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The Paradox of Forest Fragmentation Genetics   总被引:5,自引:0,他引:5  
Abstract:  Theory predicts widespread loss of genetic diversity from drift and inbreeding in trees subjected to habitat fragmentation, yet empirical support of this theory is scarce. We argue that population genetics theory may be misapplied in light of ecological realities that, when recognized, require scrutiny of underlying evolutionary assumptions. One ecological reality is that fragment boundaries often do not represent boundaries for mating populations of trees that benefit from long-distance pollination, sometimes abetted by long-distance seed dispersal. Where fragments do not delineate populations, genetic theory of small populations does not apply. Even in spatially isolated populations, where genetic theory may eventually apply, evolutionary arguments assume that samples from fragmented populations represent trees that have had sufficient time to experience drift, inbreeding, and ultimately inbreeding depression, an unwarranted assumption where stands in fragments are living relicts of largely unrelated predisturbance populations. Genetic degradation may not be as important as ecological degradation for many decades following habitat fragmentation.  相似文献   

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Conservation Genetics in the Management of Desert Fishes   总被引:3,自引:0,他引:3  
Abstract: The status and security of fishes in North American deserts have steadily declined in this century due to man's activities in this naturally fragile region. We address genetic aspects of the population structure of desert fishes as applicable to conservation and recovery programs by developing two zoogeographic models of isolation and gene flow. In the Death Valley model populations are isolated, with no chance of natural gene flow among them. Genetic diversity within populations tends to be low, but genetic divergence among populations within a species is high. In the Stream Hierarchy model, a complicated hierarchical genetic structure exists and is a function of geographic proximity and connectivity of habitats. Within-habitat genetic diversity tends to be higher, and among-habitat differentiation lower, than in the Death Valley model. These two systems must be recognized as distinct and managed differently. We also suggest three areas of experimentation needed to better understand and manage genetic stocks of desert fishes: relationships between heterozygosity and fitness, experimental mixing of similar stocks to examine effects of increased heterozygosity, and analysis of the relative roles of genetic adaptation and phenotypic plasticity in local differentiation.  相似文献   

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Population Trends and the Koala Conservation Debate   总被引:1,自引:0,他引:1  
Abstract: A critical issue affecting the long-term management of koalas is their perceived conservation status. Koalas still occur in many areas throughout their historical range, but numbers of animals are estimated to vary from <100,000 to at least one order of magnitude higher. Complex factors limit free-ranging koala populations, including food tree preferences, history of disturbance, and Chlamydia infection, all of which make longer-term population trends of many populations difficult to predict. Lack of consensus regarding the size and viability of remaining populations and regarding the extent of and reasons for decline, overabundance or in some instances, hinders the conservation task. A reappraisal of population trends suggests that, notwithstanding localized management issues in Victoria and South Australia, overall the species is "vulnerable" on the basis of current World Conservation Union criteria. Recommendations for more effective conservation of koalas include (1) acknowledging the legitimacy of differing perspectives, (2) recognizing the uncertainty and assumptions inherent in population estimates and trends, (3) applying greater rigor and developing better standards for monitoring population trends, and (4) being cautious in assigning conservation status to national, state, and regional populations.  相似文献   

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Conservation Genetics of the Endangered Isle Royale Gray Wolf   总被引:5,自引:0,他引:5  
Abstract. The small group of wolves on Isle Royale has been studied for over three decades as a model of the relationship between large carnivores and their prey. During the last ten years the population declined from 50 individuals to as few as 12 individuals. The causes of this decline may be food shortages, disease, or reduced genetic variability. We address the issues of genetic variability and relationships of Isle Royale wolves using allozyme electrophoresis, mtDNA restriction-site analysis, and multilocus hypervariable minisatellite DNA analysis (genetic fingerprinting). Our results indicate that approximately 50% of the allozyme heterozygosity has been lost in the island population, a decline similar to that expected if no immigration had occurred from the mainland. The genetic fingerprinting data indicate that the seven sampled Isle Royale wolves are as similar as captive populations of siblings. Surprisingly, the Isle Royale wolves have an mDNA genotype that is very rare on the mainland, being found in only one of 144 mainland wolves ThFF suggests that the remaining Isle Royale wolves areprobably derived from a single female founder  相似文献   

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Abstract:  Ideally, science should inform policy development in all areas of human endeavor. Nowhere is this truer than in the case of human land use and our impact on the natural environment. Unfortunately, little recent science has percolated into policy guidelines for tropical forest management in areas facing serious threats. To help science inform policy we present six guidelines, which have been empirically proven important, for the management of fragmented landscapes: (1) incorporate protection measures as part of development projects; (2) protect large areas and prevent the fragmentation of currently contiguous large patches of forest; (3) manage forest edges when creating forest patches; (4) protect gallery forests along waterways to connect isolated forest patches; (5) control the use of fire and the introduction of exotic plant species and limit the use of toxic chemicals in areas near forest patches; and (6) promote reforestation and forest cover in critical areas of landscapes. Straightforward linkages between science and policy formulation can result in simple, yet powerful, changes in land-use patterns and have a concurrent positive effect on biodiversity and natural resources.  相似文献   

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Abstract: The California Gnatcatcher (   Polioptila californica ) has become a flagship species in the dispute over development of southern California's unique coastal sage scrub habitat, a fragile, geographically restricted ecosystem with high endemism. One aspect of the controversy concerns the status of the subspecies of this bird in southern California coastal sage scrub that is currently listed as threatened under the U.S. Endangered Species Act. To investigate the recent population history of this species and the genetic distinctiveness of subspecies and to inform conservation planning, we used direct sequencing of mitochondrial DNA (mtDNA) for 64 individuals from 13 samples taken throughout the species' range. We found that coastal sage scrub populations of California Gnatcatchers are not genetically distinct from populations in Baja California, which are dense and continuously distributed throughout the peninsula. Rather, mtDNA sequences from this species contain the signatures of population growth and support a hypothesis of recent expansion of populations from a southern Baja California refugium northward into the southern coastal regions of California. During this expansion, stochastic events led to a reduction in genetic variation in the newly occupied range. Thus, preservation of coastal sage scrub cannot be linked to maintaining the genetic diversity of northern gnatcatcher populations, despite previous recognition of subspecies. Our study suggests that not all currently recognized subspecies are equivalent to evolutionarily significant units and illustrates the danger of focusing conservation efforts for threatened habitats on a single species.  相似文献   

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The gray wolf is a large, highly mobile predator whose original geographic range included most of the Northern Hemisphere. High rates of genetic exchange probably characterized even distantly-separated populations in the past, but recent population declines and habitat fragmentation have isolated previously contiguous populations, especially in the Old World. We examine mitochondrial DNA (mtDNA) variability among twenty-six populations of wolves from throughout their geographic range. We find eighteen mtDNA genotypes in gray wolves, seven of these are derived from hybridization with coyotes, four are confined to the New World, six are confined to the Old World and one is shared by both areas. Genetic differentiation among wolf populations is significant but small in magnitude. In the Old World, most localities have a single unique genotype, whereas in the New World several genotypes occur at most localities and three of the five genotypes are nearly ubiquitous. The pattern of genetic differentiation in the gray wolf contrasts with that of another large, highly vagile canid, the coyote, in which genetic differentiation among populations is not significant even among widely separated localities. We suggest that the difference between these two species reflects the rapid, recent increase in coyote numbers and expansion of their geographic range, and the coincident decline in gray wolf populations. Apparent genetic differences among extant wolf populations may be a recent phenomenon reflecting population declines and habitat fragmentation rather than a long history of genetic isolation.  相似文献   

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Freshwater bivalves are among the most endangered groups of organisms in North America. Efforts to protect the declining mussel fauna are confounded by ambiguities associated with recognition of distinct evolutionary entities or species. This, in part, is due to the paucity of reliable morphological characters for differentiating taxa. We have employed allozymes and DNA sequence data to search for diagnosably distinct evolutionary entities within two problematic genera of unionid mussels, Amblema and Megalonaias. Within the genus Amblema three species are recognized based on our DNA sequence data for the mitochondrial 16S rRNA and allozyme data (Amblema neislerii, A. plicata, and A. elliotti). Only one taxonomically distinct entity is recognized within the genus Megalonaias—M. nervosa. Megalonaias boykiniana of the Apalachicolan Region is not diagnosable and does not warrant specific taxonomic status. Interestingly, Megalonaias from west of the Mississippi River, including the Mississippi, exhibited an allozyme and mtDNA haplotype frequency shift suggestive of an east-west dichotomy. The results of this study eliminate one subspecies of Amblema and increase the range of A. plicata. This should not affect the conservation status of "currently stable" assigned to A. plicata by Williams et al. (1993). The conservation status of A. elliotti needs to be reexamined because its distribution appears to be limited to the Coosa River System in Alabama and Georgia.  相似文献   

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Conservation Genetics of the Common Snapping Turtle (Chelydra serpentina)   总被引:2,自引:0,他引:2  
Previous studies of relationships among the subspecies of snapping turtles ( Chelydra serpentina } based on morphological and osteological characters have been inconclusive. We investigated relationships among the four currently recognized subspecies using restriction endonuclease fragment patterns of mtDNA and protein electrophoresis. Sixteen six-based recognizing restriction endonucleases yielded 90 variable fragments that define 11 different haplotypes. Individuals of the two North American subspecies, C. s. osceola and C. s. serpentina , are closely related, differing by a maximum of 0.5% sequence divergence. The Central American subspecies, C. s. rossignonii and C. s. acutirostris , are more distinct, both from each other (a minimum of 1.7% sequence divergence) and from the North American samples (an average of 4.45% sequence divergence). The degree of allozymic variation among the four subspecies was found to be limited and could not be used to diagnose the four recognized subspecies. The mtDNA data presented here support the species-level distinctness of C. s. rossignonii and C. s. acutirostris from each other and from a C. s serpentina-C. s. osceola complex. The recognition of three distinctive groups of Chelydra rather than one widespread polytypic species has important conservation implications because it focuses attention on the poorly known middle and South American species.  相似文献   

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The Population Dynamics and Conservation of Primate Populations   总被引:4,自引:0,他引:4  
Abstract: Primates are among the most threatened taxa, with more than half of all species in jeopardy. In this paper we develop population models to use the kind of data on wild primates that primatologists actually collect. Our survey of recentprimate journals suggests that the average field study uses 1.5 years of data from 50 animals The models are based on the simple Leslie-Lefkovitch matrix. They suggest a simple method that allows assessment from a few years'data, of whether a population is collapsing and requires intervention To a good approximation, populations will collapse when adult survival, per inter-birth interval, is less than 70 percent.
Modifications of the basic model incorporate more realistic assumptions about social organization and densitydependent resource limitation. These allow us to identify population densities at which potential Allee effects operate, and permit more precise estimates of the minimum population sizes and compositions required for successful reintroductions to the wild The most important result is that populations of primates that live in small family groups may be more prone to "demographic" extinction than are more promiscuous species that live in more extended groups.  相似文献   

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