Population management of threatened taxa in captivity within their natural ranges: Lessons from Andean bears (Tremarctos ornatus) in Venezuela
Introduction
With the resources required for conservation of the world’s biodiversity far outstripping present allocations, there is an urgent need to ensure not only that new investments are secured, but that already-dedicated investments are made efficiently (Balmford et al., 2003). One conservation sector which has made advances in this area is that dealing with captive populations, which may aid conservation through education, fundraising, research, and breeding for release into the wild (Hutchins et al., 1995). For example, the American Zoo and Aquarium Association (AZA) and the European Association of Zoos and Aquaria (EAZA), respectively, manage over 390 and 250 species for conservation purposes, compared with just a handful in 1965 (AZA, 2005, EAZA, 2005). Zoo associations in Australia, Japan, and India are making similar advances; however, much untapped potential remains elsewhere (WAZA, 2005).
A part of this potential is represented by threatened taxa already in captivity within their natural ranges. In general, holding threatened taxa can be an efficient use of zoo resources, since populations may be managed simultaneously for a wider range of conservation goals than may non-threatened taxa (Hutchins et al., 1995). Furthermore, within-range captive populations of such groups may present distinct advantages over extra-range ones. For example, native environmental conditions may be easier to replicate, improving welfare, reproduction, and ease of reintroduction, while minimizing exposure to non-native pathogens; location close to human threats to species allows educational messages to reach the most important target audiences; and captive capacity close to natural populations may facilitate rescue and rehabilitation of valuable wild specimens (e.g. Sanz and Grajal, 1998, Wilcken et al., 2000).
However, worldwide, threatened species are presently distributed where present zoo capacity is not (Baillie et al., 2004, WAZA, 2005). For example, just 9% of the AZA’s most intensive programs are focused on threatened or endangered species native to North America (AZA, 2005). Even in the relatively prosperous Australasian region, whose zoo association focuses 54% of its 98 conservation breeding programs on native taxa, there are less than a third of the zoos in North America – despite the fact that Australasia has more than double the threatened species (Johnson et al., 2005, AZA, 2005, IUCN, 2005). The situation is even more unbalanced in South America and Africa.
In recognition of the potential advantages of within-range captive populations, extra-range programs for threatened taxa may seek deliberately to develop within-range components (e.g. US Fish and Wildlife Service, 2004, Tilson, 1998). However, many within-range captive populations of threatened taxa were initiated with no particular conservation goals in mind. The broad aim of this paper is to consider the value of such ‘happenstance’ populations: how should they be managed for maximal conservation impact, particularly if extra-range programs already exist?
One approach is to apply management techniques developed largely in the context of extra-range populations. In general, such management aims to maximize the probability of population persistence (Ballou et al., 1995). Demographically, the aim is often self-sustainability, in order to minimize the need to import wild-caught individuals (Ballou and Foose, 1996). This is achieved by controlling age/sex composition, population growth rate, and size, by manipulating parameters under managerial control (primarily breeding opportunities, acquisitions, and transfers), while taking into account less easily manipulated deterministic and stochastic factors (neonatal mortality, litter size, age at first reproduction, etc.; Foose and Ballou, 1988). At the same time, genetic management aims to maximize the retention of gene diversity, and thereby minimize inbreeding, in order to minimize inbreeding depression – and in the case of threatened taxa destined for reintroduction, also minimize adaptation to captivity and loss of evolutionary potential (Rodríguez-Clark, 1999).
However, while applying these techniques, it is important to ask: how might differences between within-range and extra-range populations be relevant? For example, is self-sustainability always a valid demographic goal? How can exchanges between within-and extra-range populations help or hinder management goals? The interaction of demographic and genetic forces, compounded with uncertainty about the future, may obscure the answers to these questions, and there are few published examples for guidance (e.g. Frantzen et al., 2001).
Here we help fill this gap by analyzing the case of captive Andean bears (Tremarctos ornatus) in Venezuela, to illustrate how within-range populations in general differ in their population management, and at the same time to address a priority identified by the action plan for T. ornatus: the integration of the Venezuelan captive population into the conservation goals for the species as a whole (Peyton, 1999). Our additional specific objectives for this study were therefore: (1) to determine the age structure and growth rate of the Venezuelan captive population, and the major factors influencing them; (2) to determine the genetic status of the population, in terms of inbreeding, kinship, and lineage distribution, relative to larger extra-range captive populations; (3) to determine the impact of past and possible future exchanges with other populations (in North America, Europe, Colombia, and the wild in Venezuela); and (4) to identify opportunities and constraints imposed by these characteristics, in order to facilitate setting realistic conservation goals for this species in captivity in Venezuela.
Section snippets
Wild Andean bears
The Andean bear (T. ornatus) is distributed throughout the Andes, from the Argentina/Bolivia border to Venezuela and the Darién region of Panama, principally between 1000 and 3600 m (Peyton, 1980, Mondolfi, 1989, Suárez, 1988). Current population estimates are based on extrapolations of data from other bear species, and suggest a total population size of ∼20,000, with the number in Venezuela less than 1000 (Peyton, 1999, Kattan et al., 2004).
The distribution and generalist diet of T. ornatus
Demographic analyses
The earliest record of an Andean bear in captivity in Venezuela is at the Zoológico Las Delicias, in Maracay in 1947 (Torres, 1991). Since then, 37 animals have been held in six Venezuelan institutions; one of these came from the North American population (195), and one from the European (397) (Fig. 1). As of August, 2005, the Venezuelan population consisted of 13 live animals in four institutions. Four of these were wild-caught males from Venezuela (orphaned cubs that hunters had either sold
Management implications for within-range populations
The present study highlights a central difference between within-range and extra-range captive populations of threatened taxa, which, if not taken into account in the application of standard management practices, could reduce the conservation value of within-range populations. This difference, in the probability of receiving recruits from the wild, has at least three general management implications. The first is the for importance of achieving demographic self-sustainability in within-range
Acknowledgements
We are grateful to many people for helping us locate information and references for the present work, including Andrés Bracho of the Red Tremarctos, Lydia Kolter and Jenny Van Leeuwen of EAZA, Caroline Lees of ARAZPA, and Mark Rosenthal Diana Weinhardt, Bob Wiese, and Kevin Willis of the AZA, as well as the dozens of individuals at Venezuelan and Colombian zoos who provided information about their specimens. We thank Laurie Bingaman-Lackey of ISIS and Robert C. Lacy of the Chicago Zoological
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