bluuebunny/crossref_metadata_2025 huggingface dataset:
Field and Genetic Survey of the Endangered Butte County Meadowfoam—Limnanthes floccosa subsp. californica (Limnanthaceae)
Authors: Dole Jefferey A. , Sun Mei
Published: March 2003

The Butte County meadowfoam (Limnanthes floccosa subsp, californica), an endangered annual endemic to vernal pools in Butte County, California, is of agronomic interest as a sperm whale oil substitute. Because it is threatened by rapid development of the community of Chico, a field and genetic survey was required to guide a conservation program. Eight new populations were discovered, bringing the total known to eleven. Population sizes varied from 220 to 45,689 plants; mean seed set per flower, a bioassay of site quality, ranged from 0.82 to 2.56 among populations. The array of associated taxa, an indicator of appropriate habitat was fairly uniform across populations. Based on allozyme and morphometric data no introgression between L. floccosa subsp, californica and L. alba subsp, alba at sympatric sites was found. Populations were remarkably monomorphic, probably due to past population bottlenecks in conjunction with high selfing rates. Electrophoretic analysis of 28 isozyme loci revealed that 96% of total genetic diversity was distributed among populations. The migration rate, Nm, calculated from the mean frequency of private alleles, (

P(1)), and from the proportion of genetic variation distributed between populations, Gst, estimated exchange between local populations of one diploid individual every 50 to 100 generations, respectively. Mean genetic identity among populations was 0.91 ± 0.068. Grouping of populations on the basis of genetic distance identified two distinct populations and three clusters of populations that deserve high priority for preservation because they are likely to have high frequencies of locally adapted alleles. The low migration rates and substantial differentiation among populations suggest a conservation plan that emphasizes preservation of as many populations as possible, at possible expense of numbers of individuals.
Protected Areas in Sweden: Is Natural Variety Adequately Represented?
Authors: NILSSON CHRISTER , GÖTMARK FRANK
Published: March 2003

Abstract: Representation of all ecosystems and species in protected areas is a major goal of nature conservation, but few countries have assessed the degree to which it has been fulfilled. We analyzed the extent to which landscape and habitat types in Sweden are represented in areas protected by the Nature Conservation Act. A total of 1175 national parks, nature reserves, and nature conservation areas comprised 4.7% of the total Swedish territory on 31 December 1986 (the proportion increased to 5.9% in 1990). Among landscape types, a very large area of alpine landscape was protected, but only a small area of river landscape. Among habitat types, subalpine birch forest and alpine heaths showed the highest degree of representation in protected areas (32% and 30%, respectively, of the total area of each habitat type). Less than 1% of the farmland and less than 2% of the coniferous forests were represented in protected areas. During an early (1909–66) and a late (1967–86) conservation period, 30% and 70%, respectively, of the protected area was established. During the early period protection of alpine areas predominated; during the late period higher proportions of the other habitat types were protected, suggesting that representation was considered increasingly important. We discuss three factors that influence the goal of representation: (1) threat to and amount of remaining habitat type, (2) cost and opportunity, and (3) evaluation criteria and history. Further inventory of communities and species as well as understanding of ecological processes, in and outside of protected areas, are necessary in future conservation work.
What Exactly Is an Endangered Species? An Analysis of the U.S. Endangered Species List: 1985–1991
Authors: Wilcove David S. , McMillan Margaret , Winston Keith C.
Published: March 2003

Critics of the Endangered Species Act have asserted that is protects an inordinate number of subspecies and populations, in addition to full species, and that the scientific rationale for listing decisions is absent or weak. We reviewed all U.S. plants and animals proposed for listing or added to the endangered species list from 1985 through 1991 to determine the relative proportion of species, subspecies, and populations, and their rarity at time of listing. Approximately 80% of the taxa added to the list were full species, 18% were subspecies, and 2% were distinct populations segments of more widespread vertebrate species. The proportion of subspecies and populations was considerably higher among birds and mammals than among other groups. The median populations size at time of listing for vertebrate animals was 1075 individuals; for invertebrate animals it was 999. The median population size of a plant at time of listing was less than 120 individuals. Earlier listing of declining species could significantly improve the likelihood of successful recovery, and it would provide land managers and private citizens with more options for protecting vanishing plants and animals at less social or economic cost.
Progress in Restoration of the Mauritius Kestrel
Authors: Cade ToM. J. , Jones Carl G.
Published: March 2003

In the 1970s, the Mauritius Kestrel (Falco punctatus) was the most endangered bird of prey in the world, at one time with only two known pairs surviving in the remnant native forest of the Black River Gorges (ca. 4,000 ha). At the end of the 1991–1992 breeding season, a minimum of 30 nesting pairs and more than 170 individuals were distributed in four separate forested areas, thanks mainly to manipulation of the reproductive potential of the wild pairs, to captive propagation, and to reintroduction (restocking). Since 1984, 139 young have been reared from 618 eggs laid by captive kestrels, and 147 from 265 wild eggs incubated and hatched in the laboratory; 235 young kestrels have been released on Mauritius by hacking and fostering. Adjustments in feeding and nesting habits of kestrels hacked and released outside the Black River Gorges in areas dominated by exotic vegetation and agriculture have allowed these kestrels to survive and reproduce in an array of previously unused habitats. Now that the kestrels have been released from dependence on the remnant and dying native forest, a viable population of more than 100 nesting pairs should be achievable in a few more years.
Forest Restoration on a Closed Landfill: Rapid Addition of New Species by Bird Dispersal
Authors: Robinson George R. , Handel Steven N.
Published: March 2003

Urban areas often contain sizeable pockets of degraded land, such as inactive landfills, that could be reclaimed as wildlife habitat and as connecting links to enhance remnant natural areas. In the northeastern U.S., many such lands fail to undergo natural succession to woodland, instead retaining a weedy, herbaceous cover for many years. We hypothesize that seed dispersal is a limiting factor, and that a form of secondary succession could be stimulated by introducing clusters of trees and shrubs to attract avian seed dispersers. As a direct test, we censused a 1.5‐ha experimental plantation on the Fresh Kills Landfill (Staten Island, New York) one year after installation, in search of evidence that the plantation was spreading or increasing in diversity. The 17 planted species, many from coastal scrub forests native to this region, were surviving well but contributed almost no seedlings to the area, in part because only 20% of the installed trees or shrubs were reproductive. Of the 1079 woody seedlings found, 95% came from sources outside the plantation; most (71%) were from fleshy‐fruited, bird‐dispersed plants from nearby woodland fringes. Although the restoration planting itself had not begun to produce seedlings, it did function as a site for attracting dispersers, who enriched the young community with 20 new species. One‐fourth of all new recruits were from nine additional wind‐dispersed species. Locations with a high ratio of trees to shrubs had proportionately more recruits, indicating that plant size contributed to disperser attraction. The density of new recruits of each species was dependent on distance from the nearest potential seed source. Introducing native species with the capacity to attract avian dispersers may be the key to success of many restoration programs.
Correlations between Human Collecting and Intertidal Mollusc Populations on Rocky Shores
Authors: Keough Michael J. , Quinn Gerald P. , King Alice
Published: March 2003

We tested whether the population structures of intertidal molluscs varied with the activity of human collectors in northern Port Phillip Bay, Victora, Australia. We examined eight sites, two of which had been protected for around 70 years by the area being used as a rifle range with the other six being visited frequently by human. The shores were examined in two different years, and in 1991 we counted humans and recorded their activities. At heavily visited shores, almost half of the people seen were simply walking, while 25% were actively collecting, despite regulations prohibiting the collection of intertidal gastritis. The remaining people were fishing or skydiving. At the protected shores, we observed only one collector and a handful of walkers over more than 20 observation periods, including weekdays, normal weekends, and holiday weekends. In 1989 and 1991, we compared size distributions of seven intertidal species between sites in the two categories. Four mollify species are taken for food and bait; the remaining three served as “controls”. The size distributions and abundance of noncarbonated species (alicized napalm, Leaderless viola, and emization ebonies) did not differ between visited and protected sites in either year, although most species did vary between individual sites. In contrast, three of the four collected species, alicize trampoliners, Austrocochlea constricta, and Nerita atramentosa, were significantly larger at the protected sites, and N. atramentosa was markedly less abundant at heavily visited sites. The fourth collected species, Turbo undulatus, has a distribution extending into the subtidal zone, and it is possible that intertidal populations ate replenished from deeper water. The changes in mean size of molluscs are well within the range reported from South America and South Africa under subsistence fishing, and they demonstrate that at least close to major urban centers, human recreational activities can have substantial effects in developed countries.
The Ethics of Ecological Field Experimentation
Authors: Farnsworth Elizabeth J. , Rosovsky Judy
Published: March 2003

Ecological field research has generated a wealth of valuable information, much of which informs conservation efforts. Such research raises ethical issues when we propose to modify or endanger the individual organism, population, species, or ecosystem we study. Yet the scientific literature contains little explicit consideration of the impact of ecological study itself on organisms or ecosystems. We propose that the lack of public ethical discourse among field scientists is due to (1) trepidation about initiating a controversy that could endanger future research efforts; (2) an assumption that the relative benefits of our research outweigh potential short‐term costs to the study object (that is, increased knowledge of the study object may inform its conservation); (3) difficulties in perceiving the potential negative impact of our work; (4) tacit assumptions about certain experiments that are simply “wrong” to do. Ethical considerations have already arisen with the collection of organisms, the effects of scientific observation on survivorship and behavior, and experimental manipulations of whole ecosystems. The literature on environmental ethics and animal experimentation, two sources that bear tangentially on the issues of ecological ethics, may afford diverse and occasionally conflicting value systems on which to build an ethic of ecological experimentation. Although methods specifically devised to minimize the impact on study subjects have been published, we find few existing formal mechanisms of external regulation or self‐regulation of research activities in the field. We suggest that ethical considerations, conservation and restoration measures that are compatible with sound scientific protocols, may be profitably incorporated into the design of field experiments. We encourage a dialogue between scientists and philosophers on this issue.
Conservation of the African Great Lakes: A Limnological Perspective
Authors: Bootsma Harvey A. , Hecky Robert E.
Published: March 2003

The limnology of Lakes Malawi Tanganyika, and Victoria is discussed with the objective of examining how the physical, chemical, and biological properties of the lakes will determine the response of these ancient great lake ecosystems to human activities. Of the physical properties discussed, large dilution capacities and long flushing times can make the detection and removal of chemical pollutants in these lakes difficult. The outflows of all three lakes are small because of high evaporation losses, and as a result lake levels are responsive to climate changes that would alter evaporation:precipitation ratios. Increased nutrient input to these lakes will likely result in a decrease in the volume of oxygenated water and available fish habitat. Plankton community composition will also change, probably toward dominance by cyanobacteria. While the effects of eutrophication on fish production are difficult to predict, changes in plankton composition would almost certainly be accompanied by changes in fish community structure. Recent studies of water chemistry and plankton productivity in Lake Victoria provide evidence of possible eutrophication. Because land use has a diffuse but potentially large impact on these lakes, conservation strategies must take into account human activities within entire drainage basins. This requires cooperation between riparian countries and technological and financial input from the international community. An immediate need is the establishment of monitoring programs to determine the impact, real or potential, of human activities around the lakes.
The Impact of Sediment Pollution on Biodiversity in Lake Tanganyika
Authors: Cohen Andrew S. , Bills Roger , Cocquyt Christine Z. , Caljon A.G.
Published: March 2003

We investigated the impact of excess sediment pollution on the biodiversity of Lake Tanganyika, Africa. The lake’s basin is undergoing deforestation at an alarming rate; rapid erosion as a consequence of this deforestation is resulting in the discharge of large volumes of sediment into normally clear‐water littoral and sublittoral environments. We determined species richness patterns among ostracodes, fish, and diatoms for undisturbed, moderately disturbed, and highly disturbed areas to see if there is a consistent pattern of lower species richness in disturbed areas. Ostracodes are significantly less diverse in highly disturbed sites than in less disturbed ones for both soft and hard substrate littoral environments, with reductions in species richness ranging from 40% to 62%. Species richness patterns for profundal ostracodes show smaller differences between low‐ and high disturbance environments (7–32%) that are not statistically significant. Fish census data show a similar pattern to ostracodes, although the sample sizes are too small to be analyzed statistically. For the four water depths where comparative transects were made, species richness was between 35% and 65% lower at high disturbance sites than at low disturbance sites. Diatoms showed only minor and statistically insignificant reductions in species richness between low and high disturbance sites (15–20%). Ostracodes and fish may be more affected by sedimentation because they are mostly endemic and may require clearwater habitats, whereas the benthic diatom species in the lake are largely cosmopolitan and in many cases also occur in turbid affluent rivers (such as the Ruzizi). Fossil and sedimentological data from short cores are required to confirm whether the low diversity observed at high disturbance sites is a consequence of increasing sedimentation rates through time. Our results have implications for establishing and managing underwater reserves in Lake Tanganyika. They suggest that lake margins adjacent to small, erosion‐resistant watersheds will be most easily protected in the event of deforestation. Conversely, lake reserves established adjacent to large and/or easily eroded watersheds should incorporate those adjacent areas as part of the reserve to prevent subsequent sedimentation damage to the reserve ecosystems.
Cascading Effects of the Introduced Nile Perch on the Detritivorous/Phytoplanktivorous Species in the Sublittoral Areas of Lake Victoria
Authors: Goldschmidt Tijs , Witte Frans , Wanink Jan
Published: March 2003

In the 1980s an explosive increase of the introduced Nile perch (Lates sp.; Harrison 1991) in Lake Victoria caused the destruction of approximately 65% of the endemic haplochromine cichlids. The eradication of approximately 200 vertebrate species in less than a decade may well represent the largest extinction event among vertebrates during this century. The introduction of the Nile perch can be considered as a large‐scale, albeit unintended, experiment. Farreaching changes in the food web are taking place. We present data on the importance of haplochromines in the ecosystem prior to the Nile perch boom. An analysis of the pelagic community in the sublittoral area of the Mwanza Gulf revealed that the phytoplanktivores formed 18% of the biomass of the total haplochromine community. In the benthic community, the detritivores that frequently included phytoplankton in their diet comprised 31% of the biomass. We examine the hypothesis that algal grazing was reduced by the disappearance of haplochromine phytoplanktivores and detritivores. The disappearance of these groups may have contributed to the recent algal blooms. To investigate this hypothesis we consider a second major change in the system. Coinciding with the decrease of the haplochromines, the number of atyid prawns, Caridina nilotica, has strongly increased. We present preliminary evidence that the stock of the detritivorous haplochromines that formerly comprised most of the demersal ichthyomass has (partially?) been replaced by the prawn. We discuss the possible mechanisms underlying this major change in the food web. With respect to the conservation of the Great African Lakes, tbe collapse of Lake Victoria’s ecosystem should serve as an example of how easily a complex ecosystem can be irreversibly destroyed.
Evaluating Biodiversity and Conserving Lake Malawi’s Cichlid Fish Fauna
Authors: Reinthal Peter
Published: March 2003

The cichlid fishes of the Great Lakes of Africa are extraordinary biological assemblages. Conservation strategies are urgently needed for these fish faunas, due to increased threats from over‐fishing, habitat degradation, and species introductions. Here I investigate the patterns of biodiversity of the rock‐dwelling cichlid fishes (known as mbuna) of Lake Malawi and present a series of recommendations to enhance their conservation. Specifically, I examine intralacustrine biogeograpbic distributions and diversity, and levels of endemism for both mbuna species and genera. The biogeographic patterns show a high degree of variation for both taxonomic designations. Significant relationships are found between diversity and distribution patterns. Speciose genera are more widespread and habitats close to other lands support higher biodiversity than in isolated islands. The results indicate that the genus level may be the appropriate taxonomic designation to consider for conservation purposes, and that areas of high generic endemism, such as the Muleri Islands, are significant for conservation. In order to account for geographic variation in biodiversity, consideration should be given to expanding Lake Malawi National Park boundaries to include areas in the northern and central parts of the lake, especially Likoma and Chisumulu Islands and Nkhata Bay. I discuss the establishment of an international park and the expansion of conservation efforts to include the non‐mbuna cichlids. An ecosystem approach to biodiversity conservation and management is advocated.
Terrestrial Arthropod Assemblages: Their Use in Conservation Planning
Authors: KREMEN C. , COLWELL R. K. , ERWIN T. L. , MURPHY D. D. , NOSS R. F. , SANJAYAN M. A.
Published: March 2003

Abstract: Arthropods, the most diverse component of terrestrial ecosystems, occupy a tremendous variety of functional niches and microhabitats across a wide array of spatial and temporal scales. We propose that conservation biologists should take advantage of terrestrial arthropod diversity as a rich data source for conservation planning and management. For reserve selection and design, documentation of the microgeography of selected arthropod taxa can delineate distinct biogeographic zones, areas of endemism, community types, and centers of evolutionary radiation to improve the spatial resolution of conservation planning. For management of natural areas, monitoring of terrestrial arthropod indicators can provide early warnings of ecological changes, and can be used to assay the effects of further fragmentation on natural areas that no longer support vertebrate indicator species. Many arthropod indicators respond to environmental changes more rapidly than do vertebrate indicators, which may exhibit population responses that do not become evident until too late for proactive management. Not all arthropod taxa are equally effective as indicators for conservation planning, and the qualities of indicators can differ for purposes of inventory versus monitoring. Assemblages of arthropod taxa used as biogeographic probes in inventories should exhibit relatively high species diversity, high endemism, and encompass the geographic range of interest. For monitoring purposes, indicator assemblages should exhibit varying sensitivity to environmental perturbations and a diversity of life‐history and ecological preferences.
Delayed Sexual Maturity and Demographics of Blanding's Turtles (Emydoidea blandingii): Implications for Conservation and Management of Long‐Lived Organisms
Authors: CONGDON JUSTIN D. , DUNHAM ARTHUR E. , VAN LOBEN SELS R. C.
Published: March 2003

Abstract: A study of Blanding's turtles conducted during 27 of the last 37 years provided demographic data sufficient to examine how life‐history characteristics may constrain population responses of long‐lived organisms. Eight independent estimates of annual adult survivorship exceeded 93%. Nest survival was variable and ranged from 0.0 to 63% annually, with a mean of 44% from 1976 to 1984 and 3.3% from 1985 to 1991. Recruitment of juveniles and adults was sufficient to replace individuals estimated to have died during the study. A life table for the population resulted in a cohort generation time of 37 years and required a 72% annual survivorship of juveniles between 1 and 13 years of age to maintain a stable population. Population stability was most sensitive to changes in adult or juvenile survival and less sensitive to changes in age at sexual maturity, nest survival, or fecundity. The results from the present study indicate that life‐history traits of long‐lived organisms consist of co‐evolved traits that result in severe constraints on the ability of populations to respond to chronic disturbances. Successful management and conservation programs for long‐lived organisms will be those that recognize that protection of all life stages is necessary. Programs such as headstarting or protection only of nesting sites, in the absence of programs to reduce mortality of older juveniles and adults, appear to be less than adequate to save long‐lived organisms such as sea turtles and some tortoises. The concept of sustainable harvest of already‐reduced populations of long‐lived organisms appears to be an oxymoron.
Isolation of Remaining Populations of the Native Frog, Rana muscosa, by Introduced Fishes in Sequoia and Kings Canyon National Parks, California
Authors: BRADFORD DAVID F. , TABATABAI FARINAZ , GRABER DAVID M.
Published: March 2003

Abstract: Rana muscosa (mountain yellow‐legged frog) was eliminated by introduced fishes early in this century in many of the lakes and streams in Sequoia and Kings Canyon National Parks, California. In waters not inhabited by fish, however, R. muscosa has disappeared from many sites within the parks during the past 30 years, and it appears to have gone extinct in some drainage systems. Fragmentation of populations may have caused or contributed to these recent extinctions, because R. muscosa populations are significantly more isolated from one another by fish at present than in prestocking conditions. A total of 312 lake‐sites in 95 drainage basins were surveyed for amphibians and fish in 1989–1990. For the 109 sites containing R. muscosa, we delineated networks of sites connected to one another via fishless streams, and we compared these present fishless networks (“present networks”) to those expected for the same sites assuming that fish had not been introduced to the parks (“former networks”). Most present networks consist of only one site (mean = 1.4), whereas the former networks average 5.2 sites. This difference represents approximately a 10‐fold difference in connectivity of populations, which is defined as the mean number of potential dispersal links (fishless streams) per network. Connectivity averages only 0.43 in present networks, in contrast to 4.15 in former ones.
Natural Die‐Offs of Large Mammals: Implications for Conservation
Authors: Young Truman P.
Published: March 2003

The viability of populations is a central concern of biological conservation. The occurrence of catastrophic die‐offs may greatly reduce the long‐term viability of populations. Theoretical extinction models and viability analyses require information on the frequency of die‐offs and on the distribution of die‐off severities. A review of literature identified 96 natural die‐offs in large mammal populations, with a die‐off being defined as a peak‐to‐trough decline in estimated population numbers of at least 25%. If such die‐offs are common, population viability analyses that ignore them may be overly optimistic. The severities of the natural die‐offs of large mammals presented here are not uniformly distributed. There is a relative overabundance of die‐offs in the 70–90% range, and an underabundance of die‐offs greater than 90%. This may indicate the presence of buffers against population extinction. The reported causes of large mammal die‐offs were significantly related to trophic level: herbivore die‐offs were more often attributed to starvation, while carnivore die‐offs were more often attributed to disease. Populations subject to large‐scale phenomena such as drought and severe winters may not be protected from die‐offs by population subdivision. On the other hand, populations subject to catastrophic disease epidemics may be protected by subdivision, and threatened by corridors between conservation areas and by translocation efforts.
A General Stochastic Model for the Prediction of Biodiversity Losses Based on Habitat Conversion
Authors: Koopowitz Harold , Thornhill Alan D. , Andersen Mark
Published: March 2003

We present a model of species extinction rates that depends on the distribution of species and rates of habitat conversion. This model allows prediction of numbers of species lost as well as current extinction rates. We apply the model to plant species in the Neotropics. We examined distribution data for 51 angiosperm taxa, comprising 4258 species from Flora Neotropica monographs. Of these, 25.7% had been recorded as occurring in a single locality, with 12.8% and 9.5% being recorded from two or three localities respectively. Assuming that 18.7% of Neotropical forested area has been cleared since 1950, when 60,000 plant species existed, the model predicts that 3020 species will have been lost by 1992. At current deforestation rates, the entire Neotropics loses between 71 and 95 plant species per year. We also apply the model to individual Neotropical countries and find annual rates of within‐country extinctions ranging from 0 per year in Belize to 63 per year in Ecuador. We suggest a means by which the model may be tested in the field.
The Prairie Dog and Biotic Diversity
Authors: Miller Brian , Ceballos Gerardo , Reading Richard
Published: March 2003

Since the turn of this century, prairie dog populations have declined as much as 98% throughout North America, largely as a result of prairie dog eradication programs. The prairie dog is a keystone species that plays an important role in maintaining the biotic integrity of the western grasslands that stretch from southern Canada to northern Mexico. The fragmentation of prairie dog distribution has degraded diversity on those prairies, and several species depending on prairie dogs have achieved listing status under the Endangered Species Act. We propose that managing the praire dog would provide an effective avenue from single‐species management to management of a system. Because prairie dogs have declined so profoundly, some form of legal protection will be required. In addition, protected areas can preserve habitat and integrate ecologically sound agricultural opportunities. Positive incentives for ranchers to manage in the interests of both livestock and wildlife will enhance the attitude change necessary for grassland conservation. These management options hinge critically on an end to U.S. government subsidies for prairie dog eradication programs. The subsidies are financially and ecologically unsound, and they only contribute to the prevailing misconceptions about the role of the prairie dog on the grasslands.
Techniques and Guidelines for Monitoring Neotropical Butterflies
Authors: Sparrow Helen R. , Sisk Thomas D. , Ehrlich Paul R. , Murphy Dennis D.
Published: March 2003

Long‐term monitoring of selected species can identify changes in biological diversity, permitting the timely adjustment of management activities to reverse or avoid undesired trends. This paper addresses several related issues bearing on the development of inexpensive and easily implemented monitoring programs for tropical butterflies. First, we discuss the use of butterflies as ecological indicators. Next, we present field evaluations of butterfly sampling techniques, indicating that: (1) light‐gap size greatly affects sampling results in forests and should be of critical concern in site selection and sampling design; (2) baited traps and visual censuses provide complementary data on butterfly abundances; (3) monitoring a subset of locally common butterfly species can provide data for comparing community composition and relative abundance of species in areas where species inventories are incomplete. Drawing on these results, we develop guidelines for designing monitoring programs. These address the formulation of explicit questions to be addressed through monitoring and the selection of appropriate study sites, study species, sampling techniques, and sampling frequency. A protocol for the ongoing butterfly monitoring program that emerged from these studies is appended. The techniques and guidelines presented here are intended to serve as an adaptable model for biologists designing monitoring projects to help guide applied conservation efforts in the tropics.
Defining Forest Fragmentation by Corridor Width: The Influence of Narrow Forest‐Dividing Corridors on Forest‐Nesting Birds in Southern New Jersey
Authors: Rich Adam C. , Dobkin David S. , Niles Lawrence J.
Published: March 2003

In studies of forest fragmentation, a fundamental inconsistency exists in the distance criterion used to define the discreteness of forest fragments. We examined three types of ubiquitous, narrow, forest‐dividing corridors for effects that influence the relative abundance and community composition of forest‐nesting birds. Fixed‐radius (100‐meter) point counts were conducted on 54 transects established along three width classes of corridors: unpaved roads (8 meters wide), paved roads (16 meters wide), and powerlines (23 meters wide). Transect locations were distributed equally among corridor edge, forest margin 100 meters from corridor edge, and forest interior 300 meters from corridor edge. Forest‐interior species of Neotropical migrants had significantly reduced relative abundances on edge transects along 16‐ and 23‐meter corridors, compared with 8‐meter corridors and with forest interior points along all three corridor‐width classes. At a landscape scale, the consequences of apparently small reductions in forest area by the presence of narrow forest‐dividing corridors may be cumulatively significant for abundances of forest‐interior species. Brown‐headed Cowbirds were more abundant than 20 of 21 forest‐interior Neotropical migrants. We found surprisingly high abundances of cowbirds associated with narrow forest‐dividing corridors, especially those with mowed grass. Corridor widths as narrow as 8 meters produce forest fragmentation effects in part by attracting cowbirds and nest predators to corridors and adjacent forest interiors. The most serious implication of this study is that narrow forest‐dividing corridors may function as ecological traps for forest‐interior Neotropical migrants. We suggest that these widespread corridors may be inconspicuous but important contributors to declines of forest‐interior nesting species in eastern North America.
Extinction Rates in Archipelagoes: Implications for Populations in Fragmented Habitats
Authors: Burkey Tormod Vaaland
Published: March 2003

To study the effect of habitat fragmentation on population viability, I used extinction rates on islands in archipelagoes and estimated the relative probability of extinction per species on single large islands and sets of smaller islands with the same total area. Data on lizards, birds, and mammals on oceanic islands and mammals on mountaintops and in nature reserves yield similar results. Species are likely to go extinct on all the small islands before they go extinct on the single, large island. In the short term, the analysis indicates that extinction probabilities may be lower on a set of small islands. This is perhaps an artifact due to underestimation of extinction rates on small islands and/or the necessity of pooling species in a focal taxon to obtain estimates of extinction rates (which may obscure area thresholds and underestimate the slope and curvature of extinction rates as a function of area). Ultimately, cumulative extinction probabilities are higher for a set of small islands than for single large islands. Mean and median times to extinction tend to be shorter in the fragmented systems, in some cases much shorter. Thus, to minimize extinction rates in isolated habitat remnants and nature reserve systems, the degree of fragmentation should be minimized
Deforestation and Its Effects on Forest‐Nesting Birds in the Florida Keys
Authors: Bancroft G. Thomas , Strong Allan M. , Carrington Mary
Published: March 2003

Uplands in the upper Florida Keys are covered by a tropical, seasonal deciduous forest containing many plant species found nowhere else in the continental United States. Before European settlement there were 4816 ha of seasonal deciduous forest in the keys. By 1991 the extent of this seasonal deciduous forest had decreased by 41%, the number of fragments increased by an order of magnitude, and the acreage in large fragments decreased by 84%. To examine the effects of fragment size on the presence of breeding birds, we censused bird populations of singing males that occurred in 27 forests that ranged in size from 0.2 ha to more than 100 ha. We also examined the occurrence of forest‐breeding species at road‐stop census points relative to nine measures of habitat around these points. Northern Cardinals (Cardinalis cardinalis) and Black‐whiskered Vireos (Vireo altiloquus) were found singing in virtually all fragments. The distribution of Red‐bellied Woodpeckers (Melanerpes carolinus) occurred independently of the size of forest fragments but was positively correlated with other measures of forest area. Great Crested Flycatchers (Myiarchus crinitus) occurred independently of fragment size and showed no correlations with other measures of habitat. White‐eyed Vireos (V. griseus) were not present in fragments smaller than 2.3 ha. Northern Flickers (Colaptes auratus) were not present in fragments smaller than 3.5 ha, but their numbers showed the highest positive correlations with the percentage of area in lawns and were negatively correlated with measures of total forest area. Yellow‐billed (Coccyzus americanus) and Mangrove (C. minor) Cuckoos were absent from fragments smaller than 7.5 ha and 12.8 ha, respectively. the effective habitat loss for the four “area‐sensitive” species exceeds the actual loss of deciduous forest. To maintain viable populations of species native to the seasonal deciduous forests of the Florida Keys will require protection of additional acreage of upland habitat from deforestation. A network of reserves that maintains dispersal possibilities among the remaining larger forest fragments is crucial.
Threatened Status, Rarity, and Diversity as Alternative Selection Measures for Protected Areas: A Test Using Afrotropical Antelopes
Authors: Kershaw Melanie , Mace Georgina M. , Williams P.H.
Published: March 2003

A major aim of conservation today is the maintenance of biodiversity. Practically, this pursuit might involve protecting a representative sample of the current biotic diversity (where diversity can have a variety of different meanings as in Vane‐Wright et al. 1991), safeguarding species with traits that may be correlated with susceptibility to extinction (see International Council for Bird Preservation 1992), or protecting those species that are currently categorized as under short‐term threat of extinction. Priority areas for conservation may vary, however, depending on which of these three approaches is taken. We investigated the designation of priority areas using these different approaches for Afrotropical antelope. Sites were selected on the basis of (1) biotic diversity—simple species richness and taxonomic diversity; (2) uniqueness of the fauna relative to other sites—how geographically restricted the component species were; and (3) degree of endangerment of the fauna. When insufficient sites to represent all the species could be selected, there was little agreement between the priority sites selected using the different methods. Sites selected by each approach were also generally poor at representing the diversity components ranked highly by other approaches. Also, many of the species were represented in only one site in the selected network, which on its own probably does not represent a viable population for the species. Therefore, it is important that the precise aims and consequences of any selection procedure be understood. A combination of different approaches, emphasizing different aspects of biodiversity and implemented sequentially, may be the best compromise for preserving a full range of biotic diversity.
Ungulate Reintroductions: Experiences with the Takhi or Przewalski Horse (Equus ferus przewalskii) in Mongolia
Authors: Van Dierendonck Machteld C. , Wallis de Vries Michiel F.
Published: March 2003

Experiences with the reintroduction of the takhi, or Przewalski horse (Equus ferus przewalskii, in Mongolia can serve as valuable lessons for reintroduction of ungulates in general. We discuss the present taxonomic, historical, and biological evidence and conclude that the takhi should be viewed as a typical steppe herbivore. Its last refuge, the Dzungarian Gobi, should therefore be seen as a marginal habitat because it consists mainly of desert and semidesert. Since 1992 two reintroduction projects have been in the acclimatization phase in Mongolia. Despite promising developments, problems with cooperation, management, habitat choice, insufficient knowledge of the ethology of the species, and current land use within the different project areas could jeopardize the successful reintroduction of takhi. We review the conditions required for a potentially successful ungulate reintroduction. The planning of a reintroduction within the framework of safeguarding an entire ecosystem with an integrated management plan appears essential. Each potential reintroduction site should be assessed thoroughly for its suitability, including size, habitat types, current land use, socioeconomics, legislation, and potential problems. Each site should be provided with one or more acclimatization facilities to harbor genetically and physically healthy, socially adapted animals in biologically sound groups. An organization structure should be established for each reintroduction site. Its objective should be to develop an effective management plan and to carefully monitor the population and its surrounding ecosystem. Special attention should be given to local socioeconomic situations, community participation, and training of staff for management, research, and ranger and warden activities.
Incidental Nest Predation and Lark Conservation in an Iberian Semiarid Shrubsteppe
Authors: Yanes Miguel , Suárez Francisco
Published: March 2003

Steppe larks are rare species in Europe, and several reserves have been established in Spain to promote their conservation. Little is known, however, about the benefits these reserves provide for Iberian larks. At Las Amoladeras Bird Reserve predation of lark nests was high according to the Mayfield method: 68–99% of nests were preyed upon, primarily by red foxes (Vulpes vulpes) and feral dogs. A negative correlation between canid abundance and daily nest survival was detected, but there was no relationship between predator abundance and lark density. There was a positive correlation between canid track abundance and rabbit density. Evidence indicated that lark nest predation in the Iberian shrubsteppes was an example of incidental predation (Vickery et al. 1992), which nevertheless has caused serious conservation problems for the larks. Lark densities in some areas decreased 80% during the 3 years of our study. Incidental predation, which is determined by rabbit abundance, is a complicating factor for the conservation of these ground‐nesting birds and should be taken into account in the management of reserves for steppe birds.
Science and Management of Rocky Mountain Grizzly Bears
Authors: Mattson David J. , Herrero Stephen , Wright R. Gerald , Pease Craig M.
Published: March 2003

The science and management of grizzly bears (Ursus arctos horribilis) in the Rocky Mountains of North America have spawned considerable conflict and controversy. Much of this can be attributed to divergent public values, but the narrow perceptions and incomplete and fragmented problem definitions of those involved have exacerbated an inherently difficult situation. We present a conceptual model that extends the traditional description of the grizzly bear conservation system to include facets of the human domain such as the behavior of managers, elected officials, and the public. The model focuses on human‐caused mortality, the key determinant of grizzly bear population growth in this region and the interactions and feedback loops among humans that have a major potential influence on bear mortality. We also briefly evaluate existing information and technical methods relevant to understanding this complex human‐biophysical system. We observe not only that the extant knowledge is insufficient for prediction (and in some cases for description), but also that traditional positivistic science alone is not adequate for dealing with the problems of grizzly bear conservation. We recommend changes in science and management that could improve learning and responsiveness among the involved individuals and organizations, clarify some existing uncertainty, and thereby increase the effectiveness of grizzly bear conservation and management. Although adaptive management is a promising approach, we point out some key—as yet unfulfilled—contingencies for implementation of a method such as this one that relies upon social processes and structures that promote open learning and flexibility in all facets of the policy process.
Contribution of Roads to Forest Fragmentation in the Rocky Mountains
Authors: Reed Rebecca A. , Johnson‐Barnard Julia , Baker William L.
Published: March 2003

The contribution of roads to forest fragmentation has not been adequately analyzed. We quantified fragmentation due to roads in a 30,213‐ha section of the Medicine Bow‐Routt National Forest in sout heastern Wyoming with several indices of landscape structure using a geographic information system. The number of patches, mean patch area, mean interior area, mean area of edge influence, mean patch perimeter, total perimeter, and mean patch shape identified patch‐ and edge‐related landscape changes. Shannon‐Wiener diversity, dominance, contagion, contrast, and angular second moment indicated effects on landscape diversity and texture. Roads added to forest fragmentation more than clearcuts by dissecting large patches into smaller pieces and by converting forest interior habitat into edge habitat. Edge habitat created by roads was 1.54–1.98 times the edge habitat created by clearcuts. The total landscape area affected by clearcuts and roads was 2.5–3.5 times the actual area occupied by these disturbances. Fragmentation due to roads could be minimized if road construction is minimized or rerouted so that its fragmentation effects are reduced. Geographic information system technology can be used to quantify the potential fragmentation effects of individual roads and the cumulative effects of a road network on landscape structure.
Genetic and Demographic Threats to the Black Rhinoceros Population in the Ngorongoro Crater
Authors: Moehlman Patricia D. , Amato George , Runyoro Victor
Published: March 2003

A resident population of 13 black rhinoceros (Diceros bicornis) persist in Ngorongoro Crater, Tanzania. The effective population size (Ne) may be as few as 5 animals. Projected growth for this population suggests that the effective population size will remain small for the near future, threatening this Iocal population with extinction due to the stochastic factors associated with small population size. A summary of historic and recent demographic data for this population reveals a population crash during the period of heavy poaching that affected this species throughout its range. Although poaching of this species has been brought under control the population remains small. These data and models of projected population growth argue for consideration of more‐intensive management within the framework of the small population paradigm. This case is an example of applied conservation resulting from this paradigm used in conjunction with rather than competing with the declining population paradigm. We identify additional monitoring, particularly of density‐dependent behaviors, that will be necessary for designing a successful management program. Finally, the use of molecular markers for developing an accurate pedigree for this population is suggested in order to maintain a genetically healthy population. These strategies have broad applicability to black rhinoceros conservation throughout Africa.