Comparing wild and reintroduced populations of the threatened orchid Diuris fragrantissima (Orchidaceae) in south-eastern Australia

Abstract

Orchids have high rates of speciation and extinction, and are over-represented on threatened species lists. Reintroductions are being used with increasing frequency as an important tool for threatened orchid recovery. The ultimate aim of these reintroductions is to create a self-sustaining population that will reduce the risk of extinction for the species. In this case study, we test the hypotheses that state transition, annual survival, and seed production rates in a reintroduced population were equivalent to those in the wild population. These hypotheses were tested using long-term demographic monitoring datasets from a wild and a reintroduced population of Diuris fragrantissima, and analysed using Bayesian multistate capture–recapture and multinomial models. The results showed that emergent plants at the reintroduction site were more likely to transition to vegetative or unobserved states, and less likely to flower in the following year, than those at the wild site. This resulted in a strong trend through time away from emergent life states at the reintroduction site. The estimated annual survival rate was >90% at the wild site, and <80% in five of the seven years at the reintroduction site. Flowering was the most frequently recorded life state at the wild site. The fate of an individual flower was not affected by site (wild or reintroduction), but an increase in rainfall increased the probability that a flower would set seed and decreased the probability that it would be browsed. The reintroduction has failed to produce a stable, sustainable, long-term population, but it has been valuable in providing information that will inform the development and improvement of future D. fragrantissima reintroductions. Improving our knowledge in these areas should increase the chances of future D. fragrantissima reintroductions being assessed as a success.