Local and Landscape Drivers of Carabid Activity, Species Richness, and Traits in Urban Gardens in Coastal California

Terrestrial invertebrate hosts of human pathogens in urban ecosystems

Terrestrial invertebrates in urban ecosystems are extremely species-rich, have many important roles in material flow and energy circulation, and are host to many human pathogens that pose threats to human health. These invertebrates are widely distributed in urban areas, including both out- and in-door environments. Consequently, humans are frequently in contact with them, which provides many opportunities for them to pose human health risks. However, comprehensive knowledge on human pathogen transfer via invertebrates is lacking, with research to date primarily focused on dipterans (e.g., mosquitoes, flies). Here, we take a broad taxonomic approach and review terrestrial invertebrate hosts (incl. mosquitoes, flies, termites, cockroaches, mites, ticks, earthworms, collembola, fleas, snails, and beetles) of human pathogens, with a focus on transmission pathways. We also discuss how urbanization and global warming are likely to influence the communities of invertebrate hosts and have flow-on risks to human health. Finally, we identify current research gaps and provide perspectives on future directions.

Dispersal limitation and environmental filtering effects: The taxonomic and functional beta diversity of ground beetles along the altitudinal gradient in Chinese warm-temperature forests

Beta diversity patterns along environmental gradients and underlying mechanisms constitute key research inquiries in biogeography. However, ecological processes often also influence the functional traits of biological communities, making the assessment of functional β-diversity crucial. Ground beetles (Coleoptera: Carabidae) are one of the most species-rich groups in the insect community, displaying strong habitat specificity and morphological differences. In this study, we explored the patterns of taxonomic and functional beta diversity in ground beetle communities along the altitudinal gradient of warm-temperature forests. By partitioning beta diversity into turnover and nestedness components, we evaluated their relationship with spatial distance. Our findings indicate a decline in species and functional trait similarity with increasing elevation and geographic distance. Further analysis attributed both types of beta diversity in carabids to a combination of dispersal limitation and environmental filtering, with elevation and geographic distance emerging as significant factors. Interestingly, forest-type variations were found to have no impact on the beta diversity of these communities. Our study reveals the impact of environmental filtering and dispersal limitation on both taxonomic and functional beta-diversity, shedding light on carabid community assembly in localized warm-temperature forest areas in eastern China.

Online toolkits for collaborative and inclusive global research in urban evolutionary ecology

Urban evolutionary ecology is inherently interdisciplinary. Moreover, it is a field with global significance. However, bringing researchers and resources together across fields and countries is challenging. Therefore, an online collaborative research hub, where common methods and best practices are shared among scientists from diverse geographic, ethnic, and career backgrounds would make research focused on urban evolutionary ecology more inclusive. Here, we describe a freely available online research hub for toolkits that facilitate global research in urban evolutionary ecology. We provide rationales and descriptions of toolkits for: (1) decolonizing urban evolutionary ecology; (2) identifying and fostering international collaborative partnerships; (3) common methods and freely-available datasets for trait mapping across cities; (4) common methods and freely-available datasets for cross-city evolutionary ecology experiments; and (5) best practices and freely available resources for public outreach and communication of research findings in urban evolutionary ecology. We outline how the toolkits can be accessed, archived, and modified over time in order to sustain long-term global research that will advance our understanding of urban evolutionary ecology.

Local Habitat Complexity and Its Effects on Herbivores and Predators in Urban Agroecosystems

In urban community gardens, cultivated vegetation provides variable levels of habitat complexity, which can suppress pests by promoting predator diversity and improving pest control. In this study, we examine three components of the structural complexity of garden vegetation (cover, diversity, and connectivity) to investigate whether higher garden vegetation complexity leads to fewer herbivores, more predators, and higher predation. We worked in eight community gardens where we quantified vegetation complexity, sampled the arthropod community, and measured predation on corn earworm eggs. We found that plots with high vegetation cover supported higher species richness and greater abundance of predatory insects. High vegetation cover also supported a greater abundance and species richness of spiders. In contrast, high vegetation diversity was negatively associated with predator abundance. While high predator abundance was positively associated with egg predation, greater predator species richness had a negative impact on egg predation, suggesting that antagonism between predators may limit biological control. Community gardeners may thus manipulate vegetation cover and diversity to promote higher predator abundance and diversity in their plots. However, the species composition of predators and the prevalence of interspecific antagonism may ultimately determine subsequent impacts on biological pest control.

Multiple ecosystem service synergies and landscape mediation of biodiversity within urban agroecosystems

Ecosystem services (ESs) are essential for human well-being, especially in urban areas where 60% of the global population will live by 2030. While urban habitats have the potential to support biodiversity and ES, few studies have quantified the impact of local and landscape management across a diverse suite of services. We leverage 5 years of data (>5000 observations) across a network of urban community gardens to determine the drivers of biodiversity and ES trade-offs and synergies. We found multiple synergies and few trade-offs, contrasting previous assumptions that food production is at odds with biodiversity. Furthermore, we show that natural landscape cover interacts with local management to mediate services provided by mobile animals, specifically pest control and pollination. By quantifying the factors that support a diverse suite of ES, we highlight the critical role of garden management and urban planning for optimizing biodiversity and human benefit.

Urban environments have species-specific associations with invasive insect herbivores

Urban forests are critically important for providing ecosystem services to rapidly expanding urban populations, but their health is threatened by invasive insect herbivores. To protect urban forests against invasive insects and support future delivery of ecosystem services, we must first understand the factors that affect insect density across urban landscapes. This study explores how a variety of environmental factors that vary across urban habitats influence density of invasive insects. Specifically, we evaluate how vegetational complexity, distance to buildings, impervious surface, canopy temperature, host availability and density of co-occurring herbivores impact three invasive pests of elm trees: the elm leaf beetle (Xanthogaleruca luteola), the elm flea weevil (Orchestes steppensis) and the elm leafminer (Fenusa ulmi). Insect responses to these factors were species-specific, and all environmental factors were associated with density of at least one pest species except for distance to buildings. Elm leafminer density decreased with higher temperatures and was influenced by an interaction between vegetational complexity and impervious surface. Elm flea weevil density increased with greater host availability, and elm leaf beetle density increased with higher temperatures. Both elm leaf beetle and elm flea weevil density decreased with greater leafminer density, suggesting that insect density is mediated by species interactions. These findings can be used to inform urban pest management and tree care efforts, making urban forests more resilient in an era when globalization and climate change make them particularly vulnerable to attack.

No evidence for innate differences in tadpole behavior between natural, urbanized, and invasive populations

Abstract

Animals are increasingly challenged to respond to novel or rapidly changing habitats due to urbanization and/or displacement outside their native range by humans. Behavioral differences, such as increased boldness (i.e., propensity for risk-taking), are often observed in animals persisting in novel environments; however, in many cases, it is unclear how these differences arise (e.g., through developmental plasticity or evolution) or when they arise (i.e., at what age or developmental stage). In the Guttural Toad (Sclerophrys gutturalis), adult urban toads from both native and invasive ranges are bolder than conspecifics in natural habitats. Here, we reared Guttural Toad tadpoles in a common garden experiment, and tested for innate differences in boldness across their development and between individuals whose parents and lineage came from rural-native, urban-native, and urban-invasive localities (i.e., origin populations). Tadpoles did not differ in their boldness or in how their boldness changed over ontogeny based on their origin populations. In general, tadpoles typically became less bold as they aged, irrespective of origin population. Our findings indicate that differences in boldness in free-living adult Guttural Toads are not innate in the tadpole stage and we discuss three possible mechanisms driving phenotypic divergence in adult boldness for the focus of future research: habitat-dependent developmental effects on tadpole behavior, decoupled evolution between the tadpole and adult stage, and/or behavioral flexibility, learning, or acclimatization during the adult stage.

Significance statement

To determine if animals can persist in urban areas or become invasive outside their native ranges, it is important to understand how they adapt to life in the city. Our study investigates if differences in boldness that have been found in adult Guttural Toads (Sclerophrys gutturalis) represent heritable differences that can also be found in early life stages by rearing tadpoles from eggs in a common garden experiment. We did not find any differences in boldness among tadpoles from rural-native, urban-native, and urban-invasive origin populations. Our findings suggest that differences in boldness are not innate and/or that boldness is a behavioral trait that is decoupled between the tadpole and the adult stage.

Bloom evenness modulates the influence of bloom abundance on insect community structure in suburban gardens

As land use change drives global insect declines, the value of enhancing habitat in urban and suburban landscapes has become increasingly important for flower-visiting insects. In order to help identify best landscaping practices, we conducted plant surveys and insect bowl-trap surveys in 34 suburban yards for 21 months in Gainesville, FL, USA, which resulted in 274 paired days of plant and insect survey data. We assessed the impact of nearest greenspace size, distance to greenspace, yard area, plant richness, plant type, bloom abundance, bloom richness and bloom evenness on insect abundance and richness. Our samples include 34,972 insects captured, 485,827 blooms counted and 774 species of plants recorded. We found that bloom evenness had a modulating effect on bloom abundance-a more even sample of the same number of blooms would have a disproportionately greater positive impact on flower visitor richness, insect richness and insect abundance. Bloom abundance was also highly significant and positively associated with flower visitor abundance, but nearest greenspace size, distance to greenspace, plant type (native vs. non-native vs. Florida Friendly), and yard area were not found to be important factors. Plant richness was a highly significant factor, but its effect size was very small.

Disentangling landscape and local drivers of ground-dwelling beetle community assembly in an urban ecosystem

Community assembly is the process by which local communities are organized and maintained from the regional species pool. Understanding processes of insect assembly are of interest in "shrinking" cities where vacant land has become abundant as a result of protracted economic decline and population loss. Vacant land represents a viable conservation space for insects such as beetles that contribute to ecosystem services including pest suppression, decomposition, and nutrient cycling. However, the inherent heterogeneity of cities may pose challenges for beetle dispersal from source populations, while quality of the urban environment may constrain establishment. The objective of this study was to investigate the constraints to ground-dwelling beetle community assembly in vacant lots and pocket prairies of Cleveland, Ohio using a functional trait-based approach. Functional traits with a strong predictive capacity for ecological functions were measured on beetle species collected via pitfall traps. Assembly of beetle communities was primarily constrained by dispersal limitations to colonization. Over 93% of species found within treatments were capable of flight, and functional diversity of beetle communities was higher across all treatments than expected by chance. Once beetles colonized, successful establishment was influenced by heavy metal contamination and mowing frequency, with these disturbances shaping communities based on body size, antennae length, and origin. Colonization of dispersal-limited species could be facilitated by increasing connectivity among greenspaces in cities, while establishment could be enhanced by managing local environmental conditions. Understanding how insect communities are structured in urban ecosystems provides context for observed patterns of biodiversity, advances conservation efforts, and fosters ecosystem services.

Natural enemy-herbivore networks along local management and landscape gradients in urban agroecosystems

Ecological networks can provide insight into how biodiversity loss and changes in species interactions impact the delivery of ecosystem services. In agroecosystems that vary in management practices, quantifying changes in ecological network structure across gradients of local and landscape composition can inform both the ecology and function of productive agroecosystems. In this study, we examined natural-enemy-herbivore co-occurrence networks associated with Brassica oleracea (cole crops), a common crop in urban agricultural systems. Specifically, we investigated how local management characteristics of urban community gardens and the landscape composition around them affect (1) the abundance of B. oleracea herbivores and their natural enemies, (2) the natural-enemy : herbivore ratio, and (3) natural-enemy-herbivore co-occurrence network metrics. We sampled herbivores and natural enemies in B. oleracea plants in 24 vegetable gardens in the California, USA central coast region. We also collected information on garden characteristics and land-use cover of the surrounding landscape (2 km radius). We found that increased floral richness and B. oleracea abundance were associated with increased parasitoid abundance, non-aphid herbivore abundance, and increased network vulnerability; increased vegetation complexity suppressed parasitoid abundance, but still boosted network vulnerability. High agricultural land-use cover in the landscape surrounding urban gardens was associated with lower predator, parasitoid, and non-aphid herbivore abundance, lower natural-enemy : herbivore ratios, lower interaction richness, and higher trophic complementarity. While we did not directly measure pest control, higher interaction richness, higher vulnerability, and lower trophic complementarity are associated with higher pest control services in other agroecosystems. Thus, if gardens function similarly to other agroecosystems, our results indicate that increasing vegetation complexity, including trees, shrubs, and plant richness, especially within gardens located in intensively farmed landscapes, could potentially enhance the biodiversity and abundance of natural enemies, supporting ecological networks associated with higher pest control services.

Landscape configuration and habitat complexity shape arthropod assemblage in urban parks

The urbanization process systematically leads to the loss of biodiversity. Only certain arthropods are resilient to the urbanization process and can thrive in the novel conditions of urbanized landscapes. However, the degree to which arthropod communities survive in urban habitats depends on landscape and local effects and biological interactions (e.g., trophic interactions). In the present study, we examined the relative importance of various factors at landscape (isolation, edge density and area of surrounding greenery) and local (size of park, canopy cover, understory vegetation cover, defoliation depth, weight of dried leaves, soil temperature, soil moisture, and soil pH) spatial scales on the diversity of ants, beetles and spiders in urban parks. Our results indicated that park edge density was negatively correlated with diversity metrics in ants, beetles, and spiders in urban parks relative to the degree of proximity with the peri-urban forest. In other words, parks that located adjacent to the peri-urban forest may not necessarily have high biodiversity. The results suggested that man-made structures have been effective dispersal barriers that limit the spillover effects of ants and spiders but not the spillover of comparatively strong fliers, such as beetles. However, the area of surrounding greenery may have facilitated the colonization of forest-dependent taxa in distant parks. Large parks with reduced edge density supported a higher arthropod diversity because of the minimal edge effect and increased habitat heterogeneity. Vegetation structure consistently explained the variability of ants, beetles, and spiders, indicating that understory plant litter is crucial for providing shelters and hibernation, oviposition, and foraging sites for the major taxa in urban parks. Therefore, efforts should focus on the local management of ground features to maximize the conservation of biological control in urban landscapes.

Competing Vegetation Structure Indices for Estimating Spatial Constrains in Carabid Abundance Patterns in Chinese Grasslands Reveal Complex Scale and Habitat Patterns

Carabid communities are influenced by landscape features. Chinese steppes are subject to increasing desertification processes that are changing land-cover characteristics with negative impacts on insect communities. Despite those warnings, how land-cover characteristics influence carabid communities in steppe ecosystems remains unknown. The aim of this study is to investigate how landscape characteristics drive carabid abundance in different steppes (desert, typical, and meadow steppes) at different spatial scales. Carabid abundances were estimated using pitfall traps. Various landscape indices were derived from Landsat 8 Operational Land Imager (OLI) images. Indices expressing moisture and productivity were, in general, those with the highest correlations. Different indices capture landscape aspects that influence carabid abundance at different scales, in which the patchiness of desert vegetation plays a major role. Carabid abundance correlations with landscape characteristics rely on the type of grassland, on the vegetation index, and on the scale considered. Proper scales and indices are steppe type-specific, highlighting the need of considering various scales and indices to explain species abundances from remotely sensed data.

Environmental and spatial filtering of ladybird beetle community composition and functional traits in urban landscapes

Urban community gardens provide habitat for biodiversity within urban landscapes. Beneficial insects, those that provide important ecosystem services like pollination and pest control, are among the many inhabitants of these green spaces. Garden management and the composition of the urban matrix in which they are embedded can affect not only the abundance and species richness of beneficial insects but also their community composition and functional traits. During 2014 and 2015 (June to September), we collected ladybird beetles (Coleoptera: Coccinellidae) in 19 community gardens in three counties of the California Central Coast. We examined the effects of garden- and landscape-level characteristics on ladybird community composition and functional traits. Out of the 19 species collected, only 3 were non-native to California (3 were not identified to species). Similarities in ladybird species composition were not driven by geographic distance between gardens, which suggest that beetles in these landscapes are not experiencing dispersal limitation. Instead, three landscape-level environmental variables and seven garden-scale ones correlated with changes in community composition. Even though we perceive cities as highly disturbed low-quality landscapes, our results suggest that highly mobile arthropods such as ladybird beetles, may not perceive the urban matrix as a barrier to movement and that urban gardens can be inhabited by native species with different sizes, diet breadths and diets. Nevertheless, our results also suggest garden specific management practices, such as altering ground cover, can affect the taxonomic and functional composition of ladybird beetles with potential implications to their ecosystem services.