ISSN:1051-0761    

DOI:10.2307/1941884

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

To meet the requirements of Congressional legislation mandating the production of a "scientifically credible" conservation strategy for the threatened Northern Spotted Owl (Strix occidentalis caurina), the Interagency Spotted Owl Scientific Committee employed scientific methods to design a habitat reserve system. Information on the current and historical distributions of the owl and its habitats was reviewed in light of economic, political, and legal constraints; results were used to develop a preliminary reserve system of habitat "polygons." A map representing these polygons and their attendant properties served as a set of hypotheses that were tested. Statistical analyses of empirical data, predictions from ecological theory, predictions from population dynamics models, and inferences drawn from studies of related species were used to test properties of the preliminary map, including the number and sizes of habitat conservation areas (HCAs), their distribution, configuration, and spacing, and the nature of the landscape matrix between HCAs. Conclusions that failed to confirm specific map properties were used to refine the reserve system, a process that continued iteratively until all relevant data had been examined and all map properties had been tested. This conservation planning process has proven to be credible, repeatable, and scientifically defendable, and should serve as a model for wildlife management, endangered species recovery, and national forest planning.

ISSN:1051-0761    

DOI:10.2307/1941885

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Understanding the factors that determine the continued survival of small populations is a central problem in conservation biology. The Acorn Woodpecker (Melanerpes formicivorus) naturally occurs in small, isolated populations throughout much of the American Southwest. In spite of this distributional pattern, the species is neither rare nor endangered. Thus it appears to have successfully "solved" the problems to the problems of habitat fragmentation. We used data from a 10—yr field study and simulation models to examine the effects of environmental stochasticity on population survival times. All simulated woodpecker populations went extinct within 49 yr, and the median survival time was only 16 yr. However, when immigration was allowed, persistence times greatly increased; with an immigrant rate of only five individuals per year, most populations lasted>1000 yr. The results of this and other analyses suggest that this population persists only because it is part of a larger "metapopulation," and because it is regularly rescued from extinction by immigration from other, independently varying, populations. This finding has important implications for the development of management strategies designed to preserve small populations that are faced with fragmented distributional patterns and high levels of environmental variation.

ISSN:1051-0761    

DOI:10.2307/1941886

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Conservation genetics utilizes the tools and concepts of genetics and applies them to problems in conservation biology. For example, molecular genetic techniques, such as protein electrophoresis, and analysis of mitochondrial DNA and highly variable nuclear genes (including DNA fingerprinting), have been important in documenting the extent and pattern of genetic variation in endangered species. We review these techniques and their advantages and disadvantages, and give examples of their application to endangered species. For captive animal populations, pedigree analysis has become the basic approach to evaluate breeding priority of particular individuals. Several pedigree analysis techniques are commonly used, but peeling and gene dropping give the most information. We compared these techniques and illustrate their value with applications to the Guam Rail, Przewalski's horse, and other endangered captive animals. The rationale for much conservation genetic interpretation is base in evolutionary genetics. We discuss the avoidance of inbreeding depression and the maintenance of genetic variation–both primary conservation genetic goals–from this perspective. In addition, we suggest aspects of these factors that deserve greater attention in their overall application to conservation planning. Finally, we briefly mention three evolutionary topics–the relationship of heterozygosity and fitness, population bottlenecks, and outbreeding depression–that have implications for conservation genetics. Although simple interpretation in these areas is appealing, we feel that because they are only generally understood and often quite controversial, their application to endangered—species management should be carefully evaluated and monitored.

ISSN:1051-0761    

DOI:10.2307/1941887

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

A geographical information system, together with a climate—driven, global, regionalized, carbon—budget model, was used to investigate climatic limitations of grassland and coniferous forest vegetation units. The climatic limitations of the fluxes net primary productivity and litter decay were considered for present climatic conditions and for scenario conditions assuming a 3.5°C temperature rise or a 10% precipitation increase, respectively. The two fluxes behave differently in respect to climatic limitations. Global grassland and coniferous forest areas are quite similar in size, but grasslands have the higher productivity while coniferous forests dominate in phytomass. Therefore, grasslands are more important for the seasonal carbon cycle. Coniferous forests have the stronger potential to influence the long—term carbon balance. The assumed climate change will strongly affect the climatic limitations of both vegetation types.

ISSN:1051-0761    

DOI:10.2307/1941888

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

As regional and global scales become more important to ecologists, methods must be developed for the application of existing fine—scale knowledge to predict coarser—scale ecosystem properties. This generally involves some form of model in which fine—scale components are aggregated. This aggregation is necessary to avoid the cumulative error associated with the estimation of a large number of parameters. However, aggregation can itself produce errors that arise because of the variation among the aggregated components. The statistical expectation operator can be used as a rigorous method for translating fine—scale relationships to coarser scales without aggregation errors. Unfortunately this method is too cumbersome to be applied in most cases, and alternative methods must be used. These alternative methods are typically partial corrections for the variation in only a few of the fine—scale attributes. Therefore, for these methods to be effective, the attributes that are the most severe sources of error must be identified a priori. We present a procedure for making these identifications based on a Monte Carlo sampling of the fine—scale attributes. We then present four methods of translating fine—scale knowledge so it can be applied at coarser scales: (1) partial transformations using the expectation operator, (2) moment expansions, (3) partitioning, and (4) calibration. These methods should make it possible to apply the vast store of fine—scale ecological knowledge to model coarser—scale attributes of ecosystems.

ISSN:1051-0761    

DOI:10.2307/1941889

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

The objective of this research was to determine which environmental resources, light, water, and/or nutrients, control understory plant production in a Pinus ponderosa forest in northeastern Oregon. A split—plot experimental design, with three 5.0—ha blocks, four treatments, and 44 plots, was established in the summer of 1985. Twenty plots (4 X 4 m) were trenched (root—reduction treatment) °1 m in depth, and 24 non—trenched plots (root—control treatment) were used to assess the effects of root competition of overstory trees on understory plants. Trees were commercially thinned (canopy—reduction treatment) in half of each block (2.5 ha) during the winter and early spring of 1986, from a density of 345 to 148 trees/ha to increase light levels to the understory. Thinning significantly increased photosynthetically active radiation, decreased midday relative humidity, and increased midday air temperatures. Xylem potential of the dominant graminoid (Carex geyeri), soil water potential, mineralizable nitrogen, and pH were increased within the root—reduction vs. the root—control treatments. Micro— and macronutrients in C. geyeri and Symphoricarpos albus, the dominant shrub, were influenced in both treatments. Increasing light did not increase understory biomass production. Reducing root competition for soil water and nutrients increased understory aboveground biomass by 53 and 94% in 1986 and 1987, respectively. This research demonstrated that belowground resources were the primary controlling factors of understory production in P. ponderosa forests in northeastern Oregon.

ISSN:1051-0761    

DOI:10.2307/1941890

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

A stochastic approach to model the spatial variability of primary productivity in a river impoundment is presented in which data from LANDSAT—TM images of reference data from the field were used as basic inputs to the model. Primary productivity is predicted here by a set of variables (chlorophyll, temperature, and turbidity) combined by means of multivated probabilistic model wherein probability distribution functions were assigned to each variable. Linear regression analysis was used to relate the field reference data to the image data used as input to the model. The model was applied using maps of the variables obtained from the digital imagery. The results was a map of primary productivity probabilities converted to absolute values utilizing the cumulative function for field measurements of primary productivity. The field data were collected over °1.5 yr at 16—d intervals at 12 sample sites. The overall r2between the model results using field—measured variables and the measured primary productivity carbon values was 0.85 with an RMS (root mean square) error of 16 mg°m—3°h—1, where the carbon values ranged from 4 to 300 mg.m—3.h—1. To test the methodology for the generation of primary productivity maps from LANDSAT imagery, two maps of primary productivity for Kentucky Lake were generated from data collected in August and December 1988. The model output was, in turn, compared to primary production carbon measurements from the reservoir. The r2s were 0.89 and 0.76 with RMS errors in these carbon values of 10 and 18 mg°m—3°h—1. No specific assumptions about Kentucky Lake were required for this approach, so the methodology is applicable to other lakes or reservoirs in similar trophic states.

ISSN:1051-0761    

DOI:10.2307/1941891

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Bush encroachment has contributed to the diminishing availability of open grassland areas and possibly caused the decline of the local wildebeest and zebra populations in a semi—arid nature reserve in South Africa. Bush was subsequently cleared to convert dense woodland to parkland savanna. Based on an ecological gradient of habitat utilization previously described for African ungulates, it was assumed that wildebeest and zebra would favor cleared areas, whereas impala and kudu would prefer naturally dense woodland vegetation. Measurements of forage production showed that dry matter yield of grasses was greater in cleared areas. Proportion similarity indices and confidence intervals, representing the monthly occurrence of ungulates in different habitats, suggested that wildebeest and zebra were selecting for cleared areas, whereas impala and kudu occurred randomly in cleared and natural habitats. Results suggested that moderate modifications of woodland savanna habitats by means of bush clearance could be advantageous to ungulates that are common in grassland habitats, while not being detrimental to resident dwellers of dense woodland. Managers, however, should consider carefully the application of bush clearance. The response of ungulates was weak, and therefore clearance might not be justified if done for the purpose of propagating grazers.

ISSN:1051-0761    

DOI:10.2307/1941892

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY