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Ischnura gemina

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA ARTHROPODA INSECTA ODONATA COENAGRIONIDAE

Scientific Name: Ischnura gemina
Species Authority: (Kennedy, 1917)
Common Name/s:
English San Francisco Forktail
Synonym/s:
Celaenura gemina (Kennedy, 1917)

Assessment Information [top]

Red List Category & Criteria: Vulnerable C2a(i) ver 3.1
Year Published: 2007
Date Assessed: 2007-03-01
Assessor/s: Abbott, J.C.
Reviewer/s: Donnelly, N., Suhling, F. & Clausnitzer, V. (Odonata Red List Authority)
Justification:
This is one of the rarest Odonates in the United States and it undoubtedly deserves a threatened status (Westfall and May 1996). Additional populations have been discovered in the San Francisco area resulting in the US Fish and Wildlife Service downgrading the species from the US Endangered category.

The species is very localized in urban areas, with probably no more than a few hundred at each site; perhaps 500 to 1,000 at the best sites (Garrison and Hafernik 1981). Several small populations have gone extinct since their discovery. Historically some populations have been extirpated due to urbanization and some habitat has naturally converted from small shallow ponds to dry pond beds; this succession is still a threat. There is also a suggested threat from hybridization with I. denticollis. The species has a relatively long life and good dispersal ability provides the opportunity to take advantage of newly formed habitats (it apparently tolerates some disturbance/pollution).

The total range of the species is probably less than 500 square miles (<5,000 km²), but there are more than 10 known locations, therefore the species cannot be listed as threatened under criterion B. The global population size is likely fewer than 2,500 (NatureServe 2006), and with 500 to 1,000 individuals at the best sites, and a declining trend (NatureServe 2006), the species meets the requirements for Vulnerable under criterion C.
History:
1996 Endangered
1994 Endangered (Groombridge 1994)
1990 Endangered (IUCN 1990)
1988 Endangered (IUCN Conservation Monitoring Centre 1988)
1986 Endangered (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description: This species is endemic to the San Francisco Bay Area, California, USA. It possibly extends north-south beyond the Bay Area (Bick 2003), with a total range area probably less than 500 square miles.
Countries:
Native:
United States (California)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Current population size is unknown.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Temporary urban pools at new construction (Garrison and Hafernik 1981). Also in depressions at the foot of steep hillsides where water seeps down (D.R. Paulson pers. comm.).
Systems: Terrestrial; Freshwater

Threats [top]

Major Threat(s): Small range, development.

Bibliography [top]

Baillie, J. and Groombridge, B. 1996. 1996 IUCN Red List of Threatened Animals. International Union for Conservation of Nature, Gland, Switzerland.

Bick, G.H. 1983. Odonata at risk in conterminous United States and Canada. Odonatologica 12(3): 209–226.

Bick, G.H. 2003. At-risk Odonata of conterminous United States. Bulletin of American Odonatology. 7(3): 41–56.

Garrison, R. and Hafernik, J. 1981. Population structure of the rare damselfly, Ischnura gemina (Kennedy) (Odonata: Coenagrionidae). Oecologica 48: 377–384.

Garrison, R. and Hafernik, J. 1981. The distribution of Ischnura gemina (Kennedy) and a description of the andromorph female (Zygoptera: Coenagrionidae). Odonatologica 10: 85–89

Garrison, R.W. 1981. Description of the larva of Ischnura gemina with a key and new characters for the separation of sympatric Ischnura larvae. Annals of the Ent. soc. of America 74(6): 525-530.

Groombridge, B. (ed.). 1994. 1994 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland and Cambridge, UK.

Hafernik, J.E. and Garrison, R.W. 1986. Mating success and survival rate in a population of damselflies: results at variance with theory? American Naturalists 128(3): 353-365.

IUCN. 2007. 2007 IUCN Red List of Threatened Species. Available at: www.iucnredlist.org. (Accessed: 12th September 2007).

Kennedy, C.H. 1915. Notes on the Life History and Ecology of the Dragonflies (Odonata) of Central California and Nevada. Proc. U.S. Nat. Mus. 52(2192): 483-635

NatureServe. 2006. NatureServe Explorer: An online encyclopedia of life [web application]. Version 6.1. NatureServe, Arlington, Virginia. Available http://www.natureserve.org/explorer. (Accessed: April 3, 2007).

Novak, K.L. and Robinson, J.V. 1996. A unique morphology, common to the penes of the Celaenura and Nanosura groups of Ischnura (Zygoptera: Coenagrionidae). Odonatologica 25(2): 183-186.

Paulson, D.R. and Dunkle, S.W. 1999. A Checklist of North American Odonata. Slater Museum of Natural History University of Puget Sound Occasional Paper Number 56.

Wells, S.M., Pyle, R.M. and Collins, N.M. (compilers) 1983. The IUCN Invertebrate Red Data Book. IUCN, Gland, Switzerland and Cambridge, UK.

Citation: Abbott, J.C. 2007. Ischnura gemina. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 24 April 2014.
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