Showing papers in "American Midland Naturalist in 1987"

Invasion of Microstegium vimineum (Poaceae), an exotic, annual, shade-tolerant, C4 grass, into a North Carolina floodplain.

Abstract: Microstegium vimineum, an Asian annual C4 grass that is very shadetolerant, has invaded floodplains, streambanks and adjacent mesic slopes in the North Carolina Piedmont during the past 30 years. A 3-year study of its invasive characteristics revealed that M. vimineum is slow to invade undisturbed vegetation, but rapidly fills disturbed, mesic, shaded areas, such as streamsides where floods scour existing vegetation or sewer-line rights-of-way which are mown once a year. Its seeds remain viable for at least 3 years in the soil seedbank and rapidly germinate to produce a new cohort if a disturbance removes an existing cohort. On fertile floodplain sites, soil fertilization in March had no effect on seed production in October. When M. vimineum seeds were sown into existing vegetation, seed production was negatively correlated with soil potassium, calcium, silt and pH, probably because the more fertile sites also supported a denser ground vegetation layer. These qualities, in addition to its cleistogamous or apomictic reproduction, help explain how M. vimineum has spread throughout the eastern U.S. since its introduction approximately 70 years ago. INTRODUCTION Microstegium vimineum (Trin.) A. Camus is an annual grass species from Asia which recently invaded floodplains, streamsides and adjacent mesic slopes in the North Carolina Piedmont. It appears to be advancing into the existing ground cover of floodplains, which consists mainly of Japanese honeysuckle Lonicera japonica Thunberg. These two species often occur in dense monospecific stands which are separated by a strikingly narrow zone of mixing. This pattern of an introduced annual grass invading established stands of Japanese honeysuckle, a perennial woody vine which is known for its aggressiveness on fertile sites of the Carolinas (Bruner and Shearin, 1964), led me to ask the following questions: (1) Is M. vimineum invading undisturbed stands of L. japonica? (2) Does M. vimineum create a seedbank? (3) Can M. vimineum invade undisturbed stands of L. japonica if its seeds are sown in the stands in large numbers? (4) What environmental variables are related to success of M. vimineum sown in stands of L. japonica? (5) Does M. vimineum respond to an increase in essential soil elements with greater reproductive success? (6) Does M. vimineum alter the soil so as to inhibit growth of L. japonica? (7) What is the role of disturbance in the invasion of M. vimineum? Microstegium vimineum is in the tribe Andropogonae, subfamily Panicoideae. It was first collected in the United States in 1919 near Knoxville, Tennessee (Fairbrothers and Gray, 1972). By 1933 it had been collected in the mountains of western North Carolina (Blomquist, 1948; Fairbrothers and Gray, 1972) and by 1964 in 35 counties in North Carolina, primarily in the Piedmont (Radford et al., 1968). By 1972 the species had spread to at least 14 eastern states, from Florida to New Jersey and W to Ohio and Mississippi (Fairbrothers and Gray, 1972), and by 1978 to Arkansas (Smith, 1978). In Asia the species occurs in Japan, Korea, China, Ryukyus, Formosa, Malaysia, India and the Caucasus (Ohwi, 1984). Microstegium vimineum is unusual in that it is a C4 plant which, unlike typical C4 plants, is adapted to low light conditions (Brown, 1977, Winter et al., 1982). Under netting which transmitted 18% full sunlight, dry matter production was not significantly reduced from production in full sunlight; at 5% full sunlight, growth was 17% of that at full sunlight (Winter et al., 1982). Apparently, the C4 pathway itself has no inherent disadvantages, compared to the C3 pathway, under conditions of low light (Pearcy, 1983; Pearcy and Troughton, 1975).

Persistence and Stability of Fish and Invertebrate Assemblages in a Repeatedly Disturbed Sonoran Desert Stream

Abstract: Persistence, a measure of presence or absence of species, and stability, an estimate of assemblage equilibrium measured as constancy in species ranks or densities, should both be considered when assessing temporal change in natural assemblages. We measured persistence and stability in two distinct animal assemblages frequently disturbed by natural and severe flooding events, the fishes and benthic invertebrates in a Sonoran Desert stream. A persistence index (derived from colonization/extinction analyses) indicates high persistence of fishes for several decades, while benthic invertebrates were persistent except in periods of severe flooding. Stability of taxon rankings (measured by Kendall's W) was high for both assemblages, even though absolute population sizes fluctuated. Fish populations resisted even the most severe flood disturbances, whereas benthic invertebrates were decimated by particularly frequent and intensive flooding. The latter were resilient, however, and quickly recovered due to life history characters favoring rapid postflood recolonization. Although absolute numbers of organisms varied through orders of magnitude, more general aspects of assemblage structure (species' presence or absence, and relative rankings) remained relatively constant despite repeated and potentially devastating natural perturbations. INTRODUCTION In their synthesis of ecological stability and persistence, Connell and Sousa (1983) emphasized the utility of a multifaceted approach in temporal analyses of community structure. Drawing upon the works of Holling (1973), Boesch (1974), Orians (1974) and Whittaker (1974), among others, they presented qualitative and quantitative criteria to be considered when assessing changes in community structure over time. Qualitatively, persistence of species focuses upon their continued presence, particularly with respect to potentially devastating forces. Quantitatively, stability is the relative constancy of species abundances over time despite disturbances. Stability may result from resistance, when relative species abundances are unchanged despite potentially disruptive forces, or resilience, rapid return to the former state following disturbance. Both persistence and stability should be considered when attempting to understand community pattern and process (Holling, 1973). The possibility of destructive disturbance is a necessary feature of communities that are used to investigate temporal change. ". . . for any situation to be included under the concept of stability . . .there must exist disturbing forces; without them, simple lack of change in numbers is of little interest" (Connell and Sousa, 1983). Consequently, responses of natural communities to disturbance are central to current ecological research (Dayton, 1971; Sousa, 1979, 1984; Matthews, 1986), and disturbance provides a framework upon which mechanistic understandings of community structure and function may be developed. We examined persistence and stability of fish and benthic invertebrate assemblages in a Sonoran Desert stream that repeatedly experiences large, quantifiable natural dis-

Helminth Parasites of Sympatric Salamanders: Ecological Concepts at Infracommunity, Component and Compound Community Levels

Abstract: Four species assemblages of desmognathine salamanders are sympatric in and along many mountain streams of the southern Appalachians. The species, Leurognathus marmorata, Desmognathus quadramaculatus, D. monticola and D. ochrophaeus, span an aquatic to terrestrial habitat continuum ranging from totally aquatic (L. marmorata) to primarily terrestrial (D. ochrophaeus). Such a system afforded the opportunity of examining concepts of helminth parasite ecology within the context of several recent theoretical predictions. Parasite infracommuinities (populations of all helminth species within individual hosts) in salamanders are isolationist in character. That is, parasite prevalence (percentage of hosts infected with a given parasite species) and mean intensity (mean number of parasites of a given species within a species of host) are low, and as a consequence there is little potential for competitive interactions. Isolationist infracommunities in salamanders arise from factors including a simple enteric system, restricted vagility and ectothermic generalist insectivory. Salamanders have a broad prey base and they do not focus on any particular prey species. Transmission of helminths by intermediate hosts is unimportant and contributes to depauperate helminth faunas dominated by nematodes with direct life cycles. The least diverse infracommunities were associated with Leurognathus marmorata while Desmognathus quadramaculatus had the most diverse fauna. Patterns of prevalence and intensity of infection revealed that salamander helminths were, in general, not host specific. Rather, they are generalists and their distributions can be correlated with host size (age), diet and habitat preferences. INTRODUCTION A principal focus of community ecology is to interpret the effects of competition, predation, mutualism and parasitism, as well as abiotic factors, in determining community structure. Ecological theory has been largely derived from studies on free-living animals with little attention focused on specialist organisms such as parasites. Price (1980, 1984) emphasized that small, highly specialized organisms are very different in many aspects of their biology from larger, more generalized animals so that communities of specialists may be organized in fundamentally different ways from generalist communities. The current literature reveals a predominance of nonequilibrial communities in nature among specialists, in which biotic interactions play a minor role in maintaining community structure (Price, 1984). These are in marked contrast to the equilibrium communities, many of which conform to the predictions of classic competition-based theory (see Strong et al., 1984; Price et al., 1984, and references therein). As stated by Price (1984), "It is valuable to examine the extent to which specialist communities support or contradict the paradigms'" Despite their biological uniqueness and complexity, helminth parasites possess certain attributes which should permit them to contribute significantly to several basic concepts in community theory. First, helminth communities have unambiguous boundaries

Opportunistic Foraging by Largemouth Bass (Micropterus salmoides)

Abstract: During 1980, adult largemouth bass diets in Peter and Paul lakes (Michigan's Upper Peninsula), included prey ranging in size from zooplankton (e.g., Daphnia) to vertebrates (fishes, amphibians, reptiles and small mammals). A partial winterkill in 1980-1981 reduced bass populations in both lakes by as much as 50%. Given the observed reduction in adult bass density and presumed reduction in intraspecific competition for food in 1981, we anticipated dietary changes as a consequence of more food being available to each surviving bass. Two approaches to foraging theory were compared in this study. Functional response models predict that density-dependent effects should be seen simply as increased numbers of each prey type eaten and that all prey will remain in the diet. By contrast, optimal foraging theory predicts that an increase in overall prey density will result in lower ranked prey items being dropped from the diet in an inverse order of ranking; the forager should become more specialized as net energy gain increases. Our data demonstrate opportunism in bass foraging behavior but provide support for the general tenets of optimal foraging theory. Large prey in the size range of the cost-curve nadir of adult bass were more abundant in the 1981 stomach samples. Lowest-ranked prey (e.g., Daphnia) became less important in 1981. Overall diet breadth of bass decreased. Growth rates of adult bass were greater in 1981 than 1980. INTRODUCTION Two somewhat different approaches to the study of diet selection have emerged in recent decades. One is based on experimental analysis of the functional components of the predation process (Ivlev, 1961; Holling, 1966). This approach is represented in reviews by Nilsson (1978), O'Brien (1979) and Dill (1983). In general, mechanistic analyses of the predator's perceptive capabilities, behavioral responses, mechanical capabilities and motivational state are combined in what are generally termed functional response models to yield predictions of predation rates on each of the available prey types. A second class of models is derived from extensions of experimental, mechanistic studies that emphasize optimization by the predator. The basic ideas of MacArthur and Pianka (1966) and Emlen (1966) have been expanded to include a theory of diet breadth or diversity (Schoener, 1971). Various published symposia and monographs include reviews of this perspective (Kamil and Sargent, 1981; Pyke, 1984) and its application to fishes (Stroud and Clepper, 1979). Laboratory and field studies have demonstrated the applicability of the optimality approach to foraging by fishes (Werner and Hall, 1974; Vince et al., 1976; Werner, 1979; Mittlebach, 1981; Stoner, 1982). Other models based simply on measures of reactive distance and the probability of successful capture (i.e., functional response models) offer equally tenable correspondence between expected and observed results (reviewed by Dunbrack and Dill, 1983). More recently, evaluation of the constraints imposed on foraging behavior has been developed to assess the roles of predator avoidance (Werner and Gilliam, 1984) and the biomechanical components of prey perception (Li et al., 1985). Although both optimality and functional components will probably

Occurrence of Vegetation on Geomorphic Surfaces in the Active Floodplain of a California Alluvial Stream

Abstract: In the active floodplain of Cottonwood Creek, an alluvial stream in California, conditions for the establishment and growth of plants are largely controlled by periodic flooding. Flooding creates and modifies erosional and depositional surfaces which are occupied by different species. To evaluate patterns of species occurrence and dominance, geomorphic surfaces on Cottonwood Creek's floodplain were defined on the basis of vertical and horizontal position relative to the stream (i.e., flood frequency), microtopography and particle size. Vegetation sampling on these surfaces provided data for classifying communities by relative cover of common riparian species. The results indicated zonation of communities dominated by different species in relation to flood-induced disturbance. Plant communities dominated by Salix hindsiana and annual grasses were found on surfaces frequently flooded and subject to severe scouring or deposition. Populus fremontii attained dominance or shared dominance with S. hindsiana on less frequently flooded surfaces and where particle size indicated less disturbance by erosion or deposition. Juglans hindsii, Quercus lobata or mixed stands of P fremontiilJ. hindsiilQ lobatalS. hindsiana were dominant on infrequently disturbed surfaces.

Pitfalls and Snap Traps for Sampling Small Mammals and Herpetofauna

Abstract: Experiments were conducted to compare the efficiency of drift-fence pitfalls with three types of snap traps for sampling small mammals and to determine the usefulness of pitfalls for sampling herpetofauna. During winter 1984, small mammal capture rates were lower in pitfalls and Victor rat traps than in Victor mouse traps (P<0.01). During summer and autumn 1984, capture rates in pitfalls were greater than in Victor mouse traps (P<0.01). During winter and summer 1985, capture rates of pitfalls and Museum Specials were similar. Pitfalls with drift fences also captured 220 individual reptiles and amphibians. INTRODUCTION Some form of trapping is often used to sample the members of a local fauna. Most authors agree that a combination of trapping methods yields the most complete data on community composition and reduces biases associated with various traps (Getz, 1961; Smith et al., 1971; Weiner and Smith, 1972). Boonstra and Rodd (1984) and others have compared conventional live traps with pitfalls for a single species of small mammal. However, we know of no studies comparing the effectiveness of snap traps and pitfalls for a large assemblage of species. We compare three snap trap types and pitfalls with drift fences as methods for collecting small mammals, and examine the effectiveness of pitfalls for sampling herpetofauna. STUDY AREAS Data were collected from Abbeville, Edgefield, Greenwood, McCormick and Saluda counties in the Piedmont Plateau Region of western South Carolina. Twenty-eight sites within young (0-21 years old), even-aged loblolly pine (Pinus taeda) stands were sampled. Criteria for site selection included seed-tree or plantation regeneration, chop-and-burn site preparation and access (Smith, 1962). Stands previously thinned or with a recent history of fire were not selected. Study sites were located on the Long Cane Division of the Sumter National Forest and lands owned by International Paper Company. Average tree age was 6.6 years (SE = 1.2 years) and tree density was 3078 pines/ha (SE = 489.0 pines/ha). Average annual temperature and precipitation in the study counties was 16.7 C and 150 cm (NOAA, 1983), respectively. Stand size varied from 4-200 ha and averaged 58.1 ha (SE = 9.95 ha). MATERIALS AND METHODS Trap locations were determined by drawing grid lines on a map of each study site and randomly selecting five lines. Pitfalls were arbitrarily placed in the center of the trap lines and equidistant from the nearest two lines. Field placement of lines and pitfalls was achieved by using a compass and pacing from the stand boundary or road intersection. By preselecting trap locations, we reduced any bias associated with subjective placement of trap lines and pitfalls. Pitfall traps. -We used pitfalls with drift fences to sample small terrestrial vertebrates. A single cross-shaped array with four fence sections was used on each site (Campbell and Christman, 1982). All fences were constructed of 5-m sections of aluminum flashing placed in a ditch 8-12 cm deep. All sections of fence were 15 m apart. Sites were randomly assigned a fence height of either 25.4 cm or 50.8 cm. A 19-liter plastic bucket was buried flush with the ground at either end of each fence section. 'Present address: Division of Life Sciences, Ferrum College, Ferrum, Va. 24088.

Food and Feeding Preferences of Rainbow and Brown Trout in Southern Appalachian Streams

Abstract: The stomach contents of Age 1 and older rainbow (Salmo gairdnert) and brown trout (S. trutta) in five southern Appalachian soft-water streams were compared with concurrent drift samples. A wide range of food items was consumed, and no prey genus comprised an average of more than 2.5% by number of the diet of either trout species. Seasonal changes in composition of drift from June to November were generally mirrored by shifts in trout diets. The contribution of terrestrial organisms to drift and to diets was highest in late summer and autumn. Averaged over all sam- ples, terrestrial taxa comprised 36, 45 and 50% of the drift, rainbow and brown trout diets, respectively. Both trout species exhibited statistically significant feeding prefer- ences for particular taxa (notably terrestrial organisms), but most prey were con- sumed in proportions similar to their abundance in the drift. Opportunistic feeding lends stability to trout populations in streams with relatively low autochthonous food production by allowing trout to capitalize on terrestrial input. Our findings empha- size the importance of both protecting riparian vegetation (which is a source of terres- trial prey) and considering aquatic habitat elements in which trout can efficiently capture surface drift when determining minimum stream flow requirements for water-diversion projects.

Tuber Size and Planting Depth Influence Growth of Potamogeton pectinatus L.

Abstract: Potamogeton pectinatus L. tubers were present to depths of 15-23 cm in sediment cores collected from three central California irrigation canals. Tuber density at a given depth varied from 0.2 -0.1 to 4.1 1.4 (mean-sE) tubers 100 cm-3 and was not significantly related to depth. But mean individual tuber weight (0.9 i 0.5 to 90.9 24.6 mg) increased with depth in the sediment for all three canals examined. In greenhouse studies, relative growth rates based on length and number of ramets and percent emergence were reduced for plants grown from small tubers (1-10 mg) planted at 10 cm or less, relative to those grown from larger tubers (31-40; 41-50; 91100). When tubers from all weight classes were planted at 20 cm the resulting plants exhibited reduced growth. Mean dry weight per plant after 30 days decreased with increased planting depth and decreased tuber size. Similar effects of tuber size and planting depth were observed for P pectinatus grown in greenhouse cultures for 11 weeks. These results indicate that planting depth and tuber size may be as important as environmental factors in regulating aquatic macrophyte population growth.

Winter Habitat Selection by North Temperate Cave Bats

Abstract: Discriminant function analysis was used to quantify both microhabitat (within-cave) and macrohabitat (among-cave) locations selected by five species of cave-dwelling bats in the limestone caves and mines of Maryland, Pennsylvania and West Virginia. Microhabitat parameters reflected microclimate, physical structure and behavioral interactions at the roosting site. Macrohabitat parameters described cave macroclimate, structure, size and external habitat features. Three discriminant functions accounting for more than 95 % of the variance were derived in the microhabitat analysis. Function I was correlated with microclimate and the tendency to cluster, function II with the exposure of the site, and function III with the draftiness of the location. There was a large degree of overlap along many of the univariate parameters, particularly temperature. Multivariate classification of the five species was 63.5% correct. Parameters that were important on a macrohabitat scale differed among species. Zones of suitable microhabitat available within a cave or mine were important factors, but presence or absence of a species at a cave or mine could not be accounted for solely by differences at this level. Cave size is shown to be important to several species in this guild. Correct multivariate classifications varied by species from 82.0 to 96.0%. INTRODUCTION Bats are primarily tropical in distribution, with only three families (Vespertilionidae, Rhinolophidae and Molossidae) occurring in temperate regions for extended periods (Koopman and Cockrum, 1967). This subset of the order Chiroptera is composed entirely of insectivorous species which must deal with seasonally fluctuating food supplies. Two ways of coping with the problem of a temporally reduced food supply are hibernation and migration (Dwyer, 1964; Davis, 1970). Selection of a site that meets the physiological requirements for hibernation is adaptive and should be favored by natural selection. Several studies of bats show that mortality rates are highest at the end of hibernation (Eisentraut, 1947; Ransome, 1968; Stebbings, 1969), when fat reserves are low and starvation may occur. Factors that contribute to an increased probability of starvation are selection of a site that is outside the thermal neutral zone (Lyman, 1970), a long winter that extends the hibernating period (Beer and Richards, 1956), and frequent disturbance of hibernating bats causing an increased metabolic rate (Hall, 1975). Caves and mines are used as winter hibernation sites (hibernacula) by large numbers of temperate bats. A number of habitat variables has been postulated to affect selection and use of specific microhabitats within these sites. These variables can be broadly grouped into microclimatic, structural and behavioral categories. Microclimatic parameters include temperature (Eisentraut, 1934; Hock, 1951; Hanus, 1959), relative humidity (Anciaux, 1948) and airflow (Kallen, 1964). Parameters of physical structure are cave wall conformation (Twente, 1955; Krzanowski, 1959; Hall, 1962) and site exposure (Krzanowski, 1959; Bezem et al., 1964; Daan and Wichers, 1968; Daan, 1973). Behavioral adaptations are cluster formation and site specificity (Twente, 1955; Hall, 1962; Daan, 1973). Previous studies of hibernation site selection have focused on microhabitat or within-cave selection, particularly with respect to microclimate (see Davis, 1970; Fenton, 'Present address: Program in Ecology, ill Ferguson Building, The Pennsylvania State University, University Park 16802.

Regeneration patterns of northern white cedar, an old-growth forest dominant

Abstract: Regeneration of Thuja occidentalis L. was examined in an old-growth dune forest on South Manitou Island, Michigan. To estimate the current status of cedar regeneration, we determined size structure of seedlings and stems and analyzed present patterns of establishment and persistence relative to substrate type. There has been a shift in the pattern of cedar establishment from soil to log substrates. While 97 % of all stems 2 15 cm dbh are associated with a soil substrate, 81 % of stems ? 2.5cm 25 cm tall. There was no significant relationship between the state of log decay and the density of seedlings >25 cm in height, indicating that long-term survival is not dependent on the degree of log decomposition. However, survival on logs is associated with canopy openings. Seedlings >25 cm tall were associated with gaps, and 78% of cedar stems (?2.5 cm dbh) on logs were associated with a single windthrow gap. Thus, current cedar regeneration in this old-growth forest depends on logs and the canopy openings associated with them.

Conditioned Aversions in a Guild of Egg Predators: Implications for Aposematism and Prey Defense Mimicry

Abstract: An assemblage of egg predators in a wildlife refuge was exposed to surrogate greater sandhill crane eggs (Grus canadensis) injected with an illness-producing substance. Although composed primarily of common ravens (Corvus corax), this assemblage also included to a lesser and more poorly measured extent: black-billed magpies (Pica pica), coyotes (Canis latrans), raccoons (Procyon lotor), long-tailed weasels (Mustela frenata) and badgers (Taxidea taxus). Both attack and consumption of surrogate eggs were reduced in treatment sites compared with control sites containing uninjected eggs. Predation in control sites generally increased as predators responded to the bonanza offered to them. The data appear to reveal a novel interaction. Intact survival of surrogate eggs was not only high in raven-breeding territories where the pair of breeding ravens avoided the eggs, but enhanced by avoidance of breeding territories in the much larger nonbreeding population. Illness-based aversions appeared to powerfully alter predation among free-ranging predators. Avoidance of surrogate eggs was measured through fluctuations in availability of alternate foods, through the critical reproductive periods of all species concerned and among consumers varying in body size, and feeding behavior. This suggests that illness-induced aversions established among predators that consume toxic prey in nature could be an important factor in prey defense.

Variation in Seed and Seedling Size in Anthoxanthum odoratum

Abstract: Success at the juvenile stage of the life cycle may have important consequences for the size-hierarchies and distribution patterns of adult plants. This study was designed to evaluate the factors contributing to variation in seed and seedling size in Anthoxanthum ordoratum. In experiments in the greenhouse and within the natural habitat of this species, significant differences in seed weight were found among inflorescences and maternal half-sib families, and marginal differences were found among populations. Larger seeds had a higher probability of germinating and individuals from them had a longer leaf length as juveniles. Covariate analysis showed that differences among populations in leaf length were caused by population differences in seed weight. Root growth was studied using plexiglass root boxes. Individuals from larger seeds tended to produce longer roots, and there were no differences among populations, maternal families, or inflorescences for root length.

Predatory Behavior and Competition Among Laboratory-Housed Largemouth and Smallmouth Bass

Abstract: moides) and smallmouth (M. dolomieui) bass were studied in order to document behav.. ioral patterns associated with locating, capturing and ingesting prey, and to evaluate differential responses to a regime of forced competition for limited food. The analyses focused on the behavioral differences associated with (a) different prey species; (b) prey size, and (c) microhabitat. Cinematography aided in the identification of species-specific searching and prey-pursuit behavioral patterns. Both species were able to capture prey using different combinations and sequences of basic functional jaw and head movements. Differences in the relative lengths of jaw bones were not reflected in a difference in the total range of prey sizes consumed by adults of the two species, but rather appeared to affect the efficiency by which various feeding modes were performed (e.g., biting, engulfing and suction). Under the competitive feeding regime, largemouth bass captured significantly higher proportions of large prey and fewer small prey than smallmouth bass in the mixed-species subadult groups. Adult basses exhibited no significant difference in the frequencies of prey captures on the basis of prey size, but did capture prey at significantly different rates from four microhabit/lts in the mixed-species group compared to the conspecific groups. Adult basses of the two species also exhibited significant differences between groups (mixed vs. single species) in the relative proportions of feeding modes used in capturing prey. For each species, there was a significant relationship between the proportions of the feeding modes used and the microhabitats where prey were seized. The microhabitat niche overlap value was 0 = 0.91 for the single species adult groups and 0 =.77 for the mixed-species adult group. Subadult basses did not separate spatially, but rather exhibited lower niche overlap for the prey size dimension in the mixed-species groups (0 =.74), compared to the single species groups (0 = .95). No significant pattern of differential prey captures between bass species was observed on the basis of the five prey species offered. The relationships between morphology, environment foraging efficiency, and behavioral variability are discussed with reference to their potential roles in natural settings.

Spawning Periodicity of the Asiatic Clam Corbicula fluminea in the New River, Virginia

Abstract: Spawning periodicity of the Asiatic clam Corbiculafluminea in the New River, Virginia, is reported. Numbers of newly recruited larvae in the New River sediment, number and life stage of larvae naturally released and collected from adults held in the laboratory, and presence of developing veligers within the brood chambers of sacrificed adults were collected weekly from May to December 1984. Abiotic data collected consist of mean weekly water temperatures, daily total daylight hours for the western Virginia vicinity and mean daily discharge rates. Density of larvae in sediment, total numbers of larvae collected from laboratoryheld adults, and brood chamber condition are all highly similar in timing, duration and intensity of spawning effort. There were three major peaks in larval abundance-late spring, midsummer and early autumn. These observations do not coincide with previously reported patterns of spring and autumn reproductive peaks by Corbiculafluminea. INTRODUCTION Since the introduction of Corbicula fluminea to the Pacific northwest coast of North America in the 1930s, the Asiatic clam has spread S and E. Its northerly migration has been limited only by winter extremes in water temperature (McMahon, 1982). Initial reports of C. fluminea in Virginia placed this species in the James River (Diaz, 1974) and the New River (Rodgers et al., 1977). Colonization of available habitats by this organism has not been limited to natural waterways but includes the establishment of viable populations in utility and industrial cooling water systems (Morton, 1979; Cherry et al., 1980). The impact of these incursions into environmental and industrial facilities has produced both ecological and economic repercussions of significant proportions that are reviewed in detail elsewhere (Ingram, 1959; Sinclair and Isom, 1963; Fuller and Imlay, 1976; Gardner et al., 1976; Fuller and Richardson, 1977; Goss and Cain, 1977; McMahon, 1977; Boozer and Mirkes, 1979; Kraemer, 1979; Smith et al., 1979; Harvey, 1981). One attribute that apparently facilitates rapid colonization is the reproductive capacity of this species. Kraemer and Lott (1977) reported that Corbicula sp. is hermaphroditic, possessing both oogenic and spermatogenic tissue. While the male and female gametes are formed in different parts of the gonads, they seem to be shed through the same ducts. This prompted the speculation that individuals may possess the ability for internal self-fertilization. Britton and Morton (1982) suggested that cross-fertilizing individuals achieve fertilization in the maternal suprabranchial chamber after spermatozoa have entered the infrabranchial chamber through the incurrent siphon. Once fertilized, eggs are either retained and incubated within the inner demibranch (gill) or discharged as conglutinates of eggs, the mode being species-specific (Sinclair and Isom, 1963). Incubatory species retain the developing embryos through the trochophore and early veliger stages prior to being expelled through the exhalant siphon as pediveligers. This study summarizes our efforts in documenting the reproductive activities of Corbicula fluminea in the New River, Virginia, during 1984. Three different approaches 'Send correspondence to F. G. Doherty. Present address: Joint Graduate Program in Toxicology. College of Pharmacy, Busch Campus, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854.

Characteristics of the Burrows of Four Species of Rodents in Undisturbed Soils in Southeastern Idaho

Abstract: Dimensions of the burrow systems of four small mammals common to southeastern Idaho (Spermophilus townsendii, Dipodomys ordii, Microtus montanus and Peromyscus maniculatus) were determined in undisturbed soils. Spermophilus constructed two distinct burrow systems: over 120 cm deep and less than 60 cm deep. The deeper systems were significantly longer and had larger volume than the shallower burrows and the systems constructed by the other species. Burrow parameters for Dipodomys were bimodal, suggesting deep and shallow burrows, but this was not demonstrated statistically. All parameters for Dipodomys burrows were similar to shallow Spermophilus burrows. Volumes of both were significantly greater than volumes for Peromyscus and Microtus. A significant portion of the variability of all parameters for Microtus and shallow Spermophilus burrows was explained by the distribution of soil particle sizes, but equations based on these were only of limited value in predicting burrow parameters.

Sex and Age-class Differences in Vocalizations of Roosevelt Elk During Rut

Abstract: Vocalizations of free-ranging Roosevelt elk (Cervus elaphus roosevelti) were studied at Gold Bluffs Beach, Prairie Creek Redwoods State Park, Humboldt Co., California, from August through November 1973. Significant differences were found in types and rates of elk vocalizations among different sex and age classes. Bull vocalizations varied with age and social status. Sonograph analyses revealed structural similarities in elk cohesion calls, bugles and yelps; bugles and yelps may be elaborations of cohesion calls. Bugling and yelping by master bulls occurred primarily in male-female encounters and may have functioned to bring cows closer together; bulls bugled most often when the harem was widely dispersed. Bulls vocalized less frequently in aggressive interactions between bulls where bugling and yelping clearly were related to male dominance. INTRODUCTION Despite extensive literature concerning mammalian vocalizations (Marler, 1955, 1967; Collias, 1960; Sebeok, 1968; Tembrock, 1968), comparatively little information exists for ungulates. Much of the recent literature on ungulate vocalizations was summarized by Kiley (1972), but quantitative descriptions of vocalizations and data on their causation were presented primarily for domestic species. Further, quantitative research on wild species often has focused on alarm vocalizations (Hirth and McCullough, 1977; Yahner, 1980; Richardson et al., 1983) or calls between mother and young (Espmark, 1971, 1975). Types and variability of vocalizations in other subspecies of Cervus elaphus have been well-documented (Murie, 1932, 1951; Darling, 1937; Johnson, 1951; Ahlen, 1965; Bubenik and Brna, 1967; Harper et al., 1967; Struhsaker, 1967; Olsen, 1979), and Peters (1980) reviewed the vocalizations of North American elk. Data on vocalizations of Roosevelt elk (C. e. roosevelti), however, were limited to qualitative descriptions (Graf, 1955; Harper et al., 1967), and information on the function and circumstances under which these sounds occurred was lacking. Further, Clutton-Brock and Albon (1979) noted that roaring by red deer (C. e. scoticus) stags occurred primarily during aggressive interactions between males, but roaring also was directed toward females in the stag's harem, suggesting a male-female function for this vocalization. Miura (1984) also noted that bugle-like "moans" of male sika (Cervus nippon) were given in response to the activities of females. The purpose of this study was to quantifv sex and age-class differences in vocalizations from a free-ranging population of Roosevelt elk during rut, and to examine the behavioral context in which vocalizations occurred. 'Present address: Institute of Arctic Biology, and Department of Biology and Wildlife, 211 Irving Building, University of Alaska, Fairbanks, Alaska 99775-1780.

Prey Size Selectivity and Food Partitioning among Zooplanktivorous Age-0 Fishes in Lake Francis Case, South Dakota

Abstract: Zooplankton prey selection and food partitioning were examined among cohabiting age-O walleyes Stizostedion vitreum, yellow perch Percaflavescens, white bass Morone chrysops and gizzard shad Dorosoma cepedianum. As these fishes grew, they consumed progressively larger zooplankton prey. Prey size appeared to be the primary factor governing zooplankton prey selection by the visual predators walleyes, yellow perch and white bass. Prey evasiveness was not important in prey selection for the visual predators but was important for the nonvisual predator, the gizzard shad. Age-O fishes partitioned food resources by prey size. Walleyes usually selected the largest prey at a given time, followed by white bass, yellow perch and gizzard shad. Diet overlap was highest between yellow perch and white bass, which had the most similar mouth gapes.

A Multivariate Analysis of Forest Communities in the Western Great Smoky Mountains National Park

Abstract: An integrated sequence of multivariate techniques was applied to the vegetation of the western Great Smoky Mountains National Park. Included in the sequence were hierarchial classification, detrended correspondence analysis and multiple discriminant analysis. Based on the importance of landform in previous research, a system of topographical quantification was developed and also used in the classification. Elevation and the topographical index, termed protection, were the most important variables associated with the 12 classified forest types. Drainage area, another topographic measurement, soil p H and water-holding capacity were also significant in the vegetation analysis. Logging and farming disturbances prior to the formation of the national park were probable causal factors for some forest types. INTRODUCTION The Great Smoky Mountains of Tennessee and North Carolina have been a focal point of vegetation analysis since 1930 (Cain, 1930). Because the Smoky Mountains provide elevation-related temperature and precipitation gradients, complex topographical patterns, and a rich woody-species composition, they have been used repeatedly in studies of the relationships of plants to the environment and within communities. Whittaker (1956) identified species associations throughout the Great Smoky Mountains National Park (GRSM) and defined their positions on a moisture complexgradient. H e concluded that the interaction of elevation, topographic shape and slope aspect determined the vegetation present at a given site. Golden (1974, 1981) approached the problem of vegetation distribution in the central G R S M with an integrated sequence of multivariate techniques (cluster analysis and similarity sorting, discriminant analysis, reciprocal averaging, ordination and canonical correlation) using quantitative environmental variables. H e found the overwhelming importance of topography and elevation as described by Whittaker was also indicated by his data and analyses. Soils data collected by Golden (1981) indicated that the p H of the A horizon and the percent clay in the B horizon were also important correlative factors. The major purposes of this paper are (1) to develop a method for quantifying topographic shape in the Smoky Mountains; (2) to provide an integrated multivariate analysis, including the topographic index, of the western Great Smoky Mountains, and (3) to examine stands disturbed by prepark logging and agriculture. Neither Whittaker (1956) nor Golden (1981) satisfactorily quantified topographic shape, which they cited as being important. Whittaker (1956) assigned a sequential order to land shapes and assumed that the order represented moisture characteristics. Golden (1981) measured the position of stands on slopes and the slope aspect but did not include slope shape. We have constructed an index of topographic shape and included it in our vegetation analysis. Most of the study area was on three major topographic features in the western 'Present address: Department of Biological Sciences, University of California, Santa Barbara, CA 93106.

Pre-European settlement forest composition in east New Jersey and southeastern New York

Abstract: A total of 5059 witness trees were counted from survey reports of "unappropriated lands" in 23 tallies from 14 towns and 13 counties of southeastern New York and East New Jersey. Southeastern New York and northern East New Jersey were dominated by oak, particularly white, red and black oaks, with hickory and chestnut common. Pre-European settlement forests in southern East New Jersey were dominated by oak and pine with cedar and maple, probably the species white cedar and red maple, common in some areas. Cedar was unrepresented in two of five S East Jersey tallies which encompass the modern white cedar-red maple swamp forest areas, while maple was common only in one of the tallies. Distribution of modern forest types and fossil pollen records were consistent with witness tree counts for oak and pine. As compared to pollen records, four tallies overrepresented walnut and underrepresented hickory.