bluuebunny/crossref_metadata_2025 huggingface dataset:
Managing Species Diversity in Tallgrass Prairie: Assumptions and Implications
Authors: Howe Henry F.
Published: March 2003

Conservation and restoration ecology efforts may conserve or restore a particular image of a community, a variety of plausible images, or maximum biological diversity. The choice is a policy decision that should reflect relevant history and sound science. Here I argue that common methods of conserving and restoring tallgrass prairie have a weak scientific rationale, are not consistent with plausible history, and threaten prairie biodiversity. Dormant‐season burns and grazer exclusion are human interventions that may promote artificially consistent dominance of large grasses utilizing the C4 photosynthetic pathway, thereby relegating hundreds of other prairie plants to small populations that are vulnerable to local extinction. I recommend an experimental approach to large remnant conservation and restoration in which varied conditions alter dominance, thereby increasing short‐term species richness. I also recommend prescribed burning during the summer, to simulate the timing of lightning fire, and light‐to‐moderate grazing by different ungulates, to simulate historical grazing history. Both should favor plants that are consistently infrequent or rare in many managed prairies. Varied regimes of burn season, burn interval, and large‐mammal grazing should promote greater overall species diversity and should more realistically represent varied conditions under which grassland taxa evolved.
Allometric Scaling of Minimal Mammal Densities
Authors: Silva Marina , Downing John A.
Published: March 2003

Minimum viable densities have rarely been determined directly. Theoretical analyses, based on empirical relationships between average mammal densities, suggest that minimum densities of viable populations are lower for larger mammals. This suggestion has been cast into doubt by other field studies showing populations of small insects and birds at very low densities. We collected 143 of the closest approximations of minimum viable density available, those of minimal, rare, and endangered mammal populations. We found that minimal density decreases as the −0.68 power of body mass. Minimal densities of small mammals are 1000 times those of the largest species. The correlation between minimum viable population density and body mass is negative in the majority of the mammalian taxonomic orders. Although minimum density is, on average, 10% of mean population density, viable population densities of herbivores are 13 times those of carnivores and insectivores. Populations in the wet tropics can apparently sustain themselves at densities much lower than those in temperate climates.
Roads and the Environmental Degradation of Tropical Montane Forests
Authors: Young Kenneth R.
Published: March 2003

Roads are often a causal agent in the degradation of tropical forests; in this paper their impact is discussed for the forested, humid montane zone. Because of their steep slopes and high elevations, these forests have disturbance regimes associated with slope instability, limited resilience, and numerous species that are elevational specialists, restricted to narrow altitudinal belts. Roads often augment slope instability and fragment ranges of specialized species. Roads can allow uncontrolled extraction of natural products and landscape conversion. Improvements are needed in the design, construction, and maintenance of these roads. Also needed are studies and mitigation efforts to reduce their effects on the specialized biota of montane forests.
Effect of High‐Intensity Wildfire and Silvicultural Treatments on Reptile Communities in Sand‐Pine Scrub
Authors: Greenberg Cathryn H. , Neary Daniel G. , Harris Larry D.
Published: March 2003

We tested whether the herpetofaunal response to clearcutting followed by site preparation was similar to high‐intensity wildfire followed by salvage logging in sand‐pine scrub. Herpetofaunal communities were compared in three replicated 5‐ to 7‐year post‐disturbance treatments and mature sand‐pine forest. The three disturbance treatments were (1) high‐intensity wildfire, salvage‐logging, and natural regeneration; (2) clearcutting, roller‐chopping, and broadcast‐seeding; and (3) clearcutting and bracke‐seeding. Animals were trapped over a 14‐month period using pitfall traps with drift fences. Microhabitat features were measured along line transects. Because amphibian (frog) occurrence appeared to be unaffected by treatment, this paper focuses only on reptile communities. Six species of lizards and one snake species were numerically dominant. Reptile species richness, diversity, and evenness did not differ among treatments or mature forest. Species composition differed markedly, however, between mature forest and disturbance treatments. Typical open scrub species such as Cnemidophorus sexlineatus, Sceloporus woodi, and Eumeces egregius, were dominant in high‐intensity burn, roller‐chopped, and bracke‐seeded stands but scarce in mature forest, and they were positively correlated with bare sand and other microhabitat features typical of open scrub. Conversely, Eumeces inexpectatus was most abundant in mature forest and was correlated with ground litter and other features typical of mature forest. With respect to the species sampled, especially the lizards (including endemic species) of open scrub, clearcutting appeared to mimic high‐intensity wildfire followed by salvage‐logging by creating microhabitat features such as bare sand. In a mirror image of the usual concept, forest maturation historically served as the fragmenting agent of an extensive open‐scrub landscape matrix that was maintained by high‐intensity wildfire. Hence, the patchwork of age classes created by current clearcutting patterns could serve as a barrier to lizard dispersal and impede metapopulation dynamics. The absence of a true control (unsalvaged burns) suggests caution in interpreting the results of this study.
Availability and Extraction of Forest Products in Managed and Primary Forest around a Dayak Village in West Kalimantan, Indonesia
Authors: Lawrence Deborah C. , Leighton Mark , Peart David R.
Published: March 2003

We examined the density and abundance of marketable products in managed forest (rubber gardens, fruit gardens, and dry rice fallows) and in primary forest surrounding the Dayak village of Kembera, near Gunung Palung National Park, West Kalimantan, Indonesia. We calculated the proportion of trees that were marketable and useful for local consumption by counting and identifying trees in each managed forest type, and we documented extraction of products through interviews. Villagers harvested four marketable tree products: tengkawang seeds (Shorea stenoptera), durian fruits (various Durio spp.), rubber (Hevea brasiliensis), and timber, especially Bornean ironwood (Eusideroxylon zwageri). We inventoried trees at least 20 cm diameter at breast height (dbh) of marketed species from 0.4‐ha plots in primary forest (n = 8) and from 0.1‐ha plots in each managed forest type (n = 10–11). With the exception of timber, the density of trees producing a marketable product was significantly higher in the forest type managed for that product than the density of the marketed species, or of similar wild species, in primary forest. Total abundance (product of density and available area) of durian and tengkawang was greater in primary forest; however, villagers gathered these products only from managed forest. We infer from this choice a greater efficiency of harvesting from trees in dense stands near the village. Historically, this choice resulted in deliberate development of fruit gardens in preference or in addition to gathering from the more distant, primary forest. Because of low product density in primary forest, extractive forest reserves or buffer zones designed to encourage the production of fruits such as tengkawang or durian may not provide a sufficient incentive for the protection of primary forest around Kembera and other Dayak villages near Gunung Palung National Park.
Implications from Mitochondrial DNA for Management to Conserve the Eastern Barred Bandicoot (Perameles gunnii)
Authors: Robinson Nicholas Andrew
Published: March 2003

On mainland Australia, the eastern barred bandicoot, Perameles gunnii, is confined to a relic wild population numbering less than 100 individuals in the city of Hamilton. Animals derived from this population are being bred in captivity in order to promote their recovery. The species also exists in Tasmania, where tittle is known of its conservation and taxonomic status. Mitochondrial DNA variability was compared within and between populations of P. gunnii using restriction fragment length polymorphisms. Genetic variability was found to be high among P. gunnii in Hamilton compared to those in Tasmania (higher diversity index, nucleotide sequence divergence, and greater number of haplotypes), despite the known decline and subdivision of the Hamilton population. Restriction fragment length polymorphisms distinguished animals from the east and the west of Hamilton and from the north and south of Tasmania. Nucleotide sequence divergence was substantial (2.2–2.5%) between Hamilton and Tasmania. Implications are that captive breeding and reintroduction should be designed to genetically represent the structure within Hamilton in order to minimize inbreeding and that the introduction of Tasmanian P. gunnii would not benefit the Hamilton population. It is concluded that mitochondrial DNA markers clearly can provide useful information about the history and current status of endangered marsupial populations, to the benefit of conservation management.
Ecological Attributes of Extinction‐Prone Species: Loss of Freshwater Fishes of Virginia
Authors: Angermeier Paul L.
Published: March 2003

I examined patterns of extirpation among Virginia’s 197 historically native freshwater fish species to address the following questions: (1) Are extinction‐prone species ecologically distinct? and (2) Are distinctive features similar to those identified for extinction‐prone species in terrestrial systems? All species were assigned to categories for a series of attributes reflecting geographical distribution, habitat use, trophic habits, life history, size, and reproductive behavior. Associations between species that had been extirpated and those that had not were examined for each attribute. Univariate associations were observed between extirpation and three ecological attributes: diadromy, limited physiographic range, and limited range of water sizes. Species specialized with respect to multiple ecological attributes also were especially likely to be extirpated. These associations reflected the effects of reduced habitat area and increased isolation (insularization), which are also important determinants of extinction in terrestrial systems. Multivariate analyses suggested that extirpated species were ecologically similar to each other, but were not completely distinct from the nonextirpated fauna. My results suggest that ecological knowledge of species can help identify extinction‐prone species and provide a basis for proactive conservation. Current approaches to conservation, which are largely reactive and piecemeal, are inadequate to protect biodiversity. Because aquatic degradation is complex and pervasive, conservation of aquatic biodiversity requires proactive comprehensive approaches to water resource management, including emphasis on protecting the ecological integrity of entire systems.
Values Associated with Management of Yellowstone Cutthroat Trout in Yellowstone National Park
Authors: Gresswell Robert E. , Liss William J.
Published: March 2003

Recent emphasis on a holistic view of natural systems and their management is associated with a growing appreciation of the role of human values in these systems. In the past, resource management has been perceived as a dichotomy between extraction (harvest) and nonconsumptive use, but this appears to be an oversimplified view of natural‐cultural systems. The recreational fishery for Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri) in Yellowstone National Park is an example of the effects of management on a natural‐cultural system. Although angler harvest has been drastically reduced or prohibited, the recreational value of Yellowstone cutthroat trout estimated by angling factors (such as landing rate or size) ranks above that of all other sport species in Yellowstone National Park. To maintain an indigenous fishery resource of this quality with hatchery propagation is not economically or technically feasible. Nonconsumptive uses of the Yellowstone cutthroat trout including fish‐watching and intangible values, such as existence demand, provide additional support for protection of wild Yellowstone cutthroat trout populations. A management strategy that reduces resource extraction has provided a means to sustain a quality recreational fishery while enhancing values associated with the protection of natural systems.
Extinction of Mammal Populations in Western North American National Parks
Authors: Newmark William D.
Published: March 2003

Patterns of local extinction of mammal populations in western North American parks were examined in relation to current biogeographic and population lifetime models. The analysis was based on species sighting records as of 1989. While western North American parks are obviously not true isolates, patterns of mammal extinction in them are nonetheless consistent with two predictions of the land‐bridge island hypothesis. First, the number of extinctions has exceeded the number of colonizations since park establishment, and, second, the rate of extinction is inversely related to park area. Factors influencing the lifetime of mammal populations were evaluated using a stepwise multivariate survival analysis procedure for censored data. Survival time for mammal populations was positively related to estimated initial population size. After accounting for population size, species within the order Lagomorpha were particularly prone to extinction. Finally, after controlling for population size and taxon variation, survival time was positively related to age of maturity, indicating that species with longer generation times—age of maturity and generation time are highly correlated in mammals—persist longer in absolute time.
Waterbird Communities and Habitat Relationships in Coastal Pastures of Northern California
Authors: Colwell Mark A. , Dodd Sarah L.
Published: March 2003

We examined waterbird assemblages (diversity, composition, and species’ densities) in 20 pastures near Humboldt Bay, California, in relation to habitat characteristics (vegetation height, soil penetrability, water depth), abundance of invertebrates (worms and other invertebrates), and presence of livestock. From October 1991 to May 1992 we observed 29 species and 10,776 birds, most (78%) of which foraged. Nonrandom pasture use by birds resulted in a highly clumped spatial distribution (s2:{ovbar>x} ratio = 42.1). Habitat characteristics of pastures correlated with this nonrandom pattern: waterbird diversity and densities of three sandpiper species and one gull species correlated negatively (r = −0.61 and r = −0.44 to −0.67, respectively) with vegetation height; densities of two plover species correlated negatively (r= −0.39 and −0.45) with soil penetrability; and waterfowl densities correlated positively with water depth (r = 0.97). Species composition varied among pastures. Wading birds used pastures with tall vegetation, shorebirds and gulls frequented short‐grass pastures, and waterfowl used flooded pastures of waterbirds and their densities increased in association with livestock.In coastal areas where much intertidal habitat has been reclaimed as postureland, pastures offered valuable habitats to nonbreeding waterbirds. We suggest that grazing in coastal pastures can be used to provide a mosaic of vegetation heights, which would yield greater waterbird diversity as well as higher densities of some species.
Overwinter Survival of Neotropical Migratory Birds in Early‐Successional and Mature Tropical Forests
Authors: Conway Courtney J. , Powell George V.N. , Nichols James D.
Published: March 2003

Many Neotropical migratory species inhabit both mature and earty‐successional forests on their wintering grounds, yet comparisons of survival rates between habitats are lacking. Consequently, the factors affecting habitat suitability for Neotropical migrants and the potential effects of tropical deforestation on migrants are not well understood. We estimated overwinter survival and capture probabilities of Wood Thrush (Hylochichla mustelina), Ovenbird (Seiurus aurocapillus), Hooded Warbler (Wilsonia citrina), and Kentucky Warbler (Oporornis formosus) inhabiting two common tropical habitat types, mature and early‐successional forest. Our results suggest that large differences (for example, ratio of survival rates (γ) ≤ 0.85) in overwinter survival between these habitats do not exist for any of these species. Age ratios did not differ between habitats, but males were more common in forest habitats and females more common in successional habitats for Hooded Warblers and Kentucky Warblers. Future research on overwinter survival should address the need for age‐ and sex‐specific survival estimates before we can draw strong conclusions regarding winter habitat suitability. Our estimates of overwinter survival extrapolated to annual survival rates that were generally lower than previous estimates of annual survival of migratory birds. Capture probability differed between habitats for Kentucky Warblers, but our results provide strong evidence against large differences in capture probability between habitats for Wood Thrush, Hooded Warblers, and Ovenbirds. We found no temporal or among‐site differences in survival or capture probability for any of the four species. Additional research is needed to examine the effects of winter habitat use on survival during migration and between‐winter survival.
Source‐Sink Models and the Problem of Habitat Degradation: General Models and Applications to the Yellowstone Grizzly
Authors: Doak Daniel F.
Published: March 2003

I used source‐sink population models to explore the consequences of habitat degradation for populations living on good and degraded habitats linked by movement. In particular, I modeled the conversion of land from good habitat quality supporting positive population growth to a degraded condition in which there was population decline. I found that with high rates of movement between good and bad quality areas populations require relatively large amounts of good habitat to remain stable. However, low movement rates resulted in greater sensitivity of population growth to habitat loss. Even small amounts of habitat degradation could result in rapid changes in overall population growth rates depending upon the rates of population increase and decline in the two habitat types. I also developed and simulated an age‐structured model for grizzly bears (Ursus arctos horribilis) existing in good and degraded habitats and fit this model to data from the Yellowstone grizzly population. I used this model to predict the ability to detect crucial amounts of habitat degradation from census data and found that when degradation is slow (e.g., 1% conversion of good to poor habitat per year), more than a decade may pass between crucial amounts of degradation—beyond which populations begin long‐term decline—and its detection, even if census data were unrealistically good. Thus these simple models indicate that, at least in some circumstances, habitat degradation can have rapid and severe impacts on population dynamics and traditional monitoring programs may not be adequate to detect the consequences of degradation.
Effects of Residential Development on Forest‐Dwelling Neotropical Migrant Songbirds
Authors: Friesen Lyle E. , Eagles Paul F.J. , Mackay R.J.
Published: March 2003

Many bird species are in local or regional decline because of habitat loss or degradation. We attempted to disentangle the effects of residential development from the effects of forest size on forest‐bird communities, with particular emphasis on Neotropical migrant species. Two variables were examined for their influence on avian diversity and abundance: forest size and the number of houses outside a forest within 100 m of the edge. We found that Neotropical migrants consistently increased in number and abundance as forest size increased. Of greater interest, we found that the number of houses surrounding a forest severely undermined its suitability for Neotropical migrants. Neotropical migrants consistently decreased in diversity and abundance as the level of adjacent development increased, regardless of forest size. The effects of development were striking: 4‐ha woodlots without any nearby houses had on average a richer, more abundant Neotropical community than did 25‐ha urban woodlots. No predictable pattern of change concerning development or forest size was observed for short‐distance migrants or permanent residents. Current planning regulations generally permit housing right up to forest edges. This practice may prevent protection of ecological features within the forest. Threshold distances for housing developments around forests need to be determined to prevent or minimize adverse effects on features and functions within the forests.
Population Declines and Range Contractions among Lowland Farmland Birds in Britain
Authors: Fuller R.J. , Gregory R.D. , Gibbons D.W. , Marchant J.H. , Wilson J.D. , Baillie S.R. , Carter N.
Published: March 2003

We used extensive atlas and census data to assess trends in the distribution and population levels of birds on lowland farmland in Britain between the late 1960s and early 1990s. Many species of farmland birds have become less widespread or have declined in numbers, or both, but few have become more wide‐spread or have increased. Of the 28 species classified as farmland birds the distributions of 24 contracted between 1970 and 1990. Of the 18 farmland species for which it was possible to assess population change, 15 were less abundant in 1990 than in 1970. Seven of the species were estimated to have undergone population decreases of at least 50%. Farmland species showing the largest population declines tended also to show substantial range contractions. Farmland species underwent an appreciably larger contraction of distribution than species associated with any other habitat. Furthermore, farmland species tended to decrease in abundance, whereas woodland species tended to increase. Population declines among farmland birds became evident in the mid‐ to late 1970s, a period when several fundamental changes were taking place in British agricultural practices. These included a great reduction in the spring sowing of cereals, a simplification of crop rotations, increased use of chemical pesticides and inorganic fertilizers, and more‐intensive grassland management. We suggest that the declines of farmland bird species have been caused or aggravated by this pervasive intensification of agriculture. Existing research on declining farmland birds, however, indicates that there is no single mechanism underlying the population changes. We identify priorities for research, focusing mainly on relationships between bird populations and agricultural practices, but we also recognize a need for a better understanding of the role of predation.
Testing the Generality of Bird‐Habitat Models
Authors: Fielding Alan H. , Haworth Paul F.
Published: March 2003

Bird‐habitat models are frequently used as predictive modeling tools—for example, to predict how a species will respond to habitat modifications. We investigated the generality of the predictions from this type of model. Multivariate models were developed for Golden Eagle (Aquila chrysaetos), Raven (Corvus corax), and Buzzard (Buteo buteo) living in northwest Scotland. Data were obtained for all habitat and nest locations within an area of 2349 km2. This assemblage of species is relatively static with respect to both occupancy and spatial positioning. The area was split into five geographic subregions: two on the mainland and three on the adjacent Island of Mull, which has one of United Kingdom’s richest raptor fauna assemblages. Because data were collected for all nest locations and habitats, it was possible to build models that did not incorporate sampling error. A range of predictive models was developed using discriminant analysis and logistic regression. The models differed with respect to the geographical origin of the data used for model development. The predictive success of these models was then assessed by applying them to validation data. The models showed a wide range of predictive success, ranging from only 6% of nest sites correctly predicted to 100% correctly predicted. Model validation techniques were used to ensure that the models’ predictions were not statistical artefacts. The variability in prediction success seemed to result from methodological and ecological processes, including the data recording scheme and interregional differences in nesting habitat. The results from this study suggest that conservation biologists must be very careful about making predictions from such studies because we may be working with systems that are inherently unpredictable.
Applying Biodiversity Gap Analysis in a Regional Nature Reserve Design for the Edge of Appalachia, Ohio (U.S.A.)
Authors: Strittholt James R. , Boerner Ralph E.J.
Published: March 2003

A biodiversity gap analysis is a method, now usually employing geographic information systems, for identifying deficiencies in existing biodiversity protection. Key principles of gap analysis were applied to a region of southcentral Ohio (U.S.A.) known as The Edge of Appalachia as part of a detailed, large‐scale (1:24,000) nature reserve design project. By combining Landsat thematic mapper imagery with ancillary data (bedrock geology, elevation, slope, aspect, and stream proximity), a rule‐based model was developed to differentiate and map the natural plant communities present in the 378‐km2 study area. The model was then used to generate a map depicting the most likely presettlement plant community distributions for the area. These two maps were compared against the 5273 ha owned and managed by state and local conservation organizations. For the current natural plant community distributions, regional land‐protection efforts represented each plant community proportionally; however, comparison with the presettlement vegetation clearly identified serious historical losses of several plant community types. Our results suggest that future land acquisitions should emphasize those plant community types that were once more widespread in the region prior to European settlement, a time when natural processes were less compromised by human activity. Current and historical plant‐community mapping results were combined and evaluated using the ownership parcel as the fundamental mapping unit. From parcel‐based desirability maps a conservation plan was developed that addressed community deficiencies using a representation target of25% for each community type, as derived from the modeled presettlement landscape.
Predictive Model of the Effects on Lake Metabolism of Decreased Airborne Litterfall through Riparian Deforestation
Authors: France R.L. , Peters R.H.
Published: March 2003

The importance of airborne allochthonous litter to the carbon and nutrient budgets of lakes has been seldom studied. We complied data on the input of terrestrial litter to develop a simple and speculative model to predict the potential consequences of riparian deforestation on one aspect of lake metabolism, specifically the balance between phytoplankton production and plankton respiration. During the autumn of 1992, 56 litter traps were deployed around the littoral zones of four oligotrophic lakes in a densely forested region of northwestern Ontario, Canada. The airborne litter input was estimated to be 32 g dry weight per meter of forested shoreline per year. Allochthonous litter input per unit offshore distance was related to the size of riparian trees, their proximity to the shoreline, and the elevation of their canopy. Combining our data with those from other studies suggests that terrestrial litter can contribute up to 15% of the total carbon supply to oligotrophic lakes and up to 10% of the total phosphorus supply to lakes with a large surface area relative to that of their drainage basin. These results were incorporated into a simple model that predicts that removal of shoreline trees could increase the ratio of plankton production to respiration in oligotrophic lakes situated within small drainage basins. Such lakes may therefore shift from allotrophy to increasing autotropy (energy self‐sustenance) following riparian deforestation.
Reproduction of a Rare New Zealand Reptile, the Tuatara Sphenodon punctatus, on Rat‐Free and Rat‐Inhabited Islands
Authors: Cree Alison , Daugherty Charles H. , Hay Jennifer M.
Published: March 2003

We compared evidence for successful reproduction of tuatara (Sphenodon punctatus punctatus) in the presence or absence of introduced Pacific rats (kiore, Rattus exulans) for islands in the Mercury Group and Hen and Chickens Group, New Zealand Tuatara were captured more frequently on the two kiore‐free islands than on the six kiore‐inhabited islands, suggesting reduced density in the presence of kiore. On the two kiore‐free islands, 22.2–30.8% of all tuatara captured were juveniles or small adults (<200 mm snout‐vent length). In contrast, juvenile tuatara were not seen on five of the six kiore‐inhabited islands and small adults were absent from three. These data support an earlier study suggesting that kiore inhibit recruitment of tuatara. Both sexes of adult tuatara were present on kiore‐inhabited islands, and plasma concentrations of sex hormones suggest that at least some adults remain reproductively active on most islands. Throughout their range, tuatara have become extinct this century on four islands inhabited by kiore, they are on the verge of extinction on two kiore‐inhabited islands sampled in this study and two kiore‐inhabited islands not sampled, and they are absent from at least six other kiore‐inhabited islands on which on biogeographic grounds they would be expected to be present. Although the data remain circumstantial, the most plausible explanation of these observations is that kiore can cause extinction of tuatara through competition for food and/or predation on eggs and juveniles. In the absence of kiore eradication the four worst‐case populations of tuatara would probably be extinct within 10–20 years and populations on three other islands would probably be relictual or extinct within 30–50 years. Kiore eradication is being carried out on most of these islands, in part to help ensure tuatara survival Well‐monitored eradication programs will enable an experimental test of the hypothesis that tuatara densities and recruitment rates are enhanced in the absence of kiore.
Fragmentation, Disturbance, and Plant Distribution: Mistletoes in Woodland Remnants in the Western Australian Wheatbelt
Authors: Norton David A. , Hobbs Richard J. , Atkins Lyn
Published: March 2003

Spatial heterogeneity and patchy distributions of species in intact landscapes are likely to lead to complex and unpredictable distribution patterns in remnants following fragmentation. We examined this proposition in relation to the mistletoe Amyema miquelii, which exhibits a clumped distribution in Eucalyptus salmonophloia woodlands in the Western Australian wheatbelt. We sampled mistletoe distribution and abundance in 14 woodland fragments ranging from 2.4 to 60.5 ha and in 14 sections of roadside corridors. These sites represent all known fragments and corridors containing E. salmonophloia in a 1680‐km2 study area. We found that large fragments were more likely to have mistletoes than small fragments, but that small fragments either contained many or few to no mistletoes, reflecting the way fragmentation “samples” the pre‐existing distribution. Superimposed on this sampling effect is the influence of disturbance. Fragments subjected to stock grazing contained no mistletoes. This indicates that grazing modified the habitat either for the mistletoe itself, through changed water relations, or for the frugivorous birds which may disperse mistletoe fruit, through removal of the shrubby understory. Only one A. miquelii plant was found on 26.3 km of roadside corridor, despite tree densities in corridors being similar to those in fragments. Roadside areas are generally considered good habitat for mistletoes, and their absence suggested that fruit‐dispersing birds either did not use the corridors or did not stay in them long enough to deposit mistletoe seeds. These results indicate that, in order to predict biotic responses to fragmentation, information on distribution patterns and scales of patchiness in the prefragmentation landscape is required and the effects of fragmentation per se are likely to be confounded by other factors such as disturbance. Furthermore, quantifying fragmentation effects is difficult because of the small sample sizes typical of highly fragmented landscapes.
Songbird Use of Gallery Woodlands in Recently Cleared and Older Settled Landscapes of the Selva Lacandona, Chiapas, Mexico
Authors: WARKENTIN IAN G. , GREENBERG RUSSEL , ORTIZ JAVIER SALGADO
Published: March 2003

Abstract:Many regions of Central America have undergone wide‐scale habitat change as land has been converted for cultivation or grazing. Clearing for agriculture often leaves a variety of regenerating and remnant patches of wooded vegetation. Of particular importance is arroyo vegetation, or strips of trees or tall shrubs growing along streams. Although it is widely acknowledged that tropical arroyo vegetation supports high densities of birds, as avian habitat it remains poorly studied. We used point counts to study populations of migrant and resident songbirds in the arroyo vegetation of settled areas of the Selva Lacandona adjacent to the Montes Azules Biosphere Reserve of southeastern México. Two study areas were established on lands that had been cleared and settled 20–35 and 10 years previously. Our objectives were to asses the value of arroyo vegetation to the conservation of avian species diversity and abundance in agricultural landscapes and to compare the composition and abundance of songbirds in cleared areas settled at different times over a 35‐year period. Arroyo vagetation had a wide diversity of songbird species that, in overall terms, differed little between those landscapes cleared recently and those cleared up to 35 years previously. In both areas we found a high abundance of habitat generalists and a smaller number of forest‐dependent species, particularly migrants. Loss of forest specialists occurs rapidly, with little further loss as the arroyos become increasingly isolated. Our data also suggest that birds do not crowd into limited habitat as the surrounding vegetation is eliminated, implying that the overall carrying capacity of the agricultural landscape is greatly enhanced as larger areas of arroyo vegetation are protected. Protection of arroyo vegetation will increase the diversity of birds living in agricultural areas and can be achieved simply by expanding upon land‐use practices currently in use.

Use de galerías boscosas por aves cantoras en paisajes recientemente clareados y en paisajes poblados con anterioridad de la Selva Lacandona en Chiapas, México
Molecular Evidence for a Unique Evolutionary Lineage of Endangered Sonoran Desert Fish (Genus Poeciliopsis)
Authors: Quattro Joseph M. , Leberg Paul L. , Douglas Michael E. , Vrijenhoek Robert C.
Published: March 2003

Efforts to restore an endangered species in its former range should be based on a sound understanding of evolutionary relationships among remaining natural populations. In this study mitochondrial (mt) DNA diversity within and among Gila River drainage populations of the endangered Sonoran topminnow (Poeciliopsis occidentalis) in Arizona was compared to that from neighboring populations in Sonora, Mexico, where the species remains locally abundant. No mtDNA diversity was detected within or among samples from the Gila River basin in Arizona. But considerable variation was found within and among populations from several river systems in Sonora. Examination of mtDNA from a population that inhabits the upper reaches of the Río Yaqui in southeastern Arizona revealed substantial divergence between it and all other populations examined. We comment on the implications of this divergent population for topminnow management in Arizona and argue for more‐detailed genetic and morphological studies to determine the distributional limits and specific status of this highly divergent form.
Ecological Correlates of Whooping Crane Use of Fire‐Treated Upland Habitats
Authors: Chavez‐Ramirez Felipe , Hunt Howard E. , Slack R. Douglas , Stehn Tom V.
Published: March 2003

The only remaining wild population of the endangered Whooping Crane (Grus americana) winters in salt marsh habitats of the Texas (U.S.) coast. Whooping Cranes are known to respond and utilize nearby upland habitats after a tire treatment has been applied. We investigated several factors that may attract Whooping Cranes to recently burned sites at Aransas National Wildlife Refuge between 1982 and 1994 and whether cranes utilize upland habitats primarily in response to a recent fire treatment or whether they occur regularly on uplands regardless of burning. We evaluated the effect of different years, burn site location, date of burn, and acorn production on crane use of specific burn sites. Crane use was determined with ground surveys from 1982 through 1985 and from weekly aerial surveys between 1986 and 1994. Whooping Cranes used fire‐treated upland habitats to a significantly greater extent than unburned sites. The response of cranes to recently burned sites was greatest immediately after fire treatment and declined with time. No significant difference was found in crane use of burned sites among different years. Similarly, time of burn and acorn production had no significant effect on crane use of fire‐treated habitats. Crane use among specific burn units differed significantly. We suggest that Whooping Cranes may be using fire‐treated upland habitats to feed on recently killed vertebrates and invertebrates plus recently exposed plant items. Because cranes primarily inhabit salt marsh habitats, the availability of alternate food sources may be of considerable importance, particularly during years when marsh foods are scarce. But because it appears that areas must be burned to facilitate use by Whooping Cranes, we suggest that the extent of prescribed burning be based on reduced availability of marsh food resources and not on acorn production estimates alone.
Effects of Tropical Cyclonic Storms on Flying Fox Populations on the South Pacific Islands of Samoa
Authors: Pierson E.D. , Elmqvist T. , Rainey W.E. , Cox P.A.
Published: March 2003

The South Pacific islands of Samoa have two extant flying fox species, Pteropus samoensis and P. tonganus. Following two severe cyclonic storms, we examined their differential behavioral responses and evaluated the effectiveness of recently established reserves in providing refugia. Although the cyclones disrupted activity patterns and foraging behavior for both species, comparisons with pre‐storm data suggested that the more common, widely distributed P. tonganus experienced more severe population declines than the endemic P. samoensis. This differential mortality could be explained by a combination of ecological and behavioral factors. P. tonganus had a greater tendency to enter villages to feed on fallen cultivated fruits, making it more vulnerable to human hunting and predation by domestic animals. In addition, P. samoensis appeared to use survival strategies not observed in P. tonganus. Leaves, which were far more available than flowers or fruits in the immediate post‐storm period, comprised a major part of the post‐storm diet of P. samoensis. This species also fed on the fleshy bracts of a storm‐resistant native liana, (Freycinetia reineckei). In contrast, a seasonally important food of P. tonganus is nectar from the delicate flowers of Syzygium inophylloides (asi), a canopy tree that is very vulnerable to wind damage and has become increasing scarce with the clearing of lowland forest. Rainforest reserves, established prior to the storms, served as adequate refugia for local P. samoensis populations, which appeared to feed relatively close to their roosts, primarily in native forest, but did not protect P. tonganus populations, which traveled outside reserves to forage in areas lacking hunting bans. Although wind damage was patchy and not consistent between storms, areas of high topographic complexity (e.g., volcanic cones and deep valleys) were the most likely to retain areas with some foliage and should be given priority in the design of future reserves.
Global Warming and the Species Richness of Bats in Texas
Authors: Scheel D. , Vincent T.L.S. , Cameron Guy N.
Published: March 2003

General circulation models provide predictions for global climate under scenarios of increased atmospheric CO2. Climate change is expected to lead directly to changes in distributions of vegetation associations. Distribution of animals will also change to the extent that animals rely on vegetation for food or shelter. Bat species in Texas appear to be restricted, in part, by the availability of roosts. We used geographic information systems and the Holdridge vegetation‐climate association scheme to model the effect of climate change on bat distributions and species richness in Texas. Habitat characteristics for each species were identified from the literature and included vegetation, topography, and availability of caves. We assumed caves and topography to be fixed relative to climate. Vegetation changes were predicted from the Holdridge vegetation‐climate association scheme. The redistribution of bats following climate change was predicted based on the new locations of suitable habitat characteristics. Under conditions of global warming tropical forests were predicted to expand into Texas; tree‐roosting bats were sensitive to this change in vegetation. Cavity‐roosting bats were less affected by changes in vegetation, but, where response was predicted, ranges decline.
The Importance of Analysis Method for Breeding Bird Survey Population Trend Estimates
Authors: Thomas Len , Martin Kathy
Published: March 2003

Population trends from the Breeding Bird Survey are widely used to focus conservation efforts on species thought to be in decline and to test preliminary hypotheses regarding the causes of these declines. A number of statistical methods have been used to estimate population trends, but there is no consensus as to which is the most reliable. We quantified differences in trend estimates or different analysis methods applied to the same subset of Breeding Bird Survey data. We estimated trends for 115 species in British Columbia using three analysis methods: U.S. National Biological Service route regression, Canadian Wildlife Service route regression, and nonparametric rank‐trends analysis. Overall, the number of species estimated to be declining was similar among the three methods, but the number of statistically significant declines was not similar (15, 8, and 29 respectively). In addition, many differences existed among methods in the trend estimates assigned to individual species. Comparing the two route regression methods, Canadian Wildlife Service estimates had a greater absolute magnitude on average than those of the U.S. National Biological Service method. U.S. National Biological Service estimates were on average more positive than the Canadian Wildlife Service estimates when the respective agency’s data selection criteria were applied separately. These results imply that our ability to detect population declines and to prioritize species of conservation concern depend strongly upon the analysis method used. This highlights the need for further research to determine how best to accurately estimate trends from the data. We suggest a method for evaluating the performance of the analysis methods by using simulated Breeding Bird Survey data.
Refugia for Endangered Fishes from an Introduced Predator in Lake Nabugabo, Uganda
Authors: Chapman Lauren J. , Chapman Colin A. , Ogutu‐Ohwayo Richard , Chandler Mark , Kaufman Les , Keiter Amanda E.
Published: March 2003

Wetlands may protect fishes from introduced predatory fishes by providing both structural and low‐oxygen refugia for prey species tolerant of the conditions that prevail in these habitats. We examined the potential of wetlands as refugia for fishes in Lake Nabugabo, Uganda, where increased numbers of an introduced predator, the Nile perch (Lates niloticus), coincided with the decline or disappearance of many indigenous species in the main lake. In 1993 and 1994 we sampled fishes in three wetland habitats: the marginal wetland ecotones of the lake, wetland lagoons separated from the lake by densely vegetated marsh habitats, and a stream separated from the lake by dense papyrus swamp. Fish distributions in these wetlands were then compared to results from two earlier fish surveys: the 1962 Cambridge expedition to Lake Nabugabo, which was conducted prior to the increase in the Nile perch population; and a 1991–1992 survey of the open lake, which reported the disappearance of 16 indigenous species. In our 1993–1994 surveys 9 of the 16 species not recovered in the 1991–1992 open‐lake survey were found in the wetland ecotones or beyond the margins of the lake in wetland lagoons and tributaries. Three of these species were found only beyond the margins of the lake in the tributaries and lagoons within extensive wetlands. Three endemic haplochromine cichlids were abundant offshore in 1962. Of these species one has disappeared and the others are now largely confined to inshore areas. Other species that were abundant in the open waters of the lake in 1962 (e.g., the lung fish Protopterus aethiopicus) are now found primarily in wetlands. Two species, the characid Brycinus jacksonii and the cyprinid Rastrineobola argentea, are still abundant in the open waters. This study highlights the need for quantitative survey work to identify wetland refugia in the Lake Victoria Basin and suggests that some species thought to have disappeared in the mass extinction of fishes in Lakes Victoria and Kyoga may still survive in refugia. Some fish populations could recover under effective ecosystem management.
Making Sense of the Policy Process for Carnivore Conservation
Authors: Primm Steven A. , Clark Tim W.
Published: March 2003

Grizzly bears (Ursus arctos horribilis), mountain lions (Puma concolor), wolverines (Gulo gulo), wolves (Canis lupus), and lynx (Felis lynx) are all top‐level carnivores in the Rocky Mountains of the northern U.S. and southern Canada. Because of their body size and high trophic position, these species require abundant prey species and large habitat areas—requirements that make their conservation a controversial public policy problem. Because the challenge of conserving these species extends beyond biological issues, it is necessary to involve other relevant disciplines and perspectives in understanding and solving the problem. Our examination of the context, content, and process of large carnivore conservation policies suggests more effective and active roles for scientists in designing solutions to the problem of landscape‐level carnivore conservation. Scientists must develop an understanding of the range of participants in the policy process and the ways in which these participants receive and utilize information. This knowledge of the policy process could help scientists to better understand their roles in framing and clarifying policy questions, projecting the consequences of various alternatives, and presenting policy information in appropriate fora.