Characterization of six polymorphic microsatellites for the polychaete tubeworm Hydroides elegans and cross‐species amplification in the congener Hydroides hexagonus

We isolated and characterized six polymorphic microsatellite loci for the polychaete tubeworm, Hydroides elegans. Two additional loci were not reliably scorable and estimates of heterozygosity were obtained for the other six. In addition, cross‐species amplification was successful for two loci using the congener H. hexagonus. Given that few microsatellite loci are available for polychaetes, these markers will be useful in assessing dispersal and gene flow in H. elegans and probably also other polychaetes.     

Resource complementation and the response of an insect herbivore to habitat area and fragmentation

Few studies have disentangled the effects of the area and fragmentation of a focal habitat type on species that use multiple habitat types within a landscape. We experimentally investigated the effects of habitat area, habitat fragmentation, and matrix composition on the movement and distribution of Melanoplus femurrubrum. Adults of this grasshopper feed preferentially on grasses, but oviposit almost exclusively in soil dominated by forbs. We compared population densities among plots that were made to vary in the area and fragmentation of clover habitat and composition of the matrix (grass or bare ground) within which clover habitat was embedded. In addition, a mark-recapture survey was conducted to examine effects of habitat area, fragmentation, and matrix composition on loss of individuals from a plot’s clover habitat and movement between clover subplots within plots. Overall densities of adult M. femurrubrum (averaged over clover and matrix) were 2.2× higher in plots where the matrix was composed of grass as compared to bare ground, and 1.8× higher in plots with 64 compared to 16 m² of clover habitat. Overall densities of nymphs were also positively influenced by greater clover area, but were unaffected by matrix composition. Within focal clover habitat embedded in grass matrix, adult densities were 2.1× higher in small clover subplots than large clover subplots. We conclude that the grass matrix had a positive effect on adult densities, but not nymph densities, because grass and forb-dominated habitats likely provide complementary resources only for adults. The aggregation of adults on small clover subplots within grass matrix was mainly attributed to a greater rate of emigration loss per unit area. In addition, this study emphasizes that a species’ response to changes in the area of a focal habitat type can depend significantly on the availability of complementary resources in the surrounding landscape. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Non-native ecosystem engineer alters estuarine communities

Many ecosystems are created by the presence of ecosystem engineers that play an important role in determining species' abundance and species composition. Additionally, a mosaic environment of engineered and non-engineered habitats has been shown to increase biodiversity. Non-native ecosystem engineers can be introduced into environments that do not contain or have lost species that form biogenic habitat, resulting in dramatic impacts upon native communities. Yet, little is known about how non-native ecosystem engineers interact with natives and other non-natives already present in the environment, specifically whether non-native ecosystem engineers facilitate other non-natives, and whether they increase habitat heterogeneity and alter the diversity, abundance, and distribution of benthic species. Through sampling and experimental removal of reefs, we examine the effects of a non-native reef-building tubeworm, Ficopomatus enigmaticus, on community composition in the central Californian estuary, Elkhorn Slough. Tubeworm reefs host significantly greater abundances of many non-native polychaetes and amphipods, particularly the amphipods Monocorophium insidiosum and Melita nitida, compared to nearby mudflats. Infaunal assemblages under F. enigmaticus reefs and around reef's edges show very low abundance and taxonomic diversity. Once reefs are removed, the newly exposed mudflat is colonized by opportunistic non-native species, such as M. insidiosum and the polychaete Streblospio benedicti, making removal of reefs a questionable strategy for control. These results show that provision of habitat by a non-native ecosystem engineer may be a mechanism for invasional meltdown in Elkhorn Slough, and that reefs increase spatial heterogeneity in the abundance and composition of benthic communities.     

垫状植物囊种草对群落物种多样性的影响

在甘肃盐池湾国家级自然保护区内海拔4137 m处,选择典型的囊种草垫状植被设置研究样地,研究了垫状植物囊种草对群落物种组成和群落物种多样性的影响,并且定量的研究了囊种草对群落物种丰富度的影响能力和维持潜力。研究结果表明:囊种草为群落中增加了新的植物种类,并且提高了部分生境一般种的多度;囊种草的出现提高了群落物种密度和物种丰富度,进而提高了群落物种多样性;囊种草斑块的增加将会引起景观水平物种丰富度的增加,表明囊种草具有为群落中引入新的植物种类进而提高群落物种丰富度的能力;在景观水平,囊种草所创造的生境多样性则成为一种保障,可以维持景观中物种丰富度从而降低物种损失的风险,表明囊种草具有较高的群落物种丰富度维持潜力。     

Ecosystem engineering by foxes is mediated by the landscape context—A case study from steppic burial mounds

In intensively used landscapes, remnant grassland fragments are often restricted to places unsuitable for agricultural cultivation. Such refuges are the ancient burial mounds called “kurgans,” which are typical landscape elements of the Eurasian steppe and forest steppe zone. Due to their hill‐like shape, loose soil structure and undisturbed status kurgans provide proper habitats for burrowing mammals. Accordingly, grassland vegetation on kurgans is often exposed to bioturbation, which can influence the habitat structure and plant species pool. In our study, we explored the effect of fox burrows and landscape context on the habitat properties and vegetation composition of small landscape elements, using kurgans as model habitats. We surveyed the vegetation of fox burrows and that of the surrounding grassland on five kurgans situated in cleared landscapes surrounded by arable lands and five kurgans in complex landscapes surrounded by grazed grasslands. We recorded the percentage cover of vascular plants, the amount of litter, and soil moisture content in twelve 0.5 m × 0.5 m plots per kurgan, in a total of 120 plots. We found that foxes considerably transformed habitat conditions and created microhabitats by changing the soil nutrient availability and reducing total vegetation cover and litter. Several grassland specialist species, mostly grasses (Agropyron cristatum, Elymus hispidus, and Stipa capillata) established in the newly created microhabitats, although the cover of noxious species was also considerable. We found that landscape context influenced the sort of species which could establish on kurgans by affecting the available species pool and soil moisture. Our results revealed that foxes act as ecosystem engineers on kurgans by transforming abiotic and biotic conditions by burrowing. Their engineering activity maintains disturbance‐dependent components of dry grasslands and increases local environmental heterogeneity.     

The effect of matrix on the occurrence of hazel grouse (Bonasa bonasia) in isolated habitat fragments

The aim of this study was to determine the effect of matrix on the occurrence of hazel grouse (Bonasa bonasia) in habitat fragments. The study was conducted in two kinds of landscape: (1) an agricultural landscape, where the censused forest habitat fragments were surrounded by farmland, and (2) in an intensively managed forested landscape, where the censused habitat fragments were surrounded by nonhabitat coniferous forest. Occupied and unoccupied habitat fragments in the agricultural landscape differed significantly in distance to the nearest suitable continuous habitat, with hazel grouse occurring only in habitat fragments closer than 100 m from continuous forest. In the intensively managed forest landscape, the effect of isolation was less evident, but there might be a threshold around 2 km. Effects of isolation occurred over much shorter distances when the surrounding habitats consisted of farmland than when it was forested habitats. The size of the habitat fragments was important in both landscapes, with larger habitat fragments more often containing hazel grouse.     

Spatiotemporal variation in benthic polychaetes (Annelida) and relationships with environmental variables in a tropical estuary

Annelida constitute a dominant functional component in soft-bottom macrobenthic communities and reveal a wide range of adaptability to different marine and coastal habitats. Analyses in different polychaete assemblages and their responses to habitat conditions reflect the biological effects of marine pollution and habitat disturbance. The present study is designed to study colonization and community structure of polychaetes in two ecologically distinct locations of the Sundarban Biosphere Reserve on the northeast coast of India. Polychaete assemblages are characteristically different at the two sites in the extreme northern (Ghusighata) and southern (Gangasagar) portions of the Biosphere Reserve. Levels of heavy metals in polychaete body tissues also reveal interspecific and regional variations. The predominant polychaete fauna exhibited a distinct and unique assemblage of two types: (i) Mastobranchus indicus – Dendronereides heteropoda in the sewage-fed substratum at Ghusighata and (ii) Lumbrinereis notocirrata – Ganganereis sootai – Glycera tesselata at Gangasagar at the mouth of the Hugli estuary where chronic anthropogenic stress and contamination with agricultural and industrial effluents occur. The faunistic composition of polychaetes and their potential for the accumulation of heavy metals from the ambient medium are distinctly different. The study demonstrates that textural composition of the sediments, together with hydrodynamic and geotechnical properties, seem to have the greatest control to quantify the differences of the polychaete community in the two study stations. An in-depth comparative study of polychaete community structure at multiple spatial scales is strongly recommended for future environmental impact assessment in this fragile environment.     

Life on the edge: conspecific attraction and recruitment of populations to disturbed habitats

Variation in the recruitment of benthic marine invertebrates is often attributed to the interaction of the supply of new individuals to a habitat and the availability of space for colonisation when they arrive. Also important in determining variation in recruitment is the response of the larvae to the characteristics of the habitat. Larvae of many benthic marine invertebrates have shown great specificity of requirements in setting their limits of distribution at the time of selection of a habitat. The tubeworm Galeolaria caespitosa shows great variation in recruitment from place to place on rocky intertidal seashores and is a gregarious animal with larvae showing directed responses to conspecific adults on the substratum. I hypothesised that, if variation in recruitment of G. caespitosa were independent of conditions on the substratum, the magnitude of recruitment in patches of the same shape but different sizes cleared within continuous mats of conspecific adults would be directly related to the area available for colonisation in the patch. Alternatively, if variation in recruitment were due to the response of larvae to conspecific adults on the substratum, the magnitude of recruitment would be a function of the perimeter of the patch, which, given patches of the same shape, is a measure of the influence of conspecific adults in that patch. To distinguish between these alternatives, small (area = 25 cm²; perimeter = 20 cm) and large (area = 225 cm²; perimeter = 60 cm) square patches were cleared within continuous mats of conspecific adults at four sites and recruitment of G. caespitosa was monitored over two seasons of recruitment. The density of recruits per unit area was, on average, almost three times greater in small than in large patches, indicating that recruitment of G. caespitosa is not directly related to the area of the patch. In contrast, the density of recruits per unit perimeter was not significantly different between small and large patches, indicating that recruitment of G. caespitosa is related to the proximity of conspecific adults in the patch. Therefore, at a given site, the perimeter of patches within mats of G. caespitosa is a better predictor of the relative magnitude of recruitment among patches than that provided by their areas. These results are contrary to many models of invertebrate recruitment that assume close linkage between available space on the substratum and settlement. Moreover, they highlight the importance of behavioural responses of animals at the time of selection of habitat in accounting for variation in recruitment. For populations of organisms that display gregarious behaviour at settlement, or conspecific attraction, this direct relationship between the perimeter of patches and recruitment could be used as a tool in restoring populations to disturbed habitats. The added benefit of such facilitative interactions in restoring populations is that they provide increasing returns to the population for a given supply of potential colonists to a habitat. Received: 1 November 1996 / Accepted: 20 January 1997     

Environmental factors structuring polychaete communities in shallow rocky habitats: role of physical stress versus habitat complexity

Polychaetes inhabiting 12 different hard bottom habitats were studied. A total of 157 species belonging to 32 families were identified. Differences among habitats in polychaete density, species richness, and diversity were analysed, as well as the relationships between these ecological indices and depth range, slope and in-bay/out-bay gradient. A high faunal homogeneity was found: all biotopes were dominated by a low number of eurytopic species. Intertidal habitats and subtidal ones with scarce algal cover were typified by vagile polychaetes (syllids, nereids), while sessile polychaetes (serpulids, sabellids) appeared typically among subtidal large macrophytes, habitats with a calcareous substrate and shaded habitats. Multivariate analyses showed that habitat complexity, determined by physical disturbance, is the main structuring factor for polychaete populations. Biotopes with the highest structural complexity displayed a high number of companion species increasing ecological indices and denoting a well-structured habitat. On the other hand, communities such as those in the upper intertidal, mainly controlled by physical environmental variables, showed a poorer polychaete fauna, dominated by ubiquitous species and a few well-adapted specialists.     

Population fluctuations in relation to seasonal habitat preferences of the Swainson's spurfowl, Pternistis swainsonii

Counts on Swainson's spurfowl Pternistis swainsonii were made during 1998–1999 within an intensive, fine‐grained, agricultural landscape to estimate population parameters, seasonal dispersion and habitat preferences. Radio‐transmitters were fitted to four birds to note habitat use and home ranges within the Summer breeding season. During Winter, population densities peaked, and birds exploited agricultural crops extensively. At the onset of Spring, densities dropped as birds paired to establish non‐overlapping breeding territories over a number of habitats with apparently sufficient cover and ‘natural’ food. Expanding grazed grassland appears to be the greatest threat to Swainson's spurfowl due to a lack of cover and food. The matrix of habitats within the landscape plays important roles in the success of this opportunistic spurfowl. Agricultural crops in the Winter sustain the population until the following Summer when natural savanna and ungrazed grasslands provide complementary foraging, nesting and roosting sites.     

Contrasting effects of natural habitat loss on generalist and specialist aphid natural enemies

The greater susceptibility of higher trophic levels to habitat loss has been demonstrated to disrupt important trophic interactions such as consumer control of prey populations. This pattern is predicted to break down for generalist species that can use matrix habitats, yet empirical studies comparing generalist and specialist enemy pressure in response to natural habitat loss are lacking. Here we examined the effects of landscape simplification resulting from habitat conversion to agriculture on nettles, Urtica dioica , their specialized aphid herbivore, Microlophium carnosum , and associated natural enemies that varied broadly in their degree of specialization. Both nettles and their specialized aphid herbivore were significantly more abundant in complex than simple landscapes. Different enemy groups showed contrasting responses. Aphid specialists (parasitic wasps and cecidomyiid midges) reached higher densities in complex than simple landscapes, and this effect was primarily related to shifts in local resource abundance (i.e. nettle aphid densities). In contrast, densities of generalists (coccinellid beetles and spiders) were significantly higher in simple landscapes, presumably due to spillover of generalists from surrounding cropland habitats. Natural enemy-prey ratios did not differ significantly across landscape types for specialist groups but were significantly higher in simple than complex landscapes for generalist groups, suggesting that enemy pressure on nettle aphids likely increases with landscape simplification. This was supported by our finding that aphid population growth rates were lower in simple than complex landscapes, and declined significantly with increasing coccinellid densities. Thus, in marked contrast to previous work, our results suggest that natural habitat loss may augment rather than disrupt consumer–prey interactions, and this will depend greatly on the degree of specialization of functionally dominant natural enemies.     

Restoration of Shorebird‐Roosting Mudflats by Partial Removal of Estuarine Mangroves in Northern Taiwan

Expansion of the monospecific mangrove, Kandelia obovata, has converted intertidal mudflats and other habitats into mangrove forests, thus reducing estuarine biodiversity in the Danshuei River estuary, northern Taiwan. Dense mangrove vegetation was removed to create a small patchwork of mudflats and a tidal creek in February 2007. Subsequent changes in sediment properties and biodiversity of the macrobenthos and avian communities were examined. The results showed that the creation of different habitats led to changes in sediment properties and biodiversity. The water content and sorting degree of the sediments differed significantly among the restored mudflat, the tidal creek, and the mangrove control site. Silt/clay, organic carbon content, and chlorophyll a concentrations varied seasonally, but not among sites. The abundance of polychaetes in the creek was greater than that in the mudflat or the mangrove (12.5 vs. 5.3 and 2.2 individuals/m², respectively), suggesting preferential colonization of infaunal polychaetes in habitats with prolonged submersion. Crabs showed seasonal changes in density, with higher densities in summer than in autumn and winter. The species richness of wintering shorebirds on the created mudflat increased dramatically from 2002 to 2007. The transformation of a vegetated area into an open mudflat appeared to benefit shorebirds by providing roosting habitat. Our study demonstrated that controlling the spread of estuarine mangrove forests could increase biodiversity, and could particularly benefit the migratory shorebird community.     

景观基质对雅江中游河谷黑颈鹤冬季觅食地选择的影响

生态系统中生境斑块并非孤立存在,而是嵌于周边景观基质中。生境内种群赖以生存的资源和环境条件不仅取决于生境本身,更与景观基质组成与结构紧密关联。黑颈鹤是青藏高原的旗舰物种,雅鲁藏布江中游河谷高寒湿地是全球最大的黑颈鹤越冬地,为其提供了良好的觅食生境。厘清该区域黑颈鹤觅食生境选择如何受景观基质组成结构的影响,对于青藏高原旗舰物种保护以及流域生态系统综合治理具有重要意义。运用景观生态学原理,以遥感影像和实地黑颈鹤种群调查数据为基础,结合景观基质多尺度缓冲区构建、相关分析以及Maxent模型,分析2000-2020年雅江中游河谷黑颈鹤国家级自然保护区（日喀则片区）景观格局时空变化和觅食地生境特征及其与黑颈鹤种群的关系,探究景观基质对黑颈鹤觅食地选择的影响,并利用关键生境因子模拟黑颈鹤生境适宜性分布。通过分析发现：（1）时间尺度上,雅江中游河谷耕地面积先增加后下降,滩地持续减少;空间尺度上,觅食黑颈鹤种群呈东多西少的集群分布特征,其分布范围与河谷内耕地分布基本吻合;（2）景观基质对黑颈鹤觅食地选择影响显著。景观结构上,黑颈鹤偏好连通性好、优势度高的景观基质;景观组成上,偏好基质中耕地和水域类型,这与黑颈鹤的觅食习性及对环境安全的生态位需求有关;（3）景观基质结构组成对黑颈鹤觅食地选择的影响具有显著的尺度效应。景观基质结构影响最显著的空间尺度为1500-2000m。但基质中耕地、草地和水域等景观组成要素对黑颈鹤的影响具有不同空间尺度效应,分别为1500m、3000m和4000m;（4）通过模型模拟,揭示出黑颈鹤适宜生境面积先增后减,但总体较2000年呈上升趋势,且基质中觅食地与耕地的距离、水域斑块密度和偏好景观组成的优势度始终是生境适宜性解释率最高的景观因子。本研究揭示出,该区域乡村规划应该统筹优化黑颈鹤栖息生境及其景观基质中的作物生产以及居民生活,形成以黑颈鹤旗舰物种保护为核心的高寒湿地生态系统综合管理模式,从而增强青藏高原高寒生态系统的稳定性和可持续性,同时也为深入研究物种生境选择机制提供了思路。     

Bird community variation across <Emphasis Type="Italic">Polylepis</Emphasis> woodland fragments and matrix habitats: implications for biodiversity conservation within a high Andean landscape

The scattered and dwindling Polylepis woodlands of the high Andean global hotspot have been identified as being of particular importance to biodiversity conservation, and yet little is known of the make-up of their faunal communities, how these vary across landscapes, and how well species might tolerate matrix/edge habitats. We examined the bird communities and vegetation characteristics of Polylepis woodlands and the surrounding matrix habitats at three sites in the Cordillera Vilcanota, southern Perú (3,400–4,500 m). The vegetation structure of woodlands varied significantly across the three sites but all were dominated by two Polylepis tree species, with mossy ground cover. Matrix habitats were treeless and dominated by ground-level puna grass-steppe or boulder scree vegetation. Bird species richness and diversity, encounter rates and the number of globally-threatened and restricted-range bird species were consistently higher in the Polylepis forests, than in matrix habitat. We used canonical correspondence analysis (CCA) to identify habitat gradients across the landscape, and to classify bird species according to their association with Polylepis, the matrix or Polylepis-matrix interface. There were few matrix-restricted bird species, but around half the bird community, including fourteen threatened or restricted-range species, were Polylepis-dependant. Many of these species had very narrow niches. The Polylepis-matrix interface was dominated by species traditionally considered invasive ecological generalists. Our study illustrates the overriding importance of Polylepis interior habitats, indicating that conservation strategies for high Andean birds must focus on patch size maintenance/enlargement, enhancement of within-patch habitat quality, and efforts to safeguard connectivity of suitable habitat across what is essentially an inhospitable puna/scree matrix.     

Polychaete fauna associated with holdfasts of the large brown alga Himantothallus grandifolius in Admiralty Bay, King George Island, Antarctic

The polychaete community associated with holdfasts of the brown alga Himantothallus grandifolius in Admiralty Bay has been studied. It is the first study of its kind in this area and only the second in the Antarctic. Samples were collected in the summer season of 1979/1980 from a depth range of 10–75 m. Seventy-eight species were found on 19 holdfasts. The community was dominated by Brania rhopalophora and Neanthes kerguelensis. Analysis of similarity showed that polychaete fauna associated with this habitat did not show any partitioning related to depth. Regression analysis showed that densities of both species and individuals decreased with increased holdfast volume. A positive correlation was found between the number of individuals and holdfast volume. Polychaetes from 10 feeding guilds were found with dominance of macrophagous motile herbivores and sessile filter feeders. The complex habitat provided by holdfasts is a shelter for a rich polychaete fauna and may function as important protection from disturbance in the shallow areas of Admiralty Bay.     

Landscape context influences the abundance of amphibians and the strength of their food web interactions in small ponds

Many species, including most amphibians, undergo an ontogenetic niche shift (ONS) from an aquatic larval stage to a terrestrial adult stage. We use the ratio of aquatic to terrestrial habitat in a landscape as a tool to understand the influence of landscape context on the population growth of ONS species. The aquatic to terrestrial ratio (ATR) of habitats can be viewed as an analog to the influence of resource ratios on the population growth of consumers and depends on the degree to which each habitat type limits the growth of a given population. Population growth rates of shorter‐lived species tend to be more limited by demographic rates in early (aquatic) life stages. As a result, increasing the ATR should lead to a higher total population size in the landscape (and higher densities in the terrestrial habitat), but have little influence on the density of individuals in any given aquatic habitat. Alternatively, population growth rates of longer‐lived species tend to be more limited by demographic rates in later (terrestrial) life stages and increasing the ATR should have little influence on the total population size in the landscape, but decrease the density of individuals in any given aquatic habitat. We show that among‐landscape variation in the breeding‐pond densities of three widespread amphibians with contrasting life histories is consistent with this framework. Within‐pond densities of Pseudacris crucifer, a species with short‐lived adults, were not influenced by ATR, whereas within‐pond densities of Hyla versicolor, a longer‐lived member of the same family (Hylidae), declined as ATR increased. Ambystoma maculatum, a long‐lived salamander, also had lower densities in ponds with higher ATR. Because A. maculatum larvae are important predators in ponds, we use structural equation modeling to show that landscape context (ATR) can moderate community structure via direct (amphibian abundances) and indirect (prey species richness) effects.     

Living on the verge: are roads a more suitable refuge for small mammals than streams in Mediterranean pastureland?

The retention of natural habitat corridors is a useful and practical conservation tool that can attenuate the effects of habitat loss and fragmentation on wildlife. Linear structures may contribute to the conservation of biodiversity by providing additional habitats for small fauna living in highly modified environments. We assessed the importance of road verges as refuge areas for small mammals, in highly intensified grazed pastures, within a Mediterranean landscape and compared the role of road verges as refuges with that of riparian galleries, which have been described as important shelter locations for small fauna. For this purpose, a small mammal trapping study was undertaken on two road verges and beside two small streams in southern Portugal. We captured 457 individuals of five different species, with Mus spretus the most common species captured, followed by Crocidura russula. Captures were 4.6-fold higher immediately beside both roads and streams than 12 m away in the surrounding matrix. Individuals captured in the matrix presented a smaller body size and lower body condition, suggesting that this suboptimal habitat is occupied mainly by subadults. M. spretus was 46% more abundant by roads than by streams, while C. russula was present in similar numbers in both habitats. M. spretus individuals were larger near streams but exhibited no difference in body condition between habitats. C. russula had a better body condition and slightly higher body lengths at roadsides. Our results show that roadside verges in intensively grazed Mediterranean landscapes act as important refuges and constitute equally vital habitats for small mammals as do riparian vegetation strips in landscapes where other suitable habitats are scarce.     

Contrasting responses of arable spiders to the landscape matrix at different spatial scales

Aim Animal communities can be influenced by the composition of the surrounding landscape through immigration. Depending on habitat preferences, however, the effect of the landscape matrix can be positive or negative and can vary with scale. We tested this idea with arable spiders and tried to infer dispersal distances from relationships between local density and landscape composition at different spatial scales. Location Thirty‐eight landscapes around the cities of Göttingen and Giessen, Germany. Methods Spiders were captured with pitfall traps in one field of winter wheat in each landscape. Landscape composition around the fields was characterized at 11 scales from 95 m to 3 km radius by land‐use mapping and subsequent GIS analysis. Correlation tests were performed between landscape composition and local densities or species richness. Results In both study regions, local species richness was enhanced by non‐crop habitats on a landscape scale. The overall densities of wolf spiders (Lycosidae), long‐jawed spiders (Tetragnathidae), crab spiders (Thomisidae), and dwarf sheet spiders (Hahniidae) increased significantly in landscapes with high percentages of non‐crop habitats. Out of the 40 species tested, 19 responded positively to the percentage of non‐crop habitats in the surrounding landscape, and five responded negatively. Depending on the species, the spatial scales with the highest explanatory power ranged from 95 m to 3 km radius around the study fields, potentially reflecting dispersal distances. Main conclusions Arable spider species showed contrasting responses to the landscape context with respect both to the direction and to the spatial scale of the relationship. The variation in landscape requirements among species ensures high spider densities in a wide range of situations, which contributes to ecosystem resilience. However, species richness of arable spiders depends on heterogeneous landscapes with high percentages of non‐crop habitats.     

Crop–noncrop spillover: arable fields affect trophic interactions on wild plants in surrounding habitats

Ecosystem processes in agricultural landscapes are often triggered by resource availability in crop and noncrop habitats. We investigated how oilseed rape (OSR; Brassica napus, Brassicaceae) affects noncrop plants in managed systems and semi-natural habitat, using trophic interactions among wild mustard (Sinapis arvensis, Brassicaceae), rape pollen beetles (Meligethes aeneus, Nitidulidae) and their parasitoids (Tersilochus heterocerus, Ichneumonidae). We exposed wild mustard as phytometer plants in two cropland habitat types (wheat field, field margin) and three noncrop habitat types (fallow, grassland, wood margin) across eight landscapes along a gradient from simple to complex (quantified as % arable land). Both landscape and local factors affected the abundance of rape pollen beetles and parasitoids. Rape pollen beetle infestation and parasitism rates on these plants were lower in noncrop habitats and higher in wheat fields and field margins, whereas beetles and parasitoids responded differently to landscape scale parameters. We found the hypothesized spillover from OSR crop onto wild plants in surrounding habitats only for parasitoids, but not for pollen beetles. Parasitism rates were not related to landscape simplification, but benefited from increasing proportions of OSR. In contrast, rape pollen beetles benefited from simple landscape structures, presumably due to multi-annual population build-ups resulting from long-term OSR planting (as part of the crop rotation). In conclusion, we showed that spillover from cropland affects parasitism rates on related wild plants outside cropland, which has not been shown so far, but can be expected to be a widespread effect shaping noncrop food webs.