Giraffe translocation population viability analysis

Abstract

Most populations of giraffes have declined in recent decades, leading to the recent IUCN decision to upgrade the species to Vulnerable status, and some subspecies to Endangered. Translocations have been used as a conservation tool to re-introduce giraffes to previously occupied areas or establish new populations, but guidelines for founding populations are lacking. To provide general guidelines for translocation projects regarding feasibility, we simulated various scenarios of translocated giraffe populations to identify viable age and sex distributions of founding populations using population viability analysis (PVA) implemented in Vortex software. We explored the parameter space for demography and the genetic load, examining how variation in founding numbers and sex ratios affected 100 yr probability of population extinction and genetic diversity. We found that even very small numbers of founders (N ≤ 10 females) can appear to be successful in the first decades due to transient positive population growth, but with moderate population growth rate and moderate genetic load, long-term population viability (probability of extinction <0.01) was only achieved with ≥30 females and ≥3 males released. To maintain >95% genetic diversity of the source population in an isolated population, 50 females and 5 males are recommended to compose the founding population. Sensitivity analyses revealed first-year survival and reproductive rate were the simulation parameters with the greatest proportional influence on probability of extinction and genetic diversity. These simulations highlight important considerations for translocation success and data gaps including true genetic load in wild giraffe populations.

The Critically Endangered El Rincon stream frog: Population viability and management actions in Patagonia, Argentina

“…Moreover, PVA provided a valuable framework for evaluating the impact of management actions on an endangered species. The use of PVA to evaluate conservation actions has been mainly focused on mammals and birds and occasionally on lizards (Kacoliris et al, 2019; Lee et al, 2020; García‐Antón & Traba, 2021). However, assessment of conservation actions through PVA is less widespread among aquatic species, including amphibians.…”

Giraffe translocations: A review and discussion of considerations

“…PVA can predict translocation outcomes and should be central to any translocation planning and decision‐making process (Dimond & Armstrong, ; IUCN, ). PVA simulations have shown that in order to establish a long‐term (100 years), genetically viable population of giraffes, a minimum of 30 females is required for the founding population (Lee et al, ). This is a substantially higher figure than is usually moved in practice (Chege, ; Muller, ).…”

“…Given the current uncertainty over giraffe taxonomy (Bercovitch et al, ; Fennessy et al, ), long‐term isolation of some populations (e.g . G. c. thornicrofti ), and deleterious effects of inbreeding depression (Lackey, ; Lee et al, ), genetic factors should be considered in giraffe translocation events. Guidance regarding taxonomic classification and distribution of giraffes is available from the IUCN SSC Giraffe and Okapi Specialist Group (http://www.giraffidsg.org), and general genetic diversity advice is available from population biologists experienced with small‐population genetics.…”

“…Translocations will be most effective if high levels of genetic diversity are maintained within subpopulations (van Niekerk et al, ), and mimic patterns of natural gene flow (Goossens et al, ). Inbreeding depression is reduced when larger numbers constitute the founding population (Lee et al, ).…”

“…Translocation events are under‐reported (but see Flanagan et al, ; Van Houtan, Halley, Aarde, & Pimm, ), so to improve future outcomes it is critical that all translocation efforts and outcomes, including planning documents, population monitoring and vegetation assessments are fully documented in a publicly available format (Parker, Ewen, Seddon, & Armstrong, ; Parlato & Armstrong, ). PVAs should be used to inform translocation planning and mitigate the effects of inbreeding depression (Lee et al, ). The complex nature of giraffe social organisation is an area which needs further research in the context of translocation events.…”