The comparative autecology of endemic, globally-rare, and geographically-widespread, common plant species: Three case studies

The autecology (species biology) of each of three federal-endangered, narrowly-endemic plant species (Echinacea tennesseensis, Iliamna corei, Solidago shortii) was compared with that of a geographically-widespread congener (E. angustifolia, I. rivularis, S. altissima) via research and/or literature reviews. The Echinacea and Iliamna species are very close relatives, and the Solidago species are in the same subsection of the genus. Particular attention was given to the Echinacea species. No differences were found in ecological, morphological, physiological, cytological, genetic, or life history characteristics per se of E. tennesseensis and E. angustifolia that reasonably could account for differences in their geographical distribution. Thus, a scenario based on historical factors was used in conjunction with the autecology of E. tennesseensis to explain development and maintenance of endemism in this species. Likewise, no difference in species biology was identified in the two fire-dependent, fire-adapted Iliamna species, and thus endemism in I. corei also probably is related to both autecological and historical factors. In contrast to the species pairs in Echinacea and Iliamna, the widespread Solidago altissima has a greater potential to form a persistent seed bank and is a better competitor than the narrow endemic S. shortii. However, these autecological differences per se should be used with caution in any attempt to explain maintenance of narrow endemism in S. shortii. We conclude that both autecological and historical factors are needed to explain endemism in many plant species.