摘要:

Typical seed caches made in the fall of the year by white—footed mice (Peromyscus leucopus) and red—backed voles (Clethrionomys gapperi) contained 20—30 pine seeds, buried beneath the litter of pine needles and in contact with mineral soil. Many caches were revisited by the mice and their contents destroyed before winter. Most caches not decimated in the fall were invaded the following spring. However, some of them escaped complete destruction and their unconsumed seeds germinated and produced seedlings. Although mice make their caches in micro—environments highly favorable to germination, their subsequent feedings on the stored seeds, both before snowfall and before and during the spring germination period, greatly deplete the number of potential germinants. Therefore, the contribution to forest regeneration of seeds stored by these small forest mammals is probably of minor significance except when bumper seed crops are produced and large numbers of caches are created. Under these circumstances, stored seeds may be of sufficient quantity to exceed food requirements of the mice. If pirating by other animals is low, then a surplus of seeds is left to help regenerate the forest.

ISSN:0012-9658    

DOI:10.2307/1933663

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

A community of adult Odonata, composed of 18 species, was studied during June and July of 1968 at a small pond in piedmont North Carolina. Studies were made on the influences of time of day, ambient temperature, and light intensity on flight activity, and on the frequencies of intra— and inter—specific interactions. Most species initiated their flying periods by mid—day and terminated them by 1930 hr with considerable variations among the species. Maximum reproductive behavior occurred near the mid—point of the patrolling period. Minimal temperature thresholds for activity ranged from 20—28°C, whereas maximal thermal thresholds were from 30—40°C. Adult activity decreased proportionally to a decrease in light intensity during cloudy periods or thunderstorms. Activity of individuals to some species was controlled chiefly by one environmental factor, but in others activity presumably was related to a combination of several factors. Intraspecific interactions, usually between males, were much more common than interspecific interactions. Threat behavior was far more prevalent than actual physical contact.

ISSN:0012-9658    

DOI:10.2307/1933664

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Shoot productivity was measured for Typha latifolia and Scirpus americanus. Samples were also subjected to chemical analyses. Tissue concentrations of chlorophylls a and b, carotenoids and most macronutrients declined as the plants aged. Net accumulation of these constituents per square meter usually continued during periods of dry matter increase, even though tissue concentrations were diminishing. Dry matter standing crop was the decisive factor determining quantities of chemical constituents per square meter. Uptake rates for macronutrients were generally not proportional to productivity rates. The most rapid uptake of several nutrients occurred earlier than maximum growth rates.

ISSN:0012-9658    

DOI:10.2307/1933665

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

The assumption of equal catchability of marked and unmarked animals in mark—recapture sampling is examined. Violation of this assumption may come from two basic sources, heterogeneity or contagion, and both produce a bias in the estimate of population size. Two approaches to this problem are discussed. First, it is noted that bias can be avoided by statistically independent sampling procedures for marking and recapturing. Second, a new regression method is presented for multiple captures on a closed population, which combines mark—recapture with "simulated" removal and tests whether the assumption of equal catchability holds, regardless of the source of bias. Furthermore, if the ratio of catchabilities between unmarked and marked animals is constant over at least two successive samples, the method provides an estimate of population size even if the assumption of equal catchability does not hold. Two suggestions are made to supplement the regression method. First, noncapture sampling to obtain the ratio of unmarked to marked animals has several advantages over trapping. Second, a subclass of the marked animals may satisfy the constant ratio assumption even when all marked animals do not. A worked example is provided to illustrate the method.

ISSN:0012-9658    

DOI:10.2307/1933666

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Shoot standing crops for Typha latifolia ranged from 428 to 2,252 g dry wt/m2. Standing crops were positively correlated with concentrations of dilute acid soluble phosphorus in hydrosoils and dissolved phosphorus in the waters. Except for a weak0 correlation for dissolved calcium, additional site fertility parameters were not correlated with standing crop. Tissue nutrient levels varied considerably, maximum values for most minerals being three or four times as great as the smallest values. Correlations between environmental levels of several nutrients and tissue concentrations were significant, but not very strong. Tissue concentrations of most nutrients were positively correlated with nitrogen content. Despite variations in tissue levels of nutrients, standing crop was the decisive factor determining quantities of nutrients per unit area of stand.

ISSN:0012-9658    

DOI:10.2307/1933667

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Laboratory experiments, conducted within a current chamber, suggest that upstream movements of the amphipod Gammarus pulex, especially in regions of slower current flow, are sufficient to compensate for the downstream displacements of animals by drift. They indicate also that drift was greater in slow—flowing than in faster waters.

ISSN:0012-9658    

DOI:10.2307/1933668

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Several examples are given to illustrate the dangers of inferring the existence of density—dependent population regulation on the basis of correlation analyses. Alternate models based on a series of random number (or random selections from some other frequency distribution) have expected correlation coefficients very close to those cited as demonstrating density dependence. A "Morris plot" can also be generated from a series of random numbers.

ISSN:0012-9658    

DOI:10.2307/1933669

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

One of the major difficulties in evaluating energy flow in natural animal populations is the determination of field metabolism. Various writers have suggested that there may be a correlation between excretion rate of a radioactive isotope and metabolism in small mammals which might be used to determine metabolism in free—ranging animals. To test this hypothesis, cotton rats confined in the laboratory and in field enclosures were injected with P32and their excretion rates were measured. Oxygen consumption also was measured in the laboratory animals. A poor correlation was found between oxygen consumption and excretion rate in the laboratory while a significant correlation was found between P32excretion rate, oxygen consumption and temperature. Assuming that this correlation held true in the field, oxygen consumption was predicted in the field population, as 2.37 cc O2/g hr—1 in July, 3.41 cc O2/g hr2o1in September and 4.02 cc O2/g hr—1in November. Oxygen consumption in the field was not significantly higher than in the laboratory, indicating that the cotton rats did not expend a significantly greater amount of energy in the field. The use of the excretion rate of a radioactive element as a predictor of metabolism was criticized due to the high variance and lack of correlation between excretion rate and metabolism at the individual level.

ISSN:0012-9658    

DOI:10.2307/1933670

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Studies of the foraging ecology of Downy Woodpeckers (Dendrocopos pubescens) at the University of Kansas Natural History Reservation indicate that there is intersexual partitioning of the foraging niche, seasonal variation in the relative frequency of the modes of foraging, variation in the mode of foraging on live versus dead trees, and seasonal variation in the use of live and dead trees. Partitioning of the foraging niches by the sexes is accomplished behaviorally by a differential use of the available substratum according to limb height and diameter. The degree to which these unisexual subniches are expressed varies on live versus dead trees. Males tend to forage on small branches, generally 5 cm in diameter or less; females tend to forage on the trunk and larger limbs. The mean foraging height of males in live trees (6.0 m) is significantly different from that of males in dead trees (8.9 m); the mean foraging height of females in dead trees (8.4 m) is not significantly different from that of females in live trees (8.1 m) or of males in dead trees. The mean foraging height of males in live trees is significantly different from that of females in live trees. A similar relationship exists among the heights of the trees in which Downy Woodpeckers forage. Both male and female Downy Woodpeckers use sub—surface foraging techniques to a greater extent during the winter and superficial techniques during the warmer months. Greater use of dead trees during winter is also indicated. Dead American elms (Ulmus americana) are used as foraging sites by both sexes to a greater extent than expected by chance. Some other tree species seem to be favored and some avoided by one or both sexes.

ISSN:0012-9658    

DOI:10.2307/1933671

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Sr/Ca ratios are given for 22 species of aquatic plants from Perch Lake, Ontario. When compared with the lake water, 16 species are found to discriminate against calcium relative to strontium. Consequently, these species introduce a strontium enrichment step into any food chain in which they participate. One species (Nymphaea odorata) however, shows a remarkable discrimination against strontium.

ISSN:0012-9658    

DOI:10.2307/1933672

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY