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The effect of habitat degradation on the long term survival of the critically endangered Madagascar spider tortoise (Pyxis arachnoides)

Journal Article


Abstract


  • Pyxis arachnoides inhabits the dry, coastal forests of southwest Madagascar; a biologically unique ecoregion

    severely threatened by unsustainable small scale agricultural practices. Using remotely sensed data

    we established vegetation loss remains unabated within our study area at 1.2% year!1; consistent with

    ecoregion wide vegetation loss between 1990 and 2000. We monitored tortoise population density on

    four occasions over 8 years and developed a stage class projection matrix to model the finite growth rate,

    matrix sensitivities and elasticities of the population. Monitoring revealed an actual mean population

    decline of 10.8% between 2003 and 2011. Our projection matrix model suggested the finite rate of growth

    to be k = 0.986, indicative of 1.4% year!1 decline for the duration of the existence of the population, with

    adult survival as the most sensitive parameter to overall survival of the population. Projection modeling

    suggests that the population would possibly become functionally non viable in approximately 170 years.

    As our study was heavily reliant on the use of surrogate data, more information is needed on pre-adult

    survival and wild reproductive rates. Our study site currently represents a population of exceptional density,

    therefore, other less dense populations, subjected to the further stresses of poaching will likely

    become functionally non viable much sooner. This study highlights the utility of population projection

    matrices in determining the vulnerability of chelonians; a globally threatened taxon. In the case of the

    spider tortoise, well coordinated development programs and tighter protected area management are

    required to address the poverty induced drivers forcing this species closer to extinction.

Authors


  •   Walker, Ryan C. J. (external author)
  •   Whitmore, Nathan (external author)
  •   Rafeliarisoa, Tsilavo H. (external author)
  •   Hamylton, Sarah

Publication Date


  • 2012

Citation


  • Walker, R. C. J., Whitmore, N., Rafeliarisoa, T. H. & Hamylton, S. (2012). The effect of habitat degradation on the long term survival of the critically endangered Madagascar spider tortoise (Pyxis arachnoides). Biological Conservation, 152 152-158.

Scopus Eid


  • 2-s2.0-84862649056

Ro Metadata Url


  • http://ro.uow.edu.au/scipapers/4292

Number Of Pages


  • 6

Start Page


  • 152

End Page


  • 158

Volume


  • 152

Abstract


  • Pyxis arachnoides inhabits the dry, coastal forests of southwest Madagascar; a biologically unique ecoregion

    severely threatened by unsustainable small scale agricultural practices. Using remotely sensed data

    we established vegetation loss remains unabated within our study area at 1.2% year!1; consistent with

    ecoregion wide vegetation loss between 1990 and 2000. We monitored tortoise population density on

    four occasions over 8 years and developed a stage class projection matrix to model the finite growth rate,

    matrix sensitivities and elasticities of the population. Monitoring revealed an actual mean population

    decline of 10.8% between 2003 and 2011. Our projection matrix model suggested the finite rate of growth

    to be k = 0.986, indicative of 1.4% year!1 decline for the duration of the existence of the population, with

    adult survival as the most sensitive parameter to overall survival of the population. Projection modeling

    suggests that the population would possibly become functionally non viable in approximately 170 years.

    As our study was heavily reliant on the use of surrogate data, more information is needed on pre-adult

    survival and wild reproductive rates. Our study site currently represents a population of exceptional density,

    therefore, other less dense populations, subjected to the further stresses of poaching will likely

    become functionally non viable much sooner. This study highlights the utility of population projection

    matrices in determining the vulnerability of chelonians; a globally threatened taxon. In the case of the

    spider tortoise, well coordinated development programs and tighter protected area management are

    required to address the poverty induced drivers forcing this species closer to extinction.

Authors


  •   Walker, Ryan C. J. (external author)
  •   Whitmore, Nathan (external author)
  •   Rafeliarisoa, Tsilavo H. (external author)
  •   Hamylton, Sarah

Publication Date


  • 2012

Citation


  • Walker, R. C. J., Whitmore, N., Rafeliarisoa, T. H. & Hamylton, S. (2012). The effect of habitat degradation on the long term survival of the critically endangered Madagascar spider tortoise (Pyxis arachnoides). Biological Conservation, 152 152-158.

Scopus Eid


  • 2-s2.0-84862649056

Ro Metadata Url


  • http://ro.uow.edu.au/scipapers/4292

Number Of Pages


  • 6

Start Page


  • 152

End Page


  • 158

Volume


  • 152