Habitat fragmentation threatens biodiversity by isolating populations and disrupting species interactions. To mitigate these negative effects, corridors - strips of habitat used to reconnect fragments - are commonly employed in conservation. Our understanding of fragmentation and corridors remains incomplete - particularly how fragmentation affects plant populations through altered plant-animal interactions and across different demographic stages. We evaluated whether fragmentation and corridors affect plant-herbivore and granivore interactions for a native asterid forb, Carphephorus bellidifolius, within a large-scale fragmentation experiment at the Savannah River Site, SC, where experimentally-fragmented landscapes contain patches connected by a corridor or isolated from each other. Previous work on mature C. bellidifolius individuals showed herbivory to occur more when closer to an edge, an effect strengthened by connectivity. Here we explore how fragmentation and herbivory impact seeds and seedlings – life stages potentially more susceptible to herbivory. We first studied how herbivory and growth of established seedlings were affected by patch connectivity, patch shape, and distance to edge – all impacts of habitat loss and fragmentation. We subsequently conducted a seed addition experiment to study how these same fragmentation effects as well as herbivory and granivory impacted seeds and germinants by sowing seeds into exclosures and pseudo-exclosures and surveying for germination and survival over the first growing season.
Despite the herbivory patterns present in mature individuals, we did not find a significant effect of connectivity, patch shape, or distance to habitat edge on herbivory or growth in our first study of established seedlings. In our second study, total germination was affected by distance to edge for seeds and first year seedlings. On average, plots near patch edges supported 142% more seedlings than plots near patch centers. We found no effect of connectivity or patch shape on germination or survival of seeds and first year seedlings. Our results demonstrate that corridors do not negatively impact C. bellidifolius through seedling-stage herbivory, but distance to an edge plays a significant role in seed germination. Coupled with past work, our findings reveal ontogenetic effects of herbivory and fragmentation, with impacts higher on early and late life stages, and less important on mid-developmental stages. This work adds to a growing understanding of how fragmentation and corridors can impact populations of plants, including through altered interactions with animals.