bluuebunny/crossref_metadata_2025 huggingface dataset:
A Biophysical Analysis of Daily and Seasonal Utilization of Climate Space by a Montane Snake
Authors: Scott John R. , Tracy C. Richard , Pettus David
Published: May 2006

A model of the energy budget for the wandering garter snake (Thamnophis elegans vagrans) was constructed from equations describing heat flows at the animal's skin surface and body core. A new method was developed for expressing the role of heat transfer from the substrate in influencing body temperature. Convection coefficients were evaluated on live snakes in a wind tunnel and determined to be essentially identical to those for cylinders. Climate space diagrams were generated from energy budget equations for snakes in their natural montane habitats at 2600 m in Larimer County, Colorado. The attainable body temperatures revealed by climate space diagrams show that the physical environments normally encountered by T. elegans are surprisingly harsh. For example, in July the maximum voluntary body temperature (35°C) would be exceeded in open microhabitats (bare ground, rocks, grass) for °5.5—6 h of each clear day. Optimum body temperatures (26—32°C) could be attained for only °1.5—2.5 h each day, and the critical thermal maximum would be exceeded for at least 3 h in bare—ground or rock microhabitats. On cool or cloudy days in May and September, a snake could barely attain the minimum optimum body temperature in any microhabitat.
A Simulation Model for Decomposition in Grasslands
Authors: Hunt H. William
Published: May 2006

A model has been developed to simulate the dynamics of decomposers and substrates in grasslands. Substrates represented are humic material, feces, and dead plant and animal remains. Except for humic material, substrates are further divided into a rapidly and a slowly decomposing fraction. The proportion of rapidly decomposing material in a substrate is predicted from its initial nitrogen content. The belowground portion of the system is divided into layers because temperature and soil water, the most important driving variables for the model, vary with depth. Decomposition rates are predicted from temperature, water tension, and inorganic nitrogen concentration. Taxonomic groups of decomposers are not distinguished, but distinction is made between active and inactive states, which differ in respiration rate, in death rate, and in that only active decomposers assimilate substrate. The model's predictions compare favorably to data on CO2 evolution and to litter bag experiments, but not to ATP estimates of active microbial biomass. The model indicates a profound influence of depth on decomposition rates and on decomposer biomass dynamics, growth yield, and secondary productivity.
Population Dynamics of a Relatively Rare Species of Milkweed Beetle (Labidomera)
Authors: Eickwort Kathleen R.
Published: May 2006

Labidomera clivicollis (Coleoptera: Chrysomelidae, Doryphorini), the milkweed leaf beetle, is relatively rare in New York State, although one of its host plants (Asclepias syriaca) is abundant. A related species, Leptinotarsa decemlineata, is an economic pest of potatoes. A comparison of the population dynamics of Labiodomera with previously published information on L. decemlineata suggests that the major differing factor controlling the two species' relative abundance is the intensity of predation to which the larvae are exposed. Predation on the young Labidomera larvae on the foliage of the host plants was the most important mortality factor in field experiments. Newly hatched beetle larvae were placed on 16 A. syriaca plants under natural conditions, in one of four treatment: (1) cage over the plant, with an open bottom; (2) sticky—trap barrier and groundcloth around the plant's base; (3) both barrier around base and cage over plant; and (4) control plants. The mortality could then be separated into four components: abiotic mortality, ground—dispersed predation, air—dispersed, and spider predation—plus—cannibalism. The rate of larval mortality on the control plants was high, averaging 35% per day; all of the 112 control larvae (on four plants) died by day 12 of the experiment. Ground—dispersed predation alone accounted for 54% of the total mortality. Important predators included Nabidae, Pentatomidae and Syrphidae (larvae); they were generalized, not specialized, arthropod predators. Another field experiment investigated the effect of different clutch sizes on larval mortality rates, with and without sticky barriers. The protective effect of the barriers, and hence the important of ground—dispersed predators, was confirmed in the second experiment. These results suggest that the beetle's preference for swamp milkweed for oviposition may be adaptive to avoid ground—dispersed predation. Swamp milkweeds frequently grow in marsh habitats with water around the base of the plants. Larvae on these plants would be protected by a "moat effect." A review of the literature on field experiments with Leptinotarsa suggests that an analogous "bare ground effect" protects the larvae on cultivated potatoes from effective predation.
A Comparison of Nonmetric Multidimensional Scaling, Principal Components and Reciprocal Averaging for the Ordination of Simulated Coenoclines, and Coenoplanes
Authors: Fasham M. J. R.
Published: May 2006

The use of nonmetric multidimensional scalings as an ordination method has been studied by the use of simulated coenoclines and coenoplanes. It was found that the method always produced better ordinations than principal components analysis and in most cases better than reciprocal averaging, providing the multidimensional scaling was calculated using a space of the same dimensions as the simulated data. For real data of which the dimensionality is unknown, the minimum spanning tree can provide a useful means of estimating this dimensionality. Nonmetric multidemensional scaling was also less susceptible to distortion of the ordination by single gradients of high beta diversity and two—gradient situations when each gradient is of a different beta diversity. A number of different similarity measures were evaluated for use in conjunction with nonmetric scaling and the cos theta coefficient was found to generally give good results. The use of a log transformation of the species values has a marginal effect while the use of a `Manhattan' distance metric in ordination space produced inferior results.
Germination, Establishment, and Demography of Coastal Bush Lupine (Lupinus Arboreus) at Bodega Head, California
Authors: Davison Eric D. , Barbour Michael G.
Published: May 2006

Lupinus arboreus is a large, fast—growing, short—lived shrub dominant in the northern coastal scrub of California. The age structure of its stands and the factors which contribute to that age structure were examined at Bodega Head, a coastal peninsula in Sonoma County, 73 km north of San Francisco. No plants older than 7 yr were found. Major causes of mortality of established plants were herbivory by two species of insect larvae and summer drought. Most plants flower and fruit after the age of 2 yr. Nearly all seeds dropped under lupine canopies are taken by mice, and the absence of establishment there is not caused by allelopathic factors or competition for light or moisture. Establishment in surrounding grassland is limited by competition with grasses for light and moisture and, again, allelopathy is not a factor. Germination was enhanced by seed burial and exposure to alternate heat and cold, wetting and drying, and salt spray. Following seedling establishment, increase in biomass is approximately exponential for the first 4 yr, then growth rate decline. The mosaic of scrub and grassland at Bodega Head appears to be approaching a steady state, following release from grazing by cattle and protection from other disturbance since 1961.
The Microdistribution and Population Trends of Larval Tanypus Stellatus Coquillett and Chironomus Frommeri Atchley and Martin (Diptera: Chironomidae) in Utah Lake, Utah
Authors: Shiozawa Dennis K. , Barnes James R.
Published: May 2006

The microdistributional patterns and life histories of larval Tanypus stellatus and Chrionomus frommeri were studied in Goshen Bay of Utah Lake, Utah, from July 1973 to August 1974. Vertical distribution data shown that over 90% of the larvae were located in the top 7.5 cm of the substratum. Depth of penetration into the substratum increased with the later instars. Chironomus frommeri larvae penetrated deeper than those of T. stellatus. Biomass was distributed bimodally. The mode at the 0—2.5—cm depth was due to high numbers of early instar larvae. The second mode, at the 17.5—20.0—cm depth was due to the presence of fourth instar C. frommeri larvae. Tanypus stellatus showed a contagious distribution in the early instars with a trend towards randomization with age. Larvae of C. frommeri rarely showed contagious distributions. This was likely related to their low abundance in the samples making detection of a contagious distribution difficult. The larvae of T. stellatus overwintered in the first and second instar. This overwintering generation emerged in early July and gave rise to a second summer generation which emerged in August. Chironomus frommeri overwinter mainly as third and fourth instar larvae. Emergence occurred throughout the summer although two strong emergence pulses were seen, one in May and the second in July—August.
Cold Hardiness and Deep Supercooling of Hardwoods: Its Occurrence in Provenance Collections of Red Oak, Yellow Birch, Black Walnut, and Black Cherry
Authors: George Milon F. , Hong Sung Gak , Burke Michael J.
Published: May 2006

Fully cold—acclimated dormant twigs from provenance collections of red oak (Quercus rubra L.), yellow birch (Betula lutea Michx. F.), black walnut (Juglans nigra L.), and wild black cherry (Prunus serotina Ehrh.) were collected in winter 1975. Stem sections from latest season's growth were evaluated for freezing of a deep supercooled fraction of their stem H2O which froze anomalously at their killing temperature. Results show that all trees within each provenance collection have low temperature freezing points for stem H2O between —38° and —47°C. Generally no correlations were found in simple linear regression analyses comparing the low temperature freezing points with average annual minimum temperature or latitude for each geographic seed source. All trees throughout the natural ranges of the species investigated are capable of attaining a freezing resistance in the vicinity of —40°C. Additional analysis on red oak demonstrated a 25% decrease in the amount of deep supercooling H2O for northern versus southern samples.
Field Response of Photosynthesis to CO"2 Enhancement in Ponderosa Pine
Authors: Green Kathleen , Wright Robert
Published: May 2006

Net photosynthesis was determined by CO2 analysis for Pinus ponderosa Laws. in situ in the San Bernardino Mountains of southern California. Leafy shoots were maintained in cuvettes under ambient and enhanced levels of CO2 on successive days. Carbon dioxide enhancement was up to 150 ppm above ambient levels. Mean response of net photosynthesis increased 84%. Responsiveness to CO2 enhancement was not altered by high temperature or decreasing soil water potential during the months June—October. The added CO2 compensated for reduction of 50% in light intensity. Severe damage from oxidant air pollution reduced but did not eliminate the response to CO2 enhancement. The evidence suggests that net photosynthesis will increase in linear relation to rising atmospheric CO2 during the next few decades.
Physiological Ecology of Desert Iguana (Dipsosaurus Dorsalis) Eggs: Temperature and Water Relations
Authors: Muth Allan
Published: May 2006

The soil environment imposes constraints on the timing of oviposition and the location of suitable sites for egg burrows of the desert iguana (Dipsosaurus dorsalis). The effects of temperature and water potential on the developmental period and hatching success of eggs were determined. Eggs hatch normally between 28° and 38°C at environmental water potentials between —50 and —1500 kPa. Predictions were derived for the timing and placement of egg clutches based on soil water potential and temperature profiles measures in the field and on the results of laboratory incubation experiments. The results suggest that egg burrows should be located at depths >22 cm in washes or possibly in sparsely vegetated areas away from creosote bushes. The biogeography of desert iguanas within the United States is discussed in relation to soil environments and tolerances of eggs. The physical factors affecting incubation may limit the geographical range of desert iguanas.
In Situ Determination of the Effect of Symbiotic Algae on the Growth of the Fresh Water Sponge Spongilla Lacustris
Authors: Frost Thomas M. , Williamson Craig E.
Published: May 2006

The freshwater sponge, Spongilla lacustris, which usually occurs in an endosymbiosis with zoochlorellae, can be rendered aposymbiotic by providing darkened conditions. Utilizing this situation, we have determined, in situ, the contribution of the algal symbiont to the growth of this association. Pigment and ultrastructure analyses demonstrated that sponges maintained under darkened conditions were effectively aposymbiotic. Growth of sponges under normal conditions was significantly greater than for aposymbiotic organisms. In two separate experiments, aposymbiotic sponges grew to only 20% and 49% of the size of normal sponges. Clearance rate determinations revealed no difference in the feeding activities of normal aposymbiotic sponges on Aerobacter aerogenes or Chlamydomonas reinhardti. The contribution from symbionts appears important to the high growth rate of this sponge and its successful utilization of soft—bottom habitats. This work represents the first in situ determination of the contribution by an algal in an endosymbiosis with an invertebrate.
The Effects of Flooding on the Swamp Forest in Lake Ocklawaha, Florida
Authors: Harms William R. , Schreuder Hans T. , Hook Donal D. , Brown Claud L.
Published: May 2006

A 26—km stretch of the Oklawaha River in north—central Florida was impounded in 1968, forming a 5265—ha reservoir and flooding 1620 ha of mixed deciduous hardwood swamp to depths up to 3 m. Carolina ash (Fraxinus caroliniana Mill.), baldcypress (Taxodium distichum [L.] Rich.), red maple (Acer rubrum [L.],) and swamp tupelo (Nyssa silvatica var. biflora [Walt.] Sarg.) were the important tree species, with smaller amounts of cabbage palm (Sabal palmetto [Walt.] Lodd), button bush (Cephalanthus occidentalis L.) and several species of oak and elm. Tree mortality 3 yr after flooding was closely related to water depth, but it alow varied with species and diameter. All trees of all species had died in those parts of the reservoir flooded in excess of 1.3 m. Mortality decreased progressively as prevailing water depth decreased below 1 m. At 0.8 m mortality averaged 41%, 0.7 m it averaged 17%, and at 0.2 m it averaged 2%, about the same as natural mortality in unflooded areas of the swamp. Baldycypress, swamp tupelo, and cabbage palm were the most flood tolerant. The oaks were least tolerant. Measurements at the end of the fourth, sixth, and seventh growing seasons showed that the rate of mortality had dropped to low but still above—natural levels. Under all flooding depths mortality was least in the larger trees, those >38 cm in diameter. Trees <13 cm in diameter suffered the greatest losses. As depth of water increased, the proportion of the root systems killed by flooding increased, and the amount of starch in tissues of living roots decreased.
Organization of a Tropical Island Community of Hummingbirds and Flowers
Authors: Kodric-Brown Astrid , Brown James H. , Byers Gregory S. , Gori David F.
Published: May 2006

We studied the temporal and spatial relationships among hummingbirds and hummingbird—pollinated flowers on southwestern Puretor Rico in order to assess the roles of competition and mutualism in the organization of this community. We recorded flowering phenology, nectar production, hummingbird and nectar—robber visits to flowers, and pollen loads, and made morphological measurements of both hummingbirds and flowers along an elevational transect during two 6—mo periods. The community consists of three species of hummingbirds and at least 13 species of plants with tubular flowers specialized for hummingbird pollination. Two large hummingbirds, Anthracothorax dominicus and A. virdis, occupy largely nonoverlapping foraging areas, habitats, and elevations but overlap in their utilization of eight species of flowers that have long tubes and secrete copious nectar. The other hummingbird, Chlorostilbon maugaeus, is much smaller and forages legitimately almost exclusively on the other five species of flowers which have shorter tubes and secreteless nectar. Thus the community consists of two largely nonoverlapping subunits. Specificity is maintained because long—tubed flowers restrict legitimate foraging to large, long—billed hummingbirds, which are attracted to their high nectar levels, and because the short—tubed flowers secrete sufficient nectar for economical foraging by small, but not large hummingbirds. Both competitive and mutualistic interactions appear to have been important in the coevolution of these two discrete subcommunities of hummingbirds and flowers.
Plant Dominance Along an Experimental Nutrient Gradient
Authors: Tilman G. David
Published: May 2006

Fertilization experiments in an 8—yr—old field demonstrated that N was the major limiting nutrient of N, P, K, Ca, and Mg, and suggested that Mg became limiting when N was added. After the fertilization experiments, this field was disturbed via thorough disking and divided into 36 plots for a Latin square design experiment on the effect of N:Mg fertilization ratios on vegetation patterns. By the second year, the major species had separated along the imposed N:Mg gradient, with Agrostis scabra dominant at the low Mg but high N end, followed by Agropyron repens, Berteroa incana, Oenothera biennis, and Aristida basiramea, which was dominant at the high Mg but low N end of the gradient. An unmanipulated resource, light availability at the soil surface, was significantly affected by the treatments. The results demonstrate that spatial heterogeneity in the relative availability of soil nutrient may be one cause of spatial heterogeneity in early successional vegetation.
Succession and Nutrient Dynamics Following Forest Cutting and Burning in Amazonia
Authors: Uhl Christopher , Jordan Carl F.
Published: May 2006

Plant establishment, plant mortality, vegetation productivity, nutrient accumulation, and nutrient leaching were studied during the first 5 yr of succesion following the cutting and burning of a forest plot in the upper Rio Negro region of the Amazon Basin. The speed and vigor of forest regeneration following disturbance of this type provide a measure of the recuperative potential of this ecosystem. The study plot (0.09 ha) was dominated by forbs during the 1st yr and then by the pioneer tree species Cecropia ficifolia Snethlage during year two. Tree mortality exceeded establishment during the 3rd yr because of C. ficifolia trees died nearly in unison. During the 4th yr, tree density increased sharply as successional and forest tree species grew in the space vacated by C. ficifolia. The canopy was dominated at that time by the pioneer species Vismia japurensis Reich. and Vismia lauriformis (Lam.) Choisy. By the 5th yr, all establishment space had apparently been preempted: there were only 0.07 new establishments/m2 during year five, while 95% of the trees present at the end of year four survived through the 5th yr. There were 56 tree species (@<2 m tall) present on the site after 5 yr. More than half of these were primary forest species. Primary forest species were most common in the understory. These trees averaged >1 m in growth height each year and should eventually grow into the canopy. Hence, it appears that most individuals that will participate in the aggrading phase of forest development were already present on the site within 5 yr of burning. Biomass was only 66 g/m2 at the end of the 1st yr, but °1000 g/m2 were added in each subsequent year. The standing crop of biomass (shoot and root) at 5 yr was 4840 g/m2, a value 16% that of the mature forest which occupied the site prior to cutting. Approximately 27% of the dead trunk and branch biomass from the pre—existing forest remained on the site after 5 yr. Litter production increased each year from 39 g/m2 (year one) to 825 g/m2 (year five) and tended to be inversely related to rainfall. Total aboveground production was highest for the 5th yr (1940 g/m2) and was probably close to a maximum for the site. Total live—plant nutrient stocks after 5 yr, as a percentage of the precut forest stocks, were 15% for N, 23% for P, 39% for K, 48% for Ca, and 45% for Mg. A large increase in the leachate concentrations of K, Mg, and NO3 occurred during the first 2 yr following burning. By the 5th yr, concentrations were not significantly different from those in the undisturbed forest. After 5 yr soil nutrient levels were also similar to those of the preburn forest. Overall, nutrient losses apparently were not great enough to destroy the site's ability to return eventually to a state similar to that which existed prior to disturbance. This does not mean that a more severe treatment, such as conversion of forest to pasture, would not affect the regrowth ability of a site.
Nutrient Budgets of Marsh Plants: Efficiency Concepts and Relation to Availability
Authors: Shaver Gaius R. , Melillo Jerry M.
Published: May 2006

The effects of variable N and P availability on nutrient uptake, nutrient recovery from dying leaves, and biomass production in three species of marsh graminoids were studied in a growth chamber experiment. "Availability" was defined as the total amount of N or P added to each pot over the duration of the experiment. The species were Carex lacustris, Calamagrostis canadensis, and Typha latifolia. Responses were evaluated in terms of three "efficiencies": (1) efficiency of uptake, or the proportion of available N or P taken up by the plants; (2) efficiency of recovery, or the removal of nutrients from dying leaves as a proportion of the N or P content of mature leaves; and (3) efficiency of use, or the ratio of total biomass of total N or P mass in the whole plant. In all three species, as N or P availability increased, all three efficiency indexes decreased. There was evidence for N ° P interaction in regulating efficiency of N or P uptake, but not the other two indexes. Implications for ecosystem nutrient cycling are discussed, with the conclusion that, as nutrient inputs to an ecosystem increase, nutrient losses from the system and nutrient turnover in the vegetation should also increase.
Effects of Abiotic Disturbance on Coexistence of Predator‐Prey Fish Species
Authors: Meffe Gary K.
Published: May 2006

Behavioral responses of animals to large—scale abiotic disturbance are poorly known. Organisms living in habitats with frequent perturbations may evolve behaviors that minimize the impact of, or exploit, the disturbance. Organisms from environments that have fewer or different perturbations should not evolve these behaviors. The Sonoran topminnow (Poeciliopsis occidentalis) a poeciliid fish native to the arid American southwest, and the mosquitofish (Gambusia affinis), a morphologically similar poeciliid introduced from the mesic central and eastern United States, occur sympatrically in a few Arizona localities. Since flash floods of the mountainous Southwest are quantitatively and qualitatively different from the typical spring floods of mesic lowland drainages, I predicted that introduced G. affinis populations would incur greater losses during Southwestern floods than would native P. occidentalis. This was supported by preflood and postflood populations surveys in a natural habitat and by subsequent laboratory simulations of floods. The native species apparently possesses innate behaviors, such as quick response and proper orientation to high discharge, that allow its persistence under flash flood conditions. Mosquitofish show little such behavior and are more easily displaced by floods. Mosquitofish typically extirpate topminnows from native habitats via predation within 1—3 yr after introduction. Replacement is most rapid in localities that rarely or never flood, while long—term coexistence may occur in frequently flooded habitats. Abiotic disturbances may promote coexistence by periodically reducing population sizes of the exotic predator before the native prey species is eliminated. This hypothesis is consistent with data from a variety of other Arizona aquatic systems containing communities of native prey and introduced predatory fishes.
Evolution of Efficiencies and Strategies of Resource Exploitation
Authors: Glasser John W.
Published: May 2006

A logistic model generalized to multiple resources as well as species was used to test ideas about the conditions under which particular efficiencies and strategies of resource use ought to evolve. I hypothesize that obligate generalization and specialization, respectively, are the optimal strategies when the mean ratio of population size to environmental carrying capacity is constantly large or small, but that facultative specialization is optimal when this ratio is variable. Facultative strategists specialize (i.e., use some subset of available resources) when their population sizes are small relative to the environmental carrying capacity, but generalize progressively as this ratio increases. These ideas were evaluated by simulating competition among otherwise identical species with different efficiencies and strategies of resource use, in environments whose resource abundances or rates of supply had coefficients of variation of 0, 1, 10, and 100%. The results confirm expectations in general (e.g., facultative strategists fare better than obligate ones only in variable environments), suggesting that consumers whose resources fluctuate in availability relative to their requirements for them should be facultative. A particularly well—studied resource—consumer interaction permits estimation of model parameters, but the dynamic observations needed to distinguish obligate from facultative strategies are anecdotal. Hence, this theory remains to be evaluated empirically.
An Experimental Analysis of Desert Rodent Foraging Ecology
Authors: Harris John H.
Published: May 2006

A series of laboratory and field experiments was conducted with the small, bipedal heteromyid Microdipodops megacephalus and the small, quadrupedal cricetid Peromyscus maniculatus to test the hypotheses that desert rodents partition seed resources by selecting different patterns of seed dispersion and that they partition them by foraging in different microhabitats. Microdipodops megacephalus has a combination of morphological features that allows a separation of the effects of body size and gait in studies on the use of microhabitat and seed—dispersion patterns. In a small laboratory arena, M. megacephalus harvested more scattered seed than clumped seed, whether the two distributions were presented simultaneously or separately. In field experiments, rodents were presented with clumped or scattered seeds in open or shrubby microhabitat. Tracks of M. megacephalus were more frequent on plots in the open than on pots near shrubs, but were equally frequent on plots with either clumped or scattered seeds. P. maniculatus occurred more frequently near shrubs when plots were unbaited or when baited plots were far from cover, but did not differentiate between plots with scattered vs. clumped seed. At a site with a relatively high density of Dipodomys spp., M. megacephalus shifted toward an increased use of scattered seed. Dipodomys had a higher fraction of exclusive use of clumped—seed plots than of scattered—seed plots, which suggests that Dipodomys may have caused the shift. Dipodomys used both open and shrubby microhabitats. These results suggest that body size is a more important factor than locomotor adaptations in the use of clumped seeds. Microhabitat use, on the other hand, appears to be related to gait, which supports the view that bipedalism and enlarged auditory bullae allow the use of open microhabitat despite the increased exposure to predators.
Demography of Belding's Ground Squirrels
Authors: Sherman Paul W. , Morton Martin L.
Published: May 2006

For 11 consecutive field seasons (1969—1979) we studied the demography of a free—living population of Belding's ground squirrels (Spermophilus belding) at Tioga Pass, in the central Sierra Nevada of California. Our research involved repeatedly capturing and directly observing individually marked, known—age animals within and between years. Here we present information on age—specific survival and dispersal rates for both sexes and age—specific fecundity and reproductive value for females. Our data indicate that: (1) The 7—8 mo hibernation period (October—May) is a hazardous time; 66—70% of juveniles and 36—39% of adults disappear during the winter. (2) Males apparently live about half as long as females; males that survive their first winter typically remain in the population an additional 1.1 yr vs. 1.6 yr for females; while few males live > yr, some females live >11 yr. (3) The sex of ration of the adult population is female—biased, especially in the older age—classes. (4) Throughout the active season (summer), males disappear more rapidly than females; this disappearance is due both to dispersal and to mortality. (5) During intrasexual combat for mates, males injure each other severely; such injuries lead directly and indirectly to male mortality. (6) Litter size and reproductive value change with female age; they are lowest for young (0—1 yr) and old (5—9 yr) female and highest for 2—4 olds. (7) The net reproductive rate (R0) for 1969—1975 was 1.36 daughters per dam, while the mean generation length (°) was 2.26 yr. Sexual asymmetries in the demographic characteristics of S. beldingi appear to result from the animals' polygynous breeding system.
The Correlation Between Ecology and Morphology in Deciduous Forest Passerine Birds
Authors: Miles Donald B. , Ricklefs Robert E.
Published: May 2006

We investigated the correspondence between feeding behavior and morphology among 19 species of passerine birds in the Hubbard Brook Experimental Forest, New Hampshire, using data in Holmes et al. (1979). Fourteen categories of foraging behavior were ordinated by reciprocal averaging. The first and second derived axes accounted for 61% of the total variance, and distinguished foraging substrate and maneuver. A morphological space was defined by eight external measurements. The correspondence between the positions of species in spaces defined by reciprocal averaging and morphology was determined by canonical correlation analysis. This analysis revealed two strong correlations: the first (R2 = 0.94) related substrate utilization to the lengths of the tarsus and midtoe, and the second (R2 = 0.70) related foraging maneuver to midtoe length. The canonical correlation analysis accounted for 83 and 74% of the variation on reciprocal averaging axes I and II; of the morphological variables, only tarsus (76%) and midtoe (64%) contributed strongly to the correlations. Therefore, although morphology predicts foraging behavior in this data set, considerable morphological variation is not related to the foraging variables that characterize the species' ecological relationships.
Gamma Radiation Effects on Nestling Tree Swallows
Authors: Zach Reto , Mayoh Keith R.
Published: May 2006

The sensitivity of Tree Swallows (Tachycineta bicolor) to the stress of ionizing radiation was investigated with growth analysis. Freshly hatched nestings were temporality removed from nests, taken to the laboratory and acutely exposed to 0.9, 2.7, or 4.5 Gy gamma radiation. Some of the unirradiated control nestlings were also taken to the laboratory, whereas other were left in the nests. Growth of all the nestlings was measured daily and analyzed by fitting growth models. There was no detectable radiation—induced mortality up to fledging, °20 after irradiation. Radiation exposure did not affect the basic growth pattern; the logistic growth model was most suitable for body mass and foot length, and the von Bertalanffy model for primary—feather length, irrespective of treatment. Parameter values from these models indicated pronounced growth depression in the 2.7—Gy and 4.5—Gy groups, particularly for body mass. Radiation also affected the timing of development. The growth depression of the 2.7—Gy group was similar to that cause by hatching asynchrony in unirradiated nestlings. The 4.5—Gy nestlings grew as well as unexposed nestlings that died from natural causes. Chronic irradiation at °1.0 Gy/d caused more severe growth effects than acute exposure to 4.5 Gy and may have caused permanent stunting. Growth analysis is a potent tool for assessing man—made environmental stresses. Observed body—mass statistics and model parameters seem to be most sensitive to environmental stresses, but coefficients of variation are not necessarily correlated with seabirds. Unfortunately, growth analysis may fail to assess the full impact of the stress, because stress factors can have effects far beyond the initial growing period.
Priority Effects in Experimental Pond Communities: Responses of Hyla to Bufo and Rana
Authors: Wilbur Henry M. , Alford Ross A.
Published: May 2006

The timing of hatching of two early spring breeding frogs, Rana sphenocephala and Bufo americanus, was controlled in a 3 x 3 factorial experiment (each species introduced early, introduced late, or not present) in a randomized block design replicated three times in an array of 27 experimental ponds. After nearly all Bufo had metamorphosed and left the ponds, but before Rana began metamorphosis, 500 hatchlings of a summer—breeding species, Hyla chrysoscelis, were added to each of the 27 ponds and to 3 more ponds that had recently been filled. Hyla had a higher survival rate, shorter mean larval period, and larger mean size at metamorphosis in the newly filled ponds than in any other treatment. The older ponds without either spring species were the next best habitat. These “old” controls were used to assay the effects of the spring—breeding species on Hyla. Bufo had a significantly adverse effect on Hyla even though the two species were not contemporaneous, this was interpreted as being due to an impact by Bufo on the trophic structure of the ponds, an impact that persisted throughout the summer. Rana had an even stronger negative effect on Hyla than did Bufo. The 2 x 2 subset of treatments consisting of Hyla with early or late Rana and early or late Bufo was analyzed separately. The combination of late Rana and late Bufo had the strongest adverse effect on Hyla and the other three combinations were about equal in their effects. These experiments demonstrate the advantages to anurans of ovipositing soon after pond filling and of colonizing ponds that have not been used previously in the season by other species. The detection of historical effect reveals that our experimental communities were not governed by stationary first—order Markov processes and that perturbations had persistent effects on their trajectories. Our results suggest that optimal seasonal patterns for reproduction exist in animals with complex life cycles that exploit temporary habitats.
Nest Predation in Forest Tracts and the Decline of Migratory Songbirds
Authors: Wilcove David S.
Published: May 2006

Nest predation has been suggested as an important cause of the decline of breeding populations of migratory songbirds in small woodlots in eastern North America. I tested this hypothesis by placing artificial nests with fresh quail eggs in forest of different sizes in Maryland and Tennessee. Predation rates were higher in small woodlots than in large tracts. Predation was especially intense in woodlots near suburban neighborhoods compared to woodlots in isolated rural areas. Experimental open—cups nests were move vulnerable to predators when placed on the ground vs. 1—2m above ground. In either position these open—cup nests were move vulnerable to predators than experimental cavity nests. Since most species of migratory songbirds construct open—cup nests, and several species place them near the ground, migratory songbirds should by strongly affected by higher predation rates in small forest tracts
Late Quaternary Aridity and Holocene Moisture Fluctuations in the Lake Valencia Basin, Venezuela
Authors: Leyden Barbara W.
Published: May 2006

Lake Valencia is one of few sites to provide paleoecological data for the Neotropical lowlands. A prior pollen analysis of late Glacial and early Holocene sediments from Lake Valencia indicated extreme aridity during the Pleistocene followed by only slightly more mesic conditions as the Holocene began. The present study confirms the aridity of the late Glacial, but suggests that the early Holocene was considerably more mesic. Data presented for the mid and late Holocene indicate that effective moisture has varied, but that climates were never again as mesic as the early Holocene. In general, arid conditions prevailed except from 5200 to 2200 BP. The vegetational record begins (°13 000 BP) with savanna surrounding a saline marsh. The watershed near the lake was not part of refugium for mesophytes, as has been suggested. As the Holocene began, halophytic littoral and shoreline communities formed around a shallow, saline lake. The coverage of savanna decline and contained scattered scrub. These communities were replaced (°9800 BP) by semievergreen and deciduous subtropical forests with Brosimum predominant. Over the past 8300 yr essentially modern vegetational associations existed with the watershed. Mesic forests retreated to higher elevations during the mid—Holocene as forests at lower elevations became more open and deciduous. Extensive weedy vegetation persisted on the unstable flood plains. Forests expanded somewhat 5200 to 2200 yr ago but have since declined in extent.
Nitrification Potentials of an Old‐Field Chronosequence in Campton, New Hampshire
Authors: Thorne James F. , Hamburg Steven P.
Published: May 2006

Successional changes in available soil nitrogen may be a key to understanding the dynamics of secondary succession. Nitrification potentials of forest floors from an old—field chronosequence in Campton, New Hampshire, were measured in the laboratory for 9 mo. Total nitrate production per unit organic matter decreased with increasing stand age. Although nitrate production decreased in older forest floors of the chronosequence, total nitrogen removals during the incubation were relatively similar. Nitrate production was strongly correlated with initial forest floor pH (°2 = 0.96, P < .001), but was not correlated with any of five different measures of litter and forest floor tannin content. It appears that decreases in nitrification potential during this secondary succession could have resulted from changing forest floor pH and its effects on microorganisms.
Competitive Effects and Responses Between Plant Species in a First‐Year Old‐Field Community
Authors: Miller T. E. , Werner P. A.
Published: May 2006

Competitive interactions involve two separate processes: the effect of a species on others in the community and the response of a species to all others. Five species from a 1st—yr field were investigated to determine if there is any correlation between competitive effect and response and if the patterns of effect and response can explain the relative success of each species in the full community. Effect and response were measured by observing the growth of individuals in all possible monocultures and two—species mixtures, using ambient densities (Year 1) and a range of densities (Year 2) for each species. Both monocultures and two—species mixtures were obtained by removing unwanted individuals at emergence, leaving naturally emerging individuals of the desired species. Competitive effect and response were found to be inversely correlated. The inverse correlation lead to a hierarchy of competitive ability, with Ambrosia artemisiifolia being the competitive dominant, followed by Agropyron repens, Plantago lanceolata, and finally the competitive subordinates Chenopodium album. Lepidium campestre (used in Year 1), and Trifolium repens (used in Year 2). The interactions were generally asymmetric, e.g. Ambrosia artemisiifolia had a large suppressive effect on the other species and demonstrated no response to their presence. The hierarchy and a lack of specificity of the interactions suggest that all the species are limited by, and competing for, the same resource or resources. The hierarchy of competitive ability appears to be a major factor in determining the abundance of each species in the full community.
A Stage‐Based Population Model for Loggerhead Sea Turtles and Implications for Conservation
Authors: Crouse Deborah T. , Crowder Larry B. , Caswell Hal
Published: May 2006

Management of many species is currently based on an inadequate understanding of their population dynamics. Lack of age—specific demographic information, particularly for long—lived iteroparous species, has impeded development of useful models. We use Lefkovitch stage class matrix model, based on preliminary life table developed by Frazer (1983), to point to interim management measures and to identify those data most critical to refining our knowledge about the population dynamics of threatened loggerhead sea turtles (Caretta caretta). Population projections are used to examine the sensitivity of Frazer's life table to variations in parameter estimates as well as the likely response of the population to various management alternatives. Current management practices appear to be focused on the least responsive life stage, eggs on nesting—beaches. Alternative protection efforts for juvenile loggerheads,such as using turtle excluder devices (TEDs), may be far more effective.
Starvation and Predation as Factors Limiting Population Size
Authors: McNamara John M. , Houston Alasdair I.
Published: May 2006

We consider a simple model in which an animal can control both its probability of starvation and its probability of predation. Probability of starvation is decreased by increasing the mean amount of food obtained in the day, but this increases the probability of predation. The optimal mean gain minimizes that total mortality. It is shown that as the amount of food that is required per day increases, the probability of starvation does not necessarily increase, and may actually decrease. This result arises because as the food requirement increases, the animal increases its predation risk in order to avoid starvation. The results suggest that it is inappropriate to argue that food alone or predation alone limits the size of a population when there is a strong interaction between them. Furthermore, the number of animals that die from starvation may not provide a reliable indication of the importance of food.
Competitive Interactions Among Adults and Juveniles in a Coral Reef Fish
Authors: Jones Geoffrey P.
Published: May 2006

Considerable discussion has arisen over whether population limitation in coral reef fishes is achieved through postrecruitment processes or through factors operating prior to recruitment that lead to insufficient numbers to saturate resources. This paper presents the results of two field experiments designed to document and measure the relative effects of recruitment and subsequent intraspecific competition on populations of the planktivorous damselfish Pomacentrus amboinensis, a common species on the Great Barrier Reef. I tested for effects of conspecifics on juvenile mortality, growth, and maturation by manipulating population densities on coral rubble patch reefs. Each experiment examined the potential for competition among juveniles and adults. The first experiment manipulated the densities of recently settled recruits; the second manipulated 1—yr—old juveniles using a similar experimental design. There were no consistent effects of juvenile density or of adult presence/absence on juvenile survivorship, during either the 0 + yr or the 1 + yr. However, there were substantial effects on growth and maturation. During the 1st 8 mo of experiment 1, grow was inversely related to initial juvenile density, but was not affected by the presence of adults. A marked negative effect of adults on juvenile growth developed as juveniles approached an age of 1 yr. This effect developed early in experiment 2. Both the mean and the variance in 1 + yr growth were reduced in the presence of adults. Adults primarily affected the growth of the initially largest, behaviorally dominant juveniles. A significantly greater number of 0 + yr and 1 + yr juveniles reached a mature size after 1 yr in treatments without adults present. The numbers maturing were not related to initial density, either with adults present or absent. It is concluded that postrecruitment competitive processes play an important role in restricting adult population size in P. amboinensis, at least over the range of densities and on the spatial scale examined. The mechanism, however, is not one of those traditionally considered in equilibrial models. That is, competition does not appear to modify recruitment or mortality patterns directly, but influences numbers maturing through density dependent effects on maturation time.
Components of Conspecific Host Discrimination Behavior in the Butterfly Battus Philenor
Authors: Papaj Daniel R. , Rausher Mark D.
Published: May 2006

The hypothesis that pipevine swallowtail butterflies (Battus philenor) discriminate among Aristolochia reticulata host plants according to their suitability for juvenile survival was investigated under field and enclosure conditions. Butterflies discriminated among host plants differing in leaf quality both before and after landing. Over 3 yr of field observations, the host plants on which females landed and oviposited were smaller, possessed longer buds, and bore a higher percentage of high—quality leaves than host plants on which females landed but left without depositing eggs. Similarly, the host plants on which females landed in those years were not a random sample of the host plants available in the habitat. Plants on which the butterflies alighted bore a higher percentage of high—quality leaves, a lower percentage of low—quality leaves, and longer buds than their nearest neighbors that were not landed upon. These characteristics were associated with differences in expected larval growth and survival. Field and enclosure experiments in which variation in certain plant characters was manipulated independently of variation in other plant characters generally confirmed these results. Enclosure studies suggested strongly that females learned to land on particular host types according to the responses those plants had elicited after previous alightings. The implications of that finding for models of the evolution of pre—alighting and post—alighting components of discrimination behavior are discussed.