Context
In fragmented landscapes, edge influence (EI) can be an important driver of ecological change. Multiple edges can interact so that distance to the nearest edge is not an accurate predictor of ...EI, an issue referred to as ‘interactive EI’. This is especially important in conservation corridors, since their linear nature puts multiple edges in close proximity.
Objectives
We assess how corridor width, an important design variable in conservation corridors, influences EI on arthropod diversity.
Methods
Arthropods were sampled along the edges of grassland corridors of different widths, and from nearby protected areas (PAs) as reference. The influence of corridor width on edge-related change in arthropod diversity was assessed. This was done at the scale of single corridors, and in comparison to nearby PAs.
Results
Corridor width influences EI strength. This was apparent at the local scale, and for those species associated with the corridor interior. At the landscape scale, distance to the nearest edge was more important for the similarity of corridors to PAs than corridor width. This was driven by edge specialists rather than grassland interior species.
Conclusions
Interactive EI influences local edge responses, especially for species which avoid edges. Future assessments should incorporate processes operating across larger scales into edge responses. We show that there is much greater conservation value in larger corridors for grassland specialists than smaller corridors, and for a given area of set-aside conservation land, we support the establishment of a few wide corridors over many narrow corridors in production landscapes.
Understanding the effects of agricultural practices on farmland biodiversity requires a landscape perspective, as local-scale processes can be influenced by the structure of the surrounding ...landscape. We assess whether amount of natural vegetation in the landscape interacts with two local-scale variables, in-crop vegetation cover and farming approach (organic vs. integrated), to influence vineyard arthropods within the Cape Floristic Region. Responses were assessed for overall arthropods and three sub-categories based on arthropod species affinity to vineyards, natural vegetation (fynbos), or both systems. There were no significant interactions between local and landscape variables that affected the species richness of arthropods. However, there was a main effect of increased in-crop herbaceous vegetation that increased the species richness of overall arthropods and ubiquitous arthropods. Furthermore, interactions between the amount of natural vegetation and local-scale processes influenced composition of arthropod assemblages. Assemblages among integrated vineyards were similar in composition irrespective of landscape context, whereas they were dissimilar among organic vineyards in landscapes with different levels of natural vegetation. Our results suggest a relatively lower homogenising effect of organic farming than non-organic farming on landscape-scale biodiversity and that maintaining non-crop vegetation in vineyards benefits arthropod diversity. These findings emphasise the importance of considering the interplay between local management and the surrounding landscape in promoting biodiversity in a farming and conservation mosaic. This is especially important where landscapes vary greatly in complexity, as in many agricultural regions worldwide.
Complementarity is crucial when prioritizing sites for biodiversity conservation. Networks of conservation corridors (CCs) can contribute to regional representativeness by complementing biodiversity ...features included in existing protected areas (PAs). We ask whether criteria important for CC management and design are effective at prioritizing complementary sites, and how the consideration of species represented in PAs influence criteria performance. We focused on species turnover of generalist and specialist dragonflies across 88 riverine sites. Criteria assessed included site-level estimates of dragonfly species richness, estimates of local habitat quality and corridor width. Measures of local habitat quality were based on either dragonfly indicator species or proportion of alien vegetation. Results showed that CCs complement dragonfly diversity in PAs by contributing unrepresented generalist species. Of the criteria, corridor width was the most efficient at prioritizing complementary sites, while prioritization based on dragonfly indicator species or species richness underperformed. When aiming to prioritize CC sites that also complement sites situated in established PAs, wide corridors with low levels of alien vegetation should be favoured.
Context
Habitat edges are integral features of conservation corridors and can influence corridor function and effectiveness. Edge orientation is linked to corridor design and can shape edge responses ...by changing habitat conditions along edges as well as contrast between conserved habitats and transformed areas.
Objectives
We assess whether corridor orientation affects butterfly assemblages in conservation corridors. To do this, we investigate how edge orientation influences butterfly diversity and abundance along forestry plantation edges, and compare this to another important design variable, corridor width.
Methods
Butterflies were recorded along the sunny austral north- and shady austral south-orientated edges in grassland conservation corridors that dissect forestry plantations, as well as corridor interior sites. Species richness, abundance and similarity to interior sites were modelled using local habitat variables (ambient temperature, floral resources, and time of day), as well as corridor design variables (corridor width, orientation and an estimate of edge contrast influenced by orientation).
Results
Both edge orientation and corridor width were important for butterfly diversity along corridor edges. Wider corridors enhanced overall species richness and promoted similarity between edge and interior habitats. Concurrently, grassland specialist species preferred the sunnier edges (i.e., north facing in the southern hemisphere) while forest- specialists showed a preference for the shadier edges (south facing edges). Edge orientation influenced resident butterflies more strongly than transient butterflies and influenced specialists more strongly than generalists.
Conclusions
Corridor orientation and width are complementary design variables for butterfly conservation. Wide corridors at a variety of orientations benefit different subsets of the butterfly assemblage, and the whole corridor (including both edges) is important to consider in conservation planning to capture all biodiversity.
Plants often form the basis of conservation planning and management. The effectiveness of plant diversity as a surrogate for arthropod diversity was assessed in natural areas in the Kogelberg ...Biosphere Reserve, a floral endemism hotspot in the Cape Floristic Region (CFR), South Africa. Arthropods and plants were sampled across 30 topographically heterogeneous sites in a spatially nested design. The relationship between plants and arthropods were quantified in terms of species richness, assemblage variation, and assemblage turnover. The influence of arthropod trophic groups, habitat association, and spatial scale were also explored. Generalized dissimilarity modelling was used to investigate differential influence of explanatory groups (geology, disturbance, local site characteristics, refuge, mesoclimate, terrain) on arthropod and plant turnover. Congruence in assemblage variation was restricted to local scales, and only present between plants and those arthropods associated with the foliar component of the habitat. Weak congruence in species turnover was due to differences in the relative importance of explanatory groups, with different variables within each explanatory group being important, and similar variables predicting different turnover patterns. For both groups, variables related to geology and fire history were important for assemblage turnover. These variables are already incorporated in conservation planning and management for plant diversity across the CFR. Overall plant diversity was a weak surrogate for the arthropod groups included in this study, suggesting that as an alternative, environmental surrogates for arthropod diversity perform better.
Habitat loss threatens insect diversity globally. However, complementary vegetation types in remaining habitat increases opportunities for species survival. We assess the extent to which indigenous ...forest patches moderate the impact of exotic commercial afforestation on grassland butterflies. Butterflies were sampled in grassland along uncorrelated gradients of landscape-scale indigenous forest and plantation cover, while controlling for variation in local vegetation composition. We separately assessed responses by butterfly groups differing in habitat preference, larval diet, and mobility. There was no effect of landscape- or local-scale variables on species richness, but there was a strong interactive effect of forest and plantation cover on butterfly assemblage structure. The effect varied according to species traits. When forest cover was high, assemblages did not differ at different levels of plantation cover. However, plantation cover significantly influenced assemblage structure when forest cover was low. Grassland with limited forest cover in the protected area supported unique assemblages with high frequency of less mobile, specialized species with herbaceous larval host plants, whereas grassland with low forest cover near plantations had a prevalence of mobile, generalist species. A positive association between forest cover and butterflies with woody larval host plants suggests that indigenous forest patches improved the suitability of fragmented grassland for a subset of butterflies, emphasising the value of natural heterogeneity in transformed areas. However, certain butterfly traits associated with large, open grassland were under-represented in grassland between plantations, underscoring the importance of open areas in the broader landscape to conserve the full diversity of species.
Understanding how biodiversity responds to fine-scale heterogeneity improves our ability to predict larger-scale diversity patterns and informs local-scale conservation practices. This information is ...important in the design of conservation set-asides in commercial forestry landscapes in the Maputaland-Pondoland-Albany biodiversity hotspot, in South Africa. We assessed how soil arthropod assemblages vary among biotopes with varying degrees of contrast in forestry landscape mosaics in this hotspot. The biotopes included dry and hydromorphic grasslands, indigenous forests and pine plantations. Assemblages were highly segregated among all biotopes for overall arthropods, and for all the feeding guilds, namely predators, herbivores, detritivores, and omnivores. There was a high degree of assemblage dissimilarity between structurally contrasting biotopes (grasslands vs. wooded biotopes) and biotopes that differ in their degree of transformation (natural biotopes vs. plantations). Yet, there was an equally high level of assemblage dissimilarity between dry and hydromorphic grasslands, which are similar in structure and undergo the same disturbance regimes, which emphasises the responsiveness of soil fauna to fine-scale habitat heterogeneity. Different biotopes favoured different feeding guilds and each biotope had species strongly associated with it, highlighting the complementarity of the biotopes. All natural biotopes had relatively high species richness, diversity, and species turnover. The diversity and turnover in pine plantations was as high as in the natural areas, suggesting that plantation conditions may favour certain soil arthropods.
Implications for insect conservation
Current delineation of conservation areas in timber estates that prioritize biodiversity-rich dry grasslands, wetlands and indigenous forests, greatly benefit soil arthropods. Approaches that promote a mix of biotopes in conservation areas and having biotopes represented across different landscapes would further maximize local heterogeneity and landscape-scale soil arthropod biodiversity.
Context
Species occurrence in transformed areas (or matrix) can be enhanced by reducing the contrast in vegetation structure between the matrix and remnant natural patches. Contrast depends on both ...structural features of remnants and that of the matrix, which can be dynamic and determined by harvesting practices.
Objectives
We assess whether structurally equivalent vegetation, as determined by structural features of the matrix relative to that of remnants in the landscape, promotes species diversity and abundance in the matrix. Furthermore, we assess the relative importance of structurally equivalent vegetation compared to features of the immediate adjacent remnant patch.
Methods
Arthropods were sampled from 34 sites situated in alien forestry plantation blocks of different ages, dissected by corridors of natural grassland and/or closed canopy woody habitats. We analysed how arthropod assemblages within plantations were influenced by structural features of remnant vegetation in the landscape, and that of remnant patches directly adjacent.
Results
The amount of structurally equivalent vegetation at the landscape level promoted arthropod abundance and diversity within plantations and was more important than either the structural contrast or biotope type of the immediate adjacent patch for promoting diversity in the forestry blocks.
Conclusions
Landscapes composed of a mosaic of structurally distinct vegetation best contribute to promoting diversity within dynamic production areas. Harvesting practices that radically change the structural features of the entire plantation should be avoided. We recommend use of rotational harvesting, so creating a variety of plantation tree ages for improved arthropod spillover from both natural grassland and woody habitats.
To ensure integrity of protected areas we need to understand how species respond to anthropogenic borders. We investigate, from a metacommunity perspective, the direct and indirect mechanisms by ...which transformed areas affect distribution patterns of ground-living arthropod assemblages inhabiting an extensive protected area adjacent to fruit orchards in an important biosphere reserve. Arthropods and environmental variables were sampled along transects perpendicular to natural-orchard edges. Influence of distance from orchard boundary, degree of impermeability of the boundary, orchard habitat quality (local scale land-use intensity), and edge-induced changes in local environmental variables on arthropod species richness and composition in non-crop habitats were assessed. Arthropod groups were assessed in terms of habitat fidelity: species associated with natural habitat (stenotopic species), those within crop habitat (cultural species), and those showing no preference for either habitat (ubiquitous species). Spillover resulted in higher cultural species richness near edges, but not higher overall species richness. Environmental filtering was important for stenotopic species composition, which was influenced by edge-induced changes in environmental variables. Ubiquitous species composition was determined by orchard impermeability. Increased orchard habitat quality was associated with higher cultural and ubiquitous species richness. The effects of orchards on assemblages in natural habitats can be variable, but predictable when using species habitat specificity in conjunction with a metacommunity framework. High intensity orchards may act as sink habitats, especially for species that readily disperse between crop and natural habitats. Here we recommend that local buffer strips are > 85 m wide, which will reduce the influence of cultural species spillover on sensitive natural ecosystems.
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•We assessed parasitoid assemblages in vineyards and adjacent remnant vegetation.•Remnants maintained rich and distinct parasitoid assemblages in vineyard landscapes.•Parasitoid ...spillover between remnant natural vegetation and vineyards was limited.•Inhospitable surrounding vineyards isolated parasitoids in remnants.•Conserving remnants and improving matrix quality can maintain parasitoid diversity.
The maintenance of remnant natural vegetation in agricultural landscapes is an important component of conservation programmes that promote farmland sustainability. Demonstrating the biodiversity value of remnant vegetation can support conservation initiatives in production landscapes. We assessed the diversity and assemblage structure of hymenopteran parasitoids in fragments of native scrubland (fynbos) within vineyard landscapes in the Cape Floristic Region of South Africa. We also aimed to detect positive effects of adjacent fynbos on vineyard parasitoids, such as elevated diversity at vineyard edges adjoining fynbos or evidence of parasitoid spillover into vineyards. Fynbos remnants had significantly higher parasitoid abundance and richness than neighboring vineyards, and supported assemblages distinct from those within vineyards. Parasitoid diversity in vineyards was not influenced by distance to remnant vegetation. Additionally, evidence for spillover was limited, as there were abrupt changes in assemblage structure at fynbos/vineyard boundaries. Surrounding vineyards therefore seem to have an isolating effect on parasitoids in remnants. This emphasises the need to increase the permeability of the vineyard matrix. Yet, our results show that remnants are important for retaining parasitoid diversity and provide refugia for certain species within the disturbed agricultural environment. Approaches that combine natural remnant conservation with arthropod-friendly activities in vineyards would be an effective way to support diverse and functional parasitoid assemblages at the landscape scale. Conservation of this diversity will be crucial for maintaining long-term ecological resilience in agricultural landscapes.
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