Topographic control of vegetation in a mountain big sagebrush steppe

Mountain big sagebrush steppes in Wyoming have strong spatial patterning associated with topography. We describe the spatial variability of vegetation in a sagebrush steppe, and test the relationship between topography and vegetation using canonical correlation. Results of the analysis suggest that the main control over vegetation distribution in this system is wind exposure. Exposed sites are characterized by cushion plant communities and Artemisia nova, and less exposed sites by the taller sagebrush species Artemisia tridentata ssp. vaseyana. Topographic depressions and leeward slopes are characterized by aspen stands and nivation hollows. Measurements of soil microclimate suggest that a major influence of topographic position on vegetation is snow redistribution and its effect on soil moisture and temperature.Abbreviations ARNO Artemisia nova - ARTRW Artemisia tridentata ssp. wyomingensis - ARTRV Artemisia tridentata ssp. vaseyana - PUTR Purshia tridentata - RIP riparian community - POTR Populus tremuloides - NIV nivation hollow community     

Effects of weather and feeding on body temperature and activity in the snake Masticophis flagellum

1. 1.|Body temperature (T_b) and activity of the snake Masticophis flagellum were studied by radiotelemetry in an outdoor enclosure.

2. 2.|Mean diurnal T_b varied little over a wide range of weather conditions, but weather variation was accompanied by major changes in sun exposure and in the timing and duration of activity.

3. 3.|Recently fed snakes reduced activity and exhibited neither a thermophilic response nor increased precision of thermoregulation compared to fasting snakes.

Infrasectional systematics of the genus Sideritis L. section Sideritis (Lamiaceae)

RIVERA NUÑEZ, D., OBON DE CASTRO, C., TOMAS-LORENTE, F., FERRERES, F. & TOMAS-BARBERAN, F. A., 1990. Infrasectional systematics of the genus Sideritis L. section Sideritis (Lamiaceae). A new taxonomic division of the section Sideritis is proposed on the basis of morphological, cytological and chemical characters. The following subsections art-recognized: Grandiflora, Ovata, Camarae, Linearifolia, Gymnocarpae, Stachydioides, Lacaitae, Hirsuta, Chamaedryfolia, Arborescens, Flavovirens, Leucantha, Angustifolia, Serrata and Scordioides . Possible evolutionary pathways are discussed.     

The medicinal leech, Hirudo medicinalis (L.) (Hirudinea: Gnathobdellae), at Dungeness, Kent

WILKIN, P. J., 1989. The medicinal leech, Hirudo medicinalis (L.) (Hirudinea: Gnathobdellae), at Dungeness, Kent . An account of the ecology and conservation of the medicinal leech ( Hirudo medicinalis (L.)) at Dungeness, Kent, is presented.     

Ecology of gorillas and its relation to female transfer in mountain gorillas

Understanding the principles that underly primate social evolution depends on integrated analysis of data on behavioral ecology, demography, life history tactics, and social organization. In this paper, data on the behavioral ecology of gorillas are reviewed and comparisons made among the three subspecies. Gorillas are selective feeders; and, their patterns of food choice are consistent with models of feeding by large generalist herbivores. They rely heavily on terrestrial herbaceous vegetation, which provides an abundant supply of densely distributed food. Availability of this food varies little in space and time; and, gorilla foraging activity can maintain its productivity. The level of frugivory and the extent of seasonal variation in diet and habitat use vary among and within populations. Low variability in food distribution patterns makes cooperative defense of foraging areas not worthwhile; but, it also means that ecological costs associated with gregariousness are low. However, demographic and life history data on mountain gorillas show that these costs may be sufficient to reduce female reproductive success as group size increases. Advantages to being with high quality males apparently can outweigh these costs. The implications of these data for the evolution of the mountain gorilla social system, and the possible roles of male protection, predation, and female/female competition in this regard, are discussed.     

Fission-fusion social organization inAteles andPan

Recent research on the ecology and behavior of free-ranging spider monkeys (Ateles paniscus chamek) allows a more detailed comparison with the chimpanzee,Pan troglodytes, than has been possible previously. Despite their distant common ancestry, chimpanzees and spider monkeys share an unusual fission-fusion social system. In this paper, I compare subgroup size and composition, social unit structure, ranging behavior, patterns of philopatry and dispersal, and social relationships in the two taxa. It is proposed that spatial and temporal patchiness in food dispersion and abundance, resulting in a high-level of feeding competition between females within a group, has been the most important ecological selection pressure leading to the evolution of fission-fusion social organization in both species.     

Modeling in the museum: On the role of remnant models in the work of Joseph Grinnell

Accounts of the relation between theories and models in biology concentrate on mathematical models. In this paper I consider the dual role of models as representations of natural systems and as a material basis for theorizing. In order to explicate the dual role, I develop the concept of a remnant model, a material entity made from parts of the natural system(s) under study. I present a case study of an important but neglected naturalist, Joseph Grinnell, to illustrate the extent to which mundane practices in a museum setting constitute theorizing. I speculate that historical and sociological analyses of institutions can play a specific role in the philosophical analysis of model-building strategies.     

流域开发生态建设发展战略

以往研究流域开发战略问题,多从流域内资源的开发利用方面考虑,而衡量其方案的优劣也多以经济效益的大小为准绳。现在,环境污染与生态危机已威胁着人类的生存与发展,因此在研究流域战略问题时,必须开拓思路,     

Isotopic Fractionation of Hydrogen in Plants

The naturally-occurring stable isotopes deuterium and hydrogen are fractionated by a number of physical and biological processes. Deuterium has a tendency to precipitate out first from a moist air mass. Thus ground water will become isotopically lighter with an increase in latitude, altitude, or distance inland. Water taken up by the plant from the soil undergoes little change until evapotranspiration results in leaf water becoming isotopically heavier. Thus hydrogen isotopes in plants can reveal something of geography (groundwater) and climate. Hydrogen isotopes undergo little fractionation by passage through the food chain, although plant parasites tend to be enriched in D as compared to their hosts, possibly due to higher rates of transpiration in the parasitic plants. The splitting of water in photosynthesis results in the lighter isotope being incorporated into organic matter. An even larger isotopic fractionation results during lipid synthesis and other processes involving the pyruvate dehydrogenase complex. Differences in metabolic pathway between species can be detected by D/H ratios. Hydrogen isotopic differences can be detected between CAM, C₄, and C₃ species. Within C₄ plants, the NADP-ME plants are isotopically distinguishable from NAD-ME and PEP-CK plants.     

Molecular tools in marine ecology

Molecular tools have diverse applications in marine ecology. In microbial systems, DNA sequences of rRNA and other genes have identified a variety of novel lineages of bacteria inhabiting marine environments that have resisted traditional culture methods. However, relatively few natural populations have been characterized due to the rather labor-intensive methodologies employed. Recent technological developments such as in situ PCR and flow cytometry promise to greatly enhance the speed at which microbial taxa can be identified and enumerated in field collected water and substrate samples; such advances will allow future work to employ the spatial and temporal field sampling required to monitor the impact of natural and anthropogenic changes in the environment. This approach also holds promise for examining physiological status of field collected cells, garnering information on such elusive parameters as growth rates and the extent of nutrient limitation under natural conditions. Studies of macrobiota have similarly benefited from the use of molecular approaches to species identification. This has been particularly true with regard to distinguishing among larval forms of closely related taxa which are nearly identical morphologically. Genetic variation within species assayed by molecular tools has been useful in examining the stability of populations through time and in assessing patterns of recruitment to geographically separated populations. Enhanced understanding of these ecological problems will also require intensive spatial and temporal monitoring of both larval and adult populations. Often, the newer techniques based on DNA sequence variation have practical advantages over allozyme techniques: e.g., PCR allows assay of minute quantities of DNA that may come from ethanol preserved samples. However, when ample allozyme variation exists to address a given issue, these older techniques may be favored on a variety of criteria, including speed and cost. Hence, choice of methodology should be based on the expected efficiency of a given approach to a specific problem rather than the apparent sophistication of the method itself.