Grassland Arthropod Communities Research Articles

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.

Changes in plant and arthropod functional traits mediate land use and precipitation effects on grassland production

• Few data were available on the mechanistic effects of land-use and rainfall on plant and arthropod productivity. • Plant and arthropod diversity and biomass showed divergent responses to land-use. • Grazing and rainfall affected plant and arthropod productivity via different pathways. • Changes in multi-trophic traits were crucial for biodiversity and ecosystem function. Much effort has been devoted to better understanding the effects of land-use and climate changes on biodiversity and ecosystem functions (BEF); however, the mechanistic pathways behind the observed changes remain largely unexplored, especially for grassland arthropod community. Using a 7-year grassland experiment in Inner Mongolian steppe, we examined the relative importance of direct versus indirect (through mediating plant and arthropod biodiversity) effects of four land-use types (growing-season grazing, spring & summer grazing, mowing and enclosure) and precipitation variation in two climatically contrasting years on plant and arthropod productivity. Our results showed that: (1) the variation patterns of species and functional diversity and productivity across land use types were significantly different between plant and arthropod communities, though both plants and arthropods had their community-weighted mean size (i.e., plant height and arthropod body size) decreased under grazing or mowing; (2) moderate grazing and plant growing-season precipitation enhanced plant productivity mainly via indirectly increasing plant functional dispersion and decreasing plant nitrogen concentration associated with the shift in dominant species, but reduced arthropod productivity majorly by direct grazing damage and less importantly by indirect mediation of arthropod body size; (3) grassland management and precipitation-induced variations in plant and arthropod productivity could be well explained by the changes in their functional traits and diversity, but not species richness. Our results indicate the importance of trait-based method in understanding the mechanisms of management and precipitation affecting plant and arthropod productivity, and suggest that biological traits in multiple trophic groups can be used as efficient indicators in the assessment of grassland ecosystem health.

Vegetation richness, diversity, and structure influence arthropod communities of native and restored northern mixed‐prairies

We studied the effects of vegetation species richness, diversity, and structure on grassland arthropod communities of 23 sites in northeastern South Dakota and southeastern North Dakota. Sites were selected to represent a vegetation species diversity gradient, and three vegetation cover types, including native unseeded grassland, low‐diversity seeding known as dense nesting cover (DNC) for waterfowl, and high‐diversity seed mix. During July of 2016, pan traps and sweep nets were used to survey the grassland arthropod community. A total of 25,521 arthropods representing 107 taxonomic families were collected. Richness, diversity, and biomass of arthropods did not differ among cover types. Vegetation richness and diversity, cover type, percent live vegetation and native cover, and litter depth were important predictors of arthropod community measures, and multivariate analysis of the arthropod community indicated significant differences between native and DNC study sites; explained by differences in vegetation richness, percent forb cover, and litter depth. Results of our study suggest that species richness of grassland restoration seeding mixes likely impacts arthropod richness and diversity, and DNC does not produce arthropod communities similar to native prairie. Additionally, because vegetation structural variables were important determinants of arthropod community measures, grassland management practices will influence the resulting arthropod community and influence the success of grassland restoration using high‐diversity seed mixes. Results of our study promote the potential for successful restoration outcomes using high‐diversity seed mixes, and indicate that low‐diversity, non‐native seed mixes, such as DNC, do not fully restore native grassland arthropod communities.

Crazy ants craving calcium: macronutrients and micronutrients can limit and stress an invaded grassland brown food web.

Nitrogen and phosphorus are thought to be the most important limiting nutrients in most terrestrial ecosystems, but little is known about how other elements may limit the abundance of arthropods. We utilized a fully factorial fertilization experiment that manipulated macronutrients (N and P, together) and micronutrients (calcium, sodium, potassium, separately), in large 30×30m plots and sampled litter arthropods via pitfall trapping to determine the nutrients that limit this group. An invasive ant, Nylanderia fulva, numerically dominated the community and increased in abundance 13% in plots fertilized by Ca. Detritivores were not limited by any nutrient combination, but macronutrients increased predator abundance 43%. We also found that some combinations of macronutrients and micronutrients had toxic or stressful effects on the arthropod community: detritivores decreased in abundance 23% with the combination of macronutrients, Ca, and K, and 22% with macronutrients and K; and N. fulva decreased in abundance 24% in plots fertilized by K and 45% in plots fertilized by the combination of Na and K. Our work supports growing evidence that micronutrients, especially Ca and K, may be important in structuring grassland arthropod communities, and suggests that micronutrients may affect whether or not invasive ants reach numerical dominance.

Is grazing always the answer to grassland management for arthropod biodiversity? Lessons from a gravel pit restoration project

Grazing by domestic stock is widely used in nature reserve management to maintain or restore characteristics of the flora. While the effects on plants are well understood, grazing effects on arthropods are in need of further investigation. We studied the effects of management on grassland arthropod communities at Needingworth, a mixture of grassland and wetland, created after gravel extraction. We hypothesised arthropod abundance and the species richness of Hemiptera and Coleoptera, would be no greater in fenced, ungrazed areas than in cattle-grazed grassland. We used suction sampling to collect grassland arthropods which were initially identified to order level, and then to species or genus level for the Coleoptera and Hemiptera. Abundance of total invertebrates and of all orders, except for Diptera, was greater in ungrazed than grazed grassland. We estimated that the presence of ungrazed grassland resulted in 14.9% greater invertebrate abundance at Needingworth. Community structure showed strong differences in relation to management, particularly in terms number of detritivores. Even the small amount of grassland management at Needingworth had distinct negative impacts arthropod abundance and community structure, and leaving ungrazed areas has the potential to benefit invertebrate biodiversity. We recommend that some grassland patches should remain unmanaged for long periods, as part of a mixed management strategy. Conservation grazing is not the only approach that should be used.

Distribution and community structure of chloropid flies (Diptera: Chloropidae) in Nearctic glacial and post‐glacial grasslands

Abstract Arthropod species inhabiting disjunct xeric grasslands in the Yukon Territory, Canada may be relicts of Pleistocene steppe assemblages widespread in Beringia during glaciation, or they may be recent remnants of northward expansion of southern grassland communities during the early‐Holocene Hypsithermal. To assess the likely origin of the Yukon grassland arthropod community, grassland‐associated Chloropidae (Diptera) were compared from three regions: the Canadian Prairies, the Peace River region of Alberta and the southern Yukon. If Yukon grassland insect communities, like those in the Peace region, result primarily from northward dispersal during the Hypsithermal, chloropid assemblages in all regions would be similar, except that species richness would decline with increasing latitude. If, however, they are primarily relicts of Pleistocene steppe communities, Yukon chloropid assemblages would be distinct from southern assemblages. There was a latitudinal gradient of decreasing species richness and Yukon assemblages were distinct from Prairie and Peace region assemblages, based on cluster analysis, non‐metric multidimensional scaling and pairwise comparisons of Morisita similarity indices. Community‐level analyses suggest that Yukon assemblages have been separated from those in the Prairies and Peace regions since before the Hypsithermal and likely contain a mix of relict populations inhabiting Pleistocene steppe remnants in East Beringia with recent northward post‐glacial dispersal from the southern Prairies. Dispersal from eastern Russia via Beringia appears to have been negligible.

Sweeping beauty: is grassland arthropod community composition effectively estimated by sweep netting?

Arthropods are critical ecosystem components due to their high diversity and sensitivity to perturbation. Furthermore, due to their ease of capture they are often the focus of environmental health surveys. There is much debate regarding the best sampling method to use in these surveys. Sweep netting and pan trapping are two sampling methods commonly used in agricultural arthropod surveys, but have not been contrasted in natural grassland systems at the community level. The purpose of this study was to determine whether sweep netting was effective at estimating arthropod diversity at the community level in grasslands or if supplemental pan trapping was needed. Arthropods were collected from grassland sites in Montana, USA, in the summer of 2011. The following three standardized evaluation criteria (consistency, reliability, and precision) were developed to assess the efficacy of sweep netting and pan trapping, based on analyses of variations in arthropod abundances, species richness, evenness, capture frequency, and community composition. Neither sampling method was sufficient in any criteria to be used alone for community-level arthropod surveys. On a taxa-specific basis, however, sweep netting was consistent, reliable, and precise for Thysanoptera, infrequently collected (i.e., rare) insects, and Arachnida, whereas pan trapping was consistent, reliable, and precise for Collembola and bees, which is especially significant given current threats to the latter's populations worldwide. Species-level identifications increase the detected dissimilarity between sweep netting and pan trapping. We recommend that community-level arthropod surveys use both sampling methods concurrently, at least in grasslands, but likely in most nonagricultural systems. Target surveys, such as monitoring bee communities in fragmented grassland habitat or where detailed information on behavior of the target arthropod groups is available can in some instances employ singular methods. As a general ecological principle, consistency, reliability, and precision are appropriate criteria to evaluate the applicability of a given sampling method for both community-level and taxa-specific arthropod surveys in any ecosystem.

Guild structure in the food web of grassland arthropod communities along an urban—rural landscape gradient

Urbanization is a major cause of ecosystem change, and arthropods are a principal component of grassland ecosystems, which are often found in human-dominated landscapes. Although higher trophic level arthropods have been expected to be the most sensitive to urbanization, researchers are debating whether this is the case. We compared the guild structure of grassland arthropod food webs along an urban—rural gradient in the Tokyo metropolitan area, the largest metropolitan area in the world. Arthropod communities were sampled, and guild types were classified by body size and food habit. The guild structure of arthropod food webs was compared among various types of grasslands, and the effects on the guild structure of the surrounding landscape and local vegetation were analyzed. The arthropod guild structure varied along the urban—rural gradient. Large carnivores were abundant in semi—natural grassland ecosystems in the traditional rural landscape, which was at one end of the studied urban-rural gradient. In contrast, small carnivores, omnivores, and detritivores were abundant in the artificial grassland ecosystems of the urban landscape at the other end of the gradient. Because very large carnivores are vulnerable to urbanization activities, rural landscapes rich in these species should be conserved.

Short-Term Effects of a Summer Wildfire on a Desert Grassland Arthropod Community in New Mexico

Surface-active arthropods were sampled after a lightning-caused wildfire in desert grassland habitat on the Sevilleta National Wildlife Refuge, Socorro County, NM. Pitfall traps (n = 32 per treatment) were used to evaluate species-specific "activity-density" indices after the June wildfire in both burned and unburned areas. In total, 5,302 individuals were collected from 69 taxa. Herbivore activity-densities generally decreased, whereas predators often increased in the burned area; pitfall trap bias likely contributed to this latter observation. Fire caused the virtual extirpation of scaly crickets (Mogoplistidae), field crickets (Gryllidae), and camel crickets (Raphidophoridae), but recolonization began during the first postfire growing season. Several grasshoppers (Acrididae) also exhibited significant postfire declines [Ageneotettix deorum (Scudder), Eritettix simplex (Scudder), Melanoplus bowditchi Scudder, and Amphitornus coloradus (Thomas)]. Some beetles showed lower activity-density, including Pasimachus obsoletus LeConte (Carabidae) and Eleodes extricatus (Say) (Tenebrionidae). Taxa exhibiting significant postfire increases in activity-density included acridid grasshoppers (Aulocara femoratum (Scudder), Hesperotettix viridis (Thomas), Trimerotropis pallidipennis (Burmeis.), and Xanthippus corallipes Haldeman); carabid beetles (Amblycheila picolominii Reiche, Cicindela punctulata Olivier), tenebrionid beetles (Eleodes longicollis LeConte, Edrotes rotundus (Say), Glyptasida sordida (LeConte), Stenomorpha consors (Casey); the centipedes Taiyubius harrietae Chamberlin (Lithobiidae) and Scolopendra polymorpha Wood (Scolopendridae); scorpions (Vaejovis spp.; Vaejovidae); and sun spiders (Eremobates spp.; Eremobatidae). Native sand roaches (Arenivaga erratica Rehn, Eremoblata subdiaphana (Scudder); Polyphagidae) displayed no significant fire response. Overall, arthropod responses to fire in this desert grassland (with comparatively low and patchy fuel loads) were comparable to those in mesic grasslands with much higher and more continuous fuel loads.

Management effects on carabid beetles and spiders in Central Hungarian grasslands and cereal fields

Modern agriculture is one of the main anthropogenic threats to biodiversity. To explore the effects of agricultural intensification we investigated carabids and spiders in two studies; in 2003 in grasslands and two years later in cereal fields in the same region. Both aimed to study the effect of management on arthropod diversity and composition at local and landscape scales. In 2003, we used a paired design for grasslands (extensively vs. intensively grazed). In 2005, a gradient design was applied with a total of seven land-use intensity categories. In both studies, sampling was carried out using funnel traps with the same sampling effort. Linear mixed models showed that high grazing intensity in grasslands had a positive effect on carabid species richness and abundance, but no effect on spiders. Landscape diversity had a positive effect only on carabid abundance. In the case of cereal fields, the management intensity (nitrogen fertiliser kg/ha) had a negative effect on spider richness and no effect on carabids. After variance partitioning, both local and landscape characteristics seem to be important for both cereal and grassland arthropod communities. Based on our results, we think that current and future agri-environmental schemes should be concentrated on cropland extensification. Low intensity croplands could act as a buffer zone around the semi-natural grasslands, at least in this biogeographic region.

Interactive effects of keystone rodents on the structure of desert grassland arthropod communities

Certain species play particularly large roles in ecosystems, and are often referred to as keystones. However, little is known about the interactive effects of these species where they co‐occur. Prairie dogs (Cynomys spp.) and banner‐tailed kangaroo rats Dipodomys spectabilis are commonly considered keystone species of grassland ecosystems, creating a mosaic of unique habitats on the landscape through ecosystem engineering and herbivory. We examined the separate and interactive effects of these species on the structure of grassland arthropod communities. We conducted a cross‐site study at two locations in the northern Chihuahuan Desert, and evaluated the impacts of these rodents on ground‐dwelling arthropod and grasshopper communities in areas where prairie dogs and kangaroo rats co‐occurred compared to areas where each rodent species occurred alone. Our results demonstrate that prairie dogs (C. gunnisoni and C. ludovicianus) and banner‐tailed kangaroo rats had keystone‐level impacts on arthropod communities both separately and interactively. Their burrow systems provided important habitats for multiple trophic and taxonomic groups of arthropods, and increased overall arthropod abundance and species richness. Many arthropods also were attracted to the aboveground habitats around the mounds and across the landscapes where the rodents occurred. Detritivores, predators, ants, grasshoppers, and rare rodent burrow inhabitants were especially associated with prairie dog and kangaroo rat activity. The impacts of prairie dogs and kangaroo rats were unique, and the habitats they created supported different assemblages of arthropods. Where both rodent species co‐occurred, there was greater heterogeneity and arthropod diversity on the landscape. Our results suggest that the interaction of multiple keystones, especially those with engineering roles, results in unique and more diverse communities in time and space.

Interactive effects of keystone rodents on the structure of desert grassland arthropod communities

Interactive effects of keystone rodents on the structure of desert grassland arthropod communities

Seasonal variation in top-down and bottom-up processes in a grassland arthropod community.

Both top-down and bottom-up processes are common in terrestrial ecosystems, but how these opposing forces interact and vary over time is poorly understood. We tested the variation of these processes over seasonal time in a natural temperate zone grassland, a field site characterized by strong seasonal changes in abiotic and biotic conditions. Separate factorial experiments manipulating nutrients and cursorial spiders were performed in the wet and dry seasons. We also performed a water-addition experiment during the summer (dry season) to determine the degree of water limitation during this time. In the spring, nutrient addition increased plant growth and carnivore abundance, indicating a bottom-up control process. Among herbivores, sap-feeders were significantly enhanced while grazers significantly declined resulting in no net change in herbivore abundance. In the summer, water limitation was predominant increasing plants and all herbivores while nutrient (N) effects were non-significant. Top-down processes were present only in the spring season and only impacted the guild of grazing herbivores. These results show that bottom-up limitation is present throughout the season in this grassland, although the specific limiting resource changes as the season progresses. Bottom-up processes affected all trophic levels and many different guilds, while top-down effects were limited to a select group of herbivores and did not extend to the plant trophic level. Our results show that the relative strengths of top-down and bottom-up processes can shift over relatively short periods of time in habitats with a strong seasonal component.

Abundance, diversity and body size: patterns from a grassland arthropod community

1.The empirical relationships among body size, species richness and number of individuals may give insight into the factors controlling species diversity and the relative abundances of species. To determine these relationships, we sampled the arthropods of grasslands and savannahs at Cedar Creek, MN using sweep nets (90 525 individuals of 1225 species) and pitfall traps (12 721 individuals of 92 species). Specimens were identified, enumerated and measured to determine body size.2.Both overall and within abundant taxonomic orders, species richness and numbers of individuals peaked at body sizes intermediate for each group. Evolution could create unimodal diversity patterns by random diversification around an ancestral body size or from size‐dependent fitness differences. Local processes such as competition or predation could also create unimodal diversity distributions.3.The average body size of a species depended significantly on its taxonomic order, but on contemporary trophic role only within the context of taxonomic order.4.Species richness (Si) within size classes was related to the number of individuals (Ii) asSi = Ii0·5. This relationship held across a 100 000‐fold range of body sizes. Within size classes, abundance distributions of size classes were all similar power functions. A general rule of resource division, together with similar minimum population sizes, is sufficient to generate the relationship between species richness and number of individuals.5.Smaller bodied species had slightly shallower abundance distributions and may, in general, persist at lower densities than larger species.6.Our results suggest there may be fewer undescribed small arthropod species than previously thought and that most undescribed species will be smaller than arthropods.

Responses of a Grassland Arthropod Community to Simulated Radioactive Fallout

Responses of an arthropod community to beta and gamma radiation from ${}^{137}{\rm Cs}\text{-tagged}$ simulated fallout and the interaction of radiation with other environment parameters are being investigated in a unique experimental facility at Oak Ridge National Laboratory. Lithium fluoride microdosimeters attached to the thorax and abdomen of insects in a fallout field indicate that closely related organisms may receive significantly different doses owing to differences in habitat or behavior. Significant differences in variation between control and contaminated communities appeared in summer 1970 (P ≤ 0.05), disappeared in autumn 1970, and reappeared in summer 1971 (P ≤ 0.01). Population densities of four arthropod taxa had been significantly (P ≤ 0.05) reduced by summer 1970. By summer 1971, three of these taxa had recovered to control levels, but four additional taxa underwent significant (P ≤ 0.05) reductions in population density. This number of affected populations is not statistically significa...