Dynamic effects of ground-layer plant communities on beetles in a fragmented farming landscape

Vegetation effects on arthropods are well recognized, but it is unclear how different vegetation attributes might influence arthropod assemblages across mixed-agricultural landscapes. Understanding how plant communities influence arthropods under different habitat and seasonal contexts can identify vegetation management options for arthropod biodiversity. We examined relationships between vegetation structure, plant species richness and plant species composition, and the diversity and composition of beetles in different habitats and time periods. We asked: (1) What is the relative importance of plant species richness, vegetation structure and plant composition in explaining beetle species richness, activity-density and composition? (2) How do plant-beetle relationships vary between different habitats over time? We sampled beetles using pitfall traps and surveyed vegetation in three habitats (woodland, farmland, their edges) during peak crop growth in spring and post-harvest in summer. Plant composition better predicted beetle composition than vegetation structure. Both plant richness and vegetation structure significantly and positively affected beetle activity-density. The influence of all vegetation attributes often varied in strength and direction between habitats and seasons for all trophic groups. The variable nature of plant-beetle relationships suggests that vegetation management could be targeted at specific habitats and time periods to maximize positive outcomes for beetle diversity. In particular, management that promotes plant richness at edges, and promotes herbaceous cover during summer, can support beetle diversity. Conserving ground cover in all habitats may improve activity-density of all beetle trophic groups. The impacts of existing weed control strategies in Australian crop margins on arthropod biodiversity require further study.     

桃园捕食性节肢动物群落结构及动态研究

【目的】探讨桃园捕食性节肢动物群落特征、结构组成及动态规律,为桃园害虫防治提供依据。【方法】在西北农林科技大学实验站选择树龄5~6年的桃园为调查对象,系统调查园内节肢动物群落的种类和数量,测定群落的相对丰富度、多样性指数(H')、均匀度指数(E)及优势集中性指数(C)等指标,研究园内捕食性节肢动物群落的变化规律。【结果】桃园捕食性节肢动物群落的多样性指数和均匀度指数表现为高-低-高-低的趋势;群落优势度(B)与优势集中性指数呈现低-高-低趋势。食蚜蝇、蜘蛛、瓢虫、步甲和草蛉是桃园主要捕食性节肢动物亚群落。大灰食蚜蝇Metasyrphus corollae和黑带食蚜蝇Episyrphus balteata是食蚜蝇亚群落的优势种群,5月中旬至6月下旬是其发生高峰期;龟纹瓢虫Propylaea japonica是瓢虫亚群落的优势种群,5月中旬至7月下旬是其发生高峰期,随后数量维持在较低水平;龟纹瓢虫鼎斑变型和锚斑变型是桃园最常见的色斑变型,分别占49.6%和29%;蜘蛛亚群落主要包括皿蛛、蟹蛛和球蛛类群,5月上中旬、8月中下旬和10月中旬是其发生高峰期;步甲亚群落的发生高峰期为5月上旬至6月下旬,随后维持在较低的水平;中华草蛉Chrysoperla sinica为草蛉亚群落的优势种群,6月上旬至8月上旬是其发生高峰期。【结论】桃园捕食性节肢动物主要包括捕食性蜘蛛、食蚜蝇、捕食性瓢虫、步甲和草蛉5个亚群落,不同天敌亚群落的结构特征随着季节和气温的变化而相互演替,共同发挥控制害虫的作用。     

A quarter of a century succession of epigaeic beetle assemblages in remnant habitats in an urbanized matrix (Coleoptera, Carabidae)

We studied the long-term (23-24 years) species turnover and succession of epigaeic beetle assemblages (Coleoptera: Carabidae, incl. Cicindelinae) in three remnant habitats [cottonwood (Populus spp.) and oak (Quercus spp.) stands, and old fields] that are embedded within highly urbanized areas in central Minnesota. A total of 9,710 beetle individuals belonging to 98 species were caught in three sampling years: 1980, 1981 and 2005 in pitfall traps in identical locations within each habitat. Results indicate that there were 2-3 times greater trap catches in 2005 than in 1980 (cottonwood and oak stands, and old fields) and 1.4-1.7 times greater species diversity of beetles in 2005 than in the 1980-1981 suggesting increased habitat association by beetles over time. Although there were no significant differences in catches between 2005 and 1981 (only cottonwood stands and old fields), there was a trend where more beetles were caught in 2005. At the species-level, 10 times more of an open-habitat carabid species, Cyclotrachelus sodalis sodalis LeConte, was caught in 2005 than in 1980. However, trap catches of five other abundant carabid species [Pterostichus novus Straneo, Platynus decentis (Say), Platynus mutus (Say), Calathus gregarius (Say), and Poecilus lucublandus lucublandus (Say)] did not change indicating population stability of some beetle species. These remnant habitats were increasingly colonized by exotic carabid species as Carabus granulatus granulatus Linneaus, Clivina fossor (Linneaus) and Platynus melanarius (Illiger), that were trapped for the first time in 2005. Species composition of epigaeic beetles was quite distinct in 2005 from 1980 with 39 species reported for the first time in 2005, indicating a high turnover of assemblages. At the habitat-level, greatest species diversity was in cottonwood stands and lowest was in old fields, and all habitat types in 2005 diverged from those in 1980s, but not cottonwood stands in 1981. As our sampled areas are among some of the last remnants of the original oak savanna habitats in central Minnesota, we hypothesize that conservation of these sites may be critical to maintaining epigaeic beetle assemblages under increased urbanization pressure.     

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.     

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.     

Effects of ecological flooding on the temporal and spatial dynamics of carabid beetles (Coleoptera, Carabidae) and springtails (Collembola) in a polder habitat

Within the scope of the Integrated Rhine Program an ecological flood gate and channel was inserted into the polder "Ingelheim" to enhance animal and plant diversity. In 2008, carabid beetles and springtails were collected, using pitfall traps, to measure the effects of ecological flooding and a strong precipitation event at a flood-disturbed and a dry location in this area. At both localities, xerophilic and mesophilic carabid beetle species were dominant throughout the study period. The total number of individuals of hygrophilic species was comparatively constant, while species number increased, partly due to the changed moisture conditions caused by ecological flooding and strong precipitation. Carabid beetle diversity and evenness decreased marginally when ecological flooding was absent. Springtails represent a less mobile arthropod order, and as such the impact of ecological flooding was stronger. An increase in both numbers of species and individuals of hygrophilic and hygrotolerant species occurred in the flood-disturbed location after ecological flooding. After the sites at both locations had dried, the number of individuals belonging to these species declined rapidly. In contrast to carabid species, the strong precipitation event showed no influence on hygrophilic springtail species. Thus, collembolan diversity and evenness decreased markedly in the absence of flooding. We showed that ecological flooding has an influence on the spatial and temporal dynamics of different arthropod groups that inhabit the polder "Ingelheim". These findings demonstrate the importance of using different arthropod groups as bioindicators in determining the ecological value of a particular polder design.     

Influence of tree species and soil properties on ground beetle (Coleoptera: Carabidae) communities

Although Carabidae is among the best-studied families of beetles in Europe from the faunistic point of view, there is still a lack of available information on the ecological requirements of the particular carabid species. The habitat preferences that determine the distribution of species are largely influenced by habitat structure and microclimate. In addition to other factors, these habitat parameters are influenced by the nature of the vegetation. Therefore, our study investigated the influence of tree species on carabid beetle communities. We conducted the research at 9 stands in the Borová Hora Arboretum (Zvolen, Central Slovakia). Each studied site represents a monoculture of one of nine tree species. At each site, some soil and leaf litter attributes (pH, conductivity, and content of H, C, N and P) were evaluated. Ground beetles were collected by pitfall trapping during the vegetation periods in 2008–2011. In total, 3012 individuals of 29 species were obtained. Significant differences in the total dynamic activity and species richness of the carabid beetle communities among the compared forest stands were revealed. The results of the research confirmed statistically significant relationships among 1) the soil conductivity and both the richness and Shannon diversity of the ground beetle communities, 2) the litter and soil N content and richness, the Shannon diversity and the species composition of the ground beetle communities. The Shannon diversity and richness were negatively related to the soil conductivity and positively related with the N content. Our research showed that dominant tree species indirectly influence diversity and composition of carabid communities via the soil properties.     

The relative effects of local management and landscape context on weed seed predation and carabid functional groups

Farmland biodiversity and its associated ecosystem services are affected by agricultural activities at multiple spatial scales. Among these services, the regulation of weeds by invertebrate seed predators has received much attention recently but little is known about the relative effect of local management and landscape context of fields on this process. We monitored seed predation on four common weed species and carabid communities in 28 winter-cereals fields during five consecutive weeks in spring 2010. These fields were situated in contrasted landscape contexts and varied in terms of intensity of pesticide treatments and soil tillage regimes. Weed seed predation was strongly and positively related to the Shannon diversity of (strictly) granivorous carabids and to the activity–density of omnivorous carabids but negatively to the richness of omnivorous carabids. Weed seed predation and granivore diversity were positively related to landscape diversity and the proportion cover of temporary grassland within a 1000 m radius around focal fields and were negatively affected by the intensity of local pesticide treatments. No-till systems sheltered higher diversity of granivorous carabids but did not show higher seed predation rates. We showed that landscape composition factors had a higher relative influence than local practices factors on weed seed predation service. Consequently, weed management strategies should not only consider the management of single fields but also the surrounding landscape to preserve carabid biodiversity and enhance weed seed predation service.     

Direct effects of tillage on the activity density of ground beetle (Coleoptera: Carabidae) weed seed predators

Ground beetles are well known as beneficial organisms in agroecosystems, contributing to the predation of a wide range of animal pests and weed seeds. Tillage has generally been shown to have a negative effect on ground beetles, but it is not known whether this is because of direct mortality or the result of indirect losses resulting from dispersal caused by habitat deterioration. In 2005, field experiments measured direct, tillage-induced mortality, of four carabid weed seed predators, Harpalus rufipes DeGeer, Agonum muelleri Herbst, Anisodactylus merula Germar, and Amara cupreolata Putzeys, and one arthropod predator, Pterostichus melanarius Illiger, common to agroecosystems in the northeastern United States. Three tillage treatments (moldboard plow, chisel plow, and rotary tillage) were compared with undisturbed controls at two sites (Stillwater and Presque Isle) and at two dates (July and August) in Maine. Carabid activity density after disturbance was measured using fenced pitfall traps installed immediately after tillage to remove any effects of dispersal. Rotary tillage and moldboard plowing reduced weed seed predator activity density 52 and 54%, respectively. Carabid activity density after chisel plowing was similar to the undisturbed control. This trend was true for each of the weed seed predator species studied. However, activity density of the arthropod predator P. melanarius was reduced by all tillage types, indicating a greater sensitivity to tillage than the four weed seed predator species. These results confirm the need to consider both direct and indirect effects of management in studies of invertebrate seed predators.     

Assessing human impact on fen biodiversity: effects of different management regimes on butterfly, grasshopper, and carabid beetle assemblages

Fens and concomitantly the associated species assemblages have undergone dramatic declines in recent decades. Given that many remaining or restored fens are currently lying fallow, an important question is which management regime, if any, is most effective in preserving fen biodiversity. Against this background we here investigate the effects of five management regimes (intensive grassland, moist meadows, summer harvested sites, winter harvested sites, fallows) on three insect taxa (butterflies, grasshoppers, carabid beetles) in riverine fens in north-eastern Germany. Butterflies and grasshoppers showed highest species numbers, diversity and numbers of threatened species on moist meadows and were detrimentally affected by high vegetation. In contrast, ground dwelling carabid beetles were less strongly affected by different management regimes, but responded very sensitive to drainage. Winter harvested sites and fallows seemed to be particularly beneficial to carabid beetles. Overall, drained, intensive grassland was not suitable for preserving fen-specific communities, while extensively managed moist meadows harboured overall the highest numbers of threatened species. We conclude that in terms of management maintaining high water tables is most important. Furthermore, some management seems necessary to maintain stands with lower vegetation turf for associated species. However, care is needed to also maintain fallows and to consider the specific demands of some highly endangered, management-sensitive species.     

Comparative analysis of two edaphic zoocoenoses (Oribatid mites and Carabid beetles) in five habitats of the ‘Pietraporciana’ and ‘Lucciolabella’ Nature Reserves (Orcia Valley,central Italy)

Oribatid mite and Carabid beetle communities were investigated at five sites in the ‘Pietraporciana’ and ‘Lucciolabella’ Nature Reserves (central Italy). In this part of southern Tuscany many attempts have been made to encourage the regeneration of native habitats and to preserve existing ones. Human-induced changes in the original forest landscape have had a direct impact on mite and carabid populations. Significant differences in species diversity and abundance among different sites were revealed throughout the sampling period. Species richness, abundance and diversity of oribatid mites decrease from woodland sites to open habitats where evenness was high. There is an inverse trend between the number of species and richness of carabid beetles and those of oribatid mites. Canonical correspondence analysis (CCA) of oribatid and carabid beetle compositions discriminated the sites, demonstrating how even small areas with different vegetation, composition, structure, environment and microclimate were characterised by distinct edaphic populations.     

Habitat structure and neighbor linear features influence more carabid functional diversity in olive groves than the farming system

The effects of land-use management and environmental features at different scales on carabid beetle diversity and trait structure were assessed across olive groves in northeastern Portugal. We selected organic and integrated olive groves that were distinct in terms of specific management practices, local linear features and landscape configurations. Besides the management intensification levels, differences in carabid diversity and community traits were mainly due to local habitat and ecological linear structures at a finer spatial scale. Carabid community traits related to disturbance, namely traits of body size and species dispersal ability, responded to land-use intensity and particular olive grove features were influencing diversity patterns. Within the olive grove patches, larger and brachypterous species were associated to plots with more dense vegetation cover while macropterous and small-sized species were more associated to open areas. Also, larger carabid species benefitted from higher patch size heterogeneity within the landscape mosaics. Our findings indicate that the effects of farming system is contingent on the specific management practices, local and linear features present in agroecosystems such as olive groves. Particularly, the influence of local features on carabid diversity patterns and community traits linked to dispersal and movement may be crucial in maintaining pest control at a landscape scale.     

Declines in a ground-dwelling arthropod community during an invasion by Sahara mustard (Brassica tournefortii) in aeolian sand habitats

Sahara Mustard (Brassica tournefortii; hereafter mustard), an exotic plant species, has invaded habitats throughout the arid southwestern United States. Mustard has reached high densities across aeolian sand habitats of southwestern deserts, including five distinct sand habitats in the eastern Coachella Valley, California. We examined trends in ground-dwelling arthropod community structure concurrent with mustard invasion in 90 plots within those habitats from 2003 to 2011 (n = 773 plot·years). We expected arthropod communities to respond negatively to mustard invasion because previous work documented significant negative impacts of mustard on diversity and biomass of native plants, the primary resource base for many of the arthropods. Arthropod abundance and species richness declined during the study period while mustard cover increased, and arthropod metrics were negatively related to mustard cover across all plots. When controlling for non-target environmental correlates (e.g. perennial frequency and precipitation) and for potential factors that we suspected of mediating mustard effects (e.g. native cover and sand compaction), negative relationships with mustard remained statistically supported. Nevertheless, arthropod richness’s relationship decreased slightly in strength and significance suggesting that mechanistic pathways may be both direct (via habitat structure) and indirect (via native cover suppression and sand compaction). However, mechanistic pathways for mustard effects, particularly on arthropod abundance, remain unclear. Most arthropod taxa, including most detritivores, decreased through time and were negatively related to mustard cover. In contrast, many predators were positively related to mustard. In total, our study provides substantial evidence for a negative effect of Sahara mustard on the structure of a ground-dwelling arthropod community.     

Differences in ground beetles (Coleoptera: Carabidae) of original and reconstructed tallgrass prairies in northeastern Iowa, USA, and impact of 3-year spring burn cycles

Ground beetle assemblages were monitored at four tallgrass prairie sites burned on 3-year cycles in northeastern Iowa. The objectives of this study were to quantify differences in carabid communities between original and reconstructed tallgrass prairies, and to determine the responses of ground beetles to 3-year cycles of early spring fire commonly used to manage tallgrass prairies. Using pitfall traps, ground beetle assemblages in two original and two reconstructed tallgrass prairies were compared between 1994 and 1998, where beetles were sampled annually (0-, 1-, and 2-year post-fire conditions) from plots burned every 3 years. When burned, the greatest abundance, activity density, and species richness of carabid beetles occurred the year immediately following a spring burn, with abundance declining steadily with increased time since burning. Overall ground beetle diversity as determined by Shannon's diversity index was greatest in original tallgrass prairies several years after a fire. Some species of ground beetles were found only in original prairies, while others were found primarily in reconstructed prairie. Similarly, some species were more abundant the year immediately following a burn, while others were found in greater abundance with increased time since fire. NMS ordination and indicator species analysis clearly show differences in carabid species between original and reconstructed tallgrass prairies, but did not show differences among burn treatments.     

Spatial and temporal variation in natural enemy assemblages on Maryland native plant species

Habitat manipulation is a branch of conservation biological control in which vegetation complexity and diversity are increased in managed landscapes to provide food and other resources for arthropod natural enemies. This is often achieved by maintaining noncrop plant material such as flowering strips and beetle banks that provide natural enemies with nectar and pollen, alternative prey, shelter from disturbance, and overwintering sites. In most cases, plant material used in habitat manipulation programs is not native to the area in which it is planted. Using native plant species in conservation biological control could serve a dual function of suppressing pest arthropod outbreaks and promoting other valuable ecosystem services associated with native plant communities. We evaluated 10 plant species native to Maryland for their attractiveness to foliar and ground-dwelling natural enemies. Plants that showed particular promise were Monarda punctata, Pycnanthemum tenuifolium, and Eupatorium hyssopifolium, which generally harbored the greatest abundance of foliar predators and parasitoids, although abundance varied over time. Among ground-dwelling natural enemies, total predator and parasitoid abundance differed between plant species, but carabid and spider abundance did not. Matching certain plant species and their allied natural enemies with specific pest complexes may be enhanced by identifying the composition of natural enemy assemblages at different times of year and in both foliar and ground habitat strata.     

Arthropod Diversity and Community Structure in Relation to Land Use in the Mekong Delta, Vietnam

Declining biodiversity in agro-ecosystems, caused by intensification of production or expansion of monocultures, is associated with the emergence of agricultural pests. Understanding how land-use and management control crop-associated biodiversity is, therefore, one of the key steps towards the prediction and maintenance of natural pest-control. Here we report on relationships between land-use variables and arthropod community attributes (for example, species diversity, abundance and guild structure) across a diversification gradient in a rice-dominated landscape in the Mekong delta, Vietnam. We show that rice habitats contained the most diverse arthropod communities, compared with other uncultivated and cultivated land-use types. In addition, arthropod species density and Simpson’s diversity in flower, vegetable and fruit habitats was positively related to rice cover in the local landscape. However, across the landscape as a whole, reduction in heterogeneity and the amount of uncultivated cover was associated, generally, with a loss of diversity. Furthermore, arthropod species density in tillering and flowering stages of rice was positively related to crop and vegetation richness, respectively, in the local landscape. Differential effects on feeding guilds were also observed in rice-associated communities with the proportional abundance of predators increasing and the proportional abundance of detritivores decreasing with increased landscape rice cover. Thus, we identify a range of rather complex, sometimes contradictory patterns concerning the impact of rice cover and landscape heterogeneity on arthropod community attributes. Importantly, we conclude that that land-use change associated with expansion of monoculture rice need not automatically impact diversity and functioning of the arthropod community.     

Effects of landscape structure and land-use intensity on similarity of plant and animal communities

Aim Species richness in itself is not always sufficient to evaluate land management strategies for nature conservation. The exchange of species between local communities may be affected by landscape structure and land‐use intensity. Thus, species turnover, and its inverse, community similarity, may be useful measures of landscape integrity from a diversity perspective. Location A European transect from France to Estonia. Methods We measured the similarity of plant, bird, wild bee, true bug, carabid beetle, hoverfly and spider communities sampled along gradients in landscape composition (e.g. total availability of semi‐natural habitat), landscape configuration (e.g. fragmentation) and land‐use intensity (e.g. pesticide loads). Results Total availability of semi‐natural habitats had little effect on community similarity, except for bird communities, which were more homogeneous in more natural landscapes. Bee communities, in contrast, were less similar in landscapes with higher percentages of semi‐natural habitats. Increased landscape fragmentation decreased similarity of true bug communities, while plant communities showed a nonlinear, U‐shaped response. More intense land use, specifically increased pesticide burden, led to a homogenization of bee, bug and spider communities within sites. In these cases, habitat fragmentation interacted with pesticide load. Hoverfly and carabid beetle community similarity was differentially affected by higher pesticide levels: for carabid beetles similarity decreased, while for hoverflies we observed a U‐shaped relationship. Main conclusions Our study demonstrates the effects of landscape composition, configuration and land‐use intensity on the similarity of communities. It indicates reduced exchange of species between communities in landscapes dominated by agricultural activities. Taxonomic groups differed in their responses to environmental drivers and using but one group as an indicator for ‘biodiversity’ as such would thus not be advisable.     

Weed vegetation of arable land in Central Europe: Gradients of diversity and species composition

Question: What are the main broad‐scale spatial and temporal gradients in species composition of arable weed communities and what are their underlying environmental variables? Location: Czech Republic and Slovakia. Methods: A selection of 2653 geographically stratified relevés sampled between 1954–2003 was analysed with direct and indirect ordination, regression analysis and analysis of beta diversity. Results: Major changes in weed species composition were associated with a complex gradient of increasing altitude and precipitation and decreasing temperature and base status of the soils. The proportion of hemicryptophytes increased, therophytes and alien species decreased, species richness increased and beta diversity decreased with increasing altitude. The second most important gradient of weed species composition was associated with seasonal changes, resulting in striking differences between weed communities developed in spring and summer. In summer, weed communities tended to have more neophytes, higher species richness and higher beta diversity. The third gradient reflected long‐term changes in weed vegetation over past decades. The proportion of hemicryptophytes and neophytes increased, while therophytes and archaeophytes decreased, as did species richness over time. The fourth gradient was due to crop plants. Cultures whose management involves less disturbances, such as cereals, harboured less geophytes and neophytes, and had higher species richness but lower beta diversity than frequently disturbed cultures, such as root crops. Conclusions: Species composition of Central European weed vegetation is mainly influenced by broad‐scale climatic and edaphic factors, but its variations due to seasonal dynamics and long‐term changes in agricultural management are also striking. Crop plants and crop‐specific management affect it to a lesser, but still significant extent.     

Ground beetle (Coleoptera: Carabidae) diversity, activity density, and community structure in a diversified agroecosystem

Diversity and abundance of ground beetles (Coleoptera: Carabidae) can be enhanced in vegetable and field intercropping systems, but the complexity of polycultures precludes the application of generalized assumptions of effects for novel intercropping combinations. In a field experiment conducted at Lacombe and Ellerslie, Alberta, Canada, in 2005 and 2006, we investigated the effects of intercropping canola (Brassica napus L.) with wheat (Triticum aestivum L.) on the diversity and community structure of carabid beetles, and on the activity density responses of individual carabid species. Shannon-Wiener diversity index scores and species evenness increased significantly as the proportion of wheat comprising total crop plant populations increased in one site-year of the study, indicating a positive response to enhanced crop plant species evenness in the intercrops, and in that same site-year, ground beetle communities in intercrops shifted to more closely approximate those in wheat monocultures as the percentage of wheat in the intercrops increased. Individual carabid species activity densities showed differing responses to intercropping, although activity densities of some potential root maggot (Delia spp.) (Diptera: Anthomyiidae) predators were greater in intercrops with high proportions of wheat than in canola monocultures. The activity density of Pterostichus melanarius (Illiger), the most abundant species collected, tended to be greater in canola monocultures than high-wheat intercrops or wheat monocultures. We conclude that intercrops of canola and wheat have the potential to enhance populations of some carabid species, therefore possibly exerting increased pressure on some canola insect pests.     

Arable weeds in organically managed wheat fields foster carabid beetles by resource- and structure-mediated effects

Arable weeds in organically managed fields may foster arthropod generalist predators by the provision of shelter and favorable microclimate (structure-mediated effects) and the provision of additional animal and floral food resources (resource-mediated effects). In three organically managed winter wheat fields in Central Germany, we investigated the impact of weed removal and introduction of artificial weed-like structure on the activity density and species richness of carabid beetles with respect to trophic groups, microclimatic conditions, and densities of potential prey. Removal of weeds reduced both carabid activity density and species richness but did not affect trophic group composition. The decline in carabid activity density was dampened by the addition of artificial structure. Mean daily surface temperature and light intensity were significantly lower under weeds and artificial plants than under wheat plants alone. Weed removal reduced the abundance of leafhoppers and true bugs, but the response was inconsistent across fields. We conclude that the presence of arable weeds in organically managed wheat fields fosters carabid activity density and species richness via resource-mediated effects, such as a higher availability of weed-borne resources (e.g. seeds and pollen) and herbivorous prey. Structure-mediated effects (altering the microclimate) add to this positive effect. The presence of weeds in organically managed wheat fields enhances carabid activity density and diversity and needs to be integrated into future management strategies for natural enemy conservation.