ISSN:0012-9658    

DOI:10.2307/1941051

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The Late Cretaceous Oldman Formation comprises sediments that were deposited along the margin of a great inland sea that covered much of the western interior of North America. The environment of deposition appears to have been tracts of fluvial marshes that separated “islands” of higher, drier ground. The climate was probably warm—temperate, and it is suggested that upland plant communities were parkland—like in aspect. The large dinosaurs of this community comprised animals that were between a hippopotamus and a large African elephant in adult weight. Some workers have suggested that dinosaurs had metabolic rates comparable to those of living birds or mammals. By extrapolating from the food consumption rates of these living endotherms it is possible to obtain crude estimates of the ingestion rates of endothermic dinosaurs. Similar extrapolations from the ingestion rates of living reptiles and amphibians provide estimates of the ingestion rates of ectothermic dinosaurs. By deriving an empirical equation relating the ratio of annual secondary productivity/average annual biomass to adult weight in living mammals, and employing estimates of adult weight and biomass for the herbivorous dinosaur populations, it is possible to estimate the annual secondary production of endothermic Oldman herbivorous dinosaurs. If the body weight vs. production/biomass relation derived for mammals can be applied to ectothermic tetrapods, it is possible to estimate annual secondary production of ectothermic dinosaur populations. These calculations suggest that the annual secondary production of endothermic herbivorous dinosaurs would have been insufficient to meet the food requirements of an endothermic carnivorous dinosaur population as large as is preserved in the Oldman Formation. However, ectothermic carnivorous dinosaurs would have been easily able to make energetic ends meet. Unfortunately, the situation is complicated by the possibility that carnivores are overrepresented in collection from the Oldman. Because of this, I cannot presently decide between ectothermy and endothermy in dinosaurs on the basis of methods presented in this paper. Alternative methods that may be more successful in this regard are discussed. It is hoped that as paleontologists collect fossils from an ecological point of view the methods presented in this paper can be employed to make realistic statements about the trophic dynamics of ancient vertebrate communities.

ISSN:0012-9658    

DOI:10.2307/1941052

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

In many space—limited systems, for instance forests, coral reefs, and mussel beds, the main biological component of the spatial matrix is provided by large—bodied species. At some point during their growth these matrix species surpass the ability of any single individual of a predator species to consume them, although they still may be overwhelmed by concentrated group attacks (i.e., by aphids, fungi, internal parasites). These species thus surpass through continued growth a size threshold limiting their consumers, and thereby attain a refuge in size. The implications of these refuges are discussed, with special reference to a predatory starfish, Pisaster ochraces, and its primary prey, the mussel, Mytilus californianus. The mean wet weight of Pisaster varies between localities from ° 150 g to 2,640g. Long—term (12—yr) observation indicates little annual variation and generally no trends within areas, yet consistent differences between areas. Five transplant experiments demonstrate that Pisaster is an indeterminate grower, andis capable of adjusting its body size through growth to local conditions. Limited recovery of individually marked starfish suggest that exchange between areas is restricted. Observations on the natural diet of Pisaster show a pronounced maximum body size limit to the mussels that can be consumed by intertidal starfish of a given size. This limit was explored experimentally in two ways. First, Pisaster was allowed to reinvade an area from which it had been manually excluded for 5 yr. In this interval those mussels comprising the matrix of the clump had attained shell lengths>8—10 cm. and could not be consumed by Piaster weighing 203 g. Second, artificial clumps of known—size mussels were protected by plastic screening, allowed to attach, and then exposed to predation. Survival was significantly greater in those mussels expected to be too large to be eaten. The significance of size—limited predation is that prey and predator can coexist in very intimate proximity, that the surviving prey often attain large sizes and probably make a reproductive contribution greater than their abundance, and that these same prey diversify the spatial structure of the environment, usually by adding a vertical dimension not otherwise present.

ISSN:0012-9658    

DOI:10.2307/1941053

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Four common species of bumblebees in central Maine each utilized the nectar from a great variety of both native and exotic flowers. The number of individuals that utilized a nectar resource was directly related to supplies available. Seasonally, ° 92% of the “standing crop” of food energy available per day was utilized in 1972. No interference competition was observed, and competition was primarily exploitative. Small wild bees generally foraged at high temperatures from the small food rewards left after Bombus exploitation. Overlap in resource utilization in the guild of bumblebees was avoided by differences in tongue length. Open (short—corolla) flowers were visited primarily by short— and secondarily by long—tongued bumblebees. Deep—corolla flowers were visited primarily by long—tongued bumblebees. Pollen flowers were utilized more by short—tongued than by long—tongued bumblebees. However, the bumblebee forager spectra on given flower species varied from one locality to the next as well as seasonally. Colony polylecty is probably a necessary correlate of social behavior, given short blooming times of the host plants relative to the long durations of the colony cycles. In turn, colony polylecty of eusocial bees may decrease species richness in the bee community due to competition.

ISSN:0012-9658    

DOI:10.2307/1941054

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The following phenology, in Maine, of 48 species of native biotically pollinated angiosperms from bogs, and 44 native species from woodland is compared with the pattern of blooming among 92 species (31% exotic) from disturbed habitats. Apportionment of the temporal blooming niches of the component plant species varied significantly (p<.005) between the three habitats. Flowering in bogs was spread fairly evenly throughout the growing season. In woodland, flowering occurred primarily before the trees leafed out, while in disturbed habitats blooming peaked in midsummer. Wind—pollinated trees and shrubs of all three habitat types had overlapping blooms in early spring. The blooming patterns of 1972 are compared with those of a few indicator species for 1973, 1974. 1975, and early spring 1976. The three types of habitats, having different presumed selective pressures on blooming time, served as mutual controls in the analysis of blooming times from the community perspective.

ISSN:0012-9658    

DOI:10.2307/1941055

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

One of the recent theories for the adaptive value of vertical migration states that migrants gain an energetic advantage over nonmigrants because by alternating between areas of high and low temperatures they are able to partition energy into growth more efficiently than nonmigrants. The energetics of the vertical migration of fourth—instar Chaoborus trivittatus larva in Eunice Lake, British Columbia was studied to identify and quantify this hypothesized energetic advantage. Fourth—instar C. trivittatus larvae undergo a regular, synchronous, diel vertical migration which exposes them to a wide range of temperature and prey density. Feeding occurs primarily at night and near the surface. Although all zooplankton in Eunice Lake are potential prey, Diaptomus kenai constitutes the majority of the biomass in the diet of fourth—instar larvae; Carbon assimilation efficiency of both copepods and cladocerans by C. trivittaus is ° 68%. Respiration rate increases linearly with temperature over the range 5—25 degrees C, although there is a suggestion of a plateau in O_2 consumption over the temperature range to which the larvae are exposed during migration. Temperature and ration size interacted to determine larval growth rate; fluctuating temperatures limited growth regardless of prey density while at constant high temperature prey density limited the growth rate. Analysis of several possible migration strategies showed that on an energetics basis alone growth will be maximized by either staying near the surface where there is food, or by vertically migrating with a physiologically determined periodicity based on individual feeding history. Laboratory growth experiments and the results of computer simulations of vertical migration show that the energetic hypothesis for the adaptive value of vertical migration does not hold for C. trivittatus larvae in Eunice Lake. These larvae do not follow either of the migration strategies that is energetically most efficient. No alternative hypothesis to explain their migration pattern is attractive. Possibly it is maintained by immigration from populations exposed to strong selection for this behavior pattern.

ISSN:0012-9658    

DOI:10.2307/1941056

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Annual production was calculated for three dominant larval odonate populations (Ladona deplanata, Epitheca spp., and Celithemis fasciata) coexisting in the littoral zone of an abandoned farm pond. Dragonfly populations and their prey were collected simultaneously with an Ekman grab at 2—wk to 1—mo intervals. Production for each dragonfly species was calculated using both the Allen curve method and the removal—summation method. Annual production for the three dominant species was ° 6 g/m2(dry wt), and total odonate production was estimated as 8 g/m2. Weekly odonate production was consistently>0.3 g/m2from July through September. With a mean annual standing stock of ° 2 g/m2, the odonate annual turnover ratio (TR) is ° 4. Weekly TRs were highest during summer months, generally declining as individual size increased. From back calculations of the amount of food required to feed the odonates, it as estimated that a minimal value of annual prey production was 18 g/m2and a minimal estimate of weekly prey production in the summer months was almost 1 g/m2. With an observed prey standing stock of 0.6 g/m2, this would necessitate an annual prey TR of 30 and a weekly summer TR>1. Since such an indirect method of calculating prey production does not account for other sources of prey mortality such as fish predation and emergence, the TRs are considered to be minimum values, perhaps only half of actual values. These relatively high TR values agree quite well with estimates based upon the amount of food required to sustain fish predators. The significance of these estimates made using indirect methods is that they are considerably higher than estimates made using more traditional direct methods. An attempt is made to resolve this discrepancy by examining sources of error associated with both approaches. Furthermore, since odonates have a standing stock frequently two to three times that of their prey and a large daily consumption capacity, I suggest that prey are saved from annihilation because they can find sufficient refuges.

ISSN:0012-9658    

DOI:10.2307/1941057

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Eight species of leafhoppers (Homoptera: Cicadellidae) of the genus Erythroneura (maculata group) breed on the American sycamore, Platanus occidentalis L. Several occur sympatrically in many areas throughout the range of their host plant even though they have been shown to compete severely for the last 9 weeks of the season in Illinois. The species are E. arta Beamer, E. bella McAtee, E. hymettana Knull, E. ingrata Beamer, E. lawsoni Robinson, E. morgani (DeLong), E. torella Robinson, and E. Usitata Beamer. Five of these are sibling species. Ecotope characteristics (niche and habitat) were examined to determine the factors which permit coexistence in this leafhopper guild on sycamore. The five niche or intracommunity factors examined were temporal utilization, distribution within the canopy, occurrence on leaves of various sizes and ages, and location of feeding sites on the leaf. There were insufficient differences between species for all five niche parameters to explain coexistence in the guild by niche segregation. Three habitat or intercommunity parameters were examined: occurrence on trees alone a moisture gradient, latitudinal distribution with respect to that of sycamore, and distribution within a given geographical locality. There were sufficient differences in the latter two parameters to explain coexistence by habitat segregation. The peak proportional abundances of seven of the eight species occurred in different latitudinal zones and the degree to which the distribution of each species was overlapped by those of all the other Erythroneura ranged from only 0.10 to 0.63 (° = 0.42). Data indicate that species whose ranges over—lapped substantially have apparently evolved differences in their manner of resource utilization, thus reducing competition through character displacement or through a shift in the adaptive mode of the population. There was a tendency for each species to become more unevenly distributed locally from its distributional center; this further reduced geographical overlap between species. Overall proportional similarities (PS), calculated for latitudinal and local distributions were low (PS range from 0.00 to 0.44; ° = 0.17 where PS_(max) = 1.0 and PS_(min) = 0.0). We infer that habitat segregation in the guild permits coexistence. Additional mechanisms which may permit coexistence are discussed.

ISSN:0012-9658    

DOI:10.2307/1941058

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Plant standing crop and productivity relations were examined for an extensive marsh complex in southern Quebec, Canada. Forty—five 1—m2plots were sampled for dry weight shoot biomass, species composition, structure (species density, diversity, height), and soil parameters including nutrient concentrations. (Ca, K, Mg, Na, N, P), pH, organic matter, and water depth. Shoot net productivity and decomposition rates were computed for 20—day intervals across the growing season. Relationships between all parameters were examined by principal components analysis. Dominant emergent species included Scirpus fluviatilis, Equisetum fluviatile, Scirpus validus, Phragmites communis, and Eleocharis palustris. For a 150—day interval, shoot net productivity averaged 6.10 g·m(—2)·day(—1) and terminal standing crop was 845 g/m2. Seasonal productivity showed a strong bimodal pattern with peaks in late July (12.90 g°m(—2)·day(—1) and midSeptember 4.73 g°m(—2)·day(—1). Species typical of deep water showed much earlier and higher peak productivity than this general pattern but net shoot productivity as of short duration. Two—thirds of annual litter production was lost by export. Complete decomposition of remaining litter occurred within the next growing season. Temperature and decomposition rate maxima coincided with peak productivity in July and decreased exponentially through October. Among edaphic parameters, soil K had the highest correlation (r = 0.49**) with standing crop while soil N had the highest correlation with shoot net primary production (r = 0.39**). Soil P correlated negatively with all production and soil nutrient parameters except soil Mg levels. It was the only nutrient with a soil concentration maximum in shallow water. Other nutrients attained maximum levels at an intermediate point on the water depth gradient. Maximum litter standing crop occurred at this point, coinciding closely with changes in soil cation levels. While shoot density and standing crop followed these trends, they coincided more closely with changes in soil anion concentrations (nitrogen, hydrogen). Sedimentation and nutrient uptake associated with high stem density and standing crop were shown to be important factors in site enrichment. Shoot net primary productivity and standing crop correlated negatively with all measures of species diversity. Variety and equitability decreased from 8.00 species and 0.96 bits/m2in Scirpus validus stands of deep water to 2.00 species and .01 bits/m2in shallow stands of S. fluviatilis. Sparse canopy cover and high levels of disturbance in S. validus stands made possible the coexistence of a rich variety of aquatic life forms not possible under conditions of intense competition typical of S. fluviatilis.

ISSN:0012-9658    

DOI:10.2307/1941059

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

An experimental ecosystem was constructed and used in studies of species coexistence in a patchy environment. This model system consisted of two species of fungi, Aspergillus nidulans and an unidentified species of Penicillium, competing for space on agar—filled petri dishes. Aspergillus was observed to overrun and infiltrate established colonies of Penicillium, and so was considered competitively dominant, while Penicillium produced a greater number of daughter colonies at an earlier age than did Aspergillus, and so was considered a better colonizer. It was hypothesized that these two species should be able to coexist in a patchy environment where local populations on occasion become extinct, with Penicillium playing the role of a fugitive species. Two different regimes (Annual and Perennial) for the generation of empty patches through the extinction of their resident species were compared with reference to the ease with which coexistence was obtained. Under the Annual regime, where all patches became empty (hence available for colonization) at the same time and where the (n + 1)st generation was seeded with spores from the nth generation alone, coexistence was not obtained. In the Perennial experiments, however, where only a fraction of patches became empty at any one time and where newly emptied patches were seeded from patches of several different ages, coexistence was easily obtained. Temporal differences in the use of single patches occurred under the Perennial transfer regime, with Penicillium colonizing from younger patches in which Aspergillus had not yet exerted its dominance, and Aspergillus colonizing from older patches. Temporal partitioning did not occur in the Annual experiments, and coexistence was not obtained. Since the pattern of disturbance and the life history patterns of the competing species combine to determine the extent to which temporal partitioning can occur, it is evident that for the fugitive species mechanism to be effective, the life history patterns of the species involved and the pattern of environmental disturbances must be well matched. Discussion of these problems is facilitated by the introduction of the notion of “coexistence bandwidth” a theoretical construct which relates in these experiments to the ease with which coexistence can be obtained, and in natural systems to the fragility or robustness of competitive associations in the face of changing environmental conditions.

ISSN:0012-9658    

DOI:10.2307/1941060

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY