Carabid Activity Density Research Articles

Proximity to non-crop vegetation increases estimates of predation frequency but not beetle numbers

Removal of non-crop vegetation (e.g., forest and grassland patches) to expand crop fields is detrimental to the natural enemies of crop pests, like the ground beetle family (Coleoptera: Carabidae), that use these areas for foraging and overwintering. An argument for maintaining non-crop vegetation is its potential to support the supply of ecosystem services, like pest control, to the surrounding crop. Pest control services from non-crop areas are usually measured using the activity-density of natural enemy species, a proxy measure for predatory activity. Evidence that predators such as ground beetles are attacking pests in crops has been less frequently studied. We distributed sentinel prey (fake ‘caterpillars’ made to look like potential prey items) along with pitfall traps at 300 stations using a spatially and temporally replicated design across 20 field sites in Alberta, Canada. The potential for pest attacks by carabids was estimated through bite marks on the sentinels. Using generalized additive modelling, we found that non-crop vegetation positively impacts carabid predation, but activity density of carabids does not explain the relationship. Instead, the non-crop vegetation affects predation frequency, likely by promoting predatory behaviours. These findings exemplify the importance of closer indicators of ecosystem services delivery than activity-density and provide evidence of the potential that ground beetles have in supplying pest control ecosystem services within agroecosystems.

Specialist carabids in mixed montane forests are positively associated with biodiversity-oriented forestry and abundance of roe deer

The ongoing transition within forest management towards more biodiversity-oriented practices, such as close-to-nature forestry and retention forestry, may benefit forest fauna such as forest-specialized ground beetles (Coleoptera: Carabidae). However, it remains unclear how forest carabids are jointly affected by these practices in Central European montane forests, which host particularly sensitive, range-restricted carabid species, and where biodiversity-oriented forestry is widely applied. Moreover, roe deer (Capreolus capreolus), the most common large herbivore in these forests, is intensively managed to reduce browsing pressure, but it is yet unknown how this may affect carabids, alongside the effect of silviculture. On 66 1-ha plots in the Black Forest region of Germany, we sampled carabids with pitfall traps, measured roe deer abundances using camera trapping, and measured several structural variables directly related to close-to-nature and retention practices, as well as variables describing microclimate and landscape-level forest cover. We found that the carabid assemblage was dominated by forest specialists, with little influence from fragmentation of the surrounding forest. Higher broadleaf share (and canopy cover for montane specialists) was correlated with higher carabid activity-density. Increasing stand maturity (and lying deadwood volume for montane specialists), was correlated with higher species richness. Plots with higher roe deer abundances showed higher carabid richness and activity-density. Assemblage composition changed along the altitudinal gradient, and both richness and activity-density increased with elevation. Thus, carabid communities, including montane specialists and several species of conservation interest, stand to benefit from close-to-nature and retention practices, if applied throughout the altitude range of montane forests. Forest carabids may additionally profit from maintaining higher roe deer abundances, but further research is needed to understand this causal link, as well as to weigh the costs and benefits of deer culling for forest biodiversity.

Inconsistent responses of carabid beetles and spiders to land-use intensity and landscape complexity in north-western Europe

Reconciling biodiversity conservation with agricultural production requires a better understanding of how key ecosystem service providing species respond to agricultural intensification. Carabid beetles and spiders represent two widespread guilds providing biocontrol services. Here we surveyed carabid beetles and spiders in 66 winter wheat fields in four northwestern European countries and analyzed how the activity density and diversity of carabid beetles and spiders were related to crop yield (proxy for land-use intensity), percentage cropland (proxy for landscape complexity) and soil organic carbon content, and whether these patterns differed between dominant and non-dominant species. <17 % of carabid or spider species were classified as dominant, which accounted for >90 % of individuals respectively. We found that carabids and spiders were generally related to different aspects of agricultural intensification. Carabid species richness was positively related with crop yield and evenness was negatively related to crop cover. The activity density of non-dominant carabids was positively related with soil organic carbon content. Meanwhile, spider species richness and non-dominant spider species richness and activity density were all negatively related to percentage cropland. Our results show that practices targeted to enhance one functionally important guild may not promote another key guild, which helps explain why conservation measures to enhance natural enemies generally do not ultimately enhance pest regulation. Dominant and non-dominant species of both guilds showed mostly similar responses suggesting that management practices to enhance service provisioning by a certain guild can also enhance the overall diversity of that particular guild.

Carabid beetles have hump‐shaped responses to disturbance and resource gradients within agricultural landscapes

Abstract Understanding the effects of the huge diversity of cropping systems on local biodiversity is challenging but necessary to implement agroecological systems. Through a functional approach, the translation of cropping systems into resource and disturbance gradients is a promising way to decipher the relationship between cropping systems and biodiversity but has never been implemented for arthropods. To investigate the contributions of resource and disturbance gradients arising from cropping systems vs environmental context (regional effect, meteorological conditions and landscape characteristics) on beneficial arthropod communities, we used a dataset collected in 60 crop fields from three French areas over a 5‐year period. It includes all farmer interventions, crop sequences, meteorological data, landscape composition and carabid samplings. We found that environmental context contributed to about 75% of explained carabid variations on average, while resource and disturbance gradients contributed to about 25% of explained carabid variations. The resource and disturbance gradients were particularly important in winter and in the spring preceding the spring–summer period to determine carabid variations. Moreover, we identified thresholds above which resource and disturbance gradients start being beneficial or detrimental for carabids. For example, increased treatment index in spring decreased the total activity density of carabids during the spring–summer period. Synthesis and applications. While implementing for the first time a functional approach to understand the effects of different facets of cropping systems on arthropods, our study also allows us to identify periods and thresholds above which specific practices affect carabids. Finally, avoiding bare soils all along the year, keeping pesticide use intensity below the identified thresholds and adopting a wide diversity of tillage strategies at the landscape scale should all contribute to enhance in‐field carabid occurrences and richness.

Can rare arable plants benefit biological pest control potential of cereal aphids in croplands?

In agricultural landscapes, arable plants are negatively affected by management intensification. These species can fulfill various ecosystem functions, such as biological pest control, by supporting predators. The ecosystem functions of common plant species are widely known. By contrast, the contribution of rare arable plants (RAPs) to biocontrol in cereal fields remains poorly understood. This study investigated the effect of RAPs on biocontrol potential. We compared cropped plots with and without sowing of rare and threatened arable plant species and investigated the effects on cereal aphids and their antagonistic predators, active hunting, and web-building spiders, as well as carnivorous/omnivorous carabids. We counted the total number of aphids on cereal shoots and trapped ground-dwelling arthropods on an experimental field and on 10 agricultural farms in the vicinity of Munich, Germany, in 2018 and 2019. The effects of the presence of RAPs were analyzed using linear mixed-effect models, whereas cover of RAPs was analyzed using structural equation models. Linear models revealed that the presence of RAPs did not significantly affect the aphid density and the activity densities of spiders and carabids. Structural equation models revealed direct negative effects of RAP cover on aphid density. However, no indirect effects via the predators of aphids were detected. Direct negative effects of active hunting spiders on aphids were determined, but not of the other potential predators. Our results suggest that RAPs may impact aphid infestation, however, the activity density of spiders and carabids were unsuitable indicators for such interactions.

The impact of maize-bean intercropping on insect biodiversity

Intensive agriculture is one of the main reasons for recent insect declines. This loss of biodiversity has created the need to develop methods of intensive cultivation that combine high yields with biodiversity conservation. One promising method in maize cultivation is intercropping with beans. The objective of this study was to determine whether maize-bean intercropping could increase insect biodiversity. We examined the activity density, species richness and Shannon diversity of bees and carabid beetles in pure and intercropped maize under both organic and conventional management. We collected carabid beetles using pitfall traps and bees by doing transect walks. The study was carried out in an agricultural landscape, on a set of 17 study sites. We found that intercropping leads to significant increases in bumblebee and honeybee activity as well as in bee species richness. Differences between pure and intercropped maize were dependent on the year of data acquisition and the management style. Solitary wild bee species activity was not significantly affected. Carabid activity density and carabid species richness also did not differ significantly between the cropping systems. We conclude that maize-bean intercropping can contribute to insect biodiversity conservation but its contribution is limited to bumblebees. Despite its relatively low contribution per hectare, maize-bean intercropping could have a surprisingly positive impact, as maize now covers large areas of German farmland. Potential exists to increase the biodiversity value of maize intercropping even further by using varied plant mixes. Our results strongly encourage further research in this direction.

Carabid activity-density and community composition, and their impact on seed predation in pulse crops

Reduced use of chemicals in weed management has been identified as a key strategy to increase overall agricultural sustainability. Carabid (Coleoptera: Carabidae) and cricket (Orthoptera:Gryllidae) weed seed predation has shown promise, but also variability, as an additional weed management tool. Therefore, it is important that carabid activity-density and weed seed predation is further explored in a wide variety of crops and cropping systems, including large conventional systems where sustainability gains may be the largest. Here we explored carabid and cricket activity-density, community, and weed seed consumption in commercial conventional pulse crop fields. Pulse crops are increasingly being incorporated in cropping rotations but weed seed predation is hardly explored in this group of crops. We sampled twenty-four large commercial lentil, pea, faba bean, and soybean fields, and found that crop type did not affect levels of seed predation or carabid activity-density but was a factor in shaping the carabid + cricket community. Crop history had an unexpectedly large impact on the community, fields previously planted to canola had relatively high Amara activity-densities. The carabid genera Amara and Pterostichus, as well as crickets were associated with volunteer canola seed predation. None of the studied carabid taxa, nor crickets, were a significant factor explaining kochia seed predation. We also explored the effects of crop canopy-driven microclimate factors on carabid and cricket activity-density and weed seed predation. The Amara, the most abundant granivorous taxon in this study, were positively related to soil temperatures but not to soil light intensity. Our study highlights the importance of cropping history on the community of beneficial insects in crop fields and indicates a taxon specific relationship with soil temperature and weed seed predation.

Undestroyed winter cover crop strip in maize fields supports ground-dwelling arthropods and predation

Intensification of agriculture, with landscape simplification and reduction of natural habitats, is known to contribute to the decline of arthropods. Implementation of agroecological practices and infrastructures in current cropping systems is expected to mitigate this biodiversity loss and provide pest regulation through natural enemies. The aim of this study was to assess the efficiency of an undestroyed strip of winter cover crop within maize fields to promote ground-dwelling arthropod spillover and their predation activity into fields. The field survey was carried out in 2019 and 2020 within 12 fields. Monitoring of ground-dwelling arthropod activity-density, richness, and predation rate, as well as slug activity-density, was conducted in the strip, in the cropped area and in a grassy field margin. The results show that activity-density of carabids, spiders, and slugs, and the predation rate were overall higher in the strip than in the cropped area or the field margin. No clear edge effect of the strip on arthropods in the cropped area was found, but predation rate was enhanced closer to the strip. We did not record a negative effect of the strip on the occurrence of slugs within the maize crop. The study shows that a mid-field strip of winter cover crops can be efficient for biodiversity conservation of ground-dwellings predators in agricultural landscapes and provide a potential pest control service in cropped fields.

Re-established grasslands on farmland promote pollinators more than predators

Agricultural intensification is among the major threats to farmland biodiversity and associated ecosystem services. Agri-environment schemes in Europe aim to counteract the continuous decrease of permanent grassland habitat and related decline of biodiversity in agricultural landscapes. We established new grasslands adjacent to permanent old grasslands to study effects on arthropod pollinators and predators. Over three years, we assessed the effects of newly established grasslands on activity density, species richness and assemblages of pollinators (syrphids, bumblebees, solitary bees) and ground-dwelling predatory arthropods (carabids, spiders, ants). Pollinator activity density and species richness of all three pollinator groups approximately doubled in newly established grasslands compared to old grasslands, indicating suitability of new grasslands as pollinator feeding habitat. Predator responses were less consistent. Species richness and activity density of carabids and ants did not increase in new grasslands, indicating slower adaptation to new habitats. Spider activity density increased in the newly established grasslands and in adjacent cereal fields, but no significant differences in species richness compared to old grasslands were observed. Bumblebees and solitary bees showed distinct distance decays in cereal fields. Syrphid activity density declined in cereal fields far away from the newly established grasslands, but not nearby. Carabids increased and ants decreased in species richness and activity density with increasing distance from old grasslands in cereal fields and newly established grasslands alike. In contrast, spider species richness and activity density decreased with increasing distance from old grasslands in cereal fields only, but there was no distance decay in newly established grasslands. While pollinators utilized the additional floral resources within the whole area of newly established grassland quickly, predators reacted much slower. Even after three years, there was no measurable response of carabid and ant activity density and only a minor response of spiders. This clearly shows that short-term measures are not sufficient to sustainably conserve farmland biodiversity. The conservation of permanent grassland and landscape heterogeneity should be prioritized. However, the restoration of new grassland should also be encouraged by agri-environment schemes as a supplement, to enhance functional biodiversity in agricultural landscapes.

Responses of ground beetle (Coleoptera: Carabidae) assemblages to stand characteristics and landscape structure in riparian poplar forests

Abstract Many carabid beetles are among the most important biocontrol agents and are biological indicators of environmental change, although relatively little is known about how local and landscape factors affect forest ground beetle assemblages. Understanding such effects of multi‐scale environmental drivers on ground beetles can promote carabid diversity and conservation. Ground beetles were sampled by pitfall trapping in 40 poplar forest stands (sampling plots) along the Irtysh River in Northwestern China. We investigated responses of carabid activity density, species diversity and functional diversity (FD) to stand characteristics and surrounding landscape structure (the overall diversity and percentage cover of vegetation productivity classes in the surrounding area of each sampling plot based on normalised difference vegetation index). While carabid activity density only responded positively to the overall diversity of vegetation productivity classes, carabid species diversity was positively associated with this landscape factor as well as vegetation cover but negatively associated with the nearest distance from sampling plot to the river. Only carabid FD responded significantly to percentage cover of vegetation productivity classes, showing a positive correlation with the proportion of medium vegetation productivity. Furthermore, overall carabid FD declined with increasing tree canopy cover. Our results can help predicting spatial patterns of ground beetles according to landscape diversity and proportions of surrounding vegetation types and improve the design of conservation strategies (such as altering canopy cover) of carabids, especially forest specialist species. Any forest management strategies for promoting carabid diversity should consider the pervasive effects of landscape composition and configuration besides local stand characteristics.

Seed Predation of Interseeded Cover Crops and Resulting Impacts on Ground Beetles.

Interseeding cover crops into standing grains can promote both agronomic and environmental benefits within agroecosystems. Producers must decide which cover crops are the best fit for their goals, and whether diverse cover crop mixtures provide benefits that are worth the increased seed cost. Broadcast seeding is an accessible strategy to try interseeding but can lead to patchy establishment; it is unknown how much seed loss is due to seed predators. In a two-year study, six cover crop species-planted as either single species or mixtures-were interseeded into standing corn. We evaluated seed predation at the time of seeding, agronomic impact through cover crop, and weedy biomass at the end of the season, and conservation impact through activity-density of ground beetles (Coleoptera: Carabidae). Cover crop seeds were vulnerable to seed predation, primarily by vertebrate seed predators, and seed loss varied across cover crop species. Cover crop biomass did not differ according to cover crop diversity and weedy biomass was not affected by cover crop presence or species. Cover crop diversity effects on carabid activity-density were inconsistent: carabids were higher in diverse mixtures in 1 year of the study, but only predicted by vegetative cover, not by cover crop, in the second year. Interseeding cover crops into corn has potential benefits for ground beetles, although the value of mixtures must be further explored.

Flowering fields, organic farming and edge habitats promote diversity of plants and arthropods on arable land

Abstract Increased farming intensity led to massive declines across multiple farmland taxa. In Europe, measures introduced to counteract these losses include those considered agronomically productive, such as organic farming, as well as those that support no direct production of crops, such as non‐crop flowering fields in conventional farming systems. We studied biodiversity effects of non‐productive flowering fields managed under conventional farming compared to both an organically managed cereal mono‐crop (organic winter spelt fields) and a flowering mixed‐crop (organic lentil mixed‐crop fields) as well as conventionally managed winter wheat fields, which served as control crop. These four crop‐use types were studied on six sites over 3 years (17 sites in total) to assess their impact on the activity density (cover for plants), species richness and community composition of wild plants, carabids, spiders, butterflies and wild bees. Species richness of wild plants was highest under organic farming and at field edges when compared to the interior. In the case of carabids and spiders, species richness was highest at the field edges, but there was no difference between the four crop‐use types. In contrast, activity density and species richness of butterflies and wild bees responded only to flowering crop‐use types, showing no edge effects. Arable land cover in 500 m buffer area also affected community composition of all taxa, with the exception of spiders, but had only minor effects on activity densities and species richness. Synthesis and applications. Our findings underline that there is no single best measure to promote biodiversity on arable land. Instead a mosaic of non‐productive and productive measures such as conventional flowering fields, organic crops and field edge habitats might be more appropriate to support the regional species pool in arable‐dominated landscapes. To support a range of complementary biodiversity‐promoting farming practices, agricultural policy should foster the coordination and collaboration between multiple farmers within the same region by covering additional costs for coordination and prioritizing collaborative schemes.

Activity density of carabid beetles along an urbanisation gradient

Several works have investigated the impact of urbanisation on carabid activity density using urban-rural gradients. Such works compared activity density recorded from green spaces located in different parts of a city and assigned to categories of increasing urban intensity, which poses two problems: (1) since the gradient is divided into categories, it is impossible to model continuous variations in biotic responses, and (2) sites representative of different urbanisation levels are not true segments of the same ecological continuum. To surpass these problems, we modelled variations in carabid activity density along an urban-rural transect within a single green space extending from the city centre of Rome to rural environments. Carabids were sampled by pitfall traps from sites distributed along the entire gradient. We used breakpoint regressions to model how (1) carabid activity density, (2) carabids/beetles ratio, (3) carabids/insects ratio and (3) carabids/arthropods ratio varied along the gradient. As already observed for various organisms in urban environments, we found that activity density of carabids and their contribution to the abundance of beetles, insects and arthropods, peaked in the middle of the gradient. This supports the intermediate disturbance hypothesis, according to which moderate urbanisation may favour diversity by increasing habitat heterogeneity.

Which Pitfall Traps and Sampling Effort to Choose to Evaluate Cropping System Effects on Spider and Carabid Assemblages?

In arable agroecosystems, arthropod communities often have a reduced abundance and diversity, which represents a challenge for sampling techniques needed to detect small differences among these simplified communities. We evaluated the suitability of pitfall traps for comparing the effects of cropping systems on arthropod communities. In a field experiment, we compared the effects of two pitfall trap diameters, the type of preserving fluid and the sampling effort on three metrics (activity density, taxonomic richness, and community weighted mean [CWM] of body size) for carabids and spiders. Trap size affected the observed composition of communities, with large traps yielding a higher proportion of spiders, and a higher richness and CWM body size for both taxa. The type of preserving fluid had a weaker effect. Simulations with various sampling efforts showed that only very different communities could be distinguished with less than 10 traps per field or less than 30 field replicates. Fewer traps were required to find differences between cropping systems for body size than for other metrics. Carabid activity density and body size, and spider genus richness, were the variables better distinguishing between cropping systems with the smallest sampling effort. A high sampling effort was required for comparing activity density and richness across cropping systems. Selection of the most appropriate trap design, metrics, and crops are the main factors for optimizing the trade-off between sampling effort and the ability to detect arthropod community responses to habitat management.

Large carabids enhance weed seed removal in organic fields and in large-scale, but not small-scale agriculture

ContextBiological weed control by seed predators is an ecosystem service reducing weed population densities in agricultural landscapes. Drivers of seed predation are manifold and may change with spatial scales considered.ObjectivesWe aimed at identifying the functional identity of seed predators, food web interactions and feeding links between weed and wheat seeds, considering the causal relationships between local and landscape-scale patterns.MethodsWe investigated direct and indirect effects of local management intensity in winter wheat fields (organic vs. conventional farming), local crop characteristics (wheat density and height), edge effects, landscape composition (measured as land-use diversity) and configuration (edge length) on carabid beetles of different body size (large vs. small carabids), and removal of weed and wheat seeds.ResultsWe showed the importance of indirect local- and landscape-scale effects for weed seed removal via the activity density, but not assemblage composition, of large, but not small carabids, which was driven by few ubiquitous species. The activity density of large carabids increased with decreasing wheat density and increasing wheat height, which was highest in organic fields and in landscapes with low compositional and configurational heterogeneity. Further, the availability of nutrient-rich wheat seeds enhanced weed seed removal rates.ConclusionsWe found highest weed seed removal via large carabids in organic fields in large-scale agricultural landscapes. Predator body size and species identity as well as the availability of additional food items need to be taken into account for better predicting the biological weed control potential and reducing the use of plant protection products.

Ground Predator Activity-Density and Predation Rates Are Weakly Supported by Dry-Stack Cow Manure and Wheat Cover Crops in No-Till Maize.

Because it keeps land in production, conservation programs that focus on in-field habitat manipulations may help farmers better support predators than by building predator habitat around fields. We investigated two in-field habitat manipulations that benefit producers and soil quality: fertilizing with dry-stack cow manure and planting a wheat cover crop. We hypothesized that, compared with inorganic fertilizer and fallow plots, both treatments augment habitat and residue and support more small arthropods that can serve as alternative prey for larger predators. As a result, we expected manure and the cover crop to increase ground-active predators. In turn, these predators could provide biological control of pests. Each year in a 3-yr field experiment, we applied manure and in 2 yr planted a wheat cover crop. We found that both planting a cover crop and applying dry-stack manure increased the plant cover in May. In the last year, this translated to greater soil mite (Acari) density. At the end of the experiment, however, neither manure nor the wheat cover crop had increased residue on the soil surface. As a result, our treatments had inconsistent effects on predator activity-density, especially for carabids and spiders. We observed strong edge effects from neighboring grass alleys on carabid activity-density. Regardless of treatment, we observed high predation of sentinel prey. We conclude that even without cover crops or organic fertilizer, the stability of no-till maize and increased weeds in fallow treatments generate sufficient habitat complexity and alternative prey to support robust predator communities.

The resilience of weed seedbank regulation by carabid beetles, at continental scales, to alternative prey

Carabids are generalist predators that contribute to the agricultural ecosystem service of seedbank regulation via weed seed predation. To facilitate adoption of this ecosystem services by farmers, knowledge of weed seed predation and the resilience of seedbank regulation with co-varying availability of alternative prey is crucial. Using assessments of the seedbank and predation on seed cards in 57 cereal fields across Europe, we demonstrate a regulatory effect on the soil seedbank, at a continental scale, by groups formed of omnivore, seed-eating (granivore + omnivore) and all species of carabids just prior to the crop-harvest. Regulation was associated with a positive relationship between the activity-density of carabids and seed predation, as measured on seed cards. We found that per capita seed consumption on the cards co-varied negatively with the biomass of alternative prey, i.e. Aphididae, Collembola and total alternative prey biomass. Our results underline the importance of weed seedbank regulation by carabids, across geographically significant scales, and indicate that the effectiveness of this biocontrol may depend on the availability of alternative prey that disrupt the weed seed predation.

Soil organic matter links organic farming to enhanced predator evenness

Balanced communities of natural enemies (i.e., greater evenness) can strengthen biological control. Natural enemy evenness is generally higher on organic than conventional farms, but the reason(s) for this are unclear. One possibility is that applications of composted manure on organic farms provide habitat for predators as well as food for detritus-feeding arthropods that are important supplemental prey. We searched for potential links between soil organic matter and ground beetle biodiversity in 65 broccoli (B. oleracea) fields, spanning the U.S. west coast, on mixed-vegetable farms using organic or conventional management practices. We measured soil organic matter in each field while also collecting predatory ground beetles (Coleoptera: Carabidae) and detritus-feeding springtails (Collembola), which are potential alternative prey resources for ground beetles. We found that carabid activity density, species richness, and species evenness were higher on organic than conventional farms. Some organic farms integrated livestock alongside vegetable production, however this did not detectably impact ground beetles, springtails, or organic matter. In a path analysis built from our on-farm data, carabid community evenness correlated with soil organic matter, and subsequently, carabid evenness positively correlated with carabid activity density. However, springtail activity-density had no apparent relationship to soil organic matter, carabid activity, or carabid evenness. It is possible that increasing organic matter improved soil microclimate to the benefit of ground beetles, although we cannot exclude the possibility that carabids on organic farms were responding to other ecological or management practices that differed from those on conventional farms. More broadly, among its myriad soil-health benefits, enhancing organic matter could be one strategy for re-balancing natural enemy densities to increase evenness.

Activity density of carabid beetles along an urbanization gradient in the city of Rome (Italy)

As concrete jungles, urban areas may be considered extreme environments for most animal groups. Yet, cities host unexpected high values of biodiversity, sometimes also in the most urbanized sectors. Several works have investigated the impact of urbanization on carabids using urban-rural gradients. However, most research has been done in north-western and central Europe, whereas urban communities in the Mediterranean region remain largely unexplored. Also, due to the high fragmentation of green spaces in urban areas, studies on the urban-rural gradient typically used data collected from several green spaces along the gradient, not from a single large area, which complicates interpretation because of the many confounding factors associated with inter-site variability. Aim of this research was to investigate the response of carabid populations to urbanization by analysing how their activity density varied along an urban-rural gradient within a single, large green space. The study was conducted in Rome (Italy), in the Appia Antica Regional Park, an urban park of 3,500 ha, which extends for some 16 km from the city centre to the rural environments out of the city. Carabids were sampled by pitfall traps from nine sites along the entire urban-rural gradient. We calculated the total carabid activity density, number of carabids/total Coleoptera (CAR/COL), and number of carabids/total insects (CAR/INS). As already observed for various organisms in urban environments, we found that carabid acitivity density peacked in the middle of the gradient, where it was more than six times higher than in the city centre and about three time higher than in the rural sites. This supports the intermediate disturbance hypothesis, according to which moderate urbanization may favour diversity by increasing habitat heterogeneity. CAR/COL and CAR/INS also peacked in the middle of the gradient, which indicates that carabids are the insect taxon most favoured by intermediate urbanization.

Carabidae assemblages in pine forests with different recreation regimes within and outside a megalopolis

The expansion of cities highlights the need for studies of the biodiversity on urban territories and factors affecting the structure and functioning of communities. In 2010–2011, we compared the abundance and diversity of carabid beetles in pine forests of natural origin within the Russian megalopolis Yekaterinburg and outside. To estimate the effects of recreation (R+: trampling, soil compaction, eutrophication) and other urbanization factors (U+: pollution, habitat fragmentation, adventive species), we selected 12 urban and non-urban forest sites with contrasting recreation regimes (U + R+, U + R−, U − R+, U − R−; three sites in each combination). We hypothesized that both urbanization and recreation decrease the abundance and diversity of carabids; the combination of two factors enhances negative effects. The total activity density of carabids and the abundances of all ecological groups increased in urban forests compared to non-urban ones. In urban forests, the Simpson dominance decreased, while Shannon diversity, total species richness, and mean number of species per site increased. The most abundant species in all forests were Pterostichus oblongopunctatus, P. mannerheimii, and P. magus, while Carabus nemoralis was abundant in urban forests only. Proportion (by the number of individuals) of forest species was lower and that of generalists and large-sized species higher in urban forests. High recreation load resulted in lower total abundance and diversity of ground beetles. Negative effect of recreation load on carabids leveled positive effect of urbanization: both abundance and diversity of ground beetles were lower at urban sites with intense recreational use compared to forest sites closed for townspeople.