ISSN:0012-9658    

DOI:10.2307/1935448

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

The effects of temperature upon phosphate absorption by marsh plants were examined along latitudinal gradients of temperature and thermal stability in order to (1) document the adaptive differentiation of a physiological system in response to environmental severity and fluctuation, and (2) elucidate the mechanisms and evolutionary implications of compensation for temperature changes occurring over different time scales. Among the species and ecotypes studied, those that had evolved in colder climates differed from their warm—adapted counterparts in having (1) lower temperature optima for root initiation, elongation, and production; (2) larger surface—to—volume ratios of roots; (3) proportionately more nutrient—absorbing tissue; (4) higher phosphate absorption capacities at given measurement and acclimation temperatures; (5) lower potential of the phosphate absorption system to acclimate in response to temperature change; and (6) less temperature sensitivity of the phosphate absorption system. When plants were acclimated to a new temperature over a period of weeks, cold—acclimated individuals had higher rates of phosphate absorption at a given measurement temperature than did warm—acclimated individuals, and temperature sensitivity of phosphate absorption was lowest in those individuals of a population acclimated to a root temperature that most closely approximated the soil temperature at the site of origin of that population. When temperatures were changed over a period of minutes, roots exposed to low temperature had a higher affinity for phosphate than did roots exposed to warm temperature. Consequently, phosphate absorption was less temperature—sensitive at ecological than at saturating concentrations of phosphate, and the change in affinity of roots for phosphate occasioned by a change in temperature compensated for that temperature change.

ISSN:0012-9658    

DOI:10.2307/1935449

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Seeds were collected from three taxa: L. divaricata from Arizona in the Sonoran desert of North America (LDNA); and L. divaricata and L. cuneifolia from northwestern Argentina, in the monte of South America (LDSA and LC). These three desert shrubs are generally not sympatric, and LDSA appears to occupy the most mesic sites. Seedlings were grown to the age of 3—7 mo in a greenhouse and compared as to root— and shoot—growth rate, photosynthesis and transpiration under high and low water stress, pathway of photosynthesis employed, leaf stomatal density, and leaf anatomy. Herbarium specimens collected from 55 sites along moisture gradients were also analyzed for path of photosynthesis, leaf stomatal density, and leaf anatomy. Under mesic conditions, LDSA had a higher growth rate, yet maintained the lowest biomass fraction in leaves and the highest in roots. There were no differences among taxa in net photosynthesis, though LDSA had a significantly higher transpiration rate. Under xeric conditions (plant pressure potential about —45 atm), the photosynthetic rates of LDSA were depressed the most, but variability within taxa prevented conclusions on differences in rates of photosynthesis and transpiration. Stomatal density was greatest for LDSA and least for LC, and these differences were maintained in the greenhouse. Reduction in stomate number seems to be a major mechanism for transpiration reduction between Larrea taxa, but within a taxon there was no relationship between site precipitation and stomatal density. The path of photosynthesis (from 13C/12C and enzyme—activity ratios) was consistently C3. Leaf cross—sections appeared to reveal mesophyll differences between LC and the two LD taxa. Two ecotone sites, where LDSA and LC share dominance, were sampled for community structure and the presence of putative hybrids. One site, with a one—to—one ratio of Larrea taxa, showed no evidence of biotic interaction between the taxa or between them and associated species, and hybrids accounted for less than 1% of all shrubs. Analysis of mass—collected random leaf samples also showed little evidence of hybridization in leaf shape or stomatal density. A second ecotone site, 600 km to the south, differed in some respects from the above, but, again, hybridization was a rare event. The basis of the mesophytic nature of LDSA might lie with its shrub architecture as well as with its physiological properties.

ISSN:0012-9658    

DOI:10.2307/1935450

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

The food—searching behavior of titmice (Paridae) was investigated in laboratory and field to determine how effective individual birds were at locating patchy sources of hidden food. A series of three experiments was performed using tame great tits, Parus major. In Experiment 1, individual birds were offered a choice among six densities of hidden food in discrete patches. The birds learned to concentrate their search strongly on the more dense patches, and five of the six birds preferred to search at the highest density. In Experiment 2, the food distribution was altered by interchanging patches of the highest and lowest density gradually. The birds initially found fewer prey per trial, but soon recovered to near their original performance by switching their search effort to the area containing the second highest prey density. Most birds failed to respond to prey appearing where they had previously been absent. Experiment 3 varied the size of prey items among four areas containing equal numbers of hidden prey. A group of six birds learned to search selectively in areas containing larger prey and, as a result, a greater total quantity of prey. In all experiments, there were marked differences in performance by individual birds. The experiments support Royama's (1970, 1971) hypothesis that great tits distribute their search effort in relation to spatial differences in the profitability of feeding sites. Field observations on a pair of great tits and a pair of blue tits, Parus caeruleus, showed that searching behavior of wild tits was also very selective in space, at least when the birds were feeding nestlings. Birds often returned to previous capture sites and were more likely to do so when they found prey there quickly. These observations suggest that the laboratory experiments have real relevance to the food searching of wild tits. The searching capacity of great tits is discussed; it is suggested that they can approach ideal responses in stable but patchy feeding environments. Some factors leading to deviations from ideal responses are discussed.

ISSN:0012-9658    

DOI:10.2307/1935451

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Marmot (Marmota flaviventris) populations are colonial or satellite. The number of adults of colonial populations is relatively stable; fluctuations occur primarily because of changes in numbers of young and yearlings. Population trends among five colonial populations are dissimilar. Satellite populations are unstable and reproduce at a lower rate than do colonial populations. Satellite marmots are shorter resident than colonial marmots. Both colonial and satellite females usually are longer resident than males. All adult colonial males are 41% of adult colonial females are recruited from other places; all satellite adults are recruited from other places. Losses of colonial marmots are attributed primarily to mortality during hibernation and emigration. Predation appears to be a minor source of mortality of colonial marmots, but may be of greater significance to satellite populations. Demographic relationships of individual colonies appear to be density—independent. Dispersal of colonial animals occurs primarily among yearlings, which have a higher expectation of reaching sexual maturity than young have. The major cause of dispersal is social pressure, but social stress is not simply density—dependent. The colonial social organization is more adaptive than the more nearly solitary (=satellite).

ISSN:0012-9658    

DOI:10.2307/1935452

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Dimension analysis was used to estimate biomass and annual net primary production for a post oak—blackjack oak (Quercus stellata—Q. marilandica) forest in central Oklahoma. Concentrations of six mineral elements in various plant tissues were determined and used with biomass and production estimates to calculate the annual cycle of N, P, K, Ca, Mg, and Mn in the forest. Total organic material in the forest is 245,000 kg/ha, of which 1.6% is leaves, 26.4% live branches, 5.9% dead branches, 44.8% trunks, 15.9% roots, 9.6% understory, and 4.4% litter. Annual net primary production is 14,900 kg/ha, distributed as follows: 32.0% leaves, 28.0% twigs and branches, 24.9% trunks, 15.1% roots, and 2.0% understory. Maximum leaf area index was 4.8. Yearly mean litterfall is 5,400 kg/ha and is distinctly biomodal, with peaks in November and March. The biomass contains 1,157 kg/ha N, 101 kg/ha P, 1,258 kg/ha K, 4,549 kg/ha Ca, 311 kg/ha Mg, and 124 kg/ha Mn. Yearly mineral budgets were determined for the six elements. Unusually high values for Ca in the biomass and in the mineral cycle were due to high concentrations of Ca in post oak bark (90,200 mg/g). High annual values for increment of biomass and for retention of mineral elements indicate that the stand has not reached a steady state, a conclusion that is confirmed by observations of stand structure.

ISSN:0012-9658    

DOI:10.2307/1935453

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

The cladoceran Bosmina Longirostris undergoes a peculiar egg—size cycle in Frains Lake. Females carry small eggs during summer, then switch to large eggs in late fall, in the process more than doubling the enclosed yolk volume. Winter generations mature at larger sizes, then shift to small eggs in early spring. The fluctuations in egg size are not strongly associated with indirect measures of nutritional conditions. Rather, they seem part of a cycle that produces small young in one seasons, large young in another, primarily as a response to changing patterns of predation.

ISSN:0012-9658    

DOI:10.2307/1935454

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

The breakdown of allochthonous leaf litter in woodland streams occurs at the community level process which is patchily distributed. Two kinds of environmental patches were tested: types of bottom sediment and sizes of leaf pack. Four sediments, aligned along parallel environmental gradients (velocity and sediment complexity), were studied: rock, gravel, sand, and silt. Five pack sizes were studied: 1, 5, 10, 20, and 40 g. Preweighed packs of white ash (Fraxinus americana) leaflets were tied to bricks and set on the sediments. These were sampled weekly for 6 wk, and the percent dry weight lost was determined. This design was followed in each of the four seasons to test the seasonal variability in leaf litter breakdown. Analysis of variance and comparison of means show that, in all seasons, sediment and pack—size effects are highly significant (P<.001). Leaf packs of all sizes were broken down less in the silt than in the other sediments. The sediment patterns are consistent with the community level effects of physical heterogeneity and stability. Though the pack—size effects were highly variable from season to season, the degree of breakdown differentiated the leaf—pack sizes in every season, at least one size displaying major differences from the others. The seasonal patterns in breakdown reflect its temperature dependence, the breakdown increasing with increasing temperature. The community level process of leaf litter breakdown in streams is patchily distributed in space. This suggests a level of organization between the population and the community, namely the patch—specific component community.

ISSN:0012-9658    

DOI:10.2307/1935455

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

The behavioral ecology of four populations of Brachycentrus occidentalis, maintained on different rations in four separate simulated stream channels, was followed daily from February to May as the larvae pupated and eclosed. Before pupation, the behavior of the population changed markedly as filtering decreased and larvae became unattached and laboratory drift increased. Cases of males were about 3 mm shorter than females. Median time within the pupal case of males and females was 34.5 and 31.0 days, respectively at 10°C. As pupation proceeded, larvae cannibalized pupae. Generally as feeding rate decreased, behavioral changes and pupation were delayed, cannibalism increased and percentage of females eclosing decreased. Females attempted cannibalism more often than males, and showed a higher percentage of successes. Of 160 pupal cases collected from Lawrence Creek, Wisconsin, approximately 9% showed evidence of cannibalism. An additional 32% were infested with Eukieffefriella sp., a small chironomid. Cannibals, predators, and parasites are considered as agents of selection pressure in connection with case construction and pupal distribution among the Trichoptera.

ISSN:0012-9658    

DOI:10.2307/1935456

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Nemophila menziesii aggr, includes three closely—related winter annual plants found in many communities in cismontane California and Oregon. The germination response is adapted to the Mediterranean climate that characterizes the region, i.e., wet winters and dry summers. The seeds germinate in late fall or early winter and are inhibited from germinating during late spring, summer, and early fall by high temperatures, long photoperiods, and low available moisture. Temperature and photoinhibition are proportional to the length of the inhibitory period and, in the case of photoinhibition, to light intensity. In combination these factors interact synergistically to inhibit the germination response. Seeds of all ages are able to germinate but germination of young seed is inhibited at temperatures that do not affect mature seed. Seed maturation is a function of high summer temperatures and aging. Populations from more northern and/or higher—elevation communities require more water and lower temperatures to germinate than more southern and/or lowest—elevation communities. These adaptations reflect the greater precipitation and cooler temperatures of the former sites as compared to the latter sites. The ecological parameters and germination responses change gradually both latitudinally and elevationally; hence the adaptations are ecoclinal in nature.

ISSN:0012-9658    

DOI:10.2307/1935457

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY