摘要:

Oncopeltus cingulifer and Oncopeltus unifasciatellus occur on the same milk—weed species in the Cauca Valley of Colombia. Adults utilize the major host, Asclepias curassavica in the same way except that O. unifasciatellus feeds somewhat more on seeds. Nymphs of O. unifasciatellus require milkweed seeds to develop whereas O. cingulifer can mature slowly while feeding only on vegetative tissues of milkweeds. Parasitism, predation, and cannibalism are responsible for heavy losses of eggs in both species. Cannibalism of unhatched eggs by their newly—hatched siblings has a complex adaptive basis involving the utilization of individuals that are otherwise doomed and the proportion of eggs parasitized in a clutch by scelionid wasps. The continuous growing season in the Cauca Valley, coupled with the asynchronous occurrence of catastrophic setbacks in different milkweed stands, results in a shifting distribution of seed abundance. The adaptive syndromes exhibited by Oncopeltus appear to be organize around their dependence on this patchy resource. Thus O. unifasciatellus, which requires seed for reproduction, is less sedentary and more phenotypically variable than O. cingulifer. It seems unlikely that two such species could coexist in a seasonal environment where seed production is synchronized over an entire region.

ISSN:0012-9658    

DOI:10.2307/1936404

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

A study of the energetics of a sururban lawn was conducted in 1972—73 in Walnut Creek, California USA. Several major components of the annual primary and secondary production were measured, including man's role as manager and experimenter in the system. The system was extremely productive with net productivity of 1,020 g/m2per yr compared to cornfields with productivity of 1,066 g/m2per yr and exceeding tall grass prairie values of around 1,000 g/m2per yr. Homopterans, with maximal values of 19 mg/m2were plentiful; other typical grassland species, like Araneida, were scarce, representing only 1% by weight of the total invertebrate population. Food utilization per unit area by suburban birds considerably exceeded natural grassland bird utilization (46 kcal/m2per yr vs. 1.01—2.33 kcal/m2per yr); lawns are ideal foraging sites for open area adapted, flock—feeding species. Man was the dominant consumer in the community, accounting for 10% of the herbivory and nearly 100% of the scavenging. Energy inputs (labor, gasoline, fertilizer, etc.) amounted to 578 kcal/m2per yr, equalling or exceeding corn production for a comparable net productivity, but not necessarily utilitarian return.

ISSN:0012-9658    

DOI:10.2307/1936405

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

A survey was made in the Sonoran Desert of yeasts living in the decaying arms of five species of cereus cacti and the four species of Drosophila that utilize them as host plants. The most common yeasts among 132 isolates from the cacti and 187 isolates from the files, respectively, were: Pichia membranaefaciens (45% and 67%), Candida ingens (17% and 4%), Torulopsis sonorensis (12% and 11%), and Cryptococcus cereanus (8% and 7%). Eighty—eight percent of the 66 initial isolates of P. membranaefaciens from Drosophila pachea and its host, senita cactus, assimilated D—xylose while only 12% of the remaining 257 initial isolates did so. Nineteen of the 20 isolates of T. sonorensis from files were found in Drosophila mojavensis and 12 of the 14 isolates of Cryptococcus cereanus came from D. pachea. The highest mean number of yeast species per cactus was 2.77 plus or minus 0.68 in organpipe cactus and per fly was 1.63 plus or minus 0.53 in D. pachea. The flies usually carried fewer yeast species than were found in the host plant but D. pachea had almost the same mean and variance as its host, senita cactus, which had 1.64 @+ 0.40. Yeast species diversity and average niche overlap have the following rank order among habitats and localities: temperate trees>temperate flies>tropical flies>desert cacti>desert flies. Habitat diversity and average niche width show: tropical flies>temperate flies and desert cacti>desert flies and temperate trees. The physiological properties of the desert yeasts are most similar to those of the tropical yeast. However, desert yeasts have similarities with yeasts of temperate trees. Both have low fermentative ability and high assimilation ability of several alcohols and acids. The genus Pichia is by far the most common yeast genus associated with Drosophila in all habitats analyzed (36% of 1,426 isolates).

ISSN:0012-9658    

DOI:10.2307/1936406

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

When larvae of the tenebrionid beetle, Zophobas rugipes, were allowed to disperse among 26 equivalent chambers in a circular dispersarium, distribution patterns were found to be a function of larval weight and number of larvae in the apparatus (N). Small larvae (x wt 250 mg) were significantly aggregated while larvae mature larvae ( 1000 mg) where highly overdispersed. Medium larvae were intermediate, being overdispersed when N was 26 and showing some aggregation within general overdispersion when N was 52. Larval distributions did not deviate significantly from randomness when N was 13, indicating weak interactions at low density. The increasing tendency to overdisperse with increasing larval weight correlates with the parallel increasing tendency to pupate. Since metamorphosis of Zophobas rugipes larvae is known to be inhibited by crowding, this weight—related overdispersal probably allows pupation by mature larvae by causing them to leave regions of high population density.

ISSN:0012-9658    

DOI:10.2307/1936407

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Polygonum pensylvanicum and Abutilon theophrasti, components of old—field communities in central Illinois were grown on a controlled soil moisture gradient to determine whether they exhibit different response centers. Germination response of a constant number of seeds per six moisture resource states, height, biomass, and reproductive response of initially constant numbers of plants per state were monitored. States, ranging from saturation down to 13.61 ± 5.53% moisture, are numbered in order of increasing drought. Maximum height of Polygonum occurred in states 4 and 5, and of Abutilon in 4, 5, 6. Vegetative and reproductive biomass maxima of Polygonum and Abutilon occurred in states 5 and 6, respectively. Abutilon reproduced only in states 5 and 6 where it overtopped the Polygonum canopy, while Polygonum reproduced in all states. Polygonum performance declined sharply in state 6. Thus, Polygonum and Abutilon response centers are displaced toward the wetter and drier ranges of the gradient, respectively. On a within—community level, Abutilon reproduces in less mesic resource states where Polygonum canopy height is reduced. In general, Abutilon reproduction may occur throughout the gradient when the Polygonum canopy opens. The performance of these species is strongly influenced by both physical and biotic conditions. Previously investigated adaptations, including drought resistance and rooting patterns in space and time, appear to underlie divergence along the moisture gradient. The response patterns found here are broad and exhibit considerable overlap as expected in fugitive strategies. The patterns of divergence shown on point and gradient scales in this and our previous work reflect a related complex of adaptations and strongly suggest that competitive divergence occurs in early successional communities.

ISSN:0012-9658    

DOI:10.2307/1936408

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

A recent article paralleling two seabird (Alcidae) communities of the North Pacific and the North Atlantic oceans in reviewed critically. The quantitative basis upon which the argument of spatial segregation is based is demonstrated to be ethereal at best. Doubts are also raised about the appropriateness of comparing a fragment of a large North Pacific community, lacking many of its important elements, with an entire North Atlantic one. The model of ecological segregation proposed for these birds in burdened with shortcomings and cannot adequately describe any significant trait of the organization of the bird communities involved.

ISSN:0012-9658    

DOI:10.2307/1936409

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Daily metabolism was calculated from food consumption in pocket mice, Perognathus longimembris, at 8 degrees C, 18 degrees C, and 31 degrees C. At temperatures below thermal neutrality for this species, daily metabolism was related to the amount of time the mice spent in torpor. Ambient temperature has no net effect on the minimum energy expenditure during a typical 5—mo hibernation season. Once an animal has accumulated a food store of 130 g of millet seeds, it has the minimum energy necessary to hibernate at any environmental temperature. Such temperature compensation results from the complex effects of temperature on (1) the ratio of time of euthermy to time of torpor, (2) the energetic cost per hour of torpor, (3) the energetic cost per hour of euthermy, and (4) the energetic cost of arousal from torpor. The amount of time spent in torpor was inversely dependent on the food supply, indicating that euthermia is preferred even during the hibernation season. Mice also maximize the time of euthermia by selecting high environmental temperatures at all times of the year. Torpor probably occurs naturally only during the winter when the highest temperatures available to the mice are below thermal neutrality. The maximization of the time of euthermia reduces the chances of freezing during hibernation and enhances the animal's ability to escape from predators.

ISSN:0012-9658    

DOI:10.2307/1936410

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Behavior of white—tailed deer (Odocoileus virginianus) in Itasca Park, north—western Minnesota, USA was analyzed for energy—conservation adaptations during winter. Track records showed a decrease in activity with an increase in perdicted heat loss when activity and heat loss were compared on a sequential basis throughout the winter. Recognition of many seasonal but gradual changes in deer characteristics, such as antler growth, reproductive condition, and molting, suggest that seasonal physiological changes occur and also effect over behavior. Energy may be conserved by reducing the general level of activity, by seeking more level land and lesser snow depths, and by walking more slowly. Such energy—conservation measures may save up to 1,000 kcal/day (= 4,184 kJ/day) for a 60 kg deer, and 0.25—0.50 kg field—weight forage. Deer should remain as undisturbed as possible in the winter; harassment by dogs and snowmobile traffic is counter to their long term physiological and behavioral adaptations.

ISSN:0012-9658    

DOI:10.2307/1936411

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Population regulation of burrowing mayflies was investigated by modeling the population dynamics of Hexagenia limbata at Tuttle Creek Reservoir, Kansas, USA. Census data were obtained for the egg, nymph, and adult life stages to construct the basic statistics for life tables. Estimates were derived for survivorship of nymphs during 4 yr and for egg and adult survivorship in four areas in 1 yr. Fecundity was estimated from a random sample of adult ♀ ♀. Density dependence between segments of the life history was tested by key factor analysis and also by discrete time simulation. Population growth rate, calculated using the exponential model, had a negative linear relationship with population density, suggesting regulation at some life stage within the cycle. Population growth rates calculated for Leslie matrices with different nymphal survivorships but constant egg and adult survivorship also had a negative linear relationship with population density. Therefore, it is concluded that the population is regulated in the aquatic environment in the nymphal portion of the life cycle.

ISSN:0012-9658    

DOI:10.2307/1936412

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

A population of Plantago lanceolata (ribwort plantain) from a roadside was found to have higher Pb tolerance than populations away from the roadside; this reflected the sharp differences in Pb content of the soil and the plants at these sites. Tolerance tests on seedlings showed that the Pb tolerance was transmitted to seed progeny. Cynodon dactylon (Bermuda grass) showed generally a higher Pb tolerance than P. lanceolata, but there was no evidence of a greater Pb tolerance of the roadside population when compared with populations from control sites. These results suggest that the Pb level found at the roadside was sufficiently high to impose selection pressure for the evolution of tolerance in a sensitive species, but no overt effect was seen in a species with a greater inherent tolerance. This provides another example of rapid and highly localized evolutionary change in plants.

ISSN:0012-9658    

DOI:10.2307/1936413

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY