Date of Award

Spring 5-1-2002

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Advisor

Peter E. Scott

Second Advisor

Steven L. Lima

Third Advisor

Marion T. Jackson

Abstract

Eastern deciduous forests have spectacular spring floral display and a diverse array of insect pollinators. From March to May, some 20-25 species of understory herbs flower in west-central Indiana. I focused on the earliest species to bloom, Erigenia bulbosa (Apiaceae), and the most abundant, Claytonia virginica (Portulacaceae), which flowers immediately after Erigenia. l characterized insect visitor assemblages in terms of species richness and relative abundance, and measured visitation rates. For Erigenia (Chapter 1), I asked whether early flowering was necessarily associated with pollinator scarcity. I examined six sites in 2000 and resampled three of these in 2001. Erigenia attracted 10 bee and 22 fly species and had an average visit rate of 3.3 insect visits per umbel per hour. Collections of most fly and bee species were significantly male-biased (by approximately 2: 1 ). Visitor species richness and visitation rates to Erigenia were high compared to studies on other very early spring wildflowers. The high species richness corroborates an early study of Erigenia's visitors (Charles Robertson, 1928), in which 63 species were recorded. Erigenia appears to be an exception to the rule that very early flowering plants have few visiting species and are rarely visited. Possible reasons include Erigenia's lack of competition during its first 2-3 weeks of flowering, its offerings of nectar as well as pollen, and its relatively high density. For Claytonia (Chapter 2), I examined the effects of.forest fragmentation on species richness, relative abundances of taxa, and visitation rates. Sites were classified IV by the percentage of forest cover in the surrounding l km 2, and placed into one of three categories: (I) low, (2) medium, or (3) high percent forest cover. In 2000 two sites were represented in each forest cover category, and in 200 l one site was represented in each category. Claytonia attracted an even more diverse set of bees (47 species) and flies (26 species) than Erigenia, and was bee-dominated. Bee species richness increased with percentage of forest cover in 2000, with high forest cover sites having more rare species. Fly species richness showed no consistent patterns between years. Relative abundances of bee taxonomic classes differed significantly among forest cover classes in 2000, but not in 2001; relative abundances of flies differed significantly among forest cover classes in both years. Visitation rates of bees and flies did not differ significantly among forest cover classes. Thus, for bees, the increase in species richness as forest cover increased was not associated with a change in visit rate. Several shared insect visitors were malebiased in Erigenia collections and female-biased in Claytonia collections, suggesting a possible indirect mutualism between the plant species.

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