Optimal Translocation Strategies for Enhancing Stochastic Metapopulation Viability

Abstract

Numerous methods have been proposed for enhancing species viability. Much attention has been given to the minimum required number of individuals, size and number of nature reserves, and value of habitat corridors. Surprisingly, however, the potential value of active management of a population through a program of translocations has only rarely been suggested, and explicit formulations of a theoretical basis for such a program are nonexistent. By drawing on the mathematical optimization technique known as dynamic programming, I develop an optimal dynamic strategy for translocation in a model population. I demonstrate this approach using a simple model for a hypothetical remnant population with two available habitat reserves incorporating demographic, environmental, and catastrophic forms of stochasticity. I then generalize the results by examining the effect on the cost and effectiveness of optimal translocation management of reserve size, population growth rate, environmental stochasticity, catastrophe size and frequency, translocation mortality rate, spatial correlation of population dynamics, and reserve size asymmetry. Simulated application of the optimal strategies, under a wide range of conditions, demonstrates that managed translocations averaging between 1 and 6 individuals/yr might dramatically enhance the probability of species persistence and reduce the required size of nature reserves, potentially by >1 order of magnitude. Given prohibitive financial and political costs of land acquisition for nature reserves, this technique could provide an important alternative for saving many endangered species.

Strategies for conserving native salmonid populations at risk from nonnative fish invasions: tradeoffs in using barriers to upstream movement

“…In general, more populations will be necessary as individual populations become more vulnerable (for example, smaller), the potential for catastrophic disturbances increases, or the potential for simultaneous disturbance across sets of local populations increases (Hanski and Gilpin 1997). Replicate populations are especially important when all are isolated above barriers, to allow reintroduction if local extinctions occur but habitats remain suitable (Lubow 1996).…”

“…This may include conserving many small populations that persist above barriers, translocating among replicates when they go extinct (Lubow 1996, Hilderbrand 2002, and working to protect or develop larger populations in remote or protected basins (see Shepard and others 2005 for an example). In the worst case, if barriers on the large populations are breached by human or natural agents and invasions proceed quickly, fish from the smaller replicate populations can be used to refound them.…”

Optimal allocation of conservation effort among subpopulations of a threatened species: How important is patch quality?

“…Stochastic dynamic programming compares different management options for each possible state of the system of interest as the system changes through time; for example, in our case, identification of which subpopulations are extant at the current time could serve as a system state variable that induces selection of a specific management action. It has been used to solve problems in several conservation studies, e.g., fire management (Richards et al 1999, McCarthy et al 2001, translocation (Lubow 1996, Tenhumberg et al 2004, Rout et al 2005, and population management (Shea and Possingham 2000).…”

Evaluating trade-offs in bull trout reintroduction strategies using structured decision making

“…We applied stochastic dynamic 302 programing (SDP) to determine the optimal management decision (Lubow 1996 (Table 4). Using these populations as starting abundances for the donor and recipient 318 population, we created every possible combination of populations that may be observed 319 in real world reintroduction scenarios, resulting in 576 (24 x 24) potential starting 320 population sizes.…”