bluuebunny/crossref_metadata_2025 huggingface dataset:
The Nature and Causes of Cyclomorphosis in a Species of the Bosmina Longirostris Complex
Authors: Black Robert W.
Published: May 2006

Cyclomorphosis was examined in the long—featured species of the Bosmina longirostris complex at an inshore site in Lake Washington, State of Washington, USA, IN 1975 and 1976. Summertime decreases were observed in the mean size and relative growth of four morphological characters in 1975 and in the mean size of three of these characters in 1976. Seasonal changes in antennule length, the number of antennule segments, mucro length, and the number of mucro sutures were determined to be unrelated to the age structure of the population. Samples of clones that were isolated from the field population and acclimated to a single set of laboratory conditions contained significant between—clone heterogeneity with respect to the mean size of three characters: antennule length, mucro length, and the number of mucro sutures. Furthermore, acclimated clone sets isolated from springtime populations contained significantly larger characters than did sets that were isolated from summertime populations and acclimated to the same conditions. These findings not only indicate that clones can be genetically distinct with respect to these three cyclomorphic characters and that the field population contained considerable genetic diversity with respect to these characters at any one time, but also show that genetic changes occurred in the population with respect to each character. Evidence suggests that these genetic changes did not occur as large—scale extinctions of clones, but probably involved the succession of morphologically distinct clones as the numerically dominant clone. Comparison of the observed cyclomorphosis with those patterns predicted by the various hypotheses for the causes of this phenomenon has revealed that the seasonal morphological changes shown by this species were probably caused by the selective predation of a temporally important predator. Cyclomorphosis in the long—featured species was not related to water temperature or oxygen stress in the manner proposed for other species by previous investigators.
An Experimental Model: Bacterial Specialists and Generalists Competing in Chemostats
Authors: Dykhuizen Daniel , Davies Maxine
Published: May 2006

An experimental model was used to test the ecological axiom that a generalist is less efficient than a specialist. The generalist in this model were strains of Escherichia coli which can use both maltose and lactose. The specialists were strains of E. coli which can use only maltose because of a deletion of the lactose genes. These generalists and specialists competing for maltose in energy—limited chemostats containing both sugars achieved coexistence under certain conditions. The equilibrium frequency depended upon the pair of strains used and the percentage of the sugar which is lactose. A genetic change was important in the outcome of these experiments: a lac constitutive mutation replaced the lac/ of the generalist. (Cells with a lactose constitutive mutation produce lactose enzyme whether or not lactose is present.) This allowed the generalist to coexist on lower amounts of lactose that it would have been able to otherwise. We propose that the lactose consititutive is selected for over the wild—type in a lactose—limited chemostat because the concentration of lactose required for growth, if the operon is constitutively depressed, is less than that required for continued depression of the lactose operon. The equilibrium frequency predicted by chemostate competition theory gave a much higher frequency of the generalist than seen in the experiments. When only the generalist was added to a chemostat containing both maltose and lactose, an equilibrium of both lac/ and lac constitutive cells was established. This implies that there exists "resource interference." Resource interference happens when an organism is not as efficient at using a resource when it is using other resources as when it was using that resource alone. When a constant for resource interference was incorporated into the equations, the theoretical predictions agreed with the experimental results. We hypothesize that this resource interferences is due to competition for permease sites.
Specialization and Foraging Efficiency of Solitary Bees
Authors: Strickler Karen
Published: May 2006

The specialist bee, Hoplitis anthocopoides, foraged for pollen from Echium vulgare, its preferred plant, more efficiently than did four generalist species. Efficiency was measured as the weight of pollen (the larval food) harvested from Echium flowers per unit handling time, divided by the weight of the discrete pollen mass required to rear one offspring. This measure of efficiency corresponds more closely to reproductive output than does the usual measure, net energy gained per unit time. The specialists produced more potential offspring per unit handling time because they manipulated flowers faster and collected more pollen per flower than did generalists. The specialists also flew between flowers more rapidly than did the generalists. The specialists did not defend the flowers against generalists. These results support the assumption in models of resource partitioning and optimal foraging theory, and in hypotheses explaining the evolution of pollen—specializing bee species, that specialists are more efficient at using their preferred resources than are generalists.
Convergence, Competition, and Mimicry in a Temperate Community of Hummingbird‐Pollinated Flowers
Authors: Brown James H. , Kodric-Brown Astrid
Published: May 2006

We studied the pollination ecology of nine species of red, tubular flowers which bloom together in different combinations in the White Mountains of Arizona, USA. All species were strikingly convergent in floral color, size, and shape. Hummingbirds, the primary pollinators, usually did not visit flower species selectively, and individual birds often simultaneously carried four or more species of pollen. Flowers may have competed interspecifically for these shared pollinators, but competition was reduced because character displacement in orientation of anthers and stigma resulted in some species using different parts of the bird to transport their pollen. Most flower species secreted nectar at similar rates, particularly when the bloomed together in mixed stands. A population of Lobelia cardinalis secreted no nectar; it attracted hummingbirds by mimicing more abundant, nectar—producing species. This temperate flower community, which resembles some associations of convergent Mullerian and Batesian mimics, appear to have evolved its characteristics convergent structure because the advantages of using similar signals and rewards to share the same hummingbird pollinators outweigh the advantages of diverging to reduce interspecific competition.
An Analysis of Elemental Concentrations in Vegetation Bordering a Southeastern United States Coastal Plain Stream
Authors: Garten Charels T. , Gentry John B. , Sharitz Rebecca R.
Published: May 2006

Mineral element concentrations were measured in the component parts of different species of plants from a floodplain community along a coastal plain stream in South Carolina, USA. Frequency distributions of concentrations of mineral elements were positively skewed, although distributions of P, K, Ca and B concentrations tended to be less skewed than those of some trace elements (Na, Al, Cs—137). Sources of variation in the elemental compositions of the major natural plant species of the floodplain were examined statistically. In herbaceous species (Scirpus cyperinus and Andropogon sp.), 52—56% of the variation in P, Mg, Mo and Na concentrations was accounted for by differences in the chemical composition of stems, leaves, roots and seeds. Seasonal variation in the mineral element composition of leaves from woody species was greater than that in stems. Concentrations of K, P, Al, Mo and Sr in leaves were significantly different among seasons in 3 woody species (Alnus serrulata, Myrica cerifera, Salix nigra). Mean concentrations of Ca, Na, Al, B, Mo and Sr in leaves tended to increase from spring to autumn, while K, Mg, N, P, Cu, Zn and Cs—137 concentrations declined. For macroelements (P, Mg, K, Ca and N) and some trace elements (B, Sr, Na and Mo), >50% of the variation in concentrations was accounted for by differences among 4 species (Polygonum punctatum, Scirpus cyperinus, Salix nigra, Sagittaria latifolia) while <12% was explained by differences among 7 locations along the creek. Discriminant function analysis showed that K concentrations, which are low in the floodplain soils, contributed more than did concentrations of 11 other elements to species differences. Concentration of elements were significantly correlated across species and locations from the floodplain community. A principal components analysis of elemental concentrations in leaves produced 2 components after varimax rotation. Principal component I was most highly correlated with concentrations of Ca and Sr, but many other elements were loaded on this component.
Presettlement Magnolia‐Beech Climax of the Gulf Coastal Plain: Quantitative Evidence From the Apalachicola River Bluffs, North‐Central Florida
Authors: Delcourt Hazel R. , Delcourt Paul A.
Published: May 2006

The presettlement vegetation mosaic bordering the Apalachicola River in the Panhandle of Florida, reconstructed from General Land Office Survey records of 1824—1825, consisted of upland pine—oak forest, open pine flatwoods, mesic hardwood hammock, tributary stream hardwoods, and Apalachicola floodplain swamp. Longleaf pine forest interspersed with blackjack, red, and post oaks occupied the sandy uplands east of the Apalachicola River. Alluvial terraces west of the river supported pine stands probably dominated by longleaf and slash pines. The mesic hammock forest of the river bluffs was comprised of an admixture of hardwood species, dominated by magnolia and beech. The tributary bottomlands community consisted primarily of bay, holly, and beech; the Apalachicola floodplain forest was dominated by bay, gum, and oak. The magnolia—beech forest of the Apalachicola River bluffs represents the second mesic upland magnolia—beech forest quantitatively documented for the original vegetational of the Gulf Coastal Plain and is the first such record for Florida. The concept of the magnolia—beech climax forest is reinstated here for the original vegetation of the southern Gulf and Atlantic coastal plains (the region of overlap in distributions of Magnolia grandiflora and Fagus grandifolia). Modern forest—management practices that include fire suppression and selective lumbering are causing both a shift from pine to hardwood dominance on sandy upland sited and a change from magnolia—beech to mixed hardwood dominance on mesic sites throughout the southern coastal plains. The "southern mixed hardwood forest climax" (sensu Quarterman and Keever 1962) thus represents a converging trend of modern and future vegetation of the South toward a new climax different from that existing in the presettlement vegetation.
Understory Structure of a Mesic Forest in Southeast Texas
Authors: Harcombe P. A. , Marks P. L.
Published: May 2006

High species richness in the understory of mesic coastal plain forests prompted examination of the vertical structure of the understory of one such forest in southeast Texas, USA. Leaves and branches (<1—cm diam) were harvested by species in an 11—m vertical transect at 50 random locations. The following points about the lower 11 m are of interest: vertical distribution of leaf weight is relatively uniform; weight of small branches shows a maximum at 1 m and a minimum at 4 m; evergreen leaves are prevalent; offspring of overstory tree species contribute strongly to understory structure; the 2 dominant species occupy different parts of the understory; and although the vertical distribution of dominant and common species is random, they are well—dispersed vertically. The high species richness in the understory may be the result partly of the relatively large amount of light reaching the understory and partly of the tendency for species to occupy different positions in the understory.
The Development and Movement of Tree Islands Near the Upper Limit of Yree Growth in the Southern Rocky Mountains
Authors: Marr John W.
Published: May 2006

Dwarfed and deformed plants of tree species occur as 'tree islands' in a matrix of tundra vegetation near the upper limit of tree growth in the Southern Rocky Mountains. Many of these islands are asymmetrical, having a surface layer of dead branches to windward and some live branches to leeward. I made repeated observations of these islands in all seasons from 1956 to 1967 along a 1.75—km belt ?20 m wide in Niwot ridge in the Front Range was of Denver, Colorado. The location of islands was mapped on a transparent overlay on an aerial photograph, annual growth of stem tips was measured, and an abundance of notes and photographs was taken. Some tree islands of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) are conspicuous because they grow in microsites in which no tree seedlings have been found, and which general observations suggest would be outside their environmental amplitude. These islands often have live branches connected to windward with dead branches, some of which have roots. These observations led to the hypothesis that some tree islands move along the ground climbing out of more moderate microsites in which a seed germinated and moving into microsites for which they are not well adapted. In this movement process, wind—exposed organs are killed, while leeward stems grow to leeward often taking root and forming an upright stem system in the process of 'stem tip layering.' Islands with interconnected live and dead stems to windward, illustrating movements of 5 m, are common; isolated dead stumps and wood fragments in a line extending to windward indicate that some islands may have moved at least 15 m. The origin of tree islands, support for the movement hypothesis, and other features of tree island ecology and discussed.
Experimental Support for Food Particle Size Resource Allocation in Heteromyid Rodents
Authors: Mares Michael A. , Williams Daniel F.
Published: May 2006

Laboratory experiments were designed to determine if heteromyid rodents of different body sizes select seeds of an average size which is correlated with the body size of the granivore. Eight types of commercial seeds were used and 6 heteromyid species were tested. Although there was no correlation of average seed size selected and the body size of the individual granivore, there was a highly significant positive correlation (r = .95) of average seed size selected versus average body size of each group of rodents of a particular species. Thus small animals of a species select seeds of the same average size as large animals of that same species. There was a tendency for individuals of larger species to take a greater variety of seeds. We suggest that differential food particle size allocation can be a mechanism for reducing interspecific competition.
Changes in the Output of Ions from a Watershed as a Result of the Acidification of Precipitation
Authors: Lewis William M. , Grant Michael C.
Published: May 2006

The average hydrogen ion input to a mountain watershed in Colorado increased by a total of 0.142 meq.m—2.wk—1 over a 150—wk study period. Over the same period, the output of bicarbonate ions from the watershed, as determined by weekly stream chemistry measurements, decreased by 0.162 meq.m—2. wk—1 after correction for a slight decrease in bicarbonate input. The output of sulfate, nitrate, ammonia, and dissolved organic matter all increased significantly. These increases are not enough to constitute a major change in watershed mass balance, but the nitrate and ammonia changes in particular could be important to the stream biota because of the low background levels of inorganic nitrogen. Output of calcium, magnesium, sodium, potassium, phosphate, and hydrogen ions showed no significant individual trends, but there is some evidence of a decrease in total cation output. It is postulated that essentially all of the hydrogenon ions entering in the form of acid precipitation combine with bicarbonate ions in the soil, and this accounts for the reduction in bicarbonate output of the watershed. This hypothesis is well supported by the match between rates of change in hydrogen ion input and bicarbonate output. Since carbonates are not present in the soil, a combination of acid with bicarbonate would lead to the production and release of free CO2 in amounts equivalent to the acid which is neutralized. Acidification of precipitation thus appears to cause a stoichiometric reduction in bicarbonate output and smaller but potentially important shifts in output of other ions as well.
An Experimental Study of Dispersal in the California Ground Squirrel
Authors: Dobson F. Stephen
Published: May 2006

Previous studies suggest three hypotheses to explain the importance of dispersal in small mammal populations: (1) regulation of density, (2) promotion of outcrossing, and (3) avoidance of competition for mates. These hypotheses were examined in an experimental study of the California ground squirrel (Spermophilus beecheyi). One ground squirrel colony was supplied with supplemental food for 3 mo, while two other colonies were monitored for reference. More adult ground squirrels moved to the supplemented colony than to the reference colonies. All young males disappeared from their natal colonies, even on two areas with different adult sex ratios (.09 and .56 male per female). Most young females remained in their natal colonies through the last month of the study. More young male immigrants were trapped at a reference colony than at the supplemented colony. More young females moved to the supplented colony than to the reference colonies; both via exploratory visits from nearby colonies and by immigration. All young resident males of the colony nearest to the supplented colony disappeared from both colony areas. The supplemented colony received visits from several young females who resided at the nearest adjacent colony. Eleven of these females took up a regular "commute" between their natal colony and the supplemental food. These results support the importance of the regulation of density relative to critical resources via young female dispersal, and the promotion of outcrossing via young male dispersal.
Structure and Primary Productivty of Lamto Savannas, Ivory Coast
Authors: Menaut J. C. , Cesar J.
Published: May 2006

Lamto savannas (Ivory Coast) are characterized by the heterogeneity of their structure and by their dynamic evolution towards forest. Life—forms and phenological cycles of herbs, shrubs, and trees reflect the constraining factors of the environment. Biomass and productivity are largely dependent on soil and climate. The specific cycles of above— and belowground biomass allow an estimate of the primary productivity. Production of shrubs and trees, obtained from size—biomass correlations and growth measures, is compared with herb production to give an insight into the ecological balance of the savanna communities.
A 19‐Year Study of Microtine Population Fluctuations Using Time‐Series Analysis
Authors: Garsd Armando , Howard Walter E.
Published: May 2006

This report involves time—series statistical analysis (including concurrent physical and community variables) of the population dynamics of 4737 voles (Microtus californicus) trapped over 19 yr while emigrating from two study enclosures on a Northern California grassland. Population fluctuation of voles, as documented in the literature as well as in this study, generally cannot be described by periodic or regularly cyclic equations, but rather are either random or occasionally pseudoperiodic where autoregressive correlation explains irregular cycles on the basis of the population's previous demographic history. For these two California vole populations, an autoregressive component accounted for approximately a third of the total variability in the population, while random extrinsic environmental variation explained almost all of the remaining variation. Weather played a key determinant role, influencing microtine populations both directly, and indirectly through an effect on vegetation. The distinction between periodic, pseudoperiodic, and random fluctuations in vole populations, and indeed in wildlife populations in general, cannot be dismissed as merely a question of semantics, because each entails a specific ecologic interpretation. The demographic characteristics of microtine rodents, although fluctuating more dramatically, were similar to those of other rodents.
Ecological Consequences of Foraging Mode
Authors: Huey Raymound B. , Pianka Eric R.
Published: May 2006

Desert lizards are typically either widely foraging or sit—and—wait predators, and these foraging modes are correlated with major differences in ecology. Foraging mode is related to the type of prey eaten by lizards. Widely foraging lizards in the Kalahari desert, the Western Australian desert, and the North American desert generally eat more prey that are sedentary, unpredictably distributed, and clumped (e.g., termites) or that are large and inaccessible (inactive scorpions) than do sit—and—wait lizards. In contrast, sit—and—wait lizards eat more prey that are active. Foraging mode also appears to influence the types of predators that in turn eat the lizards. For example, a sit—and—wait snake eats predominately widely foraging lizards. Crossovers in foraging mode thus exist between trophic levels. Widely foraging lizards may also encounter predators more frequently, as suggested by analyses of relative tail lengths; but tail break frequencies are ambiguous. Daily maintenance energetic expenditures of widely foraging lizards appear to be about 1.3—1.5 times greater than those of sit—and—wait lizards in the same habitats, but gross food gains are about 1.3—2.1 times greater. Widely foraging species also have lower relative clutch volumes, apparently in response to enhanced risks of predation. Foraging mode within one species varies with changes in food availability. Physiology, morphology, and risk of predation might generally restrict the flexibility of foraging mode. Because foraging mode constrains numerous important aspects of ecology, any general model of foraging velocity must be complex.
The Relationship between Selectivity and Food Abundance in a Juvenile Lizard
Authors: Stamps Judy , Tanaka Sanford , Krishnan V. V.
Published: May 2006

Several theoretical models of foraging behavior predict relationships between the relative abundance of a food item and a forager's selectivity for that item. Prey switching models predict that selectivity for items will be positively related to their relative abundance. Optimal foraging models based on energy optimization predict a non—negative correlation between selectivity and the abundance of valuable food items. Optimal foraging models based on nutrient constraints predict that selectivity for items should be negatively related to their relative abundance for all nutritionally important food items. The relationship between selectivity and relative abundance was investigated in the field in a juvenile lizard, Anolis aeneus. In each of 11 periods spanning the wet and dry season, sweep samples and stomach contents yielded data on selectivity, the relative and absolute abundance of different prey types in the environment, and the total abundance of food in the environment. The results tend to confirm the optimal foraging models based on nutrient constraints. All of the six important prey types eaten showed a negative correlation between selectivity and relative abundance; for four taxa the relationship was significant. In the case of four taxa, juveniles tended to eat the same proportion of the prey type regardless of its relative abundance in the habitat. In two other cases juveniles tended to eat proportionally less of a prey type as the relative abundance of that type increased in the environment. The absolute abundance of prey types also had a negative correlation with selectivity (significant for the two most frequently eaten prey types). Total food abundance was the most important determinant of selectivity in only one prey type; lizards ate more ants when food abundance was low. It is suggested that energy optimization may be relatively low priority for small ectothermic insectivores such as Anolis aeneus juveniles. Low energy demands, a relative abundance of suitable prey sizes in the environment, and low search costs may allow such animals to feed more like herbivores than like insectivorous birds or mammals.
Photosynthetic Dynamics in Varying Light Environments: A Model and Its Application to Whole Leaf Carbon Gain
Authors: Gross Louis J.
Published: May 2006

The light environment of a plant microsite can be highly dynamic with sunflecks lasting from seconds to minutes in length. Whole leaf photosynthetic response to such variations is complex and species—specific. A mathematical model based on a single enzyme pool is derived to mimic leaf response in varying light. The model is used to analyze carbon gain in Fragaria virginiana. I find that sunflecks can be responsible for an appreciable proportion of leaf carbon gain throughout a day, especially under light—limited conditions. Model results also indicate that the standard methods of estimating carbon gain in varying light using steady—state photosynthetic rates often give overestimates.
The Effect of Shade and Competition on Emigration Rate in the Ant Aphaenogaster Rudis
Authors: Smallwood Judith
Published: May 2006

Aphaenogaster rudis is a common ant in eastern United States forests that exhibits a high rate of colony relocation to new nest sites, even in the absence of nest disturbances. Field and laboratory experiments were conducted to determine if competition or reduced nest isolation, which acts to reduce internal nest temperature, could act as cues triggering colony emigrations. The field experiments tested the effect of increased food supply and artificial shade on the emigration rate. Laboratory experiments tested the effect of increased aggressive encounters with another ant species on emigration rate. Reduction in nest isolation resulted in a dramatic increase in the probability of emigration. Competition resulted in nest relocations only when it involved the invasion of the A. rudis nest site by another ant species. Changes in the amount of available food had no demonstrable effect on the probability of relocation although such changes did affect the intensity and direction of foraging activity. Seasonal trends in emigratory behavior were also observed. Emigration rate in A. rudis reached a maximum in midsummer. Also, the effect of artificially shading nests on emigration rate was the greatest in early summer and significantly less in spring and late summer.
Nonpyrogenous Climax Lodgepole Pine Communities in Yellowstone National Park
Authors: Despain Don G.
Published: May 2006

Climax lodgepole pine (Pinus contorta var. latifolia) stands are demonstrated. Size—class distribution fits a negative exponential curve, with size closely correlated to age. Maintenance of this climax does not appear to be dependent on fires. Such stands cover extensive areas in the park and may constitute a lodgepole pine zone.
Seasonal Variation in Plant‐Insect Associations: Utilization of Solanum Dulcamara by Leptinotarsa Decemlineata
Authors: Hare J. Daniel
Published: May 2006

In laboratory studies, Solanum dulcamara (nightshade) is one of the better host species for survival and growth of the Colorado potato beetle, Leptinotarsa decemlineata. The dynamics of L. decemlineata on S. dulcamara in the field, however, are far different than would be predicted from laboratory results. Therefore, a number of experiments were performed to determine the suitability of S. dulcamara for L. decemlineata under seasonal, field conditions. Field experiments showed that between 40 and 67% of first—generation adult females entered diapause without reproducing when fed S. dulcumara as both larvae and adults, although no adults entered diapause when fed S. tuberosum in both life—stages. Dispersal by first—generation adults from S. dulcamara was not observed in mark—recapture experiment. Survival of L. decemlineata on S. dulcamara did not differ significantly from survival on S. tuberosum during the part of the season corresponding to the development period of first—generation larvae. Survival on S. dulcamara was two—thirds lower during part of the season corresponding to the development period of the second—generation larvae, however. Emergence mass and larval development time varied less over the season on S. dulcamara than did survival. Analyses of extractable leaf protein, free amino acids, and glycoalkaloids showed significant seasonal variation in the concentrations of these S. dulcamara phytochemicals which are known to affect L. decemlineata feeding growth and survival. Multiple regression analyses between phytochemical concentration and larval survival showed that survival was significantly] positively associated with leaf nutritional quality (extractable protein and one free amino acid) during the first generation, and significantly negatively associated with leaf glycoalkaloid content during the second generation. Thus the seasonal variation in the suitability of S. dulcamara for L. decemlineata survival was most strongly associated with the two seasonally most variable S. dulcamara phytochemical factors. The unique and independent contribution of variation in either one to the variation in L. decemlineata survival, however, could not accurately be predicted without considering the simultaneous, independent variation in the other.
Noncanonical Distributions of Commonness and Rarity
Authors: Preston Frank W.
Published: May 2006

Some reported counts of species abundances, when tallied by octaves or other appropriate intervals, do not conform at all well to the expected normal (lognormal) distribution, but the departures therefrom seem to be by no means systematic or consistent. In the present paper we examine briefly two examples: The Audubon Christmas Bird Counts, and the counts of diatoms in freshwater streams. In some cases the departure may be due to defective, nonrandom, sampling; in others to using more than one method of sampling and then confounding the samples; in still others the sampling may be satisfactory, but the "universe" that is sampled may itself be a hybrid one, two universes (or more than two) interpenetrating one another. In the tropics the distribution of birds is lognormal but not canonical. Here the explanation must be different. The sigma values are far too low. I call these "congested" distributions. Biologically it may mean that there are more species than niches, a presumably unstable situation, possibly arising from recent (Pleistocene?) excessive speciation. Apparently some problems exist that deserve examination.
Soil Moisture Relations in the Southern California Chaparral
Authors: Ng Edward , Miller Philip C.
Published: May 2006

Contrary to previous studies of vegetation cover and environment, soil moisture was greater on a south—facing slope than on the opposite north—facing slope in southern California chaparral. Vegetation cover on the north—facing slope (mixed chaparral) was greater than the cover on the south—facing slope (Adenostoma chaparall). Precipitation on the two slopes was the same. The soil moisture profiles were analyzed to estimate soil moisture losses due to subsurface drainage, surface evaporation, and transpiration. Subsurface drainage was greater on the south—facing slope. Evaporation was greater on the south—facing slope, but transpiration was greater on the north—facing slope. The greater vegetation cover and drier soils on the north—facing slope are probably related to the drought—resistant nature of vegetation in this mediterranean climate.
Vesicular‐Arbuscular Mycorrhizae Affect Lowland Tropical Rain Forest Plant Growth
Authors: Janos David P.
Published: May 2006

In experiments with plants grown in pots, vesicular—arbuscular mycorrhizal increased seedling growth of 23 to 28 species from a lowland tropical rain forest region. Mycorrhizae improved survival in six species and cotyledon retention in five species. Mycorrhizae also increased the size of bacterial nodules and the proportion of nodulated plants among three leguminous species. Growth of seedlings lacking mycorrhizae slowed greatly or ceased after attainment of sizes correlated with average seed dry mass. Removing cotyledons from individuals of two species that are dependent on mycorrhizae, however, did not increase their response to inoculation. Thus, seed reserves are important for mycorrhiza formation as well as for seedling growth before infection. Large seeds are advantageous to plants that depend on vesicular—arbuscular mycorrhizae because they provide mineral reserves upon which the seedling can draw while awaiting infection. Seedlings of some species could not grow without mycorrhizae, but inoculation did not affect the growth of other species. Species that are least dependent on mycorrhizae have light seeds and colonize disturbed habitats.
Energetic Consequences of Sexual Size Dimorphism in Nestling Red‐Winged Blackbirds
Authors: Fiala Kent L. , Congdon Justin D.
Published: May 2006

The energy budget of nestling Red—winged Blackbirds (Agelaius phoeniceus) was determined using doubly labeled water (3HH18O) to measure field metabolic rate (FMR) and body component data to measure growth energy. Sex—specific measurements permitted the evaluation of the effects of this species' substantial sexual size dimorphism on FMR and total energetics. FMR averaged CO2 release of 5.12 mL°g—1°h—1, or 0.129 kJ°g—1°h—1, with no significant differences between the sexes. Daytime FMRs of CO2 production (5.34 mL°g—1°h—1) were higher, but not significantly so, than nighttime FMRs (4.45 mL°g—1°h—1). Water influx averaged 0.95 mL°g—1°d—1, with daytime rates (1.22 mL°g—1°d—1) significantly higher than nighttime (0.40 mL°g—1°d—1) rates. Total assimilated energy from hatching to fledging was 1014 and 797 kJ for male and female nestlings, respectively. The sexual differences in total energetics reflected differences in body size of the nestlings and suggest that there is a greater cost to the parents in raising males than in raising females.
Population Dynamics of a Pernicious Parasite: Density‐Dependent Vitality of Red Pine Scale
Authors: McClure Mark S.
Published: May 2006

The relationships between biotic and climatic factors and three parameters of fitness (survival, developmental rate, fecundity) and population density were examined for the exotic red pine scale, Matsucoccus resinosae (Homoptera: Margarodidae), in a plantation of red pine, Pinus resinosa, in Connecticut, USA, over a period of population increase and decline from 1975 to 1980. When scale density was relatively low and injury to trees was minor, measures of fitness were not correlated with density. However, when density increased markedly, each measure of fitness was significantly negatively correlated with scale density. Also, as scale density increased so too did injury to trees indicated by an increasing percentage of branches exuding resin. A greater percentage of nymphs dispersed and died as branches became resinous and unsuitable for colonization. Even though scale density decreased sharply after 1977, survival, developmental rate, and fecundity continued to decline, indicating that deterioration of red pine as a host was progressive and irreversible. The scale killed all trees in the plantation within 7 yr of its initial colonization. The single most important factor leading to the collapse of the red pine scale population was change in the magnitude of overwintering mortality incurred by nymphs. Drastic reductions in scale numbers during winter more than offset population growth during the rest of the year and resulted in overall annual population decline. Steadily increasing overwintering mortality from year to year was due to density—dependent reduction in developmental rate which resulted in nymphs overwintering in a developmental substage incapable of surviving even relatively mild winter temperatures. Natural enemies were not important to the population dynamics of M. resinosae. The only such species encountered, the cecidomyiid fly Lestodiplosis nr. grassator, consumed only 5—7% of the scale ovisacs in each year, showing no response to the changes in scale population density.
Functional Response and Fitness in a Generalist Filter Feeder, Daphnia Magna (Cladocera: Crustacea)
Authors: Porter K. G. , Orcutt J. D. , Gerritsen J.
Published: May 2006

The functional response of an organism is often assumed to maximize its fitness. We examined the relationship between functional response and body growth, survivorship, and reproduction in Daphnia magna under controlled and comparable conditions. In a previous study we determined that D. magna exhibits a Holling Type II functional response with an asymptotic increase in ingestion rate with increasing food concentration to a maximum rate at an incipient limiting concentration of °104 Chlamydomonas reinhardi cells/cm3 (measured as carbon, 0.2 mg/L) and that observed feeding activity does not follow the predictions of energy optimization models. In this study, we determined the fitness response for cohorts of D. magna (n = 20—30) at 0, 103, 104, 105 and 106 Chlamydomonas reinhardi cells/cm3 using life table methods. Most parameters indicative of fitness (e.g., body growth, fecundity, survivorship, r, and R0) were maximal at 105 cells/cm3 (2.0 mg/L). The optimum food concentration for growth and reproduction remained at 105 cells/cm3 when cohort life spans were truncated in a simulation of mass mortality due to predation or environmental deterioration. The fitness optimum occurred above the incipient limiting concentration and below the maximum food concentration encountered in nature. These appear to be "suboptimal" behavioral and reproductive responses. However, reproductive models of parthenogenesis and resting egg formation along with these feeding, growth, and reproductive responses suggest that Daphnia track the environment in that they are adapted for rapid population increase and for recovery from mass mortality in cyclical environments in conditions for optimal growth that can be expected to reoccur but are of highly variable duration.
The Structure of Guppy Life Histories: The Tradeoff between Growth and Reproduction
Authors: Reznick David
Published: May 2006

This study reports on two experiments characterizing the relationship between growth and reproduction in guppies. The first experiment compares the growth of reproducing and nonreproducing siblings raised on controlled levels of food availability. Nonreproducing females have significantly more energy in somatic tissues. The bulk of this energy is in fat tissues. Standard length and "protein" do not differ significantly. The extra energy in nonreproducers is therefore devoted predominantly to energy storage, as opposed to somatic growth. A comparison of total production, however, reveals that most of the energy "saved" by not reproducing does not appear in somatic tissues. The cause of this loss is unknown. The second experiment compares the somatic growth of different stocks of Trinidadian guppies which had previously been demonstrated to devote different quantities of energy to reproduction (Reznick 1980). Increases in the amount of energy devoted to reproduction were matched by decreases in the energy devoted to somatic tissues. Furthermore, all of the stocks have equal total production. These fish are therefore equally efficient in converting food into biomass but differ in how this biomass is allocated to growth and reproduction. A key assumption of the theory predicting the impact of certain forms of selection on life history evolution is that an increase in the resources devoted to current reproduction reduces the future capacity to reproduce. Because fecundity is directly proportional to size in guppies, the reported tradeoff between growth and reproduction satisfies this assumption. However, such theoretical treatments concentrate solely on the evolution of reproductive effort. Because growth and reproduction are complementary, it is equally plausible, especially for the guppies used in these experiments, that growth rate evolved, rather than reproductive effort.
Intertidal Zonation of Barnacles: The Influence of Planktonic Zonation of Larvae on Vertical Distribution of Adults
Authors: Grosberg Richard K.
Published: May 2006

The nonoverlapping vertical distributions of sessile species in the marine intertidal are usually considered to result from two interacting factors: (1) broadly restricted settlement of juveniles in the vertical horizon, and (2) postsettlement mortality which affects species differently. Investigated here is the role of larval behavior in molding the zonation of the acorn barnacles Balanus glandula and Balanus crenatus. I document the vertical distributions of: (a) adults, (b) newly settled spat, and (c) planktonic cyprid larvae. The data show that the vertical distribution of adults is a reflection of the vertical zonation of cyprids in the plankton and settlement patterns of spat. Although postsettlement mortality and substratum selection occur, presettlement behavior can strongly influence vertical zonation of sessile organisms.
Seed and Patch Selection by Galapagos Ground Finches: Relation to Foraging Efficiency and Food Supply
Authors: Schluter Dolph
Published: May 2006

I investigated the diets of three species of Darwin's ground finches (Geospiza Gould) on Isla Pinta, Galapagos. Diet choice was examined in relation to both the finches' handling efficiency on seed types and the profitability of patches. Handling efficiency on different seed types was related to the size of the finch species. Correspondingly, the two larger finch species generally ignored small seeds with low rewards, and the two smaller finches avoided feeding on seeds apparently too large and hard to crack. In G. fuliginosa, the smallest species, seed choice was correlated with seed depth within the range of seed sizes actually consumed. In addition, the proportion of its diet made up of given seed types was correlated with the profitability of patches within these seeds occurred. Certain seed types providing low individual returns per unit handling time were highly profitable by virtue of their high density within patches. Conversely, large search times between valuable seeds diminished the relative profitability of respective patch types. Diet breadth of G. fuliginosa was investigated in relation to seasonal changes in food supply. Results on seed choice in relation to relative densities of seed types were ambiguous, but a slight shift toward feeding on smaller seeds in the dry season was detected. However, the shift could be explained by the greater profitability of patches of the small seeds in this season. These finches did not generalize their use of patch types, despite a large seasonal decline in food abundance. This result contradicts a prediction of optimal foraging theory. Serval possible explanations for this are discussed, including an hypothesis that when food was abundant finches selected a diet that was less than maximally efficient.
Randomness, Area, and Species Richness
Authors: Coleman Bernard D. , Mares Michael A. , Willig Michael R. , Hsieh Ying-Hen
Published: May 2006

Thorough censuses have been made of breeding birds on islands in Pymatuning Lake, a reservoir at the Pennsylvania—Ohio border. Analysis of the censuses yields the conclusion that for these islands the variation of the number of resident avian species with island size is that which one would expect if the birds were distributed randomly, with the probability of a breeding pair residing on an island proportional to the area of the island and independent of the presence of other pairs. This type of random placement of individuals can yield species—area relations which differ from those commonly employed for analysis of biogeographic data.
Reconstrution of a Presettlement Giant Sequoia‐Mixed Conifer Forest Community Using the Aggregation Approach
Authors: Bonnicksen Thomas M. , Stone Edward C.
Published: May 2006

The presettlement state of a giant sequoia—mixed conifer forest community in the Redwood Creek watershed, Kings Canyon National Park, is reconstructed using in backward projection in time of plant aggregations. The most conspicuous change in the forest community from the presettlement condition (°1890) was a general increase in the area of aggregations dominated by polesize trees and mature trees, and a corresponding decrease in the area of aggregations dominated by sapling— and seedling—size trees. Aggregations dominated by white fir had both the greatest decline in area for sapling and seedling aggregations and the greatest increase in area for large mature, mature, and pole aggregations of any species in the watershed. The area of aggregations dominated by shrubs also declined, with manzanita aggregations showing the largest loss in area for any shrub species. Hardwoods were also a far more important part of the presettlement forest community than they are today.
Patterns in the Species Composition and Richness of Fish Assemblages in Northern Wisconsin Lakes
Authors: Tonn William M. , Magnuson John J.
Published: May 2006

Fish assemblage structure, and factors and mechanisms appearing important in the ecological maintence of these structures, were examined for 18 small lakes in northern Wisconsin during summer and winter. The study was focused around the following questions. Are there discrete, repeatable groups of fish assemblages? If so, are they temporally stable? What are the relations between fish assemblage structure and habitat complexity, physical disturbance, biotic interactions and the insular nature of small lakes? A comparative approach was used to generate hypotheses and propose explanations concerning the roles of these factors in structuring the assemblages. Multivariate classification, ordination, and discriminant analyses helped discern two assemblage types: Umbra—cyprinid and centrarchid—Esox. Each had a distinctive species composition and seasonal change in composition. Environmental characteristic of the lakes occupied by each assemblage type also differed consistently. The type of assemblage present in a lake appeared related to oxygen concentrations in winter, interacting with the availability of refuges from either a severe physical environment (low oxygen during winter) or from large pisvivores. Centrarchid—Esox assemblages occurred in lakes with high winter oxygen levels, and also in lakes with low oxygen if a stream or connecting lake could provide a refuge from these conditions in winter. When no refuge was present, low winter oxygen lakes lacked piscivorous fishes, but contained Umbra—cyprinid assemblages. The relationships between species richness in summer and environmental factors were generally similar for the two assemblage types, but the relative importance of individual factors differed. In winter, richness relationships in centrarchid—Esox assemblages for most environmental factors were reversed from those of summer. No significant seasonal change occurred in the Umbra—cyprinid assemblages. Habitat complexity factors, particulary vegetation diversity, were significantly related to summer species richness in both assemblage types. Lake area was also related to summer richness for both types, but the slope of the species—area regression was much steeper for Umbra—cypinid assemblages than for those in centrarchid—Esox lakes. Species richness relationships with winter oxygen concentration were negative in both seasons in Umbra—cyprinid lakes, but the relationship was positive for centrarchid—Esox assemblages in winter. A measure of lake connectedness was related to summer richness in centrarchid—Esox lakes. These patterns suggest that centrarchid—Esox assemblages are in ecological equilibrium but that a disturbance—induced disequilibrium occurs in Umbra—cyprinid assemblages.