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.

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.

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.

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.

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.

Elephant social structure is matrilineal, with family units composed only of maternally related females and their juvenile offspring, while adult males are mostly solitary and seldom congregate into bachelor herds. In such a social structure, we expect females in the same family unit to have the same mitochondrial genome, which may or may not differ from that of individuals in other family units in the population. Such social structuring also results in the mating males and females having different allele frequencies at nuclear microsatellite loci. This is manifested as an excess of heterozygotes relative to the expected Hardy-Weinberg proportions, a phenomenon which maintains genetic variation within the population by minimizing inbreeding. We analyzed mitochondrial nucleotide sequences and allele frequencies at four microsatellite loci in nine family units of the African elephant (Loxodonta africana) in Queen Elizabeth National Park and found more than one distinct mitochondrial genotype in three of the family units and no significant excess heterozygosity at microsatellite loci in eight of the families. We interpreted these findings as an indication of a breakdown in social structure of this population caused by social stress due to factors like excessive poaching that has taken place in this national park over the last three decades. Ecological and management implications of these findings for elephant populations are discussed.

Extirpated from the wild in 1972 by overhunting, Arabian oryx (Oryx leucoryx) were re-introduced in Saudi Arabia in March 1990; 17 oryx were released into Mahazat as-Sayd, a 2244 km2 fenced reserve in west-central Arabia, which lies at the periphery of their historical home range. The population has increased to 346 animals. The National Commission for Wildlife Conservation and Development, and those that manage the herd, have recently asked, ‘What is the optimal management strategy to assure long-term persistence of the species, given the absence of immigration and predation?’ Food resources, determinants of rates of mortality and birth, covary with unpredictable rainfall in Mahazat as-Sayd. Using data-driven assumptions, we developed a computer model that evaluated the probability of extinction (Pex) under various management strategies: no intervention, removing a fixed number of animals each year, removing a fixed percentage of animals each year, and removing all individuals above a threshold. In addition, we explored the probability that oryx populations would decline below two thresholds, called the probability of quasi-extinction (Pq-ex) under various management schemes. Our analyses suggested that, without intervention, the oryx population had a high Pex. Removing 15% of the current population provided a low Pex, but this method also produced high values for Pq-ex and, as a by-product, wide fluctuations in population size (N). Although it required an assessment of both N and carrying capacity (K), the most successful management plan consisted of removing all oryx above 70% of K. Adoption of this plan resulted in low Pex, low Pq-ex, and smaller fluctuations in N. Our study may provide a useful model for evaluating management plans for a variety of threatened animal populations in desert ecosystems.

Efforts to ameliorate the negative effects of introduced predators on native species depend on a clear understanding of the complex interactions between predator and prey. We illustrate the necessity of considering size variation of predators and prey and antipredator responses of prey, using a case study of an endangered fish, June sucker (Chasmistes liorus) and an introduced predator, white bass (Morone chrysops). Using a mathematical model, we assessed vulnerability of young June suckers to predation by a growing cohort of white bass. Additionally, we experimentally evaluated whether young white bass selectively occupy vegetated habitats (in contrast to adults) similar to those occupied by young June suckers. June suckers are most vulnerable to young white bass immediately after they hatch and vulnerability declines thereafter. They are vulnerable for some period of time under all combinations of predator and prey growth rates. Young white bass selected vegetated habitats, and this response was increased in the presence of adult white bass. These data suggest that young white bass may be a significant source of mortality for small June suckers, contrary to previous assumptions. Results of this study inform conservation actions designed to decrease the effect of predation on small June suckers, such as potential effects of adding vegetated refuge habitats, possible effects of manipulation of spawning time, and the design of predator-free grow-out areas.

We present results from a study of genetic variation in Utah's cougar population. Estimates were based on data for 50 animals at nine microsatellite loci with five individuals sampled for each of ten management units throughout Utah. Levels of variation were moderate (average genetic diversity across populations was estimated to be 0.4687 for all 50 individuals), and comparable with other large mammals. But this level of variation for the microsatellite loci translated into an inbreeding effective population size of only 571 animals, much lower than the current estimates of census sizes of around 2000-3000. A lack of differentiation among the sampled populations across Utah (average Nem = 6.2) indicates that gene flow occurs over a large area. Since cougars are capable of movement beyond the Utah state borders (and certainly across management units), a better understanding of migration rates and patterns of dispersal will be achieved by sampling a much larger geographic region incorporating much of the western USA. Successful management and conservation of this species will then require a far more integrated approach, involving agencies across a number of states, as opposed to current management practices involving individual units within states.

Managers trying to preserve populations of endangered carnivores are often forced to choose between restoring habitat to allow larger breeding populations or reduce risks of mortality to increase survival rates. We modelled the viability of a metapopulation of the Iberian lynx (Lynx pardinus) under several scenarios (habitat restoration, anti-poaching, reduction in road kills) in a real landscape to evaluate their relative effects. Increasing carrying capacity was highly effective when performed on the local populations that acted as sources but had no effect when carried out in the sinks. Realistic scenarios consisting of partial removal of the human-related mortality (assuming additive effects of causes) predicted high risk of extinction. When combined, the effects of both management options are highly dependent on where they are carried out. If the sinks are the only targets of carrying capacity enlargement, a complete removal of human-caused mortality is required, whereas increases in the carrying capacity of sources are always effective. The metapopulation risk of extinction decreases dramatically (from 45.5% to 2.1% in 100) if connectivity among source populations can be improved. According to our work, only a detailed knowledge of the spatial and demographic structure of the populations, combined with simulations of realistic situations, can help managers to select the a priori optimal strategy, which probably combines different management options.

The Cape Sable seaside sparrow is a Federally listed endangered species endemic to south Florida's Everglades. It nests near the ground in seasonally dry prairies. Consequently, the timing and depth of seasonal water flows determine its fate. With water management plans the central focus of Everglades' restoration schemes, the demography of this bird becomes central to hydrologic planning. In order to understand how its demography influences restoration options, we calculated survivorship, fecundity and dispersal within three of the sparrow's six populations. Nearly 40% of adult sparrows die from year to year. Sparrows can produce up to four broods per breeding season, and typically produce two (March to August). Females lay an average of three eggs per nest, two of which usually hatch. The success of these nests varies among populations such that nests in population E are more than four times as likely to fledge young as nests within population A. Nest success within population B is 26% early in the breeding season, but drops to 9% after the onset of summer rains in early June. Nests are built 16 to 21 cm from the soil surface making them vulnerable to water depths that exceed these values. Based on observations of marked individuals, sparrows generally remain within a 1 km area centred on their breeding grounds. We have never observed immigration between populations. A simple demographic model demonstrates that breeding success and duration appear to constrain sparrow population growth more than other demographic parameters. Maintaining suitable breeding conditions restricts water management options to those that will restore hydrological conditions to their original patterns.