Scale-dependent bee (Hymenoptera: Anthophila) community patterns and plant attractiveness to pollinators in the Texas High Plains

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2021-05

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Abstract

Bees (Hymenoptera: Apoidea: Anthophila) are the most important pollinators; they pollinate 80% of all flowering plants worldwide, thus helping to maintain native plant communities while contributing to pollination services in agriculture. Loss of natural habitat, pesticide over-use, invasive species, diseases, and climate change have caused managed and wild bee populations to decline worldwide. The loss of natural land cover threatens pollinator populations, especially in agricultural regions where landscape change is geographically broad. In the US High Plains in western Texas, little is known about the influence of agricultural production on pollinator communities. Moreover, growing scientific evidence has shown the importance of enhancing the pollinator habitat and floral resources in agroecosystems, particularly wildflower plantings, to support pollinators and other wildlife. However, empirical information is needed to better understand habitat associations at the local and landscape levels. The main objectives of my research were to 1) document the attractiveness of native and exotic drought-tolerant plants to foraging insect pollinators (Chapter 2); 2) determine the variation in and relationships of local and landscape habitat and land cover factors with bee communities (Chapters 3 and 4); and 3) develop a checklist and report new records of the Apoidea in farmlands in the High Plains region (Chapter 5). The attractiveness of 30 drought-tolerant plants to insect floral visitors located in 60 plant/patches was determined at an experimental plot and in restored habitats at Quaker Avenue Research Farm (Plant and Soil Science, Texas Tech University). A total of 46 insect morphospecies were observed from the experimental plots. Bees dominated the total number of pollinators; honey bees (Apis mellifera) were the most frequently observed insect and accounted for 31.1% of all observations. Russian sage (Salvia yangii) and Catmint (Nepeta x faassenii, ‘Walker's Low’) attracted the most insect visitors. Native plants attracted the highest diversity of insect species, with Indian blanket (Gaillardia pulchella) attracting 12 bees, three butterflies, and two fly species across sampling dates. The relationships of local habitat structures and native bee communities in ruderal farm habitats, pivot corners, playa edges, and fallow fields adjacent to cultivated crop fields were investigated. Bee communities and habitats were sampled across several farm types: organic and conventional cotton farms, vegetable and fruit farms, Conservation Reserve Program (CRP) lands, and vineyards. Selected habitat patches on farms were sampled during four seasons from 2016 to 2017. Pollinator communities were collected using pan traps and by hand netting across 43 habitat patches and 21 farms (i.e., homogenous habitat patches of various sizes). At each habitat patch, local floral resources (open flower heads) and the composition of vegetation along two 60m x 2m belt transects were quantified. Land cover/land use was determined for 200, 500, and 1000 m buffers surrounding each sampled habitat patch. Multivariate and mixed-effect models were used to assess the relationships of habitat, landscape variables, and wild bee and floral abundances and species richness. Across farms and sampling dates, over 17,000 bees belonging to 106 species/morphospecies and 49 genera were identified, along with 95 wildflower species/morphospecies belonging to 49 genera. Non-metric multidimensional scaling results showed high similarities in the bee communities across land use and farm types. Mixed model results showed that sites adjacent to CRP had higher bee richness and abundance by sampling seasons or when combining the data by year. The percentage of forbs was a significant factor in predicting floral and bee abundance, richness, and diversity across sampling seasons. Across sites, bee richness increased in relation to the proportion of natural land-use type, while bee diversity was reduced by the proportion of highly developed urban areas. Using data from recent collections and the current study, a checklist of the Apoidea across a 14-county region of the Texas High Plains was developed and produced a total of 286 species and 603 new county records. Information from these studies advances what is known about regional bee biodiversity and environmental drivers of communities in the region, which should inform strategies for conservation and enhancing habitat for pollinators in this important grassland and agricultural region.

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Keywords

Pollinators, Land Cover, Plant Attractiveness, Native Bees, Conservation Reserve Program, Llano Estacado, Texas High Plains

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