2018. Forest disturbance and arthropods: Small-scale canopy gaps drive invertebrate community structure and composition. Ecosphere 9(10):Abstract. In forest ecosystems, disturbances that cause tree mortality create canopy gaps, increase growth of understory vegetation, and alter the abiotic environment. These impacts may have interacting effects on populations of ground-dwelling invertebrates that regulate ecological processes such as decomposition and nutrient cycling. A manipulative experiment was designed to decouple effects of simultaneous disturbances to the forest canopy and ground-level vegetation to understand their individual and combined impacts on ground-dwelling invertebrate communities. We quantified invertebrate abundance, richness, diversity, and community composition via pitfall traps in response to a factorial combination of two disturbance treatments: canopy gap formation via girdling and understory vegetation removal. Formation of gaps was the primary driver of changes in invertebrate community structure, increasing activityabundance and taxonomic richness, while understory removal had smaller effects. Families of Collembola and Diplopoda, as well as some families of Coleoptera, increased in combined canopy and understory disturbance treatments, whereas Curculionidae and Nitidulidae were more abundant in undisturbed forest. Gaps increased light availability, height and cover of understory vegetation, and soil moisture levels, and decreased depth and cover of leaf litter compared to undisturbed forest. Decoupling of canopy and understory vegetation disturbances revealed gap formation as an important short-term driver of grounddwelling invertebrate community structure and composition. Our findings increase understanding of how ground-dwelling invertebrate communities respond to disturbance and inform sustainable management of forest ecosystems to foster biodiversity and resilience.

Emerald ash borer (Agrilus planipennis Fairmaire), an invasive wood-boring beetle native to Asia, has killed hundreds of millions of ash trees since its accidental introduction into North America, resulting in widespread formation of canopy gaps and accumulations of coarse woody debris (CWD) in forests. The objective was to quantify effects of canopy gaps and CWD caused by early stages of emerald ash borer-induced ash mortality, and their interaction on ground beetle assemblages. The impact of canopy gaps and CWD varied, as gaps affected beetle assemblages in 2011, while effects of CWD were only observed in 2012. Gaps decreased beetle activity-abundance, and marginally decreased richness, driving changes in species composition, but evenness and diversity were unaffected. Effects of the CWD treatment alone were minimal, but CWD interacted with the canopy treatment, resulting in an increase in activity-abundance of ground beetles in canopy gaps without CWD, and a marginal increase in species richness in canopy gaps with CWD. Although there were some initial changes in species composition, these were ephemeral, suggesting that ground beetle assemblages may be resilient to disturbance caused by emerald ash borer. This study contributes to our understanding of the cascading ecological impacts of biological invasions on forest ecosystems.

a b s t r a c tEmerald ash borer (EAB; Agrilus planipennis) is an invasive wood-boring beetle that causes rapid ash tree mortality, widespread formation of canopy gaps, and accumulation of coarse woody debris (CWD) in forests. The objective was to quantify the effects of canopy gaps, ash CWD and their interaction caused by EAB-induced ash mortality on the forest floor invertebrate community. A two-year manipulative experiment was conducted in forests at NASA Plum Brook Research Station in Ohio, USA. Canopy gaps caused by ash mortality decreased the activity-abundance of some taxa, such as Opiliones, Carabidae and several families of Collembola, as well as invertebrate richness and diversity, but had minor effects on community composition. CWD had minimal effects on the forest floor invertebrate community overall, but altered the activity-abundance of several invertebrate groups, and marginally increased taxonomic evenness in closed canopy treatments. The results of this study suggest that the effects of ash mortality on forest floor invertebrate communities change over time due to an inverse temporal relationship in magnitude effects of canopy gaps, which diminish over time, and accumulation of CWD, which increases over time. These findings contribute to our understanding of the effects of disturbance on ecosystems and the cascading ecological impacts of emerald ash borer invasions in forests.

We review research on ecological impacts of emerald ash borer (EAB)-induced ash mortality in the Upper Huron River watershed in southeast Michigan near the epicenter of the invasion of North America, where forests have been impacted longer than any others in North America. By 2009, mortality of green, white, and black ash exceeded 99%, and ash seed production and regeneration had ceased. This left an orphaned cohort of saplings too small to be infested, the fate of which may depend on the ability of natural enemies to regulate EAB populations at low densities. There was no relationship between patterns of ash mortality and ash density, ash importance, or community composition. Most trees died over a five-year period, resulting in relatively simultaneous, widespread gap formation. Disturbance resulting from gap formation and accumulation of coarse woody debris caused by ash mortality had cascading impacts on forest communities, including successional trajectories, growth of non-native invasive plants, soil dwelling and herbivorous arthropod communities, and bird foraging behavior, abundance, and community composition. These and other impacts on forest ecosystems are likely to be experienced elsewhere as EAB continues to spread.

A growing body of research documents the importance of plant genetic effects on arthropod community structure. However, the mechanisms underlying these effects are often unclear. Additionally, plant genetic effects have largely been quantified in common gardens, thus inflating the estimates of their importance by minimizing levels of natural variation. Using Valeriana edulis, a dioecious plant with genetically based sex determination, we conducted surveys and experiments on wild-grown individuals to document field patterns of arthropod association between the sexes and the mechanisms underlying these plant genetic effects. Three years of surveys revealed strong and consistent sex-biased arthropod association in wild-grown plants: female plants supported 4-fold, 1.5-fold, and 4-fold higher densities of aphids, aphid predators, and aphid-tending ants, respectively, compared to males. There was mixed evidence that the female bias for aphids was due to higher plant quality, while we found no difference between plant sexes in aphid preference or the top-down effects of predators and tending ants. Female bias for ants was due to both the greater attractiveness of female plants (direct effect mediated by floral nectar) and an independent, weaker effect of higher aphid abundance on females (density-mediated indirect effect). Conversely, the female bias for predators was driven solely by the greater attractiveness of female plants. We did not find interaction modification, i.e., ant-aphid and predator-aphid interactions were equivalent between plant sexes. Plant sex explained 0.24%, 2.28%, and 4.42% of the variance in aphids, predators, and ants, respectively, values comparable to but slightly weaker than those previously reported from common-garden studies. In contrast to the prediction of diminished plant genetic effects with increasing trophic level, we show how weak indirect effects on predators and parasitoids (via herbivores) can be complemented by strong direct effects via common plant traits (floral resources). In summary, we document direct and indirect effects of genetically based sex on a multi-trophic arthropod community that were expressed in wild-grown plants across multiple years.

The increase of minimally managed vacant land resulting from population loss and the subsequent removal of infrastructure is a reoccurring feature in shrinking cities around the globe. Due to the low frequency and intensity of management, these spaces create a unique environment for plant colonization, establishment, and succession. Herein we refer to these plants and the habitats they form as urban spontaneous vegetation (USV). As a form of urban green space, USV has the potential to provide a number of ecological and sociological benefits to shrinking cities, such as supporting urban wildlife, enhancing the provision of regulating ecosystem functions and services, connecting residents with nature, and improving human health and well-being. Conversely, USV can also support undesirable animals such as vectors of disease, and due to its wild and disorderly appearance, can evoke negative emotions in residents while signaling community neglect. This review aims to explore the potential ecological and sociological tradeoffs of USV within the context of shrinking cities. Through this evaluation, we aim to inform future planning and management to exploit the benefits offered by this resource while minimizing negative outcomes, thereby leading to the enhanced sustainability of shrinking cities worldwide.

Urban patch colonization and species establishment within cities are restricted by the behavioural, life history and physiological attributes of colonizing species, in conjunction with environmental filtering processes at small and large spatial scales. To enhance the local biodiversity in urban greenspaces, these filtering processes need to be assessed so that greenspace design and management can guide establishment of local species pools. We investigated the relative importance of local and landscape‐scale features on spider community assembly using a functional and taxonomic approach. Within the city of Cleveland, Ohio, USA, we established a field experiment wherein control vacant lots, urban meadows, and low‐ and high‐diversity pocket prairies were established across eight neighbourhoods (N = 32). Spiders were sampled during June–August of 2015 and 2016 using pitfall traps and vacuums. Spider functional diversity was assessed using null models, while local and landscape drivers were analysed via canonical partial least squares and clustered image maps. Increased mowing was associated with lower‐than‐expected spider functional alpha and beta diversity in 2015. Patch isolation and percentage impervious surface increased the functional dissimilarity and taxonomic diversity of spiders in 2016, resulting in higher‐than‐expected overall functional alpha diversity. We also found that increasing plant height and biomass favoured spiders with large body size and decreased the abundance of small web weavers. Synthesis and applications. Our findings suggest that increasing the amount of impervious surface in cities will act as a strong environmental filter, producing more spatially distinct spider communities at a landscape scale. Additionally, while periodic mowing in vacant lots benefits some spider taxa, it has a negative impact on the establishment of several species, mainly larger spiders and those most sensitive to disturbance. To conserve spiders and the biota depended upon them, investment in managed greenspaces such as pocket prairies that require infrequent mowing is warranted. In doing so, cities can enhance urban biodiversity and beautify local neighbourhoods.

1. Ants interact with a diversity of organisms. These interactions, coupled with their abundance, cause ants to have ecologically important effects across multiple trophic levels. 2. Empirical study of ant nutritional ecology has led to the prediction that a macronutrient imbalance will affect ant behaviour and interspecific interactions that underlie these broad‐scale effects. Excess carbohydrate relative to protein is predicted to increase ant aggressiveness, predatory tendency and foraging activity, and to decrease collection of hemipteran honeydew and plant nectar. 3. In field experiments conducted in 2009 and 2010, captive colony fragments of a native ant, Formica podzolica (Hymenoptera: Formicidae), were provided with either simulated prey or carbohydrate solution ad libitum. Foraging behaviours and interactions with flowers, myrmecophilous aphids and aphid natural enemies on wild‐grown plants were documented. 4. Strong effects of macronutrient imbalance on foraging manifested quickly and consistently across colonies; in accordance with predictions, prey‐fed foragers collected both honeydew and floral nectar, whereas carbohydrate‐fed ants ceased collecting these resources. Counter to predictions, carbohydrate‐fed ants dramatically lowered their activity levels and did not prey upon aphids. 5. Ants had no effect on aphid enemies in 2009, when the latter were relatively rare, but decreased their abundance in 2010. Despite this protection, the net effect of ants on aphids was negative (measured only in 2009). Prey‐fed ants demonstrated a strong preference for honeydew over floral nectar, thus demonstrating that a macronutrient imbalance may lead to different interactions with similar resources. 6. This study links ant nutrition and community ecology by demonstrating the rapid, asymmetric and multitrophic consequences of nutritionally mediated behaviour.