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Recovery Strategy for the Eastern Prickly Pear Cactus (Opuntia humifusa) in Canada

5. Population and Distribution

5.1 Population and Distribution Context

The range of the Eastern Prickly Pear Cactus extends from Massachusetts through extreme southwestern Ontario, west to Minnesota and south to Oklahoma and Florida (Figure 1). The Canadian population represents much less than one percent of the global abundance of this species. The species is common throughout the southern and eastern parts of its United States range. However, the species' conservation status rank is S1 (Critically imperiled) in Wisconsin and S3 (Vulnerable) in Iowa, Ohio, Pennsylvania and Connecticut (NatureServe 2009).

Figure 1: North American distribution of Eastern Prickly Pear Cactus. The arrows point to outliers in the species' range (Pinkava 1993).

Figure 1: North American distribution of Eastern Prickly Pear Cactus. The arrows point to outliers in the species' range (Pinkava 1993).

In Canada, the Eastern Prickly Pear Cactus reaches the northern edge of its range in the southern tip of Ontario. Extant, native populations are only known to occur at two locations in southwestern Ontario: two populations in Point Pelee National Park in Essex County and one in Fish Point Provincial Nature Reserve on Pelee Island (Figure 2).

Figure 2: Distribution of extant, native populations of Eastern Prickly Pear Cactus in Canada.

Figure 2: Distribution of extant, native populations of Eastern Prickly Pear Cactus in Canada.

The two distinct, native, Eastern Prickly Pear Cactus sites in Point Pelee National Park - one in primary successional shoreline areas and the other located in secondary successional, abandoned farm field sites, total 2 070 individuals (VanDerWal et. al. 2007a). A single site exists at Fish Point Provincial Nature Reserve on Pelee Island totaling 11 individuals (S. Dobbyn pers. comm. 2009). In addition to these native populations, there are five known populations of planted Eastern Prickly Pear Cactus in southwestern Ontario for which the origin is unknown, or suspected to be from one of the two native populations. Note that planted populations are not considered part of the Endangered Canadian population, but may potentially play a role in their recovery. The COSEWIC Reason for Designation considers only the two native populations (since determined to be three native populations at two locations) in its decision. There are also six populations of unconfirmed origin that are now extirpated (Table 2).

Table 2: List of extant and extirpated Canadian Eastern Prickly Pear Cactus populations.

Population - Site NameLocationOriginStatus
Fish Point Provincial Nature Reserve (1 population)Pelee Island, Essex CountyNativeExtant
Point Pelee National Park (2 populations)Point Pelee National Park, Essex CountyNativeExtant
Chatham-Kent RoadsideMunicipality of Chatham-KentUnknown (P.A. Woodliffe pers. comm. 2005)Extant
Rondeau Provincial ParkMunicipality of Chatham-KentIntroduced presumably from Fish Point Provincial Nature Reserve (P.A. Woodliffe pers. comm. 2003)Extant
Howard Township CemeteryHoward Township, Municipality of Chatham-KentIntroduced from Point Pelee National Park (White 1998)Extant
Turkey PointNorfolk CountyIntroduced from an unknown location (P. Carson pers. comm. 2003)Extant
South barrier beach of Big Creek MarshPort Rowan, Norfolk CountyIntroduced (S. Brinker pers. comm. 2008, J. Robinson pers. comm. 2008)Extant
Cedar BeachColchester South Township, Essex CountyUnknown (no voucher)Extirpated
Harwich Township CemeteryHarwich Township, Municipality of Chatham-KentIntroduced from Point Pelee National Park (White 1998)Extirpated
Bradley's MarshDover Township, Municipality of Chatham-KentUnknown (no voucher)Extirpated
West of Port StanleyElgin CountyUnknown (no voucher)Extirpated
Long PointNorfolk CountyUnknown (Macoun 1883, no voucher)Extirpated
Ruscom Shores Conservation AreaEssex CountyUnknown (P.A. Woodliffe pers. comm. 2005)Extirpated

The demographic record for Canadian populations is too inconsistent to accurately assess population trends, although some losses are known to have occurred. To more accurately estimate the size of the populations at Point Pelee National Park, population size was determined by using "microsites" as a surrogate. A microsite represents one or more groups of cacti less than 1.0 m from other groups (Lovett-Doust et al. 2004). It was estimated that each Point Pelee National Park microsite contains, on average, six individuals. Based on this, approximately 2 070 naturally established individuals occur in 345 microsites at Point Pelee National Park - 209 microsites along the west beach and 136 in the Park interior, approximately 250 m from the west beach (VanDerWal et al. 2007a). There are five microsites containing only 11 individuals at Fish Point Provincial Nature Reserve (S. Dobbyn pers. comm. 2009).

In Point Pelee National Park, the average age of microsites, the number of stems per microsite and the number of reproductive individuals in the population have declined (VanDerWal et al. 2007a). At the same time, the average number of fruits recorded per stem has increased, although this increased emphasis on sexual reproduction may be a stress response to declining habitat suitability. Based on the size, genetic variability and recruitment levels of Point Pelee National Park's existing populations, the populations are thought to be viable (L. Lovett-Doust pers. comm. 2005). In contrast, the viability of the Fish Point Provincial Nature Reserve population is questionable due to the small number of microsites and individuals and an apparent lack of recruitment (L. Lovett-Doust pers. comm. 2005).

5.2 Population and Distribution Objectives

Based on the information presented above, the population and distribution objectives for Eastern Prickly Pear Cactus are:

  • To maintain the current number of microsites (345) of the Eastern Prickly Pear Cactus in Point Pelee National Park over the next five years, and to increase the total number of microsites by 5% over the next 10 years.
  • To maintain the population size (five microsites) at Fish Point Provincial Nature Reserve on Pelee Island over the next five years.