Endemic species are critical to conservation planning and are of interest to the general public. Comparing ecological attributes of endemic species with related, widespread species can help determine causes of rarity. Evidence suggests that seed-related life history stages are often correlated with plant rarity, but few studies have tested whether the process of seed dispersal differs for rare and common species. Trillium, a genus of ant-dispersed herbs, is of interest to researchers, horticulturalists, and gardeners alike due to its status as a guild of well-known spring ephemerals. In the southern Appalachian region, several trillium species are range-restricted endemics, and many of these co-occur with widespread congeners. To investigate whether aspects of seed dispersal differ for rare and common Trillium species, we compared seed dispersal effectiveness (SDE) through assessments of dispersal rates, distances and networks, disperser preference, and seed chemistry for three co-occurring widespread-endemic species pairs in the field and laboratory.
Results/Conclusions
Results yielded some significant within-pair differences consistent with lower SDE for endemic species. Field observations showed that widespread trilliums had significantly higher numbers of seeds dispersed by ants and are characterized by more robust and diverse disperser networks than endemic congeners, although dispersal distances did not differ for endemic and widespread species pairs. In laboratory experiments, Aphaenogaster picea workers dispersed significantly more widespread seeds into nests after 24 hours, illustrating a preference for seeds of widespread species. Many of these results are consistent with the hypothesis that endemic Trillium experience lower SDE compared to widespread congeners. This study marks a novel contribution to our understanding of seed-dispersal mutualisms between ants and forest herbs and sheds light on biotic factors that are associated with plant endemism.