bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conservation of the greater glider (Petauroides volans) in remnant native vegetation within exotic plantation forest
Authors: McCarthy Michael A. , Lindenmayer David B. 
Published: February 2006

AbstractA field‐validated metapopulation model of patch occupancy was used to examine the persistence of greater gliders (Petauroides volans) in patches of remnant native eucalypt forest in south‐eastern Australia. The model was based on a system of eucalypt patches embedded within a plantation forest of exotic radiata pine (Pinus radiata) at Buccleuch State Forest, New South Wales. The probability of local extinction in occupied patches was a function of patch size. The probability of colonization of empty patches was a function of the size and proximity of occupied patches. The results of the simulations suggested that suitable habitat should occupy approximately 10% (or more) of the total landscape to ensure the persistence of greater gliders. Rates of patch occupancy were maximized when suitable habitat was clustered into larger patches. Patches <3 ha in area were predicted to be of limited value as habitat for greater gliders. The predictions of the model are consistent with the observed persistence of greater gliders in the eucalypt patch system. The system of unlogged eucalypt patches within the pine plantation is a useful model of a network of small to medium‐sized conservation reserves. Principles of reserve design can have value even in somewhat degraded and highly modified landscapes. The results demonstrate that reserved patches of native forest embedded within intensively logged forest can have significant conservation value, with important implications for the design and establishment of new softwood plantations.
Deforestation and bird extinctions in the Atlantic forest
Authors: Brooks Thomas , Tobias Joe , Balmford Andrew 
Published: February 2006

AbstractThe Atlantic forests of South America hold a great concentration of biodiversity, but most of this habitat has been destroyed. We therefore expect many species to become extinct, and yet no bird extinctions have conclusively been recorded. There could be three explanations for this. First, birds may be able to adapt to deforested landscapes. Second, many species may have become extinct before they were known to science. Third, there may be a time‐lag following deforestation before extinction occurs. We present the most complete list to date of the endemic birds of the Atlantic forests (124 forest‐dependent species), and then use the species–area relationship to predict how many species we expect to become extinct through deforestation (51 species i.e. 41%). We also count how many Atlantic forest endemic birds are independently considered ‘threatened’ with ‘a high risk of extinction in the wild in the medium‐term future’ (45 species i.e. 36%). We compare these totals and find that they are similar, suggesting that there is a time‐lag between deforestation and extinction. We go on to test the robustness of this result by varying the parameters used to make our predictions. The only parameter that varies enough to substantially weaken predictions based on deforestation is the habitat classification of Atlantic ‘forest’ birds. If we include species that can survive in secondary and non‐forest habitats then, unsurprisingly, we find that deforestation overestimates threat. Overall, not only does deforestation accurately predict threat to Atlantic forest endemic birds, but this result is robust enough to accommodate considerable variability within our data.
Assessing population structure at high levels of differentiation: microsatellite comparisons of bighorn sheep and large carnivores
Authors: Forbes Stephen H. , Hogg John T. 
Published: February 2006

AbstractUse of a new class of molecular marker for evolutionary or conservation studies may promise improved information, but it may also call for reassessment of analytical methods and empirical limitations. We used DNA microsatellites to study population structure in Rocky Mountain bighorn sheep (Ovis canadensis canadensis) and to test the ability of microsatellites to distinguish bighorn subspecies. Genetic differentiation between bighorn populations was dramatically greater than in comparable studies of brown bears and grey wolves, and these species differences are consistent with known differences in habitat use and dispersal. In bighorn, however, statistical limitations make it difficult to distinguish between moderately and highly divergent populations. As a result, only gene flow estimates greater than about one migrant per generation (OMPG) are informative about true population relatedness. In bears and wolves, apparent differentiation is so low that migration estimates are greater than OMPG continent‐wide, but factors other than high gene flow may contribute to these patterns. Despite analytical difficulties at large geographical scales and large genetic divergences, microsatellite data assist management by characterizing historical rates and patterns of dispersal on smaller scales, and by detecting population bottlenecks and regions of particularly high or low historical gene flow.
Do population size bottlenecks reduce evolutionary potential?
Authors: Frankham Richard , Lees Kelly , Montgomery Margaret E. , England Phillip R. , Lowe Edwin H. , Briscoe David A. 
Published: February 2006

AbstractSingle locus neutralist models predict that population size bottlenecks will reduce genetic variation and increase inbreeding, thereby reducing evolutionary potential. However, experimental evaluations of the effects of bottlenecks on quantitative genetic variation do not always follow predictions, especially for characters related to reproductive fitness. Populations of Drosophila melanogaster were subjected to population bottlenecks of a single pair for one or three generations, and their ability to tolerate increasing concentrations of NaCl was compared with those of their outbred base populations, and related highly inbred lines. Bottlenecked populations became extinct at significantly lower concentrations of NaCl than their non‐bottlenecked base populations. Population bottlenecks should be avoided in managing species of conservation concern.
Reproductive seasonality in the female scimitar‐horned oryx (Oryx dammah)
Authors: Morrow C. J. , Wildt D. E. , Monfort S. L. 
Published: February 2006

AbstractFaecal oestrogen and progestin analyses were used to assess ovarian activity in non‐pregnant scimitar‐horned oryx (Oryx dammah) during a 13‐month interval. Mean (± SE) luteal phase, interluteal phase and oestrous cycle duration were 18.8 (± 0.5), 5.1 (± 0.2) and 23.8 (± 1.3) days, respectively. All females exhibited a synchronized anovulatory period that ranged from 36–95 days during spring. Short ovarian cycles (10.6 (± 0.8) days) were observed intermittently throughout the year and before the spontaneous resumption of oestrous cyclicity. Periovulatory peaks in oestrogen concentrations were detected for 42.5% (31/73) of ovarian cycles. A parallel analysis of reproductive data from the North American studbook (1985–1994) revealed that captive‐held scimitar‐horned oryx gave birth throughout the year. Sex ratio at birth was male‐biased (54.4%), and 19.1% of all calves failed to survive to 6 months of age (220 out of 1149 births). Only 0.7% of births resulted in twins. Median interbirth interval was 277 days, and 75% of these intervals were less than 332 days. Interbirth interval was extended (P < 0.05) if parturition occurred from January through May. In summary, the scimitar‐horned oryx is a seasonally polyoestrous species that experiences a distinct anovulatory period during spring in north‐east America.
Reintroduction programmes: genetic trade‐offs for populations
Authors: Earnhardt Joanne M. 
Published: February 2006

AbstractReintroductions of captive‐managed animals are a vital tool for the conservation of populations and species extinct in the wild. Because genetic diversity may impact population persistence, the genetic composition of reintroduced and captive populations is critical. For captive‐managed species with known pedigrees, individual animals can be selected to create reintroduced populations with specific genetic compositions. Five genetic and demographic strategies for selecting animals were tested on four species. Selection strategies were based on criteria identified in field and theoretical studies. Simulated reintroductions of animals from captive‐breeding programmes created a genetic conflict. Among the different strategies, increases in the genetic diversity of one subpopulation were negatively correlated with changes in the genetic diversity of the other subpopulation. For example, the release of genetically over‐represented animals was the most beneficial strategy for a captive‐breeding programme, but provided the least genetic diversity for the reintroduced population. However, gains and losses in genetic diversity between populations varied with different selection criteria and different population structures. Because captive‐breeding histories vary for each species, changes in genetic composition cannot be accurately predicted and no one strategy is universally optimal. Thus, genetic trade‐offs must be assessed for each population relative to specific programme goals.
Culling and the dynamics of the Kruger National Park African elephant population
Authors: van Aarde Rudi , Whyte Ian , Pimm Stuart 
Published: February 2006

AbstractSouth Africa's National Parks Board has opted to control African elephants (Loxodonta africana) through culling in the Kruger National Park (KNP). Killing elephants is highly controversial. The Board must balance this controversy against the probable destruction of vegetation and the consequent depletion of biological diversity that high elephant densities cause. Annual aerial counts provided the population estimates on which the culling quotas were based. For management purposes, the elephant population of the Park is divided into four sub‐populations. From 1984 to 1994, the annual quota was usually taken from only one of these sub‐populations during a given year. This resulted in 3 to 5 years elapsing between culls in each sub‐population. We investigated the year‐to‐year changes in densities after culling. These changes were density dependent. Density dependence implies that immediate culls following estimated high densities may be premature. If left alone, the densities would decline naturally. Indeed, culling becomes self‐reinforcing as it moves population densities towards the level where reproduction is greatest. Data confirm this intuition: at densities greater than 0.37 elephants/km2 elephant numbers generally declined without culling. Many culls were unnecessary. Culling, as implemented in the past, may have had consequences for elephants and their habitat that were different to those expected from a mere reduction in their numbers. Densities in the year immediately after a cull tended to decline – not increase as would be expected from density dependence alone. Undoubtedly, this unexpected decline was the consequence of disturbance and subsequent emigration. In following years, the densities rose as animals moved back into the sub‐population. A management programme where culling will be instituted only when densities exceed 0.37 elephants/km2 in selected regions in the park for at least 1 year, may be more acceptable than the programme used up to 1995. However, we do not know if the vegetation of KNP can withstand the resulting episodic high densities. With densities presently exceeding the cut‐off values calculated for both the south and the northern management regions vegetation changes there need to be monitored.
Effects of southern flying squirrels Glaucomys volans on red‐cockaded woodpecker Picoides borealis reproductive success
Authors: Laves Kevin S. , Loeb Susan C. 
Published: February 2006

AbstractAnecdotal data gathered from many populations suggest that southern flying squirrel (SFS, Glaucomys volans) use of the endangered red‐cockaded woodpecker's (RCW, Picoides borealis) nest and roost cavities may negatively affect RCW populations. We conducted a controlled experiment to determine the effects of SFSs on RCW reproductive success. During the 1994 and 1995 breeding seasons, SFSs were removed from 30 RCW clusters and 32 clusters served as controls. SFSs were the most frequently encountered occupants of RCW cavities and used 20–33% of RCW cavities in control and treatment clusters over both years. Treatment groups produced significantly more successful nests (≥ 1 fledgling) than control groups in 1994. In 1995 however, there was no difference in the number of successful nests. In both years, RCW groups nesting in treatment clusters produced significantly more fledglings than groups in control clusters in each of four experimental areas, averaging approximately 0.7 additional fledglings per nesting group. Loss of entire clutches or broods, possibly as a result of predation or abandonment, was a major factor limiting reproduction in control groups in 1994. In contrast, differences in partial brood loss appeared to be the cause of differential fledging success in 1995. Usurpation of RCW roost cavities by SFSs may have placed greater energetic demands on RCWs for cavity defence or thermoregulation, thus reducing energy available for reproduction. Our results show that SFS use of RCW cavities during the breeding season has a significant impact on RCWs and that management of RCW populations should include activities that either minimize SFS populations in RCW clusters or limit access of SFSs to RCW cavities.
Conservation monitoring: estimating mammal densities in woodland habitats
Authors: Caro T. M. 
Published: February 2006

AbstractConservation and ecological monitoring programmes often estimate animal densities over time, but in wooded and forested areas practical techniques are still poorly developed. Here I have examined five simple methods of deriving densities of large and medium‐sized mammals using line transects driven through miombo woodland habitat in Africa. These methods calculated area by dividing the number of individuals seen by (i) an average of each species' sighting distances, (ii) a fixed 200 m belt width, (iii) the area visible from the centre of the transect, (iv) visible area weighted by species' vegetation preferences, and (v) by dividing the number of groups seen by area visible from the transect. Individual‐based methods produced quite divergent estimates of species' densities and overall biomass with belt transects giving the lowest values. The group method and corresponding individual‐based method gave similar values, however. Most of these calculations yielded considerably higher density estimates than aerial surveys conducted in the same area over a similar time period. Sightings of species were not distributed evenly across vegetation types although the majority of mammal species were observed more often in open habitat. These findings indicate that ground‐based conservation monitoring programmes should set transects through several vegetation types, restrict comparisons to those studies that use the same methodology, and refrain from comparing ground and aerial surveys.
Effective population sizes: missing measures and missing concepts
Authors: Crandall Keith A. , Posada David , Vasco Dan 
Published: February 2006

AbstractGenetic diversity within a population is a critical parameter for conservation biologists to assess. One approach for examining genetic diversity is through the determination of effective population sizes. Animal Conservation recently published a review of genetic approaches for estimating effective population sizes. We felt this review was incomplete both methodologically and conceptually. Here we extend that review to include coalescent‐based approaches for estimating effective population sizes. We then discuss different kinds of effective population sizes, including inbreeding, variance and eigenvalue effective sizes.
Experimental tests of minimum viable population size
Authors: Reed David H. , Bryant Edwin H. 
Published: February 2006

AbstractFitness and rates of extinction were compared among populations of the housefly, Musca domestica L., kept either at constant effective sizes of 50, 500 or 1500 or passed through extreme founder events reducing effective size to 5. Populations were maintained for 24 generations, which for small to medium‐sized mammals would be less than the 200 years suggested by Souléet al. (1986) as necessary for maintaining viable populations of endangered species. The results demonstrate that effective population sizes have to be greater than the 50 individuals suggested by Franklin (1980) to retain fitness and escape extinction, even in the short term. In contrast to populations of constant size that exhibited monotonic decreases in fitness through time, populations established with few founders rebounded from initial inbreeding depression. However, they were less adaptable to environmental stress than constant size populations, suggesting that populations founded with few numbers may do well within a single environment but may do far less well if they are reintroduced to natural environments or exposed to rapid environmental changes.
Taxonomic homogenization of the global avifauna
Authors: Lockwood Julie L. , Brooks Thomas M. , Mckinney Michael L. 
Published: February 2006

AbstractBiotic homogenization is seen as the consequence of preferential loss of native species followed by ecological replacement with widespread exotics. Homogenization is not random in its effects on higher taxa. Using Monte Carlo simulations (rather than binomial statistics) we find taxonomic patterns in the risk of extinction and probability of successful introduction among birds. Sixteen avian families selectively contain extinct or threatened birds. Eight avian families selectively contain successfully introduced birds. Eight of these 24 taxonomically selected families have not been identified in previous studies, presumably because they are species‐poor. The 22 living taxonomically selected families are classified into four homogenization categories. These categories reflect how extinction and invasion are combining in their effects at the family level. Range size, as indexed by island endemism, and human influence are the primary forces driving taxonomic homogenization patterns among birds. There is no evidence that evolutionary age influences homogenization patterns. Phylogenetic comparative analyses, which explicitly recognize the role of human influence, are needed to elucidate more detailed ecological correlates to homogenization trends.
Minimum viable metapopulation size of a beetle, Osmoderma eremita, living in tree hollows
Authors: Ranius Thomas 
Published: February 2006

Abstract Osmoderma eremita, an endangered beetle restricted to hollow trees, was surveyed in stands of different size, isolation and physical characteristics in an area in south‐eastern Sweden. To infer habitat occupancy the presence/absence of fragments of adult body parts was used. Mark–release–recapture of adults with pitfall traps set in tree hollows was carried out to estimate local population size. Habitat occupancy/tree was higher in larger stands than in smaller stands, but there was no correlation between occupancy/stand and isolation of stands. This suggests dispersal is important in the population processes within stands, but not between stands. Osmoderma eremita was found in most of the larger stands and this probably mirrors the fact that the density of old‐growth oaks has been much higher in the area than today. Habitat fragmentation over the last two centuries has disrupted the network of habitat patches, thus preventing dispersal into smaller, younger stands. A minimum number of suitable trees aggregated in stands seems to be necessary to provide long‐term viability of local O. eremita populations. To preserve viable O. eremita populations, it is therefore necessary to increase size and connectivity of stands with hollow trees.
Incorporating land cover information into regional biodiversity assessments in South Africa
Authors: Wessels K. J. , Reyers B. , Van Jaarsveld A. S. 
Published: February 2006

AbstractAnthropogenic natural habitat transformation presents the single most important threat to global biodiversity. Land cover data, based on Landsat Thematic Mapper (TM) imagery, were used to derive land use information for the Gauteng, Mpumalanga and Northern provinces of South Africa. The assessment integrated land use data with species presence data (15 × 15 minute grid cell resolution) for butterflies, mammals, birds and endemic vascular plants. The objectives of the present study were: (1) to identify areas at a regional scale where there is a possible conflict between biodiversity conservation interests and current land uses; (2) to investigate the influence of incorporating a land use constraint (LUC) into a conservation area selection algorithm, while taking cognizance of the existing reserve system; (3) to investigate the circumstances of species recorded within these conflict areas. Many grid cells identified as species richness hotspots, rarity hotspots or as part of the complementary network selected by the unconstrained algorithm were in reality largely transformed or modified. These areas should thus be avoided when striving to identify a viable conservation network. Although the LUC algorithm selected more grid cells to represent all species, it succeeded in increasing the percentage of natural vegetation within the selected conservation network and highlighted areas where potential conflicts should be thoroughly investigated at a local scale.
Implications of high intrinsic growth rate of a tortoise population for conservation
Authors: Hailey Adrian 
Published: February 2006

AbstractDemographic analyses suggest that chelonians will have a low ability to withstand harvesting, although most have been based on stationary or declining populations. In contrast to this prediction, a population of Testudo graeca grew at the instantaneous rate r= 0.137 from 1980–1990, with a doubling time of 5 years. r was similar in both adult and 10 cm animals, showing that this high rate was not due to changes in population structure, and may thus be taken as an intrinsic rate of increase (rm). rm was higher than that of most large mammals, and suggests that sustainable harvesting would be a viable conservation strategy for chelonians if tightly regulated. Ranching or farming operations for chelonians would be even more likely to succeed, given their high fecundity. A resumption of trade in Mediterranean tortoises is, however, unlikely to be economically sustainable.