摘要:

Ages and diameters were measured in mature stands for each of 507 ponderosa pine, 541 lodgepole pine, 141 limber pine, and 217 Engelmann spruce trees in the Colorado Front Range of the Rocky Mountains, USA. Cumulative age distributions were statistically different for each species. The spruce and ponderosa pine age distributions each exhibited a strong infection point at °210 and 125 yr, respectively, while neither lodgepole nor limber pine showed such a sharp inflection point. We suggest that the presence of this inflection point may be indicative ofclimax type in mature stands and interpret the age distributions of these species as reflective of their climax, colonizing and fugitive ecological patterns, respectively. Diameter distribution curves exhibited patterns markedly different from the age patterns. Ponderosa pine and Englemann spruce showed almost identical distribution despite widely disparate age structure. We interpret this result to simply that to the complex of forces which influence size distributions in forest trees is very similar in ponderosa pine and spruce although they form very different ecological communities. Lodgepole and limber pine diameter distributions were quite different. Our conjectures that the presence of a sharp inflection point in cumulative age distributions indicates aclimax stand and thatclimax species will often have coincident diameter distributions, are offered as empirically testable hypotheses.

ISSN:0012-9658    

DOI:10.2307/1937322

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Effects of the grazing activity of the gastropod Lymnaea elodes (arctica?) on animal community structure in the rocky littoral of an arctic lake were examined. In situ caging experiments on natural substrates with various snail densities resulted in shifts in faunal biomass abundance and distribution. Chironomids living in fixed tubes (Paratanytarsus) were greatly reduced at high snail loads. Free—living scrapers (Corynoneura, Crictopus cf. sylvestris, Zalutschia trigonocies, and others) fared only slightly better, while predators (Arctopelopia and Ablabesmyia) were relatively less sensitive to changes in snail density. Trichoptera larvae, Acari, and copepods were unaffected by the snails. Ostracoda and Cladocera biomass was significantly reduced by Lymnaea. All of the less sensitive groups were relatively more mobile. Reduced algal biomass and chlorophyll concentration were correlated with increased snail densities. Lymnaea production was limited by conspecific density and food.

ISSN:0012-9658    

DOI:10.2307/1937323

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Allocation models for annual plants predict that reproductive yield is maximized by an instantaneous switch from vegetative to reproductive growth. The switch is timed so that final reproductive yield is equal to the vegetative mass at the time of the switch, provided vegetative and reproductive growth efficiencies are equal. Measured allocation patterns for Plantago erecta and Clarkia rubicunda show a gradual shift from vegetative to reproductive growth in both species. This graded patter results in a 5.5% decrease in reproductive yield for Plantago relative to the theoretical maximum. The timing of that graded pattern appears optimal.

ISSN:0012-9658    

DOI:10.2307/1937324

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Concentration and export of dissolved organic carbon (DOC) were compared in streams draining four southern Appalachian watersheds with different treatment histories in 1969—1970 and again in 1979—1980. In 1969—1970 the watersheds were: old field (1 yr old), hardwood coppice (7 yr old), white pine (13 yr old), and mature hardwood (undisturbed for at least 45 yr). DOC concentrations in 1969—1970 were three to four times greater than in 1979—1980 on all watersheds, and the differences among watersheds were consistent both years: old field>hardwood>pine>coppice. Concentrations were always greater during the growing season. Annual runoff was 50% greater in 1979—1980, and annual DOC export in 1979—1980 was half the 1969—1970 value in all watersheds. Annual export was greatest from the hardwood and old—field watersheds and least from pine and coppice watersheds during both years. Although there appears to be a trend toward decreasing DOC concentration and export over the first two decades of secondary succession, differences caused by periodic variations in runoff are far more significant than any successional changes observed.

ISSN:0012-9658    

DOI:10.2307/1937325

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

The response of a stream ecosystem to disturbance in its watershed was investigated by comparing mass balances of dissolved organic carbon (DOC) for a stream draining an undisturbed watershed with a stream draining a watershed that was clear—cut 2 yr before the study began. These second—order streams are in Coweeta Hydrologic Laboratory, North Carolina. Both streams had similar, elevated DOC concentrations (from<1 to 5 mg/L) during storms. Rising and falling limbs of the hydrograph also had similar DOC concentrations. During the growing season DOC concentration increased from headwater seep to the weir in the undisturbed stream under baseflow conditions. No significant longitudinal change was observed in the stream draining the clear—cut watershed. Hence concentration was consistently lower in baseflow samples during the growing season in the stream draining the clear—cut watershed. As a result annual DOC export from the clear—cut watershed was less (9.8—11.5 kg/ha) than from the reference watershed (14.6—15.1 kg/ha). The lower DOC export was partly due to reduced DOC inputs from throughfall and leaching of fresh litter, but most importantly to lower DOC inputs in subsurface water and probably also less in—stream generation of DOC. The rate of recovery of this stream form disturbance is therefore dependent on the rate at which the terrestrial system recovers.

ISSN:0012-9658    

DOI:10.2307/1937326

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

The predictions of community matrix theory do not agree with the observed patterns of coexistence of grassland and woodland sparrows. Predictions based on the random co—occurrence of species match the observed patterns about as well as do the predictions of community theory. Predictions of both the community theory model and the random co—occurrence model are improved substantially by the addition of thresholds that account for the minimum food requirements of sparrows of different sizes. The observed patterns of species coexistence appear consistent with a model based on resource abundance and aggressive interference; however, they are also consistent with coexistence based on interspecific partitioning of seeds by size.

ISSN:0012-9658    

DOI:10.2307/1937327

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

The population biology of the tropical marine gastropod Conus pennaceus was studied off the island of Oahu in the Hawaiian Islands. Growth, fecundity, and survivorship rates were determined in the field through a combination of mark—recapture studies, regular population censuses, and direct count of ova produced by individual females. Individuals of C. pennaceus grow to a shell length of 15 mm in their 1st yr, and females may reproduce by the end of their 2nd yr at a shell length of between 20 and 25 mm. Females probably produce 1 egg mass/yr, and age—specific fecundity increases with increasing female size. By year 10, annual fecundity of females has increased to over 6000 ova, while shell growth has slowed to<1mm/yr. Although C. pennaceus has no planktonic larval stage, over 99.93% of all fertilized ova fail to survive their 1st yr. Subsequent mortality is constant at an annual rate of 0.419, and very few animals survive to the end of their 10th yr. The population examined remained relatively constant in size during the 22—mo study. This stability is attributed to the shape of the reproductive value curve of the population and to the ability of C. pennaceus to utilize a wide variety of prey species.

ISSN:0012-9658    

DOI:10.2307/1937328

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

The nitrogen dynamics in decomposing needle litter incubated in a clear—cut area were seen to be very different from those of the same types of litter incubated in a mature forest. In each stand 10 different sets of Scots pine needle litter with different initial nitrogen concentrations were incubated. A nonlinear regression model of loss and nitrogen dynamics estimates that the C/N ratio above which net immobilization and below which net mineralization takes place differs significantly between the systems (109 in the mature forest and °63 in the clear—cut area).

ISSN:0012-9658    

DOI:10.2307/1937329

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Cladophora fracta is the dominant filamentous alga in the littoral zone of Shoe Lake, Oakland County, Michigan. Seasonal and diurnal in situ productivity studies were combined with perturbations of several environmental parameters conducted in situ and in the laboratory to determine the factors that control primary productivity in this population. In situ net photosynthetic carbon fixation ranged from 0.26 to 5.39 mg°g—1°h—1, with seasonal maxima in spring and fall and diurnal patterns generally, but not always, correlating with daily insolation patterns. Phosphorus and nitrogen were above limiting concentrations throughout the year, and C. fracta was unresponsive to experimental P and N enrichments. The seasonal productivity correlated most strongly with total alkalinity (inorganic carbon content) and pH, and experimental enrichment of inorganic carbon stimulated photosynthesis during the summer. C. fracta was characterized in the laboratory as basically a C3plant on the basis of very low levels of C4acids in early14C photosynthetic products and light saturation of photosynthesis below 30 klx. In situ experiments showed oxygen inhibition of photosynthesis, but photorespiration was not directly demonstrable by evaluation of14CO2release, and the CO2compensation point was low. Release of organic photosynthate was stimulated by high oxygen, but the effect was maximal during spring and fall growth peaks rather than in the summer. Optimal photoperiod was experimentally determined to be relatively short (8 h), which correlated with the fall and spring maxima in productivity and carbon availability. Temperature in situ was below the experimentally determined optimum for photosynthesis in both spring and summer, and was associated with daily patterns of photosynthesis more closely than with the seasonal pattern. Epiphytic flora on C. fracta reduced organic carbon release to a small extent and contributed to a slight enhancement of community productivity. The productivity of C. fracta during the ice—free growing season in Shoe Lake appears to be limited principally by inorganic carbon and by oxygen inhibition of photosynthesis. C. fracta competes significantly on the basis of rapid growth capability early in the season coincident with maximal carbon availability and later possibly by minimization of photorespiration.

ISSN:0012-9658    

DOI:10.2307/1937330

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

The historical evidence for the Indians' burning the forests of the northeastern United States is reevaluated. Of 35 documents that describe vegetation or Indian life in the 16th or 17th centuries, only half mention any use of fire except for cooking. Only six purportedly first—hand accounts might refer to purposeful, widespread, and frequent use of fire. These six are all consistent with use of fire only locally near camps or villages, or with accidentally escaped fires. It is concluded that the frequent use of fires by the Indians to burn the forests was probably at most a local occurrence. The Indians' presence in the region and their use of fire for many purposes did, however, increase the frequency of fires above the low levels caused by lightning, and thus had some effect on the vegetation; for example, grasses characterized the ground cover at small, local, frequently burned sites.

ISSN:0012-9658    

DOI:10.2307/1937331

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY