Pyrodiversity begets plant-pollinator community diversity.

Global Change Biology (2016), doi: 10.1111/gcb.13236 Pyrodiversity begets plant–pollinator community diversity L A U R E N C . P O N I S I O 1 , K A T E W I L K I N 1 , L E I T H E N K . M ’ G O N I G L E 1, 2 , K E L L Y K U L H A N E K 1 , L I N D S A Y C O O K 1 , R O B B I N T H O R P 3 , T E R R Y G R I S W O L D 4 and C L A I R E K R E M E N 1 Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA 94720, USA, Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA, 3 Department of Entomology and Nematology, University of California, Davis, Davis, CA 95616, USA, 4 Department of Biology, Utah State University, Logan, UT 84322, USA Abstract Fire has a major impact on the structure and function of many ecosystems globally. Pyrodiversity, the diversity of fires within a region (where diversity is based on fire characteristics such as extent, severity, and frequency), has been hypothesized to promote biodiversity, but changing climate and land management practices have eroded pyrodiversity. To assess whether changes in pyrodiversity will have impacts on ecological communities, we must first understand the mechanisms that might enable pyrodiversity to sustain biodiversity, and how such changes might interact with other disturbances such as drought. Focusing on plant–pollinator communities in mixed-coni- fer forest with frequent fire in Yosemite National Park, California, we examine how pyrodiversity, combined with drought intensity, influences those communities. We find that pyrodiversity is positively related to the richness of the pollinators, flowering plants, and plant–pollinator interactions. On average, a 5% increase in pyrodiversity led to the gain of approximately one pollinator and one flowering plant species and nearly two interactions. We also find that a diversity of fire characteristics contributes to the spatial heterogeneity (b-diversity) of plant and polli- nator communities. Lastly, we find evidence that fire diversity buffers pollinator communities against the effects of drought-induced floral resource scarcity. Fire diversity is thus important for the maintenance of flowering plant and pollinator diversity and predicted shifts in fire regimes to include less pyrodiversity compounded with increasing drought occurrence will negatively influence the richness of these communities in this and other forested ecosystems. In addition, lower heterogeneity of fire severity may act to reduce spatial turnover of plant– pollinator communities. The heterogeneity of community composition is a primary determinant of the total species diversity present in a landscape, and thus, lower pyrodiversity may negatively affect the richness of plant–pollinator communities across large spatial scales. Keywords: bees (Hymenoptera: Apoidea), community assembly, drought, environmental heterogeneity, fire regime, fire severity Received 8 October 2015 and accepted 12 January 2016 Introduction Understanding the mechanisms underlying the main- tenance of biodiversity in natural and human domi- nated systems is critical to conservation and restoration. One fundamental and widely supported theory of biodiversity in biogeography is the idea that diversity begets biodiversity (Hutchinson, 1959; MacArthur & MacArthur, 1961; Rosenzweig, 1995). The ‘causal’ diversity here might take the form of environmental heterogeneity which could promote coexistence by facilitating resource partitioning (MacArthur & MacArthur, 1961; MacArthur & Levins, Correspondence: Lauren C. Ponisio, tel. +1 559 618 1303, fax +1 510-643 5438, e-mail: lponisio@berkeley.edu © 2016 John Wiley & Sons Ltd 1964), or it might correspond to some aspects of bio- diversity promoting other components (Whittaker, 1972; Thompson, 2005) via interactions across trophic levels (Janz et al., 2006). Disturbance diversity is also thought to promote biodiversity because shifting envi- ronmental conditions discourage dominance (i.e., the intermediate disturbance hypothesis: Connell, 1978; Huston, 1979; Martin & Sapsis, 1992). All of these mechanisms can also interact to enhance or suppress their individual effects (e.g., Rosenzweig, 1995; Collins et al., 2007; Kane et al., 2015). Fire is a disturbance that has the potential to affect biodiversity patterns both directly and indirectly via interactions between biotic and environmental heterogeneity (Martin & Sapsis, 1992; Parr & Andersen, 2006; Collins et al., 2007; Davies et al., 2012; Maravalhas