Alexandra N. Harmon-Threatt

A phylogenetically controlled analysis of the roles of reproductive traits in plant invasions

Reproductive traits are tightly linked to plant fitness and may therefore be mechanisms driving biological invasions, including the greater success of more phylogenetically novel introduced species in some systems. We present a phylogenetic comparative analysis of “Baker’s law’’, that introduced plants with the ability to reproduce autogamous or asexually may be better able to establish on introduction. We gathered data from both published and unpublished sources on pollen limitation of 141 species, including 26 introduced species and 115 native species. Our analysis compared differences in the proportion of autonomous autogamy, asexual reproduction, and pollen limitation among native, introduced noninvasive, and introduced invasive plant species, and included the phylogenetic novelty of the introduced species to the native species in that community. Introduced species were more likely to be autogamous than native species, consistent with Baker’s law. On the other hand, introduced species were less likely to have the ability to reproduce asexually. Further, among species with no autonomous autogamy, pollen limitation was greater for introduced compared to native species. Such a result is consistent with the idea that plants entering a new continent receive lower quality or quantity of services from resident pollinators than species native to that continent. Finally, more phylogenetically novel invasive species had lower pollen limitation than less novel invasive species, potentially because they experience less competition for pollinators. This is the first evidence that enhanced pollination may be one mechanism driving the greater invasiveness of phylogenetically novel introduced species observed in some systems.

Breeding system and pollination ecology of introduced plants compared to their native relatives

Identifying how plant-enemy interactions contribute to the success of introduced species has been a subject of much research, while the role of plant-pollinator interactions has received less attention. The ability to reproduce in new environments is essential for the successful establishment and spread of introduced species. Introduced plant species that are not capable of autonomous self-fertilization and are unable to attract resident pollinators may suffer from pollen limitation. Our study quantifies the degree of autogamy and pollination ecology of 10 closely related pairs of native and introduced plant species at a single site near St. Louis, Missouri, USA. Most of these species pairs had similar capacities for autogamy; however, of those that differed, the introduced species were more autogamous than their native congeners. Most introduced plants have pollinator visitation rates similar to those of their native congeners. Of the 20 species studied, only three had significant pollen limitation. We suggest that the success of most introduced plant species is because they are highly autogamous or because their pollinator visitation rates are similar to those of their native relatives. Understanding and identifying traits related to pollination success that are key in successful introductions may allow better understanding and prediction of biological invasions.

Filtering across Spatial Scales: Phylogeny, Biogeography and Community Structure in Bumble Bees

Despite the expansion of phylogenetic community analysis to understand community assembly, few studies have used these methods on mobile organisms and it has been suggested the local scales that are typically considered may be too small to represent the community as perceived by organisms with high mobility. Mobility is believed to allow species to mediate competitive interactions quickly and thus highly mobile species may appear randomly assembled in local communities. At larger scales, however, biogeographical processes could cause communities to be either phylogenetically clustered or even. Using phylogenetic community analysis we examined patterns of relatedness and trait similarity in communities of bumble bees (Bombus) across spatial scales comparing: local communities to regional pools, regional communities to continental pools and the continental community to a global species pool. Species composition and data on tongue lengths, a key foraging trait, were used to test patterns of relatedness and trait similarity across scales. Although expected to exhibit limiting similarity, local communities were clustered both phenotypically and phylogenetically. Larger spatial scales were also found to have more phylogenetic clustering but less trait clustering. While patterns of relatedness in mobile species have previously been suggested to exhibit less structure in local communities and to be less clustered than immobile species, we suggest that mobility may actually allow communities to have more similar species that can simply limit direct competition through mobility.

Bumble bees selectively use native and exotic species to maintain nutritional intake across highly variable and invaded local floral resource pools

1. Changes to plant community composition after invasion are well documented but how these shifts directly affect higher trophic levels is still poorly understood. One potentially important factor is the change in nutritional availability after an invasion. Shifts in nutrient availability could affect the nutrient intake of organisms that live in invaded habitats, causing reduced fecundity and survival.

General models for resource use or other compositional count data using the Dirichlet-multinomial distribution

Many ecological studies investigate how organisms use resources, such as habitats or foods, in relation to availability or other variables. Related statistical problems include analysis of proportions of species or genotypes in a community or population. These require statistical modeling of compositional count data: data on relative proportions of each category collected as counts. Common methods for analyzing compositional count data lack one or more important considerations. Some methods lack explicit accommodation of count data, dealing instead with proportions. Others do not handle between-sample heterogeneity for overdispersed data. Yet others do not allow general types of relationships between explanatory variables and resource use. All three components have been combined in a Bayesian framework, but for frequentist hypothesis tests and AIC model selection, maximum-likelihood estimation is needed. Here we propose the Dirichlet-multinomial distribution to accommodate overdispersed compositional count data. This approach can be used flexibly in combination with explanatory models, but the only correlations among compositional proportions that it can accommodate are the negative correlations due to the fact that proportions must sum to 1. Many existing models can be generalized to use the Dirichlet-multinomial distribution for residual variation, and the flexibility of the approach allows new hypotheses that have often not been considered in resource preference analysis, including that availability has no relation to use. We also highlight a new design for resource use studies, with multiple individual-use data sets from each of multiple sites, with different explanatory data for each site. We illustrate the approach with three examples. For two previously published habitat use data sets, we support the original conclusions and show that use is not unrelated to availability. For a data set of pollen collected by multiple bees from each of two sites, pollen use differs between the sites. Using bootstrap goodness-of-fit tests, we illustrate that the Dirichlet-multinomial is acceptable for two of the examples but unsuitable for one of the habitat use examples.

An Assessment of the Efficacy and Peak Catch Rates of Emergence Tents for Measuring Bee Nesting

Premise of the study: Emergence tents are a new tool used to understand nesting ecology of ground nesting bee species. However, many questions remain about how to use tents effectively. We assessed (a) variance in tent capture rates over time, (b) the effects of site characteristics on proportion of tents capturing bees, and (c) the effect of soil characteristics on nest site choice. Methods: Emergence tents were placed out for one week in May, June, and August and checked daily. Soil, bee, and floral characteristics were recorded. Results: Across all sites and months the average number of tents capturing bees was less than 20% during one week of sampling, but this varied between sites. Tent captures decreased after 48 h deployment, but accumulation differed seasonally, with slower accumulation of total bees caught in May than in June or August. Although capture rates were not affected by bee or floral abundance, soil moisture beneath a tent influenced where bees were captured. Discussion: Effective use of emergence tents may require adjusting the length of deployment depending on season and will require a minimum of 48 h installation to help maximize efficacy. The overall low capture rates demonstrate the need to optimize emergence tent use.

Common Methods for Tallgrass Prairie Restoration and Their Potential Effects on Bee Diversity

ABSTRACT: Habitat restoration is considered critical for maintaining and restoring biodiversity of many species groups. A better understanding of how species respond to the restoration process is imperative to identifying practices that benefit the target organisms. Using survey responses from land managers about the restoration process in tallgrass prairie habitat, we identify common restoration and management techniques. These responses are then combined with current literature on bee and plant responses to these methods in tallgrass prairie habitat. While some widely used methods, such as burning, are believed to be fairly benign to bees, there are still many knowledge gaps about how bees may respond to many common practices such as tillage, pesticides, and grazing in tallgrass prairie. Other commonly used methods, such as broadcasting of seeds, are known to significantly affect plant diversity, which could hinder bee conservation efforts. The variability in bee and plant response to commonly used methods highlights why it is necessary to better understand how management methods affect plant and bee communities.

New State Record for the Bee Species Macropis Steironematis (Robertson, 1891) (Hymenoptera, Melittidae)

The Melittidae are a relatively small family of ground-nesting, oil-collecting bees, with 14 genera and 200 described species worldwide (Michener, 2000; Michez and Patiny, 2005; Michez and Eardley, 2007). The genus Macropis Panzer, 1809 currently includes only 16 species (Michener, 1981). Macropis steironematis Robertson, 1891 is a Great Plains species and occurs in North America (Snelling and Stage, 1995), but only 39 specimen records exist from 3 counties in North America, 1 in Illinois and 2 in Kansas (GBIF.org 2017, B. Buckles pers.comm. with entomological collections in MO, KS, IA, MN, KY, MA, NE, AR, TN, GA, OK, and Washington, D.C.). Although Mitchell (1960) listed the distribution of M. steironematis as Iowa and Missouri, east to Virginia, North Carolina, and Georgia, there are no deposited specimens throughout most of this range. Additionally, efforts to relocate the species in sites where the type specimen was collected have not been fruitful (Marlin and La Berge 2001). On 19 June 2014, a female M. steironematis (Fig. 1) was collected in Missouri foraging on Rosa carolina L. (Rosaceae). The specimen was collected from Stony Point Prairie Conservation Area (37◦31.640′N, −94◦01.688′W), which is managed by the Missouri Department of Conservation using a technique called patchburn grazing. The site is burned in approximately equal patches each year in a rotational pattern and cattle are allowed to preferentially graze on the fresh plant growth in burned patches. Patch-burning could prevent loss of local disturbance-sensitive plant species and grazing may select for increased species richness (Knapp et al., 1999), however, many prairie flowers cannot tolerate grazing due to defoliation reducing growth and reproduction (Damhoureyeh and Hartnett 2002). The site this specimen was collected from (Fig. 2) had low floral richness (13 species) and diversity (Shannon diversity = 1.087) on the day sampled and none of the plant species on which it was previously collected were observed at the site. This species was previously recorded foraging on Apocynum cannabinum L. (Apocynaceae), Ceanothus americanus L. (Rhamnaceae), Lysimachia L. ( = Steironema) sp. (Primulaceae), Melilotus alba (L.) Lam. (Fabaceae), and Sericocarpus lineifolius (L.) Britton, Sterns & Poggenb. (Asteraceae) (Mitchell, 1960). This new record suggests that this rare species is able to persist in disturbed areas and has a more diverse diet than previously recorded. Collection of this individual indicates that M. steironematis is present in Missouri. This specimen is deposited at the Illinois Natural History Survey under catalog number 813861. Acknowledgments