ISSN:0012-9658    

DOI:10.2307/1933595

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Systems analysis is defined as the use of scientific method with conscious regard for the complexity of the object of study. It has strong relationships with problem solving, in that the same four phases–lexical, parsing, modelling, and analysis–are identifiable in both. Examination of each of these phases reveals some of the problems involved in the use of systems methods in ecology. A model of a precipitation—evaporation system is presented as an example. Problems in experimenting with models of systems and with control, optimization, and comparison of such models are considered.

ISSN:0012-9658    

DOI:10.2307/1933596

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Two small ponds in Bartow County, Georgia, northwest of Atlanta, originated by subsidence of unconsolidated surface deposits into solution hollows in the underlying lower Paleozoic Knox Dolomite. The pond sediments consist of copropelic clays 250—400 cm thick with well—preserved plant remains, covered by as much as 150 cm of colluvial deposits with moderately to poorly preserved plant fossils. The clays yield radiocarbon dates of 20,100 and 22,900 BP near their base, contemporaneous with the main Wisconsin glaciation. The full—glacial sediments are rich in pollen and plant macrofossils. The pollen assemblage is dominated by Pinus (pine), with small amounts of Picea (spruce), Quercus (oak), Ostrya type (hophornbeam), and herbaceous types. It closely resembles published full—glacial pollen assemblages from southeastern North Carolina. Pinus banksiana (jack—pine) and Picea sp. are represented by fossil needles at many levels, and the rich macroflora of aquatics shows a marked phytogeographical relationship with the modern flora of northern New England. A floristic displacement of about 1,100 km would be needed to account for the presence of this flora in Georgia. Deciduous trees, primarily Quercus and Ostrya type, may have had a minor role in the full—glacial vegetation. In the postglacial an early Quercus—dominated phase is followed by a Pinus—dominated phase, which lasts to the present. Familiar southern tree genera such as Liquidambar (sweet gum) and Nyssa (black gum) appear to have migrated into the region in postglacial time. Species that occur primarily on the Coastal Plain but have disjunct occurrences at the two ponds and farther into the central United States, such as Itea virginica (Virginia willow) and Psilocarya nitens (sedge), first appear in the fossil record in the postglacial. It is supposed that they and perhaps other "Coastal Plain disjuncts" migrated into their present localities during the postglacial.

ISSN:0012-9658    

DOI:10.2307/1933597

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

If aggressive behavior regulates population size in small rodents (as claimed by Chitty 1967), periodic fluctuations must be associated with behavioral changes. In an attempt to test this hypothesis, exploratory activity and aggressive behavior were measured in 645 male Microtus ochrogaster and 570 M. pennsylvanicus of 7 populations in southern Indiana from August 1965 to September 1967. Exploratory activity was measured in an open—field test under daylight conditions, and aggressive behavior was measured by fighting voles in pairs in a neutral fighting arena. Exploratory activity could not be related to the individual attributes of home range size or duration of life in males of either Microtus species. On the population level, mean exploratory activity could predict the mean rate of population growth in M. ochrogaster populations, but not in M. pennsylvanicus populations. Aggressive behavior changed significantly over the population cycle in both species, and males from peak populations were most aggressive. Multiple discriminant analysis was used to characterize the behavior patterns of males from increasing, peak, and declining populations. These discriminant scores predicted the mean rate of population growth in M. pennsylvanicus populations but not in M. ochrogaster populations. Aggressive behavior types characteristic of increase, peak, and decline phases showed differential survival rates, but no association was found with body weight or transferrin genotype in either species. Home range size was related to aggressive behavior type in M. ochrogaster but not in M. pennsylvanicus. These data on two species of Microtus do not refute the hypothesis that aggressive behavior may act to regulate population size. However, there is no information on what causes these behavioral changes, and the next step is to see if these changes occur in other populations of these two species and to determine whether they are genotypic or phenotypic.

ISSN:0012-9658    

DOI:10.2307/1933598

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

An eruptive fluctuation is defined operationally as an increase in numbers over at least two generations, followed by a marked decline. Reported eruptions in ungulates suggest that the upswing is initiated by a change in food or habitat and is terminated by overgrazing. An apparent exception–the Kaibab eruption–probably also fits this pattern. The interpretation causally linking reduction of predators on the plateau with increase of deer is an overstatement of evidence. Eruption of established populations is essentially the same process as the buildup of populations initiated by liberation, with the difference that in the second case a zone of high density migrates radially from the point of liberation. Eruption of thar (a goat—like bovid) after liberation in New Zealand was studied by sampling populations at different distances from the point of liberation. The aim was to determine trend of demographic statistics across an eruptive fluctuation that spans 50 years. Although fecundity varied across the eruption, the major influence on rate of increase was traced to variation in death rate. The major component of this variation was the rate of mortality over the first year of life. Trend in death rate, and hence in rate of increase, was associated with trends in other population statistics that are easier to measure. The most useful correlative of rate of increase is probably the level of fat reserves. While we do not know whether trends in population statistics of thar reflect those of other ungulates during an eruptive fluctuation, the generality of the reported trends may usefully serve as a testable hypothesis.

ISSN:0012-9658    

DOI:10.2307/1933599

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Concentrations of atmospheric CO2were measured continuously throughout the 1966 thaw season at two stations on the Arctic coastal plain of Alaska. A seasonal decrease in CO2of 15 ppm was demonstrated, as well as changes in concentration associated with storm frequencies and diurnal gradients. Correlation between rate of plant growth and declining CO2concentration in the atmosphere was high (r = .98). Tundra growth was initiated by mid—June and was 90% completed in mid—July. Standing crop above ground and below ground was estimated to be 82 and 100 g/m2, respectively. A 23% turnover of 273 g/m2of litter was confirmed. Gross primary production was estimated at 344 g/m2. An annual budget for CO2in an Arctic biosphere is postulated and efficiencies for both energy and carbon storage calculated. Based on seasonal net radiation a photosynthetic efficiency of 0.7% was determined, whereas atmospheric CO2was apparently used at the rate of nearly 12%. Estimates of CO2turnover due to biological activity are similar to the 10—year residence time of a molecule before absorption in the sea.

ISSN:0012-9658    

DOI:10.2307/1933600

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Total nitrogen incorporated in the shrubs of a low—fertility desert plant community (principally Acacia Gregii, Cassia armata, and Larrea divaricata) was estimated from the nitrogen content of plant parts, the total weight of plants and proportional weight of roots, stems, and leaves, and the number of plants per unit area. The average nitrogen content of shrub leaves, stems, and roots was 1.31%, .87%, and .80%, respectively. Shrub cover occupied 20% of the ground surface and contained an average of 29 kg nitrogen/ha. Legume shrubs were not significantly greater in nitrogen content than nonlegume shrubs. Soil nitrogen content decreased significantly as a function of radial distance from the center of the shrub canopy. Areas between shrubs averaged 0.19% nitrogen in the surface inch of soil. Soil nitrogen content decreased significantly from the surface to 90—cm depth and was closely related to shrub species and their root—distribution patterns.

ISSN:0012-9658    

DOI:10.2307/1933601

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Hypothetical vegetation models were made to simulate numerical changes in species populations along a single environmental gradient. A single ordination procedure was evaluated by its ability to detect the ecological information in the hypothetical models. The procedure was reasonably successful when the data were drawn from a short length of the gradient but became progressively less so as longer lengths of the environmental gradient were included in the data. This parallels an increase in the number of stands from which each species is absent in the total data set. Zero values appear to mask ecological information, and an intuitive method of assigning "degree of absence" values to the data is described. After this adjustment, ordination patterns were easier to interpret because ecological information was concentrated in fewer axes.

ISSN:0012-9658    

DOI:10.2307/1933602

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Changes in interspecific association related to variation in quadrat size, position on a gradient, and abundance measure used in calculating indices yielded information about the nature and causes of this association, and results often corroborated one another mutually. Distribution of species along the gradient and interspecific association within gradient segments appeared to be continua, with varying steepness of transition. Strong association of some rare species suggested that they are highly specific ecologically and/or controlled by few factors. Association changes related to quadrat size suggested general grouping of species on two scales. Possibly, Pteridium and litter generate this grouping between patches where they inhibit plants generally. Weaker positive correlation of cover than of presence suggests unequal competitive restriction of plastic response within the patches of high cover formed by grouping. Large and abundant species in particular seem to inhibit others. Strong positive and negative association characterized heterogeneous habitats and vegetation, extreme habitats in which small environmental differences may be critical, species whose restricted distributions along the gradient may reflect narrow tolerances and consequent microsite specificity, and extremes of species' ranges along the gradient. At these extremes, species perhaps require specific uncommon microsites, and these requirements seem to be similar for species having similar distributions along the gradient. Weak species—environment correlation may reflect low variability of environmental parameters, strong correlation between the latter suggesting that few stochastic processes and complex interactions affect them. In a bog, the major patterning element seems to be hummock—hollow microtopography.

ISSN:0012-9658    

DOI:10.2307/1933603

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Lottia gigantea, a large (up to 8 cm in length) limpet of the California and northern Mexican coast, lives in association with an approximately 1,000 cm2area of algal film in which its grazing marks can be seen, whereas the remainder of the rock surface is usually free of any visible film. These areas of algal film represent the territories of the Lottia; within them the animals do all their grazing. They keep their territories free of other organisms by shoving off any intruders: other Lottia, grazing limpets of the genus Acmaea, predatory snails, and sessile organisms such as anemones and barnacles. Within 2—3 weeks after Lottia were removed from their territories, the density of Acmaea in these territories increases to that found outside them, and the algal film disappeared. Apparently the defense of the territories against intrusions by other grazers permits the growth of a thick algal film on which the Lottia can effectively graze. Their reaction to sessile organisms prevents these animals from encroaching on and covering the territory. Their response to predatory snails may be a defense mechanisms.

ISSN:0012-9658    

DOI:10.2307/1933604

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY