bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses to Starvation in the Spiders Lycosa Lenta Hentz and Filistata Hibernalis (Hentz)
Authors: Anderson John F.
Published: May 2006

Effects of starvation were investigated in two specices of spiders to gain insight on how these predators deal with an unpredictable food supply. Comparison of weights and body dimensions of individuals from field populations with those of known nutritional status showed that lack of food is a problem for field populations of both species. Adult survival times under starvation conditions averaged 208 days for the wolf spider, Lycosa lenta, and 276 days for the cribellate web—builder, Filistata hibernalis. Potential adult life spans for fed individuals were estimated to be 305 days for L. lenta and several years for F. hibernalis. Both spiders have metabolic rates significantly lower than those of other poikilotherms of similar size, and when starving revude their metabolic rates by 30% to 40% without any apparent decrease in their normal capabilities. The difference in urvival times under starvation conditions of the two species was found to be inversely related to metabolic rate. This suggests that the relative low metabolic rates characteristic of spiders as well as their capacity to reduce these rates when starving are adaptive in survival where prey are scarce. That starved individuals have the capacity to double their body weight through ingestion of large amounts of food when available may be an adaptation to their predation.
An Advantage of Winter Flocking in the Black‐Capped Chickadee, Parus Atricapillus
Authors: Barash David P.
Published: May 2006

Field and laboratory observations of winter flocking behavior in the Black—capped Chickadee, Parus atricapillus, suggest a previously undescribed advantage to winter flocing in this species: flocked individuals are subjected to less aggression from other, solitary birds than when they are themselves solitary.
In Situ Decomposition of Roots and Rhizomes of Two Tidal Marsh Plants
Authors: Hackney Courtney T. , De La Cruz Armando A.
Published: May 2006

In situ decomposition of roots and rhizomes of the marsh plants, Juncus roemerianus and Spartina cynosuroides was investigated using litter bags. The decomposition rate was greatest in the top 10 cm (20% mass loss/yr) of the marsh soil. There was no apparent decomposition below 20 cm depth. Belowground tissues of S. cynosuroides decomposed faster than those of J. roemerianus during the first 4 mo. The rhizome decomposition rate of 27%/yr (mass loss) was faster than the 16%/yr of the roots of J. reomerianus. There was no difference between the composition rate of mixed root and rhizome materials between experiments initiated in winter and those started in the spring. This indicates a relatively constant decomposition rate during the year in the 0—10 cm soil zone. There was no apparent trend in the hydrogen, carbon, phosphorus, nitrogen, or caloric content changes of the decomposing roots and rhizomes during the study.
Water Vapor Conductance and CO"2 Uptake for Leaves of a C"4 Desert Grass, Hilaria Rigida
Authors: Nobel Park S.
Published: May 2006

Availability of soil water was the major influence on seasonal stomatal activity of Hilaria rigida (Thurb.) Benth. ex Scribn. over a 2—yr study period in the Colorado desert section of the Sonoran desert. Major stomatal opening (water vapor conductance >2mm/s) occurred for 4.6 mo in the relatively cool winter—spring (maximum daytime temperatures averaging 17°C) and for 1.7 mo in the late summer—early fall (maximum daytime temperatures averaging 31°C). The temperature optimum for CO2 uptake was generally above daytime temperatures, particularly in the winter. When the daytime growth temperature was raised from 16° to 49°C in laboratory experiments, the temperature optimum for CO2 uptake shifted from 29° to 43°C. Besides the rather high temperature optimum for CO2 uptake, H. rigoda displayed other typical C4 characteristics including Kranz anatomy, a low CO2 compensation point (12 μl/1), and a lack of light saturation of CO2 uptake at full sunlight. Under optimal field conditions, the CO2 uptake rate can be 67μmol°m—2°x—1 (106mg CO2°dm—2 h—2), higher than has been reported for any other species. The accompanying high water use efficiency (mass CO2 taken up by leaf blades/mass H2O lost) may help explain the success of this hardy grass in both the Mojave and Sonoran deserts.
Goshen Springs: Late Quaternary Vegetation Record for Southern Alabama
Authors: Delcourt Paul A.
Published: May 2006

The sediments of Goshen Springs, Pike County, Alabama, USA, provide a late Quaternary biostratigraphic record that extends from the Altonial Substage of the Wisconsinan Glacial Stage to the present. Diagrams showing percentages of palynomorphs and concentrations of plant macrofossils permit the reconstruction of both local and regional vegetation. At Goshen Springs, a drying trend during the Altonian Substage (>28 000 yr BP) resulted in the replacement of mesic—temperate forests by southern pines, oaks, and hickories. Climatic conditions of warmth and summer drought favored oak—hickory—southern pine forests from 26 000 yr BP in the mid—Farmdalian substage, through the full glacial and late glacial, until the mid—Holocene (5000 yr BP). During the full glacial, a strong climatic gradient and major vegetation ecotone extended across central Alabama and Georgia, separating northern boreal—like forests of spruce and jack pine from warm—temperate oak—hickory—southern pine forest on the Gulf Coastal Plain. The Goshen Springs record documents the persistence of many warm—temperate deciduous and broadleaf evergreen tree taxa in southern Alabama through the full and late glacial. The early Holocene forests, dominated by oak and hickory, were replaced by widespread southern pine forest on the sandy uplands of the Gulf Coastal Plain about 5000 yr ago. During the mid—Holocene, the attainment of the present climatic regime, characterized by abundant precipitation throughout the growing season, and the return of sea level to near—modern position resulted in the establishment of the southern pine forests and of widespread swamps and marshes in the Gulf and Southern Atlantic Coastal Plains.
Periphytic Community Response to Chronic Nutrient Enrichment by a Reservoir Discharge
Authors: Marcus Michael D.
Published: May 2006

Periphytic communities were investigated using glass slide substrates at four sites downstream from the montane Hyalite Reservoir, Montana, USA. Comparison of the most upstream site with the three lower sites revealed that the discharges to Hyalite Creek stimulated periphytic productivity, increased periphytic proportions of chlorophyll ° in the organic accumulations, and increased diatom species diversity and evenness. As nitrogen concentration was the only stream physiochemical parameter which correlated with periphytic variations, it is probable that ammonia nitrogen discharged from the reservoir was the primary factor influencing periphytic growth. Cocconeis placentula var. lineata dominated generally °70—80% of the diatom communities at the three downstream sites whereas only three individuals of this species were observed at the upper site. Data from two successional series following colonization of the slides suggested that species other than Cocconies had higher initial growth rates. It appears the Cocconies become dominant at the three downstream sites because of higher efficiencies for obtaining or incorporating limiting nitrogen resources: species other than Cocconeis dominated the diatom communities in which nitrogen concentrations were enriched,apparently because of higher potential growth rates which could be realized with the elevated nutrient conditions. A brief review of the literature and new data presented indicate that species diversity first increases and then decreases as a function of resource abundance.
Effects of Temperature and Photoperiod on Larval Development in Tetragoneuria Cynosura (Odonata: Libellulidae)
Authors: Lutz Paul E.
Published: May 2006

Larvae of Tetragoneuria cynosura were collected in 1965—1966 and 1969 to determine their responses to photoperiod and temperature and to elucidate the mechanisms by which seasonal regulation is achieved. Animals were subjected to experimental conditions of temperature (15°, 20°, 25°, and 30°C) and photoperiod (11, 14 hr) until emergence. Three additional groups in each collection were subjected to 11—hr, 14—hr, and natural photoperiods at lake temperatures. In larvae collected after the autumnal equinox, development progressed rapidly in animals subjected to the 14—hr day at every experimental temperature. Short—day animals experienced delayed developed especially at 15° and 30°C. Animals maintained at natural temperatures responded similarly regardless of their photoperiod regime. Short days and high temperatures induced delayed development in all animals collected in the fall and winter. For larvae collected prior to September, long days greatly retarded growth compared to short—day animals. In larvae collected from mid—September until mid—October, the rate of response to long days increases dramatically. This reversal in responseoccurred uniformly about 12 days following the autumnal equinox at 20°, 25° and 30°C. A strong correlation exists between this shift in response to experimental long days and entry into the final instar. The presence of a diapausing stage could not be fully ascertained although development was significantly delayed by experimental long days in animals collected prior to the autumnal equinox and by short days in animals collected following the equinox.
Drought Effects on a Semidesert Grassland Range
Authors: Herbel Carlton H. , Ares Fred N. , Wright Robert A.
Published: May 2006

A vegetational survey on the Jornada Experimental Range in southern New Mexico, taken annually from 1941 through 1957, is the basis for a study of the effects of the great drought of 1951 through 1956. Both cover and yields were studied. Observations were stratified into seven classes based on a consideration of land form and soil characteristics. Seasonal and annual precipitation during the drought averaged 55% of the pre—drought average. The most severe drought years were 1951, 1953, and 1956. Both the cover and yield of Bouteloua eriopoda (Torr.) Torr., the dominant species on the upland sandy soils, were greatly reduced by drought. However, drought damage was much more severe on the deep than on shallow sands. When the impermeable caliche layer occurred at shallow depths, moisture relations during drought were apparently much better than when caliche occurred at greater depths. Another result of drought was the invasion of Prosopis juliflora (Sw.) DC. in areas where grass stands have been thinned by drought. Sporobolus spp. and Aristida spp., minor components of the climax, were more susceptible to drought damage than Bouteloua eriopoda. Yields of perennial grasses per unit cover were as great during the drought as prior to the drought. Both winter—spring and summer precipitation are important in preventing death losses of black grama. In arid areas it seems necessary to consider both cover and species composition in arriving at a potential for a site.
Food‐Searching Behavior of Titmice in Patchy Environments
Authors: Smith James N. M. , Sweatman Hugh P. A.
Published: May 2006

The food—searching behavior of titmice (Paridae) was investigated in laboratory and field to determine how effective individual birds were at locating patchy sources of hidden food. A series of three experiments was performed using tame great tits, Parus major. In Experiment 1, individual birds were offered a choice among six densities of hidden food in discrete patches. The birds learned to concentrate their search strongly on the more dense patches, and five of the six birds preferred to search at the highest density. In Experiment 2, the food distribution was altered by interchanging patches of the highest and lowest density gradually. The birds initially found fewer prey per trial, but soon recovered to near their original performance by switching their search effort to the area containing the second highest prey density. Most birds failed to respond to prey appearing where they had previously been absent. Experiment 3 varied the size of prey items among four areas containing equal numbers of hidden prey. A group of six birds learned to search selectively in areas containing larger prey and, as a result, a greater total quantity of prey. In all experiments, there were marked differences in performance by individual birds. The experiments support Royama's (1970, 1971) hypothesis that great tits distribute their search effort in relation to spatial differences in the profitability of feeding sites. Field observations on a pair of great tits and a pair of blue tits, Parus caeruleus, showed that searching behavior of wild tits was also very selective in space, at least when the birds were feeding nestlings. Birds often returned to previous capture sites and were more likely to do so when they found prey there quickly. These observations suggest that the laboratory experiments have real relevance to the food searching of wild tits. The searching capacity of great tits is discussed; it is suggested that they can approach ideal responses in stable but patchy feeding environments. Some factors leading to deviations from ideal responses are discussed.
The Distribution and Dispersal of Pikas: Influences of Behavior and Climate
Authors: Smith Andrew T.
Published: May 2006

Daily and seasonal behavior in relation to local climate was analyzed for two populations of pikas, (Ochotona princeps), representing the extremes of the altitudinal range of the species in the Sierra Nevada of California. The goal of this work was to determine the relationship of a propagule to its environment at the time of dispersal, in order to evaluate the probability of successful colonization in different parts of the species range. Pikas at the high—altitude site (3,400 m) were active throughout the day, whereas at the warmer low—altitude site (2,550 m) they concentrated their activity in the morning and late afternoon. Field experiments suggest that when pikas are deprived of the opportunity to retreat to favorable microclimates in rockslides, they are unable to tolerate the high diurnal temperatures found at lower elevations. Thus, high environmental temperatures apparently constitute a major stress on dispersing individuals at low altitudes. The onset of hay storage, vocalization, and parturition, three measures of seasonality, occurred about 6 wk earlier at the low—altitude site. The timing of haying and vocalization there was correlated with the amount of precipitation during the previous winter: during dry years with little snow and an early spring pikas began and terminated their haying earlier than in wet years with a late spring. The reproductive season appeared to remain the same from year to year at the same site. The timing of dispersal of juveniles is related to the reproductive season. Most juveniles at the low—altitude site disperse during midsummer when temperatures are high and their chance of success is low. Also, during dry years most of the period suitable for gathering hay ends before a majority of the juveniles can disperse. Temperature and seasonality apparently have little effect on the dispersal of pikas at high altitude. At high altitude the pikas are wider ranging than at low altitude, and they occupy a greater proportion of available sites.
Small Mammals and Vegetation Changes After Fire in a Mixed Conifer‐Hardwood Forest
Authors: Krefting Laurits W. , Ahlgren Clifford E.
Published: May 2006

Following wild fire in northeastern Minnesota small mammals were snap—trapped on two burned and one unburned area for three nights each fall from 1955 to 1967. The deer mouse (Peromyscus maniculatus) was the most abundant species on the two burns the first 7 yr. Later the vegetation changes apparently produced a habitat less attractive to the deer mouse, while the red—backed vole (Clethrionomys gapperi) increased. Numbers of meadow voles (Microtus pennsylvanicus), jumping mice (Zapus hudsonius), and cinereus shrews (Sorex cinereus) were low and erratic on all areas. Eastern chipmunks (Tamias striatus) were abundant most years on only one of the burns.
Similarity among Avifaunas of the Galapagos Islands
Authors: Power Dennis M.
Published: May 2006

Similarity among avifaunas is calculated for both historical and current distributions of resident land birds of the Galapagos Islands. Multiple regression analysis indicates the variation in avifaunal similarity is accounted for primarily by variation in the similarity in composition of island floras and, to a much smaller degree, by isolation among islands. Thus, plant similarity and interisland distance seem the principal identifiable factors influencing avifaunal resemblance. Similarities among islands based on numbers of plant species, area, and elevation do not have a detectable effect. Variation in plant similarity among the Islands is explained largely by isolation, with area and elevation having a reduced, but significant, influence. Close to half of the variation in avifaunal similarity is unaccounted for by plant similarity and isolation. Characteristics of islands with avifaunas that deviate most from the predicted relationship suggest that small, outlying islands in a zone of infrequent and irregular rainfall may have populations of birds prone to extinction. This would have the effect of reducing similarity with most other islands. Compounding this, islands that are upwind most of the year in the prevailing trade winds of the region probably do not receive as many colonizers from other islands as do islands that are downwind. Average avifaunal similarity among congeners is less than among noncongeners. This would be expected if ecological incompatibility exists among congeneric species of the Galapagos, or if there is differentation owing, in part, to geographic isolation.
On the Significance of Clutch Size in Nidifugous Birds
Authors: Safriel Uriel N.
Published: May 2006

The average survival of young Semipalmated Sandpipers (Calidris pusilla) from experimental 5—young broods was lower than that of young from natural 4—young broods. This is predicted by a theoretical model for the determination of clutch size in nudifugous birds: precocial young are vulnerable to predation when they move around, and nudifuguous birds actively protect their young. The capacity of parents to provide protection is limited, and their protective effort is proportional to the product of the number of young times the movement rate of each young. But since the latter is inversely related to the distances between prey items, an increase in clutch size is advantageous only if accompanied by an increase in food density. However, hunting efficiency does not increase linearly with increase in food density, and above a certain level a further increase in density has a negligible effect on efficiency. Thus, the upper limit of clutch size of nudifugous birds may be set by the fact that the protection required for more young exceeds that which the parents can offer.
The Annual Cycle of Aggression in Male Microtus Pennsylvanicus, and Its Relation to Population Parameters
Authors: Turner Brian N. , Iverson Stuart L.
Published: May 2006

Intraspecific aggression of male Microtus pennsylvanicus drummondii was observed in 320 10—minute paired encounters in a neutral arena, during 17 months. Voles were drawn from a population live—trapped biweekly at Pinawa, Manitoba. The 17 months were divided into the following reproductive periods: non—breeding, testes scrotal, and littering. There were two non—breeding, two testes scrotal periods, and a single littering period. Threats, vocalizing, and mutual uprights were significantly and positively associated in all but one of the periods. Together with fighting, these three acts formed the aggressive component of the behavior recorded. All aggressive acts increased in frequency as males became reproductively active, and decreased as the breeding season ended. Latencies to aggressive acts were negatively related to the acts' frequencies. Less frequent acts (fighting, grooming other, and submissives) also showed seasonal changes associated with breeding: fighting was common throughout the breeding period, submissives most common early in the reproductive period, and grooming other most prevalent when juveniles were present in the population. Incidences of tail—wounding in the field population were significantly more common during the breeding season, and in males. A comprehensive Index of Aggression was devised by means of principal component analysis, based on the total frequencies of aggressive acts, Mean Indices of Aggression for the five periods showed that aggressive levels in the three breeding periods were significantly higher than in the two non—breeding periods. Re—tests of 53 voles showed scores from their two encounters to be positively correlated. Aggression measured in the encounters was related to population parameters derived from live—trapping results. Breeding season home ranges were larger than winter home ranges. Overwintered adults were more aggressive, had larger home ranges and survived longer than young of the year. Aggression and survival were positively related in adults but not in young. Resident voles were more aggressive than non—residents. Dominant voles were usually slightly heavier. Pairs of voles of similar weight exhibited more aggressive acts, but following was more frequent in dissimilar weight pairs. Aggressive levels did not vary consistently with population density. These observations demonstrate there is an annual cycle of intraspecific aggression synchronized with the breeding season in male M. pennsylvanicus. They support studies Peromyscus, which also showed that aggression increased with spring breeding and declined as reproduction ceased in fall; thus, behavioral density regulation seems most likely to occur during the breeding period.
Some Statistical Aspects of Sampling Throughfall Precipitation in Nutrient Cycling Studies in British Columbian Coastal Forests
Authors: Kimmins J. P.
Published: May 2006

The number of fixed collectors required to sample the volume and cation content of throughfall precipitation in the coastal forests of British Columbia was examined by means of data from 134 collectors for throughfall volume and 83 collectors for throughfall chemistry. The relative heterogeneity of throughfall parameters in four forest plant associations was also examined. It was concluded that a sampling network suitable for quantifying throughfall volume will be inadequate for quantifying throughfall chemical parameters because of the far greater spatial variability of the latter. This variability is compounded if the study area includes more than one forest plant association. The fixed—collector method was found to be far from ideal for accurate studies of the role of leaching a nutrient cycling because of the excessive number of collectors required. An analysis of the suitability of Wilm's method of roving collectors and Attiwill's modification thereof as alternatives indicated that Wilm's method is inapplicable to studies of throughfall chemistry, but that Attiwill's modification might permit a worthwhile reduction in the number of collectors required in some studies, especially those concerned with gross, long—term studies of leaching. Attiwill's method shares many of the drawbacks of Wilm's method, however, and will probably be unsuitable for many studies. The variability of the chemical data was greatest when expressed as concentrations. Conversion to kg/ha did reduce standard deviations somewhat, although the reduction was modest on all but the most highly variable study area. Sampling at longer intervals did not result in any reduction in the standard deviations of mean throughfall cation concentrations: the effect of longer collection periods on the data expressed as kg/ha was to increase standard deviations significantly. Weekly or more frequent collections are recommended for detailed studies of throughfall chemistry.
Dew Formation and Stem Flow on Common Ragweed (Ambrosia Artemisiifolia)
Authors: Shure Donald J. , Lewis Alan J.
Published: May 2006

Common ragweed (Ambrosia artemisiifolia) was found to possess an adaptation enabling the collection of dew and rainfall through stem flow. Stem wells were used to quantitively determine the incidence and extent of dew collection by this mechanism. Stem flow averaged 2.85 ml of dew/plant night during the study, which covered the later portion of the ragweed growing season. Factors influencing dew collection included plant size, stage of phenological development, microhabitats, and the duration of dew exposure. The mechanism may play a vital ecological role in old field plant relationships.
A Quantitative Evaluation of the Bray‐Curtis Ordination
Authors: Gauch Hugh G.
Published: May 2006

The Bray—Curtis ordination provides position values (x) along an ordination axis and distances (e) from the axis for samples of communities. Upon ordination, samples are displaced from their true positions on the coenocline axis into an arch the height of which increases as beta (between—habitat) diversity increases. The cause of this displacement is the fact that the similarity measure is not a linear estimator of ecological separation. The shape of this arch and the consequent effects on the x and e values are shown for various beta diversities. Refinements are suggested for the Bray—Curtis ordination.
A Niche Analysis of Colorado Ants
Authors: Culver David C.
Published: May 2006

Gregg's data on Colorado ants were examined in light of recent ecological theories. Predatory ants have high niche breadths and low niche overlaps as predicted by MacArthur and Pianka for searching predators that optimize the amount of food taken. Similar analyses were done for seed—eaters, slaves, and slave—makers.
Comparison of Oxygen‐Bomb Combustion with Standard Ignition Techniques for Determining Total Ash
Authors: Reiners William A. , Reiners Norma M.
Published: May 2006

Ash was determined in a variety of plant and organic soil samples by Oxygen—bomb combustion and by a simple muffle—furnace technique. The influence of using different drying temperatures was also assessed. Bomb combustion produced a systematic error of underestimate and a random error of variation between trials. These errors varied among the different types of material tested, but in general both types of error increased with the ash content of the material. The average systematic error of underestimate of ash content for all sampes was 1.46%, which led to an error of 1.56% when adjusting caloric coefficients to an ash—free basis. Lower drying temperatures had an insignificant effect on adjusted caloric coefficients. Independent ash determinations are recommended for materials with ash content greater than 5% to restrict the error of adjusted coefficients below 1%. The mufflefurnace technique is recommended for close approximations of absoulte ash content.
The Invisible Birds
Authors: Preston Frank W.
Published: May 2006

In a search for birds in the bush or other objects of natural history, geology, and many other things, two observers in a unit of time, or one observer in two units of time, will in most cases see > one observer in one unit. This has been known for many decades, presumably for ages. Some recently available data from the late David Lack and from Milton B. Trautman make it possible to state the matter quantitatively, treating the observations as a matter of chance sighting. Both Lack and Trautman were dealing with birds, but the theory is applicable to many other objects of search. In this paper I shall use the term "birds" to cover asteroids, mineral deposits, caterpillars, or other objects of search. We are concerned to discover how many observers can usefully be employed in a search (this depends on the efficiency or skill of the searchers), or conversely, to estimate, given the number of observers, how many objects will be missed. Reasonably skilled observers will miss 50% of the objects when observing alone, but miss only 13% of the objects when observing in 3—person census parties. The fraction of species missed similarly drops from 15% to <5% as the party size increases from one to three.
A Heliconia Insect Community in a Venezuelan Cloud Forest
Authors: Seifert Richard P. , Seifert Florence Hammett
Published: May 2006

An experimental study was designed to evaluate the importance of first—order species interactions, higher—order species interactions and habitat (flower bract) age on the survivorship of 4 species of insects living in the water—filled floral bracts of Heliconia bihai L. in a Venezuelan cloud forest. Only 3 out of 16 first—order species interactions were statistically significant and they included both competitive and symbiotic effects. A higher—order effect was found for only 1 of 4 species while habitat age was found to influence 3 of 4 species. The experimental results indicate that for 3 species survival is greater in the older habitats. These results correspond to data from field studies on nonexperimental inflorescences in which insects were found most frequently in mature floral bracts. The results of this study are similar to those of an earlier study (Seifert and Seifert 1976a) on 2 species of Heliconia from lowland Costa Rica. We propose that Heliconia insect communities in general show low levels of 1st—order species interactions, some of which are symbiotic, and that higher—order species interactions are not a general component of these communities.
Intraspecific Competition and Population Structure in Rotifers
Authors: Snell Terry W.
Published: May 2006

Competition among rotifer clones has been postulated to be an important force influencing rotifer population structure. Competition was investigated experimentally using laboratory populations of Asplanchna. Clones adapted to environments separated in space and clones adapted to environments separated in time were examined. In each case, the population dynamics of the competing clones were characterized, then the intensity of competition described. Population growth rate was found to be regulated by food availability and feeding rate was closely associated with competitive ability. Competition between clones was found to be intense whether clones were adapted to environments separated in space or time. Competitive replacement of 1 clone by another took 16 generations for the spatially separated clones and 5 generations for temporally separated clones. Strong competitive interactions among clones have definite consequences for rotifer population structure. In a competitive environment a group of conspecific rotifers in a lake at a particular time should consist of 1 or a few clones, much of the clonal variability being eliminated by competitive exclusion. Strong competitive interactions should also promote strict temporal partitioning of the environment. As a result, a rotifer species in a lake should be represented by a temporal sequence of homogeneous populations, 1 replacing another through time as the environment changes. This population structure is further suggested by evidence for restricted gene flow between populations and electrophoretic studies. Considered together, these data suggest that the model of complete genetic discontinuity is the most likely structure of rotifer populations.
Character Divergence and Convergence Among Tiger Beetles (Coleoptera: Cicindelidae)
Authors: Pearson David L. , Mury Elizabeth J.
Published: May 2006

Mandible length was found to be correlated with median prey size captured by tiger beetle species in Sulphur Springs Valley, Arizona, USA. Base resource measurements of live arthropod prey showed a relatively narrow size range (1—10.4 mm) on pond edges and a broad size range (1—30.4 mm) in upland grassland habitat within the valley. Ten of 11 tiger beetle species sympatric on the pond edge habitat showed considerable convergence in mandible length, likely in response to the narrow prey size available. The 6 grassland species, however, fit into 3 distinct size classes, 2 species in each size class. On a given grassland site, normally no more than 1 species from each size class was present. The ratio of mandible lengths for sympatric species in the grassland habitat was consistently >1.35, which corresponds to Hutchinsonian ratios. Preliminary comparisons of sympatric tiger beetles from Canada and East Africa showed divergence but with a lower ratio (1.24—1.27).
Viability of Large‐ and Small‐Sized Adults in Fluctuating Vole Populations
Authors: Boonstra Rudy , Krebs Charles J.
Published: May 2006

Peak populations of many species of lemmings and voles contain adults 20—30% larger than adults found in low populations (the Chitty effect). What is the adaptive advantage of being large? We try to answer this question by analyzing the survival rates of large— and small—size adults of 4 Microtus species. Two alternative hypotheses are proposed to explain the adaptive value of large size. Large adults may be r—selected genotypes at an adaptive advantage in increasing populations. Microtus pennsylvanicus and male M. townsendii fit this alternative because the survival advantage of large size is positively related to population growth rate and negatively related to density. Alternatively, large adults may be α—selected genotypes at an adaptive advantage in high density populations when aggression is important. Microtus californicus and M. ochrogaster fit this hypothesis because in these species the survival advantage of large size is positively related to density and negatively related to population growth rate. Thus large body size may be adaptive for quite contrary reasons in different species of cycle voles and lemmings.
Decomposition of Four Species of Leaf Litter in Response to Nitrate Manipulation
Authors: Triska F. J. , Sedell J. R.
Published: May 2006

Input of leaf litter and other allochthonous debris constitute the biological energy base of small watershed streams. The relationship of decomposition rate to nitrate inputs of a 3—4 fold magnitude was tested in three replicate experimental streams. Such a magnitude of nitrate inputs simulated possible input effects of nitrogen fertilization or logging, two common forest practices. At the levels tested, no significant increase in decomposition rate was observed on any of four litter species as a result of nitrate addition. Common parameters measured included weight loss, changes in carbon quality, absolute changes in nitrogen content, and microbial respiration measured as O_2 consumption. Results were partially confounded by growth of filamentous green algae during spring. As a result of chemical O_2 demand or leaf pack envelopment by the decaying algal mat, °° of the total O_2 consumption was not related to litter decomposition. Although not related to increases in nitrate concentration in water, decomposing litter did exhibit a twofold increase in nitrogen content following initial leaching. The mechanism of this increase, whether by biological or chemical means, remains uninvestigated.
A Comparison of Breeding Systems and Seed Physiologies in Three Species of Portulaca L.
Authors: Zimmerman Craig A.
Published: May 2006

Portulaca oleracea L. is a weed of open agricultural habitats. This paper evaluates the contribution of the plant's breeding system and seed physiology to its success as a weed by comparing these aspects of adaptation with the same aspects in two other species of Portulaca, P. grandiflora Hook., a cultivar, and P. pilosa L., a plant of comparatively limited distribution. Self—compatibility, and the seed characteristics of longevity, resistance to digestive processes, the lack of after—ripening, and overwintering proficiency combine to give the plant quick—response capability when conditions surrounding the seed are capable of supporting growth to maturity. Portulaca oleracea belongs to th group of weeds whose have specific germination requirements for environmental factors. When sufficient water is present, the majority of dormant seeds germinate upon exposure to light and to temperatures >20°C. Portulaca grandiflora seeds germinate equally well in light or dark and demonstrate a wide tolerance to temperature. Portulaca pilosa seeds require light and a temperature of 25°C for maximum germination percentages. These factors of seed production and seed physiology interact to produce large populations of P. oleracea plants that can quickly exploit open habitats that are continually supplied by man.
Stability of Species and of Community for the Benthos of two Lagoons
Authors: Peterson Charles H.
Published: May 2006

Bethnic communities (predominantly bivalve mollusks) of two southern California lagoons (Mugu Lagoon and Tijuana Slough) were sampled intensively once every 4 mo over a 37—mo period. The two lagoons differed significantly in species diversity. The lagoon with the lowest species diversity, Mugu Lagoon, was composed of species whose populations generally exhibited much greater temporal variability (showing lower stability of component species); however, the proportionate community composition of each lagoon varied to an equal degree through time (demonstrating equivalence in stability of community composition). This nearly paradoxical result can be explained in part by a higher level of synchrony in the temporal fluctuations of the species populations at Mugu Lagoon. A similar response by several species at Mugu Lagoon to an environmental perturbation, dilution after a heavy rain, contributed to this higher level of synchrony.
Selective Predation of Ephippal Daphnia and the Resistance of Ephippal Eggs to Digestion
Authors: Mellors William K.
Published: May 2006

In the spring and autumn, Daphnia populations may produce resting eggs contained in pigmented envelopes called ephippia. Pumpkinseed sunfish and yellow perch preyed selectively on ephippial over similarly sized, nonephippial Daphnia galeata mendotae Birge in Fuller Pond, Connecticut. The D. galeata mendotae with darker ephippia were consumed at a greater frequency than those with less pigmented ephippia. In the laboratory pumpkinseeds and—spotted newts preyed selectively on ephippial over nonephippial Daphnia pulex Leydig under natural light intensities. Ephippium tanning and hardening probably evolved and persisted because of the increased protection given to the resting eggs after natural release of the ephippia from the maternal Daphnia. Darker ephippia retained their normal complement of two resting eggs twice as well as less pigmented ephippia did during passage through newt and perch digestive tracts. D. galeata mendotae and D. pulex ephippial eggs hatched after passage through pumpkinseed and yellowbelly sunfish, golden shiners, and newts. Seventy percent of the 27 planktivorous fish collected from Fuller Pond in October and November contained ephippia. Large numbers of ephippia were found within the digestive tracts of some of these perch and sunfish. Daphnia pulex and D. galeata mendotae ephippial eggs hatched after passage through a Black—Crowned Night Heron and laboratory rats. This suggests a possibility for Daphnia resting egg dispersal by fish—eating birds and mammals feedings on planktivores that prey selectively on ephippial Daphnia.
Substrate Selection by Larvae of the Sessile Rotifer Ptygura Beauchampi
Authors: Wallace Robert L.
Published: May 2006

Larvae of the sessile rotifer Ptygura beauchampi begin substrate selection activities when they chemotactually sense a stimulus associated with the glandular trichomes which cover their preferred substrate, the trap door region of the largest, prey capturing organs of the carnivorous aquatic plant, Utricularia vulgaris. Four other co—occurring congeneric species (U. gibba, U. inflata minor, U. intermedia, and U. purpurea) and 2 smaller, morphologically distinct, trap types of U. vulgaris were not colonized. All of these Utricularia traps (except U. purpurea) have glandular trichomes which are nearly indistinguishable from one another. The stimulus appears to be chemical in nature, arising from the terminal head cells of trichomes as they develop. The chemical stimulus (an allelochemic agent) may be the utricularian prey—lure first proposed by Cohn in 1875. This symbiotic relationship should be termed commensal because rotifers colonize, but do not feed on the plant or its prey, and because the plant is apparently not affected by the colonization.
Reproductive Strategies in Herbaceous Plant Communities During Succession
Authors: Newell Sandra Jo , Tramer Elliot J.
Published: May 2006

Reproductive strategies of herbaceous plants were analyzed in three successional communities. The communities were a 1—yr old—field, 10—yr old—field, and forest. Analyses included measurement of community—wide reproductive effort (reproductive dry wt/total dry wt) at 3—wk intervals throughout one growing season. Reproductive effort was highest in the 1—yr field. There was essentially no difference in reproductive effort between plants in the 10—yr old—field and forest communities; both exhibited relatively low reproductive effort. Reproduction in the 1—yr and 10—yr fields was highly synchronous; there was little synchrony of reproduction in the forests. This may indicate a more efficient utilization of resources throughout the growing season in the forest. Analyses also included measurement of numbers of seeds per plant produced by dominant species in each community. Number of seeds per plant in the 1—yr and 10—yr fields was relatively high, while number of seeds per plant was comparatively low in the forest. The ratio of root:total biomass increased with successional age, reflecting a proportionately larger expenditure of energy on competitive structures in the forest. Also, goldenrods, dominants in the 10—yr field, were found to possess 1 characteristic of an r—strategy (i.e., large number of small seeds) and a characteristic of a K—strategy (i.e., low reproductive effort). This apparent paradox was explained by relating these characteristics to the selective pressures that might produce them. In addition, the empirical data provide support for expanded concepts of reproductive strategies.
Influence of Economics, Interspecific Competition, and Sexual Dimorphism on Territoriality of Migrant Rufous Hummingbirds
Authors: Kodric-Brown Astrid , Brown James H.
Published: May 2006

Migrant Rufous Hummingbirds (Selasphorus rufus) arrive in eastern Arizona in late summer and establish feeding territories from which other hummingbirds are excluded. Territories vary 100—fold in area and 5—fold in number of flowers. A simple cost—benefit model accounts for observed variation in territory size and number of flowers defended. Both sexes defend territories, but ♂ ♂ utilize denser flowers than ♀ ♀. These differences appear to be related to sexual dimorphism in wing disc loading. Selasphorus rufus appears to have sacrificed efficient flight for aggressive ability as a strategy for competing with resident hummingbird species during its migration. Comparison of feeding territories of S. rufus and other nectarivorous birds indicate similarities which suggest that these systems may be subject to similar economic constraints.
Energy Conservation by White‐Tailed Deer in the Winter
Authors: Moen Aaron N.
Published: May 2006

Behavior of white—tailed deer (Odocoileus virginianus) in Itasca Park, north—western Minnesota, USA was analyzed for energy—conservation adaptations during winter. Track records showed a decrease in activity with an increase in perdicted heat loss when activity and heat loss were compared on a sequential basis throughout the winter. Recognition of many seasonal but gradual changes in deer characteristics, such as antler growth, reproductive condition, and molting, suggest that seasonal physiological changes occur and also effect over behavior. Energy may be conserved by reducing the general level of activity, by seeking more level land and lesser snow depths, and by walking more slowly. Such energy—conservation measures may save up to 1,000 kcal/day (= 4,184 kJ/day) for a 60 kg deer, and 0.25—0.50 kg field—weight forage. Deer should remain as undisturbed as possible in the winter; harassment by dogs and snowmobile traffic is counter to their long term physiological and behavioral adaptations.
Socioecology of Marmots: Female Reproductive Strategies
Authors: Andersen Douglas C. , Armitage Kenneth B. , Hoffmann Robert S.
Published: May 2006

The relationship between female reproductive success and both spring food and hibernacula resources was examined in a high—altitude population of yellow—bellied marmots (Marmota flaviventris). The number of offspring a female weaned was significantly associated with the estimated number she could potentially produce, based on food resources. The production of young by these females is probably food limited to varying degrees. Hibernacula may be a restricted resource; young reared in an area without a hibernaculum were not recaptured as yearlings. Delaying pregnancy until forage is available fails as a strategy because young have insufficient time to accumulate fat for hibernation. Adult females deposit fat at a single maximum rate regardless of reproductive history; few females gain weight prior to weaning their young. In areas with short growing seasons, measured as the period during which nonreproductive adults gain weight, females may occasionally or regularly fail to reproduce in consecutive years. The short period of time following weaning may not permit the accumulation of fat sufficient to provide energy for hibernation, postmergence activity, and reproduction. The growth rate (g/day) of young marmots is greater at high than at intermediate elevations. This increase in growth rate warrants further examination of the hypothesis that increased sociality among marmots living in areas with short growing seasons is a response to decreased growth rates of young animals.
Population Consequences of Shell Utilization by Hermit Crabs
Authors: Fotheringham Nick
Published: May 2006

The nearshore hermit crabs Clibanarius vittatus, Pagurus pollicaris, and Pagurus longicarpus have broadly overlapping shell utilization patterns along the Texas coast. Effects of shell stress resulting from this overlap and from an overall shortage of shells on the reproductive potentials of the crabs were examined. Regression analyses indicate that shell weight and internal volume affect the clutch sizes of C. vittatus and P. pollicaris but not P. longicarpus. Clibanarius vittatus maintained in shells smaller than preferred grew more slowly than crabs maintained in shells of preferred size. Clutch size was highly correlated with crab size in this species. Several commensal animals, including polychaetes, gastropods, a hydroid, and a xanthid crab, consumed hermit crab eggs and/or zoeae in the laboratory. These egg predators were encountered in large shells occupied by ♂ ♂ more frequently than in shells in the size range utilized by ovigerous ♀ ♀. These results indicate that shell size may limit hermit crab clutch size through a variety of mechanisms.
Latitudinal Size Variation of Chilean Foxes: Tests of Alternative Hypotheses
Authors: Fuentes Eduardo R. , Jaksic Fabian M.
Published: May 2006

There are only 2 species of canids in mainland Chile: the foxes Dusicyon culpaeus and Dusicyon griseus. These 2 species are shown to diverge in body size with increasing latitude: body size of D. culpaeus increases whereas the size of D. griseus decreases south of 33° south latitude (SL). The variables latitude, temperature, annual actual evapotranspiration, and mean size of potential prey species have been previously proposed as correlates of body size in carnivores, but they do not explain the size trends exhibited by the 2 Dusicyon. Instead we found that constancy of mean size of potential prey species throughout the range, and increased habitat overlap between D. culpaeus and D. griseus south of 33° SL, are most likely to explain the size trends of these congeners. Our results suggest a trade—off between habitat and food overlap: progressive increments of interspecific habitat overlap south of 33° SL are compensated by progressively larger differences in body size and in mean prey size.