Document Type

Thesis - Open Access

Award Date

2019

Degree Name

Master of Science (MS)

Department

Biology and Microbiology

First Advisor

Charles Fenster

Keywords

Biodiversity, Ecosystem Services, Farming Practices, Landscape Heterogeneity, Pollination, Yield

Abstract

Prairies, once spanning the Upper Midwest, have now largely been replaced by agriculture. The lack of resources available to pollinators in agricultural fields and the practices employed by farmers to maximize yield has led to a decline in insect and pollinator diversity. There is a need to better understand how ecosystem services provided by a diverse insect community scale to current farming practices as they relate to crop yield. We sought to explain how landscape heterogeneity relates to insect and pollinator diversity, as well as how insect diversity relates to crop yield across common farming practices. To evaluate how farming practices relate to yield and insect diversity, we planted 35 single acre sites of Brassica carinata, a generalist flower that might be capable of supporting a diverse insect community. We randomly assigned each site with a combination of three treatments: tilling (yes/no), added honey bee hives (yes/no), and treatment with systemic neonicotinoids (yes/no). The Shannon Index of insect diversity sampled within the site, and the surrounding landscape at multiple spatial scales were calculated. We observed a significant positive relationship between insect (and pollinator) diversity with yield in the absence of any farming practice (p=0.002 and p < 0.0001, respectively). All farming practices will increase yield. However, farming practices alter the relationship between yield and diversity. The addition of seed treatment or tillage negates the relationship between insect (and pollinator) diversity with yield. Seed treatment alone results in a flat relationship between diversity and yield for all insects and a negative relationship for pollinators. Increased landscape heterogeneity results in a positive relationship between insect diversity at the 1000m scale (p=0.019) and pollinator diversity at the 3000m scale (p < 0.001), suggesting large-scale heterogeneity contributes to overall insect diversity. Lastly, there is a positive relationship between B. carinata yield and landscape diversity at the 3000m scale (p < 0.0001). Our results show that increasing large-scale landscape heterogeneity is a good way to increase diversity and that diversity can serve as a substitute for common farming practices such as application of pesticides, tilling, or added honey bee hives. Increased heterogeneity could save farmers from the input cost of treatment or tillage, by way of increased insect diversity, while still providing similar yields.

Format

application/pdf

Publisher

South Dakota State University

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