Where a male is hard to find: Consequences of male rarity in the surfgrass Phyllospadix torreyi

Abstract

Determining whether seed production is limited by pollen availability has been an area of intensive study. Past studies have focused largely on terrestrial species with biotic pollination modes, but precise causes and consequences of pollen limitation remain unknown. Here, sex ratio, seed production, seed recruitment, and viability were examined in intertidal populations of a dioecious, abiotically pollinated marine angiosperm, Phyllospadix torreyi (Torrey's surfgrass). Using field surveys and a common garden experiment, this study was conducted near Santa Barbara, California, USA, from 2007 to 2008. Reproduction and recruitment of P. torreyi primarily occur near the parental source (tens of meters) because female reproductive success ratio (RSR, measured as the ratio of fertilized ovules to total ovules) increased with local pollen production (RSR range: 0.02-0.71), and seed recruitment was predicted by local (site) seed production and elevation zone within the intertidal. Low RSR at sites with extreme male rarity (<0.3 male flowering shoots m ?2) suggests that pollen limitation is occurring within this system. Seed recruitment was predicted by local (site) seed production and elevation zone (area of potential seed recruitment within the intertidal). The occurrence of seed production and recruitment at sites with extreme male rarity suggests some dispersal of seeds and pollen extending beyond the immediate vicinity of the site. Pollen or seed dispersal over longer distances, although rare, may reduce habitat fragmentation by facilitating colonization of newly available habitat. Localized pollen availability affected seed quantity but not quality; seed germination and growth were uniform among sites. © 2012 Inter-Research.