Response of ground-dwelling beetles across logging coupe edges into streamside reserves

Streamside reserves can provide important habitat reservation in forest landscapes subject to logging. Depending on the width of streamside reserves, edge effects have the potential to compromise their effectiveness for terrestrial conservation, yet edge effects into riparian environments have rarely been assessed. It would be unwise to assume that edge effects act in the same way at streamside reserves as at the non-riparian edges of logging coupes, as interactions with riparian influences on beetles along the stream-upslope gradient might create unique edge conditions. In this study, we assess edge effects on ground dwelling beetles at four sites, using transects of pitfall traps across logging coupe edges into streamside reserves that have only been affected by logging on one side of the stream. Edge effects were found to extend further into streamside reserves in this study than into upslope habitat at the same sites from a concurrent study. Edge effects were site specific and appeared to extend as far as the stream in most cases (23–65 m). Comparison of beetle assemblage composition with adjacent unlogged streams supported the conclusion that beetles within 10 m of streams in streamside reserves were still responding to edge effects. These results suggest that streamside reserves might not contain habitat comparable with riparian areas away from the influences of nearby clearfelling, and wider reserves are recommended to maintain core habitat not compromised by edge effects.     

Spatio-temporal community structure of peat bog benthic desmids on a microscale

Significant spatial variation in species composition of microphytobenthos often occurs at scales of decimetres. This microscale variation is typically more connected with dispersal-related events than to environmental factors. In this study, 4 microscale transects were delimited at 4 temperate lowland peat bog localities to investigate spatial and temporal microscale variations in benthic desmids (Desmidiales, Viridiplantae). Significant spatial autocorrelation was detected in most of the transects taken 3 times, in September and December 2010 and March 2011. The relative abundance of species data produced more pronounced spatial patterns than the presence?Cabsence data. Spatial autocorrelation mostly decreased during the winter period, possibly due to meteorological disturbances, resulting in less spatially structured phytobenthic community in the March transects. In most cases, spatial distance accounted for a significant part of the variation in a community structure, even in analyses that controlled for the effects of environmental and temporal factors. This indicated that pure spatial factors should be considered important for structuring phytobenthic communities, even across a temporal time span of 6?months. The reduced data sets that included only 25?% of the most frequented species produced very similar patterns in spatial and temporal autocorrelation as the full data sets. Consequently, we concluded that microscale variation of benthic desmids may be sufficiently represented by dynamics of the common species.     

Dispersal of adult caddisflies (Trichoptera) into forests alongside three New Zealand streams

The abundance and taxonomic richness of adult caddisfly faunas were determined at varing distances (up to 200 m) away from three North Island, New Zealand, streams to help define appropriate forested riparian zone widths for adult aquatic insects. Adults were collected using sticky traps and ultraviolet light traps on four occasions over summer. Light traps were more effective at catching caddisflies than sticky traps, but both methods gave similar patterns of declining abundance and taxonomic richness with distance from the stream edge. Abundances of total caddisflies at 20 m were <21% of those caught at the stream edge for both trapping techniques. The same trends were evident for abundances of most common species in light traps, whereas bimodal peaks were evident with distance from the channel edge for percentage females of three common species. More than 30% of species caught at the stream edge was found in light traps at least 70 m into forest at all sites. A faster rate of decline for abundance than richness with distance away from the stream reflected the relatively large distances travelled by representatives of many species. Similar results from the three sites for numbers and species richness indicate that the main area of activity for adult Trichoptera in forested riparian zones was within 30 m of the stream edge at these sites.     

Vegetation on the edge: a gradient analysis of the riparian zone, Poerua River, New Zealand

Forest vegetation patterns alongside the Poerua River, south Westland, were studied to determine whether a distinct riparian community could be defined either immediately adjacent to the river, or out to the limit of overbank flooding. Ten randomly located 100 m transects were established perpendicular to the river at each of two sites. Ground cover of alluvial sediment indicated that annual overbank flooding occurred up to 20 m into the forest (the flood zone). No significant difference in vascular plant species richness was found between the flood zone and non-flood zone at either site, however a significant difference in species richness was found between sites, and this was attributed to recent disturbance at the edge of one site. Detrended correspondence analysis separated plots by site and indicated a gradient of species change from the river’s edge to the ends of the transects. There were inconsistent differences in the densities and/or basal areas of trees and shrubs between sites and zones. No distinct band of vegetation was recognizable as a riparian zone alongside the Poerua River. Instead, there was evidence that edge processes had influenced vegetation patterns on a gradient away from the river, fluvial processes had eroded into, and influenced the vegetated edge, and historical disturbance events had had strong effects on vascular plant community composition. The riparian zone incorporates the whole floodplain and environmental management needs to take this into consideration.     

Edge Effects Are Important in Supporting Beetle Biodiversity in a Gravel-Bed River Floodplain

Understanding complex, dynamic, and diverse ecosystems is essential for developing sound management and conservation strategies. Gravel-bed river floodplains are composed of an interlinked mosaic of aquatic and terrestrial habitats hosting a diverse, specialized, and endangered fauna. Therefore, they serve as excellent models to investigate the biodiversity of multiple ecotones and related edge effects. In this study, we investigated the abundance, composition, richness, and conservation status of beetle assemblages at varying sediment depth (0, 0.1, 0.6 and 1.1 m), distance from the channel (1, 5, 20, and 60–100 m, and 5 m within the riparian forest), and time of the year (February–November) across a 200 m-wide gravel bar at the near-natural Tagliamento River (Italy), to detect edge effects in four floodplain ecotones: aquatic-terrestrial, forest-active floodplain, sediment-air, and sediment-groundwater. We used conventional pitfall traps and novel tube traps to sample beetles comparably on the sediment surface and within the unsaturated sediments. We found a total of 308 beetle species (including 87 of conservation concern) that showed multiple, significant positive edge effects across the floodplain ecotones, mainly driven by spatial heterogeneity: Total and red list beetle abundance and richness peaked on the sediment surface, at channel margins, and at the edge of the riparian forest. All ecotones possessed edge/habitat specialists. Most red list species occurred on the sediment surface, including five species previously considered extinct – yet two of these species occurred in higher densities in the unsaturated sediments. Conservation and management efforts along gravel-bed rivers must therefore promote a dynamic flow and sediment regime to create and maintain habitat heterogeneity and ecotone diversity, which support a unique and high biodiversity.     

Anthropogenic land-use stress alters community concordance at the river-riparian interface

Organisms often respond in similar ways to environmental or spatial gradients, particularly at large spatial scales. Yet, while understanding these relationships is important for both basic and applied purposes, such as identifying surrogate taxa for conservation and monitoring purposes, patterns at finer scales and across ecotones are less certain. Our central aim was to explore patterns in community concordance at the river-riparian interface and examine whether concordance was decoupled by increasing anthropogenic stress (a gradient of local land-use intensity). We explored this at 15 sites over three years within the LTER site, Rhine-Main-Observatory, a low mountain river system in central Germany, assessing concordance between four organism groups: riparian spiders and carabid beetles, benthic macroinvertebrates, and combined aquatic macrophytes and riparian plants. This represented three different linkages: (1) predator–prey, (2) direct competition, and (3) habitat associations. While there were no correlations in richness patterns, multivariate community structure was highly concordant between all groups. Anthropogenic stress strongly reduced links between riparian spiders and carabid beetles, likely resulting from their shared resource requirements. However, increasing concordance generally occurred between plants and other groups, although inconsistently between the three groups. We posit that patterns may be resulting from two processes: (1) linkages between directly competing species decouple with increasing anthropogenic stress, and (2) stronger coupling may occur between habitat providers and dependent species when overall habitat complexity is reduced. Our results highlight the complex manner in which anthropogenic stress can influence ecosystem structure, particularly at small scales. Based on these complexities, we recommend considering the full suite of community data to adequately explore biodiversity patterns or when searching for surrogate taxa.     

Edge and land use effects on dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) in Brazilian cerrado vegetation

The Edge Influence is one of the most pervasive effects of habitat fragmentation, as many forest remnants in anthropogenic landscapes are within 100 m of edges. Forest remnants may also affect the surrounding anthropogenic matrix, possibly resulting in a matrix–edge–remnant diversity gradient for some species groups. We sampled dung beetles in 15 agricultural landscapes using pitfall traps placed along transects in matrix–edge–remnant gradients. The remnants were a native savanna-like vegetation, the cerrado, and the matrix was composed of three human-dominated environments (sugarcane, eucalyptus, pasture). More species were observed in cerrado remnants than in adjacent land uses. Dung beetles were also more abundant in the cerrado than in the landscape matrix of sugarcane and eucalypt, but not of pasture. Dung beetles were severely affected by anthropogenic land uses, and notwithstanding their high abundance in some land uses such as pasture, the species richness in these areas tended to be smaller than in the cerrado remnants. We also found that the influence of the edge was evident only for abundance, particularly in landscapes with a pasture matrix. However, this land use disrupts the species composition of communities, indicating that communities located in cerrado and pasture have a distinct species composition, and that both communities are affected by edge distance. Thus, anthropogenic land uses may severely affect dung beetles, and this impact can extend to communities located in cerrado remnants as well as to those in matrices, with possible consequences for ecological processes such as decomposition and nutrient cycling.     

Spatial and temporal patterns of carabid activity-density in cereals do not explain levels of predation on weed seeds

Seed predation is an important component of seed mortality of weeds in agro-ecosystems, but the agronomic use and management of this natural weed suppression is hampered by a lack of insight in the underlying ecological processes. In this paper, we investigate whether and how spatial and temporal variation in activity-density of granivorous ground beetles (Coleoptera: Carabidae) results in a corresponding pattern of seed predation. Activity-density of carabids was measured by using pitfall traps in two organic winter wheat fields from March to July 2004. Predation of seeds (Capsella bursa-pastoris, Lamium amplexicaule, Poa annua and Stellaria media) was assessed using seed cards at the same sites and times. As measured by pitfall traps, carabids were the dominant group of insects that had access to the seed cards. In the field, predation of the four different species of seed was in the order: C. bursa-pastoris>P. annua>S. media>L. amplexicaule; and this order of preference was confirmed in the laboratory using the dominant species of carabid. On average, seed predation was higher in the field interior compared to the edge, whereas catches of carabids were highest near the edge. Weeks with elevated seed predation did not concur with high activity-density of carabids. Thus, patterns of spatial and temporal variation in seed predation were not matched by similar patterns in the abundance of granivorous carabid beetles. The lack of correspondence is ascribed to effects of confounding factors, such as weather, the background density of seeds, the composition of the carabid community, and the phenology and physiological state of the beetles. Our results show that differences in seed loss among weed species may be predicted from laboratory trials on preference. However, predator activity-density, as measured in pitfall traps, is an insufficient predictor of seed predation over time and space within a field.     

Spatial autocorrelation analysis allows disentangling the balance between neutral and niche processes in metacommunities

One of the most popular approaches for investigating the roles of niche and neutral processes driving metacommunity patterns consists of partitioning variation in species data into environmental and spatial components. The logic is that the distance decay of similarity in communities is expected under neutral models. However, because environmental variation is often spatially structured, the decay could also be attributed to environmental factors that are missing from the analysis. Here, we use a spatial autocorrelation analysis protocol, previously developed to detect isolation‐by‐distance in allele frequencies, to evaluate patterns of species abundances under neutral dynamics. We show that this protocol can be linked with variation partitioning analyses. Moreover, in an attempt to test the neutral model, we derive three predictions to be applied both to original species abundances and to abundances predicted by a pure spatial model species abundances will be uncorrelated; Moran's I correlograms will reveal similar short‐distance autocorrelation patterns; an increasing degree of non‐neutrality will tend to generate patterns of correlation among abundances within groups of species with similar correlograms (i.e. within species with neutral and non‐neutral dynamics). We illustrate our protocol by analyzing spatial patterns in abundance of 28 terrestrially breeding anuran species from Central Amazonia. We recommend that researchers should investigate spatial autocorrelation patterns of abundances predicted by pure spatial models to identify similar patterns of spatial autocorrelation at short distances and lack of correlation between species abundances. Therefore, the hypothesis that spatial patterns in abundances are primarily due to pure neutral dynamics (rather than to missing spatiallystructured environmental factors) can be confirmed after taking environmental variables into account.     

Dung beetle communities as biological indicators of riparian forest widths in southern Brazil

Riparian forests provide important habitat for many wildlife species and are sensitive to landscape change. Among terrestrial invertebrates, dung beetles have been used to investigate the effects of environmental disturbances on forest structure and diversity. Since many studies demonstrated a negative response of dung beetle communities to increasing forest fragmentation, and that most dung beetle species had a more pronounced occurrence during warmest seasons, three hypotheses were tested: (1) Scarabaeinae richness, abundance, diversity and evenness are lower in thinner riparian zone widths than in wider widths during the warmest seasons; (2) Scarabaeinae richness and abundance are positively influenced by leaf litter coverage and height and canopy cover; and (3) Scarabaeinae composition varies with the reduction in riparian vegetation and among annual seasons. We selected four fragments with different riparian zone widths in three secondary streams in southern Brazil. In each fragment, four sampling periods were carried out seasonally between spring 2010 and winter 2011. We collected dung beetles using pitfall traps with two types of bait. We collected 1289 specimens distributed among 29 species. In spring and summer, dung beetle richness was higher in fragments with the widest riparian zone than in those with a thinner riparian zone, and it did not vary between fragments in fall and winter seasons. Dung beetle abundance did not differ among fragments with different riparian zone widths, but it was higher in spring and summer than fall and winter. Richness and abundance were positively influenced by leaf litter. While dung beetle diversity was higher in fragments with wider riparian zone widths than in those with thinner widths, the evenness was similar among fragments. Dung beetle composition differed between the fragments with the widest and thinnest riparian zones, and it also varied among the seasons. Our results suggest that decreased riparian zones affect negatively to dung beetle community structure in southern Brazil. Fragments with thinner riparian zones had lower beetle richness in warmest seasons and an altered community composition. In this sense, the dung beetles are potentially good indicators of riparian forest fragmentation since some species were indicators of a particular riparian zone width. From a conservation perspective, our results demonstrate that the new Brazilian Forest Code will greatly jeopardize not only the terrestrial and aquatic biodiversity of these ecosystems, but also countless other ecological functions.     

Flora and fauna assemblages vary with local topography in a subtropical eucalypt forest

Local‐scale spatial patterning (over hundreds of metres) in terrestrial assemblages was investigated by sampling a variety of organisms within a 400 ha eucalypt forest area in the lowlands of south‐east Queensland. Organisms were trees, shrubs, birds, insects extracted from the litter layer, and insects caught in pitfall traps. Each group was sampled using a standardized methodology, and the component taxa were counted and identified to a level commonly used in ecological studies of that organism – varying from species to order levels. Sites adjacent to drainage lines or ephemeral streams were biotically more similar to one another than they were to paired upslope sites 100–200 m distant and 15–35 m higher in altitude. This phenomenon occurred irrespective of the level of taxonomic resolution or type of organism. Within each taxonomic group, some components were mainly riparian, while others were more characteristic of upslope sites. Characteristically riparian taxa included trees in the genus Glochidion, the shrub genus Leptospermum, birds in the Pachycephalidae and Meliphagidae families, and litter invertebrates in the order Acarina. Upslope taxa included shrubs in the Rutaceae, birds in the Artamidae, and ants. Within the groups of trees, birds and litter invertebrates, more taxa were characteristic of riparian than upslope sites. Local scale biotic patterns were more strongly correlated with altitude than with measured soil characteristics; however, microtopographical differences would also be highly correlated with a large suite of covarying environmental features. The patterns of diversity and the implications for survey design and conservation are discussed.     

Effects of stream restorations on riparian mesohabitats,vegetation and carabid beetles

We investigated the effects of hydromorphological restoration measures (mainly the removal of bank fixations) on riparian mesohabitats, vegetation and carabid beetles by comparing 24 restored to nearby non-restored floodplain sections in Germany. Mesohabitats were recorded along ten equally-spaced transects, plant communities and riparian plant and carabid beetle species along three transects per section. Based on 18 indices including habitat and species diversity, taxonomic diversity and functional indices we compared the frequency and magnitude of changes following restoration, both for the overall dataset and for each site individually. Riparian habitat diversity doubled in restored sections compared to non-restored sections. The numbers of vegetation units and plant and carabid beetle species richness also doubled in restored sections, whereas changes in Shannon diversity were most pronounced for mesohabitats and riparian plants. Taxonomic diversity of carabid beetles decreased in restored sections reflecting post restoration dominance of riparian Bembidion species. Stress-tolerant pioneers of plant and especially carabid species benefit strongly from the re-establishment of open sand and gravel bars, while hygrophilous species, which also include non-riparian species, did not respond to restoration. We conclude that restoring river hydromorphology has almost generally positive effects on riparian habitats and riparian biodiversity. Riparian biota are thus well-suited indicators for the effects of hydromorphological restoration.     

Elevational Gradient in Species Richness Pattern of Epigaeic Beetles and Underlying Mechanisms at East Slope of Balang Mountain in Southwestern China

We report on the species richness patterns of epigaeic beetles (Coleoptera: Carabidae and Staphylinidae) along a subtropical elevational gradient of Balang Mountain, southwestern China. We tested the roles of environmental factors (e.g. temperature, area and litter cover) and direct biotic interactions (e.g. foods and antagonists) that shape elevational diversity gradients. Beetles were sampled at 19 sites using pitfall traps along the studied elevational gradient ranging from 1500 m–4000 m during the 2004 growing season. A total of 74416 specimens representing 260 species were recorded. Species richness of epigaeic beetles and two families showed unimodal patterns along the elevational gradient, peaking at mid-elevations (c. 2535 m), and the ranges of most beetle species were narrow along the gradient. The potential correlates of both species richness and environmental variables were examined using linear and second order polynomial regressions. The results showed that temperature, area and litter cover had strong explanatory power of beetle species richness for nearly all richness patterns, of beetles as a whole and of Carabidae and Staphylinidae, but the density of antagonists was associated with species richness of Carabidae only. Multiple regression analyses suggested that the three environmental factors combined contributed most to richness patterns for most taxa. The results suggest that environmental factors associated with temperature, area and habitat heterogeneity could account for most variation in richness pattern of epigaeic beetles. Additionally, the mid-elevation peaks and the small range size of most species indicate that conservation efforts should give attention to the entire gradient rather than just mid-elevations.     

Riparian zone as a main determinant of the structure of lizard assemblages in upland Amazonian forests

The use of lizards as model organisms in ecological studies is based on their success in occupying a great diversity of habitats, and some species are closely tied to the environment, which is disadvantaged by the legislation of several countries concerning land use. Our aim was to relate lizard species distribution patterns in rainforest environments to variation in environmental gradients, and provide ecologically based metrics for establishing buffer zones around streams. Lizards were sampled three times in 41 standardised transects near Manaus, Brazil, only in dry season, with Time Limited Visual Search associated with raking through leaf litter. We recorded 20 species from 10 families and used non‐metric multidimensional scaling to reduce the dimensionality of quantitative and qualitative compositions of species. Multiple linear regression models indicated that the environmental gradients distance to nearest stream, extent of canopy openness, vegetation density and slope did not significantly influence assemblage species distribution, with an indication of effect of litter depth. By means of piecewise linear regression, the use of riparian zone was estimated at ~190 m from quantitative species composition and ~211 m from qualitative species composition. Five species occurred only in the riparian zone. Our results suggest that conservation of the entire riparian lizard assemblage in Amazonian rainforest is likely to require protection of at least a 211 m buffer on either side of streams.     

Spatial autocorrelation as a tool for identifying the geographical patterns of aphid annual abundance

Abstract 1 A spatial autocorrelation analysis was undertaken to investigate the spatial structure of annual abundance for the pest aphid Myzus persicae collected in suction traps distributed across north‐west Europe. 2 The analysis was applied at two different scales. The Moran index was used to estimate the degree of spatial autocorrelation at all sites within the study area (global level). The contributions of each site to the global index were identified by the use of a local indicator of spatial autocorrelation (LISA). A hierarchical cluster analysis was undertaken to highlight differences between groups of resulting correlograms. 3 Similarity between traps was shown to occur over large geographical distances, suggesting an impact of phenomena such as climatic gradients or land use types. 4 The presence of outliers and zones of similarity (hot‐spots) and of dissimilarity (cold‐spots) were identified indicating a strong impact of local effects. 5 Several groups of traps characterized by similarities in their local spatial structure (correlograms, value of Moran's I_i) also had similar values for land use variables (the area occupied by agricultural zones, forest and sea). 6 It is concluded that trap data can provide information about Myzus persicae that is representative of large geographical areas. Thus, trap data can be used to estimate the aerial abundance of this species, even if the suction traps are not regularly and densely distributed.     

Influence of within-orchard trap placement on catch of codling moth (Lepidoptera: Tortricidae) in sex pheromone-treated orchards

The influence of trap placement on catches of codling moth, Cydia pomonella L., was examined in a series of studies conducted in orchards treated with Isomate-C Plus sex pheromone dispensers. Mark-recapture tests with sterilized moths released along the interface of pairs of treated and untreated apple and pear plots found that significantly more male but not female moths were recaptured on interception traps placed in the treated plots. In a second test, significantly higher numbers of wild male and female moths were caught on interception traps placed in treated versus untreated plots within a heavily infested orchard. The highest numbers of male moths were caught on traps placed along the interior edge of the treated plots. Trap position had no influence on the captures of female moths. In a third test, north-south transects of sex pheromone-baited traps were placed through adjacent treated and untreated plots that received a uniform release of sterilized moths. Traps on the upwind edge of the treated plots caught similar numbers of moths as traps upwind from the treated plots. Moth catch was significantly reduced at all other locations inside versus outside of the treated plots, including traps placed on the downwind edge of the treated plot. In a fourth test, five apple orchards were monitored with groups of sex pheromone-baited traps placed either on the border or at three distances inside the orchards. The highest moth counts were in traps placed at the border, and the lowest moth counts were in traps placed 30 and 50 m from the border. In a fifth test, the proportion of traps failing to catch any moths despite the occurrence of local fruit injury was significantly higher in traps placed 50 versus 25 m from the border. The implications provided by these data for designing an effective monitoring program for codling moth in sex pheromone-treated orchards are discussed.     

Changes in carabid beetle diversity within a fragmented agricultural landscape

The distribution of carabid and cicindelid (Coleoptera: Carabidae) beetles in five distinct habitats (riparian, mature orchard, pine windbreak, young orchard, natural veld), within Tambuti Citrus Estate (Swaziland) was examined by pitfall trapping over 18 months. Habitats with high vegetation and litter cover had the highest species diversity and larger specimens, e.g. riparian border and pine windbreak, while the lowest diversity was observed in intensively managed mature citrus orchards. While species such as Tefflus delagorguei Guérin occurred in all the habitats sampled, certain species illustrated habitat specificity; e.g. Dromica ambitiosa Péringuey was observed only in the pine windbreaks while Haplotrachelus sp. Chaudoir occurred mainly in the vegetated riparian and natural veld habitats. Four unidentified carabid beetles were exclusive to the riparian border habitat. This habitat was the only one with a distinct assemblage of species in the agricultural mosaic studied. Multivariate analyses were used to assess the role of soil and environmental variables in relation to the ground beetle diversity within the agricultural mosaic studied.     

Edge effects on ground beetles at the woodlot–field interface are short‐range and asymmetrical

• 1 Boundaries between woodlots and agricultural habitats are numerous in temperate agricultural landscapes and influence ecological processes in both woodlots and agricultural habitats.
• 2 We aimed to determine how far the species assemblage of ground beetles in woodlot and open habitats was influenced by the presence of the woodlot–field boundary.
• 3 We studied the distribution of ground beetles on both sides of the boundaries of four woodlots along transects of pitfall traps (n = 140). The depth of edge influence (i.e. the distance from the boundary at which the presence of the boundary has no more significant influence) on the species assemblage of ground beetles in each woodlot and in each agricultural habitat was determined with nonlinear canonical analysis of principal coordinates, an ordination method that is followed by nonlinear regression of the principal coordinates on distance from the boundary.
• 4 The depth of edge influence on the species assemblages of ground beetles was asymmetrical relative to the boundary: it was generally higher and had higher variability in open habitats (14.4 ± 12.3 m) than in woodlots (4.9 ± 2.3 m). Species assemblages of ground beetles in edges were a mix between both adjacent species assemblages. Edge effects in woodlots were deeper in the woodlots exhibiting a deeper penetration of open habitat species. Symmetrically, edge effects in open habitat were deeper in the open habitats with a deeper diffusion of forest species into the open habitat.
• 5 Forest ground beetles were not threatened by edge effects. Rather, edge effects are likely to benefit agriculture, mostly through the dispersal of predatory forest species into agricultural fields.

     

Even the Smallest Non-Crop Habitat Islands Could Be Beneficial: Distribution of Carabid Beetles and Spiders in Agricultural Landscape

Carabid beetles and ground-dwelling spiders inhabiting agroecosystems are beneficial organisms with a potential to control pest species. Intensification of agricultural management and reduction of areas covered by non-crop vegetation during recent decades in some areas has led to many potentially serious environmental problems including a decline in the diversity and abundance of beneficial arthropods in agricultural landscapes. This study investigated carabid beetle and spider assemblages in non-crop habitat islands of various sizes (50 to 18,000 square metres) within one large field, as well as the arable land within the field, using pitfall traps in two consecutive sampling periods (spring to early summer and peak summer). The non-crop habitat islands situated inside arable land hosted many unique ground-dwelling arthropod species that were not present within the surrounding arable land. Even the smallest non-crop habitat islands with areas of tens of square metres were inhabited by assemblages substantially different from these inhabiting arable land and thus enhanced the biodiversity of agricultural landscapes. The non-crop habitat area substantially affected the activity density, recorded species richness and recorded species composition of carabid and ground-dwelling spider assemblages; however, the effects were weakened when species specialised to non-crop habitats species were analysed separately. Interestingly, recorded species richness of spiders increased with non-crop habitat area, whereas recorded species richness of carabid beetles exhibited an opposite trend. There was substantial temporal variation in the spatial distribution of ground-dwelling arthropods, and contrasting patterns were observed for particular taxa (carabid beetles and spiders). In general, local environmental conditions (i.e., non-crop habitat island tree cover, shrub cover, grass cover and litter depth) were better determinants of arthropod assemblages than non-crop habitat island size, indicating that the creation of quite small but diversified (e.g., differing in vegetation cover) non-crop habitat islands could be the most efficient tool for the maintenance and enhancement of diversity of ground-dwelling carabids and spiders in agricultural landscapes.     

边缘效应对卧龙自然保护区森林-草地群落交错带地表甲虫多样性的影响

本文研究了卧龙国家自然保护区地表甲虫群落在天然落叶阔叶林森林边缘与森林内部和周围草地间多样性差异,在科级水平上探讨边缘效应对地表甲虫群落的影响。调查共设5个重复样带（间距大于500 m）;每个样带以距离梯度（25 m）的方式设置样点,分别由边缘深入到森林内部和草地中央100 m,共设45个样点,通过巴氏罐诱法调查地表甲虫群落组成和季节变化。本研究采集甲虫标本4 736 号,隶属于28个科,步甲科、隐翅虫科和叩甲科分别占总数的49.5%、23.5%和13.0%,共同构成本研究地区地表甲虫的优势类群。甲虫的个体数量从森林内部、边缘到周围草地依次降低,而科多样性和均匀度则依次增高,都达到了显著差异。主坐标分析（PCoA）排序表明,森林内部和周围草地间的地表甲虫群落组成差异较大;而森林边缘的群落组成与两者都有较高程度的相似性,反映了森林边缘的地表甲虫群落已经与森林内部的群落组成发生明显分化,除了森林物种成分外,还包含了若干从周围草地环境扩散来的物种成分。从季节动态看,森林边缘和森林内部在丰富度和个体数量的季节变化曲线方面相似性更高;捕食类和腐食类地表甲虫的季节变化在森林内部和边缘相似性更高,而植食类则在森林边缘和草地的相似性更高。多元回归分析表明,枯落物覆盖率是影响地表甲虫科多样性和均匀度的决定因素,枯落物厚度和林冠层覆盖率是决定甲虫个体数量分布的重要因素。以上结果表明,在科级水平上,地表甲虫群落在天然落叶阔叶林边缘已经与森林内部生境发生分化,而且正在加剧的森林片断化进程将会产生更多的森林边缘,因此,保留大面积的天然落叶阔叶林免受破坏和干扰是保护地表甲虫多样性的必要措施。