Abstract
Plant-pollinator relationships are a key part of natural ecosystems. Without pollination, plants have reduced persistence. The importance of these relationships has resulted in concern for the diversity and persistence of bee populations in natural and anthropogenic ecosystems. One ecosystem where bee diversity and persistence are of concern is the Palouse Prairie. The Palouse Prairie is a native grassland located in the Pacific Northwest consisting primarily of native bunchgrasses, early blooming forbs, and small shrubs and trees. As with many grasslands, the Palouse Prairie has experienced extreme fragmentation and habitat loss, with most of the historic prairie converted into agriculture. Due to this fragmentation, there is concern for the Palouse Prairie’s considerable bee diversity. To investigate plant-pollinator relationships and patterns of diversity, seven sites of largely intact remnant Palouse Prairie were selected for sampling. Sampling commenced in early spring and extended until late summer. Bees were collected directly from inflorescences for one hour per plant species at each site and identified to the lowest taxonomic level possible. Differences in temporal diversity between 2022 and 2023, spatial diversity among plots, and phenological diversity within a sampling season were examined using species richness, community composition, and network structure. Differences in species richness and network structure were tested using linear models. Community composition was tested using non-metric multidimensional scaling (NMDS) ordination and a permutation-based ANOVA (PERMANOVA). Between sampling years, species richness and community composition showed differences, but not network structure. Among sites, species richness varied, but not community composition. The network structure varied in unweighted indexes, but not weighted indexes, indicating that there were differences in networks qualities among sites, but not in their ultimate structure. Within the growing season, there were differences in species richness, community composition, and the average number of links members of the network had, indicating changes in diversity depending on the time of year. These results indicate that there is variation within spatial and temporal scales within the Palouse Prairie, and suggests that protecting as many fragments as feasible may be needed to preserve this ecosystem’s bee diversity.
To investigate how the plant-pollinator relationships within the prairie function, a network of plant-insect interactions was created. This network underwent a module analysis to identify which plants and insects interacted most frequently and were therefore most dependent on each other. Analysis of these modules indicated that the groups of most frequently interacting bees and plants were grouped by a combination of specialization, morphological, phenological, and taxonomic drivers. Further analysis identified several key organisms that impact network structure and frequently interact either within their own module, between modules, or both. These modules allowed the identification of key factors that impact plant-pollinator relationships within the Palouse Prairie and suggest methods to approach effective restoration and conservation within the prairie.