The Effect of Plant Patch Size and Spatial Pattern on Biodiversity, Ecosystem Functions, and Grassland Community Structure by Shannon E. Seahra A Thesis presented to The University of Guelph In partial fulfilment of requirements for the degree of Doctor of Philosophy in Environmental Biology Guelph, Ontario, Canada © Shannon E. Seahra, September, 2015 ABSTRACT THE EFFECT OF PLANT PATCH SIZE AND SPATIAL PATTERN ON BIODIVERSITY, ECOSYSTEM FUNCTIONS, AND GRASSLAND COMMUNITY STRUCTURE Shannon E. Seahra Advisor: University of Guelph, 2015 Professor J. A. Newman The interactions between plants that determine competition and coexistence are strongly influenced by their fine-scale spatial pattern. These interactions also ultimately influence diversity, function, and structure in plant communities. In areas that have undergone extensive land-use or anthropogenic degradation, such as North American grasslands, there is a critical need to understand how spatial patterning of plant species can be manipulated to maximize diversity and restoration success. The research presented in this thesis employed a novel planting strategy using conspecific patch sizes at seeding to spatially manipulate inter- and intraspecific interactions among native grassland plant species. I found that seeded patch size had strong effects on diversity maintenance, biodiversity effects, productivity, and invasion, and that the typical uniformly mixed seeding approach in biodiversity ecosystem function studies and restoration applications may not maximize these responses. Smaller patch plots tend to have strong selection effects from dominant forb species, although this may change over time. Additionally, there were species-specific and plant functional group-specific responses to patch size that should be considered in restoration of low-diversity sites. The initial fine-scale plant pattern of had measurable effects on the spatial abundance of species, functional groups, and invasion. Finally, I found that initial patch size had strong effects on the abundance several insect families that are ecologically relevant. Furthermore, the abundance of arthropod herbivores, parasitoids, and predators were significantly influenced as well, with variable relationships to patch size. These findings help to further our understanding of how plant species spatial pattern affects biodiversity, ecosystem functioning, and community structure, as well as provide novel ideas for planting strategies in grassland restoration. Acknowledgments I will always have tremendous gratitude for my advisor, Jonathan Newman, for taking a chance on me, and inviting me into his lab to study biodiversity. His guidance, knowledge, and calm reassurance throughout the years were no doubt integral to my accomplishments. Thank you to my committee member Kathryn Yurkonis, who always went above and beyond to help in all aspects of my research, despite being in another country. Her advice and encouragement, whether in person, online, or last minute, was a valuable part of my progress throughout the years. Thanks to my parents who introduced me to science at a very young age (Billions and Billions!), and never stopped pushing me forward. Their immense support over the years, throughout all of my mistakes, will never be forgotten. Thanks to my sister, Nicole, for being a great friend, although to me you will always be little Coee. To my partner, Rick Thompson, thank you for putting up with me, for always making dinner when I was too occupied, for all the morning coffees, and for making me a better person. Thank you as well for helping with biomass drying, and for learning to appreciate insects (and Collembola) the way I do. Thanks to our Lagomorpha babies/monsters for distracting me at the best of times, and the worst of times. My life would be incomplete without Jezebel, Rocco, and Garth. Thank you to the Newman lab group, both past and present members, for their support and camaraderie. Dr. Kim Bolton was an esteemed supervisor both in the field and the lab, and hosted some of the best parties. Thanks to Aurora Patchett for being an important field member in nearly all projects, and for entertaining my insect interests, no matter how obsessive. Thanks to Dr. Heather Hager for sharing her expertise in multivariate stats. Thanks to Dr. Simone Harri, Dr. Emily Robinson, Dr. Gerry Ryan, and Kruti Shukla for welcoming me into the lab all those years ago. Thank you to Neil Rooney, my co-advisor, for his outgoing help and support since my undergraduate years. Without him, I would have not applied to graduate studies at SES. Thank you to my committee member Alex Smith, for providing guidance in my arthropod research, and helpful feedback during the grueling writing stage. Finally, thank you to my sweet Haze. I dedicate my thesis to him. iv List of Tables Table 2.1. Results from repeated measures ANOVA of seeded species patch size treatment effects on aboveground biomass (natural log transformed), proportion of invaders (arcsine square root transformed), overyielding ln(Di), biodiversity effects (selection and complementarity, square root transformed with sign preserved), and Simpson’s diversity. Linear contrasts between patch size treatments were based on the natural-log of the seeded patch edge to area ratio and excluded mixed seeding plots. Values are F-statistics and degrees of freedom, which were reduced for variables with two growing seasons of data. Table 2.2. Results from repeated measures ANOVA of patch size treatment effects on interspecific association, the natural-log of total conspecific patches and the natural-log of total interspecific edges. Mixed plot treatment was not included in the analyses. Linear contrasts were based on the natural-log of the resident patch edge to area. Values are F-statistics and degrees of freedom. Table 3.1. Species loadings from the RDA of relative spatial abundance of seeded species in relation to patch treatment and time for 2011-2012. Response variable (Resp.) coordinates correspond to axes in Fig 3.1 composition biplot. Table 3.2. Species loadings from the RDA of relative spatial abundance of seeded species in relation to patch treatment for 2011. Response variable (Resp.) coordinates correspond to axes in Fig 3.2 composition biplot. Table 3.3. Species loadings from the RDA of relative spatial abundance of seeded species in relation to patch treatment for 2012. Response variable (Resp.) coordinates correspond to axes in Fig 3.3 composition biplot. v Table 3.4. Standard least squares regression results from analysis of proportional change in number of conspecific clusters of seeded species and patch size, year, and patch × year. Table 3.5. Effect tests from repeated measures ANOVA for relative spatial abundance of plant functional groups and patch size treatment (m) (patch trt) across 2011-2012. Table 3.6. Standard least squares regression results from analysis of relative spatial abundance of functional groups and patch edge to area ratio (m/m2), year, and patch edge to area ratio × year. Table 3.7. Standard least squares regression results from analysis of invader species relative spatial abundance and number of clusters using terms: patch edge to area ratio (m/m2), year, and patch edge to area ratio × year. Table 4.1. Trophic group designations for arthropod taxon groups, based on published literature. Groupings were assigned based on the majority of described grassland species. Table 4.2. Species loadings from the RDA of arthropod family (or taxon group) abundance in relation to patch treatment, block, and year. Response variable (Resp.) coordinates correspond to axes in Fig 4.1 composition biplot. Table 4.3. Species loadings from the RDA of arthropod family (or taxon group) abundance in relation to patch treatment and block for year one (2011). Response variable (Resp.) coordinates correspond to axes in Fig 4.2 composition biplot. Table 4.4. Species loadings from the RDA of arthropod family (or taxon group) abundance in relation to patch treatment, block for year two (2012). Response variable (Resp.) coordinates correspond to axes in Fig 4.3 composition biplot. vi Appendix Table 1. Species list (n = 16) of grassland perennials selected for experiment, including authority, family, common name, seeds/g, plant functional and reproductive group, and distribution in Southern Ontario according to the Ontario Ministry of Natural Resources (Bradley, 2013). Seeds/g was calculated based on the mass of 100 seeds (n=10) for each species. All species are native to Southern Ontario except for S. arundinaceus. vii List of Figures Figure 2.1. Effect of initial patch edge to area ratio (m/m2) of seeded species on a) aboveground biomass (g) (untransformed mean ± SE) over three growing seasons, and b) the selection effect (square root transformed mean with sign preserved ± SE), in the second (2011) and third (2012) growing seasons. Means with the same letter are not significantly different (LSD, P < 0.05). Plots were divided into patches 1, 0.5, 0.25 and 0.125 m on an edge, which corresponds to an edge to area ratio of 4, 8, 16 and 32 m/m2 for the seeded patches. Mixed seed plots (represented by the × symbol) developed an average patch edge to area ratio of 28.2 m/m2. Figure 2.2. Effect of initial patch edge to area ratio (m/m2) of seeded species on a) Simpson’s diversity (mean ± SE) in the second (2011) and third (2012) growing seasons, and b) the proportion of non-seeded (invader) species (untransformed mean ± SE) over three growing seasons. Means with the same letter are not significantly different (LSD, P < 0.05). Plots were divided into patches 1, 0.5, 0.25 and 0.125 m on an edge, which corresponds to an edge to area ratio of 4, 8, 16 and 32 m/m2 for the seeded patches. Mixed seed plots (represented by the ×symbol) developed an average patch edge to area ratio of 28.2 m/m2. Figure 2.3a) Patch treatment (m) and interspecific association (mean ± SE) in 2010- 2012, see Methods for measurement and calculation of intersection association.