Mf. Mckenna et G. Houle, Under-saturated distribution of Floerkea proserpinacoides Willd. (Limnanthaceae) at the northern limit of its distribution, ECOSCIENCE, 7(4), 2000, pp. 466-473
Habitat availability and dispersal ability are commonly the major factors c
ontrolling the distribution of habitat specialists. However, these species
often have an "under-saturated" distribution, i.e., their habitat is more f
requent than their populations. Floerkea proserpinacoides is an annual spri
ng ephemeral plant of the deciduous forest of eastern North America. It is
considered rare in most of its range. In Quebec (Canada), where the species
reaches the northern limit of its distribution, F. proserpinacoides is mos
tly restricted to rich, low woods on islands of the St. Lawrence River. To
elucidate the factors responsible for this peculiar distribution, we determ
ined the dispersal ability of F. proserpinacoides nutlets and attempted to
establish new populations at apparently suitable, but unoccupied sites with
in the species range in Quebec. Primary dispersal is barochorous and nutlet
s have no accessory structures to assist in dispersal. Secondary dispersal
is also limited, and nutlets typically move distances < 50 cm from their or
iginal point of fall. Yet, nutlets are buoyant and hydrochory is a possible
means of long-distance dispersal. When nutlets were introduced at apparent
ly suitable but unoccupied sites, the seeds could germinate and the individ
uals completed their life cycle. However, nutlets from different population
s did not have the same success. The under-saturated distribution of F. pro
serpinacoides in Quebec is not related to a lack of suitable habitat. Inste
ad, long-distance dispersal events may be too infrequent to allow the occup
ation of all potential sites, or conditions may be too variable among years
on certain sites to allow for population persistence.