The translocation trade-off for eastern sand darter (Ammocrypta pellucida): balancing harm to source populations with the goal of re-establishment

The use of translocations to recover populations requires a sufficiently large number of individuals from source populations, but removing too many individuals could lead to source population collapse. To understand the trade-off between the probabilities of source population extirpation and translocation success, matrix population models that incorporate Allee effects, density dependence, and demographic and environmental stochasticity were combined with a model that simulates removals from source populations. We apply these models to eastern sand darter (Ammocrypta pellucida; Species at Risk Act status: Threatened) translocation scenarios in Canada. The results suggest that translocations most often require source populations >20 000 individuals, as source population extirpation probability increased with the number and frequency of removals. Transport mortality or losses immediately following introduction further affected translocation success. Uncertainty around life-history parameters and the strength of Allee effects led to additional uncertainty about the required source population size. Although stochastic processes affected the probability of translocation success, factors such as stocking density and frequency can be controlled, and translocation may therefore be a viable strategy for eastern sand darter recovery, even when applying cautious thresholds to guard against uncertainty. Si l'utilisation de deplacements pour retablir des populations necessite un nombre suffisamment grand d'individus de populations sources, le retrait de trop d'individus peut mener a l'effondrement de ces populations. Pour comprendre le compromis entre les probabilites de disparition de populations sources et le succes du deplacement, des modeles demographiques matriciels qui integrent des effets Allee, la dependance a la densite et une stochasticite demographique et environnementale ont ete combines a un modele qui simule des retraits de populations sources. Nous appliquons ces modeles a des scenarios de deplacement de dards de sable (Ammocrypta pellucida; etat de la Loi sur les especes en peril: menaces) au Canada. Les resultats donnent a penser que les deplacements necessitent le plus souvent des populations sources de plus de 20 000 individus, puisque la probabilite de disparition d'une population source augmente parallelement au nombre et a la frequence des retraits. La mortalite liee au transport ou les pertes immediatement apres l'introduction ont egalement une incidence sur le succes du deplacement. L'incertitude entourant des parametres du cycle biologique et la force d'effets Allee accroissent l'incertitude associee a la taille requise des populations sources. Bien que des processus stochastiques aient une incidence sur la probabilite de succes du deplacement, des facteurs comme la densite et la frequence d'ensemencement peuvent etre controles, de sorte que le deplacement pourrait etre une strategie viable pour le retablissement du dard de sable, meme si des seuils prudents sont appliques pour contrer l'effet de l'incertitude. [Traduit par la Redaction]
Introduction The number of species that are currently at heightened risk of extinction continues to rise (Chapin et al. 2000; Rockstrom et al. 2009). Reversing this trend requires rigorous evaluation [...]