape context.     

BIODIVERSITY RESEARCH: Native and introduced fish species richness in Mediterranean streams: the role of multiple landscape influences

Aim To examine the role of multiple landscape factors on the species richness patterns of native and introduced freshwater fish. Location Mediterranean streams, south‐western Iberian Peninsula, Europe (c. 87,000 km²). Methods We used a dataset of fish occurrences from 436 stream sites. We quantified the incremental explanatory power of multiple landscape factors in native, introduced, and overall local species richness using regression analysis. First, we related variation in local species richness across river basins to regional species richness (here, the basin species pool), area and factors of climate and topography. Second, we related within‐river basin local species richness to site’s climate and topography, and spatial structure derived from Principal Coordinates of Neighbour Matrices approach, after testing for species richness spatial autocorrelation; predicted local richness was mapped. Results Patterns of local species richness across river basins were strongly associated with regional species richness for overall, native and introduced species; annual rainfall showed a significant incremental contribution to variation in introduced species richness only. Within river basins, environmental factors were associated with local richness for the three species groups, though their contributions to the total explained variation were inferior to those of spatial factors; rainfall seasonality and stream slope were the most consistent environmental correlates for all species groups, while the influence of spatial factors was most prevalent for native species. Main conclusions Landscape factors operating among and within river basins seem to play a relevant role in shaping local species richness of both native and introduced species, and may be contingent on basin‐specific contexts. Nevertheless, local factors, such as habitat characteristics and biotic interactions and human‐induced disturbances may also be at play. Multiscale approaches incorporating a multitude of factors are strongly encouraged to facilitate a deeper understanding of the biodiversity patterns of Mediterranean streams, and to promote more effective conservation and management strategies.