bluuebunny/crossref_metadata_2025 huggingface dataset:
Floodplain rehabilitation in North Cameroon: Impact on vegetation dynamics
Authors: Scholte Paul , Kirda Philippe , Adam Saleh , Kadiri Bobo
Published: May 2006

Abstract. Since the construction in 1979 of a dam in the Logone floodplain in the Sahelo‐Sudanian zone of Cameroon, annual inundations have decreased, reducing perennial vegetation as important grazing source for nomadic herds and wildlife during the dry season. Presently, possibilities exist to release excess water for floodplain rehabilitation. In 1994 a pilot release was executed, reflooding 200 km2, to verify predicted advantages. Vegetation has been studied from 1984 onwards along a transect covering flooded, recently reflooded and desiccated parts of the floodplain. Since 1993, the floristic composition has also been monitored in a grid in the centre of the impact zone. Cover of perennial grasses, most notably Echinochloa pyr amidalis and Oryza longistaminata increased from 41 to 61% in the reflooded zone. Vetiveria nigritana, a tussock grass that used to be dominant, disappeared slowly after the dam construction and has not shown a comeback. The cover of annual species, most notably Sorghum arundinaceum, a dominant annual grass only since the mid‐1980s, decreased in the reflooded zone from 58% to 34%. If the present conversion rate of annual into perennial grassland is extrapolated, recovery towards a 100% perennial state may be reached after the 2003 flooding season. Apart from favourable climatic conditions, recovery might be dependent on the restoration of soil fertility, limiting an approach focusing on flooding depth only.
Restoration of the understorey layer of recent forest bordering ancient forest
Authors: Bossuyt Beatrijs , Hermy Martin
Published: May 2006

Abstract.Recently established forests are commonly characterized by an impoverished understorey. Restoration is mostly based on spontaneous secondary succession, but little is known about the time period needed to achieve a community species pool with species composition equal to that of ancient forests.

Vegetation in transects of 197 plots in 13 recent forest stands contiguous to the Meerdaalwoud ancient forest complex was surveyed. The recent forest stands ranged in age from 36 to 132 yr. The community species pool was described with an ecological, functional and phytosociological approach and based on groups derived from a CCA. Differences in community species pool between age classes of recent forest stands were analysed.

During establishment of a new forest competitive species, forest edge species and species with high Ellenberg values for light and nitrogen and a more persistent seed bank will dominate the understorey. After 90 yr of succession the cover by these species decreases and reaches equal values to ancient forest after ca. 105 yr. A large number of forest species will be able to colonize the forest in less than 90 yr. Some typical forest species, however, have very low colonization rates and still have low cover in recent forest more than 105 yr old, so that complete restoration of the understorey requires a time period of over a century. Anthropogenic introduction of forest plant species may reduce the time required for ancient forest vegetation equality.
Hydrology of Dutch Cirsio‐Molinietum meadows: Prospects for restoration
Authors: Jansen A.J.M. , Grootjans A.P. , Jalink M.H.
Published: May 2006

Abstract. Fen meadows (Cirsio dissecti‐Molinietum) are seriously threatened by desiccation, acidification and eutro‐phication. In The Netherlands several projects were launched to restore damaged fen meadows. This review describes how successes and failures of these restoration projects depend on hydrological systems. Six hydrological systems have been distinguished, which all provide the site conditions required by this community. Nowadays, the best developed fen meadows are found in the higher Pleistocene landscape of The Netherlands, where they depend on base‐rich groundwater discharging from local or large groundwater systems. Fen meadows of the lower Holocene landscape usually occur in man‐made surface water systems. Almost all stands have been severely deteriorated. Restoration of fen meadows in the Pleistocene landscape is promising when the hydrology is only slightly disturbed or when hydrological measures are taken in combination with sod cutting. Restoration prospects of fen meadows in the Holocene landscape are low. Until now a complete regeneration of Cirsio‐Molinietum meadows has not been realized. Restoration measures failed to restore high pH values in the top soil. It is hypothesized that viable seeds of many target species lack in the soil seed bank. In addition, the dispersal capacities of these species seem to be limited.
The influence of different grazing regimes on Phragmites‐ and shrub vegetation in the well‐drained zone of a eutrophic wetland
Authors: Vulink J. Theo , Drost Hans J. , Jans Luc
Published: May 2006

Abstract. The effects of grazing by cattle and horses on vegetation development were studied in the well‐drained border zone of the Oostvaardersplassen nature reserve, a managed eutrophic wetland in the young Zuidelijk Flevoland polder in The Netherlands.

At the start of the study period, 12 yr after the area was enclosed by dykes, the vegetation was dominated by Phragmites australis and tall herbs, particularly Cirsium arvense. Over the next 8 yr, different plant communities developed under different grazing regimes. In all communities, C. arvense was gradually replaced by Urtica dioica, and stands dominated by these two species expanded at the expense of P. australis. The shrub Sambucus nigra invaded the stands of C. arvense and U. dioica.

Grazing affected the rate of these developments and the degree to which the grass Poa trivialis became dominant. When cattle were enclosed at a relatively high stocking rate in an area of Phragmites australis and tall herbaceous vegetation during summer, P. trivialis became dominant within 4 yr. The introduction of herbivores led to a faster spread of S. nigra, which contains cyanogenic glycosides which only ruminants can detoxify. Horses, as hind‐gut fermenters, did not feed on S. nigra.

Grazing pressure and herbivore species, therefore, are two important variables that can be used to manage the development of Phragmites‐ and shrub vegetation: the greater the grazing pressure by cattle or horses the greater the area dominated by grasses, and a relatively high grazing pressure by cattle will retard S. nigra expansion.
Phenological mapping in a topographically complex landscape by combining field survey with an irradiation model
Authors: Chytrý Milan , Tichý Lubomír
Published: May 2006

Abstract. A phenological map has been prepared for the Podyjí/Thayatal National Park, located on the border between the Czech Republic and Austria. The area is characterized by V‐shaped river valleys deeply incised into a gently undulating landscape. Five stages of phenological development were defined, based upon phenological spectra of plant communities in late April; 96 sites, more or less regularly spaced over the area, were assigned to one of these stages using field observations of these spectra. Potential direct solar irradiation was calculated from a digital elevation model for a 25 m x 25 m grid extending over the study area. A method was developed for interpolation of phenological observations by weighted regression of phenology on the irradiation model. This interpolation enables the prediction of the local stage of phenological development across the study area without levelling out phenological patterns dependent upon small‐scale topographic variation. Spring phenological events appear to be more advanced in the valleys (except for steep north‐facing slopes) than in the adjacent landscape. Possible climatic processes underlying this pattern are discussed with emphasis on temperature inversions in the river valleys. Cold‐air‐drainage inversions reported from the valleys are probably too infrequent and of too short duration to delay plant phenology. The combined effects of advanced phenology and the increased risk of spring frost injury due to these inversions in the valleys may be an explanation for local distributional patterns of flora and vegetation.
Estimation of primary production of subhumid rangelands from remote sensing data
Authors: Paruelo José M. , Oesterheld Martín , Di Bella Carlos M. , Arzadum Martín , Lafontaine Juan , Cahuepé Miguel , Rebella César M.
Published: May 2006

Abstract. Above‐ground Net Primary Production (ANPP) is the main determinant of forage availability and hence of stocking density. A tool to track the seasonal and interannual changes in ANPP at the paddock level will be very important for livestock management. We studied the relationship between field ANPP data and the Normalized Difference Vegetation Index (NDVI) for rangelands of the Flooding Pampa of Argentina using spectral data provided by sensors on board of two satellites: NOAA/AVHRR and Landsat TM. The relationship between NDVI and ANPP was linear both for data derived from NOAA/AVHRR and Landsat TM. Changes in ANPP accounted for a large proportion of the temporal and spatial variation of NDVI: 71% of NOAA/AVHRR data and 74% of Landsat TM data. By inverting these models, ANPP may be inferred from NDVI data at a seasonal and paddock scale. NOAA/AVHRR data captured better the seasonal variation in ANPP and were less sensitive to local variations than Landsat TM data. In contrast, Landsat TM data were more sensitive to inter‐site differences in primary production, except for the winter months. Thus, combining information from these two sources offers a good alternative for monitoring rangeland production at high temporal and spatial resolution.
Livestock exclusion increases the spatial heterogeneity of vegetation in Colorado shortgrass steppe
Authors: Adler P.B. , Lauenroth W.K.
Published: May 2006

Abstract. Spatial heterogeneity, an important characteristic in semi‐arid grassland vegetation, may be altered through grazing by large herbivores. We used Moran's I, a measure of autocorrelation, to test the effect of livestock grazing on the fine scale spatial heterogeneity of dominant plant species in the shortgrass steppe of northeastern Colorado. Autocorrelation in ungrazed plots was significantly higher than in grazed plots for the cover of the dominant species Bouteloua gracilis, litter cover and density of other bunchgrasses. No species had higher autocorrelation in grazed compared to ungrazed sites. B. gracilis cover was significantly auto‐correlated in seven of eight 60‐yr ungrazed exclosures, four of six 8‐yr exclosures, and only three of eight grazed sites. Autocorrelograms showed that B. gracilis cover in ungrazed sites was frequently and positively spatially correlated at lag distances less than 5 m. B. gracilis cover was rarely autocorrelated at any sampled lag distance in grazed sites. The greater spatial heterogeneity in ungrazed sites appeared linked to patches characterized by uniformly low cover of B. gracilis and high cover of C3 grasses. This interpretation was supported by simple simulations that modified data from grazed sites by reducing the cover of B. gracilis in patches of ca. 8 m diameter and produced patterns quite similar to those observed in ungrazed sites. In the one exclosure where we intensively sampled soil texture, autocorrelation coefficients for sand content and B. gracilis cover were similar at lag distances up to 12 m. We suggest that the negative effect of sand content on B. gracilis generates spatial heterogeneity, but only in the absence of grazing. An additional source of heterogeneity in ungrazed sites may be the negative interaction between livestock exclusion and B. gracilis recovery following patchy disturbance.
Computing Clear Day Solar Radiation Spectra for the Terrestrial Ecological Environment
Authors: McCullough Edwin Charles , Porter Warren P.
Published: May 2006

Clear sky (cloud—free) horizontal plane terrestrial solar radiation spectral fluxes can be computed for any time of day and year, geographic location (latitude and longitude), and elevation upon inputing the optical properties of the atmosphere and reflecting properties of the underlying surface. Consideration is given to the problem of diffuse terrestrial radiation spectra for non—sea level elevations and where the terrestrial atmosphere cannot be regarded as being purely a Rayleigh atmosphere. Computation of terrestrial spectra for "large" zenith angles (Z > or = 72 degrees) is considered along with a discussion of irradiation patterns peculiar to polar zones (i.e., long days and nights). Selected results from the integration of these concepts into a computer program include the computation of total diffuse—to—direct flux ratios for radiation from a Rayleigh atmosphere at any solar zenith angle and selected elevations with typical mean ground albedos. Comparisons of integrated energy predictions with measurements in the literature agree favorably.
Crown Distortion and Elephant Distribution in the Woody Vegetations of Ruhuna National Park, Ceylon
Authors: Mueller-Dombois Dieter
Published: May 2006

A major wild elephant refuge occurs in the southeastern dry zone of Ceylon. The effect of the elephants on the woody vegetation is manifested in crown distortions mainly of the 2— to 5—m—tall woody plants. A survey of this phenomenon was made in 18 sample stands of four different structural woody vegetation types. A species crown—distorion index was established from summing the number of crown—distorted individuals in each species across the structural vegetation types. A list of species from high to low crown—distortion index is presented, which may serve as a guide to preferential elephant food plants for southeastern Ceylon. A stand crown—distortion index was established for each vegetation sample by summing the number of crown—distortion individuals per stand and relating these to the total number available. It was found that crown distortion is particularly high among earlier seral rather than late seral species, and stands, in spite of equal availability of both. This shows that the elephant is more strongly associated with disturbed and developing vegetation than with late seral or near—climax, evergreen, sclerophyll monsoon forest. Periodic elephant feces unts in wet and dry seasons indicated a shift and spread—out of current elephant activity into all structural woody vegetation types in the dry season, while during the wet season, elephant activity is more concentrated in areas of greater vegetation diversity with ready access to short—grass covers. Year—round centers of maximum activity were found in open Feronia (woodapple) scrub stands on grumusols and in evergreen forest—scrub on dunes.
Environment and Communiy Organization in Grasslands of Canyonlands National Park
Authors: Kleiner Edgar F. , Harper K. T.
Published: May 2006

Sixty uniformly distributed stands in adjacent areas, 40 in Virginia Park (virgin) and 20 in Chesler Park (grazed), were analyzed. Cryptogamic and vascular species were recorded; cover was analyzed by the point sampling method, and frequency by means of 25 quadrats (each 0.125 m2) per stand. The prevalent species (26 in Virginia, 23 in Chesler) were selected on the basis of a constancy—times—frequency index. Interspecific association patterns were determined by means of simple procedures based on quadrat frequency values for each species in the individual stands. Major environmental variables were recorded at each stand, and soil samples from four depths were collected at each site. Soil samples were analyzed for texture, bulk density, pH organic matter, total nitrogen, and available K+, PO4°, and Ca++. Although the parks are similar in gross environment and vascular plant cover, cryptogamic vegetation and community structure differ markedly between the areas. Many vascular species occur in greater abundance in one park than the other. Floristically, Virginia was much richer than Chesler Park. Cryptogamic cover was about seven times greater in the ungrazed park. The lichen and moss ground cover is apparently important in stabilization of the highly erodable, sandy soils against wind and water erosion. Cryptogams also have a important influence on chemical characteristics of the surface 5 cm of soil, and the difference in surface soils between the parks may be related to the presence of these species. Community pattern in the virgin park is more definite than in the adjacent, grazed park, a condition which is contrary to the concept that minimum association between species (pattern) is to be expected in stable as opposed to successional vegetations.
Fascicle Density and Needle Growth Responses of Red Pine to Water Supply Over Two Seasons
Authors: Garrett Peter W. , Zahner Robert
Published: May 2006

The ontogeny of terminal growth in red pine (Pinus resinosa Ait.) suggests that the growing season in Michigan be divided into three 2—month periods: April—May,June—July, and August—September. It is during the middle period that mitotic activity at the shoot apex initiates dwarf shoot primordia in the bud for the subsequent season's foliage; thus, preconditioning one year has a strong effect on next year's growth. Water was applied to or withheld from the soil under 23—year—old trees in various combinations of the 2—month periods over two growing seasons. All effects of drought were greatest on the terminal shoot of the main stem, diminishing on terminals of branches with distance from the apex, and disappearing at the base of the crown. Shoot extension was governed equally by conditions of the middle period of the previous year and of the early period of the current year. Each year fascicle density was regulated only by water conditions of the early period of the current year, regardless of preconditioning. Spacing of needles on shoots depended on elongation of the stem internodes between dwarf shoots, and was independent of the number of fascicles. Number of fascicles per shoot was governed only by conditions of June—July of the previous year, with drought during this period reducing the number of 30%. Length of needles was related to two factors: the number of fascicles produced per shoot and the water treatment of the period during which needles elongated. Thus when the water supply of the middle of the previous year was deficient, fewer but longer needles were produced currently; when water during the middle of the current year was deficient, needles were reduced in length by about 30%. It is concluded that the interaction of two seasons' water supply are usually compensative, rarely additive. The average net effect on foliage production is along—term, year—to—year stability in photosynthetic potential for red pine.
Biomass and Nutrient Content of Hazel Undergrowth
Authors: Tappeiner John C. , John Hugo H.
Published: May 2006

Studies in hazel undergrowths in five Minnesota pine stands provided techniques for estimating total hazel biomass and its three components (leaves, aerial stems, underground parts). Regression equations were developed for estimating total biomass and the three components based on measurements of aerial stem weight, aerial stem basal area, or number of aerial stems. Nutrient concentrations in the three biomass components were not well enough correlated with biomass nor with each to allow estimation using regression techniques. Total hazel biomass ranged from 4,600 to 15,000 kg/ha representing 4% to 7% of the total above ground weight of the stands. Compared to the overstory, hazel appeared to be rich in Ca, P. and Mn and contained from 2% to 22% of the weight of the nutrients in the above—ground parts of the vegetation.
Some Factors Affecting Germination of Swamp Tupelo Seeds
Authors: DeBell Dean S. , Naylor Aubrey W.
Published: May 2006

The effects of three temperature levels (15°, 21°, and 33° C) in combination with four soil—water regimes (moist—drained, surface—saturated, flooded—stagnant, and floodedaerated) on the germination of seeds of swamp tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.) were investigated. Germination was rapid in the moist—drained regime at temperatures of 21° and above. No germination occurred in potted soil where water levels were at or above the soil surface, regardless of temperature or whether the water was aerated. However, seeds germinated under water in the absence of soil, and aeration and partial removal of the seedcoat enhanced under water in the absence of soil, and aeration and partial removal of the seedcoat enhanced germination and early growth of the radicle. Seeds that had been submerged in flooded soil for up to 5 weeks germinated when placed in moist sand, but the germination response of such seeds was substantially reduced at 33° C.
Food as a Limited Resource in Competition between Two Species of Terrestrial Salamanders
Authors: Jaeger Robert G.
Published: May 2006

The terrestrial salamander Plethodon richmondi shenandoah occurs primarily in areas of talus, apparently excluded from surrounding areas of deep soil by Plethodon cinereus. Although the two species are closely related P. r. shenandoah grows to a longer body length and has a broader head. All ages classes of P. r. shenandoah emigrate out of the talus and are found within 3 m of the talus edge, but only adults which are as large as or larger than the largest P. cinereus are able to survive farther than about 3 m from the talus. This distribution is not explained by a tendency for large adults to wander more than juveniles. The large P. r. shenandoah in the soil take prey that are significantly larger than prey taken by conhabiting P. cinerueus, indicating that food may be the limited resource for which competition occurs. Both species are euryphagic and prey upon the same taxa of small animals. Food is periodically limited in availability, but not in abundance. Following a rain, salamanders forage freely and consume a large quantity of prey, based on stomach contents, but prey become increasingly unavailable as the soil and leaf litter dry and the salamanders are restricted to isolated pockets of moisture. Stomachs remain virtually empty until the next rain, at which time they are full again indicating that the abundance of prey is not greatly affected by the intervening dryness. Food may periodically become a limited resource during long dry seasons and as such may affect the survival of the salamanders or their ability to produce eggs. It is not clear whether interspecific competition is through differential exploitation of the limited resource or through interference. Lack of evidence for interspecific aggression may indicate that the former occurs, although it could not be demonstrated experimentally. Contiguous allopatry between the two species seems to result from an interaction of competitive exclusion and differential tolerance to dryness; P. cinereus is presumably a superior competitor for food in the soil and excludes P. r. shenandoah to areas of talus which P. cinereus cannot enter due to its tolerance of drier conditions in the rocks.
Metabolism of Weasels: The Cost of Being Long and Thin
Authors: Brown James H. , Lasiewski Robert C.
Published: May 2006

Metabolism of cold stressed weasels is 50—100 per cent greater than that of normally shaped mammals of the same weight. This can be attributed to their greater surface area, shorter fur, and inability to attain a spherical resting posture. In evolving an elongate shape which enables them to enter confined spaces in search of prey, weasels have sacrificed energetic efficiency. Increased ability to obtain prey, made possible by elongate shape and sexual dimorphism in body size, apparently more than compensates for the energetic cost of being long and thin. The information on weasels indicates that body surface area is an important determinant of heat loss in small homeotherms and suggests that energetic efficiency has played a significant role in the evolution of body shape and size.
Litter Production and Energy Accumulation in Three Plantations of Longleaf Pine (Pinus Palustriis Mill)
Authors: Wiegert Richard G. , Monk Carl D.
Published: May 2006

Three plantations of longleaf pine (Pinus palustris Mill) in South Carolina, 7, 11, and 13, years old, produced 298, 1,669, and 2,525 kcal/m2 per year of litter, respectively. The total standing crop of tree material was 3,171, 17,795, and 43,277 kcal/m2, respectively. The 7—year—old stand had the lowest density of trees and had not achieved a closed canopy. Annual needle fall average 57% of the spring standing crop of living needles. During the 7— to 13—year period the rate of net biomass accumulation per tree did not decrease, although the production of leaves to woody tissue decreased from 32% to 10%. The production characteristics of P. palustris differ markedly from those of a Virginia pine (P. virginiana) stand from the southeastern coastal plain of the United States.
Continuous Measurement of Carbon Dioxide Evolution From Partitioned Forest Floor Components
Authors: Edwards Nelson T. , Sollins Phillip
Published: May 2006

Loss rates of organic detritus in ecosystems can be determined by measuring rates of CO_2 release from decomposing organic substrates. We used an open system employing inverted boxes and an infrared gas analyzer (IRGA) to obtain continuous measurements of CO_2 evolution from the floor or a mixed mesophytic forest. Plexiglass sheets were used to partition respiratory activity of two litter horizons (01 and 02) and soil. Root respiration rates were determined with a differential respirometer. We compared the open system with a closed system in which KOH was used as the CO_2 absorber. Respiration measurements with KOH were 63% of IRGA values at 20 degrees C and 90% at 12 degrees. Flow rates (28 to 340 liters hr—1) had no effect on rates of CO_2 evolution. Nighttime CO_2 evolution rates were generally higher day—1. Preliminary data indicate annual CO_2 evolution of 3.8 kg m—2 (48% from litter, 17% from soil, and 35% from roots). This estimate is equivalent to 2.3 kg m—2 organic mass catabolized, assuming a carbohydrate substrate, which is 11% higher than independent estimates of the organic detritus annually available for catabolism.
Effects of Shading on the Migratory Behavior of the Florida Harvestor Ant, Pogonomyremex Badius
Authors: Carlson Douglas M. , Gentry John B.
Published: May 2006

Shading of the mound surfaces of a series of Pogonomyrmex badius colonies caused an increase in the number of migrations to new colony sites. Only 18% of the control colonies moved, while all of the shaded colonies moved at least once. The shading caused a reduction in soil temperature to a depth of 50 cm. It is speculated that the reduction in soil temperature interfered with the normal development of the brood and the colonies' response was migration to a new site. Since it invokes a predictable response, shading may be an excellent tool for future experimental studies into the behavior of P. badius.
Microhabitat Selection During Nesting of Hummingbirds in the Rocky Mountains
Authors: Calder William A.
Published: May 2006

The importance of nest location in reducing heat loss by radiation and convection is indicated by a preliminary examination of the nest sites of Broad—tailed and Calliope hummingbirds with regard to chilling nights in the Rocky Mountains. Radiation losses are estimated from surface temperatures. Nest diameter and weight increase as a function of time in the nesting season.
The Growth and Development of Montane Species at Near‐Freezing Temperatures
Authors: Kimball Steven L. , Bennett Bryce D. , Salisbury Frank B.
Published: May 2006

Studies were conducted to determine species response to low—temperature environments. Apical development was found to progress at near—freezing temperatures throughout the winter except when the plants were encased in a solid soil—ice matrix. Claytonia lanceolata and Nemophila breviflora shoots developed above the soil surface, under snow cover. In both species, chlorophyll content was inversely proportional to depth of snow cover. Spectrophotometric analysis of light penetration through snow indicated about 10% penetration through shallow layers (ca. 3.5 cm), and 0.01% through layers of 69 cm. C. lanceolata, Orogenia linearifolia, and Erythronium grandiflorum plants developed complete floral structures during the winter months, these being protected by leaves or an apical sheath (Orogenia).
Phenological Events and Their Environmental Triggers in Mojave Desert Ecosystems
Authors: Beatley Janice C.
Published: May 2006

Phenological events in Mojave desert systems are triggered by heavy rains (>25 mm [1 in]). The most predictable and consequential of these is a regional rain between late September and early December. This rainfall event is usually the precursor of successful vegetative and reproductive growth of shrubs the next spring, and is usually necessary for all growth phenomena of herbaceous perennials and winter annuals during the following winter and spring. For most plant components in most years, the growing season is synchronized within the autumn—winter—spring period, and the relative biological success each spring is dependent upon the occurrence or failure of occurrence of events of the preceding autumn. Under certain conditions rainfall during other seasons may trigger growth and reproduction of the primary producers and permit at least moderate or local successes every season. The relationships are stated in a flow diagram for the rainfall and phenological events, as documented for 13 yr in the Mojave desert of southern Nevada.
Fallout 137CS in the Soils and Sediments of Three Small Watersheds
Authors: Ritchie Jerry C. , McHenry J. Roger , Gill Angela C.
Published: May 2006

A budget for the distribution of fallout 137Cs was calculated for three small watersheds in northern Mississippi. The cover in one contributing watershed is predominantly forest, in the second it is predominantly grass, and in the third predominantly grass and crops. Of the total 137Cs input, 97%, 88%, and 85%, respectively, remained in the forest, the grass, and the grass—crop watersheds. The concentration of 137Cs per unit area in the reservoir sediments was 2.8, 3.8, and 4.0 times that of the soils from the respective contributing watersheds, indicating that the reservoirs are acting as "traps" for 137Cs. Of the 137Cs eroded from the three contributing watersheds, 57%, 38%, and 25% was found in the respective sediments. The calculated loss of 137Cs per unit area was in this order: eroded soils > croplands > grass > forest.
Flight Patterns among Eleven Species of Diurnal Lepidoptera
Authors: Scott James A.
Published: May 2006

Flights (movements from place to place) were studied in 11 species of Lepidoptera which differed in size, mate—locating behavior, food plants of larvae and adults, oviposition behavior, population size, areal extent of populations, and habitat features possibly limiting flights. and population size were quantified. Mate—locating behavior influences the difference in flights of ♂ ♂ and ♀ ♀; males tend to remain in sites favorable for mating, while ♀ ♀ tend to disperse more than ♂ ♂. Multibrood polyphagous species feeding on early successional plants had the farthest flights. Conversely, single—brood species feeding as larvae on perennial trees or shrubs had short flights. There is apparently a genetic component to flight distances; taxonomically similar species had similar distances, flights of several species were similar in successive years, and flights of reared individuals were similar to those of native individual. Two species in different superfamilies occupying the same habitat convergently developed similar flight distances. A migratory species had more unidirectional flight than the nonmigrants. There is a strong positive correlation between the size of the area in which the majority of individuals of a population are concentrated and flight distances for the 11 species. No correlation exists with population size, but mean densities are inversely correlated with flight distances. The significance of these correlations is discussed. It ispostulated that heritable behavioral mechanisms and local extinction influence the relationships between flights, area, and density.
Competition among Sympatric Erythroneura Leafhoppers (Homoptera: Cicadellidae) on America Sycamore
Authors: McClure Mark S. , Price Peter W.
Published: May 2006

Eight species of leafhoppers (Homoptera: Cicadellidae) in the genus Erythroneura (maculata group) breed on the American sycamore, Platanus occidentalis L.; several of these species occur sympatrically in many areas throughout the range of their host plant. The eight species are E. arta Beamer, E. bella McAtee, E. hymettana Knull, E. ingrata Beamer, E. lawsoni Robinson, E. morgani (DeLong), E. torella Robinson, and E. usitata Beamer. Population densities of these leafhoppers in mid—September reached an average of 72 adults per 10 leaves at the West Vienna site in southern Illinois USA. This was 28 time greater than at the Golconda site approximately 48.3 km away where weather severely reduced spring population levels. By early August at West Vienna food resources at the customary feeding sites, within 2 mm distance of the main veins, had been 95% depleted. This apparent food shortage was experienced by 86% of the total leafhoppers collected during the year. By mid—September the total leaf surface area utilized by feeding leafhoppers reached 98%. Similar levels of feeding damage were common throughout Illinois. Feeding was concentrated in the lower canopy. In the upper canopy (12 m aboveground) of a tree which had supported a relatively low leafhopper population throughout the season, there was no damage to leaves while in the lower portion (2 m aboveground) 59% of the leaf surface area was utilized. We infer that during the period of peak leafhopper abundance there are severe food limitations on these insects. Single species and mixed species rearing experiments in the field demonstrated that these leafhoppers compete at population densities comparable to those commonly observed throughout Illinois from August to October. At West Vienna 86% of the total leafhopper population probably experiences competition for about 9 wk in the year. For each species the number of progeny produced per ♀ under single species conditions was reduced even at low densities (2 ♂ ♂/leaf), at 6 ♀ ♀/leaf reproductive success was reduced by >70%, at 14 ♀ ♀/leaf no progeny matured. For mixed species rearings at comparable densities trends were similar. However, certain species pairs were less adversely affected by high density than others, suggesting slight differences between these species in the manner in which they utilize to explain coexistence by niche segregation. The relative rates of dispersal and extinction among competing species may explain coexistence in the sycamore leaf—feeding guild. The competitive ability of the Erythroneura leafhoppers may be frequency—dependent since at high densities each species adversely affected its own fitness more than it did that of its competitor in mixed species rearings.
Effects of Insect Seed Predators on Astragalus cibarius and Astragalus utahensis (Leguminosae)
Authors: Green Thomas W. , Palmbald Ivan G.
Published: May 2006

The genus Astragalus (Leguminosae) is noted for a wide diversity of compounds toxic to animals and for varied fruit morphology. Seed predation by insects was measured in mixed populations of Astragalus cibarius (browse milkvetch or locoweed), a toxic species with glabrous fruits, and Astragalus utahensis (Utah milkvetch), a nontoxic species with pubescent fruits. The study was conducted for 3 yr in areas where both species were sympatric, allowing direct comparison of insect faunas. The major seed predator on both species was a seed beetle (Acanthoscelides fraterculus, Coleoptera: Bruchidae) which destroyed 74% of the A. cibarius seeds and 60% of the A. utahensis seeds examined. Additional A. cibarius seed destruction, principally the result of predation by a seed chalcid wasp (Bruchophagus mexicanus, Hymenoptera: Eurytomidae), averaged 25%. Differential predation on the two plant species may be due to differences in phenology, seed and pod energy content, internal pod temperature, chemicals in the pods, and pod morphology. As A. cibarius and A. utahensis individuals apparently compete for a number of resources when they occur sympatrically, the differential predation rate probably influences the population dynamics of both species. Selection pressure by seed—eating insects may account for much of the chemical an morphological diversity exhibited by the genus Astragalus at the present time.
Age Distribution in Virgin Red Spruce and Northern Hardwoods
Authors: Leak W. B.
Published: May 2006

Age distributions are given for four species in a virgin spruce—fir stand in New Hampshire together with comparative data from virgin northern hardwoods. Three distinct forms of age distribution were found: (1) essentially linear relationships of numbers of stems (log) vs. age (log) denoting stationary populations with a power function form of survivorship; (2) concave age distributions indicative of increasing populations; and (3) convex to bell—shaped age distributions reflecting declining populations with a low birth date. Picea rubens, Abies balsamea, Betula papyrifera var. cordifolia, and Sorbus americana all exhibited stationary age distributions in the virgin spruce—fir stand. In virgin northern hardwoods, Fagus grandifolia and Acer saccharum appeared to be stationary or increasing, respectively, while P. rubens and Betula alleghaniensis had age distributions typical of declining populations.
Coexistence of Salamanders in the Genus Plethodon: A Variation of the Santa Rosalia Theme
Authors: Fraser Douglas F.
Published: May 2006

Two sympatric species of Plenthodon (P. hoffmani and P. punctatus), dissimilar in size as adults, were used to investigate the general problem of how two species that differ in size as adults but overlap in certain life history stages may avoid significant, size—related overlap in ecological requirements. The following three hypotheses were tested: (1) that size differences between adults lead to resource partitioning adequate to explain the coexistence of adults; (2) that co—occurring, similarly sized juveniles of the large species and adults of the smaller lack significant resource partitioning; and (3) that alternatives to resource partitioning are likely to be of importance in promoting coexistence in these salamanders. Analysis of food and surface habitat utilization shows overlap values that are low enough for adults of the two species to coexist but too high for coexistence between juveniles of the larger species and adults of the smaller. Because subadults and juveniles make up a substantial proportion of the population of the largest species, it appears that salamanders with long developmental periods and without temporal staggering during periods of development, probably cannot use adult size differences alone as an avenue along which to ameliorate interspecific competition for food or space. On the other hand staggered feeding schedules (noncoincident feeding) in all individuals, coupled with the partioning of the structural habitat by adults of the two species, appear to be factors of major importance in reducing inter— and intraspecific competition.
Recolonization of Red Sea Corals Affected by Natural Catastrophes and Man‐Made Perturbations
Authors: Loya Y.
Published: May 2006

The recovery patterns of hermatypic corals following an unpredicted catastrophic low tide were studied on two reef flats in the northern Gulf of Eilat, Red Sea: (1) the nature reserve of Eilat, Israel which is chronically polluted, and (b) a control reef which is pollution—free. The coral community structure and species diversity in both reefs were studied in 1969 and served as a base for comparing the extent of mortality during the low tide (1970), and the extent of recovery 3 years later (1973). In 1969 no significant differences were found (p > 0.05) between the coral community structure of the nature reserve and the control reef when the average number of species, number of colonies, living coverage, and diversity (H'n) per transect were taken into account. During the low tide both reefs suffered mass mortalities of corals (85% at the nature reserve and 81% at the control reef). Although the extent of mortality in both reefs did not differ significantly (p > 0.05), a marked difference was observed in their recovery 3 years later. The extent of coral recolonization was 23 X greater at the control reef, but no significant difference (p 0.05) was found in the extent of coral community regeneration in both places (15% at the nature reserve and 19.2% at the control reef). While the number of colonies, number of species, living coverage, and H'n are drastically decreased at the nature reserve 3 years after the catastrophic low tide, the control reef exhibited an outstanding fast recovery (full recovery is expected 5—6 years from the low tide). The commonest species on the control reef in 1969 showed the highest rates of recruitment in 1973, which might indicate the opportunistic life history of these species. I conclude that one of the differences between man—made polluting activities and natural catastrophes on coral reefs, is the possibility that the human—perturbed environment will not return to its former configuration, while reconstruction of reef areas denuded by natural disturbances is mainly a function of time. The higher coral diversity recorded on the control reef in 1973 (H'N = 2.403) as compared to 1969 (H'N = 2.206) may reflect a succession pattern in which diversity continues to increase in time after a catastrophe, until space becomes limiting and competitive interactions between species cause a decline in diversity. The unpredictable and extremely low tides at the Gulf of Eilat seem to interfere with this scheme and prevent monopolization of the reef flat by competitively superior species. I suggest that catastrophic low tides act as an important diversifying force on the reef flats of Eilat, in a similar way as other biological and physical disturbances affect coral communities (Porter 1974)
Lakes as Islands: The Distributional Ecology of Two Aquatic Plants, Lemna Minor L. and L. Trisulca L.
Authors: Keddy Paul A.
Published: May 2006

Groups of lakes can be considered archipelagos, and island biogeographic theory can be used to explain the distribution of aquatics within them. Two species of duckweed, Lemma minor and Lemna tremex, were studied as examples. Both are found in southern Ontario, but L. minor occurs much more frequently than L. trisulca. It is this difference the experiments were designed to explain. Colonization capability of each species was defined as its ability to: (1) withstand desiccation, (2) quickly populate a new habitat, and (3) inhibit the other species competitively. Lemna minor was clearly fat superior to L. trisulca in abilities (1) and (2), and in (3) it was judged superior or equal to L. trisulca. Wherever L. minor and L. trisulca are still colonizing recently deglaciated habitats, superior colonization capability alone can explain the more frequent occurrence of L. minor. Southern Ontario lakes may already have reached equilibrium, where the rate of species colonization is balanced by the rate of species extinction. Increases in summer pH above 8 occur, and as both species die above this point, pH could be the major cause of mortality. The observed frequencies of occurrence could therefore be the result of a balance between different rates of colonization and approximately equal rates of extinction.
Biochemical and Transplantation Studies of the Growth Form of Spartina alterniflora on Connecticut Salt Marshes
Authors: Shea M. L. , Warren R. S. , Niering W. A.
Published: May 2006

In southern New England Spartina alterniflora occurs as a tall grass (1.25—2m) within the intertidal zone and as a short form (0.3—0.4 m) within pannes on the high marsh. By means of electrophoretic comparisons of total soluble proteins and selected enzymes, along with reciprocal field transplants, an attempt was made to clarify the ecotype versus ecophene status of these different forms. All data obtained suggest that the tall and short forms are genetically indistinguishable and therefore merely reflect physiological responses to the environmental differences between the intertidal and panne sites.
Behavioral and Ecological Aspects of Shore‐Level Size Gradients in Thais Lamellosa and Thais Emarginata
Authors: Bertness Mark D.
Published: May 2006

Four intertidal carnivorous gastropods in the Puget Sound region. Thais lamellosa, Thais emarginata, Thais canaliculata, and Searlesia dira, exhibit intraspecific shore—level size gradients, with shell size increasing with decreasing tidal height, on a majority of the 13 beaches examined. Thais lamellosa and T. emarginata respond by photo—orthokinesis and geotaxis to gradients of light and beach elevation to establish and maintain their nonrandom size—class distributions. A previously published hypothesis that size gradients place the prereproductive members of a population in the least stressful portion of a species' intertidal range is examined. Evidence suggests that thaid size gradients are in response to similar size gradients in their major food source, Balanus spp. This promotes an energetically efficient predator—prey size selection relationship and facilitates intra and interspecific resource partitioning.
Observational Learning and the Feeding Behavior of the Red Squirrel Tamiasciurus Hudsonicus: The Ontogeny of Optimization
Authors: Weigl Peter D. , Hanson Elinor V.
Published: May 2006

The red squirrel is a food opportunist, exploiting the seed resources in many types of forest and possessing the capacity for learning new feeding techniques. Two groups of naive, individually isolated squirrels were presented with hickory nuts for the first time. One group could observe an experienced squirrel (Model) feeding. Comparisons of the metabolic cost of feeding. times, and techniques after 6 wk showed that the group with the Model expended half the time and energy used by other group while feeding and approached the Model in time and technique. The improved performance persisted after removal of the Model. While feeding techniques may develop by trial and error, observational learning (for example, from a parent or other conspecific) is more efficient in terms of energy and time and may be crucial to the safe and rapid exploitation of new foods and habitats.