bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioenergetic and Community Changes in Intertidal Aufwuchs Grazed by Littorina Littorea
Authors: Hunter R. Douglas , Russell-Hunter W. D.
Published: May 2006

Grazing by Littorina littorea on Aufwuchs grown on glass substrata resulted in substantial changes in the bioenergetics and community structure of the microalgae. At all grazer densities (13—504 snails/m2) standing crop biomass of the Aufwuchs was markedly reduced compared to that on control (ungrazed) substrata. Both in situ dry mass and organic carbon per square decimetre decreased as snail density increased; however, nutritional quality was improved with increase in density of grazers. Carbon per unit dry mass of Aufwuchs was higher at all grazer densities than for controls, and nitrogen per unit dry mass increased as grazer density increased. C:N ratio of the Aufwuchs decreased from 10:1 at 13 snails/m2 to 2:1 at 504 snails/m2. A computed assessment of Aufwuchs productivity based on snail intake necessary for bioenergetic maintenance derived from respiration measurements indicated that grazing at moderate levels increased microalgal productivity by 88% over control. Both microalgal abundance and richness decreased as Littorina density increased. Grazing reduced the number of taxa to 50% of that of control Awfwuchs at low snail densities and to <30% of that of controls at high snail densities. Five taxa (including the genera Achnanthes, Nitzschia, Amphora, and Cocconeis) appeared resistant to grazing and in terms of number of cells per square centimetre comprised 73% of the cells on highly grazed substrata, compared to 7.5% on control substrata. Grazing by Littorina littorea on Aufwuchs involves ingestion of a mixture of prey; possibly only passive selectivity; bioenergetic increase in certain nutritional parameters such as proportion of organic carbon, nitrogen, and possibly per unit mass productivity; and reduction in community parameters such as abundance richness, and diversity.
Ant Protection of a Host Plant's Defoliator: Consequence of an Ant‐Membracid Mutualism
Authors: Fritz Robert S.
Published: May 2006

Black locust (Robinia pseudoacacia) is extensively defoliated by the locust leaf—mining beetle (Odontota dorsalis) in western Maryland. This plant is also the host of Vanduzea arquata (Membracidae), a gregarious, sap—feeding treehopper, which is tended by the ant Formica subsericea. Aggression by F. subsericea reduced adult density and density of egg masses of O. dorsalis on branches with Vanduzea tended by Formica (ant branches) compared to non—ant branches. Observations and staged encounters also showed that Formica ants excluded Nabicula subcoleoptrata, an important predator of O. dorsalis larvae, from branches with Formica and Vanduzea. Thus, ants indirectly protected the beetle larvae from this predator. In both 1980 and 1981 survivorship of beetle larvae was significantly higher in the presence of ants. In 1980 this resulted in nearly twice as many beetle larvae surviving on ant branches even when egg mass density was initially lower. In 1981 beetle survivorship was higher on branches with ants, although numbers of larvae remained higher on nonant branches compared to ant branches. There was no apparent net benefit or harm to black locust in having Formica ants and Vanduzea treehoppers, although these results suggest a mechanism by which ant attendance could harm the plant indirectly. These results are contrary to previous studies of ant—Homoptera—plant associations.
Patterns of Resource Use and Tests for Competitive Release in a Spider Community
Authors: Riechert Susan E. , Cady Alan B.
Published: May 2006

Determinations were made of the temporal, functional (diet), and spatial niche relations of four web—building spider species comprising 98.3% of the individuals of a sandstone rock outcrop community. Three of the species were found to be potential ecological equivalents; despite dissimilar web structures, significant overlaps (60—85%) were exhibited in their diets, timing of activity, and microhabitat use. Investigation of the degree to which various resources were in limited supply to these species during the course of the study indicates that: (1) space was a potentially limiting factor, while (2) prey availability appeared to be in excess of the needs of the populations. We complete removal experiments to seek evidence for changes in various demographic parameters of the populations (i.e., in adult and juvenile densities and in egg production) and in use of various microhabitats in the absence of heterospecifics. No evidence for competitive release was observed on the single—species cliffs during the 11—mo period of the experiments. Data are presented that suggest interspecific effects present may be masked and/or offset by the operation of other impinging effects (e.g., [1] the fact that by removing all other spiders from the experimental cliffs, we were removing a major source of food to one of the species and [2] the presence of potentially limiting intraspecific competitive effects to three of the species populations).
Ecological Aspects of the Reproductive Biology of Eastern Kingbirds: Geographic Comparisons
Authors: Murphy Michael T.
Published: May 2006

A geographic comparison of the ecology of Eastern Kingbirds (Tyrannus tyrannus) breeding in New York (NY), and Kansas (KS), USA, was conducted in 1979 and 1980, respectively Emphasis was placed on relating variation in reproductive parameters, both within and between sites, to season and weather. Superimposed on the geographic comparison was a severe drought in KS in 1980. In both populations egg laying peaked at the end of the 1st wk of June, and modal clutch size was three. seasonal declines in clutch size were also nearly identical. Clutch size differences were not significant. Eggs were significantly larger in NY than in KS. The difference was not related to either adult size or annual variation in weather. Egg mass was only weakly correlated with environmental variables (date and temperature), but interruptions in laying followed days of below—average temperatures. Egg mass increased With the order of laying in NY, but decreased in KS. This apparently reflected the stressful conditions for laying females in KS. Incubation was significantly shorter in KS, probably due to warmer air temperatures since an inverse relationship was found between air temperature and incubation length in NY. Smaller egg size in KS may also have contributed to the shorter incubation period. Nestling growth was relatively slow, and despite large mass differences (eggs were heavier in NY) growth rates were nearly identical. Absolute tarsus growth was also significantly greater in NY, but development of the ninth primary was significantly greater in KS. Nestling period length was inversely correlated with primary length in both populations. Emphasis on primary development in KS, where nest success was lower, vs. mass gain in NY, where starvation was more frequent, discussed in terms of tradeoffs to balance losses to predators (KS) and starvation (NY). Growth was negatively correlated with brood size in both populations, but in KS also with date, i.e., seasonal changes probably related to the drought. Productivity was greater in NY, but in neither population did it exceed 1.5 fledglings per nesting attempt. Mortality of fledglings is near zero in both populations due to intense postfledging parental care. Weather has important influences on the breeding biology of kingbirds, yet geographic variation in most traits was small. Hence, kingbird reproduction is not highly adapted to differences in average weather conditions between the sites. Occasional periods of severe weather probably preclude narrow specialization to local conditions. Kingbirds are therefore best characterized as a bet—hedging species. Patterns of growth and reproduction match hypothetical and independently derived predictions based on other aerial insectivores, thus providing support for several recent predictions for life history evolution.
A Multivariate Approach to the Analysis of Factorial Fertilization Experiments in Alaskan Arctic Tundra
Authors: Lechowicz M. J. , Shaver G. R.
Published: May 2006

Canonical analysis was used to analyze the results of factorial NPK fertilization trials on size species growing in arctic tundra at Eagel Creek, Alaska, USA (latitude 65°10'N, longitude 145°30'W): the graminoids Eriophorum vaginatum and Carex bigelowii, the deciduous shrubs Betula nana and Vaccinium uliginosum, and the evergreen shrubs V. vitis—idaea and Ledum palustre. In an extension of early univariate analyses, multivariate comparisions were made based on shoot concentrations of N, P, K, Ca, and Mg as a measure of overall nutrient balance. In the unfertilized controls, the graminoids were richer in K than the other growth forms, deciduous shrubs had higher concentrations of N relative to P and Ca than the evergreen shrubs, and the deciduous—evergreen contrasts were greatest early in the growing season. An NKP fertilization triggered disproportionate increases in K concentration in the graminoids and increases N relative to P and Ca in the evergreen shrubs. The effect of fertilization on nutrient balance of the deciduous shrubs in the spring following fertilization was like that of the evergreen shrubs but by late summer had shifted to the graminoid pattern. Nitrogen and phosphorus consistently produced contrasing shifts in the nutrient balance in all three growth forms. In contrast to the two Vaccinium shrubs, the nutrient balance of the graminoid E. vaginatum was strongly affected by any fertilization involving potassium. In general, factorial combinations of N, P, and/or K produced shifts in the nutrient balance qualitatively intermediate to those resulting from the nutrients added singly. Many differences among growth forms apparent here were not discerned in the earlier univariate analyses of these fertilization trials. Particularly when combined with factorial fertilization experiments, canonical analysis can provide considerable insight into the response of nutrient balance to fertilization and help elucidate the ecological significance of these response patterns.
The Dynamics of a Colonizing Population of Poa Annua
Authors: Law Richard
Published: May 2006

This paper describes a demographic analysis of a colonizing population of Poa annua. The population was characterized by a burst of growth growing the first autumn of colonization, after which there was little further change, apart from small seasonal oscillations. Recruitment of seedlings also increased towards a ceiling during the first autumn, after which it showed marked seasonal oscillation, with peaks in spring and autumn. During colonization there was an increase in numbers of old individuals in the population, and the age structure developed a wake—like pattern, corresponding to the seasonal peaks and troughs of recruitment. Reproduction decreased as population density increased and was much influenced by season, tending to be greatest in the summer. Mortality increased with population density and was also influenced by season, tending to be greater in the autumn. Overall, the analysis draws attention to the interdependence of the spatial and temporal dimensions in plant populations.
Control of Morphotype Frequency Distributions in Populations of the Rotifer Asplanchna Sieboldi: Factors Influencing the Production of the Tocopherol‐Dependent Cruciform and Campanulate Morphotypes
Authors: Gilbert John J.
Published: May 2006

When the diet of A. sieboldi contains tocopherol and certain types of prey, such as congeners, females develop into one of two morphotypes–cruciform or campanulate. The frequency with which these morphotypes can be produced in a population is a function of: probabilities that the daughters of amictic (asexual) cruciforms and campanulates will be cruciform and campanulate; the probabilities that cruciforms and campanulates will be amictic and mictic; and the birth rates of amictic cruciforms and campanulates. These reproductive parameters wee determined from laboratory observations on individuals from populations maintained on a diet of A. brightwelli with d—α—tocopherol at 10—7 mol/L. A Markovian model was developed and, when used with these data and initiated with a single amictic cruciform, showed that an equilibrium distribution of 34.8% amictic cruciforms, 51.0% mictic cruciforms, 8.5% amictic campanulates, and 5.7% mictic campanulates was approached at a rapidly decelerating rate and finally attained after 15 generations. Varying the inputs to this model showed that very high equilibrium frequencies of campanulates could be produced if most campanulates were amictic and had predominantly campanulate daughters, even if almost all daughters of cruciform parents were cruciform, but could not be produced even by dramatically increasing either the probability of cruciforms bearing campanulate offspring or the reproductive rate of amictic campanulates relative to that of amictic cruciforms. The high proportions of campanulates often observed in natural populations could not be produced if the reproductive parameters of the amictic cruciforms and campanulates were similar to those determined in this study, unless the cruciforms were preferentially eliminated through cannibalism or predation. Shifts in the frequency distributions of cruciforms and campanulates, such as have been noted in natural populations, could be due to: progressions to equilibrium distributions; variations in the types of prey available; changes in environmental factors that differentially affect the redproductive parameters of the two amictic morphotypes; different intensities of selective, intermorphotypic cannibalism; successions of invertebrate and vertebrate predators that differentially ingest the two morphotypes; and clonal replacements that alter characteristics of the two morphotypes affecting reproduction and survival.
Nitrogen Immobilization in Decomposing Needle Litter at Variable Carbon: Nitrogen Ratios
Authors: Berg B. , Ekbohm G.
Published: May 2006

The nitrogen dynamics in decomposing needle litter incubated in a clear—cut area were seen to be very different from those of the same types of litter incubated in a mature forest. In each stand 10 different sets of Scots pine needle litter with different initial nitrogen concentrations were incubated. A nonlinear regression model of loss and nitrogen dynamics estimates that the C/N ratio above which net immobilization and below which net mineralization takes place differs significantly between the systems (109 in the mature forest and °63 in the clear—cut area).
Tropical Territorial Damselfishses: Is Density Limited by Aggression or Recruitment?
Authors: Doherty Peter J.
Published: May 2006

The spatial distributions of two common damselfishes, Pomacentrus wardi and P. flavicauda, suggest that they compete for common resources within lagoons of the southern Great Barrier Reef. Both fishes are herbivores that defend territories on rocky substrata covered with shallow water, but are segregated by microhabitat. When young P. flavicauda recruit into the habitat where P. wardi are most numerous, they have lower persistence than counterparts on reefs where conspecifics predominate. Several experiments were done, using as replicates that large patch reefs populated by P. wardi, to determine what effects territory—holding individuals have on the distribution and abundance of conspecifics, P. flavicauda, and other grazing fishes. Total and selective removal of the numerically dominant P. wardi revealed that these reefs are mostly repopulated by larval fishes (recruitment), rather than by already recruited fishes (immigration). P. wardi are the most frequent recruits. The removals also showed that resident P. wardi do not determine the numbers of conspecific larvae invading their territories, and do not reduce their survival after recruitment (at least for 300—400 d). They do determine the growth of such juveniles. Despite this interaction, there was no evidence that either density or biomass is usually regulated in these populations. Both measures vary greatly among replicate reefs. The lack of numerical equilibrium, within the study period, was caused by a patchy and limiting supply of larval recruits. Manipulations also showed that resident P. wardi do not limit the recruitment or reduce the postrecruitment survival of P. flavicauda on large patch reefs. An unknown density—independent cause is implicated in the observed habitat—segregation and in the failure of P. flavicauda to reach breeding size on such reefs. The removal of P. wardi produced different results for the fish grazers from other families, depending upon their feeding strategy. For example, solitary acanthurids concentrated their grazing activities on reefs with fewer damselfishes, but a schooling parrotfish did not. The outcomes of these perturbations support a nonequilibrial view of reef fish communities, rather than hypotheses that emphasize the importance of competition among populations usually at carrying capacity.
Analysis of the Differential Response of Five Annuals to Elevated CO2 during Growth
Authors: Garbutt K. , Williams W. E. , Bazzaz F. A.
Published: May 2006

In order to investigate the effects, without competition, of CO2 on germination, growth, physiological response, and reproduction, we focussed on co—occurring species that are prominent members of an annual community in Illinois. Five species of old field annual plants—Abutilon theophrasti (C3), Amaranthus retroflexus (C4), Ambrosia artemisiifolia (C3), Chenopodium album (C3), and Setaria faberii (C4)–were grown for their entire life cycle as individuals at CO2 concentration of 350 @mL/L, 500 @mL/L, and 700@mL/L. Emergence time, growth rate, shoot water status, photosynthesis, conductance, flowering time, nitrogen content, and biomass and reproductive biomass were measured. There was no detectable effect of enhanced CO2 on timing of emergence in any of the species. Amaranthus relative growth rate (RGR) was always higher at 700 @mL/L CO2 than at 350 @mL/L. In both Abutilon and Ambrosia, RGR was greater at 700 @mL/L than at 350 @mL/L during the first half of the experimental period, but during the second half of the period the reverse was true. Shoot water potential significantly increased (became less negative) with increasing CO2 in Amaranthus and Setaria. Similar but statistically nonsignificant trends were found in Chenopodium and Abutilon. Overall rate of photosynthesis increased with CO2 but there were no significant effects, at the species level, of CO2 on photosynthetic rates. Stomatal conductance decreased with increased CO2 at both high and low light levels in C3 species but only at high light levels in C4 species. In all species, intercellular CO2 increased with external CO2. Amaranthus flowered significantly earlier at 700 @mL/L than at 350 @mL/L, and Setaria flowered significantly later at 700 @mL/L than at either of the other CO2 levels. Both Abutilon and Ambrosia showed a trend towards earlier flowering but this was not statistically significant. Of the morphological characters measured at the final harvest only specific leaf area (SLA) showed a consistent response to CO2, decreasing with increasing CO2. Significant CO2 x species interactions were also found for leaf area, leaf biomass, biomass of reproductive parts, and seed biomass indicating species—specific responses for these characters. The proportion of nitrogen declined with increasing CO2: there was also a significant CO2 x species interaction caused by the different rates of decline in proportion of nitrogen among the species. The response of most characters had a significant species x CO2 interaction. However, this was not simply caused by the C3/C4 dichotomy. Reproductive biomass (seed, fruits, and flowers) increased with increasing CO2 in Amaranthus (C4) and in Chenopodium and Ambrosia (both C3), but there was no change in Setaria (C4), and Abutilon (C3) showed a peak a 500 @mL/L. Species of the same community differed in their response to CO2, and these differences may help explain the outcome of competitive interactions among these species above ambient CO2 levels.
Characteristics of Three Populations of a Swamp Annual Under Different Temperature Regimes
Authors: Christy E. Jennifer , Sharitz Rebecca R.
Published: May 2006

This study was undertaken to examine rapid evolution in an herbaceous plant species in response to strong selection associated with increases in temperature. Differences in growth and reproduction in three populations of Ludwigia leptocarpa (Nutt.) Hara, an herbaceous plant dominant along the edges of streams receiving heated nuclear reactor effluent on the United States Department of Energy's Savannah River Plant (SRP) in South Carolina, USA, were examined for two growing seasons. Two populations of this semi—aquatic herb were in areas with elevated water temperatures, and one population was in an undisturbed swamp. In each of the populations in warmer water, growth and reproductive output were significantly higher than in plants from the undisturbed site. Total percentage germination under controlled temperatures from 22° to 42°C did not differ among the three populations; however, initiation of germination was delayed in all three at 22°. Seedlings from all three populations showed similar growth responses at 22°, whereas at 32° seedlings from the higher temperature locations grew more rapidly. At 42°C, survivorship of seedlings from all three seed populations was low. These results indicate selection for temperature—tolerant ecotypes in the disturbed areas.
Habitat Requirements and Growth of Striped Maple (Acer Pensylvanicum L.)
Authors: Hibbs David E. , Wilson Brayton F. , Fischer Burnell C.
Published: May 2006

Surveys of distribution and habitat characteristics, growth patterns, and growth in recently logged areas of striped maple (Acer pensylvanicum L.) were made in western Massachusetts, USA. Highest densities at a given altitude were found on mesic sites on middle and upper slopes. Density increased with increasing slope and altitude but was not affected by aspect or light conditions. Ninety percent of the striped maples were found in the northern hardwood—hemlock forest type although the type covered only 52% of the study area. Optimum height growth occurred at intermediate light intensities, on higher and more northerly slopes, and on mesic sites. Half of the plants in the nonlogged areas were growing <3 cm/yr in height. In logged areas, 75% of the plants present before overstory removal were released by removal, but most subsequent new seedlings were suppressed. The distribution and growth patterns of striped maple suggest that it is a gap—phase replacement species that utilizes temporary forest openings for growing space.
Biomass Distribution and Production Budget for a Nonaggrading Forest Ecosystem
Authors: Gosz James R.
Published: May 2006

A fundamental question in current ecosystem research is the extent to which net organic matter increment (net ecosystem production, NEP) controls nutrient input—output behavior. The large uncertainties associated with net primary production (NPP) and heterotrophic respiration (RsH) make it very difficult to verify statistically an ecosystem as steady—state (NPP — RsH = 0). The aspen (Populus tremuloides Michx.) ecosystem reported on here appears to be degrading (i.e., negative NEP), a condition which would allow an important test of the influence of NEP on the nutrient regulation of an ecosystem. Total NPP was estimated at 11 740 kg°ha—1°yr—1, RsH was 13 800 kg°ha—1°yr—1, and NEP was —2060 kg°ha—1°yr—1. The standard error of the estimate for the sum of woody biomass increment and litter fall was 119 kg°ha—1°yr—1. Extravagant estimates were used for other components of NPP and underestimates used for components of RsH to ensure a conservative estimate of a degrading condition.
Metamorphic Responses to Changing Food Levels in Two Species of Hylid Frogs
Authors: Leips J. , Travis J.
Published: May 2006

We investigate how changes in food availability during development affected the timing of and body size at metamorphosis in two closely related species of tree frogs that use different larval habitats. We raised tadpoles of Hyla gratiosa (a temporary—pond breeder) and Hyla cinerea (a permanent—pond breeder) at two different temperatures on either constant resources or a regime in which we altered food levels at one of three different times during development. For both species, larval period was affected only by early changes in food level; early increases shortened larval period, and decreases lengthened it. The timing of metamorphosis of Hyla gratiosa showed greater plasticity than that of Hyla cinerea, because of its greater overall response to any food—level change and not because of any difference between species in the duration of the sensitive period. The two species showed comparable levels of plasticity in body size at metamorphosis; increases in food level produced larger body sizes, and decreases produced smaller sizes. However, in contrast to the pattern seen in larval period, later changes in food level had the greatest effect on body size. These results force a reexamination of current ideas about the adaptive significance of plasticity in the timing of metamorphosis in response to food availability in larval anurans. We offer a model of dynamic allocation that accommodates the extant data on this issue.
Developmental Changes in Resistance to Herbivory: Implications for Individuals and Populations
Authors: Kearsley Michael J. C. , Whitham Thomas G.
Published: May 2006

The hypothesis that individual plants undergo predictable changes in their resistance to herbivory as they mature was experimentally tested. The performance of two species of insects transferred onto different—aged trees of the same naturally occurring clones of narrowleaf cottonwood, Populus angustifolia, showed opposing and significant changes in host resistance as a function of tree age. The gall—forming aphid Pemphigus betae was 70 times as common on mature trees as on juvenile trees. Transfer experiments demonstrated that this pattern is adaptive; survivorship on mature trees was 50% higher than on juvenile trees. The leaf—feeding beetle Chrysomela confluens exhibited opposite distribution on hosts, with densities 400 times as high on juvenile as on mature trees. This is also adaptive; larvae transferred to mature hosts had 50% lower survival and took 25% longer to reach adulthood than those transferred to juvenile trees. These survivorship and performance data and our inability to support the hypotheses of other mechanisms that would produce the observed distributions suggest that the distributions result from the insects' preferences for different—aged hosts. Several basic implications emerge. (1) Developmental changes in resistance and susceptibility of hosts are important components in determining the distribution of herbivores. (2) A single plant can change rapidly in its resistance traits with age such that a 10—fold change in resistance can occur over a 2—yr period. (3) As trees mature, increased and decreased resistances to different herbivores can produce nonoverlapping herbivore distributions that could be misinterpreted as being the result of competition (e.g., in this study, beetle abundance was strongly, negatively correlated with aphid abundance). (4) While host maturation processes have large effects on within— and between—tree variation in resistance to herbivores, the implications for herbivore population dynamics and community structuring have not been generally appreciated.
Population Biology of a "Noncycling" Population of Prairie Voles and a Hypothesis on the Role of Migration in Regulating Microtine Cycles
Authors: Abramsky Zvika , Tracy C. Richard
Published: May 2006

As part of the US/International Program Grassland Biome study in northeastern Colorado, six 1—ha plots of shortgrass prairie were manipulated for 6 yrs (1971—1976) through the addition of N, water, or both. Two additional 1—ha plots served as controls. Microtus ochrigaster invaded the 2 N + water treatment plots in 1971, and increased in annual peak densities (occurring in late summer or fall each year) linearly through the completion of this study in 1976. These vole populations exhibited no multiyear cycles in population density usually common in microtines, but they did undergo exaggerated annual fluctuations in density. Patterns in reproduction, mortality, sex ratios, body weight, annual population fluctuations, and dispersal were analyzed and compared with those of populations reported in the literature to exhibit 2—4 year cycles in population density. Only small differences in these parameters were found between the Pawnee populations and multiyear cyclic populations. The N + water plots represented "islands" of suitable vole habitat in a "sea of shortgrass prairie," which is apparently inhospitable for voles. Thus, these semi—isolated populations of noncyclic (or annually cyclic) prairie voles allowed us to speculate on several aspects of the Chitty/Krebs theory of self—regulation in microtine populations. This theory (as modified by Krebs) implicates emigration as an important determinant of 2—4 year cycles. We propose that the importance of emigration is in regulating population size while immigration is probably responsible for the existence of the cycle.
Population Dynamics, Bioenergetics, and Role of Lepidostoma Quercina Ross (Trichoptera: Lepidostomatidae) in an Oregon Woodland Stream
Authors: Grafius E. , Anderson N. H.
Published: May 2006

The aim of this study was to gather quantitative field and laboratory data on the utilization of deciduous leaves as food by Lepidostoma quercina Ross (Trichoptera: Lepidostamatidae) and estimate the effect of this food processing on the stream ecosystem. Samples were taken monthly in a riffle—pool section of Berry Creek, Benton County, Oregon. Maximum larval density was 382 per m2, instantaneous growth rate was 2.7% per day, instantaneous mortality rate was 1.4% per day, and production was 0.19 g·—2·—1. The life cycle of L. quercina and its period of maximum larval growth correspond closely with the period of maximum availability of its prefered food (alder leaves) in the stream. Consumption and fecal production rates were measured gravimetrically. Rates (mg·—1·—1) increased with temperature, food quantity, and conditioning time of the leaves, and decreased with increased size of the larvae. Mean respiration rates of larvae were higher at 10°C than at 5°, but there was no significant difference in mean rates at 10, 15, or 20°C. Respiration rate decreased with increased size of the larvae. Size—specific respiration rates showed regulation of respiration with respect to temperature for small individuals (present in the field in September and October when temperatures are variable) and little or no regulation by large individuals (present in December and January). Stimulation modeling of larval growth based on laboratory data demonstrated that growth and production of L. quercina in the field may be limited by a lack of high—quality food (alder leaves) in late summer and early fall. Consumption of leaves by the simulated population was estimated as 3.1 g·—2·—1. Lepidostama quercina comprised only a small part of the secondary production in Berry Creek (0.19g·—2·—1, vs. 2.2 g·—2 for simuliids) and processed only a small portion of the allochthonous input to the stream. However, significant quantities of fecal material were produced and it was estimated that these fine particle would be sufficient to support ¼ to ½ of the production of simuliids, the dominant riffle species in Berry Creek.
Thermal Ecology, Behavior, and Growth of Gypsy Moth and Eastern Tent Caterpillars
Authors: Knapp Rosemary , Casey Timothy M.
Published: May 2006

Eastern tent caterpillars (Malacosoma americanum) are behavioral thermoregulators while gypsy moth caterpillars (Lymantria dispar) are thermal conformers. Differences in thermal ecology can be related to differences in the environments these species encounter. Temperature sensitivity of growth rates differs in a predictable manner; the growth rates of gypsy moth caterpillars are temperature independent at ecologically relevant temperatures of 25°—30°C, and the growth of the tent caterpillars is very temperature dependent. Growth rates of tent caterpillars in the field are greater than that expected for the average ambient temperature of 15°, and closely approximate growth in the laboratory at 25°, near the average Tb exhibited in the field. The higher growth rates are a result of the tent caterpillars' elevated body temperatures. These data are used to develop hypotheses for the evolution of caterpillar thermal responses.
Feeding Relationships Among Bison, Pronghorn, and Prairie Dogs: An Experimental Analysis
Authors: Krueger Kirsten
Published: May 2006

Bison (Bison bison), pronghorn (Antilocapra americana), and prairie dogs (Cynomys ludovicianus) form a grazing association on the northern United States mixed—grass prairie. Marked similarities in diet and spatial use between bison and prairie dogs on dog town edges and between pronghorn and prairie dogs on town centers create a high potential for interspecific interactions. Observational data were deemed insufficient to detect and properly characterize such interactions, and an experimental analysis was undertaken for this purpose. Two sets of exclosures, built on centers and edges of active and poisoned prairie dog towns, and on uncolonized prairie sites, were used to evaluate foraging relationships among bison, pronghorn, and prairie dogs feeding within and adjacent to exclosures and in control areas. Bison foraging groups were largest, nearest neighbor distances least, and foraging efficiency (bite: step ratios) highest among bison foraging in town edge control areas of the active towns, suggesting that these were the best areas for bison foraging. Prairie dogs showed smaller nearest neighbor distances and higher bite: step ratios when foraging in these areas than when foraging within adjacent exclosures, suggesting that bison foraging on town edges improved prairie dog foraging there. These results indicate a mutually positive relationship between bison and prairie dogs on town edges. Nearest neighbor distances and bite: step ratios of prairie dogs on town centers (within and adjacent to exclosures) suggested that pronghorn foraging did not appreciably affect prairie dog foraging. However, comparisons of pronghorn foraging between active and poisoned town centers showed nearest neighbor distances always smaller and bite: step ratios often higher on the poisoned town centers, suggesting that the presence of prairie dogs on town centers may have slightly degraded pronghorn foraging there. This indicates a complex relationship on town centers between pronghorn and prairie dogs, which was neutral for prairie dogs but slightly negative for pronghorn under the conditions of the study. Results of vegetation analyses within exclosures and in control areas showed significant enhancement of shoot nitrogen in plants growing on areas subject to heavy grazing pressure, such as active dog towns and control areas on dog towns, and may partially explain improvements in prairie dog and bison foraging there.
Alternation of Oviposition Behavior by Battus Philenor Butterflies in Reponse to Variation in Host‐Plant Density
Authors: Rausher Mark D.
Published: May 2006

As host—plant density increases, the oviposition rate of Battus philenor butterflies increases, then levels off. By contrast, alighting rates continues to increase with host density approximately linearly. The leveling off of oviposition rates is caused by a decline in the probability that a female will oviposit once she alights on a plant. Evidence is presented indicating that these phenomena are due to an increase in female selectivity as plant density increases, rather than to a limit on oviposition rate imposed by the rate of egg maturation. This type of behavioral response to host density is a mechanism that can explain in part the tendency of many herbivorous insects to aggregate to a greater degree in low—density than in high—density stands of host plants.
The Unpredictability of the Marine Phytoplankton
Authors: Hulburt Edward M.
Published: May 2006

The focus of this paper is on what appears to be a large and partly inherent measure of unpredictability in marine phytoplankton species. Thus, if a species is frequently abundant and occasionally undetectable or if instead it is frequently undetectable and occasionally abundant, it behaves unpredictable in its occasional failure or in its occasional success. The option of abundant or unabundant of below detection, with resolution to just one of these at any given place, results in the close juxtaposition of abundances of a given species (°3.0 cells/cm3) with unabundances or undetectable amounts (the last °0.03 cells/cm3), often under conditions of excess nutrient, and attests to its fast—growing but unpredictable behavior. Such species occur in the Slope Water off the coast of southern New England. Farther away, in the mid—Atlantic, a different lot of predictable but slowly growing species occurs. In terms of a single midocean species an appropriate formula is: if it is a predictable species, then it is a slow grower implying if it is not a slow grower, then it is not a predictable species, with the parts before and after implying reserved for a single Slope Water species. One purpose of this paper is application of a philosophical explanation of an observed concentration of a given species. Such an observation is a resolution of abundant or unabundant or below detection to just one of these. A second purpose is clarification of scientific explanation (Hempel 1970), wherein theory formation is considered to be a suppositional process, as in the if—then sequences of the above formula.
Ophiuroids in a Bahamian Saltwater Lake: The Ecology of a Paleozoic‐like Community
Authors: Aronson Richard B. , Harms Craig A.
Published: May 2006

This study examined predation pressure as a determinant of ophiuroid abundance in Carribean shallow marine communities. The density of Ophiothrix oerstedii in Sweeting Pond, a saltwater lake on Eleuthera Island, Bahamas, was orders of magnitude higher (mean density up to 434.2 individuals/m2) than at nearby coastal sites (maximum density 3.21 individuals/m2). Ophiothrix occurred cryptically off the coast but fully exposed in the lake. Experiments in which ophiuroids were placed in open arenas revealed that Ophiothrix off the coast experienced dramatically higher predation pressure from fishes than they did in the lake, which contained none of the common Caribbean reef predators. Analysis of the diets of potential Ophiothrix predators in Sweetings Pond confirmed that the predation rate on these brittlestars was negligible. Density was directly related to the degree of microtopographical heterogeneity in Sweetings Pond. When the heterogeneity of experimental plots was artificially increased in a flat area of the lake by adding artificial bivalve clumps, introduced Ophiothrix remained in those plots, whereas they emigrated from unmanipulated control plots. Raised surfaces appear to confer an advantage to the suspension—feeding Ophiothrix. This population is strongly reminiscent of certain Paleozoic crinoid— and ophiuroid—dominated communities, and the absence of predatory fishes may have been important to the persistence of those fossil communities as well.
Crowding and Host Plant Nutrition: Environmental Determinants of Wing‐form in Prokelisia marginata
Authors: Denno Robert F. , Douglas Larry W. , Jacobs Dan
Published: May 2006

Prokelisia marginata is a wing—dimorphic planthopper that feeds on the phloem sap of the intertidal marsh grass Spartina alterniflora. Populations are comprised of two wing—forms: flightless brachypters and macropters, which can fly. Macropters migrate between permanent and temporary stands of Spartina. Brachypters, because of their immobility and early age at first reproduction, are the successful morph as long as conditions remain suitable in the current patch of host plants. Wingform in planthoppers is not inherited according to any simple genetic rule; there is a strong environmental component. Various environmental cues acting on the nymphal stage trigger a developmental switch that determines adult wing—form. We investigated the wing—form response to two environmental cues, crowding and host plant nutrition, by raising planthoppers at five levels of crowding on nutritionally superior and inferior seedlings of Spartina. Percentage of macroptery was density—dependent in females but not in males. Even when raised in isolation a significant number of males eclosed as macropters. There was no consistent main effect of host plant nutrition on wing—form. However, there was a significant crowding x host nutrition interaction, which suggest that the density—dependent migration response observed at high densities is dampened if planthoppers feed on nutritionally superior hosts. The roles of crowding and host plant nutrition in the population dynamics and migration behavior of P. marginata are discussed.
Sampling Properties of Gower's General Coefficient of Similarity
Authors: Lim T. M. , Khoo H. W.
Published: May 2006

The sampling properties of Gower's general coefficient of similarity were investigated. Artificial communities were created and the effects of sample size and species number on the sampling distribution of the coefficient were studied using a computer simulation technique. It was found that the index tends to overestimate low similarity and to underestimate high similarity. The bias of the index increased with species number, while the standard deviation was independent of species number. Increasing sample size increased the accuracy and the precision of the index in estimating community similarity.
Age‐Specific Energetics of Yellow‐Bellied Marmots
Authors: Webb D. R.
Published: May 2006

Juvenile and adult yellow—bellied marmots (Marmota flaviventris) were studied at 15 locations in the deserts and mountains of central and eastern Oregon. Maintenance of homeothermy by juveniles usually required a metabolic power output above the basal rate; adults only rarely needed to increase their power output above basal. Absolute power required per adults was greater than that for juveniles in thermoneutral environments, but juveniles required more power per animal at moderate to high wind speeds. Absolute energy requirements per animal were typically only slightly greater for adults than for juveniles and were reduced for some components of the energy budget. Juveniles foraged for longer periods per day than adults at all sites.
Influences of Territory Composition and Interspecific Competition on Red‐Tailed Hawk Reproductive Success
Authors: Janes Stewart W.
Published: May 2006

In north—Central Oregon, Red—tailed Hawks (Buteo jamaicensis) exhibited a high degree of stability in territory occupancy and territorial boundaries over a 10—yr period. Long—term reproductive success varied markedly among territories and was correlated primarily with the dispersion and density of perches used as foraging sites and secondarily with the abundance of ground squirrels, Principally the Belding's Ground Squirrel (Spermophilus beldingi). These results imply that prey availability is more important to reproductive success than absolute prey abundance. Pairs in territories with few or poorly dispersed perches did not rely more on energetically expensive aerial foraging. However, poor dispersion of perches resulted in both decreased flight time and in decreased foraging energy expenditure. Thus it is likely that Red—tailed Hawks in territories with few or poorly dispersed foraging perches deplete the prey near the perches that are present. Territory size was not correlated with reproductive success. Red—tailed Hawks coexisted with Swainson's Hawks, and showed strong interspecific territoriality. Some pairs of Red—tailed Hawks lost portions of their territories to the later arriving Swainson's Hawks each year. Yet the contention at territorial boundaries and loss of territory to Swainson's Hawks had no observable effect upon Red—tailed Hawk reproductive success.
Woody Plant Growth Related to Planting Time and Clipping of A C_4 Grass
Authors: Bush J. K. , Van Auken O. W.
Published: May 2006

The density of woody plants has increased in grasslands throughout the world, but the cause has been elusive, although changes in herbivory seem central. In this study, the importance of relative time of planting and clipping of Bouteloua curtipendula, a C4 grass, on Prosopis glandulosa, a woody seedling, was evaluated in a 2—yr field study in central Texas, USA. Secondarily, effects of planting date, presence of the woody seedling and clipping of the grass on the growth of the grass were evaluated. Relative growth rates (RGRs) of Prosopis glandulosa (honey mesquite) seedlings grown alone were seasonal, generally high in spring and decreasing as summer progressed. When P. gladulosa was planted earlier than Bouteloua curtipendula (side—oats grama), the grass had little or no effect on the woody seedlings RGRs. However, the dry mass of P. glandulosa increased 2.3 times when the grass was clipped but was reduced 54% when the grass was unclipped. When the two species were started at the same time and the grass was not clipped, P. glandulosa RGRs decreased and remained zero over the 2 yr, dry mass was reduced 99.8%, and mortality was 80%. If both species were started at the same time and the grass was clipped, 1st— and 2nd—yr growth of P. glandulosa was comparable to that of seedlings grown alone; however dry mass was reduced 79%. When planted later than the clipped grass, dry mass of P. glandulosa was reduced 98% compared to dry mass when planted alone, while in unclipped plots there was 100% mortality. When B. curtipendula was planted early in the growing season, clipping increased aboveground grass dry mass 1.63 times; there was no increase when the grass was planted late. Evidence suggests that woody seedling growth in undisturbed C4 grasslands would be very limited, and establishment requires gap formation.
The Effect of Alternative Prey on the Functional Response of Notonecta Hoffmani
Authors: Chesson Jean
Published: May 2006

Continuous observations were made to determine the effect of alternative prey on the functional response of the aquatic bug Notonecta hoffmani to mosquito larvae (Culex pipiens). Mosquito larvae and two alternative prey, the zooplankter Daphnia pulex and vestigial—winged Drosophila (representing terrestrial prey trapped on the water surface), were presented to the predator at various densities. Preference, searching times, capture times (searching time per prey captured), and handling times for mosquito larvae were estimated. The predator showed a significant preference for Daphnia relative to mosquitoes in three of the nine prey combinations tested, and a significant preference for Drosophila relative to mosquitoes in all prey combinations tested. The presence of Daphnia did not significantly affect searching or capture times for mosquitoes, whereas the presence of Drosophila was associated with a significant decreased in searching time and a significant increase in mean capture time. Mosquito handling time decreased slightly as Daphnia density increased. The results predict that Drosophila will have a greater effect than Daphnia on the ability of notonectids to control mosquito larvae. The prediction was supported by a longer term experiment in which the largest number of mosquitoes reached the pupal stage when Drosophila were present as alternative prey. The study shows that relative preferences alone are not sufficient to predict the effect of alternative prey on a predator's functional response. Factors such as handling time (which affects searching time) and behavioral changes such as a change in capture time, must also be considered when assessing the role of alternative prey in a biological control program.