bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution and Cycling of Nutrients in a Natural Pinus Banksiana Ecosystem
Authors: Foster N. W. , Morrison I. K.
Published: May 2006

Data on dry matter and N, P, K, Ca, and Mg contents and movements in soil and ground vegetation in a 30—yr—old natural Pinus banksiana Lamb. stand in northern Ontario are presented, together with previously published aboveground data. Dry matter and N, P, K, Ca, and Mg contents of trees were 90,700; 165; 14; 82; 112; and 18 kg/ha, respectively–less than in many Pinus spp. of comparable age in other parts of the world. A comparison with nutrient contents in younger (20 yr) and older (65 yr) stands on the same site indicated that most nutrient accumulation in vegetation takes place in the first decades of stand development. Annual nutrient uptake by all vegetation was 32 kg N, 2 kg P, 18 kg K, 21 kg Ca, and 3 kg Mg per hectare. Between 71% and 89% of the elements taken up annually by trees were returned to the soil by litterfall and leaf wash. There was a buildup of forest floor organic matter with stand age and N, P, and Mg accumulated in this material faster than the other elements. Soil reserves of plant—available or mineralizable nutrients were maintained by nutrient replenishment from precipitation and vegetation—soil nutrient cycling. Thus, we conclude that removal of elements from the ecosystem by logging or burning should not result in significant impoverishment of this site.
Mechanisms of Interference and Foraging Among Colonies of the Harvester ant Pogonomyrmex Californicus in the Mojave Desert
Authors: De Vita Joseph
Published: May 2006

This report examines patterns of competition and foraging dynamics among colonies of the harvester ant Pogonomyrmex californicus. Two components of harvesting efficiency are defined: total harvesting efficiency (i.e., all food items considered) and seed harvesting efficiency (only seeds considered). Throughout the summer, total harvesting efficiency remained constant, whereas seed—harvesting efficiency exhibited an increase as a result of changes in the relative availability of the dominant seed crop, Erodium cicutarium. Several aspects of interference were studied. Colonies were uniformly spaced, and nest relocations significantly increased nearest—neighbor distance. Of encounters between ants from different colonies, 81% resulted in some form of aggression and 7% were fatal to one or both foragers. In a particular study, forager mortality rate was estimated at 0.06 deaths per ant foraging hour, thus indicating that such aggression may have a substantial impact on colony size. Furthermore, following an encounter involving physical struggle, ants returned to and remained in their nests for an extended period of time, thereby reducing seed input to the colony. The above—mentioned components of interference are examined to their potential effects on colony density, distribution, and size.
Intrapopulation Variation in the Body Size at Metamorphosis and Timing of Metamorphosis in the Bullfrog, Rana Catesbeiana
Authors: Collins James P.
Published: May 2006

Variation in body size at metamorphosis and the time of metamorphosis were studied for 3 yr in a population of bullfrogs at the E. S. George Reserve, Michigan, USA. The size at metamorphosis and the week of metamorphosis were positively related through the 1972 activity season and the last half of the 1973 activity season. During the first half of 1973 and all of 1974 there was no significant relationship between size and metamorphosis and time of metamorphosis. The data suggest that the 1971 larval year class transformed during 1972 and 1973, the 1972 year class during 1973 and 1974 and the 1973 year class during 1974. Variation in length of the larval period and body size at metamorphosis varied with density of conspecifics and time of oviposition during spring and early summer. Data for the Michigan population of frogs are consistent with predictions derived from a model of amphibian metamorphosis proposed by Wilbur and Collins (1973). A review of the literature indicates that length of the larval period among populations of bullfrogs in the United States is negatively correlated with mean length of the frost—free period.
Changes in Forest Floor Organic Matter and Nutrient Content Following Clear Cutting in Northern Hardwoods
Authors: Covington W. Wallace
Published: May 2006

A secondary succession sequence of 14 northern hardwoods stands was sampled for forest floor organic matter and nutrient content. During the first 15 yr following clear cutting, the forest floor decreased by 30.7 Mg/ha, a decline of over 50%. The decrease in the forest floor and slash (logging residue) may be greater than the increase in the living biomass. During the next 50 yr the forest floor increased by 28.0 Mg/ha and by year 64 was within 5% of an asymptote of 56.0 Mg/ha. Nutrients were analyzed in 6 of the 14 stands. Magnesium, potassium, and nitrogen concentrations showed no successional pattern. However, calcium concentrations were significantly higher in the stands in which forest floor mass was low. The initial decrease in forest floor mass is attributed to lower leaf and wood litter fall and to more rapid decay resulting from higher temperature, moisture content, and nutrient levels and to early successional litter being more easily decomposed. The recovery of the forest floor is explained primarily as resulting from the rapid increase in the quantity and diameter of wood litter fall. JABOWA, the northern hardwood forest growth simulator, predicts a maximum rate of increase in woody litter by years 10—20 with a leveling off by years 30—50. An apparent asynchrony in function of the forest floor and slash as nutrient sources may be important to the recovery process. During the first 15 yr the forest floor is a major source of nutrients, releasing a net amount of approximately 800 kg/ha of nitrogen. During this period nitrogen immobilization in the decay of slash may account for as much as one—half of the nitrogen released from the forest floor. After year 15 the forest floor is no longer a source but a sink for nutrients as nutrients and organic matter accumulate. By year 15 the slash probably shifts in function from a sink to a source, providing nitrogen for the continuing rapid nitrogen accumulation in vegetation beyond year 15.
Phenological Properties of Wind‐ and Insect‐Pollinated Prairie Plants
Authors: Rabinowitz Deborah , Rapp Jody K. , Sork Victoria L. , Rathcke Beverly J. , Reese Gary A. , Weaver Jan C.
Published: May 2006

The number of flowering stems for 82 species on a transect 2 x 400 m was counted twice weekly during 1978 at Tucker Prairie, Callaway County, Missouri, USA, a tall—grass prairie remnant. Phenological curves (number of flowering stems vs. day of the year) are narrower (smaller standard deviations) for wind—pollinated species than for insect—pollinated species. Symmetry (g1) does not differ significantly for wind— and insect—pollinated species. The curves are largely either symmetric or begin abruptly and end gradually (right—skewed). Overlap, measured as the fraction of the area under the curves occupied by two or more species, does not differ significantly for wind— and insect—pollinated species, among 20 groups of five randomly drawn species. Dates of peak flowering are distributed randomly over the season (May to November 1978) and their distributions do not differ for wind— and insect—pollinated species. Dates of peak flowering are also randomly distributed for grasses, legumes, and composites considered separately. Thus, although species with different pollination modes show different shapes for phenological curves, the species aggregated into the community do not have ensemble patterns of temporal dispersion or overlap and cannot be distinguished from a random collection.
Web Orientation in the Spider Micrathena Gracilis (Araneae: Araneidae)
Authors: Biere J. Michael , Uetz George W.
Published: May 2006

Web orientation (direction that spiders faced) in a forest—dwelling orb web—building spider, Micrathena gracilis (Araneidae), was related to the microhabitat where webs are constructed. Individuals in shaded (closed) microhabitats faced predominantly north/south, while those in well—lighted microhabitats (open and patchy) faced east/west. Several variables were examined in an effort to explain the patterns that emerged. Wind speeds were found to be so low within the interior of the forest that available instrumentation could not measure them. Nethertheless, webs were not aligned with prevailing winds. There were no significant differences in web site parameters (height, bridge thread distance) between microhabitats. Artificial web studies indicate that prey abundance is greater in open microhabitats and at lower heights, though prey movement through all microhabitats is nondirectional. Spider body temperature, however, was positively correlated with the amount of solar radiation striking the animal, which varied with both microhabitat and direction of orientation. The compass orientation of a spider's web influenced the amount of radiation to which the spider was exposed, and thus affected its body temperature. A model is proposed that relates the time an individual spider can spend on its web to the amount of heat accrued by the spider. Both too little or excessive body heat might affect activity. Since time on the web is positively correlated with total prey captured, more time spent on the web effectively increases the availability of prey. Web orientation is suggested as a behavioral thermoregulatory mechanism which allows Micrathena gracilis enough flexibility to exploit a variety of microhabitats and to maximize its time on the web, thus optimizing its prey take in each habitat.
Food Plant Selection by a Generalist Herbivore: The Moose
Authors: Belovsky Gary E.
Published: May 2006

A model of food plant selection by a generalist herbivore was developed. The model was designed to predict the species composition of the diet of an herbivore based upon the joint probabilities of whether or not an individual of a plant species satisfied two threshold values: some nutritional minimum and a size limit (both minimum and maximum), and the probability that it was encountered while foraging. The model was tested using moose (Alecs alces) at Isle Royale National Park, Michigan, USA. Initially the threshold values for food selection were determined empirically from the moose's observed behavior, but these empirical values were later shown to be based upon time—energy considerations. Although the model satisfied some of the criteria of optimal foraging contingency models, it appeared that the perfect knowledge assumption was not met. Rather, moose appeared to utilize a strategy of risk aversion.
An Analysis of Competitive Interactions in a Patch Back‐Reef Environment
Authors: Williams Ann Houston
Published: May 2006

Manipulative field experiments were used to test for the existence of competitive interactions between three abundant herbivore species in a shallow back—reef zone. Densities of the territorial threespot damselfish, Eupomacentrus planifrons, and two sea urchins, Diadema antillarum and Echinometra viridis, were altered through addition and removal experiments conducted within patches of staghorn coral, Acropora cervicornis. Removals of each urchin species resulted in population increases of the other urchin. Additions of each urchin species tended to inhibit increases of the other species. Removals of damselfish resulted in increases of the other species. Removals of damselfish resulted in increases in Diadema density within 24 h, while Echinometra density increased during the 3rd d following the perturbation. Dry biomass of algae on ceramic tiles in the lower strata of damselfish removal patches was reduced by 62% as compared with algal biomass in these strata in the presence of damselfish. Wire mesh cages were utilized over a 2—mo period to test the effect of predation on competition at the herbivore level. No significant alteration of species numbers was observed in the absence of predation. Therefore, predation did not appear to affect significantly the distributions and abundances of the adult members of the community. Low predation levels on adults within this system do not appear to alter the competitive interactions between these herbivores. Interference competition by the threespot damselfish appears to mediate competition between the two echinoids, allowing coexistence of all species. The presence of damselfish may reduce destructive echinoid grazing pressure on the coral substrate.
Seasonal and Site Variation in Costa Rican Euglossine Bees at Chemical Baits in Lowland Deciduous and Evergreen Forests
Authors: Janzen D. H. , DeVries P. J. , Higgins M. L. , Kimsey L. S.
Published: May 2006

By attracting male euglossine bees with cineole, eugenol, methyl salicylate, methyl cinnamate, and benzyl acetate in Costa Rican lowland deciduous forest and rain forest, we found no indication of change in the composition and numbers of rain forest attractable bee species during different seasons, but within the deciduous forest both abundance and species richness declined in the dry season. Within each major forest type there were substantial differences in the abundance and species composition of attractable bees among habitats: baits in estuarine swamp forest and open pasture in the rain forest attracted very few bees as compared with nearby forest understory sites. In the deciduous forest, at least 15 species of male euglossine bees were attracted that apparently do not have breeding populations in this forest and that do not visit orchids in this forest; we hypothesized that they normally find females and chemical resources elsewhere in distant habitats or forest types.
Root Productivity in an Amazonian Rain Forest
Authors: Jordan Carl F. , Escalante Gladys
Published: May 2006

Average rate of root biomass accumulation in the surface root mat of an Amazonian rain forest near San Carlos de Rio Negro, Venezuela was 117 g°m—2°yr—1, and total root biomass increment was 201 g°m—2°yr—1. Root growth was higher in the surface root mat when fresh litter was present. Root growth rates relative to shoot growth rates at San Carlos were similar to ratios for a temperate forest near Oak Ridge, Tennessee, USA. However, turnover rates of roots were higher at the San Carlos site. High turnover rates result in a relatively large proportion of the roots in smaller size classes, which have a large surface area in relation to their volume and thus area efficient nutrient traps. High efficiency of nutrient trapping is important in the nutrient—poor San Carlos forest.
Heat Exchange Influence on Foraging Behavior of Zonotrichia Flocks
Authors: DeWoskin Robert
Published: May 2006

The heat exchange of individuals in a foraging mixed population of Zonotrichia leucophrys and Z. atricapilla in western Oregon is analyzed for its influence on the direction of stance and feeding location. Values for heat gain or loss in the field were generated from a model that estimates the equivalent blackbody temperature (Te) and from previous laboratory findings for the effects of air temperature, solar radiation, and wind speed on metabolism. Observations were recorded at 1—min intervals throughout the daylight hours with samples at weekly intervals from January to March 1978. A summation of 1500 observations on direction of stance subjected to a g test for randomness supports the hypothesis that spatial orientation of individuals is not random. Maximum differences in Te for different stances with respect to the wind direction were only 1°C because of the low winter values for incoming shortwave radiation. More important factors than heat exchange influencing the direction of stance were food availability, social interactions, and the location of the hedge in the area used for cover. Placing a trace line of food perpendicular to the most frequently observed direction of stance caused a significant change in percentage of time spent facing each direction for that location. Individuals were facing the same direction as the majority of their neighbors within a 2—m radius during 68% of the total number of recorded observations for a nonrandom flock orientation. Heat loss was affected by changes in the microhabitats at the site. Differences in wind speed, air temperature, and solar radiation were large enough to increase metabolic rate as much as 20% for the open area foraging as compared to the hedge. Instead of feeding in the open area during midday where the shortwave radiation is greatest, the flock would often move into the hedge, thus occupying each location when the thermal conditions were least advantageous. Factors that may influence this feeding behavior could be a decreased cost—to—gain ratio for caloric intake in the open area in conjunction with circadian rhythms for metabolic rate and energy needs.
Effect of Cloudcover on Photosynthesis and Transpiration in the Subalpine Understory Species Arnica Latifolia
Authors: Young Donald R. , Smith William K.
Published: May 2006

Analysis of solar radiation data for three summers (1978—1980) revealed that cloud—cover was present for at least 10% of the daytime on 85% of the days in the Medicine Bow Mountains of southeastern Wyoming and occurred most frequently from 1000 to 1800. Although cloudcover caused a major reduction in direct—beam irradiance as well as a 30% decrease in daily integrated photon flux density at the forest floor, substantial increases in diffuse photon flux density were measured. The understory herb Arnica latifolia had a 37% greater carbon gain on representative cloudy days than on clear days with an 84% reduction in transpiration, which resulted in more than a sevenfold increase in water use efficiency when compared to clear days. The increase in carbon gain may have been the result of photosynthetic rates that were still near saturation even under the diffuse light of cloudy days. Thus, photosynthesis and water relations of A. latifolia may be enhanced by the natural occurrence of afternoon clouds which prevent potential increases in transpiration without decreasing in carbon gain.
Foraging Ecology of Temperate‐Zone and Tropical Woodpeckers
Authors: Askins Robert A.
Published: May 2006

The foraging behavior of 11 species of woodpeckers in Guatemala, Maryland, and Minnesota was studied in order to test the seasonal stability hypothesis. This hypothesis predicts that specialization and species richness should be no greater for tropical wood—excavators than for those in the temperate zone because wood—excavators in both regions are buffered against seasonal change. Niche breadth values for six variables that describe foraging methods and perches were calculated by two methods. Unweighted niche breadth values were similar for tropical and temperate woodpeckers for all variables except foraging techniques; in this case the temperate species are more specialized. With weighted niche breadth values temperate species are more specialized for two variables and less specialized for two others. Thus there is no consistent tendency for tropical species to be more specialized. However, the excavating guild includes twice as many species in Guatemala as in either of the northern study sites. Two of the three additional species in Guatemala use a configuration of foraging methods and perches not used by northern woodpeckers. Hence the large number of tropical woodpecker species can be attributed partly to the greater range of resources available in the structurally complex rain forest.
Colonizing Abilities of 'Biennial' Plant Species in Relation to Ground Cover: Implications for their Distributions in a Successional Sere
Authors: Gross Katherine L. , Werner Patricia A.
Published: May 2006

The "biennial" plant series Verbascum thapsus, Oenothera biennis, Daucas carota, and Tragopogon dubius are all found in abandoned agricultural fields, but they differ in their time of first appearance, peak abundance, and length of time populations persist. In experimental field studies these species showed differences in their abilities to colonize various types of ground cover. Seedling emergence, survival, and growth were highest for all four species in patches of bare ground. The small—seeded species, Verbascum and Oenothera, survived only in bare ground. In contrast, the large—seeded species, Daucus and Tragopogon, survived in several ground cover types. Relative coverage of three ground cover types and differences in seedling performance in these cover types were compared in a 1—yr and 15—yr old field. Verbascum and Oenothera became established only in the 1—yr old field where bare ground was abundant and not in the 15—yr old field where these patches were rare (°1% of area). When bare—ground patches were created experimentally in the 15—yr old field, both species were able to establish, supporting the conclusion that it is availability of bare ground rather than age of field per se that confines these two species to recently disturbed areas. In contrast, Daucus and Tragopogon became established in both fields, although seedling emergence, survival, growth, and reproductive output were higher in the 1—yr old field. Under nonexperimental conditions, however, these two species are not generally found in newly abandoned fields. Their absence is due to the fact that they produce seeds that, although broadly dispersed, do not survive in the soil for >1—2 yr and are not often present in a newly distributed area. Once dispersed to and established in an area, they can persist for several generations because their seedlings can survive in several types of ground cover, including those with thick vegetation.
The Effect of Competition on Foraging Activity in Desert Rodents: Theory and Experiments
Authors: Mitchell William A. , Abramsky Zvika , Kotler Burt P. , Pinshow Berry , Brown Joel S.
Published: May 2006

We studied, both theoretically and empirically, the effect of intra— and interspecific competition on the foraging effort of individuals. We considered two models, one for a time—minimizer satisfying an energy requirement, the other for an animal maximizing fitness as a function of multiple inputs subject to a time constraint. The goal of satisfying an energy constraint predicts that foraging effort should increase with increased competition. The goal of maximizing fitness subject to a time constraint on multiple inputs may also predict that foraging effort should increase with increased competition because of the missed opportunity cost that results when different inputs are complementary. However, if the fitness—maximizer with multiple inputs incurs an energy cost of foraging (in addition to missed opportunity costs), then it should often reduce foraging effort in response to an increase in competition. We experimentally tested the foraging response to increased competition by two species of gerbils, Gerbillus allenbyi and G. pyramidum, over a range of manipulated population densities in field enclosures located in the Negev Desert of Israel. Our results support the cost—benefit model when the additional energy cost of foraging is important. Per capita activity (as measured by spoor) declined as a function of intraspecific density for each species and as a function of interspecific density for G. allenbyi. We detected no interspecific effect, however, on G. pyramidum.
Recruitment Regulates Demographic Variation in a Tropical Intertidal Barnacle
Authors: Sutherland John P.
Published: May 2006

I studied populations of the barnacle Chthamalus fissus on the central Pacific coast of Costa Rica to determine the relative importance of pre— and post—settlement processes in determining patterns of distribution and abundance. Populations were studied at 10 sites representing five different microhabitats on one shore. Sites were censused photographically from 1983 to 1985 at 1—3 mo intervals, yielding data on recruitment, growth, and mortality. Mortality after settlement (=after day 1) was density independent for at least 90 d, so recruitment reflected settlement. Abundance appeared limited by sparse recruitment since considerable bare space was available at most sites during much of the study. Intraspecific competition (preemptive and adult—adult) was weak, except after occasional peaks of dense recruitment. Interspecific interactions were also weak, except for localized, intense predation by the thaidid gastropod Acanthina brevidentata near cracks and crevices, and sporadic competition with the small mussel Brachidontes semilaevis. In large part, demography of C. fissus was regulated by events in the water column affecting settlement and subsequent recruitment. Similar communities are found on rocky shores in the Bay of Panama, in central Costa Rica, and in the northern Gulf of California. Recruitment of Chthamalus spp. is very sparse in the Bay of Panama, sparse with occasional peaks in central Costa Rica, and consistently dense in the northern Gulf of California. Post—settlement processes involving Chthamalus spp. (competition and predation) appear strong and pervasive only in the northern Gulf of California. Abundance of Chthamalus fissus in Central America is regulated by events in the water column that determine the number of cyprids arriving to the substratum, an example of supply—side ecology.
Response to Fertilization by Various Plant Growth Forms in an Alaskan Tundra: Nutrient Accumulation and Growth
Authors: Shaver G. R. , Chapin F. S.
Published: May 2006

The fertilization responses of six tundra species belonging to three plant growth forms were compared to test the hypothesis that species of the same plant growth form are more similar to one another than to other growth forms in their response to a controlled perturbation. The controlled perturbation was a complete factorial NPK fertilization experiment in tussock tundra at Eagle Creek, Alaska, USA. We compared deciduous shrubs, evergreen shrubs, and functionally deciduous graminoids in terms of mineral and total nonstructural carbohydrate (TNC) concentrations, and annual production per stem or tiller. Species differed in the extent to which nutrient and TNC concentrations were altered by fertilization, although concentrations were usually changed in the same direction in all species in response to a given nutrient addition. Growth forms were not consistently different from each other in the responses of nutrient and TNC concentration, and frequently the two species from the same growth form responded differently. Growth per stem or tiller was stimulated most strongly by N and/or N + P fertilization in five of six species, with small and usually insignificant differences in magnitude but not direction of the response among species. Nutrient concentrations generally responded without interaction between fertilization treatments but the growth response was usually characterized by the N*P interaction, indicating that individual nutrient concentrations may vary widely and independently but that growth at Eagle Creek requires a balanced plant nutrition with first N and then P as the principal limiting factors. Decreases in TNC with fertilization suggested that carbon supply was not strongly limiting to plant growth. We conclude that species respond individually to fertilization in terms of nutrient and TNC accumulation, but that the species or growth forms studied are not distinctive from each other on the basis of limiting nutritional factors for growth.
Factors Influencing the Juvenile Demography of a Coral Reef Fish
Authors: Forrester Graham E.
Published: May 2006

A notable recent development in marine ecology has been the suggestion that the size of demersal populations is limited and that patterns in demersal abundance are determined by the settlement of pelagic larvae (recruitment). Here I examine some factors potentially limiting and determining population density in a small coral reef fish. An experimental study of the demography of juveniles of a small planktivorous damselfish, the humbug Dascyllus aruanus (Pomacentridae), was done at One Tree Reef, southern Great Barrier Reef, Australia. Recently settled fish were transplanted to replicate units of habitat at three lagoonal sites. The interactive effects of initial recruit density, the presence of adults, and supplemental feeding on the growth, survival, migration, and maturation of the recruits were examined over the following 10 mo. Migration was apparently rare and thus unimportant. Effects of the factors on the growth and survival of recruits were complex. Survival of recruits was generally inversely related to their density but enhanced in the presence of adults. Average survival also varied among locations. Mean growth was generally depressed at high recruit densities and in the presence of adults but was enhanced by supplemental feeding. Maturation was related to size and so was influenced by effects on growth. The results suggest that regulatory interactions and shortages of food may limit the size of adult populations via their effect on growth rates. Effects of the factors on survival were slight. Total abundance may thus be limited primarily by recruitment unless effects on growth are ultimately translated to effects on demersal mortality. As a result of the effects on survival, there was some modification of the initial pattern of recruit abundance. The importance of these effects in determining patterns of abundance in unmanipulated populations depends on variation in recruitment at similar scales. The number of recruits entering the adult population under different treatments was highly modified from the pattern of initial recruit density. The number of recruits that became mature by the end of the experiment was totally unrelated to their initial density. In addition, that number was reduced in the presence of adults, and was limited by the availability of food. The results suggest that complex effects of these factors on juvenile demography can modify recruitment patterns at small spatial scales. They also suggest that these factors may have different effects on the adult and total demersal populations. In general terms, both recruitment and postrecruitment processes influence patterns in abundance.
A Colonization Strategy in Field Voles (Microtus Agrestis): Reproductive Traits and Body Size
Authors: Ebenhard Torbjorn
Published: May 2006

Populations of the field vole (Microtus agrestis) in the Stockholm Archipelago in the Baltic (southern Sweden) are highly dynamic, with frequent extinctions and recolonizations of islands. In order to investigate the demography of such a successful island colonizer, I studied reproductive traits in two breeding colonies of Swedish field voles, one mainland and one from the archipelago, which I kept in a laboratory for 3 yr. Insular voles, as compared to mainland voles, were characterized by a larger adult body size, more rapid growth, larger and heavier litters, and a larger reproductive effort relative to body size. The two colonies were similar in gestation time, litter mortality, and age at sexual maturation. A large body size in combination with a high reproductive investment can be predicted neither from large—scale interspecific allometric relationships, nor from r—K—selection in its wider sense. It is instead argued that both the large body size and the reproductive traits are coevolved components of an island colonization strategy.
A Case of Insect Grazing Affecting Plant Succession
Authors: McBrien Heather , Harmsen Rudolf , Crowder Adele
Published: May 2006

The effect of phytophagous beetles on plant succession in an old—field community in southeastern Ontario was investigated over a 5—yr period. An experimental comparison of insecticide treated and untreated plots indicates that grazing by Trirhabda spp. on the goldenrod Solidago canadensis resulted in a reduction in precent cover of this species (from 40—70% to °1%), and a significant increase in percent cover of a number of earlier stage successional species.
Processes of Soil Organic‐Matter Accretion at a Mudfloe Chronosequence, Mt. Shasta, California
Authors: Sollins P. , Spycher G. , Topik C.
Published: May 2006

Amounts of carbon and nitrogen were measured in bulk soils and compenent density fractions from four mudflows (A, B, D, E) of increasing age at Mt. Shasta, California, in order to gain insight into mechanisms of soil organic—matter accretion. Soil was divided into a light fraction (specific gravity < 1.65 g/cm3) in which organic matter consisted mainly of root fragments and other plant remnants and a heavy fraction in which most of the organic matter was adsorbed on mineral surfaces and occluded within organomineral microaggregates. In bulk soil and the heavy fraction, amounts of C and N increased consistently with flow age and were even greater at an older, mineralogically similar site previously studied in the Oregon Cascade Range. Amounts of light—fraction C and N increased from flow A to D but were lower at flow E. Regardless of soil age, the heavy fraction contained 55—88% of the total soil N and 37—72% of the total soil C. Thus, the heavy fraction is the major long—term sink for N and an important sink for C. Soil properties and vegetation were exceptionally variable at the D and E flows. A multiple regression on rockiness of the soil (volume of fragments > 2mm) and a tree index (reflecting number and size of trees near each soil—sampling point and their proximity) accounted for 50—80% of the variability in light—fraction C and N at the D and E flows but not at the A and B flows, where all parameters were less variable. Rockiness and tree index accounted for little of the variability in heavy—fraction C and N, indicating that light— and heavy—fraction organic—matter accumulate in response to different factors. It appears that mass and composition of light—fraction organic matter correlate with short—term changes in biological activity, whereas heavy—fraction organic matter accumulates steadily and correlates with long—term processes such as mineral weathering and soil horizon formation.
Partitioning Genetic and Environmental Components of Reproduction and Lifespan In Artemia
Authors: Browne Robert A. , Sallee Stephen E. , Grosch Daniel S. , Segreti Wendy O. , Purser Susan M.
Published: May 2006

Reproductive and lifespan characteristics were determined for 12 populations of the brine shrimp, Artemia. Based upon geographical distribution and reproductive mode these could be separated into three distinct groups: obligate parthenogenetic populations, Old World sexual populations, and New World sexual populations. The three groups were found to be distinctly different in regard to reproductive and lifespan characteristics. Variance levels were compared between uniparental and biparental populations, allowing estimates to be made of the relative contribution of the genetic and environmental components for 11 life history traits. The environmental portion was estimated to be 100% for encystment traits and for the length of the prereproductive period, while the number of offspring produced (both as a lifetime total and a production rate) and the recovery period between broods had genetic components for variance °50%. To test for the interrelatedness of life history traits, a correlation coefficient matrix was constructed. In contradiction to most theoretical assumptions, extremely now correlation coefficients were found between the length of the female prereproductive period and the remaining lifespan and reproductive traits. However, recovery time between broods showed a significant positive correlation with number of broods produced, total offspring produced, and female lifespan.
Reproductive Hierarchies in Erodium: Effects of Variation in Plant Density and Rainfall Distribution
Authors: Rice Kevin J.
Published: May 2006

Reproductive hierarchies in even—aged plant monocultures often reflect the dynamics of intraspecific competition and, by their influence on effective population number, can alter significantly the relative importance of genetic drift in the evolution of plant populations. In experimental populations of Erosium boytrs and E. brachycarpum, I examined the interactive effects of intraspecific competition and rainfall variability on the development of reproductive hierarchies in these annual species. Reproductive inequality within monocultures of both species increased with increasing plant density and plant productivity, as measured by seed production, was determined by rainfall distribution. The magnitude of reproductive inequality was dependent on the interaction of sowing density, reproductive inequality was greatest in populations that experienced early autumn precipitation and lowest in populations exposed to drought during flowering. In contrast, at the lowest sowing density there was no significant effect or rainfall pattern on reproductive inequality. Effective population number was relatively insensitive to increases in population density because of increased inequality in reproduction at higher population densities. Reproductive variance could be a major contributor to drift variance in dense populations of both Erodium species.
Plant Drought Stress and Outbreaks of Spider Mites: A Field Test
Authors: English-Loeb Gregory M.
Published: May 2006

I conducted a field experiment to clarify the relationship between drought stress of bush beans, Phaseolus vulgaris, and outbreaks of the twospotted spider mite, Tetranychus urticae, in the presence or absence of an important spider mite predator, Phytoseiulus persimilis. Spider mite populations were highest on well—watered and on severely stressed bean plants and lowest on slight—to—moderately stressed plants, indicating a nonlinear relationship. The predator exaggerated this pattern, reducing mite populations the most on moderatley stressed plants and having the least impact on mites from severely stressed plants. Number of mites per unit leaf mass (a measure of mite injury to plants) was highest on severely stressed plants, lowest on slightly stressed plants, and intermediate on well—watered plants. Bean yield was negatively influenced by drought stress, with those plants that experienced high numbers of mites per unit leaf mass appearing to be more sensitive to drought than plants with low numbers of mites. The implications of these data for understanding the causes of pest outbreaks are discussed.
The Regulation of Morphological Plasticity in Tropical Reef Algae by Herbivory
Authors: Lewis Sara M. , Norris James N. , Searles Richard B.
Published: May 2006

Many tropical algal species exhibit considerable morphological variation associated with different coral reef habitats, but the factors contributing to such variation have not been identified. Two strikingly distinct morphologies are described here for the common Caribbean alga Padina jamaicensis. These distinct morphologies are characteristically found in different reef habitats, and are shown to represent phenotypic responses to different levels of herbivorous fish grazing. Experimental reduction of grazing intensity in a high—herbivory reef habitat resulted in a rapid (96 h) morphological shift from a prostrate, highly branched turf morphology to an erect foliose morphology. Transplant experiments indicated that foliose Padina plants were preferentially consumed by herbivorous parrotfishes. These results suggest that morphological plasticity may represent an important adaptive strategy in some tropical algal species, enabling plants to persist in intensely grazed reef habitats while maintaining the ability to respond rapidly to spatial or temporal fluctuations in herbivory.
Predation, Breeding Asynchrony, and the Outcome of Competition Among Treefrog Tadpoles
Authors: Morin Peter Jay
Published: May 2006

Densities of a predatory salamander (0, 2, or 4 Notophthalmus viridescens/m3) and a spring—breeding frog tadpole (100, 200, or 400 Hayla crucifer/m3), were controlled in a 3 x 3 factorial experiment replicated three times in 27 artificial ponds. Shortly before all Hyla crucifer metamorphosed from the ponds, 200 hatchlings of a summer—breeding frog, Hyla versicolor, were added to each artificial pond. Differences among ponds in growth and survival of H. versicolor provided a bioassay for the effects of predators and previously established competitors. Increased predator density decreased the survival and increased the mean mass at metamorphosis of H. versicolor, regardless of H. crucifer density. Increased H. crucifer density decreased the survival and mass at metamorphosis of H. versicolor in ponds without predators. Increased H. crucifer density decreased the mass at metamorphosis of H. versicolor adjusted for variation among ponds in the density of surviving H. versicolor, over all artificial ponds. Total H. versicolor biomass was negatively correlated with the biomass of H. crucifer metamorphs, in artificial ponds without predators. This experiment demonstrates strong competition between two species of asynchronously breeding treefrogs in predator—free ponds, and thereby compromises the traditional assumption of weak interspecific competition among temporally separated species. However, predation greatly reduces the intensity of competitive interactions among asynchronously breeding species.
Modelling The Effect of Host Patch Size on Mexican Bean Beetle Emigration
Authors: Turchin Peter B.
Published: May 2006

The resource concentration hypothesis states that specialized herbivores are more likely to find remain in pure, large, and/or dense stands of their hosts plants. This study examined whether in fact herbivores tended to remain longer in large vs. small patches of host plants and attempts to explain in the results by modelling herbivore movement. Both movement within a patch and emigration of marked Mexican bean beetles (MBBs) were studied by releasing beetles into small (19 plants) and large (61 plants) patches. Beetles left small patches at a faster rate than large patches, but the difference was not statistically significant. A stochastic model that was developed translates individual patterns of MBB movement into population patterns of beetle distribution within a patch, and predicts how this distribution changes with time. Estimating and testing a model on two separate sets of data provides a more rigorous test than applying the model to the data set on which it was developed. The parameters of the model, therefore, were estimated from data collected in the large patches, and the model was tested by comparing the predicted with the observed spatial distribution of beetles in small patches (i.e., a novel situation). Predicted distribution were very similar to the observed distributions; the predicted proportion of insects remaining in a patch at each census time differed from the observed by @<10% on the average. The model predicts that MBB emigration rate should decrease with patch size, confirming the observed trend.
The Effect of the Manipulation of Social Structure on Reproduction in House Mice
Authors: DeLong Karl T.
Published: May 2006

The influence of social and demographic parameters on reproduction was examined by removing either adult ♂ ♂, breeding ♀♀, or subadults of both sexes from pairs of populations for 15 mo; the 4th pair of 8 populations was not manipulated. Removal of ♂ ♂ was associated with a decreased proportion of adult ♀♀ which became parous, low body growth rates for maturing ♀ ♀, low association of perforate and nonperforate ♀♀ with adult ♂ ♂, and a high association of adult ♂ ♂ with nonperforate ♀ ♀. Removal of parous ♀♀led to earlier maturation and breeding of ♂ ♂, negative association between perforate ♀♀ and adult ♂ ♂, and higher levels of aggression in the populations. Multiple regression techniques indicated that estrous cycling and lactation were best explained by the activity of nonperforate ♀♀ and their association with adult ♂ ♂, the number of young weaned the previous month, the percentage of adult ♂ ♂ in the populations, and the aggressive tendency of these ♂♂. Aggressive tendency was measured in ♂ ♂ removed from the populations and paired with nonaggressive control mice. Nulliparous ♀ ♀ were more sensitive than parous ♀ ♀ to changes in social] behavior or demography of a population; litters born to previously nulliparous ♀ ♀ were clustered on certain months, whereas litters of parous ♀ ♀ were born randomly. Although most ♀ ♀ failed to reproduce during the later stages of population growth, this inhibition of reproduction was not always permanent; when nonbreeding ♀ ♀ were removed from the populations, transferred to small cages, and paired with adult ♂♂ from the populations, one half reproduced within 1 mo. Nestling survival was influenced negatively by the number of aggressive acts, the proportion of adults of either sex in the population, and the proportion of perforate and lactating ♀ ♀. Only ♂ dominance had a positive correlation with litter survival. The sex ratio of recently weaned mice varied greatly and was similar to that found among adults, even when the removal of adults of 1 sex caused the adult sex ratio to be markedly unequal.
Nutritional Ecology of the California Vole: Effects of Food Quality on Reproduction
Authors: Batzli George O.
Published: May 2006

California voles primarily eat the green shoots of grasses during the wet, breeding season (winter) and switch to grass seeds during the dry, nonbreeding season (summer). This suggest that nutritional factors control the timing of breeding, but until now there has been no indication of which nutrients are responsible. This paper reports the results of experiments conducted to test the following hypotheses: (1) grass seeds will not support extensive reproduction by California voles, and (2) low calcium and sodium concentrations in grass seeds can account for reduced reproduction on seed diets. In 12—wk feeding trials neither multiparous adults nor nulliparous subadults produced as many pups when fed grass seeds as when fed a laboratory diet (rabbit chow). Subadults fed grass shoots had intermediate success. Concentrations of calcium and sodium, but not protein and phosphorus, were lower in seeds than in rabbit chow, grass shoots, and diets recommended for laboratory rodents. Subadult animals had positive net balances of nitrogen and phosphorus, but not of calcium and sodium, when fed grass seeds. Although subadult females generally produced fewer young than adult females, subadult voles fed grass seeds and supplemental calcium and sodium in their drinking water reproduced as well as adult voles fed rabbit pellets. All these results were consistent with the hypotheses given above and lend credence to previous suggestions that nutrition (particularly mineral nutrition) exerts important influences on the population densities of lemmings and voles.