Showing papers in "American Midland Naturalist in 1992"

Anthophilous fly distribution across an elevation gradient

Abstract: -Flower-visiting Diptera are abundant in montane and Arctic areas. This research, conducted on the western slope of the Colorado Rocky Mountains: (1) characterizes the predominant anthophilous fly taxa in comparison with other high-elevation and highlatitude sites; (2) examines changes in fly abundance with elevation, and (3) examines the potential of flies as pollinators by examining quality and quantity of pollen loads. Flies collected from 66 flowering species were identified to species to produce a data base containing taxonomic information, elevation and floral records. Malaise trap censuses were conducted in three elevational zones. Pollen carried by flies and pollen in their guts were quantified and examined to determine the number of plant species represented. Proportional representation of dipteran families changed in a similar manner in different mountain systems and the Arctic. The predominance of flies on flowers at high elevations appears to be due to a decrease in representation of other orders of insects. Most fly taxa fed at multiple plant species, but gut contents indicated that individual flies fed largely on a single pollen type. Total pollen loads of flies and solitary bees were similar although flies collected on Linum lewisii carried less pollen than bees.

The Influence of Precipitation on Reproduction by Myotis Bats in British Columbia

Abstract: -We compared the timing of reproduction by insectivorous bats in 1990, a wet year, with previously published data to test the prediction that reproduction is delayed by excess precipitation. The latest date of first capture of lactating, postlactating and juvenile bats occurred in 1990, whereas the earliest records for lactating females occurred in the driest year (1979). More important, the proportion of reproductive female Myotis lucifugus and M. yumanensis was significantly lower in 1990 than 1982. We conclude that high levels of precipitation delays reproduction and may induce some individuals to forego breeding altogether. Given the potential lifespan of temperate bats, this may be the best way of maximizing lifetime reproductive success.

Soil Seed Bank of a Semiarid Texas Grassland Under Three Long-Term (36- Years) Grazing Regimes

Abstract: -Species composition and density of the readily germinable soil seed bank of three long-term (36-yr) grazing treatments (heavy continuous, moderate deferred rotation and ungrazed exclosure) were determined for a summer and spring period for a semiarid grassland of the western Edwards Plateau, Texas. Total seed densities (2252 to 4409 seeds/ mi2) did not differ among grazing treatments, but did vary seasonally. Species composition varied among treatments. Heavy continuous grazing had a high proportion of early-seral, annual-dicot taxa, whereas the ungrazed treatment had a high proportion of late-seral, perennial-monocot taxa. Seeds of late-successional midgrass species (e.g., Bouteloua curtipendula, Eriochloa sericea) were not stored in the soil of any treatment and appeared to be transient. Many other species appeared to maintain persistent seed banks, including seeds of the current mid-successional dominant shortgrass, Hilaria belangeri. Similarity of composition between germinable seeds in the soil and existing plant communities was low. Soil seed bank is a primary control of secondary succession in these grasslands, and absence of late-successional species in the seed bank impairs the rate of succession.

Sugar maple invasion of an old-growth oak-hickory forest in southwestern Illinois.

Abstract: -Analysis of presettlement land survey records in an area surrounding a present 7.2 ha old-growth oak-hickory forest, Weaver's Woods, in southwestern Illinois showed dominance by Quercus alba and Q. velutina. Weaver Woods developed into a Q. velutina, Q. rubra, Carya ovata forest by 1956, and into an Acer saccharum, C. ovata, Quercus spp. forest with a basal area of 32.7 m2 ha-' by 1983. Woody stem inventories were based on trees >30.5 cm dbh in 1956, and on all woody plants >6.6 cm dbh in 1967 and 1983 along with the sampling of understory and herbaceous vegetation. Stand density has fluctuated and in 1983 was 459 trees ha-'. Size-class distribution of all species combined has not changed. Size-class distributions of individual species show a changing composition and structure of the forest. Size-class distributions of the oaks and hickories best fit a normal or Gaussian curve, with little or no recent regeneration. Acer saccharum was the dominant species in the forest in 1983 and had a negative exponential size-class structure reflecting abundant regeneration. Asimina triloba was the dominant species in the understory in 1983, heavily shading much of the forest floor. If current trends continue, Acer saccharum will dominate the canopy and oaks and hickories will decrease to remain as scattered large individuals. The size-class distributions of Weaver's Woods over the past 27 yr, plus future trends and old-growth status related to presettlement forests in the area, are discussed. INTRODUCTION Changes in composition of a 7.2-ha forest remnant, Weaver's Woods, in Union County of southwestern Illinois are examined in relation to the status of old-growth, oak-hickory forests in the midwest. Weaver's Woods is one of the best-documented upland forests in southern Illinois. A decline in oaks, particularly Quercus rubra and Q. velutina, and an increase in Acer saccharum has been observed in remaining midwestern old-growth, oak-hickory forests (Weaver and Ashby, 1971; Weaver and Robertson, 1981; Schlesinger, 1976, 1989; Boggess, 1964; Boggess and Bailey, 1964; Ebinger, 1968; Ebinger and Parker, 1969; Johnson and Bell, 1975; and Schmelz et al., 1975). Well-documented studies of changes in old-growth forests provide benchmarks for ecologists and natural heritage managers to evaluate natural processes. They provide valuable data for better understanding the effects of climatic change, manipulative practices and anthropogenic pollutants on this type of ecosystem. Forest inventories in 1956, 1967 and 1983 are used to evaluate the changes in forest composition and structure of Weaver's Woods over 27 years. The objectives were to: (1) I Present address: Ft. Lucy School System, Ft. Lucy, Florida 34983 2 Present address: Department of Forestry, Wildlife and Fisheries, University of Tennessee, Knoxville 37901-1071

Dynamics of a small mammal community in a fragmented forest.

Abstract: -Community structure [species richness (S) and numbers of individuals captured] of a small mammal community were studied in July and August, 1987-1989, on a 1166-ha forested area in central Pennsylvania, which was divided into reference and treated sectors of comparable size. The reference sector was uncut, whereas the treated sector contained two areas with 50% and 75% fragmentation, respectively, resulting from forest clear-cutting in winter 1985-1986 and 1986-1987. I examined whether community structure of small mammals differed among years (1987-1989) or among forested areas that varied in extent of fragmentation. In addition, I compared community structure in 1987-1989 to that obtained on the same study site in 1982-1984 when extent of forest fragmentation was considerably less (25% and 50%) on the treated sector. Four-hundred nine individuals of seven species were captured during 4500 trap nights in 1987-1989, including white-footed mice (Peromyscus leucopus) (67.3% of total individuals), southern red-backed voles (Clethrionomys gapperi) (13.3%), and masked shrews (Sorex cinereus) (12.0%). Numbers of individuals captured of all species combined and of the three common species were significantly (P < 0.05) lower in 1988 than in 1987 and 1989, which I attributed to a drought in 1988 that presumably reduced the availability of terrestrial arthropods as a food resource. Although S was similar in 1987-1989 among areas of forest fragmentation and between 1982-1984 and 1987-1989, numbers of P. leucopus and C. gapperi captured were significantly (P < 0.05) higher in 1987-1989, especially in the area with 75% fragmentation. Numbers of P. leucopus were greater in 1987-1989 than in 1982-1984, perhaps because of a greater variety of microenvironments created by clear-cutting and increased availability of mast (acorns of oaks [Quercus] spp.) in 1987-1989. Numbers of C. gapperi likely were higher in 1987-1989 than in 1982-1984 because of moist microenvironments resulting from abundant low vegetation in clear-cut plots on the treated sector. I conclude that forests fragmented into small, even-aged plots can benefit P. leucopus and C. gapperi by increasing abundance of these two

Contrasts in Density of Benthic Invertebrates Between Macrophyte Beds and Open Littoral Patches in Eau-Galle Lake, Wisconsin

Abstract: -Small areas that are barren of plants commonly occur amidst dense littoral zone vegetation of lakes. This study compared the benthic invertebrate communities of nonvegetated patches to those in the surrounding vegetated sediments in a Wisconsin lake. Mean benthic invertebrate densities in the sediments of Ceratophyllum demersum and Potamogeton nodosus beds were 13 and seven times, respectively, those of nearby nonvegetated areas within the littoral zone. The contrast in densities was especially striking for the gastropods Amnicola limosa and Gyraulus parvus, which were collected below Ceratophyllum at 162 times and 48 times, respectively, their densities in open areas. The conjecture that these density differences were due to a lack of a detrital food base in the nonvegetated areas was not supported by our investigation. The most likely explanations for such a contrast in invertebrate densities are: (1) disturbance effects in areas lacking plants, and (2) increased predator efficiencies in the open zones. Removal of macrophytes by herbicides, drawdown or mechanical means creates large expanses of open areas; our data indicate that macrophyte removal would result in a less diverse and much less abundant invertebrate fauna in littoral zone sediments. More than 90% of the invertebrates in 0-1 5 cm cores were found within the top 5 cm in nonvegetated areas as well as in sediments below a rooted macrophyte (Potomageton nodosus) and a nonrooted macrophyte (C. demersum). Despite the presence of its root system, which might oxidize the sediments, proportional abundances of invertebrates deeper in the sediments below Potamogeton were not greater than those below Ceratophyllum or in the open zones.

Fire, Vegetation Changes, and Population Fluctuations of Townsend's Ground Squirrels

Abstract: -Townsend's ground squirrels (Spermophilus townsendii) are important prey for raptors and other predators in the Snake River Birds of Prey Area in southwestern Idaho, an area undergoing drastic vegetation changes induced by fire. We used 54 transects of burrow entrances done in 1982 and recensused in 1986-1989 to determine how the vegetation changes were affecting squirrel populations and if Townsend's ground squirrels will continue to provide a stable prey base for these predators. The mean number of active burrow entrances/ha decreased from 194 in 1982 to 68 in 1988. Burrow densities were highest and had the lowest annual variation in winterfat (Ceratoides lanata)-Sandberg's bluegrass (Poa secunda) communities. Big sagebrush (Artemisia tridentata)-dominated communities had intermediate burrow densities, whereas shadscale (Atriplex confertifolia) communities had the lowest burrow densities. Burrow densities were highly variable in exotic annual communities, and negatively correlated with cheatgrass (Bromus tectorum) and other exotic annuals in all communities. Widespread conversion of desert shrublands to exotic annualdominated communities by wildfires appears to be creating an increasingly unstable prey base for raptors in the Snake River Birds of Prey Area.

Effects of grazing on cryptogamic crusts in pinyon-juniper woodlands in Grand Canyon National Park

Abstract: -Previously grazed pinyon-juniper woodlands in Grand Canyon National Park, northern Arizona, were studied to determine the effects of past and present grazing. The occurrence and biomass of cryptogamic crust were compared for five sites in and around the Park along a continuum from never grazed to recently grazed. All sites were similar in soil characteristics, elevation and overstory dominants. Cryptogamic crust was quantified using visible cover estimates and the chlorophyll a content of the crust as an indicator of biomass. Visible crust cover was reduced almost 80% on grazed (5.2%) as compared to ungrazed (23.3%) sites. Crust biomass, as estimated by chlorophyll a content, was reduced on grazed (3.1 ,tg cm-2) compared to ungrazed (9.9 ,tg cm-2) sites. There were no significant differences in species presence and absence data. Significant correlations existed between cryptogamic crust cover and the composition of the respective vascular plant communities, marked by a reduction of grasses and an increase of bare soil.

A comparison of presettlement and present-day forests on two bigtooth aspen-dominated landscapes in northern Lower Michigan

Abstract: -Forest composition within a local landscape is influenced by physical site characteristics and prevailing disturbance regime. In many areas of eastern North America, the natural disturbance regimes that influenced presettlement forest composition have been altered by human activities associated with European settlement. These alterations have led to substantial changes in composition and the development of successional pathways markedly different from presettlement conditions. In this study we examined presettlement and presentday forest composition of two bigtooth aspen-dominated landscapes in northern Lower Michigan. Our objectives were to: (1) reconstruct and relate presettlement forest composition to the potential natural disturbance regime of each landscape; (2) compare presettlement and present-day forest composition of each landscape; and (3) assess the influence of postsettlement disturbance history on the development of the current forests and the potential successional pathways of the two landscapes. Presettlement forest composition, reconstructed using General Land Office survey records, differed substantially between the two landscapes. Landscape 1 was dominated by firesensitive eastern hemlock and American beech, while landscape 2 was dominated by firedependent red pine, white pine and jack pine. Compositional differences may have been related to differences in presettlement fire frequency, or to differences in physical site characteristics or regional climates. The present-day overstories of both landscapes were dominated by bigtooth aspen, red oak and red maple species that were of minor importance in the presettlement forests of the study areas. Compositional convergence was attributed to the similar influence of postsettlement disturbance history on each landscape. Logging and wildfires eliminated advanced regeneration and many remnant seed sources of hemlock, beech and pines and favored the development of forests dominated by bigtooth aspen, red oak and red maple. Individuals.of the latter species survived the disturbance and proliferated vegetatively in the postsettlement landscape. Differences in seed source availability in the present-day forests have led to marked differences in species recruitment in the understories of the two landscapes. Changes in seed rain and fire exclusion in the two landscapes are apparently leading to development of forest types markedly different from the presettlement conditions. The results illustrate how human-induced changes in disturbance regimes can have important, long-lasting effects on forest composition.

Winter Activity of Bats at a Mine Entrance in Vermillion County, Indiana

Abstract: -Activity of bats was investigated at the entrance to an abandoned clay mine in Vermillion County, Indiana, between 21 November 1989 and 17 March 1990. The mine serves as a hibernaculum for little brown bats Myotis lucifugus, eastern pipistrelles Pipistrellus subflavus, and northern bats M. septentrionalis. Two methods of sampling were employed, both using a double-frame Tuttle trap. The first was used to test the assumption that little bat activity occurred at the entrance to the mine after 15 November. The trap was left in place continuously from 21 November 1989 to 11 March 1990, and was checked at first daily, then sporadically. Totals of 55 little brown bats (30 males, 25 females), 78 northern bats (42 males, 36 females) and 10 pipistrelles (6 males, 4 females) were taken. Tending of traps was instituted to get more specific information when the first method indicated much activity was occurring. The trap was tended from dusk to 0100 h on 11 nights between 16 January and 17 March (3 in January, 4 in February and 4 in March). A total of 184 bats were taken in approximately 77 h of observation, 133 of them entering and 51 of them leaving the mine. These included 3 pipistrelles (1 male, 2 females), 50 little brown bats (32 males, 18 females), and 131 northern bats (106 males, 25 females). Outside temperatures on these 11 nights ranged from -6 C to 24 C. Activity increased in direct proportion to temperature. There was little activity by pipistrelles, but a few little brown and northern bats were flying outside the mine throughout the winter. Northern bats showed greatly increased activity in mid-March. Limited data indicated no feeding occurred until mid-

Spatial and Temporal Patterns in Fish Assemblage Structure of an Intermittent Texas Stream

Abstract: -Fish were sampled monthly at seven sites for 1 yr in Sister Grove Creek, an intermittent prairie stream in N-central Texas. Despite drastic seasonal fluctuations in discharge, abundance of individual species varied more spatially among sites than temporally at individual sites. Spatial differences in assemblage structure were attributed to differences in habitat and to migration from a downstream reservoir. The preponderance of spatial variation in species abundances combined with minimal temporal variation suggests: (1) temporal consistency of species abundance throughout the year, and (2) the highly dynamic hydrologic regime may not be a disturbance for Sister Grove Creek fishes.

Factors Affecting Home-Range Size in House Mice (Mus musculus domesticus) Living in Outdoor Enclosures

Abstract: -Home range size was investigated in wild house mice living in outdoor enclosures using powder-tracking and radio-tracking. We obtained 19 home-range estimates for juvenile mice using powder-tracking, and 43 estimates for adults using both techniques. Juvenile males, juvenile females and adult females did not differ in home-range size, but ranges of adult males were larger than those of the other three groups. Changes in homerange size were examined with trend analysis using body weight as an indicator of age. Home ranges of males had a positive linear relationship with body weight, whereas home ranges of females fit a negative quadratic trend with body weight. Population density was not an accurate predictor of home-range size of all mice, nor was adult-male density a predictor of adult-male home-range size. Powder-tracking and radio-tracking yielded equal estimates of home ranges for adult mice.

Vulnerability of Ground Nests to Predation on an Agricultural Habitat Island in East-Central Illinois

Abstract: -Predation of artificial ground nests (n = 388) was studied in 1986 and 1987 in E-central Illinois. The 61-ha study area included small tracts of old field, native and introduced grasses and cropland. Thirty-five percent of all nests were destroyed during 10day trials; 51% within the 1st 2 days. Nest predation was influenced by heterogeneity of vegetation and nest concealment. The fate of a given nest was related to the fate of nearby nests although distance to the nearest nest and nest densities were not significant factors. Distances from nests to boundaries (changes in one cover type to another) did not affect nest outcome. Nest predation was relatively low along roadsides leading away from the study area.

Response of five deciduous forest herbs to partial canopy removal and patch size.

Abstract: -Forest canopy was partly removed [33% or 66% removal of canopy tree basal area (BA)] from patches of three sizes (0.015, 0.053, 0.196 ha) to determine whether the frequency of five deciduous forest herbs was affected by patch size. Herb frequency, irradiance and woody stem density were recorded after canopy removal and 2 yr later. Irradiance and woody stem density both increased more in large (0.196 ha) patches than in smaller patches (0.015 and 0.053 ha) with 33% and 66% of tree BA removed. In contrast, where 66% of tree BA was removed, the frequency of four herbs increased more in smaller patches than in large patches and the frequency of the fifth herb was unaffected by patch size. Where 33% of tree BA was removed, herb frequency also increased more in smaller patches than in large patches for one herb and by about the same amount in all patches for another herb. The remaining three herbs each increased more in medium-sized patches (0.053 ha) than in small or large patches. These results indicate that the frequency of perennial forest herbs does not increase more in large canopy openings than in smaller openings. Although irradiance was higher in large patches than in smaller patches, woody stem density was greater in large patches as well and competition from more woody plants in large patches may explain why herbs did not increase more in large patches than in smaller patches.

Water Level Variability and Litterfall Productivity of Forested Freshwater Wetlands in Louisiana

Abstract: -Litterfall was measured in an impounded swamp and a managed wooded crayfish pond swamp in S central Louisiana from mid-December 1976 through mid-December 1981 and in a natural swamp and a "restored" swamp from mid-December 1977 through mid-December 1981. Hydrological patterns were different from area to area and water depths (measured from May 1977 to May 1981) varied considerably in three of the areas depending upon rainfall. In the crayfish pond, the water regime was maintained by pumping. Average leaf litterfall was greatest in the crayfish pond swamp (579 g/m2/yr) and least (293 g/m2/yr) in the impounded area. Average litterfall values were intermediate and similar in the natural swamp and the "restored" swamp areas (405 and 401 g/m2/yr, respectively). Yearly litterfall declined throughout the study in the impounded swamp until 1981. The progressive decline is likely related to permanent flooding conditions which have caused tree mortality. The increase in litterfall in 1981 in all areas was probably related to drought conditions that year which for the first time in many years allowed the sites to dry out, thus improving growing conditions. These results suggest that productivity of Louisiana coastal forested wetlands will decrease in the future due to waterlogging related to regional subsidence.

Sparse buried seed bank in a southern Appalachian oak forest: implications for succession.

Abstract: -Samples of leaf litter, humus and surface soil were collected from sites on six steep NE-facing slopes to determine the density and species composition of the buried seed bank on Brush Mountain (Jefferson National Forest, Montgomery Co., Va.) and its potential contribution to postdisturbance forest regeneration. An average of only 0.43 seeds/ m2 was found at the sites, with significantly more seeds occurring in the humus layer than either the leaf litter or soil. Seeds of forest herbs were more common than those of forest trees, forest shrubs or even ruderals. There were also differences in seed density and species composition among sites. These results were unexpected, and probably due to the cumulative long-term effects of a variety of factors including: (1) the lack of past cultivation; (2) past low-intensity ground fires; (3) the scarcity of nearby sources of ruderal and early-successional seeds, and (4) the inherently short longevities of seeds of forest species. The sparse seed bank, particularly the virtual absence of seeds of early successional species, indicates that succession should be strongly dependent upon vegetative reproduction and postdisturbance seed dispersal.

Seed Dispersal by a Generalized Herbivore: Rabbits as Dispersal Vectors in a Semiarid California Vernal Pool Landscape

Abstract: The possible role of rabbits as seed dispersal agents was investigated in a chaparral-coastal sage scrub landscape containing vernal pools (small temporary wetlands) in coastal San Diego County, California. Rabbit pellets were collected from the pools and placed in temperature-controlled chambers to determine their content of germinable seeds. Seeds of 18 species germinated, 10 of which occur primarily or exclusively in or near vernal pools. Although the germinable seed content of pellets is low, ca. 87 germinable seeds per 1000 pellets, the long-term and large-scale impact of rabbit dispersal may be important to species that lack dispersal-enhancing traits. We conclude that dispersal by rabbits may influence the distribution and long-term dynamics of these species.

The effects of light environment on herbivory and growth in the dioecious shrub Lindera benzoin (Lauraceae).

Abstract: -Measurements of total leaf area, herbivory, number of herbivores, and growth on male, female and vegetative individuals of the dioecious shrub Lindera benzoin were made in different light environments. Herbivore abundance did not differ across habitat types and sexual morphs. Herbivory was greater in shade habitats than in sun habitats, and vegetative plants suffered greater herbivory than did flowering males or females which did not differ in the amount of leaf material eaten. Branch growth rates were higher in the sun than in the shade, and females grew less than male or vegetative plants. Because allocation to defense, growth and leaf characteristics are likely to be confounded, rates of herbivory may not always be predicted based on growth rate or gender alone.

Climate-vegetation Relationships between the Great Plains and Great Basin

Abstract: -Conditions responsible for vegetative differences between the Great Basin and Great Plains are poorly understood. Two hypotheses for the differences are (1) the geophysical barrier of the Rocky Mountains and a slow rate of dispersal of taxa restrict interchange of taxa between the Great Basin and Great Plains, even where gaps in the mountains occur; and (2) differences in climate between the two regions limit floristic intermixing. We examined relationships for both hypotheses using vegetative data from 14 study sites in Idaho, Colorado, Wyoming and Montana. Canopy cover of graminoids, forbs and shrubs was regressed against selected climatic variables and distance of each study site from the Rocky Mountains. Shrub cover diminished, graminoid cover increased and forb cover remained roughly constant on a west-to-east gradient. Graminoid cover increased and forb cover remained roughly constant on a west-to-east gradient. Graminoid cover was positively correlated with summer precipitation, and shrub cover was positively correlated with winter precipitation and negatively correlated with summer precipitation. These vegetative variables were more highly correlated with climatic data than with distance from a broad gap in the Rocky Mountain chain. Current distributions of Great Plains and Great Basin taxa suggest that the Rocky Mountains have not been an effective barrier to plant dispersal in Wyoming. Our data suggest that seasonality of precipitation restricts dispersal of taxa between the Great Basin and Great Plains.

Diameter growth of Taxodium distichum (L.) Rich. and Nyssa aquatica L. from 1979-1985 in four Louisiana swamp stands.

Abstract: -Annual diameter growth of baldcypress and water tupelo trees in four swamp stands in S central Louisiana were measured from 1979 to 1985. Seasonal patterns of growth were also monitored during 1979 and 1980 using vernier tree bands. Most growth occurred from late April to early July for both species, with baldcypress exhibiting the greatest growth in all sites. Trees of both species on the site with the least hydrological alteration, had the lowest growth rate. Trees in the crayfish pond (water level managed by pumping) and the impounded area (permanently flooded) had much higher growth rates than the control area. Annual defoliation by the forest tent caterpillar probably accounted for the low water tupelo growth rates compared to baldcypress. It is becoming more difficult to relate annual growth differences to hydroperiod alone in S Louisiana because of changes in tree growth and successional patterns due to increased waterlogging as a result of eustatic sea level rise and subsidence combined with insect herbivory and human manipulation of the environment.

Factors Affecting Tree Growth on Three Lowland Sites in Southern Illinois

Abstract: -This article reports a three year study (1985-1987) assessing environmental factors controlling seasonal and historical tree growth on floodplain forested sites in southern Illinois. Radial growth increment was related to temperature, precipitation, soil moisture, depth to water table and solar radiation during each growing season. Growth ceased early during dry and later during wet years. During the wettest year, growth was negatively correlated with water table depth but during the driest year (1987), precipitation was positively correlated with growth. High water tables that occurred in the winter and early spring did not negatively affect tree growth. Historical tree growth was measured using standard dendrochronological techniques to analyze increment core data from individuals of eight Quercus species growing in three floodplain sites along the Big Muddy, Mississippi and Cache rivers in southern Illinois. Growth indices were negatively correlated with June temperature for most species on each site. Late spring or summer (May, June or July) precipitation was positively correlated with growth in many species-site groups. Tree species adapted to wet floodplain sites were not significantly related to precipitation but did respond significantly to summer temperature. Tree growth was positively correlated with river discharge on two sites; this relationship is likely due to the increased moisture available to the trees at high discharge. The lack of significant relationships at Horseshoe Lake may be the result of the hydrological control on the Mississippi River or because the river discharge is not strongly related to local precipitation.

Effects of Soil Surface Microtopography and Litter Cover on Germination, Growth and Biomass Production of Chicory (Cichorium intybus L.)

Abstract: -A greenhouse experiment was conducted to determine the effect of soil surface and litter cover on germination, survival and biomass production of chicory (Cichorium intybus L.). Surface treatments which had more microtopographical relief (soil covered with clods or rocks) were better for germination and growth compared to treatments in which surfaces were smooth or covered with fine or coarse litter. Seeds germinated in crevices formed where clods or rocks interfaced with the soil surface creating "safe sites" which retained moisture and provided seedling roots an opportunity to become established. Optimal experimental treatments were similar to chicory's roadside habitat which appears to be hot, dry and inhospitable, but provides the topographical heterogeneity necessary for successful germination and seedling establishment.

Pattern of Nest Occupancy of the Prairie Vole Microtus ochrogaster in Different Habitats

Abstract: -Size and composition of social groups of the prairie vole, Microtus ochrogaster, were studied during October and November 1989 in alfalfa and bluegrass that are high and low food resource habitats, respectively, for this species. Similar data were also collected in February 1990 in tallgrass prairie, a very low food resource habitat for M. ochrogaster. Average social group size, prevalence of communal groups, and proportion of known philopatric offspring were similar in alfalfa and bluegrass. Group size and composition in alfalfa and bluegrass in 1989 were similar to those observed in alfalfa in the same months during 1981-1987. Social group size and prevalence of communal groups in tallgrass prairie were similar to those recorded in alfalfa during February 1981-1987. We conclude that food resource availability is not a proximate factor influencing formation of communal groups in M. ochrogaster.

Life History Traits of a Riverine Population of the Asian Clam Corbicula fluminea

Abstract: -Monthly collections of Corbicula fiuminea were taken for 1 yr from a small river (depth range 0.1-1.1 m) near Charlottesville, Virginia. Mean densities ranged from 173-2990 clams m2, with an annual mean of 677 clams m2. Based on the time-series of shell-length frequency distributions and from dissections of adults, it appeared that there was one generation produced per year with the first detectable newborns (shell length z 0.4 mm) settling in the substrate during July. Maximum lifespan was 2-3 yr during which clams reached average shell lengths of 11.1 mm in the 1st yr and 17.6 mm in the 2nd yr of life. Other studies have most often reported two generations produced per year with lifespans of 2-4 yr and maximal shell lengths of 30-60 mm. It is suggested that much of the variation in life history displayed by this introduced species in phenotypic.

Plant-animal Interaction: The Effect of Permian Megaherbivores on the Glossopterid Flora

Abstract: -With the appearance and diversification of dinocephalian and anomodont terrestrial herbivores in the Permian, plants responded to this intense herbivory by deterrence and escape. Plant defenses recognized in glossopterids include: increase in undigestible carbon in the leaves, reduction in leaf size (microphylly), woodiness, chemical defense and protection of reproductive structures. This resulted in lower quality of herbage, requiring herbivores to evolve various feeding strategies. In Permian herbivores this is reflected in diversity of skull morphology, body size, body weight and bite size. In addition, high activity rates and possibly homeothermy may have evolved in these herbivores. This would permit the herbivores to respond to changing conditions in the quality and quantity of the herbage and dissipate excess heat due to high activity rate and stomach microbes.

Patterns of Weevil Herbivory on Male, Monoecious and Female Inflorescences of Sagittaria latifolia

Abstract: -The weevil Listronotus appendiculatus lays eggs on immature inflorescences of Sagittaria latifolia, which, in the study area, may be male, monoecious or female. The weevil lays the same numbers of eggs on male as on monoecious inflorescences, and in both cases the larvae create a strong vertical gradient in the success of male flowers, with basal flowers more successful in presenting pollen. The monoecious inflorescences have female flowers in the basal positions that are the safest for male flowers. The interference of these female flowers with male success is low, however, because the number of female flowers per monoecious inflorescence is small. The weevil lays many fewer eggs on female than on male or monoecious inflorescences, and the potential for damage to female success is much lower on female than on monoecious inflorescences. The male parts of a monoecious inflorescence seem to "attract" egg laying, which subsequently interferes with the female success of that inflorescence. In these ways each gender on a monoecious inflorescence interferes with the escape of the other gender from herbivory. This pattern of herbivory may help to select for the unisexuality found in the taxon.

Diet and Nesting Success of Barn Owls Breeding in Western Nebraska

Abstract: -We analyzed the diet of barn owls (Tyto alba) in Lincoln County, Nebraska during nesting seasons of 1984 through 1986 and their nest success in 1985 and 1986. Nesting attempts were made at 9 of 13 nest sites checked in 1985 and at 12 of 15 nest sites in 1986. Microtus ochrogaster comprised 32.7% of 10,140 prey items overall with marked increase in percent from 1985 to 1986. Barn own reproduction increased from 1985 to 1986 with more nests initiated, a higher proportion of successful nests and higher mean number of young fledged per nest attempt. Proportions of prey in the diet were significantly different from proportions of prey captured by trapping. Microtus ochrogaster was overrepresented and Peromyscus maniculatus underrepresented in the diet. Annual percentages of M. ochrogaster and Perognathus hispidus in the diet were negatively correlated with Reithrodontomys megalotis and with P. maniculatus but were not correlated with each other. Reithrodontomys megalotis and P. maniculatus were not correlated with each other. Reithrodontomys megalotis decreased and P. hispidus increased in the diet each year. A number of factors influence barn owl reproductive success including diet, quality of nest site and foraging ability of

Nests and Daytime Refugia of Cotton Mice (Peromyscus gossypinus) and Golden Mice (Ochrotomys nuttalli) in South-central Florida

Abstract: -Daytime refuge selection, nest construction, and patterns of refuge use of cotton mice (Peromyscus gossypinus) and golden mice (Ochrotomys nuttalli) were studied in S-central Florida. Of 95 P. gossypinus refugia examined, 67 were burrows of the gopher tortoise (Gopherus polyphemus), 23 were ground holes, and five were hollow tree cavities. Of 77 0. nuttalli refugia examined, 75 were on the ground under leaf litter and two were aboveground in shrubs. Neither species differed in seasonal refuge selection. Peromyscus gossypinus built platform and spherical nests of saw palmetto (Serenoa repens) fibers, lichens and cotton, and 0. nuttalli built spherical nests of saw palmetto fibers, Spanish moss, leaves, twigs, grasses and cotton. Winter 0. nuttalli nests were significantly larger and heavier than summer nests. Individuals of both species used a similar number of refugia, and refuge fidelity was greater for both species during winter. The greater versatility of refuge selection in P. gossypinus may contribute to its ability to exploit a wider variety of habitats than 0. nuttalli. Based on the extreme differences in refuge selection observed between these species, it is unlikely that competition for daytime refugia occurred in this study.