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Population and community-level rarity have opposing effects on pollinator visitation and seed set

Citation

Brown, Kaitlyn; Gilbert, Benjamin (2020), Population and community-level rarity have opposing effects on pollinator visitation and seed set, Dryad, Dataset, https://doi.org/10.5061/dryad.8sf7m0cj7

Abstract

  1. When can small, isolated populations overcome the negative consequences of rarity? Despite considerable effort to understand threats to rare species, few studies consider how community context alters these threats. Plant-pollinator interactions offer the opportunity to test the effect of community context on rare species success, as plant-pollinator dynamics are thought to be influenced by neighboring plants, both through competition for pollinators (reducing success in small populations) and attraction of potential pollinators (increasing success in small populations). Here, we test these predictions by experimentally decoupling community-level rarity (relative abundance) from population-level rarity (population size) in experimental two-species fragments.
  2. We created experimental plant communities varying independently in population rarity (population size) and community rarity (relative abundance) of two annual plant species. We isolated plant roots to eliminate resource competition. We then compared the effects of population size vs. relative abundance on pollinator visitation rates and an estimate of seed production.
  3. Both species had greatest pollinator visitation in large populations, but the negative effects of population rarity on visitation were partially offset when the neighboring species was more abundant – community rarity offset the impacts of population rarity for the most common group of pollinators, solitary bees. These visitation trends impacted seed production for one species. When at low relative abundance, Polanisia dodecandra had higher seed set, matching increased visitation by solitary bees. Chamaecrista fasciculata showed no change in seed production with population- or community level rarity.
  4. Synthesis: Our results suggest that the surrounding community can offset the negative effects of low absolute abundance on fitness when neighboring species are more abundant, and may ultimately maintain diversity even in fragmented ecological communities.

Funding

Natural Sciences and Engineering Research Council of Canada, Award: Discovery Grant

Natural Sciences and Engineering Research Council of Canada, Award: CGS-M