bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of Myriophyllum: Sediment or Lake Water as the Source of Nitrogen and Phosphorus
Authors: Best Mary D. , Mantai Kenneth E.
Published: May 2006

A series of laboratory culture experiments was designed to investigate uptake of phosphorus and nitrogen by roots and shoots of Myriophyllum spicatum in a number of lake water/substrate and nutrient medium/substrate environments. The plants were compared with respect to biomass, physical dimensions, and total P and N in the plant tissues. It appears that Myriophyllum spicatum can meet its requirements for N by root uptake from the sediment as well as by absorption from the water itself through stem and leaf tissue. It was also seen that Myriophyllum can absorb considerable quantities of P from the sediment via the root system and transport it to the shoot regions of the plant. Growth data suggest that N was growth—limiting for sand—grown plants in nitrate—deficient media, even though tissue N was high. Growth was not decreased in low—phosphate media, suggesting that phosphate—limiting conditions were probably not attained in these experiments. A synergistic relationship between P and N was noted; P in the water clearly affected the ability of Myriophyllum plants to take up nitrate from the water. These data suggest that the limiting concentration of nitrate for Myriophyllum might vary considerably depending in part on the phosphate concentration.
Comparative Population Regulation of Two Planktonic Cladocera (Holopedium Gibberum and Daphnia Catawba)
Authors: Tessier Alan J.
Published: May 2006

The abundance of two planktonic grazers (Holopedium gibberum and Daphnia catawba) fluctuated seasonally in a nonparallel manner in Lake Lacawac, Pennsylvania. Holopedium gibberum was abundant in early and midsummer, while D. catawba was common only in spring and late summer. I sought to explain this seasonal succession by identifying seasonal factors which regulate each population. I monitored population abundance, individual energy reserves (lipid content), egg production, and body size distributions in plankton samples from April to October in three years. Food resources and vertebrate predator abundance were also examined seasonally. Results of experimental manipulations of food availability and predators, conducted seasonally in both small (6.4—L) and large (6000—L) enclosures, supported interpretations drawn from descriptive data. Contrasting seasonal abundance patterns of the species are explained by differences in the intensity of food stress and predation affecting each species. Food supply restricted population growth of H. gibberum at most times. In the spring of each year, starvation was a major cause of mortality; during summer, individual energy reserves and fecundity were near zero for H. gibberum. Predation losses were negligible for adult H. gibberum, but neonate (smallest age class) mortality by fish was occasionally large. Daphnia catawba experienced a seasonal change in the intensity of regulating factors; food supply restricted population growth only in spring and late summer, but predation controlled growth during summer. During late summer, predation on D. catawba was reduced and its population abundance increased sharply. Experimental removal of fish caused a comparable increase of D. catawba during midsummer. At peak animal densities in late summer, both species were food stressed Life table experiments conducted at this time suggest that competition for food occurs between D. catawba and H. gibberum, and results in a reduction of H. gibberum density.
An Energy Budget for the Zoobenthos of Mirror Lake, New Hampshire
Authors: Strayer David , Likens Gene E.
Published: May 2006

We combined our data on abundance, biomass, and diet of benthic animals in Mirror Lake with estimates of annual P/B (production/biomass) ratios to construct a model of energy flow through the zoobenthos of this small, oligotrophic lake. Because we included the rarely study meiofauna (all metazoans < 0.5 mm), our model provides the first accounting of energy flow through an entire zoobenthic community in freshwater. In Mirror Lake, about half of the zoobenthic assimilation of carbon (14 g°m—2°yr—1) is due to the meiofauna. Although detritivory supports about half of community assimilation, benthic algae are an important energy source to the zoobenthos, especially in the littoral zone. We suggest that the importance of benthic algae in lacustrine energy budgets has been underestimated. Major fates of zoobenthic production in Mirror Lake include invertebrate predation, insect emergence, and fish predation. Invertebrate predation is the dominant fate and accounts for 80% of zoobenthic production.
Resource Regulation by a Stem‐Galling Sawfly on the Arroyo Willow
Authors: Craig Timothy P. , Price Peter W. , Itami Joanne K.
Published: May 2006

We studied the impact of the stem—galling tenthredinid sawfly, Euura lasiolepis, on the growth and branch age structure of the arroyo willow, Salix lasiolepis. Normally, as willows age they become less susceptible to galling, but heavy Euura galling maintains willows at a young, relatively susceptible juvenile stage. The Euura form more galls and long shoots. Long shoots are found on clones with young branches. Heavy galling stunts or kills growth distal to the gall, stimulating sprouting by indefinitely dormant buds located near branch bases. The resulting young branches keep the clone susceptible to further galling. In contrast, increasing branch age of lightly galled clones confers resistance to galling. We term this model of gall—induced resource maintenance the resource regulation hypothesis. Resource regulation is the maintenance or increase of high—quality resources by an herbivore species that impacts immediately subsequent generations of the same herbivore species on the same plant.
Nocturnal Bee Abundance and Seasonal Bee Activity in a Panamanian Forest
Authors: Wolda Henk , Roubik David W.
Published: May 2006

Bees were monitored weekly for 7 yr at light traps in the tropical monsoon forest of Barro Colorado Island. Fifty species and 17 genera were recorded, including nocturnal Megalopta and crepuscular Rhinetula (Halictidae) and Ptiloglossa (Colletidae). Twenty—eight native meliponines and African Apis mellifera in traps increased the known resident highly social bees to 32 species. Most of the 11,860 bees were Megalopta; these species were present throughout the year, as were Rhinetula and Ptiloglossa. Abundance of Megalopta was lowest during the dry season; this was its only consistent seasonality. Peak abundance occurred at various times during dry—to—wet—season transition and in the first half and the end of the wet season. Centris and Epicharis, large, solitary anthrophorid bees, were present in the early wet season and absent in the late wet season and most of the dry season. The highly social bee Trigona aff. cupira was aseasonal but had abundance peaks during all but the mid—to—late wet season. Megalopta genalis abundance and M. ecuadoria abundance were highly positively correlated within years, and weekly correlated with abundances of other bees. Pairwise correlations between years were low for each Megalopta species and for combined bees of other genera. A singularly large catch of Megalopta genalis in 1978 corresponded to flowering of the monocarpic tree Tachigalia versicolor near light traps. Fluctuation of bee abundance at light traps probably indicates local flower availability for this species and, to a lesser extent, for the other bees. The data suggest large year—to—year variation in seasonal abundance of resources used by nocturnal bees and by bees in general, but are limited to indicating the presence or absence of most other bee species. The yearly variances in abundance of a stingless bee species and of Megalopta in Panama are comparable to those of eight temperate bumble bee species studied in England, but combined diurnal and crepuscular bee abundance is considerably less variable. The African honey bee arrived on Barro Colorado Island in mid—1982 and has produced no noticeable changes in abundance of other bees but has yet to reach its potential, numbers there; light—trap studies could provide perhaps the most reliable information on its impact.
Niche Partitioning in Spittlebugs (Homoptera: Cercopidae) Sharing Shelters on Host Plants
Authors: McEvoy Peter B.
Published: May 2006

Resource exploitation was measured for two spittlebugs using shelters on host plants. Approximately 80% of the older nymphs of Philaenus spumarius and Lepyronia quadrangularis lived cradled in leaf axils. Manipulative experiments showed the preference for leaf axils over adjacent internodes is related to shelter rather than food, and that spittlebugs favor wide over narrow axils. Preference for a host species was correlated with the quality of shelter provided by the host's axils. Leaves reduce runoff and evaporation of spittle, the frothy excrement that surrounds and protects the nymph. Sampling of old—field vegetation indicated that the two spittlebug species concentrated in shelters at different heights in the vegetation; the larger species (L. quadrangularis) extended beyond the vegetation height range of the smaller (P. spumarius), and overlap between the species was greatest on short plants (<25 cm). Overlap was greater on tall (>50 cm) than intermediate (25—50 cm) stems. Tall stems offer less available stem length because hard lower stem tissues make stylet penetration difficult. The supply of shelters far exceeded demand even after excluding axils made useless by narrow width, trichomes, tissue hardness, and distance from the occupied site. Despite the abundance of empty axils, individuals of the same or different spittlebug species often lived together in the same axil. Crowding did not delay development or stunt growth; in field samples, the instar and dry mass of nymphs were independent of density over the observed range in density among spittlemasses (1—12 nymphs per spittlemass) and among stems (1—17 nymphs per stem). In accord with recent reviewers who conclude that competition for food rarely occurs among insect herbivores, this study demonstrates that use of shelters is similarly characterized by high overlap, undersaturation, and absence of density—dependent effects on growth and development.
Nitrogen‐Limited Growth in Plants from Different Successional Stages
Authors: Tilman David
Published: May 2006

The effect of nitrogen availability on the plant growth was studied using nine plant species, some of which are commonly found in recently abandoned old fields while others are more characteristic of native prairie. Each species was grown by itself in nine different soil mixtures in which total soil nitrogen (as N) per unit soil mass ranged from 20 to 850 mg/kg, spanning the range of total soil nitrogen observed in a chronosequence of old fields at Cedar Creek Natural History Area, Minnesota. For each species there was a significant (P < 0.5), positive correlation between the biomass attained after 12 wk of growth and the total soil nitrogen. These data allowed the species to be ranked, from those that attained the greatest biomass as seedling at low nitrogen levels to those that attained the least, as follows: Ambrosia artemisiifolia, Achillea millefolium, Chenopodium album, Agropyron repens, Agrostis scabra, Poa pratensis, Sorghastrum nutans, Schizachyrium scoparium, and Liatris aspera. There was a highly significant tendency for early successional species to grow more rapidly at low nitrogen levels and to acquire more nitrogen per plant from nitrogen—poor soils than late successional species. However, late successional species did not grow more rapidly at high nitrogen levels than early successional species. These results are consistent with the hypothesis that early successional species are dominant following old field abandonment at Cedar Creek because of their ability to compete for soil nitrogen.
Timing of Seed Production and Dispersal Geranium Carolinianum: Effects on Fitness
Authors: Roach Deborah Ann
Published: May 2006

The importance of the timing of seed production and of seed dispersal to the fitness of an annual plant was examined using Geranium carolinianum in the piedmont of North Carolina. Mature seeds were collected from naturally growing plants on four dates in May and June and were then sown back into the population on five dates in late May, June, and July. The mean mass of seed produced varied during the growing season and this had important consequences for fitness. Seeds produced early were heavier, but lighter seeds germinated earlier. Seedlings that emerged earlier developed into larger plants with relatively higher reproductive output. Timing of seed dispersal had no effect on date of emergence, plant size, or fecundity.
Predator Avoidance and Community Structure: Interactions among Piscivores, Planktivores, and Plankton
Authors: Turner Andrew M. , Mittelbach Gary G.
Published: May 2006

We present the results of an experiment designed to examine the role predator—avoidance behaviors play in structuring a community. Previous studies have shown that small bluegills (Lepomis macrochirus) shift their habitat use in the presence of their predator, the largemouth bass (Micropterus salmoides). The addition of bass causes small bluegills to make greater use of structured (vegetated) habitats and reduces their use of open (limnetic) habitats. We hypothesized that these effects of bass on bluegill behaviors should lead to an increase in the abundance and mean size of zooplankton when bass are present. We tested this prediction in two ponds by stocking small bluegills with and without bass. Pronounced differences in zooplankton abundance and size structure developed between treatments, with three cladocerans (Daphnia, Diaphanosoma, and Ceriodaphnia), and the phantom midge Chaoborus, becoming more abundant with bass. These effects of bass were not due to changes in bluegill abundance, as very few bluegills were eaten by the bass, and bluegill densities did not differ between treatments. Calculation of bluegill feeding rates shows that the fish exerted substantial mortality on zooplankton and that cladocerans experienced lower per capita death rates (due to bluegill) in the presence of bass. We discuss these results in light of current theory predicting how foragers should deplete prey among habitats that differ in mortality risk.
Behavioral and Life‐Historical Responses of Larval American Toads to an Odonate Predator
Authors: Skelly David K. , Werner Earl E.
Published: May 2006

This study examines the responses of larval American toads (Bufo americanus) to the non—lethal presence of an odonate predator (Anax junius). We performed a laboratory experiment where toad larvae were raised at four food rations crossed with the non—lethal presence (i.e., constrained Anax) and absence of the predator. Tadpoles facultatively responded by metamorphosing at smaller sizes in the presence of the predator and at lower food rations. Tadpoles also responded behaviorally to the presence of predators by reducing activity and altering spatial distribution. These latter reactions appeared to contribute to reduced growth rates in the presence of the predator at a given food level. We attempted to separate the effect of the predator on size at metamorphosis into components due to the effect on growth and to more direct effects of the predator, by comparing size at metamorphosis for individuals growing at the same rate in the presence and absence of the predator (i.e., at different food levels). Our data suggest that the metamorphic response may be mediated primarily through the behavioral effects on growth, which then affect size at metamorphosis. These results are consistent with theories of amphibian metamorphosis that predict that size at metamorphosis should depend on the relation between growth opportunities and risk of mortality in the larval and adult habitats. We discuss the importance of non—lethal effects of predators on prey performance, species interactions, and the evolution of prey defenses.
Nitrogenase Activity, Nitrogen Fixation, and Nitrogen Inputs by Lupines at Mount St. Helens
Authors: Halvorson Jonathan J. , Franz Eldon H. , Smith Jeffrey L. , Black R. Alan
Published: May 2006

We measured the timing and magnitude of nitrogenase activity and N2 fixation by lupines colonizing early successional volcanic sites at Mount St. Helens. Nitrogenase activity (measured by acetylene reduction) in Lupinus lepidus growing at a pyroclastic site exhibited significant diurnal trends, with lowest ethylene evolution rates at night. Nitrogenase activity also followed seasonal trends, with high rates in June, very low levels in August, the dry warm part of the season, and a partial recovery of nitrogenase activity in September after precipitation resumed. A comparison of typical nitrogenase activities measured at several sites suggested that rates of N2 fixation were highest in L. lepidus growing at disturbed low N sites. Adult lupine C and N composition also varied during the growing season, with trends correlated with seasonal patterns of nitrogenase activity. Seasonal N2 fixation in L. lepidus and L. Latifolius was measured using 15N isotope. Both species fixed °60% of their N during the first season of growth with some evidence of preferential allocation to aboveground biomass. N fixation by Lupinus lepidus individuals was ° 18.1 mg/g biomass or an average of 15.4 mg per plant, while L. latifolius fixed an average of 16.3 mg/g biomass, equivalent to 22.9 mg per plant. Average net C fixation during the same period was 355 and 589 mg per plant for L. lepidus and L. latifolius, respectively. Despite these rates, the current distribution of L. lepidus into a few, small patches that occupy <1% of the surface area indicates that annual N inputs by lupines are <0.05 kg/ha and thus probably not the primary source of N input into developing Mount St. Helens pyroclastic sites except at a local scale.
Effects of Microhabitat Selection on Feeding Rates of Net‐Spinning Caddisfly Larvae
Authors: Georgian Ted , Thorp James H.
Published: May 2006

Net—spinning caddisfly larvae of the family Hydropsychidae are known to prefer microhabitats with large, stable substrate and high water flow velocity. It is often assumed that net spinners in high—velocity microhabitats have higher feeding or growth rates than larvae in less preferred sites, but there is no direct evidence to support this assumption. We hypothesized that net—spinning caddisflies would select microhabitats that offered the greatest feeding rates. This hypothesis was tested by field experiments in which we determined if net—spining caddisfly larvae preferred high—velocity sites even when substrate size and type were held constant. We then measured feeding rates of net spinners in microhabitats with different flow characteristics. High—flow positions were selected by 96% of hydropsychid arvae colonizing artifical moss substrates. Artemia nauplii released into the water column were captured by individual larvae in high—flow sites at a rate of 0.016%/m, significantly higher than the capture rate in low—flow sites. Combing this rate of prey capture with mean hydropsychid densities of 1125 individuals/m2, we estimate that hydropsychid larvae in riffles remove drifting invertebrate prey at a rate of ° 18%/m. Assuming exponential prey removal, a prey item in the drift would travel an average of only 5.5 m before being consumed. This study is one of the first to show that the distribution of a stream filter feeder is related to the feeding rates obtainable in different microhabitats.
Spatial Heterogeneity and Individual Variation In Diet of an Aquatic Top Predator
Authors: Zerba Kim E. , Collins James P.
Published: May 2006

Since habitats are generally spatially heterogeneous, and important component of niche variation may be determined by the relationship between individual variation in feeding among and within habitats. We characterized variation in diet among and within individual tiger salamander larvae (Ambystoma tigrinum nebulosum) among and within sites in natural ponds. We also analyzed prey variation among sites. There was significant variation in diet among sites, controlling for variation in larval size among sites. Prey taxa varied significantly among sites. There were also significant size—associated differences in diet within sites. Controlling for larval size we found no further evidence of significant interindividual differences in diet within sites. Intrapopulation variation in diet among sites is likely a consequence of adaptive phenotypic plasticity in feeding behavior of individuals on a spatially variable prey assemblage. This result supports Van Valen's hypothesis that selection should favor multiple phenotypes within populations. Variation in diet among sites is directly analogous to the within— and between—phenotype components of niche variation defined by Roughgarden. Size—associated differences in diet represent a significant ontogenetic component to niche variation in feeding within populations of larval salamanders. Studies of food web structure that ignore predator diet and prey differences among sites are an incomplete summary of predator—prey linkages. In addition, phenotypic plasticity in feeding behavior as a source of niche variation has implications for traditional ecological theory of intra— and interspecific interactions, which has rarely included variation other than morphological size differences among animals.
Selection on Fledging Mass in the Collared Flycatcher and the Great Tit
Authors: Linden Mats , Gustafsson Lars , Part Thomas
Published: May 2006

The selection on residual mass (relative to body size) at fledging was investigated in the Collared Flycatcher Ficedula albicollis and the Great Tit Parus major. Directional selection for high fledging mass was evident in 6 of 7 yr in Collared Flycatchers but only in 1 of 5 yr in Great Tits. Three different methods of demonstrating and testing stabiilizing selection are compared. Stabilizing selection on relative mass occurred in both species, but the frequency with which this was established depended on which method was used. None of the methods seemed to be universally reliable, and the problem of defining and testing stabilizing selection is discussed. In Collared Flycatchers mass seemed to be most important for juvenile survival. Also in Great Tits mass was important, but in addition other traits (e.g., hatching date) strongly influenced juvenile survival in this species. This possible difference between the two species is suggested to relate to differences in their territory establishment.
Nonrigorous Foraging by Robbing Egrets
Authors: Kushlan James A.
Published: May 2006

The premise that a species will maximize its net energy intake over the short term was tested by studying the robbing behavior of the Great Egret. In wading—bird feeding aggregations of the southern Florida Everglades, the 5 most common species robbed other birds, and this behavior consumed 10% of the feeding time of the Great Egret. When an egret robbed other birds, it got larger prey, but it took longer, caught fewer prey, and expended more energy than it did feeding in more typical fashion by slow walking or standing. Nonrobbing behavior had a gross energy intake per time 3.1 x greater than robbing. The cost—benefit ratio of robbing was 70% larger than for standing feeding. The combined used of both standing feeding and robbing resulted in a cost—benefit ratio 10% larger than for standing feeding alone. The use of a nonoptimal behavior is interpreted to suggest that energy return need not always be optimized over the short term. Minimizing cost—benefit ratios, optimizing time budgets, or maximizing net energy gain may occur only intermittently during an animal's annual cycle. The existence of a less—than—optimal behavior within the egret's foraging repertoire suggests that, under circumstances other than those studied, it might contribute to foraging optimization. It is predicted that an animal should attempt to capture each prey that it encounters when the occurrence of a prey item is a relatively rare and random event and if the potential penalty were small. Under these conditions, which would occur during periods of nonrigorous foraging, an animal can use a nonoptimal behavior.
Components of Avian Diversity Along a Multifactorial Gardient
Authors: Rotenberry John T.
Published: May 2006

It has been suggested that "regulation" of species diversity occurs through variation in either its richness or evenness component with the former occurring in predictable, nonrigorous environments and the latter under the opposite conditions. This hypothesis is tested by examining the variations in components of bird—community diversity along a derived gradient of climatic variability and rigor. The gradient consist of the first axis of a principal component analysis of 15 weather variables, and accounts for 53.8% of the total variation in those variables. Factor loadings of the original variables (which were taken from stations throughout the Pacific Northwest) suggest that the gradient represents a cline between the mild, most, uniform weather of the Oregon and Washington coast, and the severe, arid, variable climate of interior southern Oregon and Idaho. Correlations of avian community attributes (diversity, richness, and evenness) with their geographic position along the derived gradient show that species diversity decreases significantly along the gradient from mild—moist—stable to severe—arid—unstable climates. Unlike several other studies, however, diversity changes as a result of variation in its evenness rather than its richness component. The results are consistent with the suggestion that in less—stable environments spatial heterogeneity or habitat patchiness may be more important than resource limitation and subsequent interspecific competition in determining bird community structure.
Regulation of a Northern Grey Squirrel (Sciurus Carolinensis) Population
Authors: Thompson Donald C.
Published: May 2006

The parameters of a northern grey squirrel (Sciurus carolinensis) population were examined. The objective was to determine the factor(s) that controlled population size. Adult death rates were constant and were less than those of young. More young produced that subsequently entered the breeding population. The number of young recruited into the adult population was the main parameter which determined population size. The dispersal of young was the factor that determined the number of young which survived to recruit. The essential conclusion is that established squirrels interact with young to regulated recruitment through dispersal, and, in turn, population numbers.
Food Availability as a Proximate Factor Influencing Individual Growth Rates in the Iguanid Lizard Sceloporus Merriami
Authors: Dunham Arthur E.
Published: May 2006

Von Bertalanffy, logistic—by—length, and logistic—by—weight models of individual growth for 2 populations of Sceloporus merriami were estimated from 3 yr (1974—1976) of mark—recapture data using nonlinear regression. The logistic—by—weight model was found to provide the best fit to observed growth rates. Abundance of arthropod prey was estimated by 2 techniques and found to be serially correlated with seasonal precipitation. Prey abundance was correlated with annual precipitation. Individual foraging success was found to be correlated with estimated prey abundance. Parameters of logistic—by—weight growth models were compared for the 3 yr of the study and revealed that variation in food availability resulted in predictable variation in individual growth rates. Individual growth rates were positively correlated with active—season and annual precipitation and with estimates of food availability. The limitations of using stationary growth models to describe a potentially nonstationary process such as individual growth are discussed.
The Influence of Male‐Defended Oviposition Sites on Early Embryo Mortality in Bullfrogs
Authors: Howard Richard D.
Published: May 2006

Field studies were conducted on factor affecting embryo mortality in bullfrogs, Rana catesbeiana, in 1975 and 1976 at the E. S. George Reserve of the University of Michigan. Larger ♀ produced significantly larger clutches than smaller ♀ (6000 to >20,000). Older ♀ produced 2 clutches each year with 2nd clutches containing significantly fewer eggs than 1st clutches. Egg size appeared to be unrelated to ♀ size; however, 2nd clutches contained significantly smaller eggs than initial clutches for all ♀♀. Embryo mortality depended on ♀ choice of oviposition sites. Such sites were controlled by territorial ♂♂. Larger ♂ ♂ controlled oviposition sites that had significantly lower embryo mortality than the sites of smaller ♂ ♂. Sources of embryo mortality included developmental abnormalities and predation. Choice of oviposition sites included: (a) advance of areas with high water temperatures (>32 degrees C) that result in increased developmental abnormalities and (b) preference for areas that increase embryo survival by increasing developmental rate and/or decreasing efficiency of predation on embryos by the leech. Macrobdella decora.
Fungal‐Small Mammal Interrelationships with Emphasis on Oregon Coniferous Forests
Authors: Maser Chris , Trappe James M. , Nussbaum Ronald A.
Published: May 2006

Most higher plants have evolved with an obligatory symbiotic relationship with my corrhizal fungi. Epigeous mycorrhiza formers have their spores dispersed by air currents, but hypogeous mycorrhizal fungi are dependent upon small mammals as primary vectors of spore dissemination. Mammalian mycophagists defecate within the coniferous forest ecosystem, spreading the viable spores necessary for survival and health of the conifers. As one unravels and begins to understand the interrelationships between small—mammal mycophagists and mycorrhizal fungi, it becomes apparent that the various roles of small mammals in the coniferous forest ecosystem need to be reeevalutaed. One can no longer accept such simplistic solutions to timber management as poisoning forests rodents to "enhance" tree survival. One must consider the direct as well as the indirect costs and benefits of timber management decisions if one is to maintain balanced, healthy coniferous forests.
Role of Tannins in Defending Plants Against Ruminants: Reduction in Protein Availability
Authors: Robbins C. T. , Hanley T. A. , Hagerman A. E. , Hjeljord O. , Baker D. L. , Schwartz C. C. , Mautz W. W.
Published: May 2006

We tested the hypothesis that tannins defend plants against large herbivores by decreasing protein availability. Digestion trials were conducted with mule deer (Odocoileus hemionus) and results from previous trials with white—tailed deer (O. virginianus), moose (Alces alces), caribou/reindeer (Rangifer tarandus), and elk (Cervus elaphus) were summarized to evaluate dietary factors affecting protein availability. The digestibility of plant protein in feeds with minimal tannins, such as grasses and agriculturally produced legumes and grains, was a highly predictable function of the total protein content and the amount of nondigestible, fiber—bound protein. Digestible protein in plants containing significant tannins was lower than predicted from regressions for low—tannin feeds. The reduction in digestible protein was proportional to the protein—precipitating capacity of the plant tannins. Deciduous browse stems collected in winter had very low levels of protein—precipitating tannins and only a slightly lower protein availability than predicted. Tannins are not important in the defense of most deciduous tree shrub stems consumed by these herbivores. Tannins in flowers and forb, tree, and shrub leaves markedly reduced protein availability. Tannins must be considered in understanding the defensive strategies of leaves and flowers. Voluntary intake of the high—phenolic forages was significantly reduced below ingestion rates for grasses, legumes, and pelleted diets. It is hypothesized that soluble phenolics that do not inhibit digestion but are absorbed and reduced intake through their toxicity are more important in defending some plant parts against ruminants than are digestion—reducing tannins.
Fire and Mammalian Secondary Succession in an Australian Coastal Heath
Authors: Fox Barry J.
Published: May 2006

A species—rich small—mammal community on 7 ha of diverse coastal heath in Myall Lakes National Park, New South Wales, Australia, was studied for 7 mo before the area burned in a wildfire (August 1974) and has subsequently been monitored for 5 yr since the fire. Species regularly trapped were the dasyurids Antechinus stuartii and Sminthopsis murina, the peramelid Isoodon macrourus, and the native murids Pseudomys novaehollandiae and P. gradcilicaudatus, together with the introduced Mus musculus. Pseudomys species, M. musculus, and S. murina reached greater abundance on early seral stages, while the abundance there of both Rattus fuscipes and R. lutreolus was much reduced. Species reach peak abundance in an orderly replacement sequence exhibiting a mammalian secondary succession. A habitat accommodation model is proposed with species entering the succession and reaching peak abundance as externally controlled changes in the vegetation fulfil the habitat requirements of each species. Species leave the succession or are greatly reduced in abundance when these local physical conditions move out of the optimal range for the species. This study shows that a major perturbation of a small—mammal community can produce a variety of responses among species, suggesting that regeneration time may represent a resource axis subdivided by community members in this secondary succession. The rapid recovery illustrated by the total number of individuals, as a measure of community response, support the suggestion that fire and fire frequency have been major factors in producing a fire—adapted, species—rich small—mammal community on this heathland.
Effects of Winter Feeding on Limpets by Black Oystercatchers, Haematopus Bachmani
Authors: Frank Peter W.
Published: May 2006

Black Oystercatchers fed on limpets in an intertidal boulder field at a rate of 2 limpets°m—2°yr—1. The birds exert a major influence on the microdistribution of these molluscs. Where accessible to oystercatcher predation, limpets are unlikely to survive over a winter once they reach moderate size (10—14 mm). Collisella pelta are exceptional in having refuge in large size. Oystercatchers thus produce and reinforce patchy limpet distributions. Adaptations of the limpets include crypsis and habitat selection of setting larvae. Spatial heterogeneity on local, regional, and broader geographic scales complicates these effects, especially since settlement behavior is constrained from making distinctions between all levels of heterogeneity, e.g., between cliffs where limpets will be relatively safe and boulders where they are at high risk. Locally the effects of bird predation are most notable for Notoacmea persona, but N. scutum, C. digitalis, and C. pelta are also consumed in significant numbers. The resulting microdistribution of limpets affects algal cover, which tends to be effectively removed by their grazing on steep and vertical walls, but which can maintain itself on large horizontal and gently sloping surfaces. Feeding in this locale was confined to the birds' nonbreeding season, fall and winter. By its end the limpets were reduced in number and the birds foraged elsewhere and on other prey. Limpet recruitment may be insufficient to allow year—round feeding in such areas by these birds, whose foraging may represent an adaptive seasonal adjustment to local conditions.
Regulation of Fruit Maturation Pattern in an Annual Legume, Cassia Fasciculata
Authors: Lee T. D. , Bazzaz F. A.
Published: May 2006

This study investigated the extent of and basis for selective fruit maturation in the annual legume, Cassia fasciculata Michx. Demographic analysis of flowers and fruit in field populations demonstrated that fruit did not necessarily mature in the order initiated, although early initiated fruit were more likely to mature. Fruit initiated early in the season tended to grow slowly at first, whereas those initiated later tended to grow rapidly; this growth pattern dampened the effect of the order fruit initiation on maturation sequence. Two experiments were conducted to test the hypothesis that more outcrossed fruit matured than selfed fruit, but in both cases the hypothesis was rejected. Other experiments were performed to determine if (a) fruit resulting from pollination by a particular plant mature more rapidly than do those resulting from pollination by other plants, and (b) fruit resulting from mixed pollen loads mature more readily than those pollinated by a single plant. These ideas were also rejected. Two experiments were conducted to test the hypothesis that fruit with a large number of percentage of fertilized ovules are selectively matured. This hypothesis was supported by both glasshouse experiments and field observations. Percentage of fertilized ovules seemed to be more clearly related to fruit growth and maturation than was number of fertilized ovules. Natural selection may favor individuals that selectively mature fully fertilized fruit because such fruit (1) may be more resource—efficient because they contain less pericarp per seed, (2) may provide better dispersal of seed, or (3) may contain high—quality seed owing to increased gamete competition.
Abalones, Shells, and Sea Otters: Dynamics of Prey Populations in Central California
Authors: Hines Anson H. , Pearse John S.
Published: May 2006

Densities, sizes, and species composition of abalones, Haliotis refescens, H. walallensis, and H. kamtschatkana, remained stable from 1972 to 1981 within a sea otter habitat in central California. Almost all censused abalones were in crevices, with densities averaging 1.8 animals/10 m2. Live abalones and empty abalone shells resulting primarily from predation by sea otters averaged 7.5 and9 cm length, respectively. In contrast, out of the range of sea otters, live abalones were over twice as large and were numerous outside crevices (when protected from human predation). At our study site within their range, sea otters selected abalones larger than were proportionately available in crevices, and they broke many large shells with stone tools. An average of 55 freshly produced empty abalone shells, equivalent to °20% of the crevice population of live abalones, were found each month in our study area over a 12—mo period. Indirect calculations of feeding rates of sea otters also indicated a high production rate of abalones, as did observations of abalones in mapped crevices. The high production rates of abalones must result from high rates of juvenile recruitment and growth, and are indicative of a highly dynamic population, with a turnover time of 1—3 yr.
Effects of Rainfall Variability and Gopher Disturbance on Serpentine Annual Grassland Dynamics
Authors: Hobbs Richard J. , Mooney Harold A.
Published: May 2006

We studied the dynamics of a serpentine annual grassland in northern California in relation to disturbance by pocket gophers (Thomomys bottae) and interannual variation in rainfall over the period 1982—1988. Mapping of gopher mound formation indicated that the probability that gophers would disturb any given area during the 6—yr study period had a near normal distribution with a peak at two disturbances during that period. Disturbance levels varied considerably from year to year and spatially, and thus the disturbance regime is complex. Exclosure experiments indicated that gopher disturbance had a significant effect on the abundances of many of the grassland annuals, perennial grasses, and cormaceous species. Aboveground herbivores had no detectable effects. Over the period of the study annual rainfall varied threehold and plant community dynamics were strongly affected by this. In particular, Plantago erecta decreased and Lasthenia californica increased in abundance with increasing rainfall. Abnormally high rainfall in 1982—1984 allowed the buildup of populations of Bromus mollis, the only nonnative species that invades the serpentine significantly. B. mollis was, however, subsequently virtually eliminated from the serpentine grassland by two consective years of severe drought. Invasion of B. mollis was found only on gopher mounds formed in 1983. In subsequent years recolonization of gopher mounds was predominantly by other species, in particular Lotus subpinnatus. Interannual variability in species abundances was most apparent on disturbed microsites. Our results provide a longer term perspective from which to view shorter term experimental and modelling work and highlight the need for long—term observations of ecological systems.
Responses to Simulated Leaf and Root Herbivory by A Biennial, Tragopogon Dubius
Authors: Reichman O. J. , Smith Stan C.
Published: May 2006

Removal of 25 or 75% of leaf or root tissue, and 25% of both, was used to simulate above— and belowground herbivory on Tragopogon dubius. Plants with 25% of their leaf tissue removed did not differ significantly from controls in total biomass; those with any root tissue trimmed produced significantly less biomass while the 75% leaf removal treatment was intermediate. A similar pattern was exhibited for plant mortality and flower production. Plants that had one or more flowers removed by herbivores grew significantly larger and produced significantly more flowers than plants that lost no flowers, regardless of treatment. The greatest differences between treatments in nutrients allocation patterns occurred 1 d after manipulations were applied. Subsequently, differences between treatments moderated, and values tended to converge by 98 d postmanipulation, when the plants were harvested. Seeds had significantly higher nitrogen concentration levels than leaf or root tissue.
Interspecific Interactions among High Marsh Perennials in a New England Salt Marsh
Authors: Bertness Mark D.
Published: May 2006

High marsh habitats in New England exhibit conspicuous zonation of vascular plants. Spartina patens and Juncus gerardi dominate the seaward and terrestrial borders of the high marsh, respectively, whereas Distichlis spicata is common in disturbed habitats. In this paper I examine the role of interspecific interactions among these marsh perennials in maintaining marsh plant zonation. Removal and transplant experiments were performed to examine species interactions in dense stands. In both types of experiments J. gerardi competitively dominated S. patens and D. spicata, while S. patens competitively dominated D. spicata. Each of these perennials showed maximum growth when transplanted into the J. gerardi zone without neighbors. J. gerardi appears to dominate the terrestrial border of the marsh by competitively excluding S. patens to lower marsh levels, while D. spicata is competitively restricted to disturbed habitats by boty J. gerardi and S. patens. Species interactions during the colonization of bare patches were strikingly different than those found in dense vegetation. Colonization of bare patches by boty S. patens and D. spicata facilitated the colonization of J. gerardi, the competitive dominant in dense vegetation. Bare patches in the high marsh are typically hypersaline due to increased surface evaporation in the absence of plant cover. Patch colonization by competitive subordinates, which are relatively salt tolerant, appears to reduce substrate salinity by passively shading the substrate and, as a by—product, facilitate the invasion of a superior competitor. With interspecific competition in dense vegetation dictates the zonation of New England perennials in the high marsh, secondary succession in this assemblage may commonly be driven by facilitations. This scenario may not be uncommon among assemblages in harsh physical environments where plants or sessile animals ameliorate their physical environment.
Temporal Variation in a Paleolimnological Record Arising from a Trophic Cascade
Authors: Carpenter Stephen R. , Leavitt Peter R.
Published: May 2006

A food—chain model based on trophic cascade theory predicts substantial variance in ecosystem function at time scales near the lifespan of the dominant predator. We tested this prediction using time series (1889—1982) of algal pigment concentrations in annually laminated sediments from a lake dominated by planktivorous fishes with lifespans of 3—5 yr. For pigments that are deposited in sediments mainly by herbivory and are known to be direct indicators of the trophic cascade (alloxanthin, pheophorbide a), variance was pronounced at scales similar to the fish lifespan, consistent with predictions of the model. Several other sedimentary pigments that have mainly pelagic sources (native chlorophylls, a—carotene) also had variance peaks consistent with predictions of the model. Pigments with multiple sources (fucoxanthin, lutein—zeazanthin, b—carotene, pheophytin c) had only weakly significant or nonsignificant variance peaks. Pigments with mainly terrestrial sources (pheophytins a and b) had no variance peaks. These results indicate that some of the variance in this paleolimnological record is due to the trophic cascade. Since the scale of this variance component is °3—5 yr, a 5—yr moving average filters out variance due to the trophic cascade. Residuals from the 5—yr moving average accentuate variance due to the trophic cascade. Filtering the pheophytin time series revealed longer—term cycles (°15 yr), which may arise from terrestrial or climate processes.
The Adaptive Significance of Egg Size and Laying Date in Thick‐Billed Murres Uria Lomvia
Authors: Birkhead T. R. , Nettleship D. N.
Published: May 2006

The effect of egg size and laying date on the fledging mass of Thick—Billed Murre chicks was examined at Cape Hay, Bylot Island, and Coburg Island, Northwest Territories, Canada, to test the idea that late—laying females face a trade—off between the time of egg laying and egg size. There was a seasonal decline in egg volume, and egg volume was correlated with mass and size (wing length) of chicks soon after hatching. Partial correlations showed that larger eggs hatch into heavier, but not larger chicks. Chics hatched early in the season fledged at heaver masses than late—hatched chicks. Hatching mass contributed significantly to this effect, but other factors (e.g., energy intake) were probably also important. A model, based on a multiple regression of the effects of hatching mass and hatching date on fledging mass, shows the possible combinations of egg size and timing of breeding while maintaining a constant fledging mass. Data on the replacement interval and size of replacement eggs suggest that females that lay late may do better (in terms of fledging mass of their chick) to minimize the delay in laying by producing a small egg earlier, rather than delay laying further in order to produce a larger egg. This is because they are unable to accumulate nutrients at a fast enough rate to make a delay worthwhile. This suggests that the seasonal decline in egg size is an adaptive response to a seasonal deterioration in environmental conditions.