Thursday, 3 January 2013

Reintroduction or ecological replacement? Or both?

Firstly, happy new year and apologies for the break in posts as a result of my baby girl falling ill (she's now better) and Christmas. Normal weekly service will now resume and I have a backlog of posts to bring you of which this is the first.

The idea for this post was prompted by a widely-reported paper on the genetic legacy of Lonesome George, the last known purebred individual of Chelonoidis abingdoni, or Galapagos giant tortoise native to Pinta Island (Edwards et al. 2013, authors webpage here). The discovery of individuals with very similar genetic ancestry on another island (Isabela Island) provides hope that hybrids with C. abingdoni parents could be taken into captive breeding programmes to produce tortoises that might be translocated to 'back' Pinta Island. The authors suggest an interesting strategy of tiered translocation whereby any individuals with a very high genetic similarity to the extinct Pinta Island tortoises are saved for the captive breeding whilst hybrids that are further removed (offspring of hybrids rather than purebreds) are moved directly to Pinta, the former constituting reintroduction albeit with a little genetic mixing, the latter being an example of ecological replacement (see page on definitions). This would be motivated by the need to restore giant tortoises as ecosystem engineers and would hopefully improve the habitat quality prior to release of the 'purer' individuals.

On reading this, I went back to another paper from three years ago (Hansen et al. 2010) in which the authors discuss the pros and cons of a range of translocations of large and giant tortoises. Back then, Lonesome George had mated unsuccessfully with females of a similar subspecies but there was still hope that
the Pinta tortoise genes might be salvageable. Meanwhile the Floreana tortoise C. elephantopus provided an early warning of where the Pinta tortoises would be once Lonesome George had died.  The Floreana tortoise is another species lost from Galapagos but having extant hybrid descendents. In this case Hansen et al. propose that the restoration of tortoises to Floreana is a dichotomous choice - they present the 'dilemma' as a decision to either "repatriate Floreana with available extant tortoises to restore lost dynamics as soon as possible, or initiate a long-term breeding programme to create a lineage of tortoises [genetically] similar to the extinct species". To me, it is Edwards et al.'s approach that makes sense - instead of choosing one intervention over another, we should recognise that with threatened species management, there are usually several motivations for undertaking conservation, and that these will be prioritised differently depending on the timescales over which they operate. Using an armoury of conservation tools to address the various targets and motivations is the only way to adequately protect species and importantly, the role they play in maintaining functioning and resilient ecosystems.

Edwards, D. L., Benavides, E., Garrick, R. C., Gibbs, J. P., Russello, M. a., Dion, K. B., Hyseni, C., et al. (2013). The genetic legacy of Lonesome George survives: Giant tortoises with Pinta Island ancestry identified in Gal├ípagos. Biological Conservation, 157, 225–228. doi:10.1016/j.biocon.2012.10.014

Hansen, D. M., Donlan, C. J., Griffiths, C. J., & Campbell, K. J. (2010). Ecological history and latent conservation potential: large and giant tortoises as a model for taxon substitutions. Ecography, (March), no–no. doi:10.1111/j.1600-0587.2010.06305.x

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