Macoun’s meadowfoam (Limnanthes macounii) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

Since the completion of the1988 COSEWIC status report, the writers made 150 field trips that involved revisiting old known subpopulations of Macoun’s meadowfoam and search for new ones. During the winter 2002/2003 all the Macoun’s meadowfoam sites (with the exception of one or two) were visited again and the size of each subpopulation was either counted or estimated.

The exact locality of the population from which Macoun’s type specimen was collected (“Victoria, ditches”) is not known. The efforts to find Macoun’s meadowfoam at Dallas Road & Victoria Breakwater (reported by C.F. Newcombe in 1920’s) and at West Burnside Road (Macoun’s 1875 record) failed.

Since the 1988 COSEWIC report, seven new sites (populations) have been discovered: Church Point [4], Williams Head [6], Saxe Point [18], Government House [19], Arbutus Grove [25], Gabriola Island [31], and Hornby Island [32]. New finds of Macoun’s meadowfoam on Gabriola Island and Hornby Island extended the known distribution of Macoun’s meadowfoam about 100 km in a northwestern direction. With the exception of these populations listed above, most new populations and sub-populations were found in the vicinity of previously known populations. A large proportion of newly discovered sub-populations came from the military areas as a result of a more intensive search conducted there since the 1988 report. The majority of new sub-populations were found on DND property with the largest number found at any one site being at the Rocky Point DND property.

Abundance

Based on the latest fieldwork, Macoun's meadowfoam is known globally from 28 extant populations (= locations). About a third of these populations consist of two or more sub-populations each; a total of 84 extant sub-populations (out of a total of 99 documented) are presently known (see Appendix).

The original 1988 status report listed 52 “populations” many of which should be treated as mere sub-populations. Applying the present concept of populations (based on a separation of about 1 km), the original 1988 COSEWIC report would have consisted of 24 populations. Four populations known in 1988 have been destroyed and seven new populations have been found (based on increased search effort) and one was restored.

The majority of all plants are concentrated in twelve large populations that all together host over one half of all plants documented in Canada. The majority of “large” populations have less than 2000 individuals. Only about 8 populations have more than 2000 plants (subpopulations 5.12, 5.4, 7.1, 14.1, 18.1, 24.1, 24.3, 29.3). It is estimated that there are presently a total of about 10,000 plants in Canada.

Fluctuations and trends

Annual plants vary widely from season to season and absolute numbers of plants in each population change from year to year. In the 1988 COSEWIC report, three size classes were distinguished to characterize population size:

  • Small: 1-50 plants;
  • Medium: > 50 - 200 plants;
  • Large: > 200 plants

The writers’ experiences monitoring Macoun’s meadowfoam populations since 1987 has shown that these categories reflected the size of populations reasonably well. Variation of plant numbers from year to year usually remain within the size limits of the respective categories (i.e., small, medium and large), in spite of the fluctuation from one generation to another in absolute numbers, typical for annual plants.

Of the 52 occurrences that were reported in the 1988 COSEWIC report (as “populations”), 29% (15) disappeared, 27% (14) declined, 19% (10) remained about the same and 23% (12) increased. The majority of subpopulations that disappeared were small and most of them were outcompeted by introduced perennial grasses.

Rescue effect

There is no possible rescue effect from populations outside Canada since the species is an endemic.

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