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Understanding the multiple resource needs of leaf-cutter bees to inform pollinator conservation and the restoration of reclaimed mines

Ballas, John Peter, II
http://rave.ohiolink.edu/etdc/view?acc_num=osu1587416286314145

Abstract Details

2020, Master of Science, Ohio State University, Evolution, Ecology and Organismal Biology.
Loss of habitat is one of the drivers of bee declines worldwide. However, conservation and habitat recreation often solely focus on the establishment of forbs as a pollen and nectar source while disregarding other resources that bees need to gather from their landscapes. The family Megachilidae is a large and diverse assemblage of bee species, the majority of which require non-floral resources for nest building. Leaf-cutter bees (genus Megachile) are perhaps the most well-known bees within the family, using cut pieces of leaves to build their nests. Like all bees, Megachile are central place foragers, requiring all of their food plants, as well as suitable leaves for nest construction, within a limited foraging range of their nest. Each female builds her nest within a tunnel in wood or a hollow stem where she constructs a linear series of brood cells lined with cut discs of leaves that protect her offspring and pollen provisions from parasites and desiccation. Poor quality leaves incur fitness costs for the female bee, including longer processing time and excessive mandibular wear. These costs drive strong preferences for specific species of leaves. I investigated the leaf traits that influence preference in Megachile to better understand how variation in vegetation surrounding the nest might limit bee success through the availability of high-quality leaves. This study focuses on reclaimed coal surface mines in Eastern Ohio because they exhibit variation in vegetation at a landscape scale relevant to bee foraging. Reclaimed mines also present novel ecological conditions that can be used to establish habitat for bee conservation. First, I described the physical characteristics of leaves found on a reclaimed mine in order to determine traits associated with leaf choice. This study focused on a representative species of leaf-cutter bee, Megachile rotundata, because of its abundance at the study site and the availability of published data on the species of leaves it uses for nesting. The 59 surveyed species of leaves were divided into two groups: those which are used by M. rotundata at the study site or in the literature, and those that are not used. By measuring the toughness, trichome density, useable area, and other traits of each leaf, species used and not used by M. rotundata were compared via ordination. The physical characteristics of used and unused leaves differed, but no one trait completely distinguished the two groups. Other untested traits may contribute to preference. The interactions of traits are complex, but toughness is a large factor determining usability. By ordinating leaf species from their traits, differences were clearly visualized. This study also documented species of plants used by M. rotundata that have not yet been observed, including the petals of multiple forbs. In order to learn how the availability of leaves affects leaf-cutter bee nesting behavior, I tested how variation in landscapes and plant composition affected the leaf foraging durations of M. rotundata. Building on prior observations about M. rotundata’s preferences for specific leaves and higher rates of reproduction closer to forest edges, I tracked bee foraging duration at different distances from the forest to compare the time investment towards leaf collection in different landscapes. The prediction that bees nesting closer to forest would spend less time foraging for leaves was supported, likely a result of the forest offering a large and apparent source of suitable leaves. Bees nesting far from the forest would be required to search the complex matrix of their surrounding grassland to find suitable leaves, leading to long foraging trip durations. The study also provides rigorous documentation of foraging patterns mentioned anecdotally in earlier literature. These observations verify that bees consistently foraged for leaves by making a series of “short” trips, interspersed by occasional “long” trips. Regardless of site location, “short” trips varied little in duration. However, the “long” trips lasted more than 7 times longer on average and were more variable in duration for bees nesting further from the forest. The abundance of floral resources did not predict the duration of long foraging bouts, refuting previous hypotheses that long trips represented combined leaf and nectar foraging bouts. These results are consistent with the idea that bees are limited by leaf choices in large reclaimed grasslands and that the forest edge is a particularly valuable habitat for Megachile.
Karen Goodell, PhD (Advisor)
Rachelle Adams, PhD (Committee Member)
Frances Sivakoff, PhD (Committee Member)
Rebecca Swab, PhD (Committee Member)
64 p.
Biology; Conservation; Ecology; Entomology; Environmental Management
bee; leaf-cutter bee; Megachile; Megachile rotundata; Megachilidae; leaf; preference; choice; habitat; landscape; foraging; nesting; reclaimed mine; grassland; forest

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Citations

  • Ballas, II, J. P. (2020). Understanding the multiple resource needs of leaf-cutter bees to inform pollinator conservation and the restoration of reclaimed mines [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587416286314145

    APA Style (7th edition)

  • Ballas, II, John. Understanding the multiple resource needs of leaf-cutter bees to inform pollinator conservation and the restoration of reclaimed mines. 2020. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1587416286314145.

    MLA Style (8th edition)

  • Ballas, II, John. "Understanding the multiple resource needs of leaf-cutter bees to inform pollinator conservation and the restoration of reclaimed mines." Master's thesis, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587416286314145

    Chicago Manual of Style (17th edition)

osu1587416286314145
361
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