396 • AMERICAN JOURNAL OF BOTANY 103(3): 396–407, 2016; http://www.amjbot.org/ © 2016 Botanical Society of America AMERICAN JOURNAL OF BOTANY RESEARCH ARTICLE Te movement of pollinators between plants in multispecies plant communities can result in the transfer of pollen from heterospecif- ics as well as conspecifcs (e.g., Feinsinger et al., 1986; Montgomery and Rathcke, 2012; Fang and Huang, 2013). However, the likeli- hood of heterospecifc pollen (hereafer, HP) receipt varies widely among species. For instance, a review of published studies (Ashman and Arceo-Gómez, 2013) revealed variation among species in both the percentage of fowers that received any HP (2–100%), as well as in the average intensity of HP receipt (% HP in total stig- matic pollen load: 0.1–80%). Furthermore, Fang and Huang (2013) uncovered variation among species within a single community not only in HP load size, but also in the number and identity of HP donors. Some species received large multispecies loads, while oth- ers received small monospecifc loads of HP (Fang and Huang, 2013). Variation in HP receipt among individuals within a single species can also be extensive (e.g., 1–95% of total load in Mimulus 1 Manuscript received 6 April 2015; revision accepted 9 July 2015. 2 4249 Fifh Ave, Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA; 3 Department of Tropical Ecology, Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán, Km. 15.5 Carretera Mérida-Xtmakuil, Mérida, Yucatán, México 97000; and 4 Estación Biológica de Doñana, Consejo Superior de Investigaciones Científcas (EBD- CSIC). Avda. Américo Vespucio s/n, E-41092, Sevilla, Spain 5 Author for correspondence (e-mail: tia1@pitt.edu) doi:10.3732/ajb.1500155 INVITED PAPER For the Special Issue: Ecology and Evolution of Pollen Performance Patterns of among- and within-species variation in heterospecifc pollen receipt: The importance of ecological generalization 1 Gerardo Arceo-Gómez 2 , Luis Abdala-Roberts 3 , Anneka Jankowiak 2 , Clare Kohler 2 , George A. Meindl 2 , Carmen M. Navarro-Fernández 4 , Víctor Parra-Tabla 3 , Tia-Lynn Ashman 2,5 , and Conchita Alonso 4 PREMISE OF THE STUDY: Cofowering plants are at risk for receiving pollen from heterospecifcs as well as conspecifcs, yet evidence shows wide variation in the degree that heterospecifc pollen transfer occurs. Evaluation of patterns and correlates of among- and within-species variation in heterospecifc pollen (HP) receipt is key to understanding its importance for foral evolution and species coexistence; however, the rarity of deeply sampled multispecies comparisons has precluded such an evaluation. METHODS: We evaluated patterns of among- and within-species variation in HP load size and diversity in 19 species across three distinct plant communi- ties. We assessed the importance of phenotypic specialization (foral phenotype), ecological specialization (contemporary visitor assemblage), and con- specifc fower density as determinants of among-species variation. We present hypotheses for diferent accrual patterns of HP within species based on the evenness and quality of foral visitors and evaluated these by characterizing the relationship between conspecifc pollen (CP) and HP receipt. KEY RESULTS: We found that within-species variation in HP receipt was greater than among-species and among-communities variation. Among species, ecological generalization emerged as the strongest driver of variation in HP receipt irrespective of phenotypic specialization. Within-species variation in HP load size and diversity was predicted most often from two CP-HP relationships (linear or exponentially decreasing), suggesting that two distinct types of plant–pollinator interactions prevail. CONCLUSIONS: Our results give important insights into the potential drivers of among- and within-species variation in HP receipt. They also highlight the value of explorations of patterns at the intraspecifc level, which can ultimately shed light on plant-pollinator-mediated selection in diverse plant communities. KEY WORDS co-fowering community; diversity; ecological generalization; foral specialization; heterospecifc pollen; foral visitor assemblage; pollinator sharing