Demographic models and the management of endangered species: a case study of the critically endangered Seychelles magpie robin

Abstract

Summary1. Demographic models are assuming an important role in management decisions for endangered species. Elasticity analysis and scope for management analysis are two such applications. Elasticity analysis determines the vital rates that have the greatest impact on population growth. Scope for management analysis examines the effects that feasible management might have on vital rates and population growth. Both methods target management in an attempt to maximize population growth. 2. The Seychelles magpie robin Copsychus sechellarum is a critically endangered island endemic, the population of which underwent significant growth in the early 1990s following the implementation of a recovery programme. We examined how the formal use of elasticity and scope for management analyses might have shaped management in the recovery programme, and assessed their effectiveness by comparison with the actual population growth achieved. 3. The magpie robin population doubled from about 25 birds in 1990 to more than 50 by 1995. A simple two-stage demographic model showed that this growth was driven primarily by a significant increase in the annual survival probability of first-year birds and an increase in the birth rate. Neither the annual survival probability of adults nor the probability of a female breeding at age 1 changed significantly over time. 4. Elasticity analysis showed that the annual survival probability of adults had the greatest impact on population growth. There was some scope to use management to increase survival, but because survival rates were already high (> 0·9) this had a negligible effect on population growth. Scope for management analysis showed that significant population growth could have been achieved by targeting management measures at the birth rate and survival probability of first-year birds, although predicted growth rates were lower than those achieved by the recovery programme when all management measures were in place (i.e. 1992-95). 5. Synthesis and applications. We argue that scope for management analysis can provide a useful basis for management but will inevitably be limited to some extent by a lack of data, as our study shows. This means that identifying perceived ecological problems and designing management to alleviate them must be an important component of endangered species management. The corollary of this is that it will not be possible or wise to consider only management options for which there is a demonstrable ecological benefit. Given these constraints, we see little role for elasticity analysis because, when data are available, a scope for management analysis will always be of greater practical value and, when data are lacking, precautionary management demands that as many perceived ecological problems as possible are tackled.

Evolutionary conservation advice for despotic populations: habitat heterogeneity favours conflict and reduces productivity in Seychelles magpie robins

“…Until recently, it survived only on the 210 ha island of Fregate (Norris & McCulloch 2003), from where it has been successfully translocated to three new islands: Cousin, Cousine and Aride. The entire world population of the species has been individually monitored since July 1988, during which time the population has grown from 23 individuals on a single island to 149 on four islands by December 2004(BirdLife International 2005.…”

Análise da estrutura de comunidades arbóreas de uma floresta amazônica de Terra Firme aplicada ao manejo florestal

“…A atividade de manejo tem procurado estabelecer práticas silviculturais mais adequadas aos processos ecológicos (Buschbacher, 1990;Rodriguez, 1998;Uhl & Vieira, 1989), especialmente aqueles que podem afetar o crescimento ou a viabilidade das populações (Noris & McCulloch, 2003).…”

Biodiversity in the context of ecosystem services: the applied need for systems approaches

“…From 1988 onwards, a programme of research and conservation has seen the population recover from 23 individuals on Frégate to over 120 individuals on five islands in recent years (figure 1a) [24,26]. Ecological studies provided the basic evidence to support a package of conservation measures including predator removal, habitat restoration, supplementary feeding, nest-site provision and the translocation of birds to other potentially suitable islands.…”