Using manipulation of density-dependent fecundity to recover an endangered species: the bearded vulture Gypaetus barbatus as an example

摘要

1. Endangered species subjected to reintroduction programmes often occur as small and isolated populations with local high density and depressed fecundity. Variation in territory quality may lead to this low fecundity owing to increasing occupation of suboptimal territories as population density grows, known as the habitat heterogeneity hypothesis (HHH). In this context, food supplementation in poor territories may be used to produce extra young which could be allocated to reintroduction programmes. 2. We analyse the density-dependent fecundity pattern and the underlying mechanism in a small population of bearded vultures Gypaetus barbatus in Aragón (northeast Spain). We then use population simulations to examine the viability of a hypothetical reintroduction programme using extra young produced by supplementary feeding on poor-quality territories and the effect on the donor population. We also compare the economic cost of such a reintroduction programme in relation to the cost of a traditional captive breeding programme. 3. The wild population showed clear negative, density-dependent fecundity regulation driven by the HHH mechanism. Simulations showed that extractions for translocations had no relevant long-term effects on the donor population viability, but a marked population reduction during the extraction period. However, the implementation of supplementary feeding to produce extra young for translocation lessened significantly this expected initial population reduction. 4. Analyses showed that the annual budget of a captive breeding programme for this species could be seven times more expensive than the translocation of extra young produced by food supplementation. 5. Synthesis and applications. Reintroduction programmes based on translocation of wildreared individuals, after a supplementary feeding programme oriented to poor-quality territories, provide a source of young at least seven times cheaper than those from captive breeding programmes. The use of this approach would decrease initial effects on donor population avoiding public criticism. Increasing the number of young released during the first years of the reintroduction decreases total financial cost and increases the final population size in the new area.