bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation, Stability, and Diversity in A Model Experimental Microcosm
Authors: Luckinbill Leo S.
Published: May 2006

The stability, regulating factors, and dynamics of an experimental community of protozoans are examined here. The predator Didinium nasutum is found to coexist in microcosms with its prey, Colpidium campylum. Prey are limited by the quantity of bacteria and nutrients available. Didinium proves to be an ineffective predator and is limited by the availability and/or quality of prey as food. Enrichment of this community with bacteria or nutrients results in the extinction of prey and starvation of the predator. Increasing diversity of the lower trophic level by adding alternative prey species destabilizes this community, also causing extinction. Stability depends here on the characteristics of the particular species serving as prey and not simply the diversity of species present.
Ecology of Subtidal Algae on Seasonally Devastated Cobble Substrates off Ghana
Authors: Lieberman Milton , John David M. , Lieberman Diana
Published: May 2006

The growth of subtidal algae on calcareous cobbles is restricted to a short (2—4 mo) growing season. Most algae are destroyed during rainy season storms due to surge and cobble tumbling; algal density is low throughout the year. Significant interspecific competition does not occur on cobbles, and no species/area relationship could be demonstrated. The number of species per cobble is correlated with cobble moment of inertia (resistance to tumbling) during the rainy season. Species diversity on cobbles is significantly higher than on neighboring rocky reefs. Available evidence suggests an annual floristic cycle, although biomass and diversity are closely related to short—term weather conditions. Ephemerals, annuals, pseudoannuals, and prennials appear sequentially during the growing season. Species with greater potential size reach peak abundance late in the growing season, although many never reach maximum size or reproduce on cobbles. These longevity and size trends cannot be said to constitute adaptive strategies on cobbles. The high species diversity observed on cobbles is adequately explained by seasonal disturbance.
Male Quality and Female Choice of Mate in the Red‐Winged Blackbird (Agelaius Phoeniceus)
Authors: Yasukawa Ken
Published: May 2006

Male Red—winged Blackbird pairing success was studied to determine the role of male quality in female choice of territory and mate. Data on date of first nest, harem size, and proportion of territorial males surviving to subsequent breeding seasons did not support the hypothesis that territory quality alone determines female choice of mate. Male reproductive experience and body size were significantly positively correlated with harem size, but correlations between male age and harem size, and male courtship intensity and harem size, appeared to occur because females preferred territories defended by experienced males. There was no evidence that male aggressiveness tendencies influenced female choice of mate. Although these data indicate that females were influenced by male characteristics, it is suggested that a complex interaction of male and territory quality determines female choice of mate in the Red—winged Blackbird.
Trichopteran Communities of Streams Associated with Aspen and Conifer Forests: Long‐Term Structural Change
Authors: Molles Manuel C.
Published: May 2006

A comparison of the trichopteran communities of streams associated with aspen, spruce—fir, and mixed—conifer forests demonstrated significant differences in structure. Though tricophteran species composition in aspen—associated and spruce—fir associated streams was virtually identical, relative abundances of shredder and grazer Trichoptera differed significantly in the two types of streams. The ratio of shredder to grazer trichopteran biomass in aspen streams was °1:17 while in conifer streams, the dominance was reversed with a shredder to grazer biomass ratio of 3:1. The difference in dominance of functional groups in the two types of streams was attributed to the order—of—magnitude greater standing crops of detritus found in the conifer streams. It is hypothesized that the greater accumulation of detritus in conifer streams is the result of habitat modification by logs. Five times the number of logs were found in conifer streams as compared to aspen streams. The greater accumulation of logs in the conifer streams is attributed to lower rates of decomposition of conifer wood. The data suggest a general model for long—term structural change in trichopteran communities of the southern Rocky Mountains and I suggest that these long—term changes result from changes in quantity and quality of wood inputs during forest succession.
A Model for the Dynamics of a Plant Population Containing Individuals Classified by Age and Size
Authors: Law Richard
Published: May 2006

In many populations of plants, reproduction and mortality depend both on age and size. This paper develops a model to describe the dynamics of such a population, classifying individual both by age and size. It is based on a model originally proposed by Goodman (1969) as an extension to the Leslie matrix. The model allows a projection of the transient dynamics of a population from an arbitrary set of starting numbers. It also allows some asymptotic properties of the population to be determined, namely, the finite rate of increase, the stable age/size distribution, and the reproductive values. In the special case of reproduction and survival being independent of size, the model reduces to a Leslie matrix. In the special case of reproduction and mortality being independent of age, it yields results which approximate to a form of the stage projection matrix (Lefkovitch matrix). The main results of the model are illustrated with an example based on a plant with a monocarpic life history.
Mixed‐Function Oxidase Activity in a Generalist Herbivore in Relation to Its Biology, Food Plants, and Feeding History
Authors: Ahmad Sami
Published: May 2006

A general—purpose detoxification enzyme system, known as the mixed—function oxidase (MFO) system, apparently protects generalist herbivores from defensive plant allelochemics. Previous studies limited to lepidopterous larvae show that the MFO system has the attributes of an effective biochemical defense, mainly because this system has been shown to occupy a key position in the primary degradation and inactivation of a wide variety of exogenous lipophilic substances, and its level increases rapidly via introduction by plant allochemics. The gut microsomal MFO system of the highly polyphagous Japanese beetle, Popilia japonica, is induced rapidly, attaining maximal level within 24 h of feeding on host plants. The order of induction is: field polyphagouf beetles > laboratory—simulated polyphagy > single—plant feeding. However, apparently the induction is not related to host preference of this herbivore, but probably occurs in response to host allelochemics. Single—plant feeding of three host plants: sassafras, broccoli, and phlox, as a group, produced MFO induction that was 83 and 67%, respectively, of the level achieved in mixed plant feeding on a natural polyphagy. The Implication of this mode of substantial induction in single—plant feeding, in relation to the beetles' feeding habits immediately after emergence, is discussed. The beetle larvae clearly show that under faculatative monophagy, the MFO level is significantly lower than in polyphagy. Taken together, these data show that the MFO system in the Japanese beetle is highly flexible and is responsive not only to overall breadth of the diet, but also to the immediate feeding history.
Behavioral Modification of Evaporative Water Loss by a Puerto Rican Frog
Authors: Pough F. Harvey , Taigen Theodore L. , Stewart Margaret M. , Brussard Peter F.
Published: May 2006

Leptodactylid frogs (Eleutherodactylus coqui Thomas) reduce rates of evaporative water loss threefold by adjusting their postures and activities in response to changing conditions of availability of water during their nocturnal activity periods. Frogs that do not make these adjustments experience a potentially lethal loss of body water on a rainless night. Dehydration of a frog's body tissues increases its resting metabolic rate and lowers its maximum rate of aerobic metabolism. Water is reabsorbed from urine in the bladder to maintain tissue water content on dry nights. Use of water—conserving postures precludes vocalization by male frogs and response to calling males by females. Frogs in water—conserving postures feed less readily than active frogs. Frogs in the forest canopy experience higher rates of evaporative water loss than those in the understory, but there are more anthropods in the canopy, and leaf surfaces are twice as likely to be wet by rain. Despite these potential benefits of activity in the forest canopy, most frogs remain in understory vegetation. In that microhabitat their behavioral and physiological adjustments permit them to occupy their normal perches despite wide fluctuations in hydric conditions.
Costs and Benefits of Flower Abscission and Fruit Abortion in Asclepias Speciosa
Authors: Bookman Susan Stone
Published: May 2006

Costs and benefits associated with flower abscission (dropping of flower prior to postfertilization ovary enlargement) and fruit abortion (shriveling of ovary after postfertilization enlargement) are examined in Asclepias speciosa, in which °97% of the ovaries fail to develop into mature pods. The cost in terms of mineral nutrients of producing flowers and initiating pods was low relative to mature pod production as both abscised flowers and initiated pods that aborted containing °3.2% of the amount of N, P, K, or Mg in mature pods. Abortion of initiated pods sometimes entailed an additional loss of nutrients over that entailed in flower abscission, as large aborted pods contained two to seven times the amount of N, P, K, or Mg is abscised ovaries that did not initiate surplus pod development. The relatively low cost of producing surplus ovaries and initiating surplus pods is partially opposed by the benefits of selective pod maturation. Within umbels, smaller developing pods contained less N, P, K, and water than did larger pods of the same age, and slower growing pods had a lower percentage of N and, at certain stages, less P, K, and water than faster growing pods of the same size. Smaller pods within umbels also contained both fewer and lighter seeds. These results suggest that pods differ in ability to compete for limiting resources. Through selective elemination of the poorest competitors (the slower growing, smaller pods) at an early age, pod abortion may result in survival of the fittest offspring.
Plant Adaptation in an Ecosystem Context: Effects of Defoliation, Nitrogen, and Water on Growth of an African C4 Sedge
Authors: McNaughton S. J. , Wallace Linda L. , Coughenour Michael B.
Published: May 2006

Clones of a C4 sedge, Kyllinga nervosa Steud., from a semiarid location in the Serengeti region of Tanzania were propagated vegetatively and grown at 12—h photoperiods, 30°C maximum daytime temperature and 15° minimum nighttime temperature, simulating conditions at the native site. Clipping height, clipping frequency, nitrogen concentration of the nutrient medium, and watering frequency were varied in an unbalanced factorial experiment. Plants were harvested after 5 mo of sustained treatment. Each yield component was principally regulated by a different environmental factor. Yield to grazers (amount clipped off) was controlled by nitrogen supply, yield to producers (residual biomass) was controlled by water, and yield to decomposers (litter and standing dead) was controlled by clipping height and nitrogen. Plant growth was stimulated by defoliation. Plants overcompensated for amounts removed at moderate defoliation at high nitrogen, undercompensated at severe defoliation, and just compensated under other conditions. Therefore, increments of energy flow to grazers can be additive in ecosystem budgets due to compensatory growth of affected plants. The most important mechanisms accounting for compensatory growth of K. nervosa were activation of plant meristems and stimulated rates of leaf elongation in defoliated plants. Allocation of residual plant biomass to various organs was virtually independent of environment, indicating genetic control of physiological processes tending to balance allocation over a broad environmental range.
Niche Dynamics and Organization of Waterfowl Guilds in Variable Environments
Authors: Nudds Thomas D.
Published: May 2006

Factors influencing the diversity of coexisting ducks in the prairie—pothole region of North America were investigated. Thirty—five years of census data and data on breeding—habitat use for each of two guilds (diving and dabbling ducks) from aspen—parkland and mixed—prairie habitats were analyzed to investigate the means by which species were accommodated in diverse assemblages. There was a regular increase in the temporal variability of breeding habitats of each guild in this order: parkland divers < parkland puddle ducks < grassland divers < grassland puddle ducks. A positive relationship between a multivariate measure of niche separation derived from discriminant function analysis and species diversity, suggesting competitively induced adjustments to niche parameters, was found only for parkland diving ducks. Species diversity was better correlated with total niche space for guilds occupying more variable breeding habitats. Niche separation and species diversity were never inversely related, suggesting that competition for limited resources in evolutionary time sets the limits to species' similarity in resource use, but the importance of competition as a factor influencing community structure in ecological time depends on environmental variability. Evidence that duck populations may be in long—term equilibria with resource levels in breeding areas is presented.
Morphology, Surface Temperatures, and Northern Limits of Columnar Cacti in the Sonoran Desert
Authors: Nobel Park S.
Published: May 2006

Interspecific morphological differences and intraspecific morphological changes with latitude were evaluated to help examine the distributional ranges of Carnegiea gigantea, Lemaireocereus thurberi, Lophocereus schottii, Pachycereus pecten—aboriginum, and P. pringlei in the Sonoran Desert (USA and Mexico). A computer model, which predicted the average surface temperature of the stem within 1°C of that measured hourly throughout a 24—h period, was particularly useful in studying the thermal relations of the stem apex, where the lowest surface temperature occurred. Simulated increases in stem diameter raised the minimum apical temperature for C. gigantea and may help account for the extension of its range to higher latitudes than the other species studied. However, diameter increases led to a slight decrease in minimum apical temperatures for Lophocereus schottii. The immature stems of L. schottii are morphologically distinct from the mature stems which caused minimum apical temperatures to be 1.6°C lower for the immature stems under given environmental conditions; thus, freezing damage to the immature stems could limit the northward extension of the range of this species. As the apical pubescence in the simulations was increased up to the normal amount (10 mm), the minimum apical temperature for the stem of C. gigantea increased 2.4°C. Simulated increases in spine shading of the apex also raised the minimum apical temperatures, again indicating the influence of morphological features on the temperature of the meristematic region. Under the same environmental conditions the minimum apical temperatures were 7.7°C, 5.9°C, and 3.9°C for C. gigantea, Lemaireocereus thurberi, and immature stems of Lophocereus schottii, respectively, which is the same relative order as their northernmost limit (34°56'N, 32°38'N, and 31°55'N respectively). The northern limit for these three species, but not for Pachycereus pectenaboriginum and P. pringlei, may well be determined by the low temperatures occurring at the stem apex.
Territory Size in Western Gulls: Importance of Intrusion Pressure, Defense Investments, and Vegetation Structure
Authors: Ewald Paul W. , Hunt George L. , Warner Molly
Published: May 2006

Variation in territory size in a low—density colony of Western Gulls (Larus occidentalis) was analyzed in terms of costs and benefits accruing to owners. Spatial variation in intrusion rate per unit area best explains variation in territory size; the highest intrusion rate and smallest territories occurred near undefended gathering spots. Killing of chicks by neighbors was more frequent on small territories than on large territories. However, owners of large territories spent more time in territorial defense and more time per act of defense than owners of small territories. Intrusion elicited aggression from owners more frequently on small territories than on large territories, and intruders remained on large territories for longer periods of time. Territory size was positively correlated with the amount of visually obstructive vegetation. This correlation was apparently a result of gathering spots occurring in areas with little cover.
An Experimental Analysis of Interspecific Competition Among Marine Filter Feeders in a Soft‐Sediment Environment
Authors: Peterson Charles H. , Andre Stephen V.
Published: May 2006

Transplants in Mugu Lagoon, California, USA of a deep—dwelling bivalve, Sanguinolaria nuttallii, into experimental enclosures containing various combinations of other filter—feeding bivalves demonstrate that linear growth in Sanguinolaria is reduced by °80% over a 2—mo period when it is confined with two other deep—dwelling species, Tresus nattallii and Saxidomus nuttalli. Sanguinolaria growth is unaffected by the presence of a shallow—dwelling species, Protothaca staminea. Results also suggest a tendency for Sanguinolaria to emigrate away from areas of high Treasus and Saxidomus density. These interactions may explain why Sanguinolaria is uncommon in natural beds of Tresus and Saxidomus, although it is abundant elsewhere within Mugu Lagoon. In contrast to Sanguinolaria, Protothaca growth is not significantly influenced by the presence of either Sanguinolaria or Tresus and Saxidomus. Thus, while no apparent interactions occur between species which occupy different living positions in the sediments, species which share a similar depth stratum interact strongly, suggesting that competition for space is the primary mechanism of interaction in this system. This assumption is partially supported by the results of another experiment in which the growth rate of Sanguinolaria is significantly depressed by the presence of unoccupied shells of dead Tresus and Saxidomus, placed in normal living position in the sediments.
Life Histories of Mammals: An Analysis of Life Tables
Authors: Millar John S. , Zammuto Richard M.
Published: May 2006

We quantitatively test theoretical predictions concerning mammalian life histories, using published data on survival, reproduction, and body mass for 29 eutherian mammals. Larger mammals have a greater age at maturity, greater generation length, greater life expectancy, lower reproductive value at maturity, and smaller litters than do smaller mammals. Residual reproductive value at maturity is not correlated with adult body mass or survival. Litter size varies inversely with generation length and adult survival. Age at maturity is positively correlated with life expectancy. Twenty—seven of 29 mammals display a generation length longer than their life expectancy at birth, and the same proportion shows a greater life expectancy at maturity than at birth. A fairly high proportion (76—82%) of the variation in these dependent variables is attributable to adult mass. Many life table characteristics of mammals are interrelated, although not necessarily in the ways predicted by theory. Design constraints may preclude significant differences in life history patterns among mammals, so that the life table characteristics of only a few species may depict the pattern of life table evolution in most eutherian mammals.
Livestock Grazing‐Fire Regime Interactions within Montane Forests of Zion National Park, Utah
Authors: Madany Michael H. , West Niel E.
Published: May 2006

Major differences were found between the vegetation structure of ponderosa pine—dominanted communities on the Horse Pasture Plateau and those on the nearby but isolated Church and Greatheart Mesas in Zion National Park. The Horse Pasture Plateau was heavily grazed by livestock in the late 19th and early 20th centuries, while the mesas were never grazed. Conditions on the mesas now approximate the pre—European situation of the region as described in the earliest written accounts. Pine, oak, and juniper sapling density and cover were much higher on the formerly grazed plateau than on the relict mesas. Herbaceous species dominated the groundlayer in mesa ponderosa pine savanna stands, while grass and forb cover was low on analogous sites of the plateau. Age—class distributions of major tree species further substantiated that major physiognomic changes have occurred on the plateau since the arrival of European man. Analysis of fire scars showed that prior to 1881, the mean fire—free interval for ponderosa pine stands on the plateau was 4 to 7 yr, while the interval for Church Mesa was 69 yr. Since there were no recorded fires on Church Mesa between 1892 and 1964, and yet no corresponding increase in sapling density, the increased understory density of plateau stands should not be attributed primarily to cessation of fires. Instead, heavy grazing by livestock and associated reduction of the herbaceous groundlayer promoted the establishment of less palatable tree and shrub seedlings, Fire, however, played an important secondary role in maintaining savanna and woodland communities.
Geographic Variation in Seedling Douglas‐Fir (Pseudotsuga Menziesii) from the Western Siskiyou Mountains of Oregon
Authors: Sorensen Frank C.
Published: May 2006

Patterns of geographic variation for seed and seedling traits of Douglas—fir from four elevations on west and east aspects of first and second ridges away from the ocean (latitude °42°30'N) were observed under two air—temperature regimes in a common garden. Size and germination rate were recorded for seeds; phenological and size data were recorded on seedlings through two growing seasons. The pattern of genetic variation appeared to be determined by adaptation to local moisture and temperature regimes. In east—west comparisons (inland ridge vs. coastal ridge or east aspect vs. west aspect), seeds of east aspect or inland origin were larger and germinated more rapidly than seeds of more westerly origin. Similarly, plants of inland origin or from east aspects tended to start and end elongation earlier and have smaller top : root ratios, compared to plants from the coastal ridge or west aspects. Genetic differences were generally greater between the west and east aspects of the coastal ridge than between the two aspects of the inland ridge. Variation in data of bud set and plant size was also related to elevation. The change associated with elevation was greater on the coastal ridge than on the inland ridge. Evidence is presented that indicates length of growing season and heat accumulation may change more with elevation and latitude near the ocean than inland in the Pacific Northwest. This in turn may result in steeper elevational and latitudinal gradients of genetically based variability near the ocean than inland.
Physiological Integration among Intraclonal Ramets in Solidago Canadensis
Authors: Hartnett D. C. , Bazzaz F. A.
Published: May 2006

Clones of Solidago canadensis were studied to determine the degree of physiological interdependency among interconnected ramets. Ramets severed from their parental clone in the field experienced reductions in growth, survivorship and flowering, relative to intact controls. The results show that new daughter ramets are physiologically dependent upon resources translocated from their parental clone and that this dependency declines with time. When one of the ramets within each of several connected pairs was shaded to 10% of full sunlight, rates of photosynthesis increased in the remaining illuminated ramets. This and patterns of ramet survivorship and growth indicate that during periods of light limitation ramets become reintegrated. Shaded ramets become supported by the translocation of assimilates from other ramets within the clone. There is a tradeoff between rhizome number and length. When ramets become resource limited they produce fewer but longer new rhizomes. This results in the placement of daughter ramets at a location distant from the parent and may improve their probability of encountering more favorable conditions. The physiological integration among intraclonal ramets reduces the establishment risks of new daughter ramets and enables a genet to integrate local heterogeneity in resource availability. The result is that establishment and competitive ability are increased equitably among genets, and genets are buffered against localized patch—specific selection. This reduction in genetic deaths may be one mechanism resulting in the maintenance of variation in clonal populations.
Vegetation Change in Response to Extreme Events: The Effect of a Short Interval between Fires in California Chaparral and Coastal Scrub
Authors: Zedler Paul H. , Gautier Clayton R. , McMaster Gregory S.
Published: May 2006

This study describes changes in the abundance of shrub species after two fires in 1979 and 1980 on Otay Mountain in San Diego County, California. The 1979 fire burned a large area of dense chaparral and coastal sage scrub. The 1980 fire burned a portion of the 1979 fire area that had been seeded with annual ryegrass (Lolium multiflorum) as an erosion protection measure. Changes in the vegetation caused by the 1979 fire alone were similar to those commonly seen in chaparral wildfire, but the reburning of the vegetation in 1980 caused drastic changes in some areas. Ceanothus oliganthus was almost completely eliminated from the area of the 1980 burn. Adenostoma fasciculatum, the most abundant shrub at the study site, was reduced in density by up to 97%. Even Xylococcus bicolor, which normally resprouts with complete success after fire, suffered substantial mortality with reburning. It is concluded that the changes brought about by the 1980 fire will certainly persist for many decades. While sudden shifts in vegetation composition probably occurred without human intervention, we believe that human activity, especially after the introduction of aggressive annual grasses 200 yr ago, has caused an increase in the instances of abrupt change.
A 12 000‐Year Record of Forest History form Cahaba Pond, St. Clair County, Alabama
Authors: Delcourt Hazel R. , Delcourt Paul A. , Spiker Elliott C.
Published: May 2006

A 650—cm sediment sequence from Cahaba Pond, St. Clair County, Alabama spans the past 12 000 yr and has yielded a pollen and plant—macrofossil record indicating major changes in forest composition during the Holocene interglacial. Both pollen and plant macrofossils from sediments of this 0.2—ha pond primarily reflect changes in local and extralocal forests within the surrounding watershed. Four distinct pollen assemblage zones were recognized: a Fagus—Ostrya zone from 12 000 to 10 200 BP, a Pinus—Magnolia zone from 10 200 to 10 000 BP, a Quercus—Carya zone from 10 000 to 8400 BP, and a Nyssa—Pinus zone from 84 BP to the present. Forests of the early Holocene (12 000 to 10 000 BP) were mesic and predominantly composed of broadleaved deciduous trees, dominated by beech (Fagus grandifolia) and with substantial representation of hornbeam (Ostrya/Carpinus), oak (Quercus), hickory (Carya), elm (Ulmus), and ash (Fraxinus). Atlantic white cedar (Chamaecyparis thyoides), today a coastal species, extended inland to St. Clair County during the early Holocene. Eastern white pine (Pinus strobus), hemlock (Tsuga), striped maple (Acer pensylvanicum), and mountain maple (Acer spicatum), today rare or absent in Alabama, extended southward of their present ranges into central Alabama 10 000 yr ago. Outliers of mixed, mesic hardwood communities in the southern Ridge and Valley and Piedmont provinces may be relicts that date from the early Holocene, a time with high species richness and equable climate. After 10 000 BP, forests became more xeric, with oaks and hickories predominant. Cahaba Pond, formerly dominated by submersed aquatics such as Najas gracillima, became shallower, and floating—leaved and emergent aquatics became abundant. A decrease in effective precipitation is inferred for the time period between 10 0000 and 8400 BP. After 8400 BP, black gum (Nyssa sylvatica), southern pines (Diploxylon Pinus), red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), buttonbush (Cephalanthus occidentalis), and other elements of the modern flora became established locally. Water levels in the pond became higher, and sedimentation rate diminished, as observed in other pond sites in the region. An increase in effective precipitation in the late Holocene reflects the establishment of the modern atmospheric circulation patterns, including increased frequency of hurricanes developing in the Gulf of Mexico and the equatorial Atlantic Ocean.
Some Comments on Niche Analysis in Canonical Space
Authors: Carnes Bruce A. , Slade Norman A.
Published: May 2006

Discriminant functions have been used to identify axes of niche separation, and dispersion of locations on these axes have, in turn, been interpreted as representing niche width and specialization. We discuss the influence of sampling scheme and choice of niche measures on the results of an analysis conducted in canonical space. Specifically, habitat variables measured at random locations should provide a more representative measure of habitat available than would recording habitat only where animals are observed. Species presence information alone tends to bias the mean habitat toward the one where the most common species is found. If niche specialization is to be measured by distance from the overall mean habitat, each sampling station should receive equal weighting. The most straightforward measure of habitat breadth seems to be the variance or standard deviation of canonical scores. The mean squared distance from the species centroid can then be used as a comparable multidimensional breadth measure. Finally, we suggest that niche overlap be measured via a joint probability density function rather than by area of overlap of concentration ellipses.
Drought‐Induced Changes in Avian Community Structure Along a Montane Sere
Authors: Smith Kimberly G.
Published: May 2006

Avain community structure was studied along a meadow—aspen—fir—spruce subalpine sere in northern Utah and southern Idaho during the breeding seasons of 1976, 1977, and 1978. During 1977 one of the worst droughts of this century occurred in the western United States, and comparative changes in avian community structure were documented during and after drought in the four seral stages. The number of breeding species declining most markedly during drought in aspen. Breeding communities on the forested plots during drought were least similar to predrought communities; pre and postdrought communities were consistently most similar. Densities of singing males declined more markedly on all plots during drought than did number of species, and remained below predrought levels in 1978. Changes were also noted in avian trophic structure during drought: insectivores generally declined in number, nectivorous hummingbirds completely disappeared, and the number of granivorous cardueline finch species increased. These changes can be related to changes in food resources. During drought, insect species composition and densities changed, flower phenology was 5 wk early, and one of the best coniferous cone crops in 30 yr occurred in northern Utah. Direct effects of lack of water were observed, and many bird species probably experienced water stress. Although difficult to document, indirect effects of drought on food resources are suggested for insectivores, nectivores, and possibly carnivores. The result indicate that a drought can represent an "ecological crunch" to and affect the structure of, temperature avain communities. However, separating the variation due to drought from inherent variation is difficult without comparative long—term studies. Avian communities in deciduous vegetation may be greatly affected by drought than those in coniferous vegetation.
How Aphids Choose Leaves: The Roles of Phenolics in Host Selection by a Galling Aphid
Authors: Zucker William V.
Published: May 2006

The aphid Pemphigus betae does not induce galls at random on leaves of its host plant, Populus angustifolia (narrowleaf cottonwood). Probability of stem mother success in forming a gall, body mass of stem mother and progeny, number of progeny, development rate of progeny to maturity and numbers of embryos in mature progeny are all correlated positively with leaf size at maturity. Leaf size at maturity is predictable from leaf position in the shoot at bud burst (Whitham 1978, 1980). The major secondary compounds of the host plant are known phenol glycosides. Using the Folin Denis assay for total phenol determination, a strong inverse correlation has been established between the concentration of total phenols and suitability of a tree, leaf, or leaf section for galling at the time of bud burst, when the colonizing stem mothers are at the peak of their activity. Expanding leaves within the same shoot have different phenol concentrations; the potentially largest leaves have lower phenol levels. Leaves containing one or more incipient galls have lower phenols levels than leaves without galls. Phenol concentrations in leaves are not uniform; the existence of phenol gradients in leaves is demonstrated. In a comparison between two neighboring trees that are differentially infested with colonizing aphids, the tree with the higher aphid numbers per leaf has lower phenol levels in its leaves. These same leaves were shown to posses different average phenol gradients, suggesting that phenol gradients play a role in microhabitat selection. These findings are consistent with the known biology and territorial behavior of the aphid and provide a chemical basis for continuing studies on aphid habitat selection and fitness.
On the Comparative Allocations of Biomass, Energy, and Nutrients in Plants
Authors: Abrahamson Warren G. , Caswell Hal
Published: May 2006

The objective of this study was to test the assumption that biomass allocation, energy allocation, and nutrient element allocation are equivalent for studies involving ecological—strategy analysis in plants. The results for the semelparous Verbascum thapsus and five iteroparous Solidago species show that the mineral elements examined are allocated differently than biomass. Thus, in a study aimed at estimating the allocation strategy of plants within a population, it would not be prudent to measure biomass allocation and assume that it reflected nutrient allocation. More important, there are significant nutrient X population interactions, which means that between—population trends in biomass allocation do not reflect qualitative trends in mineral element allocation. The results of this study do not identify a given mineral element, biomass, or energy as the best measure of resource allocation patterns, but the study indicates that further research along the lines of the "currency" of allocation is greatly needed. Results with Solidago show strong correlation between biomass allocation and energy allocation. The reemphasizes Hickman and Pitelk's (1975) conclusion that calorimetry is not necessary to determine energy allocation patterns within populations in plants with primarily carbohydrate seed reserves. There was an overall lack of correlation between soil nutrients and the chemical composition of Solidago plant organs or whole plants.
Prey Selection and Handling in Two Neotropical Hover‐Gleaning Birds
Authors: Sherry Thomas W. , McDade Lucinda A.
Published: May 2006

Prey handling and prey selection were studied by releasing over 150 live insects to wild White—fronted Nunbirds (Monasa morphoeus, Bucconidae) and a caged Bright—rumped Attila (Attila spadiceus, Tyrannidae). Handling time was determined for each insect taken and the relationship between handling time and several prey characteristics was examined. Log—transformed x— and y—axes (power function) better linearized the relationship between handling time and prey size than log—transformed y—axis (exponential function) or untransformed axes did for acridid—tettigoniid Orthoptera, the insect group used to compare handling abilities of the two species. The species power function slopes were statistically indistinguishable, but y—intercepts differed such that the smaller attila (40 g) required significantly longer than nunbirds (108 g) to handle prey of a given mass or width. An energetic cost—benefit analysis using these handling time regressions showed that handling costs wer negligible compared with benefits and could not explain the upper limit to prey size (2—6 g) for nunbirds. The cost/benefit functions of the two species largely coincided, and the energetics of prey handling would not likely predispose these two species to take different mean prey sizes. The most important difference between the two species should be the range of sizes effectively utilized; the larger predator can consume much larger prey then the smaller predator can. For all insects successfully handled, prey body width was the best predictor of handling time in both species. We argue that the primary function of prey handling in these birds is to render prey swallowable. Thus gape size sets a limit to the largest noncreshable prey, and determines how much handling is required for malleable prey. A variety of insects were rejected by nunbirds because of the insect size and/or shape in combination with hardness and distastefulness. Knowledge of prey—handling behavior in these birds predicts effective insect morphologies to impede avian handling abilities.
Harmonious Coexistence of Hispine Beetles on Heliconia In Experimental and Natural Communities
Authors: Strong Donald R.
Published: May 2006

Hispine beetles that live as adults in the rolled leaves of Heliconia plants are prime suspects for interference competition among species, based upon theory developed by vertebrate ecologists. These beetles are tropical, long—lived, and very closely related, eat the same food, and use the same habitat. However, hispines do not conform to this theory: 1) Rolled—leaf hispines are not aggressive intra— or interspecifically, and are not displaced or intimidated by encounters between individuals. 2) Adults are not segregated by species into different leaf subsets of host populations. Species mingle together in patterns that do not suggest interspecific competition. 3) Number of species does not affect interspecific association. 4) Pairwise correlations indicate that only one beetle (Cephaloleia) of the 13 species studied is even weakly segregated from others. It prefers leaves on younger plants than those preferred by other species, and its segregation is a result of subtle habitat differences rather than competition. 5) Interspecific segregation among hispanies does not increase with density in leaves. 6) No higher order interactions were detected in species associations. 7) Experiments showed that habitat heterogeneity does not measurably influence interspecific association in hispine communities as delimited by a single host species. Experimental communities in nature were constructed with minimal habitat heterogeneity, and no mor segregation or aggregation between hispine species occurred in experimental than in natural communities. Additional observations suggest that levels of food and habitat are commonly not limiting to hispine populations, which suffer heavy parasitism and predation. I infer that community structure of hispines on Heliconia is affected greatly by natural enemines. Heliconia is not chemically noxious to hispines, and experiments show that hispines grow at maximum rates on the relatively low nitrogen content of Heliconia. Theories of community structure based upon interspecific competition, and those based upon allelochemical protection of host plants against adapted insects, are not suitable for hispine communities on Heliconia. My conclusions largely agree with those of Hairston et al. 1960. Additional work with parasitism, predation and other factors that may affect hispine populations, such as the weather, migration, and spacing of host plants, is necessary to establish key and regulatory factors for these tropical insects.
Cryptomeria Japonica: Glacial Refugia and Late‐Glacial and Postglacial Migration
Authors: Tsukada Matsuo
Published: May 2006

Cryptomeria japonica had multiple refugia in Japan where relatively moist, cool climates prevailed during the last glacial period. Its expansion began from scattered full—glacial centers of distribution °15 000 yr ago, reaching its maximum abundance from °7000—2000 yr ago. On one migration pathway, along the southwestern Japan Sea coast, the movement was initially from the coastal refugia to the interior mountains, and was then toward the southern limit of modern distribution; however, the arrival of the species was greatly delayed in Kyushu and Tsushima Islands. Here, the initial stock of Cryptomeria plants was probably brought from Honshu by prehistoric man °2500 yr ago. Cryptomeria reached its northern limit by 3000 yr ago through the coastal route along the Sea of Japan. The population which migrated from the Izu Peninsula area along the Pacific coast did not arrive in Sendai until °1500 yr ago. In Shikoku, Cryptomeria stands were probably continuous with those on the Kii Peninsula during the full—glacial period, but have been isolated for about the last 12 000 yr. After its arrival at each site, a population of Cryptomeria behaved in either of two ways: in a less moist area, it increased slowly in abundance, hardly reaching the 20% pollen frequency level at its maximum occurrence, while in a humid area (> 2000 mm annual precipitation) it increased logistically to an asymptote (represented by generally 50% of the fossil pollen spectra).
Production Strategies in Antarctic Inland Waters: Phytoplankton Eco‐Physiology in a Permanently Ice‐Covered Lake
Authors: Vincent Warwick F.
Published: May 2006

Three distinct population strategies were observed within the summer algal plankton of Lake Fryxell (Taylor Valley, South Victoria Land, 77°35'S, 163°15'E). Phytoplankton immediately under the ice (Ochromonas and Chlamydomonas) were adapted to relatively bright light but were limited by nitrogen availability. A deep maximum of Chroomonas and Pyramimonas was recorded at the bottom of the euphotic zone. This community did not respond to nitrogen or phosphorus enrichment. It was highly shade adapted but at this depth ambient irradiance was below that required to saturate photosynthesis. Net population increases in both the upper and lower euphotic communities occurred very early in the season. Flagellated algae in the middle of the oxygenated water column swam up to depths of greater light during the day and returned to lower depths of greater nutrient supply at night. These mid—euphotic populations continued to grow throughout midsummer. Comparisons with other Dry Valley lakes suggest that nutrient supply, rather than in situ light or temperature, determines the large lake—to—lake and depth variations in primary productivity. Nutrient availability appears to control algal biomass, but in contrast to arctic ecosystems, low light rather than low temperature dampens algal photosynthesis to cellular rates that are well below those recorded at lower latitudes. The complexity of production strategies in Lake Fryxell, and the occurrence of population maxima early in the season when sampling is logistically difficult, challenge the view that the desert lakes of Antarctica offer ideal and simple systems for limnological study.
Movement and Microdistribution of Sida Crystallina and Other Littoral Microcrustacea
Authors: Fairchild G. Winfield
Published: May 2006

Littoral invertebrates of Cochran Lake, Michigan were either highly plant—associated, and found infrequently away from aquatic macrophytes, or free—swimming among the plants. Plant—associated taxa were distributed according to available surface area. Numbers of periphyton and detritus feeders, chiefly chydorid Cladocera and chironomid midge larvae, were highly correlated with diatom density, whereas filter—feeding Cladocera attached to the plants (Sida, Simocephalus) were not. Cyclopoid copepods characteristic of the littoral during the day (Macrocyclops, Eucyclops, and Microcyclops) were also found primarily on aquatic plant surfaces. Abundances of the chydorid Cladocera increased slightly at night, while other taxa showed little diurnal variation. Free—swimming species in the littoral (Bosmina, Ceriodaphnia) sometimes formed large patches covering many square metres. Large species (Mesocyclops, Diaptomus, Epischura) greatly increased the numbers and diversity of this community at night. Sida crystallina, a filter feeder typically attached to plant surfaces, nonetheless swims frequently and well if disturbed. Juveniles moved between substrates more frequently than adults, and were found nearer the surface. Sites for reattachment were located visually. Frequent and often extensive episodes of swimming, especially by juveniles, provided a plausible explanation for the high concentrations of Sida observed on isolated plants, particularly those on the margins of stands of aquatic vegetation.
Factors Controlling Photosynthetic Productivity in a Population of Cladophora Fracta (Chlorophyta)
Authors: Cheney Caralee , Hough R. Anton
Published: May 2006

Cladophora fracta is the dominant filamentous alga in the littoral zone of Shoe Lake, Oakland County, Michigan. Seasonal and diurnal in situ productivity studies were combined with perturbations of several environmental parameters conducted in situ and in the laboratory to determine the factors that control primary productivity in this population. In situ net photosynthetic carbon fixation ranged from 0.26 to 5.39 mg°g—1°h—1, with seasonal maxima in spring and fall and diurnal patterns generally, but not always, correlating with daily insolation patterns. Phosphorus and nitrogen were above limiting concentrations throughout the year, and C. fracta was unresponsive to experimental P and N enrichments. The seasonal productivity correlated most strongly with total alkalinity (inorganic carbon content) and pH, and experimental enrichment of inorganic carbon stimulated photosynthesis during the summer. C. fracta was characterized in the laboratory as basically a C3 plant on the basis of very low levels of C4 acids in early 14C photosynthetic products and light saturation of photosynthesis below 30 klx. In situ experiments showed oxygen inhibition of photosynthesis, but photorespiration was not directly demonstrable by evaluation of 14CO2 release, and the CO2 compensation point was low. Release of organic photosynthate was stimulated by high oxygen, but the effect was maximal during spring and fall growth peaks rather than in the summer. Optimal photoperiod was experimentally determined to be relatively short (8 h), which correlated with the fall and spring maxima in productivity and carbon availability. Temperature in situ was below the experimentally determined optimum for photosynthesis in both spring and summer, and was associated with daily patterns of photosynthesis more closely than with the seasonal pattern. Epiphytic flora on C. fracta reduced organic carbon release to a small extent and contributed to a slight enhancement of community productivity. The productivity of C. fracta during the ice—free growing season in Shoe Lake appears to be limited principally by inorganic carbon and by oxygen inhibition of photosynthesis. C. fracta competes significantly on the basis of rapid growth capability early in the season coincident with maximal carbon availability and later possibly by minimization of photorespiration.