摘要:

Rates and energies of consumption (C), egestion (F), assimilation (A), respiration (R), growth (Pg), production of exuviae (Pev), and production of egg masses (Pr) with associated efficiencies, and effects of seasonal temperature, weight and life—history stage upon them were examined for a typical individual and cohort of Corydalus cornutus (L.) from a stream in north—central Texas. Dobson flies are univoltine with 11 larval instars. Emergence, oviposition, and hatching occurred from late May into August. The typical dobson fly hatched in mid—June, grew rapidly until November, and again in March, reaching adult size prior to pupation in early June. A0dult females fed to provide energy to yolk eggs, produce cases and for maintenance during their week of reproductive activities. Metabolic compensation enabled larval dobson flies to maintain fairly constant rates of R during winter (6.07 J g—1h—1, 5—15°C) and summer (16.15 J g—1h—1, 20—30°C); with a seasonal acclimatization threshold occurring between 15—20°C. Metabolic constancy is adaptive and probably contritubed to high ratios of P/R (1.94) and P/A (66%) for individual larvae. Rates of C, F, A, and R, but not assimilation efficiency (AE = A/C X 100), were influenced by temperature and size. The energy budget for a typical dobson fly during the 47 wk as a larva was: C = 17,435, A = 14,401, F = 3,033, Pg= 8,682, Pev= 828 and R = 4,892 J. Embryos respired 0.45 J/wk, prepupae 1,494 J/wk, male pupae 2,130 J/wk, female pupae 1,900 J/wk, male adults 2,615 J/wk and female adults 3,075 J/wk. Prepupal and pupal exuviae were 602 J and 502 H respectively. The average adult female's minimal reproductive effort was 2,791 J for eggs and 774 J for egg cases, 54 and 100% of her A and P respectively, 17% of her life—history A. Annual energetics of the larval population were; C = 165,343, A = 136,574, F = 28769, Pg= 54,610, Pev= 15,096, Pr= 1,502—1,711 and R = 66,869 J m—2.

ISSN:0012-9658    

DOI:10.2307/1938225

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Female Common Grackles (Quiscalus quisculaL.) laying clutches of 2, 3, and 4 eggs show different patterns of initial investment in offspring than those laying clutches of 5 and 6. Females laying small clutches do not increase egg size with laying sequence and hatch young synchronously by starting incubation after the last egg is laid. Such parents usually raise the entire brood. Females laying clutches of 5 and 6 increase provisioning of yolk and albumen with laying sequence, start incubation before the clutch is complete, and have variable success in space and time. Few raise the entire brood. Late—hatching young are favored by large egg size, but disadvantaged by hatching order because older siblings are fed first and grow faster. Youngest members of a brood are maintained as long as possible, but differentially starve if food is scarce. A review of the literature suggests that similar patterns may be widespread in passerine birds. Antagonistic forms of parental investment and brood reduction are interpreted as “bet—hedging” tactic for minimizing losses of parents attempting to raise large broods during periods of uncertain food availability. The most common clutch of 5 in Common Grackles is, on the average, the most productive of fledglings. But complete success of small broods and variability in the success of adults laying "the most productive clutch" suggest selection for individual optima related to demographic or ecological circumstances. Population averages emphasized in the literature appear as effects of such selection.

ISSN:0012-9658    

DOI:10.2307/1938226

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

We report on differences in foraging and recruitment patterns among 6 stingless bee species simultaneously exploiting a large grid of baits in a tract of tropical dry forest in Costa Rica. Comparative data for the species were obtained on the following parameters of foraging: time to initial bait discovery, rate of discovery of additional baits, rate of worker recruitment, time till attainment of approximate steady—state number of workers and visited baits, frequency of number of workers per bait, degree of site constancy of foraging within and between days, and responses to presence of intraspecific and interspecific rivals at baits. All species had unique aspects to their foraging, which reflected whether the species mark food sources and lay trails with pheromones, the degree to which workers forage solitarily, and their use of aggression. The behavior of Trigona fuscipennis, the pheromone—using group forager, was particularly distinctive. It found baits the most slowly, was the most site constant, and excluded all other bees from its baits. We hypothesize that in group foragers, extreme localization of workers and resultant slowness of discovery of new food sources represent a trade—off for the advantages of group defense of good sources. Other responses to rival bees included bullying tactics by lone, marauding workers of the large, facultative recruiter, Trigona silverstriana, and persistent, opportunistic insinuation by small, solitary foraging species. Spatial segregation of foraging location between the species increased over time on each day of the experiment, especially among interspecifically aggressive species. The observed diversity of tempo and mode of foraging reinforces the hypothesis that coexistence among these apparently food—limited social bees does not result from the simple partitioning of food resources by size or taxon, but from rather subtle partitioning based upon diversity in the timing, persistence, renewal rate, and spatial dispersion of their limited food resourves.

ISSN:0012-9658    

DOI:10.2307/1938227

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

We investigated the effects of seasonal variation in food abundance on food partitioning among Darwin's ground finches of the genus Geospiza. Finch populations, the availability of seed of fruits, and finch feeding habits were measured during 2 visits to each of 4 study sites on 3 Galapagos islands. Our 1st visit was made near the end of the 1973 rains at a time of seasonal food abundance and the 2nd, 6—8 mo later, when food was scarce. If interspecific competition prevails, finch populations should decline from wet to dry season in response to declining food availability. At 2 sites where food supplies declined sharply, so did an index of finch numbers; at the other 2 sites, both food supplies and finch numbers remained high. Total finch biomass at 5 dry—season study sites was correlated with food abundance but was not at 8 wet—season study sites. If interspecific competition is stronger, diets of finch species should diverge as food becomes scarce, but if intraspecific competition is stronger, diets should expand and overlap among species increase. At all 4 sites, finch species diverged in their diets and took a narrower range of foods in the dry season. All species shifted from a common wet—season diet of soft, easy—to—handle seeds and fruits to different diets reflecting the morphological specializations of each species. The results are consistent with interspecific competition for food occuring at all sides, but other explanations cannot be ruled out. Even where food remained relatively abundant, species diets changed and overlapped less. Intense competition was not, therefore, a necessary condition for seasonal diet changes; these may have been simple proximate responses to food availability. Existing foraging theory does not predict these results or others, because the assumption that available foods do not change qualitatively between seasons is violated. Where food greatly decreased, inter— and intraspecific competition may have caused the death or dispersal of most of the finches in the wet—season populations and diet divergence minimized interspecific competition are probably complemented by year—to—year differences caused by the unpredictable Galapagos rainfall.

ISSN:0012-9658    

DOI:10.2307/1938228

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Comparisons between modern pollen and tree—inventory data from northeastern North America show how the clear portrayal of vegetational patterns in pollen data depends upon several choices made in selecting and preparing these data. These choices concern the size and location of the area studied, the types of pollen examined, the quantitative measure of pollen used, the types of sediments sampled, the number of analysts contributing samples to the data set, and the degree of smoothing applied to the data either by adding samples together or by combining pollen types into groups. Our results show that these choices can control not only what scale of vegetational pattern will appear on maps of pollen data but also whether these maps portray vegetational patterns at all. Of the choices examined, the most important were those concerning the size of the area studied, the types of pollen examined, and the amount of smoothing used. Before presenting the results, we introduce an expression for a signal—to—noise ratio that contrasts the degree of vegetational variation affecting the pollen data with the size of the uncertainties and nonvegetational variation (e.g., changes in pollen dispersal) that also influence these data. The effects of the different choices in data selection are discussed in light of their effect on this ratio.

ISSN:0012-9658    

DOI:10.2307/1938229

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The leaf galling aphid, Pemphigus betae can be highly resource and habitat limited and has evolved to reduce these limitations. Over a 3—day period in spring as much as 83% of the overwintering population migrates to immature leaves of Populus angustifolia where individuals are rapidly entombed by expanding leaf tissue. The size of the mature leaf is critical to ultimate fitness of the individual colonizing stem mother. Probability of stem mother failure, body weight of stem mother and progeny, number of progeny, development rate of progeny to maturity, and number of embryos in mature progeny are all correlated with leaf size. Due to these selection pressures, stem mothers search out and colonize large leaves. Thirty—two percent of the tree's leaves were so small as to result in an 80% probability of total aphid failure. Nearly all of these leaves were avoided. In comparison, only 1.6% of the tree's leaves were so large as to result in a 0% probability of failure, and 100% of these leaves were colonized. Even though most stem mothers were forced to colonize. Even though most stem mothers were forced to colonize suboptimal leaves because competitor density (35/100 leaves) was much>the availability of optimal leaves, the average stem mother colonized a leaf 60%>the mean leaf size of the tree. Resulting from this degree of selectivity, the minimum increase in fitness was 2 times>expected if leaves had been selected at random. At low competitor densities reproductive output would still be limited by energy intake such that if there were only 1 gall on a tree, the colonizing stem mother and her progeny would still be resource limited. Apparently, no leaf produced by the tree is so large that a further increase in leaf size would not result in a further increase in fitness. Thus, even at low competitor densities, resources would still be important in the habitat selection process and in determining the parasite distribution.

ISSN:0012-9658    

DOI:10.2307/1938230

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Pattern sampling (Whiteside and Williams 1975) was employed to study the population changes, habitats and spatial arrangements (pattern) of littoral cladocera in Lake Itasca, Minnesota during 1974. Population dynamics of the 19 most abundant species of chydorids had changes similar to other populations studied in north—temperate lakes. All species had either spring or fall maxima, or both, a mid—summer low in numbers. Population trends were the same for vegetative and mud habitats. In a comparison of Chara vs. mud habitat we found Chydorus piger, Leydigia leydigi, Alona quadrangularis, Pleuroxus aduncus, and Alona circumfibriata to live mainly in littoral mud. Kruzia latissima, Camptocerus rectirostris and Chydorus faviformis were most restricted to the vegetative habitat, while other species were more ubiquitous. Pielou's (1974) terms describing pattern, phase, mosaic, grain, and intensity are discussed. We redefined intensity as describing the visual effect of density. The changes of intensity accompanying changes in density typified 1974 patterns, while no changes in the other parameters were evident. Preliminary experiments exploring the behavior of chydorids suggest that visual stimuli are very important in directing movements, followed by tactile and chemical clues.

ISSN:0012-9658    

DOI:10.2307/1938231

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Seasonal changes in reproductive output of house sparrows, Passer domesticus, were studied at 2 localities: Lawrence, Kansas, USA and Calgary, Alberta, Canada. In both localities the most productive clutch (6 eggs) was larger than the modal clutch (5 eggs). Most variation in clutch size could be attributed to within—individual seasonal changes. Laying of 6—egg clutches was generally restricted to the middle of the breeding season. Clutch size changes were not consistently synchronized with trends in predictable environmental variables such as photoperiod and temperature. Because seasonal trends in clutch size and fledging success were poorly correlated, there is no evidence that seasonal changes in clutch size represent adaptations to maximize the number of adequately nourished offspring. Although clutch size is ultimately determined by contribution to future generations, it is probably proximately controlled by resources at the time of oogenesis.

ISSN:0012-9658    

DOI:10.2307/1938232

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The response of the soil microbial community in a short Spartina alterniflora salt marsh to selected, long term perturbations was examined. Alternative hypotheses of linkage between macrophyte production and the microbial community biomass and activity were tested. In 2 perturbation experiments macrophytic primary production was removed from marsh plots by clipping shoots and printing beneath ground parts for periods up 10 18 mo. In a third experiment monthly enrichments of glucose, ammonium nitrate and their combination were made for 5 mo to both clipped and pruned plots as well as unclipped control plots. The state of the microbial community was monitored by adenosine triphosphate and total adenylate concentration, community adenylate energy charge ratio and anaerobic uptake of14C—glucose by mud slurries. The overall responses of the various parameters were consistent with the hypothesis that the soil microbial community is relatively unlinked to plant growth. This "unlinking" appears responsible for the observed resistance to change by the microbial community in the face of perturbations to the marsh system. Two mechanisms of resistance were postulated. First, while the microbial community resides in a large reservoir of organic matter, most of this organic matter may be relatively refractory. Hence, the microorganisms would be nutrient limited by the slow transformation of this material. Such a large resource pool with a long turnover time would promote resistance to perturbations that alter plant productivity. Second, the microbial community would be resistant to changes rather than nutrient status if in fact it were limited by physiochemical, spatial constraints rather than nutrients. While neither hypothesis could be totally rejected, our results give greater support to the second hypothesis.

ISSN:0012-9658    

DOI:10.2307/1938233

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Based on the general premise that the genus represents an ecological, as well as a morphological type, a number of generalizations are developed concerning the use of food resources in fresh waters by Trichoptera and some other aquatic orders of the Nearctic fauna. There are more genera of the Nearctic order Trichoptera (144) than in the orders Ephemeroptera (59), Odonata (84), or Plecoptera (88). Trichoptera have a wide range of habitats and a broader range of trophic categories than any of these other wholly aquatic orders. This relatively high ecological diversity is attributed to the many uses of silk by trichopteran larvae. Genera of 3 families of filter—feeding Trichoptera show differences in distribution which are correlated with the type of food particle. Most of these genera are found in the eastern deciduous forest biome and all sizes of organic particles are filtered. In the western montane forest biome, generalist filter feeders are absent or underrepresented; predacious genera or those filtering very fine particles have been more successful. Possibly there are differences in the quality and quantity of fine particulate detritus between eastern and western forest which account for the above distributions. In the trichopteran family Limnephilidae, genera of the detritivorous shredders have exploited lotic, lentic, and even terrestrial habitats; grazer genera are mostly confined to cool lotic habitat. Grazers in other families of Trichoptera are also more diverse in upstream areas, and grazer genera are particularly well—represented in the western montane forest biome. In streams of the eastern deciduous forest biome, the relative proportions of feeding categories shown by trichopteran genera appear to agree with a general trophic model of benthic invertebrate communities in that dominance of shredder—collector genera in upstream sections gives way to grazer—collector dominance downstream. In western montane streams, trichopteran generic distributions conform to the model downstream, but show relatively more grazers than the model would predict for upstream areas. Periphyton growth, and thus food for grazers, may be more abundant in the western coniferous forest than in the shaded streams of the eastern deciduous forest. In general, an ecological analysis of Nearctic Trichoptera at the generic level appears to provide a reasonable indication of the energy resources available in aquatic habitats.

ISSN:0012-9658    

DOI:10.2307/1938234

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY