Genetic variation within a stick-insect species associated with community-level traits.

Phenotypic variation within species can affect the ecological dynamics of populations and communities. Characterizing the genetic variation underlying such effects can help parse the roles of genetic evolution and plasticity in "eco-evolutionary dynamics" and inform how genetic variation may shape patterns of evolution. Here, we employ genome-wide association (GWA) methods in Timema cristinae stick insects and their co-occurring arthropod communities to identify genetic variation associated with community-level traits. Previous studies have shown that maladaptation (i.e., imperfect crypsis) of T. cristinae can reduce the abundance and species richness of other arthropods due to an increase in bird predation. Whether genetic variation that is independent of crypsis has similar effects is unknown and was tested here using genome-wide genotyping-by-sequencing data of stick insects, arthropod community information, and GWA mapping with Bayesian sparse linear mixed models. We find associations between genetic variation in stick insects and arthropod community traits. However, these associations disappear when host-plant traits are accounted for. We thus use path analysis to disentangle interrelationships among stick-insect genetic variation, host-plant traits, and community traits. This revealed that host-plant size has large effects on arthropod communities, while genetic variation in stick insects has a smaller, but still significant effect. Our findings demonstrate that (1) genetic variation in a species can be associated with community-level traits but that (2) interrelationships among multiple factors may need to be analyzed to disentangle whether such associations represent causal relationships. This work helps to build a framework for genomic studies of eco-evolutionary dynamics.

Latitudinal variation in the diversity and composition of various organisms associated with an exotic plant: the role of climate and plant invasion.

Climate and plant invasion can shape biotic communities at large spatial scales. Yet, how diverse groups of organisms associated with an invasive plant change simultaneously with latitude and the roles of climate and plant invasion remains unclear. We conducted a field survey of plants (native vs exotic), soil fungi (pathogenic, saprotrophic, arbuscular mycorrhiza fungi (AMF) and ectomycorrhizal (EcM) fungi) and arthropods (herbivores, predators and detritivores) associated with the invasive plant Alternanthera philoxeroides at 49 sites spanning 14 latitudinal degrees in China. Results showed that diversity and composition of these functional groups changed differently with latitude, partially due to their specific responses to climate, invasion of A. philoxeroides and other biotic environments. Moreover, A. philoxeroides invasion and/or composition of other plants, rather than climate, predicted the diversity and richness of major functional groups and partly explained variance in composition of putative fungal pathogens. Our results suggest that climate and plant invasion could affect the diversity and composition of diverse groups of organisms simultaneously and their relative importance might vary among functional groups. Thus, it is necessary to explore latitudinal patterns and underlying drivers of diverse groups of organisms simultaneously to improve our ability to predict and mitigate threats posed by plant invasion and climate change.

Edge effects on trophic cascades in tropical rainforests.

The cascading effects of biodiversity loss on ecosystem functioning of forests have become more apparent. However, how edge effects shape these processes has yet to be established. We assessed how edge effects alter arthropod populations and the strength of any resultant trophic cascades on herbivory rate in tropical forests of Brazil. We established 7 paired forest edge and interior sites. Each site had a vertebrate-exclosure, procedural (exclosure framework with open walls), and control plot (total 42 plots). Forest patches were surrounded by pasture. Understory arthropods and leaf damage were sampled every 4 weeks for 11 months. We used path analysis to determine the strength of trophic cascades in the interior and edge sites. In forest interior exclosures, abundance of predaceous and herbivorous arthropods increased by 326% and 180%, respectively, compared with control plots, and there were significant cascading effects on herbivory. Edge-dwelling invertebrates responded weakly to exclusion and there was no evidence of trophic cascade. Our results suggest that the vertebrate community at forest edges controls invertebrate densities to a lesser extent than it does in the interior. Edge areas can support vertebrate communities with a smaller contingent of insectivores. This allows arthropods to flourish and indirectly accounts for higher levels of plant damage at these sites. Increased herbivory rates may have important consequences for floristic community composition and primary productivity, as well as cascading effects on nutrient cycling. By interspersing natural forest patches with agroforests, instead of pasture, abiotic edge effects can be softened and prevented from penetrating deep into the forest. This would ensure a greater proportion of forest remains habitable for sensitive species and could help retain ecosystem functions in edge zones.

Efectos de Borde sobre las Cascadas Tróficas en los Bosques Tropicales Resumen Los efectos en cascada de la pérdida de la biodiversidad sobre el funcionamiento ecosistémico de los bosques se ha vuelto más evidente. A pesar de ésto, no se ha establecido cómo los efectos de borde moldean estos procesos. Evaluamos cómo los efectos de borde alteran las poblaciones de artrópodos y la fuerza de cualquier cascada trófica resultante sobre la tasa de herbivoría en los bosques tropicales de Brasil. Establecimos siete pares de sitios interiores y en el borde del bosque. Cada sitio tuvo un lote de encierro de vertebrados, uno procesal (un marco de trabajo de encierro con muros abiertos) y uno de control (total de 42 lotes). Los fragmentos de bosque estuvieron rodeados por potreros. Los artrópodos del sotobosque y el daño a las hojas fueron muestreados cada cuatro semanas durante once meses. Usamos el análisis de vía para determinar la fuerza de las cascadas tróficas en los sitios interiores y los del borde. En los encierros ubicados al interior del bosque la abundancia de artrópodos depredadores y herbívoros incrementó en un 326% y 180% respectivamente (comparada con los lotes de control) y hubo efectos relevantes de cascada sobre la herbivoría. Los invertebrados habitantes del borde respondieron débilmente al encierro y no hubo evidencia de la cascada trófica. Nuestros resultados sugieren que la comunidad de vertebrados en los bordes del bosque controla las densidades de invertebrados en un grado menor de lo que lo hace al interior del bosque. Las áreas del borde pueden mantener comunidades de vertebrados con un contingente menor de insectívoros. Ésto permite que los artrópodos florezcan y explica indirectamente los niveles más altos de daño a las plantas en estos sitios. El incremento de las tasas de herbivoría puede tener consecuencias importantes para la composición de la comunidad y para la productividad primaria, así como para los efectos cascada y el ciclo de nutrientes. Si intercalamos los fragmentos de bosque con agrobosques, en lugar de hacerlo con potreros, los efectos abióticos del borde pueden reducirse y se puede prevenir que penetren profundamente en el bosque. Esto aseguraría que una mayor proporción de bosque permanezca como habitable para las especies sensibles y podría ayudar a retener las funciones del ecosistema en las zonas de borde.

The interplay of landscape composition and configuration: new pathways to manage functional biodiversity and agroecosystem services across Europe.

Managing agricultural landscapes to support biodiversity and ecosystem services is a key aim of a sustainable agriculture. However, how the spatial arrangement of crop fields and other habitats in landscapes impacts arthropods and their functions is poorly known. Synthesising data from 49 studies (1515 landscapes) across Europe, we examined effects of landscape composition (% habitats) and configuration (edge density) on arthropods in fields and their margins, pest control, pollination and yields. Configuration effects interacted with the proportions of crop and non-crop habitats, and species' dietary, dispersal and overwintering traits led to contrasting responses to landscape variables. Overall, however, in landscapes with high edge density, 70% of pollinator and 44% of natural enemy species reached highest abundances and pollination and pest control improved 1.7- and 1.4-fold respectively. Arable-dominated landscapes with high edge densities achieved high yields. This suggests that enhancing edge density in European agroecosystems can promote functional biodiversity and yield-enhancing ecosystem services.

Impacts of rainfall extremes predicted by climate-change models on major trophic groups in the leaf litter arthropod community.

Arthropods in the leaf litter layer of forest soils influence ecosystem processes such as decomposition. Climate-change models predict both increases and decreases in average rainfall. Increased drought may have greater impacts on the litter arthropod community. In addition to affecting survival or behaviour of desiccation-sensitive species, lower rainfall may indirectly lower abundances of consumers that graze drought-stressed fungi, with repercussions for higher trophic levels. We tested the hypothesis that trophic structure will differ between the two rainfall scenarios. In particular, we hypothesized that densities of several broadly defined trophic groupings of arthropods would be lower under reduced rainfall. To test this hypothesis, we used sprinklers to impose two rainfall treatments during three growing seasons in roofed, fenced 14-m2 plots and documented changes in abundance from initial, pre-treatment densities of 39 arthropod taxa. Experimental plots were subjected to either LOW (fortnightly) or HIGH (weekly) average rainfall based upon climate models and the previous 100 years of regional weekly averages. Unroofed open plots, our reference treatment (REF), experienced higher than average rainfall during the experiment. The two rainfall extremes produced clear negative effects of lowered rainfall on major trophic groups. Broad categories of fungivores, detritivores and predators were more abundant in HIGH than LOW plots by the final year. Springtails (Collembola), which graze fungal hyphae, were 3× more abundant in the HIGH rainfall treatment. Taxa of larger-bodied fungivores and detritivores, spiders (Araneae), and non-spider predators were 2× more abundant under HIGH rainfall. Densities of mites (Acari), which include fungivores, detritivores and predators, were 1.5× greater in HIGH rainfall plots. Abundances and community structure of arthropods were similar in REF and experimental plots, showing that effects of rainfall uncovered in the experiment are applicable to nature. This pattern suggests that changes in rainfall will alter bottom-up control processes in a critical detritus-based food web of deciduous forests. Our results, in conjunction with other findings on the impact of desiccation on arthropods and fungal growth, suggest that drier conditions will depress densities of fungal consumers, causing declines in higher trophic levels, with possible impacts on soil processes and the larger forest food web.

Increased grassland arthropod production with mammalian herbivory and eutrophication: a test of mediation pathways.

Increases in nutrient availability and alterations to mammalian herbivore communities are a hallmark of the Anthropocene, with consequences for the primary producer communities in many ecosystems. While progress has advanced understanding of plant community responses to these perturbations, the consequences for energy flow to higher trophic levels in the form of secondary production are less well understood. We quantified arthropod biomass after manipulating soil nutrient availability and wild mammalian herbivory, using identical methods across 13 temperate grasslands. Of experimental increases in nitrogen, phosphorus, and potassium, only treatments including nitrogen resulted in significantly increased arthropod biomass. Wild mammalian herbivore removal had a marginal, negative effect on arthropod biomass, with no interaction with nutrient availability. Path analysis including all sites implicated nutrient content of the primary producers as a driver of increased arthropod mean size, which we confirmed using 10 sites for which we had foliar nutrient data. Plant biomass and physical structure mediated the increase in arthropod abundance, while the nitrogen treatments accounted for additional variation not explained by our measured plant variables. The mean size of arthropod individuals was 2.5 times more influential on the plot-level total arthropod biomass than was the number of individuals. The eutrophication of grasslands through human activity, especially nitrogen deposition, thus may contribute to higher production of arthropod consumers through increases in nutrient availability across trophic levels.

Genetically based latitudinal clines in Artemisia californica drive parallel clines in arthropod communities.

Intraspecific variation in plant traits has been clearly shown to drive the structure of associated arthropod communities at the spatial scale of individual plant populations. Nevertheless, it is largely unknown whether plant trait variation among populations drives landscape-scale variation in arthropod communities, and how the strength of such plant genetic effects compares to, and interacts with, those of environmental variation. We documented the structure of arthropod communities on Artemisia californica for two consecutive years in a common garden of plants sourced from five populations along a 5° latitudinal gradient and grown under precipitation treatments approximating the four-fold difference between the north and south range margins for this species. Previous study of plant traits from this garden documented clinal genetic variation, suggesting local adaptation to this environmental gradient, as well as effects of precipitation manipulation that were consistent among populations (i.e., no genotype-by-environment interaction). Within the common garden, arthropod density, evenness, and diversity increased clinally with population source latitude, and arthropod community composition (i.e., species relative abundance) showed a north-south divide. The 2.6-fold cline of northward increase in arthropod density in the common garden was mirrored by a 6.4-fold increase in arthropod density on wild plants sampled along the species range. In contrast to the strong influence of plant genotype, the precipitation manipulation only influenced arthropod community composition, and plant genetic effects on arthropods operated independently of precipitation regime (no genotype-by-environment interaction). Accordingly, we conclude that the strongest driver of landscape-level variation in arthropod communities in this foundational plant species is not variation in the abiotic environment itself, but rather variation in plant traits underlain by the evolutionary process of plant local adaptation.

Taxonomic and functional composition of arthropod assemblages across contrasting Amazonian forests.

Arthropods represent most of global biodiversity, with the highest diversity found in tropical rain forests. Nevertheless, we have a very incomplete understanding of how tropical arthropod communities are assembled. We conducted a comprehensive mass sampling of arthropod communities within three major habitat types of lowland Amazonian rain forest, including terra firme clay, white-sand and seasonally flooded forests in Peru and French Guiana. We examined how taxonomic and functional composition (at the family level) differed across these habitat types in the two regions. The overall arthropod community composition exhibited strong turnover among habitats and between regions. In particular, seasonally flooded forest habitats of both regions comprised unique assemblages. Overall, 17·7% (26 of 147) of arthropod families showed significant preferences for a particular habitat type. We present a first reproducible arthropod functional classification among the 147 taxa based on similarity among 21 functional traits describing feeding source, major mouthparts and microhabitats inhabited by each taxon. We identified seven distinct functional groups whose relative abundance contrasted strongly across the three habitats, with sap and leaf feeders showing higher abundances in terra firme clay forest. Our novel arthropod functional classification provides an important complement to link these contrasting patterns of composition to differences in forest functioning across geographical and environmental gradients. This study underlines that both environment and biogeographical processes are responsible for driving arthropod taxonomic composition while environmental filtering is the main driver of the variance in functional composition.

Host-plant sex and phenology of Buddleja cordata Kunth interact to influence arthropod communities.

Intraspecific variation in plants is expected to have profound impacts on the arthropod communities associated with them. Because sexual dimorphism in plants is expected to provide consistent variation among individuals of the same species, researchers have often studied the effect it has on associated arthropods. Nevertheless, most studies have focused on the effect of sexual dimorphism in a single or a few herbivores, thus overlooking the potential effects on the whole arthropod community. Our main objective was to evaluate effects of Buddleja cordata's plant-sex on its associated arthropod community. We surveyed 13 pairs of male and female plants every 2 months during a year (June 2010 to April 2011). Every sampling date, we measured plant traits (water content and leaf thickness), herbivory, and the arthropod community. We did not find differences in herbivory between plant sex or through time. However, we found differences in water content through time, with leaf water-content matching the environmental seasonality. For arthropod richness, we found 68 morphospecies associated with female and 72 with male plants, from which 53 were shared by both sexes. We did not observe differences in morphospecies richness; however, we found sex-associated differences in the diversity of all species and differences on the diversity of the most abundant species with an interesting temporal component. During peak flowering season, male plants showed higher values on both parameters, but during the peak fructification season female plants showed the higher values on both diversity parameters. Our research exemplifies the interaction between plant-phenology and plant-sex as drivers of arthropod communities' diversity, even when plant sexual-dimorphism is inconspicuous, and highlighting the importance of accounting for seasonal variation. We stress the need of conducting more studies that test this time-dependent framework in other dioecious systems, as it has the potential to reconcile previous contrasting observations reported in the literature.

Assessing the drivers of grassland ground-dwelling arthropod community composition: Integrating landscape-scale farming intensity and local environmental conditions.

Grasslands are essential habitats for preserving arthropod communities in agricultural landscapes. The environmental state of grassland, their farming practices, and land cover heterogeneity in landscape around grassland are three factors that influence ground-dwelling grassland arthropod communities. However, the impact of the intensity of farming practices at the landscape scale has not yet been fully explored. In this study, (i) we studied complex relationships between environmental variables that describe the local conditions (i.e., grassland environmental state and farming practices) and land cover heterogeneity (i.e., land cover and landscape-wide intensity) of our study area in north-east France; and (ii) estimated the relative effect weight of landscape-wide intensity compared to other local and landscape variables on arthropod communities. We identified 14 taxonomic families, with Lycosidae, Carabidae and Staphylinidae as the families most represented in communities. We have highlighted a positive correlation between the different variables of landscape-wide intensity, as well as a positive correlation between sampled grassland intensity and the quantity of grassland in the landscape. Using Partial Least Squares Path Modelling (PLS-PM) analysis, we observed a positive effect of landscape-wide intensity on arthropod abundance-activity in grassland, indicating a potential concentration effect in the grasslands surrounded by an intensive landscape. Also, we have shown that the effect of landscape-wide intensity was at least as strong as that of other local and landscape variables. Our study is one of the first to consider land cover and farming practices simultaneously at the landscape scale. We demonstrate the importance of considering farming practices at the landscape scale to explain the state of ground-dwelling arthropod communities, and the need to take them into account when designing landscapes that are favourable to biodiversity. We argue that further studies are needed to explain the mechanisms involved in the relationship between arthropod communities and farming practices at the landscape scale.

Habitat characteristics and climatic factors influence microhabitat selection and arthropod community structure in a globally rare central Appalachian shale barren.

The central Appalachian shale barrens, a globally unique habitat type restricted to the eastern United States, presents an insular and physiologically stressful environment with sparse vegetation and extreme ground surface and air temperatures. Despite the high levels of plant species endemism within these systems, information on invertebrate communities and habitat preferences is extremely limited.Through this study, we aimed to better understand a shale barren arthropod community, microhabitat selection, and the influence of habitat characteristics and climatic factors. We employed pitfall traps to sample epigeic arthropods during the 2016 growing season in a shale barren habitat.Arthropod community composition was driven by overstory trees, mediated through accumulated leaf litter and availability of shaded microhabitats. Ambient air temperature also influenced the surface activity of various taxa with spiders decreasing at higher temperatures and ants, crickets, flies, and harvestmen all increasing in relative abundance.Habitat integrity of the central Appalachian shale barrens is threatened by forest succession and mesophication, encroaching invasive plant species, and rising ambient air temperatures, all of which can alter the extent of overstory vegetation and availability of shaded microhabitats. These biotic and physical pressures will subsequently affect epigeic arthropod community composition, depending on adaptive capacity of individual taxa.To the authors' knowledge, these findings constitute only the second published work on arthropod communities and the first to focus on epigeic taxa in this globally rare habitat type. Continued conservation of these unique, insular habitats and their adapted inhabitants requires a multifaceted approach that considers current and future conditions.

Effects of Two Invasive Weeds on Arthropod Community Structure on the Central Plateau of New Zealand.

Heather (Calluna vulgaris) and broom (Cytisus scoparius), originally from Europe, are the main invasive plants on New Zealand's North Island Central Plateau, where they threaten native flora and fauna. Given the strong link between arthropod communities and plants, we explored the impact of these invasive weeds on the diversity and composition of associated arthropod assemblages in this area. The arthropods in heather-invaded areas, broom-invaded areas, and areas dominated by the native species manuka (Leptospermum scoparium) and Dracohyllum (Dracophyllum subulatum) were collected and identified to order. During summer and autumn, arthropods were collected using beating trays, flight intercept traps and pitfall traps. Diversity indices (Richness, Shannon's index and Simpson's index) were calculated at the order level, and permutational multivariate analysis (PERMANOVA) was used to explore differences in order-level community composition. Our results show a significant variation in community composition for all trapping methods in both seasons, whereas invasive plants did not profoundly impact arthropod order richness. The presence of broom increased arthropod abundance, while heather was linked to a reduction. Under all possible plant pairings between heather, broom, manuka, and Dracophylum, the impact of neighbouring plant identity on arthropod community composition was further explored for the samples collected using beating trays. The results suggest that during plant invasion, arthropod communities are affected by neighbouring plant identity and that impacts vary between arthropod sampling methods and seasons.

Crop Diversity at the Landscape Level Affects the Composition and Structure of the Vegetation-Dwelling Arthropod Communities in Naked Oat (Avena Chinensis) Fields.

The expansion of agriculture and intensive mechanized production have resulted in the loss of habitats and biodiversity, which has led to the loss of ecological services such as the biological control of pests and diseases, and insect-borne pollination. Current studies mainly focus on the impact of small-scale crop diversity (such as intercropping) on ecological service but lack research on the effects of crop diversity at the landscape scale. In this study, vegetation-dwelling arthropods in naked oat (Avena chinensis) fields under different planting patterns were collected at different growth stages by standardized sweep netting sampling, and the differences in arthropod communities and temporal dynamics were analyzed. Taking this information as an example, the effects of crop diversity at the landscape scale caused by different planting patterns on arthropod communities were studied. It was found that herbivores were the most abundant functional group in the arthropod community in naked oat fields, accounting for 70.13% of the total abundance, followed by natural enemies, accounting for 23.45%, and, finally, other insects. The abundance and species richness of natural enemies in naked oat fields under diversified planting pattern were significantly higher than those under intensive planting pattern, while the abundance and species richness of herbivorous pests showed no significant difference between the two planting patterns. Planting patterns significantly affected the composition and structure of arthropod communities in naked oat fields. Significantly higher ratio of natural enemy to pest and more diverse natural enemies under the diversified planting pattern have shown better biological control potential and the significance of biodiversity protection.

The importance of dung beetles and arthropod communities on degradation of cattle dung pats in eastern South Dakota.

BACKGROUND: Dung accumulation in rangelands can suppress plant growth, foul pastures, and increase pest pressure. Here, we describe the arthropod community of dung in eastern South Dakota, and quantify their contributions to dung degradation using an exclusion cage design. METHODS: Various arthropod community and degradation characteristics were measured in caged and uncaged dung pats over time in early and late summer. RESULTS: A total of 86,969 specimens were collected across 109 morphospecies (13 orders) of arthropods, and cages effectively reduced arthropod abundance, species richness, and diversity. Uncaged dung pats degraded significantly faster than the caged pats, with the largest difference occurring within 2 d of pat deposition. Dung organic matter was degraded more slowly (by 33-38 d) in the caged pats than where insects had free access to the pats. Although dung beetles only represented 1.5-3% of total arthropod abundance, they were significantly correlated to more abundant and complex total arthropod communities. DISCUSSION: A diverse community contributes to dung degradation in rangelands, and their early colonization is key to maximizing this ecosystem service.

Genetic-Based Susceptibility of a Foundation Tree to Herbivory Interacts With Climate to Influence Arthropod Community Composition, Diversity, and Resilience.

Understanding how genetic-based traits of plants interact with climate to affect associated communities will help improve predictions of climate change impacts on biodiversity. However, few community-level studies have addressed such interactions. Pinyon pine (Pinus edulis) in the southwestern U.S. shows genetic-based resistance and susceptibility to pinyon needle scale (Matsucoccus acalyptus). We sought to determine if susceptibility to scale herbivory influenced the diversity and composition of the extended community of 250+ arthropod species, and if this influence would be consistent across consecutive years, an extreme drought year followed by a moderate drought year. Because scale insects alter the architecture of susceptible trees, it is difficult to separate the direct influences of susceptibility on arthropod communities from the indirect influences of scale-altered tree architecture. To separate these influences, scales were experimentally excluded from susceptible trees for 15 years creating susceptible trees with the architecture of resistant trees, hereafter referred to as scale-excluded trees. Five patterns emerged. (1) In both years, arthropod abundance was 3-4X lower on susceptible trees compared to resistant and scale-excluded trees. (2) Species accumulation curves show that alpha and gamma diversity were 2-3X lower on susceptible trees compared to resistant and scale-excluded trees. (3) Reaction norms of arthropod richness and abundance on individual tree genotypes across years showed genotypic variation in the community response to changes in climate. (4) The genetic-based influence of susceptibility on arthropod community composition is climate dependent. During extreme drought, community composition on scale-excluded trees resembled susceptible trees indicating composition was strongly influenced by tree genetics independent of tree architecture. However, under moderate drought, community composition on scale-excluded trees resembled resistant trees indicating traits associated with tree architecture became more important. (5) One year after extreme drought, the arthropod community rebounded sharply. However, there was a much greater rebound in richness and abundance on resistant compared to susceptible trees suggesting that reduced resiliency in the arthropod community is associated with susceptibility. These results argue that individual genetic-based plant-herbivore interactions can directly and indirectly impact community-level diversity, which is modulated by climate. Understanding such interactions is important for assessing the impacts of climate change on biodiversity.

Long-term resource addition to a detrital food web yields a pattern of responses more complex than pervasive bottom-up control.

BACKGROUND: Theory predicts strong bottom-up control in detritus-based food webs, yet field experiments with detritus-based terrestrial systems have uncovered contradictory evidence regarding the strength and pervasiveness of bottom-up control processes. Two factors likely leading to contradictory results are experiment duration, which influences exposure to temporal variation in abiotic factors such as rainfall and affects the likelihood of detecting approach to a new equilibrium; and openness of the experimental units to immigration and emigration. To investigate the contribution of these two factors, we conducted a long-term experiment with open and fenced plots in the forest that was the site of an earlier, short-term experiment (3.5 months) with open plots (Chen & Wise, 1999) that produced evidence of strong bottom-up control for 14 taxonomic groupings of primary consumers of fungi and detritus (microbi-detritivores) and their predators. METHODS: We added artificial high-quality detritus to ten 2 × 2-m forest-floor plots at bi-weekly intervals from April through September in three consecutive years (Supplemented treatment). Ten comparable Ambient plots were controls. Half of the Supplemented and Ambient plots were enclosed by metal fencing. RESULTS: Arthropod community structure (based upon 18 response variables) diverged over time between Supplemented and Ambient treatments, with no effect of Fencing on the multivariate response pattern. Fencing possibly influenced only ca. 30% of the subsequent univariate analyses. Multi- and univariate analyses revealed bottom-up control during Year 1 of some, but not all, microbi-detritivores and predators. During the following two years the pattern of responses became more complex than that observed by Chen & Wise (1999). Some taxa showed consistent bottom-up control whereas others did not. Variation across years could not be explained completely by differences in rainfall because some taxa exhibited negative, not positive, responses to detrital supplementation. DISCUSSION: Our 3-year experiment did not confirm the conclusion of strong, pervasive bottom-up control of both microbi-detritivores and predators reported by Chen & Wise (1999). Our longer-term experiment revealed a more complex pattern of responses, a pattern much closer to the range of outcomes reported in the literature for many short-term experiments. Much of the variation in responses across studies likely reflects variation in abiotic and biotic factors and the quality of added detritus. Nevertheless, it is also possible that long-term resource enhancement can drive a community towards a new equilibrium state that differs from what would have been predicted from the initial short-term responses exhibited by primary and secondary consumers.

Temporal dynamics of the arthropod community in pear orchards intercropped with aromatic plants.

BACKGROUND: Increasing attention has been paid to enhancing biological control through habitat management in agricultural systems for enhanced pest management. Pest management benefits can be realised by intercropping, which can increase natural enemy abundance and, in turn, reduce pest abundance. In this study, the composition and temporal dynamics of arthropod communities in pear orchards when intercropped with aromatic plants were investigated, and the effectiveness and applicability of aromatic plants as intercrops for enhancing insect control were assessed. RESULTS: When compared with natural grasses or clean tillage, intercropping significantly reduced pest abundance and increased the ratio of natural enemies to pests. Intercropping also shortened the occurrence duration and depressed the incidence peak in annual dynamics curves of the pest subcommunity and the arthropod community, mainly because of the repellent effects of aromatic plants. Equally important, intercropping significantly reduced the numbers of major pests, such as Psylla chinensis, Aphis citricola and Pseudococcus comstocki, while their incidence period was delayed to varying degrees, and the numbers of their dominant natural enemies (Coccinella septempunctata, Phytoseiulus persimilis and Chrysoperla sinica) increased. CONCLUSION: Intercropping with aromatic plants led to a considerable improvement in arthropod pest management by enhancing the activity of the beneficial arthropod community within the pear orchard ecosystem.

Effects of understory structure on the abundance, richness and diversity of Collembola (Arthropoda) in southern Brazil / Efeitos da estrutura do sub-bosque na abundância, riqueza e diversidade de Collembola (Arthropoda) no sul do Brasil

The purpose of this study was to investigate the effects of different landscape structures on the understory Collembola community. Four different forest physiognomies were compared: Pinus spp. plantation, Eucalyptus spp. plantation, Araucaria angustifolia plantation, and a remaining native Araucaria forest. Three areas containing two sampling units (25 m x 2 m each) were selected in each forest physiognomy. Understory Collembola collection was done with a 1 x 1m canvas sheet held horizontally below the vegetation, which was beaten with a 1m long stick, seasonally from September 2003 to August 2004. We evaluated the influence of forest physiognomies on the abundance, richness and diversity of Collembola communities. It was also verified if the habitat structure of each physiognomy was associated with the composition of the Collembola community. A total number of 4,111 individuals were collected belonging to the families Entomobrydae and Tomocerida (Entomobryomorpha), and Sminthuridae (Symphypleona), and divided in 12 morphospecies. Pinus plantation presented the highest richness, abundance and diversity of Collembola and it was associated to diverse understory vegetation. The abundance of Entomobrydae and Sminthuridae was associated to the presence of bushes, while Tomoceridae abundance was associated to the presence of trees. The habitat structure, measured through understory vegetation density and composition, plays an important role on the determination of the structure and composition of the Collembola community.

O propósito deste estudo foi investigar os efeitos da estrutura do sub-bosque na comunidade de colêmbolos. Foram comparados quatro ambientes florestais distintos: plantações de Pinus spp., plantações de Eucalyptus spp., plantações de Araucaria angustifolia e áreas de floresta ombrófila nativa remanescente. Para cada fisionomia vegetal houve três áreas com duas unidades amostrais de 25 m × 2 m cada. As coletas foram realizadas com guarda-chuva entomológico, medindo 1 m × 1 m, no período de setembro de 2003 a agosto de 2004. Investigou-se se a abundância, a riqueza e a diversidade da comunidade de colêmbolos foram influenciadas pelas fisionomias vegetais. Também verificou-se se a estrutura do habitat de cada tipo de floresta teve associação com a composição da comunidade de colêmbolos. Foram coletados 4111 indivíduos, pertencentes às famílias Entomobryidae, Tomoceridae e Sminthuridae, divididos em 12 morfoespécies. A plantação de Pinus spp. apresentou maior riqueza, abundância e diversidade de colêmbolos, devido à maior quantidade de vegetação disponível no sub-bosque. A composição de colêmbolos esteve associada aos tipos vegetacionais, com Entomobryidae e Sminthuridae associados aos arbustos, e Tomoceridade às árvores. A estrutura do habitat, medida através da densidade e composição da vegetação do sub-bosque mostrou-se um fator importante na determinação da estrutura e composição da comunidade de Collembola.