bluuebunny/crossref_metadata_2025 huggingface dataset:
Time‐Delay Versus Stability in Population Models with Two and Three Trophic Levels
Authors: May Robert M.
Published: May 2006

If a biological or other system has a potentially stabilizing negative feedback mechanism, which, however, is applied with a time lag long compared to the natural time scale of the system, the result is instability, not stability. This theme is developed in detail for vegetation—herbivore and vegetation—herbivore—carnivore systems in which the stabilizing resource—limitation effect operates on the herbivore population with a time lag. Under certain conditions, which are commonly met in nature, the vegetation—herbivore—carnivore system is stable (with population fluctuations being damped out), while the vegetation—herbivore system with no predators is unstable. This model, which can be supported with some observational data, suggests inter alia that herbivore population numbers may often be set neither by predators alone nor by vegetation alone, but by an explicit interplay between both effects.
Demography of Gregariously Roosting Populations of the Nymphaline Butterfly Marpesia Berania in Costa Rica
Authors: Benson Woodruff W. , Emmel Thomas C.
Published: May 2006

Populations of the daggerwing butterfly, Marpesia berania (Hewitson) (Nymphalidae; Nymphalinae), assemble nightly in roosts of up to 68 individuals in the tropical rain forest of the Osa Peninsula, Costa Rica. Gregarious nocturnal roosting in butterflies in uncommon, and reported almost exclusively in supposedly distasteful species. We studied two roosts, using a marking technique that permitted visual censusing. The butterflies maintained roosting sites in the same general locations and regularly returned to them before evening, during life spans of over 5 months. The sex ratio was unity, and the rates of population recruitment and mortality were apparently the same for both sexes. The instantaneous mortality rates were approximately 0.0126 (on a daily basis) over the study period, and the recruitment rates for the two roosts were 0.907 and near 0.15 butterfly per day for March and April, 1968 (the last month of the dry season and the first month of the wet season). In the following 3 months of the wet season, recruitment decreased to near zero. The empirically determined rates of recruitment and mortality accurately predicted the initial population size, indicating that the adult population was under equilibrium conditions during the dry season and the first month of the wet season.
The Foraging of Small Populations of Yellow Warblers and American Redstarts
Authors: Morse Douglass H.
Published: May 2006

I studied the foraging of Yellow Warbler (Dendroica petechia) and American Redstarts (Setophaga ruticilla) on several small islands of varying vegetational composition off the coast of Maine. Both species used deciduous growth more than predicted by chance alone. Yellow Warblers foraged slightly lower than Redstarts; Redstarts used dead limbs and hawked for insects more often than Yellow Warblers. On islands with mixed forests both species fledged young regularly; there they set up largely exclusive territories. Partitioning appeared to be in response to certain vegetational characteristics; little evidence was obtained that direct interactions were of major importance in this regard. Most male Redstarts in the latter areas were adults; most males on small spruce—clad islands had first—year plumage. Only one species occupied any small spruce—clad island, and seldom did it fledge young. Usually a male did not attract a female in such cases. No clear correlation occurred between the size of the standing insect crop, the tendency of these species to occupy an island, and their ability to fledge young. While Parula (Parula americana), Myrtle (Dendroica coronata), and Black—throated Green (D. virens) warblers displayed a highly developed vertical division of space and a well—defined interspecific social hierarchy (Morse 1971), Yellow Warblers and Redstarts divided space horizontally and did not demonstrate a well—defined interspecific social hierarchy. Correspondingly, one may find up to three species of spruce—woods warblers on an island too small to support more than one pair of a given species, but never both Yellow Warblers and Redstarts in such a situation.
Establishment of Invertebrate Communities on Log Substrates in the Kaskaskia River, Illinois
Authors: Nilsen Henry C. , Larimore R. Weldon
Published: May 2006

Development of invertebrate communities on log substrates was investigated in three habitats. In slowly moving, shallow water, standing crops (weights) of colonizing invertebrates followed a sigmoid growth curve during a 6—week exposure period. Initial colonization was rapid, followed by 2 weeks of slow growth, a rapid increase during the next 2 weeks, and then a leveling off at 1,650 mg/m2 during the final week. Numbers followed a similar pattern of growth, attaining a high of approximately 100,000/m2 by the end of the 5th week. Chironomid larvae colonized first and in the greatest numbers, followed sequentially be sessile rotifers and oligochaetes. These three organisms had the greatest influence on standing crops and total numbers. In a riffle, colonization was also rapid: 569 mg and 8,830 individuals per m2 at the end of four weeks . The riffle community was dominated by Taeniopteryx nivalis, hydropsychid larvae, chironomid larvae, and simuliid larvae. In a pool, the standing crop was largest on logs at an intermediate depth, next largest near the surface, and smallest near the bottom. The oligochaete, Aeolosoma sp., attained their largest population on logs at the greatest depth, chironomid larvae and taeniopterygid naiads attained their largest population at or above the intermediate depth. Communities on naturally occurring logs contained more planaria and insects of the families Hydropsychidae, Heptageniidae, and Elmidae than on the experimental logs in slowly moving, shallow water. Communities on the introduced logs did not reach a climax stage during the experimental period because organisms, organic detritus, and slit were constantly accumulating or sloughing off, the substrate was slowly decomposing, and changes were occurring seasonally in the chemical and physical condition of the water, all of which modified the habitat and influenced community development.
The Stability of Predator‐Prey Systems
Authors: Smith J. Maynard , Slatkin M.
Published: May 2006

The interactions between a predator and prey species have been analyzed by computer simulation of a model in which there are discrete breeding seasons, separated by a winter during which the predator must be able to find prey at a certain minimum rate or starve. The model is intended to represent a warm—blooded vertebrate predator and its prey. The main conclusions are: (1) Coexistence of predator and prey is possible, but if so, the number of prey present will not be substantially below the equilibrium number in the absence of predators. Mutual regulation of predator and prey, with the latter substantially below the carrying capacity of the environment, is unstable. (2) Coexistence is more likely if there are differences in hunting ability between different individual predators–for example, between young and old predators. (3) Cover for the prey enables the prey species to survive the extinction of the predator, but does not make coexistence more likely.
Diversity and Evenness: A Unifying Notation and Its Consequences
Authors: Hill M. O.
Published: May 2006

Three commonly used measures of diversity, Simpson's index, Shannon's entropy, and the total number of species, are related to Renyi's definition of a generalized entropy. A unified concept of diversity is presented, according to which there is a continuum of possible diversity measures. In a sense which becomes apparent, these measures provide estimates of the effective number of species present, and differ only in their tendency to include or to ignore the relatively rarer species. The notion of the diversity of a community as opposed to that of a sample is examined, and is related to the asymptotic form of the species—abundance curve. A new and plausible definition of evenness is derived.
A Centrifuge Method for Determining Live Weights of Aquatic Insect Larvae, With a Note on Weight Loss in Preservative
Authors: Stanford Jack A.
Published: May 2006

A reproducible centrifuge drying method for determining live or preserved weights of aquatic insect larvae is described. An attempt was made of derive a conversion factor for weight loss in preservative. Results showed a great interspecific variation in weight loss over a period of time due to the effect of preservative.
An Optimization Equation for Predation
Authors: Marten Gerald G.
Published: May 2006

A general equation is derived for the quantity of different foods a predator consumes in response to food preference and food abundance. It is supposed the predator apportions its efforts among different search modes in order to minimize the discrepancy between actual and desired quantities of each food consumed. Included are the conflict between quantity and composition of the diet and the competition between feeding and nonfeeding activities. The properties of the equation are examined and discussed in light of the literature.
Relationship of (65)ZN Excretion and Egg Production in Trichoplusia NI (Hubner)
Authors: Mason William H. , McGraw Katherine A.
Published: May 2006

Egg production and (65)Zn excretion were measured in cabbage loopers, Trichoplusia ni (Hubner), at constant temperatures of 23 degrees C and 27 degrees C and at a fluctuating temperature ranging from 22 degrees C to 37 degrees C (X = 27 degrees C). Correlation coefficients (r) of =0.88 (P=<.0005) and +0.92 (P = <.0005) were calculated for constant—temperature and fluctuating— temperature groups, respectively. It appears that egg production could be accurately estimated on the basis of measuring (65)Zn loss in released and recaptured animals.
Structures and Dynamics of Populations of the Salamader Desmognathus Ochrophaeus Cope in Different Habitats
Authors: Tilley Stephen G.
Published: May 2006

Two populations of Desmognathus ochrophaeus, one inhabiting a wet rockface created during the construction of a tunnel portal on the Blue Ridge Parkway and the other a wooded cover 145 m away, were compared with respect to size at maturity, growth rates, age structure, and fecundity. Woodland animals are larger at maturity than rockface animals. This is because of their faster juvenile growth rates, not delayed maturity as previously believed. Woodland juveniles then continue to grow faster than rockface individuals after they mature, possibly because food resources are more extensive and dependable in leaf litter than on wet rockfaces. In the rockface population, growth rates appear to vary slightly from year to year. Body sizes and egg production are positively correlated in both populations, and the larger body sizes of woodland females enables them to achieve a mean clutch size nearly 50% greater than that of the rockface population. Body—size variation among populations of D. ochrophaeus is a complex phenomenon, possibly involving genetic differentiation of populations at different elevatons as well as non—evolutionary differences in growth rates between populations in different habitats. Further studies will be required to show whether other differences among rockface populations and between rockface and woodland populations have genetic bases. In the rockface population, proportions of second—summer juveniles and males in their 1st yr of sexual maturity appear to decrease during the summer. The cause of this phenomenon is unknown, and there is no evidence for it in the woodland population. Both populations have similar age structures in the early summer, before changes in the structure of the rockface population have occurred. Continued sampling of the rockface population over four successive summers resulted in a decline in the ratio of adult males to 1st yr juveniles, especially after the summer of 1971 when collecting was particularly intense. Estimates of the normal number of adult males in the population and the amount of yearly recruitment were made from capture—release—recapture data on another rockface population of similar density. Sustained collecting, which should have resulted in a greater decline in mean number of testis lobes per male than was observed, showed that older males may have been underrepresented in samples because of their more secretive habits.
Colonization Curves for Planar Marine Islands
Authors: Schoener Amy
Published: May 2006

Marine fouling and successional studies, documenting species changes on flat, isolated objects, provide some additional data on island colonization. Plotting numbers of species on these planar islands over time allows construction of several colonization curves. Contrary to the MacArthur—Wilson equilibrium model, in many cases these curves do not convincingly approach an equilibrium number of species during colonization. This contrasts with findings for most, but not all, three—dimensional islands. Continuing increases in the number of species on these two—dimensional islands is probably attributable to the large number of species available relative to the number accumulating on these small panel islands, rather than to successional changes on the islands themselves. Evidence indicates that in areas of substantial seasonal temperature change the shape of the colonization curve varies seasonally: in warmer months the colonization curve initially rises more rapidly than during colder months.
Sand‐Beach Energetics: Importance of the Isopod Tylos Punctatus
Authors: Hayes Willis B.
Published: May 2006

The isopod Tylos punctatus dominates the supratidal sand—beach communities at a number of locations in southern California and northern Mexico. It feeds on the giant kelp Macrocystis pyrifera, which appears to be the major source of organic input for these beaches. Field measurements on kelp input and on the kelp consumption and assimilation rates of the isopods indicated that the animals were consuming an average of only 4%—5% of the edible kelp input. Assimilation efficiencies were high, however, averaging 64%. Approximately 88% of the assimilated energy could be accounted for by metabolic activity and growth. The beaches investigated appear to be of only minor importance in the degradation of nitrogen compounds (e.g. proteins) to NH4+—N and the recycling of this material to the nearshore waters.
Plant Resources and Butterfly Habitat Selection
Authors: Sharp Margaret A. , Parks David R. , Ehrlich Paul R.
Published: May 2006

The microdistribution of adult subalpine butterflies was examined in relation to several components of the mountain meadow flora in Gunnison County, Colorado. With the exception of two small, sedentary species, there was no significant correlation between the microdistribution of the butterflies and that of their larval food plants. Similarly, correlational studies indicated no strong habitat selection on the basis of nectar source abundance. The diversity of the butterfly fauna was, if anything, negatively correlated with overall floral diversity. It thus seems that most of the butterflies studied treat a wide array of meadow—vegetation associations as suitable habitat.
Caloric, Elemental, and Nutritive Changes in Decomposing Juncus Roemerianus Leaves
Authors: de la Cruz Armando A. , Gabriel Benjamin C.
Published: May 2006

In situ decomposition rate of Juncus roemerianus (Juncaceae) leaves determined by litterbag method was 40% per year. Caloric, elemental, and proximate nutritive analyses of leaves at various stages of life and decay–classified as young, mature, standing dead, partially decayed, decomposed fragments, and particulate detritus–showed the following: (a) an increase in caloric content (4630—4911 g cal/ash—free g); (b) a decrease in carbon (49.75%—6.38%), nitrogen (1.09%—0.57%), and phosphorus (0.22%—0.17%); and (c) a decrease in crude fiber (37%—9%), carbohydrate (52%—11%), protein (9%—4%) and fats (2.0%—0.85%). Particulate detritus retrieved from litterbags decomposed in incubation flasks at the rate of 50% in 36 days. At intervals of 0, 5, 13, 25, and 36 days, analyses of detritus showed the following: (a) a decrease in organic content (67%—32%) and carbon (5.6%—3.2%); and (b) an increase in nitrogen (0.44%—1.21%) and respiration rates (0.11%—1.10 mg O2 hr—1 ash—free g—1). The increase in nitrogen of detritus and consequently protein is attributed to conversion of plant tissue to microbial protoplasm as evidenced by increased respiration rates.
Anolis Cupreus: The Response of a Lizard to Tropical Seasonality
Authors: Fleming Theodore H. , Hooker Roderick S.
Published: May 2006

Seasonal changes in the population ecology of Anolis cupreus, a sexually dimorphic lizard, were studied over a 2—yr period in a deciduous and riparian forest ecosystem in western Costa Rica. This tropical environment undergoes strong seasonal changes, including a 6—mo yr dry season during which maximum air temperatures, hours of daily sunshine, and heavy winds occur. Many aspects of the ecology of A. cupreus undergo striking seasonal changes in response to this climatic seasonality. Both sexes were sexually active for about 6 mo of the year, with the ♀ cycle coinciding with the wet season. Fat body cycles in both sexes were inversely related to the reproductive cycles. Males and ♀ ♀ attain sexual maturity at 1 yr or less, and the population apparently undergoes an annual turnover. Population density was high (> 1,200 anoles/ha) in the dry season, but in part because of changes in the structural habitat of ♂ ♂ and territorial behavior, density was much lower in the wet season. In the dry season social interactions were rarely seen, both sexes perched at or near ground level, and ♀ ♀. In contrast, in the wet season social interactions occupied a majority of the ♂ ♂ time as they defended territories and courted ♀ ♀. At this time of the year ♂ ♂ perched much higher than ♀ ♀ fed primarily on the ground; ♂ ♂ obtained at least half their food up to 6 m aboveground in the wet season. Because of seasonal changes in perch heights and size of prey items eaten, intrasexual (seasonal) values of place x food niche overlap were lower than intersexual values. The response of this anole to stressful climatic conditions is analogous to that of its Temperate Zone congener, Anolis carolinensis. Whereas A. carolinensis hibernates to avoid low winter temperatures, A. cupreus becomes inactive during periods of high winds and air temperatures.
Germination Response of Legume Seeds Subjected to Moist and Dry Heat
Authors: Martin Robert E. , Miller Robert L. , Cushwa Charles T.
Published: May 2006

Prescribed burning is used in southeastern USA to promote growth of leguminous plants which produce seed important as quail food. These seed are characterized by a hard seed coat and the ability to remain dormant but viable for a long time. This study was conducted to determine the effect of heat on germination of seed from several of these legume species. Seeds of 18 species and two varieties were subjected to moist and dry heat treatment. Moist heat increased germination in eight species and two varieties, and dry heat increased germination in seven species and two varieties.
Studies of a Simple Laboratory Microecosystem: Effects of Stress
Authors: Ferens M. Catherine , Beyers Robert J.
Published: May 2006

Inocula from an established microcosm were subjected to acute gamma radiation levels of 105 and 106 rads. Microcosms developed from these inocula were sampled through the 40—day successional period to determine effects of radiation stress. Chlorophyll "a" content, biomass, and community metabolism were measured. Significant reduction in chlorophyll "a" was found when each treatment level was compared to its control. Biomass was significantly reduced throughout succession for both treatment levels except for the last sample of 106 rad microcosms. Net productivity and nighttime respiration varied similarly and were significantly reduced during early succession at both treatment levels. Comparison of treatment effects revealed that the 105 rad level microcosms responded to the stress with a greater reduction in parameters measured than the 106. Explanation of this phenomenon may lie in inhibitory interactions among microcosm components at 105 rads. Elimination of certain species at 106 rads may have limited this interaction. The action of radiation at the community level was similar to that of other forms of stress in that radiation can differentially affect the organisms comprising a community and subsequently change community structure. The present study illustrates the idea that stress changes species dominants and succession. In addition, it emphasizes the significance of changes in interactions among community components when a community is stressed.
Influence of Corals in the Dispersion of the Pomacentrid Fish, Dascyllus Aruanus
Authors: Sale Peter F.
Published: May 2006

Coral colonies suitable for use as shelter are an important resource for the pomacentrid reef fish, Dascyllus aruanus. Each fish restricts its movements to the vicinity of a single colony which may be shared with several other individuals. This paper examines the pattern of distribution of individuals of this species among corals. The correlation between the number of fish in a group and the area of the colony used by the group was determined for 16 locations on a reef. The strength of this correlation varied greatly, but a significant relationship (P<0.01) existed between its strength and the intensity of use of the corals in each sampling area. In those places where use of coral was most intense, the correlation between the number of fish in a group and the area of the coral used by the group approached unity. The results indicate that the available suitable corals are fully used in only some parts of a reef, but than in these parts, an efficient dispersion of fish among corals is achieved. The behavioral mechanisms by which the dispersion might be attained are discussed.
Effect of Cover on Agonistic Behavior of a Reef Fish: A Possible Spacing Mechanism
Authors: Sale Peter F.
Published: May 2006

Each Dascyllus aruanus shelters in a colony of coral on a reef. The fish restricts its movements to the vicinity of this colony, which may be shared with several other individuals. In areas where suitable coral colonies are in short supply, the fish are efficiently spaced over the available coral (Sale 1972). The mechanism by which this dispersion might be attained is examined in the present paper. If the tendency of a fish to be aggressive were controlled by the degree to which it was crowded while sheltering in its coral, the pattern of emigration and immigration among neighboring groups would be influenced. Groups in one area would approach a common ratio between the number of fish they contained and the size of the coral they occupied. An experiment tested whether the frequency or intensity of agonistic behavior of a group of D. aruanus was affected by the amount of shelter provided for them. Agonistic behavior was observed when groups of two, four or six fish were placed with one, two, or three units of synthetic coral. In addition to the expected effect of group size on the level of agonistic behavior (P < 0.005), a significant effect of the amount of shelter (P < 0.005) and a significant interaction (P < 0.005) were detected. The results are interpreted as supporting the proposed mechanism.
Competition between Microtus: A Behavioral Hypothesis
Authors: Conley Walt
Published: May 2006

Behavioral and demographic parameters were studied in Microtus longicaudus and M. mexicanus during 1969 and 1970. Microtus longicaudus was at peak density (120/ha) in 1969 and decline density (30/ha) in 1970. Microtus mexicanus remained at low density (30/ha) during both years. Sex ratios, and survival rates were different between years in M. longicaudus, not different in M. mexicanus. Intraspecific agonistic behavior in M. longicaudus was consistent with hypotheses of intrinsic regulation. Behavioral reactions related to contention for space were measured. These values support an hypothesis relating space to interspecific competition in these species.
Body Size Differences Between Populations of the Chuckwalla, Sauromalus Obesus
Authors: Case Ted J.
Published: May 2006

Body size of chuckwallas, Sauromalus obesus (measured as the upper decile snout—vent length, UDL) at 12 locations throughout the species' range is highly correlated with average winter rainfall. The coefficient of variation of rainfall and average seasonal temperatures did not significantly aid winter rainfall in accounting for populational body size differences. Two populations with the highest (Little Lake) and the next to lowest (Amboy) UDL were studied in detail. The larger Little Lake chuckwallas appear to grow faster but do not live longer than chuckwallas at Amboy. This enhanced growth was allied to the more diverse and abundant food regime at Little Lake. Surprisingly, chuckwallas at Little Lake maintain relatively smaller fat bodies than animals at Amboy. This may be an adaptation to Amboy's more severe and less productive environment.
Character and Significance of Forest Tree Root Exudates
Authors: Smith William H.
Published: May 2006

Root exudates from the unsuberized tips of new woody roots were collected from mature Betula alleghaniensis, Fagus grandifolia, and Acer saccharum in a northern hardwood forest. Numbers of new woody root tips were also determined for these three species. Exudates were fractioned into carbohydrates, amino acids/amides, organic acids, and 9 inorganic ions. Considerable species variation characterized the quantitative and qualitative nature of the organic fraction. Organic acids were the most abundant component. Fagus grandifolia released the largest amount of amino and organic acids per hectare, while B. alleghaniensis exuded the largest amount of carbohydrates. Sodium (possibly anomalous), K, and Ca dominated the cationic fraction, while the anionic fraction was chiefly SO4 and Cl. Betula alleghaniensis and F. grandifolia released considerably greater quantities of inorganic ions than A. saccharum, but the inorganic root exudate patterns of the three species were relatively uniform. These results indicate root exudates have some role in intrasystem nutrient cycling.
Seasonal Fat Reserves of Bats in Two Tropical Environments
Authors: McNab Brian K.
Published: May 2006

Seasonal fat deposits were examined in eight species of bats from two localities in Jamaica. All species, except the nectarivore Monophyllus redmani, have a significant decrease in fat reserves during the dry season. In insectivorous bats, ♀ ♀ generally have more fat than ♂ ♂ during periods of maximal fat reserves; this difference normally disappears during the dry season. Bats with other food habits show no sexual dimorphism in fat deposition and appear to have smaller annual variations in the size of fat reserves. These data are compatible with the interpretation that insectivorous species face the greatest seasonal variation in food availability, which is derived from studies of the metabolism, temperature regulation, and reproduction of tropical bats. It is suggested that the tropical bats most likely to invade a temperate environment ate those whose habits expose them to the most seasonal food supplies.
Seasonal and Diurnal Water Relations of Selected Forest Species
Authors: Cline Richard G. , Campbell Gaylon S.
Published: May 2006

Leaf diffusive conductance, leaf water potential, and leaf osmotic potential measurements were made on one tree species and three woody brush species on north and south aspects in the Priest River Experimental Forest of northern Idaho. Douglas maple (Acer glabrum) and western white pine (Pinus monticola) occurred on both aspects. Sitka alder (Alnus sinuata) and mallow ninebark (Physocarpus malvaceus) occurred only on north and south aspects, respectively. Physocarpus on the south aspect attained osmotic and leaf water potentials near ‐30 bars and daytime leaf diffusive conductances (reciprocal of resistance) near 0.3 cm/s. The Pinus on this site attained osmotic and leaf water potentials near °25 bars and leaf diffusive conductances near 0.06 cm/s. Osmotic potential and leaf water potential decreased to a minimum specific to each deciduous species as the season progressed. The Alnus and Acer species exhibited osmotic potentials near ‐16 bars with the Acer leaf water potential decreasing further to near ‐20 bars. The Pinus maintained a uniform osmotic potential between ‐20 and ‐25 bars throughout the year. Leaf diffusive conductance appeared to be controlled during the day by a combination of atmospheric demand, soil moisture availability, and plant adaptation to water stress. Stomatal control of leaf water potential was evident in Pinus on both aspects and in the brush species on the north but not on the south aspect.
Two‐Dimensional Microdistribution or Cellular Slime Molds in Forest Soil
Authors: Eisenberg Robert M.
Published: May 2006

Four sample series consisting of 101 small samples (° wet wt = 0.2 g) of forest soil were examined for the presence of cellular slime molds. Although each sample series contained 5 cellular slime mold species, the distribution of species among the samples indicates that on a microlevel, 5, 4, or even 3 species seem seldom to co—occur. The results also demonstrate the extreme patchiness or cellular slime mold distribution in nature.
Selection of Roost Sites by Honduran White Bats, Ectophylla Alba (Chiroptera: Phyllostomatidae)
Authors: Timm Robert M. , Mortimer Jeanne
Published: May 2006

Ectophylla alba H. Allen (Chiroptera: Phyllostomatidae), the Honduran white bat, was found to alter the leaves of five species of Heliconia (H. imbricata, H. laptispatha, H. pogonantha, H. tortuosa, and an undescribed species) for use as diurnal roosts. By cutting the side veins extending out from the midrib, the bats cause the two sides of the leaf to fold down around the midrib forming a tent. More tents were found on H. imbricata and H tortuosa than on the other three species, but these were the most abundant species at the Costa Rican locality. The bats appeared to be selecting size—class of leaves for tent construction rather than leaves of a particular species of Heliconia. Honduran white bats were found roosting in groups of 1—6 individuals. It appeared that a colony of bats roots in a number of tents scattered within the forest. An hypothesis of leaf size selection, tent utilization, and evolution of tent construction is presented.
Ecology, Flowering Phenology, and Hummingbird Pollination of Some Costa Rican Heliconia Species
Authors: Stiles F. Gary
Published: May 2006

Nine hummingbird—pollinated species of Heliconia occur together at Finca La Selva, in the wet Caribbean lowlands of Costa Rica. In forest habitats, Heliconia clumps (clones) are typically small; in more open areas, many clumps attain large size. This probably reflects differences in light intensity and degree of vegetative competition in these habitats. Nine species of hummingbirds regularly visit Heliconia flowers at La Selva. The four hermits are nonterritorial, traplining foragers with long, curved bills. Non—hermits frequently hold territories at Heliconia clumps, and have short, straight bills. Pollination by hermits tends to produce more cross—pollination; territorial hummingbirds increase self—pollination. Different Heliconia species appear to be specialized for pollination by either hermits on non—hermits, largely through components of the caloric phenotype: amount and timing of nectar production, rate of inflorescene and flower production, and morphological paramerters that affect the energetic efficiency of nectar—harvesting hummingbirds. Habitat may influence pollination systems through its effects on clump size and thus on the number of flowers a clump can have at any one time. Ultimately, specialization for hermits or non—hermits may depend on the degree of self—compatibility of the different Heliconia species. Hermit—pollinated Heliconia mostly show sequential and nonoverlapping flowering peaks, probably resulting from competition for pollinators and/or selection against hybridization. Two hermit—pollinated species bloom simultanesoulsy, thereby inducing the birds to utilize an other—wise little—used microhabitat. Heliconia species pollinated by non—hermits bloom in the early to middle rainy season, and are mostly separated by habitat. Isolating mechanisms among sympatric Heliconia species involve both spatial and temporal patterns of partioning available pollinators. Floral parameters include mechanical (different site of pollen deposition on the bird) and ethological (caloric and visual factors affecting flower choice) mechanisms. Selection for pollinator specificity may result in convergence of blooming peaks, provided that other isolating mechanisms are present. Human activity has broken down some habitat barriers by producing large areas of second growth.
Comparative Dynamics and Life Histories of Coexisting Dragonfly Populations
Authors: Benke Arthur C. , Benke Susan S.
Published: May 2006

Several species of coexisting dragonfly larvae were studied for four consecutive years in a 1—ha old farm pond. Larval development, emergence patterns, and adult flight patterns showed that the most abundant species were univoltine and developed relatively synchronously (i.e., like a cohort). Three of the common species emerged in early spring, and the others emerged later in the summer. The common genera with the most similar microhabitat had a distinct temporal separation that may serve in reducing interspecific competition. However, coexisting congeneric species had almost identical life histories, supporting the hypothesis that ecological homologues can coexist because of "errors of exploitation" of the dominant species. The larval population dynamics of each dominant species (Ladona deplanata, Epitheca spp., and Celithemis fasciata) was characterized by a constant percentage numerical decline, coupled with a dramatic biomass increase from time of hatching to final instar. Larval mortality during this period averaged 92% per annum, but population biomass increased at least tenfold during the same period for each species. Comparison of larval estimates with emergence data revealed that at least 80% of the final instars die just before leaving the water to emerge. Life history variations among species smoothed out composite density and biomass trends which averaged about 1,000 individuals/m2 and 2 g dry wt/m2, respectively. In general, population dynamics from year to year were quite consistent, indicating a relatively high degree of stability in terms of species composition and densities.
Sucessional Status and the Palatability of Plants to Generalized Herbivores
Authors: Cates Rex G. , Orians Gordon H.
Published: May 2006

Theoretical considerations and evidence from the literature suggest that early successional plant species should make a lesser commitment of resources to defense against herbivores, and should then provide better food sources for generalized herbivores than later successional and climax plants. Commitment to defense by plants is estimated by determining short—term palatabilities to two slug species; one native to western Washington, Ariolimax columbianus, and one introduced from Europe, Arion ater. Results of tests with 100 plant species of three growth forms and from different seral stages indicated that early successional annuals were significantly more palatable than early successional perennials which were significantly more palatable than later successional species. No correlation was found between palatability and evolutionary association of the herbivores with the plant species.
Residual Nutrient Discharge in Streamwaters Influenced by Sewage Effluent Spraying
Authors: Perkins Michael A. , Goldman Charls R. , Leonard Robert L.
Published: May 2006

The disposal of secondary sewage effluent on a subalpine forest floor was investigated in terms of its relationship to nutrient discharge in a Tahoe basin watershed. Heavenly Valley Creek showed significant increases in NO3—1—N and ultraviolet absorbance downstream form a site that had been used for land disposal 5 yr prior to this study. These increases were traceable to subsurface discharge from the sprayed area. Evidence indicated that substances present in the spray area discharge and the streamwater are inhibitory to algal photosynthesis at in situ concentrations. This effect may be due in part to NO3—1—N which undoubtedly becomes stimulatory through dilution in the lake. Discharge from the spray area can be traced into Lake Tahoe by following patterns of UV absorbance which correlate closely with patterns of primary productivity. This correlation, combined with estimates of continuing heavy NO3—1—N loading of Lake Tahoe by Heavenly Valley Creek, reveals the long—term impact of land disposal of effluent on the ultra—oligotrophic lake.
Time and the Number of Herbivore Species: The Pests of Sugarcane
Authors: Strong Donald R. , McCoy Earl D. , Rey Jorge R.
Published: May 2006

Previous analyses have established that host species range in the most important determinant of plant— and animal—associated parasite species richness, and that the age of a host species within a region is, at most, much less important in determining this richness. However, these previous analyses were not able to completely rule out age as a cause, because the available host age estimations were crude and few host groups were available for comparison. This paper examines the arthropod pests of sugarcane (Saccharum officinarum) in 51 regions for which dates of introduction, areas in cultivation, and associated pest data are available. The sugarcane data are more complete and extensive than those for previously investigated host—parasite associations, and they make possible a more detailed analysis of the causes of species richness. Multiple regression analyses of these data cannot identify time to have any measurable influence upon the species richness of sugarcane pests. This implies pest species accumulation to reach an asymptote within, at most, a few hundred years. The asymptote is set by the geographic range of host species. The results of this study are consistent with those of four other analyses of host—parasite associations. We suggest sufficient evidence has accumulated to justify abandoning nonasymptotic species accumulation models (the "time) and "stability—time" hypotheses), at least for parasite communities. We caution against invoking "time" hypotheses for the explanation of diversity variation in other ecological systems where the influence of area and immigration rates cannot be dealt with. The "time" hypothesis also often involves virtually untestable assumptions about habitat constancy over very long periods of time.
Interactions of Food Level and Population Density in Rana Sylvatica
Authors: Wilbur Henry M.
Published: May 2006

Tadpoles of the wood frog, Rana sylvatica were reared in the laboratory at four densities (1, 2, 4, and 8/dish) and at four food levels (1, 2, 4 and 6 multiples of a ration) in a randomized 4—block design for a factorial analysis of variance. Both food and density had significant effects on growth rate and body size at metamorphosis. The length of the larval period was significantly correlated (r=.81) between pairs of larvae reared together but was not significantly associated with either food or density. At low ratios of supply (food level) to demand (density level) body weight increased with food availability. At high supply: demand ratios the excess food caused a pollution effect which reduced growth, body size at metamorphosis and survival. At different densities maximum growth was achieved at different supply: demand ratios. In natural populations, body size decreases with density as if food were in short supply.
A New Vegetation Map of Kansas
Authors: Kuchler A. W.
Published: May 2006

A new vegetation map of Kansas has been prepared, accompanied by a commentary. In the latter, some historical remarks on mapping the vegetation of Kansas are followed by a presentation of some basic aspects of vegetation. Comments on Kansas vegetation units, a discussion of vegetation boundaries, and the description of the vegetation types help the reader of the new vegetation map to appreciate its content. In an elaboration of the map legend, each vegetation type is described threefold: its physiognomy and structure, the dominant species (in English and Latin), and other characteristic components (Latin only). A brief comment on location and habitat and a photograph of each vegetation type complete the legend elaboration.
The Structure of Hardwood Forest Ecosystems of Prince Edward County, Virginia
Authors: Gemborys Stanley R.
Published: May 2006

A phytosociological investigation was conducted in the hardwood forests of Prince Edward County, Virginia, to determine the structural aspects of these ecosystems and to determine the relationships of these communities to edaphic and topographic characters. In all, 32 stands were studied, located entirely within the Piedmont, representing habitats ranging from those of wet bottomlands to dry upland sites.

Stands were positioned on the X, Y, and Z axes of a vegetational mosaic according to the technique described by Bray and Curtis. Environmental parameters were then superimposed over this mosaic in an attempt to determine which, if any, of these factors showed distributions associated with the vegetatively determined array. Density, basal area, depth of litter, percent organic matter, pH, soluble salts, calcium, magnesium and depth of the "A" horizon were found to be correlated with one or more of these axes.
Primeval Magnolia‐Holly‐Beech Climax in Louisiana
Authors: Delcourt Hazel R. , Delcourt Paul A.
Published: May 2006

An early American Land Office Survey (1821) has provided a reliable basis for reconstruction of early settlement forest patterns within West Feliciana Parish, Louisiana. Application of the statistical test, analysis of variance, in the evaluation of surveyor bias in selection of bearing trees is a refinement of previous methods. Distribution of forest communities has been delineated on the basis of edaphic and topographic relationships. A forest community of tupelogum and cypress occurred in the alluvial plain of the Mississippi River. Upland portions of West Feliciana supported a magnolia—holly—beech mixed hardwoods on thick loess deposits. A second distinct association of magnolia, beech, and holly existed in ravine and river lowlands of the loess hills. Occurrence of a mixed white oak—pine—beech forest was restricted to the northeastern portion of the present parish. This study represents the first quantitative evidence to support the existence of a late—successional, or climax, magnolia—holly—beech forest in the original vegetation of upland mesic sites within a portion of the Gulf Coastal Plain, U.S.A.
Rate of Development and Viability of Hybrids Between Drosophila Pavani and Drosophila Gaucha under Competitive Conditions
Authors: Brncic Danko , Budnik Myriam
Published: May 2006

In experiments on competitive ability of the preadult hybrids between the sibling species, Drosophila pavani and D. gaucha with a limited supply of food and space, the egg—to—adult survival of the hybrids is higher than that of the corresponding parental species, when the preadults are reared alone. When these hybrids are reared together with the parental species, there is a decrease in their variability, especially with respect to D. gaucha. The developmental period of the hybrids tends to shorten in the presence of D. gaucha, but in the presence of D. pavani and at high densities the hybrids show prolonged development. On the other hand, D. pavani and D. gaucha increase their viability significantly in the presence of the hybrids at high densities. The conclusion is that the growth of hybrids is strongly interfered with the presence of the parental species under overcrowded conditions, while the parental species, D. pavani and D. gaucha, are facilitated."
Parametric Models for Line‐Transect Estimators of Abundance
Authors: Quinn Terrance J. , Gallucci Vincent F.
Published: May 2006

The estimation of the abundance of animal populations with the line—transect sampling method requires that a sighting model be postulated to represent the decreased probability of a sighting as its distance from the transect line increases. The development of parametric sighting models and estimation techniques is reviewed, and general procedures for variance estimation are given. Two new models and their corresponding abundance estimators are developed. The half—normal model provides a useful alternative to the widely used exponential model. The generalized exponential model contains the half—normal and exponential models as special cases and has the flexibility to account for a wide range of sighting phenomena. The new models are applied to transect surveys of porpoise schools and the results are related to sampling and ecological conditions. Criteria for model selection and transect design are discussed.
Comparative Error Analysis of Six Predator‐Prey Models
Authors: Gardner R. H. , O'Neill R. V. , Mankin J. B. , Kumar D.
Published: May 2006

Six models were devised for a hypothetical predator—prey system. The models differed in functional forms, but were calibrated to display similar output for a standard annual cycle. Parameters were assumed to be measured with error, and this uncertainty was propagated through the models by Monte Carlo simulation. Total uncertainty on model output was partitioned, for each model, into six component sums of squares, and components were examined as they changed over the simulated annual cycle. The results indicate that the models differ in their error propagation properties with more complex functions often generating greater uncertainty on output. The contribution of a specific model term to overall error is dependent on its mathematical form (especially, the partial derivative of the term with respect to the parameter) and also its position within the total model. No single model showed the smallest output uncertainty for all possible modeling objectives. The results indicate that the most useful data for testing a model should be gathered during periods of the year when the state variables are changing most rapidly.