bluuebunny/crossref_metadata_2025 huggingface dataset:
Littoral Fish Communities in Lake Tanganyika: Irreplaceable Diversity Supported by Intricate Interactions among Species
Authors: Hori Michio , Gashagaza Masta Mukwaya , Nshombo Muderhwa , Kawanabe Hiroya
Published: March 2003

The rocky littoral areas of Lake Tanganyika harbor diverse fish communities, mainly composed of cichlids. Their stability, structure, and organizing mechanism were examined at three locations by census, behavioral observations, and dietary analyses. These fish communities were stable, characterized by their persistence during a 10‐year period and resilience after a perturbation. Partitioning of spawning sites among substrate spawners was evident, which might be a factor in their ability to coexist. The fish communities were consistently composed of 12 food‐habit groups, but composition of species in each group differed from location to location. Among species of different food‐habit groups, facultative commensalisms were prevalent. Although aggressive interactions are common among fishes of the same food‐habit group, each predatory fish obtained an advantage in feeding efficiency from the different feeding behaviors of other species of the same group. This mutualism and the facultative commensalism should both increase species richness in different parts of the communities. These intricate interactions among species may be a base of stability of the fish communities. We assert that maintenance of ecological networks among species are most important for conservation of biodiversity in tropical regions.
Population Structure of Loggerhead Turtles (Caretta caretta) in the Northwestern Atlantic Ocean and Mediterranean Sea
Authors: BOWEN BRIAN , AVISE JOHN C. , RICHARDSON JAMES I. , MEYLAN ANNE B. , MARGARITOULIS DIMITRIS , HOPKINS‐MURPHY SALLY R.
Published: March 2003

Abstract: To assess population genetic structure and evolutionary relationships among nesting populations of loggerhead turtles (Caretta caretta), we analyzed mitochondrial (mt) DNA variation in 113 samples from four nesting beaches in the northwestern Atlantic Ocean and from one nesting beach in the Mediterranean Sea. Significant differences in haplotype frequency between nesting populations in Florida and in Georgia/South Carolina, and between both of these assemblages and the Mediterranean nesting colony, indicate substantial restrictions on contemporary gene flow between regional populations, and therefore a strong tendency for natal homing by females. Nonetheless, this regional genetic structure appears shallow, indicating recent evolutionary connections among rookeries. Data from tag returns and mtDNA, as well as geological considerations, suggest that over short evolutionary time scales (perhaps a few thousand years), dispersal by female loggerheads is sufficient to allow colonization of appropriate habitat in proximity to established rookeries but is too low to significantly affect the population dynamics of rookeries on a contemporary time scale. These data indicate that nesting populations of the loggerhead turtle must be managed as demographically independent units. The population subdivisions based on mtDNA analyses are concordant with previously reported distinctions between Florida and Georgia/South Carolina nesting populations based on environmental markers, tag recaptures, and morphology.
The Pending Extinction of the Uncompahgre Fritillary Butterfly
Authors: Britten Hugh B. , Brussard Peter F. , Murphy Dennis D.
Published: March 2003

Previous mark‐recapture studies and population size estimates indicated that in the 1980s populations of the endangered Uncompahgre fritillary (Boloria acrocnema) declined precipitously, apparently leading to extirpation at its type locality. This locality and a nearby second site, both high in the San Juan Mountains of southwestern Colorado, constitute the total known range of B. acrocnema. A survey of 20 presumptive allozyme loci from one B. acrocnema population and seven populations of the closely related B. improba, sampled along the Rocky Mountain cordillera from the Yukon Territory, Canada, to the Wind River Range of Wyoming, revealed that B. acrocnema populations are less variable genetically than are B. improba populations in the northern part of that species’ North American range. Genetic variability was also assayed at 18 presumptive allozyme loci in populations of Boloria titania, which were sampled from five of the same locations for comparison with the B. improba‐B. acrocnema clade. Low estimates of heterozygosity indicate that genetic and demographic factors preceded by historic human disturbance are causing the decline of B. acrocnema. In addition, persistent drought conditions in southwestern Colorado throughout the 1980s probably contributed to the population declines. Conservation recommendations include strict enforcement of the ban against collecting pursuant to the Endangered Species Act, careful monitoring of known B. acrocnema sites, and possible translocations. Extreme measures beyond these will be costly and may be inappropriate for this relict species, which has an unknown capacity to persist in the face of local weather fluctuations and predicted regional warming trends.
Ecological Correlates of Species Success in Modified Habitats May Be Disturbance‐ and Site‐Specific: The Primates of Tiwai Island
Authors: Fimbel Cheryl
Published: March 2003

I compared primate abundances in an old forest and in adjacent regenerating farm clearings abandoned by slash‐and‐burn agriculturalists in Sierra Leone, West Africa. Univariate correlation procedures were used to identify socioecological characteristics of primate species that best explained success (abundance) of primates in regenerating farm clearings adjacent to old forest. A highly frugivorous diet was the single most significant primate characteristic correlated with use of abandoned farms (rs = 0.886, p = 0.019). In contrast, other studies of primates in disturbed habitats determined that a frugivorous diet was strongly negatively correlated with primate use of selectively logged forest and other disturbed habitats. These contrasting results expose the hazard of generalizing about ecological correlates of primate success in disturbed habitats, which may be site or disturbance specific. Although this warning is derived from studies of primates, it may apply to other taxa as well.
Lyme Disease and Conservation
Authors: Ginsberg Howard S.
Published: March 2003

Lyme disease is a tick‐borne illness that is widespread in North America, especially in the northeastern and northcentral United States. This disease could negatively influence efforts to conserve natural populations in two ways: (1) the disease could directly affect wild animal health; and (2) tick control efforts could adversely affect natural populations and communities. Lyme disease affects several domestic animals, but symptoms have been reported in only a few wild species. Direct effects of Lyme disease on wild animal populations have not been reported, but the disease should be considered as a possible cause in cases of unexplained population declines in endemic areas. Methods available to manage ticks and Lyme disease include human self‐protection techniques, manipulation of habitats and host species populations, biological control, and pesticide applications. The diversity of available techniques allows selection of approaches to minimize environmental effects by (1) emphasizing personal protection techniques, (2) carefully targeting management efforts to maximize efficiency, and (3) integrating environmentally benign techniques to improve management while avoiding broad‐scale environmentally destructive approaches. The environmental effects of Lyme disease depend, to a large extent, on the methods chosen to minimize human exposure to infected ticks. Conservation biologists can help design tick management programs that effectively lower the incidence of human Lyme disease while simultaneously minimizing negative effects on natural populations.
Viability Analysis in Biological Evaluations: Concepts of Population Viability Analysis, Biological Population, and Ecological Scale
Authors: Ruggiero Leonard F. , Hayward Gregory D. , Squires John R.
Published: March 2003

Environmental protection strategies often rely on environmental impact assessments. As part of the assessment process biologists are routinely asked to evaluate the effects of management actions on plants and animals. This evaluation often requires that biologists make judgments about the viability of affected populations. However, population viability analyses that are analytically comprehensive require extensive ecological data. Such data are usually unavailable and impossible for wildlife managers to collect given limitations of time and money. In this paper we present a conceptual framework to help managers assess population viability given the reality of limited information and resources. Our framework includes a series of steps that facilitate assessment of management impacts on population viability while stressing the importance of reconciling disparities between the geographic scale of management actions and the scale of ecological responses. We argue that a gross mismatch of scale between local management actions (e.g., timber sales) and geographically extensive ecological responses (e.g., species viability) reduces the reliability of environmental analyses. Our framework stresses “biological populations” as the most appropriate level of ecological organization for conducting impact analyses. We argue that in most cases environmental analyses of local management actions should assess the ecological responses of populations rather than the responses of entire species, as is now commonly the case. We also present ecological concepts that have been used effectively by biologists in making judgments about management effects and in developing conservation plans. Although not completely generalizable we believe these concepts, summarized from the conservation biology literature, can aid in evaluating population viability: (1) connected habitats are better than disjointed habitats; (2) suitable habitats in close proximity to one another are better than widely separated habitats; (3) late stages of forest development are often better than younger stages; (4) larger habitat areas are better than smaller areas; (5) populations with higher reproductive rates are more secure than those with lower reproductive rates; and (6) environmental conditions that reduce carrying capacity or increase variance in the growth rates of populations decrease persistence probabilities.
Genetic Diversity in a Threatened Wetland Species, Helonias bullata (Liliaceae)
Authors: Godt Mary Jo W. , Hamrick J.L. , Bratton Susan
Published: March 2003

Genetic variation was examined in Helonias bullata, a threatened perennial plant species that occurs in isolated wetland habitats. Fifteen populations representing the species’ geographic range were sampled. Genetic diversity was low for the species (Hes = 0.053) as well as within populations (Hep = 0.029). Of the 33 allozyme loci examined, 11 (33%) were polymorphic, while on average only 12.8% (4) of the loci were polymorphic within populations. The number of alleles per polymorphic locus was 2.36 for the species and averaged 2.09 across populations. For every genetic parameter calculated, variation in H. bullata was lower than that typically found for narrowly distributed plant species. The lowest levels of genetic diversity were found in northern areas that were colonized following the last glacial epoch. The number of genotypes detected per population ranged from three to 21, with a mean of 13 for this clonally reproducing species. We found a relatively high proportion of total genetic diversity (30.6%) among populations and a significant correlation (p < 0.002) between genetic distance and geographic distance. Genetic drift phenomena appear to play a major role in the population genetics of this species. Anomalously, several populations that appeared most limited in size and vigor were genetically most variable, perhaps because they represent older, relictual populations. Life‐history characteristics of H. bullata coupled with low levels of genetic diversity and the degradation and disappearance of wetlands threaten the existence of this species.
The Roles of Introduced Rats and Commercial Fishing in the Decline of Ancient Murrelets on Langara Island, British Columbia
Authors: Bertram Douglas F.
Published: March 2003

I examined the decline of Ancient Murrelets (Synthliboramphus antiquus), a small, burrow‐nesting seabird, at Langara Island. The island’s seabird colony was historically one of the largest colonies of Ancient Murrelets in British Columbia—perhaps in the world—with an estimated 200,000 nesting pairs. I reviewed historical information and compared the results of surveys from 1981 and 1988 that employed the same census protocol. The extent of the colony, a potential index of population size, declined from 101 ha in 1981 to 48 ha in 1988. Burrow density increased during the same period, however, suggesting that the colony bad consolidated. In 1988, the population estimate was 24,200 ± 4000 (S.E.) breeding pairs compared to 22,000 ± 3700 in 1981. in 1988, 29% of the burrows that were completely searched contained bones of Ancient Murrelets. Bones were most common in burrows located in abandoned areas of the colony and were least common where burrow occupancy was high. The discovery of adult Ancient Murrelets killed in their burrows by introduced rats, combined with the high proportion of burrows with bones, suggests that rats (Rattus rattus and R. norvegicus) have contributed significantly to the decline of the population. In addition, the presence and activities of a salmon‐fishing fleet in the 1950s and 1960s may also be linked to the decline of the Langara Ancient Murrelet population during that period because these fisheries are known to have caused heavy mortality through fatal light attraction and drowning in gill nets. The combined effects of ongoing predation by introduced rats and—to a lesser extent—previous, episodic fishery‐induced mortality are probable causes for the population decline.
Sixty Years of Change in Californian Conifer Forests of the San Bernardino Mountains
Authors: Minnich Richard A. , Barbour Michael G. , Burk Jack H. , Fernau Robert F.
Published: March 2003

We revisited 68 plots of forest vegetation in the San Bernardino Mountains that had been quantitatively described in 1929‐1935, from the California Vegetation Type Map (VTM) Survey. By using the same sampling methods, we documented changes—over approximately 60 years and during a period of fire suppression management—in tree density by both species and size class. In general, we found increasing stand densities, a transformation from old‐growth age structure to young growth, and a compositional shift from Pinus ponderosa and P. jeffreyi to Abies concolor and Calocedrus decurrens. Density of trees of more than 12 cm diameter at breast height (dbh) increased by 79%, including three to ten‐fold increases in the youngest cohorts 12–66 cm dbh. The magnitude of change depended upon initial forest composition and local annual precipitation. Monotypic stands of P. jeffreyi or those initially dominated by Abies concolor showed the least change in species composition; the most xeric stands of P. jeffreyi showed the least gain in density; and mesic mixed P. ponderosa stands showed the most dramatic change in composition and density. We compared these data to records of past and present forests in the Sierra Nevada and found parallel trends, but magnified by the increased precipitation of the Sierra Nevada. We also compared VTM data from the San Bernardino Mountains to mixed conifer forests in the Sierra San Pedro Martir of Baja California. These Mexican sites and forests are ecologically similar to those in California, but they still experience unmanaged fire regimes. Californian forests of 60 years ago are remarkably similar to modern forests in the Sierra San Pedro Martir. Thus, we conclude that forest changes in the San Bernardino Mountains are primarily due to lengthening fire intervals. Forest changes as a result of fire suppression have important conservation consequences for bird species diversity in general and for Spotted Owl and Neotropical migrants in particular.
Control of Abundant Native Vertebrates for Conservation of Endangered Species
Authors: Goodrich J.M. , Buskirk S.W.
Published: March 2003

Abundant native vertebrates, which we define as those that have increased in abundance due to human‐induced changes in communities or ecosystems, have contributed to the decline of rare vertebrates through predation, competition, habitat change, disease transmission, and hybridization. Recent literature dealing with the negative effects of abundant native vertebrates on rare native vertebrates argues for population control by killing or translocating animals. We identify several potential problems with these methods, including the high cost of population control, community changes such as mesopredator release that favor other harmful vertebrate species, and increases in diseases harmful to the rare species. Also, public opposition to and lack of species specificity in population control techniques often make population control difficult. We propose alternatives to population reduction/or management of abundant native vertebrates, including techniques that prevent abundant vertebrates from causing harm, and community and ecosystem rehabilitation and restoration. The latter provide the best solutions to problems caused by abundant native vertebrates because community and ecosystem degradation are the primary factors responsible for some species becoming rare and others becoming abundant. These solutions are long term, biologically sound, and involve little direct human intervention into ecosystem processes. But population control may be necessary as a short‐term solution when abundant vertebrates pose an immediate threat to the survival of a rare species. We conclude that those involved in the conservation of rare species should consider population control of abundant native vertebrates only as a last resort.
The Role of Traditional Agroforests in the Conservation of Rain Forest Bird Diversity in Sumatra
Authors: Thiollay Jean‐Marc
Published: March 2003

Bird community composition and structure were compared among three different types of traditionally managed agroforests and the nearby primary forests in southwestern Sumatra during the breeding season. The agroforests were dominated respectively by rubber tree (Hevea brasiliensis), damar (Shorea javanica), and durian (Durio zibethinus) and were managed for cash crops (latex, resin, fruits, spices, coffee and timber). Although planted on formerly clearfelled and cultivated areas, these agroforests were highly diversified and structurally complex. Species relative abundance was obtained in 112 random samples of 50 individuals within limited census areas. The species were classified according to size, main diet, and observed habitat use. Eighty‐three percent of all the regional pool of resident species were recorded at least once (excluding aerial, nocturnal, and aquatic species). Species richness, diversity, and equitability were all significantly lower (12% to 62% less) in every agroforest than in the primary forest, and the coefficients of similarity between the natural and managed forest communities were low (0.43–0.55). Less than half the lowland primary forest species known from western Sumatra were recorded in at least one agroforest. Among the 216 species occurring in samples, 56% significantly decreased in or disappeared from agroforests, whereas only 22% appeared or increased. The species most affected by the conversion of primary forests were large frugivores and large insectivores of the canopy and low understory, or terrestrial interior forest specialists. Species thriving in agroforests were small frugivores, foliage insectivores, and nectarivores often originally associated with gaps. The factors affecting biodiversity in agroforests may involve reduced tree height, canopy foliage volume, vertical diversity of the vegetation structure, floristic richness, and associated variety of food resources. High hunting pressure may also be a factor. These multipurpose, traditionally managed agroforests still are a valuable compromise between conservation of tropical forest biodiversity and sustainable use of natural resources. They also function as buffer zones between densely populated and protected areas and are one of the most successful examples of silviculture of dipterocarps. Yet they are not equivalent to primary forests.
Implications of Intratropical Migration on Reserve Design: A Case Study Using Pharomachrus mocinno
Authors: Powell George V.N. , Bjork Robin
Published: March 2003

As habitat loss continues, natural protected areas will become islands in human‐modified landscapes; maintenance of functional communities and ecosystems will depend on properly designed protected areas. We demonstrate that incorporating regional habitat linkages that allow for seasonal migrations of intratropical resident species must be a major design criterion for establishing protected areas. Using radiotelemetry, we monitored the seasonal movements of one such migrant, the Resplendent Quetzal (Pharomachrus mocinno), a large, frugivorous bird, one of many tropical residents known to migrate altitudinally within Mesoamerica. Based on three years of data we determined that quetzals followed a complicated local migration that linked four montane life zones. Using this species as an indicator revealed that the configuration of the Monteverde reserve complex in the Tilaran Mountains in west‐central Costa Rica lacked sufficient habitat distribution to conserve montane biodiversity. On the basis of these results, we propose that the three‐step process proposed by Soulé and Simberloff (1986) for estimating minimum sizes of reserves be amended to include a fourth step: The critical habitats used throughout the annual cycles of target or keystone species must be identified and adequately protected. Natural protected areas can be considered adequately designed only when sufficient area with a full complement of ecologically linked habitats is included.
Edge Effects and Isolation: Red‐Backed Voles on Forest Remnants
Authors: Mills L. Scott
Published: March 2003

Negative effects of habitat edge have been advanced as an important proximate cause of extinction, and a growing literature calls attention to the matrix surrounding habitat remnants as a critical factor determining population persistence. I examined spatial distribution of California red‐backed voles (Clethrionomys californicus) on 13 forest remnants and five control sites in southwestern Oregon. The species was virtually isolated on remnants, making little use of the regenerating clearcuts surrounding the remnants. The effects of the clearcut also impinged on the remnants as edge effects: six times more voles were captured per trap in the interior of remnants than on the edge. Consequently, the density of voles per unit area on remnants increased with remnant size, despite the potential buildup of population density in small isolates due to limited emigration. I explored potential mechanisms of the negative edge effect on voles and found that the biomass of coarse woody debris, per se, did not explain the vole distribution because both number and volume of logs increased from the interior to the edge of remnants. However, the distribution of the vole's primary food item, hypogeous sporocarps of mycorrhizal fungi, did correspond to the vole edge effect
Assessment of Forest Fragmentation in Southern New England Using Remote Sensing and Geographic Information Systems Technology
Authors: Vogelmann James E.
Published: March 2003

Spatial patterns and rates of forest fragmentation were assessed using digital remote sensing data for a region in southern New England that included 157 townships in southern New Hampshire and northeastern Massachusetts. The study area has undergone marked population increases over the last several decades. Following classification of 1973 and 1988 Landsat Multispectral Scanner data into forest and nonforest classes, data were incorporated into a geographic information system. The natural logarithms of forest area to perimeter ratios, referred to as the forest continuity index, were used to assess patterns and trends of forest fragmentation across the region Forest continuity index values were extracted from each township for both data sets and compared with population data. Forest continuity index values were found to decrease with increasing population density until about 200 persons per square kilometer, after which the relationship stabilized. With slight population increases at low densities forest continuity index values declined sharply, implying abrupt increases in forest fragmentation. Results from the study indicated good negative correlations (r2 values of 0.81 and 0.77) between the Multispectral Scanner‐derived forest continuity index and natural logs of township population density. Socioeconomic indicators such as affluence and commuting patterns did not appear to correlate well with forest fragmentation estimates. Decreases in forest continuity index values occurred throughout much of the study region between 1973 and 1988, suggesting that forest fragmentation is occurring over large regions within the eastern United States. It is technologically feasible to assess patterns and rates of forest fragmentation across much larger areas than analyzed in this study; such analyses would provide useful overviews enabling objective assessment of the magnitude of forest fragmentation.
Impact of Market Hunting on Mammal Species in Equatorial Guinea
Authors: FA JULIA E. , JUSTE JAVIER , DEL VAL JAIME PEREZ , CASTROVIEJO JAVIER
Published: March 2003

Abstract: The impact of commercial hunting on forest mammals was studied in two regions on Bioko and Rio Muni in Equatorial Guinea, west Africa. Harvests were assessed from carcass counts in the main markets in the areas. A total of 10,812 carcasses of 13 species were recorded in Bioko, and 6160 carcasses of 30 species were recorded in Rio Muni. Biomass of harvested mammals was 111,879.63 kg in Bioko and 66,447.87 kg in Rio Muni. For the 12 prey species selected for study in Bioko, harvests totaled 7.15 animals/km2 or 62.93 kg/km2. Harvests for the 17 prey species in Rio Muni were 3.22 animals/km2 or 24.06 kg/km2. We used a model developed by Robinson and Redford (1991) to estimate potential harvests based on animal production rates. Total production was 147.90 animals/km2 and 139.12 animals/km2 in Bioko and Rio Muni, respectively. Potential harvest figures varied considerably by species. Comparison of actual and potential harvests showed that five primate species (Cercopithecus erythrotis, Cercopithecus nictitans, Cercopithecus pogonias, Cercopithecus preussi, and Mandrillus leucophaeus) and one ungulate (Cephalophus ogilbyi) in Bioko were being hunted unsustainably. Only two of the 17 species (Cercopithecus nictitans and Cephalophus dorsalis) in Rio Muni were being hunted unsustainably. Percent deviation of actual from potential harvests averaged 4.98 times greater than sustainable harvest in Bioko and 1.03 times greater in Rio Muni. For the two sites together figures ranged from close to 28 times greater than potential to 0.08% of the potential harvest. Although hunting methods and the commercialization potential of species may affect their presence in markets, these figures show that Bioko animals are heavily exploited, some of them unsustainably. This poses severe risks for the conservation of the island's unique fauna that must be addressed immediately.

Impacto de la caza comercial sobre las especies de mamíferos en Guinea Ecuatorial
Hybridization and the Extinction of Rare Plant Species
Authors: Levin Donald A. , Francisco‐Ortega Javier , Jansen Robert K.
Published: March 2003

Much has been written about the role of interspecific competition, disease, herbivory, and the loss of key mutualisms in the extinction of rare plant species. Interspecific hybridization rarely is considered among the biotic interactions that promote extinction. We show how hybridization may contribute to the demise of rare plant species through demographic swamping and genetic assimilation by an abundant congener. We contend that the growth of the hybrid subpopulation is the key to rare species assimilation, and we show how the production of hybrid seed, the fitness of hybrids, and pest pressure affect hybrid proliferation. We also discuss how habitat disturbance, unspecialized pollinators, and weak crossing barriers promote hybridization, and how the negative consequences of hybridization are unlikely to be compensated for by immigration from conspecific populations. We also illustrate stages in the demise of species in island floras. We suggest that hybridization is an increasing threat to rare species because ecological barriers are being disrupted by human activities.
Invertebrate Morphospecies as Surrogates for Species: A Case Study
Authors: Oliver Ian , Beattie Andrew J.
Published: March 2003

Environmental monitoring and conservation evaluation in terrestrial habitats may be enhanced by the use of invertebrate inventories, but taxonomic and logistic constraints frequently encountered during conventional taxonomic treatment have greatly restricted their use. To overcome this problem we suggest that nonspecialists may be used to classify invertebrates to morphospecies without compromising scientific accuracy. To test this proposition, large pitfall and litter samples of ants, beetles, and spiders from four forest types were sorted to morphospecies by a nonspecialist and to species by specialists. These data were used to generate morphospecies and species inventories and to estimate richness (α diversity) and turnover (β diversity), information frequently used in the above activities. Our results show that the estimates of richness of ants and spiders varied little between morphospecies and species inventories. Differences between estimates of beetle richness were largely influenced by errors of identification in two families, Curculionidae and Staphylinidae. But morphospecies and species inventories yielded identical ranking of forest type using richness. Turnover was assessed by sample ordination, which revealed similar clusters regardless of the type of inventory. Analysis of similarities of assemblages of ants and beetles showed significant differences between all forest types. Spider assemblages showed a lower level of discrimination. The assessment of turnover was consistent among inventories but different between the major taxa. Our findings suggest that morphospecies may be used as surrogates for species in some environmental monitoring and conservation, in particular when decisions are guided by estimates of richness and the assessment of turnover.
Command and Control and the Pathology of Natural Resource Management
Authors: Holling C.S. , Meffe Gary K.
Published: March 2003

As the human population grows and natural resources decline, there is pressure to apply increasing levels of top‐down, command‐and‐control management to natural resources. This is manifested in attempts to control ecosystems and in socioeconomic institutions that respond to erratic or surprising ecosystem behavior with more control. Command and control, however, usually results in unforeseen consequences for both natural ecosystems and human welfare in the form of collapsing resources, social and economic strife, and losses of biological diversity. We describe the “pathology of natural resource management,” defined as a loss of system resilience when the range of natural variation in the system is reduced encapsulates the unsustainable environmental, social, and economic outcomes of command‐and‐control resource management. If natural levels of variation in system behavior are reduced through command‐and‐control, then the system becomes less resilient to external perturbations, resulting in crises and surprises. We provide several examples of this pathology in management. An ultimate pathology emerges when resource management agencies, through initial success with command and control, lose sight of their original purposes, eliminate research and monitoring, and focus on efficiency of control. They then become isolated from the managed systems and inflexible in structure. Simultaneously, through overcapitalization, society becomes dependent upon command and control, demands it in greater intensity, and ignores the underlying ecological change or collapse that is developing. Solutions to this pathology cannot come from further command and control (regulations) but must come from innovative approaches involving incentives leading to more resilient ecosystems, more flexible agencies, more self‐reliant industries, and a more knowledgeable citizenry. We discuss several aspects of ecosystem pattern and dynamics at large scales that provide insight into ecosystem resilience, and we propose a “Golden Rule” of natural resource management that we believe is necessary for sustainability: management should strive to retain critical types and ranges of natural variation in resource systems in order to maintain their resiliency.
Darwin’s Fox: A Distinct Endangered Species in a Vanishing Habitat
Authors: Yahnke Christopher J. , Johnson Warren E. , Geffen Eli , Smith Deborah , Hertel Fritz , Roy Michael S. , Bonacic Cristian F. , Fuller Todd K. , Van Valkenburgh Blaire , Wayne Robert K.
Published: March 2003

The temperate rain forest of Chiloé Island, Chile, is inhabited by an endemic fox (Dusicyon fulvipes) first described by Charles Darwin and now designated Darwin’s fox. Despite morphological differences, Darwin’s fox has been considered only an insular subspecies of the mainland chilla fox (D. griseus). This follows the assumption that the island population, with an estimated population of less than 500, has been separated from the mainland chilla fox for only about 15,000 years and may have received occasional immigrants from the mainland. Consequently, this island population has not been protected as endangered or bred in captivity. Recently, a population of Darwin’s fox was discovered on the Chilean mainland 600 km north of Chiloé Island. This population exists in sympatry with chilla and possibly culpeo (D. culpaeus) foxes, which suggests that Darwin’s fox may be reproductively isolated. To clarify the phylogenetic position of Darwin’s fox, we analyzed 344 bp of mitochondrial DNA control‐region sequence of the three species of Chilean foxes. Darwin’s foxes from the island and mainland populations compose a monophyletic group distinct from the two other Chilean fox species. This indicates that Darwin’s fox was probably an early inhabitant of central Chile, and that its present distribution on the mainland may be a relict of a once much wider distribution. Our results highlight the ability of molecular genetic techniques to uncover historical relationships masked by recent events, such as local extinctions. The “rediscovery” of Darwin’s fox as a distinct species implies that greater significance should be given to the protection of this species and its unique habitat and to documenting the extent of its mainland distribution.
Collapse of a Regional Frog Fauna in the Yosemite Area of the California Sierra Nevada, USA
Authors: Drost Charles A. , Fellers Gary M.
Published: March 2003

There has been much concern about widespread declines among amphibians, but efforts to determine the extent and magnitude of these declines have been hampered by scarcity of comparative inventory data. We resurveyed a transect of the Sierra Nevada mountains in western North America that was carefully studied in the early 1900s. Our comparisons show that at least five of the seven frog and toad species in the area have suffered serious declines. One species has disappeared from the area entirely and a second species, formerly the most abundant amphibian in the area, has dwindled to a few small remnant populations. These declines have occurred in a relatively undisturbed, protected area and show some of the same patterns noted in other reports of amphibian declines. Introduced predatory fish, possibly interacting with drought‐induced loss of refuge habitats, have contributed to the decline of some species. However, the overall cause of these dramatic losses remains unknown.
The Quantitative Incidence Function Model and Persistence of an Endangered Butterfly Metapopulation
Authors: Hanski Ilkka , Moilanen Atte , Pakkala Timo , Kuussaari Mikko
Published: March 2003

The incidence function model is derived from a linear first‐order Markov chain of the presence or absence of a species in a habitat patch. The model can be parameterized with “snapshot” presence/absence data from a patch network. Using the estimated parameter values the Markov chain can be iterated in the same or in some other patch network to generate quantitative predictions about transient metapopulation dynamics and the stochastic steady state. We tested the ability of the incidence function model to predict patch occupancy using extensive data on an endangered butterfly, the Glanville fritillary (Melitaea cinxia) Parameter values were estimated with data collected from a 50‐patch network in 1991. In 1993 we surveyed the entire geographic range of the species in Finland, within an area of 50 × 70 km2, with 1502 habitat patches (dry meadows) of which 536 were occupied. Model predictions were generated for the 1502 patches and were compared with the observed pattern of occupancy in 1993. The model predicted patch occupancy well in more than half of the study area, but prediction was poor for one quarter of the area, probably because of regional variation in habitat quality and because metapopulations may have been perturbed away from the steady state. The incidence function model provides a practical tool for making quantitative predictions about metapopulation dynamics of species living in fragmented landscapes.
Tropical Diversity and Conservation
Authors: Briggs John C.
Published: March 2003

The superior diversity of the tropics is well known and, for the largest marine and continental areas, there appears to be a positive relationship between area and species diversity (richness). There are certain portions of the tropics, however, in which species diversity has reached unusually high levels. Such areas apparently function as centers of evolutionary origin. In the ocean the largest of the four tropical shelf regions is the Indo‐West Pacific, which stretches almost two thirds of the distance around the globe. Within that expanse by far the greatest diversity is found within the relatively small East Indies Triangle. From the Triangle an evolutionary radiation has reached many other parts of the marine world. On land the Neotropical, Ethiopian, and Oriental biogeographic regions demonstrate very high levels of species diversity. Various major groups of animals and plants have originated in these regions and subsequently spread to other parts of the world. There is no accepted scientific agreement on a conservation strategy for these areas. By focusing our attention on centers of origin, we can save the areas containing species that apparently have the greatest evolutionary potential.
Effects of Population Size, Mating System, and Evolutionary Origin on Genetic Diversity in Spiranthes sinensis and S. hongkongensis
Authors: Sun Mei
Published: March 2003

Hong Kong once supported more than 109 species of wild orchids, of which approximately 30% were endemic. Most of the local wild orchids have now become rare or endangered. I conducted a comparative study of genetic diversity in two closely related terrestrial orchids, an allotetraploid, Spiranthes hongkongensis, and its diploid progenitor, S. sinensis, to assess the effects of the population bottleneck associated with the origin of the polyploid and to investigate the relationships between number of breeding individuals, mating system, and level of isozyme variation in their populations. Nearly complete genetic uniformity was observed both within and among populations of S. hongkongensis. In contrast, S. sinensis had high levels of genetic variation for all of the genetic parameters examined. Regression analysis of population size and several components of genetic diversity in S. sinensis revealed that, among various measures of within‐population variation, the proportion of polymorphic loci (P) and average number of alleles per locus (A) or per polymorphic locus (Ap) were the most sensitive to population size (R2 = 0.942, p = 0.001; R2 = 0.932, p = 0.002; and R2 = 0.923, p = 0.002 respectively). The highly negative correlation (r = −0.999, p < 0.01) between population size and the mean frequency of private alleles in pairwise population comparisons,

p(1), indicated that population size may also be used to predict the extent of population differentiation caused by random genetic drift. Conservation of genetic diversity in S. sinensis could be maximized by protecting several of both large and small populations, whereas fewer populations may be needed to achieve this goal for S. hongkongensis.
Factors Leading to Different Viability Predictions for a Grizzly Bear Data Set
Authors: Mills L. Scott , Hayes Stephen G. , Baldwin Calib , Wisdom Michael J. , Citta John , Mattson David J. , Murphy Kerry
Published: March 2003

Population viability analysis programs are being used increasingly in research and management applications, but there has not been a systematic study of the congruence of different program predictions based on a single data set. We performed such an analysis using four population viability analysis computer programs: GAPPS, INMAT, RAMAS/AGE, and VORTEX. The standardized demographic rates used in all programs were generalized from hypothetical increasing and decreasing grizzly bear (Ursus arctos horribilis) populations. Idiosyncracies of input format for each program led to minor differences in intrinsic growth rates that translated into striking differences in estimates of extinction rates and expected population size. In contrast, the addition of demographic stochasticity, environmental stochasticity, and inbreeding costs caused only a small divergence in viability predictions. But, the addition of density dependence caused large deviations between the programs despite our best attempts to use the same density‐dependent functions. Population viability programs differ in how density dependence is incorporated, and the necessary functions are difficult to parameterize accurately. Thus, we recommend that unless data clearly suggest a particular density‐dependent model, predictions based on population viability analysis should include at least one scenario without density dependence. Further, we describe output metrics that may differ between programs; development of future software could benefit from standardized input and output formats across different programs.
Effects of Water Management on the Wetlands of the Colorado River Delta, Mexico
Authors: Glenn Edward P. , Lee Christopher , Felger Richard , Zengel Scott
Published: March 2003

The lower delta of the Colorado River has been severely affected by the upstream diversion of water for human use. No river water is officially appropriated to support delta wetlands, yet large marsh areas of conservation interest still exist below the agricultural fields in Mexico. These are supported by flood water, agricultural drainage water, municipal sewage effluent, and seawater in the intertidal zone. From 1973 to 1993 the area of freshwater and brackish marsh varied widely, from 5800 to 63,000 ha. A new opportunity exists to restore wetlands in the delta now that the upstream water impoundments on the Colorado River are filled and flood flows are once again being directed to the delta. But flood control structures now channel most of the flood water directly to the sea, and most of the effluent waters are deposited in evaporation basins rather than used to support wetlands. If the Yuma Desalting Plant in the United States becomes operational and if the Rio Hardy wetlands continue to be drained, the area of brackish wetlands could decrease to less than 2000 ha in the near future. Preserving the remaining wetlands will require a binational water management plan. The plan should maximize the benefits to wetlands of flood and irrigation return flows that enter the delta, and it should minimize flood risks.
A Century of Plant Species Loss from an Isolated Fragment of Lowland Tropical Rain Forest
Authors: Turner I.M. , Chua K.S. , Ong J.S.Y. , Soong B.C. , Tan H.T.W.
Published: March 2003

An isolated 4‐ha fragment of lowland tropical rain forest has been preserved in the Singapore Botanic Gardens since their founding in 1859. The Botanic Gardens’Jungle has recently had enumerated all woody stems 5 cm diameter at breast height (dbh) and larger and the complete vascular plant flora inventoried. This inventory can be compared with the historic record of the flora of the Gardens’Jungle obtained from the extensive collection of herbarium specimens dating back to the 1890s. Of the 448 historically recorded native species, 220 are still present. Ninety‐four native species for which there were no historic records and 80 introduced species were also recorded in the recent inventory. The 50.9% loss of plant species richness over approximately the last century has not been distributed uniformly across plant life‐form groups. Tree species have been less likely to go extinct than shrubs, climbers, or epiphytes. But half of the tree species present in 1994 were represented by only one or two individuals ≥ 5 cm dbh and larger. Individual longevity may be the major correlate with persistence of plant species in isolated forest fragments. Shade‐tolerant understory shrubs (mostly Rubiaceae) and rattans (Palmae) have been particularly prone to extinction. Some species have probably proliferated during the period of isolation. The tree Calophyllum ferrugineum currently constitutes one quarter of all woody stems. A group of climbers has become very common and covers large areas, probably inhibiting tree regeneration. We conclude that tiny fragments will act as refuges for tropical rain‐forest plant species for decades, possibly even centuries after isolation but on their own they will not provide a permanent guarantee of the conservation of tropical biodiversity.
Directions in Conservation Biology: Comments on Caughley
Authors: Hedrick Philip W. , Lacy Robert C. , Allendorf Fred W. , Soulé Michael E.
Published: March 2003

The recent review by Caughley (1994) on approaches used in conservation biology suggested that there are two: the small population paradigm and the declining population paradigm. We believe that this division is overly simplistic and that it should not be perpetuated. Both the deterministic factors that reduce population size and the stochastic factors that lead to the final extinction of a small population are critical to consider in preventing extinction. Only through an overall and comprehensive effort, which we call inclusive population viability analysis, can extinction processes be understood and mitigated. In this context we discuss Caughley’s comments about genetics, demography, and general population viability, with particular attention to cheetahs (Acinonyx jubatus) and Pacific salmon (Oncorhynchus sp.).