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Pyrgulopsis trivialis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA GASTROPODA LITTORINIMORPHA HYDROBIIDAE

Scientific Name: Pyrgulopsis trivialis
Species Authority: (Taylor, 1987)
Common Name(s):
English Three Forks Springsnail

Assessment Information [top]

Red List Category & Criteria: Critically Endangered B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v) ver 3.1
Year Published: 2012
Date Assessed: 2012-03-05
Assessor(s): Cordeiro, J.
Reviewer(s): Bohm, M., Collen, B. & Seddon, M.
Contributor(s): Dyer, E., Soulsby, A.-M., Whitton, F., Kasthala, G., McGuinness, S., Milligan, HT, De Silva, R., Herdson, R., Thorley, J., McMillan, K., Collins, A., Offord, S., Duncan, C. & Richman, N.
Justification:
Pyrgulopsis trivialis has been assessed as Critically Endangered under criterion B1ab(i,ii,iii,iv,v) and B2ab(i,ii,iii,iv,v) due to the small range of the species (meeting thresholds for both extent of occurrence and area of occupancy for this species), which counts as a single location in the face of continuing threats of habitat degradation as a result of grazing animals and habitat alteration and predatory pressure by the invasive crayfish. The spring system in which this species occurs has an extent of no more than 1 acre and extirpations of subpopulations have been reported recently, indicating a declining population trend. Site protection and management is therefore vital in order to ensure the continued survival of this species.
History:
1996 Data Deficient
1994 Indeterminate (Groombridge 1994)

Geographic Range [top]

Range Description: The species is restricted to a single spring complex from areas of the Upper Black River drainage (tributary to the Gila River) in Apache County, southeastern Arizona (Taylor 1987, Hershler 1994). Some degree of decline has been observed with extirpation confirmed from two spring sources (NatureServe 2009). The total extent of the spring complex is less than an acre (USFWS 2003, NatureServe 2009).
Countries:
Native:
United States (Arizona)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Population estimates in the last several years have concluded that the total population size is 129,135 snails (standard error = 31,511), at a density of 213.09 per m² (M.A. Martinez unpublished data, cited in USFWS 2003). The recent extirpation of two subpopulations confirms the declining population trend of the species (USFWS 2003), although population trend data is not available to accurately infer the rate of decline of the species. Martinez (2009) made three population estimates in 2002 at 129,135, 30,130 and 164,234 snails but noted they may underestimate the true population size.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: This species occurs at an unusually high elevational habitat (8,400 feet) (Taylor 1987) in spring-rich meadows with springs and creeks of various sizes that flow into a 200 foot pond at temperatures of 15°C (springs) to 17°C (pond). The species is limited to the pond and spring rich meadow perched above the steep canyon of the North Fork of the East Fork of the Black River. Substrate is firm and includes cobble, gravel, woody debris, and aquatic vegetation are essential for egg-laying and grazing. Aquatic vegetation includes watercress (Nasturtium sp.), Ranunculus, and algae. Associated species in the spring include Physa gyrina, Pisidium casertanum and a few Physa insigne; and in the pond include Valvata humeralis, Physa gyrina, Radix auricularia, Gyraulus parvus, Pisidium casertanum, Pisidium compressum, and Pisidium variabilis as well as Anodonta californiensis in pools and at depths greater than 4 inches (Taylor 1987, Hershler 1994). Preliminary analysis of substrate influence on Three Forks springsnail density, based on data collected during the summer of 2001, revealed snail densities were significantly higher in gravel/cobble substrate versus sand/silt substrate, particularly when watercress was present (Martinez and Myers 2002, cited in USFWS 2003).
Systems: Freshwater

Use and Trade [top]

Use and Trade: This species is not utilised.

Threats [top]

Major Threat(s): The greatest threat to this species is likely to be habitat loss (human created and due to trampling by livestock and crayfish burrowing). Throughout most of the 20th century, Three Forks and Boneyard Springs have been subjected to various levels of livestock grazing which degraded the aquatic environment and has been implicated in the extirpation of other hydrobiid snails. In the mid- and late 1990s livestock were fenced out of the immediate areas containing the spring complexes, although trespass livestock may occasionally gain access to springsnail sites. The degradation of spring run banks due to excessive ungulate trampling continues, however (particularly at Boneyard Springs, less so at Three Forks), and crayfish burrowing contributes to accelerated sedimentation and high turbidity resulting in changes to microhabitat conditions such as shifts in substrate composition. Habitat invasion by non-native crayfish (Orconectes virilis) contributes to unnatural predatory pressure. In May 2000, field investigations at Three Forks Springs revealed that the Three Forks springsnail is entirely absent from at least two boxed spring heads within which it was previously abundant.  These extirpations coincide with the introduction of exotic crayfish into the area. Unauthorized bait bucket releases and dish washing by recreationists potentially contributes to introduction of non-native organisms and/or pollutants. Three Forks Springs has also been affected by modifications of natural spring head integrity. During the 1930s concrete boxes were constructed around four of the spring heads at the Three Forks site. However, it does not appear that these modifications have negatively affected habitat suitability for the species and springsnails have been known to be locally abundant within spring boxes and associated outflows (USFWS 2003). The species' restricted range makes it particularly vulnerable to stochastic events.

Conservation Actions [top]

Conservation Actions: This species is listed under NatureServe as G1 - Critically Imperilled, is listed as a Species of Special Concern by the state of Arizona and has a monitoring programme in place (USFWS 2003). Long-term management strategies, however, are not currently in place. Site management and protection is required to prevent further habitat degradation and ensure the species' survival (NatureServe 2009).

Citation: Cordeiro, J. 2012. Pyrgulopsis trivialis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 01 October 2014.
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