Bee communities and pollination services in adjacent crop fields following flower removal in an invasive forest shrub.

The habitat boundaries between crops and seminatural areas influence bee movements and pollination services to crops. Edges also provide favorable conditions for invasive plants, which may usurp pollinators and reduce visitation to native or crop plants. Alternatively, floral displays of alien plants may facilitate, or increase, the pollination success of adjacent plants by attracting more pollinators to the area. Therefore, pollination services of bees from seminatural habitats to crop areas should vary with the presence of invasive floral resources and distance from habitat edges. To test the hypothesis that floral resources of invasive forest shrubs affect the bee community and pollination services in adjacent crop fields, we conducted a 2-yr field experiment along forest-crop edges at five isolated forest remnants. We removed flower buds from a dominant invasive shrub, Lonicera maackii (Amur honeysuckle), along forest-crop edges and paired removals with controls of intact flowers. The bee community, their pollination services, and flower visitation rates were quantified along a 200-m gradient into an adjacent crop field using pan traps and sentinel cucumber plants. Impacts to the bee community were dependent of bee functional traits. Larger bees visited fewer sentinel cucumber flowers in flower removal plots, which corresponded with decreased cucumber pollination compared to plots with honeysuckle flowers at distances >100 m from forest edges. Small-bodied and weaker flying bees visited sentinel plants more frequently closer to the forest edge and increased pollination services to cucumber at distances <100 m from L. maackii shrubs in flower removal plots. After 2 yr, bee abundance and species richness increased within flower removal plots across all distances. High functional diversity of the bee community increased pollination services to sentinel plants and increased cucumber production within 200 m from forest remnants. Our findings suggest that dense floral resources of invasive shrubs suppressed forest-edge bee communities and their pollination services, but also attracted large-bodied generalist bees, which were effective pollinators. This study helps explain how life histories and functional attributes of bees can predict either facilitation or suppression of pollination services to crop or native plants in response to invasive floral resources.

Experimental effects of white-tailed deer and an invasive shrub on forest ant communities.

Ungulate browse and invasive plants exert pressure on plant communities and alter the physical and chemical properties of soils, but little is known about their effects on litter-dwelling arthropods. In particular, ants (Formicidae) are ubiquitous in temperate forests and are sensitive to changes in habitat structure and resources. As ants play many functional roles, changes to ant communities may lead to changes in ecosystem processes. We conducted a long-term experiment that controlled white-tailed deer (Odocoileus virginianus) access and presence of an invasive understory shrub in deciduous forests located in southwestern Ohio, USA from 2011 to 2017. Several leaf-litter ant community responses and litter biomass were measured in five paired deer access and exclosure plots, each with a split-plot removal of Amur honeysuckle (Lonicera maackii). Ant abundance and species richness increased with time in deer exclosures, but not in deer access plots. Honeysuckle removal reduced abundance and richness of ants. There were additive effects of deer and honeysuckle on ant richness, and interactive effects of deer and honeysuckle on ant abundance. Deer exclusion reduced variation in ant composition relative to access plots. There was little evidence that treatments directly influenced species diversity of ants. However, all ant measures were positively related to litter biomass, which was greater in deer exclosures relative to access plots. Our results indicate strong indirect effects of herbivores and honeysuckle on litter-dwelling ants, mediated through changes in litter biomass and likely vegetation structure, which may alter ant-mediated ecosystem processes.

Invasive earthworm and soil litter response to the experimental removal of white-tailed deer and an invasive shrub.

Recent studies have shown that complex species interactions can regulate above- and belowground processes in terrestrial systems. Ungulate herbivory and invasive species are known to have strong effects on plant communities in some systems, but their impacts on soil biota and belowground processes are lesser known. Growing evidence suggests white-tailed deer (Odocoileus virginianus) and invasive plants facilitate increased abundance of exotic earthworms in temperate forests of the eastern United States. We conducted an experimental study that manipulated deer access and the presence of an invasive understory shrub in an eastern deciduous forest of southwestern Ohio, USA, from 2013 to 2017. Earthworm density and biomass, and standing litter biomass were measured in five paired deer access and exclosure plots, each with a split-plot removal of Amur honeysuckle (Lonicera maackii). Earthworm density declined in response to the experimental exclusion of deer, with earthworm density decreasing over time in the deer exclosure plots relative to deer access plots. Deer exclusion produced greater variation in earthworm species composition relative to access plots. Multivariate analyses indicated that larger earthworms in the genus Lumbricus were associated with deer exclosure plots, while smaller endogeic species were ubiquitous in both treatments. Standing litter biomass decreased over time in the deer-access plots. In contrast, honeysuckle removal had little effect on earthworm density and standing litter biomass. There was an interaction between deer and honeysuckle treatments on earthworm biomass, with honeysuckle removal reducing earthworm biomass when deer were excluded. Our results demonstrate strong effects of herbivores on invasive earthworms and ecosystem processes, but indicate a weaker influence of invasive shrubs. Further, our findings suggest that the effects of deer overabundance in forest ecosystems are potentially reversible with long-term intervention.

From dispersal to predation: A global synthesis of ant-seed interactions.

Ant-seed interactions take several forms, including dispersal, predation, and parasitism, whereby ants consume seed appendages without dispersal of seeds. We hypothesized that these interaction outcomes could be predicted by ant and plant traits and habitat, with outcomes falling along a gradient of cost and benefit to the plant. To test this hypothesis, we conducted a global literature review and classified over 6,000 pairs of ant-seed interactions from 753 studies across six continents. Linear models showed that seed and ant size, habitat, and dispersal syndrome were the most consistent predictors. Predation was less likely than parasitism and seed dispersal among myrmecochorous plants. A classification tree of the predicted outcomes from linear models revealed that dispersal and predation formed distinct categories based on habitat, ant size, and dispersal mode, with parasitism outcomes forming a distinct subgroup of predation based on seed size and shape. Multiple correspondence analysis indicated some combinations of ant genera and plant families were strongly associated with particular outcomes, whereas other ant-seed combinations were much more variable. Taken together, these results demonstrate that ant and plant traits are important overall predictors of potential seed fates in different habitat types.

The Effects of Dispersal and Predator Density on Prey Survival in an Insect-Red Clover Metacommunity.

Trophic interactions are often studied within habitat patches, but among-patch dispersal of individuals may influence local patch dynamics. Metacommunity concepts incorporate the effects of dispersal on local and community dynamics. There are few experimental tests of metacommunity theory using insects compared to those conducted in microbial microcosms. Using connected experimental mesocosms, we varied the density of the leafhopper Agallia constricta Van Duzee (Homoptera: Cicadellidae) and a generalist insect predator, the damsel bug (Nabis spp., Heteroptera: Nabidae), to determine the effects of conspecific and predator density and varying the time available to dispersal among mesocosms on predation rates, dispersal rates, and leafhopper survival. Conspecific and damsel bug density did not affect dispersal rates in leafhoppers, but this may be due to leafhoppers' aversion to leaving the host plants or the connecting tubes between mesocosms hindering leafhopper movement. Leafhopper dispersal was higher in high-dispersal treatments. Survival rates of A. constricta were also lowest in treatments where dispersal was not limited. This is one of the first experimental studies to vary predator density and the time available to dispersal. Our results indicate that dispersal is the key to understanding short-term processes such as prey survival in predator-prey metacommunities. Further work is needed to determine how dispersal rates influence persistence of communities in multigenerational studies.

Effectiveness of Winkler Litter Extraction and Pitfall Traps in Sampling Ant Communities and Functional Groups in a Temperate Forest.

Selection of proper sampling methods for measuring a community of interest is essential whether the study goals are to conduct a species inventory, environmental monitoring, or a manipulative experiment. Insect diversity studies often employ multiple collection methods at the expense of researcher time and funding. Ants (Formicidae) are widely used in environmental monitoring owing to their sensitivity to ecosystem changes. When sampling ant communities, two passive techniques are recommended in combination: pitfall traps and Winkler litter extraction. These recommendations are often based on studies from highly diverse tropical regions or when a species inventory is the goal. Studies in temperate regions often focus on measuring consistent community response along gradients of disturbance or among management regimes; therefore, multiple sampling methods may be unnecessary. We compared the effectiveness of pitfalls and Winkler litter extraction in an eastern temperate forest for measuring ant species richness, composition, and occurrence of ant functional groups in response to experimental manipulations of two key forest ecosystem drivers, white-tailed deer and an invasive shrub (Amur honeysuckle). We found no significant effect of sampling method on the outcome of the ecological experiment; however, we found differences between the two sampling methods in the resulting ant species richness and functional group occurrence. Litter samples approximated the overall combined species richness and composition, but pitfalls were better at sampling large-bodied (Camponotus) species. We conclude that employing both methods is essential only for species inventories or monitoring ants in the Cold-climate Specialists functional group.

Species traits and environmental characteristics together regulate ant-associated biodiversity.

Host-associated organisms (e.g., parasites, commensals, and mutualists) may rely on their hosts for only a portion of their life cycle. The life-history traits and physiology of hosts are well-known determinants of the biodiversity of their associated organisms. The environmental context may strongly influence this interaction, but the relative roles of host traits and the environment are poorly known for host-associated communities. We studied the roles of host traits and environmental characteristics affecting ant-associated mites in semi-natural constructed grasslands in agricultural landscapes of the Midwest USA. Mites are frequently found in ant nests and also riding on ants in a commensal dispersal relationship known as phoresy. During nonphoretic stages of their development, ant-associated mites rely on soil or nest resources, which may vary depending on host traits and the environmental context of the colony. We hypothesized that mite diversity is determined by availability of suitable host ant species, soil detrital resources and texture, and habitat disturbance. Results showed that that large-bodied and widely distributed ant species within grasslands support the most diverse mite assemblages. Mite richness and abundance were predicted by overall ant richness and grassland area, but host traits and environmental predictors varied among ant hosts: mites associated with Aphaenogaster rudis depended on litter depth, while Myrmica americana associates were predicted by host frequency and grassland age. Multivariate ordinations of mite community composition constructed with host ant species as predictors demonstrated host specialization at both the ant species and genus levels, while ordinations with environmental variables showed that ant richness, soil texture, and grassland age also contributed to mite community structure. Our results demonstrate that large-bodied, locally abundant, and cosmopolitan ant species are especially important regulators of phoretic mite diversity and that their role as hosts is also dependent on the context of the interaction, especially soil resources, texture, site age, and area.

Fine-scale spatial patterns of genetic relatedness among resident adult prairie voles.

Characterizing the spatial arrangement of related individuals within populations can convey information about opportunities for the evolution of kin-selected social behaviors, the potential for inbreeding, and the geographic distribution of genetic variation. Prairie voles (Microtus ochrogaster) are socially monogamous rodents that sometimes breed cooperatively. Individuals of both sexes are highly philopatric, and among natal dispersers, the average dispersal distance is about 30 m. Such limited natal dispersal can result in the spatial clustering of kin and we used microsatellite data to estimate genetic relatedness among resident adult prairie voles in 2 natural populations to test the hypothesis that limited natal dispersal of male and female prairie voles results in the spatial clustering of kin. Spatial autocorrelation analyses of nest residency and microsatellite data indicated that proximate same-sex adult residents of both sexes were significantly more related than more spatially distant resident same-sex adults in Kansas. In Indiana, adult female voles residing less than 20 m apart were also significantly more related than more spatially distant resident adult females but spatial clustering of kin was not detected among resident adult males. The spatial clustering of kin indicates that opportunities for kin-selected behaviors exist in both populations, especially among females. Differences in the patterns of spatial genetic structure among resident males between the Kansas and Indiana populations may be due to population differences in factors such as demography and mating system, as well as in the extent of natal philopatry.

Predator interference alters foraging behavior of a generalist predatory arthropod.

Interactions between predators foraging in the same patch may strongly influence patch use and functional response. In particular, there is continued interest in how the magnitude of mutual interference shapes predator-prey interactions. Studies commonly focus on either patch use or the functional response without attempting to link these important components of the foraging puzzle. Predictions from both theoretical frameworks suggest that predators should modify foraging efforts in response to changes in feeding rate, but this prediction has received little empirical attention. We study the linkage between patch departure rates and food consumption by the hunting spider, Pardosa milvina, using field enclosures in which prey and predator densities were manipulated. Additionally, the most appropriate functional response model was identified by fitting alternative functional response models to laboratory foraging data. Our results show that although prey availability was the most important determinant of patch departure rates, a greater proportion of predators left enclosures containing elevated predator abundance. Functional response parameter estimation revealed significant levels of interference among predators leading to lower feeding rates even when the area allocated for each predator was kept constant. These results suggest that feeding rates determine patch movement dynamics, where interference induces predators to search for foraging sites that balance the frequency of agonistic interactions with prey encounter rates.

Landscape moderation of biodiversity patterns and processes - eight hypotheses.

Understanding how landscape characteristics affect biodiversity patterns and ecological processes at local and landscape scales is critical for mitigating effects of global environmental change. In this review, we use knowledge gained from human-modified landscapes to suggest eight hypotheses, which we hope will encourage more systematic research on the role of landscape composition and configuration in determining the structure of ecological communities, ecosystem functioning and services. We organize the eight hypotheses under four overarching themes. Section A: 'landscape moderation of biodiversity patterns' includes (1) the landscape species pool hypothesis-the size of the landscape-wide species pool moderates local (alpha) biodiversity, and (2) the dominance of beta diversity hypothesis-landscape-moderated dissimilarity of local communities determines landscape-wide biodiversity and overrides negative local effects of habitat fragmentation on biodiversity. Section B: 'landscape moderation of population dynamics' includes (3) the cross-habitat spillover hypothesis-landscape-moderated spillover of energy, resources and organisms across habitats, including between managed and natural ecosystems, influences landscape-wide community structure and associated processes and (4) the landscape-moderated concentration and dilution hypothesis-spatial and temporal changes in landscape composition can cause transient concentration or dilution of populations with functional consequences. Section C: 'landscape moderation of functional trait selection' includes (5) the landscape-moderated functional trait selection hypothesis-landscape moderation of species trait selection shapes the functional role and trajectory of community assembly, and (6) the landscape-moderated insurance hypothesis-landscape complexity provides spatial and temporal insurance, i.e. high resilience and stability of ecological processes in changing environments. Section D: 'landscape constraints on conservation management' includes (7) the intermediate landscape-complexity hypothesis-landscape-moderated effectiveness of local conservation management is highest in structurally simple, rather than in cleared (i.e. extremely simplified) or in complex landscapes, and (8) the landscape-moderated biodiversity versus ecosystem service management hypothesis-landscape-moderated biodiversity conservation to optimize functional diversity and related ecosystem services will not protect endangered species. Shifting our research focus from local to landscape-moderated effects on biodiversity will be critical to developing solutions for future biodiversity and ecosystem service management.

Disentangling the drivers of ß diversity along latitudinal and elevational gradients.

Understanding spatial variation in biodiversity along environmental gradients is a central theme in ecology. Differences in species compositional turnover among sites (ß diversity) occurring along gradients are often used to infer variation in the processes structuring communities. Here, we show that sampling alone predicts changes in ß diversity caused simply by changes in the sizes of species pools. For example, forest inventories sampled along latitudinal and elevational gradients show the well-documented pattern that ß diversity is higher in the tropics and at low elevations. However, after correcting for variation in pooled species richness (γ diversity), these differences in ß diversity disappear. Therefore, there is no need to invoke differences in the mechanisms of community assembly in temperate versus tropical systems to explain these global-scale patterns of ß diversity.

Functional landscape heterogeneity and animal biodiversity in agricultural landscapes.

Biodiversity in agricultural landscapes can be increased with conversion of some production lands into 'more-natural'- unmanaged or extensively managed - lands. However, it remains unknown to what extent biodiversity can be enhanced by altering landscape pattern without reducing agricultural production. We propose a framework for this problem, considering separately compositional heterogeneity (the number and proportions of different cover types) and configurational heterogeneity (the spatial arrangement of cover types). Cover type classification and mapping is based on species requirements, such as feeding and nesting, resulting in measures of 'functional landscape heterogeneity'. We then identify three important questions: does biodiversity increase with (1) increasing heterogeneity of the more-natural areas, (2) increasing compositional heterogeneity of production cover types and (3) increasing configurational heterogeneity of production cover types? We discuss approaches for addressing these questions. Such studies should have high priority because biodiversity protection globally depends increasingly on maintaining biodiversity in human-dominated landscapes.

Navigating the multiple meanings of ß diversity: a roadmap for the practicing ecologist.

A recent increase in studies of ß diversity has yielded a confusing array of concepts, measures and methods. Here, we provide a roadmap of the most widely used and ecologically relevant approaches for analysis through a series of mission statements. We distinguish two types of ß diversity: directional turnover along a gradient vs. non-directional variation. Different measures emphasize different properties of ecological data. Such properties include the degree of emphasis on presence/absence vs. relative abundance information and the inclusion vs. exclusion of joint absences. Judicious use of multiple measures in concert can uncover the underlying nature of patterns in ß diversity for a given dataset. A case study of Indonesian coral assemblages shows the utility of a multi-faceted approach. We advocate careful consideration of relevant questions, matched by appropriate analyses. The rigorous application of null models will also help to reveal potential processes driving observed patterns in ß diversity.

Diversity partitioning without statistical independence of alpha and beta.

Diversity partitioning has become a popular method for analyzing patterns of alpha and beta diversity. A recent evaluation of the method emphasized a distinction between additive and multiplicative partitioning and further advocated the use of multiplicative partitioning based on a presumed independence between alpha and beta. Concurrently, additive partitioning was criticized for producing dependent alpha and beta estimates. Until now, the issue of statistical independence of alpha and beta (in either type of partitioning) has not been thoroughly examined, partly due to confusion about the meaning of statistical independence. Here, we adopted a probability-based definition of statistical independence that is essentially identical to the definition found in any statistics textbook. We used a data simulation approach to show that alpha and beta diversity are not statistically independent in either additive or multiplicative partitioning. However, the extent of the dependence is not so great that it cannot be overcome by using appropriate statistical techniques to control it. Both additive and multiplicative partitioning are statistically valid and logically sound approaches to analyzing diversity patterns.

Life-history traits predict species responses to habitat area and isolation: a cross-continental synthesis.

There is a lack of quantitative syntheses of fragmentation effects across species and biogeographic regions, especially with respect to species life-history traits. We used data from 24 independent studies of butterflies and moths from a wide range of habitats and landscapes in Europe and North America to test whether traits associated with dispersal capacity, niche breadth and reproductive rate modify the effect of habitat fragmentation on species richness. Overall, species richness increased with habitat patch area and connectivity. Life-history traits improved the explanatory power of the statistical models considerably and modified the butterfly species-area relationship. Species with low mobility, a narrow feeding niche and low reproduction were most strongly affected by habitat loss. This demonstrates the importance of considering life-history traits in fragmentation studies and implies that both species richness and composition change in a predictable manner with habitat loss and fragmentation.

Butterfly abundance and movements among prairie patches: the roles of habitat quality, edge, and forest matrix permeability.

The spatial distribution of patchy insect populations is partly caused by behavioral patterns of insect movement that are influenced by habitat quality, isolation, and the permeability of the surrounding matrix. We recorded insect movements, abundance, and edge behaviors in two species of butterflies, the great-spangled fritillary (Speyeria cybele F., Lepidoptera: Nymphalidae) and the pearl crescent (Phyciodes tharos Drury, Lepidoptera: Nymphalidae), inhabiting remnant prairies surrounded by a forest matrix in south-central Ohio. We also determined the number of forest matrix types present and recorded the permeability of the different types to butterfly movement. The great-spangled fritillary exhibited a relatively high number of interpatch movements, a higher abundance at patch edges, and a propensity to cross the prairie-forest edges, and the forest matrix had a high permeability to butterfly movement. The pearl crescent, in contrast, rarely crossed edge boundaries, moved infrequently among patches, and was more abundant within the patch interior and in patches with high host-plant and flower densities. There were three structurally different forest matrix types separating habitat patches, which in previous studies would have been classified as a single deciduous forest matrix. Butterfly movement and edge behaviors mechanistically interact with patch quality, isolation, and the matrix permeability to determine the spatial structure of these populations in fragmented habitats.

Resource complementation and the response of an insect herbivore to habitat area and fragmentation.

Few studies have disentangled the effects of the area and fragmentation of a focal habitat type on species that use multiple habitat types within a landscape. We experimentally investigated the effects of habitat area, habitat fragmentation, and matrix composition on the movement and distribution of Melanoplus femurrubrum. Adults of this grasshopper feed preferentially on grasses, but oviposit almost exclusively in soil dominated by forbs. We compared population densities among plots that were made to vary in the area and fragmentation of clover habitat and composition of the matrix (grass or bare ground) within which clover habitat was embedded. In addition, a mark-recapture survey was conducted to examine effects of habitat area, fragmentation, and matrix composition on loss of individuals from a plot's clover habitat and movement between clover subplots within plots. Overall densities of adult M. femurrubrum (averaged over clover and matrix) were 2.2x higher in plots where the matrix was composed of grass as compared to bare ground, and 1.8x higher in plots with 64 compared to 16 m(2) of clover habitat. Overall densities of nymphs were also positively influenced by greater clover area, but were unaffected by matrix composition. Within focal clover habitat embedded in grass matrix, adult densities were 2.1x higher in small clover subplots than large clover subplots. We conclude that the grass matrix had a positive effect on adult densities, but not nymph densities, because grass and forb-dominated habitats likely provide complementary resources only for adults. The aggregation of adults on small clover subplots within grass matrix was mainly attributed to a greater rate of emigration loss per unit area. In addition, this study emphasizes that a species' response to changes in the area of a focal habitat type can depend significantly on the availability of complementary resources in the surrounding landscape.

Habitat specialization, body size, and family identity explain lepidopteran density-area relationships in a cross-continental comparison.

Habitat fragmentation may strongly affect species density, species interactions, and the rate of ecosystem processes. It is therefore important to understand the observed variability among species responses to fragmentation and the underlying mechanisms. In this study, we compare density-area relationships (DARs) for 344 lepidopteran species belonging to 22 families (butterflies and moths). This analysis suggested that the DAR(slope) is generally positive for moths and negative for butterflies. The differences are suggested to occur because moths are largely olfactory searchers, whereas most butterflies are visual searchers. The analysis also suggests that DARs vary as a function of habitat specialization and body size. In butterflies, generalist species had a more negative DAR(slope) than specialist species because of a lower patch size threshold. In moths, the differences in DAR(slope) between forest and open habitat species were large for small species but absent for large species. This difference is argued to occur because the DAR(slope) in large species mainly reflects their search mode, which does not necessarily vary between moth groups, whereas the slope in small species reflects population growth rates.