Ecological sorting and character displacement contribute to the structure of communities ofClarkiaspecies

Abstract

Despite long-standing interest in the evolutionary ecology of plants that share pollinators, few studies have explored how these interactions may affect communities during both community assembly (ecological sorting) and through ongoing, in situ evolution (character displacement), and how the effects of these interactions may change with community context. To determine if communities display patterns consistent with ecological sorting, we assessed the frequency of co-occurrence of four species of Clarkia in the southern Sierra foothills (Kern County, CA, USA). To investigate potential character displacement, we measured pollination-related traits on plants grown in a greenhouse common garden from seed collected in communities with one, two or four Clarkia species. Among the four species of Clarkia in this region, the two species that are often found in multi-species communities also co-occur with one another more frequently than expected under a null model. This pattern is consistent with ecological sorting, although further investigation is needed to determine the role of pollinators in shaping community assembly. Patterns of trait variation in a common garden suggest that these two species have diverged in floral traits and converged in flowering time where they co-occur, which is consistent with character displacement. Trait variation across community types also suggests that the process and outcome of character displacement may vary with community context. Because community context appears to affect both the direction and magnitude of character displacement, change in more species-rich communities may not be predictable from patterns of change in simpler communities.

Emission rates of species-specific volatiles change across communities ofClarkiaspecies: Evidence for character displacement in floral scent

“…These species, C. unguiculata and C. 94 cylindrica, co-occur more frequently than expected by chance in the southern foothills of the 95 Sierra Nevada (Kern County, CA, USA). Where they co-occur, these species have converged in 96 flowering time and diverged in flower size (Eisen and Geber 2018). This pattern of divergence in 97 flower size provides an opportunity to test if character displacement occurs on multimodal floral 98 signals.…”

Molecular Assays of Pollen Use Consistently Reflect Pollinator Visitation Patterns in a System of Flowering Plants

“…Though these Clarkia have distinct adult phenotypes, their pollen grains are morphologically indistinguishable. The Clarkia also co-occur with each other more often than they occur alone in plant communities in their range of sympatry, and assemblages can contain one to four species of Clarkia (Eisen and Geber 2018). Finally, Clarkia bloom much later in the growing season than the vast majority of co-occurring flowering annual plants, and as such are often the only flowering plants where they occur.…”

Character displacement drives floral variation inPelargonium(Geraniaceae) communities

“…; Calsbeek and Cox ; Kooyers et al. ; Eisen and Geber ). Phenotypic divergence can also evolve to reduce reproductive interference and is then termed reproductive character displacement (RCD; Levin ; Kawano ; Kirschel et al.…”

“…Antagonistic interactions have long been thought of as important drivers of organismal diversification (Darwin 1859;Brown and Wilson 1956;Levin 1970;Grant 1972;Schluter 2000a;Pfennig and Pfennig 2012). In particular, ecological character displacement (ECD) can occur when phenotypic divergence evolves to reduce competition for resources (Slatkin 1980;Dayan et al 1989;Grant 1994;Adams and Rohlf 2000;Losos 2000;Marchinko et al 2004;Calsbeek and Cox 2010;Kooyers et al 2017;Eisen and Geber 2018). Phenotypic divergence can also evolve to reduce reproductive interference and is then termed reproductive character displacement (RCD; Levin 1985;Kawano 2002;Kirschel et al 2009;Hopkins 2013;Stanger-Hall and Loyd 2015).…”

“…2 of Stuart and Losos 2013). There is a particular dearth in character displacement studies on plants, with only 11 plant studies displaying some evidence for character displacement mediated through pollinators (see table 1 of Eisen and Geber 2018).…”