bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses to Nutrient Pulses of Two Colonizers Requiring Different Disturbance Frequencies
Authors: Miao S. L. , Bazzaz F. A.
Published: May 2006

Using a congeneric pair of colonizing perennial species, we tested the prediction that Plantago major, a species from frequently disturbed habitats, would respond to pulses of nutrient availability with greater increases of growth and shifts in biomass allocation to reproduction than would P. rugelii, a species from less frequently disturbed habitats. The two species were maintained at two nutrient levels, and plants were pulsed once each at five different times during the course of the experiment. Net photosynthesis was measured before plants were harvested at four intervals. It was found that the timing of nutrient pulses affected leaf and root relative growth rates (RGR) of P. major plants differently. At the high nutrient level, nutrient pulses given to P. major plants before the reproductive stage resulted in increased leaf RGR at the expense of root growth, whereas the opposite was observed at the low nutrient level. However, P. rugelii generally exhibited similar change in leaf and root RGR following nutrient pulses. P. major pulsed during the reproductive stage exhibited higher increases of RGR, total biomass, and leaf/root ratio, and different patterns from those plants pulsed before the reproductive staged. In contrast, P. rugelii generally exhibited similar change in these characters. At the final harvest, P. major plants significantly increased allocation to spike biomass in response to nutrient pulses, whereas P. rugelii did so only at specific times. For P. major, there were significant negative correlations between proportional allocation to vegetative (both leaves and roots) and reproductive organs, while for P. rugelii, the negative correlation was found only between proportional allocation to roots and spikes. The differences in response to nutrient availability of the two colonizers are commensurate with the degree and frequency of disturbance of the sites on which they grow in the field.
Plant Resistance to Insect Herbivores: A Field Test of the Environmental Stress Hypothesis
Authors: Louda Svata M. , Collinge Sharon K.
Published: May 2006

We tested the hypothesis that environmental stresses decrease overall plant resistance to insect herbivory in the field and evaluated biochemical mechanisms proposed to explain insect response to stressed plants. To impose a stress treatment, we severed lateral roots and rhizomes of a native crucifer (bittercress, Cardamine cordifolia) and quantified plant and herbivore responses for treatment and control clones. Severing roots and rhizomes once, early in the growing season: (1) produced moderate, but detectable, changes in plant physiological traits, specifically greater transient leaf water decicits at midday (P < .05) and elevated nitrate—nitrogen concentrations (P < .05); (2) altered plant quality, by causing an increase in soluble carbohydrates (P < .003), isoleucine concentrations in leaves (P < .01), and possibly glucosinolate concentration (P < .10), but made no differences in most primary nutrient concentrations, including total nitrogen, total free amino nitrogen, total amino acids, proline, and leaf water content; and (3) led to increase herbivory by chewing and leaf—mining (P < .001), but not by sap—feeding, insect herbivores. Trends toward decreased plant stature and fruit reproduction were not significant after 1 mo. In addition to the significant effect of our treatment, we found extensive variation in the magnitude of response to stress and herbivory among replicates. We hypothesize that environmentally induced physiological variation among plants within a plant population commonly distributes insect herbivory disproportionately onto a subset of the individuals, and in so doing influences the demography, distribution, and evolution of that plant population.
Influence of Thermal Ecology on the Mycosis of a Rangeland Grasshopper
Authors: Carruthers Raymond I. , Larkin Timothy S. , Firstencel Heidi , Feng Ziding
Published: May 2006

The clearwinged grasshopper, Camnula pellucida, exploits incident solar radiation to raise internal body temperatures above ambient levels. Under adequate temperature and light conditions, grasshopper body temperatures may exceed air temperatures by 10°—15°C with both nymphs and adults preferring to thermoregulate near 40°C, their optimal temperature for development. Comparison of age—specific phenology data collected from field sites with projections from computer simulation studies on grasshopper development, indicated that incident solar radiation can highly accelerate maturation of grasshoppers. Also, prolonged exposure to temperatures above 35°C is beneficialto grasshoppers, as it is detrimental to the fungal pathogen Entomophaga grylli (US pathotype I), which is a major cause of natural mortality in many species. E. grylli protoplasts grew little or not at all if incubated at a constant 35°C in tissue culture medium. Studies, conducted in vivo at constant temperatures, verified that E. grylli has an upper thermal limit of survival and development near 35°C. IN nature, however, these organisms are exposed to fluctuating temperatures. Further in vitro studies revealed that protoplast survival and development were significantly affected by incubation at 40°C for as little as 2 h per day and almost totally inhibited by 40°C for 8 h each day. In vivo incubation studies also showed an increase in the incubation period and a decline in the proportion of grasshoppers dying of E. grylli mycosis with increased daily exposure to 40°C. Infected grasshoppers were also held at 25°—30°C and allowed to range freely between shaded and lighted areas, so body temperatures could be raised through normal basking activity. Compared to a control group held in diffuse light, E. grylli mycosis was almost totally eliminated from the basking grasshoppers. The few individuals treated with solar radiation that died from E. grylli infection survived significantly longer then infected individuals not exposed to the solar simulator. Computer simulations using field—collected temperature, moisture, and solar radiation data revealed that behaviorally regulated thermal effects on E. grylli survival and development could limit disease development in some locations and seasons. Although it is unclear that the behavioral trait of basking is an adaptive response to selection pressures caused either by the pathogen or by other selective factors, it is clear that thermoregulatory behavior provides survival advantages to C. pellucida. In addition to their specific biological significance, these results demonstrate that behavioral exploitation of a physical resource in the environment can be used to profoundly alter biological relationships between species in this case, allowing one organism to eliminate an antagonist by causing its mortality.
Effects of Herbivore Gut Surfactants on Kelp Polyphenol Defenses
Authors: Tugwell S. , Branch G. M.
Published: May 2006

The idea that plant polyphenols act as digestibility—reducing compounds is well entrenched. This hypothesis has recently been countered with the proposal that the presence of surfactants in the gut fluids of herbivores may preclude the digestibility—reducing effects of plant polyphenols. We examined three marine isopods, three limpets, and a rock lobster, and established that surfactants are present in the digestive fluids of all of these organisms. However, further determinations of the efficacy with which these surfactants can prevent the complexation of proteins by brown—algal polyphenols in vitro revealed substantial differences between species. Moreover, in cases where the surfactants were ineffective, polyphenols reduced in vitro digestibility in a dose—dependent manner. We therefore conclude that the presence of gut surfactants does not necessarily preclude protein precipitation by polyphenols in vivo. Thus polyphenols might still be regarded as digestibility—reducing compounds, since gut surfactants only counter these effects in some cases.
How Distribution and Abundance Influence Fertilization Success in the Sea Urchin Strongylocentotus Franciscanus
Authors: Levitan Don R. , Sewell Mary A. , Chia Fu-Shiang
Published: May 2006

Many organisms reproduce by releasing gametes into the environment. However, very little is known about what proportion of released eggs become fertilized. We examined the influence of spawning group size, degree of aggregation, position within an aggregation, and water flow, on in situ fertilization in the sea urchin Strongylocentrotus franciscanus. This study was conducted at a depth of 9 m on the west coast of Vancouver Island, British Columbia, Canada. Males were simulated by syringes filled with sperm; females were simulated by sperm—permeable containers filled with eggs. Individuals were placed 0.5 or 2.0 m apart within a 2 x 2 or 4 x 4 (group size of 4 or 16 individuals) experimental array. The results indicate that group size, degree of aggregation, position within a spawning group, and water flow all affect fertilization success. Fertilization success. Fertilization success ranged from 0 to 82%. Increases in group size and aggregation, decreases in flow velocity, and central and downstream positions within an aggregation all lead to increase in fertilization success. Thus, individual reproductive performance is dependent on, and highly sensitive to, population parameters and environmental conditions.
Two‐Stage Life Histories in Fish: The Interaction Between Juvenile Competition and Adult Performance
Authors: Osenberg Craig W. , Mittelbach Gary G. , Wainwright Peter C.
Published: May 2006

Punpkinseed sunfish (Lepomis gibbosus) typically exhibit a strong ontogenetic diet shift. Small (juvenile) pumpkinseeds feed primarily on soft—bodied littoral invertebrates and compete with small bluegill (L. macrochirus), while large (adult) pumpkinsees feed extensively on sanils. We compared pumpkinseed and snail populations in two Michigan lakes that contain bluegill (Three Lakes II and Three Lakes III) with populations inhabiting Wintergreen Lake, a lake lacking bluegill. In the absence of bluegill, pumpkinseeds were abundant and juveniles grew well; however, snail abundances were low and adult pumpkinseeds grew poorly. Furthermore, no ontogenetic diet shift to snails occurred in Wintergreen Lake, and the pharyngeal muscles and bones used to crush snails were smaller than in fish from Three Lakes II. Pumpkinseeds from Wintergreen Lake also required significantly more time to crush and handle thick—shelled snails, but not thin—shelled snails and nongastropod porey, than did fish from Three Lakes II. In a field caging experiment in Wintergreen Lake snail densities increased fourfold when pumpkinseeds were excluded. Historical data as well as the among—lake comparisons suggest that the changes in Wintergreen Lake occurred in response to the selective elimination of the pumpkinseed's juvenile—stage competitor, the bluegill, via a winterkill event in the late 1970s. It appears that removal of bluegill released juvenile pumpkinseeds from competition and increased pumpkinseed recruitment into the adult stage, which resulted in the overexploitation of the adults' snail resource. These events then led to changes in adult pumpkinseed diet, growth, morphology, and feeding ability. These data are consistent with predictions from a two—stage life history model developed for the pumpkinseed—bluegill interaction and illustrate some of the important indirect consequences of interactions involving stage—structured populations.
Predation and Habitat Shift in the House Mouse, Mus Domesticus
Authors: Dickman C. R.
Published: May 2006

This study investigates the responses of house mice (Mus domesticus) to two species of introduced mammalian predators in Western Australia, the red fox (Vulpes vulpes) and cat (Felis catus), and to an endemic carnivorous marsupial, the western quoll (Dasyurus geoffroii). In four study areas containing no mammalian predators, mice showed little discrimination between traps bearing fecal odors of the predators and traps bearing conspecific odors or no odor. Mice in these areas also used sites of different vegetation density roughly in proportion to their abundance, irrespective of the intensity of lunar illumination or whether densities of predator feces were high or low. These results suggest that predator—naive mice do not respond to predator odors or to different levels of predation risk. In contrast, mice in 12 other study areas containing one to three species of mammalian predators avoided traps with predator adors, and generally selected relatively dense vegetation. They also used sites of greater vegetation density on moonlit compared to dark nights, and in two study areas where the density of cat feces had been experimentally increased. These results indicate that mice in areas exposed to mammalian predators distinguish predator odors and use denser vegetation when the preceived risk of predation is increased. In further experiments, I introduced predator—naive and predator—experienced mice to study areas containing cats and foxes. Survival rates of experienced mice a month after release were 2½ times higher than those of their naive counterparts, and hence support the hypothesis that a habitat shift to dense vegetation is an effective anti—predator response.
Stability of the Interaction Between Didinium and Paramecium: Effects of Dispersal and Predator Time Lag
Authors: Maly Edward J.
Published: May 2006

Experiments to test effects of dispersal ability and predator time lag on the stability of the interaction between the predatory Didinium nasutum and Paramecium caudatum were performed in depressions which could be connected by capillary tubes. The basic interaction is shown to be unstable. Dispersal rates are variable, but generally high; dispersal does not alter stability in a 2—compartment system but increases stability in a multicompartment system. Predaton numerical time lag to changed food supply decreases stability to a small extent, but dispersal time lag may increase stability. The results suggest that spatial or temporal complexity is necessary for stability of this predator—prey interaction; the latter probably controls dynamics in natural conditions.
Aboveground Production of Seven Marsh Plant Species in Coastal Louisiana
Authors: Hopkinson Charles S. , Gosselink James G. , Parrando Rolando T.
Published: May 2006

Results of a 2—yr evaluation of aboveground production of 7 plant species commonly found in Louisiana's coastal marshes show a generally higher level of production compared to other studies. In 5 of the 7 species significant growth occurred throughout the year. Calculated annual production in grams per square metre for each species was; Distichlis spicata–3237; Juncus roemerianus–3416; Phragmites communis–2318; Sagittaria falcata–1501; Spartina alterniflora–2658; Spartina cynosuroids—1355; and Spartina patens–6043. Sampling variability, expressed as the ratio of the standard error to the mean x 100, averaged between 8 and 18 different species. Instantaneous loss rates (mg x g(—1) x day(—1)) of dead vegetation from the marsh, averaged over the year, ranged from 4.7 for P. communis to 25.2 for S. falcata.
Differentiation Among Nine Populations of Phlox: Response to Environmental Gradients
Authors: Schwaegerle Kent E. , Bazzaz F. A.
Published: May 2006

To investigate the extent of ecological differentiation in the annual Phlox drummondii, nine populations were characterized for response along six controlled environmental gradients. Statistically significant heterogeneity among populations in survival, vegetative growth, and flowering was observed in response to different levels of moisture, light, nutrients, and competition. Differences in germination were observed in response to temperature and nutrient levels. Analysis of response along each gradient indicated that some populations are more sensitive to different environments than others, a significant genotype—environment interaction. Differences among populations were teste for adaptive significance by examining the relationships between response along gradients and a set of environmental measurements performed at the site of each population. Soil was characterized for five nutrients, organic matter, and texture. Percent plant cover, extent of surface disturbance, density of P. drummondii, and species diversity were also measured. Climatic differences were established from meteorological records. Correlation was used to examine relationships between site characteristics and population response along gradients. Despite highly significant differences among populations in response along gradients and significant differences in the environment at the sites of populations, we found no evidence that the differentiation among populations is adaptive. These results suggest that in situations where no single, consistent environmental factor has an overriding influence on the distribution and abundance of a species, a certain amount of indeterminancy arises between environment and adaptations exhibited by the organism. This situation may be common among plant species.
Development of Dead Leaf Foraging in a Tropical Migrant Warbler
Authors: Greenberg Russell
Published: May 2006

The Worm—eating Warbler (Helmitheros vermivorus), a neotropical migrant bird, specializes during the nonbreeding season in searching dead curled leaves that hang in the understory of tropical forest. How such a specialization might develop in individual warblers was investigated in an experimental study of hand—raised birds. In these experiments I measured the preference that juvenile warblers showed in visiting various micro—habitats. The experiments produced the following results. (1) Juvenile warblers, prior to any self feeding, showed a highly stereotypic ranking of preference for exploring different "microhabitats," visiting dead leaf clusters nearly three times as frequently as the next most preferred microhabitat types. Such as strong stereotyped order of preference was not found in similar experiments using the ecologically less specialized Carolina Chickadee (Parus carolinensis). (2) The same individual Worm—eating Warblers showed consistent preferences for visiting certain microhabitats at the age when they would normally be arriving in the tropics. However, dead curled leaves were no longer strongly preferred over other foliage types. (3) With other factors held constant, Worm—eating Warblers spent significantly more time manipulating curled versus uncurled foliage, but did not respond to either texture or color differences between live and dead leaves. (4) Worm—eating Warblers spent over half of their active time manipulating substrates, particularly foliage; this activity varied little among birds and among experiments and was also not extinguishable through elimination of food reinforcement. (5) Preference for a particular foliage type (including dead leaves) increased with positive reinforcement with food. These results suggest that young Worm—eating Warblers enter the world with a rigidly determined preference for dead leaves during the period of unreinforced exploration. I suggest that this preference is relaxed when birds are self—feeding because, with their highly manipulative behavior, they can readily track changes in abundance of dead—leaf and live—leaf arthropods. In this case, a consistent and apparently species—typical preference for dead curled leaves appears to be learned.
Ecological and Physiological Differentiation Among Low‐Artic Clones of Daphnia Pulex
Authors: Weider Lawrence J. , Hebert Paul D. N.
Published: May 2006

A distributional survey of obligately parthenogenetic clonal groups belonging to the Daphnia pulex complex was conducted on rock bluff and tundra ponds near Churchill, Manitoba. Clonal distributions were spatially heterogeneous. The clonal patterns of microgeographic heterogeneity suggested a strong association of Daphnia clonal type with salinity/conductivity gradients in pond habitats that varied in their proximity to Hudson Bay. Acute salinity tolerance experiments showed significant differences in survivorship of six clonal isolates at salinities encountered in nature. Clones from high—salinity ponds had greater survivorship at high salinities than clones from low—salinity ponds. There were no significant differences in clonal survivorship at low salinities. Clonal differences were also found in hatching success of ephippial eggs at different salinities. Laboratory measurements of hemolymph osmolality from these clones indicated significant differences in oscmoregulatory capacity. Coupled with morphological and electrophoretic data, the ecophysiological differences among D. pulex clones from Churchill suggest strongly that this Daphnia complex consists of physiologically different "ecotypes." The ecological and evolutionary implications of these data are discussed.
Structure and Species Composition of Desert Heteromyid Rodent Species Assemblages: Effects of a Simple Habitat Manipulation
Authors: Thompson Steven D.
Published: May 2006

Habitat manipulation demonstrates that a reduction in the distance between desert shrubs can produce a marked change in the structure and composition of a desert rodent species assemblage. After placement of small cardboard shelters in open areas between shrubs the dominant heteromyid rodent, Dipodomys merriami, declined in abundance and an intermediate—size species, Perognathus fallax, became established. The reduction in interplant distance also produced successful invasion by two species of generalist cricetine rodents belonging to the genus Peromyscus. Reduction of distances between safe foraging sites, which may decrease the risk of predation, increases the number of strategies of spatial utilization available to desert rodents. Thus, predation risk can be an important determinant of both structure and species composition of desert rodent species assemblages.
Influence of Stream Temperature and Seston on the Growth and Production of Overwintering Larval Black Flies (Diptera: Simuliidae)
Authors: Merritt Richard W. , Ross Douglas H. , Larson Grahame J.
Published: May 2006

The influence of stream temperature and seston on larval growth and production of the univoltine black flies Prosimulium mixtum Syme and Davies, P. fuscum Syme and Davies, and Stegopterna mutata (Malloch) was studied in a southcentral Michigan first—order stream. Black files were sampled quantitatively with artificial substrate for production estimates and qualitatively estimate instar—specific dry mass. Length—mass equation obtained for each species and most instars indicated that maximum growth occurred in the later stadia. Production estimates (as dry mass per square metre of artificial substrate, with 95% confidence interval) for two cohorts of P. mixtum/fuscum were 696 ± 95 and 1939 ± 339 mg°m—2°yr—1. On artificial substrates, mean standing stock biomasses for the two cohorts were 110 and 507 mg/m2, and the cohort P/B ratios were 6.32 and 3.83, respectively. Seston concentration (AFDM) during the winter and early spring were highly dependent on stream discharge and ranged from 0.81—8.33 mg/L, with a mean of 3.73 mg/L. Particles <45 μm comprised >92% of the total organic seston, and larvae ingested particles in the 0.45—45 μm size class almost exclusively, with 85% of the particles in larval guts <10 μm in diameter. No significant differences existed in the size frequency distributions of particles in the guts among instars or between species, suggesting that the quantity of seston in the 0.45–45 μm size class was not limiting. Over 81% of P. mixtum/fuscum annual production occurred during the last two larval stadia and was attributed to increases in stream temperature and seston organic content during the late winter and early spring.
Waterborne Nutrient Flow Through an Upland‐Peatland Watershed in Minnesota
Authors: Verry Elon S. , Timmons D. R.
Published: May 2006

Water and nutrient flow were measured on a complex upland—peatland watershed in north central Minnesota. Annual water budgets for upland and peatland components and for the total watershed were developed. Nutrient input and output budgets were developed for each component on a seasonal basis, using net precipitation inputs, and an annual nutrient budget was developed for the entire watershed, using gross precipitation and total outputs. Both components evapotranspire water near potential rates. The upland converts 34% of the water input to water yield, while the peatland (a bog in a lower topographic position) converts 55% of its water input to water yield. The upland annually retains some N, P, K, and Ca from net precipitation, but passes through Mg and supplies Na in excess of inputs. The peatland is a nutrient trap retaining 36—60% of all nutrient inputs annually. There are striking differences in the seasonal retention of nutrient forms between the upland and bog. The total watershed accumulates P and (apparently) N but loses more K, Ca, Mg, and Na than it receives in gross precipitation. Nutrient flow is interpreted for the design of nutrient—added technologies (fertilization and sewage treatment) and as a bench mark for nutrient—depleted technology (whole—tree harvesting).
Patterns of Disturbance in Some Old‐Growth Mesic Forests of Eastern North America
Authors: Runkle James Reade
Published: May 2006

To characterize the disturbance regime of one type of vegetation, study areas in which relatively small—scale disturbance predominates were chosen in several old—growth mesic forests in the eastern United States. Canopy openings covered 9.5% of total land area. New gaps were formed at an average of 1% of total land area per year; old gap area closed at a similar rate primarily by sapling height growth. With increasing gap size, vegetation within gaps increased in woody species diversity, total basal area, and total number of stems. Stems also showed accelerated growth into larger size classes. As gaps aged, stems grew into larger size classes and basal area increased. Species responses to canopy gaps varied. Some species survived and became established in fairly small gaps (50—100 m2). Although in large gaps (up to 2009 m2 in the present study) these species usually increased in total number of stems and basal area, they declined in importance relative to species which rarely survived in small gaps but grew rapidly in large gaps. The disturbance regimes in the forests studied favored tolerant species but allowed opportunists to persist at low densities.
A Comparison of Thermoregulation and Evaporative Water Loss in the Hispid Cotton Rat. Sigmodon Hispidus texianus, From Northern Kansas and South‐Central Texas
Authors: Scheck Stephen H.
Published: May 2006

Thermoregulatory abilities were examined in adult, laboratory—reared F1 offspring of wild caught adult hispid cotton rats, Sigmodon hispidus texianus, from northern Kansas and south—central Texas. These regions are representative of the northern and southern areas of the distribution of the subspecies. Responses of Kansas and Texas adults subjected to ambient temperatures Ta's) of 0—30°C are significantly different. Kansas animals have a basal metabolic rate (BMR), measured as oxygen use, of approximately 0.83 mL°g—1°h—1, which is 85% of the value predicted by mass. The BMR of Texas animals (1.03 mL°g—1°h—1) is 103% of the value predicted by mass and is significantly higher than that determined for Kansas animals. Thermoneutral zones extend between 29.5—33.7° and 33.5—35° in Kansas and Texas animals, respectively. Total and dry conductances are significantly lower in Kansas animals. Total conductances (as O2) for both Kansas (0.078 mL°g—1°h—1°°—1) and Texas (0.082 mL°g—1°h—1°°C—1) animals are higher than values predicted by body masses (113% and 115%, respectively). Body temperature is similar (38.1°) at Ta's below 35° in both Kansas and Texas animals. Evaporative water loss is similar at all Ta's, but the percentage of endogenous heat dissipated by evaporative water loss is significantly greater in Kansas animals than in Texas animals. The significantly lower metabolism and thermal conductance in the Kansas animals probably represent an adaptation for conservation of water in the more arid regions of the distribution of S. hispidus texianus. Furthermore, these adaptations are thought to have permitted S. hispidus texianus to expand its range into cooler regions of the Great Plains within the past century.
Mycorrhizal Role in Net Primary Priduction and Nutrient Cytcling in Abies Amabilis Ecosystems in Western Washington
Authors: Vogt Kristiina A. , Grier Charles C. , Meier Calvin E. , Edmonds Robert L.
Published: May 2006

The potential contribution of mycorrhizal fungi (as sporocarps and mycorrhizal sheaths) to total ecosystem biomass and turnover and nutrient distribution and turnover was examined in a 23—yr—old and a 180—yr—old Pacific silver fir (Abies amabillis) stand in western Washington. While mycorrhizal fungi contributed roughly 1% a total ecosystem biomass in both stands, the percentage of net primary production (NPP) in the mycorrhizal fungal component was roughly 14% in the younger stand and 15% in the mature stand. Mycorrhizal fungi plus conifer fine roots contributed °45% of NPP in the young stand and °75% in the mature stand. Sclerotia production (2700 kg°ha—1°yr—1) contributed the largest proportion of total mycorrhizal fungal production in both stands followed by mycorrhizal sheath production (°350 kg°ha—1°yr—1 and 430 kg°ha—1°yr—1 in the young and mature stands, respectively). Potentially, 27 kg°ha—1°yr—1 of N is cycled through sporocarps in the young stands and 41 kg°ha—1°yr—1 in the mature stand. Annually, fine roots (including mycorrhizae) cycle at least 60, 10, 20, 30 and 10 kg°ha—1°yr—1 of N, P, K, Ca, and Mg, respectively, in the young stand. In contrast, 110, 20, 20, 30 and 10 kg°ha—1°yr—1 of N, P, K, Ca and Mg, respectively, are cycled through fine roots in the mature stand.
Asexual Reproduction in Anthopleura Elegantissima (Anthozoa: Actiniaria): Seasonality and Spatial Extent of Clones
Authors: Sebens Kenneth P.
Published: May 2006

The sea anemone Anthopleura elegantissima (Brandt) forms clonal aggregations in the field by binary longitudinal fission. The fission process leaves a noticeable scar which develops body—wall adhesive verrucae and returns to normal appearance over a month or more. The incidence of new division scars (without verrucae) and that of old scars (with developing verrucae) were used to examine the seasonality of the division process at Cattle Point, San Juan Island, Washington State, USA. Divisions can occur at any time of year but are most frequent during August to February. Body size increased over the spring and summer (April—August) and decreased over the fall and winter (September—March) in population samples and in monitored experimental clones. Frequency of division was positively correlated with a seasonal decrease of anemone basal diameter in the field. Division was least common during the period of rapid individual growth in the spring and early summer. When compared at the annual peak of body size it was the larger individuals that went on to divide over the fall and winter. Agonistic interactions (acrorhagial response, Francis 1973b) were used to examine the spatial extent of clonal aggregations at three field sites. Single clones were often discontinuous and were distributed over areas up to 100 m2. Clone size increased from exposed to protected locations and from exposed (convex) to protected (concave) microhabitat.
Role of Planktonic and Benthic Factors in the Population Dynamics of the Bryozoan Membranipora Membranacea
Authors: Yoshioka Paul M.
Published: May 2006

The bryozoan Membranipora membranacea possesses a long—lived planktonic larva and occurs in encrusting colonies in the Macrocystis pyrifera kelp canopies on southern California. Seasonally Membranipora populations varied from >1000 to less than one colony per kelp blade in late winter and late summer, respectively. Populations often varied by more than an order of magnitude in 2 wk. Several planktonic and benthic factors play important roles in the population dynamics of Membranipora. Upwelling conditions and the presence of two nudibranch predators accounted for 55% of the variability in larval abundance relative to adult population size. In turn, low recruitment rates relative to larval abundance corresponded with periods of high surface temperatures. The combined effect of larval abundance and surface temperature accounted for 79% of the Vaccinium in recruitment. Although a field transplant experiment demonstrated that predation plays a major role in the survival of colonies, recruitment was a major factor underlying population fluctuations and accounted for 75% of the variability in reproduction as indexed by the production of zooids by Membranipora colonies. A 12—fold density—dependent effect on reproduction attributable to space limination and to the density—dependent component of predation was observed over the 1000—fold range in recruitment resulting from density—independent factors. A population model based on field—derived relationships accounted for 64% of the observed variability in colony density. Temperature, as it affects recruitment, was the major factor controlling the seasonal fluctuations in Membranipora populations. Over longer, multiseasonal time scales the small density—dependent effect was capable of maintaining model populations within the range of values observed in the field and therefore was sufficient to regulate Membranipora populations. The results of this study emphasize the importance of small density—dependent effects in the regulation of single—species populations.
The Effect of Soil Fauna on Litter Mass Loss and Nutrient Loss Dynamics in Arctic Tundra at Barrow, Alaska
Authors: Douce G. Keith , Crossley D. A.
Published: May 2006

Litterbags and arthropod defaunation techniques were used to evaluate the effects of soil—litter fauna on loss of dry matter and nutrient elements from native litter in arctic tundra. A control and a naphthalene—treated plot were established in each of three microhabitats. Faunal populations, litter dry mass and % N, and the concentration of Ca, Na, Mg, Mn, P, Zn, and K in the litter were measured from each litterbag. Litterbags were collected at 10—d intervals during the 1974 nonfrozen season and twice in 1975. Litter mass and nutrient loss differed among habitats and exhibited differing responses to defaunation, as did dry mass loss. Generally greater dry mass loss and less nutrient loss occurred from the litter in the control than in the corresponding defaunated plot. Nutrient loss was greater in plots that are subjected to natural periodic flooding than in plots never flooded. Loge regression lines of percent mass loss vs. days are reported for each plot on a calendar year and a nonfrozen season basis. Results of this study are compared with results from decomposition studies in other arctic and temperate systems.
Reproductive Strategies: Food Availability as a Source of Proximal Variation in a Lizard
Authors: Ballinger Royce E.
Published: May 2006

Reduced food availability in 1974 significantly altered the reproductive characteristics of a population of Urosaurus near Animas, Hidalgo County, New Mexico compared to 1973. Relative food availability, which was monitored using sticky traps, was attributed to reduced precipitation levels. Fat storage prior to reproduction was greatly reduced in 1974. As a result, size of the first clutch was reduced from 10.9 (1973) to 6.8 eggs, and clutch frequency was reduced from two clutches by most females (90%) in 1973 to only one clutch in 1974 (8.7% produced two). The reproductive strategy in this population of Urosaurus compared to that previously presented for a Texas population differs primarily by a restriction of the reproductive season and reduced clutch frequency but an increase in clutch size. The limited reproduction in a low resource year may represent an adaptation to reduce risk and effort when current reproduction is less profitable than survivorship and future reproduction
Patch by Gray Squirrels and Optimal Foraging
Authors: Lewis Allen R.
Published: May 2006

The use of a naturally patchy distribution of tree seeds by gray squirrels was investigated. In most patches the acorn species allowing the highest rate of energy intake was consumed disproportionately in relation to its low abundance. Foraging was particularly intense in patches where an acorn species offering a lower rate of energy intake was abundant. Calculations made with a model of optimal foraging show that these heavily used patches were those yielding high patch—specific rates of energy intake. The squirrels selected patches yielding high rates of energy intake even though these patches were not sites of concentration of the preferred food.
Habitat Varition Within Sympatric Snake Populations
Authors: Reinert Howard K.
Published: May 2006

Radiotelemetry was used to monitor the habitat use of 21 timber rattlesnakes (Crotalus horridus) and 20 northern copperheads (Agkistrodon contortrix mokeson) during a 3—yr period beginning in 1979. Habitat was quantitatively defined on the basis of 14 structural environmental factors. To examine intraspecific habitat variations, species groups were subdivided by sex and the female subgroup was further separated into gravid and Nodulated segments. The nongravid female A. c. mokeson subgroup was deleted from the analysis because of its small sample size. A random series of habitat samples was obtained from the study site for comparison with the remaining five subgroups. A Muesebeck analysis of variance of six groups with 14 variables indicated that group centroids differed significantly (P < .01). The first three discriminant functions accounted for 94% of the total variance and represented the following respective habitat gradients: (1) rocky, open sites to heavily forested sites with few rocks, (2) sites predominantly covered with leaf litter to sites with dense forest—floor vegetation, and (3) sites with large—diameter overstory trees to sites with small—diameter trees. Gravid specimens of both species were most closely associated in discriminant space and clearly separated from other segments of their respective species groups. The utilization of rocky, sparsely forested sites and decreased variation in site selection were associated with gravidity. A two—group discriminant—function analysis using melanistic and nonmelanistic male C. horridus indicated a gradient in habitat utilization from mature forest sites with numerous fallen logs to young forest sites with predominant leaf litter cover. Melanistic specimens preferred the former and nonmelanistic specimens the latter. The results suggested that A. c mokeson was poorly adapted to the study site due to the preference of all population segments for open sites and young forest stands. In contrast, C. horridus was better adapted, utilizing a broad range of the available habitat. The analyses serve to emphasize the importance of physiological factors in determining the spatial relationships of snakes in temperate environments.
Effects of Predatory Sculpin on the Chironomid Communities in an Arctic Lake
Authors: Hershey Anne E.
Published: May 2006

To determine the importance of fish predation and habitat heterogeneity in structuring the chironomid community of an arctic lake, I used a combination of field and laboratory experiments in conjunction with field sampling data. Chironomid density was consistently °1.5 times as high in macrophyte—covered as in bare sediments in the soft—sediment littoral zone of arctic Toolik Lake. In laboratory experiments, most chironomid taxa showed no preference for one habitat over the other, but schulpins, the major predators on larval chironomids, were more efficient foragers in bare sediments than in macrophytes. Field exclosure experiments in macrophyte and bare—sediments habitats indicated that macrophytes afforded chironomids a refuge from their sculpin predators. At the end of a 21—d experiment, chironomid density in unenclosed areas significantly lower than in fish exclosures in bare sediments, but this was not so in macrophytes. This difference was due to an effect of sculpin on chironomids that are small rather than on large chironomids or on any single chironomid taxon or broad trophic group (predaceous vs. nonpredaceous). Small chironomids were probably more available as prey because of their tube—dwelling and sediment—penetrating behaviors.
Local and Regional Richness of Cynipine Gall Wasps on California Oaks
Authors: Cornell Howard V.
Published: May 2006

Regional herbivore richness is defined as the total number of herbivore species associated with a host plant in any part of its range. Local richness is the number of species associated with a host population or clump at a single site. These are roughly equivalent to @a and @c diversity. Understanding the mechanisms operating on local richness required a knowledge of the relationship between these two variables, and, specifically, an answer to the question of whether the same processed determine both regional and local richness. When local ecological interactions are weak and herbivore species are widespread, the correlation between richness at these two spatial scales should be strong. If local interactions are strong and herbivore species have restricted ranges due to habitat specialization, then the correlation should be weak. The relationship between local and regional richness was studied in California in the cynipid gall—forming wasps, which are highly specialized on the oak genus, Quercus. Regressions of presence—absence data suggested that geographic range and host taxonomic isolation explain the majority of regional richness variation in this group. Moreover, the very strong correlation between local and regional richness indicated that there is no upper limit to local richness independent of the regional pool. In terms of @a, @b, and @c diversity,@b (between—habitat) diversity does not increase with @b diversity. Instead, there is an unabated increase in @a diversity as @c diversity increases, suggesting that excess niche space is available on host oaks for additional cynipine species, and that limits to similarity of coexisting cynipines have not been reached. This indicates that sufficient information on the causes responsible for local herbivore richness cannot be gained by studying the local host population in isolation. The spatial dynamics of the system are such that measures of the regional pool from which the local assemblage is drawn must also be taken. Finally, cynipine habitat specialization and local interactions are not predictable from regional richness, but may influence local richness on certain oak species independently of regional richness.
Ontogenetic Niche Shifts in Old‐Field Annuals
Authors: Parish J. A. D. , Bazzaz F. A.
Published: May 2006

To learn whether niche breadths change during the life of a plant, we tested the responses of three age—classes of six annual plants on four environmental gradients. Several ontogenetic niche shifts were observed. The differences in response among age—classes of a species were larger than the differences in response among other species of similar ages. The species were very similar in their germination responses to the moisture and nutrient gradients, but were quite different from each other on the temperature gradient. The biomass response of seedlings was the broadest of the three age—classes only on the nutrient gradient. The responses of the species were very similar. On the temperature gradient, responses of the species were also similar to each other, but response breadths were low. On the light gradient there were more differences among the species as seedlings than on the other gradients. The reproductive responses of mature plants were most sensitive to changes in nutrient concentration, resulting in narrower responses than for the other two age—classes. Responses of mature plants were relatively broad on the moisture, temperature, and light gradients. The co—occurrence of different ages of plants in a given locality makes these ontogenetic shifts in response to resource gradients important in the outcome of interactions between neighbors.
Nitrogen Dynamics During Succession in a Desert Stream
Authors: Grimm Nancy B.
Published: May 2006

Nitrogen dynamics of Sycamore Creek, Arizona, a lowland Sonoran Desert stream, are described by seven diel input—output budgets at different stages of postflood succession. Hydrologic inputs and outputs of nitrogen and N storage in periphyton, macroinvertebrates, and fish were measured over 24—h periods. Total nitrogen storage in this desert stream (3—9 g/m2) was lower than that in forest streams of Oregon (12 g/m2) and Quebec (22 g/m2). While >99% of nitrogen in the latter systems is in allochthonous detritus, benthic algae and autochthonous detritus comprised °90% of the total nitrogen pool in the desert stream. Up to 14% of nitrogen was in consumer organisms. Inputs of nitrogen to the stream ecosystem were dominated by dissolved nitrogen, of which 19—60% was inorganic, primarily nitrate. Particulate nitrogen in transport (4—15%of total input) was mostly autochthonous. Inputs of nitrogen exceeded outputs on most study dates. Rates of ecosystem nitrogen retention were as high as 400 mg°m2°d—1 and outputs exceeded inputs on only one study date. Retention was primarily of inorganic nitrogen and was presumed due to autotrophic assimilation. Nitrogen retention data from the seven budgets were used to evaluate the Vitousek and Reiners (1975) model that patterns of nitrogen retention during succession reflect patterns of net ecosystem production and biomass accumulation. Biomass and stored nitrogen increased asymptotically during a postflood successional sequence at a single site; nitrogen retention during this period accounted for increases in storage. Nitrogen retention among the seven study dates exhibited the predicted successional patterns of increases from early to middle successional stages, followed by late stage declines.
Theoretical Analysis of the Long‐Term Dynamics of Carbon and Nitrogen in Soils
Authors: Agren Goran I. , Bosatta Nesto
Published: May 2006

Carbon and nitrogen turnover in soils having continuous inputs of litter is described using theory developed for single cohorts of litter. Fresh litter is characterized by its quality (how easily it is decomposed by microbes) and its N:C ratio. The decomposition process is described as a continuum and no transition between litter and humus is recognized. Equations are derived for the amounts of carbon and nitrogen in the soil at steady state. Depending upon the microbial production—to—assimilation ratio when substrate of the lowest quality (most—degraded litter) is decomposed, steady state implies either constant or linearly increasing amounts of soil carbon and nitrogen. Comparisons are made between theoretically estimated and observed relations between soil carbon and nitrogen turnover rates for a large range of terrestrial ecosystems, as well as carbon and nitrogen stocks in a Scots pine forest soil.
Variation in Host Preference Affects Movement Patterns Within a Butterfly Population
Authors: Thomas C. D. , Singer M. C.
Published: May 2006

Within a population of the butterfly Euphydryas editha, there is variation in post—alighting oviposition preference. After alighting, most females prefer to lay eggs on Pedicularis semibarbata, while a minority prefer another host, Collinsia torreyi. This variation in preference was correlated with variation in movements to and from patches of the two host species. Females were likely to leave areas without preferred hosts and stay where preferred hosts were present. This association between preference and movement increases the correlation between oviposition preference and host use, and increases the likelihood of host race formation. This study also shows an effect of habitat quality on movement, independently of other factors. Interpretation of the correlation between preference and movement requires knowledge of the relationship between encounter and preference. We present evidence that repeated encounters with one or the other host species have no influence on acceptance for oviposition of either host.