PARENT SESSION
Poster Session 31: Rare, Threatened, and Endangered Species
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Are North American pteridophytes rarer than they should be?

Wild, Matthew¹, Gagnon, Daniel¹, Bouchard, André², ¹ Université du Québec à Montréal, Montreal, Quebec, Canada² Université de Montréal, Montreal, Quebec, Canada

ABSTRACT- Several recent studies have suggested that rare species are not randomly distributed throughout plant taxa. This would appear to apply to North American pteridophytes, which are constantly over-represented on local lists of rare, threatened and endangered plant species. However, such lists often paint a skewed portrait of the true situation because of our tendency to recognize the rarity of well known and charismatic species while ignoring that of lesser known species. In order to verify if this over-representation of pteridophytes on rare plant lists is a real and consistent trend throughout North America, we used data from what we consider to be the most objective and complete available database: NatureServe (http://www.natureserve.org/). The NatureServe system, also known as the Heritage rankings, is based on criteria such as number of occurrences, population size, severity of threats and intrinsic vulnerability. From this database, we counted total vascular plant species, total pteridophyte species as well as rare vascular plant species and rare pteridophyte species for each North American sub-national (Canadian province or US state) flora. Rare species were defined as those belonging to one of NatureServe's "at risk" categories (S1, S2, S3, SX or SH). The same methods were used to analyse several taxa, including the Pteridophyta, the Filicinophyta and pteridophyte families with more than 40 species occurring in North America: Dryopteridaceae (132 spp.), Pteridaceae (99 spp.), Aspleniaceae (61 spp.) and Ophioglossaceae (47 spp.). The null hypothesis that the contribution of a given taxon to total rare species did not differ from its contribution to the total vascular flora was assessed using 2. Out of 64 sub-national floras, rare pteridophytes are over-represented in 55 cases. Of these 55, 31 differ significantly from their expected values. Only one is significantly lower than expected, and that is the particular case of Hawaii. We obtained similar results for all analysed taxa, suggesting that North American pteridophytes are rarer than expected. We postulate and discuss several hypotheses that could explain this phenomenon, including causes stemming from biological (life history traits), historical (evolutionary advancement), and geographical (distributions and disjunctions) aspects.

Key words: pteridophytes, ferns, rarity, natureserve