Cost-efficient conservation for the white-banded tanager (Neothraupis fasciata) in the Cerrado, central Brazil

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Abstract

Population viability analyses are widely used to support decisions for the management of single species, but there are few studies that explicitly take into account realistic economic costs. In this study we determine the most cost-efficient conservation management options for the white-banded tanager (Neothraupis fasciata) in the protected areas of the Cerrado in central Brazil. We use the PVA model VORTEX to simulate the ability of different management options to improve population persistence and then assess the effectiveness of each option given a fixed budget. We discover that the best strategy for improving the viability of white-banded tanager populations is to use fire management and nest protection to increase fecundity. In small reserves and a low budget then fire management alone is the best strategy, but if the budget is larger fire management with nest protection as a mixed strategy is better. In large reserves the best strategy is to do nest protection and with large budgets there is a negligible difference between spending all the money on nest protection versus a mixed strategy. If we had not included financial considerations in our analysis of management options then we would have discarded fire management as an option, even though it can be the best strategy.

Introduction

Developing cost-efficient management strategies for the world’s avifauna is going to become an increasingly important global problem. Of all the bird species in the world 12% are considered threatened and 8% are listed as Near Threatened (Baillie et al., 2004). Most threatened species need to be actively managed to persist in the long term. Some species are restricted to captive populations with low chances of being successfully re-introduced in natural environments. For example, the Spix’s Macaw project in the Caatinga biome (Brazil) failed to save the last wild individual and re-introduction has not been successful so far (Galetti et al., 2002). This species was considered extinct in the wild in 2000 with less than 60 individuals existing in captivity (Galetti et al., 2002). Although captive populations can offer insurance against extinctions, it would be foolhardy to assume that these species can be easily re-introduced back into the wild to form viable populations (Baillie et al., 2004). Additionally, many populations of common bird species are in decline around the world (BirdLife International, 2004). In many cases, habitat protection on its own is not sufficient, and therefore intensive management will be required to stop populations falling to a point where they no longer play their functional role in ecosystems (Redford, 1992).

Population viability analysis (PVA) is a quantitative approach to assessing the viability of populations and the factors that affect that viability (Possingham et al., 1993, Beissinger and Westphal, 1998). The original purpose of PVA was to determine the minimum population size of a viable population (Shaffer, 1981). PVA can be applied to estimate persistence probabilities of populations under different conditions using life history data and knowledge about the influence of environmental factors (Shaffer, 1981, Reed et al., 1998). A PVA model provides the means for assessing the magnitude of changes in parameters such as survival, fecundity and resource availability that precipitate important biological effects (Burgman, 2000). By incorporating elements of uncertainty these models provide a stochastic projection of a population’s fate (Brito and Fernandez, 2000). Although this assessment of extinction risk is useful, authors have questioned this traditional use of PVA arguing that it is generally difficult to accurately predict extinction probabilities (Possingham et al., 1993, Beissinger and Westphal, 1998). Although there are concerns about their predictive power, PVAs can be used to uncover the importance of different model parameters (McCarthy et al., 1995, Brito and Fernandez, 2000), and optimize conservation programmes (Cross and Beissinger, 2001, Morris and Doak, 2002).

PVA can be usefully applied in conjunction with decision support tools to evaluate and compare conservation strategies (Clark et al., 1991, Drechsler and Burgman, 2004). By simulating a range of possible scenarios that a species may face in the future, PVAs can be used to compare alternative management options (Lindenmayer et al., 1993, Lindenmayer and Possingham, 1996, Burgman, 2000). Another benefit of PVA models is that they can help us determine which type of data would be the most useful to collect in the future to reduce uncertainty about our choice of management action (Possingham et al., 1993, Morris and Doak, 2002).

Despite the call to use PVA in conservation decision making, there are few studies where it has been done with realistic economic costs (e.g. Larson et al., 2003, Tisdell et al., 2005). Conserving biodiversity requires significant financial resources and countries with large number of threatened species must spend their limited resources prudently (Baillie et al., 2004). Conservation decisions that ignore costs may be very expensive to implement and draw substantial resources away from other more cost efficient conservation actions (Baxter et al., 2006). By incorporating cost in the decision analysis it is possible to determine the action expected to deliver the best viability within a constrained budget (Noon and McKelvey, 1996, Possingham et al., 2001, Yokomizo et al., 2003, Haight et al., 2004, Yokomizo et al., 2004, Yokomizo et al., 2007).

This paper determines the most cost-efficient management option for populations of a Near Threatened bird species (the white-banded tanager, Neothraupis fasciata) in central Brazil. We assume that the best conservation strategy is the one that maximizes population persistence for a fixed budget. In other words, it achieves the vital rates required for population persistence while minimizing financial costs. In this paper we focus on the economic costs of different management options and consider the efficiency of different strategies for decreasing the chance of extinction.

Brazil has a high diversity of bird species and contains the highest number of threatened bird species of any country in the Neotropics (Collar et al., 1997, Marini and Garcia, 2005, IUCN, 2006). The Cerrado region is the most extensive woodland/savanna region in South America, and also the only biodiversity hotspot that largely consists of savanna, woodland/savanna and dry forest habitat (Mittermeier et al., 2005). It is the second largest South American biome, and one of the most threatened ecosystems in South America (Silva and Bates, 2002, Klink and Machado, 2005). The primary threat to its biodiversity is the accelerated process of conversion to agriculture and a deficiency in the extent and representativeness of the protected area system (Silva et al., 2006). Recent estimates suggest that most of the unreserved natural habitat in the Cerrado will be destroyed by 2030 if the current rate of destruction continues (Machado et al., 2004). Most of the Cerrado’s endemic species can be considered as threatened because of the high rate of habitat loss even though some have not been officially red listed (Garcia and Marini, 2006). This is one region where cost-efficient management strategies are urgently needed for endemic species.

In this paper we: (1) assess the extinction risk of the white-banded tanager population in ‘Estação Ecológica de Águas Emendadas’ using data from three years of field research; (2) determine the management strategy which maximizes viability within a limited budget or minimizes financial costs while reaching the vital rates required for population persistence and (3) identify the most important future research. The study is generalized by assessing the extinction risk of other populations of this species in protected and unprotected areas in the Cerrado.

Section snippets

Study area

The field study that provided information for the PVA was conducted in a 10,547 ha protected area called “Estação Ecológica de Águas Emendadas” (ESECAE) (15°29′–15°36′S and 47°31′–47°41′W), located in Distrito Federal, Brazil. This contains a little over 6000 ha of suitable white-banded tanager habitat (Duca, 2007). ESECAE is one of the most important protected areas in central Brazil, with 301 bird species including 16 Cerrado endemic (Bagno, 1998, Lopes et al., 2005) representing 37% of the

Population persistence

VORTEX simulations suggest that the white-banded tanager population in ESECAE has a very low chance of becoming quasi-extinct in the next 100 years (quasi-extinction probability = 0.038, basic scenario). In spite of the low quasi-extinction probability, the population trend (stochastic growth rate) for all scenarios was negative (Table 2). Decreasing the carrying capacity increases the extinction probability. When the area drops below about 2000 ha, the quasi-extinction probability becomes higher

Population persistence

The sensitivity analysis indicated that fecundity and adult survival have the greatest impact on the population persistence of the white-banded tanager. Variation in adult survival invariably has the greatest impact on persistence probabilities for long-lived vertebrates (e.g. Goldingay and Possingham, 1995, McCarthy, 1996, Lunney et al., 2002, Larson et al., 2002), but intriguingly fecundity appears to be the most important vital parameter for the white-banded tanager in ESECAE. Fecundity was

Conclusion

Our results confirm previous research that stresses the importance of considering costs when making conservation decisions (Possingham et al., 2001, Frazee et al., 2003, Baxter et al., 2006, Wilson et al., 2006). We conclude that the best strategy for the conservation of the white-banded tanager is to increase its fecundity and this goal can be achieved most cost efficiently by doing only fire management and/or nest protection. The amount spent of each activity depends on the budget available

Acknowledgements

This study was funded by the ‘Fundação O Boticário de Proteção À Natureza’. ‘PEQUI – Pesquisa e Conservação do Cerrado’ provided institutional support. We thank the ESECAE/SEMARH for authorization to conduct this study. C. Duca was supported by a fellowship from CAPES/CNPq, and M.Â. Marini is supported by research fellowship from CNPq. We thank all people from ‘Laboratório de Ornitologia’ at Universidade de Brasília during field work. This work has been supported by a Grant-in-Aid for

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