Bolander’s quillwort (Isoetes bolanderi) COSEWIC assessment and status report: chapter 9

Population Sizes and Trends

Search Effort

Surveys for Isoetes bolanderi were done in 2002 and 2003 of lakes in Waterton Lakes National Park and in Akamina Provincial Park in adjacent British Columbia (Appendix 1). Initially, a list of 32 potentially suitable lakes was assembled and screened against criteria based on similarity of environmental characteristics with Summit Lake. A detailed search of the most likely 26 lakes was done, occupying usually 1-3 hours per lake, by Cheryl Bradley, Cyndi Smith and Peter Achuff, but failed to find any additional populations.


Abundance

The first population estimate of Isoetes bolanderi at Summit Lake was a minimum of 600 000 and a maximum of 1.8 million along 50-90% of the shoreline, based on plants observed growing to a depth of ca. 1.5 m (Brunton 1994). This suggests a maximum of about 4 million plants, based on 1.8 million for 50% of the shoreline.

A comprehensive survey was done in August 2002 (Smith and Bradley 2003).

"Ten transects were randomly established, and data were collected from 101 quadrats. About 78% of the quadrats (79 of 101) contained at least one I. bolanderi plant and only those quadrats were included in calculations because the plants are not randomly distributed around the lake. Quadrats with coarse rocky substrate, or that supported other vascular plant species, did not contain I. bolanderi plants. Six thousand plants were counted, and the mean number per quadrat was 75.9 (S.E. ±6.5). The range was 1 to 265, and the median number was 61."

"To estimate the population size from the sample mean, we had to calculate the total number of possible sampling units. Transects did not extend beyond 1.2 m depth, but along all transects I. bolanderi plants were observed beyond that depth. As the maximum depth of the lake is 2.0 m, we assumed that there were no depth limitations to where plants would be found. We also assumed the same average frequency of quadrats with I. bolanderi as in the quadrats that we sampled."

"We sampled 10.1 m2 (0.5%) of the 2.03 ha lake. The lake could have approximately 203 000 sampling units (quadrats at 0.1 m2), but as only 78% of the quadrats had Isoetes bolanderi plants present, we estimate the total number of possible sampling units to be 158 340. We multiplied these 158 340 possible quadrats by the sample mean of quadrats with plants (75.95) to estimate the population size for Summit Lake to be 12 025 923 plants ± 2 058 614 (95% C.I.)."

The difference (12 million vs. 4 million) is almost certainly due to differences in estimation techniques, not a three-fold increase in population size.

In 2004, the population was monitored using the presence/absence of plants in random quadrats. The protocol was designed to have a 95% probability of detecting a 30% change in presence, with a 10% chance of making a false-change error (Smith and Bradley 2003). The 2004 survey had an 87% presence, compared with 78% in 2002 (Smith pers. comm.) This difference is not significant and the population apparently is stable over the two-year period.


Fluctuations and Trends

The Summit Lake population appears to be stable over the period 2002-2004.

Trends of Isoetes bolanderi populations in the USA are unknown. However, the species has not been considered to present a significant conservation concern on a global scale (Cronquist et al. 1972, Lellinger 1985, Taylor et al. 1993).


Rescue Effect

The only extant population currently known in Canada is at Summit Lake. The nearest population is at Dutch Lakes, Glacier National Park, Montana, about 30 km away (Lesica 2002). The status of this population is unknown.

Colonization from the Dutch Lakes population to suitable habitat in Canada is highly unlikely given the limited dispersal capacity of this species. Although plants from Dutch Lakes probably would be adapted to survive in southern Canada, it is not clear that sufficient, suitable habitat for migrants to establish exists in Canada outside of Summit Lake. Summit Lake is the most northerly population of Isoetes bolanderi and, presumably, other suitable habitat would already have been colonized from the Summit Lake population.

In summary, rescue effect from outside populations is highly unlikely.

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