Frequency-dependent fitness and reproductive dynamics contribute to habitat segregation in sympatric jewelflowers

Abstract

Coexistence results from a complex suite of past and contemporary processes including biogeographic history, adaptation, ecological interactions and reproductive dynamics. Here we explore drivers of local micro-parapatry in which two closely related and reproductively isolated Streptanthus species (jewelflower, Brassicaceae) inhabit continuous or adjacent habitat patches and occur within seed dispersal range, yet rarely overlap in fine-scale distribution. We find some evidence for abiotic niche partitioning and local adaptation, however differential survival across habitats cannot fully explain the scarcity of coexistence. Competition may also reduce the fitness of individuals migrating into occupied habitats, yet its effects are insufficient to drive competitive exclusion. Experimental migrants suffered reduced seed production and seed viability at sites occupied by heterospecifics, and we infer that heterospecific pollen transfer by shared pollinators contributes to wasted gametes when the two congeners come into contact. A minority disadvantage may reduce effective colonization of patches already occupied by heterospecifics, even when habitat patches are environmentally suitable. Differential adaptation and resource competition have often been evoked as primary drivers of habitat segregation in plants, yet negative reproductive interactions—including reproductive interference and decreased fecundity among low-frequency migrants—may also contribute to non-overlapping distributions of related species along local tension zones.

Joint effect of phylogenetic relatedness and trait selection on the elevational distribution of Rhododendron species

“…4B, a, b; Table S1), a result that seems contrary to the expectation that for species coexistence to occur, species differences should be maximized across biologically important niche dimensions (Lasky et al, 2014;Salazar et al, 2016). However, in addition to a suite of ecological factors, biotic interactions among sympatric species, including competition for reproductive resources, can influence their fine-scale distribution (Christie & Strauss, 2020). Coexisting congeneric plant species require reproductive isolation to minimize interspecific reproductive interference and maintain species integrity (Huang & Shi, 2013;Paudel et al, 2018).…”

Co‐occurrence patterns at four spatial scales implicate reproductive processes in shaping community assembly in clovers

“…Frameworks of coexistence have largely centred on resource competition (Adler et al, 2018;Chesson, 2000); yet, reproductive dynamics among co-occurring species are also intimately tied to fitness (Kishi & Nakazawa, 2013;Schreiber et al, 2019). A growing number of studies suggest that reproductive interactions might affect the ability of plants to co-occur (de Waal et al, 2015;Hersh et al, 2016;Katsuhara & Ushimaru, 2019;Muchhala et al, 2014;Whitton et al, 2017), especially in close relative with similar floral phenotypes and habitat preferences (Ashman & Arceo-Gómez, 2013;Carvalheiro et al, 2014;Christie & Strauss, 2020;Toll & Willis, 2018).…”

“…Our analyses were only based on the presence/absence of different Trifolium species, not on local abundances, which may profoundly affect localized pollen pools and the likelihood of heterospecific interactions. There is strong reason to believe that reproductive process, including reproductive interference might be frequency-or density-dependent (Briscoe Runquist & Stanton, 2013;Christie & Strauss, 2020;Levin, 1975). High conspecific abundance could dilute the possibility of reproductive interference, if for example, a large-flowered species vastly outnumbered another co-occurring congener.…”

How does the magnitude of genetic variation affect eco-evolutionary dynamics in character displacement?

“…reproductive exclusion: (Pfennig and Pfennig 2009)) by empirical (Kawatsu andKishi 2018, Christie andStrauss 2020) and theoretical (Kuno 1992, Yoshimura and Clark 1994, Kishi and Nakazawa 2013, Schreiber et al 2019 approaches. Reproductive character displacement produces a locally stable coexistence equilibrium with minority disadvantage (Fig.…”

“…In addition, we showed that the magnitude of genetic variance is more important in reproductive character displacement due to positive frequency-dependence (Figures 1-4). While previous studies on character displacement and species coexistence tended to focus on competitive exclusion, recent studies have revealed that reproductive interference is an important factor that promotes extinction of rare species via positive frequency-dependence (i.e., reproductive exclusion: (Pfennig and Pfennig 2009)) by empirical (Kawatsu and Kishi 2018, Christie and Strauss 2020) and theoretical (Kuno 1992, Yoshimura and Clark 1994, Kishi and Nakazawa 2013, Schreiber et al 2019) approaches. Reproductive character displacement produces a locally stable coexistence equilibrium with minority disadvantage (Fig.…”