bluuebunny/crossref_metadata_2025 huggingface dataset:
Life Histories and Natural Selection in Populations of the Salamander Desmognathus Ochrophaeus
Authors: Tilley Stephen G.
Published: May 2006

Populations of Desmognathus ochrophaeus Cope in the vicinity of Mt. Mitchell, Yancey County, North Carolina, differ from one another with respect to age at first reproduction, a trait in which variation can strongly affect individual fitness. Maturity is delayed in high elevation populations relative to low elevation populations, and in low elevation woodland populations relative to low elevation rockface populations. Juvenile growth rate appears to vary but slightly between populations, so that delay maturity results in individuals being larger at maturity. This may be responsible for the altitudinal size clines noted in D. ochrophaeus by other authors. Body size is positively correlated with clutch size, so that delay reproduction enhances subsequent age—specific fecundity. When populations are compared, indications of delayed maturity are usually accompanied by adult male age structures indicative of higher survivorship. In woodland populations such indications occur in samples from habitats where higher survivorship would be expected. High elevation woodland populations also exhibit higher adult growth rates, which in turn enhance female age—specific fecundities. The degree to which interpopulational differences in life history patterns are genetically based is unknown. The differences which occur are however, compatible with predictions drawn from current theory on the adaptive nature of life history patterns. Specifically, theory predicts that delayed maturity should be adaptive in relative stable environments and where it is accompanied by increased survivorship and fertility. The evolutionary ecology of Desmognathus ochrophaeus is such that these conditions may be met in high elevation woodland environments in southern Appalachians. Evidence for earlier maturity on low elevation rockfaces created by man's activities during 1938—39 suggest that, if these differences are genetically based, natural selection affects are at maturity with great effectiveness. Whether interpopulational differences in age at maturity prove to be genetic or not, interdemic variation in a trait to which fitness is potentially so sensitive is of theoretical interest.
Coexistence, Coevoluation and Convergent Evolution in Seabird Communities
Authors: Cody Martin L.
Published: May 2006

Ecological isolating mechanisms based on differences in size or breeding season operate in many groups of related sympatric seabirds, but not in the alcid species (Aves: Fam. Alcidae) found together in Washington State. At least three of the six coexisting species have similar diets, and all six breed at the same time of year. They differ, however, in their foraging zones at sea and appear to have reduced interspecific competition by this means. Diverse aspects of the breeding biology, behavior morphology and ecology of these alcids can be explained by reference to two sets of selective factors–interspecific competition for food and predation upon the eggs, chicks and adults. Species that fish inshore guard their chicks in exposed cliff sites grouped into ubiquitous but small colonies. They carry fish to chicks singly and frequently throughout the day. These young develop rapidly to about one—third adult weight, at which time they quit the nest site. At the other extreme, species that feed far offshore provide burrows for the chick and nest in large colonies on only a few off—shore islands. Chicks are visited at night by adults whose bills are adapted for carrying many fish. These chicks grow slowly and reach close to adult weight before leaving the nest. These patterns are repeated with considerable fidelity in the six—species alcid community of Northern Iceland, but southern hemisphere seabirds are, in general,differently organized.
The Ecology of the Pollinators and Predators of Frasera Speciosa
Authors: Beattie A. J. , Breedlove D. E. , Ehrlich P. R.
Published: May 2006

Frasera speciosa is a conspicuous perennial in the Rocky Mountains where it forms discrete colonies whose inflorescences are characterized by almost total absence in some years and greater abundance in others. This sporadic yet synchronous flowering was the most conspicuous feature of the reproductive biology of the species and its adaptive value was worth investigation. In a three—mile stretch of the East River Valley, Colorado, the following data were gathered over a period of three years: the distribution and abundance of colonies, the floral biology, the dispersal of insect visitors among the flowers of Frasera and its floral associates, the frequency of floral predation and seed—set. Although the percentage of plants with inflorescences was always very low and despite the occasional wide spatial separation of individuals, Frasera invariably attracted the greatest number and diversity of floral visitors and never yielded less than 52% seed—set. It was also shown that pollination was affected by a wide variety of inset visitors that maintained cross—pollination at a frequency of approximately 15%. In no colonies was floral predation nearly as heavy as in its sympatric associate Lupinus and it was concluded that seed—set Frasera was not significantly affected by predispersal herbivory. The local synchrony revealed by the occurrence of discrete colonies and the overall synchrony revealed in the almost total absence of floral colonies in some years and their abundance in others is viewed as a strategy for predator avoidance. These mechanisms, together with other aspects of the reproductive biology, also reduce pressure from sympatric species competing for pollinators. It is out that they confer reproductive advantage to a minority species which may otherwise rapidly decline to extinction in the presence of intense competition. The flowering regime of Frasera combines a predator avoidance system which yields widely dispersed colonies in space and in time with a pollination system which successfully exploits the maximum diversity of floral visitors and maintains excellent seed—set whenever and wherever the colonies appear. The systems are clearly complementary in preventing the build—up of predator populations while maintaining an attractive forage source for potential pollen vectors. The combined effect is to maintain the abundance of the species in a variety of stress environments, in turn resulting in a remarkably wide geographic success. It is considered likely that similar systems will turn out to be very common among entomophilous plants in both temperate and tropical regions.
Clipping Effects on Bermuda Grass Biomass
Authors: Dittmer Howard J.
Published: May 2006

Clipping Bermuda grass every few days in its first year of growth to keep it at 6 different heights resulted in a variation of weights for both roots and tops in the harvested plants. The higher the grass was permitted to grow the greater the weight of both roots and tops but the root/shoot ratio remained constant at about 40% roots to tops. The dry weight of tops in unclipped plots was about 2.35 times and the roots 2.0 times those in plots maintained at 12 mm.
Clumps of Heliconia Inflorescences as Ecological Islands
Authors: Seifert Richard P.
Published: May 2006

Previous theoretical and field studies have identified quantifiable relationships between migration, extinction, island size, and distance to mainland with species richness on islands. Some of these relationship hold for insects living in spatially and temporally separated Heliconia inflorescences. Analysis of 45 clumps of Heliconia wagneriana and 77 clumps of Heliconia imbricata using MacArthur and Wilson's (1967) island biogeography theory indicates that area—species richness curves are more similar to those of true islands than to those of mainland areas. Other island relationships such as distance influences could not be found. It is postulated that beta diversity (the diversity due to the number of habitats available) is more important in increasing species richness of animals in Heliconia clumps than is alpha diversity (the diversity due to the number of species using a given resource). The reduction of evenness as area size increases indicates that increasing ecological island size increases populations of common insects more rapidly than new species can invade these ecological islands.
Nutrient Concentrations in Plants in the Brookhaven Oak‐Pine Forest
Authors: Woodwell G. M. , Whittaker R. H. , Houghton R. A.
Published: May 2006

Distribution of nutrient elements (N, P, K, Ca, Mg, S, Fe, and Na) varied substantially among the tissues and species of a late successional oak—pine forest at Brook—haven, New York. Mean nutrient concentration in the biomass was 2.3 times higher in Vaccinium angustifolium than in Pinus rigida; but in net production mnean nutrient concentrations were high in Quercus alba and Q. ilicifolia, intermediate in Q. coccinea, Gaylussacia baccata, Vaccinium angustifolium, and V. vacillans, and low in P. rigida and Kalmia angustifolia. With the exception of Kalmia the species of the lower strata and earlier woody successional stages of the forest higher mean nutrient concentrations in the biomass than did the upper strata and climax tree species. Among tissues flowers, leaves, and fruits contained the highest concentrations; heartwood, the lowest. Weighted mean nutrient concentrations were higher for net primary production than for biomass by "enrichment ratios" mostly between 1.5 and 3.0 in the Bookhaven forest and comparable forests for which data are available. Nutrient element profiles showed the contrats in concentrations of different elements in species as deviations from the means for the forest as a whole. The contrasting nutrient profiles may express niche difference in nutrient use among the plant species of the community.
The Importance of Respiration Losses in Controlling the Size Distribution of Marine Phytoplankton
Authors: Laws Edward A.
Published: May 2006

Large single phytoplankton cells are likely to catabolize a smaller fraction of their biomass than do small phytoplankton cells. Under certain environmental conditions, this characteristic may be highly important in regulating the growth rates of large versus small phytoplankton. A model is developed incorporating experimental data on phytoplankton growth, respiration, and sinking rates as a function of cell size. Application of the model to specific oceanic regions shows that the net growth rate of large cells may exceed that of small cells when the mixed layer is relatively deep, despite the larger gross production rates characteristics of the smaller cells.
Ecological and Nutritional Effects of Food Scarcity on a Tropical Frugivorous Bird and its Fruit Source
Authors: Foster Mercedes S.
Published: May 2006

The Long—tailed Manakin (Chiroxiphia linearis) was studied from 1971 to 1974 in Guanacaste Province, Costa Rico. From late April until early June 1973 the normal food of this species, i.e., ripe fruits of Ardisia revoluta Humboldt, Bonpland, and Kunth (Myrsinaceae) and Stemmadenia donnell—smithii (Rose) Woodson (Apocynaceae), was unavailable. The birds switched to a diet of green Ardisia fruits upon which they normally do not feed. The primary components of the normal and alternate diets (fruits and varying ripeness) were analyzed to determine differences in nutrient and energy contents in an attempt to quantify the impact of the food shortage. Birds needed to eat 6.6x as many green fruits of A. revoluta to obtain the same metabolizable energy contained in a ripe fruit and 4.5, 8.5, and 18.6x as many to obtain comparable amounts of H2), protein, and trichloroacetic acid—soluble carbohydrates, respectively. The birds had to eat 1.4, 8.3, 4.8, and 5.8 x as many green A. revoluta fruits to obtain the same amounts of water, lipids, protein, and metabolizable energy contained in one feeding unit of ripe S. donnell—smithii. Feeding on green fruit probably is the best way for Long—tailed Manakin to cope with a period of food scarcity for several reasons. The fact that the birds maintained their normal weights during this period supports this idea. Experiments showed that seeds from green and ripe fruits germinated with almost equal frequency. Maturation appears to influence primarily the speed of germination. It also enhances dispersal by making the fruits more attractive to dispersal agents.
Environmental Factors Controlling Duration of Larval Instars in Tetragoneuria Cynosura (Odonata)
Authors: Lutz Paul E.
Published: May 2006

Groups of Tetragoneuria cynosura larvae were subjected to combinations of experimental and natural temperatures and photoperiods until emergence. For each of the later instars, responses to the various regimens by larvae in each collection were analyzed to determine instar receptivity of these environmental factors. Final instar duration for larvae subjected to a 11—hr day varied inversely with the temperature at which the animals were maintained. For larvae collected prior to the autumnal equinox and maintained at a 14—hr photoperiod, final instar development was greatly delayed when compared to responses of short—day animals. Long—day larvae collected after the equinox responded significantly faster than their short—day counterparts. This dramatic reversal in response occurred shortly following the equinox. Significantly delayed the development attributable to long days was noted in the F—1 (penultimate) instar and to diminishing degrees in earlier in stars. For larvae at lake temperatures, long days retarded development in the F—1 and F—2 (antepenultimate) instars compared to short days. Final instar duration was compensatory to the rates of development in earlier instars since all animals at lake temperatures emerged together regardless of their photoperiodic regime. The equinox, a crucial synchronizing mechanism for this species, induced both the populations to molt synchronously into the final instar and establised a larval physiological sensitivity to spring photoperiods. Rising vernal water temperatures served as a second synchronizing element. Animals collected prior to the equinox were in a radically different physiological state from larvae that had experienced the equinox in nature _kw Tetragoneuria cynosura
Properties of Food Webs
Authors: Pimm Stuart L.
Published: May 2006

On the assumption that systems of interacting species, when perturbed from equilibrium, should return to equilibrium quickly, one can predict four properties of foods web; (1) food chains should be short, (2) species feeding on more then one trophic level (omnivores) should be rare, (3) those species that do feed on more than one trophic level should do so by feeding on species in adjacent trophic levels, and (4) host—parasitoid systems are likely to be exceptions to (1)—(3) when interaction coefficients permit greater trophic complexity. By generating random, model food webs (with many features identical to webs described from a variety of marine, freshwater, and terrestrial systems), it is possible to generate expected values for the number of trophic levels and the degree of omnivory within webs. When compared with these random webs, real world webs are shown to have fewer trophic levels, less omnivory, and very few omnivores feeding on nonadjacent trophic levels. Insect webs are shown to have a greater degree of omnivory than other webs. The confirmation of all these predictions from stability analyses suggests that system stability places necessary, though not sufficient, limitations on the possible shapes of food webs.
Natural Selection and the Distribution of Nematode Sizes
Authors: Kirchner Thomas B. , Anderson Richard V. , Ingham Russell E.
Published: May 2006

Habitat constraints, life history strategies, and physiology of nematodes, examined by habitat type and trophic guild, affect size—frequency distributions. Although unimodal size—frequency distributions have been found for many animal taxa, nematodes have a strongly biomadal size—frequency distribution, apparently because of the dichotomy in life history strategies between vertebrate parasites and other nematodes.
Life History Variation Among Populations of an Amphipod (Hyalella Azteca)
Authors: Strong Donald R.
Published: May 2006

Inheritable differences in life history features are shown among three groups of populations of Hyallela azteca from Oregon. Hyallela individuals of coastal populations are relatively small as eggs, as young, and as adults. They grow slowly as young and adults, and the regression of clutch size on female size is relatively steep. Hyallela individuals from the Cascade Mountains are large as eggs, as young, and as adults. They grow rapidly as young and adults, and the regression of clutch size on female size is relatively less steep. A population of Hyalella from a hot springs is made up of animals that are intermediate in these characteristics. The maturation period and the rate of production of egg volume does not differ among the populations investigated. Selection for inconspicuousness, generated by visually orienting predaceous fish, is probably responsible for the small, slow—growing end of the character spectrum (coastal populations). Hyallela is a grazer and deposit feeder, it does not filter. Evidence indicates that larger Hyalella do not have a competitive advantage in predator—free environments, as do larger planktonic filter feeders.
Effects of Species Removal on an Old‐field Plant Community
Authors: Pinder John E.
Published: May 2006

The effect of removing the dominant grasses on the net productivity of subordinate forb species was investigated in the perennial—grass stage of old—field succession. Removing the dominants increased the net productivity of subordinate species from 0.49 g/m2°day to 1.44 g/m2°day. The increased net productivity of subordinates was due to increased productivity by almost all subordinate species. This increase was not sufficient to equal the total net productivity of the unaltered community (2.26 g/m2°day). Net productivity by subordinates in the absence of dominants was less than that reported for earlier successional stages where the forbs are the dominant producers. However, this difference might have been caused by relatively low rainfall at the time of this experiment.
Respiration of a Sublittoral Community
Authors: Smith K. L.
Published: May 2006

Respiration of a sublittoral community was examined off Sapelo Island, Georgia, from July 1969 through July 1970. Total community respiration ranged from 53.7 ml O_2 m(—2)hr(—1) in January to 92.7 ml O_2 m(—2)hr(—1) in July. A positive correlation was found between community respiration and water temperature. Annual community respiration was estimated to be 676.6 liters O_2 m(—2)yr(—1). The macrofauna consisted of 103 species representing ten phyla. Species abundance ranged from 744 individuals/m2 in July to 14,213 individuals/m2 in March. Biomass (ash free dry wt) increased from 7.3 g/m2 in October to 20.2 g/m2 in March. Macrofaunal respiration comprised from 5 to 26% of community respiration. Bacteria were the major functional component of the community accounting for 30% to 60% of the total respiration. Meiofaunal—microfaunal—microfloral respiration contributed from 25% to 58% to total community respiration. Sediment chemical oxidation was responsible for 2.8 ml O_2 m(—2)hr(—1) in January to 8.5 ml O_2 m(—2)hr(—1) in July of the total oxygen uptake.
Population Dynamics of Two Gorgonian Corals
Authors: Grigg Richard W.
Published: May 2006

The gorgonian corals Muricea calofirnica and Muricea fruticosa, co—occur at shallow depths along the western coasts of the Americas. Their northern geographic limit is Point Conception in California; the southern limits are unknown but may be Peru. In California, the depth range of both species is 1—30 m. Their abundances range up to 7.90 and 2.35 colonies/m2, respectively. Both species spawn once each year at a time which corresponds to annual peak temperature, which corresponds to annual peak temperature, which in California occurs later in the year for deeper segments of the population. Depth—staggered spawning has the effect of extending its duration from 2 to about 6 mo. During the larval stages of both species, mortality rates are low and nearly constant. Field records that detachment and abrasion rather than predation are the major sources of mortality for sessile stages. Several lines of evidence suggest that recruitment is generally spaced limited. In habitats where space is fully occupied, space limitation may regulate recruitment. In such habitats recruitment and mortality of populations of Muricea are nearly constant (i.e. in steady state), and their actual rates of natural increase are close to zero. In contrast, intrinsic rates of natural increase (rmax) are very high: 0.92 for M. californica and 1.45 for M. fruitcosa. These enormous rates of potential increase are offset by high rates of larval mortality in the plankton. Although M. californica is significantly more longevous than M. fruticosa, both species share similar patterns of life history. Competition for settlement and living space rarely occurs between the two species rather, it often takes place with other plants and invertebrates. These interactions may be sufficiently unpredictable for either species of Muricea to develop a competitive advantage over the other and hence may explain their coexistence. Thus, in the absence of significant direct competition between the two species, their similarities in life history may simply represent similar adaptations to the same set of environmental variables. Both species exhibit life history correlates of both K—selection (iteroparity, delayed reproduction, and relative great longevity) and r—selection (high (rmax). Life history at tributes of a single species may be located at different points along the r—K continuum. In fact, their colonial habit allows for combination of good characteristics of both patterns of selection and may be explain the evolutionary success of this type of life history, phenomena.
Seed Weight of Amaranthus Retroflexus in Relation to Moisture and Length of Growing Season
Authors: Schimpf David J.
Published: May 2006

Correlation analysis suggest that moisture availability is more important than length of growing season as a selective force for seed weight in Amaranthus retroflexus populations from eastern and central North America. Larger seeds are associated with drier environments, probably due to their capacity to establish seedlings from deeper soil horizons, where moisture is more reliable. Seed weights correlate better with long—term moisture availability than with more recent moisture patterns, indicating that populations do not track short—term climatic fluctuations very closely. A previously reported strong relationship between length of growing season and A. retroflexus seed weight is confounded by high correlation between dryness and short growing season, as well as by genotype interaction with abnormal photoperiods. Populations in flood— or furrow—irrigated regions do not have smaller seeds than those in the driest nonirrigated regions. This may be due to enhanced dispersal of large seeds by irrigation systems.
Lizard Energetics and Diet
Authors: Pough F. Harvey
Published: May 2006

In the families Agamidae, Gerrhosauridae, Iguanidae, and Scincidae, species that weigh more than 300 g are almost all herbivores, whereas those weighing less than 50—100 g are carnivores. Juveniles of large herbivorous species tend to be carnivorous until they reach body weights of 50—300 g. Diet is compared to metabolic expenditure in these lizards. Although smaller animals have higher weight—specific metabolic rates, the greater total metabolicrate of larger animals requires a greater caloric intake. Juvenile animals and species of small body size are primarily insectivorous. It is postulated that larger animals of these families are unable to get caloric demands on a diet of insects, have no practical alternative animal prey, and rely instead on vegetation. The families Anguidae, Chamaeleontidae, Helodermatidae, Teiidae, and Varanidae do not include herbivorous species, although each family has species that weigh more than 300 g. Morphological, ecological, and physiological specializations in these families account for the absence of herbivorous species. For an unspecialized lizard, evolution of large body size both requires and permits an herbivorous diet.
The Impact of Forest Fire on the Nutrient Influxes to Small Lakes in Northeastern Minnesota
Authors: Wright Richard F.
Published: May 2006

The Little Sioux fire of May 1971 burned most of the mixed coniferous—deciduous forest on the watersheds of Meander and Lamb lakes, two small, low conductivity lakes located in the Boundary Waters Canoe Area (BWCA) of northeastern Minnesota, USA. During 1972, hydrologic and chemical (Ca, Mg, K, Na, and P) budgets were determined for the terrestrial watersheds of Meander and Lamb lakes and for the lakes themselves. Budgets were also measured for Dogfish Lake, a lake physically and chemically similar to Meander Lake but whose watershed was not burned in the Little Sioux fire. These budgets show that the atmosphere supplies a significant fraction of the cations and phosphorus (Ca, 90%; Mg, 35%; K, 95%; Na, 55%; P, 95%) to the BWCA watersheds, with the remainder coming from chemical weathering. The budgets are similar to those reported for other Canadian Shield lakes and watersheds. The impact of the Little Sioux fire on nutrient fluxes was evaluated by comparing the budgets measured at Dogfish Lake with those measured at Meander Lake. This comparison showed that as a result of the burning of Meander Lake watershed, runoff increased 60% and the K and P exports increased 265% and 93%, respectively. The exports of Ca, Mg, and Na did not change significantly. The increase in runoff, probably due to the reduction in vegetative transpiration, is comparable to that measured after the 1970 Entiat fire (western Washington) and to that resulting form clear—felling experiments at Hubbard Brook (New Hampshire) and Coweeta (North Carolina). The increased nutrient losses after fire are less than those observed at Hubbard Brook and Coweeta. There was no indication of a drastic increase in nitrate export such as occurred after the Entiat fire and at Hubbard Brook. The increase in phosphorus loading of Meander Lake due to the fire was 38% (to 25 mg/m2°yr), a value that probably falls within the natural year—to—year variation in supply, and it did not represent a major impact on Meander Lake. Fire is a natural part of the BWCA forest ecosystems. The results of this study indicate that nutrient losses after the Little Sioux fire were minimal, perhaps because it was a spring fire. Fall fires may cause larger nutrient losses because more of the forest—floor material is likely to be consumed and revegetation does not begin until the following spring.
Environmental Stability and Fish Community Diversity
Authors: Kushlan James A.
Published: May 2006

Seasonal fluctuation of water level is the most critical environmental factor affecting the fish community of the Everglades marshes. During a 27—mo period of water—level stability, fish density decreased but biomass, average size of fish, species richness, and species diversity increased. These changes were accompanied by a functional shift from the dominance of small sized omnivorous species to the dominance of larger sized carnivorous fish. The changes resulted from immigration of large carnivorous species poorly adapted for survival in fluctuating marshes. Increased predation assumed the determining role in restructuring the community under environmentally stable conditions. The fish community of Everglades marshes oscillates between opposing tendencies of species domination, which depend on the degree of water level stability.
Fitness and Optimal Body Size in Zooplankton Population
Authors: Lynch Michael
Published: May 2006

A measure of fitness which is an explicit function of feeding efficiency and vulnerability to predation is introduced. Feeding efficiency is a function of feeding and respiration rates and the nature of the food supply. Defining fitness as a function of body size reveals several potential explanations for the evolution of life—histories and for mechanisms of competition in zooplankton populations. Utilizing availability data for Daphnia pulex and evaluating fitness for several temperatures, food—size distributions, and predatory regimes gives results which are very consistent with what is known of the ecology and demography of this species. A large variability in fitness is shown to exist between size classes, very small and very large individuals being particularly prone to food limitation. Thus, for a specified environment, there is an optimal body size at which an organism maximizes its contribution to the persistence of the population in terms of survival and/or reproduction. I suggest that natural selection should lead to maximum reproductive effort at this size at the expense of growth, and present several examples which support this idea. As alternative to the size—efficiency hypothesis, I suggest several mechanisms whereby small species may outcomplete or coexist with larger ones.
Feeding Strategies of the Little Brown Bat, Myotis Lucifugus, in Southern New Hampshire
Authors: Anthony Edythe L. P. , Kunz Thomas H.
Published: May 2006

Feeding strategies of the little brown bat, Myotis lucifugus, were investigated in southern New Hampshire USA from early May through late 1974. Nightly food consumption was estimated by comparing mean prefeeding body weights with postfeeding weights taken as individuals returned to the roost from their first feeding period (at 2200 to 2400h) and from a subsequent foraging period (at 0330 to 0500 h). Pregnant bats consumed an average of 2.5g of insects (2.72kJ/g prefeeding body weight) nightly. lactating females ate 3.7 g (4.23 kJ/g), and juveniles ingested 1.8 g (2.47 kJ/g). Increased food consumption in lactating bats accommodated reproductive energy demands and was facilitated by rising food availability. Increasing levels of independent food consumption in juveniles accompanied weaning. Fecal analysis revealed that diets of individual bats were diverse. All available insects 3 to 10 mm in body length were accepted as food items. Nematoceral Diptera were by far the most common insects taken in light—trap samples, and constituted a major portion of the diet throughout the summer. Coleoptera, Trichoptera, Lepidopter, Ephemeroptera, and Neuroptera were also consumed in appreciably numbers. Comparison of dietary composition with prey availability indicates that pregnant bats consumed 3—10 mm prey in approximate proportions encountered during June, when insect availability was low and unpredictable. However, lactating, postlactating, and nonproductive ♂ ♂ exhibited more selective feeding in July, when insects were more abundant. This increase in selectivity reflected exploitation of beetles and mayflies, which were uncommon in trap samples. In August, juveniles approximated random feeding patterns, as they learned to forage. We suggest that increased resource availability allowed selective feeding in adult bats during July, as predicted by presy selection models. However, reduced discriminatory abilities may prevent similar levels of prey selection in juveniles.
Ecological Significance of the Shapes of Abundance‐Frequency Distributions for Coexisting Phytoplankton Species
Authors: Lewis William M.
Published: May 2006

Abundance—frequency distributions for 31 phytoplankton species form Lake Lanao, Philippines, are constructed on the basis of 65 weekly samples. All of the distributions have a positive skew. The shapes of the distributions are quantified in terms of the coefficient of variation and a skew statistic. CV (the coefficient of variation) and skew are highly correlated for the 31 species and vary over approximately an order of magnitude between species. High CV and skew are interpreted as evidence of an opportunistic demographic strategy and low CV and skew as evidence of conservative strategy. Relationships are tested between CV or skew and three sets of variables: (1) mean abundance measured as biomass or numbers, (2) morphofunctional properties such as size and surface: volume ratio, and (3) niche descriptors. Niche descriptors are variables which give the average position of a species on an environmental gradient when net growth of the species is positive. The results of the analysis on the 3 sets of variables are as follows. (1) The mean abundance of a species is not statistically related to the CV or skew of its frequency distribution. This indicates that rate species are as likely to have an opportunistic strategy as common species. (2) Three specific morphofunctional characteristics (volume, surface area, and S:V ratio) are not related to CV or skew, but two general morphofunctional characteristics (morphotype and taxonomic affinity) are related to CV and skew. Filamentous morphotypes and diatoms have the most opportunistic patterns (high CV and skew), while coenobial morphotypes and chlorophytes have the most conservative patterns. (3) Among 5 different niche descriptors, CV and skew are related only to those which incorporate some measure of attrition, especially grazing. Periods of high attrition correspond with success of conservative species, and periods of low attrition with succes of opportunisticii species. Attrition due to grazing is the mechanism by which the general morphofunctional variables (morphotype, taxon) are related to shape of the abundance—frequency distribution.
The Determination of the Rate Constants of Island Colonization
Authors: Gilroy D.
Published: May 2006

Insular colonization is described in terms of simple Langmuirian equations for immigration and extinction. Possible techniques for the determination of the respective rate constants, k1 and k—1, of these processes, and of the transition times are discussed. The recolonization experiments of Wilson and Simberloff have been re—examined to illustrate some aspects of the model. The results show that k—1 is identical on five of the six islands throughout the period of regular monitoring. On the other island the same k—1 is observed initially, and later behavior may indicate the transition towards an assortive equilibrium. The effect of unobserved immigrations and extinctions on the experimental value of k—1 is of lower magnitude than previously suggested. The departure of the immigration process from "ideal" behavior is related to the defoliation damage produced by the defaunation. The species pool or source must be described by an activity" parameter, as well as by the number of species. In the experiments discussed, neither quantity is constant, and the effects of island area, and distance from source cannot be properly evaluated.
Influence of Precipitation on Perennial Grass Production in the Semidesert Southwest
Authors: Cable Dwight R.
Published: May 2006

Perennial grass production in the semidesert grass—shrub type (with and without a velvet mesquite (Prosopis juliflora var. velutina [Woot.] Sarg.) overstory) was dependent primarily on current summer rainfall and previous summer rainfall. The influence of previous summer rainfall was an interaction effect–not a direct effect. The best overall relationship involved current August rainfall, previous June through September rainfall, and the interaction product of these two. However, in interaction product along yielded estimates essentially as good as the multiple regression, and explained 64%—91% of the year—to—year variability in grass production. Winter precipitation had no consistent effect on perennial grass production the following summer. The degressing effect of mesquite on perennial grass production was most noticeable at low rainfall levels, but became minor at high rainfall levels.
Functional Roles of Schizoporella and Styela in the Fouling Community at Beaufort, North Carolina
Authors: Sutherland John P.
Published: May 2006

The functional roles of Schizoporella, an encrusting bryozoan, and Styela plicata, a solitary tunicate, were investigated by continuously removing each species from the developing community for 15 months. Observations were also made on the undisturbed community after the cessation of removals. Two experiments are reported here, initiated in October 1972 and 1973, respectively, and terminated in December 1976. When dense, Schizoporella excluded other species from the space it occupied, resulting in a patch with fewer species and with fewer changes in species composition through time. The maximum persistence time appeared to be °2 years and Schizoporella was unable to invade space occupied by other species. Styela also excluded other species from the community when dense, but its larvae were capable of invading space occupied by other species. The attachment sites of Styela on other organisms were often unable to support the large animals resulting from a summer of rapid growth. Thus, Styela often sloughed off in the fall, (even though the individuals may have been healthy) taking other organisms with it. In a short time frame, Styela stabilized the community, resisting invasion as did Schizoporella, but destabilized the community on a different time scale because of the approximately annual slough—offs.
The Role of Seed Banks in the Vegetation Dynamics of Prairie Glacial Marshes
Authors: van der Valk A. G. , Davis C. B.
Published: May 2006

The presence of viable seed in 24 substrate samples from Eagle Lake, a marsh in north—central Iowa, was tested by placing subsamples of each sample under 2 environmental conditions. One set of subsamples was placed underwater (submersed treatment). Seeds of 20 species germinated and grew in this treatment. On the average, there were 8.3 species/sample. The 2nd set of subsamples was kept moist, simulating conditions on an exposed mud flat (drawdown treatment). In the drawdown treatment, on the average, seeds of 12.9 species germinated/sample. Altogether seeds of 40 species germinated in this treatment of which only 24% were also found in the submersed treatment. By combining the results from the 2 treatments, the seed banks in the 6 vegetation types studied were estimated to range from 21,445 to 42,615 seeds/m2 on the average in the upper 5 cm of soil. Field studies at Eagle Lake (1974) and Goose Lake (1976), when these marshes had no standing water, revealed that the most abundant species whose seeds germinated on exposed mud flats were the same as the most abundant species in the experimental drawdown samples from Eagle Lake. In 1975, when Eagle Lake had standing water again, the submersed and floating species that were found were the same as those found in the experimental submersed samples from Eagle Lake. The seed—bank results and vegetation sampling reveal that there are 3 types of species present in prairie marsh seed banks: emergent species (Typha, Scirpus, Sparganium, Sagittaria) germinate on exposed mud flats or in very shallow water; submersed and free—floating species (Lemna, Spirodela, Ceratophyllum, Naias, Potamogeton) whose dormant seeds or turions can survive on exposed mud flats for a year and which germinate when there is standing water; and mud—flat species (Bidens, Cyperus, Polygonum and Rumex) which are ephemerals whose seeds can only germinate on exposed mud flats during periods when no standing water exists in the marsh because of drought or water level manipulation. When the marsh refloods, these species are eliminated from the visible marsh flora. Primarily because of the fluctuating water levels and muskrat damage, prairie marshes have cyclical changes in their vegetation during which mud—flat, emergent, or submersed and free—floating species replace each other as the dominant type of species in a marsh.
Differential Acceptance of Toxic Jojoba Seed (Simmondsia Chinensis) by Four Sonoran Desert Heteromyid Rodents
Authors: Sherbrooke Wade C.
Published: May 2006

Selected native heteromyid rodents were placed on diets of jojoba seeds (Simmondsia chinensis), which contain cyanogenic glucosides, to determine their ability to utilize the wild seed crop. Perognathus baileyi ate jojoba seeds and lived on a diet of seeds or meal for several weeks. Perognathus penicillatus, Perognathus intermedius, and Dipodomys merriami refused jojoba seed diets and lost weight rapidly. Apparently P. baileyi has a detoxification mechanism not possessed by the other species. Cyanogenic glucosides in jojoba seeds may function as a defense in seed predation. The development of detoxification mechanisms by P. baileyi could have been a coevolutionary response to the development of seed toxicity in jojoba. Biogeographically their distributions are broadly overlapping. Jojoba seed storage by P. baileyi may function to disperse seeds and facilitate germination and seedling survival. It is hypothesized that jojoba seed toxicity is an important factor in resource allocation among coexisting seed—eating rodents in jojoba habitats.
Fish Predation, Interspecific Predation, and the Distribution of Two Chaoborus Species
Authors: von Ende Carl N.
Published: May 2006

In sampling 22 lakes in the Upper Peninsula of Michigan, I found that 2 species of Chaoborus, C. punctipennis and C. americanus, never co—occurred (von Ende 1975). Chaoborus punctipennis was found only in lakes with fish whereas C. americanus occurred along in stained, bog lakes without fish. Third and 4th instar C. americanus lack extensive diel, vertical migratory behavior and are found near the surface waters in stained bog lakes. Adults of this species emerge in the middle of May. Third and 4th instar C. punctipennis exhibit diel, vertical migration. They are benthic during the day. This species emerges at the end of June. In situ rearing experiments indicate the Chaoborus americanus larvae can survive in lakes with fish, when isolated from the fish. Fish (Umbra limi) added to a lake with C. americanus eliminated this Chaoborus species from the lake. It is concluded that the absence of C. americanus from lakes with C. punctipennis is due to fish predation on the older larvae of C. americanus. Chaoborus punctipennis adults are able to disperse to lakes from which their larvae are absent. In situ experiments indicate C. punctipennis can survive on the zooplankton in a stained, fishless bog lake, but is subject to heavy predation by 3rd and 4th instar C. americanus larvae. It is concluded that because of early recruitment by C. americanus, as well as its lack of extensive vertical migration, this species excludes C. punctipennis from stained, fishless bog lakes.
Effect of Grazing and Browsing Fishes on the Zonation of Corals in Guam
Authors: Neudecker Steve
Published: May 2006

Controlled coral transplant experiments were used to determine the effect of piscine corallivores on growth, zonation, and distribution of scleractinian corals in Guam. Pocillopora damicornis L. generally occurs only on the reef flat, reef margin (crest), and in lagoon habitats of the Indo—West Pacific. Although P. damicornis grows in deeper reef habitats in the eastern Pacific, it is seldom found in fore reef zones of the Indo—West Pacific. Colonies were transplated from a depth of 1.3 m in a barrier reef lagoon to depths of 15 and 30 m in fore reef zones of three fringing reefs, where P. damicornis was absent. All transplanted colonies were heavily fed upon and branch tips were removed primarily by chaetodontid and balistid fishes, but none of the colonies was killed. This feeding removed about one—fourth of the colony wet weight in 1 wk (°x 23.7% ± 2.4, .99 confidence limits, N = 118). There was a very significant differnt in the amount of fish feeding on transplants between three different study reefs (Fs = 459.30, P < .001). There was no significant difference in the amount of feeding between the two depths at each site on any one run. Polyp and mucus browsing by species which do not physically damage the corol skelton was also substantial. When colonies of P. damicornis from Apra Harbor (1.3 m) were transplanted with colonies of Pocillopora sp. from Fafai Reef (15 m), to Double Reef and attached to naturally occurring Pocillopora verrucosa colonies (15 m), fish discriminated between the three similar species and fed only on P. damicornis. While some authors have indicated that these species may comprise a species complex, the fish clearly discriminted between the species. Coral feeding by many reef fishes is a regular event and exerts great influence upon reef community structure. Although P. damicornis can survive and grow well in deeper habitats in fish exclusion cages, it generally does not occur in these zones in the Indo—West Pacific. It is therefore concluded that piscine corallivores are important in restricting the growth, local zonation, and general distribution of some coral species.
Energetics of Yellow‐Bellied Marmot Populations
Authors: Kilgore Delbert L. , Armitage Kenneth B.
Published: May 2006

The energy dynamics of 2 colonies of yellow—bellied marmots (Marmota flaviventris) were studied in the Rocky Mountains of central Colorado in 1969 and 1970. The Intake—Rejecta and Maintenance—Production models, which included an analysis of seasonal variations in energy flow parameters, yielded similar estimates of population energy flow. Colony energy flow ranged from 64.0 to 94.6 KJ°m(—2)°yr(—1). Differences between colonies in annual energy flow can be explained by variations in biomass. Peak energy flow occurred at different times in the 2 colonies and the timing was related to reproductive conditions. The marmot populations consumed 94.6 to 119.2 kJ°m(—2)°yr(—1), which represented 0.8 to 3.1% of the aboveground primary production. The efficiency with which the marmot populations exploited the available net primary production was 2 to 6.4%. Seventy—one to 75% of the energy ingested by the populations was assimilated; only 77% of the assimilated energy went into maintenance of the population biomass. Tissue growth efficiency averaged 16.8%, °5x greater than typical homeotherms. The production/maintenance ratio averaged 29.6%. The marked differences in the respiration efficiencies, tissue growth efficiencies, and production: maintenance ratios between the heterothermic marmot and typical homeotherms suggest that heterothermy represents a distinct strategy in secondary production.
Binary Discriminant Analysis: A New Method for Investigating Species‐Environment Relationships
Authors: Strahler Alan H.
Published: May 2006

Binary discriminant analysis (BDA) is a readily understood, easily used technique for identifying binary variables and their common trends which are most important for discriminating between groups. For the plant ecologist, the technique can be used on species lists to reveal similar patterns of preference or avoidance among species responding significantly to a multistate environmental parameter such as soil type, rock type, or aspect. In Q—mode BDA, orthogonal canonical factors are obtained which represent uncorrelated floristic trends best separating the groups. Scores of species on the factors can be plotted in multidimensional hyperspace, showing how each species responds to the floristic trends. In R—mode BDA, groups of species with similar responds to the environmental parameter are identified. These groups may be interpreted as statistical associations or community components comprised of species with similar ecologies. An example using lists of woody species from the Maryland Piedmont and Coastal Plain sorted according to underlying rock type produces floristic trends which are easily interpreted and species groups which are readily understandable.
An Analysis of Species Dissimilarity Using Multiple Environmental Variables
Authors: Dyer David P.
Published: May 2006

A linear model is developed for species dissimilarity. The model, which potentially can be used in conjunction with any species dissimilarity index, is designed for data sets which involve both multiple species and multiple environmental variables. The total species dissimilarity is divided into components with 1 component being assigned to each environmental variable or interaction of environmental variables. Unbiased estimates for the variance of each component are provided.