bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential replacement vegetation: an approach to vegetation mapping of cultural landscapes
Authors: Chytrý Milan
Published: May 2006

Abstract. The concept of mapping potential replacement vegetation (PRV) is proposed as a parallel to potential natural vegetation (PNV). Potential replacement vegetation (PRV) is an abstract and hypothetical vegetation which is in balance with climatic and soil factors currently affecting a given habitat, with environmental factors influencing the habitat from outside such as air pollution, and with an abstract anthropogenic influence (management) of given type, frequency and intensity. For every habitat, there is a series of possible PRV‐types corresponding to the different anthropogenic influences, e.g. grazing, mowing, trampling or growing cereals.

The PRV‐concept is especially useful in large‐scale mapping (scales > 1 : 25 000) of small areas where replacement vegetation is the focus of attention for managers and land‐use planners, for example in nature reserves where the aim is conservation of replacement vegetation managed in a traditional way, or in restoration ecology where the concept may be used for defining restoration goals and evaluating the success of restoration efforts. At smaller scales, PRV‐mapping may be useful for revealing the biogeographical patterns of larger areas which may be different from the corresponding PNV patterns, because replacement vegetation and natural vegetation may respond to environmental gradients at different scales. An example of medium‐scale PRV‐mapping through the coincidence of diagnostic species of vegetation types, based on species distribution grid data, is presented.

In cultural landscapes, the advantage of using the PRV‐concept instead of PNV is its direct relationship to the replacement vegetation. In the habitat mapping with respect to the replacement vegetation, the PRV concept yields more valuable results than the mapping of actual vegetation, as the latter is strongly affected by spatially variable anthropogenic influences which may be largely independent from climatic and soil factors.
Environmental controls of NDVI and sheep production in the Tierra del Fuego steppe of Argentina
Authors: Posse Gabriela , Cingolani Ana María
Published: May 2006

Abstract. We analysed vegetation dynamics in Tierra del Fuego steppes using Normalized Difference Vegetation Index (NDVI) data provided by advanced very high‐resolution radiometer (AVHRR) on board the National Oceanic and Atmospheric Administration (NOAA) polar satellite. Our objective, at a regional scale, was to analyse the spatial variability of NDVI dynamics in relation to parent material and geographic location, representing the fertility and climate gradients respectively; at a local scale, it was to analyse the inter‐annual variability associated with climate and its relation with sheep production indices. The general pattern of NDVI dynamics was analysed with Principal Component Analysis. We found that the geographic location was more important than landscape type in explaining NDVI dynamics despite the fact that the variation in landscape type reflects a fertility gradient strongly associated with floristic composition and secondary productivity.

Discriminant Analysis was performed to identify the variables that better distinguish geographic units. The Northern region (with the lowest precipitation and the highest temperatures) had lower NDVI values over the year. In the Central region, NDVI reached the highest value of the season, surpassing both other regions. The Southern region (the coldest and moistest) had its growth pattern displaced towards the summer. For the Central region we analysed 10 years of monthly NDVI data with PCA. We found that precipitation from August to December and winter temperature are the most important determinants of overall NDVI values. Lamb production was correlated with spring and early summer NDVI values. Sheep mortality is affected by low NDVI values in late summer and high annual amplitude. Satellite information allowed us to characterize the vegetation dynamics of three ecological areas across the Fuegian steppe.
Effects of Thermal Additions from the Yellowstone Geyser Basins on the Bacteriology of the Firehole River
Authors: Zeikus J. Gregory , Brock Thomas D.
Published: May 2006

A series of stations was established on the Firehole River where it flows through the main geyser basins of Yellowstone Park, and temperature, pH, alkalinity, conductivity, and phosphate were measured. The temperature of the water gradually increased as it flowed through the thermal area, at its warmest averaging about 16°C higher than in the cool area (10° to 26°C). Alkalinity, conductivity, pH, and phosphate also increased markedly. The growth rates of periphtic bacteria measured in situ on glass slides were virtually identical at different stations despite the wide differences in temperature. The effect of temperature on the incorporation of 14C—glucose by benthic bacteria populations at the different stations demonstrated that the temperature optimum for this process increased in parallel with the temperature of the habitat. It is thus concluded that the bacteria are near—optimally adapted to the temperature of their habitat and that despite wide differences in temperature the rate of bacterial activity is the same. In another study, samples of water were placed on agar media and incubated at temperatures of 25°, 55°, and 70°C to obtain estimates of the number of bacteria able to grow at these temperatures. The thermophilic organisms developing at 55°C were primarily Bacillus stearothermophilus at those at 70°C primarily Thermus aquaticus. Thermophiles were not present in water which had not received thermal additions, but both kinds of thermophiles were found in the warm water, and numbers increased progressively as more thermal water entered. In the recovery zone downstream from the thermally region, the numbers of thermophilic bacteria decreased markedly. The possible value of these thermophilic bacteria as indicators of thermal pollutions is discussed. It is suggested that the Firehole River is an excellent model for long—term studies on the ecological consequences of thermal pollution.
Coexistence in Laboratory Populations of Paramecium Aurelia and Its Predator Didinium Nasutum
Authors: Luckinbill Leo S.
Published: May 2006

Previous attempts at the prolonged laboratory study of predator—prey systems lacking refuges or physical complexity have been unsuccessful. The addition of Methyl Cellulose to interacting laboratory populations of Paramecium aurelia and its predator, Didinium nasutum, prolongs coexistence by reducing the frequency of contact between predator and prey. The study of this system under controlled conditions revealed the perturbing influence of a time delay in the predator population that resulted in oscillations of increasing amplitude terminating with D. nasutum's extinction. Enrichment of the system by supplying excess bacteria resulted in the extinction of P. aurelia. The perturbing effect of D. nasutum's time delay was counteracted by reducing the amount of bacterial food for Paramecium. In this system, prey became food—limited at their peak density, resulting in limit cycle oscillations of predator and prey at approximately constant amplitude. The medium used for these experiments lack physical inconsistencies that might act as barriers to movement and did not provide the prey with a superior dispersal ability. Coexistence of the predator and prey in this experimental system did not result from the introduction of refuges or physical complexity.
Species Diversity of Stream Insects of Fontinalis SPP. Compared to Diversity on Artificial Substrates
Authors: Glime Janice M. , Clemons Roger M.
Published: May 2006

Two types of artificial mosses (string and plastic) were compared with Fontinalis spp. for their insect inhabitants. These communities were sampled on six dates at eight stream sites and compare by community coefficients, information theory analysis, and rank correlations. These results showed that those insects which were abundant on moss were also abundant on the artificial substrates. Fewer species and fewer individuals were present on the latter.
Diversity and Pattern in Plants and Insects
Authors: Murdoch William W. , Evans Francis C. , Peterson Charles H.
Published: May 2006

The plants and Homoptera on three old fields in southeast Michigan were sampled. Within fields, correlations between plant and insect diversity were generally weak. But using all samples from three fields, evenness (J) and diversity (H) of the insects were highly correlated with plant evenness and plant diversity, respectively. For example, 72% of the variance in insect H could be accounted for by variation in plant H. Number of species (S) showed a positive but weaker correlation. When correlations were based on the pooled samples from each field, all three statistics for insects were highly correlated with those for the plants. Insect H was also highly correlated with plant structure (foilage height diversity FHD) over all three fields. These two measures of plant diversity (H and FHD) were highly correlated and were equally good correlates of insect H. Together they accounted fir 79% of the variance in insect H. This extends to insects a correlation between plant and animal diversity, already well established for birds and possibly true for lizards and rodents. It leaves open the unresolved question as to whether plant structure or plant species diversity is more important.
Factors Affecting Spruce Beetles during a Small Outbreak
Authors: McCambridge William F. , Knight Fred B.
Published: May 2006

In 1957, spruce beetles, Dendroctonus rufipennis developed into outbreak numbers in logging slash at a north—central Colorado site, entered living spruce trees, but remaining epidemic for only two years. Reduced beetle fecundity was the first indication of outbreak decline; this was caused by nematodes and unknown agents. Significant summer mortality agents were pitch, intra— and interspecific competition for food, predation by woodpeckers and flies, and parasitism by wasps. Desiccation of both food and beetle larvae, enhanced by woodpecker feeding activity, contributed significantly to outbreak decline. Winter mortality was attributed mainly to woodpeckers, although temperature of —29°C caused additional losses. The effects of the outbreak on the spruce were considerable. Large diameter trees in small patches were killed, and species composition was altered in favor of subalpine fir and lodgepole pine, but mean tree diameter was not significantly reduced.
Vegetation and Soils of Shell Middens on the Coast of British Columbia
Authors: Sawbridge David F. , Bell M. A. M.
Published: May 2006

Six vegetation dominance types were recognized on 23 shell middens. Combinations of the dominants Alnus rubra Bong., Acer macrophyllum Pursh, Gaultheria shallon Pursh, Mnium insigne Mitt., Picea sitchensis (Bong.) Carr., Poa trivialis L., Polystichum munitum (Kaulf.) Presl., Pseudotsuga menziesii (Mirbel) Franco, Rhytidiadelphus triquetrus (Hedw.) Warnst., Rubus spectabilis Pursh, Tellima grandiflora (Pursh) Dougl., Thuja plicata Donn, Tsuga heterophylla (Raf.) Sarg., and Urtica dioica var lyalli (Wats.) C.L. Hitchc. characterize each vegetation type. A chart is included for rapid field identification. The major factors influencing vegetation variation are probably moisture regime and logging disturbance. Apart from lower concentrations of total nitrogen in midden horizons of Tsuga—dominated stands, no significant relationships are apparent between vegetation type or individual dominants and midden age since occupation, soil pH, soil particle—size ratio, organic carbon, total nitrogen, carbon—to—nitrogen ratio, exchangeable calcium, or available phosphorus. Midden horizons contain large quantities of mollusc shell, often with ash and other cultural detritus, and have high levels of exchangeable calcium (5,125—14,350 ppm) and high pH (6.9—7.2). Vegetation on adjacent areas with comparable topography is frequently similar to midden vegetation; thus shell deposits appear to have little influence on composition and structure of forest communities in this area. Radiocarbon age estimates of upper shell deposits in 13 middens ranged from 770 ± 90 to 6,250 ± 110 years B.P. (before 1950). Organic carbon, total nitrogen, and exchangeable calcium values apparently decrease with increasing bidden age. Further study is required to facilitate the development of a fast, inexpensive method for approximate dating of bidden deposits.
Censusing Mouse Populations by Means of Tracking
Authors: Marten Gerald G.
Published: May 2006

A new approach based on mark—and—sample tracking is presented that may substantially reduce errors in censusing small mammals. A test is included to check the underlying assumption of equal tracking from marked and unmarked mice. A procedure for applying the tracking approach to estimating births and deaths between samples is also presented. The tracking approach was demonstrated on a population of Peromyscus maniculatus. The number of tracks left nightly by males was significantly greater than by females. However, the tracking rate was about the same each night for all individuals of the same sex, even though tracking fluctuated from night to night. The test revealed no strong difference in the tracking rates of marked and unmarked mice. It is concluded that population estimates based on tracking can be highly precise and are far superior to estimates based on trapping alone.
A Critical Variable Formulation of Population Dynamics
Authors: Streifer William , Istock Conrad A.
Published: May 2006

A single—species population model which admits a more realistic and complete description of the internal structure and changes of a population as well as a more complete description of the external influences gathered about the population is presented. The basic idea is to identify the characteristics which most critically affect the population dynamics. Coupled differential equations for the total population and the means and variances of the critical variables, such as age and mass, are formulated. Thus the means and variances of the critical variables change with time. After the derivation of the equations an examples is given. The examples illustrates that the behavior of the population and its equilibrium depend on quantities which have ecological significance.
Early Stages of Plant Succession Following Logging and Burning in the Western Cascades of Oregon
Authors: Dyrness C. T.
Published: May 2006

Vegetative changes were documented for 7 years on permanent milacre plots located in three clearcut logged units in the western Cascade Mountains of Oregon. Plant cover and composition were observed the year prior to logging the old—growth Pseudotsuga menziesii forest, after logging but before burning, and during each of five growing seasons following broadcast slash burning. Total plant cover was 15.2 49.3, and 75.5% in the first, second and fifth years after slash burning, respectively. Invading herbaceous species dominated from the second through fourth growing seasons after burning but by the fifth year residual herbaceous species regained dominance. Differences in disturbance from logging and burning strongly influenced successional trends. In undisturbed soil areas, residual species, such as Acer circinatum, Oxalis oregana, and Gaultheira shallon, dominated. Areas disturbed by logging but unburned supported a wide variety of both residual and invader species. Light to severely burned sites were largely occupied by invaders such as Ceanothus velutinus, Epilobium angustifolium, and E. paniculatum. Although often obscured by varying degrees of disturbance, relationships between early stages of succession and prelogging plant community were discernible. For example, of the species considered characteristic of five undisturbed plant communities, only 13 percent were absent from the plots 5 years after burning. The invaders Ceanothus velutinus, Agoseris grandiflora, and Gnaphalium microcephalum var. thermale were restricted to sites previously supporting rather xeric communities; while Rubus leucodermis and Anaphalis margaritacea were found on plots characteristic of the more mesic communities.
Some Effects of Soil Type and Water Regime on Growth of Tupelo Seedlings
Authors: Harms William R.
Published: May 2006

Two—year—old swamp tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.) and water tupelo (N. aquatica L.) grown in large tanks in a silty clay loam soil from a river swamp or a sandy loam soil from a non—alluvial headwater swamp were subjected to continuous flooding at depths of 20 cm above the soil surface with moving water, 20 cm above the soil surface with stagnant water, or at the soil surface with moving water. Height growth of water tupelo averaged 1.8 times greater and dry weight 2 to 3 times greater in the more fertile soil from the river swamp than in soil from the headwater swamp. Soil type had no effect on growth of swamp tupelo. Growth and dry weight of both tupelos were poorest in the regime with stagnant water, which also had the highest CO_2 and lowest O_2 contents. Swamp tupelo grew 50 cm more in height in the surface—flooded regime with moving water than in either deep—flooded regime. Water tupelo in both regimes with moving water grew 37 cm taller than those in the stagnant regime.
Effects of Logging on Periphyton in Coastal Streams of Oregon
Authors: Hansmann Eugene W. , Phinney Harry K.
Published: May 2006

Changes in the stream algal flora were observed during a multi—disciplinary logging study of small watersheds in Oregon. Clearcut logging was applied to one watershed of 71 hectares, while a second watershed of 304 ha was patch—out leaving a buffer—strip of vegetation along the stream channel. A third watershed of 203 ha was not logged but remained as a control. Pre—logging and post—logging oxygen levels, temperature, and sedimentation loads were analyzed. Access roads were built in 1963, and logging completed in 1966. Analysis of the algal communities of the three watershed streams prior to the logging operation of 1966 indicated that the communities were predominantly a periphyton type composed mainly of diatoms. Immediately following the yarding operation of the clearcut watershed, large quantities of Sphaerotilus natans colonized all debris and mud in the stream, and a change in the algal floral appeared to take place. Large mats of green algae were observed colonizing all mud and slash. Results from glass substrates indicate that some changes may have taken place in the diatom community.
The Relationship Between Basal Fire Scars and Crown Damage in Giant Sequoia
Authors: Rundel Philip W.
Published: May 2006

A strong correlation exists between the presence of basal fire scar in giant sequoia and the occurrence of snag—tops in mature trees. The percentage of snag—top trees is directly related to the size of the basal fire scar. Approximately 50% of trees with the fire scars greater 100 ft2 possess a snag—top. Evidence indicates that the physiological basis for the formation of snag—tops is a response to high water stresses in the uppermost crown of a mature tree. Fire damage at the base of the tree destroys large amounts of active xylem tissue, thereby reducing the rate of water absorption. When water stress exceeds the physiological tolerance limits for giant sequoia, the top of the main trunk is the first area damaged. The critical level of water potential at the top of a mature giant sequoia has not been determined, but evidence indicates that trees may survive xylem pressure potentials somewhat lower than —20 bars for short periods of time at midday without damage. Water potentials lower than this may provide a significant limiting factor in determining the upper height limits of these trees.
Feeding Ecology of a Temperate Insectivorous Bat (Myotis Velifer)
Authors: Kunz Thomas H.
Published: May 2006

The feeding behavior and ecology of the cave bat, Myotis velifer, in south—central Kansas are investigated. Emergence behavior and foraging patterns varied according to sex, age, reproductive condition, season, and colony size. Females had one synchronous period of departure in late states of pregnancy. Two feeding periods usually were evident in summer with a major period of activity soon after sunset and a reduced secondary period before sunrise. Pregnant females emerged sooner than lactating females and adults departed before juveniles when the latter first began to fly. Adult—like emergence and foraging behavior developed in juveniles within 2 wk after flight was initiated. Adult females consumed greater quantities of food than adult males, and juveniles were less efficient at insect capture than adults. Nearly 80% of daily food consumption can be accounted for in the first 2 hr following emergence. Seasonal changes in consumption corresponded to changing energy demands imposed by pregnancy, lactation, molt, and the availability of food resources. Levels of food consumption in both sexes were lowest in spring and autumn when insect densities were low. Adult females increased their daily levels of consumption throughout most of gestation, although in the terminal days of pregnancy daily food consumption was reduced. Maximum daily levels of food consumption in adult females (approximately 25—30% of body weight) was reached near the time that young were weaned in late July and early August. Adult males achieved maximum levels of consumption (20—25% of body weight) in June, at the time molt and spermatogenesis were initiated. Young bats began foraging for insects at the age of 4 wk although their meager diet of insects was supplemented with milk for 2 wk after foraging was initiated. By the age of 6 to 8 wk their daily level of consumption increased to adult proportions. Food habits based on stomach content analysis revealed that in volume and in actual numbers, beetles (Coleoptera) and moths (Lepidoptera) comprised the major prey items in the diet. Colony size and dispersal distances may be adjusted to reduce intraspecific competition, with most individuals from large colonies dispersing nightly to greater distances than individual from smaller colonies. Emigration of males from nursery colonies in late spring and early summer and emigration of adult females soon after young were weaned may provide a mechanism to reduce competition for available food. Small and widely—scattered transient colonies in early spring and later autumn may be important in reducing competition for food at a time when food resources are scarce.
Behavioral and Environmental Factors in the Spatial Distribution and Popualtion Dynamics of a Yellow‐Bellied Marmot Population
Authors: Svendsen Gerald E.
Published: May 2006

Behavioral and environmental factors in the spatial distribution and population dynamics of a yellow—bellied marmot (Marmota flaviventris) population were studied in 1971 and 1972 in Gunnison Co., Colorado. Yellow—bellied marmots are generally considered to be colonial; however, this is not their only option, depending upon the marmots' behavioral profile and the size and composition of the habitat. Of the adult—yearling group 75% lived as members of colonies, 16% lived at satellite sites, and 8% were transients. Satellite sites differed from colonies mainly in size and topographic diversity; they may be considered mini—habitats, with the most limited resources being burrow sites. Marmots can be classified, by means of mirror—image stimulation (MIS), as aggressive, social, and avoider. Aggressive females tended to occupy small harems at large sites, or to live as solitary individuals regardless of the size of the site. Social females occurred primarily at large sites, in harems. Avoider females lived in peripheral burrows at colonies, or in satellite sites. All behavioral types reproduced successfully, but reproductive fitness was correlated with social structure. Aggressive females were most fit in small harems or at satellite sites, whereas social females were most fit in large social groups. Avoiders were least fit in all social situations. Data presently available fails to show that the behavioral profile of the female is reflected in the social tendencies of her young. In general, social behavior is a major factor affecting the distribution and dynamics of populations of yellow—bellied marmots, but dispersion is also related to the distribution of suitable habitat.
Explicit Calculation of the Rarefaction Diversity Measurement and the Determination of Sufficient Sample Size
Authors: Heck Kenneth L. , van Belle Gerald , Simberloff Daniel
Published: May 2006

An explicit means of calculating the expected number of species [E(Sn)] and the variance of (Sn) in a random sample of n individuals from a collection containing N individuals and S species is presented. An example illustrates a new use of E(Sn): determination of the sample size required for any desired degree of accuracy in collecting species known to occur in a particular area.
Niche Width and Niche Overlap: A Method for Measuring Them
Authors: Pielou E. C.
Published: May 2006

Suppose r different animal species are found in some or all of c different habitats. Observations on the numbers of occurrences of the animals in the habitats can be tabulated in an r ° c table. The overall "diversity" of the table, HT say, is defined as Brillouin's information measure with the r ° c table's cell frequencies of the different "symbols." It is shown that HT may be split into two components in two different ways. The first way splits HT into HA, the diversity of the animal species, plus the weight mean of the within—species habitat diversities. The second way splits HT into HB, the diversity of the habitats, plus the weighted mean of the within—habitat species diversities. The weighted mean of within—species habitat diversities constitutes a measure of the average niche width of the r species of animals. The weighted mean of within—habitat species diversities constitutes a measure of the average niche overlap among the c habitats examined. The measures are of actual, realized niche widths and niche overlaps and are therefore inevitably affected by the relative abundances of the species and the habitats. A method of standardizing them is proposed. An example is given using data on the occurrences of several species of aphids on several host plants of the genus Solidago (goldenrods).
Competition among Fugitive Species in a Harlequin Environment
Authors: Horn Henry S. , MacArthur Robert H.
Published: May 2006

We examine the qualitative behavior of differential equations for the proportion of insular patches of each of two kinds of habitat occupied by each of two species with characteristics rates of migration between patches and of local extinction within a habitat. Certain migration and extinction rates result in stable coexistence, even of closely similar species; others lead to competitive exclusion, even when each species is competitively superior in one kind of habitat. For a community of many species in many habitats, we surmise qualitative limits to the subdivision of resources, and alternative stable communities. Our results extend to species that live in successional or ephemeral habitats. We therefore conjecture equilibrial theories for the number of patches of habitat occupied by insular species, fugitive plants and invertebrates, or infesting parasites.
Root Production and Root Turnover in a Wet Tundra Ecosystem, Barrow, Alaska
Authors: Shaver G. R. , Billings W. D.
Published: May 2006

The wet tundra near Barrow, Alaska, is dominated by three species of graminoids: Dupontia fischeri, Carex aquatilis, and Eriophorum angustifolium. Root production, root turnover, and root distribution patterns of these three species were studied by direct observations of growing roots and by analysis of whole, interconnected tiller systems dug from the soil. Root weight per unit length and density of individual tillers were also measured in the field. Production of new roots was found to be strongly correlated with age of individual tillers, each species having a distinctive pattern and phenology. Root turnover rates also varied considerably; the range is from an annual turnover in E. angustifolium to 6—8(10) yr in C. aquatis. An estimated of root turnover on an ecosystem basis is about 100 g ° m—2 ° yr—2, or 25% of the live root biomass. Species with the shallowest and longest lived roots have the greatest weight per unit length of root, and vice versa. Each species has a characteristic root distribution pattern with depth and in relation to the progress of soil thaw.
Plant Species Diversity in Old‐Field Successional Ecosystems in Southern Illinois
Authors: Bazzaz F. A.
Published: May 2006

In old—field ecosystems in the deciduous forest, plant species diversity generally increases with succession and reaches a maximum during the forest stage when structural diversity is highest and at the time when both shade—tolerant and shade—intolerant species are present together. Species diversity may be exceptionally high in succesional communities when there is a high degree of vertical and horizontal heterogeneity. Diversity may be exceptionally low in old—field ecosystems when there is strong dominance by species with alleolopathic chemicals or other effective interference methods. Species distribution curves are geometric during the first few years of succession and gradually change to lognormal as more species are added to the community, the process resulting in a high degree of evenness.
Relative Diversity Indices
Authors: Peet Robert K.
Published: May 2006

Diversity indices are frequently applied in the form of ratios of absolute diversity to the maximum diversity possible. Regardless of whether the maximum diversity is defined to be limited by the number of species or by the number of individuals present, the resultant indices can be shown to possess mathematically undesirable qualities. All such indices, including equitability as measured by Pilou's J and J', Lloyd and Ghelardi's ratios, redundancy, and the scaled diversity formulations of Fager, are inappropriate for most ecological applications.
Energy Costs of Reproduction in the Cotton Rat, Sigmodon Hispidus
Authors: Randolph Polley Ann , Randolph J. C. , Mattingly Kevin , Foster Margaret Mead
Published: May 2006

Individual organism costs of reproduction were investigated by a series of observations and experiments with the cotton rat, Sigmodon hispidus. Energy budget techniques, including respirometry, showed that ingestion in pregnant rats was increased 25%, while that in lactating rats was increased 66%, over nonreproductive rats. Digestive efficiency of rats fed a commercial standard diet was 84% and did not change as a result of pregnancy or lactation. Respiration per gram of reproductive rats was not significantly different from nonreproductive rats. Twenty—six days of pregnancy required an average additional ingestion of 221.8 kcal [=928.0 kJ]; 12 days of lactation required an extra 270.7 kcal[=1,132.6 kJ]. Total cost per offspring 12 days of age was 100.5 kcal[=420.5 kJ]. The total cost of producing a litter was a linear function of litter size. Two—thirds of the energy accumulated by a pregnant rat was not in the neonates but deposited as storage and mobilized during lactation when the precocial young grew faster than the maternal assimilation alone could support. This use of stored energy increased the apparent efficiency of lactation above that found in other wild rodents. Neonatal litters of cotton rats contained two to seven young (Z = 5). The sizes of these individuals were not affected by litter size although their subsequent early growth rates were. Individuals from larger litters grew more slowly.
Selection for Optimal Life Histories. II: Multiple Equilibria and the Evolution of Alternative Reproductive Strategies
Authors: Schaffer William M. , Rosenzweig Michael L.
Published: May 2006

In a recent theoretical study of life history evolution, it was suggested that, for some species, there might exist more than one set of age—specific reproductive expenditures corresponding to local maxima in fitness. The present paper points out that the argument supporting this conclusion was in error, but that the conclusion itself is correct. In addition, the suggestion that the same adaptive landscape can obtain local optima corresponding to both semelparity and iteroparity is confirmed. The circumstances under which variation in reproductive efforts should be canalized are also discussed.
Diel Patterns of Aggregative Behavior in Tadpoles of Bufo Americanus, in Relation to Light and Temperature
Authors: Beiswenger Ronald E.
Published: May 2006

Tadpoles of the American toad, Bufo americanus, undergo a diel cycle of distribution and activity. Tadpoles spend the night scattered throughout all but the shallowest parts of ponds, where it is cooler than in nearby deeper areas. They begin swimming and feeding more frequently as light intensity increases in the morning, and when shallow areas begin to warm, they move into them. Most are in aggregations in the upper 1—2° of temperature gradients through midday. During late afternoon, they move from shallow water and by evening are scattered and inactive. This diel cycle is closely correlated with changes in light. Light triggers activity in the morning, and swimming and feeding are depressed on cloudy days. Diminishing light causes individuals to disperse from aggregations and become inactive. Once active, tadpoles are attracted to particular microhabitats by heat and light. Temperature gradients are primarily responsible for bringing tadpoles together in sufficient density for aggregations to develop, but thermal effects do not act along in controlling aggregations.
The Presettlement Forest and Natural Disturbance Cycle of Northeastern Maine
Authors: Lorimer Craig G.
Published: May 2006

Land survey records of 1793—1827 containing forest data for 1.65 x 106 ha of northern Maine were analyzed for species composition, successional status, and frequency of large—scale disturbance. Quantitative data consists of 1,448 sample trees spaced 1.6 km apart along a 9.7— x 9.7—km grid. Species which each comprised > 10% of the total were Picea spp., Fagus grandifolia, Abies balsamea, Thuja occidentalis, and Betula lutea. These forests appeared to be largely in a climax state as indicated by the dominance of shade—tolerance species and the small percentage (8%) of intolerant or early successional species. However, 9.3% of the tract was burned land and birch—aspen forest at the time of the survey, mostly the result of large fires in 1803 and 1825. Windfalls occurred along 2.6% of the surveyed distance. If the amount of disturbed forest at this time was typical of the natural disturbance regime, then the average recurrence interval of fire and large—scale windthrow for a given site would be 800 and 1,150 years, respectively. Data on the structure of remnant virgin stands in the region likewise suggest that the time interval between severe disturbances was much longer than that needed to attain a climax, all—aged structure.
Simulation of Vegetation Response to Modified Hydrologic Regimes: A Probabilistic Model Based on Niche Differentiation in a Floodplain Forest
Authors: Franz Eldon H. , Bazzaz F. A.
Published: May 2006

This study was initiated to develop a model for predicting the relative impacts of alternative reservoir designs on vegetation in the backwater zone. The result is a probabilistic model based on niche differentiation in the floodplain forest. Existing methodologies provided estimates of the flooding regime modifications produced by variable backwater conditions during reservoir operation. The model is exercised, with hydrolic modifications as input, to simulate shifts in species distribution. The model has been applied to evaluate the impact of a proposed reservoir on the vegetation of Robert Allerton Part, a 607 km2 natural area in east—central Illinois. Comparison of simulations for three alternative plans for the reservoir provides a basis for distinguishing among them, and suggests that the impact of one would be substantially less than the other two.
The Population Ecology of the Lizard Anolis Acutus
Authors: Ruibal Rodolfo , Philibosian Richard
Published: May 2006

Populations of Anolis acutus, the only anole on St. Croix, U.S. Virgin Islands, were studied for three years. A mark and resight method, used to estimate population size, was tested twice by capturing the entire population studied; the error in estimating the adult population was 3% and 13%. Structural and climatic habitats, diurnal activity, distance to nearest neighbor, migration, survival, and homing were also studied. The species has one of the densest lizard populations known, at one locality an average of 0.4 lizards/m2–density ranged 2,000—5,600 lizards/ha, biomass 13—23 kg/ha. A single tree may have a population of 80 adult lizards and a biomass of 300 g. Anolis acutus has a broader structural habitat than other solitary anoles, occupying a range of perches from near ground level to the tops of the highest trees. The lizards are active from before sunrise to after sunset with no peaks of activity or basking behavior. Territories are small; they mean distance to nearest neighbor was 1.5 m for males, 0.7 m for females, and 0.5 m for male—female pairs. The mean survival over 12 mo was 12% for adult males and 37% for adult females. Adult males homed rapidly; 50% returned when displaced 71—90 m. Migration rate of adults is low. Attempts to relocate adults were unsuccessful since the lizards deserted the new site. Adults are sedentary and once having established a territory on a tree rarely move from that tree. Immigration into a tree devoid of resident lizards is primarily by juveniles. The habibat partitioning results from the adults excluding juveniles from trees. Egg and/or juvenile mortality may function to regulate the population size.
Zooplankton Competition and Predation: An Experimental Test of the Size‐Efficiency Hypothesis
Authors: Dodson Stanley I.
Published: May 2006

Twelve 42—liter plankton cages were used in an alpine Colorado pond to test a size—efficiency hypothesis: to determine why small herbivorous zooplankton species tend not to coexist with large species. The size—efficiency hypothesis, that large species exclude the smaller ones through competition for food, was not substantiated. An alternate hypothesis extends the understanding of the importance of size—selective predators to include invertebrates selecting small prey. A predaceous copepod Diaptomus shoshone excluded the small Daphnia minnehaha from an association with the large D. middendorffiana within 1 mo. By implication, the predacious copepod is responsible for the absence of the small species in ponds occupied by the large Daphnia species.
Algal Zonation in the New England Rocky Intertidal Community: An Experimental Analysis
Authors: Lubchenco Jane
Published: May 2006

Zonation patterns of plants, including marine algae, have commonly been attributed solely and directly to physical factors. Experimental investigations of the factors affecting zonation of macroscopic, benthic algae in the New England rocky intertidal region demonstrated that biological factors set the lower limits of these plants. The mid zone at all but very exposed sites is usually dominated by brown fucoid algae. These plants are virtually absent in the low zone, which is dominated by the red alga Chondrus crispus (Irish moss). Total removal of Chondrus (including the prostrate holdfast) results in establishment of Fucus vesiculosus or F. distichus ssp. edendatus in the low zone. Fucus grows faster in the low than in the mid zone, appears healthy, and reproduces. Thus competition from Chondrus sets the lower limit of Fucus, not changes in light intensity or immersion time, per se, as previously assumed. If herbivores (primarily the perinwinkle snail Littorina littorea) are absent where Chondrus is removed, Fucus can settle very densely and occupy 100% of the space. If herbivores are present, Fucus colonizes, but less abundantly. Thus competition is the primary determinant of the zonation pattern (affecting presence or absense) and herbivory is of secondary importance (affecting abundance). Other experimental evidence suggests that the upper limit of Chondrus is determined by desiccation. The lower limit of Chondrus has not been investigated except where a sharp lower limit exists at the low intertidal—shallow subtidal interface. Experiments demonstrate that this is due to the grazing by sea urchins (Stronglyocentrotus droebachiensis) where they are locally abundant. Normally, Chondrus extends well into the subtidal region. These results parallel experimental studies of animal zonation in rocky intertidal regions in which biotic factors also set lower bathymetric limits. It is suggested that biogeographic ranges of some species may be similarly affected by biotic factors.
Ecological Shifts in Sympatry: Kalahari Fossorial Lizards (Typhlosaurus)
Authors: Huey Raymond B. , Pianka Eric R. , Egan Michael E. , Coons Larry W.
Published: May 2006

Two species of legless, fossorial skinks (Typhlosaurus) are partially sympatric in the Kalahari Desert. Typhlosaurus lineatus occur both in the sandridge and flatland geographic provinces of the Kalahari, in dune streets and on sandridgesmicrogeographically in sympatry, and primarily under log and leaf litter microhabitats. Typhlosaurus gariepensis, always microgeogrphically, and primarily in basal roots of bunch grass microhabitats. Microhabitat overlap in sympatry is low. Morphologically, T. lineatus differ from T. gariepensis in being longer and in having a longer and wider head. Snout—vent lengths, head dimensions, and proportional head lengths of sympatric T. lineatus are larger than those of allopatric T. lineatus; thus T. lineatus displace from T. gariepensis in sympatry. Both species are viviparous, have one brood per year, and give birth in summer after a 5—mo gestation period. Maturity is reached at minimum ages of one and two—thirds yr. Mean litter size of T. lineatus is 1.6, whereas T. gariepensis have but one young. A response to competition between the two species is suggested by the facts that offspring of sympatric T. lineatus are significantlyheavier than those of allopatric females, and that fewer sympatric T. lineatus females are reproductive than allopatric females. Because Typhlosaurus are termite specialists (92.4% of diet by volume), termitesin guts were identified to species and caste. Compared with sympatric T. lineatus, T. gariepensis eat more Psammotermes workers, fewer Allodontermes major workers, and scarcely any Hodotermes. Sympatric T. lineatus eat fewer Psammotermes workers and more Allodontermes major workers than do allopatric T. lineatus. Prey size differences parallel lizard size differences. Because of dietary shifts by T. lineatus in sympatry, dietary overlap with T. gariepensis is substantially reduced for females and immatures, although not for males. Strong morphological and dietary evidence support, for T. lineatus females and immatures, the hypothesis that behavioral and morphological character displacement has occurred which reduces dietary overlap with T. gariepensis. Dietary data for male T. lineatus are possibly conflicting.
Seasonality in Ovarian Cycles among Tropical Anolis Lizards
Authors: Gorman George C. , Licht Paul
Published: May 2006

Ovarian cycles were studied in six species of Anolis lizards from Puerto Rico. All are markedly seasonal, with egg production dropping in the autumn—winter months. Marked interspecific and intraspecific differences in onset, duration, and extent of cycling correlated with altitude. In general, upland populations decline earlier, more severely, and for a longer time than sea level populations. In most lowland populations some females are gravid throughout the year; among most upland populations there are usually one or two months when virtually no females are gravid. Rainfall has previously been implicated as the most important environmental variable to explain ovarian cycles of tropical lizards. Rainfall does not explain the patterns observed on Puerto Rico, but temperature or a combined photothermal effect does. Reconsideration of previously published data on ovarian cycles in tropical anoles strongly suggests that the initial decline is not because of changing rainfall patterns but is again a response to a thermal or photothermal cue.
Demography of Yellow‐Bellied Marmont Populations
Authors: Armitage Kenneth B. , Downhower Jerry F.
Published: May 2006

Marmot (Marmota flaviventris) populations are colonial or satellite. The number of adults of colonial populations is relatively stable; fluctuations occur primarily because of changes in numbers of young and yearlings. Population trends among five colonial populations are dissimilar. Satellite populations are unstable and reproduce at a lower rate than do colonial populations. Satellite marmots are shorter resident than colonial marmots. Both colonial and satellite females usually are longer resident than males. All adult colonial males are 41% of adult colonial females are recruited from other places; all satellite adults are recruited from other places. Losses of colonial marmots are attributed primarily to mortality during hibernation and emigration. Predation appears to be a minor source of mortality of colonial marmots, but may be of greater significance to satellite populations. Demographic relationships of individual colonies appear to be density—independent. Dispersal of colonial animals occurs primarily among yearlings, which have a higher expectation of reaching sexual maturity than young have. The major cause of dispersal is social pressure, but social stress is not simply density—dependent. The colonial social organization is more adaptive than the more nearly solitary (=satellite).