bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Niche Breadth and Overlap: The Colwell‐Futuyma Method
Authors: Sabath Michael D. , Jones J. Micheal
Published: May 2006

The Colwell—Futuyma niche metrics are examined by means of data on microgeographic distribution of 25 species of drosophilid flies. Niche metrics based on a variety of weighting factors (circular, non—circular, absolute, and relative) are highly positively correlated. Unweighted metrics are highly correlated with all weighted metrics. The niche breadth and overlap values with drosophilids as weighting factors are highly positively correlated to metrics using drosophilids matched with co—occurring plants, even though the weights are slightly negatively correlated. Increasing the number of species in the resource matrix (species X resource states table) decreases the variation in weights of resource states and they approach uniform distinctness. Most drosophilid species are broad niched for all calculation methods used. Samplig error may account for some skewing of breadth values because flies might be attracted into otherwise unfavorable environments by the baits.
Diel Rhythms in Edaphic Community Metabolism in a Delaware Salt Marsh
Authors: Gallagher John L. , Daiber Franklin C.
Published: May 2006

An endogenous rhythm in edaphic salt marsh community photosynthesis was demonstrated but no evidence for a similar respiratory rhythm was found. Photosynthesis exhibited both temperature— and light—modulated rhythms. Light saturation of the system did not occur at less than 50% of full sunlight. Respiration also exhibited light— and temperature—induced rhythms.
Population Dynamics of Two Competing Annual Plant Species
Authors: Sharitz Rebecca R. , McCormick J. Frank
Published: May 2006

Population attributes including density, distribution, biomass, seed production, and survival were measured at significant stages throughout the life cycles of natural and experimental populations of Sedum smallii (Britt.) Ahles (Crassulaceae) and Minuaritia uniflora (Walt.) Matif. (Caryophyllaceae). These two species along with Viguiera porteri (A. Gray) Blake (Asteraceae) are dominant in island communities on granite outcrops in the southeastern United states. Actuarial life tables and survivorship curves were constructed for natural populations of both Sedum and Minuarita. On the basis of field studies the hypothesis was proposed that the population dynamics of dominant outcrop species are primarily influenced by interspecific competition for soil moisture in habitats of varying soil depth. This hypothesis was tested by growing both species under varying levels of soil moisture, soil depth, and competition in a programmed environment. Final verification of cause—and—effect relationships was obtained through experiments under modified field conditions. Strict zonation of Sedum smallii and Minuartia uniflora along intensity gradients of soil depth and soil moisture in the island communities is due to (1) high tolerance of Sedum to low moisture levels in soils less than 4 cm deep; (2) the competitive superiority of Minuartia over Sedum under more favorable moisture levels prevailing at soil depths from 4 cm to 10 cm; and (3) the competitive disadvantage of Minuartia at high moisture levels in deeper soils that support larger annual and perennial species. Sedum smallii is a primary invader in granite outcrop succession because of adaptations which allow it to exist under low moisture conditions in shallow soil unfavorable for growth of other outcrop species. Minuartia uniflora is less resistant to abiotic stress and invades later. Both Sedum and Minuartia exhibit high reproductive potentials typical of colonizing species. Early juvenile stages are the most vulnerable periods in the life cycles of both species. Washout of seeds and seedlings from the communities and the sensitivity of these juvenile stages to moisture stress are the major causes of early mortality. Sedum plants are stunted by increased abiotic stress although population densities may remain high. On the other hand, interspecific competition causes increased mortality. In Minauritia stunting is largely a response to severe environment, whereas mortality is caused by both abiotic stress and interspecific competition. Species zonation and outcrop community structure are therefore a consequence of shifting competitive superiority as physical conditions shift.
Response Surface Methodology Applications to Biological Data From Field Measurements
Authors: Menke Warren W.
Published: May 2006

Response surface methodology has a practical application in analyzing experimental data when the experimental responses are confounded by unrecorded, uncontrolled factors. the data analyzed were population counts from field experiments to investigate population control strategies for the beetle, Haltica sp. by nonpesticidal treatments. Confounding was caused by the unrecorded effects of the Haltica sp. environment. Population contour maps were obtained that not only described the efficacy of the control strategy but also described the Haltica sp. life cycle in its natural environment. Viable regions for future experiments were identified in order to be able to define the control mechanisms more precisely.
Influence of Fire on Soil Nutrients in a Ponderosa Pine Type
Authors: Wagle R. F. , Kitchen J. H.
Published: May 2006

Plant bioassays, with lettuce and ponderosa pine seedlings as indicator plants, and chemical analyses were used to investigate differences in macronutrient availability in soils from areas of different wildfire burn histories. Soils originating from the same parent material were collected from unburned areas consisting of a large control area, having no known history of burning, and two small relict unburned areas, located within two large areas that had been burned over by a severe wildfire at different times in their history. The vegetation, litter, and soil profiles of the relict areas suggested that the soils of these areas were very similar to those of the control area, which indicated that the soils of all three areas were alike before the advent of wildfire into the two burned—over areas. The assays essentially substantiated this conclusion. Soils were collected from the same three areas, with the difference that two were from central locations in the large areas burned over by wildfire. Thus representative soils were obtained from areas with no known history of burning, an old burn (over 12 years old), and a recent burn (3 years old). Assays indicated that nutrient availablility in these soils was completely different, and this difference apparently was due to the effect of wildfire on the soils. Fire, through its effect on soil nutrients, could thus exert a profound effect on the nature and growth of the surface vegetation.
Behavioral Indices of Adrenal Gland Weight in the California Ground Squirrel
Authors: Adams Lowell , Finn Joseph A.
Published: May 2006

The behavioral characteristic time—in—sight promises to be a reliable, objective index to the weight of the adrenal gland in California ground squirrels. Time—in—sight is defined as the percentage of time during scheduled observation periods that a squirrel is actually in view. The more an animal is available to be seen, the smaller its adrenal, and vice versa (correlation coefficient r=—0.835). Another promising index of gland weight is based on the experienced observer's subjective evaluation of the squirrel's behavior. The initial study included observations of male squirrels in one locality and in one season only. Further validation is needed with regard to variations in sex, season, and locality. Establishment of a behavioral index of adrenal gland size eliminates the need to kill to obtain gland weights in studies of social biology and population dynamics. With such an index ongoing studies of living animals are possible.
Environment, Population Size and Vital Statistics: An Analysis of Demographic Data from 18th Century Villages in the Province of Reggio Emilia (Italy)
Authors: Matessi Carlo , Menozzi Paolo
Published: May 2006

We have analyzed a set of crude vital statistics from six of the years between 1690 and 1793 for a number of villages in the province of Reggio Emilia (Italy). These statistics were computed from population counts and registered baptisms and burials. We investigated the relationship between these vital statistics and population size for evidence of population regulation by density—dependent mechanisms. Since the villages were located in three quite distinct environmental zones (mountains, hills and plains), we also investigated the existence of environmental effects. The statistical results indicate that: (1) birth rates do not depend on population size but increase significantly from mountains to hills and plains; (2) death rates increase significantly with population size, also increasing by environmental zone in the same order as birth rates; (3) consequently, growth rates depend significantly on both environment and population size. However, the last relation does not emerge so strongly as for death rates alone because growth rates include the statistical variations in both the birth and death rates.
Effects of Grazing by the Sea Urchin, Centrostephanus Coronatus, on Prey Community Composition
Authors: Vance Richard R.
Published: May 2006

Individuals of Centrostephanus coronatus, a diadematid sea urchin, restrict their grazing to relatively confined areas on subtidal rock surfaces. To determine the effects of Centrostephanus grazing on the composition and diversity of the attached biota within these areas, I removed sea urchins from an experimental site and photographically monitored subsequent events in marked quadrats at monthly intervals for 27 mo. Grazed and ungrazed control sites were similarly monitored. These observations were supplemented by dietary data obtained from grazed control site urchins at the end of the experiment, permitting assessment of food preferences through the use of electivity indices. Taxonomic composition in the exclusion site changed dramatically following urchin removal nearly converging to that of the ungrazed control site. Algae, sponges, tunicates, and erect bryozoa replaced encrusting coralline algae and encrusting bryozoa as the dominants. The urchin's diet includes all of these taxa, and the most preferred ones increase most upon urchin removal. Taxonomic diversity increased in the exclusion site as a result of replacement of a small number of taxa which can withstand urching grazing by a larger number of competitively superior ones which cannot. Thus the effect of Centrostephanus on the community is to decrease diversity where it actually grazes, but to increase diversity in the community as a whole by creating local environmental patches favorable to otherwise rare taxa.
Effects on Sevin on Arthropods in an Agricultural and an Old‐Field Plant Community
Authors: Suttman Cheryl E. , Barrett Gary W.
Published: May 2006

The pesticide Sevin was applied to 4 of 8 0.1 ha plots of oats. These plots were left to normal ecological succession and the application process repeated during the old—field stage of succession. Arthropods in the oats field exhibited greater decreases in density and biomass than did arthropods in the old—field community following treatment. This response, however, was followed by a shorter recovery period than in the old—field community. The herbivorous arthropod response was usually immediate, pronounced, and short—term in duration, whereas the carnivorous response was normally delayed, less pronounced, and long—term in duration. Carnivorous Coleoptera were the most severely affected by pesticide treatment in both fields. Pesticide application produced a greater total effect on both species richness and species apportionment indices within the oats community as compared to the old—field community. The old—field community appeared to show more resilience than the oats community. This resilience, however, cannot be accounted for by plant diversity.
A Short‐Focus Telescope for Ground Cover Estimation
Authors: Reynolds K. C. , Edwards K.
Published: May 2006

A short—focus telescope that allows point quadrat sampling for ground cover assessment with a high degree of accuracy has been developed for use in pasturelands. The equipment is sufficiently accurate and precise to allow it to be used as a standard for the correction of assessments carried out with established techniques yet it is easy to use and can be value for survey work.
Factors Influencing Cannibalism, a Mechanism of Population Limitation in the Predator Notonecta hoffmanni
Authors: Fox Laurel R.
Published: May 2006

Factors influencing cannibalism rates in the freshwater insect predator Notonecta hoffmanni were analyzed in a series of field and laboratory experiments. Starvation was rejected as a cause of nymphal mortality. Cannibalism was related to both the relative and absolute abundances of alternative food, the cannibal's age, and the presence of refuges for the vulnerable nymphs, although the predator's state of hunger also influenced cannibalism rates. Cannibalism occurred when there was physical proximity between different age—classes even if alternative food were abundant. Long—term feeding history had no effect on cannibalism, which is a rapid response to rapid response to immediate food availibility. The population consequences of cannibalism seem analogous to those of dominance and spacing behavior, causing a decline in population size before animals are actually killed by the limiting resource, and increasing the chances that at least some relatively well—fed individuals will survive and reproduce successfully.
The Influence of Food Abundance on Territory Size in the Iguanid Lizard Sceloporus jarrovi
Authors: Simon Carol A.
Published: May 2006

This study was designed to determine how food abundance affects territory size for the insectivorous lizard Sceloporus jarrovi. Observations and experiments were performed in the field in southeastern Arizona during 1971 and 1972 summers. Territories were defined as defended areas, and the convex polygon method was used to determine territorial boundaries. Preliminary studies showed that all adult and most juvenile lizards defended territories against lizards of the same species, size, and sex. Sex and body size influenced territory size. Within size classes, territories of ♂ ♂ averaged more than twice territory size of ♀ ♀. Lizards in the larger size class had territories more than twice those of smaller animals. Natural food abundance, determined with adhesive—coated Masonite® boards, was inversely correlated with territory size. Summer territories compressed significantly when food was added even through natural food supplies seemed adequate. Terrtories returned to initial sizes with the removal of additional food. Experiments involving the locations of concentrated food sources within the territory provided some evidence for the hypothesis that ease of food obtainment may be an important factor in determining summer territorial size and location.
Switching in the Parasitoid Nasonia Vitripennis and Its Effects on Host Competition
Authors: Cornell Howard , Pimentel David
Published: May 2006

Switching behavior of the parasitoid wasp Nasonia vitripennis was investigated for its effects on the competitive outcome of 3 fly host species, Phormia regina, Phaenicia sericata, and Musca domesticia, interacting in laboratory ecosystems. The investigation was carried out in 2 stages: (1) examination of factors which altered Nasonia's innate preference for each host species when hosts were offered in pairwise combinations, (2) examination of the effect of Nasonia's attack pressure on host competitive outcome. In stage (1), Nasonia showed a strong innate preference for P. regina (4.45:1) when offered with M. domestica, a weak innate preference for P. regina (1.41:1) when offered with P. sericata, and a weak innate preference for P. sericata (2.71:1) when offered with M. domestica. In all 3 tests, Nasonia's preference for a given host was increased if Nasonia had a previous feeding experience on that host. In the switching tests, Nasonia concentrated its attacks on the most abundant host as its ratio in the diet increased from 1:7 to 7:1. Both strong and weak preference combinations showed similar switching effects. Increasing parasitoid density was found to obscure gradually the expression of switching. At maximum parasitoid densities the parasitoid population became host limited, and all host individuals were attacked regardless of host ratio offered. In stage (2), parasitoid host interaction systems were established with Nasonia attacking the 3 competing host species. Under some conditions, Nasonia attack pressure can induce a reversal of dominance in the competitive outcome, but stable coexistence between the host species was not achieved in these tests. The results of these investigations partly confirm previous conclusions about switching and partly expand the switching concept to include more situations.
Geographic Variation in Artificial Island Colonization Curves
Authors: Schoener A. , Long E. R. , DePalma J. R.
Published: May 2006

Colonization of identical marine—fouling—panel "islands" is compared at several shallow—water Northern Hemisphere localities in tropical, subtropical, temperate and subarctic regions. Because these sites differ in total number of species available for colonization, the equilibrium number of species on these islands predicted by an extension of the MacArthur—Wilson model is expected to differ as well. Initially the number of sessile species of marine invertebrates and algae accumulating on panels is inversely related to the availability of potentially colonizing species; in most cases this implies an inverse relation to latitude. By the end of the study equilibrium species number shows minimal differences between sites, appearing to converge on similar values at all localities. Thus, colonization curves are more peaked in species—rich regions such as the tropics than in poorer ones.
Phytosociological Changes after Timber Harvest in a Southern Pine Ecosystem
Authors: Blair Robert M. , Brunett Louis E.
Published: May 2006

Changes in the plant community following a selection timber harvest in an all—aged pine—hardwood ecosystem were studied for 11 yr on 218 hectares of rolling uplands in central Louisiana, USA. Pine and selected hardwoods were harvested. Prior to the study, stands were harvested at 10—yr intervals by the single—tree selection method. Fire had been excluded for 30 yr. Principal tree species were Pinus taeda, Pinus echinata, Quercus alba, Quercus falcata, Nyssa sylvatica, and Liquidambar styraciflua. In the shrub layer pertinent species were Callicarpa americana, Vitis rotundifolia, Acer rubrum, Vaccinium elliottii, and Ostrya virginiana in association with reproduction of the principal tree species. In the absence of fire and hardwood arrest, periodic selection harvest, primarily of pine, was enhancing a definite shift from pine to hardwood. In the postharvest stand hardwoods averaged 84% of the tree density and 49% of the basal area. Residual pine in the dominant and codominant canopies will be harvested at the next cutting with hardwoods largely being potential sucessors. The density of young pine < 21.72 cm dbh (diameter at breast height) in the transgressive layers averaged 67.0%. Of the major hardwood species 93.5% of the average density consisted of young replacement trees < 21.72 cm. Among trees < 36.96 cm dbh, the percentage importance of hardwoods, as a group, was higher than the value for pine. In the shrub layer the relative dominances of pine regeneration progressively increased for 9 yr then declined appreciably as the species became intolerant to the high level of community competition. The net primary productivity (NPP) of herbaceous and woody species in the herb and shrub layer crested 2 yr after timber harvest. At this time NPP of the relatively sparse herbaceous dry matter averaged 111.9 kg/ha and that of woody species was 327.6 kg. Thereafter, NPP decreased progressively as many stems of tree reproduction grew above the shrub layer and the density and basal area of the tree stratum increased. Within 11 yr after the stand disturbance herbaceous growth was very sparse, with a NPP of 21.0 kg dry matter/ha. NPP of woody species declined to 116.6 kg dry matter/ha. The vegetative response among woody species in the herb and shrub layer after logging was primarily a general growth decline with increasing competition and not an elimination of established species nor an introduction of new species.
An Analysis of the Yeast Flora Associated with Cactiphilic Drosophila and their Host Plants in the Sonoran Desert and Its Relation to Temperate and Tropical Associations
Authors: Heed William B. , Starmer William T. , Miranda Mary , Miller Martin W. , Phaff Herman J.
Published: May 2006

A survey was made in the Sonoran Desert of yeasts living in the decaying arms of five species of cereus cacti and the four species of Drosophila that utilize them as host plants. The most common yeasts among 132 isolates from the cacti and 187 isolates from the files, respectively, were: Pichia membranaefaciens (45% and 67%), Candida ingens (17% and 4%), Torulopsis sonorensis (12% and 11%), and Cryptococcus cereanus (8% and 7%). Eighty—eight percent of the 66 initial isolates of P. membranaefaciens from Drosophila pachea and its host, senita cactus, assimilated D—xylose while only 12% of the remaining 257 initial isolates did so. Nineteen of the 20 isolates of T. sonorensis from files were found in Drosophila mojavensis and 12 of the 14 isolates of Cryptococcus cereanus came from D. pachea. The highest mean number of yeast species per cactus was 2.77 plus or minus 0.68 in organpipe cactus and per fly was 1.63 plus or minus 0.53 in D. pachea. The flies usually carried fewer yeast species than were found in the host plant but D. pachea had almost the same mean and variance as its host, senita cactus, which had 1.64 @+ 0.40. Yeast species diversity and average niche overlap have the following rank order among habitats and localities: temperate trees > temperate flies > tropical flies > desert cacti > desert flies. Habitat diversity and average niche width show: tropical flies > temperate flies and desert cacti > desert flies and temperate trees. The physiological properties of the desert yeasts are most similar to those of the tropical yeast. However, desert yeasts have similarities with yeasts of temperate trees. Both have low fermentative ability and high assimilation ability of several alcohols and acids. The genus Pichia is by far the most common yeast genus associated with Drosophila in all habitats analyzed (36% of 1,426 isolates).
Vegetation of the Mima Mounds, Washington State
Authors: Del Moral Roger , Deardorff David C.
Published: May 2006

The vegetation patterns on the undulating topography of the Mima Mounds, Washington, USA exist on at least three scales. At the smallest scale the distribution of individuals is determined primarily by microtopographic features which provide small, but significant habitat variation. An Intermediate scale is dependent upon exposure and elevation. Mounds alter drainage and insolation to create moisture gradients to which all species respond. The largest scale involves the shift of species distributions with respect to mounds as one moves from the prairie to a zone of Pseudotsuga menziesii invasion. Conditions become more mesic as a consequence of reduced insolation and wind in this ecotone, resulting in an increase in mesophytes and a decrease in xerophytes. Both ordination and classification methods are applied in this study. The analyses are complementary and provide insight into the nature of factors controlling vegetation. A method of detailed mapping is proposed which involves the description of a small sample of the area to be mapped, preliminary clustering, the application of discriminant analysis to perform reallocation of samples, and the construction of a key to the resultant associations. The key is used in the field to assign samples to the proper association.
Population Ecology of the Gray Bat (Myotis Grisescens): Factors Influencing Growth and Survival of Newly Volant Young
Authors: Tuttle Merlin D.
Published: May 2006

Growth success and survival of newly volant young Myotis grisescens were observed in colonies traveling a variety of distances between the roost cave and foraging areas (0.0—6.6 km). Foraging occurred primarily over large rivers and reservoirs. Quality of the foraging area, climatic conditions, and cave temperatures were thought to be some of the potential factors influencing growth and survival, most noticably when distances traveled were minimal; however, when distance became excessive relative to the other variables, it was found to be a highly significant factor. Success in growth, percent of low—weight young, and mortality were closely correlated with the distances traveled by the colonies to their feeding areas.
The Effects of Predator Functional Response and Prey Productivity on Predator‐Prey Stabillity: A Graphical Approach
Authors: Armstrong Robert A.
Published: May 2006

A new graphical technique is developed for predicting the stability of predator prey systems. In this method the prey's productivity curve and the predator's functional response curve enter the analysis directly and independently. This method yields new insights into the relationship between prey productivity, predator functional response, and the stability of predator—prey systems.
Genetic Variability in the Pelagic Environment: A Paradox?
Authors: Ayala Francisco J. , Valentine James W.
Published: May 2006

The pelagic environment is often regarded as rather homogeneous by comparison with shallow—water benthic environments. Species of krill of the pelagic genus Euphausia (Crustacea) display a trend in genetic variability from low in high latitudes to high in low latitudes, closely similar to trends displayed by shallow—water benthic invertebrates. We interpret the trends as genetic strategies, with few functionally—broad alleles in high latitude species or in species that range widely ecologically, and numerous functionally—narrow alleles in low latitude species that are narrowly restricted ecologically. The functionally—narrow alleles are maintained by forms of balancing selection and permit a high degree of specialization. Therefore the tropical kill species is highly sensitive to spatial heterogeneities within the pelagic zone, which does not appear homogeneous to selection.
Some Sampling Properties of the Fager Index for Recurrent Species Groups
Authors: Hayes Willis B.
Published: May 2006

A Monte Carlo technique was used to produce sets of samples from a series of artificial 2—species communities. The Fager recurrent group index was calculated for these samples. The effects of sample numbers were assessed by comparing the sample indices to size—corrected population index values. A small negative bias was noted for indices calculated from the smaller sample sets, particularly in those communities where the species were rare. The index appears to give conservative estimates of affinity when only a small number of samples are taken.
Selective Feeding of Red Phalaropes on Zooplankton of Arctic Ponds
Authors: Dodson Stanley I. , Egger David L.
Published: May 2006

Food preferences and feeding rate coefficients were estimated for five Red Phaloropes (Phalaropus fulicarius) eating zooplankton. Birds were captured in the Barrow, Alaska, area and put into enclosures containing a known amount of zooplankton. Predation preference and intensity was calculated from the rate of disappearance of zooplankton from the cages. Results indicated phalaropes are size—selective predators on zooplankton, and reaffirm the size—selection predation model previously applied to fish and salamander populations.
Nitrogen Fixation and the Nitrogen Balance in Peatland Ecosystems
Authors: Waughman G. J. , Bellamy D. J.
Published: May 2006

A survey of heterotrophic nitrogen fixation was carried out using the acetylene reduction assay on peat from mires in Canada, England, Scotland, Ireland, Norway, Germany, Italy, and Malaysia. A detailed study of the relationship between nitrogen fixation and peatland ecology was carried out on the German sites. Nitrogenase activity was detected in all 16 fen sites examined, with the highest rates of activity being >100 nmol C2H4°mL peat—1°d—1 . Lower rates were found in both extreme rich fen and poor fen sites, with the lower rates found in bogs. A multiple regression analysis indicated pH and K to be positively correlated with nitrogenase activity whilst the correlation with Ca was negative. These results suggest that the systems as a whole may be in balance with regard to nitrogen. The rate of nitrogenase in peat from lower latitudes is greater than in peat from higher latitudes when temperatures are allowed for. The concentration of soluble nitrogen was higher, and the rate of nitrogenase activity lower in peat from beneath fen woodland than in peat from the early unwooded phase of succession. The estimated amount of nitrogen fixed annually by heterotrophic bacteria in peat from the south German mires is as follows (mg N/m2): fen, 2100; poor fen, 530; and bog, 70.
Demography and Dispersal in Island and Mainland Populations of the Deer Mouse, Peromyscus Maniculatus
Authors: Sullivan Thomas P.
Published: May 2006

If dispersal is reduced on islands, then the demography of island populations of deer mice should be different from that of mainland populations. Areas of 1.1 hectare were periodically cleared of mice on Samuel Island (206 ha) and Saturna Island (3, 102 ha) in the Gulf Islands of southwestern British Columbia. A similar experiment was conducted on the mainland at Maple Ridge, British Columbia. The average density of mice per hectare on Saturna (43.5) was 2° that on Samuel Island (22.0) and nearly 2.5° higher than that on the mainland (18.7). The reproductive rate, as measured by length of breeding season, number of successful pregnancies, proportion of breeding animals, and number of recruits surviving to breed, was much higher on Samuel Island that on either Saturna or the mainland. Survival was lowest on Samuel Island, with little difference between the mainland and Saturna Island. Mice on Samuel Island grew more than 5° faster than mainland animals, and Saturna growth rates were double those on the mainland. Dispersal (or colonization) rate was reduced on the two islands compared with that on the mainland. Recruitment of young animals occurred throughout the breeding season on the islands but was delayed until the end of breeding on the mainland. Seasonal changes in aggressiveness of the adult population may be sufficient but are not necessary to determine breeding density in deer mice. Regulatory processes in populations of Peromyscus maniculatus may be different on islands.
Enegry Value, Elemental Composition, and Productivity of Belowground Biomass of A Juncus Tidal Marsh
Authors: De La Cruz Armando A. , Hackney Courtney T.
Published: May 2006

Belowground standing crop of a Juncus roemerianus marsh in Mississippi ranged from 9.7 to 12.4 kg dry wt/m2 with the peak biomass occurring in April. Annual productivity estimated from expected maximum minus expected minimum biomass fitted into a periodic regression model was 1.36 kg/m2. Ninety—four percent of the productivity was within the top 20 cm indicating that the bulk of the materials found beyond this depth consisted of dead tissues. Energy, carbon, hydrogen, nitrogen, and phosphorus contents of belowground materials did not vary significantly during the year, but patterns of differences in samples taken from different depths were evident. The productivity of belowground materials in Juncus marshes is comparable with aboveground productions reported in the literature with respect to dry biomass. The probability that large portions of the underground production enter the aqueous system and become incorporated in estuarine energetics merits further consideration.
Energetics of the Straling (Sturnus Vulgaris) In a Pine Woods
Authors: Kelty Michael P. , Lustick Sheldon I.
Published: May 2006

Field and laboratory studies were conducted during the winter of 1975—76 to assess and quantify the energetic determinants of the communal roosting behavior of the Starling (Sturnus vulgaris) in a pine woods. Of the microclimate factors measured, only the wind velocity varied significantly between the recordings obtained outside of the pine woods and in areas within the woods that were used extensively as roost sites. Subjection to wind velocities of 2.9, 7.3, and 15.1 km/h at ambient temperatures of —10.0°, 0.0°, and 5.0°C caused significant increases in metabolism of the 30 Starlings tested. Selection of microclimates where wind velocity is virtually eliminated confers upon roost inhabitants the energetic advantage derived from minimized forced convective heat loss. The reduction in daily existence metabolism is estimated to range from 12% to 38% under environmental conditions that are normally presented in temperate latitudes during winter nights.
Phenologic Influences on Cohort‐Specific Reproductive Strategies in Mice (Peromyscus Polionotus)
Authors: Dapson Richard W.
Published: May 2006

Breeding seasons and birth cohorts were defined for two populations of mice (Peromyscus polionotus). Cohort—specific differences in reproductive effort were correlated with residual reproductive value. In one population, mice lived nearly 2 yr, reproduced at moderate rates, and showed few differences in cohort—specific reproductive strategy. Mice from the other population lived <1 yr, and spring—, summer—, and fall—born females exhibited markedly different reproductive strategies. Cohorts able to breed in a future season had moderate reproductive efforts, which did not increase risk of mortality. Extraordinary efforts (being pregnant and lactating simultaneously), which seriously increased mortality rate, were undertaken when residual reproductive value became zero. Nestling mortality increased with litter size when there were more than three young per litter, but larger litters still resulted in more weaned young than did smaller litters. These observations provide additional confirmation of the model of Pianka and Parker (1975). It is possible that populations of very short—lived mammals characteristically have seasonal cohorts operating under different reproductive strategies.
Forests of the Southeastern United States: Quantitative Maps for Abovegound Woody Biomass, Carbon, and Dominance of Major Tree Taxa
Authors: Delcourt Hazel R. , West Darrell C. , Delcourt Paul A.
Published: May 2006

Summary maps presented in this paper depict the current distribution patterns of aboveground woody biomass and carbon content of commercial forests in the southeastern United States. Contour maps of dominance of 10 important southeastern tree taxa are included. These maps were complied from growing—stock volume data available from the Continuous Forest Inventories (CFI) of the United States Department of Agriculture (U.S.D.A.) Forest Service, Southern and Southeastern Forest Experiment Stations. The maps of woody biomass and carbon establish the current for standing crop and carbon storage within forests of the southeastern United States, an area comprising 15% of the temperate forest zone of the earth. The contour maps of tree dominance quantify variation in composition within and between forest types previously mapped only qualitatively by the Forest Service. These dominance maps illustrate the individualistic nature of the distributions in response to gradients of environmental factors and effects of land management practices.
Influences of Photosynthetically Active Radiation on Cladode Orientation, Stem Tilting, and Height of Cacti
Authors: Nobel Park S.
Published: May 2006

Stem orientation and morphology were investigated for 14 species of cacti in Chile, Ecuador, Mexico, and the United States. The interception of photosynthetically active radiation (PAR) was specifically considered for cladodes (flattened stems) of platyopuntias, for tilted cylindrical stems, and in the presence of surrounding vegetation. Terminal cladodes of Opuntia chlorotica had a statistically significant tendency to face north—south at specific sites in the Mojave desert and east—west in the Sonoran desert. There was also a tendency for cladodes of three varieties of O. echios in the Galapagos Islands, Ecuador, to face east—west, while three times more cladodes of O. stricta var. dillenii faced within 15° of east—west than within 15° of north—south in Florida. In all cases, the orientation increased PAR absorption at times of the year favorable for growth. The longitudinal axes of ceroid cacti with multiple stems were vertical in both the northern (Carnegiea gigantea, Lemaireocereus thurberi, and Lophocereus schottii) and southern (Trichocereus chilensis) hemisphere. However, the longitudinal axes of barrel—shaped cacti with single cylindrical stems tended to tilt southward in the northern hemisphere (Ferocactus acanthodes, F. covillei, F. viridescens, and F. wislizenii) and northward in the southern hemisphere (Copiapoa cinerea var. columna—alba, C. lembckei, and Eriosyce ceratistes). Although equatorial tilting can increase the temperature of the apical region for certain cacti in the wintertime, for other species it has relatively little influence of minimum or maximum stem temperatures. Also, it tends to reduce the total amount of PAR intercepted by the sides of stem. Hence, equatorial tilting may not be of adaptive advantage for all cacti. The maximum stem height of O. echios varied 2—fold in a series of communities extending over 16 km on Santa Cruz island in the Galapagos Islands, and the maximum height of T. chilensis varied 4—fold over 12 km in central Chile. Changes in stem height were positively correlated with changes in the height of the surrounding vegetation (r ° .98) and negatively correlated with PAR in the vertical planes of the stems at 2 m (r ° —.96). The diurnal change in tissue acidity of these Crassulacean—acid—metabolism (CAM) plants was 90% light—saturated for a total daily PAR of about 20 mol of quanta.m—2.d—1 which is approximately the average PAR that unshaded vertical stem would receive on clear days. Hence, the increase in height of these cacti accompanying increases in height of the surrounding vegetation helps to insure that they receive adequate PAR. In fact, for these and other cacti, PAR is often limiting for CO2 uptake, even in the high—radiation environment of deserts.
Feeding Habits and Prey Consumption of Three Setipalpian Stoneflies (Plecoptera) in a Mountain Stream
Authors: Allan J. David
Published: May 2006

The feeding ecology of predaceous stoneflies was investigated over 18 mo in Cement Creek, Colorado, USA. Three species were studied at each of three sites over their entire life cycles to elucidate any differences due to species and site. Diet typically changed, over the course of development, from diatoms and chrionomids in the earliest instars, to primarily chironomids, to a broader diet in which mayflies increased in importance relative to chironomids. Stonefly diet was similar in individuals of a given size at a particular site, regardless of species, but differed among size categories and sites within a species. Two factors appeared to determine what prey were eaten. The maximum size of prey ingested increased with size of stonefly, at approximately 10% of predator body mass. No evidence of preference for larger prey was observed within a predator size category, however. Rather, the availability of prey depends upon the abundance of the vulnerable size class, which in turn is affected by the juxtaposition of predator and prey life cycles. The mass of a full foregut was related to mass of stonefly by the power law for each species. By combining these estimates of gut clearance rate, total prey consumption by stoneflies at each site was estimated to range from 2.7 to 3.3 g°m—2°yr—1 (dry mass). While prey availability is notoriously difficult to measure, this appears to be substantial predation pressure.
Habitat Selection and Interspecific Competition in Two Species of Plethodontid Salamanders
Authors: Keen W. Hubert
Published: May 2006

A series of field enclosure and laboratory experiments was conducted to test the hypothesis that intespecific interference competition plays no role in the microhabitat utilization and activity patterns of the plethodontid salamanders Desmognathus fuscus and Desmognathus monticola. Single—species and mixed—species groups were tested to determine if the presence or absence of potential competitors influence either species' selection of substrate texture, selection of substrate moisture, utilization of cover object sizes, proximity to the stream bed, magnitude of activity and temporal activity patterns. In single—species groups significant differences were found between species in all of the variables tested except temporal activity pattern. Relative species differences in micro—habitat utilizations shown experimentally during this study reflect closely those commonly observed in the field for the two species. The preferences of each species for substrate texture, substrate moisture, and cover object sizes were independent of the presence or absence of potential competitors; temporal activity patterns were also independent of the composition of test groups. Evidence for interspecific interference was found, however, in the proximity of individuals to a stream bed, and in magnitude of activity. D. fuscus utilized microhabitats farther than from the stream bed and was significantly less active in the presence of D. monticola than when the latter species was absent. These two species of Desmognathus possess distinctly different patterns of hbatiat utilization and activity which could account for the field distributions observed; yet evidence for interspecific interference points to competition as another factor in their spatial distributions.
Reproductive Tactics in Relation to Life‐Cycle Bioenergetics in Three Naturla populations of the Freshwater Snail, Leptoxis Carinata
Authors: Aldridge David W.
Published: May 2006

Regular sampling of three populations of the riverine prosobranch snail, Leptoxis carinata, revealed it to be a slow—growing, semelparous biennial. Copulation and egg laying are restricted to 23—mo—old individuals. Growth is restricted to two 3—mo periods during their 25—mo life cycle. Mean numerical fecundity at the three sites (170—330 eggs per female life—span) is inversely correlated with adult density. Experimental evidence indicates that differences in adult density (over moderate levels) have no direct effect on numerical fecundity whereas increasing egg density has a marked negative effect. Egg C:N ratio decline (less nonprotein stores) as numerical fecundity increases. Survivorship of eggs and young is very low but improves after 8 mo of age. Female reproductive effort (reproductive biomass as a percentage of growth) is relatively low in Leptoxis. The mean reproductive effort values range from 12 to 19% for carbon and 6 to 11% for nitrogen. The life—cycle traits of Leptoxis (semelparity after long prereproductive life; and low reproductive effort combined with relatively low numerical fecundity) reflect a compromise strategy imposed by severe environmental periodicities and concomitant physiological constraints (including low growth rates).
Reproductive Isolation in Clearwing Moths (Lepidoptera: Sesiidae): A Tropical‐Temperate Comparison
Authors: Greenfield Michael D.
Published: May 2006

To elucidate the factors promoting reproductive isolation in a diverse tropical community of clearwing moths (Lepidoptera: Sesiidae), I compared the results of pheromone trapping studies conducted in Panama with previously published studies involving Wisconsin Sesiidae. Pair—forming behavior in sesiids is facilitated by female—emitted sex pheromones which serve as long—range attractants for conspecific males. Pheromones of the various species appear to be closely related in terms of chemical structure. Prior work in Wisconsin demonstrated that species maintain reproductive isolation through specificity in sex pheromone chemistry and differences in seasonal or daily pattern of sexual activity. In both Wisconsin and Panama, data were obtained by trapping male sesiids with synthetic pheromone baits. An objective comparison of reproductive isolation in the two regions is accomplished through an application of metrics (breadth, overlap) developed originally to measure niche segregation. The atmospheric channel along with sex communication occurs is considered as an entity, and the chemical and temporal axes along which the communication channels of species may differ are viewed as dimensions. Interspecific differences in channels along a dimension constitute a reproductive isolating mechanism. The calculations of channel breadths and overlaps along these dimensions permit a quantitative comparison of isolating mechanisms. Theory predicts that in species—rich communities either breadths are narrower, overlap greater, or channel availability (space) is more extensive along one or more dimensions. Species richness of sesiids was significantly greater in Panama on both a regional and a local basis. Seasonal breadths of sesiids were greater in Panama than in Wisconsin. However, when seasonal breadths were standardized to account for the extended favorable season in Panama, values in both regions were equivalent. Chemical breadths of species that apparently utilized mixtures of different compounds as sex pheromones (binary species) were comparable in Panama and Wisconsin, as were overlaps along the seasonal and chemical dimensions. However, a higher proportion of the Panamaian fauna were binary isomer species, and Panamanian sesiids appeared to utilize a greater diversity of compound mixtures as pheromones. This indication that greater channel space distinguishes two communities differing is species richness agrees with several recent findings, regarding niche segregation, in other taxa.
The Role of Drift Dispersal in Production Ecology of a Stream Mayfly
Authors: Hall Ronald J. , Waters Thomas F. , Cook Edwin F.
Published: May 2006

The role of drift behavior in the production ecology of the mayfly Tricorythodes atratus McDunnough was investigated in a headwater reach of the Mississippi River in northern Minnesota, USA. Comparison of drift and bottom samples revealed that larger nymphs exhibited a greater propensity to drift; in bottom samples, small immatures (1—2 mm) were predominant in a study riffle, whereas larger nymphs (>2 mm) were relatively more abundant in a downstream pool. Annual production was 8.56 g.m—2.yr—1 (dry mass) and the annual turnover ratio (annual production/annual mean biomass) was 26; the species was bivoltine. Errors in production rate estimation resulting from sampling a single habitat were substantial when differential size dispersal of nymphs occurred.