Plant-pollinator interactions across California grassland and coastal scrub vegetation types on San Bruno Mountain, San Mateo County

Abstract

Animal pollination of plants is a crucial ecosystem service for maintaining biodiversity and ecosystem function, worldwide. High pollinator abundance and diversity can likewise improve the reproductive success of the plant community. Plant-pollinator interaction networks have the potential to identify dominant, specialist, and generalist pollinator species within a system, and their host plant counterparts. Understanding these relationships is paramount for buffering natural systems from biodiversity loss in a world where pollinator abundance continues to decline rapidly. San Bruno Mountain (SBM) in San Mateo County, California, is one of the last natural, open spaces in the urban landscape in the northern San Francisco Peninsula. I conducted a series of timed meanders and vegetation surveys at eight sample sites within SBM (four grassland and four coastal scrub sites) to identify plant species prevalence and pollinator species visitation of flowering plants. I employed a multivariate approach for investigating plant and pollinator species richness, plant and pollinator community composition, and trophic-level interactions across the SBM landscape, and I evaluated differences in these relationships between grassland and coastal scrub habitats. A total of 59 pollinator species and 135 plant species were inventoried over the course of the study. While species richness did not vary significantly between vegetation types, the nonmetric multidimensional scaling results revealed significant differences in species composition and key indicator species between vegetation types. The bipartite analyses identified Bombus vosnesenskii, Eriophyllum stachaedifolium, Grindelia hirsutula and others as generalist pollinator and plant species that are 4 important for the long-term biodiversity conservation of SBM due to their interactions with a diverse array of other plant and pollinator taxa. In the future, adaptive restoration activities could be used at SBM and other similar habitats to bolster the abundance of herbaceous flowering plants for pollinators to conserve biodiversity and promote ecosystem health in a world that continues to experience declines in pollinator abundance.