bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth, Mortality, Fecundity, Biomass and Productivity of Four Lake Populations of the Prosobranch Snail, Viviparus Georgianus
Authors: Browne Robert A.
Published: May 2006

Studies were carried out on natural populations of the freshwater prosobranch snail, Viviparus georgianus, located in 4 mesotrophic lakes in upstate New York. Viviparus are among the dominant members of the benthic fauna at the second trophic level in these localities. A growth survey involved regular sampling for measurements of growth, fecundity, mortality, and biomass production. Viviparus georgianus were variable in ♀ life span, with 2 populations having a 36—mo maximum life and the remaining 2 populations having a 28—mo maximum life. Maximum life span of ♂ ♂ was similar in all populations at 21—22. Analyses of growth and biomass production as organic carbon and total nitrogen were utilized to estimate standing crop biomass leading to productivity rates, and of changing C:N ratios during growth and reproduction. Productivity ranged from 0.911 to 8.303 mg C/(m2°day). The ♀ portions of the populations were °5x as productive as the ♂ portions. The lower life span, growth rates and productivity of ♂ ♂ are believed to be linked to increase ♂ mobility during the breeding period, with subsequent decrease in filter—feeding during spring primary productivity. Reproduction in V. georgianus was iteroparous and vivaparus, with a gestation time of °9 mo. Fecundity varied seven—fold between the populations, with reproductive output paralleling the productivity rate. Fecundity of ♀ ♀ approximates a 1:3:2 ratio for 1—, 2— and 3—year—old ♀ ♀ respectively. Reproductive output with respect to ♀ age is discussed.
Productivity and Decomposition of the Dominant Salt Marsh Plants in Louisiana
Authors: White David A. , Weiss T. Edward , Trapani John M. , Thien Leonard B.
Published: May 2006

Net primary production and decomposition of the 4 dominant salt marsh plants found in Louisiana were determined. Live and dead standing crops were calculated by the harvest method over an annual cycle. Litterbags were used to estimate loss rates of vegetation from the marsh. Peak standing crops were: 1164 g/m2 for Distichlis spicata, 2194 g/m2 for Spartina patens, 1959 g/m2 for Juncus roemerianus and 1473 g/m2 for Spartina alterniflora. Net production estimates using the Smalley (1958) method were from 1291 g.m(—2). yr(—1) for D. spicata, 1342 g.m(—2).yr(—1) for S. patens. 1740 g.m(—2).yr(—1) for J. roemerianus and 1527 g.m(—2).yr(—1) for S. alterniflora. Using the Wiegert and Evans' (1964) method net production for the 4 species was: 1162 g.m(—2).yr(—1), D. spicata; 1428 g.m(—2).yr(—1), S. patens; 1806 g.m(—2).yr(—1), J. roemerianus and 2895 g.m(—2)°yr(—1) for S. alterniflora. It is estimated that these 4 species of Louisiana marshland plants produce 146 x 105 metric tons/yr of plant material. This accounts for approximately one—half of 17,050 km2 of marshes in the state. In general production was higher for this Louisiana marsh than reported in Atlantic Coast marshes. Also, decomposition rates were considerably higher. Spartina alterniflora decomposed most rapidal with 100% removal in 7 mo; 24%/yr for D. spicata, 36%/yr for S. patens and 20%/yr for J. roemerianus. In additional a belowrgound standing crop analysis was undertaken on new S. alterniflora roots.
Floral Ecology in Relation to Plant Species Diversity in the Wasatch Mountains of Utah and Idaho
Authors: Ostler W. Kent , Harper K. T.
Published: May 2006

An analysis of the relative abundance of the prevalent species in 25 major plant communities of the Wasatch Mountains demonstrates that variation in species diversity is significantly correlated with many floral characteristics. Wind—pollinated flowers decrease in abundance whereas animal—pollinated flowers increase along the diversity gradient. The relationship is statistically significant. Color diversity and species diversity are significantly and positively correlated in open communities bur are unrelated in forest communities. The percent sum frequency of yellow flowers decreases with increasing species diversity whereas blue flowers increase. Also, zygomorphic flowers and flowers in which access to the nectar supply is restricted by morphological barriers are positively correlated with species diversity. It is shown that species with wind—pollinated flowers and zoophilous species having open flowers are significantly better represented in the higher frequency classes than animal—pollinated species whose nectaries are morphologically restricted. The results suggest that many floral characteristics impart a reproductive advantage to species growing in communities of high diversity. That the relationships observed can be predicted with reasonable confidence within a small geographic area implies that the selective forces are local and strong.
Lianas as Structural Parasites: The Bursera Simaruba Example
Authors: Stevens George C.
Published: May 2006

The Fecundity of female Bursera simaruba (L.) Sarg. (Burseraceae) trees was found to be negatively correlated with their degree of coverage by lianas in the deciduous forests of Santa Rosa National Park, Guanacaste Province, Costa Rica. Experimental reduction of the liana of heavily overgrown trees resulted in an increase in fruit production. The finding that lianas are detrimental to the fecundity of their hosts, coupled with the fact that lianas require physical contact with trees as a consequence of their growth form, suggests that lianas should be viewed as structural parasites of the trees that support them.
Distribution‐Abundance Relationships of Some Arizona Landbirds: A Matter of Scale?
Authors: Bock Carl E.
Published: May 2006

Distribution and local abundance of 62 landbird species were measured in winter across an elevational gradient in the Huachuca Mountains of southeastern Arizona. The number of 35—m radius plots and the number of habitats occupied by the species were positively correlated with their average abundances within occupied plots and habitats. Common species were no more conspicuous than rare ones, as measured by detectability on variable distance point counts. The same species that were most abundant locally also were most abundant on Christmas bird counts across Arizona and throughout the western United States. The positive correlation between distribution and abundance of winter landbirds appear to be neither an artifact of conspicuousness, nor a consequence of the geographic scale of comparison. Rather, it seems to be an intrinsic property of the species themselves, and one that has important ecological and evolutionary implications. An individualistic approach to avian ecology is indicated, emphasizing comparisons of rare and common species.
Daily Variation in the Body Temperatures of Free‐Ranging Garter Snakes
Authors: Peterson Charles R.
Published: May 2006

This study describes how the body temperatures (Tb) of individual garter snakes varied on a daily basis under field conditions. Temperature—sensitive radio transmitters were surgically implanted into 10 Thamnophis elegans vagrans in eastern Washington. The snakes were released and monitored at 15—min intervals for periods of up to several days from June 1979 to May 1980. Operative environmental temperatures were estimated with painted metal models and were used to indicate possible Tb's. The combination of telemetered body temperatures with operative temperature data permitted detailed description of Tb variation and evaluation of the relative importance of the physical environment and behavior in determining that variation. The physical environment usually prevented the snakes from attaining preferred (selected) Tb's and thus limited when and where they could be active and potentially reduced their physiological performance. On cool days or at night, when operative temperatures (Te) were <15°C, the snakes remained underground and body temperatures changed gradually. On moderate days (15° < Te < 30°), the snakes usually emerged but were unable to maintain preferred body temperatures, and Tb variation was marked. On warm days (Te > 30°), the snakes selected Tb's within their preferred temperature range, and variation in Tb was small (e.g., range = 28.0°—32.5° X = 29.9°, SD = 1.32°). The snakes stayed within their preferred temperature range >90% of the time when Te > 30°. Their high thermoregulatory precision and thermal utilization presumably maintained high levels of physiological performance on warm days. Delays in emergence accounted for most instances in which the snakes did not utilize available thermal opportunities.
Rotifer Threshold Food Concentrations and the Size‐Efficiency Hypothesis
Authors: Stemberger Richard S. , Gilbert John J.
Published: May 2006

Using published data, we develop a physiological explanation for the positive relationship between threshold food concentration (the food concentration at which the population growth rate is zero) and body mass in planktonic rotifers. The exponent describing maximum clearance rate as a function of body mass is similar to the exponent expressing energy intake rates at low food concentrations. The former exponent (0,42) is considerably lower than the exponent for respiration (0.66). Consequently, the difference between energy intake and metabolism should decrease with increasing body size at low food concentrations. Rotifer swimming speeds are rather uniform for a wide range of body sizes and species. Consequently, length—specific swimming speeds (body lengths moved per unit time) and, particularly, mass—specific swimming speeds (distance moved per unit time per unit mass) decrease rapidly with increasing body size. We conclude that swimming speed, which is under the energy constraints of ciliary locomotion and which directly determines the rate of food encounters, provides the mechanism for the positive relationship between body size and threshold food concentration.
Stable Population Structure and Reproductive Value for Populations with Complex Life Cycles
Authors: Caswell Hal
Published: May 2006

Classical demographic theory was developed to describe age—classified populations, in which knowledge of an individual's age accurately specifies its demographic state. In many species (e.g., plants, insects, fish) individuals of the same age may be in very different states; classical theory is inappropriate for such populations. In this paper, I present general formulae for the stable stage distribution (the analogue of the stable age distribution of classical demography) and the stage—specific reproductive value distribution for populations with arbitrarily complex life histories. The results are obtained by use of z—transforms of a simple graphical representation of the life cycle. They yield literal formulae, which can be used to draw qualitative conclusions about the general properties of the life history. They will also provide quantitative results if numerical values for the parameters are available. Since the selective pressures on life history traits can be expressed simply in terms of the stable stage distribution and reproductive value, these results render complex life cycles amenable to evolutionary analysis. The reproductive value formulae can sometimes be used to calculate optimal schedules of stage—specific reproductive effort.
Bias in Estimating Niche Overlap
Authors: Smith Eric P. , Zaret Thomas M.
Published: May 2006

Bias refers to the accuracy of a particular estimator. We evaluate bias, using analytic and simulation technics, for six measures of overlap: the likelihood ratio measure, the chi—square measure, the measure based on the Freeman—Tukey statistic, Morisita's adjusted index, Morista's original index, and Horn's information index. We present an exact formula for a seventh, the percentage similarity measure. We consider bias due to resource a sample size, total number of different resources, and evenness of resource distribution. Results indicate that of the seven measures, changes in evenness of resource of distribution produce significant bias only in the percentage similarity measure and Morista's adjusted index. All measures show increasing bias with increasing number of resources. For estimating unbiased overlap, Morisita's original measure of overlap gives the most accurate results, especially when using small sample sizes. The percentage similarity measure, one of the most commonly used measures among ecologists, is also one of the most biased and for this reason is not preferred.
Regulation of Fruit and Seed Production in An Annual Legume, Cassia Fasciculata
Authors: Lee T. D. , Bazzaz F. A.
Published: May 2006

This study examines the factors that limit female reproductive function (fruit and seed production) in the annual plant, Cassia fasciculata Michx. (Leguminosae), an hermaphroditic herb that inhabits prairies, open woods, and waste places in the eastern USA. Removal of competitors and addition of water to plants in the field showed that resource levels prior to fruit influence plant size which, in turn, is positively related to the number of fruit matured. Manual addition of pollen to flowers in the field did not increase the number of fruit matured, suggesting that fruit production was not pollinator limited. Removal of rapidly growing fruit resulted in growth and maturation of fruit that normally would not have matured, indicating that resources limited fruit production. In four populations studied, 24—70% of initiated fruit matured, 12—40% aborted or died, 3—31% were still developing at the time of plant death, and 61—12% were lost to predators. In fruit that matured, between 23% and 73% of initiated seeds reached maturity, 22—43% were aborted, and 0—49% were lost to seed predators. These data indicate that seed production was limited by resources and seed predators. It is hypothesized that overinitiation of fruit in C. fasciculata is an adaptive response to either; (1) the loss of juvenile fruits to seed predators, (2) variation in fruit quality coupled with the ability of the plant to selectively mature high—quality fruit, or (3) unpredictability of resource levels and survival during fruit filling. The generally low levels of predation on juvenile fruits make the first hypothesis unlikely for C. fasciculata. Plants did, however, selectively mature fruit with large numbers of developing seeds. Furthermore, variation in the number of fruit matured per inflorescence seemed to be related to variation in precipitation and plant survival through the fruit—filling period. Thus, the data support both the second and third hypotheses.
Factors Regulated Nitrification in Primary and Secondary Succession
Authors: Robertson G. Philip
Published: May 2006

A six—point primary sere developed on sand dunes and a four—point secondary sere developed on old fields were studied to examine the regulation of nutrification in succession. Soils from sites along the seres were incubated in funnel—microlysimeters leached weekly with NH4Cl and other nutrient solutions. Nitrate output in soils from the youngest sites along the primary sere was rapidly simulated by NH4+—N additions. Nitrification in soils from all four sites of the secondary sere was also stimulated by added ammonium. Added NH4+—N had no effect on the last primary sere site; in this CaCO3 was the only treatment that stimulated potential nitrification. The possibility that labile inhibitors of nutrification were present in these sites was assessed by applying soil, litter, and whole—leaf washings, and whole—leaf and litter extracts to incubated soils. Soils amended with oxidizable carbon and pH—buffer solutions served as controls. Clear evidence for ecologically meaningful allelochemical inhibition of nitrification was found only in some subsites in the next—to—last site of the primary sere, which in previous incubations had had higher rates of nitrate production than any other site along this sere. No evidence for inhibition was found in the secondary sere. The effects of moisture and temperature on the rates of nutrification in these sites were also investigated. Results suggested that laboratory incubations may overestimate relative field rates of nutrification for early primary sere sites. Nitrification appears to be controlled by ammonium availability in at least the first four sites of the primary sere and perhaps the fifth. Allelochemical inhibition may also be important in this fifth site. A lag in nitrification that is counteracted by CaCO3 is an important regulator of nitrification in the last site. In the secondary sere NH4+—N availability appears to control nitrification in all sites.
Temporal and Spatial Patterns of Abundance of the Chydoridae (Cladocera) in Lake Itasca, Minnesota
Authors: Williams James B.
Published: May 2006

The chydorid populations of Lake Itasca, Minnesota, were monitored over a 2.5—yr period by pattern sampling. Of the 24 species collected, 15 were sufficiently abundant to allow analysis of population trends. Chydorid species have two basic patterns of abundance. One group of species exhibits only a summer density peak. The second group shows one abundance peak in summer and a second peak in fall or winter. All species experience a precipitous decline in density following the summer peak. Population growth in chydorids is limited by different factors during different times of the year. During periods of ice cover most species are apparently limited by a reduction in primary productivity due to reduced light penetration rather than by water temperature. Spring chydorid populations are limited by temperature. Summer populations, at least for abundant species, are limited by predation. Chydorid species are distributed patchily within Chara beds. Patchiness is moderate in spring, declines to low levels during summer, and peaks in the fall for most species. Patchiness remained about constant during the summer decline in density. Experimentation showed that heterogeneity of the physical habitat is not a necessary cause of patchiness. A Bray—Curtis—type ordination was performed on data from a complete year of monitoring. The primary component of variation extracted from the data matrix is due to temporal differences in abundance among species. The second major source of variation is due to spatial differences in abundance (habitat preference). The most abundant chydorid species tent to have similar habitats and temporal patterns of abundance.
Ecological Consequences of Song Matching: Breeding Success and Intraspecific Song Mimicry in Indigo Buntings
Authors: Payne Robert B.
Published: May 2006

Mating and breeding success of males that matched the song of a neighbor were compared with success of nonmatching song individualists in Indigo Buntings (Passerina cyanea) in southern Michigan. Adult males had higher success than 1st—yr males that matched the song of an adult on a neighboring territory had significantly greater mating success, nesting success, and fledging success than did nonmatching 1st—yr males. First—year males with blue plumage did better than 1st—yr males with browner plumage. Song matching raised the success of the browner males by 50% to equal that of the nonmatching bluer males, and song matching in the bluer 1st—yr males increased their success to that of the adults. The advantage in birds that mimic was restricted to birds that copy an adult and remain on a territory near the song model, and was most pronounced in the mimics that resembled the song model in plumage as well as in song. This increase in success in the song—matching males cannot be explained by variation in body size, time of arrival, or habitat. No apparent disadvantage fell to the older male buntings that were mimicked. As the structure and function (territoriality and mate attraction) of song in the individualist 1st—yr males did not differ from that in the song mimics, the increased success of song mimics apparently resulted from matching the adult neighbor's song and not simply from a behavioral maturation of song learning. The mechanisms through which song matching enhances biological success appear to involve competitive mimicry and deceit of other males through mistaken identity based on the older territorial male model's song.
Environmental Limits on Aboveground Net Primary Production, Leaf Area, and Biomass in Vegetation Zones of the Pacific Northwest
Authors: Gholz Henry L.
Published: May 2006

Mature vegetation from eight of the 12 major vegetation zones in Oregon and Washington was sampled along a transect from the Pacific Coast to the east slopes of the Cascade Mountains. Six stands were in forest, one in woodland, and one in the shrub—steppe. Aboveground—over—story net primary production) (NPP, estimated as the sum of annul stem, branch, and foliage production) ranged from <1 to 15 Mg°ha—1°yr—1, aboveground biomass from 3 to 1500 Mg/ha, and area of all sides of leaves from 1 to 47 ha/ha; minima were in the shrub—steppe zone and maxima in the coastal forest zone. Maximum leaf area index, biomass, and NPP were all strongly related both to a simple index of growing season water balance and to mean minimum air temperatures in January. In the subalpine conifer zone, though, cold winter temperatures apparently have a stronger influence than summer water availability. Of the water balance components, evaporative demand alone could account for >90% of the variation in leaf area index. Although annual precipitation ranged from 20 cm in the shrub—steppe to 260 cm at the coast, it was a relatively poor predictor of stand structure and production. Biomass and NPP increased linearly up to a leaf area of °30 ha/ha; above this point, biomass continued to increase while NPP decreased. Except in the coastal forest zones, NPP was less than maximum values reported for other mature systems elsewhere in the world for the same range in leaf area indices. Compared to other forested regions of the temperate zone with the same NPP, these systems receive more annual precipitation, and average twice the basal area and biomass.
Decomposition and Nutrient Exchange of Litter in an Alluvial Swamp Forest
Authors: Brinson Mark M.
Published: May 2006

Weight loss from cellulose sheets was measured monthly at three sites (river, swamp floor, natural levee) of a North Caroline swamp forest dominated by Nyssa aquatica. Rates of loss were significantly different seasonally and between sites. Both temperature and moisture appeared to be important in controlling decomposition rates. For Nyssa leaves, dry weight decreased to 25% of original after 48 wk while twigs fell to 80% of original after 56 wk. Three modes of nutrient exchange were found: (1) accumulation of N, Ca, and Fe by both leaves and twigs, with stronger leaf accumulation of these elements; (2) strong leaf accumulation with rapid twig loss of P; and (3) losses by both leaves and twigs of K and Mg. Final atomic ratios of C:N and C:P were about 15:1 and 500:1, respectively, suggesting that P may be in short supply. The significance of nutrient accumulation is that there was little or not net release of P, N, Ca, and Fe from autumn leaf fall until tree growth in the spring. Conservation and recycling of nutrients appear to be tight even in swamps open to flooding during tree dormancy.
Comparative Experimental Study of Seed Dispersal on Animals
Authors: Bullock Stephen H. , Primack Richard B.
Published: May 2006

Studies of the plants Achyranthes aspera, Bidens sp. and Petiveria alliacea establish examples of seed attachment and detachment on dispersal surfaces that occur continuously during movement of a dispersal agent. In uniform one—species stands, dynamic saturation points for the dispersal surfaces were demonstrated. A parameter termed the retention rate (R) was determined for each species in various habitats, and was used to calculate mean distances of dispersal. Within and around established populations of Achyranthes, for example, the mean dispersal distance ranged from < 5 m to > 2.4km, showing that settlement is selective and depends on the structure of existing vegetation. This relationship is also affected by the vertical distribution of seeds on the disperser.
An Experimental Analysis of Biological Factors Contributing to Stream Community Structure
Authors: Peckarsky Barbara L. , Dodson Stanley I.
Published: May 2006

Densities of invertebrates were manipulated within stony substrate filled cages in a Wisconsin and a Colorado stream to test the effects of prey densities on colonizaiton of the cages by invertebrate predators and potential competitors. There was no difference between the number of predators colonizing cages with high initial prey densities and that the colonizing cages with zero initial prey density, for any trial, during any season, in either stream. This observed lack of predator response to prey density has been termed a "null numerical response," characteristic of predator populations limited by factors other than prey availability. Food resource, then, was not responsible for the observed distributions of invertebrate predators in these two streams. Physical habitat cues or mutual interference among predators may explain the observed colonization pattern of these predators. Wisconsin stream prey preferentially colonized cages with zero initial densities compared to cages with potential competitors, but only when those cages excluded predators. The presence of spatial refuges from predators enhanced the effect of potential competitors upon prey colonization in this stream. The cage colonization by prey populations in the Colorado stream was reduced by the presence of potential competitors regardless of the availability of spatial refuges. Possible reasons for differences between the responses in the two streams are discussed.
Chaos, Asymmetric Growth and Group Selection for Dynamical Stability
Authors: Thomas William R. , Pomerantz Mark J. , Gilpin Michael E.
Published: May 2006

Mathematical chaos in simple growth models has grave consequences for theoretical ecology. Much effort has recently been directed towards delimiting the conditions under which chaos exists. We have performed an empirical search for chaos among 27 drosophilid species at two temperatures, and found that single—species laboratory populations invariably exhibited dynamical stability. We argue that chaos and stable limit cycle behavior are maladaptive, and propose an evolutionary mechanism whereby group selection for stability occurs.
Effects of Predation and Competition on Survivorship, Fecundity, and Community Structure of Desert Annuals
Authors: Inouye Richard S. , Byers Gregory S. , Brown James H.
Published: May 2006

Effects of rodent and ant granivores, watering, and thinning were studied in a diverse community of winter annuals in the Sonoran Desert. Seed predation considerably reduced plant densities, but ants and rodents had qualitatively different effects on the plant community. Ants increased species diversity of annuals by differentially harvesting the numerically dominant species, while rodents preyed selectively on species which dominated the community in terms of biomass. Competition among annual plants reduced growth rate, biomass, and fecundity, but had no significant effect on mortality. One species, Euphorbia polycarpa, apparently increased in density when the density of competing Erodium species was reduced by rodent predation.
Herbivore Effect on Stature, Fruiting, and Leaf Dynamics of a Native Crucifer
Authors: Louda Svata M.
Published: May 2006

The impact of a native, leaf—feeding chrysomelid beetle (Phaedon sp. nr. oviformis) on bittercress (Cardamine cordifolia: Cruciferae), was evaluated in an exclusion experiment. Multivariate statistical analysis showed a significant increase in plant performance in the rotenone exclusion compared to performance in the paired control treatment. Plant response to the reduction of herbivory was a complicated, interrelated syndrome of changes. When insects were excluded, the amount of missing leaf area decreased significantly (3.6—fold; 3.2—0.9 cm2 per plant), and the total leaf area increased 5.7—fold (12.9—73.4 cm2 per plant). Plant height (5.7—20.3 cm) and fruit production (0.1—3.9 siliques per plant) also increased significantly when the number of insects was reduced. Furthermore, the 570% expansion in leaf area due to the exclusion of insects involved signficant increases both in the initiation of new leaves and in the survival of mature leaves. Nevertheless, insect herbivory at a level well below complete defoliation (25% of the leaf area) changed leaf demography (both phenology and dynamics) and reduced plant perfomance by decreasing the plant stature, leaf area, and fruit production of this native forb. Thus, further experimental assessment is necessary before generalizations can be made regarding the effects of herbivory on plant dynamics.
Salinity Stresses Along a Complex River Continuum: Effects on Mayfly (Ephemeroptera) Distributions
Authors: Magdych William P.
Published: May 2006

The saline—stressed Washita River in western Oklahoma was evaluated to test the River Continuum Concept (RCC). Physical, chemical, and biological, variables were monitored at six sites in the river over 14 sampling periods during 1980 and 1981. Physical parameters represented stream discharge, sediment particle sizes, organic content of the sediment, and related factors. Chemical variables were conductance, pH, and concentrations of major salts (calcium, sulfate, sodium, and chloride). Biological variables were densities of mayfly genera from dredge samples. Two—dimensional ordinations were produced for the physical, chemical, and biological groups of variables using the ALSCAL model of three—way non metric multidimensional scaling. The ALSCAL model summarized variation over the 14 sampling periods. Rank correlations of the dimensions from all ordinations suggest that both river gradient and local effects influence the structure of the benthic community. River gradient dimensions for physical and chemical variables were highly correlated with one biological dimension. The remaining biological dimensions was correlated with local salinity effects. Benthic community structure is influenced by physical gradients. Saline effects, although governed by geomorphological processes, do not conform to the typical river gradient. This localized saline impact influences the benthic community structure. Therefore, the RCC must be modified to allow for multiple gradients if it is to be useful in the generation of ecological models in regions with high river salinity.
An Experimental Analysis of Mixed‐Species Flocking in Birds of Deciduous Woodland
Authors: Berner Theodore O. , Grubb Thomas C.
Published: May 2006

Two general models have been developed concerning the adaptive advantage of participating in mixed—species foraging groups. One model emphasizes the increased feeding efficiency to be obtained in heterospecific groups, while the other model advances the antipredator advantages of participation in such species complexes. From these models, two conflicting predictions were made about the consequences of providing a superabundant of food resource to birds that normally engage in mixed—species flocking. We tested these predictions over the course of two winters birds in two central Ohio woodlots, provisioning one of the two woodlots with a superabundant supply of sunflower seeds and beef suet during the second winter of the study. In addition, we examined the effects of added food on the density of bird species, and on the size and composition of heterospecific flocks. Carolina Chickadees, White—breasted Nuthatches, Brown Creepers, Tufted Titmice, and Downy Woodpeckers all exhibited significant decreases in mixed—species flocking in the area with added food relative to the controls. These results reject protection from predators as a sufficient cause for mixed—species flocking, and support the view that either increased feeding efficiency alone or feeding efficiency and predation protection in combination cause animals to forage in mixed—species groups.
The Successional Status of a Southern Wisconsin Oak Woods
Authors: McCune Bruce , Cottam Grant
Published: May 2006

We examined the applicability of concepts of succession to 27 yr of tree growth and demographic data from an oak woods. From 1956 to 1983 tree population dynamics in Noe Woods, a black oak—white oak woods in southern Wisconsin, were heavily influenced by oak wilt disease. Between 15 and 20% of the black oaks, many of them large, died in each 5—yr period; much of this mortality was due to wilt. White oak increased in basal area but declined slowly in numbers. Regeneration was dominated by black cherry, boxelder, and American elm; these species are either short—lived and small—statured or threatened by disease, and are, the therefore, unlikely to form a new canopy. None of the species in the woods seems capable of filling the role of a self—replacing climax species in the classical sense. We hypothesize that the absence of a climax species in Noe Woods and other areas of the prairie—forest transition is due to the changed disturbance regime. Decreased fire frequency has created an unprecedented opportunity for shade—tolerant species in dry woods. This opportunity has apparently been met by expansion of shade—tolerant native species from other habitats, invasion of exotic species, and increased abundance of some short—lived and small—statured native species.
Fine Roots, Net Primary Production, and Soil Nitrogen Availability: A New Hypothesis
Authors: Nadelhoffer Knute J. , Aber John D. , Melillo Jerry M.
Published: May 2006

The relationships between above— and belowground net primary production and soil nitrogen availability were studied at nine temperate forest sites. Annual allocations of nitrogen (N) and net primary production to leaf litter, perennial tissues (wood + bark), and aboveground biomass all increases significantly (P < .01) in relation to apparent N uptake by vegetation (N"u) as calculated using field measurers of net N mineralization (Nm) and other major N fluxes to and from available N pools. Mean annual N content and biomass of fine roots @<3.0 mm diameter) were both negatively correlated with Nu (° = —0.71, P < .05; ° —0.63, ° < .10, respectively). However, only °50% of Nm at each site could be accounted for by allocation to aboveground litter and perennial tissues. Assuming that mineralized N not accounted for by allocation to these components was taken up by vegetation and allocated to fine roots, annual N allocation to fine roots (Nfr) was a constant fraction of N uptake. Therefore, Nfr increased in absolute terms with both Nm and apparent N uptake. Fine—root N turnover rates (or Nfr/fine—root N content) also increased as Nm and Nu increased. Provided that fine—root biomass and N turnover rates were similar within sites, allocation of production to belowground biomass also increased relative to increases in soil N availability. Furthermore, the proportion of total net production allocated to belowground biomass did not decrease with increased N availability.
Geomys Bursarius Burrowing Patterns: Influence of Season and Food Patch Structure
Authors: Andersen Douglas C.
Published: May 2006

The relationship between belowground food resources and the pattern and pace of soil excavation by Geomys bursarius, the plains pocket gopher, was assessed during spring and autumn using replicated 18 x 18 m enclosures containing uniform arrays of food plants (Daucus carota) at spacings assumed to result in burrowing being energetically profitable (25 and 50 cm) or unprofitable (100 cm and empty). Soil excavation rate, measured in terms of either daily additions to tunnel length or volume, or the maximum volume excavated during a 3—d interval, varied greatly among individuals. No significant effect due to season or density of belowground plant biomass was detected when burrowing was profitable. Individuals readily initiated aboveground travel in unprofitable treatments. Soil bulk density was negatively related and animal body mass positively related to excavation rate. Individuals deposited from 41 to 87% of excavated soil on the ground surface; the remainder was used to backfill previously created tunnels or chambers. Plant size, but not plant spacing, affected the ratio of the volumes deposited aboveground and belowground. There was no evidence that animals in enclosures disturbed soil in a manner quantitatively or qualitatively different from free—ranging adults. The large proportions and absolute quantities (up to 30 L/d) of soil involved suggest that backfilling may affect ecosystem structure and functioning as much as surface mound—building.
Barn Swallow Coloniality: A Net Cost for Group Breeding in the Adirondacks?
Authors: Shields William M. , Crook Janice R.
Published: May 2006

To explore the costs and benefits of groups living in a facultatively social bird, we studied the reproductive ecology of a marked population of Barn Swallows (Hirundo rustica) as the Cranberry Lake Biological Station in the Adirondack Mountains of New York State. Throughout its range, the Barn Swallow breeds solitarily or in small groups. From 1979 through 1985 we gathered reproductive and mortality data in colonies varying in size and density. Birds living in larger colonies tended to be younger and to breed later, on average, than solitary breeders. Breeding success was less for birds in large colonies than for birds breeding solitarily or in small groups. Larger colonies did not provide obvious benefits that offset the reduced reproductive success. Nests in larger colonies were infested more by a bloodsucking blow fly larva (Protocalliphora hirundo) than were nests in smaller colonies. The fraction of nests infested and the mean number of parasites per nestling also increased as the breeding season progressed. Since parasitism appeared to be the major source of nestling mortality, the increased parasite loads were probably the major cost of living in larger groups in our area. Birds in large colonies suffered a net reproductive loss relative to those breeding alone or in smaller groups. Thus, our data consistent with Snapp's (1976) conclusion that shortages of nesting habitat rather than direct benefits of group living are responsible for swallow coloniality.
Thermal Requirements for Development in Chrysopa Oculata: A Geographically Stable Trait
Authors: Tauber Catherine A. , Tauber Maurice J. , Nechols James R.
Published: May 2006

Chrysopa oculata from five widespread localities (southern Canada to montane Mexico), exhibited remarkable similarities in their thermal requirements for nondiapause development. Lower thermal thresholds (t) varied by only 1.2°C., and the degree—days required for total preimaginal development (K) differed among the populations by °85°d. Despite the similarities among populations, the results suggest that the thermal requirements for development are genetically variable. However, two factors may limit the geographical expression of this variation: (1) the multivoltine life cycle could result in seasonal oscillations in the magnitude and projection of directional selection on the nondiapause thermal responses, and/or (2) the thermal thresholds for development and the rates of development above the thresholds may be functionally correlated and constrained in their evolution. Males from all populations emerged slightly but consistently earlier than females. Temperature did not affect sex or survival, other than at 15.6.° where mortality was significantly increased. Among the five populations, only one large difference occurred in the thermal responses; under low temperatures, a relatively high proportion of the two northern populations entered diapause. The differences in diapause induction resulted from the differential effect of temperature on the critical photoperiod for diapause induction, rather than on the developmental rates.
Interspecific Competition Lowers Fitness in Collared Flycatchers Ficedula Albicollis: An Experimental Demonstration
Authors: Gustafsson Lars
Published: May 2006

The definition of interspecific competition requires that the fitness of individuals that are exposed to such competition be reduced. However, the effects of interspecific competition on individual fitness under natural conditions has rarely, if ever, been demonstrated in rigorous experimental tests. Here I report a study on the effects of Great and Blue Tits on the fitness of Collared Flycatchers, at the natural density, or at artificially high densities. When densities of tits were experimentally reduced, the number and mass of Collared Flycatchers fledglings increased, compared to those on control plots. Collared Flycatchers breeding under reduced competition contributed more recruits to the breeding population than did those breeding in control plots. The mechanism presumably was differential access to food for the young during both the nestling and postfledging periods. The combined fitness value of recruited young and surviving adults was significantly higher in low—competition plots. Interspecific competition affected the reproductive success of the Collared Flycatchers more than did intraspecific competition.
A Geometric Model of Vertebrate Dispersal: Tests and Implications
Authors: Buechner M.
Published: May 2006

A model of vertebrate nata dispersal is developed and compared to observed patterns of dispersal distances for a variety of animals. The model, which has the same basic formulation as Waser's competition model of dispersal, is based on assumptions of the divisibility of the habitat into discrete units capable of supporting a resident, and of a constant probability of a disperser stopping as it crosses each of these units. This probability is decomposed into the probability of settling and the probability of dying. Comparisons to observed data indicated that the model is adequate to describe the pattern of dispersal distances observed in many vertebrates. This model has advantages over other treatments in that it is simple to manipulate mathematically, and it has parameters that are relatively easy to estimate from field data and are directly relevant to the behavior, ecology, and demography of dispersing animals. In addition, the theoretical distribution is in a form that makes statistical tests of the fit to observed data straightforward. Comparisons of parameter values and deviations from the geometric pattern between groups within taxa indicated that males and females may follow different patterns of dispersal. Comparisons among taxa indicated that mammals and birds show consistent differences in dispersal distributions. These results are relevant to discussions of natal philopatry, inbreeding avoidance, and proximate mechanisms of dispersal.
Intraguild Predation and Competition Among Desert Scorpions
Authors: Polis Gary A. , McCormick Sharon J.
Published: May 2006

Interactions among four species of desert scorpion were analyzed over a 9—yr period at two sites in the Coachella Valley, California. Although potential competitors that feed on similar anthropod prey, these species also eat one another (i.e., engage in intraguild predation); heterospecific scorpions were found to form 8—21.9% of the diet. Size differences determine scorpion—scorpion predation. Larger individuals of any species were always the predator, and prey scorpions were most frequently males and individuals that were in motion. Intraguild predation was most frequent when food availability was low. The numerically dominant scorpion, Paruroctonus mesaensis (>95% of all individuals), killed and ate 8 and 6% of two smaller scorpion species (Paruroctonus luteolus and Vaejovis confusus, respectively) and 10% of all the observed newborn of another scorpion species, Hadrurus arizonensis. Mortality due to P. mesaensis was generally an inverse function of the density of P. luteolus and of V. confusus. During a 29—mo experiment, >6000 P. mesaensis were removed from 300 100—m2 quadrats. There were significant increases in the populations of P. luteolus and V. confusus (but not of Hadrurus) in the removal quadrats, compared to control quadrats. The hypothesis that species compete exploitatively for food was also tested. Although there was extensive evidence that food limited feeding, growth, adult size, and reproduction, there was no evidence that food use by one scorpion depleted the availability of prey to other scorpions: abundance of prey (determined by trapping), percent feeding (number of individuals observed with prey ° total number of individuals observed), and mean body sizes were not greater in the removal vs. control quadrats. We conclude that intraguild predation rather than exploitation competition is the major factor structuring the observed patterns of distribution and abundance of these scorpions. We suggest that aspects of foraging behavior and the spatial and temporal patterns of surface activity of smaller scorpion species and age classes have coevolved largely to avoid predation by P. mesaensis. Many assemblages of scorpion species exhibit intraguild predation, and we speculate that this process produces behavioral and activity patterns similar to those observed in this study.
Ecological Scale and Habitat Use
Authors: Morris Douglas W.
Published: May 2006

Population density can respond to habitat at different scales. If habitat selection occurs as a consequence of resource exploitation, the density of fine—grained consumers should reflect microhabitat variation. But if habitat use is controlled by a variety of selective pressures, it is no longer apparent whether density should respond to micro— or macrohabitat. These two alternatives can be tested simultaneously by multiple regression models where macrohabitats are represented by dummy variables. When the local densities of two Temperate Zone rodents were analyzed in this way, macrohabitat and temporal effects were consistent significant predictors of rodent density; microhabitat was not. This analysis suggests species whose patterns of resource and habitat use probably depart from classical interpretations of species coexistence. It is probably premature to assess the role of habitat selection in the structure of ecological systems until the results of further tests of habitat scaling are reported.
Paedomorphosis in the Salamander Ambystoma Talpoideum: Effects of a Fish Predator
Authors: Jackson Mary E. , Semlitsch Raymond D.
Published: May 2006

We examined the expression of metamorphic and paedomorphic phenotypes of the salamander Ambystoma talpoideum in relation to a fish predator. We measured the effects of fish density and time of introduction on larval activity, growth, survival, and body size, and the percentage of larvae metamorphosing or becoming paedomorphic, i.e., maturing as larvae. In addition, a laboratory experiment measured refuge use by larvae according to varying amounts of chemical cues from fish. There was no effect of fish density or time of introduction on survival and growth rate of larvae, nor on final density of zooplankton. Percentage of individuals becoming paedomorphic or metamorphosing was positively related to mean body size in ponds. An analysis of covariance, after removing the effect of body size, revealed a significant effect of fish density on the expression of the paedomorphic phenotype, but not on that of metamorphosis. The proportional decline of paedomorphs was related to the increase of larvae. The laboratory experiment indicated that refuge use by larvae was proportional to the amount of fish stimuli. Activity of larvae in the ponds, however, was not affected by fish density, but rather showed that larvae became habituated to fish. Our experiment demonstrated that expression of the paedomorphic phenotype is reduced in the presence of fish, not by increasing the number of metamorphs as expected, but by increasing the number of individual that remained as larvae. These results indicate that models of amphibian metamorphosis based on growth and mortality are not adequate to explain paedomorphosis. We propose that trade—offs with reproductive traits such as size and age at first reproduction must be incorporated into models predicting metamorphosis as an alternative life history pathway to paedomorphosis.