bluuebunny/crossref_metadata_2025 huggingface dataset:
Determinants of Variation in Tropical Forest Primate Biomass: New Evidence from West Africa
Authors: Oates John F. , Whitesides George H. , Davies A. Glyn , Waterman Peter G. , Green Steven M. , Dasilva Georgina L. , Mole Silon
Published: May 2006

To explore sources of variation in tropical forest primate biomass, and, in particular, to test the hypothesis that soil conditions are a major ultimate determinant of the biomass of colobine monkeys and other primates, we compared data on the soils, vegetation, and primate community at a site in West Africa (Tiwai Island, Sierra Leone) with information from other sites, especially two other African sites (Douala—Edea in Cameroon, and Kibale Forest in Uganda). The biomass of eight anthropoid primate species in old secondary high forest on Tiwai was estimated from data on population densities assessed by transect samples combined with data on social group densities and individual body masses. Samples of soil and tree foliage were collected at the same site, and subjected to a variety of chemical and mechanical analyses. Our estimate of anthropoid biomass at Tiwai is 1229—1529 kg/km2, including 682—889 kg/km2 of colobines. This is one of the highest primate biomasses recorded anywhere. The soils at Tiwai were found to be relatively high in sand content and low in pH, and to have low levels of mineral nutrients. Levels of condensed tannins in the mature foliage of the trees comprising a major part of the forest canopy were higher than at other sites, but the ratio of protein to fiber in this foliage was also higher than at any other site except Kibale. It is argued that a wide range of environmental factors affect primate population densities, and that nutrient—poor soils and high tannin levels in tree foliage do not necessarily produce a low primate (or colobine) biomass, as some earlier studies had suggested. Furthermore, seeds (an important food source for Tiwai colobines) are apparently a common part of the colobine dietary repertoire and are not consumed largely as a response to a scarcity of digestible foliage.
Gastrointestinal Helminth Communities of Bobwhite Quail
Authors: Moore Janice , Simberloff Daniel
Published: May 2006

We found 12 species of intestinal helminths in 158 Northern Bobwhites (Colinus virginianus) in northern Florida (1983—1984). Of these, six species were common: the cestodes Raillietina cesticillus and R. colinia, the cecal nematodes Heterakis isolonche and Trichostrongylus tenuis, the proventricular nematode Dispharynx nasuta, and the gizzard nematode Cyrnea colini. Four pairs of species had statistically significant numerical associations: the cestodes were negatively associated, and positive associations existed between the cecal nematodes, R. cesticillus—D. nasuta, and H. isolonche—C. colini. When either cecal nematode was present in high densities, H. isolonche shifted its location, indicating a possible negative interaction. There were some intraspecific relationships between cestode density and mean location, variance, and biomass. In addition, R. cesticillus biomass was negatively correlated with R. colinia density. This community, while not characterized by high species richness, is readily colonized and exhibits evidence of inter— and intraspecific interaction. It does not conform to current models of parasite community structure.
Food Provisioning by White‐Tailed Tropicbirds: Effects on the Developmental Pattern of Chicks
Authors: Schaffner Fred Charles
Published: May 2006

Food provisioning of White—tailed Tropicbird (Phaethon lepturus) chicks by their individually identified parents was studied at Cayo Luis Pena, Puerto Rico, in 1985—1986. This paper describes the pattern of this provisioning from the perspectives of both the chick receiving the food, and the individual parents delivering the food. The interval between feedings delivered by an individual adult was more variable than food payload mass (higher coefficients of variation), and there was no day—to—day relationship between the feeding interval and feed mass. Moreover, adults demonstrated the ability to lift and transport food payloads substantially larger than the mean feed mass. Energetic considerations suggest that there is strong selection for parents to decrease the feeding frequency and increase feed mass, to some limit imposed by either the limits of the parents' delivery capabilities, or the limits of the chick's food receiving (swallowing) capabilities (the volume a chick can ingest in one feeding bout). In fact, the limits of the chick's swallowing capabilities occur well before the parents' delivery limits are reached, and thereby set the feed mass at a weight and volume that is easily within the adults' lifting and transporting capabilities. The mean feed mass is viewed as reflecting a particular “target” payload mass that parents strive to collect as quickly as conditions, and their own individual foraging abilities, will allow, and is a practical compromise between the short—term interests of the chick and those of the adult. While parents are able to collect an abundance of food for their single chick, their pelagic foraging creates an intermittent, or “feast or famine” feeding situation for the chick which promotes the characteristic developmental pattern of slow growth and large fat accumulations. The developmental pattern of White—tailed Tropicbirds and other pelagic birds may be better understood by examining the temporal pattern of feeding, and thus there is a need for more comparative and experimental ecological and physiological studies focusing on patterns of food delivery and their possible effects, as well as the average rate of energy flow.
Functional Interactions among Traits that Determine Reproductive Success in a Native Annual Plant
Authors: Farris Michael A. , Lechowicz Martin J.
Published: May 2006

We grew cocklebur, Xanthium strumarium L. (Compositae), in an experimental garden and monitored a variety of morphological, physiological, and phenological traits known to have a significant influence on plant productive success. We used a hierarchical series of multiple regression analyses to generate a path diagram explaining the interacting contributions of individual traits to the numbers and size of fruits produced by individual plants. Fruit production was strongly positively correlated with plant vegetative biomass, and fruit size was negatively correlated with the total number of fruits produced. Although larger plants produced more fruit, there was also a significant direct effect of the timing of anthesis on total fruit numbers; plants in this determinate species that flowered later produced more fruit. The influence of all other traits on reproductive success was indirect through their influence on plant size. Plants with higher water—use efficiencies early in the season produced leaves more quickly, while plants which emerged earlier grew more rapidly in height. These faster growing plants had a higher vegetative biomass and consequently a greater reproductive success. Latter emergence also had a direct positive influence on plant size, demonstrating that a single trait can have significant but counteracting influences on final reproductive success. These results demonstrate the utility of an inductive approach in analyzing the actual functional pathways by which diverse traits influence growth and reproduction at the whole plant level.
Prey Size Selection in Dungeness Crabs: The Effect of Claw Damage
Authors: Juanes Francis , Hartwick E. B.
Published: May 2006

We investigate prey size selection by Cancer magister, a decapod crustacean, feeding on Protothaca staminea, a hard—shelled venerid clam, and test predictions of the optimal diet model using three different currencies. We also evaluate the effect of claw damage on crab feeding efficiency. To model parameters measured were: energy content of the prey, energy cost of predation, and handling time. All of these variables were positive exponential functions of clam size. The different measures of prey value (or profitability) provided contrasting prey rankings. Both net and gross rates of energy intake [(Benefit–Cost)/Time and Benefit/Time, respectively] predicted that the largest clams were the most profitable. Energetic efficiency (Benefit/Cost) predicted that the smallest claim sizes were the most profitable. Prey—size selection experiments, offering crabs mixtures of two or three clam size classes, showed that crabs always ate more clams from the smallest clam size class offered. Thus the predictions from the energetic efficiency model provide the best fit to the results. The use of energetic efficiency as a currency requires energy cost to be limiting over the animal's lifetime. In this study we propose claw damage, defined as chela breakage and claw—tooth wear, as a consequence of fatigue failure (breakage of a structure due to repeated loading), to be a limiting cost. A field study of a natural population of C. magister indicated that levels of wear and breakage were significant, and were related to sex and molting state. Laboratory experiments showed that crabs with broken claws were unable to crack clams. Crabs with artificially worn claw teeth had significantly longer handling times than undamaged crabs. Finally, the ecological effects of claw breakage in decapods are evaluated with reference to growth, molting ability, regeneration load, and reproductive success.
The Effects of Variable Settlement and Early Competition on Patterns of Kelp Recruitment
Authors: Reed Daniel C.
Published: May 2006

Recruitment from newly settled propagules is an important process in the population dynamics of many species especially those living in highly disturbed areas and subjected to frequent local extinctions. For many primitive plants such as kelps (large brown algae in the order Laminariales), the process of recruitment (i.e., the first appearance of macroscopic individuals) is quite complex and requires the successful completion of an alternate microscopic free—living sexual stage. To experimentally investigate the consequences of variable spore settlement and early (i.e., prerecruit) competition on the recruitment patterns of the sympatric sublittoral kelps Macrocystis pyrifera and Pterygophora californica, I seeded bare rock substrates with known densities of spores of the two algae in both single— and mixed—species assemblages. Results from 12 field experiments done over 3 yr indicated that for both kelps, a minimum density of at least 1 spore/mm2 was needed for successful recruitment. This minimum density was probably determined in part by the maximum distance that could separate male and female gametophytes while still allowing fertilization to occur. Although greater spore density often resulted in higher numbers of sporophyte recruits, strong density—dependent mortality still occurred whenever there was recruitment. The requirement for spores to settle at relatively high densities (i.e., >1 spore/mm2), coupled with the drastic difference in size between spores (0.01 mm) and early recruits (20 mm), insures that density—dependent mortality will occur at early stages in these algae.

“Safe sites” for the recruitment of kelp were highly variable in time; recruitment of both kelps varied significantly among experiments and was negatively correlated with the natural recruitment of ephemeral species of filamentous brown algae. Differences in postsettlement mortality between Macrocystis and Pterygophora often caused patterns of sporophyte recruitment to vary from those of initial spore settlement. In monospecific treatments, the recruitment rates of the two kelps usually differed in the same experiment, indicating they responded differently to the same environmental conditions. In mixed—species treatments, interspecific competition between microscopic prerecruit stages also caused species—specific differences in early mortality. Pterygophora spore settlement generally inhibited the recruitment of Macrocystis at both high (750—1500 spores/mm2) and low (10—20 spores/mm2) densities. Competition between the two kelps was asymmetrical; Macrocystis settlement had no effect on Pterygophora recruitment. Thus, changing environmental conditions and competition among early microscopic stages modified the ways in which spore settlement influenced sporophyte recruitment. The effects of these factors on kelp recruitment were interactive, and their relative importance will undoubtedly vary with species, location, and time.
Species Packing in Caribbean and North Temperate Ant Communities
Authors: Culver David C.
Published: May 2006

Short—term competition was examined in ant communities in West Virginia, Michigan, Puerto Rico, and St. John (U.S. Virgin Islands), by baiting with tuna fish. Species in Puerto Rico, where resource accrual was more rapid, had broader niches than in West Virginia. Niche breadths were not related to colony size, worker size, or aggressiveness. In forest areas, there was good agreement between observed and expected numbers of species per area estimated from the mean value of the competition coefficients (α) and the covariance of α. Niche breadths of ant communities in grassy areas were reduced by aggression between species. Given lack of aggression, competition coefficients predicted more species than observed in the grassy areas, an indication that aggression reduced species diversity. Competition for nest sites increased between—habitat diversity and foraging niche breadth.
Comparative Photosynthetic and Respiratory Gas Exchange Characteristics of Atriplex Lentiformis (Torr.) Wats. in Coastal and Desert Habitats
Authors: Pearcy R. W. , Harrison A. T.
Published: May 2006

Field measurements of the photosynthetic gas exchange characteristics of Atriplex lentiformis (Torr.) Wats. were conducted in both a coastal and an interior desert habitat. Despite large differences in habitat temperature, the diurnal course of CO2 exchange of the coastal and desert shrubs were remarkably similar. Maximum CO2 uptake rates and stomatal conductances to water vapor were similar in both habitats and occurred during midday when irradiance was highest. Measurement of the temperature dependence of photosynthesis revealed marked differences between the coastal and desert shrubs. The thermal optima for photosynthesis were 32°C in the coastal and desert shrubs respectively. At temperatures below 36°C rates of CO2 uptake were higher in the coastal shrubs than in desert shrubs, whereas at higher temperatures the reverse was true. These differences in temperature dependence coupled with the differences in leaf temperatures in the coastal and desert habitats result in nearly equal rates of CO2 uptake measured under temperature and light regimes similar to natural conditions in the respective habitats.
Quantitative Genetic Models for the Coevolution of Character Displacement
Authors: Taper Mark L. , Chase Ted J.
Published: May 2006

The evolution of character displacement in competition communities was simulated with two quantitative genetic models. The first model is identical to that of Slatkin (1980) but we extend his analysis. The second model allows for the evolution of all niche attributes that affect interspecific competition along a resource axis. These are: the mean position of each species along the axis, the variation in position between phenotypes within each species, and the width of resources used by each phenotype. In addition, explicit dynamics for the resources are included in the model. This model predicts that character displacement can occur in coevolutionary communities. It also predicts that the relative niche separations between species (d/w ratios; d = distance between peaks of two species' niches on the resource (niche) axis, w = total niche width of a species) can be quite large, that the d/w values should decrease as species number increases, that at the evolutionary equilibrium, the within—individual component of the niche width will be much larger than the between—individual component, and that niche separation should be substantially smaller than character separation. These predictions are all in agreement with field observations surveyed from the literature.
Resource Utilization by Desert Quail: Time and Energy, Food and Water
Authors: Goldstein David L. , Nagy Kenneth A.
Published: May 2006

Time—energy budgets (TEB) of Gambel's Quail (Callipepla gambelii) were compiled during two summers in the Colorado Desert of California. Quail spent 6.77 h/d foraging, 6.2 h/d inactive during daylight hours, and 11.02 h/d inactive at night. Field metabolic rate (FMR) calculated from this activity budget was 81.8 kJ/d. Of this, 47.3 kJ/d was expended during foraging, 12.6 kJ/d in daytime inactivity, and 20.4 kJ/d in nighttime inactivity. Despite the extremely hot thermal environment (maximum ambient temperature °45°C), there was no energy cost above resting levels for thermoregulation. FMR was also measured simultaneously with doubly labeled water (DLW), and averaged 90.8 kJ/d. TEB and DLW values agreed to within 6% when differences in measurement period were taken into account. A laboratory validation study indicated that DLW and balance methods agreed to within 5%. The FMR of C. gambelii was only 40% of that predicted for a bird of its body mass. This low FMR is primarily the result of a low resting metabolic rate (RMR): 51% of the predicted basal rate in 1981, and 70% of predicted in 1982. The basis and significance of this low and variable RMR are unclear. Energy assimilation efficiency, measured in laboratory feeding experiments with a mixed seed and arthropod diet, was 60.3%. An individual quail in the field thus required 150.3 kJ/d in its diet, representing a dry matter intake of 8.1 g/d. A diet of seeds alone provides insufficient water for Gambel's Quail in summer, so they must either incorporate moist food items in their diet or drink free water. It was calculated that over the course of a year, a population of Gambel's Quail consumes seeds with a total energy content °15% as great as that in seeds consumed by a population of desert rodents or harvester ants in the same area. Gambel's Quail thus may be important factors in the competition for resources among desert granivores, particularly because they can eat one of their competitors (harvester ants).
Responses to Anoxia during Simulated Hibernation in Northern and Southern Painted Turtles
Authors: Ultsch Gordon R. , Hanley Robert W. , Bauman Thomas R.
Published: May 2006

The painted turtles, Chrysemys picta, with four subspecies, have the largest range and most northern distribution of any North American freshwater turtle. C. p. bellii in Canada may hibernate for as much as 6 mo, while C. p. dorsalis on the Gulf Coast may not hibernate at all. We subjected both subspecies to simulated hibernation conditions by submerging them in anoxic water at 3°C without access to air to compare physiological responses. Initial acid—base and ionic statuses of animals acclimated to 3° were the same in both subspecies. As anoxia continued, both subspecies showed similar changes in all measured parameters, but the rates of change were greater in dorsalis than in bellii. By day 46, the plasma pH of dorsalis had fallen to 6.96, a change that required °180 d in bellii. By day 38, the acidosis was entirely due to lactate formation in both groups, and it had induced compensatory changes in ionic concentrations, particularly large increases in total Ca and total Mg in the blood. We conclude that the only adaptation required of bellii to enable it to endure longer winters than dorsalis is an ability to limit lactate accumulation, by having either a lower metabolic rate and/or a great ability to eliminate lactate. It is known that hibernation in a normoxic environment would be less stressful physiologically than in an anoxic one, but turtles apparently choose the latter. We suggest that the physiological stress of prolonged anoxia and the requirements of subsequent recovery in the spring are outweighed by considerations of predator avoidance during the winter. Tolerance of the physiological perturbations resulting from prolonged anoxia may limit the northern distribution of freshwater turtles.
Settlement Cues and Determination of the Vertical Limit of an Intertidal Barnacle
Authors: Raimondi Peter T.
Published: May 2006

The settlement behavior of the barnacle Chthamalus anisopoma near its upper intertidal limit was investigated using field surveys and experiments. The upper limit of Chthamalus was found to be extremely variable, ranging from 1.5 to 2.6 m above MLW. Chthamalus showed increased settlement in response to chemical cues produced by several species whose vertical distributions overlapped with its vertical distribution. Within a single species there was significantly more settlement in response to cues associated with Nertia funiculata that occurred with Chthamalus than to N. funiculata that occurred only above the vertical limit of Chthamalus. Another species that induced settlement, Acanthina angelica, is the major predator of adult Chthamalus. Acanthina may be a good settlement cue because it is a reliable indicator of the vertical distribution of Chthamalus and because (1) the clusters of Acanthina that induced settlement may move away before the new barnacles become edible; and (2) Chthamalus can develop a predator—resistant morphology in responses to Acanthina. I was also able to induce Chthamalus recruitment into areas well above their normal upper limits using a conspecific extract, indicating that conspecifics function as a strong settlement cue. The evolution of larval attraction to settlement cues should be dependent on the reliability of the cues and the consequences of not using them. Reliable cues and harsh consequences should lead to the development of "strong" (i.e., attractive) cues. However, reliable cues may be conservative; their absence may not indicate a "bad" settlement site. Therefore, a variable distribution of strong settlement cues could lead to temporal and spatial variability in a species regardless of other factors such as pre— and postsettlement physical conditions or biological interactions.
Structural Function of Buttresses of Tachigalia Versicolor
Authors: Warren Steven D. , Black Hal L. , Eastmond David A. , Whaley Wayne H.
Published: May 2006

To the test the hypothesis that buttresses serve as tension members for structural support of lowland tropical trees, measurements were made of 518 buttresses from 100 Tachigalia versicolor trees. Buttress size, particularly buttress height, increased at a more rapid rate than tree size or number of buttresses. No significant polar orientation was found in the distribution of individual buttresses relative to prevailing wind direction or to the direction of tree lean. However, buttresses that were, by chance, oriented into the prevailing wind, or located on the side of a tree opposite the direction of a visually perceptible lean, tended to be longer, taller, and more voluminous. The concentration of buttress tissue on the windward side of trees and on the side opposite the direction of declination suggests that proliferation of buttresses is a response to wind—induced and lean—induced stresses and that buttresses serve a function as tension members providing structural support to this species. While direction of lean was somewhat dependent upon wind direction, the constant unidirectional stress exerted by a leaning bole was more significantly related to buttress size proliferation than was the stress exerted by wind alone.
Population Development of Rain Forest Trees on a Chronosequence of Hawaiian Lava Flows
Authors: Drake Donald R. , Mueller-Dombois Dieter
Published: May 2006

The purpose of this study was to compare forest structure on a series of geologically similar larva flows that differed in age, but not in climate or in accessibility to pioneer plants. The data were then used to infer the patterns of forest development over 3000 yr on a single flow. Stand structure was measured for populations of Metrosideros polymorpha, other canopy tree species, and tree ferns on a chronosequence of lava flows aged 47, 137, °300, °400, and °3000 yr, in the montane rain forest zone on Mauna Loa, Hawaii. The upper stratum of vegetation at all sites was dominated by M. polymorpha; populations of other trees were relatively sparse throughout the study area. For M. polymorpha populations, the basal area per hectare increased, at an ever—decreasing rate, as flow age increased; population densities of seedlings, samplings, and trees peaked on the 137—yr flow, then declined, apparently through self—thinning and wind—throw, with further increases in flow age. The decrease in M. polymorpha population density on older flows was accompanied by an increase in the density of tree ferns, which formed a closed subcanopy on the 3000—yr flow, and may have inhibited regeneration of M. polymorpha. Among M. polymorpha trees there was a successional transition from pubescent varieties on the three youngest flows to glabrous varieties on the oldest flow. A comparison between plant populations on the chronosequence and on one other flow, aged °1400 yr but containing some volcanic ash, indicated that ash may alter some aspects of forest development.
Geographic Variation in Winter Fat of Dark‐Eyed Juncos: Displacement to a Common Environment
Authors: Rogers Christopher M. , Nolan Val , Ketterson Ellen D.
Published: May 2006

Main small temperature—zone birds fatten in winter and use this reserve when food becomes unavailable. The winter body mass of migratory Dark—eyed Juncos (Junco hyemalis) usually is greater where severe weather is more frequent, i.e., at higher latitudes or altitudes. The mechanism responsible for this geographic variation is unknown, and we asked whether geographically separated populations are composed of birds with different capacities or tendencies to fatten. We sampled the lipid index (LI, grams of lipid per gram of lean dry mass) of free—living juncos at three latitudes in two winters and found geographic variation. However, the pattern of variation in LI at the three latitudes was not consistent, either within or between winters. We also displaced wintering juncos from northern, intermediate, and southern sites and exposed them to a common environment in Indiana. One group of displaced birds was released in natural junco habitat (during three winters), and another was held outdoors in captivity (during two winters). Many released birds remained nearby, and when we recaptured some of them in late winter the LIs of the three geographic subgroups were statistically indistinguishable. It was also indistinguishable from the LI of juncos sampled at that time from the free—living Indiana population. Among the displaced birds that we held captive, we found no differences among the geographic subgroups either in LI or total body mass. In one of the years, late—winter LI and body mass of the captives did not differ from values for the released group or from values of newly caught Indiana juncos, but in the second year values for the captives were lower. Our results indicate the geographic variation in winter fattening of juncos is not a population—specific trait that persists independently of current environmental information and that it probably reflects a response to local environmental conditions. To our knowledge, this is the first experiment using free—living birds to test the role of the environment in maintaining geographic variation in a life history trait in the nonbreeding period.
Diatom Community Structure Along Physicochemical Gradients in Saline Lakes
Authors: Blinn Dean W.
Published: May 2006

Relationships between diatom assemblages and physiocochemical factors were examined in 63 saline lakes in western North America. Sodium was the overwhelmingly dominant cation in the lakes examined; lakes above 47° latitude were dominated by SO4—2, and lakes below 47° were dominated by CO3—2 and Cl—1. This latitudinal gradient for anions was correlated with the distribution and community structure of diatoms. Sixty—two taxa comprised >85% of the total diatom relative abundance in the saline environments. There were strong negative correlations between specific conductance and diversity and species richness, however pH and major cations showed limited predictive value. Cluster analyses identified diatom assemblages along specific conductance and major anion gradients. Indices for specific conductance and major anions were also developed for 62 diatom taxa. These diatom indices provide useful information to interpret past and present physicochemical conditions in lacustrine ecosystems. Greatest diversity was found in habitats with ionic concentrations < seawater and ion composition similar to marine environments. Principal components analyses comparing loadings for major cations and anions, ionic concentration, and diatom community structure suggested that shallow saline lakes may have provided evolutionary pathways for speciation of marine pennate diatoms into athalassic (nonmarine) environments.
Nutrient Dynamics in Slash Pine Plantation Ecosystems
Authors: Gholz H. L. , Fisher R. F. , Prichett W. L.
Published: May 2006

Changes in the distribution and cycling of N, P, K, Mg, and Ca were investigated in plantations of splash pine (Pinus elliottii var. elliottii) using an age sequence of replicated stands 2, 5, 8, 14, 18, 26 and 34 yr old. All stands had a similar history of management and occurred within 20 km on somewhat poorly drained Ultic Haplaquod soils in northern Florida. Because of the rapid colonization of these sites by grasses, plant nutrient uptake was already high at age 2 yr. Thereafter, uptake of N, P, K, and Mg increased <50% to a maximum at 8 yr, around the time that maximum leaf area for these stands is reached. Ca uptake increased 130% over this time. Uptake declined after age 8 yr for all elements. Nutrient return in litterfall remained relatively constant after 5 yr. Canopy leaching, estimated as the difference between bulk precipitation and throughfall, was negligible for N and P, but highly significant for all three cations. K leaching from the canopy was greatest and amounted to °60% of litterfall in mature stands. Internal redistribution of mobile elements (N, P, K) in the vegetation was negligible until the pine canopy closed, but then increased greatly. From 2 through 26 yr, vegetation nutrient contents increased much more than nutrient uptake rates. The surface soil of the youngest stands appeared to be enriched by material added during site preparation. The nutrient content of the Bh horizon increased through the 8th yr, indicating a downward movement of the added material. Soil contents (to 100 cm depth) of total N and double—acid extractable P and cations then decreased over time, with the greatest decline during the first 18 yr. Forest floor contents increased at a constant rate, with no plateau indicated through 34 yr. Annual precipitation inputs of nutrients varied from 0.3 kg/ha for P to 13.5 kg/ha for N, with cation values of 2.6—5.0 kg/ha. Annual ecosystem balances of N, P, K, and Ca appeared slightly positive, while the content of Mg appeared to decline. Nutrient use efficiencies (net primary production ° uptake) increased greatly with time and were very high in older stands, especially for P. However, it appears that mineralization processes in these very nutrient—poor systems and the small atmospheric inputs cannot supply the annual nutrient requirements of mature stands, especially for P; this leads to a cessation of vegetative biomass increment around age 26 yr.
Local Coexistence of Deciduous‐Forest Groundlayer Species Growing in Different Seasons
Authors: Rogers Robert S.
Published: May 2006

In 10 stands of deciduous forest, evidence was sought for competitive inhibition between groundlayer species photosynthetically active in different seasons. In each stand, the forest floor had probably not been disturbed catastrophically for >50 yr, thus favoring detection of cumulative competitive effects. The underlying hypothesis was that long—lived species occupying the same microsites but not competing directly for light may, nevertheless, interfere with each other's growth by seasonal depletion of labile soil nutrients. For a plot size that holds, on average, two species, coefficients of rank correlation were computed, stand by stand, between the cover values of (1) species that are in leaf only through early spring, and (2) species that leaf out later in the growing season. Fewer than 5% of the correlations were significantly negative at the 5% level, indicating that competition between phenologically distinct plants may be too weak or sporadic to affect local species patterns. The magnitude of negative correlations, or the percentage of significant negative correlations, was, however, greater than average between certain abundant species thought to be liberal in uptake of labile nutrients. This was most pronounced for correlations between Erythronium americanum, a spring—ephemeral herb, and Parthenocissus quinquefolia, a summer—active shrub with relatively indeterminate shoot growth. Another result suggesting nutrient—based competitive inhibition was a 50% lower mean cover for two nutrient—demanding summer—active species (Acer saccharum and Ulmus rubra, both abundant as groundlayer plants) in plots with an exceptionally high density of shoots in early spring. In contrast, the pooled cover sums for all summer—active species were unaffected by locally high densities of shoots in early spring.
Fruit‐Size, Gape Width, and the Diets of Fruit‐Eating Birds
Authors: Wheelwright Nathaniel T.
Published: May 2006

In most animals, especially those that must swallow food items whole, prey size is related to predator size. This paper examines gape limitation and the influence of fruit size on diet in fruit—eating birds, drawing on data gathered over a 5—yr period on 70 bird species and 171 plant species in the lower montane forests of Monteverde, Costa Rica. The results suggest that fruit—eating birds face many of the constraints imposed on other gape—limited foragers, but have an unusual minimum—size relationship with their food because of the unique characteristics of fruits. Fruit—eating birds with broad gapes consumed more lauraceous fruit species and a larger mean and maximum size of fruits overall than narrow—gaped birds. However, the size of the smallest fruits eaten was not correlated with gape width; large—gaped species commonly fed on diminutive fruits. Birds effectively selected among individual fruits within a tree on the basis of fruit size, dropping bulky fruits beneath the tree. Effective size selectivity also occurred among trees of different species in the same family and among plant species in various families. The diet of broad—gaped birds was not comprised differentially of large fruit species. For example, Three—wattled Bellbirds favored medium—sized fruits, whereas Long—tailed Manakins took individual fruits in the same proportions as they took fruit species of different mean fruit diameters. Gape limitations and effective size selectivity have obvious consequences for seed dispersal patterns: Plants with large fruits attracted fewer species of birds than plants with small fruits. Moreover, the broad—gaped bird species on which large—fruited plants specialized were those with the most generalized diets.
Asynchronous Hatching in the Pied Flycatcher: An Experiment
Authors: Amundsen Trond , Slagsvold Tore
Published: May 2006

David Lack's “brood reduction hypothesis” to explain asynchronous hatching has recently been tested experimentally on several altrical species of birds. However, for most studies it is not known whether a food shortage occurred or not. We induced food shortage by removing the male parent shortly after hatching, in Pied Flycatcher (Ficedula hypoleuca) broods with experimentally reduced and increased asynchrony. The broods were adjusted to an initial size of five. Broods with reduced and increased asynchrony showed a similar degree of partial mortality, fledging on average 3.3 and 3.5 young, respectively. In broods with both parents present and a normal level of asynchrony, all the young fledged. Mean fledgling body masses in reduced (12.6 g) and increased asynchronous (13.1 g) uniparental broods were also similar, and significantly lower than that of biparental broods (14.6 g). Pronounced nestling size hierarchies developed in both types of experimental broods, and female body mass losses during the nestling period were similar. The results demonstrate that, in the Pied Flycatcher, asynchronous hatching is not necessary for the achievement of brood reduction. The differences between broods with reduced and increased asynchrony in numbers and body masses of fledged young were not statistically significant, but were in the direction predicted by the brood reduction hypothesis. The results are inconsistent with Lack's original formulation of the hypothesis, but not with a recent life history modification, which states that asynchrony increases parental efficiency rather than within—season nestling survival.
Numerical and Functional Responses of Kestrels, Short‐Eared Owls, and Long‐Eared Owls to Vole Densities
Authors: Korpimaki Erkki , Norrdahl Kai
Published: May 2006

We studied numerical and functional responses of breeding European Kestrels (EK) (Falco tinnunculus), Short—eared Owls (SO) (Asio flammeus), and Long—eared Owls (LO) (Asio otus) during 1977—1987 in 47 km2 of farmland in western Finland. The pooled mean yearly breeding density varied from 0.1 to 2.4 pairs/km2. The number of nesting EKs (range 2—46 pairs), SOs (0—49), and LOs (0—19) fluctuated in close accordance with the spring density of Microtus (M. agrestis and M. epiroticus) voles. The mean yearly number of fledglings produced per pair ranged from 0.4 to 3.8 and, for each species, was positively correlated with spring density of Microtus voles. Due to their high degree of mobility, EKs, SOs, and LOs were able to track the population fluctuations of their microtine prey without time lags. An increase in microtine densities caused a rapid immigration into the study area and a decrease caused a rapid emigration from the area. Microtus voles were the most important prey group by mass in the diet of each species. Water voles, bank voles, shrews, and small birds were the most frequent alternate prey. The spring density of Microtus spp. was positively correlated with the percentage of these voles in the diet of EK, SO, and LO. The pooled functional response curve of these three raptor species to the fluctuating densities of Microtus spp. was close to linear, indicating that consumption rates are independent of vole densities. Breeding EKs, SOs, and LOs seemed to take a larger proportion of voles available in peak years than in low ones.
Interactions Between the Salamander Siren Intermedia and the Keystone Predator Notophthalmus Viridescens
Authors: Fauth John E. , Resetarits William J.
Published: May 2006

Is the ability to function as a keystone predator a property of a species or an emergent property of the community? We discussed this question in a temporary—pond community where the broken—striped newt Notophthalmus viridescens dorsalis is known to act as a keystone predator on larval anurans. We independently manipulated the initial density of adult Notophthalmus (two or four) and the presence or absence of one adult Siren intermedia in a set of 20 artificial ponds to determine if this additional predator affected the ability of Notophthalmus to function as a keystone predator. Each pond received a diverse assemblage of larval anuran prey: a spring—breeding assemblage of 275 Rana utricularia, 100 Pseudacris crucifer and 25 Bufo americanus tadpoles, and a summer assemblage of 200 Hyla chrysoscelis and 150 Gastrophryne carolinensis tadpoles. Two additional pond received neither predator, to assay the outcome of competition among the tadpoles. The effect of the salamander Siren on Notophthalmus survival and fecundity depended on the density of Notophthalmus. At low newt density Siren had no effect on survival, but at high newt density competition reduced the survival and growth rates of Notophthalmus. The density of Notophthalmus and the presence of Siren interacted to determine the fecundity of Notophthalmus. At low newt density Siren reduced Notophthalmus reproductive success by preying on larvae. At high newt density Siren indirectly enhanced reproductive success by reducing survival of adults, thus releasing larvae from intraspecific competition and cannibalism. Notophthalmus density had no effect on adult Siren survival or growth rate in this experiment, but other evidence indicates that competition with Notophthalmus reduces the growth rates of Siren. Notophthalmus acted as a keystone predator on the assemblage of spring—breeding anurans; it increased the number of metamorphs of the weak competitor Pseudacris crucifer by releasing them from interspecific competition. Siren preyed on tadpoles in a nonselective manner. An additive model was sufficient to describe the effects of Siren and initial density of Notophthalmus on the structure of the tadpole assemblage. In our system of experimental ponds, the strong interaction between Siren and Notophthalmus density did not extend its effects to lower trophic levels, and the direct and indirect effects of Siren did not alter the role of Notophthalmus as a keystone predator.
Effects of Geothermal Groundwater on Nutrient Dynamics of a Lowland Costa Rican Stream
Authors: Pringle Catherine M. , Triska Frank J.
Published: May 2006

Spatial and temporal variability of surface and groundwater nutrient chemistry was contrasted between two tributaries of the Salto River, which drain the terminus of Pleistocene lava flows in the Atlantic slope foothills of Barva Volcano, Costa Rica. Some riparian zones along the Salto are saturated by subsurface inflows of phosphorus—rich, geothermal groundwater of the sodium—chloride—bicarbonate type. The heterogenous pattern of solute—rich groundwater inflows results in dramatic differences in soluble reactive phosphorus (SRP) concentration between stream waters of two closely adjacent tributaries. SRP levels also vary dramatically in the water table and in soils across stream riparian zones on a scale of metres. The Salto River (SRP 50—200 mg/L) receives steady phosphorus—rich groundwater inflows that become diluted with increasing precipitation. The Pantano lacks three inputs and retains a low background SRP concentration (typically <10 mg/L). SRP levels in waters of the Salto were strongly negatively correlated with discharge (r = —0.86), while in the Pantano there was no correlation. In situ nutrient bioassays of algal periphyton growth indicated that both nitrate and SRP were at growth—saturating levels in the Salto while, in the Pantano, algal growth was phosphorus limited. The Pantano had a high retention capacity for phosphorus as measured through a whole—stream tracer injection experiment. SRP concentration was reduced by 17 and 94% of injected phosphate over 40 and 800 m reaches, respectively. Results indicate the important linkage between geothermal activity and hydrogeochemical features of the volcanic landscape and their role in regulating ecological processes in these streams.
Seasonal Variation in Pollination Dynamics of Sexually Dimorphic Sidalcea Oregana SSP. Spicata (Malvaceae)
Authors: Ashman Tia-Lynn , Stanton Maureen
Published: May 2006

We explored the combined effects of seasonal variation in both pollinator assemblage and availability of pollen donors on pollination in a gynodioecious species, Sidalcea oregana ssp. spicata (Malvaceae). Hermaphrodites produced flowers with significantly larger petals but maintained fewer open flowers per inflorescence than females. Flowers of hermaphrodites produced 50% more nectar sugar in the 24 h after anthesis than the flowers of females. Nectar sugar production was also significantly and positively correlated with petal length. Pollinator visitation rates were influenced more by differences in petal length than by differences in flower number per inflorescence. Consequently, hermaphrodites experienced higher visitation rates on a per—flower basis. Female flowers tended to receive pollen at a lower rate than hermaphrodites, but remained in the receptive female—phase longer than hermaphrodites. On average, the length of the period of flower receptivitiy declined as pollen deposition rate increased. These opposing processes resulted in the sex morphs receiving equivalent levels of pollination. Seasonal variation in the rate of pollen reception was more strongly influenced by the efficiency of the available pollinator pool than by rates of visitation. Dramatic seasonal shifts in the composition of the pollinator assemblage and pollen availability were correlated with increased pollination intensity as the season progressed. Not only were more pollen grains received, but they arrived in a shorter period of time and the number of potential pollen donors (hermaphrodites) increased. These findings suggest that pollen competition in both sex morphs may be more intense late in the season.
Plant Size Effects on Female and Male Function in Hermaphroditic Sabatia Angularis (Gentianaceae)
Authors: Dudash Michele R.
Published: May 2006

Variation in the contribution of different—sized individuals to female and male function was examined for the extremes of a size—structured population of hermaphroditic Sabatia angularis (Gentianaceae). Local populations of S. angularis at Miller Dunes, Indiana consisted of 10—15% large plants (>25 flowers) and °50% small plants (<7 flowers). Components of female function studied were (1) pollen grain deposition of stigmas, (2) probability of fruit set, (3) seed production per fruit, (4) average seed mass per fruit, and (5) seed dispersal distributions. Components of male function examined were (1) pollen production on a per flower basis, (2) pollen removal rates, and (3) pollinator observations and fluorescent dye experiments to infer pollen movement. Large plants contributed disproportionately through female and male function to the production of offspring compared to small plants. In one of the two years examined, the proportion of flowers developing into fruits was significantly greater in large plants than small plants. Seed production per fruit was overall twofold greater for fruits of large plants than small plants. Plant size had no effect on mean seed mass per fruit or the distance of primary and secondary seed dispersal. Flowers of large plants produced significantly more pollen per flower and had significantly more pollen grains deposited on their stigmas than flowers of small plants. However, there was no difference in the proportion of pollen removed from flowers of small and large plants, although the absolute number of pollen grains removed was greater for large plants. Large plants appeared to have the potential for more geitonogamous pollinations than small plants.