Non-crop Habitats Research Articles

Effects of landscape complexity on pollinators are moderated by pollinators' association with mass-flowering crops.

Conserving and restoring semi-natural habitat, i.e. enhancing landscape complexity, is one of the main strategies to mitigate pollinator decline in agricultural landscapes. However, we still have limited understanding of how landscape complexity shapes pollinator communities in both crop and non-crop habitat, and whether pollinator responses to landscape complexity vary with their association with mass-flowering crops. Here, we surveyed pollinator communities on mass-flowering leek crops and in nearby semi-natural habitat in landscapes of varying complexity. Surveys were done before and during crop bloom and distinguished between pollinators that visit the crop frequently (dominant), occasionally (opportunistic), or not at all (non-crop). Forty-seven per cent of the species in the wider landscape were also observed on leek flowers. Crop pollinator richness increased with local pollinator community size and increasing landscape complexity, but relationships were stronger for opportunistic than for dominant crop pollinators. Relationships between pollinator richness in semi-natural habitats and landscape complexity differed between groups with the most pronounced positive effects on non-crop pollinators. Our results indicate that while dominant crop pollinators are core components of crop pollinator communities in all agricultural landscapes, opportunistic crop pollinators largely determine species-richness responses and complex landscapes are local hotspots for both biodiversity conservation and potential ecosystem service provision.

How does habitat diversity affect ground-dwelling arthropods assemblages in Douro Demarcated Region terraced vineyards?

We investigated the impact of neighborhood non-crop habitats (NCHs) and cover vegetation in the Douro Demarcated Region terraced vineyards on ground-dwelling arthropods communities. Arthropods were sampled using pitfall traps located either in NCH as inside vineyards, at three distances (5, 25 and 50 m from NCH). Vegetation cover and plant species richness were evaluated around each trap. Omnivores (Formicidae) and detritivores (mainly Collembola), accounted for 42.0% and 33.7% of the sample, respectively. Predators, mainly dominated by Scydmaenidae (Coleoptera) and Araneae, accounted for 19.4% of the sample. The abundance of omnivores and predators was higher in NCH than in vineyards. In Formicidae, the generalist/opportunist group dominated, being highly represented by Pheidole pallidula. This group occurred mainly in NCH and its abundance was positively correlated either with plant richness as with percentage of fresh and total cover vegetation. This study indicates that preserving NCH close to the vineyards, as well as promoting native vegetation, enhances the presence of ground-dwelling arthropods.

Non-crop habitats promote the abundance of predatory ladybeetles in maize fields in the agricultural landscape of northern China

Ladybeetles are promising contributors of biological control services in agricultural landscapes, potentially providing significant economic gains in agricultural production. In northern China, ladybeetles are the most common predators in the annual double-crop rotation system, where the dominant crops are wheat in the spring and maize and cotton in the summer. Land-use features at the landscape level affect ladybeetle populations in a number of ways, and our previous studies have estimated the effects of landscape composition on ladybeetles abundance in wheat and cotton fields in northern China. However, these landscape effects on ladybeetle abundance in maize remain insufficiently documented in this specific agro-ecosystem. We assessed the relationships between ladybeetle abundance and landscape composition at four spatial scales (0.5, 1.0, 1.5, and 2.0 km) in a summer maize system at the whorl stage (the main period for ladybeetle colonization). We found that both semi-natural habitats (woodlots and grasslands) and vegetation around water bodies increased the abundance of ladybeetles in maize fields, and maize area played a dilution effect on ladybeetle abundance in this crop. These non-crop habitats might serve as source of emigrants that disperse to maize fields. The smallest scale (0.5 km) studied was the most predictive spatial scale in this colonization period for ladybeetles. Propylaea japonica, the dominant ladybeetle, showed response to landscape variables in a similar way as the whole ladybeetle population did. These findings suggest that leaving some non-crop habitats and reducing human disturbance to this vegetation within a landscape will enhance ladybeetle abundance in maize fields. Consistent with our previous studies in wheat and cotton fields in the same system, maintaining the continuity in time and space of functional habitats was essential for the persistence of ladybeetle populations within the landscape. In the future, habitat management and landscape design to ensure resource continuity should be encouraged to maximize the conservation of ladybeetles in agricultural ecosystems in northern China.

Pond management enhances the local abundance and species richness of farmland bird communities

Agricultural intensification and the associated loss of non-cropped habitats have caused a major decline in UK farmland bird populations since the 1970s. As a consequence, there is an urgent need to implement effective conservation and habitat restoration measures in agricultural landscapes. Over the last 40–50 years, due to the cessation of traditional management practices, the majority of UK farmland ponds have become highly terrestrialised, resulting in major reductions in the diversity and abundance of aquatic plant and invertebrate assemblages. Recent research undertaken at farmland ponds in early summer, has shown restored open-canopy, macrophyte-dominated ponds support an increased abundance and diversity of farmland birds, compared to non-managed, overgrown ponds.Here, we expand on this previous research with a year-long field study to assess the implications of pond management for farmland birds by comparing bird diversity, abundance and activity at managed open-canopy ponds with those at unmanaged overgrown ponds. Driven strongly by pond management and connectivity to semi-natural landscape features such as hedgerows and woodland patches, bird abundance and species richness, as well as foraging and parental behaviour, were all significantly higher at managed open-canopy ponds. Further, a wider landscape analysis found that terrestrial land-use patterns in the vicinity of the ponds were not significant predictors of bird communities at the pond sites.In light of the numerous potential benefits to conservation-listed birds and other wildlife, we conclude that farmland pond management has been undervalued as a conservation measure to assist farmland birds. Consequently, we conclude that future agri-environment schemes, should more fully embrace farmland ponds.

Spatial organisation of habitats in agricultural plots affects per-capita predator effect on conservation biological control: An individual based modelling study

A highly advocated approach to enhance pest control by indigenous predators is to add or maintain appropriate non-crop plant habitats in agrosystems. Although the addition of non-crop plant habitats can enhance the number of predators in crop by increasing their food resources or shelter, the effect is often insufficient to reduce pest abundance or damage. A number of explanations were identified in previous studies; the ability of such habitats to enhance predators, in particular, is affected by the spatial organisation of the habitats at the landscape level. Here, we explore how intra-plot spatial patterns of non-crop habitats affect the per-capita predator effect on pest control. We use a spatially explicit and individual-based model to simulate the foraging movements of an earwig-like predator in a banana field. Predator movements within a day were based on a simple non-specific behavioural assumption: movement is a correlated random walk affected by habitats and edges. Population dynamic processes occurring at larger time or spatial scales, such as reproduction and immigration, were not considered. In this model, non-crop habitats added to plots were considered favourable to predators: movements were slower and more sinuous in non-crop habitat than in unfavourable habitats. The intra-plot spatial patterns of the non-crop habitat were built and characterised using landscape ecology concepts and metrics. We found that the per-capita predator effect was strongly affected by a spatial dilution of predators, induced by non-crop habitat addition, but this negative effect could be partially or fully mitigated by the spatial organisation of the non-crop habitat. At the banana plant level, a long edge length between the crop and non-crop habitat can compensate for this dilution effect by reducing the duration of the periods between predator visits to the banana plant. At the plot level, the best plots (i.e., those in which all banana plants were often visited by predators) were those with non-crop strips in the banana plant rows. Overall, the results support the idea that the spatial organisation of non-crop habitats at the plot level, characterised by the metric edge length in particular, can be managed to minimise the negative impact of the dilution effect.

Landscape structure alters the abundance and species composition of early-season aphid populations in wheat fields

Agricultural landscape composition is reported to have effects on the occurrence of natural enemies in fields, but the responses of herbivorous pests to landscape features have rarely been studied. Our previous landscape-level study in northern China found that natural enemies had no significant effects on the population growth of wheat aphids at the colonization stage. Hence, we hypothesised that the initial aphid population in wheat fields may largely depend on immigration events from other habitats. In this study, we investigated the effects of landscape pattern on wheat aphid abundance and species composition at the colonization stage by surveying population densities of different aphid species along a landscape gradient. We found that noncrop habitats such as woodlots, fallow lands and vegetation around dwellings or wetlands in the landscape all had positive correlations with aphid abundance in wheat fields because they provided a source for aphid colonization. More specifically, the proportion of woodlots, fallow lands, dwellings, and other crops increased the abundance of Rhopalosiphum padi (L.), and the existence of water and dwellings in an agricultural landscape facilitated the occurrence of Sitobion avenae (Fabricius). Likewise, the abundance of Schizaphis graminum (Rondani) in wheat fields was found to be significantly promoted by the presence of water. The habitats around water and dwellings usually provide the overwintering sites for the aphids. Furthermore, wheat production acreage had a significant negative correlation with the abundance of R. padi, S. avenae and S. graminum. Landscape characteristics had a significant effect on the species composition of wheat aphids. Our study suggests that noncrop habitats in a landscape enhance aphid occurrence at the population colonization stage, and differences in overwintering host plants among aphid species may be responsible for the differing responses of the abundance of different aphids to landscape variables, which greatly altered aphid population composition across different landscapes. These results highlight the need for taking landscape effects on the pest itself into consideration when designing landscape-level pest management strategies.

Habitat preference of Drosophila suzukii across heterogeneous landscapes

In temperate regions, generalist insect pests are expected to use multiple habitats and host plant species over the different seasons. Landscape composition and configuration can also provide a diversity of thermal resources and host plants that can modify insect activity and movement. Here, we described the seasonal spatial distribution of a destructive invasive pest, spotted wing drosophila (SWD), along a gradient of landscape composition (i.e. proportion of forest habitat) and configuration (i.e. length of forest edge). We selected a triplet of habitat patches (forest, vineyard and grassland) in 17 landscapes in North-eastern Italy characterised by different proportions of forest and forest edge length and monitored pest activity density for 1 year. We found that during the cold season, SWD mostly occupied forest habitats, which were suitable overwintering sites due to ideal microclimatic conditions. During plant-growing season, SWD occurred equally in the three habitats, probably due to warmer temperatures in open areas as well as high food and host availability. In summer, when high temperatures can be limiting, landscapes with large forest edge length presented an increase in activity density compared to landscapes with less amount of edges, irrespective of the total cover of forest. Large edge length indicated landscapes with high contact zones between forest and open habitats, probably favouring spillover of individuals in SWD. In the light of these results, pest control in crop fields located in landscapes with complex configurations can be particularly challenging. The high density in non-crop habitats suggests that this invasive species can have pervasive impact also on wild plant species occurring in semi-natural and natural habitats.

Possibilities and requirements for introducing agri-environment measures in land consolidation projects in China, evidence from ecosystem services and farmers' attitudes

The reductions of ecosystem services (ES) initiated by land consolidation towards intensive agriculture has been recognized in many parts of the world. Land consolidation in China is experiencing a transformation towards sustainability, which may be promoted by learning the experience of Europe to introduce agri-environment measures (AEM). This paper focused on the typical engineering works of land consolidation projects (LCP) to discuss the requirements and possibilities of introducing AEM in LCP in China. Evidence was sought through the ES changes and farmers' attitudes. Based on a database collected from the literature, the changes of ES under LCP across China were evaluated. Household interviews were conducted to identify farmers' perception of ES changes under LCP and their preference of AEM in LCP. In consisted with our expectation, our study demonstrated the negative impacts of LCP on the environment, that the present agricultural-focused LCP in China have typically generated increases in the arable land but decreases in non-crop habitats, and extensively caused growths in food supply ES but reductions in biodiversity maintenance ES. This tendency would threaten the provision of multiple ES and the ultimate sustainability of agriculture. It reflected the urgent requirements of environment integration in LCP in China, for which AEM are efficient instruments. Our results further illustrated the high possibilities of introducing AEM in LCP based on the evidence that the AEM welcomed by the majority of farmers involved all the engineering works, although the farmers selected AEM mainly due to their pursuit of aesthetic instead of biodiversity consideration. To promote land consolidation in China towards sustainability, it is essential to integrate ES into the goals of land use policy, set up the quantitative parameter controlling for non-crop habitats, and introduce AEM in LCP guidelines.

Dominance of cropland reduces the pollen deposition from bumble bees

Intensive agricultural landscapes can be hostile for bees due to a lack of floral and nesting resources, and due to management-related stress such as pesticide use and soil tillage. This threatens the pollination services that bees deliver to insect-pollinated crops. We studied the effects of farming intensity (organic vs. conventional, number of insecticide applications) and availability of semi-natural habitats at the field and landscape scale on pollinator visits and pollen delivery to pumpkin in Germany. We found that wild bumble bees were the key pollinators of pumpkin in terms of pollen delivery, despite fivefold higher visitation frequency of honey bees. Critically, we observed that the area of cropland had stronger effects on bees’ pollen deposition than the area of seminatural habitats. Specifically, a 10% increase of the proportion of cropland reduced pollen delivery by 7%. Pumpkin provides a striking example for a key role of wild pollinators in crop pollination even at high numerical dominance of honey bees. In addition, our findings suggest that habitat conversion to agricultural land is a driver of deteriorating pollination. This underlines the importance to maintain sufficient areas of non-crop habitats in agricultural landscapes.

Grass management intensity affects butterfly and orthopteran diversity on rice field banks

Agricultural intensification through landscape homogenization has been identified as one of the main drivers of the recent biodiversity decline in European farmlands. In particular, the loss of non-cropped habitats has often deprived farmland species of feeding and nesting sites, refuge areas, and dispersal corridors. In this framework, well-managed field margins may play a key role for wildlife conservation in agroecosystems, providing additional suitable habitat patches for many species, which also include several natural agents of pests’ biological control. In rice crops, paddy banks are usually heavily managed by farmers, which remove vegetation through chemical or mechanical procedures, with a consequent limitation of the potential role of levees in maintaining a functional agroecosystem. The aim of this study was to investigate the response of butterfly and orthopteran diversity to different grass management practices on rice field banks, namely herbicide spraying, mowing, and no management. Between April and September 2016, we sampled butterflies and orthopterans on 30 and 22 paddy levees respectively, located in three sites within the intensive rice crop district of northern Italy. Herbicides spraying proved to be the most detrimental practice for these insects, producing a considerable reduction in species richness and abundance in comparison with unmanaged and mown banks. The impacts of mowing were less pronounced than those of chemical treatments; however, frequent cutting caused a significant reduction in butterfly and orthopteran diversity on levees. Our results highlight the importance of unmanaged banks in preserving insect diversity in rice crops, while herbicide spraying should be avoided. Low frequency and rotational mowing could represent sustainable management solutions to meet biodiversity and husbandry requirements in this agroecosystem.

Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win-win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win-win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies.

Bt rice plants may protect neighbouring non-Bt rice plants against the striped stem borer, Chilo suppressalis.

The area planted with insect-resistant genetically engineered crops expressing Bacillus thuringiensis (Bt) genes has greatly increased in many areas of the world. Given the nearby presence of non-Bt crops (including those planted as refuges) and non-crop habitats, pests targeted by the Bt trait have a choice between Bt and non-Bt crops or weeds, and their host preference may greatly affect insect management and management of pest resistance to Bt proteins. In this study, we examined the oviposition preference of the target pest of Bt rice, Chilo suppressalis, for Bt versus non-Bt rice plants as influenced by previous damage caused by C. suppressalis larvae. The results showed that C. suppressalis females had no oviposition preference for undamaged Bt or non-Bt plants but were repelled by conspecific-damaged plants whether Bt or non-Bt. Consequently, C. suppressalis egg masses were more numerous on Bt plants than on neighbouring non-Bt plants both in greenhouse and in field experiments due to the significantly greater caterpillar damage on non-Bt plants. We also found evidence of poorer performance of C. suppressalis larvae on conspecific-damaged rice plants when compared with undamaged plants. GC-MS analyses showed that larval damage induced the release of volatiles that repelled mated C. suppressalis females in wind tunnel experiments. These findings suggest that Bt rice could act as a dead-end trap crop for C. suppressalis and thereby protect adjacent non-Bt rice plants. The results also indicate that the oviposition behaviour of target pest females should be considered in the development of Bt resistance management strategies.

Interactive effects of local and landscape factors on farmland carabids

AbstractAs a result of migration and spillover from noncrop habitats, predacious insects in agricultural fields respond locally to adjacent field margins and on a larger spatial scale to habitats in the surrounding landscape. However, the relative importance of local and landscape effects and their possible interactions have rarely been studied. We studied carabids in 18 pumpkin fields bordered by different field margins, along a gradient from simple to structural rich landscapes. Carabids were caught in pitfall traps along transects from the adjoining semi‐natural habitat towards the field centre. Although estimated species richness generally increased towards the field edges, carabid abundance increased towards adjacent woody margins and other crop fields. By contrast, abundance decreased towards adjacent herbaceous margins. Estimated carabid species richness in organically managed fields increased with increasing landscape heterogeneity, whereas this effect was absent in conventional fields. However, estimated species richness did not differ between organic and conventional fields. The differential response of carabid abundance to distance from the field edge in accordance with the type of field margin may explain the variability of patterns reported in the literature. The results of the present study show that both local and landscape parameters must be taken into account to promote carabids as natural enemies of crop pests.

When beggars are choosers-How nesting of a solitary bee is affected by temporal dynamics of pollen plants in the landscape.

Wild bees are declining in intensively farmed regions worldwide, threatening pollination services to flowering crops and wild plants. To halt bee declines, it is essential that conservation actions are based on a mechanistic understanding of how bee species utilize landscapes. We aimed at teasing apart how foraging resources in the landscape through the nesting season affected nesting and reproduction of a solitary bee in a farmland region. We investigated how availability of floral resources and potentially resource‐rich habitats surrounding nests affected nest provisioning and reproduction in the solitary polylectic bee Osmia bicornis. The study was performed in 18 landscape sectors dominated by agriculture, but varying in agricultural intensity in terms of proportion of organic crop fields and seminatural permanent pastures. Pasture‐rich sectors contained more oak (Quercus robur), which pollen analysis showed to be favored forage in early season. More oaks ≤100 m from nests led to higher proportions of oak pollen in nest provisions and increased speed of nest construction in early season, but this effect tapered off as flowering decreased. Late‐season pollen foraging was dominated by buttercup (Ranunculus spp.), common in various noncrop habitats. Foraging trips were longer with more oaks and increased further through the season. The opposite was found for buttercup. Oak and buttercup interacted to explain the number of offspring; buttercup had a positive effect only when the number of oaks was above the mean for the studied sectors. The results show that quality of complex and pasture‐rich landscapes for O. bicornis depends on preserving existing and generating new oak trees. Lignose plants are key early‐season forage resources in agricultural landscapes. Increasing habitat heterogeneity with trees and shrubs and promoting suitable late‐flowering forbs can benefit O. bicornis and other wild bees active in spring and early summer, something which existing agri‐environment schemes seldom target.

Creation of bunchgrass, sagebrush, and perennial grassland habitats within a semi-arid agricultural setting: Implications for small mammals

Native habitats of the semi-arid intermontane grasslands and shrub-steppe rangelands of the Pacific Northwest of North America are disappearing owing to agricultural, urban, and recreational development. A major small mammal occupying these habitats is the montane vole (Microtus montanus), along with the deer mouse (Peromyscus maniculatus), northwestern chipmunk (Neotamias amoenus), house mouse (Mus musculus), and two less common species at risk. To help restore these native habitats and small mammals, we tested three hypotheses (H) that non-crop habitats of native bunchgrasses, sagebrush (Artemisia tridentata), and perennial grasslands (alfalfa and mix of forage grasses) would: (H1) establish in an agricultural setting, (H2) conserve small mammal species, and (H3) limit vole damage to tree fruit production in orchards. Linear habitats of these non-crop treatments, within a semi-arid agrarian setting in south-central British Columbia, Canada, were sampled for all vascular plants and small mammals from 2006 to 2010. Mean abundance of bunchgrasses declined after the second year owing to competition from orchard herbs, but sagebrush and pasture grasses became well established, thereby partially supporting H1. Alfalfa established initially but then declined potentially owing to consumption by voles. Conservation of the three major small mammal species, but not less common species, partially supported H2. Alfalfa and pasture grasses provided optimum habitat for montane voles, but their high numbers did not result in feeding damage to tree fruit production, thereby supporting H3. Creation of non-crop habitats within as well as adjacent to agricultural settings should become a major endeavour to restore native habitats, enhance small mammal populations, and maintain biodiversity.

Contrasting effects of landscape composition on crop yield mediated by specialist herbivores.

Landscape composition not only affects a variety of arthropod-mediated ecosystem services, but also disservices, such as herbivory by insect pests that may have negative effects on crop yield. Yet, little is known about how different habitats influence the dynamics of multiple herbivore species, and ultimately their collective impact on crop production. Using cabbage as a model system, we examined how landscape composition influenced the incidence of three specialist cruciferous pests (aphids, flea beetles, and leaf-feeding Lepidoptera), lepidopteran parasitoids, and crop yield across a gradient of landscape composition in New York, USA. We expected that landscapes with a higher proportion of cropland and lower habitat diversity would lead to an increase in pest pressure of the specialist herbivores and a reduction in crop yield. However, results indicated that neither greater cropland area nor lower landscape diversity influenced pest pressure or yield. Rather, pest pressure and yield were best explained by the presence of non-crop habitats (i.e., meadows) in the landscape. Specifically, cabbage was infested with fewer Lepidoptera in landscapes with a higher proportion of meadows likely resulting from increased parasitism. Conversely, cabbage was infested with more flea beetles and aphids as the proportion of meadows in the landscape increased, suggesting that these pests benefit from non-crop habitats. Furthermore, path analysis confirmed that these landscape-mediated effects on pest populations can have either positive or negative cascading effects on crop yield. Our findings illustrate how different pest species within the same cropping system show contrasting responses to landscape composition with respect to both the direction and spatial scale of the relationship. Such tradeoffs resulting from the complex interaction between multiple-pests, natural enemies, and landscape composition must be considered, if we are to manage landscapes for pest suppression benefits.

Bringing diversity back to agriculture: Smaller fields and non-crop elements enhance biodiversity in intensively managed arable farmlands

Agricultural intensification has substantially reduced multi-scale habitat heterogeneity, including increased field size and loss of semi-natural structures, thus resulting in large-scale deterioration of farmland biodiversity. Biodiversity conservation in farmland has therefore become a conservation priority on a regional as well as continental scale. The effect of habitat heterogeneity on biodiversity on different trophic and niche levels is poorly understood, particularly in agricultural regions with simple arable patterns, where biodiversity has declined most conspicuously. To investigate the effects of habitat heterogeneity on biodiversity in an intensively managed arable-dominated agricultural landscape, we measured the abundance and species richness of spiders, butterflies, birds and European hares as well as the fine-scale habitat composition on various spatial scales. Additionally, we examined correlations between species richness and abundance among taxonomic groups to investigate if any of the biodiversity parameters provided a good indicator of overall farmland biodiversity. We found that smaller patch sizes and larger areas of non-cropped elements (margins, hedges and grasslands) were related to higher farmland biodiversity of different taxonomic groups but habitat diversity was not. The positive effect of these factors was recorded on both spatial scales and in a separate analysis considering groups with different habitat requirements and dispersal abilities. Biodiversity parameters (i.e. species richness and abundance) of the taxonomic groups were positively correlated with one another. In particular, butterfly species richness correlated with bird, butterfly and spider abundance and with bird species richness, suggesting that it may be a good indicator of general farmland biodiversity in intensively managed arable landscapes. Our results suggest that enhancing the heterogeneity of farmed landscapes by decreasing field size and increasing the availability of non-cropped habitats may be a valuable tool for conserving farmland biodiversity in intensive arable farmlands.

Secondary crops and non-crop habitats within landscapes enhance the abundance and diversity of generalist predators

An agricultural landscape is usually composed of multiple crops and non-crop habitats, and many studies have examined the effects of main crops and non-crop habitats on arthropod communities. However, secondary crops are also important features in argoecosystems, but how they affect generalist arthropod predators in an agricultural landscape has rarely been considered, especially in landscape dominated by small-scale farming. In this study, we applied a principal component analysis to interpret the landscape composition, and we performed a multiple regression analysis basing on Akaike’s information-theoretic selection criterion to assess the effects of secondary crops (other crops besides maize and cotton) as well other landscape component factors (e.g., landscape diversity, non-crop habitats) on the abundance and diversity of generalist predators in Bt cotton fields, across multiple spatial scales in 49 study sites covering at least 600 km2 in northern China. We found that a high proportion of secondary crops significantly enhanced the abundances of lacewings and vegetation-dwelling spiders within a 0.5 km radius, and an increasing proportion of urban habitats supported a high abundance of these spiders, in contrast to the negative effect that high landscape diversity had on spider abundance. However, we failed to find a significant landscape variable response on the abundances of lady beetles and Orius spp. Furthermore, high proportions of both non-crop habitats and urban areas enhanced hoverfly abundance at a 1.5 km radius, while a high proportion of urban areas also supported high diversity but a low dominant species concentration of the predator community at the 2 km scale. Our results suggest that predator abundance and community structure diversity may benefit from secondary crops, non-crop habitats and urban areas in agricultural landscapes, and these habitats and areas will improve the potential ecosystem services of these predators in a pest management program.

Plant species, functional assemblages and partitioning of diversity in a Mediterranean agricultural mosaic landscape

Agricultural landscapes represent mosaics of different habitats that can harbour high plant diversity where plant traits and trait syndromes can be used for predicting either plant responses to agricultural intensification or plant functional effects on other organisms. Understanding the spatial components of diversity within an agricultural mosaic can help to select the appropriate spatial scale for conserving species and ecological functions such as the provisioning of resources for pollinators. We hypothesize that trait syndromes aimed at provisioning resources for pollinators are positively related to non-crop habitats and negatively related to increasing agricultural intensification. We sampled plant species in 140 patches distributed among seven habitats (abandoned fields, boundaries, roadverges, and edges and inner alfalfa and cereal fields) that were classified into three levels of agricultural intensification: Low, Medium and High. We examined differences in species and functional assemblages, splitting response and effect traits, across various habitats and levels of agricultural intensification. Species richness and functional diversity of response and effect traits were partitioned along spatial scales. Both species and functional assemblages changed across habitats and with different levels of agricultural intensification. Non-cropped habitats and low levels of agricultural intensification promoted trait syndromes with trait-overdispersion mainly linked to the provisioning of resources for pollinators. The species turnover did not imply a functional turnover. Our study shows that traits are determined by agricultural intensification, and no further details on field position and habitat variability are needed to promote vegetation types with trait syndromes able to support pollinating insects.

Change in ladybeetle abundance and biological control of wheat aphids over time in agricultural landscape

The improvement of biocontrol services provided by natural enemies is important for realizing sustainable agriculture. While it has been well demonstrated that landscape context affects the occurrence of natural enemies in agricultural ecosystems, the response of natural enemies and their ability to suppress pest population growth over time has rarely been studied in relation to landscape composition and diversity. In this study, we investigated natural enemy (ladybeetle) and pest (wheat aphids) population abundance in wheat fields in the early period (defined as the main period for aphid colonization) and the late period (i.e., the main period for aphid reproduction) in different landscapes. Non-crop habitats surrounding wheat fields were found to enhance ladybeetle abundance. More specifically, the proportion of dwellings and woodlots were positively correlated with ladybeetle abundance in early period, and those of fallow and woodlot habitats were positively associated with ladybeetle abundance in late period. The most predictive spatial scales of ladybeetle abundance were landscape features within 0.5 and 2.0 km of wheat fields in the early and late periods, respectively. In contrast with the significantly negative correlation between ladybeetle abundance and aphid population growth during the late period, the relative low density of ladybeetles in the early period appeared to have no effect on aphid population growth. These findings suggest that non-crop habitats have differing effects on ladybeetle populations, both in their spatial scale and over time, and the continuity of functional habitat types is essential to support ladybeetle populations. While ladybeetles do indeed suppress aphid growth in the later part of the cycle, aphid control is also dependent on early colonization and constrained by external circumstances.