摘要:

Radiotracking and live—trapping techniques were used to determine the movement patterns of Dipodomys spectabilis in central New Mexico, USA. In contrast with the live—trapping results which suggest extensive home range overlap, 133 h of radiotracking over a 2—yr period revealed that most individuals exclude other bannertails from a circular home range of approximately 0.05 ha with a centrally located burrow. Home range size remained relatively constant during the warmer months. The extent and intensity of activity varied greatly among rats, and although the contents of food caches changed qualitatively during the year, no seasonal foraging pattern was evident. The average bannertail spent 58% of the night hours inside or on the mound and less than 22% of the time more than 6 m from the mound. There was no evidence that moonlight affected activity. Foraging is an efficient process, perhaps accomplished concurrently with other activities. The tendency of this species to store large quantities of seed heads collected at an optimal stage of development from a feeding territory suggests that the bannertial may manage its food resources to an extent seen in few other rodent species.

ISSN:0012-9658    

DOI:10.2307/1936601

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Controlled coral transplant experiments were used to determine the effect of piscine corallivores on growth, zonation, and distribution of scleractinian corals in Guam. Pocillopora damicornis L. generally occurs only on the reef flat, reef margin (crest), and in lagoon habitats of the Indo—West Pacific. Although P. damicornis grows in deeper reef habitats in the eastern Pacific, it is seldom found in fore reef zones of the Indo—West Pacific. Colonies were transplated from a depth of 1.3 m in a barrier reef lagoon to depths of 15 and 30 m in fore reef zones of three fringing reefs, where P. damicornis was absent. All transplanted colonies were heavily fed upon and branch tips were removed primarily by chaetodontid and balistid fishes, but none of the colonies was killed. This feeding removed about one—fourth of the colony wet weight in 1 wk (°x 23.7% ± 2.4, .99 confidence limits, N = 118). There was a very significant differnt in the amount of fish feeding on transplants between three different study reefs (Fs= 459.30, P<.001). There was no significant difference in the amount of feeding between the two depths at each site on any one run. Polyp and mucus browsing by species which do not physically damage the corol skelton was also substantial. When colonies of P. damicornis from Apra Harbor (1.3 m) were transplanted with colonies of Pocillopora sp. from Fafai Reef (15 m), to Double Reef and attached to naturally occurring Pocillopora verrucosa colonies (15 m), fish discriminated between the three similar species and fed only on P. damicornis. While some authors have indicated that these species may comprise a species complex, the fish clearly discriminted between the species. Coral feeding by many reef fishes is a regular event and exerts great influence upon reef community structure. Although P. damicornis can survive and grow well in deeper habitats in fish exclusion cages, it generally does not occur in these zones in the Indo—West Pacific. It is therefore concluded that piscine corallivores are important in restricting the growth, local zonation, and general distribution of some coral species.

ISSN:0012-9658    

DOI:10.2307/1936602

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

The interaction of insolation, wind, and ambient temperature on the energetics and behavior of juvenile Herring Gulls was studied. At low ambient temperatures gulls can reduce their energy expenditure for thermoregulation as much as 29% by basking. Insolation at ambient temperatures above 15°C was stressful to the gulls because the thermal gradient was into the bird. The feet were found to be an important means of heat loss in birds at high and moderate ambient temperatures receiving insolation. Under natural conditions the use of the microhabitat is extremely important in minimizing the effects of radiation both during the day and at night.

ISSN:0012-9658    

DOI:10.2307/1936603

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Classical nearest neighbor analysis, assuming points, underestimates expected mean nearest neighbor distance for circles and overestimates its standard error. The extent of distortion may be sufficient to lead to incorrect conclusions, such as regularity for an arrangement which is, in fact, clumped. Analytic expressions are derived which are accurate for small circles, and the results of simulations are plotted for use when circles are large.

ISSN:0012-9658    

DOI:10.2307/1936604

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Horned lizards, Phrynosoma cornutum, were observed between sunrise and sunset in order to record the time spent at different behaviors and the prey taken. Two ant species, Pogonomyrmex desertorum and Pogonomyrmex rugosus, were the most important prey. The behavioral responses of these prey species were studied by subjecting them to varying levels of simulated predation. The lizards fed most often on ants that were not associated with nest discs or foraging columns and took only a few ants at any one place. Lizards moved on average of 46.8 m/d, remaining in the vicinity of any group of ant nests<15 min. In artificial predation experiments, Pogonomyrmex desertorum ceases activity for periods of up to 5 d following losses of °25% of the forager population when foragers were removed at a rate of 5/d or 10/d. Pogonomyrmex rugosus did not respond to loss of 25% of the forager population, ceased activity of losses of 50% of the forager population, and exhibited frenzied activity upon loss of 75% of the forager population. The horned lizards have evolved a foraging strategy that allows maximization of prey availability over weeks or a month rather than per hour or day. Estimates of horned lizard densities, ingestion rates, and numbers of potential prey suggest that horned lizard numbers are regulated by the availability and productivity of Pogonomyrmex spp. These estimates also suggest Pogonomyrmex spp. colonies are extremely productive, essentially replacing the entire worker population each year.

ISSN:0012-9658    

DOI:10.2307/1936605

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

The concentrations of inorganic nitrogen ions were measured in the tidal water flushing Flax Pond, an estuarine marsh on the north shore of Long Island, New York, USA. The basic sampling unit was one tidal cycle during which eight subsamples were taken, four on the flood and four on the ebb. The sampling was approximately weekly during 20 mo. Concentrations of the three forms of nitrogen (nitrate, nitrite, and ammonium) varied seasonally and with the periodic occurrence of algal blooms. Concentrations were highest in winter and lowest in spring and early summer, but details of the pattern of abundance differed among the ions. There was a net discharge of nitrogen in the ammonium form from Flax Pond during summer and fall and a net input from the Sound in winter and spring. The net exchanges during 1 yr were zero for nitrite, an influx of nitrate of about 1 g N/m2to the marsh, and a release of about 2 g ammonium—N/m2into the Sound. The net total exchange was a release into Long Island Sound of approximately 1 g N/m2of marsh, an amount not statistically different from zero. Crude estimations of the total inorganic N—budget of Long Island Sound suggest that estuaries, precipitation, and rivers each contributed approximately equal inputs in earlier times.

ISSN:0012-9658    

DOI:10.2307/1936606

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Currently used niche measures of overlap and breadth are shown to be inappropriate for analyzing field data. Previously proposed measures assume resources are equally available, but this assumption is unwarranted in field studies. Comparisons of different measures of either breadth or overlap are also not valid. A measure of niche breadth is derived by asking how likely it is that a species' utilization of resources could have been drawn from the available resources in the environment. An overlap measure is derived in a similar manner and represents the likelihood that the utilization of resources by one species is identical to the utilization by another species. Tests for comparing different measures are given.

ISSN:0012-9658    

DOI:10.2307/1936607

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

This study uses morphological data relating to many aspects of the niche to study community organization in assemblages of stream fishes from three separate drainages. Mean values for all morphological features were compared statistically for coexisting species pairs, and those features which had significantly different means were assumed to indicate ecological differentiation that exists between the species under consideration. Average niche overlap as defined by the percentage of morphological features not differing significantly between species pairs was constant for these assemblages regardless of a nearly twofold difference in number of species present. Similarly, the average Euclidean distance between the centers of morphologically defined niches for all sympatric common species was approximately the same for all three assemblages. Moreover the distribution of Euclidean distances between species was the same in all three drainages and different than a distribution that would result from a random division of resources. Together, these results indicate that consistent patterns do exist in the organization of these stream communities, and that the species currently living together are not a random assortment of species and do not randomly divide their resources. The presence of higher numbers of species in a community seems not to be accompanied by increased packing of the niches, but rather by an occupation of more total niche space by the community as a whole.

ISSN:0012-9658    

DOI:10.2307/1936608

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

The intestinal protozoan faunas of 11 social groups of Cercocebus albigena, 3 groups of Ceropithecus mitis, 3 groups of Cercopithecus ascanius, 2 groups of rain forest and 4 groups of savannah Papio anubis are documented. All individuals in a particular social group exhibit identical protozoan faunas. All social groups of each species, except the savannah P. anubis, exhibit intergroup differences in the composition of their protozoan faunas. The number of intestinal, protozoan species in Cercocebus albigena social groups is a function of group size. The similarity between the protozoan faunas of different C. albigena groups is related to the density of the social groups and types of land tenure in particular localities. Past social history of C. albigena groups may have some influence on the level of similarity of different groups' faunas. Entrance of a nongroup member into a group of Cercopithecus mitis resulted in an increase in the species richness of the group's protozoan fauna. Group fission may result in reduction of a group's protozoan species richness. All groups of savannah Papio anubis exhibit identical protozoan faunas. I argue that this is because savannah P. anubis has a higher rate of exchange of individuals between groups than has been recorded for the rain forest primates under consideration. I hypothesize that the differing rates of exchange are due to disease—related selection against traits which result in high rates of individual exchange among rain forest primate groups. Primate social groups are functionally biological islands; the species of their protozoan faunas changes according to group size and levels of protozoan migration between groups.

ISSN:0012-9658    

DOI:10.2307/1936609

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

This report examines patterns of competition and foraging dynamics among colonies of the harvester ant Pogonomyrmex californicus. Two components of harvesting efficiency are defined: total harvesting efficiency (i.e., all food items considered) and seed harvesting efficiency (only seeds considered). Throughout the summer, total harvesting efficiency remained constant, whereas seed—harvesting efficiency exhibited an increase as a result of changes in the relative availability of the dominant seed crop, Erodium cicutarium. Several aspects of interference were studied. Colonies were uniformly spaced, and nest relocations significantly increased nearest—neighbor distance. Of encounters between ants from different colonies, 81% resulted in some form of aggression and 7% were fatal to one or both foragers. In a particular study, forager mortality rate was estimated at 0.06 deaths per ant foraging hour, thus indicating that such aggression may have a substantial impact on colony size. Furthermore, following an encounter involving physical struggle, ants returned to and remained in their nests for an extended period of time, thereby reducing seed input to the colony. The above—mentioned components of interference are examined to their potential effects on colony density, distribution, and size.

ISSN:0012-9658    

DOI:10.2307/1936610

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY