Pollen carryover, pollinator movement, and spatial context impact the delivery of pollination services in apple orchards.

Assessing the relative contributions of different pollinator taxa to pollination services is a central task in both basic eco-evolutionary research and applied conservation and agriculture. To that end, many studies have quantified single-visit pollen deposition and visitation frequency, which together determine a pollinator species' rate of conspecific pollen delivery. However, for plant species that require or benefit from outcrossing, pollination service quality further depends upon the ratio of outcross to self-pollen deposited, which is determined by two additional pollinator traits: pollen carryover and movement patterns among genetically compatible plant individuals. Here, we compare the pollination capacities of managed honey bees, native bumble bees, and native mining bees in apple-a varietally self-incompatible commercial crop-when pollen carryover and pollinator movement patterns are considered. We constructed simulation models of outcross pollen deposition parameterized using empirically measured single-visit pollen deposition, visitation frequency, and probabilities of intertree movement exhibited by each pollinator type, as well as pollen carryover patterns simulated based on parameters reported in the literature. In these models, we also explicitly specified the spatial relationships among cross-compatible trees based on field-realistic orchard layout schemes. We found that estimated pollination service delivery was considerably reduced for all pollinator types when pollen carryover and pollinator movement patterns were considered, as compared to when only single-visit pollen deposition and visitation frequency were considered. We also found that the performance of different pollinator types varied greatly across simulated orchard layout schemes and pollen carryover scenarios, including one instance where bumble and mining bees reversed their relative rankings. In all simulations, native bumble and mining bees outperformed managed honey bees in terms of both outcross pollen delivery per unit time and per flower visited, with disparities being greatest under scenarios of low pollen carryover. We demonstrate the degree to which pollination studies may reach inaccurate conclusions regarding pollination service delivery when pollen carryover and pollinator movement patterns are ignored. Our finding of the strong context dependence of pollination efficiency, even within a single plant-pollinator taxon pair, cautions that future studies in both basic and applied pollination biology should explicitly consider the ecological context in which pollination interactions take place.

Ten-year trends reveal declining quality of seeded pollinator habitat on reclaimed mines regardless of seed mix diversity.

Plant-pollinator interactions represent a crucial ecosystem function threatened by anthropogenic landscape changes. Disturbances that reduce plant diversity are associated with floral resource and pollinator declines. Establishing wildflower plantings is a major conservation strategy targeting pollinators, the success of which depends on long-term persistence of seeded floral communities. However, most pollinator-oriented seeding projects are monitored for a few years, making it difficult to evaluate the longevity of such interventions. Selecting plant species to provide pollinators diverse arrays of floral resources throughout their activity season is often limited by budgetary constraints and other conservation priorities. To evaluate the long-term persistence of prairie vegetation seeded to support pollinators, we sowed wildflower seed mixes into plots on a degraded reclaimed strip-mine landscape in central Ohio, USA. We examined how pollinator habitat quality, measured as floral abundance and diversity, changed over 10 years (2009-2019) in the absence of management, over the course of the blooming season within each year, and across three seed mixes containing different numbers and combinations of flowering plant species. Seeded species floral abundance declined by more than 75% over the study, with the largest decline occurring between the fifth and seventh summers. Native and non-native adventive flowering plants quickly colonized the plots and represented >50% of floral community abundances on average. Floral richness remained relatively constant throughout the study, with a small peak one year after plot establishment. Plots seeded with High-Diversity Mixes averaged two or three more species per plot compared with a Low-Diversity Mix, despite having been seeded with twice as many plant species. Within years, the abundance and diversity of seeded species were lowest early in the blooming season and increased monotonically from June to August. Adventive species exhibited the opposite trend, such that complementary abundance patterns of seeded and adventive species blooms resulted in a relatively constant floral abundance across the growing season. Seeded plant communities followed classic successional patterns in which annual species quickly established and flowered but were replaced by perennial species after the first few summers. Long-term data on establishment and persistence of flower species can guide species selection for future-oriented pollinator habitat restorations.

Non-native honey bees disproportionately dominate the most abundant floral resources in a biodiversity hotspot.

Most plant-pollinator mutualisms are generalized. As such, they are susceptible to perturbation by abundant, generalist, non-native pollinators such as the western honey bee ( Apis mellifera), which can reach high abundances and visit flowers of many plant species in their expansive introduced range. Despite the prevalence of non-native honey bees, their effects on pollination mutualisms in natural ecosystems remain incompletely understood. Here, we contrast community-level patterns of floral visitation by honey bees with that of the diverse native pollinator fauna of southern California, USA. We show that the number of honey bees visiting plant species increases much more rapidly with flower abundance than does that of non-honey bee insects, such that the percentage of all visitors represented by honey bees increases with flower abundance. Thus, honey bees could disproportionately impact the most abundantly blooming plant species and the large numbers of both specialized and generalized pollinator species that they sustain. Honey bees may preferentially exploit high-abundance floral resources because of their ability to recruit nest-mates; these foraging patterns may cause native insect species to forage on lower-abundance resources to avoid competition. Our results illustrate the importance of understanding foraging patterns of introduced pollinators in order to reveal their ecological impacts.

The worldwide importance of honey bees as pollinators in natural habitats.

The western honey bee (Apis mellifera) is the most frequent floral visitor of crops worldwide, but quantitative knowledge of its role as a pollinator outside of managed habitats is largely lacking. Here we use a global dataset of 80 published plant-pollinator interaction networks as well as pollinator effectiveness measures from 34 plant species to assess the importance of A. mellifera in natural habitats. Apis mellifera is the most frequent floral visitor in natural habitats worldwide, averaging 13% of floral visits across all networks (range 0-85%), with 5% of plant species recorded as being exclusively visited by A. mellifera For 33% of the networks and 49% of plant species, however, A. mellifera visitation was never observed, illustrating that many flowering plant taxa and assemblages remain dependent on non-A. mellifera visitors for pollination. Apis mellifera visitation was higher in warmer, less variable climates and on mainland rather than island sites, but did not differ between its native and introduced ranges. With respect to single-visit pollination effectiveness, A. mellifera did not differ from the average non-A. mellifera floral visitor, though it was generally less effective than the most effective non-A. mellifera visitor. Our results argue for a deeper understanding of how A. mellifera, and potential future changes in its range and abundance, shape the ecology, evolution, and conservation of plants, pollinators, and their interactions in natural habitats.

Floral visitation by the Argentine ant reduces bee visitation and plant seed set.

Ants often visit flowers, but have only seldom been documented to provide effective pollination services. Floral visitation by ants can also compromise plant reproduction in situations where ants interfere with more effective pollinators. Introduced ants may be especially likely to reduce plant reproductive success through floral visitation, but existing experimental studies have found little support for this hypothesis. Here, we combine experimental and observational approaches to examine the importance of floral visitation by the nonnative Argentine ant (Linepithema humile) on plant species native to Santa Cruz Island, California, USA. First, we determine how L. humile affects floral visitor diversity, bee visitation rates, and levels of pollen limitation for the common, focal plant species island morning glory (Calystegia macrostegia ssp. macrostegia). Second, we assess the broader ecological consequences of floral visitation by L. humile by comparing floral visitation networks between invaded and uninvaded sites. The Argentine ant and native ants both visited island morning glory flowers, but L. humile was much more likely to behave aggressively towards other floral visitors and to be the sole floral occupant. The presence of L. humile in morning glory flowers reduced floral visitor diversity, decreased rates of bee visitation, and increased levels of pollen limitation. Network comparisons between invaded and uninvaded. sites revealed differences in both network structure and species-level attributes. In. invaded sites, floral visitors were observed on fewer plant species, ants had a higher per-plant interaction strength relative to that of other visitors, and interaction strengths between bees and plants were weaker. These results illustrate that introduced ants can negatively affect plant reproduction and potentially disrupt pollination services at an ecosystem scale.

Floral visitation by the Argentine ant reduces pollinator visitation and seed set in the coast barrel cactus, Ferocactus viridescens.

Mounting evidence indicates that trade-offs between plant defense and reproduction arise not only from resource allocation but also from interactions among mutualists. Indirect costs of plant defense by ants, for example, can outweigh benefits if ants deter pollinators. Plants can dissuade ants from occupying flowers, but such arrangements may break down when novel ant partners infiltrate mutualisms. Here, we examine how floral visitation by ants affects pollination services when the invasive Argentine ant (Linepithema humile) replaces a native ant species in a food-for-protection mutualism with the coast barrel cactus (Ferocactus viridescens), which, like certain other barrel cacti, produces extrafloral nectar. We compared the effects of floral visitation by the Argentine ant with those of the most prevalent native ant species (Crematogaster californica). Compared to C. californica, the Argentine ant was present in higher numbers in flowers. Cactus bees (Diadasia spp.), the key pollinators in this system, spent less time in flowers when cacti were occupied by the Argentine ant compared to when cacti were occupied by C. californica. Presumably as a consequence of decreased duration of floral visits by Diadasia, cacti occupied by L. humile set fewer seeds per fruit and produced fewer seeds overall compared to cacti occupied by C. californica. These data illustrate the importance of mutualist identity in cases where plants balance multiple mutualisms. Moreover, as habitats become increasingly infiltrated by introduced species, the loss of native mutualists and their replacement by non-native species may alter the shape of trade-offs between plant defense and reproduction.

A globally synthesised and flagged bee occurrence dataset and cleaning workflow.

Species occurrence data are foundational for research, conservation, and science communication, but the limited availability and accessibility of reliable data represents a major obstacle, particularly for insects, which face mounting pressures. We present BeeBDC, a new R package, and a global bee occurrence dataset to address this issue. We combined >18.3 million bee occurrence records from multiple public repositories (GBIF, SCAN, iDigBio, USGS, ALA) and smaller datasets, then standardised, flagged, deduplicated, and cleaned the data using the reproducible BeeBDC R-workflow. Specifically, we harmonised species names (following established global taxonomy), country names, and collection dates and, we added record-level flags for a series of potential quality issues. These data are provided in two formats, "cleaned" and "flagged-but-uncleaned". The BeeBDC package with online documentation provides end users the ability to modify filtering parameters to address their research questions. By publishing reproducible R workflows and globally cleaned datasets, we can increase the accessibility and reliability of downstream analyses. This workflow can be implemented for other taxa to support research and conservation.

California Native Perennials Attract Greater Native Pollinator Abundance and Diversity Than Nonnative, Commercially Available Ornamentals in Southern California.

While many factors have been implicated in global pollinator decline, habitat loss is a key driver of wild pollinator decline in both abundance and species richness. An increase in and diversification of pollinator habitat, even in urban settings, can assist in the conservation of pollinator populations. In Southern California, a highly fragmented and urbanized landscape with a rich yet threatened native pollinator fauna, the availability of food resources for native pollinators hinges largely upon the selection of ornamental plants grown in the urban landscape. To examine the pollinator attractiveness of ornamental plants in a Southern California context, we installed an experimental garden with common California native and nonnative ornamental perennials and observed floral visitation and visitor community composition for 3 yr. Our study demonstrates that while native pollinators visited common ornamental perennials native to California at a higher rate than they visited nonnative ornamentals, introduced honey bees showed no significant preference for either native or nonnative species. Native plants also received a greater diversity of visitor taxa, including a richer suite of native bees. Plant species differed dramatically in attractiveness, by as much as a factor of 12, even within the native status group. Our results suggest that including a data-driven selection of both native and non-native ornamental perennials in the urban landscape can diversify the assemblage of native pollinators, provide critical floral resources throughout the year, and reduce the impact of honey bee landscape foraging dominance by providing plants highly attractive to native pollinators and less so to honey bees.

Joint Impacts of Drought and Habitat Fragmentation on Native Bee Assemblages in a California Biodiversity Hotspot.

Global climate change is causing more frequent and severe droughts, which could have serious repercussions for the maintenance of biodiversity. Here, we compare native bee assemblages collected via bowl traps before and after a severe drought event in 2014 in San Diego, California, and examine the relative magnitude of impacts from drought in fragmented habitat patches versus unfragmented natural reserves. Bee richness and diversity were higher in assemblages surveyed before the drought compared to those surveyed after the drought. However, bees belonging to the Lasioglossum subgenus Dialictus increased in abundance after the drought, driving increased representation by small-bodied, primitively eusocial, and generalist bees in post-drought assemblages. Conversely, among non-Dialictus bees, post-drought years were associated with decreased abundance and reduced representation by eusocial species. Drought effects were consistently greater in reserves, which supported more bee species, than in fragments, suggesting that fragmentation either had redundant impacts with drought, or ameliorated effects of drought by enhancing bees' access to floral resources in irrigated urban environments. Shifts in assemblage composition associated with drought were three times greater compared to those associated with habitat fragmentation, highlighting the importance of understanding the impacts of large-scale climatic events relative to those associated with land use change.

Ecological filtering in scrub fragments restructures the taxonomic and functional composition of native bee assemblages.

Predicting the long-term consequences of habitat alteration for the preservation of biodiversity and ecosystem function requires an understanding of how ecological filters drive taxonomic and functional biodiversity loss. Here, we test a set of predictions concerning the role of ecological filters in restructuring native bee assemblages inhabiting fragmented coastal sage scrub ecosystems in southern California, USA. In 2011 and 2012, we collected native bees in scrub habitat belonging to two treatment categories: large natural reserves and small habitat fragments embedded in an urban landscape. We compared bee assemblages in reserve and fragment sites with respect to their taxonomic and functional alpha diversity, beta diversity, assemblage composition, and mean geographical range size estimated via distribution maps compiled for this study from digitized specimen records. We found multiple lines of evidence that ecological filtering drove bee diversity loss in fragments: a disproportionate loss of functional diversity relative to taxonomic diversity, shifts in assemblage composition driven largely by the preferential extirpation of reserve-associated indicator species, and disproportionate loss of range-restricted species. However, we found no evidence of taxonomic or functional homogenization across fragment bee assemblages, suggesting that filtering was not sufficiently strong to cause a subset of functional traits (and their associated species) to dominate assemblages in fragments. Our results suggest that ecological filtering altered bee assemblages in habitat fragments, even when such fragments contained well-preserved native plant assemblages, underscoring the importance of preserving large areas of natural habitat for the conservation of bees (especially range-restricted taxa) and their associated ecological functions.

Urbanization-induced habitat fragmentation erodes multiple components of temporal diversity in a Southern California native bee assemblage.

Despite a large number of ecological studies that document diversity loss resulting from anthropogenic disturbance, surprisingly few consider how disturbance affects temporal patterns of diversity that result from seasonal turnover of species. Temporal dynamics can play an important role in the structure and function of biological assemblages. Here, we investigate the temporal diversity patterns of bee faunas in Southern California coastal sage scrub ecosystems that have been extensively fragmented by urbanization. Using a two-year dataset of 235 bee species (n = 12,036 specimens), we compared 1-ha plots in scrub fragments and scrub reserves with respect to three components of temporal diversity: overall plot-level diversity pooled over time (temporal gamma diversity), diversity at discrete points in time (temporal alpha diversity), and seasonal turnover in assemblage composition (temporal beta diversity). Compared to reserves, fragments harbored bee assemblages with lower species richness and assemblage evenness both when summed across temporal samples (i.e., lower temporal gamma diversity) and at single points in time (i.e., lower temporal alpha diversity). Bee assemblages in fragments also exhibited reduced seasonal turnover (i.e., lower temporal beta diversity). While fragments and reserves did not differ in overall bee abundance, bee abundance in fragments peaked later in the season compared to that in reserves. Our results argue for an increased awareness of temporal diversity patterns, as information about the distinct components of temporal diversity is essential both for characterizing the assemblage dynamics of seasonal organisms and for identifying potential impacts of anthropogenic disturbance on ecosystem function through its effects on assemblage dynamics.

A new species of Triepeolus (Hymenoptera: Apidae), with comments on T. utahensis (Cockerell) and T. melanarius Rightmyer.

Triepeolus matildae Rightmyer, sp. nov., from Mexico (Baja California) and USA (California) is described and both genders are differentiated from the closely related species T. utahensis (Cockerell) using morphological characters. The synonymy of T. utahensis and T. heterurus was established in Rightmyer (2008); however, the younger name was used in that treatment, an error that is corrected herein. Males of both T. matildae and T. utahensis are additionally differentiated from T. melanarius Rightmyer, which is morphologically similar in that gender only. DNA barcoding evidence supporting the recognition of the new species is additionally presented.