Contorted-pod evening-primrose (Camissonia contorta) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

A total of approximately 100 hours (not including travel time) were spent searching for Camissonia contorta at 3028 locations in 2002, 2003 2and 2004 (Figure 4). The principal surveyors were Matt Fairbarns, Phil Henderson, Frank Lomer, Erica Wheeler, Heidi Guest, Adolf Ceska and Oldriska Ceska; all of whom are familiar with the species.

Figure 4. Search effort for Camissonia contorta.

Figure 4. Search eEffort for Camissonia contorta.

The surveys were conducted throughout the known extent of occurrence. Surveys were also conducted on sand dunes and flats at coastal locations in the Gulf Islands and along the southwest coast of Vancouver Island, where rare associates such as yellow sand-verbena (Abronia latifolia) were already known to occurand Camissonia contorta might have been overlooked.

Botanists unfamiliar with the species may have difficulty spotting the diminutive plants, especially on cloudy days and in late afternoon when most flowers are closed. Plants may also be hard to find on very bright days when glare off bare sand may be troublesome. Nevertheless, botanists familiar with the species had little trouble finding the plants because of their high habitat specificity, the scarcity of appropriate habitat and the sparse nature of the associated vegetation. This held true even when the plants are not in flower, since the deep red foliage present on most plants is relatively easy to detect. Typically, if plants were present on a site they were found within the first 30 minutes of searching.

Abundance

In 2004 there were an estimated 3,500-4,500 mature individuals of Camissonia contorta in Canada (Table 1). Non-reproductive plants were very short-lived and could not be counted before they died. The number of mature individuals per population varied from approximately 20 at site 7 to as many as 2,000 at site 5.

Table 1. Population Data
Population Number and Name Area of Ooccupancy Number of Mature Individuals Observed Number of Mature Individuals Estimated Total Number of Mature Individuals
Total
78,400 m²
3,500 - 4,500
1 Metchosin
100
253
253
2 Saanich A
2,000 m²
500-1,000
500-1,000
3 Northern Gulf Island A
500 m²
190
200-250
200-250
4 Northern Gulf Island B
800 m²
696
700-750
700-750
5 Saanich B
35,000 m²
2,000
2,000
6 Saanich C
40,000 m²
100
100
7 Saanich D
1 m²
20
20
8 Saanich E
extirpated
extirpated
extirpated
extirpated

Fluctuations and trends

Past records of Camissonia contorta are not sufficiently detailed to determine fluctuations or declines, overall, in the Canadian population. However,some inferences can be made from known habitat losses.  The most extensive occurrence, Saanich C, now consists ofabout 100 widely scattered plantsrestricted to small, intact areas within a recently roughed-in golf course. About 95% of theareais now so heavily altered that it provides very poor quality habitat for C. contorta. The former population size at Saanich C is estimated at 2,300 plants according to an extrapolation assuming the same density observed at Saanich B (a similar, nearby site). The smaller population at Saanich E completely disappeared in recent years. Overall, the Canadian population of C. contorta has declined by an estimated 30-35% in recent years.

Rescue effect

The only nearby extra-territorial population occurs on San Juan Island in Washington State. There, it occurs as a healthy population sporadically distributed along a 10 km stretch of sand dunes and glacial outwash deposits. This extended population is more than 10 km from the nearest point in Canada and about twice that distance from the nearest Canadian population of Camissonia contorta. The intervening area is open ocean. Given the very limited dispersal distance of this species, there is negligible likelihood that seeds from the San Juan populations would be able to migrate to Canada. There is negligible likelihood of a natural rescue effect from Washington populations should the Canadian populations become extirpated. 

Page details

Date modified: