摘要:

The inornate ringlet butterfly, Coenonympha inornata, is highly constrained by temperature in its activity, and even on sunny days may spend a major portion of its time grounded. Thermoregulation in these lateral baskers can consume the major portion of their time; males alternate between basking and flying, and at 16°C spend 73% of their time basking and only 27% of their time flying. At high ambient temperatures (Ta), on the other hand, they spend most (>80%) of their time in flight. Active butterflies were followed for up to 52 min in the field to determine foraging behavior, mating success, and time investments for thermoregulation. Foraging was a minor component of their flight activity. Most of the flight activity was associated with mate—seeking. Thoracic temperatures were measured in the field on individuals tethered to thermocouples that permitted flight and basking behavior. Basking at low Taallowed the maintenance of higher thoracic temperatures than could be maintained in continuous flight, and the butterflies then adopted a sit—and—wait strategy in mate chasing. In contrast, at high Tathey used a search strategy for mate seeking instead.

ISSN:0012-9658    

DOI:10.2307/1937682

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

Eastern tent caterpillars (Malacosoma americanum) are behavioral thermoregulators while gypsy moth caterpillars (Lymantria dispar) are thermal conformers. Differences in thermal ecology can be related to differences in the environments these species encounter. Temperature sensitivity of growth rates differs in a predictable manner; the growth rates of gypsy moth caterpillars are temperature independent at ecologically relevant temperatures of 25°—30°C, and the growth of the tent caterpillars is very temperature dependent. Growth rates of tent caterpillars in the field are greater than that expected for the average ambient temperature of 15°, and closely approximate growth in the laboratory at 25°, near the average Tbexhibited in the field. The higher growth rates are a result of the tent caterpillars' elevated body temperatures. These data are used to develop hypotheses for the evolution of caterpillar thermal responses.

ISSN:0012-9658    

DOI:10.2307/1937683

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

While the physical environment is often viewed as that with which an organism must contend, and the biotic environment as including resources that may be exploited, interactions occurring between the physical and biotic portions of animal niches suggest that animals also exploit their physical environments. The space and time required for physiological optimal interactions with the environment represent units with which the thermal environment can be quantified as an ecological resource. Characteristics of the thermal environment that an animal experiences within its home range have been incorporated into measures to quantify the quality of the home range with respect to temperature relations, to evaluate the importance of thermal transients to an animal, and to assess temporal aspects of habitat exploitation. Since the thermal environment is physiologically important to animals, and since there can be competition for space and time, this approach provides a bridge between physiological and population/evolutionary ecology.

ISSN:0012-9658    

DOI:10.2307/1937684

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

The "principle of allocation" underlies much of current life history theory, but has never been critically tested. Although the cockroaches Periplaneta americana and P. brunnea are closely related and morphologically very similar, P. brunnea produces an ootheca nearly twice the mass of P. americana's. The principle of allocation predicts that P. brunnea should take longer to produce an ootheca, or that some other factor must be traded off. The principle was tested by comparing the mass budgets of Periplaneta americana and P. brunnea fed artificial diets under controlled conditions. Although dissections confirmed their morphological similarity, P. brunnea had a rate of dry biomass production of 11.2 mg/d, whereas that of P. americana was only 4.4 mg/d. The gross production efficiency of P. brunnea (38%) was also higher than that of P. americana (29%). These results challenge the generality of the principle of allocation. P. brunnea was much less resistant to starvation than P. americana. Although growth of the two species was similar on an adequate diet, P. brunnea grew faster but suffered higher mortality than P. americana on low—protein diets. The results suggest a view of organism design based on safety factors and adjustment to levels of key resources, as an alternative to a perspective of maximized production.

ISSN:0012-9658    

DOI:10.2307/1937685

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

Aquatic insect secondary production, emergence, and export of adults to the adjacent terrestrial ecosystem were assessed in Sycamore Creek, Arizona, by means of benthic sampling, emergence traps, and catch—nets that passively sampled adults falling into the stream. Annual secondary production was 120.9 ± 18.0 g°m—2°yr—1an emergence was 23.1 g°m6—2°yr—1(in dry mass units). The ratio of annual emergence to annual production (E/P) varied among taxa and ranged from 2 to 29%. Chironomids comprised 48.2% of production and 59.7% of emergence and mayflies accounted for 45.9 and 19.2%, respectively. Approximately 3% of emergent insect biomass returned to the stream; thus 22.4 g°m—2°yr—1was transferred to the adjacent terrestrial ecosystem. The transfer of a significant portion of aquatic insect biomass to the terrestrial habitat reduced insects available to stream insectivores while providing prey for insectivores in neighboring terrestrial ecosystems.

ISSN:0012-9658    

DOI:10.2307/1937686

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

We tested the prediction that decreased fruit density would lead to decreased parasitism of Cornus amomum fruits by Rhagoletis cornivora flies in a field manipulation. Fruit density following manipulation ranged from no reduction to 88% reduction. We found no evidence of parasitism decreasing with fruit density. Instead, the relationship was inversely density dependent. Although individual tephritid fruit flies concentrate attacks on fruits in areas of high fruit densities, the searching behavior of individual flies apparently does not result in a density—dependent pattern of parasitism at the population level.

ISSN:0012-9658    

DOI:10.2307/1937687

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

Differences in replacement patterns and frequencies of treefalls were investigated for subalpine fir (Abies lasiocarpa) and Englemann spruce (Picea engelmannii) in the Colorado Front Range. In seven old—growth unlogged stands, data were collected on age and size of trees, frequencies of fallen trees, growth rates of trees, and sizes and abundances of occupants of treefall gaps. Subalpine fir accounted for 74.5% of the potential successors in the 125 treefall gaps sampled. The much greater abundance of subcanopy trees of subalpine fir implies more frequent recruitment into the canopy. However, its greater recruitment rate into the canopy is approximately balanced by its greater loss from the canopy; even though subalpine fir accounted for only 37% of the canopy trees it accounted for 76% of the fallen trees. The consistently lower frequency of Engelmann spruce as treefalls and its great longevity compared to subalpine fir imply a lower adult mortality rate for the spruce. Consequently, the greater proportion of young subalpine fir does not imply that it will gradually replace Engelmann spruce in old—growth stands unaffected by large—scale exogenous disturbance. The results of this study provide empirical support for the coexistence of ecologically similar species by means of different life history strategies.

ISSN:0012-9658    

DOI:10.2307/1937688

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

We used frequently repeated measurements of growth characteristics in undisturbed study plots, and replicated harvests of shoots from nearby plots, to measure biomass accumulation of Typha latifolia in 1978 and 1979. The data were used to calculate net annual aboveground production (NAAP) using seven computational procedures: peak biomass; the Milner and Hughes; Smalley; Valiela et al.; a modified Wiegert and Evans; Allen curve; and the summed shoot maximum which we devised for this study. The procedures were evaluated with respect to their sensitivity to differences in sampling frequency by repetitively calculating NAAP using different sequential subsets of the study plot and harvesting data sets. Year—to—year differences in the relative accuracy of some methods (peak biomass; Milner and Hughes; Smalley; and Valiela et al.) were affected by cohort structure of the population. The Allen curve NAAP estimates were not affected by the differences in cohort structure. Our modified Wiegert and Evans method overestimated NAAP, and is inappropriate for use with Typha. As apparent sampling frequency declined, NAAP estimates for most methods declined and were more variable, especially for the more complicated methods. Relative to the standard used in this study (the summed shoot maximum), most methods underestimated NAAP by 18—38%, even with 1—3 wk sampling intervals. Underestimates were due to inadequate corrections for early shoot mortality, leaf turnover, and losses of portions of individual leaves. The procedure of estimating each cohort's production by plotting shoot number vs. mean biomass per shoot over time (Allen curve method) has inherent advantages relative to the other methods examined and was comparatively insensitive to changes in sampling frequency.

ISSN:0012-9658    

DOI:10.2307/1937689

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

The contribution of woody stems to the aboveground net primary production (NPP) of several species of tundra shrubs was documented at four sites in northern and central Alaska. To measure stem secondary growth, a new method was developed based on the ability to measure the changes in mass per unit length of stem segments or known age. Net accumulation of N and P in woody stems was also estimated, from additional measurements of changes in element concentration with stem age. Results showed that stem secondary growth was an important component of NPP in all species and sites, ranging from 13 to 49% of total aboveground NPP for individual species. The most productive species and sites had the highest proportions of NPP accounted for by secondary growth. Accumulation of N and P in woody stems occurred at slower rates, presumably due to internal reuse of these elements, but still accounted for 5—19% of the annual net aboveground N accumulation and 6—24% of the P accumulation. One implication of these results is a faster rate of N and P turnover in the vegetation than previously believed, and a greater annual nutrient demand. The relative contribution of each age class of stem segments to the total woody biomass was due to an interaction between the number of stem segments surviving to a given age and the annual percentage increase in mass per unit length. Older stem segments also tended to be longer than younger segments.

ISSN:0012-9658    

DOI:10.2307/1937690

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY

摘要:

Litterfall, litter standing crop, and leaf decomposition of basin mangrove sites with mixed associations of Avicennia germinans, Rhizophora mangle, and Laguncularia racemosa adjacent to bay waters were compared to monospecific stands A. germinans located inland of the mixed associations. The objective was to determine whether basin mangroves with low tidal amplitude are characterized by lower litter productivity, longer litter residence times, and increased nitrogen recycling. Litterfall rates for the two mixed forests averaged 8.10 Mg°ha—1°yr—1compared to 4.44 Mg°ha—1°yr—1in the three monospecific sites. Peak litterfall occurred from August to October after increases in soil water salinity during June and July. Seasonal changes in surface litter mass occurred only in the monospecific forests and corresponded with higher leaf decomposition rates when tidal inundation frequency increased. As a result, surface leaf litter in a monospecific site>200 m from the bay had a longer residence time than in two monospecific sites<100 m inland. The rates of dry mass loss and organic carbon leaching of R. mangle leaves were lower than those for A. germinans, resulting in higher residence times of leaf litter in mixed (0.5 yr) than monospecific (0.2 yr) forests located<100 m from the bay. Leaf nitrogen decreased during senescence, and absolute nitrogen increased in leaf litter during decomposition on the forest floor. As a result, turnover rates of nitrogen in surface litter were lower than for dry mass. A comparison of litter dynamics and nitrogen recycling among riverine, fringe, and basin mangroves suggests that the relative influence of export and decomposition on litter dynamics depends on the magnitude of tidal inundation. Inland basin mangroves have low nitrogen recycling efficiency in litterfall, but higher internal recycling of litter on the forest floor, due in part to a longer litter residence time, nitrogen retranslocation prior to leaf senescence, and nitrogen immobilization during litter decomposition and peat deposition.

ISSN:0012-9658    

DOI:10.2307/1937691

出版商:Ecological Society of America    

年代:1986

数据来源: WILEY