bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical Evaluation of the Jackknife Estimate of Diversity when Using Quadrat Samples
Authors: Heltshe James F. , Forrester Nancy E.
Published: May 2006

The jackknife estimation procedure is used to estimate Brillouin's and Simpson's indices of diversity when sampling is done by selecting quadrats. Using simulated data, a sampling plan is set up to study effects of quadrat size, sample size, and sampling area. The estimates are evaluated by estimating bias, standard error, and mean square error, and by comparing expected 95% confidence interval coverage with observed 95% confidence interval coverage. Smaller quadrats tend to give less biased and smaller variance estimates of Brillouin's index. The jackknife estimate of Simpson's index is unbiased using quadrat samples, but the estimates of standard error appears to be an overestimate for large samples, causing overcoverage (>95%) for observed confidence intervals.
Competition among Larval Dragonflies: A Field Enclosure Experiment
Authors: Johnson Dan M. , Crowley Philip H. , Bohanan Robert E. , Watson Charles N. , Martin Thomas H.
Published: May 2006

Tetragoneuria cynosura and Celithemis elisa dominate the larval dragonfly assemblage of Bays Mountain Lake, Tennessee, USA, where they coexist in the extensive submersed macrophyte and allochthonous detritus habitats despite relatively high overlap in both seasonal occurrence and diet. Field enclosure experiments, designed to determine the intensity of intraspecific and interspecific competition at approximately natural densities, were conducted during September 1981 and April 1982. Survival rate for both species was dependent on intraspecific density in September, and that for C. elisa was also affected by the presence of T. cynosura. These effects are attributed to interference (encounter) competition rather than to exploitation (consumption) competition. The mechanism of competition seems to be predation by larger larvae on smaller larvae. No evidence of either exploitation or interference competition was found in the April experiment.
A Geochemical Perspective on the Causes and Periodicity of Mass Extinctions
Authors: Moses Carl O.
Published: May 2006

Environmental change, including changes in biogeochemical cycles, climate, and sea level, is the primary cause of extinctions that result from mechanisms external to evolutionary dynamics. Evidence that extraordinary tectonism, including volcanism, sea—floor spreading, and eustatic sea level changes, took place prior to and at the Cretaceous–Tertiary boundary (K–TB) is sufficient to account for the environmental changes that led to mass extinctions. A coincident impact of an extraterrestrial object cannot be conclusively ruled out. Some mineralogic evidence suggests a scenario that includes impacts, but this does not rule out tectonism. The K–TB is certainly the best studied and most often discussed extinction boundary, but study of other extinction episodes and other potential extinction causes will now shed more light on mechanisms than continued study of the K–TB.
Repeated Reversals During Spatial Competition Between Corals
Authors: Chornesky Elizabeth A.
Published: May 2006

On many tropical reefs, competition for space among sessile animals is common and is generally thought to influence the population and community ecology of reef corals. A 20—mo photographic study revealed frequent temporal reversals in the observable outcome of interspecific spatial competition between some of the most abundant Caribbean corals. These reversals apparently were not due to seasonal changes or to other environmental effects on relative competitive ability. Rather, they resulted from inherent differences between the competing species in response time and competitive mechanism employed. Specifically, encounters between individuals of Agaricia agaricites and Porites asteroides or between individuals of A. agaricites and Montastraea annularis are characterized by a repeated cycle of attack by one opponent using digestive filaments, and subsequent retaliation by the initially wounded coral when it develops and deploys fighting tentacles. The resulting bilateral injuries increase the distance separating competing colonies. Active competition then ceases temporarily until the corals grow back into proximity, and the cycle of reciprocal injury is re—initiated. This phenomenon has several important implications. Because the advances and retreats occurring along competing coral margins are temporary, short—term or infrequent observations might misleadingly suggest one or the other opponent was continuously "winning" these interactions. Similarly, the distances competing edges advance and retreat during these repeated reversals are small (millimetres). If observed at too great a spatial scale, these dynamic competitive interactions might incorrectly appear to be a case in which adjacent animals have simply ceased growth along their common margin (i.e., a standoff). Over time, interactions involving repeated reversals result in no or only a very slow exchange of spatial resources, and may potentially enhance the coexistence of competing colonies. Nevertheless, despite having little direct effect on the occupation of space by competitors, ultimately such interactions may indirectly influence coral distributions by costing competitors reduced fecundity, growth, or survivorship.
Contrasting Windstorm Consequences in Two Forests, Itasca State Park, Minnesota
Authors: Webb Sara L.
Published: May 2006

Thunderstorm winds (°25—35 m/s) often damage scattered trees in northern Minnesota forest. Following one moderate windstorm on 3 July 1983, I surveyed damaged trees within two Itasca Park study areas (1) to identify mortality patterns and their correlates, (2) to evaluate windstorm consequences for shade—intolerant species, and (3) to investigate formation of light—gaps. Risk of direct wind damage was predicted best by tree size (in both stands) and either tree species (in a Pinus/Acer stand) or species wood strength (in a Pinus/Abies stand). However, the overall risk or mortality, combining direct with damage and damage from falling trees, was more complex, Tree mortality in the Pinus/Acer study area was related to tree size, species, species wood strength, and incidence of species—specific fungal pathogens. Mortality in the Pinus/Abies study area, where many understory trees were killed, was not predictable on the basis of tree size, but mortality risk was affected by tree species and species wood strength (data on fungal pathogens were unavailable for this stand). Within most populations, the size distribution off windstruck trees differed from the population size distribution. However, mortality risk, including that from falling trees, increased with tree size only for Populus tremuloides. In one study area, smaller trees were most vulnerable within the Picea and Pinus strobus populations. The difficulty of generalizing about windstorm consequences is illustrated by large intraspecific variation in amount of damage between different populations of Betula papyrifera. Pinus resinosa, and Pinus strobus. For shade—intolerant species expected to benefit from disturbance, windstorm consequences differed in the two stands, despite shared postfire origins and several tree species in common. In the Pinus/Acer forest, heavy mortality to shade—intolerant Populus tremuloides, Pinus resinosa, and Pinus strobus combined with a well—developed, windfirm understory and infrequent light—gap formation to benefit existing shade—tolerant, windfirm Acer saccharum and tall shrubs. In the nearby Pinus/Abies forest, the windstorm produced more regeneration opportunities for shade—intolerant species (Betula papyrifera, Populus tremuloides, Fraxinus pennsylvanica), because the shade—tolerant understory species of this stand (Abies balsamea, Picea glauca) were more heavily damaged, and because more light—gaps formed, although such light—gaps were small relative to published gap size thresholds for tree establishment. Differences between the two communities in their responses to the same storm event appear to result from differences in forest structure and differences in the windfirmness of shade—tolerant understory taxa.
Lifetime Impacts of Herbivory for a Perennial Plant
Authors: Doak Daniel F.
Published: May 2006

In spite of widespread interest in the impact of herbivores on plants, few studies have addressed the lifetime consequences of attack for perennial plants. I have addressed this issue by studying the interaction between dwarf fireweed, Epilobium latifolium, and its principal herbivore in south—central Alaska, Mompha albapalpella (Momphidae Lepidoptera). Fireweed is a long—lived, clonal herb that grows as clumps of connected shoots, and suffers from chronic attack by Mompha. I used a Markov Process (transition matrix) model, in combination with 3 yr of experimental data, to simulate expected changes in size and fecundity for clumps growing under different frequencies and intensities of damage. These analyses indicate that fireweed suffers fairly little reduction in growth from low intensity attacks, even if these attacks are quite frequent, but that high intensity attacks suppress growth even at very low frequencies. Damage greatly reduces seed production and also increases the inequality of seed output from different clumps. Because the patterns in which damage is meted out are crucial in determining herbivory's effects, kniwong only average amounts of tissue loss will be insufficient to predict the impacts of herbivory. My results show that short—term impacts of herbivory canopy simply be extrapolated to longer time spans; a quantitative, modeling approach is necessary to understand herbivory's complicated effects.
Variation in the Vulnerability of Prey to Different Predators: Community‐Level Consequences
Authors: Power Mary E. , Marks Jane C. , Parker Michael S.
Published: May 2006

Midge larvae (Diptera, Chironomidae) that weave filamentous algae into retreats of tufts, are dominant primary consumers in a river food web. In a previous study, densities of tuft—weaving midges increased in the presence of large fish. In the absence of large fish, midges decreased as densities of predatory invertebrates built up, and higher standing crops of algae were maintained. To examine the mechanisms underlying these dynamics, we compared the vulnerability of tuft—weaving midges (naked or in algal tufts) to fish and predatory invertebrates, in field and laboratory experiments. When midges were exposed for 1 h in the river to fish, 15 out of 15 midges in tufts survived, while 15 of 15 naked midges were consumed. Tufts afforded only partial protection to midges exposed to invertebrate predators, however. After 1 h, enhancement of survivorship by tufts was moderately significant for midges exposed to aeshnids, and insignificant for midges exposed to lestids and naucorids. We suggest that the vulnerability of tuft—weaving midges to invertebrate predators, and their relative invulnerability to fish, sets the stage for trophic cascades observed in the system. Fish, by consuming small predators, release midges, which graze down algae. The strong effects of fish as fourth—level consumers would not be predicted from their diets, in which algivorous mayflies dominate (>60% of the insect biomass found in each of the two most common fish species). Nevertheless, fish in this food web act as fourth—level, rather than third—level, consumers because of the differential vulnerability of one guild of primary consumer, which, when released from predation, can suppress plants.
Niche Parameters and Species Richness
Authors: Fox Barry J.
Published: May 2006

This study examines how spatial niche parameters change as functions of species richness. The basis of the study was the partitioning of space by a community of small mammals in eastern Australian coastal heathland. Live—trapping was carried out in 13 habitat patches with two to seven coexisting species of small mammals on a 6.4—ha study area. Data from the 1st 2 mo of this 5—yr study are analyzed in detail. Spatial niche parameters were calculated using trapping stations as resource states. Mean niche breadth and mean niche overlap were negative functions of species richness while mean niche separation was a positive function of species richness. Spatial niche separation was estimated using nearest—neighbor analysis. Total spatial niche overlap increased to a peak and then decreased as the number of species increased. The field results were tested against two null hypotheses of noninteraction between species, one with and one without habitat selection, while a third considered the species—abundance effect using equally abundant species. The simulation values showed similar trends for the first three parameters and a continued increase for total overlap. However, field values had significantly steeper slopes, and parameter values at the extremities were usually significantly different form simulated values. Simulated niche parameters became independent of species richness when species were equally abundant, but showed increasing dependence as habitat partitioning and then microhabitat partitioning were introduced into the models. The results support Pianka's niche overlap hypthesis; mean overlaps were significantly higher than expected with a few species and significantly lower with many species, suggesting diffuse competition. Unsaturated patches showed an opposite effect, when space did not appear to be limiting, strongly implying that interspecific interactions play an important role in limiting the closeness of species packing in this community. Additional species are accommodated by significantly increasing mean spatial niche separation, thus decreasing mean spatial overlap. The rate of change in mean spatial niche breadth is not significantly different from the simulated rates.
Seasonal Patterns in Production and Drift of Gammarus Pseudolimnaeus in Valley Creek, Minnesota
Authors: Waters Thomas F.
Published: May 2006

The stream amphipod, Gammarus pseudolimnaeus Bousfield, was sampled monthly for five consecutive years, 1968—1973, in Valley Creek, Minnesota, USA, and seasonal patterns in production rate, drift, standing stock, and growth were observed. Several modifications of the instantaneous growth rate method were attempted, and one, the Length Increment Alternative, employing size—frequency historgrams (both in numbers and biomass) to determine instantaneous growth rates, was selected as the most accurate to estimate production at approximately monthly intervals. Production, drift, and growth correlated well in a pronounced seasonal periodicity, with maxima in the warm months. A serious siltation occurred about midway in the study, reducing the population standing stock, production, and drift. During the 1st 2 yr prior to the siltation, when the stream was in normal condition, daily production (dry mass) reached summer maxima of about 0.12—0.14 g/m2, and maximum drift about 120—220 g dry mass°d—1°m—3°s—1, both falling to zero, or near, in winter. Daily instantaneous growth rate reached maxima of about 0.03 in all years, with zero growth in winter. Annual dry mass production by the Length Increment Alternative was 271, 238, 123, 57, and 91 kg/ha for the 5 yr, respectively. Calculations comparing daily drift to production indicated that production rates were sufficient to provide the observed drift without the necessity of compensatory upstream migration.
Annual Experimental Evaluation of the Effect of Invasion History on Community Structure
Authors: Robinson James V. , Edgemon Michael A.
Published: May 2006

Fifty—four communities were developed from repeated introductions of 28 phytoplankton species in three different orders of invasion at three different rates. Variation in species richness values in these communities was assignable to invasion order, invasion rate, and the timing between interspecific invasions. Invasion rate was most influential, explaining 21.8—78.8% of the variation on any give date; invasion order never explained >4.3%, and timing explained between 19.7 and 74.9%. All three facets of invasion had significant effects. One of the low—rate invasion categories developed a unique community structure that was dominated by Chlamydomonas. Communities in this category were invulnerable to the invasion of many species and as a result had low species richness values. The relative abundance patterns of species in categories having low or moderate invasion rates but identical invasion orders clustered more closely to each other than they did to their high invasion rate counterparts. In this sense, invasion order is more influential where immigration rates are relatively low (e.g., on islands) than it is where dispersal from outside sources is high (e.g., on continents). Because invasion history was controlled, the methodology used here provides interpretable data concerning the potential importance of chance historical events that occur during community assembly. The data indicate that idiosyncrasies in community structure often may be explained on the basis of the random invasion patterns of organisms to different habitats.
Density‐Related Changes in Survival of Philopatric and Dispersing Kangaroo Rats
Authors: Jones W. Thomas
Published: May 2006

Seven years of mark—recapture data from a population of banner—tailed kangaroo rats (Dipodomys spectabilis) revealed lower survival of dispersing juveniles at high population density than at low density. Acquisition of the maternal burrow and food caches provided survival advantages of high density but not at low density. These differences were significant in both sexes, but they were more pronounced in females. A previous report found shorter dispersal distances at higher density. The present study shows that this pattern was due partially to a tendency to move less at high density, especially in males, and partially to lowered survival to maturity of individuals that dispersed at high density, especially in females. These results support the hypothesis that dispersing animals' chances of successful recruitment are inversely related to density, and that high—density saturated conditions favor philopatry over dispersal. Moreover, this effect of saturation on the advantages and frequency of philopatry was greater in females, the sex that is usually philopatric in mammals.
Sapling Diameter Growth in Gaps for Two Nothofagus Species in New Zealand
Authors: Runkle James R. , Stewart Glenn H. , Veblen Thomas T.
Published: May 2006

We quantified the effects of position within treefall gaps, gap size, and sapling size on sapling radial increment (most recent 5 yr, using tree cores) for two species of Nothofagus (southern beech) on the South Island, New Zealand (42°13' S). Mean radial growth rates of the species and characteristics of the gaps in which they occurred were similar. Based on regression analysis, stems (1.4—26 m tall) of both species grew faster in larger gaps than smaller gaps (canopy gap area range 16—528 m2) and larger stems grew faster than smaller ones, the latter more true of N. fusca than N. menziesii. N. fusca grew fastest near gap center; N. menziesii grew fastest south of gap center. Smaller stems of both species grew faster south of gap center and large ones faster at, or even north of, gap center. For all size classes, the optimum location for N. menziesii growth was further south than for N. fusca. N. fusca grew faster than N. menziesii near gap center; N. menziesii grew faster than N. fusca south of gap center. These results are intermediate between literature predictions of best growth in gap center (based on soil moisture, soil nutrients and diffuse radiation) and best growth near the south gap edge (based on direct beam radiation and without considering shading).
Predation by Didinium Nasutum: Effects of Predator and Prey Size
Authors: Hewett Steven W.
Published: May 2006

Experimental manipulation of the size of Didinium nasutum, a protozoan predator, feeding on large and small Paramecium species was used to examine the effects of predator and prey size on predator behavior and capture success. Didinum size is a function of prey size; large and small Didinium were obtained by conditioning predators on large or small prey species prior to experimentation. The predatory behavior of large and small predators feeding on large and small prey was monitored through an entire division cycle. Large Didinium had shorter handling times and encounter times on both sizes of prey than small Didinium. Large Didinium made more captures per division on either size of prey. Large prey required longer handling times, longer engulfing times, and were encountered more frequently than small prey for both sizes of predator. First captures were more difficult than subsequent captures for all predators. Small predators were more successful initially in capturing small prey than were large predators; first captures by large predators on small prey were particularly difficult. Encounter times, the number of encounters per capture, capture times, and handling times varied with the size of the predator and also varied within the division cycle of the predator. The effect of time within the division cycle may be due to increasing size as prey are captured and/or to adaptations to the specific prey species following initial captures. Didinium may adapt to new prey species through morphological changes in the oral apparatus, chemoreceptors, or extrusive organelles, in addition to shifts in size. That each size of Didinium had more successes per encounter on the size of prey to which it had been conditioned suggests that the size shift improves that aspect of the predatory behavior. However, other aspects (such as handling time and time to each encounter) show a clear advantage to large size. Large size also improves survival ability of Didinium under conditions of starvation (Hewett 1987). For large predators to maintain a large size on small prey would require a substantial increase in the division time. Selection forces favoring fast division rates, may impose restraints, making the size of Didinium on any prey species a compromise.
Compensatory Scope and Resource Allocation in Two Species of Aquatic Snails
Authors: Rollo C. David , Hawryluk Mark D.
Published: May 2006

The resource allocation strategies of the freshwater snails Stagnicola elodes and Physella gyrina were examined using artificial diets diluted to various degrees with cellulose. Even when nutrients were diluted by 50 or 75%, both species showed remarkable maintenance of their rates of assimilation (94 to 294% of controls) and production (82 to 140% of controls). This was mainly achieved by varying rates of feeding (148 to 397% of controls) and respiration (76 to 839% of controls). S elodes was twice as large as P. gyrina and had slower rates. The hypothesis that this endows S. elodes with greater compensatory scope (i.e., a greater range of response in feeding or respiration rates) was strongly supported. This observation has broad implications for theories of evolution and niche breadth. Particular attention was devoted to trade—offs between somatic and reproductive support. With 75% dietary dilution, the two species showed exactly inverse strategies. S. elodes supported growth more than reproduction (90 and 59% of controls, respectively), whereas P. gyrina supported reproduction over growth (116 and 38% of controls, respectively). Their strong compensatory ability suggests that these snails normally operate at submaximal rates that are homeostatically maintained. Shifts in resource allocation may be engaged as "anticipatory" safety measures, even before absolute shortages arise.
The Distribution of Marine Invertebrate Larvae Near Vertical Surfaces in the Rocky Subtidal Zone
Authors: Graham Krista R. , Sebens Kenneth P.
Published: May 2006

The realized dispersion patterns of marine invertebrate larvae were examined in the field for a range of larval types that differ in their potential for dispersal. Plankton samples were collected near three subtidal rock walls over a 2—yr period. Larvae to sessile invertebrates were identified and counted in each sample and analyzed for density differences among: (1) three distances from the rock surface; 1—5 cm, 1 m, and >200 m, (2) 1—5 cm above crustose coralline algae—covered surfaces and 1—5 cm over invertebrate—covered surfaces and, (3) 1—5 cm and 1 m from rock surfaces on days of high flow speed vs. days of low flow. Larvae with short dispersal times, such as ascidian tadpole larvae and hydroid actinula larvae, were more abundant 1—5 cm away from rock walls than 1 or >200 m away from rock surfaces. They were usually more abundant over invertebrate—covered surfaces than over crustose coralline algae—covered surfaces as well. Larvae with long planktonic dispersal times, but which were competent to settle (e.g., mussel pediveligers) were more abundant 1—5 cm away from rock walls than at 1 or >200 m away from rock walls. These larvae were often more abundant over invertebrate—covered surfaces than over crustose algae—covered surfaces also. Larvae with long planktonic dispersal times, but which were not competent to settle (e.g., Anomia veligers and mussel veliconcha—stage veligers) had similar densities at all distances from rock surfaces. These larvae occurred at similar densities over both invertebrate—covered surfaces and crustose algae—covered surfaces. Larvae that exhibited differences in density with distance from vertical walls, such as ascidian larvae, mussel pediveligers, and hydroid actinula larvae, were more thoroughly mixed into the mainstream flow away from rock surfaces on days of high flow compared to days of low—flow conditions.
Environmental Changes Affecting the Migratory Timing of American Shad and Sockeye Salmon
Authors: Quinn Thomas P. , Adams Dean J.
Published: May 2006

The rate of evolution and the scope of phenotypic plasticity can be assessed by studying the adaptation of an introduced population to a new habitat and the response of established populations to progressive environmental change. Adult American shad (Alosa sapidissima), and introduced species, and sockeye salmon (Oncorhynchus nerka), a native species, migrate up the Columbia River (northwestern United States) in late spring and early summer to spawn. Based on records from Bonneville Dam, the river's spring warming has occurred progressively earlier since ≈ 1950, coinciding with a reduction in spring discharge. The date when 50% of the shad migrated past the dam is correlated with this shift inthermal and flow regimes; they now ascend the river ≈38 d earlier than they did in 1938. However, the mean temperature that they experience has actually decreased by 1.8$deg;C in 45 yr, indicating that the change in their migratory timing has outstripped the rate of environmental change. The upriver migration of sockeye salmon is also earlier than in past years, but their change in time (≈6 d since 1949) lags behind the rate of environmental change, and they are now experiencing ≈2.5°C warmer temperatures than in past years. We hypothesize that the differences in response to changing environmental conditions between these species arise from differences in their migration patterns and early life histories. Shad spawn soon after they enter the river in its main stem where environmental conditions of the larvae will closely mirror those experienced by upstream—migrating adults. They may therefore have evolved a migratory pattern that allows greater behavioral response to environmental fluctuations than sockeye salmon, which spawn in distant locations many months after their upriver migration. Sockeye salmon migration may be more strongly controlled by innate responses to photoperiod, migrating at the time of year which is best on average because conditions in the lower river will not be indicative of those to be experienced by incubating embryos and juveniles.
Habitat Distributions of Wintering Sparrows: Foraging Success in a Transplant Experiment
Authors: Repasky Richard R. , Schluter Dolph
Published: May 2006

Why do birds partition habitats? Possible explanations include nonoverlapping food distributions, interspecific competition, and predation. If food limits distributions, species should forage most successfully in their preferred habitats and should experience poorer food intake rates elsewhere. These same predictions hold if species distributions are shaped by exploitative competition. We tested the foraging success hypothesis and exploitative competition hypothesis as explanations of the habitat distributions of Sage Sparrows (Amphispiza belli), Black—throated Sparrows (A. bilineata), and Dark—eyed Juncos (Junco hyemalis), which spend the winter in different habitats along an elevational gradient in the Sonoran Desert of southern California. Individuals of each species were transplanted between habitats in a portable aviary and observed while foraging on naturally occurring seeds. Predictions of the foraging success hypothesis and exploitative competition hypothesis were not confirmed. Only Dark—eyed Juncos achieved their highest foraging success in their preferred habitat. Black—throated Sparrows experienced nearly identical foraging success in all three habitats, yet are confined to only one of them naturally. Sage Sparrows foraged more successfully in habitats other than that in which they naturally occur. We conclude that immediate foraging gains do not explain habitat distributions of these birds, and that interference competition, predation, or other unknown factors are responsible. We contrast this finding with that seen in Galapagos finches in which bird distributions closely matched food supply.
Delayed Inducible Resistance in Mountain Birch in Response to Fertilization and Shade
Authors: Ruohomaki K. , Chapin F. S. , Haukioja E. , Neuvonen S. , Suomela J.
Published: May 2006

Delayed inducible resistance (DIR) is triggered by artificial or herbivore—caused foliar damage and is manifested as decreased performance of herbivore generation(s) feeding on the trees subsequent to the generation during which the damage took place. DIR is associated with increase in concentrations of foliage phenolics and decrease in nitrogen. The growth—differentiation balance hypothesis, and the carbon—nutrient balance (CNB) hypothesis contained in it, claim that DIR is caused by nutritional stress after defoliation of trees growing on nutrient—poor soils. In these environments, nutrient uptake limits plant growth more strongly than does photosynthesis; that is, carbon—based secondary metabolites (e.g., phenolics) are prone to accumulate. According to the CNB hypothesis, an excess of limiting nutrient(s) or reduced photosynthetic rate should lead to elimination of DIR. We tested this using same—aged Betula pubescens ssp. tortuosa trees of five open—pollinated families growing in a common arboretum in northernmost Finland. In addition to unmanipulated control trees, we had three nutritional treatments during three successive growth seasons: N—fertilization, PK—fertilization adding all nutrients except N, and shading to decrease carbon assimilation. Half of the trees in each treatment were artificially defoliated (50% leaf area) in the second study year, one year before the growth trial with geometrid (Epirrita autumnata) larvae. Tree growth measurements showed that N is the growth—limiting nutrient in our study area. N—fertilization and shading of the trees affected foliage chemistry generally as proposed by the CNB hypothesis. For example, they reduced foliar concentrations of total phenolics and condensed tannins. The birch families differed significantly in foliage chemistry, suggesting genetic differences, but the differences were not associated with fertilizations, shading, or defoliation of the trees. Contrary to fertilizing—shade treatments, changes in leaf chemistry and E. autumnata performance caused by defoliation were not consistent with the CNB hypothesis. For example, defoliation caused significant DIR irrespective of N—fertilization or shading. There were no significant differences among the birch families in performance of the moth larvae or in effects of fertilization, shade, or defoliation on larval performance. These responses to defoliation contrast with those of some other studies, especially those on the Betula resinifera—Rheumaptera hastata system in Alaska, which provide clear support for the CNB as an explanation of DIR. We find methodological differences to be an unlikely explanation for the different results but are unable to propose any single mechanism that will explain the diverse plant responses.
Assessment of Preference among a Range of Options Using Log Ratio Analysis
Authors: Elston D. A. , Illius A. W. , Gordon I. J.
Published: May 2006

Animals generally exhibit preference from among the resources available to them. Preference data are compositional, since they describe the proportion of some resource, such as time or energy, which has been allocated to each option, and the sum of these proportions must be 1. The unit—sum constraint places a restriction on the types of analysis that are appropriate. The method of log ratios provides a transformation that leads to analyses in which the unit—sum constraint is automatically satisfied. This paper describes a form of log ratio analysis that allows estimation of the relative preferences for the options available and the influence on these preferences of the conditions under which the options are presented. The method is most suitable for application to data from controlled experiments in which options are presented in pairs, as equal availability of the choices can best be achieved and standard regression techniques can be used to fit the proposed models. The proposed analysis is demonstrated by a simple example in which the main difficulty of log ratio analysis, namely, unutilized options, is addressed and overcome.
Timing of Metamorphosis in a Freshwater Crustacean: Comparison with Anuran Models
Authors: Twombly Saran
Published: May 2006

Many crustaceans have complex life cycles characterized by a metamorphosis, yet variation in metamorphic traits, and the causes and consequences of this variation, have rarely been examined. Food concentrations were changed during specific larval stages of the freshwater copepod Mesocyclops edax Forbes (Copepoda: Cyclopoida) to examine whether age and size at metamorphosis remain flexible or become fixed during the larval period. Results were compared to predictions of both flexible (the Wilbur—Collins model) and fixed (Leips—Travis model) rate models for the timing of amphibian metamorphosis. Age and size at metamorphosis were variable in all treatments, and age was always more variable than size. Changes in food concentration early in larval development resulted in significant differences in age at metamorphosis among treatments, but changes initiated when 60% of the larval period had passed had no effect on age at metamorphosis. Development appeared to become fixed later in the larval period, before the ultimate larval stage was reached. These results support predictions of the Leips—Travis model. Early changes in food concentrations had significant effects on size at metamorphosis, but changes initiated during the penultimate larval stage (50—60% of larval development) had no effect on metamorph size. Size at metamorphosis in M. edax also appeared to be fixed before the ultimate larval stage was reached. Fixation of size at metamorphosis during development is not predicted by either model and may be unique to organisms with rigid exoskeletons that constrain growth within any stage. Patterns of covariation between age and size at metamorphosis suggest that food conditions early in larval development exert a large effect on metamorphic traits, in contrast to patterns observed in several amphibian species. The Wilbur—Collins model places a fitness premium on delaying metamorphosis to achieve a maximum size, when growth conditions are favorable; it thus may not apply to crustaceans. Selection pressures on the timing of metamorphosis in crustaceans may differ substantially from those identified for amphibians and other organisms. Because of these differences, incorporating crustaceans into studies of metamorphosis will help to clarify the factors affecting this life cycle transition.
Origins of Dioecy in the Hawaiian Flora
Authors: Sakai Ann K. , Wagner Warren L. , Ferguson Diane M. , Herbst Derral R.
Published: May 2006

Because of its presumed high levels of dioecy (separate male and female plants), study of the native Hawaiian angiosperm flora has been important in development of many hypotheses about conditions favoring the evolution of dioecy. The importance of ecological correlates with dioecy has proven difficult to assess, however, because of lack of data on the origins of dioecy in the Hawaiian Islands. Clearly, these correlations are of greater interest in taxa where dioecy evolved in the Hawaiian Islands (autochthonous evolution of dioecy) than in taxa that are the result of dioecious colonists with subsequent speciation in the Hawaiian Islands. Because the Hawaiian flora is small and extremely isolated, colonists can be identified and their breeding systems hypothesized, thus allowing inferences on the origins of dioecy. Using current taxonomic information, the incidence of dioecy in native Hawaiian angiosperm species is 14.7%, lower than previous estimates, but still the highest of any known flora worldwide. Ten percent of the colonists were sexually dimorphic (dioecious, gynodioecious, polygamodioecious, and subdioecious), and over half (55.2%) of current dimorphic species are in lineages arising from dimorphic colonists, showing that dimorphism is high in part because colonists were dimorphic. Autochthonous evolution of dimorphism occurred in at least 12 lineages (e.g., hermaphroditic colonists of Bidens (Asteraceae), the Hawaiian Alsinoideae (Caryophyllaceae), and Hedyotis (Rubiaceae) led to species—rich lineages that include many dimorphic species). One—third (31.8%) of current dimorphic species are in lineages arising from monomorphic colonists. Dioecy in the Hawaiian Islands is a result of both dimorphic colonists as well as evolution of dioecy in Hawaiian lineages from hermaphroditic colonists. The high incidence of dimorphism is not because dimorphic colonists evolved more species per colonist than monomorphic colonists. Detailed studies of individual lineages are critical to elucidate causal factors in the evolution of dioecy.
The Roles of Density, Stage, and Patchiness in the Transmission of an Insect Virus
Authors: Dwyer Greg
Published: May 2006

Although the importance of insect viruses in the population dynamics of their hosts is widely acknowledged, ecologists are still relatively ignorant of the factors determining the rate of transmission of insect viruses in the field. I performed a series of field experiments in which I investigated the transmission dynamics of the nuclear poly— hedrosis virus (NPV) of Douglas—fir tussock moth, Orgyia pseudotsugata (Lepidoptera: Lymantriidae), in northern Idaho, USA. In these experiments, I reared healthy and infected healthy larvae that became infected as a measure of transmission. I explored the influences of density, stage structure, and spatial structure on transmission by manipulating the density and stage distribution of healthy and infected hosts, and the spatial distribution of infected hosts. The experiments indicate that transmission is strongly affected by the densities of both healthy and infected hosts, but the effect depends on the instar of each. Late instars are both more infectious and more likely to become infected than are early instars, so that the NPV is more likely to spread in populations of late—instar tussock moth larvae. I also found that transmission is affected by the spatial distribution of infected hosts, and this effect also depends on the instar of healthy hosts. That is, transmission to healthy early instars decreases with increasing patchiness of infected hosts, but transmission to healthy late instars is essentially unaffected by patchiness. I discuss how these results can be in— terpreted in terms of behavioral differences among instars, and relate the results to the mathematical theory of disease and the use of viruses in biological pest control.
Effects of Maternal Nutrient Pulse on Reproduction of Two Colonizing Plantago Species
Authors: Miao S. L. , Bazzaz F. A. , Primack R. B.
Published: May 2006

Plantago major and P. rugelii maternal plants were grown at two background nutrient levels and received nutrient pulses given at different times during their life—span. The influences of these maternal treatments on the reproduction of progeny were examined in four different progeny environments represented by two treatments: with and without competition, and with and without a nutrient pulse. We found that the effects of maternal nutrient pulses on the two species were related to the environments of both parents and progeny. When grown without competition, progeny from parent P. major plants maintained at the low background nutrient level and given a nutrient pulse had a higher spike biomass and a higher proportional allocation to spikes than did progeny from parents that did not receive a nutrient pulse. In contrast, the progeny of parents that were maintained at the high nutrient level showed no response to a nutrient pulse. In P. rugelii the effect of maternal nutrient pulses on the total and leaf biomass of the progeny was related to both maternal background nutrient levels and nutrient pulse treatments to the progeny. For both species, the timing of maternal nutrient pulses had no significant effect on the characters studied. In competition, for P. major, the progeny from parents given a nutrient pulse during fruit maturation consistently produced a greater amount of spike biomass relative to their neighboring plants from parents that did not receive nutrient pulses, regardless of both the maternal background nutrients and progeny pulse treatments. However, for the progeny from parents given a nutrient pulse during the vegetative and flowering stages, their competitive ability relative to their neighbors depended on both the timing of maternal pulse and the progeny pulse treatment. For P. rugelii, the performance (leaf biomass) of the two neighboring progeny depended on maternal background nutrient levels. These results show that maternal nutrient, conditions can influence competitive interactions in the progeny generation. The effects may have ecological and evolutionary implications particularly for initial colonization of infertile sites and for the ability of natural selection to act on phenotypic variation. The strength of these maternal effects depends on both the maternal environment and the progeny environment.
Diurnal Photosynthesis Cycle in Cam and Non‐Cam Seasonal‐Pool Aquatic Macrophytes
Authors: Keeley Jon E. , Sandquist Darren R.
Published: May 2006

Seasonal pools undergo marked diurnal changes in pH, free carbon dioxide, and oxygen levels. Previous studies showed that Isoetes howellii utilized crassulacean acid metabolism (CAM) photosynthesis as a means of assimilating carbon at night when ambient carbon dioxide levels are high. However, much of the pool flora is not CAM. We hypothesized that coexistence under extreme carbon—limiting conditions would select for other photosynthetic characteristics in these non—CAM species. Quantitative carbon uptake measurements wee made in the field on the CAM Isoetes howellii and the non—CAM Eleocharis acicularis, Downingia bella, and Plagiobothrys undulatus. Despite wide phylogenetic separation, thee species are structurally convergent in that they all produce aquatic stage with an isoetid growth form. They are functionally similar in that none appear to utilize bicarbonate, and all are carbon limited through much of the day, as indicated by a marked midday depression in carbon uptake that last through the afternoon. All four species were capable of carbon fixation at night, although only in Isoetes howellii was this accompanied by an overnight accumulation of acid. It was estimated that dark fixation in I. howelli contributed up to 40% of its total carbon gain under submerged conditions, but was <1% under aerial conditions. The role of dark fixation in the other three, non—CAM, species is unknown. Short—term (1 s) steady—term (1 s) steady—state 14C tracer studies in the laboratory revealed that, under submerged conditions in the light, all species assimilated carbon into the C3 photosynthetic product phosphoglycerate (PGA) and the C4 photosynthetic products of malate, citrate, and aspartate. The proportion of label fixed into C4 organic acids was greatest in E. acicularis. The ratio of RuBP carboxylase/PEP carboxylase was broadly similar in all species, ranging from 8.8 to 11.5. When the pools dried down and the plants became aerial, photosynthetic rates increased and a midday depression such as occurred under submergence was not observed. Carbon fixation in the dark became negligible, and the RuBP carboxylase/PEP carboxylase ratio increased. Seasonal changes in biomass showed I. howellii and E. acicularis dominated the pools early in the season, and the biomass of the other two species increased later when the pools dried. The latter species, D. bella and P. undulatus, also had higher rates of photosynthesis under aerial conditions.
α‐methylstyrene hydrogenation in a flow‐through membrane reactor
Authors: Purnama H. , Kurr P. , Schmidt A. , Schomäcker R. , Voigt I. , Wolf A. , Warsitz R.
Published: May 2006

The hydrogenation of α‐methylstyrene (AMS) was carried out in a flow‐through membrane reactor at: 45–50°C, 1–40 bar, and 18 vol % AMS in heptane. An α‐Al2O3 membrane tube of defined pore size was used as catalyst support material. A wet impregnation method was used to prepare the active membrane with palladium as catalyst. Experiments with a spherical Pd/Al2O3 egg‐shell catalyst in a slurry reactor were carried out under similar reaction conditions for comparison. Results from the flow‐through membrane reactor were also compared to results from other types of reactors described in the literature. Application of the flow‐through membrane reactor exhibits an enhanced performance with respect to the productivity (reaction rate per mass of palladium) relative to that of other types of membrane reactors and other conventional reactors, such as a slurry reactor, a trickle‐bed reactor, and a bubble‐column reactor. © 2006 American Institute of Chemical Engineers AIChE J, 2006
Human skin‐color sexual dimorphism: A test of the sexual selection hypothesis
Authors: Madrigal Lorena , Kelly William
Published: May 2006

Applied to skin color, the sexual selection hypothesis proposes that male preference for light‐skinned females explains the presence of light skin in areas of low solar radiation. According to this proposal, in areas of high solar radiation, natural selection for dark skin overrides the universal preference of males for light females. But in areas in which natural selection ceases to act, sexual selection becomes more important, and causes human populations to become light‐skinned, and females to be lighter than males. The sexual selection hypothesis proposes that human sexual dimorphism of skin color should be positively correlated with distance from the equator. We tested the prediction that sexual dimorphism should increase with increasing latitude, using adult‐only data sets derived from measurements with standard reflectance spectrophotometric devices. Our analysis failed to support the prediction of a positive correlation between increasing distance from the equator and increased sexual dimorphism. We found no evidence in support of the sexual selection hypothesis. Am J Phys Anthropol 2006. © 2006 Wiley‐Liss, Inc.
How neutrals can overcome the psychology of disputing: The effect of framing and reactive devaluation in mediation
Authors: Korobkin Russell
Published: May 2006

More advice for neutrals: In the conclusion of his two‐part article, Russell Korobkin, of Los Angeles, describes two more impediments to mediation settlement. He also provides interventions that mediators can deploy to offset resistance to offers and further negotiations