Negative Edge Effects Research Articles

Geodesigning landscape linkages: Coupling GIS with wildlife corridor design in conservation planning

Conservation planners continue to face challenges in quantifying and ameliorating the negative ecological effects of landscape fragmentation on species populations. While significant methodological and technological advancements have led to more analytically robust assessments of landscape connectivity, the end result of these efforts is often the demarcation of corridor areas void of any significant detailed physical design of their interiors. To address this shortcoming, this work proposes the creation of a hybrid geodesign and connectivity conservation framework and the development of a new tool, or Automated Design Model (ADM), for use in wildlife corridor design. The ADM's primary purpose is to generate detailed vegetation planting designs that may be applied to the interiors of previously modeled corridors. When coupled with existing methods for delineating the spatial extents of biologically best corridors, ADM derived vegetation designs may prove useful in mitigating negative edge effects and enhancing species movement, thus potentially improving the corridors connectivity function. Using a series of geospatial models and rule-based pattern generators, the ADM derived designs are highly customizable to locally specific landscape conditions, varied focal species requirements, and differences spatial structures known to facilitate wildlife movement.Moreover, the automated nature of the ADM allows for detailed design at the landscape-scale, has broad applicability in connectivity conservation and landscape restoration, and may help in filing data gaps necessary for moving towards planning and design implementation. Towards this end, this work proposes a basis for developing a common understanding of what constitutes geodesign, proposes the development of a hybrid geodesign/conservation planning framework, and discusses the development of the ADM as a mechanism for improving the functional design of wildlife corridors.

Intraguild predator drives forest edge avoidance of a mesopredator

AbstractInteractions between top predators and mesopredators of the same guild often result in habitat segregation restricting interactions to shared habitat edges. Although negative edge effects are recognized as important spatial patterns in the ecology of fragmented landscapes, the underlying mechanisms of predator–prey interactions resulting in negative edge effects remain unknown. To disentangle top‐down effects of intraguild predators and bottom‐up effects of shared resources on mesopredator spatial distribution, we recorded the occurrence of tawny owls Strix aluco in forests and their prey, the little owl Athene noctua in adjacent open areas over 2 yr across 687 km2 in Southern Germany. We developed a new, asymmetrical dynamic two‐species occupancy model investigating spatial interactions while accounting for imperfect detection. Little owl occupancy was strongly reduced within 150 m of forests, but only in the presence of tawny owls. Analysis of over 30 000 telemetry locations of 275 little owls showed that little owls strongly avoided areas closer than 150 m from the forest during range use. These results suggest that the negative edge effect is due to forest edge avoidance rather than direct predation. Potential confounding mechanisms such as food depletion or habitat avoidance at forest edges can be ruled out. Thus, top‐down effects caused by avoidance of intraguild top predators shape the spatial distribution of mesopredators such as the little owl. While habitat complexity mitigates multitrophic interactions within habitats, it is expected to reinforce multitrophic interactions between habitats, potentially leading to the suppression of mesopredators from suitable habitats.

The “edge effect” phenomenon: deriving population abundance patterns from individual animal movement decisions

Edge effects have been observed in a vast spectrum of animal populations. They occur where two conjoining habitats interact to create ecological phenomena that are not present in either habitat separately. On the individual-level, an edge effect is a change in behavioral tendency on or near the edge. On the population-level, it is a pattern of population abundance near an edge that cannot be explained in terms of either habitat in isolation. That these two levels of description exist suggests there ought to be a mathematical link between them. Here, we make inroads into providing such a link, deriving analytic expressions describing oft-observed population abundance patterns from a model of movement decisions near edges. Depending on the model parameters, we can see positive, negative, or transitional edge effects emerge. Importantly, the distance over which animals make their decisions to move between habitats turns out to be a key factor in quantifying the magnitude of certain observed edge effects.

Retention patch size and conservation of saproxylic beetles in boreal white spruce stands

Green tree retention is thought to conserve biodiversity in harvested landscapes; however, the amount and distribution of retention that best meets conservation goals remains unclear. To clarify size of retention patches needed to effectively conserve saproxylic (i.e., deadwood-associated) beetles in western Canada, we compared beetle assemblages among patches of three size categories (small: 0.63–1.06ha, medium: 1.43–2.93ha, and large: 3.34–5.93ha) left in harvested areas with those from intact forests and harvested matrix. To understand edge effects as a potential driver of faunal changes associated with patch size, we also compared assemblages from edges and centers of retention patches. Saproxylic beetle assemblages similar to those in intact forests were well maintained in all patch centers, but assemblages in small and medium patches were strongly influenced by edge effects and were least similar to those in intact forests. Particular trophic guilds showed distinct responses to patch size. Predator assemblages showed negative edge effects in small and medium patches, while phloeophage assemblages did not differ between edges and centers of different patch sizes. Although smaller patches may better emulate historical size distributions of fire skips, conservation value is likely maximized in large patches, mainly by decreasing edge effects. Our study dealt mainly with ‘initial colonizers’, but further studies to define minimum patch size for retention harvest must be conducted over time to incorporate effects on species associated with well-decayed deadwood.

Microclimatic conditions at forest edges have significant impacts on vegetation structure in large Atlantic forest fragments

Forest fragmentation creates forest edges, and the effect of those edges increases as the size of forest fragments decreases. Edge effects include changes to microclimatic conditions at the forest edge, which affect vegetation structure. No previous studies have directly tested the relationship between microclimate and vegetation structure (for instance, basal area, trees mean height, dead trees and damage trees) at the edge of forest fragments in the Atlantic Forest domain. We tested the following three hypotheses: (i) the microclimatic conditions differ between the edge and the interior of the forest, (ii) the forest structure differs between the edge and the interior of the forest and (iii) changes to microclimatic conditions at the forest edge negatively affect vegetation structure at the edges. Our results demonstrate that edge habitats are significantly more susceptible to strong winds, lower humidity and higher air temperatures than forest interiors. The microclimate may be considered the principal factor that explains the difference between the vegetation structure of the forest edge and the forest interior. Our results suggest that even large forest fragments in the Brazilian Atlantic Forest may be impacted by negative edge effects.

Potential negative ecological effects of corridors.

Despite many studies showing that landscape corridors increase dispersal and species richness for disparate taxa, concerns persist that corridors can have unintended negative effects. In particular, some of the same mechanisms that underlie positive effects of corridors on species of conservation interest may also increase the spread and impact of antagonistic species (e.g., predators and pathogens), foster negative effects of edges, increase invasion by exotic species, increase the spread of unwanted disturbances such as fire, or increase population synchrony and thus reduce persistence. We conducted a literature review and meta-analysis to evaluate the prevalence of each of these negative effects. We found no evidence that corridors increase unwanted disturbance or non-native species invasion; however, these have not been well-studied concerns (1 and 6 studies, respectively). Other effects of corridors were more often studied and yielded inconsistent results; mean effect sizes were indistinguishable from zero. The effect of edges on abundances of target species was as likely to be positive as negative. Corridors were as likely to have no effect on antagonists or population synchrony as they were to increase those negative effects. We found 3 deficiencies in the literature. First, despite studies on how corridors affect predators, there are few studies of related consequences for prey population size and persistence. Second, properly designed studies of negative corridor effects are needed in natural corridors at scales larger than those achievable in experimental systems. Third, studies are needed to test more targeted hypotheses about when corridor-mediated effects on invasive species or disturbance may be negative for species of management concern. Overall, we found no overarching support for concerns that construction and maintenance of habitat corridors may result in unintended negative consequences. Negative edge effects may be mitigated by widening corridors or softening edges between corridors and the matrix. Other negative effects are relatively small and manageable compared with the large positive effects of facilitating dispersal and increasing diversity of native species.

Spatial distribution and nutritional requirements of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) in a Mediterranean Nanozostera noltii (Hornemann) meadow

Sulphur-oxidising endosymbiont-bearing bivalves often inhabit seagrass meadows, where they can control sulphide levels and variably contribute to carbon cycling, by feeding on endosymbiotic bacteria and/or on particulate organic matter from the water column. The patterns of variability in their feeding mode and their spatial distribution within the seagrass meadows are however poorly studied. Seagrass beds form naturally patchy habitats with seagrass-sand edges that may have variable effects on different organisms. The present study aims at understanding differences in feeding mode and abundance of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) as well as the physiological conditions of its endosymbiotic populations between edge and inner portion of meadows of the eelgrass Nanozostera noltii (Hornemann). In July 2010, Loripes specimens were sampled in 4 eelgrass patches at 2 different locations in the Thau lagoon, South of France. There was a clear negative edge effect on the abundance of small individuals of Loripes, while large individuals were homogeneously distributed between edge and inner part of the meadow. Although Loripes isotopic signatures (δ13C and δ15N) were always closer to those of its symbiotic bacteria than to those of suspension-feeding bivalves, eelgrass edge enhanced mixotrophic behaviour of small animals, which assimilated less bacterial carbon and nitrogen at the edge than in the inner part of the eelgrass meadow. No differences related to eelgrass edges were instead found for the bacterial populations harboured by Loripes. Rather, flow cytometry revealed large variability at small spatial scales. Although bacteria were always important for the nutrition of Loripes, these findings showed that seagrass edges may contribute to regulate feeding mode and population structure of Loripes, which may have implications for seagrass functioning.

Balancing the edge effects budget: bay scallop settlement and loss along a seagrass edge

Edge effects are a dominant subject in landscape ecology literature, yet they are highly variable and poorly understood. Often, the literature suggests simple models for edge effects-positive (enhancement at the edge), negative (enhancement at the interior), or no effect (neutral)--on a variety of metrics, including abundance, diversity, and mortality. In the marine realm, much of this work has focused on fragmented seagrass habitats due to their importance for a variety of commercially important species. In this study, the settlement, recruitment, and survival of bay scallops was investigated across a variety of seagrass patch treatments. By simultaneously collecting settlers (those viable larvae available to settle and metamorphose) and recruits (those settlers that survive some period of time, in this case, 6 weeks) on the same collectors, we were able to demonstrate a "balance" between positive and negative edge effects, resulting in a net neutral effect. Scallop settlement was significantly enhanced along seagrass edges, regardless of patch type while survival was elevated within patch interiors. However, recruitment (the net result of settlement and post-settlement loss) did not vary significantly from edge to center, representing a neutral effect. Further, results suggest that post-settlement loss, most likely due to predation, appears to be the dominant mechanism structuring scallop abundance, not patterns in settlement. These data illustrate the complexity of edge effects, and suggest that the metric used to investigate the effect (be it abundance, survival, or other metrics) can often influence the magnitude and direction of the perceived effect. Traditionally, high predation along a habitat edge would have indicated an "ecological trap" for the species in question; however, this study demonstrates that, at the population level, an ecological trap may not exist.

The landscape matrix modifies the effect of habitat fragmentation in grassland butterflies

The landscape matrix is suggested to influence the effect of habitat fragmentation on species richness, but the generality of this prediction has not been tested. Here, we used data from 10 independent studies on butterfly species richness, where the matrix surrounding grassland patches was dominated by either forest or arable land to test if matrix land use influenced the response of species richness to patch area and connectivity. To account for the possibility that some of the observed species use the matrix as their main or complementary habitat, we analysed the effects on total species richness and on the richness of grassland specialist and non-specialist (generalists and specialists on other habitat types) butterflies separately. Specialists and non-specialists were defined separately for each dataset. Total species richness and the richness of grassland specialist butterflies were positively related to patch area and forest cover in the matrix, and negatively to patch isolation. The strength of the species-area relationship was modified by matrix land use and had a slope that decreased with increasing forest cover in the matrix. Potential mechanisms for the weaker effect of grassland fragmentation in forest-dominated landscapes are (1) that the forest matrix is more heterogeneous and contains more resources, (2) that small grassland patches in a matrix dominated by arable land suffer more from negative edge effects or (3) that the arable matrix constitutes a stronger barrier to dispersal between populations. Regardless of the mechanisms, our results show that there are general effects of matrix land use across landscapes and regions, and that landscape management that increases matrix quality can be a complement to habitat restoration and re-creation in fragmented landscapes.

Filling evidence gaps with expert opinion: The use of Delphi analysis in least-cost modelling of functional connectivity

Assessment of landscape functional connectivity is increasingly important for planning landscape scale conservation measures. However, measuring the functional connectivity of landscapes is challenging due to the lack of data on species landscape interactions and because connectivity is species-specific. We developed parameters for a connectivity indicator using Delphi analysis, and critically examine the use of Delphi analysis in this context. To calculate the connectivity indicator we used the following parameters: maximum dispersal distance, negative edge effects of different land cover, and relative permeability of different land cover. Delphi is a technique designed to numerically synthesise expert opinion in data-poor environments and is based on repetitive questionnaires interspersed with controlled feedback. Three panels of experts were assembled, one covering each of three habitats of interest. Experts found the process challenging especially fixing exact numbers given the potential range of values. However, panels generally assigned higher permeability and low edge effects to semi-natural land cover classes, assigning low permeability and high edge impacts to more modified land cover. During the Delphi process we found that experts were prepared to alter their answers in response to feedback from the previous round. Participants’ answers which did change between rounds generally changed to approach the group median, and when they did, the associated confidence score was more likely to rise than to fall. After three rounds, answers were generally stable. Delphi proved a useful method to use to generate parameter values for the connectivity indicator, with the method particularly acceptable to stakeholders of the indicator project.

Relating Microclimate to Epiphyte Availability: Edge Effects on Nesting Habitat Availability for the Marbled Murrelet

Industrial timber harvesting typically creates forest edges with altered microclimate regimes, causing reduced growth and survival of some canopy epiphytes. This process has implications for the marbled murrelet (Brachyramphus marmoratus), a threatened seabird that nests on moss platforms in old-growth forests of the coastal Pacific Northwest in North America. We investigated microclimate and epiphyte availability in old-growth forests of southwestern British Columbia, Canada. We contrasted mean and maximum temperature, mean humidity, mean vapor pressure deficit (VPD) and mean epiphyte cover and platform tree density between forest edge and interior plots at hard edges (recent clearcuts), soft edges (regenerating forest) and natural edges (rivers and avalanche chutes). Differences measured in VPD and epiphyte availability varied due to edge proximity and edge-type. Hard edges had fewer trees with suitable marbled murrelet nest platforms relative to adjacent interiors, and hard-edged patches had the lowest epiphyte cover overall. This suggests that microclimate edge effects and substrate availability can negatively impact epiphyte growth and survival, and may reduce the availability of marbled murrelet nest sites. These negative effects may decrease with time as forests regenerate, as edge effects were lower in magnitude at soft-edged patches. In contrast, natural-edged patches had the greatest levels of epiphyte cover and platform tree density, suggesting that these areas provide an abundant source of potential nest sites. Minimizing the ratio of anthropogenic edge to suitable interior habitat, and maintaining natural edges will limit negative edge effects on moss availability and provide nesting habitat for marbled murrelets.

Edge effect and matrix influence on the nest survival of an old forest specialist, the Brown Creeper (Certhia americana)

Conservation strategies should be based on a solid understanding of processes underlying species response to landscape change. In forests fragmented by agriculture, elevated nest predation rates have been reported in many forest bird species, especially near edges. In intensively-managed forest landscapes, timber harvesting might also be associated with negative edge effects or broader “context” effects on some species when the matrix provides additional resources to their major nest predators. In this study, we hypothesized that proximity to a forest edge and proportion of cone-producing plantations will increase nest predation risk in fragments of relatively undisturbed forest. We focused on the Brown Creeper (Certhia americana), an indicator species of late-seral forests. We compared habitat configuration and composition at four spatial scales (0.14, 0.5, 1 and 2 km) around 54 nests and related daily nest survival rate to the distance to the nearest forest edge, mean patch size of late-seral forest (r = 141 m), proportion of non-forested lands (r = 141 m), density of maintained roads (r = 1 km), proportion of cone-producing spruce plantations (r = 2 km), and year. The best model included distance to the nearest edge and proportion of cone-producing plantations. Distance of nests to the nearest edge was the best individual predictor of daily nest survival. A larger sample of nests showed a significant threshold in distance to the nearest forest edge; nests located at least 100 m away were more likely to fledge young. These results suggest that even in managed forest landscapes, matrix effects can be important and some bird species may exhibit negative edge effects.

Islands of fear: effects of wooded patches on habitat suitability of the striped mouse in a South African grassland

Summary 1. As a fundamental unit within a landscape, habitat patches create spatial heterogeneity. On a gradient of habitat patch size, one sees patches of denser vegetation cover occurring in otherwise open habitats (e.g. bushes in the desert, forest fragments in grasslands). 2. The resulting habitat fragmentation and consequent edge effects continue to concern conservation biologists, landscape ecologists, and wildlife managers due to their role in influencing wildlife abundance and distribution on broad geographic scales. 3. Although ecological processes near habitat edges often differ from processes away from edges, an animal’s suitable habitat may increase or decrease by ‘positive’ or ‘negative’ edge effects. Such effects can be measured using behavioural indicators and experiments based on the costs and benefits of foraging under diminishing returns. 4. We used live trapping, giving‐up densities [amount of food left behind in experimental food patches – giving‐up density (GUD)] and geographic information system (GIS) analyses to test for spatial and temporal habitat selection by the four‐striped grass mouse (Rhabdomys pumilio) inhabiting a grassland containing distinct ‘islands’ of woody vegetation (500 m2 of average area). We investigated how these woody islands influence the quality of the grassland in terms of activity patterns, feeding opportunities, predation risk and habitat suitability. We used R. pumilio’s GUDs to explicitly map and measure habitats of varying quality using GIS. 5. Our results showed that R. pumilio perceived the wooded patches as habitats with no opportunities and yet highly risky when opportunities are provided. Furthermore, the wooded patches had a negative edge effect, their unsuitability extended for 1–3 m into the otherwise suitable habitats. 6. The combination of live‐trapping and giving up densities provided an unbiased and controlled measure of a prey’s perception of habitat use and foraging costs when equal opportunities are simultaneously provided. These techniques and concepts should be broadly applicable by conservationists and ecologists interested in understanding and managing edge effects. 7. This approach aims to effectively quantify edge effects and extrapolate predation risk on a landscape scale, thereby developing recommendations for managers to improve the quality or amount of edges for wildlife.

Associations between distance to forest and spatial and temporal variation in abundance of key peatland breeding bird species

Capsule Negative forest edge effects were detected for Willow Ptarmigan (Red Grouse) Lagopus lagopus and Dunlin Calidris alpina. Aims To investigate the effects of distance to forest on the abundance and changes in abundance of four key peatland breeding bird species, and to measure changes in predatory bird numbers, in the peatlands of northern Scotland. Methods Bird surveys were carried out in 2000 at 34 plots, covering 197 km2 of peatland, and 80 forestry point‐count sites, first surveyed in 1988. Habitat data were also collected in 2000. We used multi‐model inference to investigate the associations between forest distance and other habitat variables, and the abundance, and changes in abundance, of four bird species of economic or conservation importance: Red Grouse, European Golden Plover Pluvialis apricaria, Dunlin and Common Greenshank Tringa nebularia. Results There was strong evidence that distance to forest was negatively associated with Dunlin abundance and changes in Red Grouse abundance, but only weak evidence for negative associations with Golden Plover abundance and changes in Dunlin abundance. There was no evidence of a forest distance effect on Greenshank. Among predatory birds, there were no significant increases either on peatland plots or in new forestry plantations. Conclusions This study provides evidence that, for a given habitat quality, Dunlin densities are lower, and Red Grouse declines more likely, near to forest edges, but weak evidence only that Dunlin declines are more likely, and Golden Plover abundance lower, near to forests. These results suggest that for at least two key peatland breeding birds, forest removal is likely to benefit birds breeding on adjacent unafforested peatland.

Distance to edges, edge contrast and landscape fragmentation: Interactions affecting farmland birds around forest plantations

Afforestation often causes direct habitat losses for farmland birds of conservation concern, but it is uncertain whether negative effects also extend significantly into adjacent open land. Information is thus required on how these species react to wooded edges, and how their responses are affected by edge and landscape characteristics. These issues were examined in Mediterranean arable farmland, using bird counts at 0, 100, 200, 300 and >300 m from oak, pine and eucalyptus edges, embedded in landscapes with variable amounts and spatial configurations of forest plantations. Bird diversity declined away from edges, including that of woodland, farmland and ground-nesting birds. Positive edge responses were also found for overall and woodland bird abundances, and for five of the nine most widespread and abundant species ( Galerida larks, stonechat, linnet, goldfinch and corn bunting). Strong negative edge effects were only recorded for steppe birds, with reduced abundances near edges of calandra larks and short-toed larks, but not of little bustards and tawny pipits. Edge contrast affected the magnitude of edge effects, with a tendency for stronger responses to old and tall eucalyptus plantations (hard edges) than to young and short oak plantations (soft edges). There were also species-specific interactions between edge and fragmentation effects, with positive edge responses tending to be strongest in less fragmented landscapes, whereas steppe birds tended to increase faster away from edges and to reach the highest species richness and abundances in large arable patches. Results suggest that forest plantations may increase overall bird diversity and abundance in adjacent farmland, at the expenses of steppe birds of conservation concern. Clustering forest plantations in a few large patches and thus reducing the density of wooded edges at the landscape-scale might reduce such negative impacts.

Influence of Landscape Elements in Riparian Buffers on the Conservation of Semiaquatic Amphibians

Studies on riparian buffers have usually focused on the amount of land needed as habitat for the terrestrial life stages of semiaquatic species. Nevertheless, the landscape surrounding wetlands is also important for other key processes, such as dispersal and the dynamics of metapopulations. Multiple elements that influence these processes should therefore be considered in the delineation of buffers. We analyzed landscape elements (forest cover, density of roads, and hydrographic network) in concentric buffers to evaluate the scale at which they influence stream amphibians in 77 distinct landscapes. To evaluate whether our results could be generalized to other contexts, we determined whether they were consistent across the study areas. Amphibians required buffers of 100-400 m of suitable terrestrial habitat, but interspecific differences in the amount of habitat were large. The presence of amphibians was related to roads and the hydrographic network at larger spatial scales (300-1500 m), which suggests that wider buffers are needed with these elements. This pattern probably arose because these elements influence dispersal and metapopulation persistence, processes that occur at large spatial scales. Furthermore, in some cases, analyses performed on different sets of landscapes provided different results, which suggests caution should be used when conservation recommendations are applied to disparate areas. Establishment of riparian buffers should not be focused only on riparian habitat, but should take a landscape perspective because semiaquatic species use multiple elements for different functions. This approach can be complex because different landscape elements require different spatial extents. Nevertheless, a shift of attention toward the management of different elements at multiple spatial scales is necessary for the long-term persistence of populations.

The Boundary‐Quality Penalty: a Quantitative Method for Approximating Species Responses to Fragmentation in Reserve Selection

Aggregation of reserve networks is generally considered desirable for biological and economic reasons: aggregation reduces negative edge effects and facilitates metapopulation dynamics, which plausibly leads to improved persistence of species. Economically, aggregated networks are less expensive to manage than fragmented ones. Therefore, many reserve-design methods use qualitative heuristics, such as distance-based criteria or boundary-length penalties to induce reserve aggregation. We devised a quantitative method that introduces aggregation into reserve networks. We call the method the boundary-quality penalty (BQP) because the biological value of a land unit (grid cell) is penalized when the unit occurs close enough to the edge of a reserve such that a fragmentation or edge effect would reduce population densities in the reserved cell. The BQP can be estimated for any habitat model that includes neighborhood (connectivity) effects, and it can be introduced into reserve selection software in a standardized manner. We used the BQP in a reserve-design case study of the Hunter Valley of southeastern Australia. The BQP resulted in a more highly aggregated reserve network structure. The degree of aggregation required was specified by observed (albeit modeled) biological responses to fragmentation. Estimating the effects of fragmentation on individual species and incorporating estimated effects in the objective function of reserve-selection algorithms is a coherent and defensible way to select aggregated reserves. We implemented the BQP in the context of the Zonation method, but it could as well be implemented into any other spatially explicit reserve-planning framework.

Edge effects on flower‐visiting insects in grapefruit plantations bordering premontane subtropical forest

Summary Over the last decade, there has been much concern about the decline in pollinator abundance and diversity caused by different types of anthropogenic disturbances, including deforestation and habitat fragmentation. However, little empirical information exists documenting this decline and its consequences for cultivated flowering crops. We tested the hypothesis that remnants of natural habitats act as a source of flower‐visiting insects for neighbourhood crops. Over 3 consecutive years we evaluated flower‐visiting insect diversity, visitation frequency and composition in four grapefruit Citrus paradisi Macf. plantations at increasing distances (edge, 10, 100, 500 and 1000 m) from remnants of subtropical premontane forest in NW Argentina. The frequency of visits to grapefruit flowers decreased by more than twofold as distance to the forest increased and the flower‐visiting fauna became more depaupurate. Even the feral africanized honeybee Apis mellifera, the dominant flower visitor to grapefruit flowers, showed a decline at distances > 500 m from the forest edge. However, the greatest relative declines occurred among stingless and solitary bees as well as other native flower visitors, which were rarely seen a few hundred metres inside the plantations. In addition, flower‐visiting insect faunas among plantations became more homogeneous as distance from the edge increased. These trends were consistent over years and among plantations up to 50 km apart. Thus, we can conclude that negative forest edge effects on flower‐visiting insects inside grapefruit plantations are widespread in the increasingly deforested landscape of NW Argentina. Synthesis and applications. This study provides empirical evidence for considering remnants of natural habitats as a source of both native and alien flower‐visiting insects that can be potential pollinators for agriculture. Increasing edge density in agricultural lands, through preservation and restoration of natural habitats, can foster stocks of diverse and abundant insect pollinators.

Effects of Forest Fragmentation on Pteridophyte Diversity in a Tropical Rain Forest in Brazil

The impacts of forest fragmentation on the pteridophyte communities of the Una region of Bahia, Brazil, were investigated by comparing species richness and ensemble diversity among areas of large forest fragments (>900 ha), small forest fragments (<100 ha), and landscape matrix. We inventoried the pteridophytes below 1 m in height in interiors of small fragments, interiors of large fragments (control areas), edges of fragments, edges of continuous forest, capoeiras (initial stages of forest regeneration) and cabrucas (cocoa plantations). All ferns were collected following the plot method (plots of 120 · 10 m, each). Sampling units were established in the six main ecotypes of the Una region. These units were allocated within three sampling blocks of 5 per 5 km, which were chosen in order to include the largest forest patches that still remain. Results suggest that fragmentation has a negative impact on species richness at the matrix and the edges of forest remnants. A similar negative matrix end edge effect is reported for diversity of those sites measured by the a Log-series Index. However, small forest fragments have pteridophyte species richness and diversity rates similar to large ones so they should be considered of utmost importance to the conservation of forest-related species in the region.

Edge effects on nesting success of cavity-nesting birds in fragmented forests

Forest fragmentation leads to the creation of isolated forest patches and habitat edges with subsequent impact on forest-interior bird species. Although the effects of fragmentation and edge on avian nesting success are well documented for open cup-nesting species in eastern deciduous forests in North America, it is unclear whether these effects are common for all birds nesting in predominantly forested landscapes. In particular, edge effects on nesting success of cavity-nesting birds are poorly understood. Using natural cavity nests, we examined nesting success of four species of cavity-nesting birds (two nonexcavators and two excavators), the yellow-rumped flycatcher (Ficedula zanthopygia), the great tit (Parus major), the great spotted woodpecker (Picoides major), and the grey-faced woodpecker (Picus canus) in relation to forest edges in Zuojia Nature Reserve, Jilin province, northeastern China. Our primary objective was to assess whether distance to the edge of agricultural lands was related to nesting success for cavity-nesting birds in fragmented forests. A total of 439 natural cavity nests of the four species were located and monitored during four breeding seasons. Probability of nest success was influenced by distance to forest edge for nonexcavators, but not for excavators. The rate of nesting success of the two nonexcavators, yellow-rumped flycatcher and the great tit, increased with distance from the edges. For all cavity nests, nesting success was 0.43 at 0–100m, 0.56 at 101–200m, 0.68 at 201–300m, 0.61 at 301–400m, 0.77 at 401–500m from the edges. Nesting success ranged from 0.57 for the yellow-rumped flycatcher to 0.89 for the Grey-faced Woodpecker. Failed nests were often occupied by nest-site competitors (accounting for 68%). However, predation only accounted for 20% of all nest failures. Our results suggest that negative edge effects do exist for some cavity-nesting birds, especially for nonexcavator species.