Hill's pondweed (Potamogeton hillii) COSEWIC assessment and status report: chapter 11
Technical Summary
Potamogeton hillii
Hill’s pondweed – Potamot de Hill
Range of Occurrence in Canada:
Ontario
Extent and Area Information
Extent of occurrence (EO) (km²)
ca. 20,000 km² including extirpated site 3; <10,000 km² excluding site 3 [1300 km² if EO includes only 3 restricted areas around the extant sites – est. by K. Makkay]. [Note: revised GIS estimate by E. Haber of polygons for southern Ontario mainland and Manitoulin Island]
Specify trend in EO
unknown
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km²)
<<1 km² (19.7 ha) [sum of aquatic habitats at extant localities]
Specify trend in AO
unknown, possible decline
Are there extreme fluctuations in AO?
unknown
Number of known or inferred current locations
12-18
Specify trend in #
unknown, possible decline
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat
unknown
Population Information
Generation time (average age of parents in the population)
unknown
Number of mature individuals
estimated at 55,000 at sites where verified by the occurrence of fruits plus 64,600 including sites where identification is based on vegetative characters only [Note: The estimate is very crude due to the difficulties of obtaining estimates of abundance in an aquatic habitat in which destructive sampling would have to be undertaken to obtain more precise figures; plants are intertwined, moving or stagnant water conditions add to the difficulty of counting plants and other similar pondweeds are present. E. Haber]
Total population trend:
unknown, possible decline
% decline over the last/next 10 years or 3 generations.
unknown
Are there extreme fluctuations in number of mature individuals?
unknown
Is the total population severely fragmented?
somewhat fragmented
Specify trend in number of populations
unknown, possible decline
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each:
See Appendix 1
Threats (actual or imminent threats to populations or habitats)
Degradation of habitat observed at one site; overall, threats to habitat primarily potential.
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
USA – ranks in adjacent states are: Michigan (S2), New York (S2), Ohio (S1), Pennsylvania (S1)
Is immigration known or possible?
unlikely
Would immigrants be adapted to survive in Canada?
yes
Is there sufficient habitat for immigrants in Canada?
yes
Is rescue from outside populations likely?
No
Quantitative Analysis
[provide details on calculation, source(s) of data, models, etc.] n/a
Current Status
COSEWIC:Special Concern (May 2005)
Status and Reasons for Designation
Status: Special Concern
Alpha-numeric code: N/A
Reasons for Designation: An inconspicuous, rooted, aquatic plant currently known from fewer than 20 Canadian populations and occupying a very small total area of habitat. No imminent limiting factors have been identified that would have significant impacts on this globally rare species, but invasive exotic plants may be impacting some populations.
Applicability of Criteria
- Criterion A (Declining Total Population): Insufficient data.
- Criterion B (Small Distribution, and Decline or Fluctuation): The larger, revised extent of occurrence takes into consideration that the species may be more widespread than is indicated by the extant populations documented; it is still, however, below the threshold level for threatened and the area of occupancy is below critical values for both endangered and threatened. The criterion is not met because there are > 10 locations and these are not considered severely fragmented due to the possibility of propagule dispersal by waterfowl or by natural dispersal within a given riparian system; the lack of monitoring has resulted in little information on decline of populations; some degradation of habitat has been noted and can be inferred to continue in the future. No extreme fluctuations are known.
- Criterion C (Small Total Population Size and Decline): Population size has been determined to be larger than 10,000 plants but uncertainties in the manner of extrapolation from a single small test sample, the likely presence of mixed populations of pondweeds of similar appearance, and the occurrence of asexual reproduction makes the data unreliable for determining population size of mature individuals and level of risk under this criterion.
- Criterion D (Very Small Population or Restricted Distribution): May meet threatened D2 based on an area of occupancy < 1 km² and there is some indication of habitat degradation but overall there appear to be limited or few threats documented to the 12-18 populations currently reported; the species may be regarded best as one of special concern. This species is difficult to distinguish from other similar species and may be present at additional sites if a more intensive survey were to be conducted. Fruiting specimens collected for this study were, however, verified for the report writer by a highly competent botanist.
- Criterion E (Quantitative Analysis): Not applicable.