bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectral Absorption of Solar Radiation in Alpine Snowfields
Authors: Curl Herbert , Hardy John T. , Ellermeier Ronald
Published: May 2006

We measured penetration of solar radiation into snow at various times of the year with a spectral radiometer. We found that light absorption obeys a y = axn law where n varies from 0.71 to 2.10. The absorption coefficient n decreases with increasing snow density. The 1% of surface value of total energy occurs at a snow depth of approximately 18 cm in winter, increasing to a maximum of 110 cm in late summer when snow density is near its maximum. Penetration of 0.1% of the surface radiation is shown to coincide with the approximate date and depth of snow pack for the first spring bloom of snow algae, implying that increasing light penetration may initiate germination of overwintering stages.
Morphological and Physiological Mechanisms of Temperature Compensation in Phosphate Absorption along a Latitudinal Gradient
Authors: Chapin F. Stuart
Published: May 2006

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.
Egg‐Size Cycle of a Cladoceran
Authors: Kerfoot W. Charles
Published: May 2006

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.
Behavioral Ecology of Brachycentrus Occidentalis Banks during the Pupation Period
Authors: Gallepp G. W.
Published: May 2006

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.
Response to Predation by Colonies of the Florida Harvester Ant, Pogonomyrmex Badius
Authors: Gentry John B.
Published: May 2006

The effect of predation (by the systematic removal of forager ants) on the behavior and population structure of Pogonomyrmex badius colonies was studied during the summer of 1965. For 23 wk, 50 workers per day were removed from one group of 10 colonies and 10 ants per day from another group of 10 colonies. Another 10—colony group served as a control. No effects of removal were observed in the 10/day group. Within a week after removal began, aboveground activity was reduced drastically in many of the 50/day colonies and the removal of a complete sample each day was impossible. Later, colonies underwent extended periods (3 wk or more) of complete inactivity aboveground. The mean dry weight of workers removed at the rate of 10 per day increased over the removal period. The mean dry weight of workers removed at the rate of 50 per day increased for the first 9 wk and then decreased rapidly over the rest of the removal period. As removal continued, craters became smaller and many disappeared; nest entrances were shifted under the overhang of grass clumps and were covered with dried leaves. Intercology conflicts became common at most 50/day colony sites. After the 23—wk removal period, five colonies from each treatment group were randomly selected for excavation. Significantly fewer ants were excavated from both the 10/day and 50/day colonies compared to the controls. Significantly more ants altogether were produced (removed plus excavated) by the 10/day and 50/day colonies. However, the increase in the number of ants produced could not immediately counteract the loss of the ants to aboveground removal. At excavation, workers in the 50/day colonies weighed less than those in the control and 10/day group. In each treatment group, workers collected from the top 20 cm of the nest system weighed less than those collected from the remainder of the nest system. Also, in the 10/day group, workers collected at the surface during the removal phase weighed less than those present in the top 20 cm of the nest at excavation. No such difference existed in the colonies of the 50/day group. By midsummer of the next year (1966), the remaining experimental colonies appeared to be back to normal strength. Although the forager population was greatly reduced, the colonies were able to survive until more foragers could be produced. Such an adaptive strategy is possible because of a highly developed social behavior which results in a well—defined division of labor within the ant colony.
Biogeographic Range Comparisons and Evidence of Geographic Variation in Host‐Parasite Relations
Authors: Pielou E. C.
Published: May 2006

A test for judging whether a parasite's geographic range is as extensive as that of its host is described. Suppose hosts have been examined at M / N sites and infested specimens have been found at only M of them. Let a map of the area be divided into blocks by drawing boundary lines through the N clean sites. Each block contains one or more infested sites, or is empty; but a block cannot contain any clean sites since, owing to the method of block construction, all clean sites are on block boundaries. Now count the number of empty blocks. One may compute the probability of finding at least as many empty blocks on the null hypothesis that the risk of a host's infestation is independent of its geographic location, and hence tests the hypothesis. The test is then applied to data on the ranges of several aphid species that attack species of Solidago (goldenrod) in Nova Scotia and Prince Edward Island (NS / PEI). Data on plant—aphid relations obtained in NS / PEI are compared with previously collected data from southeastern Ontario. One of the Solidago species constitutes an empty niche in Ontario, either because the aphids that attack it in NS / PEI have small geographic ranges, or because Ontario plants of the species are aphid—resistant. One of the aphid species, with greater geographic range than its three host species, attacks different (though closely related) Solidago's in the different regions.
Dark Sulfate Uptake and Bacterial Productivity in a Subalpine Lake
Authors: Jassby Alan D.
Published: May 2006

Dark uptake of 35SO4 was investigated as a possible method for estimating bacterial production rates in Castle Lake, California. Assuming a fixed cellular sulfur; carbon ratio, bacterial productivities determined in this manner ranged from 2.5 to 28 mg C°m.—3°day—1 in 48 in situ measurements in the summer of 1972. Average production rates increased throughout the sampling period and corresponded in part to increasing levels of dissolved organic carbon. Production rates were stimulated by addition of NH4Cl and vitamin B12 to water samples, but not by thiamine, biotin, SO4, NO3, PO4 or a trace metal mix. Further studies on the sulfur content of bacteria and the role of phytoplankton in SO4 uptake are required before dark 35SO4 uptake is used for routine field measurements.
The Evolution of Oviposition Tactics in the Bean Weevil, Callosobruchus maculatus (F.)
Authors: Mitchell Rodger
Published: May 2006

A sizeable fraction (7%—17%) of the mung beans that are the preferred food of Callosobruchus maculatus are not large enough to support two larvae. Whenever two or more eggs are on a bean, development takes 40 days rather than 33 days, and only 8% of the second eggs develop even in beans with resources enough for two larvae. This larval competition confers an advantage on females that disperse eggs uniformly. Females tend to avoid adding second eggs as long as there are unusued beans. Survivorship of single eggs on beans increase with weight (l1 = .—005 mg + .368) and females oviposit on the largest of the unused beans first. Survivorship of the second egg (l2 = .31), due principally to mortality of the first egg, is about half that of the first egg; a second or third egg is added after nearly all the beans carry one or two eggs respectively. With these constraints the beetle may maximize fitness if it knows the weights and egg loads of all available beans. The actual performance falls short of achieving maximum fitness and the oviposition of the beetle fits a computer simulation that makes decisions after comparing the weight and egg load of the present bean with the last bean encountered. The performance of the beetle can be appropriately evaluated against models of unspecialized beetles that ovipost randomly and for beetles with maximum fitness. This shows that the beetle gains about 70% of the fitness that it could evolve.
Wildfires in Northern Yellowstone National Park
Authors: Houston Douglas B.
Published: May 2006

A sample of 40 fire—scarred trees was used to reconstruct the frequency and size of fires during the past 300—400 years in northern Yellowstone National Park. Best estimates of frequency suggested mean intervals of about 20—25 years between fires, after adjustments had been made for the recent influence of modern man. Agreement in fire dates over wide areas suggested the occurence of 8 or 10 extensive fires in the past 300—400 years. Euro—American man has substantially reduced the natural fire frequency for about 80 years and has thus contributed to changes in plant succession.
The Soil Arthropod Community of a Chicago Expressway Margin
Authors: Lussenhop John
Published: May 2006

Soil arthropods were collected at each of eight stations along a 21—km, E—W expressway margin in Chicago, Illinois. Community diversity and species distribution are not affected by proximity to the city. Expressway margin soil arthropod species are more aggregated than species in a Wisconsin prairie collection. The expresswey margin population is less diverse, and composed of greater proportions of soil—surface and root—feeding individuals than is the prarie population.
Spatial Distribution of Yearlings in a Richardson's Ground Squirrel Population
Authors: Michener Gail R. , Michener Daniel R.
Published: May 2006

Yearlings constituted 56%—67% of an adult Richardson's ground squirrel population in southern Saskatchewan. On the average 101 female yearlings were located 64 m from their site of original capture as young. Whether or not the mother was present after hibernation did not affect the distance moved by female yearlings. If the mother was present the average distance between mother and her female yearling offspring on closest capture dates was 40 m. Six male yearlings whose mothers did not survive hibernation were 25 m from their site of original capture as young, compared with 353 m for three male yearlings whose mothers did survive. Twenty—eight male yearlings whose mothers were unknown fell into two groups: 18 that moved less than 150 m from original caputure site (average 63 m) and 10 that moved more than 150 m (average 439 m). Laboratory experiments established that mothers and yearlings are able to identify each other as familiar or unfamiliar after a 7—8 month separation over hibernation. The data suggest that for a full understanding of the organization of adult ground squirrel populations the relationships between the animals must be known.
Egg Development, Growth, and Metabolism of Sigara Alternata (Say) (Hemiptera: Corixidae) in Fluctuating Thermal Environments
Authors: Sweeney Bernard W. , Schnack Juan A.
Published: May 2006

Egg development and growth of Sigara alternata in southeastern Pennsylvania, USA were evaluated in six fluctuating temperature regimes with daily maxima ranging from 12.0° to 21. 5°C. Developmental rate was positively correlated with increased magnitude of the diel temperature pulse. Developmental acceleration was most apparent for environments pulsing beyond 15.0°C for both stages. Oviposition rates were studied at natural temperatures during the initial days of reproduction. Egg deposition was sporadic but highly correlated with maximum diel temperatures. A critical temperature region of 11.0—12.5°C was observed for initiation and maintenance of egg laying. Metabolic rates were measured using a different respirometer. The thermal response of metabolism varied with animal soze and the range of test temperatures. The energy demand per uniy weight of tissue was inversely related to body size at all temperatures. Adult population metabolism decreased exponentially during the peak reproductive period due to high mortality. Energy budgets were determined for nymphal development in all thermal regimes. Net growth efficiencies and production/respiration ratios for Sigara alternata ranged from 49.7—73.4% and 0.9—2.7 respectively. Assimilation rates increased with rinsing temperatures and varied between 1.05 and 3.52 J.mg—1.day—1 [=0.25 —0.84 cal.mg—1.day—1]. Net growth efficiencies tended to decrease with increased temperatures due to higher maintenance costs. The significance of fluctuating temperatures to the bioenergetics, developmental dynamics, and ecology are discussed .
Species Diversity of Seed‐Eating Desert Rodents in Sand Dune Habitats
Authors: Brown James H.
Published: May 2006

The seed—eating rodent faunas were sampled on 18 dunes of semistabilized, wind—drifted sand in eastern California, Nevada, and western Utah. These dunes were similar in general appearance and in the form and spacing of vegetation, yet the number of common species of granivorous rodents ranged from 1 to 5. The faunas of all dunes were characterized by a regular spacing of body sizes, and the difference in size between coexisting species was inversely related to the number of species present. Differences in species diversity between dunes can be attributed to ecological, biogeographic, and evolutionary processes. A common pool of species had equal opportunity to colonize 13 of the dunes. The numbers of species inhabiting these dunes are determined primarily by ecological factors. Species diversity is most closely correlated with the predictable amount of annual rainfall, the best available estimate of the abundance of seeds. At least three dunes apparently are biogeographically depauperate; biogeographic barriers have prevented colonization of particular species that probably could exist on those dunes. Two of the dunes occur at high altitudes and these appear to be depauperate in an evolutionary sense; although these dunes seem to be capable of supporting additional rodent species, it is likely that no existing species possess the adaptations necessary to colonize them.
Salt Spray and Mineral Cycling in Two California Coastal Ecosystems
Authors: Clayton James L.
Published: May 2006

Windblown salt aerosols are a significant input to the mineral cycle along coastal areas. Cationic ratios of aerosol salts differ markedly from the same ratios in sea water. Resulting salt inputs to inland ecosystems reflect initial ion separation during sea—water bubble bursting and subsequent fallout of particulate salts until a base—level aerosol concentration is achieved. Inputs of aerosols to Baccharis brushland ecosystems are concentrated in plants and soil. Cations are trapped on leaf surfaces where they are available for foliar absorption and in some cases, translocation. Tracer studies with 22Na indicated that the greatest accumulation of retained 22Na was in the roots of Baccharis plants. Of the total applied dose of 22Na, 12% was either exuded or leached from roots of hydrophonically grown Baccharis over a 25—day period. This phenomenon may be considered a potential pathway for inputs of large amount of Na to soil near shorelines. The surface ionic content of soils reflects nutrient release from litter fall. At 1— to 2—m depths ionic losses from leaching occur in approximately the same ratios as inputs of salt spray. This suggests a steady state with regard to cycling of Na, K, Mg, and Ca.
Some Implications of Leaf Tearing in Musaceae
Authors: Taylor S. Elwynn , Sexton Owen J.
Published: May 2006

Leaf temperatures associated with torn and untorn leaves of Musaceae were taken in both dry and wet seasons at Barro Colorado Island, Canal Zone. Transpiration rates and leaf resistance to water—vapor diffusion were determined. Energy—budget analysis is used to describe the relationship of leaf dimension and leaf resistance to thermal survival and water usage. Gas—exchange theory is applied to predict the photosynthetic implications of leaf tearing. The analyses showed that leaves less than 10 cm wide are not subject to critical heat stress, have lower water loss, and higher ratios of photosynthesis to water expended than do leaves of widths greater than 10 cm. In wet season, leaves have lower resistance to the diffusion of water vapor and accordingly are less subject to excessive heating.
Nitrogen Metabolism in the Height Forms of Spartina Alterniflora in North Carolina
Authors: Mendelssohn Irving A.
Published: May 2006

Selected aspects of the nitrogen nutrition of salt marsh cordgrass, Spartina alterniflora, were investigated in Oak Island Marsh, North Carolina, USA. Nitrate was of minor importance as a nitrogen source for Spartina in this marsh as indicated by low soil interstitial water nitrate concentrations and low plant tissue nitrate concentrations and nitrate reductase activities. However, Spartina did have the capability of assimilating nitrate nitrogen when available. Interstitial water and plant tissue ammonium concentrations were 1—2 orders of magnitude > that for nitrate which strongly indicated that ammonium was the dominant inorganic nitrogen source. Leaf and root nitrogen constituents (total nitrogen, soluble nitrogen, ammonium, and nitrate) and nitrogen metabolism measured via glutamate dehydrogenase activity indicated that the nitrogen status of the short height form of Spartina was deficient relative to that of the tall form.
Geographic Variation and Its Climatic Correlates in the Sex Ratio of Eastern‐Wintering Dark‐Eyed Juncos (Junco Hyemalis Hyemalis)
Authors: Ketterson Ellen D. , Nolan Val
Published: May 2006

The sex ratio of Dark—eyed Juncos wintering in the eastern and central United States and Canada varies clinally along a latitudinal gradient. The percentage of @V @V among both museum skins and live—caught birds is °70% in the south, 20% in the north. When abundance according to latitude is also considered, an average ♀ appears to winter farther south than an average ♂ and hence probably tends to migrate farther. Latitude alone is an excellent predictor of sex ratio (r2 = 85%), and latitude plus 13 other measures of climate explain virtually all the variation (r2 = 96.6%). Extreme measures of climate, as compared to mean measures, are equally predictive. Principal component analysis indicates that snowfall, temperature, and latitude are the most important climatic variables associated with sex ratio. Because ♂ ♂ average larger than ♀ ♀ and are concentrated northward, mean wing length increases with latitude and is significantly correlated with climatic measures that vary with latitude. Further, larger birds within each sex may select higher altitudes as wintering sites. Sex ratio does not vary measurably with date in wintering populations. Among possible explanations for clinal variation in sex ratio are sex—associated differences in (1) advantages of early arrival on the breeding or wintering grounds, (2) impacts of inter— and intrasexual competition, and (3) effects of low temperature and intermittent food availability. Comparison of ♂ ♂ and ♀ ♀ with respect to potential fasting endurance, a size—related metabolic parameter, indicates that at 0 degrees C an average ♂ should be able to fast 4% longer (1.6 h) than an average ♀ at standard metabolic rates. An extremely heavy 7 ♂ might endured fasting up to 29% (10.7 h) longer than a very light ♀. These differences may confer greater survival ability upon the ♂ at latitudes where snow cover can often preclude feeding.
Community Structure in Sympatric Rodents
Authors: M'Closkey Robert T.
Published: May 2006

Species diversity, microhabitat separation, microhabitat shifts and body size patterns are examined in seven sympatric rodent species. Habitat separation and seasonal shifts are identified by multiple—group discriminate analysis on microhabitat variables representing shrub structure and substrate patchiness. The rodents form two functional groups. Four permanent, year—round residents (Peromyscus eremicus, Neotoma lepida, Neotoma fuscipes, and Dipodomys agilis) show significant separation on habitat structure and some temporal habitat shifts. Three seasonal residents (Peromyscus maniculatus, Peromyscus, and Reithrodontomys megalotis) show no microhabitat shifts and have a greater frequency of microhabitat overlap with one another and with permanent residents. There is no relationship between niche breadth and population density for any given species; however, as a group, seasonal residents show reduced breadth with increased population density. The significance of this pattern is discussed with respect to ecological opportunism of seasonal residents. The pattern of body size differences within the fauna is examined in light of habitat structure. Pairwise differences in habitat structure and body size are positively correlated. The data show that permanent residents are more different from one another in body size and structural habitat than pairs in which at least one species is a seasonal resident. Increased similarity in body size and microhabitat structure may not favor year—round coexistence in some pairs of species. The most similar—sized pair of species are congeneric deer mice (P. eremicus and P. maniculatus), and in addition to seasonal separation, they show niche difference by habitat structure.
Species Diversity and Community Organization in Desert Seed‐Eating Ants
Authors: Davidson Diane W.
Published: May 2006

Patterns of species diversity and community organization in desert seed—eating ants were studied in 10 habitats on a longitudinal gradient of increasing rainfall extending from southeastern California, through southern Arizona, and into southwestern New Mexico. Local communities of harvester ants include 2—7 common species, and at least 15 species from five genera of Myrmecines compose the total species pool in these deserts. Ant species diversity is highly correlated with mean annual precipitation, an index of productivity in arid regions. Communities are structured on the basis of competition for food, and interspecific differences in worker body sizes and colony foraging strategies represent important mechanisms of resource allocation. Seed size preferences, measured for native seeds in food choice experiments with seeds of different size but uniform nutritional quality, are highly correlated with worker body sizes. Species of similar body size can coexist within local habitats if they differ in foraging strategy. Interspecific aggression and territorial defense and microhabitat partitioning all appear to be relatively unimportant in these and communities. Patterns of species diversity and community organization in harvest ants are strikingly similar to those reported for communities of seed—eating rodents that occupy many of the same desert habitats. Separate regressions of within—habitat species diversity against the precipitation index of productivity for the two groups correspond closely in slope, intercept, and proportion of explained variation. Resource allocation on the basis of seed size characterizes local communities of both ants and rodents. Parallels between these two groups suggest that limits to specialization and overlap may be specified by parameters such as resource abundance and predictability that effect unrelated taxa similarly.
Effect of Host Plant Density on Populations of a Specialzied, Seed‐Sucking Bug, Oncopeltus Fasciatus
Authors: Ralph Carol Pearson
Published: May 2006

To assess the role of host plant density in the life of a specialized herbivore, natural populations of the large milkweed bug, Oncopeltus fasciatus, were monitored in 5 paired study plots of high and low milkweed density (Asclepias syriaca). At all sites the plot with a higher density of milkweed pods supported more O. fasciatus per pod. At some sites, O. fasciatus load (cumulative biomass of bugs/pod) correlated positively with pod density within plots, and milkweed below a certain density escaped O. fasciatus exploitation. However, at a site that recevied an exceptionally large influx of colonizing bugs, almost all pods were heavily fed upon, regardless of their dispersion. This herbivore clearly demonstrates the resource—concentration effect. The effect orginates with the oviposition patterns of colonizing ♂ ♂ and its strengthened by differential mortality of nymphs searching for suitable feeding spots. Since these behaviors are common in other insects herbivores, the resource—concentration effect may be an important organizing factor in many natural, as well as cultivated plant—athropod associations.
Seed Production, Seed Populations in Soil, and Seedling Production After Fire for Two Congeneric Pairs of Sprouting and Nonsprouting Chaparal Shrubs
Authors: Keeley Jon E.
Published: May 2006

A study of seed production, seed storage in the soil, and seedling production after fire was undertaken for a sprouting and a nonsprouting congenerica pair of species of Ceanothus and Arctostaphylos. All species exhibited large fluctuations in annual seed production. There was a significant correlation between fruit production and precipitation in the previous year. It is hypothesized that high carbon gain in years of high precipitation results in high numbers of floral primordia which, in these species, remain dominant until the following year. It was also noted that high fruit production was not dependent upon high precipitation the same year; suggesting that the fruits were utilizing carbon stored from the previous year. All 4 species were capable of producing more seeds in a single season than were stored in the soil. Apparently the soil seed pools do not represent a steady accumulation of seeds in the soil but rather are the result of dynamic fluctuations in seed inputs and outputs. Each species also had more seeds in the soil, by several orders of magnitude, than seedlings after fire in an adjacent burned stand. The sprouting and seeding productive strategies are quite different in the two genera. The information from this study coupled with that from other studies indicate 4 reproductive modes: sprouting and seedling production (C. leucodermis), abundant seedling production (C. greggii), low seedling production but better "equipped" seedlings (A. glauca), and predominantly sprouting (A. glandulosa).
How Southern Cowpea Weevil Larvae (Bruchidae: Callosobruchus Maculatus) Die on Nonhost Seeds
Authors: Janzen Daniel H.
Published: May 2006

Callosobruchus maculatus bruchids (southern cowpea weevils) oviposited on the seed coats of 63 species of nonhosts in the laboratory. The first—instar larvae were unable to penetrate the seed coats of 17%, made a shallow pit in 30%, made a deep pit in 13%, and passed through the seed coats of the remaining 41%. Even when the seeds were cut in half, so that the eggs were laid directly on seed contents, the larvae died very shortly after mining into the seed contents of 92% of the 63 species. In only 1 case (Rhynchosia calycosa) did the bruchid develop normally and emerge from an intact seed. In 3 cases (Delonix regia, Parkinsonia aculeata and Schizolobium parahybum), the bruchid developed to a full—sized larva or an adult in the embryo of the seed but was unable to emerge by itself. In 9 species, the ♀ beetles refused to ovipost on the seeds, apparently because they were too small or because they were tomentose. It appeared that larvae failed to penetrate seed coats both because of their hardness and their toxicity. This demonstration that seed coats can be a barrier to a bruchid complicates the interpretation of the toxicity of seed contents and emphasizes the need to analyze seed contents separately from seed coats.
Stability of Small Unisexual‐Bisexual Populations of Poecilipsis (Pisces: Poeciliidae)
Authors: Moore William S.
Published: May 2006

All—female species of Poeciliopsis depend upon ♂ ♂ of closely related species for sperm. The relationship creates a competitive situation in which bisexual ♀ ♀ compete with unisexual ♀ ♀ for sperm from ♂ ♂ of the bisexual species. Earlier studies demonstrated a sufficient mechanism inherent in the behavior of ♂ ♂ for allowing coexistence in mixed unisexual—bisexual populations. Courtship preference of ♂ ♂ for conspectific ♀ ♀ is dynamically countered by social interaction among ♂ ♂: subordinate males mate with unisexual ♀ ♀ in impetuous courtships. The Poeciliopsis monacha—Poeciliopsis 2 monacha—lucida complex occurrs naturally in small isolated populations where stochastic factors are not negligible. This paper evaluates the stability of small populations of this complex by laboratory population experimentation and stochastic computer simulation. Three small mixed populations persisted in the laboratory for 2 yr but extinction of the bisexual species occurred in four of nine simulated replicates of these experiments. Life tables and fitness values calculated from estiamtes of birth and death rates showed the all—female species to be much more fit in the laboratory populations than was the bisexual species. Additional simulations done at relative fitness values more characteristic of natural populations indicated that extinctions in small isolates would be rare in nature. Isolated demes can become confluent during the annual rainy season. It was expected that this confluence, by effectively increasing population size, might enhance stability by reducing the effect of stochastic factors; simulations of two and four demes mixed annually did not support this hypothesis.
A Model for Tropic Interaction
Authors: DeAngelis D. L. , Goldstein R. A. , O'Neill R. V.
Published: May 2006

A nonlinear function general enough to include the effects of feeding saturation and intraspecific consumer interference is used to represent the transfer of material or energy from one trophic level to another. The function agrees with some recent experimental data on feeding rates. A model using this feeding rate function is subjected to equilibrium and stability analyses to ascertain its mathematical implications. The anaylses lead to several observations; for example, increases in maximum feeding rate may, under certain circumstances; result in decreases in consumer population and mutal interference between consumers is a major stabilizing factor in a nonlinear system. The analyses also suggest that realistic classes of consumer—resource models exist which do not obey Kolmogorov's Criteria but are nevertheless globally stable.
Behavioral Ecology of Mating in the Male Gila Topminnow, Poecilipsis Occidentalis (Cyprinodontiformes: Poeciliidae)
Authors: Constanz George D.
Published: May 2006

Males of the fish family Poeciliidae cease growth upon attainment of sexual maturity. Because position in fish social hierarchies is in large part size—dependent, Poeciliopsis occidentalis ♂ ♂ which mature at a small body size may be locked into subordinate status. As an apparent consequence of disparate competitive abilities, ♂ ♂ at extremes of body size exhibited contrasting mating strategies. Females were courted by large, territorial ♂ ♂. Tiny ♂ ♂ remained at a distance prior to dashing toward ♀ ♀ for a copulatory attempt. The accuracy of sneak copulatory attempts by tiny ♂ ♂ appeared to be enhanced by a relatively longer intromittent organ. Quantitative data on territory size and rates of social encounters indicated possible costs and benefits of such alternate strategies. Possible ultimate causes of these contrasting behaviors are the cost—benefit balance of a particular strategy and underlying genes. Possible proximate factors include the growing season, sex ratio, and the competitive environment.
Flowering Ecology of Some Spring Woodland Herbs
Authors: Schemske Douglas W. , Willson Mary F. , Melampy Michael N. , Miller Linda J. , Verner Louis , Schemske Kathleen M. , Best Louis B.
Published: May 2006

Fecundity characteristics, phenology, and behavior of insect flower—visitors were studied for 7 early flowering woodland herbs: Claytonia virginica, Dentaria laciniata, Dicentra canadensis, Dicentra cucullaria, Erythronium albidum, Isopyrum biternatum, and Sanguinaria canadensis. Sanguinaria canadensis is facultatively autogamous, the Dicentras are obligate outcrossers, and the remainder are self—compatible, at least within a stem. All are insect pollinated except sometimes S. canadensis. The numbers of ovules per flower and flowers per stem tended to be inversely correlated, and large—seeded species (S. canadensis, E. albidum, I. biternatum) had lower numbers of potential seeds per stem than did small—seeded species. Flowering of all species typically occurred during the first prolonged period of weather suitable for pollinator activity and ceased by the time the canopy closed. Annual differences in flowering times were associated with differences in average temperatures (i.e., early blooming in a warm, early spring), but cumulative degree—hours or degree—days of air or soil temperatures were not well correlated with flowering times. Other constraints on flowering phenology are discussed, including the predictability of suitable conditions, a proposed "fail—safe" mechanism that may assure flowering before canopy closure even if temperatures are abnomally low, and the importance of nontemperature factors in defining suitable conditions. Flowering time was not very finely tuned to the temperature regime and pollinator activity; flowers blooming during the flowering peak often had low seed production and the fertilization rate of most species was low. Evidence that seed production may have been pollinator limited for several species was obtained by comparing the success of hand pollination and of natural pollination, rarity of certain specialized pollinators, and estimates of the abortion rates of fertilized ovules. We suggest that flowering in early spring is a high—risk option in terms of insect—mediated sexual reproduction. Certain flower—visiting insects favored D. laciniata out of proportion to its abundance, but no effect on seed set of other species was detectable. Honeybees were abundant and active flower visitors with the potential for disrupting ecological/evolutionary relationships between native insects and flowers.
Plant Selection and Foraging Patterns in Two Species of Leaf‐Cutting Ants (Atta)
Authors: Rockwood Larry L.
Published: May 2006

Three colonies each of two species of leaf—cutting ants (Atta colombica Guer. and Atta cephalotes L.) were studied for 1 yr in the Guanacaste Province of Costa Rica to determine the following: (1) Do colonies of Atta cut leaves from a limited number of species (i.e., are they selective)? (2) What determines which plant species are attacked? (3) Do leaf—cutters optimize foraging in terms of energy expended by attacking palatable plants closest to the nest or do they distribute their efforts more or less evenly throughout their foraging territory? Several line of evidence support the hypothesis that A. cephalotes and A. colombica are selective in terms of plant material attacked. The ants sampled a large majority of the plant species present, but concentrated their foraging on a restricted subset of species. The mature leaves of only 31.4% and 22.0% of the species present were readily acceptable to A. colombica and A. cephalotes, respectively. The new leaves of another 12—16 plant species were acceptable. Different colonies of the same Atta species consistently attacked the same plant species if they were available, cut leaves from the same species at similar rates, and even attacked the same species of plants at the same time of year. The amount of material cut from host plant species was not correlated with host plant abundance in four of the six colonies studied, and was even slightly negatively correlated in two of these four. An analysis of plant distance from the nest versus amount harvested shows that palatable plant species close to the nest have a greater probability of being visited by the ants, but do not necessarily suffer more defoliation than other such plants within 50—60 m of the nest. Amount harvested decreases greatly for plants farther than 60—80 m from the nest. Thus colonies of Atta do not normally concentrate their efforts on plants closest to the nest, but foraging cannot be described as evenly distributed either. The factor responsible for selectivity in colonies of Atta is probably the internal chemistry of the material selected. An Atta colony must provide the fungus garden when a proper balance of nutrients and moisture without overlapping it with secondary compounds from the plants selected. The ants' attempt to solve this problem may explain some of the complexities of leaf—cutter foraging behavior.
Soil Arthropod Response to Prairie Burning
Authors: Lussenhop John
Published: May 2006

Soil arthropod response to altered litter production in a Wisconsin prairie was examined after a long established biennial spring burning program was modified by substituting raking for burning in some experimental blocks, and substituting no disturbance for burning in others. Very few species were favored by increased surface litter in undisturbed blocks. After two biennial burnings or rakings, a drop in species numbers, density of individuals, and diversity of herbivore—decomposers occurred in undisturbed, and to a lesser extent, in raked blocks. Predatory soil arthropod species showed no response. These results suggest that soil detritus levels dropped slowly in response to decreased plant productivity in undisturbed blocks. The drop in soil arthropod community diversity which occurred in undisturbed blocks indicates a direct productivity—diversity relationship. Other field experiments show the same direct productivity—diversity relationship among consumers or terrestrial producers, but an inverse relationship among aquatic producers.
The Life‐Styles of Tropical Milkweed Bugs, Oncopeltus (Hemiptera: Lygaeidae) Utilizing the Same Hosts
Authors: Root Richard B. , Chaplin Stephen J.
Published: May 2006

Oncopeltus cingulifer and Oncopeltus unifasciatellus occur on the same milk—weed species in the Cauca Valley of Colombia. Adults utilize the major host, Asclepias curassavica in the same way except that O. unifasciatellus feeds somewhat more on seeds. Nymphs of O. unifasciatellus require milkweed seeds to develop whereas O. cingulifer can mature slowly while feeding only on vegetative tissues of milkweeds. Parasitism, predation, and cannibalism are responsible for heavy losses of eggs in both species. Cannibalism of unhatched eggs by their newly—hatched siblings has a complex adaptive basis involving the utilization of individuals that are otherwise doomed and the proportion of eggs parasitized in a clutch by scelionid wasps. The continuous growing season in the Cauca Valley, coupled with the asynchronous occurrence of catastrophic setbacks in different milkweed stands, results in a shifting distribution of seed abundance. The adaptive syndromes exhibited by Oncopeltus appear to be organize around their dependence on this patchy resource. Thus O. unifasciatellus, which requires seed for reproduction, is less sedentary and more phenotypically variable than O. cingulifer. It seems unlikely that two such species could coexist in a seasonal environment where seed production is synchronized over an entire region.
Latitudinal Trends in the Metabolic Adjustments of the House Sparrow
Authors: Kendeigh S. Charles
Published: May 2006

Between latitudes 9 degrees and 59 degrees in North America, the House Sparrow, Passer domesticus, shows progressive increases northward in energy expenditures for temperature regulation, existence metabolism, reproduction, daily energy budget, permanent residency, and mobilizable energy. Energy requirements are greater in the winter than in the summer for temperature regulation, existence metabolism, daily energy budget, and mobilizable energy. Seasonal acclimatization to winter temperatures brings lower rates at equivalent temperatures in existence metabolism. However, latitudinal adaptation at colder northern latitudes brings higher rates at equivalent temperatures in existence metabolism. The number of broods produced per year is inversely proportional to the energy cost per brood, and the energy expended by the species for reproduction is approximately the same at all localities. The reduction in work capacity at high ambient temperatures increases southward, but is greater in desert climates with large daily and seasonal fluctuations in temperature than in the tropics with their uniform climates. The species may be limited in dispersal into desert regions by daily maximum temperatures that approach or surpass its upper limit of tolerance, but is capable of dispersing through the Central American tropics into South America. The species is limited northward by low temperatures at which it is unable to mobilize sufficient energy for existence and/or reproduction except where it makes use of artificial man—made shelters and food supplies. These variations and adjustments noted between geographic populations of the House Sparrow probably apply to bird species generally.
Microheterotrophic Activity in a Salt‐Marsh Estuary, Sapelo Island, Georgia
Authors: Hanson Roger B. , Synder James
Published: May 2006

Uniformly 14C—labelled glucose was used to estimate maximum potential uptake kinetics (WMAX) in unfractionated and <64 μm, and <10 μm screened water samples. Most of the activity in the estuary was found in the size fraction >10 μm, in the summer, and in the tidal creeks. The uptake (VMAX) of labelled lactic acid was > glucose > glycolic acid > aspartic acid and alanine. Glycolic acid was respired most rapidly, followed by aspartic acid, lactic acid, alanine and glucose. Most of the particulate organic carbon (POC), adenosine triphosphate (ATP), and platable bacterial cells (CFU) were in the 10 μm fraction. Glucose VMAX values were significantly correlated with ATP and CFU, and lactic acid VMAX values with CFU only. VMAX and turnover times in the unfractionated water were 57% lower and 29% greater, respectively, than in the <64 μm fraction sample, and (K / Sn) values were at times very dissimilar among fractions of the same water. These results were attributed to the physical separation of the plankton community, nutrient fluctuation in the sample, and microheterotroph diversity and distribution on particles.
Behavior of a Predator and its Prey: The Horned Lizard (Phrynosoma Cornutum) and Harvester Ants (Pogonomyrmex Spp.)
Authors: Whitford Walter G. , Bryant Martha
Published: May 2006

Horned lizards, Phrynosoma cornutum, were observed between sunrise and sunset in order to record the time spent at different behaviors and the prey taken. Two ant species, Pogonomyrmex desertorum and Pogonomyrmex rugosus, were the most important prey. The behavioral responses of these prey species were studied by subjecting them to varying levels of simulated predation. The lizards fed most often on ants that were not associated with nest discs or foraging columns and took only a few ants at any one place. Lizards moved on average of 46.8 m/d, remaining in the vicinity of any group of ant nests <15 min. In artificial predation experiments, Pogonomyrmex desertorum ceases activity for periods of up to 5 d following losses of °25% of the forager population when foragers were removed at a rate of 5/d or 10/d. Pogonomyrmex rugosus did not respond to loss of 25% of the forager population, ceased activity of losses of 50% of the forager population, and exhibited frenzied activity upon loss of 75% of the forager population. The horned lizards have evolved a foraging strategy that allows maximization of prey availability over weeks or a month rather than per hour or day. Estimates of horned lizard densities, ingestion rates, and numbers of potential prey suggest that horned lizard numbers are regulated by the availability and productivity of Pogonomyrmex spp. These estimates also suggest Pogonomyrmex spp. colonies are extremely productive, essentially replacing the entire worker population each year.
The Flax Pond Ecosystem Study: Exchanges of Inorganic Nitrogen Between An Estuarine Marsh and Long Island Sound
Authors: Woodwell G. M. , Hall C. A. S. , Whitney D. E. , Houghton R. A.
Published: May 2006

The concentrations of inorganic nitrogen ions were measured in the tidal water flushing Flax Pond, an estuarine marsh on the north shore of Long Island, New York, USA. The basic sampling unit was one tidal cycle during which eight subsamples were taken, four on the flood and four on the ebb. The sampling was approximately weekly during 20 mo. Concentrations of the three forms of nitrogen (nitrate, nitrite, and ammonium) varied seasonally and with the periodic occurrence of algal blooms. Concentrations were highest in winter and lowest in spring and early summer, but details of the pattern of abundance differed among the ions. There was a net discharge of nitrogen in the ammonium form from Flax Pond during summer and fall and a net input from the Sound in winter and spring. The net exchanges during 1 yr were zero for nitrite, an influx of nitrate of about 1 g N/m2 to the marsh, and a release of about 2 g ammonium—N/m2 into the Sound. The net total exchange was a release into Long Island Sound of approximately 1 g N/m2 of marsh, an amount not statistically different from zero. Crude estimations of the total inorganic N—budget of Long Island Sound suggest that estuaries, precipitation, and rivers each contributed approximately equal inputs in earlier times.