Showing papers in "American Midland Naturalist in 1977"

Factors Affecting Seed Reserves in the Soil of a Mojave Desert Ecosystem, Rock Valley, Nye County, Nevada

Abstract: During 1972, a 2nd year of low herb production, there was a significant variation of seed reserves in the upper 2 cm of soil, with a doubling from February to June and a density-independent halving by October. In October 1972 there were 8 X 106 seeds/ha (5.3 kg/ha). After very high herb production in the spring, seed densities in October 1973 were 10-16 times greater under shrubs and 23-27 times greater in exposed areas (max 187.5 X 106 seeds/ha, 84.3 kg/ha). The increase was principally by the winter annual grass, Festuca octoflora. In 1972, when there was a small difference in rodent density between two plots (0.8:1.0), there was no effect of rodents on seed density. In 1973, when there was a 1:17.8 ratio of rodent densities, there was a significant effect on seeds under shrubs. Then from October 1973 to October 1974, seed reserves in exposed areas between shrubs decreased by 20% in the plot with few rodents, and by 40% in the plot with many rodents. Eating of seeds by rodents accounted for 30 to 80% of the seed reserve decreases observed. Germination losses were no more than 25%. There is slight evidence that pocket mice selectively decrease abundance of the heavier species of seeds. Seed density was at least five times greater under shrubs than in exposed areas ; density was significantly correlated with the size of shrub canopy. There was also a significant effect of the species of shrub on the density of seeds. During years of low production, under-shrub areas are a refuge for herb seed production, and in such years shrub seeds form a larger portion of the seed crop and new reserves. The difference in response of shrubs and herbs to weather increases the stability of seed reserves. In May 1973 the number of herbs per 100 seeds in the previous October was 16.8 under shrubs and 43.6 in exposed areas; this implies a minimum germination of 24% of seeds over the whole habitat. It takes an exceptional coincidence of events, even in deserts, to cause a severe depletion of seed reserves.

Changes in Structure, Pattern and Diversity Associated with Climax Forest Maturation in Piedmont, North Carolina

Abstract: During 1951 and 1952 the position and diameter were recorded for each tree on a 140 ? 140 m plot of immature climax oakhickory forest in the Duke Forest, Durham, North Carolina. To ascertain the changes in structure associated with climax forest maturation, this plot was remapped in 1974 and the two maps compared. In general, tree density, particularly of overstory trees, decreased while total basal area increased from 1951-52 to 1974. The most notable changes were a 75% reduction in density of Carya spp. and a 230% increase in density of Acer rubrum. Many dominant species showed significant reduction of numbers in smaller size classes in 1974. Tree-by-tree analysis of mortality and recruitment revealed low rates of population recruitment and high mortality rates in these smaller size classes. Tree pattern, analyzed by quadrat and point-to-neighbor methods, was clumped in smaller size classes and random or regular in larger size classes on both maps. However, total tree pattern shifted from random in 1951-52 to regular in 1974. This shift was the result of significantly higher mortality in the smaller size classes which had clumped distributions. Species diversity, H', decreased during this time; however, pattern diversity (Pielou, 1966) increased. Decreased species diversity resulted from diminished equitability, whereas increased pattern diversity was probably due to shifts in tree pattern.

Soil water withdrawal and root characteristics of big sagebrush.

Abstract: The volume of soil important to an individual big sage- brush (Artemisia tridentata) plant as a soil water reservoir was identi- fied and compared with the root system of the same plant. Experimental sites were located near the bottom, midway and crest of a N-facing slope. The effective winter precipitation at these sites was 511, 368 and 102 mm, respectively, because of relocation of snow by wind. Soils at the three sites belonged to different series despite their proximity and similar parent material. The primary water reservoir for an individual plant extended later- ally 91 cm from the trunk and 91 cm deep. Moisture use zones shifted from surface soil near the plant early in the season, outward and down- ward as the season advanced. Water use decreased sharply in early August after vegetative growth was complete. More than 90% of the root weight for individual big sagebrush plants was located in the volume of soil identified as an important water reservoir. Roots at each study site had a maximum lateral spread of 122-152 cm from the trunk and extended 183-213 cm deep at the two lower sites. Roots were less than 152 cm deep at the upper site, a reflec- tion of the limited water supply and rocky substratum. Maximum lateral root spread was usually in the surface 30.5 cm of soil.

The effect of burial by squirrels on germination and survival of oak and hickory nuts

Abstract: Field experiments designed for analysis of variance demonstrated that surface predators significantly reduced survival of both white oak acorns (Quercus alba) and pignut hickory nuts (Carya glabra), while fossorial predators significantly affected only the acorns. Pr?dation on hickory nuts was much more intense than on acorns. Burial of acorns resulted in increased survival from pr?dation, but not increased germination. Burial of hickory nuts did not significantly affect survival or germination. Germination was higher for acorns than hickory

Food Habits and Competitive Relationships of the Bandfin Shiner in Halawakee Creek, Alabama

Abstract: The bandfin shiner (Notropis zonistius) showed highest feeding activity between 0300 and 0600 hr and 1400 and 1700 hr in Halawakee Creek. The bulk of the diet over the 24-hr period was composed of terrestrial insects (allochthonous material). Feeding intensity was lowest in winter and highest in summer. Fish less than 35 mm fork length fed mostly on dipteran larvae in spring through autumn. Ephemeropteran nymphs were important in the diet in summer and winter. Collembola were consumed only in winter. The diet was most diverse in summer and winter and least in spring. Fish larger than 35 mm ate mostly terrestrial insects and were more specialized feeders. Dipteran larvae, ephemeropteran nymphs and odonate nymphs were consumed in moderate quantities in some seasons. The diet was most diverse in winter and least in summer. The diet of the bandfin shiner was compared quantitatively with that of the rough shiner (Notropis baileyi), a cyprinid recently introduced in Halawakee Creek. Indices of food similarity indicated a significant overlap in their diets in some seasons. Nilsson's hypothesis of interactive segregation and the principle of competitive exclusion are discussed.

A Comparison of the Pattern of Herb and Shrub Growth in Comparable Sites in Chile and California

Abstract: Two physiognomically similar but floristically dissimilar brushland areas of central Chile and southern California were compared to test the hypothesis that where the dominant overstory vegetations are structurally and functionally similar, the understory or herbaceous vegetations will also be similar. This hypothesis was tested in a relatively undisturbed site, a heavily disturbed site and a burned site within each study area. Values of percent ground surface covered and relative density were obtained using the line-intercept method. Two modifications of this method were used to determine the relationship between herb species location and canopy cover. In the Chilean site herbs were best developed beneath the shrub canopy, were predominantly perennial (75% of the most commonly found species) and were sparse following fire. In the California site few herbs were present in the mature chaparral. But in the 1st year following a fire an abundant herbaceous flora was observed; 75% of the most common species were annuals. The role of man-caused disturbance, climatic differences, floristic histories and the role of fire are discussed as possible explanations for the differences observed.

Population Dynamics of the White-footed Mouse in Floodplain and Upland Forests

Abstract: Comparative observations of the density and demography of two populations of the white-footed mouse (Peromyscus leucopus) were made in a floodplain forest and adjacent upland. There was little exchange of individuals (<3%) between populations. Fluctuations of density were greater in the floodplain because better recruitment in autumn produced higher densities than in the upland, and poor recruitment in winter and spring produced lower densities. In other respects ? breeding season, adult survival and age structure ? the populations were similar. Contrary to expectations, the floodplain population served as a small source of recruits for the upland rather than the reverse. Recruitment patterns and population fluctuations were probably related to food availability; the best survival of young occurred in autumn after the mast crop had fallen. Poor recruitment in the floodplain was related to extensive flooding. Neither population bred during the coldest months, December and January. General food habits of the two populations were similar, and the proportion of seeds in the diet and fat content of carcasses were high during the most successful recruitment period (autumn). Overall, the two populations were surprisingly similar. Greater fluctuations of density in the floodplain, while agreeing with theoretical predictions for an unstable habitat, occurred primarily because the floodplain was more productive in autumn rather than because of poor survival. Thus, floodplain forests should not be considered marginal habitat for these mice.

Morphometry, benthos, and sedimentation rates of a floodplain lake in Pool 9 of the Upper Mississippi River

Abstract: Big Lake is a shallow (mean depth = 0.89 m in 1973) 256-ha backwater lake on the floodplain of the Mississippi River in NE Iowa. During the summers of 1973 and 1974 Sphaerium and Hexagenia made up 81% of the benthic macroinvertebrate abundance and 92% of the benthic biomass; both taxa had greatly reduced abundance and biomass within stands of emergent Sagittaria along the lake margin. During July 1974 the Sagittaria net productivity was about 19 g/m/sup 2//day. Cesium-137 levels were determined in sediment samples showing that between 1896 and 1973 about 76 cm of sediment had accumulated in Big Lake, and the recent sedimentation rate (1964-1974) was about 1.7 cm/year. The calculated annual reduction in lake volume of about 37,400 m/sup 3//year suggests that the physical and biological components of this productive aquatic habitat will be greatly modified during the next few decades.

Mutualism between Three Species of Tropical Piper (Piperaceae) and Their Ant Inhabitants

Abstract: Three species of the genus Piper (P. cenocladum G.DG., P. fimbriulatum G.DG., P. sagittifolium G.DG.) from the wet evergreen forest of Costa Rica are associated with ants of the genus Pheidole in what appears to be a coevolved mutualistic relationship. The ants live in petiolar cavities and in the stems which they hollow out; the plant produces lipid-rich food bodies inside the petiolar cavities on which the ants feed. The ants appear to increase the competitive fitness of the plants by removing encroaching vines. More importantly, it seems that the plant may receive a nutritional benefit from the ants' presence by absorbing nutrients released from decaying nest material inside the stem. Ant-plant mutualisms involving several plant families have been described in the Old and New World tropics (Hocking, 1970; Janzen, 1967, 1969a, 1972, 1973a, 1975; Rehr et al., 1973; Whiffin, 1972). The swollen-thorn acacia and its obligate ant inhabitant, Pseudomyrmex, is the most thoroughly studied ant plant, or myrmecophyte (Janzen, 1967, 1969a, b). However, most of the ant-plant associations described in the New World tropics are facultative. It is often the case that the plant produces extrafloral nectaries and is associated with aggressive ants that feed on the nectar source and in turn presumably protect the plant from herbivory (Bequaert, 1922; Carroll, 1974; Whiffin, 1972). We describe a situation involving three species of plants of the genus Piper (P. cenocladum C. DC, P. fimbriulatum C. DC, P. sagittifolium C. DC) that are always associated with ants of the genus Pheidole in what appears to be a coevolved mutualistic relationship. The occurrence of ants in these Piper species has been previously noted (Burger, 1972), but there are no* descriptions of the benefits that both ants and plant derive from the relationship. Piper cenocladum and P. fimbriulatum are slender shrublike plants that grow commonly to a height of 4 m, although P. fimbriulatum sometimes reaches a height of 7-8 m. Both species live in the understory of the wet evergreen forest of Costa Rica between sea level and approximately 1100 m altitude. Piper cenocladum is endemic to Costa Rica and is found only on the Caribbean coast, while P. fimbriulatum is found only on the Pacific coast of Costa Rica and in western Panama (Burger, 1971). Piper sagittifolium is a smaller herbaceous plant seldom exceeding 1.5 m in height and has only been recorded from the 1 Present address : Department of Zoology, University of Michigan, Ann

The Life Cycle, Habitat and Variation in Selected Web Parameters in the Spider, Nephila clavipes Koch (Araneidae)

Abstract: A field study of the ecology and natural history of the spider, Nephila clavipes, was conducted between May 1972 and September 1973. The habitat of Nephila clavipes on the Texas Coastal Plain is described,, as well as its life cycle, monthly variation in selected web parameters, and abundance in a study area. Height of the web aboveground, magnetic orientation, degree of slant, and density of weblines all exhibited consistent changes during the year. Numerical density of the spiders was approximately constant during the year, suggesting that adult female Nephila are relatively immune to pr?dation and that there are only a finite number of suitable web sites within the study area.

Effects of the Mound Nests of the Ant, Formica obscuripes, on the Surrounding Vegetation

Abstract: Plant species richness, diversity and abundance were measured in quadrats at varying distances from active mound nests of the ant, Formica obscuripes. Most species were distributed throughout the study areas but seven were associated with mounds. In areas dom- inated by juniper, species richness and diversity were negatively cor- related with distance from nests; this was not true of areas dominated by grasses. Species abundance, as measured by stem and tiller number, reached a peak 1.5 m from mounds in juniper areas, beyond which it decreased linearly. Species abundance and distance from nests showed less obvious patterns in grass areas. Seed dispersal by ants is unimpor- tant in determining vegetation structure, but altered soil conditions in the vicinity of mounds are partially responsible for the observed patterns of plant distribution. In general, local disturbances caused by ant mounds increase the heterogeneity of the plant community. This effect is strongest in early successional communities.

The Pharyngeal Bones and Teeth of Catostomid Fishes

Abstract: Examination of the pharyngeal apparatus of 22 species of catostomids reveals three types of bones and teeth associated with different dietary habits. The mollusk feeders Moxostoma hubbsi and M . carinatum have 21-42 large, molariform teeth on each of the heavy pharyngeal bones. The teeth occlude with a chewing pad borne by the basioccipital and are well-adapted for crushing shells. Most catostomids (other Moxostoma, Cycleptus, Hypentelium, Lagochila, Catostomus, Chasmistes, Erimyzon, Xyrauchen and Minytrema) have 43-90 moderately compressed teeth arranged in comblike fashion on each bone. These species feed primarily on benthic macroinvertebrates including aquatic insect larvas and small mollusks. In addition to mastication, the teeth of this group probably serve to manipulate and hold food during the rejection of inorganic matter inadvertently taken in with the food. The teeth of Ictiobus and Carpiodes are extremely small and numerous (134184)., and the pharyngeal bones are correspondingly delicate. These specle5 are microphagous filtm feeders with a well-developed selectory apparatus consisting of gill rakers, gill arches and palatal organ. The teeth are capable of masticating small food items and may also function as strainers. An analytical key based only on pharyngeal bone and tooth characteristics is provided, and the bones and teeth of several species are illustrated. Catostomid pharynqeal bones and teeth have some limited use in specimen identification. They are usually reliable at the tribe or genus level. In certain trophically specialized forms (Moxostoma hubbsi, M . carinatum and Ictiobus cyprinellus) they are significant at the species level. INTRODUCTION Freshwater fishes of the family Catostomidae, commonly known as suckers, are represented by 11 genera with about 63 species in North and Central America and the single relict genus Myxocyprinus in China. Catostomids probably diverged from a cyprinid ancestor sometime before the Eocene (Uyeno and Smith, 1972). Most are suctorial bottom-feeders with small, extensible, ventroterminal mouths. These fishes lack both oral teeth and a stomach. They do, however, possess pharyngeal teeth arranged in a single row on each of the two pharyngeal bones located posterior to the fourth pair of gill arches. Certain aspects of catostomid morphology are well-documented; for example, osteological information for some species has been provided by Sagemehl (1891 ) , Edwards (1926), Gregory (1933), Nelson (1948, 1949, 1955), Ramaswami (1957), Weisel (1960, 1967a), Branson (1962), Smith (1966) and Smith and Koehn (1971). However, catostomid pharyngeal bones and teeth, of considerable trophic and possible taxonomic significance, have never been adequately treated. Le Sueur (1817) was aware of the existence of catostomid pharyngeal bones and teeth, but only later did ichthyologists begin to recognize the potential taxonomic value of these structures (Agassiz, 1855; Bleeker, 1860; Cope, 1870; Jordan, 1878). More recently, fossilized catostomid pharyngeal bones and teeth have been found in several localities in the southwestern United States (C. L. Smith, 1954, 1958; G. R. Smith, 1963). This family represents the second-most abundant fish group in North American Pleistocene deposits, and most of these fossils are osteologically indistinguishable from living species (Miller, 1965). Therefore, descriptions of pharyngeal structures from Recent species provide valuable information for interpreting material from archaeological (Trautman, 3 957:262) and paleontological (cf. Rutte, 1962, for Old World cyprinids) sites. With the exception of comments by Forbes (1888: 440-441) and Forbes and Richardson (1908 :63-64), the structural diversity of catostomid pharyngeal bones and teeth has generally not been appreciated by ichthyologists, nor has their form in the various species been related to diet or to specializations in ancillary pharyngeal structures. I undertook this investigation to rectify this situation as well as to assess the utility of pharyngeal bones and teeth in specimen identification. All 11 American genera are represented in the study. Special emphasis is accorded to Moxostoma carinatum, Catostomus commersoni and Carpiodes cyprinus because the pharyngeal morphology of each of these species is considered typical of one of the three levels of trophic adaptation seen in the pharyngeal complex. MATERIALS METHODS AND For the most part, the 22 species (135 specimens) used in this study represent a typical Great Lakes assemblage of catostomids (Table I ) . Many were collected from the waters of Minnesota with a 0.25-inch mesh seine. Most of the Moxostoma, Ictiobur and Carpiodes cyprinus were netted in Lake St. Croix, Washington Co., Minn., by a commercial fisherman. Other northern species were borrowed from the James Ford Bell Museum of Natural History at the University of Minnesota. Rare species were obtained from Cornell University (CU) ; Museum of Comparative Zoology, Harvard University (MCZ) ; University of Michigan Museum of Zoology (UMMZ) ; University of Oklahoma Museum of Zoology (UOMZ) ;and National Museum of Natural History, Washington, D. C. (USNM). Pharyngeal bones were removed, thoroughly cleaned of adhering tissue, dehydrated in ethanol, and degreased in acetone. The number of teeth per bone was counted with the aid of a dissecting microscope. Broken and missing teeth were included in the count. In addition, the pharyngeal region was dissected in representatives of all but the rare species (Moxostoma hubbsi, M. valenciennesi, Ictiobus niger, Xyrauchen texanus and Lagoclzila lacera). Most specimens studied were sexually mature adults. Whenever possible, gut contents were examined and major groups of food items were identified. For rare species, however, it was necessary to refer to the literature (Forbes. 1888; Forbes and Richardson, 1908; Carlander, 1969) for dietary information. Illustrations were prepared with the use of a drawing tube attachment on a Wild M-7 stereomicroscope. The pharyngeal bones of some species were too large to be drawn by this method; in such cases, the specimens were photographed and a tracing was made from a print. In order to assure uniformity in illustrative procedures, the bones were positioned so that the surface facing posteriorly in life, Chu's (1935) ventral surface, was nearest the illustrator. I n many species the presence of numerous small, dorsal teeth made it impossible for the illustrations to reflect the correct tooth count as given in Table 1. Illustrations of the most ventral tooth of each species are also provided. Many catostomid teeth bear conical projections or hooks on their anterior (inner) margins; these are subject to wear, however, and are shown only when they are a constant and diagnostic feature in a given species. The catostomid classification used in this paper is that of Hubbs (1930). This was amended by Nelson (1948, 1949) and subsequently employed by Miller (1958). Figures 8-21 are arranged according to this sequence. Skull bone nomenclature is that of Harrington (1955) with the exception that the pharyngobranchials are referred to as infrapharyngobranchials (Nelson, 1969). Weisel's (1960) work on the skull of Catostomus macrocheilus was also helpful. Although the pharyngeal bone nomenclature proposed by Chu (1935) was formulated with respect to cyprinids, it is employed here because it is easily adaptable to catostomid bones. Pharyngeal tissues studied histologically were fixed in 10% formalin with subsequent dehydration in ethanol, clearing in xylene, and embedding in paraffin. Sections were cut to a thickness of 6 pm and then stained with hematoxylin and eosin or Weigert's elastica (for sirnultaneous demonstration of collagen, elastin and muscle). Mounting was in Permount. GENERALANATOMY THE REGION OF PHARYNGEAL The pharyngeal bones and teeth.-Fish teeth are generally involved in the seizing, manipulating, masticating and swallowing of food. Catostomid pharyngeal teeth participate in all but the first of these actions. The teeth are arranged in a single row on each of the two pharyngeal bones. These falcate bones, representing fifth ceratobranchials, are joined at their ventral tips to each other and to ventral gill arch elements by means of a cartilaginous copula. There are only muscular connections between the pharyngeal bones and the skull, vertebral column and pectoral girdle. Cyprinoid pharyngeal teeth are unusual among vertebrate teeth in that the \"enamel organs\" are of endodermal rather than ectodermal origin, developing from the deeper columnar layer of the pharyngeal epithelium representing the endoderm of the primitive foregut (Edwards, 1929). The crowns of the teeth are probably composed entirely of dentin (Cheprakova, 1958). This material, termed modified dentin by Peyer (1968), functionally substitutes for enamel in most teleost teeth. Bony ankyloses, several millimeters long, unite the crowns to the pharyngeal bone. The ankyloses are partially resorbed by osteoclasts prior to tooth loss and reformed during tooth replacement. ~atostomid pharyngeal teeth are replaced continuously throughout life. Weisel's (196713) study of the form and attachment sequence of the teeth in larval and juvenile Catostomus indicates that the replacement is rapid at these stages of life with at least the first and second generations of replacement teeth resembling the conical hooked teeth of immature cyprinids. .In most catostomids the form of the teeth varies with their position on the bone. The more dorsally situated teeth are generally more distinctly hooked on the anterior (inner) margin than are the ventral teeth. Masticatory activity, however, may sometimes obliterate the hooks. Conversely, recently ankylosed crowns may not have worn sufficiently to exhibit the flat masticatory surfaces characteristic of, for example, the teeth of Moxostoma hubbsi and M . carinatum (Figs. 14-

Aspects of the Life History and Ecology of the Olympic Salamander, Rhyacotriton olympicus (Gaige)

Abstract: Life history attributes of two populations of Rhyacotriton olympicus were studied in western Oregon. A population in the Coast Range had (1) smaller eggs; (2) smaller metamorphic size; (3) smaller size at maturity; (4) smaller mean adult size; (5) smaller maximum size, and (6) higher fecundity, compared to a population in the Columbia River Gorge. Also, the population in the Coast Range is thought to have smaller hatchlings and lower age at maturity. Females are larger in both populations. Spermatophores were found in females in all months except August, September, December and January, indicating an ex- tended courtship season. Similarly, oviposition may occur at almost any time,, although there is a peak of courtship and egg-laying activity in May in both populations. Data on growth, density and movement of marked larvae are given for the population in the Columbia River Gorge. Females reproduce annually and apparently do not attend the embryos. In many respects, the reproductive mode of R. olympicus is more like that of hemidactyliine plethodontids than other ambys- tomatids.

Energy Allocation Patterns of a Sprouting and a Nonsprouting Species of Arctostaphylos in the California Chaparral

Abstract: The r- and K-selection theory was used to generate test- able hypotheses about patterns of energy allocation in two chaparral shrubs of different reproductive strategies. Terminal-branchlet vegeta- tive and reproductive biomass of the nonsprouting Arctostaphylos glauca and the sprouting A. glandulosa were sampled in a 23-year-old and a 90-year-old stand of chaparral to test the predictions that: (1) the ter- minal vegetative growth (g dry weight/m2 of areal coverage) would be equal in the two species, in both stands; (2) oven dry weight (g) of reproductive parts/m2 of areal coverage would be greater in A. glauca than in A. glandulosa in both aged populations; (3) allocation to repro- ductive parts by the shrubs in the 23-year-old stand would be greater than (or equal to) that of the 90-year-old shrubs. The amount of ter- minal vegetative growth was equal for both species in the 23-year-old and the 90-year-old stands. There was no statistically significant differ- ence in the weight of fruits produced by the two species in the 23-year- old stand. However, fruit production by A. glauca was significantly greater than by A. glandulosa in the 90-year-old stand. Fruit produc- tion was also significantly greater for the older A. glauca shrubs than for those in the 23-year-old stand. The relationships of rainfall pattern and age of shrubs to fruit production are discussed.

Responses of caddisfly larvae (Brachycentrus spp. ) to temperature, food availability and current velocity

Abstract: Larvae of the stream caddisflies, Brachycentrus americanus and Brachycentrus occidentalis, were studied in eight simulated stream channels to determine their behavioral responses to temperature, food availability (brine shrimp) and current velocity. For both species, filtering, withdrawn and case-building were the primary behavior patterns of larvae that had attached their cases to the substrate. Most larvae not attached to the substrate were crawling or holding. As temperatures increased above 8 C, B. occidentalis larvae filtered more frequantly; but above 20 C the percentage of larvae filtering steadily decreased and the percentage withdrawn increased dramatically with increasing temperature. Percentages of larvae case-building and unattached generally decreased over the range of 4 to 27 C. Despite this decrease in case-building, B. occidentalis larvae generally grew faster as temperature increased from 4 to 16 C. Behavior of B. americanus as a function of temperature was similar to behavior of B. occidentalis. Both species responded to decreased ration by increasing the percentage of time filtering. Although many larvae were unattached and probably grazing in Lawrence Creek, few larvae were unattached in the laboratory, even at the lowest ration (1.2 percent of the body weight per day). Growth and case-building activity of B. americanus larvae weremore » directly related to ration. Over the range of current velocities of 7 to 26 cm/sec, behavior of B. occidentalis changed little. At 5 cm/sec fewer larvae filtered and more were unattached; this suggested a threshold response to current velocity. Increasing temperatures from 10 to 20 C caused the percentage withdrawn at low velocities to increase; however, this trend was hardly noticeable at velocities above 10 cm/sec. In these tests, Brachycentrus were more responsive to temperature and food availability than to current velocity.« less

Burrow System Structure of Pappogeomys castanops (Geomyidae) in Lubbock County, Texas

Abstract: Burrow systems of Pappogeomys castanops differed from burrow systems of the other two genera of North American geomyids (Geomys and Thomomys) in possessing grass and feces mound plugs, and in lacking a distinct shaft to a deep tunnel system. The single nest- opening was similar to that of Geomys and contrasted with multiple nest-openings of Thomomys. A single functional nest per burrow system was characteristic.

Some Ecological Characteristics of the Ants of a Desert-Shrub Community in Southeastern Arizona

Abstract: Ants were studied principally by analysis of collections at 66 stations on a 30.3-m grid baited with honey solution and peanut butter. Twenty-three species were collected, which is an exceptionally diverse ant fauna for a small area. Analyses suggest there are several bases for coexistence of these species: (1) Mean body weights of most species are significantly different from each other, and always so within three general feeding categories (seeds; nectar, honeydew and insects; omnivorous). The mean ratio of dry weight of workers of pairs of nearest species was 1.66 within feeding categories and 1.28 between categories. (2) Forage items showed some distinctiveness of food habits among species. (3) Some species were clearly diurnal and others nocturnal in August. (4) Only four species were active up in shrubs in the daytime, and they had their peak numbers in different months or different species of shrubs. (5) Hierarchical classification of stations by species characteristics showed some patterns of distribution of groups of sites according to topography and unknown factors. Other data are given on importance curves, enrichment of species collected with time and space sampled1, species-area relationship, species interactions, and patterns of daily dispersal of workers. Introduction Ants are often assumed to be important components of ecosystems, and in a few cases their importance has been specifically documented, e.g., in terms of energy flow (Golley and Gentry, 1964), modification of soil chemistry and plant distribution (Gentry and Stiritz, 1972), and effects on microsuccession and composition of vegetation (Talbot, 1953; Tevis, 1958). This study concerns a particularly diverse fauna of 23 species of ants within a creosote bush desert community in southeastern Arizona. Simple techniques were used to determine the general ecological characteristics of the ant fauna of the study site, as a prelude to a more extensive study. In particular, ants were collected at bait stations, intensively over a short period of time in August 1972. The collections provided information on species diversity and equitability of the fauna, importance curves, body sizes of species, patterns of diel activity and foraging, patterns of distribution of species in space, and interactions of species. These data, together with information on food habits and activity through a year's time, provide a good initial understanding of the possible bases of coexistence of the ant species of the community. Since the fieldwork was done, several authors have shown that the use of baits, in spite of their artificiality, is a productive way of determining some aspects of ant ecology (Pressick, 1972; Hunt, 1973; Culver, 1974). 33 This content downloaded from 157.55.39.111 on Sat, 17 Sep 2016 06:12:02 UTC All use subject to http://about.jstor.org/terms 34 The American Midland Naturalist 98(1)

Reproduction, Fecundity, Sexual Dimorphism and Sex Ratio of Etheostoma fonticola (Osteichthyes: Percidae)

Abstract: Etheostoma fonticola is an endangered species of fish which spawns year-round in the relatively constant temperature headwaters of the San Marcos River and in Spring Lake (impounded origin of the river), Hays Co., Texas. However, the species appears to have two spawning peaks, one in August and the other in late winter to early spring. Proposed explanations for this observed spawning periodicity are a slight increase in water temperature and/or a decrease in flow. Ripe ovaries of preserved Etheostoma fonticola contain three distinct classes of ova based on their size and appearance. The number of mature ova (Size Group I) is positively correlated with total length of the fish while the mean diameter of mature ova is not positively correlated. Etheostoma fonticola provides no parental care to the ova and has very low fecundity (mean fecundity was 19). Sexual dimorphism is evident in the shape and size of the genital papillae and the pelvic fins and in the intensity of body coloration. The sex ratio of Etheostoma fonticola is 1.39:1.00 (M:F).