Abstract
BackgroundCaptive facilities such as zoos are uniquely instrumental in conservation efforts. To fulfill their potential as bastions for conservation, zoos must preserve captive populations as appropriate proxies for their wild conspecifics; doing so will help to promote successful reintroduction efforts. Morphological changes within captive populations may be detrimental to the fitness of individual animals because these changes can influence functionality; thus, it is imperative to understand the breadth and depth of morphological changes occurring in captive populations. Here, we conduct a meta-analysis of scientific literature reporting comparisons of cranial measures between captive and wild populations of mammals. We investigate the pervasiveness of cranial differences and whether cranial morphological changes are associated with ecological covariates specific to individual species, such as trophic level, dietary breadth, and home range size.ResultsCranial measures of skull length, skull width, and the ratio of skull length-to-width differed significantly between many captive and wild populations of mammals reported in the literature. Roughly half of captive populations differed from wild populations in at least one cranial measure, although the degree of changes varied. Carnivorous species with a limited dietary breadth displayed the most consistent changes associated with skull widening. Species with a more generalized diet displayed less morphological changes in captivity.ConclusionsWild and captive populations of mammals differed in cranial morphology, but the nature and magnitude of their cranial differences varied considerably across taxa. Although changes in cranial morphology occur in captivity, specific changes cannot be generalized for all captive mammal populations. The nature of cranial changes in captivity may be specific to particular taxonomic groups; thus, it may be possible to establish expectations across smaller taxonomic units, or even disparate groups that utilize their cranial morphology in a similar way. Given that morphological changes occurring in captive environments like zoos have the potential to limit reintroduction success, our results call for a critical evaluation of current captive husbandry practices to prevent unnecessary morphological changes.
Highlights
Captive facilities such as zoos are uniquely instrumental in conservation efforts
Literature search An exhaustive literature search with key words “zoo”, “captive”, “mammal”, “animal”, “skull”, “cranium”, “morphology”, and “size” revealed 515 potentially relevant publications examining differences in the cranial morphology of a population of captive mammals, of which 17 met the complete search criteria and included all applicable data required for inclusion in at least one of the size or shape-related trait analyses (Table 1)
Each of the meta-analyses were conducted as independent models with and without the inclusion of ecological covariates, which may influence the degree of morphological differentiation between captive populations and their wild counterparts
Summary
Captive facilities such as zoos are uniquely instrumental in conservation efforts. To fulfill their potential as bastions for conservation, zoos must preserve captive populations as appropriate proxies for their wild conspecifics; doing so will help to promote successful reintroduction efforts. We investigate the pervasiveness of cranial differences and whether cranial morphological changes are associated with ecological covariates specific to individual species, such as trophic level, dietary breadth, and home range size. Captive facilities such as zoos are important hubs for in situ and ex situ conservation where animals are often maintained in an effort to preserve species as faithful representatives of their wild counterparts so that captive populations can sustain the functionality and fitness of the species and perhaps, one day, be considered for reintroduction [39, 64, 75, 92, 117]. Morphological changes in captivity have been reported in the literature, the nature (i.e., directionality and magnitude) of cranial differences and the ecological factors that may drive these differences (i.e., ecological covariates) have remained unclear
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