Individual study: Captive propagation of the endangered Socorro isopod Thermosphaeroma thermophilum at the Socorro Isopod Propagation Facility, Socorro, New Mexico, USA
Lang B.K., Douglas A. Kelt D.A. & Shuster S.M. (2006) The role of controlled propagation on an endangered species: demographic effects of habitat heterogeneity among captive and native populations of the Socorro isopod (Crustacea: Flabellifera). Biodiversity and Conservation, 15, 3909-3935
The endangered Socorro isopod Thermosphaeroma thermophilum is endemic to an isolated freshwater warm spring in New Mexico, southwest USA. Habitat loss and degradation resulted in extirpation of the wild population near Socorro, NM. This event prompted controlled propagation to initiate recovery of the species. Age-specific microhabitat segregation of this isopod was examined in artificial and native habitats, short- and long-term demographic patterns of captive populations in response to induced habitat manipulations, and overall experimental results of propagation as an effective method for management of this endangered species.
Propagation facility: The Socorro Isopod Propagation Facility was established in 1990. The facility consists of two separate systems of four small artificial pools (0.53 m wide x 1.63 m long x 0.75 m high) connected by pipes that are supplied with water from the native spring.
Habitat treatments and population responses: Captive populations (eight) were exposed to four artificial habitat treatments: control (no treatment); rocks only; plants only; rocks and plants. These were repeated over two 50-month experimental periods (Trial 1: July 1995 to August 1999; Trial 2: August 1999 to September 2003). Quantitative measures (benthic and sweep samples) of population density and age structure were compared among these managed subpopulations using the native population as a demographic baseline.
The native population remained significantly more abundant than captive subpopulations during the 100-month study. Population trends among artificial habitats differed slightly between the trials, but the captive populations responded to habitat quality, i.e. pools with plants supported higher densities than other treatments. Isopod age structure was most heterogeneous in pools with plants suggesting that vertical structural diversity is necessary to maintain long-term viability in captivity.
Observations of “breeding huddles” in all artificial habitats implied that propagation may affect the social basis of the species’ mating system, as this behaviour was not observed in wild populations.This could be a behavioural response to selection on body size that may reduce predation risks from larger cannibalistic males, or to increase fitness of both sexes under spatially altered sex ratios of artificial environments.
Conclusions: Habitat condition in controlled environments evidently plays a critical role, significantly affecting Socorro isopod body size and genetic affinities between captive and native population of this isopod.
Suggested reading: Shuster S.M., Miller M.P., Lang B.K., Zorich N., Huynh L. & Keim P. (2005) The effects of controlled propagation on an endangered species: genetic differentiation and divergence in body size among native and captive populations of the Socorro isopod (Crustacea: Flabellifera). Conservation Genetics, 6, 335-368.
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