Rarity and reproductive biology: habitat specialists reveal a complex relationship

Abstract

Understanding how species with historically fragmented populations are able to persist will provide insights into which factors may be important for the maintenance of newly fragmented populations. Plants with fragmented and isolated populations, such as habitat-specialist (HS) species, are likely less attractive to pollinators and may have adaptive traits that compensate for these distributional challenges, such as larger flowers and more specialized pollination systems. If they do not have these adaptations, HS species are predicted to have lower reproductive success and be more pollen limited than widespread species. Here, I test three predictions concerning differences in reproductive traits that are known to affect attractiveness to pollinators, pollen receipt, and reproductive success, by comparing three HS species to congeneric species with broader habitat use (HT, habitat tolerators). Two of the three HS species lend partial support to the predictions that HS species have larger floral displays and more specialized pollination systems. The third HS species did not have either of these traits but did have lower relative seedset compared to its matched HT. These results provide preliminary support for a positive relationship between habitat specificity and pollination specialization, and for the role of low fecundity in contributing to range restriction of HS species.