Research Article
Patterns of mtDNA and microsatellite variation in an island and mainland population of guanacos in southern Chile
- Ronald J. Sarno, William L. Franklin, Stephen J. O'Brien, Warren E. Johnson
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- Published online by Cambridge University Press:
- 18 May 2001, pp. 93-101
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The archaeological record indicates that guanacos inhabited the Patagonia of Chile and Argentina about 13,600 years ago, but were unable to migrate further south owing to the presence of glacial and water barriers that covered much of southern South America including the island of Tierra del Fuego. As environmental and ecological conditions improved, guanacos, along with other large mammals including horses, colonized the area. As a result of continued world-wide glacial melting, ocean levels rose and Tierra del Fuego became isolated from the mainland approximately 8000 years ago. Although island populations generally exhibit lower levels of genetic variation than their counterpart mainland populations, it is difficult to predict how much less variation island populations will exhibit. An analysis of mitochondrial cytochrome b and ATPase-8 sequences and 15 nuclear microsatellite loci revealed that both populations retained appreciable genetic diversity. The island population, however, exhibited much less variation than the mainland population. Measures of genetic variation revealed modest, but significant genetic differentiation, consistent with separation of the two populations approximately 8000 years ago. The assessment of levels of genetic diversity and population differentiation among populations of the wild South American camelids is becoming increasingly important as interest mounts in their utilization as a renewable resource.
Reduced genetic variation in insular northern flying squirrels (Glaucomys sabrinus) along the North Pacific Coast
- Allison L. Bidlack, Joseph A. Cook
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- Published online by Cambridge University Press:
- 26 November 2001, pp. 283-290
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Nearshore oceanic archipelagos are natural laboratories that could provide valuable insight into the role of evolutionary processes such as founder effects and incipient speciation in biotic conservation. The Alexander Archipelago of Southeast Alaska is an example of such a complex, yet few biological investigations have been conducted. For the past 50 years, the region has experienced intense anthropogenic disturbances (particularly timber harvesting), causing habitat fragmentation and potential disruption of biotic communities. As part of a series of studies of mammals endemic to Southeast Alaska, we examined mitochondrial DNA sequences from 118 flying squirrels to investigate genetic diversity across Southeast Alaska. Mitochondrial sequence divergence corroborates the subspecific designation of the endemic Prince of Wales flying squirrel (Glaucomys sabrinus griseifrons). This island lineage exhibits severely reduced genetic variation and may be the result of an early Holocene founder event. Nearly all of the animals we examined on Prince of Wales Island and ten islands to the west had identical cytochrome b (52 of 53) and control region (21 of 21) sequences. In contrast, substantial polymorphism and little genetic structuring were found in comparable populations on the mainland of Southeast and Interior Alaska. Because flying squirrels in the Pacific Northwest are associated with old-growth forest, forest-use plans should aim to conserve this unique lineage of island squirrels.
A mitochondrial DNA control region phylogeny of the Cervinae: speciation in Cervus and implications for conservation
- Ettore Randi, Nadia Mucci, Françoise Claro-Hergueta, Amélie Bonnet, Emmanuel J. P. Douzery
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- Published online by Cambridge University Press:
- 30 March 2001, pp. 1-11
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Sequences from complete mitochondrial control regions (mtDNA CR) were used to infer phylogenetic relationships in 25 Cervinae taxa. Cervus splits into clades that are partially discordant with current species delimitations. Nominate Cervus elaphus includes two divergent clades that must be referred to as species elaphus (European elaphoid deer) and canadensis (Eurasian and North American wapitoid deer). Cervus nippon splits into Japanese and continental plus Taiwan sika. Père David's deer is nested within Cervus, suggesting that Elaphurus should be merged with Cervus. European and Persian fallow deer are genetically divergent and distinct species. Sequence length varied due to a CR-I insertion, tandemly repeated twice in rusa and sambar deer, sika and wapiti, and repeated up to six times in a clade of Japanese sika. Variable copy numbers of this repeat are also fixed in different sika subspecies, and could be used as a diagnostic marker for subspecies. Sequence variability at the mtDNA CR is informative for defining species and subspecies boundaries, and for locating the geographical origin of captive-reared stocks. Natural and farmed populations of some species have been deeply affected by human management and the conservation of deer populations would be aided by the appropriate identification of the different evolutionary and taxonomic units.
Water vole in the Scottish uplands: distribution patterns of disturbed and pristine populations ahead and behind the American mink invasion front
- Jon Aars, Xavier Lambin, Rebecca Denny, A. Cy Griffin
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- Published online by Cambridge University Press:
- 29 August 2001, pp. 187-194
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The invasion of Britain by American mink has had a catastrophic impact on water vole populations. We surveyed and live-trapped water voles over 2 years in eight c. 25 km2 blocks in the upland of Scotland behind and ahead of the mink invasion front. Water voles had a similar distribution in the Grampian Mountains of north-east Scotland, on the edge of the invasion front, and in the Assynt area of north-west Sutherland well beyond the front. Water voles occurred in small, discrete colonies. Median nearest-neighbour distance between colonies was 0.6-0.7 km in both areas. Colonies experienced a high degree of turnover with extinction and colonization being commonplace and only a fraction of suitable sites were occupied at a given time. High dispersal rates connecting numerous (> 30) colonies over large areas (> 25 km2) enable water voles to persist in such circumstances. Synchronized fluctuations in occupancy not caused by mink also occurred at the regional scales of the Grampian Mountains and Assynt areas. Localized mink invasions have fragmented a previously continuous metapopulation into smaller clusters and this may indirectly affect the likely persistence of water vole colonies not directly exposed to predation by mink.
Differences in the impacts of dams on the dynamics of salmon populations
- Phillip S. Levin, Nicholas Tolimieri
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- Published online by Cambridge University Press:
- 26 November 2001, pp. 291-299
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Modern concrete dams have devastated fish populations world-wide. However, dams vary greatly in how they are engineered and operated, and thus pose a range of threats to riverine fauna. Understanding the differences in the impacts of dams is critical for setting conservation priorities. We used a modified BACI (before-after-control-impact) sampling design as a means to quantify the effects of dams on spring/summer chinook salmon in two watersheds (Snake and Upper Columbia Rivers) of the Columbia River Basin, USA. The construction of four dams in the Columbia River Basin from 1966 to 1975 allowed us to test the hypothesis that the presence of these dams does not affect the abundance, survival and population growth of chinook salmon. In both the Snake and Upper Columbia Rivers, there was a significant decline from the period before dams were constructed (1959-65) to the period after dams were constructed (1980-90). In the Upper Columbia River, declines in productivity or population performance (measured as recruits per spawner or Ricker function residuals) were greater than in the control region. On the other hand, patterns of fish productivity in the Snake River were similar to those seen in the control region. The disparity between fates of Upper Columbia and Snake River populations points to the differences between regions in current efforts to reduce fish mortality associated with dams. Our analysis suggests that dams in the Upper Columbia River, but not Snake River, are a potential force preventing recovery of endangered salmon populations.
Parasite resistance and genetic variation in the endangered Gila topminnow
- Philip W. Hedrick, Timothy J. Kim, Karen M. Parker
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- Published online by Cambridge University Press:
- 18 May 2001, pp. 103-109
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In recent years, it has become apparent that introduced or novel pathogens or parasites may have a significant negative impact on endangered species. Here we examine experimentally the effect of an exotic fluke from guppies on the endangered Gila topminnow. Populations from different sources showed variable responses (although statistically non-significant) to the fluke and, in particular, the most homozygous population had high fluke infections and high subsequent mortality. Homozygotes for a MHC (major histocompatibility complex) gene had lower (although statistically non-significant) survival when infected with flukes than did heterozygotes. An inbred line from one of the populations had statistically significant lower survival and higher fluke infection than did a simultaneous outbred control. Overall, Gila topminnows appear quite susceptible to infection by the non-native fluke compared to other related species. In addition, it was shown that Gila topminnows can be infected by casual contact with infected guppies. This is another example of the potential detrimental effects of a parasite on an endangered species, a threat that may constitute a particular problem for species with low genetic variation, either in general, for important MHC genes, or for populations with a past history of inbreeding.
Effect of anthropogenic low-frequency noise on the foraging ecology of Balaenoptera whales
- Donald A. Croll, Christopher W. Clark, John Calambokidis, William T. Ellison, Bernie R. Tershy
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- Published online by Cambridge University Press:
- 30 March 2001, pp. 13-27
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The human contribution to ambient noise in the ocean has increased over the past 50 years, and is dominated by low-frequency (LF) sound (frequencies <1000 Hz) from shipping, oil and gas development, defence-related and research activities. Mysticete whales, including six endangered species, may be at risk from this noise pollution because all species produce and probably perceive low-frequency sound. We conducted a manipulative field experiment to test the effects of loud, LF noise on foraging fin blue (B. musculus) and (Balaenoptera physalus) whales off San Nicolas Island, California. Naive observers used a combination of attached tracking devices, ship-based surveys, aerial surveys, photo-identification and passive monitoring of vocal behaviour to examine the behaviour and distribution of whales when a loud LF source (US Navy SURTASS LFA) was and was not transmitting. During transmission, 12-30% of the estimated received levels of LFA of whales in the study area exceeded 140 dB re 1 μPa. However, whales continued to be seen foraging in the region. Overall, whale encounter rates and diving behaviour appeared to be more strongly linked to changes in prey abundance associated with oceanographic parameters than to LF sound transmissions. In some cases, whale vocal behaviour was significantly different between experimental and non-experimental periods. However, these differences were not consistent and did not appear to be related to LF sound transmissions. At the spatial and temporal scales examined, we found no obvious responses of whales to a loud, anthropogenic, LF sound. We suggest that the cumulative effects of anthropogenic LF noise over larger temporal and spatial scales than examined here may be a more important consideration for management agencies.
Conservation breeding for reintroductions: assessing survival in a captive flock of houbara bustards
- Yolanda van Heezik, Stéphane Ostrowski
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- Published online by Cambridge University Press:
- 29 August 2001, pp. 195-201
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Conservation breeding for reintroduction is becoming a popular option for restoring threatened populations. Whereas post-release results are widely reported in the conservation literature, little empirical information is presented on the captive populations that often make such releases possible, even though fecundity, fertility and survival rates can have an impact on the outcome and cost of wild population re-establishment. We present results of survival analyses carried out on a captive population of houbara bustards to determine peak periods of mortality, and by identifying sources of variations in mortality to recognize the potential impact of management practices on productivity. There were two main mortality peaks: during incubation (53% survival of fertile eggs), and by 6 months post-hatching (75% survival of hatchlings). Management-related variables influencing survival of eggs and chicks included the year when laid, the cohort of females laying them, and possibly sex. Most post-hatching deaths were due to trauma and infectious diseases. Trauma-related deaths usually follow collisions with cages, and imply selection for the captive environment, an undesirable trend in populations maintained for reintroductions. Reducing losses during incubation would have the largest impact on production of birds for reintroduction, enabling the release of more birds, and reducing the overall costs of the project.
Attracting endangered species to ‘safe’ habitats: responses of fairy terns to decoys
- D. S. Jeffries, D. H. Brunton
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- Published online by Cambridge University Press:
- 26 November 2001, pp. 301-305
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The New Zealand fairy tern (Sterna nereis davisae) is considered an endangered subspecies. The aims of this study were to quantify fairy tern responses to decoys and sound recordings and determine the viability of decoys as a technique for re-establishment of this species in protected habitat. Sixteen decoy trials were conducted in an area suitable for nesting from 9 September to 2 October 1999 at Papakanui Spit, New Zealand (36°26′S, 174°13′E). The decoy models were effective in attracting fairy terns to a specific area. There was a significant effect due to decoys with >80% of landing episodes occurring in the decoy plots. There was no effect due to individual plots. A planned contrast between decoys with and without recordings showed no significant difference. The behaviour of the fairy terns towards the decoys paralleled live tern interactions, e.g., erect postures, one aggressive response and a possible courtship feeding. Fairy terns appear to be less social than other members of the Laridae family (although their population numbers make the level of gregariousness difficult to determine). Despite low numbers, the response to the decoys was highly significant. We suggest that decoy techniques could be used as a simple and effective management tool for a wide range of group-living species. Such techniques will become particularly important as the availability of suitable habitat declines owing to anthropogenic effects. Finally, regardless of whether the attraction of fairy terns towards these decoys encourages residence and nesting in this area, the effectiveness of attracting terns to a specific location results in a safe and efficient means of trapping adults away from the nest and/or outside the breeding season.
Conservation genetics of the endangered Shenandoah salamander (Plethodon shenandoah, Plethodontidae)
- Daniel W. Carpenter, Robin E. Jung, Jack W. Sites, Jr
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- Published online by Cambridge University Press:
- 18 May 2001, pp. 111-119
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The Shenandoah salamander (Plethodon shenandoah) is restricted to three isolated talus outcrops in Shenandoah National Park, VA, USA and has one of the smallest ranges of any tetrapod vertebrate. This species was listed as endangered under the US Endangered Species Act in 1989 over concern that direct competition with the red-backed salamander (Plethodon cinereus), successional habitat changes, and human impacts may cause its decline and possible extinction. We address two issues herein: (1) whether extensive introgression (through long-term hybridization) is present between the two species and threatens the survival of P. shenandoah, and (2) the level of population structure within P. shenandoah. We provide evidence from mtDNA haplotypes that shows no genetic differentiation among the three isolates of P. shenandoah, suggesting that their fragmentation is a geologically recent event, and/or that the isolates are still connected by occasional gene flow. There is also no evidence for extensive introgression of alleles in either direction between P. cinereus and P. shenandoah, which suggests that P. shenandoah may not be in danger of being genetically swamped out through hybridization with P. cinereus.
Predator, prey and pathogen interactions in introduced snail populations
- J. Gerlach
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- Published online by Cambridge University Press:
- 29 August 2001, pp. 203-209
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The introduction of the carnivorous snail Euglandina rosea to Pacific islands by biological control programmes has had a devastating effect on native snail populations. In most areas the target species, Achatina fulica, has not been affected, although some unsubstantiated reports have led to E. rosea being viewed as an effective control agent. Data from recent laboratory and field studies of E. rosea were combined into a simple model of the interactions between populations of E. rosea and A. fulica and a disease agent. Predictions from the model correspond closely with field data from a number of sites. The model suggests that apparent reductions in A. fulica numbers following E. rosea introduction are the result of a combination of predation and disease effects, and that although the maximum population levels are reduced the population is stabilized at a relatively high level. The model predicts that both A. fulica and E. rosea populations will persist. Partulidae will decline following E. rosea invasion although Samoana spp. may persist at reduced densities. More effective control of A. fulica can be achieved through manual collecting. Control of E. rosea requires the imposition of a significant novel mortality factor.
Determining the species status of one of the world's rarest frogs: a conservation dilemma
- Andrew Holyoake, Bruce Waldman, Neil J. Gemmell
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- Published online by Cambridge University Press:
- 04 April 2001, pp. 29-35
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New Zealand's native frogs (genus Leiopelma) are considered to be archaic amphibians of exceptional scientific interest that appear to have remained virtually unchanged for 160-200 million years. They are among the rarest extant amphibians and are highly restricted in distribution, confined to isolated, highly disjunct, populations on the North Island and a few small offshore islands in Cook Strait. Previous investigations have suggested, based on patterns of allozyme variation, that the Stephens Island frog (Leiopelma hamiltoni) and Archey's frog (L. archeyi) are sister taxa to the exclusion of the Maud Island frog, a species in close geographical proximity to the Stephens Island frog and previously viewed as a population of this species. As a consequence of these data, a new species, L. pakeka, the Maud Island Frog, has been described. This new species definition has dramatically enhanced the conservation status of L. hamiltoni, of which there are probably fewer than 150 individuals. In this study we re-examine the systematics of the Leiopelmatidae using mtDNA sequence analyses. Partial 12 S ribosomal RNA and cytochrome b (Cyt b) gene sequences were obtained for 57 frogs from six populations representing all four extant Leiopelma species. Contrary to previous reports we find L. pakeka and L. hamiltoni to be monophyletic. The amount of variation evident between these present species (<1% for Cyt b) is comparable to that seen between populations of L. archeyi. Based on these data, classification of L. pakeka and L. hamiltoni as separate species appears to be unwarranted, but they may be sufficiently distinct to warrant classification as evolutionarily significant units.
Could translocation aid hen harrier conservation in the UK?
- Mark Watson, Simon Thirgood
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- Published online by Cambridge University Press:
- 04 April 2001, pp. 37-43
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Translocation is increasingly used in conservation to re-establish or augment populations of threatened species or to remove individual animals from areas of human-wildlife conflict. We assess the feasibility and utility of translocating hen harriers (Circus cyaneus) in the UK to enhance their distribution and abundance whilst simultaneously reducing the impact of harrier predation on red grouse (Lagopus lagopus scoticus) populations and shooting bags. Current knowledge of hen harrier feeding ecology, dispersal, survival and recruitment suggests that they would be suitable subjects for translocation with the aim of increasing their distribution in the UK. Assessment of habitat and food availability suggest that there are suitable recipient sites beyond the current range of the hen harrier in the UK. However, translocation would not be a sustainable method of reducing predation on grouse moors because it would have to continue indefinitely as long as grouse moors attracted harriers. Translocation of harriers to grouse moors where they have been locally extirpated would not be appropriate until levels of illegal control are reduced. Establishing new harrier populations through translocation away from grouse moors may become desirable if initiatives to reduce human-raptor conflicts on grouse moors are unsuccessful, or as an interim measure to accelerate the recovery of hen harriers in the UK.
Birds on edge: avian assemblages along forest-agricultural boundaries of central Victoria, Australia
- Monica J. Campi, Ralph MacNally
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- Published online by Cambridge University Press:
- 17 May 2001, pp. 121-132
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Habitat clearance generally produces fragmented landscapes. A major consequence is the creation of large amounts of new ‘edge habitat’, often of a kind not previously existing, such as abrupt forest- agricultural land interfaces. Much work from around the world suggests that proliferation of edge habitat seriously affects birds reliant on large forest blocks to persist, and the intrusion of edge specialists into areas they did not previously occupy. These processes often generate avifaunal gradients in which assemblages change from the interior to the edge. This effect is explored in the largest remnant block of box-ironbark forest of central Victoria, Australia (about 30,000 ha). Eight radially oriented survey lines were established around the periphery of the block. Along each survey line, five transects with long axes oriented parallel to the edge were positioned with midlines at 40 m, 160 m, 280 m and 400 m into the forest, and one transect 80 m into the agricultural land, yielding a total of 40 transects. Six identical transects were located deep within the forest (> 2 km). There was little evidence of a change in the avifauna from interior to edge, although mean richness was depressed in the edge habitats compared with forest interior transects. These results were essentially the same for ‘all species’ or ‘forest dependent’ species. Thus, there is little evidence for marked edge effects on the avifauna of these large forest blocks, although work in intermediate sized remnants (100-1000 ha) is needed to identify thresholds at which edge effects begin to be manifested.
Feral pigs facilitate hyperpredation by golden eagles and indirectly cause the decline of the island fox
- Gary W. Roemer, Timothy J. Coonan, David K. Garcelon, Jordi Bascompte, Lyndal Laughrin
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- Published online by Cambridge University Press:
- 26 November 2001, pp. 307-318
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Introduced species can compete with, prey upon or transmit disease to native forms, resulting in devastation of indigenous communities. A more subtle but equally severe effect of exotic species is as a supplemental food source for predators that allows them to increase in abundance and then overexploit native prey species. Here we show that the introduction of feral pigs (Sus scrofa) to the California Channel Islands has sustained an unnaturally large breeding population of golden eagles (Aquila chrysaetos), a native predator. The resulting increase in predation on the island fox (Urocyon littoralis) has caused the near extirpation of three subspecies of this endemic carnivore. Foxes evolved on the islands over the past 20,000 years, pigs were introduced in the 1850s and golden eagles, historically, were only transient visitors. Although these three species have been sympatric for the past 150 years, this predator-prey interaction is a recent phenomenon, occurring within the last decade. We hypothesize that this interaction ultimately stems from human-induced perturbations to the island, mainland and surrounding marine environments.
High effective inbreeding coefficients correlate with morphological abnormalities in populations of South Australian koalas (Phascolarctos cinereus)
- Ayesha M. Seymour, Margaret E. Montgomery, Brian H. Costello, Sonja Ihle, Greg Johnsson, Barbara St. John, David Taggart, Bronwyn A. Houlden
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- Published online by Cambridge University Press:
- 29 August 2001, pp. 211-219
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Koalas have undergone a series of sequential founding events on islands in south-eastern Australia in recent times. Populations in South Australia at the Eyre Peninsula and Mt Lofty Ranges were founded in the 1960s from a colony on Kangaroo Island. The Kangaroo Is. colony was derived from animals introduced to French Island from mainland Victoria over a century ago. In this study, we first use microsatellite markers to quantify levels of genetic variation within the South Australian koala populations and the relatively unperturbed Strzelecki Ranges population from mainland Victoria. This analysis revealed low levels of allelic diversity (1.7 ± 0.2 to 2.7 ± 0.5) and heterozygosity (0.208 ± 0.088 to 0.340 ± 0.110) in the three South Australian koala populations relative to the Strzelecki Ranges population, which has the highest levels of allelic diversity (4.7 ± 1.1) and heterozygosity (0.476 ± 0.122) in Victoria. Second, we measured the incidence of testicular aplasia, a unilateral or bilateral failure in testicular development, in the Eyre Peninsula and Kangaroo Is. populations, and in the ultimate founding population at French Is. Testicular aplasia was present at a frequency of 4.3% in French Is., 12.8% in Kangaroo Is. and 23.9% in the Eyre Peninsula, but was undetectable in the non-bottlenecked Pilliga State Forest population of New South Wales. The incidence of testicular aplasia correlated positively with effective inbreeding coefficients derived from heterozygosity values (0.13 ± 0.06 in the Pilliga State Forest, 0.57 ± 0.17 in French Is., 0.63 ± 0.12 on Kangaroo Is. and 0.77 ± 0.12 in the Eyre Peninsula), which may indicate inbreeding depression. These findings are of concern when evaluating the long-term conservation and viability of the South Australian koala populations, which may benefit from genetic augmentation in the future. Finally, unconfirmed reports suggested that animals from other states in Australia were introduced into the Mt Lofty Ranges population. Therefore, we quantified differentiation between the three South Australian populations and the Strzelecki Ranges and French Is. populations, based on microsatellites and mtDNA d-loop region variation. R-statistics and Goldstein's delta mu square distance revealed that differentiation at nuclear loci between populations paralleled known recent population history, except for the close relationship between Mt Lofty Ranges and French Is. This suggested a recent contribution to the Mt Lofty Ranges populations of animals derived from the French Is. translocation program. Furthermore, mtDNA d-loop analysis found no evidence of contributions to the gene pool from animals of New South Wales or Queensland stock, implying that the population was derived exclusively from Victorian stock.
Beyond eight forms of rarity: which species are threatened and which will be next?
- Lisa L. Manne, Stuart L. Pimm
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- Published online by Cambridge University Press:
- 29 August 2001, pp. 221-229
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We tabulate three measures of rarity: local abundance, breeding range size and elevational extent for the passerine birds of the New World. We determine what fraction of species is threatened with extinction within the combinations of these three measures. Species with smaller ranges, lower abundances and narrower elevational bands suffer higher levels of threat across lowland, montane and island species. For a given range size, lowland species suffer higher levels of threat than island or montane species. (This is counter to the intuition that island species — and those isolated on mountain tops — might be ecologically naïve.) When all three factors are considered together, there is only a slight tendency for lowland species to be disproportionately more threatened. Simply, island and montane species tend to be relatively common within their restricted ranges and their increased abundance reduces their likelihood of being threatened. Elevation is a consistent but relatively unimportant factor in determining threat; abundance and range size are much more important, and have an interactive effect on threatened status. We calculate the number of humans with which each species shares its breeding range, and find that this number does not aid in predicting threat status.
Inbreeding depression in captive bighorn sheep
- S. T. Kalinowski, P. W. Hedrick
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- Published online by Cambridge University Press:
- 26 November 2001, pp. 319-324
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We estimated the extent of inbreeding depression for juvenile survival in 589 captive-born bighorn sheep, and, unlike an earlier report, found no evidence of significant inbreeding depression. There did not appear to be any overall effect of year of birth, place of birth, subspecies, sex or ancestral inbreeding upon the viability of inbred animals as compared to non-inbred animals. However, for the first few years of data, there was lower survival for inbred than non-inbred offspring. After this period, there was an increase in the viability of inbred offspring, probably reflecting a general improvement in husbandry conditions in the zoos. It should be emphasized that the lack of significant inbreeding depression does not necessarily imply that there may not be inbreeding depression for other traits or in a less benign or more natural environment for juvenile viability.
Role of human population size in raising bird and mammal threat among nations
- Michael L. McKinney
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- 04 April 2001, pp. 45-57
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It is commonly held that species loss is linked to human population size but there are surprisingly few quantitative studies that measure the strength and nature of this linkage. In a study of about 150 nations, a highly significant positive relationship (P << 0.01) was found between population size and threat levels of birds and mammals. For continental nations, log population explains 16-33% of the variation in threat level among nations. The pattern of the continental population-threat correlation indicates that per capita human impacts are initially very high and asymptotically diminish with increasing population size. No population-threat correlation was found for island nations, since human impacts are apparently so catastrophic that human population size is largely irrelevant. Surprisingly, for both islands and continents, area does not affect the level of threat after human population size is accounted for. Thus, even on continents the harmful impacts of humans, for a given population size, are evidently so profound that no amount of added area provides compensatory refugia for native species. Major regional differences in levels of threat are shown, with nations in Asia and the Middle East having generally higher proportions of threatened species than nations in Africa. The causes of these differences are only partly related to population size. Other factors not related to population size are that Asian nations tend to have much higher rates of mammal over-harvesting and Middle Eastern nations tend to have statistically lower percentages of area set aside as preserves. Threat proportions are correlated between birds and mammals among nations implying that one group may be a proxy indicator of impacts on the other. The slope of this relationship indicates that mammals suffer more losses during initial human impacts but proportions of threatened birds increase more rapidly than mammals as human impacts become more widespread.
An assessment of annual mortality rates in adult-sized migrant houbara bustards (Chlamydotis [undulata] macqueenii)
- Olivier Combreau, Frédéric Launay, Mark Lawrence
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- Published online by Cambridge University Press:
- 18 May 2001, pp. 133-141
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Between the years 1994 and 2000, we assessed the mortality rate of adult-sized, migrant Asian houbara bustards (Chlamydotis [undulata] macqueenii) via banding and satellite tracking programmes. The birds were captured either on their breeding grounds in Kazakhstan (Taukum desert and Buzachi peninsula) and in China (Jungar basin) or on their wintering grounds in Pakistan (Cholistan desert) and in the United Arab Emirates (Baynunah area). For the banding programme, 104 houbara bustards were marked and statistical analysis was performed on the number of transmitters and rings returned by falconers. This allowed us to calculate a 0.045 (SD 0.061) annual mortality rate attributable to hunting activities. The tracking programme analysed the fate of 41 houbara bustards equipped with satellite transmitters (PTTs). Overall, the satellite-tracked birds were followed for 10,965 days and had travelled all over the distribution range of the species in Asia. The causes of mortality were assessed from the interpretation of the ARGOS data relayed by the sensors embarked on the PTTs. The annual mortality rate was derived from the calculation of the average finite daily survival rate using the Trent & Rongstad (1974) method. With this method, the overall annual mortality rate in adult-sized houbara bustards migrating through Asia was 0.283 (95%lcl 0.186-95%ucl 0.404). The hunting and poaching pressure could explain 73.5% of the observed mortality. The mortality rate during winter, when the houbara is under severe hunting pressure, was 11.2 times higher than during the breeding season. Houbara appear to be especially at risk in Pakistan, Afghanistan and Iran. A VORTEX simulation showed that under current hunting and poaching pressures, the probability of extinction of the houbara population modelled can be anticipated at 50 years with a 94% probability. The maximum sustainable yield was estimated at 7.2% of the adult-sized population whereas as much as 20.8% is currently taken. This work stresses the need for conservationists and Arab falconers to take appropriate concerted measures as soon as possible.