Abstract
Pollinators are introduced to agroecosystems to provide pollination services. Introductions of managed pollinators often promote ecosystem services, but it remains largely unknown whether they also affect evolutionary mutualisms between wild pollinators and plants.Here, we developed a model to assess effects of managed honey bees on mutualisms between plants and wild pollinators. Our model tracked how interactions among wild pollinators and honey bees affected pollinator and plant populations.We show that when managed honey bees have a competitive advantage over wild pollinators, or a greater carrying capacity, the honey bees displace the wild pollinator. This leads to reduced plant density because plants benefit less by visits from honey bees than wild pollinators that coevolved with the plants.As wild pollinators are displaced, plants evolve by increasing investment in traits that are attractive for honey bees but not wild pollinators. This evolutionary switch promotes wild pollinator displacement. However, higher mutualism investment costs by the plant to the honey bee can promote pollinator coexistence.Our results show plant evolution can promote displacement of wild pollinators by managed honey bees, while limited plant evolution may lead to pollinator coexistence. More broadly, effects of honey bees on wild pollinators in agroecosystems, and effects on ecosystem services, may depend on the capacity of plant populations to evolve.
Highlights
Pollinators provide billions of dollars in global pollination services annually (Goulson, Nicholls, Botias, & Rotheray, 2015; Losey & Vaughan, 2006) and promote plant biodiversity (Burkle, Marlin,& Knight, 2013)
Our results show plant evolution can promote displacement of wild pollinators by managed honey bees, while limited plant evolution may lead to pollinator coexistence
Negative effects of honey bees on wild pollinators may stem from aggressive interactions at floral resources (Cairns, Villanueva-Gutierrez, Koptur, & Bray, 2005; Geslin et al, 2017), resource competition (Geldmann & Gonzalez-Varo, 2018; SteffanDewenter & Tscharntke, 2000; Torne-Noguera, Rodrigo, Osorio, & Bosch, 2016), and through displacement of wild species to low-reward nutrients (Magrach et al, 2017; Schaffer et al, 1983; Thorp, 1996)
Summary
Pollinators provide billions of dollars in global pollination services annually (Goulson, Nicholls, Botias, & Rotheray, 2015; Losey & Vaughan, 2006) and promote plant biodiversity In selection experiments, Sahli and Conner (2011) observed that variation in pollinator exposure can drive variations in rapid evolution, with honey bees stimulating greater anther exsertion than smaller wild bees, and reduced stamen dimorphism relative to bumblebees Together, these studies suggest that managed honey bees may induce evolutionary changes in plants that impact wild pollinators. When the evolutionary benefit to one species comes at a cost to a mutualist partner (e.g., pollinators evolving a better ability to deplete a flower of its resources), evolution may be expected to alleviate that cost by reducing the environmental effects on the mutualist partner's abundance (Northfield & Ives, 2013) While these studies focused on pair-wise evolution between mutualistic partners, theoretical research on complex pollination networks suggests that indirect interactions can play an important role in altering the evolution of species embedded within a network (Guimaraes, Pires, Jordano, Bascompte, & Thompson, 2017). We present each mechanism separately, along with resulting evolutionary changes, so hypotheses can be tested for each and scenarios identified which allow for the coexistence of managed honey bees and wild pollinators
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