Risa Sargent

Associate Professor

Research Classification

Research Interests

Biological control
community ecology
evolutionary ecology
Floral trait evolution
Flowering plants
Pollinator-mediated interactions

Relevant Thesis-Based Degree Programs


Graduate Student Supervision

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Effects of honey bees (Apis mellifera L.) on the structure of plant-pollinator networks (2024)

Global biodiversity is under threat from a variety of factors, including habitat loss, land use change, climate change, and invasive species. Pollinators are crucial for biodiversity maintenance and global food security and are experiencing declines. One pollinator, the Western honey bee (Apis mellifera L.; Hymenoptera: Apoidea) is nearly ubiquitous in human altered landscapes. Despite honey bees being geographically widespread, knowledge of their impacts on plant-pollinator communities is incomplete. My study represents the first macroanalysis of honey bee competition in plant-pollinator networks from around the globe. Using an open-access database, I summarized bipartite network statistics for 123 plant-pollinator networks to test whether the proportion of interactions with honey bees in a network is associated with changes in network topology. Specifically, I calculated the normalized degree of interactions with honeybees (NDHB), defined as the total number of interacts divided by the richness of plant species. I predicted higher NDHB would be associated with (1) increased connectance (the realized proportion of possible interactions), (2) decreased modularity (degree of compartmentalization of subcommunities), and (3) increased nestedness (the amount of redundancy of interactions between specialist and generalist) of networks. I quantified these associations for entire networks containing all pollinators, as well as for Hymenopteran sub-networks. I also investigated whether honey bee normalized degree was associated with increased plant generalization (i.e., the mean number of links per species), and decreased pollinator generalization within Hymenopteran sub-networks. Overall, I found that honey bees were widespread, present in 77% (95/123) of networks worldwide. Results revealed that higher honey bee normalized degree was associated with decreased modularity, as well as increased plant generalization and increased pollinator generalization. Contrary to expectations, honey bee introduction was not associated with changes to network connectance or nestedness. While the results are correlational, they suggest that this widely introduced species is capable of modifying the structure of plant-pollinator networks leading to the homogenization of interactions, which could impact the persistence and coexistence of native plants and pollinators.

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Floral strips support ecosystem services in pepper production (2024)

Agriculture intensification, characterized by increased pesticide use and ecological simplification, has raised concerns due to its adverse effects on non-target organisms and biodiversity. Biodiversity loss compromises essential ecosystem services, including pollination and biological pest control, which are crucial for agricultural productivity. To mitigate the consequences of agricultural intensification, there is a growing interest in adopting ecological intensification approaches that reduce reliance on synthetic chemicals and promote ecosystem services.This study investigated whether floral strips, a form of habitat enhancement within crops, supported biological pest control and pollination services in a replicated field pepper cropping experiment. The research took place across multiple sites on UBC’s Point Grey Campus in Vancouver, British Columbia, Canada. The results revealed that floral strips were associated with higher ground beetle activity density, lower foliar herbivory, and lower pepper damage, evidencing biological pest control was supported. The floral strips also successfully attracted more pollinators, but with no associated increases in pepper weight, width, or length detected, nor a difference in the total number of peppers per plant was observed. The findings highlight the role floral strips can play in positively impacting agricultural ecosystems by promoting beneficial insect activity, and thereby potentially supporting ecosystem services. Future studies should incorporate factors that impact pollination services to assess how to achieve the greatest performance for their distinct floral strip.

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Current Students & Alumni

This is a small sample of students and/or alumni that have been supervised by this researcher. It is not meant as a comprehensive list.

Membership Status

Member of G+PS
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Program Affiliations

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