Date of Award

January 2020

Degree Type

Open Access Thesis

Document Type

Master Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

David R. Brown

Department Affiliation

Biological Sciences

Abstract

Tropical forests are among the biologically richest ecosystems on Earth, but how most organisms in these forests will respond to a warming climate remains uncertain. Insects are expected to be highly responsive to climate change due to their short life cycles that are strongly influenced by temperature. Plants depend on pollinators to set seed and reproduce, and many animal populations rely on the resources provided by flowering plants. There is an urgent need to document elevational distributions and thermal specialization for tropical bee species to understand how these important pollinators may respond to warming temperatures. My four-year study (2016-2019) aims to quantify bee abundance differences across an elevational gradient. I focus on the two bee tribes comprising the most abundant species collected, Tribes Meliponini and Ceratinini. Bee species of these two tribes are also important pollinators of tropical forest plant species. Three adjacent roadsides, separated by 1 km each, were used as replicate elevational gradients. Each elevational gradient spans 750-1150 m elevation and are located in the seasonally dry Pacific slope forests of Costa Rica. The study area represents a mixture of smallholder farms, pasture, and forest patches, and is located in a conservation area. Bees were sampled at each 100 m elevation change using both active and passive collection methods in an effort to effectively survey the bee community. My results suggest that many species in these tribes exhibit elevational range specialization, and a canonical correspondence analysis indicates that elevation and site explain ~42% of the variation in the community composition of Meliponini and Ceratinini (Fpseudo(3,8) = 1.91, p = 0.002). Mountain-dwelling species are expected to exhibit shifts to higher elevations and cooler temperatures over time due to global temperature increases. My study is one of the first to provide evidence of elevational specialization in several bee species. These findings indicate that bee species of tropical montane landscapes could be at high-risk due to warming temperatures or changing patterns of precipitation, as species with narrow elevational ranges or specialization within a narrow portion of their elevational range are predicted to be more vulnerable to range shifts.Beyond my assessment of elevation specialization in Neotropical bee species, I conducted an additional study to identify the important pollinators of Persea americana and Cucurbita pepo within their native ranges. Observations were conducted during December of 2018 and 2019 for P. americana, and during the wet and dry seasons of 2019 for C. pepo, and resulted in the collection of 145 pollinators visiting P. americana and 223 pollinators visiting C. pepo. My results suggest that species belonging to the tribe Meliponini are important pollinators for my focal crop species, as they represent approximately 75% of the pollinators visiting both P. americana and C. pepo; however, species accumulation curves indicate the need for additional sampling in order to accurately determine the entire pollinator assemblage visiting each focal crop species. Community similarity analyses also indicate that elevation may be an important factor in determining the pollinator assemblages of each focal crop species, as a low degree of similarity was detected among communities present at each sampled elevation category. My results support the importance of natural area management, sustainable farming, and conservation of plant- pollinator mutualisms in order to sustain wild bee species abundance and diversity.

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