bluuebunny/crossref_metadata_2025 huggingface dataset:
Predatory Copepods and Bosmina: Replacement Cycles and Further Influences of Predation Upon Prey Reproduction
Authors: Kerfoot W. Charles , Peterson Carolyn
Published: May 2006

In the days of large lakes, populations of cladocerans and rotifers often appear to undergo seasonal morphological changes. In the past, these transformations were thought to reflect phenotypic plasticity within lineages (cyclomorphosis). However, in Union Bay populations of Bosmina, the transformations clearly involve regular seasonal replacements (termed "taxocene cycles") by genetically different lineages. In Union Bay, Washington, USA, selective predation by both visually foraging and blindly grasping predatrory copepods, combined with reproductive and competitive costs associated with prey defense, created a spatial and temporal environment where the seasonally fluctuating selective regimes exceed the ability of individual lineages to adapt phenotypically to changes. Genetically different clones, some derived from biologically isolated populations, rapidly replace one another in time and space. While most clones remain extant throughout the year, even times of relatively small density differences are punctuated by rapid clonal replacement. Detailed study of the clonal replacements disclosed that: (1) phenotypes generally fall into three modal classes (short—, intermediate—, and long—featured forms); (2) the short and longs are separate species; and (3) intermediates are not the results of crosses between extremes, but are heterogeneous mixtures of convergent lines derived from the other two species. While there is limited sexual activity, and certainly opportunity for mating between clones, there is no electrophoretic evidence for crossing. The distinctive nature of certain secondary sexual features seems associated with mate choice and thus aids the isolation of various lineages. In general, the frequency of sexual activity, the evolution of the brood chamber, and the transparent ephippium all appear intimately associated with predation and the selective advantage of rapid reproductive responses.
Bat Activity and Pollination of Bauhinia Pauletia: Plant‐Pollinator Coevolution
Authors: Heithaus E. Raymond , Opler Paul A. , Baker Herbert G.
Published: May 2006

The relationship between the pollination biology of a tropical plant, Bauhinia pauletia, and the foraging strategies of the nectarivorous bats visiting it was studied. At least two bat species are pollen vectors, Phyllostomus discolor and Glossophaga soricina. Artibeus jamaicensis and Sturnira lilium were also captured near Bauhinia flowers. Larger bats (P. discolor) drain flowers of nectar and forage in groups, while smaller bats (G. soricina) make brief visits and forage independently. These foraging strategies should optimize energetic gain for the bats and promote outcrossing for the plant. Bauhinia pauletia is self—compatible, but is found where conditions favor outcrossing. Andromonoecism(the preence of hermaphrodite and male flowers) in this species appears to be anadaptation to pollination by large pollinators that also promote outcrossing.
Distribution and Activity of the Desert Cockroach Arenivaga Investigata (Polyphagidae) in Relation to Microclimate
Authors: Edney E. B. , Haynes Stuart , Gibo David
Published: May 2006

Arenivaga investigata is abundant in sand dunes of the Colorado desert at the foot of Mount San Jacinto, California. Measurements of temperature and humidity were made in its habitat at various depths in the sand over 24—h periods at least once each month from July 1967 to July 1968. At the driest and hottest times of the year (surface temperature 72°C, RH < 10%), relative humidities of 82% and above were available only 45 cm below the surface, and temperatures below 40°C occurred at —7.5 cm or lower. Since the insects can absorb water vapor from 82% RH or above, their source of water is assured. Onset of subsurface activity towards nightfall may be correlated with the movement downward of the temperature inversion, but this is not proved. The insects are found much more commonly in the sand near or under shrubs than in open sand. Their vertical distribution shows a maximum at —12.5 cm in July, and at —5 cm in November. In July most insects were found at temperatures between 30° and 35°C, whereas in November they were most frequent from 22° to 26°C. This seasonal difference in distribution, which could be attributed to acclimation, awaits further analysis.
The Relationship Between Net Primary Production and Accumulation for a Peatland in Southeastern Manitoba
Authors: Reader R. J. , Stewart J. M.
Published: May 2006

Two functional attributes of an ecosystem, net primary production and subsequent dry matter accumulation, were examined in four peatland types (lagg, bog, muskeg and bog forest) located in southeastern Manitoba. A preliminary peat accumulation budget was constructed by relating the amount of litter present after a single year of decomposition to the initial litter income and annual net primary production. Annual litter “income” in the four vegetation zones ranged from 489 gm/m2, which represented 69% to 90% of the calculated net primary production. Decomposition losses in the following year amounted to approximately one quarter of the original income. An average annual accumulation rate of 26 gm/m2/yr to 51 gm/m2/yr was calculated from radiocarbon—dated peat cores, thus suggesting that less than 10% of the annual net primary production will remain as peat.
Competition and Mechanism of Coexistence in Three Sympatric of Intertidal Hermit Crabs
Authors: Vance Richard R.
Published: May 2006

During monthly intervals over a 1—year period, 12,000 empty snail shells were added to a small, isolated, rocky intertidal reef in the San Juan Islands of Washington. The shells added were species normally used by the high intertidal hermit crab, Pagurus hirsutiusculus, and were placed in locations accessible to that species. The shell additions resulted in an increase in density of P. hirsutiusculus at the experimental reef, whereas no density change occurred at a nearby control reef, indicating the importance of shells as a limiting resource. To establish the generality of shell limitation, the hermit crab populations of four unmolested rocky intertidal sites (three of which are typical hermit crab habitats) were quantitatively samples to obtain species compositions and size distributions of hermit crabs, their shells, and unoccupied shells. Shell preference experiments determined the preferred shell sizes and species for each hermit crab species. Except for small size classes, empty shells were rate at the three typical areas. In addition, hermit crab size distributions followed shell size distributions, and all but small hermit crabs of three species occupied shells smaller than the preferred size. These results support the conclusion that empty shells are a limiting resource for these hermit crabs. Since shells constitute a common, necessary resource in short supply, these hermit crabs are in competition for available shells. The fourth area, chosen for its unusual shell—availability characteristics, exhibited a different pattern of shell utilization not suggesting shell limitation. Shell occupancy at the three representative intertidal sites was examined to determine the strength of the relationship between hermit crab species composition and resource availability. Though resource partitioning was demonstrated, the presence and numbers of each hermit crab species and its preferred shell types were poorly correlated. Differences in hermit crab species composition are explained by differences in the physical habitat, and collections from other areas show that the same shell species can support different hermit crab species in different but adjacent habitat types. Thus, the mechanism allowing coexistence apparently involves both resource and habitat partitioning.
A Transformation for Species Response to Habitat Factors
Authors: Forsythe W. L. , Loucks O. L.
Published: May 2006

This study develops a data—transformation method useful in correlating species importance with habitat factors. The relative basal area of six major tree species is examined in relation to data on eight environmental factors. A parabola transformation makes the domeshaped species—importance response into a more linear relationship. The transformed data then are examined by a multiple regression of the response of each species to eight factors. The regression yields a numerical estimate of the relative influence of each factor in increasing or decreasing the importance of each species. The regression also yields a numerical estimate of the relative influence of each factor in increasing or decreasing the importance of each species. The regression also yields an estimate of the extent to which variation in species importance is accounted for by the environmental influences present in the study area. Regression with parabola transformation accounts for as much as 80% of the variation in individual species importance. Simple linear multiple regression accounts for no more than 65% of the variation.
The Covering Response to Surge, Sunlight, and Ultraviolet Light in Lytechinus Anamesus (Echinoidea)
Authors: Lees Dennis C. , Carter Gerald A.
Published: May 2006

Examination of the covering reaction (masking or heaping with shells) of Lytechinus anamesus in response to ultraviolet irradiation, sunlight, and surge suggests that most previous hypotheses explaining this reaction are inadequate or incomplete. Shaded L. anamesus initially reacts to short wavelength ultraviolet light (254 nm) with a fairly strong masking response, which is followed by death after an exposure of several days. Long wavelength ultraviolet light (360 mm) elicits moderate covering, while the nonirradiated controls rarely covered. These responses to ultraviolet light are probably artifacts, as L. anamesus and other sea urchins are seldom exposed to that factor in nature. There is a strong and immediate covering response to direct sunlight. Application of surge induces a cover response nearly equal to that of sunlight, regardless of light conditions. The intensity of covering during periods of surge appears to increase during the exposure period. Cessation of surge results in a rapid reduction in covering and a marked increase in movement. We suggest that covering is important in increasing the stability of this echinoid during periods of increased surge by effectively increasing its specific density, reducing its surface area, and changing the configuration it presents to surge forces. Sunlight intensity may be used as a cue that indicates directly the risk of displacement by surge action.
Cold Hardiness of Twigs of Quercus Rubra L. As a Function of Geographic Origin
Authors: Flint Harrison L.
Published: May 2006

Cold hardiness of twigs of young tress of Quercus rubra L. grown from seeds collected form 38 different geographic origins and growing on a single site varied widely from October to December, 1968, and was strongly related to estimated average annual minimum temperature of the origin. By March, 1969, differences among sources had disappeared. Hardening again was apparent as early as August 23, 1969, accompanied by a significant differentiation related to climate of the origin. Multiple regression analyses showed twig hardiness to be closely related to latitude of the origin. Longitude and elevation had significant but secondary effects in autumn. Average annual minimum temperature (AAMT), extreme minimum temperature (EMT), length of frost—free period (FFP), and biotemperature (BIOT) as defined by Holdridge, were highly correlated with each other and with latitude of the origin. All were strongly related to cold hardiness in autumn. Cold hardiness in all cases was greater than that required by climate of the origin, suggesting that twig hardiness in established trees is not an important factor currently in natural selection.
Energy Balance Investigations on Native Range Vegetation in the Northern Great Plains
Authors: Aase J. Kristian , Wight J. Ross
Published: May 2006

Evapotranspiration (ET) to net radiation (Rnv) ratios for native vegetation on semiarid western rangeland were less than 1 throughout the season except for a rainy period, illustrating the contributing role of semiarid range to downwind advection. Ratios of pan evaporation (Ep) to net radiation over an evaporation pan (Rnp) were consistently greater than 1, indicating the contribution of advective energy to free water evaporation. Net radiation over both vegetation and an evaporation pan were similar except for early and late growing season. The relationship between Rnv and solar radiation (R8) was highly variable. with Rnv:R8 ratios ranging from 0.2 to 0.7.
Environmental Patchiness and the Breakdown of Leaf Litter in a Woodland Stream
Authors: Reice Seth R.
Published: May 2006

The breakdown of allochthonous leaf litter in woodland streams occurs at the community level process which is patchily distributed. Two kinds of environmental patches were tested: types of bottom sediment and sizes of leaf pack. Four sediments, aligned along parallel environmental gradients (velocity and sediment complexity), were studied: rock, gravel, sand, and silt. Five pack sizes were studied: 1, 5, 10, 20, and 40 g. Preweighed packs of white ash (Fraxinus americana) leaflets were tied to bricks and set on the sediments. These were sampled weekly for 6 wk, and the percent dry weight lost was determined. This design was followed in each of the four seasons to test the seasonal variability in leaf litter breakdown. Analysis of variance and comparison of means show that, in all seasons, sediment and pack—size effects are highly significant (P < .001). Leaf packs of all sizes were broken down less in the silt than in the other sediments. The sediment patterns are consistent with the community level effects of physical heterogeneity and stability. Though the pack—size effects were highly variable from season to season, the degree of breakdown differentiated the leaf—pack sizes in every season, at least one size displaying major differences from the others. The seasonal patterns in breakdown reflect its temperature dependence, the breakdown increasing with increasing temperature. The community level process of leaf litter breakdown in streams is patchily distributed in space. This suggests a level of organization between the population and the community, namely the patch—specific component community.
Effects of Territoriality on Breeding in a Population of Cassin's Auklet
Authors: Manuwal David A.
Published: May 2006

There are approximately 105,000 breeding Cassin's Auklets (Ptychoramphus aleuticus) on Southeast Farallon Island, California. Burrow density is high, from 1.09 to 0.02 burrows per square meter. Removal experiments conclusively showed a surplus population capable of reproducing. This floating population has an equal sex ratio, and 50% of the floaters were paired before or immediately after entering a recently vacated burrow. Fifty percent of the floating population is adult and 80% have no previous breeding experience. Most floaters do not maintain active permanent territories, but instead roost in areas where there are no territory—holders. Other floaters actively search for empty burrows. Fifty percent of the floaters fledged young, and at least 44% of 1970 floaters in the removal experiment returned to breed in 1971. Floaters enter the population at the rate of about 19% per year. It is clear that territorial behavior limits breeding density in this population of Cassin's Auklet.
Qualitative Stability and Digraphs in Model Ecosystems
Authors: Jeffries Clark
Published: May 2006

Roughly speaking, an ecosystem is called qualitatively stable" when one may conclude solely on the basis of the qualitative effects of member species on each other, that the system is stable. The conditions for qualitative stability are rather severe, particularly for ecosystems with great species diversity. Nonetheless, qualitative stability conditions may be met in nature by very simple ecosystems. In a recent paper, R. M. May (1973) presented necessary but insufficient conditions for qualitative stability. In this report, sufficient conditions are expressed in terms of the food web design viewed as a signed digraph."
The Allelopathic Influences of Sassafras albidum in Old‐field Succession in Tennessee
Authors: Gant Robert E. , Clebsch Edward E. C.
Published: May 2006

Allelopathy seems to be the mechanism that allows Sassafras albidum to maintain itself in relatively pure stands through many stages of old—field succession. Field studies revealed that 10 species consistently occurred exclusively outside of clump canopies and 7 other species predominated beneath the sassafras canopy. We suggest that annual herbs are being effectively excluded from the understory flora. 2—pinene, α—phellandrene, eugenol, safrole, citral, and d—camphor were isolated were within and outside of sassafras stands from leaves, litter, soil, and roots. Germinating seeds watered with aqueous leachates of leaves, litter, and canopy washings showed varying degrees of radicle reduction during germination. Germination on soil discs from beneath sassafras stands was significantly lower in four of the test species; in seeds overwintered in sassafras litter it was significantly lower in all species. There was a positive correlation between α—phellandrene concentration and reduction in radicle growth in Acer negundo and Ulmus americana. Sufficient incoming and buried seeds were available to support a richer and more abundant understory flora than was found in the vegetational survey. The different modes of sassafras for releasing phytotoxins into the environment at different times of the year operate to continually influence its surroundings.
Biogeography of the Puerto Rican Bank: Species‐Turnover on a Small Cay, Cayo Ahogado
Authors: Heatwole Harold , Levins Richard
Published: May 2006

The equilibrium species—number of plants on Cayo Ahogado, a small sand cay east of Puerto Rico, is 11.2 if all species are considered, and 6.8 if only established species are counted. Establishment is defined in terms of reproductive success and presence on the island for at least two consecutive visits. There were only five species in the permanent flora. Species—turnover rates of plants were high, migration being on the average 14.4 species/year (all species), or 1.6 species/year (established species only). Extinction rates were 17.2 and 0.8 species/year for total species and established species respectively. Immigration is chiefly by flotation, particularly of propagules released by flood waters in Puerto Rico; extinction is caused by failure to find suitable habitat, wave erosion, and hurricanes. Nine individuals of three species of lizard arrived, probably by flotsam as time of arrival correlated with flooding in Puerto Rico, and persisted for varying times up to 5 months. No reproduction occurred. Species turnover of invertebrates was high. Eighty—one species (77 terrestrial, 1 marine water strider, and 3 semiterrestrial crustacea) were recorded from the cay. Equilibrium number was 9.8 for established species and 14.2 for total species. Direct flight was probably the most imporrant mode of immigration for the entire fauna because of the large number of strong fliers among the ephemerals. If only established species are considered, flotsam transport becomes important. Human transport and passive dispersal by wind were relatively insignificant. Trophic structure of the fauna remained relatively constant although taxonomic structure varied. It is postulated that species—numbers on small cays are determined in part by the type of trophic structure which can be built upon available energy reserves, and that establishment of immigrants is influenced by whether they fit into the trophic scheme.
Comparative Production of Larrea Divaricata Cav. on Three Geomorphic Surfaces in Southern New Mexico
Authors: Burk J. H. , Dick-Peddie W. A.
Published: May 2006

Net above—ground productivity was measured for 3 years on creosotebush (Larrea Divaricata Cav.) occuring on three different geomorphic surfaces. Rates of stem elongation, fruit production, flower production, and accumulation of secondary wood were ascertained for each of the geomorphic surfaces. Growth rates varied among plants of the different surfaces, but when the net production of stands were compared, rates for the surfaces were remarkably similar. Statistically significant differences were present in both growth and net productivity between years. Creosotebush seems to have a great capacity for adjusting to sites of broad ecological amplitude with no apparent effect upon its ability to fix energy.
Changes in Patterns of Seasonal Growth of Microtus Pennsylvanicus
Authors: Brown Ernest B.
Published: May 2006

A field study of growth, in terms of both linear dimensions and weight, was made by successively trapping the small winter—active mammals found in a study area in a region with persistent winter snow cover. The animals trapped were primarily Microtus pennsylvanicus, with some data also on Blarina brevicauda, Clethrionomys gapperi, and Peromyscus sp. The reliability of the field measurements was determined by comparing successive measurements made on individual animals within short time spans. The results of these comparisons indicate that linear measurements can be made accurately on live, conscious animals in the field, and that linear measurements are much more reliable than weight measurements. Microtus pennsylvanicus young born in the spring and early summer reach adult size in 12 weeks or less. These animals undergo a fall loss in weight. Animals born in middle to late summer stop growing in the fall, maintain their weight and linear dimensions throughout the winter, and resume growth again in the spring. Blarina brevicauda individuals grow little in linear dimensions after entering the trappable population and do not appear to lose weight in the fall.
A Grasshopper Model for a Grassland Ecosystem
Authors: Rodell Charles F.
Published: May 2006

A state variable, process—oriented model is presented that considers the effect of grasshoppers on a grassland ecosystem. The model considers that interactions with producer, decomposer, and other consumer components via the mechanistically implemented flow of carbon through the system. The primary driving variables that influence the grasshopper model are air temperature and precipitation. Grassphopper have a direct effect on producers through diet selection, herbivory, and damage as the result of feeding. Interactions with the decomposers are the result of death and feces production. Grasshoppers interact with other consumers as the result of competition for food and predation on the grasshooper population. The major objectives addressed in the model are estimates of the grasshopper population dynamics, the effects grasshoppers have on the total grassland system, and the amount of energy flow through the grasshopper population. The age structure of the grasshopper population is considered only where information exists to indicate that age groups are functionally different and can be represented within the resolution of the model. The model is formulated in first—order difference equations in the simulation language SIMCOMP. Simulation results of the model are presented and discussed.
Acclimatization of Thermoregulation in Desert‐Inhabiting Jackrabbits(Lepus Alleni and Lepus Californicus
Authors: Hinds David S.
Published: May 2006

Seasonal physiological responses to ambient temperature were determined for the black‐tailed jackrabbit, Lepus californicus and the antelope jackrabbit, Lepus alieni at Tucson, Arizona. Both species exhibited similar responses to changes in season although differences were noted. From winter to summer the thermoneutral zone shifted upwards, with the shift occurring at both critical temperatures in L. californicus and at only the lower critical temperature in L. alieni. Standard metabolism above thermoneutrality was higher in winter than in summer, while below thermoneutrality it was lower in winter than in summer. Basal metabolism in winter was 15% lower in L. alieni and only slightly lower in L. californicus. Water losses during the summer were higher than in winter at ambient temperatures below 20°C and lower at the higher air temperatures. During both seasons all metabolic heat production was dissipated by evaporative heat Joss at an ambient temperature of ≈ 40°C. Seasonal differences in body temperature were not apparent except that in summer L. alieni exhibited hypothermia at ambient temperatures < 20°C. The dry‐heat‐transfer coefficients were higher during summer below 30°C; they also increased at higher ambient temperatures than in winter and at a faster rate. The dry‐heat‐transfer coefficient in L. alieni decreased during summer when ambient exceeded body temperature. This was not the case in winter for L. alieni or in either season for L. californicus.
Seasonal Maintenance and Net Production of Two Sympatric Species of Subarctic Microtine Rodents
Authors: Whitney Paul
Published: May 2006

Estimates were made of production and productivity (rate of production) of net biomass and metabolic rates for two species of mocrotine rodents in interior Alaska. Net production was estimated at two—wk intervals for natal, nestling, juvenile, subadult and adult components of each population. Maintenance energy requirements of nestling and adults were estimated on a seasonal basis using metabolic rates measured in the laboratory at concurrent field temperatures and photo—period. Maximum densities of Clethrionomys rutilus were nearly equal during each year of the study (° 60/hectare), yet yearly net production (1969 = 11565 kJ/hectare, 1970 = 6363 kJ/ha, 1971 = 1168 kJ/ha) varied nearly twofold. Yearly variability was due to a delay in production or a shorter production season. Net productivity during the low production year (1970) was significantly greater than the following high production year. As a result production intensity (maximum bimonthly production) was similar for each year studied. The density of Microtus oeconomus was not similar during each year of the study. A peak density during 1969 (° 80/ha) was followed by 2 yr of very low density and an increase during 1972. Net production during 1969 was 31359 kJ/ha. The average net production for high and low density years was approximately the same as the average yearly production for Clethrionomys rutilus. Maintenance production values are quite different from those cited for other microtine populations in two respects: First, seasonal maintenance estimates for the Clethrionomys rutilus population indicate that those of summer periods were lowest in spite of the cost of reproduction. Second, winter individual maintenance was nearly 2x summer maintenance for both species. Production estimates for the two microtine populations suggest that low species density typical of northern habitats should not always imply low production over a 3— 4—yr cycle, from year to year or even on a short term (bimonthly) basis. Dispersal and weight loss are discussed as possible mechanisms for regulating production variability.
Interspecific Agonism in Two Parapatric Species of Chipmunks (Eutamias)
Authors: Meredith Don H.
Published: May 2006

The chipmunk species Eutamias minimus oreocetes and Eutamias amoenus luteiventris are altitudinally parapatric in the Rocky Mountains of southern Alberta; E. m. oreocetes occupies the alpine, E. a. luteiventris occupies forest. During simultaneous introductions of these subspecies into a large structurally complex arena, E. a. luteiventris was dominant in a majority of matches. During matches in which E. m. oreocetes was introduced 1 day prior to the introduction of E. al luteiventris, both species won the same number of matches. Habitat structure appeared to influence the outcome of interactions. Prior residence of a nonforest habitat may provide E. m. orecetes with sufficient advantage in agonistic interactions to exclude E. a. luteiventris from such habitat. Eutamias minimus borealis and E. amoenus ludibundus are geographically parapatric in the Rocky Mountains of central Alberta, Canada; both species occupy forest habitats. During simultaneous introductions of these subspecies into the arena, E. a. ludibundus was dominant in a majority of matches. A comparison of three studies of interspecific agonism between various subspecies of E. minimus and E. amoenus indicates that E. minimus is generally subordinate to E. amoenus regardless of habitats occupied. The distributions of the four subspecies in Alberta suggest that E. amoenus luteiventris displaced E. minimus borealis from the montane forest of southern Alberta, and E. minimus oreocetes may represent refuge populations of E. minimus borealis that successfully excluded E. amoenus ssp. from the alpine.
Turnover Rates in Insular Biogeography: Effect of Immigration on Extinction
Authors: Brown James H. , Kodric-Brown Astrid
Published: May 2006

Demographic and genetic contributions from conspecific immigrants tend to reduce extinction rates of insular populations. The MacArthur—Wilson model of island biogeography is modified to provide for this effect of immigration on extinction, which we call the rescue effect. This new model predicts that when immigration rates are high relative to extinction rates, turnover rate is directly related to the distance between an island and the source of colonizing species. A field study of the distribution of arthropods among isolated plants supports the model.
The Solar Radiation Balance of Scrub Forest and pasture on the Carmel Mountain, Israel: A Comparative Study
Authors: Stanhill G. , Israeli Miriam , Rosenzweig D.
Published: May 2006

Differences in the solar radiation balance of scrub forest and pasture vegetation were investigated. Three years of measurement showed small but consistent differences which were, however, at the limits of the radiometer's absolute accuracy. The mean annual short wave reflectivity of the pasture plot was 0.18, varying between a spring maximum of 0.20 and a midsummer minimum of 0.16. The reflectivity of the woody vegetation averaged 0.15, varying from a maximum of 0.16 to a minimum of 0.14 at approximately the same seasons, which coincided with the periods of maximum and minimum vegetative growth. Annual values of net radiation measured above the forest vegetation were 11% greater than above the pasture, differences increasing to 15% on cloudless days. Nighttime differences were much smaller, but of similar sign. Maximum differences in net radiation of 65 cal cm(—2) day(—1) were measured in early May, when differences in vegetation cover and evapotranspiration rate were also at their maximum; minimum differences were found in early winter, when vegetative activity was minimal. Net radiation was highly correlated with global radiation under both cloudless and average conditions; no statistical advantage in prediction accuracy was found by including a heating coefficient. Annual totals of net terrestrial long—wave radiation during daylight hours were 21% greater from the pasture than from the scrub forest plots: during the night the flux from the two vegetation types was similar but much smaller. Maximum daily differences of 60 cal cm(—2) day (—2) occurred in May and showed that differences in long—wave emission from the two plots, rather than differences in short—wave reflectivity, were the cause of differences in the radiation balance. The mean daily radiative surface temperature of the pasture plot was calculated to be 4oC above that of the scrub forest during this period, assuming an equally high emissivity for the two surfaces. The radiant energy available to the scrub forest during the 6 rainless months (April to September) was 8.52 kcal cm(—2) more than that retained by the pasture. During the same period, evapotranspiration measurements indicated that the scrub forest utilized 7.14 Kcal cm(—2) more latent heat of vaporization than did the pasture plot. The latent—to—radiant heat ratios imply diffusive resistances of water vapor transport of 8.3 sec cm(—1) for the pasture plot and 5.4 sec cm(—1) for the scrub forest. It is concluded that differences in the evapotranspiration rate of the two vegetation surfaces are the cause rather than the result of differences in their radiation balance.
Field Studies on Photosynthesis of Cladophora Glomerata (Chlorophyta) in Green Bay, Lake Michigan
Authors: Adams Michael S. , Stone Walter
Published: May 2006

Net photosynthesis of Cladophora glomerata was measured at three sites in lower Green Bay, Lake Michigan, from late spring through summer, 1971. Lower levels of productivity occurred early in the season at two of the sites, when water temperatures were lowest. At the third site water temperature and productivity varied the least. Contrary to other reports, we found that Cladophora made relatively efficient use of low illumination. Under statistically similar temperature and irradiance levels, productivity was higher with increasing proximity to the mouth of the Fox River. Nitrogen, calcium, strontium, sodium, and zinc also were highest in concentration in plants receiving the greatest amount of effluents from the Fox River in comparison with the site receiving the least. Site differences in productivity appear to be related to nutrient levels, whereas seasonal differences in productivity are probably most closely related to seasonal temperature differences.
Interterritorial Habitat Variation in Grasshopper and Savannah Sparrows
Authors: Wiens John A.
Published: May 2006

Individual variation in features of habitat structure among territories of breeding grasshopper sparrows and savannah sparrows in a southern Wisconsin grassland was examined. Grasshopper sparrow territories established late in the breeding season were larger than those occupied earlier. In savannah sparrows, time of establishment had no significant effect upon territory size, but variation in the amount of grass cover was highly correlated with size differences. There was considerable inter—territorial variation in habitat features in both species, but patterns relating to territory size, position in the breeding population, and time of territory establishment were well—defined in savannah sparrows, whereas grasshopper sparrow territories generally showed little systematic pattern of variation. Although these species occupied similar habitat situations after breeding populations stabilized in mid—June, they initially established territories in quite different portions of the habitat spectrum.
Leaf Area Dynamics of a Shortgrass Prairie in Colorado
Authors: Knight Dennis H.
Published: May 2006

Leaf area changes were studied at the Prawnee Grassland in northern Colorado. Specific objectives were (1) to measure seasonal changes in leaf area during 1970 and 1971, (2) to estimate the influence of irrigation, irrigation plus nitrogen fertilization, and grazing on leaf area, and (3) to calculate average daily above—ground productivity per unit of leaf area during the peak of the growing season. The point—quadrat method was used for leaf area measurement. Peak leaf area was reached in mid—June of both years, with a maximum Leaf Area Index of 0.55 in 1970. Both years were drier than average, but seasonal distribution of rainfall was different with a corresponding seasonal difference in LAI. Irrigation alone increased LAI about two—thirds, and irrigation plus fertilization increased LAI approximately tenfold. Different grazing treatments had little effect on total leaf area values. Above—ground productivity per unit leaf area averaged about 5 g/day/l2 of leaf area in May and about 4 g in June and July 1970.
Diversity, Floristic Richness, and Species Evenness During a Secondary (Post‐Fire) Succession
Authors: Shafi M. I. , Yarranton G. A.
Published: May 2006

Diversity, species richness, and species evenness were analyzed in II boreal forest areas that had been burned from 0 to 44 years previously. The values of the information measure of diversity, H'. and Hurlbert's probability of interspecific encounter. Delta_1, obtained here are highly correlated. Both show a long—term declining successional trend, but exhibit relatively high values for the period 4 to 11 years after burning. Fluctuations in both appear to be attributable to variations in richness rather than evenness, supporting Pielou and Hurlbert's contentions that the two components of diversity should be analyzed separately. Delta_1 is preferred to H' because, if used in conjunction with a knowledge of spatial heterogeneity, it can provide information about the levels of competition in a community. The results indicate a slight increase in the amount of intraspecific competition during the course of succession, contrary to what might be expected as the outcome of evolution. It is argued that the species present are adapted to the occurrence of frequent catastrophes, particularly fires, so that prevailing evolutionary pressures and their outcome differ from those in more stable environments.
Half‐Saturation Constants for Uptake of Nitrate and Ammonia by Reservoir Plankton
Authors: Toetz Dale W. , Varga Louis P. , Loughran Edward D.
Published: May 2006

Observations were made in order to learn if the uptake of NH_4 and NO_3 by freshwater plankton can be described by the Michaelis—Menten expression. Uptake of NO_3 and NH_4 by reservoir plankton was estimated at 5 concentrations using (15)N Tracer techniques. A hyperbola results when the uptake velocity (v) of NO3 and NH4 is plotted against concentration (S). The S/v vs S transformation of the Michaelis—Nenten expression was used to estimate K_s. For a mixed population of blue—green algae in Lake Carl Blackwell, Oklahoma, K_s was about 43 mg NO_3 — N (m)(—3), when the initial concentration was 7.53 mg NO_3 — N (m)(—3). In Lake Keystone, where the initial concentration of NO_3 — N was 419.17 mg (m)(—3), enrichment with NO_3 increased v in a similar way, suggesting use of the Michaelis—Nenten model may not be realistic.
Food Preferences of Squirrels
Authors: Smith Christopher C. , Follmer David
Published: May 2006

Gray and fox squirrels show similar preferences for various types of natural foods. Their preferences are based on a combination of two factors; the speed with which they can ingest food energy and the digestibility of the food eaten. The two species of squirrels have essentially the same ability to digest their natural foods. However, five species of nuts differ in their digestibility, ranging in percentage of energy assimilated from about 78% for white oak to 95% in shagbark hickory. The squirrels' efficiency in digesting the kernels of different species of nuts is correlated with the lipid content of the kernels. The niche differences between gray and fox squirrels are not based on food preference or feeding efficiency. Instead, they are probably related to differences in foraging behavior and predator escape behavior which adapt fox squirrels to open forests and forest edges and gray squirrels to dense forests. The annual activity pattern of gray and fox squirrels make the hard—shelled nuts of hickory and walnut the most efficient food in fall and spring and acorns the most efficient food in winter. This change in the relative efficiency of foods results in the squirrels acting as dispersing agents for the seeds of both oaks and hickories in mixed stands of trees.
Fiber Tracheid Length and Wood Specific Gravity of Seedlings as Ecotypic Characters in Liquidambar Styraciflua L.
Authors: Winstead Joe E.
Published: May 2006

Fiber tracheids of first—year seedlings of Liquidambar styraciflua from geographically diverse seed sources grown under controlled conditions differed in length. The longest tracheids were found in seedlings from Mexico populations; tracheids in plants from New Jersey, North Carolina, and Texas were shorter and showed a latitudinal trend, the shortest being northernmost. Cell lengths varied with the environmental conditions, those of the United States populations being more reduced in length under short day—lengths, cooler temperatures, and low light intensity. Populational differences in specific gravity of wood were evident in seedlings grown under controlled conditions. Lower specific gravity was correlated with decrease in latitude of origin. A possible relationship between fiber tracheid length, cell diameter, and latitude of origin is suggested.
Parasitiods Utilizing the Same Host: Adaptive Nature of Differences in Size and Form
Authors: Price Peter W.
Published: May 2006

Eleven hymenopterous parasitoid species commonly exploit one sawfly host, Neodiprion swainei. A comparison of the area of forewing, structure of ovary, and length of ovipositor of some of these species is revealing. The three guilds of parasitoids that attck the larval, eonymphal, and cocoon stages of the host, respectively, face different problems in host exploitation. Females of the larval parasitoid guild have large egg production and large wings. They are adapted to exploit a relatively abundant, easily discovered stage of the host, but their progeny are subject to high mortality while in the host. Females of the cocoon parasitoid guild have small wings and low egg production. They seek a scarcer, well—concealed stage of the host, and their progeny sufer less mortality. Members of the eonymphal parasitoid guild show intermediate characteristics. Among the cocoon parasitoids, the species have different ovipositor lengths, presumably allowing them to utilize segments of the host population, either different size classes or hosts that are buried at different depths in the forest litter. Comparison of ovipositor lengths indicates how similar the species can be in size, and therefore larval food exploitation, before competitive displacement prevents coexistence.
Bioenergetics of Lotic Filter‐Feeding Insects Simulium SPP. (Diptera) and Hydropsyche Occidentalis (Trichoptera) and their Function in Controlling Organic Transport in Streams
Authors: McCullough Dale A. , Minshall G. Wayne , Cushing Colbert E.
Published: May 2006

This study derives a set of bioenergetic parameters for the blackfly Simulium spp. (Diptera: Simuliidae) and the caddisfly Hydropsyche occidentalis (Trichoptera: Hydropsychidae) and evaluates the impact of these filter feeders on the lotic environment. In addition, comparison is made between field— and laboratory—derived estimates of ingestion and between 2 methods of calculating assimilation rate. Digestion (gut—clearance) time for Simulium ranged between 0.33 and 1.25 h compared to 1.54 to 2.63 h for Hydropsyche. Mean ingestion rate for Simulium in a series of experiments ranged from 1.36 to 54.74 mg DW/mg DW/h. The mean assimilation efficiency for diatoms was about 55% as measured by the dual—label technique. Mean ingestion rates of diatoms for Hydropsyche in 3 experiments were 31.3, 31.0 and 29.2 mg DW/mg DW/h, respectively; low values (3 mg DW/mg DW/h) from a 4th experiment were associated with high concentrations of green algae. An assimilation rate for diatoms of 7.5 mg AFDW/mg DW/h was derived for Hydropsyche. Measurements of growth rates of Hydropsyche under natural conditions were 3.6 to 4.4 mg DW/mg DW/h. Respiration rate of Hydropsyche for water >62% O2 saturation was about 2.3 μl O2/mg DW/h at 20°C. The results of this research in combination and literature derived values, yielded the following mean energy budgets for Simulium and Hydropsyche, respectively (J/mg/h): ingestion (C) 0.318, 0.393; respiration (R) 0.092; 0.042; growth (G) 0.092, 0.100; assimilation (A) (as C x AE) 0.182, 0.192; (as G / R) 0.184, 0.142 (values times 0.239 = cal/mg/h). The role of these filter feeders is discussed in terms of their processing of suspended organic material and in directing energy to higher trophic levels. Simulium and Hydropsyche (with net growth efficiencies of 49.5 and 69.6%, respectively) are shown to be comparable to bacteria in terms of metabolic removal of organic C from food sources. During the months in which they were present, the mean biomass and density of Hydropsyche occidentalis in Deep Creek (station 2), Idaho, were 2.45 g DW/m2 and 1786/m2 and of Simulium were 0.22 g DW/m2 and 1699/m2. Based on all 12 monthly samples, Hydropsyche comprised 44% of the total invertebrate standing crop biomass of 4.84 g DW/m2. From mean biomasses and numbers of invertebrates in riffles of Deep Creek and mean ingestion rates for Simulium and Hydropsyche (30.5 and 80 mg/mg/h, respectively) it was calculated that the filter—feeders remove °1% of the seston flowing over them each day. The filter—feeders also are an important energy based for feeding by carnivorous insects and fish in Deep Creek.
Nutrient Limitation of Algal Standing Crops in Shallow Prairie Lakes
Authors: Haertel Lois
Published: May 2006

Environmental control of algal standing crops in two non—stratified prairie lakes in South Dakota and Minnesota, USA was investigated by season for 3 years. Multiple regression analysis was performed using chlorophyll a concentration and cell counts as dependent variables. In both lakes physical factors (light, temperature, wind stress and rainfall) were more frequently correlated with changes in algal standing crops than were nitrogen and phosphorous. Both lakes indicated occasional positive correlations with nitrogen. The correlations were greater in the deeper lake. Phosphorous was positively correlated during one season in the deeper lake, never in the shallower lake. Multiple regression analyses using concentrations of nitrate, ammonia, and orthophosphate as dependent variables and physical factors, algal abundance and zooplankton abundance as independent variables showed positive correlations between increases in orthophosphate and nitrate and prior rainfall and wind stress. Ammonia showed strongest correlations with wind stress. The correlations between wind stress and nutrient levels are assumed to result from recirculation of nutrients released at the sediment surface by circulation of the water column and by direct stirring of sediments in shallow water by wave action. The more extensive direct stirring of sediments in the shallower lake is assumed to partially account for the much higher levels of nutrients observed. Depth of lake relative to depth of wave action determines to what extent the sediments of a shallow lake are subject to direct stirring.
Ground Vegetation Biomass, Production, and Efficiency of Energy Utilization in Some Northern Wisconsin Forest Ecosystems
Authors: Zavitkovski J.
Published: May 2006

The aboveground biomass of the herb stratum, including woody species up to 30 cm tall, was determined by harvesting annually over a 4—yr period (1969—72) in aspen, maple—aspen—birch, birch, northern hardwood, and logging road communities. Average aboveground biomass in the respective community types was 117.5, 63.0, 51.0, 37.6, and 80.6 g/m2. Root biomass was determined by harvesting the belowground part on selected plots in 1971. Cumulative solar energy received at the sample points was measured with a chemical integrating light meter (petroleum ether chlorophyll extracts). Phenological observations indicated that net annual production in the four forest types was essentially equal to their end—of—season standing crop biomass. Average root:top ratios ranged from 2.98 to 4.79 and were higher in the dry communities (birch and northern hardwood) than in the other more mesic forest. Except for the logging road, two to five species accounted for most of the biomass in each community. Significant positive correlations were found between incident solar energy and aboveground biomass. Efficiency ranged from 0.82% to 2.19% based on May—October cumulative energy in the visible spectrum and cover adjusted aboveground biomass.