Karen Goodell

The Role of Resources and Risks in Regulating Wild Bee Populations

Recent declines of bee species have led to great interest in preserving and promoting bee populations for agricultural and wild plant pollination. Many correlational studies have examined the indirect effects of factors such as landscape context and land management practices and found great variation in bee response. We focus here on the evidence for effects of direct factors (i.e., food resources, nesting resources, and incidental risks) regulating bee populations and then interpret varied responses to indirect factors through their species-specific and habitat-specific effects on direct factors. We find strong evidence for food resource availability regulating bee populations, but little clear evidence that other direct factors are commonly limiting. We recommend manipulative experiments to illuminate the effects of these different factors. We contend that much of the variation in impact from indirect factors, such as grazing, can be explained by the relationships between indirect factors and floral resource availability based on environmental circumstances.

Shading by invasive shrub reduces seed production and pollinator services in a native herb

Plant invasions disrupt native plant reproduction directly via competition for light and other resources and indirectly via competition for pollination. Furthermore, shading by an invasive plant may reduce pollinator visitation and therefore reproduction in native plants. Our study quantifies and identifies mechanisms of these direct and indirect effects of an invasive shrub on pollination and reproductive success of a native herb. We measured pollinator visitation rate, pollen deposition, and female reproductive success in potted arrays of native Geranium maculatum in deciduous forest plots invaded by the non-native shrub Lonicera maackii and in two removal treatments: removal of aboveground L. maackii biomass and removal of flowers. We compared fruit and seed production between open-pollinated and pollen-supplemented plants to test for pollen and light limitation of reproduction. Plots with L. maackii had significantly lower light, pollinator visitation rate, and conspecific pollen deposition to G. maculatum than biomass removal plots. Loniceramaackii flower removal did not increase pollinator visitation or pollen deposition compared to unmanipulated invaded plots, refuting the hypothesis of competition for pollinators. Thus, pollinator-mediated impacts of invasive plants are not limited to periods of co-flowering or pollinator sharing between potential competitors. Geranium maculatum plants produced significantly fewer seeds in plots containing L. maackii than in plant removal plots. Seed set was similar between pollen-supplemented and open-pollinated plants, but pollen-supplemented plants exhibited higher seed set in plant removal plots compared to invaded plots. Therefore, we conclude that the mechanism of impact of L. maackii on G. maculatum reproduction was increased understory shade.

Pollen limitation and local habitat-dependent pollinator interactions in the invasive shrub Lonicera maackii.

Many nonnative plants require pollinators to produce the seed needed to establish beyond their native range. Local variation in pollination can cause variation in mating patterns, reproductive output, genetic diversity, and selection, which can influence invasion dynamics. We quantified pollinator visitation, pollen deposition, and pollen limitation of reproduction in the invasive shrub Lonicera maackii in adjacent forest edge and forest interior habitats. Flowers in edge habitats received as many or more pollinator visits than those in interior habitats, resulting in twofold greater pollen deposition and nearly twice as many seeds produced per flower. Supplemental pollination increased seed production over open pollination by 37%–145% in both edge and interior habitats. Edge flowers produced more seed than interior flowers. Despite greater pollen deposition in edge habitats, the magnitude of pollen limitation was similar to interior plants. Thus, different mechanisms of pollen limitation characterize these habitats. Pollen receipt and other resources limited reproduction of interior plants, which were located in a shady environment. Pollen quality likely limited reproduction of edge plants, because pollinators visited more flowers per plant and likely delivered more geitonogamous pollen in this habitat than in the interior. Therefore, local variation in abiotic conditions influenced reproduction in this invasive plant, both directly and indirectly via pollinators.

Plant–pollinator interactions between an invasive and native plant vary between sites with different flowering phenology

Floral displays of invasive plants have positive and negative impacts on native plant pollination. Invasive plants may also decrease irradiance, which can lead to reduced pollination of native plants. The effects of shade and flowers of invasive plant species on native plant pollination will depend on overlap in flowering phenologies. We examined the effect of the invasive shrub Lonicera maackii on female reproductive success of the native herb Hydrophyllum macrophyllum at two sites: one with asynchronous flowering phenologies (slight overlap) and one with synchronous (complete overlap). At each site, we measured light availability, pollinator visitation, pollen deposition, and seed set of potted H. macrophyllum in the presence and absence of L. maackii. At both sites, understory light levels were lower in plots containing L. maackii. At the asynchronous site, H. macrophyllum received fewer pollinator visits in the presence of L. maackii, suggesting shade from L. maackii reduced visitation to H. macrophyllum. Despite reduced visitation, H. macrophyllum seed set did not differ between treatments. At the synchronous site, H. macrophyllum received more pollinator visits and produced more seeds per flower in the presence of co-flowering L. maackii compared to plots in which L. maackii was absent, and conspecific pollen deposition was positively associated with seed set. Our results support the hypothesis that co-flowering L. maackii shrubs facilitated pollination of H. macrophyllum, thereby mitigating the negative impacts of shade, leading to increased seed production. Phenological overlap appears to influence pollinator-mediated interactions between invasive and native plants and may alter the direction of impact of L. maackii on native plant pollination.

Documenting bee decline or squandering scarce resources.

V. J. Tepedino,∗ ¶ Susan Durham,† Sydney A. Cameron,‡ and Karen Goodell§ ∗Department of Biology, Utah State University, Logan, UT 84322-5305, U.S.A. †Ecology Center, Utah State University, Logan, UT 84322-5205, U.S.A. ‡Department of Entomology and Program in Ecology, Evolution and Conservation (PEEC), University of Illinois, Urbana, IL 61801, U.S.A. §Department of Evolution, Ecology and Organismal Biology, The Ohio State University, Newark, OH 43055, U.S.A.

Demographic consequences of greater clonal than sexual reproduction in Dicentra canadensis.

Abstract Clonality is a widespread life history trait in flowering plants that may be essential for population persistence, especially in environments where sexual reproduction is unpredictable. Frequent clonal reproduction, however, could hinder sexual reproduction by spatially aggregating ramets that compete with seedlings and reduce inter‐genet pollination. Nevertheless, the role of clonality in relation to variable sexual reproduction in population dynamics is often overlooked. We combined population matrix models and pollination experiments to compare the demographic contributions of clonal and sexual reproduction in three Dicentra canadensis populations, one in a well‐forested landscape and two in isolated forest remnants. We constructed stage‐based transition matrices from 3 years of census data to evaluate annual population growth rates, λ. We used loop analysis to evaluate the relative contribution of different reproductive pathways to λ. Despite strong temporal and spatial variation in seed set, populations generally showed stable growth rates. Although we detected some pollen limitation of seed set, manipulative pollination treatments did not affect population growth rates. Clonal reproduction contributed significantly more than sexual reproduction to population growth in the forest remnants. Only at the well‐forested site did sexual reproduction contribute as much as clonal reproduction to population growth. Flowering plants were more likely to transition to a smaller size class with reduced reproductive potential in the following year than similarly sized nonflowering plants, suggesting energy trade‐offs between sexual and clonal reproduction at the individual level. Seed production had negligible effects on growth and tuber production of individual plants. Our results demonstrate that clonal reproduction is vital for population persistence in a system where sexual reproduction is unpredictable. The bias toward clonality may be driven by low fitness returns for resource investment in sexual reproduction at the individual level. However, chronic failure in sexual reproduction may exacerbate the imbalance between sexual and clonal reproduction and eventually lead to irreversible loss of sex in the population.

Mating Patterns and Pollinator Communities of the Invasive Shrub Lonicera maackii: A Comparison between Interior Plants and Edge Plants

Premise of research. It is known that outcrossing rates and mating structure are important factors determining the genetic structure of populations. Moreover, the composition and abundance of pollinator communities visiting flowers determine the distances over which the pollen is likely to be dispersed, which in turn affects the genetic structure of plant populations. For invasive plants, high outcrossing rates produce genetically diverse propagules for the colonization of uninvaded areas and facilitate the establishment of novel gene combinations that may affect their invasive ability. Here, we examine how differences in pollinator communities visiting flowers of the invasive shrub Lonicera maackii (Caprifoliaceae), growing along the edge and in the interior of a woodlot, affect their outcrossing rates and mating structure. Methodology. Five microsatellite marker loci were used to determine the outcrossing rates, levels of biparental inbreeding, and effective number of pollen donors siring the seed crop of plants growing along the edge and in the interior of an invaded woodlot. Pivotal results. We found that L. maackii is a predominantly outcrossing plant. Despite dissimilarities in composition and abundance of pollinator communities, there were no differences in outcrossing rates and biparental inbreeding between plants along the edge of the woodlot and those in the interior. However, the seed crop of plants in the interior was sired by more pollen donors than that of plants along the edge. Our findings suggest that plants differ in their ability to sire seeds, as maternal allele frequencies are different from those that sired their seeds. Conclusions. Lonicera maackii plants showed high outcrossing rates regardless of their position in the woodlot. Differences in the number of donors siring the seed crop between plants in the interior of the woodlot and those along the edge are most likely due to disparities in the abundance and composition of the pollinator communities.

Using a Centrality Index to Determine the Contribution of Restored and Volunteer Plants in the Restoration of Plant-Pollinator Mutualisms on a Reclaimed Strip Mine

The restoration of ecosystem function relies, at least partly, on restoring services provided by mutualists. If the goal of restoration is to assemble functional and stable communities, particular care should be taken to identify and attract those species that contribute most to long-term community stability. Land managers and ecologists can use centrality indices, a group of network statistics that measure the relative importance of individuals within a community, to objectively determine the contribution of particular plant species to overall restoration efforts. Our objective was to compare the role of flowers planted as part of the restoration effort to those plants volunteering at the restoration site, either native adventives or non-native invaders, in support of the pollinator community. Further, we sought to determine how this relationship varied with changes in relative floral abundance. We found that plants cultivated as part of the restoration effort were preferred by pollinators, attracted the greatest abundance and richness of pollinators, and were the most central in our plant-pollinator networks compared to volunteers, despite the greater abundance of volunteer plants across the site. We also found that the role of all plants was density dependent; plants of every group attracted more pollinators in plots where they had greater relative abundance. We conclude that centrality indices provide a tool for planning and monitoring the restoration of important functional relationships and allow land managers and ecologists to objectively determine the contribution of particular plants to overall community structure and function.