bluuebunny/crossref_metadata_2025 huggingface dataset:
Successional Development of the Forest Floor and Soil Surface on Upland Sites of the East Gulf Coastal Plain
Authors: Switzer G. L. , Shelton M. G. , Nelson L. E.
Published: May 2006

The forest floor and Soil surface were studies in 40 forest stands representing secondary succession from old fields to the oak—hickory—pine climax in eastern Mississippi, USA. Forest succession proceed from coniferous to deciduous communities and is divided into early, middle, and late stages. The compositional change of the vegetation is linearly related to stand age, and the shift from coniferous to deciduous dominance occurs at °130 yr. The physical and chemical properties of the forest floor and soil surface changes during succession and make extensive recoveries from the levels reported for old fields at abandonment. However, no overall pattern of change emerges since change varies by specific property of the forest floor and soil surface. Generally, the properties of the forest floor layers are more reflective of compositional changes than are the properties of the soil surface. Organic matter, C, N, P, and K approach equilibrium in the forest floor in early succession while the equilibrium of Ca and Mg is not reached until late succession. The equilibrium levels of organic matter and C are principally determined by decomposition rates since the inputs to the forest floor remain relatively constant throughout succession. Organic matter and C approach equilibrium levels in the succession. The rapid recovery indicates the restorative properties of the communities of early succession and the resilient properties of these sites.
Functional Relationships of Macroinvertebrates in Heterotrophic Systems with Emphasis on Sewage Sludge Decomposition
Authors: Mitchell Myron J.
Published: May 2006

The general functional roles of macroinvertebrates in heterotrophic systems are outlined with special reference to sewage sludge decomposition. Specific energetic parameters of an isopod, Oniscus asellus, and an earthworm, Eisenia foetida, and four sludges were determined under a variety of conditions. Oxygen consumption rates for O. asellus, E. foetida, and sludge were measured from 5° to 30°C and found to fit an exponential formulation expressed as Q10. The earthworm had a 39% lower respiration rate when food was present. The respiration rate of sludge was directly proportional to its moisture content although the history of the moisture regime also affected oxygen consumption with recently wetted sludge having the highest rate. The aging of sludge brought about an exponential decline in respiration rate. Egestion rates for O. asellus and E. foetida were determined gravimetrically from 5° to 37°C. Egestion was maximal at 20°C for O. asellus and 15°C for E. foetida. The effect of temperature on egestion was formulated as a modified Krogh curve. Moisture above a threshold level was found to have no effect on egestion. Sludge type had a market effect on egestion rate with one sludge even being toxic, although egestion rates were generally similar to those found for other substrates. Sludge egested from the macroinvertebrates had a respiration rate 2.82 times greater than non—eaten sludge. Using the derived functional relationships and constant, along with published values of assimilation efficiency, a FORTRAN simulation model INDEC was constructed for predicting the effect of macroinvertebrate feeding on decomposition. Model predictions were compared with values obtained from sludge—invertebrate microcosms, and a high correlation (r = .916, N = 60) was found. The importance of macrocoinvertebrates in stimulating biological activity in heterotrophic systems was discussed and related to specific parameters of the INDEC model. The roles of specific energetic conversions, such as secondary production, in affecting decomposition processes were demonstrated.
Territorial Behavior of Eastern Chipmunks (Tamias Striatus): Encounter Avoidance and Spatial Time‐Sharing
Authors: Getty Thomas
Published: May 2006

The structure and dynamics of chipmunk home ranges were characterized by focal—animal observation. Neighboring animals were territorial, but their home ranges overlapped extensively and did not have exclusive core areas. Established neighbors avoided encountering each other. Their pattern of encounter avoidance with extensive spatial overlap resulted in spatial time—sharing. Territorial interference with the timing of space—use did not affect the total utilization of shared areas within a resident's home range. Distance and patch structure were important proximate determinants of space—use intensity. The result suggest that territorial interference is more important as a mechanism for deterring the immigration of nonneighbors than as a continuously operative competitive mechanism between established neighbors. The concept than the proximate object of interference competition is access to space is questioned.
Small‐Mammal Associations in Forested and Old‐field Habitats: A Quantitative Comparison
Authors: Anthony Robert G. , Niles Lawrence J. , Spring Jeffrey D.
Published: May 2006

Population densities, physical condition, and several parameters (diversity, niche breadth, and ratio of dominance) of small—mammal communities were documented for two old—field and two forested sites from fall 1974 to spring 1977. White—footed mice (Peromyscus leucopus) were the most numerous species in forested habitats, and populations fluctuated asynchronously and were noncyclic. Physical condition indices were not significantly different between the two forested sites, but values were significantly higher for adults than juveniles and significantly different between different sample periods. Seasonal changes in physical condition were not correlated with population fluctuations. Meadow voles (Microtus pennsylvanicus) were the most numerous species in old—field habitats, and populations were cyclic and fluctuated synchronously with a 2—yr duration between peaks. Physical condition indices were not significantly different between different census periods, but were significantly higher for adults than juveniles. Seasonal changes in physical condition were not significantly correlated with population fluctuations. There was a negative correlation between average niche breadth and the number of species occurring in each census period for both Peromyscus— and Microtus—dominated communities, which suggested the occurrence of species packing. Niche breadth of species was positively correlated with their abundance of both forested and old—field habitats. Species diversity was negatively correlated with meadow vole density, suggesting that at high densities voles competitively excluded other species of small mammals. Species diversity of small—mammal communities in both habitats were extremely variable spatially and temporally. There were significant differences in diversity indices between sites within the same habitat but not between habitats.
How Well Does the Edmonson‐Paloheimo Model Approximate Instantaneous Birth Rates?
Authors: Lynch Michael
Published: May 2006

An equation independently derived by Edmondson and Paloheimo for estimating instantaneous birth rates without a knowledge of mortality rates has been extensively employed by zooplankton ecologists. This expression is exactly true only under the unlikely conditions that the age distribution is stable and that egg mortality is equal to that averaged across the entire population. Here I compare estimates of instantaneous birth rates (b) using the Edmondson—Paloheimo equation to those determined with a general model which accounts for age structure instability and egg mortality in two Daphnia pulex populations. Despite the fact that the assumptions of the Edmondson—Paloheimo models are rarely met, it mimics the seasonal pattern of b quite well, with few exceptions. An analysis of variance suggests that the model will provide an adequate approximation of the true population birth rate when a variance in b of 0.003 can be tolerated. A much more critical factor in the analysis of instantaneous rates in plankton populations is the development of accurate sampling techniques.
A Method for the Statistical Analysis of Time‐Energy Budgets
Authors: Travis Joseph
Published: May 2006

In this paper I outline a method for estimating the sampling variance of estimates of mean daily energy expenditure of free—ranging animals, based on time—energy budgets. This method combines estimated components of variation from laboratory and field observations into a single estimate of the overall sample variance. An approximate confidence region for the mean daily expenditure can be constructed as well. I illustrate these methods by applying them to the energy budget of the Golden—winged Sunbird (Nectarinia reichenowi) originally published by Gill and Wolf (1975). The total sample variance of the mean daily energy expenditure, when that expenditure is estimated from the time—energy budget approach, is a sum of many terms, including the products of the variances of individual variables, the squared estimates of the mean of individual variables, and the products of the estimated means and covariances among the variables. Thus, the estimated sample variance will usually be large. Any biases in estimation will be propagated throughout the calculations, and errors of staggering magnitude can result. Knowlege of the components of total sampling variance and the sensitivity of these estimates to the various sources of bias should aid field biologists in designing time—energy budget studies so that the maximum possible reliability can be achieved.
The Costs of Reproduction in Brine Shrimp
Authors: Browne Robert A.
Published: May 2006

Brine shrimp were subjected to one of four reproductive regimes: complete absence of mating, mating postponed for 20 d or 40 d past sexual maturity, or continuous breeding upon sexual maturity (controls). Each of the four reproductive regimes was further subdivided into low and high feeding groups (1:10 feeding ratio). Under low food, female lifespan was negatively correlated with the length of the reproductive period. However, no such relationship was found among the four high food groups; no intrasex differences were found in survival curves or mean length of lifespan. Fertile females in the delayed reproduction groups gave birth to approximately the same total number of offspring as controls, not by lengthening lifespan but by producing larger broods, with fewer days between broods. The results indicate that although some reproductive costs are unavoidable, nutritional resources play a critical role in determining how extensively reproduction will affect lifespan.
Results of Experimental Density Manipulation in An Arizona Lizard Community
Authors: Tinkle Donald W.
Published: May 2006

A study of three species of sceloporine lizards (Sceloporus clarki, S. undulatus, and Urosaurus ornatus) was begun in 1971 and continued into 1977 in a very diverse (at least 11 species) lizard community in central Arizona, USA. The present paper reports the results of a density manipulation experiment carried out with these three lizards to ascertain whether direct evidence for interspecific competition could be found in a community of lizards in which circumstantial evidence suggested its importance. In May 1975 the study area was divided along a natural constriction into an experimental area and a control area and an attempt was made to remove all U. ornatus and S. clarki from the experimental areas. This experimental treatment was maintained until the termination of the experiment in 1977. Patterns of habitat utilization, population density, survivorship, and individual body size of S. undulatus on experimental and control areas both before and after the removals were analyzed for evidence of competitive interactions. There were no detectable effect of the removal of S. clarki and U. ornatus on habitat selection, perch height, survivorship, population density, or individual body size of S. undulatus inhabiting the removal area. Implications of these results for studies of lizard community structure are discussed.
Seasonal Water Potential Components of Sonoran Desert Plants
Authors: Monson Russell K. , Smith Stanley D.
Published: May 2006

Seasonal water potential components were measured for seven Sonoran Desert plant species representing a variety of growth forms. Three of the species (Amsinckia intermedia, Erodium cicutarium, and Baccharis sarothroides), which occupy the most mesic microhabitats, possessed the highest osmotic potentials and lowest pressure potentials, with very little seasonal adjustment in either parameter. In constrast, two species (Larrea tridentata and Atriplex polycarpa), which experienced substantial periods of water stress, had relatively low osmotic potentials and high pressure potentials with seasonal adjustments occurring in both. Two species (Encelia farinosa and Olneya tesota) exhibited intermediate responses for dawn plant water potential. Encelia also exhibited intermediate osmotic and pressure potential values. However, in Olneya these latter values were very similar to those for Larrea and Atriplex. The capacity for osmoregulation was noted in four of the seven species, with fluctuations in the osmotic potential at full turgor ranging from 0.3 to 0.8 MPa. Adjustments in tissue elasticity and pressure potential were also noted in four of the species. In general these adjustments allow the species to maintain higher turgor pressures at most relative water contents during periods of drought stress. The results indicate that a plant's capacity to avoid water stress is reflected in its water potential components.
Experimental and Observational Studies of Patch Choice at Different Scales by the Crab Spider Misumena Vatia
Authors: Morse Douglass H. , Fritz Robert S.
Published: May 2006

We studied patch choice of adult female crab spiders (Misumena vatia) on common milkweed (Asclepias syriaca) at three different scales: among umbels (inflorescences), among stems, and among clones. Spiders occupied the umbel on a stem with the most insect prey (and most nectar—producing flowers) (=high quality) more often than predicted by chance and captured most of their prey there. However, even if sample patch choices (umbels) of greatly varying quality were provided, 30% of the spiders did not select high—quality umbels within a day, although choices required movements of only several centimetres. The distribution of spiders on these umbels most closely resembled that predicted if spiders responded to the number of times insect prey visited an umbel. Many spiders move to higher quality stems, upon which most prey were caught, as the last flowers on their own stems senesced. Significantly more spiders remained on high—quality stems than did those on stems with only senesced umbels; however, 25% of the spiders placed on high—quality stems nevertheless moved. Many spiders that moved did not immediately occupy stems of higher quality than the ones they had just left, but by continuing to move, their probability of eventually occupying a high—quality stem markedly increased. Thirty—five percent of the spiders on stems with only senesced umbels did not move within a day. Clones of milkweed were several metres apart, and there was no evidence that spiders moved between them during their last instar. We argue that stochastic factors (unpredictable visits to flowers by prey) may account for the nonuniform response in the simple umbel choice experiments. They may also account for part, but not all, of the variance in the stem choice experiments.
Hardwood Seedling Survival Under Plantations of Scotch Pine and Red Pine in Central New York
Authors: Tobiessen Peter , Werner Mary B.
Published: May 2006

Hardwood seeds germinate under both red pine and Scotch pine plantations, but few reach larger size classes under red pine. The environment of the plantation floor cannot explain this difference in hardwood survival. Differences were found in chlorophyll, nitrogen, and phosphorus content of leaves of hardwood seedlings growing under the two pine species, with the phosphorus content in the seedlings growing under red pines suggesting limitation of growth. Endomycorrhizal colonization was not found in 1st—yr hardwood seedlings growing under red pines, whereas it was found in all examined seedlings growing under Scotch pines. Laboratory experiments confirmed these findings. We suggest that this lack of endomycorrhizal colonization reduces the phosphorus uptake by the hardwood seedlings growing under the red pines to levels which limit their growth, eventually contributing to the observed seedling mortality.
On the Quantitative Theory of Resource Partitioning in Rhizomatous Perennial Plants: The Influences of Canopy Structure, Rhizome Branching Pattern, and Self‐Thinning
Authors: Armstrong Robert A.
Published: May 2006

Here I develop a geometry—based quantitative theory of energy partitioning between seed production and rhizome production in energy—limited herbaceous rhizomatous perennial plants. This theory makes two basis predictions. The first prediction concerns species in which additional energy devoted to rhizome production substantially increases the leaf area index of the genet. In such species, the functional relationship between seed production and leaf area index should be well approximated by a steep power law with a slope > 2. The second prediction concerns plants in which increased energy devoted to rhizomes increases the radial growth rate of clones much more strongly than it increases leaf area index and in which genets self—thin in response to crowding. In such plants, the ratio of seed production to rhizome production should be relatively constant across environments and should be strongly influenced by the relationship between the level of investment in rhizomes per ramet and the length of the resulting rhizomes. An investment ratio on the order of 1:2 is often to be expected.
A Multivariate Study of the Relationship of Parental Age to Reproductive Success in California Gulls
Authors: Pugesek Bruce H. , Diem Kenneth L.
Published: May 2006

Breeding biology of a California gull population was investigated on Bamforth Lake, Albany County, Wyoming. Data on hatching success, 1st and 2nd wk survival, and fledging success were collected in 1979 and 1980 for 295 breeding pairs. Breeding success increased with parental age as a result of larger clutches and reduced offspring mortality. Linear regressions indicated that nest sites with shrub shelter, central location in the colony, and high nest densities correlated positively with many measures of breeding success. These types of nest sites were most commonly obtained by old parents. Multivariate analyses, however, indicated that while parental age had a major influence on breeding success, all other variables that correlated with breeding success did so through covariation with parental age. Thus, results did not support a hypothesis that more experienced parents have greater breeding success because they obtain better nest sites.
Foraging Patterns of Nesting Gila Woodpeckers
Authors: Martindale Steven
Published: May 2006

Movement patterns, activities, and nest deliveries of Gila Woodpeckers (Melanerpes uropygialis) in nature were monitored in order to determine the mechanisms involved in substrate selection, the effects of distance from the nest on foraging behavior, and the ecological differences between sexes of this dimorphic species. The woodpeckers found insects in clumps, and tended to return to the same area and same substrate type after a successful delivery, but tended to switch substrates if no capture was made. They delivered saguaro pollen and fruit and preferred cacti with many fruits. Substrate selection also depended on the ambient temperature, however; at higher temperatures, the birds spent more time resting on the shady sides of saguaro cacti, where they had low rates of prey capture. Thus, while the birds selected substrates partly on the basis of searching efficiency, they were constrained by the physiological necessity of evading the desert heat. Optimal foraging theory predicts that to maximize the delivery rate to nestlings, foragers using small prey should select higher—quality patches, hunt longer, and deliver larger loads when farther from the nest. From greater distances, the Gila Woodpeckers did select more profitable substrates and deliver larger insects, as predicted by the theory. Visit duration increased only slightly with distance, but at greater distances, foraging effort was greater: the birds spent more of their time searching and pecking for insects rather than scanning or resting, had higher capture rates, and delivered a greater proportion of insects rather than fruits. The sexes differed in their foraging behaviors, in the selection of substrates, and in the composition of deliveries to the young. Males spent more of their foraging time pecking for insect larvae, whereas females spent more time searching for insect adults. Moreover, the sexes performed different parental roles; males spent much of their time guarding the nest, while the females primarily forged. This division of labor resulted in sexual differences in the effects of distance on substrate selection and on the activities performed on the substrates.
Niches of Adult and Juvenile Deer Mice (Peromyscus Maniculatus) In Seral Stages of Coniferous Forest
Authors: Van Horne Beatrice
Published: May 2006

I analyzed food habits and habitat utilization patterns of deer mice (Peromyscus maniculatus) in seral stages of coastal coniferous forest in southeast Alaska. Adult deer mice consumed a higher proportion of hard—bodied arthropods than did juveniles. Juveniles consumed a lower proportion of soft—bodied arthropods in high—density populations than in low—density populations. High—and low—density habitats were described for adults and juveniles using discriminant function analysis. Adult high—density habitat had more cover than juvenile high—density habitat and was more favorable, as evidenced by a greater overwinter survival of both juveniles and adults. Intraspecific competition appeared to responsible for niche displacement of juvenile deer mice along food and habitat dimensions.
Estimating Survivorship when the Subjects are Visited Periodically
Authors: Bart Jonathan , Robson Douglas S.
Published: May 2006

Statistical methods for estimating and comparing constant survival rates are developed here for sampling designs in which survival of a subject is checked at irregular intervals. The maximum likelihood estimator is derived and shown to be readily calculated using an iterative procedure that starts with the Mayfield (1975) estimate as a trial value. Sampling distributions of this estimator and of the product of two or more estimates are skewed, and normalizing transformations are provided to facilitate valid confidence interval estimation. The sampling distribution of the difference between two independent estimates is found to be sufficiently normal without transformation to allow valid use of conventional normal theory procedures for testing differences and determining sample size for specified power. Statistical validity under the variable intensity sampling design does require that the duration of intervisit periods vary independently of observer perceptions concerning the survival status of the subject and, in order to achive robustness with respect to the assumption of constant survivorship, sampling intensity must vary independently of any temporal changes in the daily survival rate. Investigators are warned not to return earlier than planned to subjects thought to have died, as this observer behavior may cause serious bias in the survivorship estimate.
The Effect of Native Vegetation on the Susceptibility of Aristolochia Reticulata (Aristolochiaceae) to Herbivore Attack
Authors: Rausher Mark D.
Published: May 2006

Plants growing in dense stands of native vegetation are often less susceptible to herbivore attack than isolated plants or plants growing in monoculture. Three mechanisms have been suggested that may account for this phenomenon; (1) maintenance of a complex predator fauna in dense vegetation; (2) inhibition by complex vegetation of the ability of an herbivore to discover its host plants; and (3) decreased residence time of herbivores on plants growing in diverse vegetation. This study demonstrates that for both adults and larvae of the pipevine swallowtail butterfly, Battus philenor, inhibition of discovery is the primary cause of decreased susceptibility of its host plants, Aristolochia reticulata, to attack when grown amid native vegetation. In addition, this study demonstrates that a seasonal decrease in the susceptibility of host plants to discovery by adults is correlated with a seasonal increase in the height and density of the native vegetation. A similar inverse correlation between vegetation structure and susceptibility to discovery by larvae was detected. However, seasonal changes in vegetation structure do not influence susceptibility to larval discovery. This differential effect of changing vegetation structure on searching efficiency is probably due to differences in the way larvae and adults search.
Ecological Community Theory and the Coexistence of Sparrows
Authors: Pulliam H. Ronald
Published: May 2006

The predictions of community matrix theory do not agree with the observed patterns of coexistence of grassland and woodland sparrows. Predictions based on the random co—occurrence of species match the observed patterns about as well as do the predictions of community theory. Predictions of both the community theory model and the random co—occurrence model are improved substantially by the addition of thresholds that account for the minimum food requirements of sparrows of different sizes. The observed patterns of species coexistence appear consistent with a model based on resource abundance and aggressive interference; however, they are also consistent with coexistence based on interspecific partitioning of seeds by size.
Reproductive Consequences of Insect Seed Predation in Hamamelis Virginiana
Authors: De Steven Diane
Published: May 2006

Through the use of populations of marked individuals over a 4—yr period, I studied the demographic impact on a temperate forest shrub, witch—hazel (Hamamelis virginiana), of predispersal seed predation by a host—specific weevil (Pseudanthonomus hamamelidis). The general consequences of seed predation for witch—hazel recruitment are dependent upon the interaction of seed predation with the pattern of annual fruit production. Fruit production was poor in 1977 and 1978, and in these 2 yr, seed predation intensities (percent fruits attacked per crop) averaged 80—90%. In 1979, fruit crop sizes increased dramatically, resulting in only 45% seed predation on average. Fruit production declined again in 1980, and the weevils were able to attack nearly 100% of the available fruit. Thus at the population level, successful seed production is episodic, with large numbers of seeds being produced in the occasional good fruiting year through satiation of seed predators. The host specificity of Pseudanthonomus provides a mechanism for direct limitation of weevil population size in poor fruiting years. I also evaluated the effect of seed predation on the relative contributions of different witch—hazel individuals to successful seed production. The distribution of individual plant fecundity in any given year is highly skewed, with only a few plants in the population large fruit crops. In any given year, more fecund plants incur neither higher nor lower percent fruit attack on average than less fecund individuals. Seed predation therefore does not change the relative contributions of different—sized individuals to annual seed production; more fecund plants produce more viable seeds than do less fecund plants, and the few highly fecund individuals in the population make a disproportionately large contribution. Between—plant variation in witch—hazel fecundity is thus significant demographically, even though it may not be subject to natural selection from seed predation pressure in these populations. The spatial distribution of witch—hazel is highly clumped, with few individuals being very isolated from conspecifies. Spatial isolation reduced the probability of a plant's location by weevils only in the case of small, low—fecundity individuals; large individuals, in contrast, were likely to be found regardless of distance from other conspecifics. Among the larger plants there were slight but nonsignificant tendencies for percent fruit attack to be lower with increased distance from conspecifics. Spatial isolation in this system seems important in lowering seed predation intensity only in interaction with individual plant fecundity.
Foraging Ecology of Bees in an Old Field
Authors: Ginsberg Howard S.
Published: May 2006

In an abandoned field near Ithaca, New York, bee species partitioned the available flower resources, primarily by foraging at different times of the season and by visiting different flower species. Honey bees (Apis mellifera) concentrated on different flower species than did native bees. In spring, most flowers bloomed along roadsides, in cultivated fields, or in forests. Many were clustered in spatial distribution and had short blooming times. Spring—flying native bees included many species adapted to forage on native flower species that bloom before the tree canopy closes. Apis mellifera, an introduced species, appeared to outcompete native bees at large clusters of attractive flower species such as apple and the crucifer Barbarea vulgaris. Blooming of introduced herbs increased in the field in early summer. This period of resource abundance was exploited primarily by primitively eusocial halictine bees. The multivoltine seasonal cycle of these bees allowed them to build populations over the season and to forage in large numbers in early and mid summer. Halictus ligatus was the most common early summer halictine. This species concentrated its foraging on different flowers than did other early summer bees, probably because of differences in innate flower preferences. A profuse bloom of native goldenrods in late summer was the seasonal peak of resource abundance. Honey bees partitioned goldenrod species with late summer native bees on the basis of flowering time. Native bees must complete their seasonal cycles and enter diapause before the killing frost. They therefore foraged on early—blooming goldenrod species such as Solidago juncea. In contrast, honey bees overwinter as active bees within their hives. They were most common on later—blooming goldenrods, where they collected much of the nectar required for overwintering. Competition among foraging bees was probably most important in the spring at this site. Partitioning of flower species and differences in seasonal flight times resulted primarily from differences in innate flower preferences, number of generations per season, and means of overwintering.
Soil Mining by Pocket Gophers along Topographic Gradients in a Mima Moundfield
Authors: Cox George W.
Published: May 2006

To account fully for the pattern of translocation of soil by pocket gopher activity in Mima moundfields, I investigated soil mining in relation to location along the mound—intermound topographic gradient. From September 1986 to November 1987, at Miramar Mounds National Landmark in coastal San Diego County, California, the total soil mined by pocket gophers (Thomomys bottae) was estimated by measuring the mass of soil deposited in surface heaps and counting the number of plugged surface—access tunnels on mound and intermound zones associated with 10 Mima—type mounds. Surface heap deposition was greatest in late fall and early winter, whereas the digging of surface—access tunnels was most frequent in spring and early summer. Both the mass of soil in surface heaps per unit area and the number of surface—access tunnels per unit area tended to decrease with distance from the center of mounds. When the areas of concentric zones at increasing distance from the mound center were taken into account, however, the total mas of soil mined increased with distance from mound centers. At this site, deposition of soil in surface heaps estimated to be 8.23 Mg°ha—1°yr—1 and subsurface deposition to be 20.31 Mg°ha—1°yr—1, so that total soil mining equalled 28.54 Mg°ha—1°yr—1. Total mass of soil mined bore a log—linear relation to distance from the mound center. This relation was combined with that relating distance of movement of mined soil to mound height and distance from the mound center, to give a preliminary model of mound growth dynamics as influenced by pocket gopher activity. This model suggests that maximum mound size is largely determined by the pattern of soil mining and translocation by these mammals.
Spatial Patterns in Sizes of Seeds Collected by Four Species of Heteromyid Rodents
Authors: M'Closkey Robert T.
Published: May 2006

This research was designed to provide information on the spatial variation in size of seeds collected by four species of heteromyid rodents. During summer 1975, rodents (Dipodomys merriami, Perognathus amplus, P. baileyi, and P. penicillatus) were live—trapped on several Sonoran Desert habitats at the Saguaro National Monument in southern Arizona, USA. In 1976 and 1977 a single study area containing all four rodent species was live—trapped to provide information on microhabitat and seed use among coexisting species. Any seeds contained in the cheek pouches of the rodents were identified and their linear dimensions were measured. Microhabitats were quantified by enumeration of shrubs and measurement of their size. Much of the variation in collection of different—sized seeds is attributable to habitat and microhabitat differences between rodent species. Not only do rodent species collect seeds of different size among different habitats, but within a habitat, locally coexisting rodent species collect seeds of different size. As a test of the concept of independent use of two resources (seed size and microhabitat) by coexisting species, seed size differences were compared to microhabitat differences between all pairs of heteromyid rodents. The results show that the difference between rodent species in the size of seeds they collect depends upon the difference in microhabitat selection of the species. Hence, these two components of the niche (seed size and microhabitat) of coexisting heteromyid rodents reduce to a single dimension.
Multalism between Harvester Ants and a Desert Ephemeral: Seed Escape from Rodents
Authors: O'Dowd Dennis J. , Hay Mark E.
Published: May 2006

The harvester ants Veromessor pergandei and Pogonomyrmex californicus modify the highly localized seed shadow of the Sonoran Desert ephemeral Datura discolor (Solanaceae) through (1) attraction to food bodies attached to seeds released beneath the parent plant, (2) immediate transport of disapores to the ant nest, (3) subsequent removal of the food body in underground granaries, and (4) final expulsion of intact seeds onto the colony midden. D. discolor seed without food bodies are not attractive to ants and remain beneath the parent canopy. At Nude Wash, California, USA, diaspore removal distances are generally small, averaging 2.3 m away from the nearest D. discolor canopy in March—May 1977. Two lines of evidence indicate that this limited transport has a large effect on seed detection and utilization by rodents: (1) seeds placed in ant—proof dishes beneath the D. discolor canopy were about 10 times more likely to be removed by nocturnally foraging rodents than seeds placed in locations similar to those where ants locate their nests; (2) using D. discolor as bait, significantly more rodents were trapped beneath the plant canopy than in open areas where seeds were transported by ants. Manipulation of the density of D. discolor seed in these tests suggests that seed utilization by rodents is distance—responsive to the parent canopy rather than dependent on the density of seeds. Disapore analyses indicate that investment in the transport system is relatively small and represents <5% of the total investment in seeds.
Structure and Biomass Dynamics of Epiphytic Lichen Communities of Balsam Fir Forests in New Hampshire
Authors: Lang Gerald E. , Reiners William A. , Pike Lawrence H.
Published: May 2006

Changes in species composition, cover, biomass, and elemental pools in space and time were determined for epiphytic lichens associated with balsam fir (Abies balsamea [L.] Mill.) forests on Mt. Moosilauke, New Hampshire, USA. Thirty—three species of epiphytic lichens were present; none was able to fix atmospheric nitrogen. Between 45 and 94% of the total lichen flora occurred in any given stand. Hypogymnia physodes, H. krogii, Bacidia chlorococca, Platismatia glauca, Hypotrachyna revoluta, and Parmelia saxatilis were the leading dominants in all stands and accounted for 74—93% of the bole cover. Each species exhibited an individualistic pattern of vertical distribution. Lichen cover was least in the lower part of the bole (<15%) and peaked in the mid— or top—canopy position (42—58%). Species richness, average percent bole cover, and epiphytic lichen biomass increased with stand age owing to change in stand structure. Lichen biomass ranged from 120 to 1603 kg/ha, with °80% of the biomass located on branches. Nitrogen and phosphorus concentrations increased with increasing canopy height, while no obvious trends were noted for calcium, magnesium, or potassium. Elemental pool sizes (average biomass multiplied by average lichen tissue concentration) were: 10.7 kg/ha for nitrogen, 3.34 for potassium, 1.26 for calcium, 1.20 for phosphorus, and 0.25 for magnesium. Epiphytic lichens contribute little (<1.0%) to biomass and elemental pool sizes within the balsam fir ecosystem.
Ecotope Differentiation in a Guild of Sap‐Feeding Insects on the Salt Marsh Grass, Spartina Patens
Authors: Denno Robert F.
Published: May 2006

Niche and habitat differentiation are studied in seven sap—feeding insects (mostly leafhoppers and planthoppers) that inhabit the salt marsh grass Spartina patens. The microhabitat niche dimension is well partitioned. Four species of sap—feeders occur primarily in the upper stratum of the grass system, while three others are abundant in and beneath the lower thatch layer. Conversely, the seasonal niche dimension is poorly partitioned and most species show similar phenologies. The elevational habitat dimension is also poorly partitioned where most of the sap—feeders occur most abundantly on patches of grass within 10 cm of mean high water level. There are sufficient differences in resource utilization along niche and habitat dimensions as well as body size to explain the coexistence of all sap—feeders but two. The niches and body sizes of Amplicephalus simplex and Aphelonema simplex are very similar. One of these species, the leafhopper, Am. simplex, is the only species that fully retains the ability to fly. Populations of the other seven species are composed mostly of flightless brachypterous wing—morphs. It is hypothesized that Am. simplex is able to coexist in the guild because it is able to efficiently colonize relatively empty (competitor—free) patches of grass created by the catastrophic effects of storm tides.
Influences of Predatory Fish on the Drift Dispersal and Local Density of Stream Insects
Authors: Forrester Graham E.
Published: May 2006

Researchers have recently suggested that frequent prey dispersal into and out of an area can swamp the local effect on predation. Where prey are mobile, the extent of prey movement can therefore explain variation in the apparent effect of predators on local prey density. I compared the effect of the dominant predator in a temperate stream (brook charr, Salvelinus fontinalis Mitchill) on five insect prey taxa (mayflies: Ephemeroptera), to test the prediction that the extinct of density reduction should be less for prey taxa dispersing more frequently. The propensity of the mayflies to disperse by drifting downstream in the water column was measured in unmanipulated areas of the stream. Relative propensity to drift of the five mayflies was, from greatest to least: Baetis, Paraleptophlebia, Ephemerella, Eurylophella, Stenonema. I then tested effects of charr on the mayflies by manipulating charr density in fenced 35—m sections of the stream. Charr densities were adjusted to zero, medium, and high levels relative to natural densities. Rates of predation by charr in stream sections did not vary among the five mayfly taxa. Charr caused a large reduction in the density of Baetis, had a smaller effect on Paraleptophlebia, but had no detectable effect on the density of the other mayflies. Drift dispersal into the stream sections did not differ among charr densities. Effects of charr on prey densities could thus have been caused by direct predation or by increases in emigration from areas containing charr. Charr caused increased drift dispersal of Baetis and of Paraleptophlebia, but had no influence on drift of the other three mayflies. The reduction in density of Baetis by charr was due more to the charr—induced increase in drifting of Baetis than to direct predation on Baetis. The hypothesis that frequent prey dispersal swamps the effects of predators assumes that predators influence prey density primarily by consuming prey. In this system charr also influenced prey densities by causing increases in prey drift rates, affecting the mayflies that drifted most frequently. For this reason, the mayflies drifting less frequently were not, as predicted, the ones most strongly affected by charr. Variation in the effect of predators on prey density may thus be partially explained by both (1) changes in prey dispersal not related to predators, as proposed in the initial hypothesis, and (2) influences of predators on prey dispersal.
Despotic Distribution, Unequal Reproductive Success, and Population Regulation in the Jay Garrulus Glandarius L.
Authors: Andren Henrik
Published: May 2006

A population of European Jays (Garrulus glandarius L.) in south—central Sweden occupied territories in most forest habitats. However, there was a strong preference for dense forest, characterized by trees older than 10 yr and a composition of >30% Norway spruce (Picea abies Karst.). Individuals having territories in this preferred habitat exhibited the highest breeding success. This supports the Fretwell—Lucas model of ideal—despotic distribution. Differences in nest predation, and perhaps also in food abundance and adult predation, caused higher breeding success in forest dominated by Norway spruce than in other forests. Despots were not distinguished by size, but age might be more important in long—lived species like the Jay. Territoriality means that certain individuals monopolize some resources at the expense of other individuals, which results in unequal resource partitioning. Following current ideas of population regulation due to unequal resource partitioning in a heterogeneous environment, I discuss the effect of having the preferred habitat unequally divided among individuals, which will result in a density—dependent breeding output, and also suggests a possible system of population regulation.
An Analysis of the Spatial Structure of Mammalian Distribution Patterns in Texas
Authors: Owen James G.
Published: May 2006

I examined mammalian distribution patterns and species richness in the state of Texas, USA, along two major environmental gradients. I drew a system of square quadrats on a map of the state. I recorded the presence of absence of each native mammalian species and fifteen environmental variables. I analyzed these data using classification and ordination procedures and by statistical regression methods. The purpose of the analysis was to determine if a hierarchical classification explains the spatial structure mammalian distributions well, or if they are best understood as a continuum resulting from the individual responses of species to history and environmental conditions. I used quadratic response surface analysis to relate changes in species richness to environmental gradients and to test ecological hypotheses that richness is explained by climatic stability and primary productivity. Correlation analysis of community ordination axes with a suite of environmental variables indicated that mammalian species distributions differentiate along two major clines: a dominant east—to—west gradient of decreasing precipitation and productivity, and a south—to—north gradient of decreasing mean annual temperature, increasing winter cold, and increasing seasonal variation of temperature. Mammalian community—units, as identified by hierarchical cluster analysis, are essentially continuous with each other. This interpretation is reinforced by the substantial boundary overlap of 95% confidence ellipses about the association centroids. Quadrat ordination scores, contoured on a map of the study area, exhibited rather even patterns of species turnover in both east—to—west and north—to—south directions. This indicates that there are no zones of rapid species replacement followed by areas of faunal homogeneity. The distributions of species that range widely within quadrat sets show little fidelity to the areas to which they are most highly associated. Species appear to be geographically distributed in an individualistic manner according to the vicissitudes of history and their own ecological tolerances. These findings are consistent with the continuum concept community structure for mammals. Quadratic response surface analysis of species richness (bats, rodents, carnivores, and all mammals) with environmental variables estimating productivity and stability of temperature did not support either the productivity or stability hypotheses of species richness. The relationship of these four taxa to a resource gradient of increasing productivity shows that the curvilinear models used by Grime (1979), Huston (1979), and Tilman (1982) for plants apply also to mammals.
Problems in Detecting Chaotic Behavior in Natural Populations by Fitting Simple Discrete Models
Authors: Morris William F.
Published: May 2006

In order to predict the long—term qualitative dynamics of natural populations with discrete generations, ecologists have used short—term field data to estimate the parameters of simple difference—equation models whose behaviors are then examined. Three problems complicate the model—fitting approach: (1) the parameter estimates, and hence the predicted dynamics, may be sensitive to the estimation procedure used; (2) different models may fit the data equivalently well and yet make different predictions about population behavior; and (3) even when the best—fit parameters are used, a simple model may fail to capture the observed dynamics of the field population. I illustrate these problems using data from published insect life—table studies. I then discuss the limitations these problems impose upon the prediction of the qualitative behavior of natural populations by means of simple best—fit models. I conclude that, given these limitations, inferences about the presence or absence of chaos in natural insect populations that rely on simple best—fit models and premature.
Transient Dynamics of Populations with Age‐ and Size‐Dependent Vital Rates
Authors: Law Richard , Edley Michael T.
Published: May 2006

The transient dynamics of a population containing individuals with age— and size—dependent vital rates are considered. It is shown that there are two sequential phases in the dynamics. During the first phase the dynamics are determined by both the age and size dependence of the vital rates. This phase can operate only so long as individuals initially present remain alive, and is followed by a second phase in which the age dependence of the vital rates alone governs the dynamics. In view of this rapid collapse into an age—dependent mode, it is argued that the approximation to the transient dynamics given by the age—dependent Leslie matrix is likely to be closer than that given by the size—dependent Lefkovitch matrix. The results are illustrated with data from a clonal population of Daphnia magna.