The contribution of lateral aquatic habitats to insect diversity along river corridors in the Alps

River floodplains are among the most threatened ecosystems globally. Understanding the mechanisms that create and maintain biodiversity and ecosystem functioning of floodplains, is therefore a prerequisite for developing scientifically-sound management and conservation strategies. We quantified the spatial distribution of lateral aquatic habitats (i.e. tributaries, ponds, backwaters) and the associated insect assemblages (Ephemeroptera, Plecoptera, Trichoptera) along three Alpine river corridors (Tagliamento, Thur, and Rhône). Our objective was to assess the relative contribution of lateral habitats to river corridor diversity, and to identify the scale that contributed the most to regional (Alpine scale) species diversity. The number of lateral habitats decreased by 72 % from the near-natural Tagliamento (101) to the Thur river (42) and the regulated Rhône river (28). More than 50 % of the total species richness along each river was restricted to lateral habitats, which also exhibited higher taxon turnover rates (Whittaker’s beta diversity) than the associated main channel. Hierarchical diversity partitioning revealed that beta diversity among corridors was higher than expected, and accounted for 48 % of regional richness, partly reflecting biogeographical differences among catchments. However, diversity partitioning, excluding catchment-specific effects, showed that beta diversity among habitat types contributed significantly to regional richness (79 %). The present study is among the first to quantify the distribution and biodiversity of floodplain habitats along entire river continua. Our results demonstrated that biodiversity would be best preserved by protecting multiple catchments, and that lateral floodplain habitats contribute disproportionally to species richness at the river corridor and regional scale.     

Application of the diminishing returns concept in the hydroecologic restoration of riverscapes

Increasing our knowledge of unplanned anthropogenic synergies, which have affected ecosystems since prehistory, may facilitate ecological restoration. Predictive relationships between spatial pattern and ecosystem processes and functions in riverscapes have the potential to inform applied ecosystem restoration planning and design, where principles are needed for large-scale river reconnections. Although synergistic, additive, and antagonistic interactions affect ecosystems, the role of such interactions in restoration rarely has been evaluated. Using hydrodynamic modeling, we experimentally examine the aggregate effects of reestablishing hydrologic connections in a tidal freshwater tributary on the floodplain of the Columbia River, USA, which is currently undergoing dike breaching to restore juvenile salmon habitat. Sets of dike breaches yielded average wetted floodplain areas conforming to a two-parameter hyperbola (r ² = 0.93). These findings demonstrate that the yield of inundated floodplain habitat area from dike breaching can conform to the well-established “law of the diminishing increment,” developed in the study of agriculture and economics. Furthermore, the influence of spatial configuration on yield was strong, with midstream breaches yielding 63% and upstream breaches 2% of the wetted area produced by downstream breaches, although conditions of extreme high river flow were not studied. Opening the dike at 26% of the historically present channel outlets provided the maximum return on investment for the study riverscape. Verification of this relationship elsewhere in tidal areas of the Columbia River and on other large river floodplains would contribute to cost-benefit analyses in ecological restoration program planning and have implications for effects on biota.     

Spatial correlates of amphibian use of constructed wetlands in an urban landscape

Many amphibian species rely on both aquatic and terrestrial habitats to complete their life cycles. Therefore, processes operating both within the aquatic breeding habitat, and in the surrounding uplands may influence species distributions and community composition. Moreover, changes in land use adjacent to breeding site may degrade aquatic habitats. To assess land use effects on pond-breeding amphibian assemblages, we investigated relationships between land use, breeding habitat conditions, and breeding amphibian use of constructed wetlands in urban environments of the Baltimore metropolitan area, USA. Forest and impervious surface associations with species richness and occurrence occurred at spatial scales ranging from 50 to 1,000 m, with strongest relationships at 500 m. Forest and impervious surface cover within 1,000 m of ponds were also related to water and sediment quality, which in turn were capable of explaining a proportion of the observed variation in species richness and occurrence. Taken together, our results suggest that forest and other land covers within relatively proximal distances to ponds (i.e., within 50–1,000 m) may be influencing species richness directly via the provisioning of upland habitat, and indirectly via influences on within pond habitat quality. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Connectivity providers for semi-aquatic vertebrates: the case of the endangered otter in Italy

Modeling habitat connectivity for conservation of semi-aquatic vertebrates is a particularly challenging task, due to the fine-scale and linear distribution of riverine habitats and to the capacity of species to move both on freshwater and terrestrial realms. We showed how the integrated analytical framework provided by the habitat availability (reachability) metrics and their fractions can be used to effectively evaluate the distinctive roles and contributions of both habitat patches (aquatic and riparian) and linkage areas (permeable land matrix) to the connectivity and functioning of a complex system composed of multiple river catchments. Analysis focused on the Eurasian otter (Lutra lutra L.), one of the most endangered mammals in Italy. We developed a network connectivity model based on suitable otter habitats and multiple least-cost paths between catchments. A graph analytical approach was used to identify critical nodes and links for the potential expansion and long-term viability of the species in the region. Our results showed that few basins concentrate most of the importance for sustaining the overall habitat connectivity, due to the extension of suitable habitats they contain, their strong connections with other basins, and their importance as stepping stones that uphold ecological fluxes between otherwise weakly connected habitats. The potential contribution of each basin to enhance the dispersal and expansion of otters in the area strongly depended on the key functional paths (sequences of links and nodes) among the catchments. We identified vacant basins that could be colonized by otters in the near future, and connecting areas in the intermediate matrix that might be preferentially used to conduct and promote dispersal movements and gene flow in the area. The novel approach here adopted could be easily extended to other semiaquatic species and catchment systems, offering a management strategy to preserve the hydrographic network as an integrated system, as well as a joint evaluation of the role of both the river courses and the matrix in between in a single landscape model.     

Observed and modeled directional change in riparian forest composition at a cutbank edge

Lateral migrations of river meanders create transient, spatially transgressive edges where the advancing cutbank edge encroaches upon interior floodplain forest communities. This spatial movement of edge toward the forest interior should initiate directional changes in species composition within a forest plot as it is affected by a changing microclimate and hydrological regime. We found that cutbank edge and forest interior sites in an Iowa floodplain contained markedly different plant assemblages. Species commonly associated with later stages of succession dominated interior sites while cutbank edge sites favored secondary, successional species. Assuming that the cutbank edge sites once contained vegetation similar to that surveyed in the floodplain interior, the observed changes in community structure accompanying channel migration are suggestive of retrograde succession, or retrogression. To link cutbank erosional processes with retrogressional processes, we modified a computer simulation model already in use for floodplain environments. We incorporated the changing edge effects and compared model projections with the data collected from the field sites using detrended correspondence analysis. Without changes, the simulation projected a site compositionally similar to the sampled interior forest. When the changes were initiated, the simulated site progressively took on compositional characteristics similar to the riparian edge sites. Because we included only those forcing functions that would be initiated by cutbank erosion, the model supports the hypothesis that the spatially progressive edge effect results in a directional change in forest community composition analogous to retrogression. Our results demonstrate an interesting linkage between successional and fluvial-geomorphic processes and indicate that site dynamics may be controlled differently in landscapes where sites are progressively created and destroyed than where recurrent disturbances affect the same site.     

Landscape ecology: a framework for integrating pattern and process in river corridors

Investigations of European floodplain rivers demonstrate how landscape ecology can provide an effective framework to integrate pattern and process in river corridors, to examine environmental dynamics and interactive pathways between landscape elements, and to develop viable strategies for river conservation. The highly complex and dynamic nature of intact river corridors is particularly amenable to a landscape ecology perspective. Analysis of spatial patterns has provided considerable insight into environmental heterogeneity across river corridors and is an essential prelude to examining dynamic interactions. For example, data from aerial photographs, digitized maps and year-round field measurements in a glacial flood plain, enabled us to distinguish six channel types, based on the correspondence between connectivity and physicochemical attributes. Spatial data were also used to analyze longitudinal changes in landscape elements along the course of a morphologically-intact riverine corridor, providing insight into the structural complexity that must have characterized many Alpine rivers in the pristine state. Landscape indices were employed to investigate seasonal dynamics in a glacial flood plain of the Swiss Alps which exhibits a predictable expansion/contraction cycle, with corresponding shifts in flow paths (surface and subsurface) and water sources (snowmelt, englacial, subglacial, alluvial aquifer, hillslope aquifer). Surface connectivity exhibited an unexpected biphasic relationship with total channel length, whereas riverscape diversity progressively increased along the entire range of channel length. Reconstituting the functional integrity that characterizes intact river corridors should perhaps be the major goal of river conservation initiatives. Although understanding functional processes at the landscape scale is essential in this regard, few data are available. In the Alluvial Zone National Park on the Austrian Danube, three phases of hydrological connectivity were identified (disconnection, seepage connection and surface connection) that corresponded to the predominance of three functional processes (biotic interactions, primary production and particulate transport) within the river corridor.     

A riverscape perspective on habitat associations among riverine bird assemblages in the Lake Champlain Basin,USA

The riverscape perspective recognizes the heterogeneous habitat types within the stream corridor as a single, integrated ecological unit operating across spatial scales. Although there is ample evidence that the riverscape notion is appropriate in understanding the physical phenomena of stream corridors, significantly less attention has focused on its ecological ramifications. To this end, we surveyed riverscape habitat variables and bird community characteristics in the Champlain Valley of Vermont, USA. From the data collected, we used information theoretic methodology (AIC_c) to model relationships between bird community attributes and key habitat variables across the riverscape. Our models with the greatest support suggest that riverine bird communities respond to a suite of characteristics; representing a variety of riverscape habitats at the in-stream, floodplain, and riparian levels. Channel slope, drainage area, percent conifers, and in-stream habitat condition were among the most influential variables. We found that piscivores are potentially important indicators of riverscape condition, responding to a host of variables across the riverscape. Our results endorse a holistic approach to assessing and managing the mosaic of patches in the riverscape and suggest that a riverscape approach has significant conservation potential.     

Overwintering in a megacity: Urban green areas and migratory birds in Mexico City

Nearctic-Neotropical migratory birds are threatened by land-use change throughout their complex annual cycles. While urbanization is an essential driver of land-use change, it is unclear how it affects migrant birds. Although migratory birds are more diverse in non-urban patches of native vegetation than in urban areas, neotropical cities can host diverse assemblages of overwintering migrant birds. Migratory birds in neotropical cities tend to be closely associated with urban green areas (UGAs). However, how their presence and abundance are affected by the habitat elements of UGAs and the urban matrix of neotropical cities is poorly understood. In this study, we compared the migratory bird species richness and abundances among UGAs and the urban matrix of the southern section of the megacity of Mexico City and native vegetation sites outside the city. Our results show that UGAs in neotropical cities provide habitats capable of maintaining complex overwintering migratory bird assemblages with local trees as critical features. We also assess the role that UGAs' characteristics play in determining migrant bird assemblages. We conducted bird censuses and measured habitat traits to determine how migrant bird assemblages are related to the habitat features of our study sites. We measured local, buffer, and spatial habitat features of each UGA. We found 23 overwintering migrant species in the three habitats, with 22 present within UGAs. Both UGAs and urban matrix sites had higher estimated species richness of migrant birds than non-urban native vegetation sites located outside the city. Only local features of UGAs affected migrant birds. While tree abundance in UGAs was positively associated with migratory bird species richness, the proportion of tree coverage was positively related to bird abundance. Our results show that UGAs in neotropical cities can maintain complex overwintering migratory bird assemblages, with trees being the most critical habitat feature. As a result, UGA management focused on maintaining trees and increasing their numbers can improve habitat conditions for migratory birds overwintering in neotropical cities.     

Physico-chemical heterogeneity in a glacial riverscape

Spatio-temporal heterogeneity in physico-chemical conditions associated with the annual expansion/contraction cycle in a complex glacial flood plain of the Swiss Alps was investigated employing a landscape approach. The diverse and dynamic aquatic habitats of the flood plain were visualized as an aquatic mosaic or riverscape. Based on samples collected at ca. monthly intervals for 1.5 yr along 17 floodplain transects, the 3 components of riverscape heterogeneity, extent, composition, and configuration, were quantified using categorical maps and indices of landscape patterns for turbidity and specific conductance. Changes in the spatial heterogeneity of 13 other physico-chemical parameters were further analyzed by means of a within-dates principal component analysis. Riverscape heterogeneity (RH), quantified by applying several indices of landscape pattern to turbidity and specific conductance data, was minimum during groundwater-dominated base flow in winter. Despite an increase in surface connectivity in the channel network with rising discharge, RH rose in spring and summer as additional chemically-distinct water sources (i.e., snowmelt runoff and glacial ablation) contributed to surface flow within the flood plain. Most other physico-chemical variables measured during this study exhibited the same spatio-temporal heterogeneity as turbidity and specific conductance. Overall, the glacial flood plain shifted from a monotonous physico-chemical riverscape in winter to a complex mosaic in summer, this seasonal pattern being clearly driven by hydrological factors operating at the catchment scale rather than by autogenic processes within individual water bodies. Although RH exhibited a predictable annual pattern in response to the seasonal flow regime, we expect the channel network to undergo future modifications from stochastic factors associated with flood events and long-term changes reflecting movements of the glaciers.     

Floodplain ecosystem response to climate variability and land-cover and land-use change in Lower Missouri River basin

This contribution aims at characterizing the extreme responses of Lower Missouri River basin ecosystems to land use modification and climate change over a 30-year temporal extent, using long term Landsat data archives spanning from 1975 to 2010. The inter-annual coefficient of variation (CoV) of normalized difference vegetation index was used as a measure of vegetation dynamics to address ecological consequences associated with climate change and the impact of land-cover/land-use change. The slope of a linear regression of inter-annual CoV over the entire time span was used as a sustainability indicator to assess the trend of vegetation dynamics from 1975 to 2010. Deduced vegetation dynamics were then associated with precipitation patterns, land surface temperature, and the impact of levees on alluvial hydrologic partitioning and river channelization reflecting the links between society and natural systems. The results show, a higher inter-annual accumulated vegetation index, and lower inter-annual CoV distributed over the uplands remaining virtually stable over the time frame investigated; relatively low vegetation index with larger CoV was observed over lowlands, indicating that climate change was not the only factor affecting ecosystem alterations in the Missouri River floodplain. We cautiously conclude that river channelization, suburbanization and agricultural activities were the possible potential driving forces behind vegetation cover alteration and habitat fragmentation on the Lower Missouri River floodplain.     

Effects of landscape composition and connectivity on the distribution of an endangered parrot in agricultural landscapes

The extent and connectivity of individual habitat types strongly affects the distribution and abundance of organisms. However, little is known of how the level of connectivity and the interactions between different habitat types influences the distribution of species. Here, we used the geographically restricted and endangered regent parrot Polytelis anthopeplus monarchoides as a case study to examine the importance of composition and connectivity between different elements in 39 complex landscape mosaics (each 10 km radius). We compiled a database of 674 regent parrot nesting records, regional vegetation maps and measures of multipath connectivity between core vegetation types under different scenarios of resistance to movement provided by landscape elements. The occurrence of regent parrot nests was strongly affected by landscape composition, being positively related to the extent Eucalyptus camaldulensis riverine forest, but negatively related to the extent of semi-arid woodlands dominated by Eucalyptus largiflorens. Connectivity between E. camaldulensis forest (principal nesting habitat) and mallee (preferred feeding habitat) was a strong predictor of nest locations. Our study shows that the suitability of fragmented agricultural landscapes for supporting species can be greatly affected by connectivity and interactions between preferred and non-preferred habitats. For species that require complementary habitats such as the regent parrot, conservation management activities may be ineffective if they simply focus on a single core habitat type or the impacts of human land uses without regard to the interrelationships among landscape elements. While increasing the amount of primary preferred habitat should remain a cornerstone goal, increasing the extent and improving connectivity with alternative landscape elements also should be priority management objectives.     

Context is more important than habitat type in determining use by juvenile fish

Context

Habitat characteristics are often equated with habitat function for animals. However, in heterogeneous landscapes, similar habitat types occur in different environmental contexts. In the marine realm, landscape studies have been confined to particular environments, rather than encompassing entire seascapes, due to incompatible sampling methods required in different situations.

Objectives

We examined the interactive structuring effects of local habitat characteristics and environmental context on assemblage composition.

Methods

We used a single technique—remote underwater video census—to explore the importance of habitat type (biotic structural components, substrate, and depth) and environmental context (marine vs estuarine) in structuring juvenile fish assemblages throughout an entire coastal region. In this model system, a range of structural habitat types were present in both estuarine and marine contexts.

Results

The 1315 video surveys collected show a clear hierarchy in the organisation of juvenile fish communities, with assemblages first distinguished by environmental context, then by habitat type. Marine and estuarine mangroves contained entirely different assemblages, and likewise for rocky reefs and submerged aquatic vegetation. Our results suggest that two functionally different ‘seascape nursery’ types exist at local scales within a single region, defined by their context.

Conclusions

The context of a location can be of greater significance in determining potential habitat function than what habitat-forming biota and substrates are present, and apparently similar habitat types in different contexts may be functionally distinct. These findings have important implications for local-scale management and conservation of juvenile fish habitats, particularly in regard to offsetting and restoration.

     

The relative influence of catchment and site variables on fish and macroinvertebrate richness in cerrado biome streams

Landscape and site-scale data analyses aid the interpretation of biological data and thereby help us develop more cost-effective natural resource management strategies. Our study focused on environmental influences on stream assemblages and we evaluated how three classes of environmental variables (geophysical landscape, land use and cover, and site habitat), influence fish and macroinvertebrate assemblage richness in the Brazilian Cerrado biome. We analyzed our data through use of multiple linear regression (MLR) models using the three classes of predictor variables alone and in combination. The four MLR models explained dissimilar amounts of benthic macroinvertebrate taxa richness (geophysical landscape R ² ≈ 35 %, land use and cover R ² ≈ 28 %, site habitat R ² ≈ 36 %, and combined R ² ≈ 51 %). For fish assemblages, geophysical landscape, land use and cover, site habitat, and combined models explained R ² ≈ 28 %, R ² ≈ 10 %, R ² ≈ 31 %, and R ² ≈ 47 % of the variability in fish species richness, respectively. We conclude that (1) environmental variables differed in the degree to which they explain assemblage richness, (2) the amounts of variance in assemblage richness explained by geophysical landscape and site habitat were similar, (3) the variables explained more variability in macroinvertebrate taxa richness than in fish species richness, and (4) all three classes of environmental variables studied were useful for explaining assemblage richness in Cerrado headwater streams. These results help us to understand the drivers of assemblage patterns at regional scales in tropical areas.     

A modeling approach for identifying recolonisation source sites in river restoration planning

Context

The colonization of restored river reaches by benthic macroinvertebrates and fish depends strongly on the proximity of source sites. Central European river networks have been fragmented over decades and populations of sensitive species have been eradicated from large parts of the catchments.

Objectives

Identification of remaining source sites (i.e., near-natural river stretches with populations of sensitive organisms) allows to protect them and reconnect them to degraded or restored stretches. We developed an approach to identify source sites of fish and benthic invertebrates and applied it to large parts of Germany.

Methods

The approach is based on identifying source sites from sampling data (5919 benthic invertebrate and 2584 fish monitoring sites) depending on the occurring number of sensitive species. For river stretches that have not been sampled we conducted statistical modeling with environmental data (e.g. land use, river habitat data) using boosted regression trees to identify source sites characterized by similar environmental conditions.

Results

The results are presented as maps on the level of the federal states. Statistical modeling allowed identification of stream type-specific environmental parameters and their thresholds. The maps allow a visual estimation of the recolonisation potential for river sections considered for restoration.

Conclusions

The results provide valuable insight into the perspective of restoration in different regions. For restoration planning we suggest application on a catchment level using environmental data with higher resolution and consideration of additional parameters (e.g. fine sediment input) in lowland regions.

     

Tree-grass coexistence in a flood-disturbed, semi-arid savanna system

The coexistence of trees and grasses in savanna ecosystems is a contentious phenomenon. Fire and herbivory disturbances are often cited as major structuring forces that create a sustainable tree–grass relationship. However, periodic flooding of savanna patches may also enable coexistence. The aim of this study was to investigate the effects of flood-disturbance on the recruitment patterns of Acacia karroo trees in a semi-arid savanna system in South Africa. We analysed the spatial coincidence of A. karroo seedlings with tussocks of the tall spiny grass Stipagrostis namaquensis in the riverbed and related herbivory intensity to spatial position. The data showed that A. karroo seedlings were significantly positively associated with S. namaquensis (Chi-square test, $ \chi_{1}^{2} = 4 5. 20 $ , n = 118, P < 0.001); A. karroo seedlings growing inside of tussocks experienced less browsing pressure than those growing in the floodplain (Kruskal–Wallis test, H = 11.90, n = 118, P < 0.01); and recruitment success of A. karroo trees was spatially discrete (K–S test, D = 0.78, n = 196, P < 0.01). We suggest that floods create an enemy-free zone, which S. namaquensis colonises and then facilitates successful A. karroo establishment. High levels of A. karroo recruitment in the riverbed may replenish the woodlands fringing the river, which appear to be sink areas for A. karroo seedlings. Thus, the interaction between disturbances at different spatial and temporal scales (flooding versus herbivory) seems to maintain the inherently unstable coexistence of tree and grass species in this ecosystem. These findings also suggested that flood disturbances alter the tree–grass relationship.     

Spatial scaling of core and dominant forest cover in the Upper Mississippi and Illinois River floodplains, USA

Different organisms respond to spatial structure in different terms and across different spatial scales. As a consequence, efforts to reverse habitat loss and fragmentation through strategic habitat restoration ought to account for the different habitat density and scale requirements of various taxonomic groups. Here, we estimated the local density of floodplain forest surrounding each of ~20 million 10-m forested pixels of the Upper Mississippi and Illinois River floodplains by using moving windows of multiple sizes (1?C100 ha). We further identified forest pixels that met two local density thresholds: ??core?? forest pixels were nested in a 100% (unfragmented) forested window and ??dominant?? forest pixels were those nested in a >60% forested window. Finally, we fit two scaling functions to declines in the proportion of forest cover meeting these criteria with increasing window length for 107 management-relevant focal areas: a power function (i.e. self-similar, fractal-like scaling) and an exponential decay function (fractal dimension depends on scale). The exponential decay function consistently explained more variation in changes to the proportion of forest meeting both the ??core?? and ??dominant?? criteria with increasing window length than did the power function, suggesting that elevation, soil type, hydrology, and human land use constrain these forest types to a limited range of scales. To examine these scales, we transformed the decay constants to measures of the distance at which the probability of forest meeting the ??core?? and ??dominant?? criteria was cut in half (S _1/2, m). S _1/2 for core forest was typically between ~55 and ~95 m depending on location along the river, indicating that core forest cover is restricted to extremely fine scales. In contrast, half of all dominant forest cover was lost at scales that were typically between ~525 and 750 m, but S _1/2 was as long as 1,800 m. S _1/2 is a simple measure that (1) condenses information derived from multi-scale analyses, (2) allows for comparisons of the amount of forest habitat available to species with different habitat density and scale requirements, and (3) can be used as an index of the spatial continuity of habitat types that do not scale fractally.     

Historical influence of man on the riparian dynamics of a fluvial landscape

Man's influence, over the last three centuries, has gradually influenced the dynamics of forest cover along the valley of the Garonne, a seventh order river in Southern France. The vegetation cover of the floodplain depends on topographical levels which govern the frequency and duration of submergence during flooding. Along the valley, forest patches vary from a continuous ribbon of riparian wood along the river to a mosaic of groves towards the upland terraces. In the floodplain, the forest dynamics are influenced by floods, appear to be reversible, and are subject to dominant allogenic processes. On the contrary, forest dynamics on the terraces, which are not influenced by floods, are irreversible and subjected to dominant autogenic processes. Since the end of the 17th century, the structure of riparian woods has been modified by navigation and agriculture leading to a fragmentation of forest cover in the floodplain. Modern agriculture and urbanization have accentuated these tendencies by modifying the hydrologic regime of the river. These historical changes result in a fragmentation of forest cover and a substitution of species in the riparian zone, the forest dynamics being still reversible in the floodplain.     

Beetle’s responses to edges in fragmented landscapes are driven by adjacent farmland use,season and cross-habitat movement

Context

Farming practices influence the degree of contrast between adjoining habitats, with consequences for biodiversity and species movement. Little is known, however, on insect community responses to different kinds of edges over time, and the extent of cross-habitat movement in agricultural landscapes.

Objective

To determine temporal changes in beetle responses to different farmland-woodland edges, and document cross-habitat movement.

Methods

We examined species richness, abundance, and movement across edges between remnant woodlands and four farmland uses (plantings, fallow, annual crops, woody debris applied over crops post-harvest) in southeastern Australia. We used directional pitfall traps to infer movement, and sampled at edges, and 20 and 200 m on both sides of edges, during spring and summer.

Results

Detritivore and predator abundance varied between seasons across the edge between woodlands and all farmlands, but seasonal differences were weaker for fallow-woodland and woody debris-woodland edges. Detritivores moved from farmlands towards woodlands, but not across fallow-woodlands and woody debris-woodlands edges during summer. During summer, predators showed short-range movement towards edges from all farmlands except plantings, and towards woody debris from woodlands. Edges showed temporally stable predator richness and higher herbivore richness than adjoining habitats.

Conclusions

Farmland use and season interactively affect beetle abundance across farmland-woodland edges. Woody debris can reduce seasonal fluctuations in beetle edge responses and increase permeability for cross-habitat movement, while plantings provide habitat during summer. Edges provide important resources for beetles in adjoining habitats, however, seasonal movement of predators specifically into edges may affect prey assemblages—a link requiring further study.