Communities In Agroecosystems Research Articles

Molecular and ecological perspectives of nitrous oxide producing microbial communities in agro-ecosystems

Nitrous oxide (N2O) is a potent greenhouse gas. Agricultural soils are the major source of N2O contributing more than 70% of the global N2O emissions. In soil, N2O is mainly produced during the microbial mediated nitrification and denitrification processes. These processes are influenced by several factors. Nitrification is governed by a few species of bacteria, archaea, and fungi, whereas, several species are involved in the denitrification process. Recently, several improved molecular approaches particularly different omics technologies namely genome sequencing, proteomics, metagenomics, meta-transcriptomics, etc. are being used for microbial diversity assessment, identification of metabolic pathways as well as recovery of the abundant uncultivable microbial genomes along with the genes involved in N2O production but also necessary for mitigation of N2O emission from agricultural soils. Various studies on the N2O production pathways and factors affecting from the agricultural soils are being elaborately documented. However, the molecular perspective of the N2O production in agricultural soils is not well-addressed. Thus, a better understanding of N2O production pathways, factors affecting, and identification of soil microbial and ecological diversity will provide great insight into the mitigation of N2O emission from agricultural soils. This review aims to explore in detail the published literature for a better understanding of soil microbial dynamics in both aerobic and anaerobic environment and how nitrogen saturation disrupts microbial and ecosystem functioning. The impact of impending climate change on soil microbiome along with their interaction with soil environment and plant communities is also discussed.

Arable Weed Patterns According to Temperature and Latitude Gradient in Central and Southern Spain

(1) Background: In agro-ecosystems, the success of the crops has a strong connection to biodiversity in the landscape. In the face of climate change, it is important to understand the response to environmental variation of weed species by means of their distribution. In the last century, biodiversity has been impacted due to a variety of stresses related to climate change. Although the composition of vegetation tends to change at a slower rate than climate change, we hypothesize species present in weed communities are distributed in diverse patterns as a response to the climate. Therefore, the general aim of this paper is to investigate the effect of temperature, using latitude as an indicator, on the composition and distribution of weed communities in agro-ecosystems. (2) Methods: Weeds were monitored in georeferenced cereal fields which spanned south and central Spanish regions. The graphic representation according to latitude allowed us to identify groups of weeds and associate them to a temperature range. We classified weeds as generalist, regional, or local according to the range of distribution. (3) Results: The monitoring of species led to the classification of weeds as generalist, regional or local species according to latitude and associated temperature ranges. Three weed species that were present in all latitude/temperature regions, were classified as generalist (Linaria micrantha (Cav) Hoffmanns & Link, Sonchus oleraceous L., and Sysimbrium irium L.). The species were classified as regional or local when their presence was limited to restricted latitude/temperature ranges. One weed, Stellaria media (L.) Vill., was considered a local species and its distribution dynamics can be considered an indicator of temperature. (4) Conclusions: The novel methodology used in this study to assign weed distribution as an indicator of climatic conditions could be applied to evaluate climate gradients around the world.

Pollinator monitoring in agroecosystems – general methods for evaluations in field studies

Extensive knowledge of the occurrence, condition and population changes of wild bee communities in agroecosystems is important. The knowledge is needed to understand the complexity of potential exposure routes to plant protection products in specific crops and agricultural scenarios or to evaluate possible impacts of treatments at a landscape scale taking into account other influencing parameters like the cultivation system or management practices.

Long-term fertilization rather than plant species shapes rhizosphere and bulk soil prokaryotic communities in agroecosystems

The rhizosphere microbiome plays an important role in disease-suppressive soils and is closely related to plant health. While a key role of plant-related factors in shaping the rhizosphere microbiome is well known for natural ecosystems and similarly fertilized agricultural systems, the interaction between fertilization and plant species effects on rhizosphere microbial communities has less been determined. Here, we assessed the influence of plant- and fertilization-related factors on the abundance, biomass and composition of rhizosphere and bulk soil prokaryotic communities. Soil samples were collected from the bulk soil and the rhizosphere of maize, potato, and white mustard under mineral (N180P150K150 per year) and organic (50 t ha−1 of fresh cattle manure) fertilization treatments within a long-term microplot experiment. Total (DNA) and potentially active (RNA) prokaryotic communities were analyzed using RT-PCR and Illumina MiSeq amplicon sequencing. Both NPK and manure fertilization systems led to the similarity of the prokaryotic community structures in rhizosphere and bulk soil. Long-term application of manure increased significantly prokaryotic abundance and diversity due to development of many underrepresented taxa. NPK significantly reduced prokaryotic diversity and the total number of species. Our findings suggest that fertilization is a more important factor in determining the abundance and diversity of prokaryotic communities in the rhizosphere than plant species. Thus, the traditional concept of the key role of plant species in shaping prokaryotic communities in the rhizosphere which is valid for non-cultivated plant species was not confirmed for the agricultural ecosystems and crops investigated here.

Elevated air temperature shifts the interactions between plants and endophytic fungal entomopathogens in an agroecosystem

Abstract The possible effects of climate change on species interactions remain a very complex and challenging subject in community ecology. Here, we comparatively examine the interactions between maize (Zea mays) and an endophytic fungal entomopathogen (Beauveria bassiana) in a typical agroecosystem under both ambient and elevated air temperatures. We found that under ambient temperature certain key biological characteristics in maize (i.e., height, relative growth rate, biomass, and defense enzymes) and B. bassiana (i.e., conidia yield, germination rate of conidia, and virulence) were positively related to each other. Under elevated air temperature, however, we only detected positive effects of maize on B. bassiana (i.e., conidia yield, germination rate of conidia, and virulence), but little effect of B. bassiana on maize. These observations suggest that elevated air temperature could shift the interactions between plants and the endophytic fungal entomopathogens, possibly even from mutualism to commensalism. Both the nature and strength of species interactions are important for better understanding and predicting structure and stability of ecological communities in agroecosystems under climate change.

Change in ground-dwelling arthropod communities in agroecosystems in Wang Nam Khiao, Nakhon Ratchasima province, Thailand

Change in ground-dwelling arthropod communities in agroecosystems in Wang Nam Khiao, Nakhon Ratchasima province, Thailand

Habitat conversion affects beta diversity in frugivorous butterfly assemblages

ABSTRACT Tropical dry forests are diverse ecosystems that are globally threatened but are rarely protected. The main threat to this habitat is conversion for agricultural use. Here we evaluate the effects of environmental conversion, comparing patterns of beta diversity of butterflies in unconverted dry forest ecosystems (protected areas) and in agroecosystems (sugarcane and pasture). Butterflies were collected for 720 traps/day in 2018, using baited traps. Contrary to expectations, temporal beta diversity in sugarcane was higher than in forests. Nevertheless, the community in sugarcane contained mainly generalist species and its temporal dissimilarity was driven mainly by differences in species abundance. As expected, the spatial beta diversity between forest ecosystems and agroecosystems was high. Environmental conversion led to species loss, affecting mainly specialist species, which are more restricted to forest habitats, and resulted in a high degree of nesting of communities in agroecosystems. Our results emphasize the conservation value of protected natural areas and the importance of maintaining such areas as an essential strategy for conserving biodiversity.

Biodiversity of soil fungal communities in agro-ecosystems using DNA metabarcoding

Soil fungi are key component of soil biota having an important role in many ecological processes. As pathogens, decomposers and plant mutualists they can affect plant and soil health in agro-ecosystems significantly. The impact of crop management practices on soil fungal communities is diverse and still poorly studied. The lack of knowledge is mainly related to their hidden life mode, high phenotypic diversity, the great heterogeneity of soil microhabitats, difficulty for culturing and species identification. Collecting data with high accuracy to detect effects relevant to ecosystem management is an ongoing challenge for soil ecological studies and biomonitoring. However, the combination of DNA-based identification methods and Next Generation Sequencing technology was recognized as a powerful tool to evaluate biodiversity in environmental samples, especially soil biodiversity. In the frame of the National Research Program "Healthy Foods for a Strong Bio-Economy and Quality of Life", soil microbiome diversity (fungi, prokaryotes and archaea) will be used as indicator for assessing soil and plant health, and ecosystem services in several agricultural ecosystems. Four crop types (apple, lavender, rose and pea) located in southern Bulgaria, and managed by conventional and organic farming have been selected. Two general objectives related to soil biodiversity study were envisaged: to examine the impact of cropping systems on microbiome structural and functional diversity, and to propose management measures and agronomic practices improving soil and plant health. to examine the impact of cropping systems on microbiome structural and functional diversity, and to propose management measures and agronomic practices improving soil and plant health. Here we present some preliminary results on soil fungal communities evaluated by using amplicon DNA sequencing of the internal transcribed spacer 2 (ITS2) rDNA region. Multiple core soil samples were collected from 18 sampling plots in June 2019. Fungal diversity and community structure were evaluated at different taxonomic levels. The most common and abundant taxa at all sites were Fusarium Link 1809, Solicoccozyma X.Z.Liu, F.Y.Bai, M.Groenew. & Boekhout 2015, Cladosporium Link 1816, Alternaria Nees ex Wallroth 1816, and Mortierella E.Coemans 1863. The multivariate statistics (PCA) comparing the overall microbial composition revealed loose clusters linked to crops and localities. The study provides a new comprehensive overview of soil fungal communities (composition and diversity) from Bulgarian agro-ecosystems using high-throughput DNA sequencing.

Relationships between soil morpho-chemical parameters and earthworm community attributes in tropical agro-ecosystems in the Centre-West region of C\xf4te d\u2019Ivoire, Africa

This study was carried out to investigate the relationship between earthworm trophic groups and soil morphology and chemical attributes, and moreover, to determine which of these attributes would be most significant in explaining the distribution of earthworm communities in agro-ecosystems in the Centre-West region of Côte d’Ivoire. Earthworms' soil morphology and soil samples were studied in three agro-ecosystems: 20-year-old cocoa plantations, 5-year-old mixed cocoa plantations and mixed crop-fields. The semi-deciduous forests near the agro-ecosystems were also sampled and considered as control plots. Earthworm global densities varied on average between 53.9 ± 7.9 and 86.0 ± 19.0 individuals m−2 and biomass between 16.5 ± 3.1 and 20.6 ± 4.1 g m−2 under these ecosystems. Path analysis produced a significant model: soil morphology and chemical attributes under different agro-ecosystems affected the density and biomass of earthworm trophic groups, and these attributes are potential regulators of the fauna communities. The morphological components related to dead leaves (r2 = 0.73, P < 0.05) and fine woods quantities (r2 = 0.71, P < 0.05) are most decisive for detritivore abundances, whereas geophageous mesohumic abundances were positively affected by soil organic carbon (r2 = 0.79, P < 0.05) and N (r2 = 0.84, P < 0.05) and geophageous polyhumic abundances were positively affected only by soil N (r2 = 0.63, P < 0.05). In agro-ecosystems the relationship between soil conditions and earthworm communities varied between earthworm trophic groups, so detritivores were more affected by litter quantity, whereas shallow geophageous populations were guided by soil organic matter.

Consortia of anti-nematode fungi and bacteria in the rhizosphere of soybean plants attacked by root-knot nematodes.

Cyst and root-knot nematodes are major risk factors of agroecosystem management, often causing devastating impacts on crop production. The use of microbes that parasitize or prey on nematodes has been considered as a promising approach for suppressing phytopathogenic nematode populations. However, effects and persistence of those biological control agents often vary substantially depending on regions, soil characteristics and agricultural practices: more insights into microbial community processes are required to develop reproducible control of nematode populations. By performing high-throughput sequencing profiling of bacteria and fungi, we examined how root and soil microbiomes differ between benign and nematode-infected plant individuals in a soybean field in Japan. Results indicated that various taxonomic groups of bacteria and fungi occurred preferentially on the soybean individuals infected by root-knot nematodes or those uninfected by nematodes. Based on a network analysis of potential microbe–microbe associations, we further found that several fungal taxa potentially preying on nematodes (Dactylellina (Orbiliales), Rhizophydium (Rhizophydiales), Clonostachys (Hypocreales), Pochonia (Hypocreales) and Purpureocillium (Hypocreales)) co-occurred in the soybean rhizosphere at a small spatial scale. This study suggests how ‘consortia’ of anti-nematode microbes can derive from indigenous (resident) microbiomes, providing basic information for managing anti-nematode microbial communities in agroecosystems.

Neonicotinoid insecticidal seed-treatment on corn contaminates interseeded cover crops intended as habitat for beneficial insects.

Neonicotinoid seed treatments are extensively used to systemically protect corn from invertebrate herbivory. Interseeding cover crops can promote beneficial insect communities and their ecosystem services such as predation on pests, and this practice is gaining interest from farmers. In this study, cereal rye (Secale cereale) and hairy vetch (Vicia villosa) were planted between rows of early vegetative corn that had been seed-treated with thiamethoxam. Thiamethoxam and its insecticidal metabolite, clothianidin were quantified in cover crop leaves throughout the growing season. Thiamethoxam was present in cereal rye at concentrations ranging from 0 to 0.33 ± 0.09 ng/g of leaf tissue and was detected on six out of seven collection dates. Cereal rye leaves contained clothianidin at concentrations from 1.05 ± 0.22 to 2.61 ± 0.24 ng/g and was present on all sampling dates. Both thiamethoxam and clothianidin were detected in hairy vetch on all sampling dates at rates ranging from 0.10 ± 0.05 to 0.51 ± 0.11 ng/g and 0.56 ± 0.15 to 9.73 ± 5.04 ng/g of leaf tissue, respectively. Clothianidin was measured at a higher concentration than its precursor, thiamethoxam, in both plant species on every sampling date. Neonicotinoids entering interseeded cover crops from adjacent treated plants is a newly discovered route of exposure and potential hazard for non-target beneficial invertebrates. Future research efforts should examine the effects of systemic insecticides on biological communities in agroecosystems whose goal is to diversify plant communities using methods such as cover cropping.

The Influence of Bt Maize Cultivation on Communities of Arbuscular Mycorrhizal Fungi Revealed by MiSeq Sequencing.

The cultivation of transgenic Bacillus thuringiensis (Bt) has received worldwide attention since Bt crops were first released. Its ecological risks on arbuscular mycorrhizal fungi (AMF) have been widely studied. In this study, after cultivation for five seasons, the AMF diversity and community composition of two Bt maize varieties, 5422Bt1 (event Bt11) and 5422CBCL (event MO10), which both express Cry1Ab protein, and their isoline non-Bt maize 5422, as well as Bt straw after cultivation had been returned to subsequent conventional maize variety, were analyzed using Illumina MiSeq sequencing. A total of 263 OTUs (operational taxonomic units) from 511,847 sequenced affiliated with the AMF which belonged to Mucoromycota phylum Glomeromycotina subphylum were obtained. No significant difference was detected in the AMF diversity and richness (Shannon, Simpson, ACE, and Chao 1 indices) and community composition in rhizosphere soils and roots between Bt and non-Bt treatment revealed by NMDS (non-metric multidimensional scaling) and NPMANOVA (non-parametric multivariate analysis). Moreover, Glomus was the most dominant genus in all samples. Although there was no significant difference in the AMF community in roots and rhizosphere soils between the Bt and non-Bt maize treatments, total phosphorus (TP), total nitrogen (TN), organic carbon (OC), and pH were driving factors affecting the AMF community, and their composition varied between rhizosphere soils and roots during the maturity period of the fifth season. Compared to our previous study, the results were identical. In conclusion, no significant difference was observed between the Bt and non-Bt treatments, and the Illumina MiSeq method had higher throughput and higher quality read cover, which gave us comprehensive insight into AMF communities in agro-ecosystems.

Evidence for multi-trophic effects of pesticide seed treatments on non-targeted soil fauna

The use of pesticide seed treatments containing neonicotinoid insecticides is widespread in large-scale row crop agriculture. Recently, use of pesticide seed treatments has come under scrutiny due to concerns over non-target impacts on beneficial insects (e.g., honey bees) and the environment. Amidst these growing concerns, however, few studies have examined how pesticide seed treatments may impact soil faunal communities across multiple feeding guilds and the soil processes they regulate. We grew corn and soybean with and without pesticide seed treatment for three years and measured the response of the soil faunal detritivore, herbivore, mixed, and predator feeding guilds, nitrogen mineralization, and surface litter decomposition at three time points each year. We found the effects of seed treatment on the soil faunal community varied in direction and magnitude by year and feeding guild and were most apparent in the predator and detritivore guilds. Guild-level effects tended to be strongest soon after planting but remained apparent throughout the crop growing season, particularly in the predator and mixed feeding guilds. We found no evidence that pesticide seed treatment affected the herbivore guild—the intended target of the seed treatment, or nitrogen mineralization, surface litter decomposition, or grain yields. Collectively, these data suggest that pesticide seed treatments can alter the abundance, richness, and diversity of all non-targeted soil faunal guilds. Additional research will be necessary to determine the longer-term significance of pesticide seed treatment-driven changes in non-target soil faunal communities in agroecosystems.

The anurofauna of a vanishing savanna: the case of the Brazilian Cerrado

The second largest biome in Brazil, the Cerrado has been transformed into a highly mechanized and intensive agricultural area, with little public opposition. The native anurofauna is rich in species number and endemisms, but has long been regarded as a generalist community originated from neighboring biomes. The accelerated degradation of Cerrado habitats caused by agriculture is bound to affect local anuran communities. This review aims to investigate the effects of anthropogenic activities on local amphibians. Despite a clear paucity, the existing studies indicate that, while this community may be more resilient to some anthropogenic activities (e.g. fire) than their forest counterparts, agricultural environments are strongly dominated by generalist species. Susceptibility to agro-cattle land-uses appears to be determined by specializations, especially regarding habitat and breeding strategies. Natural vegetation fragments are important for maintaining diverse anuran communities in agroecosystems. Agrochemicals cause histopathologic alterations and potential decreased fitness. Chytridiomycosis has been recorded in species extant in the biome, including endemics. The anurofauna appears to be especially sensitive to hydroelectric dams, as even previously common, widespread and generalist species declined or disappeared after dam flooding. Latest predictions indicate the occupation of the Cerrado will proceed northward, which, coupled with climate change, will cause great loss of biodiversity. Only a small portion of suitable natural habitats will remain in northern Cerrado, with amphibian richness being reduced to less than half. We conclude that less popular biomes may benefit from trait-oriented reviews to assess and guide future scientific and conservation projects.

In-Field Habitat Management to Optimize Pest Control of Novel Soil Communities in Agroecosystems.

The challenge of managing agroecosystems on a landscape scale and the novel structure of soil communities in agroecosystems both provide reason to focus on in-field management practices, including cover crop adoption, reduced tillage, and judicial pesticide use, to promote soil community diversity. Belowground and epigeal arthropods, especially exotic generalist predators, play a significant role in controlling insect pests, weeds, and pathogens in agroecosystems. However, the preventative pest management tactics that dominate field-crop production in the United States do not promote biological control. In this review, we argue that by reducing disturbance, mitigating the effects of necessary field activities, and controlling pests within an Integrated Pest Management framework, farmers can facilitate the diversity and activity of native and exotic arthropod predators.

Effects of Organic Pesticides on Enchytraeids (Oligochaeta) in Agroecosystems: Laboratory and Higher-Tier Tests

Enchytraeidae (Oligochaeta, Annelida) are often considered to be typical forestliving organisms, but they are regularly found in agroecosystems of the temperate regions of the world. Although less known than their larger relatives, the earthworms, these saprophagous organisms play similar roles in agricultural soils (but at a smaller scale), e.g., influencing soil structure and organic matter dynamics via microbial communities, and having a central place in soil food webs. Their diversity is rarely studied or often underestimated due to difficulties in distinguishing the species. New genetic techniques reveal that even in anthropogenically highly influenced soils, more than ten species per site can be found. Because of their close contact with the soil pore water, a high ingestion rate and a thin cuticle, they often react very sensitively to a broad range of pesticides. Firstly we provide a short overview of the diversity and abundance of enchytraeid communities in agroecosystems. Afterwards, we explore the available data on enchytraeid sensitivity towards pesticides at different levels of biological organization, focusing on pesticides used in (mainly) European agroecosystems. Starting with non-standardized studies on the effects of pesticides on the sub-individual level, we compile the results of standard laboratory tests performed following OECD and ISO guidelines as well as those of higher-tier studies (i.e., semi-field and field tests). The number of comparable test data is still limited, because tests with enchytraeids are not a regulatory requirement in the European Union. While focusing on the effects of pesticides, attention is also given to their interactions with environmental stressors (e.g., climate change). In conclusion, we recommend to increase the use of enchytraeids in pesticide risk assessment because of their diversity and functional importance as well as their increasingly simplified use in (mostly standardized) tests at all levels of biological organization.

Conversion from long-term cultivated wheat field to Jerusalem artichoke plantation changed soil fungal communities

Understanding soil microbial communities in agroecosystems has the potential to contribute to the improvement of agricultural productivity and sustainability. Effects of conversion from long-term wheat plantation to Jerusalem artichoke (JA) plantation on soil fungal communities were determined by amplicon sequencing of total fungal ITS regions. Quantitative PCR and PCR-denaturing gradient gel electrophoresis were also used to analyze total fungal and Trichoderma spp. ITS regions and Fusarium spp. Ef1α genes. Results showed that soil organic carbon was higher in the first cropping of JA and Olsen P was lower in the third cropping of JA. Plantation conversion changed soil total fungal and Fusarium but not Trichoderma spp. community structures and compositions. The third cropping of JA had the lowest total fungal community diversity and Fusarium spp. community abundance, but had the highest total fungal and Trichoderma spp. community abundances. The relative abundances of potential fungal pathogens of wheat were higher in the wheat field. Fungal taxa with plant growth promoting, plant pathogen or insect antagonistic potentials were enriched in the first and second cropping of JA. Overall, short-term conversion from wheat to JA plantation changed soil fungal communities, which is related to changes in soil organic carbon and Olsen P contents.

Soil Microbiome Is More Heterogeneous in Organic Than in Conventional Farming System.

Organic farming system and sustainable management of soil pathogens aim at reducing the use of agricultural chemicals in order to improve ecosystem health. Despite the essential role of microbial communities in agro-ecosystems, we still have limited understanding of the complex response of microbial diversity and composition to organic and conventional farming systems and to alternative methods for controlling plant pathogens. In this study we assessed the microbial community structure, diversity and richness using 16S rRNA gene next generation sequences and report that conventional and organic farming systems had major influence on soil microbial diversity and community composition while the effects of the soil health treatments (sustainable alternatives for chemical control) in both farming systems were of smaller magnitude. Organically managed system increased taxonomic and phylogenetic richness, diversity and heterogeneity of the soil microbiota when compared with conventional farming system. The composition of microbial communities, but not the diversity nor heterogeneity, were altered by soil health treatments. Soil health treatments exhibited an overrepresentation of specific microbial taxa which are known to be involved in soil suppressiveness to pathogens (plant-parasitic nematodes and soil-borne fungi). Our results provide a comprehensive survey on the response of microbial communities to different agricultural systems and to soil treatments for controlling plant pathogens and give novel insights to improve the sustainability of agro-ecosystems by means of beneficial microorganisms.

Clay-to-Carbon Ratio Controls the Effect of Herbicide Application on Soil Bacterial Richness and Diversity in a Loamy Field

Soil texture and soil organic carbon (OC) influence the bacterial microenvironment and also control herbicide sorption. A field-scale exploratory study was conducted to investigate the potential interaction between soil texture parameters, herbicides, and soil bacterial richness and diversity. Glyphosate and bentazon were used to evaluate the herbicidal effect on bacterial community under different conditions created by clay and OC gradients in a loamy field. Metabarcoding by high-throughput sequencing of bacterial rDNA was used to estimate bacterial richness and diversity using OTUs, abundance-based coverage (ACE), Shannon diversity index, and phylogenetic diversity. In general, bacterial richness and diversity increased after bentazon application and decreased after glyphosate application. There was no significant effect for field locations with Dexter n (the ratio between clay and OC) values below 4.04 (the median of the values in the field study). The correlation coefficient (r) between bacterial richness and clay decreased after bentazon application, but increased after glyphosate application. Correlations between Dexter n and bacterial indices followed the same pattern, decreasing after bentazon application and increasing after glyphosate application. This indicated that the specific chemical nature of individual herbicides affected bacterial communities. This study reinforced the importance of including soil physical and chemical characteristics to explain the influence of pesticides on the variation in soil bacterial communities in agroecosystems.

Field density and distribution of weeds are associated with spatial dynamics of omnivorous ground beetles (Coleoptera: Carabidae)

Soil seedbanks contribute to development of weed communities in agroecosystems and thus, understanding their regulation contributes to weed management strategies. In this context, the impacts of beneficial seed-consuming arthropods like carabids may contribute to sustainable long-term weed management. We were interested in assessing the spatial relationship between carabid beetles, weeds, and weed seeds in canola (Brassica napus L.), one of the most widely grown crops in Canada. To do this, we collected spatially referenced count data representing the activity-density of seed predatory carabid species and data regarding weed density and weed seed density. We used Spatial Analysis by Distance Indices (SADIE) to explore spatial distributions of carabids in four commercial canola agroecosystems in western Canada. Carabids and weed populations were highly clustered. Moreover, there was significant spatial overlap between activity-density of carabids and patches of high weed density, with an association index, X, ranging between 0.40 and 0.71. Patterns of spatial association also became generally stronger with more advanced crop development. Our results suggest that presence of weedy patches of vegetation in cropped areas contributes to biodiversity by conserving populations of carabids, which also increases rates of weed seed predation.