Optimal release strategies for cost-effective reintroductions
Article first published online: 22 APR 2014
© 2014 The Authors. Journal of Applied Ecology © 2014 British Ecological Society
Journal of Applied Ecology
Volume 51, Issue 4, pages 1107–1115, August 2014
How to Cite
Canessa, S., Hunter, D., McFadden, M., Marantelli, G., McCarthy, M. A. (2014), Optimal release strategies for cost-effective reintroductions. Journal of Applied Ecology, 51: 1107–1115. doi: 10.1111/1365-2664.12253
- Issue published online: 17 JUL 2014
- Article first published online: 22 APR 2014
- Accepted manuscript online: 15 MAR 2014 08:09AM EST
- Manuscript Received: 15 SEP 2013
- Manuscript Accepted: 12 MAR 2013
- NSW Government
- Australian Government
- National Heritage Trust
- age structure;
- captive breeding;
- growth rate;
- Leslie matrix;
- population viability analysis;
- post-release effects;
Ex situ programmes for endangered species commonly focus on two main objectives: insurance against immediate risk of extinction and reintroduction. Releases influence the size of captive and wild populations and may present managers with a trade-off between the two objectives. This can be further complicated when considering the costs of the captive population and the possible release of different life stages.
We approached this decision problem by combining population models and decision-analytic methods, using the reintroduction programme for the southern corroboree frog Pseudophryne corroboree in Australia as an example. We identified the optimal release rates of eggs and subadults which maximized the size of the captive and reintroduced populations while meeting constraints. We explored two scenarios: a long-term programme for a stable age-distributed captive population and a short-term programme with non-stable age distribution and limited budget. We accounted for uncertainty in the estimated vital rates and demographic stochasticity.
Assuming a stable age distribution, large proportions of individuals could be released without decreasing the captive population below its initial size. The optimal strategy was sensitive to the post-release survival of both life stages, but subadult releases were generally most cost-effective, producing a large wild population and requiring a cheaper captive population. Egg releases were optimal for high expected juvenile survival, whereas mixed releases of both life stages were never optimal.
In the short-term realistic scenario, subadult releases also produced the largest wild population, but they required a large increase in the size and cost of the captive population that exceeded the available budget. Egg releases were cheaper but yielded smaller numbers in the wild, whereas joint releases of both life stages provided more wild individuals, meeting budget constraints without depleting the captive population.
Synthesis and applications. Optimal release strategies for endangered species reflect the trade-offs between insurance and reintroduction objectives and depend on the vital rates of the released individuals. Although focusing on a single life stage may have practical advantages, mixed strategies can maximize cost-effectiveness by combining the relative advantages of releasing early and late life stages.