bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of Algal Biomass in Dominant Odd‐ vs. Even‐Link Lake Ecosystems
Authors: Mazumder Asit
Published: May 2006

Foodchain models predict strong positive response of algal biomass to total phosphorus (TP) in odd—link ecosystem where grazers are controlled by planktivores and no significant response of algal biomass in even—link ecosystem where grazers are released from planktivore predation. On the other hand, resource— or ratio—dependent models predict proportional increase in algal biomass with increasing TP. These predictions were tested with field data from a large number of north temperature lake ecosystems exhibiting a wide range of TP. Instead of using the traditional approach of the number of trophic links present in an ecosystem, I used the presence vs. absence or near absence of large Daphnia and planktivorous fish to indicate the function dominance of odd vs. even links. Results showed that algal biomass response to TP is stronger in dominant odd—link ecosystems than in dominant even—link ecosystems, which is consistent with the predictions of foodchain models. The significant positive slope of the relationship of algal biomass to total phosphorus for dominant even—link ecosystems is not consistent with foodchain models. In addition, a nonlinear response pattern of algal biomass to total phosphorus appears to be inconsistent with both foodchain and ratio—dependent models. Results also showed that even—link ecosystems produce proportionately lower algal biomass, demonstrating that grazers can modify ratio dependence of algal biomass. Overall, algal biomass appears to be both predator and ratio dependent because grazers are capable of modifying algal response to nutrients, and algae show positive response to nutrients even in the presence of larger grazers.
Habitat Segregation in Ground Crickets: Experimental Studies of Adult Survival, Reproductive Success, and Oviposition Preference
Authors: Howard Daniel J. , Harrison Richard G.
Published: May 2006

The closely related ground crickets Allonemobius allardi and A. fasciatus provide a striking example of habitat segregation. Both species are abundant in pastures and grasslands in the northeastern United States, but they occupy different parts of these habitats. At a site in northwestern Connecticut, we found nearly pure single—species populations at the extremes of a moisture gradient. Allonemobius allardi occurred in dry pasture, A. fasciatus in wet pasture. Distribution patterns remained constant from one developmental stage to another and from year to year. We undertook a series of experiments to define the factors that determine habitat associations in these crickets. By introducing single—species and mixed—species populations into enclosures in both wet and dry areas, we could demonstrate no significant differences in adult survival or reproductive success between species. Both A. allardi and A. fasciatus can survive and reproduce in wet and dry habitats. Laboartory choice experiments indicate that differences in oviposition preference also cannot account for field distribution patterns. Indeed, oviposition preference may be a consequence rather than a cause of habitat association.
The Flight and Migration Ecology of the Red Milkweed Beetle (Tetraopes Tetraophthalmus)
Authors: Davis Mark A.
Published: May 2006

Laboratory experiments showed that female Tetraopes beetles possess greater flight capacity than males and that flight capacity is positively correlated with size. Take—off tendency, however, is higher in males and is negatively correlated with size. Both flight capacity and take—off tendency decline with age. Flight capacity is diminished markedly by starving for 48 h, and, in females, was not found to be influenced by oogenesis. The laboratory findings are consistent with field data showing that males move more often within patches (mate—searching flights) while females move more between patches (migration flights). The data suggest that the flight and migration ecology of short—flying sedentary species, like Tetraopes, may differ markedly from that of long—flying fugitive species.
Aboveground Production and N and P Cycling Along a Nitrogen Mineralization Gradient on Blackhawk Island, Wisconsin
Authors: Pastor John , Aber John D. , McClaugherty Charles A. , Melillo Jerry M.
Published: May 2006

Net aboveground production (4.1—9.5 Mg°ha—1) across a series of edaphic climax forests was highly correlated with field measurements of soil N mineralization (26—84 kg°ha—1°yr—1; r2 = 0.902, P < .001) and with soil silt + clay content (5—74%; r2 = 0.883, P < .001). Soil N mineralization was positively correlated with litter production and N and P return in litter. Soil N mineralization was negatively correlated with litter C:N and C:P ratios and with efficiency of P use in litter production. Efficiency of N use in litter production declined with increasing N mineralization except for inefficient use of N in a hemlock stand at low N mineralization. Changes of litter quality across the mineralization—soil texture gradient were due to species replacement rather than changes in litter quality within each species. Nitrification was not correlated with aboveground production. Both mineralization and nitrification were highly correlated with humus P content. Differences in nitrification among the soils appeared to be related to PO4—P supply in the spring and early summer and to NH4—N supply in mid— to late summer.
The Nitrogen Pathway in a Penguin Rookery
Authors: Lindeboom H. J.
Published: May 2006

The most important nitrogen sources for the Marion Island ecosystem are the excreta of birds that forage at sea. Eighty percent of the nitrogen excreted by penguins during their molt fast appeared to be uric acid, with the remaining 20% mainly proteins and ammonia. The uric acid is rapidly degraded by aerobic and anaerobic microorganisms, and no uric acid could be detected in the penguin rookery deposit. Nitrification, followed by denitrification, occurs in the rookery deposit. However, laboratory experiments showed that both nitrification and denitrification are relatively unimportant processes in the rookery. Models of the nitrogen cycle in both a Macaroni Penguin and a King Penguin rookery during the molt fast and breeding season are given. In both rookeries the degradation of uric acid into ammonia and the subsequent evaporation are, quantitatively, the most important processes. The ammonia production in the rookeries of Macaroni Penguins as well as the heavy rains and the predominantly westerly winds have produced an "ammonia shadow" around the rookery where a vigorous plant growth occurs. The vegetation has formed a thick peat layer around the penguin rookery. 14C dating of this peat layer has shown that the Macaroni Penguins first bred on Marion Island °7000 yr ago.
Litterfall, Nutrient Cycling, and Nutrient Limitation in Tropical Forests
Authors: Vitousek Peter M.
Published: May 2006

Patterns of nitrogen, phosphorus, and calcium cycling through litterfall were evaluated using published information from 62 tropical forests. In general, lowland tropical forests have more nitrogen and lower dry mass/nitrogen ratios in litterfall than most temperate forests, while nitrogen return in montane tropical forests is comparable to that in temperate forests. Calcium return is also high in most tropical forests studied, but many tropical forests (lowland and montane) have little phosphorus return and very high dry mass/phosphorus ratios in litterfall compared to most temperate forests. Phosphorus appears to be cycled highly efficiently in such forests. Fine litterfall in the range of tropical forests studied was predicted from climate, and the residuals of this regression were positively correlated with phosphorus but not nitrogen concentrations in litterfall. The amount of fine litterfall (uncorrected for climate) was also significantly correlated with phosphorus concentrations in moist and wet lowland tropical forests. These analyses suggest that phosphorus but not nitrogen availability limits litterfall in a substantial subset of intact tropical forests. Sites on old oxisols and ultisols, especially those in Amazonia, appear to be particularly low in available phosphorus.
Vegetation Change on a Northeast Tidal Marsh: Interaction of Sea‐Level Rise and Marsh Accretion
Authors: Warren R. Scott , Niering William A.
Published: May 2006

Increasing rates of relative sea—level rise (RSL) have been linked to coastal wetland losses along the Gulf of Mexico and elsewhere. While such losses have yet to be reported for New England tidal marshes, rapidly rising RSL may still be affecting these systems. Studies of the Wequetequock—Pawcatuck tidal marshes over four decades have documented dramatic changes in vegetation that appear to be related primarily to differential rates of marsh accretion and sea—level rise. Other environmental factors such as sediment supply and anthropogenic modifications of the system may be involved as well. When initially studied in 1947—1948 the high marsh supported a Juncus gerardi—Spartina patens belting pattern typical of many New England salt marshes. On the most of the marsh complex the former Juncus belt has been replaced by forbs, primarily Triglochin maritima, while the former S. patens high marsh is now a complex of vegetation types–stunted Spartina alterniflora, Distichlis Spicata, forbs, and relic stands of S. patens. These changes are documented by vegetation sampling that closely followed the 1947—1948 methods and by peat core analysis. Marsh elevations were determined by leveling, and the mean surface elevation of areas where the vegetation has changed is significantly lower than that of areas still supporting the earlier pattern (4.6 vs. 13.9 cm above mean tide level). The differences in surface elevation reflect differences in accretion of marsh peat. Calculations based on sandy overwash layers deposited during historically recorded storms as well as on experimentally placed marker horizons of known age indicate that stable areas have been accreting at the rate of local sea—level rise, 2.0—2.5 mm/yr at least since 1938; changed areas have accreted at about one half that rate. Lower surface elevations result in greater frequency and duration of tidal flooding, and thus in increased peat saturation, salinity, and sulfide concentrations, and in decreased redox potential, as directly measured over the growing season at both changed and stable sites. It is proposed that these edaphic changes have combined to favor establishment of a wetter, more open vegetation type dominated by to distinctive communities–Stunted S. alterniflora and forbs. Changes documented on the Wequetequock—Pawcatuck system have been observed on the other Long Island Sound marshes and may serve as a model for the potential effects of seal—level rise on New England tidal salt marshes.
Biomass and Nutrient Dynamics Associated with Slash Fires in Neotropical Dry Forests
Authors: Kauffman J. Boone , Sanford Robert L. , Cummings Dian L. , Salcedo I. H. , Sampaio E. V. S. B.
Published: May 2006

Unprecedenteded rates of deforestation and biomass burning in tropical dry forests are dramatically influencing biogeochemical cycles, resulting in resource depletion, declines in biodiversity, and atmospheric pollution. We quantified the effects of deforestation and varying levels of slash—fire severity on nutrient losses and redistribution in a second—growth tropical dry forest ("Caatinga") near Serra Talhada, Pernambuco, Brazil. Total aboveground biomass prior to burning was °74 Mg/ha. Nitrogen and phosphorous concentrations were highest in litter, leaves attached to slash, and fine wood debris (<0.64 cm diameter). While these components comprised only 30% of the prefire aboveground biomass, they accounted for °60% of the aboveground pools of N and P. Three experimental fires were conducted during the 1989 burning season. In these treatments consumption was 78, 88, and 95% of the total aboveground biomass. As much as 96% of the prefire aboveground N and C pools and 56% of the prefire aboveground P pool was lost during combustion processes. Nitrogen losses exceeded 500 kg/ha and P losses exceeded 20 kg/ha in the fires of the greatest severity. With increasing fire severity, the concentrations of N and P in ash decreased while the concentration of Ca increased. This indicates greater amounts of these nutrients were volatilized (i.e., greater ecosystem losses occurred) with increasing fire severity. Following fire, up to 47% of the residual aboveground N and 84% of the residual aboveground P were in the form of ash, which was quickly lost from the site via wind erosion. Fires appeared to have a minor immediate effect on total N, C, or P in the soils. However, soils in forests with no history of cultivation had significantly higher concentrations of C and P than second—growth forests. Based upon the measured losses of nutrients from these single slash—burning events, it would likely require a century or more of fallow for reaccumulation to occur. However, current fallow periods in this region are 15 yr or less.
Size‐Dependent Competition: Effects on the Dynamics Vs. The End Point of Mussel Bed Succession
Authors: Wootton J. Timothy
Published: May 2006

I manipulated relative body size of mussels (Mytilus californianus) and gull (Larus glaucescens) predation pressure within gaps in a mussel bed to determine (1) whether size differences could cause shifts in competitive dominance between goose barnacles (Pollicipes polymerus) and Mytilus, species with indeterminate growth, and (2) if the late recruiting Mytilus required gull predation on established adult Pollicipes to attain dominance. Increasing relative body size enhanced the area and the rate of change in area covered by both Pollicipes and Mytilus. Preventing gull feeding enhanced Pollicipes and reduced Mytilus cover, slowing the rates of succession and reducing the frequency of disturbance. However, even in the absence of predators on Pollicipes and with an initial size disadvantage, Mytilus maintained positive rates of change in cover, probably because adult recruitment into the gap altered the initial size hierarchy of competitors. These results indicate that bird predation and initial size asymmetries can alter the dynamics, but not the eventual end point, of intertidal succession. They also highlight the importance of choosing the right comparison (differences between treatments vs. deviations in rates from 0) when testing alternative modes of succession (i.e., facilitation, tolerance, or inhibition). Although gull predation does not change the end point of succession locally, it may have important regional effects by altering the dynamics of disturbance and recovery. Such regional effects cannot be determined by experiments on a local scale.
Stopping Rules in Principal Components Analysis: A Comparison of Heuristical and Statistical Approaches
Authors: Jackson Donald A.
Published: May 2006

Approaches to determining the number of components to interpret from principal components analysis were compared. Heuristic procedures included: retaining components with eigenvalues (λ) > 1 (i.e., Kaiser—Guttman criterion); components with bootstrapped λ > 1 (bootstrapped Kaiser—Guttman); the scree plot; the broken—stick model; and components with λ totalling to a fixed amount of the total variance. Statistical approaches included: Bartlett's test of sphericity; Bartlett's test of homogeneity of the correlation matrix, Lawley's test of the second λ bootstrapped confidence limits on successive λ (i.e., significant differences between λ); and bootstrapped confidence limits on eigenvector coefficients (i.e., coefficients that differ significantly from zero). All methods were compared using simulated data matrices of uniform correlation structure, patterned matrices of varying correlation structure and data sets of lake morphometry, water chemistry, and benthic invertebrate abundance. The most consistent results were obtained from the broken—stick model and a combined measure using bootstrapped λ and associated eigenvector coefficients. The traditional and bootstrapped Kaiser—Guttman approaches over—estimated the number of nontrivial dimensions as did the fixed—amount—of—variance model. The scree plot consistently estimated one dimension more than the number of simulated dimensions. Barlett's test of sphericity showed inconsistent results. Both Bartlett's test of homogeneity of the correlation matrix and Lawley's test are limited to testing for only one and two dimensions, respectively.
Putting Things in Even Better Order: The Advantages of Canonical Correspondence Analysis
Authors: Palmer Michael W.
Published: May 2006

Canonical Correspondence Analysis (CCA) is quickly becoming the most widely used gradient analysis technique in ecology. The CCA algorithm is based upon Correspondence Analysis (CA), an indirect gradient analysis (ordination) technique. CA and a related ordination technique, Detrended Correspondence Analysis, have been criticized for a number of reasons. To test whether CCA suffers from the same defects, I simulated data sets with properties that usually cause problems for DCA. Results indicate that CCA performs quite well with skewed species distributions, with quantitative noise in species abundance data, with samples taken from unusual sampling designs, with highly intercorrelated environmental variables, and with situations where not all of the factors determining species composition are known. CCA is immune to most of the problems of DCA.
Evolution of a Flower Dimorphism: How Effective is Pollen Dispersal by "Male" Flowers?
Authors: Podolsky Robert D.
Published: May 2006

Many plants produce more flowers than will set fruit. In some species, a subset of flowers are actually female—sterile and morphologically distinct; these flowers are presumed to enhance fitness primarily through pollen donation. Individual plants of the hummingbird—pollinated shrub Besleria triflora produce both long—styled and short—styled flower morphs, characteristic of these "andromonoecious" sexual systems. Short—styled flowers set fruit rarely when hand—pollinated and are therefore functionally staminate. To test the hypothesis that selection for increased male function maintains flower dimorphism, I measured relative pollen dispersal per unit investment by staminate vs. perfect (long—styled) flowers. In the field, anthers of perfect flowers dispersed pollen for a significantly longer time than did those of staminate flowers. In laboratory experiments, hummingbirds transferred more pollen per visit from perfect flowers than from staminate flowers, in part due to differences in flower—morph pollen production. As a result, perfect flowers dispersed substantially more pollen than staminate flowers over an average flower lifetime. The two flower morphs did not differ in the amount of biomass invested through the time of corolla abscission, suggesting that staminate flowers do not conserve resources substantially. These results fail to support the "male—function" hypothesis for the evolution of andromonoecy. Staminate flowers contribute relatively little to plant reproductive success directly through male function, suggesting they are maintained for reproductive functions other than pollen donation.
Stable Isotopes Resolve the Drift Paradox for Baetis Mayflies in an Arctic River
Authors: Hershey Anne E. , Pastor John , Peterson Bruce J. , Kling George W.
Published: May 2006

The colonization cycle hypothesis states that stream ecosystems would become depleted of insects if flying adults did not compensate for drifting immatures. Using long—term drift and benthic abundance data, we show that a Baetis mayfly nymph population moves downstream during development in the Kuparuk River in arctic Alaska. Baetis relative benthic abundance decreased from early to late season in an upstream unfertilized river section, while simultaneously increasing in the downstream fertilized section. Baetis nymphs drifted significantly more in the upstream unfertilized section, compared to the downstream fertilized section where food was more abundant. Approximately one—third to one—half of the nymph population drifted at least 2.1 km downstream during the arctic summer. A stable isotope tracer experiment and mathematical models show that about one—third to one—half of the adult Baetis population flew 1.6—1.9 km upstream from where they emerged. These results provide a quantitative test of the colonization cycle for the dominant grazer/collector in the Kuparuk River. Quantifying the colonization cycle is essential to understanding stream ecosystem function because offspring of downstream insects are needed for nutrient cycling and carbon processing upstream. Since downstream drift and upstream flight are important components in recovery of streams from disturbances, our results provide a quantitative method for predicting recolonization rates from downstream, essential to estimating recovery.
Bacterial‐Algal Relationships in Streams of the Hubbard Brook Experimental Forest
Authors: Findlay Stuart , Howe Karin , Fontvielle Dominique
Published: May 2006

Epilithic bacteria appear to be an important trophic component in many streams ecosystem, but it is not clear whether bacterial abundance and growth covary within epilithic algae, one potential carbon source for bacteria. Epilithic bacterial abundances and growth rates were measured for 2 yr in two streams with contrasting trophic bases at the Hubbard Brook Experimental Forest. The reference stream (Bear Brook) has a closed canopy Low epilithic primary production, and a high standing stock of detrital organic matter. A nearby stream in a clear—cut catchment had experienced algal blooms in the early years following cutting, and rates of primary production measured during our study period were 5 times greater than in Bear Brook. Chlorophyll a concentrations on tiles did not differ between streams, indicating that algal abundance was limited by factors other than light availability. Bacteria were not consistently correlated with algal abundances in either stream. Bacterial abundance and growth did not differ statistically between streams despite the large differences in rates of primary production. A shading experiment conducted in both streams was successful in reducing chlorophyll levels but did not reduce bacterial growth rates. A laboratory experiment involving nutrient additions and high light levels greatly stimulated algal abundance and carbon fixation, but there was no parallel increase in bacterial abundance or growth. Apparently, in contrast to planktonic systems, there is not a tight trophic connection between algal and bacterial productivity in these streams.
Daphnia Growth on Varying Quality of Scenedesmus: Mineral Limitation of Zooplankton
Authors: Sterner Robert W.
Published: May 2006

Because the biochemical content of primary producers varied with their growth rate, herbivores feeding on foods of high growth rate have different diets than herbivores feeding on foods of low growth rate. Herbivores' food quality is thus related to their resource's growth rate. Here, the growth in body mass of individuals of the herbivore Daphnia obtusa was measured for a variety of foods, which consisted of the chlorophyte Scenedesmus acutus cultured under a suite of N— and P—limited growth rates. Food quantity (measured as carbon) was held constant at 0.5 mg/L. In general, low growth rate algae were poorer in quality than high growth rate algae. The logarithm of Daphnia mass was well predicted by the logarithm of algal growth rate. Algal growth rates at <50% of resource saturation demonstrated marked reductions in quality. Animals feeding on low growth rate foods, and which themselves tended to grow slowly, nevertheless accumulated lipid to a higher degree than faster growing animals. A biochemical analysis of elemental (C, H, N, and P) and biochemical (protein, carbohydrate, and ash) content (all as percentage of total dry mass) suggested the nutritional basis for these differences in food quality. Phosphorus content was especially well correlated with food quality. Daphnia mass was explained with an r2 of 0.97 by a regression model with P, C, and H content. Algal foods of >1% P were high in quality, while foods lower than this exhibited reduced quality. These results are consistent with P limitation of Daphnia growth when feeding on foods of low P content.
Intraspecific and Cross‐Superorder Responses to Chemical Alarm Signals by Brook Stickleback
Authors: Mathis Alicia , Smith R. Jan F.
Published: May 2006

Fathead minnows (Pimephales promelas) and brook stickleback (Culaea inconstans) are often sympatric, occupy similar microhabitats, and share common predators. Therefore, individuals that detect alarm signals of both conspecifics and heterospecifics should gain antipredator benefits. We conducted a series of experiments to determine the extent to which these species respond to chemical alarm signals from conspecifics and heterospecifics. In laboratory experiments, brook stickleback responded to chemical stimuli from injured conspecifics with increased shoaling, but did not increase shoaling following exposure to chemical stimuli from injured swordtails (Xiphophorus helleri), an unfamiliar tropical fish that is not closely related to either stickleback or fathead minnows. These data are the first to document a chemical alarm signal for fishes in the order Gasterosteiformes. Brook stickleback also exhibited fright responses to extracts from injured fathead minnows in both laboratory and field tests. Stickleback did not exhibit a fright reaction following exposure to chemical stimuli from fathead minnows that had been treated with testosterone to decrease the concentration of alarm substance cells. This result suggests that the minnow alarm pheromone is the active component rather than some other constituent of the minnow skin extracts. In contrast to the response of the stickleback, fathead minnows did not respond to extracts from brook stickleback with a fright response. These data suggest that brook stickleback may benefit from close proximity with fathead minnows by gaining early warning of danger.
Ontogenetic Loss of Phenotypic Plasticity of Age at Metamorphosis in Tadpoles
Authors: Hensley Frank R.
Published: May 2006

Amphibian larvae exhibit phenotypic plasticity in size at metamorphosis and duration of the larval period. I used Pseudacris crucifer tadpoles to test two models for predicting tadpole age and size at metamorphosis under changing environmental conditions. The Wilbur—Collins model states that metamorphosis is initiated as a function of a tadpole's size and relative growth rate, and predicts that changes in growth rate throughout the larval period affect age and size at metamorphosis. An alternative model, the fixed—rate model, states that age at metamorphosis is fixed early in larval life, and subsequent changes in growth rate will have no effect on the length of the larval period. My results confirm that food supplies affect both age and size at metamorphosis, but developmental rates became fixed at approximately Gosner (1960) stages 35—37. Neither model completely predicted these results. I suggest that the generally accepted Wilbur—Collins model is improved by incorporating a point of fixed developmental timing. Growth trajectories predicted from this modified model fit the results of this study better than trajectories based on either of the original models. The results of this study suggest a constraint that limits the simultaneous optimization of age and size at metamorphosis.
Animal Dispersal Patterns: A Reassessment of Simple Mathematical Models
Authors: Porter John H. , Dooley James L.
Published: May 2006

Attempts to fit simple mathematical models of animal movement to observed distributions of movements have been extremely successful. However, the extent to which these results were influenced by use of potentially distance—weighted sampling methods has not been evaluated. Of the 15 field studies used to test model fits, 13 used methods that sample unevenly over distance. We use a simple Monte—Carlo simulation model to evaluate the effects of unequal sampling over distance on results obtained from simple mathematical models of animal movement. For three data sets that provide detailed maps of observation sites, the effects of unequal sampling are profound. Prior to sampling, data simulated by our model follow a uniform distribution, but a geometric model adequately fits the "sampled" simulated data. Following corrections to the field data to mitigate the effects of distance—weighted sampling, in only one of five studies do simple mathematical models adequately fit the observed distribution of movements.
A General Test for Interaction Modification
Authors: Adler Frederick R. , Morris William F.
Published: May 2006

How can measurements of population dynamics be used to deduce the mechanisms of interaction in an assemblage of species? We present a technique to use such measurements to distinguish among assemblages of species with no direct interactions, sets of species influenced predominantly by pairwise interactions, and communities with significant interaction modification. We define the interaction coefficients and show that their dependence on the population sizes of the various species reveals and pinpoints interactions. Our technique distinguishes non—additivity in the statistical sense from interaction modification in the biological sense.
The Effect of Relatedness on Spacing Behavior and Fitness of Female Prairie Voles
Authors: Sera Wendy E. , Gaines Michael S.
Published: May 2006

Numerous behavioral hypotheses have been suggested to explain population cycles in microtine rodents. Charnov and Finerty (1980) proposed that preferential behavior toward relatives drives population cycles through kin selection. Their hypothesis makes three assumptions: (1) individuals behaviorally discriminate kin from non—kin, (2) kin associate, and (3) kin benefit from this association. These assumptions were tested in female prairie voles (Microtus ochrogaster) in eastern Kansas. An equal number of laboratory—born females and males were released into 12 fenced enclosures; 6 enclosures contained groups of littermate sisters and 6 contained groups of unrelated females. Space use, reproductive success, and survival were monitored during two replications of the experiment (Fall 1989 and Spring 1990). Female survival and reproductive success were not affected by relatedness, although more young were born in the Spring than in the Fall. Home range size and overlap were greater for females in related groups than those in unrelated groups. Home range size also was larger in the Fall than in the Spring. Prairie vole sisters associated spatially, but our measurements showed no fitness benefits conferred by these associations. Although the kin—selection hypothesis could not be demonstrated in this experimental population, relatedness in local neighborhoods may have consequences for small mammal population ecology.
Tropical Forest Disturbance: Paleoecological Records from Darien, Panama
Authors: Bush Mark B. , Colinvaux Paul A.
Published: May 2006

The first paleoecological data from the Darien of Panama, a remote region rich in endemic species and purported to be one of the last untouched neotropical wilderness, demonstrate a 4000—yr history of human disturbance. Unstable climate is recorded as changes in precipitation inferred from the diatom record, but a more important source of disturbance has been human activity. Pollen, and phytoliths of Zea mays, and charcoal from grass fires confirm historical and archaeological judgments that the region has a long history of human settlement.The data are consistent with depopulation and abandonment of most agriculture following the Spanish conquest, showing that the local modern forest has developed in recent centuries. Four millennia of disturbance that preceded the decline of human populations may have had a profound effect upon the modern forest associations. The apparently pristine forests appear to have regrown in just 350 yr, probably from populations fragmented by previous agricultural disturbance. However, the modern richness of the Darien forests suggests that local biodiversity was maintained throughout 4000 yr of indigenous agriculture.
A Comparison of Plotless Density Estimators Using Monte Carlo Simulation
Authors: Engeman Richard M. , Sugihara Robert T. , Pank Larry F. , Dusenberry William E.
Published: May 2006

We conducted an extensive simulation study to compare the performance of a large group of plotless density estimators (PDEs) to obtain clarification of their relative performance in a diversity of sampling situations. The PDEs studied included well—known ones from the literature plus some extensions and modifications introduced here. The simulations cover 96 combinations of 6 spatial patterns, 4 sample sizes, and 4 population densities. We made comparisons within classes of similar estimators, and we indicate the best—performing PDEs out of the complete set studied. Over all spatial patterns, the angle—order estimator with measurements to the third—closest individual in each quadrant had the lowest relative root—mean—squared error (RRMSE), followed by the same estimation method with measurements to the second closest individual in each quadrant. Also performing well were the variable area transect, the ordered distance estimator using the third closest individual, and an extension of the Kendall—Moran estimator that searches for the second nearest neighbor and pools search areas from all sample points. Opinions and recommendations are given as to which PDEs perform well enough and are practical enough to deserve strong consideration for use in the field.
Density Dependence is Better Than Ratio Dependence
Authors: Gleeson Scott K.
Published: May 2006

Ratio—dependent models make very specific assumptions that prevent them from serving as a foundation for general consumer—resource theory. Traditional density—dependent models can be, and have been, modified to incorporate similar alternative assumptions and many others.
The Fallacies of "Ratio‐Dependent" Predation
Authors: Abrams Peter A.
Published: May 2006

It has recently been claimed that the functional response of predators depends on the numbers of prey and predators only via their ratio. Contrary to this claim, I argue that such “ratio—dependent” functional responses are very unlikely to occur on theoretical grounds and have not been shown empirically. Previous justifications for ratio—dependent functional responses ignore the role of these responses in determining prey population dynamics. Patterns in the abundances of trophic levels and experimental results that have been cited as support for “ratio—dependent” predation are consistent with numerous other explanations. These other explanation do not suffer from the pathological behaviors and lack of a plausible mechanism that afflict ratio—dependent models. Furthermore, ratio—dependent functional responses, because of their lack of mechanistic basis, do not provide a good basis for developing more detailed models. Nor can the use of ratio—dependent models be justified as a limiting case of more general predator—dependent models.
The Enemies Hypothesis: Tritrophic Interactions and Vegetational Diversity in Tropical Agroecosystems
Authors: Letourneau Deborah K.
Published: May 2006

The effects of vegetational diversity on the abundance of natural enemies of herbivores were studied in a traditional agroecosystem in tropical Mexico. Visitation patterns of parasitic Hymenoptera and densities of predators were compared between monocultures of squash and maize and mixed assemblages of maize, cowpea, and squash. The impact of parasitoid visitation was assessed by monitoring the percent parasitism of a target herbivore in the system: Diaphania hyalinata (L.) (Lepidoptera: Pyralidae), a cucurbit specialist. The "Enemies" hypothesis predicts a positive correlation between plant species richness and natural enemy abundance, which results in the regulation of herbivores at lower levels in diverse vegetation than in pure stands. The specific questions addressed in this study were: (1) are the major groups of natural enemies more abundant in patches of diverse vegetation than in monocultures?; (2) if so, does an increase in either abundance or diversity of natural enemies cause a concomitant increase in herbivore regulation?; (3) are the effects of vegetational diversity uniform over major enemy groups? The activity of hymenopteran parasitoids was affected by cropping pattern. Malaise trap captures of parasitoids in general, and of those species that attack D. hyalinata on squash, were consistently greater in tricultures than in squash monocultures, but were also greater in maize monocultures. Parasitism rates of eggs and larvae were higher on squash interplanted with maize and cowpea. These data partially support the "Enemies" hypothesis in explaining lower herbivore levels in diverse vegetation. However, the effects of diversity, per se, do not seem to be as important as the presence of maize in the system. The responses of natural enemies to vegetational diversity were not uniform. Most predators were not significantly influenced by cropping patterns, and some were more abundant in squash monocultures. The results of this study are discussed in terms of possible routes by which members of the third trophic level are influenced by plants in association.
Breeding Birds of Isolated Woodlots: Area and Habitat Relationships
Authors: Blake John G. , Karr James R.
Published: May 2006

We investigated breeding bird communities of isolated woodlots (1.8—600 ha) in east—central Illinois during three summers (1979—1981) to compare the influence of area and habitat on community structure. Woodlots supported from 9 to 43 species and composition was relatively constant among years. Ecological generalists dominated small woodlots, while more specialized species increased in importance with area. Area accounted for most variation (86—98%) in total species number in each year and the species—area relationship did not change significantly among years. The amount of variance accounted for by area was greater than in previous studies. Neither habitat nor woodlot isolation explained significant additional variation in total species richness after area. Area accounted for most variation in number of species in different migratory and breeding habitat categories, except for short—distance migrants, which correlated most strongly with habitat. Variation in habitat was not related to woodlot area and habitat accounted for additional variation in bird species numbers in most cases. Abundances of one—third to one—half of species examined correlated with woodlot area, but a greater proportion (66—72%) were influenced more strongly by habitat variables. Results from Illinois support previous conclusions that species that breed in forest interior habitat and winter in the tropics are most likely to be adversely affected by a reduction in forest habitat. Results also show that bird communities in isolated tracts of forest are not random assemblages, but rather that species found in smaller woodlots are subsets of species found in larger forests.
A Spurious Correlation in an Interpopulation Comparison of Atlantic Salmon Life Histories
Authors: Myers Ransom A. , Hutchings Jeffrey A.
Published: May 2006

We tested two hypotheses concerning geographical variation in Atlantic salmon (Salmo salar) life histories: (1) mean age at first reproduction is positively correlated with growth rate at sea and (2) within—population variation in age at first reproduction first increases and then decreases with latitude. Data on growth and age at first reproduction were compiled from 41 populations in eastern North America. Data reliability was checked by a redetermination of ages based on scale examination. The proportion of fish that were incorrectly aged was small (°0.7%); however, aging errors were primarily of one kind; salmon that had previously spawned were misclassified as virgin fish of an older age class. Growth rate at sea was found not to be positively correlated with age at maturation. Schaffer and Elson's (1975) positive correlation between growth and age at first reproduction can be attributed to a subtle statistical artifact caused by aging errors. We also found that within—population variation of age at maturation was not related to latitude. We conclude that tests of life history theories should not assume constancy in life history traits, such as mortality, among populations.
Utilization of Freshwater and Ocean Water by Coastal Plants of Southern Florida
Authors: Sternberg Leonel da Silveira Lobo , Swart Peter Koenraad
Published: May 2006

The coastal vegetation of southern Florida is undergoing dramatic changes due to the instability of the ocean water—freshwater boundary. These vegetation changes will be determined by the response of each particular species to saline ocean water, particularly whether it can use ocean water or not. In this study, isotopic data were used to determine the relative usage of freshwater or ocean water by plants in the Florida keys. The results indicate that, with some exceptions, plants toward the interior of the keys were using freshwater while those toward the edge were using ocean water. A plot of the hydrogen and oxygen isotopic composition of the plant water yielded a mixing line between typical freshwater values and those of ocean water. In general, the isotopic ratios of stem water for species found in hardwood hammocks were confined to the freshwater end of the line, followed by values of stem water from mangrove margin species. found in mangroves, however, had water with extremely variable isotopic ratios, ranging from values typical of ocean water to values typical of freshwater. This variability is consistent with the hypothesis that mangroves are fully capable of growing in freshwater, but are limited to saline habitats because of competitive exclusion by fast—growing glycophilic plants.
Clonal Integration and Population Structure in Perennials: Effects of Severing Rhizome Connections
Authors: Schmid B. , Bazzaz F. A.
Published: May 2006

Short rhizomes in perennial plants lead to compact genet architecture and populations consisting of monoclonal patches. Long rhizomes lead to spreading genets and polyclonal patches. To test if shoot integration within genets was higher in the first case than in the second, we compared shoots of connected genets to artificially disconnected shoots for three Aster species (spreading genets), Solidago canadensis (compact genets), and S. gigantea (intermediate) grown in high and low density, pure and mixed sands. Severing rhizome connections stimulated plant growth in S. canadensis but had only small effects on growth in Aster and S. gigantea. In low density, the production of new rhizome and shoot modules of S. canadensis, and to a lesser degree of S. gigantea, was restricted by integration. Aster performed better and S. canadensis worse in mixed than in pure stands. Intact connections did not increase the competitive ability of s. canadensis grown in mixture. Shoots of S. canadensis, but not of S. gigantea and Aster, were more variable if connected in pairs than if isolated (or connected in fours). The results confirm the prediction that integration increases with increasing genet compactness, i.e., Aster < S. gigantea < S. canadensis. They further indicated that destroying physical connections in integrated genets may decrease between—shoot competition rather than between—shoot cooperation. Ecological consequences of high vs. low clonal integration in perennial plants are discussed.
Comparative Analyses of Carbon Dynamics in Native and Cultivated Ecosystems
Authors: Buyanovsky G. A. , Kucera C. L. , Wagner G. H.
Published: May 2006

Plant productivity, litter decomposition rates, and soil organic matter accumulation for winter wheat and for unbroken tallgrass prairie in Central Missouri were analyzed and compared. As measured in this 3—yr study, annual production of dry matter above— and belowground for the cultivated system averaged slightly higher than that for the natural vegetation burned every 3—4 yr. Prairie was characterized by greater year—to—year fluctuation of productivity, which in some years exceeded productivity of the cultivated system. More litter and structural biomass older than 1 yr occurred in the prairie, reflecting the perennial nature of the root system. Principal pathways of carbon transfer in both ecosystems were modeled, and mean residence time in major storage compartments estimated. Combined CO2 losses from above— and belowground litter decay, expressed as a percentage of total soil respiration, were twice as great under wheat as for native prairie. A relatively greater fraction of net primary production was available for synthesis of soil organic matter in native prairie. Under equilibrium conditions, decomposition constants for this compartment, however, were similar. Contrasts in community structure and phenology, seasonal dynamics of litter decay, and levels of soil disturbance are suggested influences affecting transfer and storage characteristics.
Site‐Related ^(13)C of Tree Leaves and Soil Organic Matter in a Temperate Forest
Authors: Balesdent Jerome , Girardin Cyril , Mariotti Andre
Published: May 2006

In order to relate the isotopic composition of soil organic matter to parent vegetation and soil type, we measured the carbon stable isotope ratios of tree leaves and soil C and 14 locations in a temperate forest. Sites were selected over a wide variety of soil types and related vegetation associations, but within a single regional climate. The δ13C of the bulk leaf material falling on the soil varied among sites, ranging from —29.5 to —26%. Within this range, differences up to 1.5% were attributable to differences in three species. Further differences were related to site. The δ13C values of soil organic matter cover the range —29.8 to 24.3% and varied with both parent vegetation δ13C and depth. Transformation and decay of organic C within the litter layers led to no isotope enrichment, irrespective of vegetation and humus type: mull, hydromull, moder, or anmoor. The difference between woody and leaf material in litter was low, 0.23 ± 0.35% (mean ± SD). On the other hand δ13C in mineral horizons always increased with depth, reaching values richer than litter by 1.0 ± 0.5% at 20 cm and up to +1.5% at 1 m. The trend was independent of the soil physico—chemical characteristics, whether aerobic, anaerobic, eutrophic, oligotrophic, or podzolic. Isotope ratios of soil organic C in forests appear to provide useful estimators of tree isotopic composition. When compared to the measurements of the vegetation, they offer the advantage of an easily obtained value that naturally integrates over plant material, time and, eventually, local area.
The Orgins and Evolution of Predator‐Prey Theory
Authors: Berryman Alan A.
Published: May 2006

Predator—prey theory is traced from its origins in the Malthus—Verhulst logistic equations, through the Lotka—Volterra equations, logistic modifications to both prey and predator equations, incorporation of the Michaelis—Menten—Holling functional response into the predator and prey equations, and the recent development of ratio—dependent functional responses and per—capita rate of change functions. Some of the problems of classical predator–prey theory, including the paradoxes of enrichment and biological control, seem to have been caused by the application of the principle of mass action to predator–prey interactions. Predator–prey models that evolved from logistic theory or that incorporate ratio—dependent functional responses do not have these problems and also seem to be more biologically plausible.