Effects Of Patch Size Research Articles

Patch size effects on avian foraging behaviour: implications for tropical forest restoration design

Summary 1. Active restoration to rehabilitate degraded tropical lands often involves planting tree seedlings, an effective but expensive approach if large areas are planted. Planting small patches of vegetation (tens to a few hundred square metres) has recently been suggested as a more economical restoration technique that mimics natural regeneration processes. However, few studies have examined the consequences of restoration patch size on animals, whose presence and activities are often key to successful ecosystem recovery. 2. We examined the effects of patch size on the foraging behaviour of four resident tropical bird species in a replicated forest restoration experiment in southern Costa Rica. We also measured arthropod abundance and anti‐predator vigilance behaviour to assess whether variation in food availability or predation risk could explain patch size effects on foraging behaviour. 3. Prey attack rates were highest, and the effort required to find prey was lowest, in larger patches for three of the four bird species. Arthropod density was approximately twice as great in larger patches (>3500 m2) compared with smaller patches (<350 m2). Evidence for patch size differences in predation risk was more limited but risk may be higher in smaller patches. The results indicate that food availability is the primary mechanism driving patch size effects on foraging behaviour, with predation risk being an additional influence for some species in some years. 4. Synthesis and applications. As demonstrated in this study, patches of tens to a few hundreds of metres squared are likely to provide fewer food resources and potentially less cover from predators for vertebrates that use woody habitat, compared with patches of a few thousand square metres. The more limited resources in smaller patches are likely to have short‐term and, potentially, long‐term consequences for the fitness of organisms. When considering restoration project design, the potential economic and other benefits of planting in smaller patches must be weighed with the potentially negative ecological effects on some taxonomic groups. To increase the probability that patches provide adequate habitat for the largest number of species, we recommend that when financial resources are available, patches of at least a few thousand square metres be planted.

The effects of forest patch size and ownership structure on tree stand characteristics in a highly deforested landscape of central Poland

Forest structure is influenced by the origin, history and manner of forest management. All these aspects may affect the occurrence of many forest dwelling organisms. We investigated the simultaneous impact of forest patch size and ownership structure on selected forest characteristics in central Poland. We sampled stand composition, the DBH of particular tree species, basal area, species number and species diversity in all 32 forest patches found in a farmland-dominated area of 150 km2. Forest ownership status was linked to patch size: large patches were state-owned and small ones were private. Ownership status also affected the average DBH and basal area of all tree species pooled, with lower DBH and basal area found in private forests. The share of deciduous trees was negatively affected by forest size, while pine was positively affected, which could suggest that forest management and economic interests may be related to this factor. The share of non-native species was higher in state forests. Our results showed that forest patch size could be associated with its ownership status, which is commonly ignored in research on the relationship between forest size and species occurrence. Historical as well as sociological aspects related to private forests in Poland are also presented.

Effects of patch size and density on flower visitation and seed set of wild plants: a pan‐European approach

Summary 1. Habitat fragmentation can affect pollinator and plant population structure in terms of species composition, abundance, area covered and density of flowering plants. This, in turn, may affect pollinator visitation frequency, pollen deposition, seed set and plant fitness. 2. A reduction in the quantity of flower visits can be coupled with a reduction in the quality of pollination service and hence the plants’ overall reproductive success and long‐term survival. Understanding the relationship between plant population size and/or isolation and pollination limitation is of fundamental importance for plant conservation. 3. We examined flower visitation and seed set of 10 different plant species from five European countries to investigate the general effects of plant populations size and density, both within (patch level) and between populations (population level), on seed set and pollination limitation. 4. We found evidence that the effects of area and density of flowering plant assemblages were generally more pronounced at the patch level than at the population level. We also found that patch and population level together influenced flower visitation and seed set, and the latter increased with increasing patch area and density, but this effect was only apparent in small populations. 5. Synthesis. By using an extensive pan‐European data set on flower visitation and seed set we have identified a general pattern in the interplay between the attractiveness of flowering plant patches for pollinators and density dependence of flower visitation, and also a strong plant species‐specific response to habitat fragmentation effects. This can guide efforts to conserve plant–pollinator interactions, ecosystem functioning and plant fitness in fragmented habitats.

Phragmites australis (Common Reed) Invasion in the Rhode River Subestuary of the Chesapeake Bay: Disentangling the Effects of Foliar Nutrients, Genetic Diversity, Patch Size, and Seed Viability

The invasion and expansion of the introduced haplotype of Phragmites australis across North America is of growing concern. Previous studies in the Chesapeake Bay region found that Phragmites was more abundant, had higher foliar nitrogen, and produced more viable seeds in brackish wetland subestuaries with more anthropogenic development of the watershed. Here, we focus on a different scale and address issues related to the invasion of Phragmites within a single subestuary, the Rhode River. We evaluated patterns in seed viability, foliar nutrient concentrations, patch size, and genetic variation in ten Phragmites patches in wetlands that occur in the side of the subestuary that is surrounded by forest and 10 patches in wetlands that are in the side of the subestuary that has extensive anthropogenic development. Seed viability varied from 0–60% among the 20 patches but did not differ significantly between patches on the developed vs. forested sides of the Rhode River. Foliar nutrients also did not differ between patches on the two sides of the Rhode River. Seed viability, however, was negatively related to foliar nutrients. Most Phragmites patches consisted of >1 genotype. Larger patches had multiple genotypes, and patches with more genotypes produced more viable seeds. Our study indicates that the Rhode River subestuary behaves as one system with no differences in the measured Phragmites variables between the forested vs. developed sides of the watershed. Our findings also suggest a cyclical process by which Phragmites can spread: larger patches contain more genetic diversity, which increases the chances for cross-fertilization. The subsequent increased production of viable seeds can increase local levels of genetic diversity, which can further facilitate the spread of Phragmites by seed.

The importance of past and present landscape for Japanese hares Lepus brachyurus along a rural-urban gradient

This study evaluated the effects of landscape on the distribution of Japanese hares Lepus brachyurus Temminck, 1845 hares along a rural-urban gradient. We surveyed the presence of hares in 62 forest patches in the Tama Hills, which spreads from forested mountains to the urban core, and found signs of hares in 23 patches. We evaluated the effects of habitat patch size, connectivity, and land cover of the surrounding area (forest, residential and few agricultural area) by logistic regression. To select the most appropriate spatial scale and time period, we conducted a variable selection for all combinations of buffer size (250-, 500-, 1000- and 2000-m radius), and year (1974, 1984 and 1994). We calculated Akaike weight for the best model to measure the importance of each variable. The model for the best combination of buffer size and year was 500 m in 1994. We conclude that recent landscape determines the occurrence of hares. Forest patch size and percentage of forest cover were important variables in the best model. To protect the wild hare population in suburban areas, it is important to conserve areas of forest that have at least 500 m radius. These areas must be continuously maintained, as hares respond rapidly to changes in landscape.

Does the type of matrix matter? A quantitative review of the evidence

It has been increasingly recognized that the type of matrix surrounding habitat patches can affect biodiversity in landscapes, but there were only qualitative reviews of the subject focused on particular taxonomic groups. We present a quantitative review of studies from 1985 to 2008 that compared effects of different matrix types on individuals, populations and communities. We compiled 104 studies, most on animals, covering a broad range of landscape types and spatial scales. Most studies were empirical, focused on individuals and communities, and evaluated abundance/richness in the patch as the dependent variable. The type of matrix surrounding habitat patches influenced the studied parameters in 95% of the studies, but such effects were overall smaller compared to patch size or isolation effects. Matrix type effects were strongly species-specific, with different species responding differently to matrix type in 96% of studies comparing species or group of species. In 88% of studies, matrix types more similar in structure to the patch had higher quality for the studied organisms from the point of view of functional connectivity. Overall, the type of matrix is important, but patch size and isolation are the main determinants of ecological parameters in landscapes. Matrix quality generally increases with increasing structural similarity with habitat patches, a pattern that could be used as a general guideline for management of the matrix in fragmented landscapes.

Relative contribution of edge and interior zones to patch size effect on species richness: An example for woody plants

In order to understand the capacity of habitats to conserve species, many authors have searched for a species–area relationship (SAR) to evaluate the effect of patch size on species richness in habitat fragments. However, a range of different processes may underlie or obscure this relationship. For woody plant species in forest fragments, as for other taxa, considering forest edges separately in the investigation of SAR is particularly relevant. The objective of our study was to evaluate edge influence on SAR in a fragmented forest landscape in south-western France. To achieve this objective, we considered SAR in two separate spatial portions of the forest fragment: the edge and the forest interior. We also considered SAR for different ecological groups of species based on their shade tolerance and their mode of dispersal, as species can respond differently to habitat reduction depending on their ecological characteristics. In 40 woodlands in an agricultural landscape, we observed the presence/absence of all woody species along parallel walking transects 20-m wide to inventory the total number of species in each woodlot. Vegetation surveys resulted in the identification of 53 woody species, with a total of 23 trees and 30 shrubs, and a number of species per woodlot ranging from 18 to 44. The species richness found in a given woodlot was significantly correlated with its area. When considering the edge and the interior parts of the woodlot separately we found a steeper increase in species richness with area for the part we considered as the edge, compared with the increase found in the interior part of the forest. Our results confirm the contribution of forest edge to forest fragment SAR. Results also underlined the importance of two additional processes that may contribute to SAR: a possible extinction debt of shade-tolerant species in forest edge zones and colonisation by light-demanding species in forest interior zones probably due to disturbances. This approach underlines the importance of taking the edge effect into account when studying the influence of patch size on species richness and the dynamic of species richness pattern.

Predicting Forest Microclimate in Heterogeneous Landscapes

Forest microclimate plays an integral role in ecosystem processes, yet a predictive understanding of its spatial and temporal variability in heterogeneous landscapes is largely lacking. In this study, we used regression kriging (RK) to analyze the degree to which physiographic versus ecological variables influence spatio-temporal variation in understory microclimate conditions. We monitored understory temperature in 200 forest plots within a 274 km2 environmentally heterogeneous region in northern California (0.55 obs/km2). For each plot location, we measured four physiographic influences (elevation, coastal proximity, potential solar radiation, topographic wetness index) and three ecological drivers (forest patch size, proximity to forest edge, tree abundance). Temperature observations were aggregated to three time scales (hourly, daily, and monthly) to examine temporal variability in microclimate dynamics and its effect on spatial prediction. The obtained prediction models included both physiographic and vegetative effects, although the relative importance of individual effects varied greatly between the different models. Across time scales, elevation and coastal proximity had the most consistent physiographic effects on temperature, followed by the vegetative effects of forest patch size and distance to forest edge. RK captured significantly more landscape-scale variability in understory temperature than a regression-only approach with considerably better model performance at hourly and daily time scales than at a monthly scale. Using varied sampling density scenarios our results also suggest that predictive accuracy drops considerably at densities less than 0.34 obs/km2. This research illustrates how geospatial and statistical modeling can be used to distinguish physiographic versus ecological effects on microclimate dynamics and elucidates the spatial and temporal scales that these processes operate.

Patch size effects on plant species decline in an experimentally fragmented landscape

Understanding local and global extinction is a fundamental objective of both basic and applied ecology. Island biogeography theory (IBT) and succession theory provide frameworks for understanding extinction in changing landscapes. We explore the relative contribution of fragment size vs. succession on species' declines by examining distributions of abundances for 18 plant species declining over time in an experimentally fragmented landscape in northeast Kansas, U.S.A. If patch size effects dominate, early-successional species should persist longer on large patches, but if successional processes dominate, the reverse should hold, because in our system woody plant colonization is accelerated on large patches. To compare the patterns in abundance among patch sizes, we characterize joint shifts in local abundance and occupancy with a new metric: rank occupancy-abundance profiles (ROAPs). As succession progressed, statistically significant patch size effects emerged for 11 of 18 species. More early-successional species persisted longer on large patches, despite the fact that woody encroachment (succession) progressed faster in these patches. Clonal perennial species persisted longer on large patches compared to small patches. All species that persisted longer on small patches were annuals that recruit from the seed bank each year. The degree to which species declined in occupancy vs. abundance varied dramatically among species: some species declined first in occupancy, others remained widespread or even expanded their distribution, even as they declined in local abundance. Consequently, species exhibited various types of rarity as succession progressed. Understanding the effect of fragmentation on extinction trajectories requires a species-by-species approach encompassing both occupancy and local abundance. We propose that ROAPs provide a useful tool for comparing the distribution of local abundances among landscape types, years, and species.

Remote sensing of small and linear features: Quantifying the effects of patch size and length, grid position and detectability on land cover mapping

The accurate mapping of small, often fragmented and linear vegetation patches is of key importance for natural resource management because of their ecological significance. However, due to their small size and the quantised nature of remote sensing imagery they may be under-represented in the landscape when mapped using earth observation. This paper investigates the effect of patch area and patch elongation on the accurate mapping of these vegetation patches. Using synthetic images to simulate sub-pixel patch location, we investigated classification accuracy and extraction probability resulting from differences in the geometric properties of the raster grid and the feature alone. We simulated the effect of grid position, detectability, feature size and shape on classification. This represents the highest achievable accuracy using the remote sensing raster grid, where other factors influencing classification such as classification algorithm, radiometric calibration and sensor characteristics are excluded. We found that mapping error was highest when the scale of the feature and the raster grid coincided. We showed that the spatial resolution of the grid should be many times finer in order to extract these features accurately. For square patches with a mean classification accuracy of 75%, the grid pixel area was 11 times smaller than patch size. When patches were small and/or elongated, the probability of extraction was reduced, mapping accuracies decreased and variability in accuracy due to the effects of grid position increased. For example, a square shaped patch needed an area of at least 11 pixels to achieve a mean accuracy of 75%, whilst a linear patch with a width to length ratio of 4 needed an area of 12.3 pixels. This paper quantifies the limitations of remote sensing for the accurate detection of small and linear features and provides guidelines on the appropriate spatial resolution required to map these features. Using our results, map users can estimate the probability of a map classifying small and linear features independently of the error matrix. Furthermore, we provide a more precise estimate of the size of the smallest discernable feature taking into account the random position of the remote sensing grid with respect to the feature as well as its shape. An understanding of this phenomenon is critical for making good land management decisions based on a thorough understanding of the limitations of remote sensing data.

Effects of Patch Size and Type of Coffee Matrix on Ithomiine Butterfly Diversity and Dispersal in Cloud‐Forest Fragments

Determining the permeability of different types of landscape matrices to animal movement is essential for conserving populations in fragmented landscapes. We evaluated the effects of habitat patch size and matrix type on diversity, isolation, and dispersal of ithomiine butterflies in forest fragments surrounded by coffee agroecosystems in the Colombian Andes. Because ithomiines prefer a shaded understory, we expected the highest diversity and abundance in large fragments surrounded by shade coffee and the lowest in small fragments surrounded by sun coffee. We also thought shade coffee would favor butterfly dispersal and immigration into forest patches. We marked 9675 butterflies of 39 species in 12 forest patches over a year. Microclimate conditions were more similar to the forest interior in the shade-coffee matrix than in the sun-coffee matrix, but patch size and matrix type did not affect species richness and abundance in forest fragments. Furthermore, age structure and temporal recruitment patterns of the butterfly community were similar in all fragments, independent of patch size or matrix type. There were no differences in the numbers of butterflies flying in the matrices at two distances from the forest patch, but their behavior differed. Flight in the sun-coffee matrix was rapid and directional, whereas butterflies in shade-coffee matrix flew slowly. Seven out of 130 recaptured butterflies immigrated into patches in the shade-coffee matrix, and one immigrated into a patch surrounded by sun coffee. Although the shade-coffee matrix facilitated movement in the landscape, sun-coffee matrix was not impermeable to butterflies. Ithomiines exhibited behavioral plasticity in habitat use and high mobility. These traits favor their persistence in heterogeneous landscapes, opening opportunities for their conservation. Understanding the dynamics and resource requirements of different organisms in rural landscapes is critical for identifying management options that address both animals' and farmers' needs.

Abundance of an Herbivorous Beetle: Factors Affecting Dispersal and Local Reproduction

A current challenge for ecologists is identifying the relative effect of factors affecting abundance in spatially segregated populations. I investigated the effects of variables affecting dispersal (current patch size, interpatch distance and patch quality) and reproduction (previous female abundance, previous patch size and their interaction) on the local abundance of an herbivorous beetle, Tetraopes tetrophthalmus. Mark-release-recapture methods were used to monitor beetle populations in a 40 ha landscape containing numerous patches of the beetles' host plant, Asclepias syriaca. Factors affecting dispersal and reproduction were compared using statistical models, and the relative effects of each factor were evaluated by examining the joint and unique deviance explained. Over 3 y, 3952 individuals were captured 10,715 times. The models explained over 80% of the deviance in beetle abundance with significant contributions from factors affecting both dispersal and reproduction. Current patch size and number of females in a patch the previous generation had the largest effects on abundance. Immigration exceeds emigration in larger patches resulting in higher abundance in larger patches, but a large effect of current patch size was also due to confounding with factors affecting reproduction. Abundance also increased with habitat quality and connectivity through their effects on dispersal. The abundance of females in the previous generation affected current abundance directly and via interactions with resources. In a low density year (1995) there was a positive interaction between female abundance and patch size (resources) such that large patches with an abundance of females had high abundances the next generation (1996). In a higher density year (1996) abundance the next generation increased with female abundance, but showed either a negative interaction with patch size (male beetle abundance) or a negative effect of patch size in 1996 (female). For patchy populations a combination of landscape and population factors are needed to understand local abundance.

Short-term consequences of spatial heterogeneity in soil nitrogen concentrations caused by urine patches of different sizes

The scale of spatial heterogeneity in soil nitrogen (N) concentrations varies considerably in grazed systems, because grazers vary in the volume of urine they excrete. This could affect how urine-N is processed, and subsequently how much N is lost from the system, as diffusion and plant effects on soil nutrient concentrations can be scale-dependent. Two field experiments were performed; one measured the impact of urine patch size (small, medium or large) on soil inorganic N pools and fluxes over time, and the other assessed whether urine patch size affected plant responses and system N retention even if the same total amount of urine was applied. Soil from inside small urine patches retained inorganic N for shorter amounts of time, resulting in lower plant biomass and N uptake than that inside larger patches. Although system nitrogen retention was not affected by patch size, it appeared that larger patches had a greater potential to lose N due to the longer period over which soil inorganic N concentrations remained high. This suggests that systems grazed by larger organisms are more prone to lose N through patch size effects than those grazed by smaller ones.

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.

Modelling carbon storage in highly fragmented and human-dominated landscapes: Linking land-cover patterns and ecosystem models

To extend coupled human–environment systems research and include the ecological effects of land-use and land-cover change and policy scenarios, we present an analysis of the effects of forest patch size and shape and landscape pattern on carbon storage estimated by BIOME-BGC. We evaluate the effects of including within-patch and landscape-scale heterogeneity in air temperature on carbon estimates using two modelling experiments. In the first, we combine fieldwork, spatial analysis, and BIOME-BGC at a 15-m resolution to estimate carbon storage in the highly fragmented and human-dominated landscape of Southeastern Michigan, USA. In the second, we perform the same analysis on 12 hypothetical landscapes that differ only in their degree of fragmentation. For each experiment we conduct four air-temperature treatments, three guided by field-based data and one empirically informed by local National Weather Service station data. The three field data sets were measured (1) exterior to a forest patch, (2) from the patch edge inward to 60 m on east-, south-, and west-facing aspects, separately, and (3) interior to that forest patch. Our field-data analysis revealed a decrease in maximum air temperature from the forest patch edge to a depth of 80 m. Within-patch air-temperature values were significantly different ( α = 0.01) among transects (c.v. = 13.28) and for all measurement locations (c.v. = 30.58). Results from the first experiment showed that the interior treatment underestimated carbon storage by ∼8000 Mg C and the exterior treatment overestimated carbon storage by 30,000 Mg C within Dundee Township, Southeastern Michigan, when compared to a treatment that included within-patch heterogeneity. In the second experiment we found a logarithmic increase in carbon storage with increasing fragmentation ( r 2 = 0.91). While a number of other processes (e.g. altered disturbance frequency or severity) remain to be included in future experiments, this combined field and modelling study clearly demonstrated that the inclusion of within-patch and landscape heterogeneity, and landscape fragmentation, each have a strong effect on forest carbon cycling and storage as simulated by a widely used ecosystem process model.

Effects of landscape composition and configuration on northern flying squirrels in a forest mosaic

Habitat loss and sometimes habitat fragmentation per se affect species survival, reproduction, dispersal, abundance and distribution. However, understanding the independent effects of fragmentation (i.e., landscape configuration) has been limited because it is frequently confounded with landscape composition (i.e., habitat amount). We assess the independent effects of landscape composition and configuration on the occurrence of northern flying squirrels ( Glaucomys sabrinus) in New Brunswick, Canada after controlling for local site conditions. We measured landscape structure using an “organism-based” approach; landscape structure was characterized quantitatively using a spatially explicit local-scale distribution model for northern flying squirrels. Flying squirrels occurred more frequently in old forest, at sites with mixed coniferous–deciduous microhabitat composition and greater amounts of habitat cover at the neighbourhood (within home-range) scale. Squirrels were less likely to occur at sites surrounded by greater proportions of non-habitat matrix (non-treed or early seral open areas). The occurrence of flying squirrels was not strongly correlated with patch size or edge contrast. We detected no interaction between the effects of patch size and habitat composition. Landscape composition was clearly a more important predictor of flying squirrel distribution than configuration. We conclude that management practices that maximize the amount of old forest cover, maintain diverse tree species composition and minimize the creation of open areas should enhance the conservation value of landscapes for northern flying squirrels. Manipulating landscape pattern though forest management likely has limited use in mitigating the negative influence of habitat loss on this species.

Linking edge effects and patch size effects: Importance of matrix nest predators

The edge effect is usually considered to be the proximate cause of area sensitivity in forest birds. We tested if birds nesting in large patches are less vulnerable to the edge effect using a simple model that assumes an increase in patch size reduces the probability of a matrix predator moving to the core areas of forest and that larger perimeter/area ratios result in a higher number of matrix predators per unit of area. The probability of a nest being successful decreased asymptotically with an increase in either the patch penetration distance of predators or predator density, but those effects were reduced when patch size was increased. Large patches have a lower probability of being affected by an Allee effect and they can function as sink habitats only if penetration distance and predator density are largely increased. However, the transition from an Allee effect to a sink condition occurs with a small increase in penetration distance and predator density. Since birds nesting in large patches are less vulnerable to an increase in matrix predator populations, persistence of bird populations may be possible by increasing the size of habitat patches that can act as source populations.

The impact of habitat characteristics on bird presence and the implications for wildlife management in the environs of Ottawa, Canada

Urban forestry is increasingly vital for both wildlife conservation and human use, despite frequent conflicts between these functions. A fundamental task in urban habitat and recreation forestry is the identification of those habitat characteristics important for animal species and the evaluation of these within the geographies of human presence, urban proximity and land cover variation and change. This paper examines the habitat characteristics for birds in urban built, green and greenbelt areas of Ottawa, Canada, and an area of continuous Ontario forest, to determine the effects of vegetation density and patch size, and human presence on bird presence. Bird presence was measured by point counts, and land cover was mapped using field observation and aerial photographs (1955 and 1999). At the species level, the pre-dominantly forest birds were affected by human presence and were primarily associated with tree stands in the greenbelt and continuous forest. In dense urban areas there were larger numbers of a few ‘generalist’ species. Both forested and urban (residential/commercial) environments increased in area between 1955 and 1999, creating the two types of land cover favouring the largest number of birds, while the less habituated grass/farmed areas declined in area. More informed bird conservation and recreation management will depend on paying greater attention to vegetation cover combinations with urban development.

Habitat influences on urban avian assemblages

Urbanization is increasing across the globe and there is growing interest in urban ecology and a recognition that developed areas may be important for conservation. We review the factors influencing urban avian assemblages, focusing on habitat type and anthropogenic resource provision, and analyse data from a common bird monitoring scheme to assess some of these issues. The review suggests that (1) local factors are more important than regional ones in determining the species richness of urban avian assemblages, raising the potential for the management of urban sites to deliver conservation; (2) habitat fragmentation frequently influences urban avian assemblages, with the effects of patch size being greater than those of isolation, and (3) urban bird assemblages appear to respond positively to increasing the structural complexity, species richness of woody vegetation and supplementary feeding, and negatively to human disturbance. Data from Britain's Breeding Bird Survey, combined with habitat data obtained from aerial photographs, were used to assess a number of these issues at the resolution of 1‐km squares. Green‐space constituted 45% of these squares, and domestic gardens contributed 50% of this green‐space, though their contribution to large continuous patches of green‐space was negligible. There was no significant positive correlation between the densities of individual species in urban areas and surrounding rural areas. Rural species richness declined with increasing latitude, but urban species richness was not correlated with latitude. This contrast contributes to slightly higher avian species richness in rural squares in Southern England than urban ones. Occupancy and abundance were strongly positively correlated in urban avian assemblages, and some indicator species of conservation concern occurred in few urban areas and at low densities. Such species will require conservation action to be precisely targeted within urban areas. Of the urban indicators of conservation concern, only the House Sparrow Passer domesticus and Common Starling Sturnus vulgaris were more abundant in urban than rural areas. Moreover, the densities of these two species were strongly and positively correlated, indicating that they may be limited by shared resources, such as nest‐sites or supplementary food. There was little evidence that high densities of nest‐predating corvids were associated with reduced densities of their prey species. Species richness and the densities of individual species frequently declined with an increasing number of buildings. Current trends for the densification of many British urban areas are thus likely to be detrimental for many bird species.

Mating system, reproduction mode and diaspore size affect metacommunity diversity

1 Metapopulation persistence and metacommunity diversity in patchy dynamic landscapes critically depend on efficient dispersal. Dispersal strategies could involve trade-offs that result in different species responses to habitat fragmentation, alteration in habitat quality and changes in landscape dynamics. 2 We studied spatial structuring in species richness of obligate epiphytic bryophytes in 135 deciduous forest patches in a largely coniferous landscape in Sweden. We tested the effects of forest patch size (0.01–15 ha), patch quality and present and historic connectivity (as revealed by air photographs) on species richness of species groups with different mating systems, reproduction modes and diaspore sizes. 3 Present connectivity to other deciduous forest patches had positive effects on richness of dioecious species with predominant asexual reproduction, whereas richness of monoecious species with predominant sexual reproduction was affected by historic connectivity only. The scale of spatial structuring in species richness increased with decreasing diaspore sizes. Forest patch quality affected richness of monoecious species reproducing sexually but not of dioecious species reproducing asexually. 4 Our results suggest shorter dispersal distances, but higher establishment rates, of large asexual diaspores than of small sexual ones. In monoecious species with sexual reproduction, it may take several decades from establishment to first spore production, and this may explain the strong effect of historic, but not present, forest patch connectivity on species richness of this group. This suggests a trade-off between dispersal distance and age at first reproduction, which may explain the parallel evolution of asexual reproduction and monoecism in species inhabiting patchy, transient habitats. 5 Synthesis. We conclude that dispersal success of metacommunity members is influenced both by species traits and habitat characteristics. In patch-tracking metacommunities, trade-offs in species traits may have evolved as a consequence of conflicting selection pressures imposed by habitat patchiness and dynamics. Syndromes of interrelated species traits imply that fairly small changes in habitat conditions may lead to distinct changes in metacommunity diversity: Species reproducing asexually may drastically decline with increasing distances among patches, whereas sexually reproducing species may decline with increasing patch dynamics.