Showing papers in "American Midland Naturalist in 1975"

Death feigning by ducks in response to predation by red foxes (Vulpes fulva)

Abstract: Predation by captive red foxes (Vulpes fulva) on approximately 50 ducks comprised of five species was observed in tests conducted at the Northern Prairie Wildlife Research Center, Jamestown, North Dakota. Most ducks were attacked from a rear or lateral position and seized in the cervical or thoracic region. All birds became immobile (death-feigned) immediately when seized and with few exceptio'ns remained motionless during prey-handling and for varying lengths of time thereafter. Initial death feints lasted from 20 sec to 14 min. Recovery was delayed by tactile, visual and, possibly, auditory cues from the foxes. Death-feigning birds appeared alert and often took advantage of escape opportunities. Twenty-nine birds survived initial capture and handling by the foxes. Naive foxes were wary of ducks during initial confrontations, but experienced foxes showed little hesitation in attacking them. After capture, most ducks were taken alive to, lay-down sites where they were mouthed and often killed. Then the ducks were usually cached or taken to, dens or pups. Several birds were cached alive. Red foxes appear to have adapted to the escape of death-feigning ducks by learning to kill some birds soon after capture and by the evolution of an appendage-severing behavior. Death feigning appears to be a highly developed antipredator behavior of ducks that facilitates the escape of some birds after capture by red foxes. INTRODUCTION The so-called immobility or hypnotic reaction of animals was first described in the mid-1600's (Gilman and Marcuse, 1949), and since then the phenomenon has been observed in many species (Armstrong, 1965; Ratner, 1967). Among vertebrates, the reaction has been studied most intensively in birds; Armstrong (1965) cites examples of immobility in over 20 species. Perry (1938, p. 142-143) described the reaction of ". . . a wild eider drake . . ," presumably a common eider (Somateria moltissima), that became motionless ". . . as if he were dead . . ." when handled. There have been numerous theoretical explanations of the immobility reaction, including hypnosis, reflex response and cerebral inhibition, sleep, spatial disorientation, paralysis of fear and death feigning (see review by Ratner, 1967). Evidence is mounting, however, that such a reaction is an innate fear response that serves as a defense against predators (Gallup, 1972; Gallup et al., 1972; Gallup et al., 1971a; Gallup et al., 1971b; Ratner, 1967). Several studies have shown that predators may elicit immobility reactions among prey (Francq, 1969; Gallup et al., 1971a); however, Gilman et al. (1950, p. 110) stated, "There is little real evidence to show that dead animals, or animals who appear dead, will not be eaten by preying ones." Others have suggested that immobility may serve to minimize stimulation for further attack (Gallup, et al., 1971a) or that

An Analysis of the Relationship Between Stress and Parasitism

Abstract: The impact of stress upon the dynamics of host and parasite populations is varied. It may be expressed physiologically or behaviorally in either the host or the parasite. The outcome of stress may be an increase or a decrease in natality and mortality which may then result in significant changes in the densities of the involved popula- tions. At the ecosystem level, stress may be manifested either directly or indirectly on individuals or populations, but the outcome is change in natality or mortality and, hence, in the density of the affected species. The varied response to stressor input at the individual, population and ecosystem levels is dictated by the capacity for adaptability present at each level; the response may be modified, however, by the unique com- bination of environmental characteristics at the time of stressor input.

Size-biomass relationships of several Chihuahuan desert shrubs

Abstract: Rapid, nondestructive methods are needed to quantify plant biomass dynamics Methods known as dimension analysis can be used to establish regression relationships between plant biomass and easily obtained plant measurements Regression analyses were used to estimate the dry weight of foliage, living and dead stems and roots from canopy area and volume for eight desert shrubs The results show that volume and canopy area are generally suitable estimators Regression equations developed for Larrea tridentata compare favorably with equations in similar studies in Arizona and Nevada, suggesting that our results might be applicable in other desert regions, at least for shrubs with well-defined growth forms Other considerations when using these techniques are discussed

Seasonal and Microseral Variations in the Insect Populations on Carrion

Abstract: Microseral and seasonal variations in the carrion insect microcommunity were examined in 39 small-mammal carcasses in a red oak-basswood-sugar maple forest in Illinois from June 1968 through October 1969. Four stages of decomposition were described for the carcasses: Fresh, Bloat, Decay and Dry. These stages are the result of the activity of the arthropods, especially the insects. Four orders of arthropods (Coleoptera, Diptera, Hymenoptera and Acarina) accounted for over 90% of the organisms associated with carrion. The successional pattern of these arthropods on the carcass is discussed. Each of the major families found in the carrion microcommunity was represented by a few common species. Even though the families followed a fairly regular successional pattern, the species involved within a given family depended upon the season of the year. The specific times of abundance are discussed. INTRODUCTION When the organisms in a community die, their remains form an important habitat. Such a habitat and its associated organisms may be referred to as a microcommunity (Allee et at., 1949). Successional patterns of these organisms occur and the overall seral sequence is called a microsere (Mohr, 1943). This seral sequence or microsere can usually be divided into a series of definable stages which are called microseral stages (Mohr, 1943). Microcommunities eventually lose their identity during their last microseral stage. When this occurs, they become a homogeneous part of the major community. This is an important differentiation for separating a microsere from a sere (Allee et a!., 1949). Carrion is an important microcommunity in any terrestrial community and is a source of food and shelter for many organisms. These are primarily insects which play an important role in the return of organic material to the community. Papers dealing with the succession of insects in carrion include Fuller, 1934; Reed, 1958; Payne, 1965; and Payne and Crossley, 1966. This paper will describe both the basic microseral pattern and the seasonal changes of abundance in the populations of the important members of the carrion microcommunity. To understand fully the ecology of the carrion microcommunity, it is not only important to study how the populations change serally but also, 'how they change during the year (seasonally). MATERIALS AND METHODS This study was conducted from 30 June 1968 through 1 November 1969 in Carle Woods, a red oak-basswood-sugar maple forest in DesPlaines, Illinois (Arlington Heights Quad.; R12E, T41N, NW1/4S9).

Relative Importance of Factors Controlling Germination and Seedling Survival in Adenostoma Chaparral

Abstract: Environmental factors affecting germination and growth in the understory of mature stands of Adenostoma fasciculatum H. & A. were examined in the Santa Ynez Mountains near Santa Barbara, California. Nomenclature follows Munz and Keck (1959). Using a multifactor plot design, the effects of animal grazing, soil heating and soil fertility were examined under the shrub cover. Seed germination was greatly stimulated in several species by heat. Seedling growth was enhanced by nutrient enrichment similar to that observed in burned chaparral. Animal grazing had drastic effects on seedling survival. None of the seedlings exposed to animal grazing survived. Growth under the shrub cover was apparently suppressed, even in fertilized plots, by shrubderived toxins and decreased light levels. No single factor can, by itself, account for the entire pattern of germination and growth of all species beneath Adenostoma. The environmental complex under the shrub cover is such that the probability of survival of any single seedling is very low. These selective forces have resulted in the evolution of very efficient seed dormancy mechanisms in several species.

Climates and Vegetation Pattern across the Mojave/Great Basin Desert Transition of Southern Nevada

Abstract: Plant communities of the transition between the Mojave and Great Basin deserts of southern Nevada are under the primary control of climatic variables. Rainfall increases and temperature decreases according to large increments of increase in elevation of the drainage basins from S to N. Within the basins, the climates and vegetation pattern are primarily under the control of patterns of air circulation and nocturnal cold air accumulations and secondarily, of edaphic factors. Minimum temperature and maximum mean rainfall tolerances of Mojave Desert Larrea (creosote bush) communities are exceeded across this transition as, apparently, are the mean maximum temperature and minimum rainfall tolerances of the Great Basin Artemisia (sagebrush) communities. In those communities which characterize the transition (Coleogyne, Grayia-Lycium andersonii, Lycium pallidumGrayia, Lycium shockleyi), the Mojave and Great Basin temperature and rainfall regimes occur in various definable combinations. Only Atriplex confertifolia (shadscale) communities cannot be so defined; these occur along topographic gradients in both Mojave and Great Basin Desert climates. Contrasts in temperature regimes and their effects on vegetation in the lowlands of closed basins are illustrated by air temperature and plant data from two adjacent sites, with only 1.5 m elevation difference, near the playa of Frenchman Flat. All relationships are inferred from data collected during 10 years on a network of study sites on the Nevada Test Site of central-southern Nevada, whose drainage basins encompass the transition from the Mojave to the Great Basin Desert. INTRODUCTION In the basin and range topography of western United States the pattern of desert shrub vegetation of the intermontane valleys is often conspicuously defined and repeated from basin to basin. The area comprises the Basin and Range province of Fenneman (1931), which in part includes the Great Basin of Billings (1951) and most of the Great Basin Division of Cronquist et al. (1972). In the southern part-the Mojave, Sonoran and Chihuahuan deserts-the bajadas are mostly dominated by creosote bush (Larrea tridentata) communities. Along an irregular boundary extending from southwestern Utah across southern Nevada to southern California, these communities are replaced to the N by mostly sagebrush (Artemisia tridentata) and shadscale (Atriplex confertifolia) vegetation-the Great Basin Desert. These broad vegetation zones were recognized, mapped and described by Billings (1949, 1951) in relation to the macroclimate, topography 1 Work performed under U. S. Atomic Energy Commission Contracts AT (04-1) Gen-12 and AT(ll-1) 2307, and at the Nevada Test Site as a part of CETO Proj. 61.5.4.

Productivity and flowering of winter ephemerals in relation to Sonoran Desert shrubs

Abstract: Ephemeral plant biomass and density on a Sonoran Desert hill near Cave Creek, Arizona, vary relative to shrub canopy type and shrub density. Higher shrub density associated with increased elevation appears to decrease both ephemeral biGmass productivity and density, while ephemeral growth is enhanced under a shrub canopy if it is not too dense or low-hanging. Phenology of ephemerals on the desert study site shows early cool-season germination, low tolerance to heat, and early flowering when compared to shrubs and succulents in the same area. INTRODUCTION The Sonoran Desert of North America is characterized by a hot, dry climate; small mountain ranges rising out of fairly level basins, and a vegetation of shrubs, small trees, cacti and associated ephemerals. Information on desert ephemerals includes studies of germination (Went, 1948, 1949; Went and Westergaard, 1949; Capon and Van Asdall, 1967), growth and longevity (Tevis, 1958; Beatley, 1967), responses to moisture stress (Klikoff, 1966; Adams, et al., 1970) and interspecific associations with herbs (both annual and perennial), shrubs and small trees (Went, 1942; Muller, 1953; Muller and Muller, 1956; McDonough, 1963; Beatley, 1966, 1969; Cable, 1969; Harris and Wilson, 1970). The prime objective of this study was to relate ephemeral productivity and density to varying densities of shrubs in the central Arizona portion of the Sonoran Desert; in addition, phenological observations were made. STUDY AREA This study was conducted on the N side of a small desert hill near Cave Creek which lies N of the Salt River Valley in central Arizona. The hill is approximately 1.2 km wide at its base and rises 162 m above a base of 610 m elevation. The geologic substrate is composed of schist of igneous origin, and the soils, typical Aridosols, generally are shallow with small amounts of organic matter, little clay development and a layer of "caliche" in the lower portion of the profile. The climate of this area is desert-like, but modified by itg proximity to mountainous terrain to the N. Data taken from the Weather Bureau at Cave Creek, Arizona, show a mean annual precipitation of approximately 300 mm. Precipitation peaks occur during the summer from 1 Present address: Department of Botany, University of Rhode Island,

Carbon Dioxide Flux from Tundra Soils and Vegetation as Related to Temperature at Barrow, Alaska

Abstract: Measurements of total CO2 flux from a vegetated tundra surface using a dark chamber approach have shown diurnal patterns which are correlated linearly with soil temperature. Evidence is presented for the importance of microsite differences and seasonality in total dark CO2 flux from tundra soils and vegetation. The relative contributions of aboveground and belowground CO2 sources to the total dark CO2 flux from tundra soils and vegetation are estimated at between 36 and 46% for the aboveground contribution and between 54 and 64% for the belowground contribution on a polygon meadow during late June. Contributions of root respiration to total dark CO2 flux from wet tundra are likely to be overestimated if based entirely on controlled laboratory measurements now available. INTRODUCTION The use of carbon in energy capture and storage makes the study of carbon transfers of fundamental importance to, assessing energy flow through an ecosystem. Several aspects of the dynamics of CO2 transfer have been studied for the Barrow tundra ecosystem. Tieszen (1973) has measured the rates of photosynthesis and respiration for those graminoid plant species which constitute most of the vegetation. Coyne and Kelley (1972) have studied CO2 exchange using an aerodynamic approach. Billings et al. (1973) and Billings et al. (1974) have measured root respiration of the dominant graminoids. Microbial respiration and decomposition have been investigated by Benoit et al. (1972) and by Flanagan and Scarborough (1973). The sizes of the various carbon pools in the Alaskan tundra also have been estimated. Dennis and Johnson (1970) and Dennis and Tieszen (1972) have studied the aboveand belowground carbon pools while Tieszen (1972) has measured aboveground primary productivity. Integration of such information should lead to a higher degree of resolution in the knowledge of energy flow and possibly to a predictive model of the carbon transfers in this tundra ecosystem. The results reported in this paper concern the CO2 flux from tundra soils and vegetation to the atmosphere and the relative importance of root respiration and total subsurface CO2 production to the total flux. Sources of CO2 evolved from a vegetated surface may be grouped into three general categonies: 1. CO2 from nonbiological sources, i.e., release of dissolved CO2 from warming water or CO2 displaced from soil pore space by water. 2. CO2 from aboveground respiration, i.e., plant dark respiration and photorespiration, and animal respiration. 3. CO2 from belowground respiration, i.e., root respiration and respiration of soil organisms.

The Selective Advantage of the Defensive Posture of the Newt, Taricha granulosa

Abstract: The newt, Taricha granulosa (family Salamandridae) is toxic and noxious; bright ventral coloration is exhibited by a rigid defensive posture (unken reflex). Feeding studies using Taricha were conducted to determine if the bright ventral coloration and the defen- sive posture are important aposematic cues eliciting avoidance by birds. Trials were conducted using three groups of five chickens, previously conditioned to eat palatable salamanders (Desmognathus). Anesthe- tized Taricha were offered to each group in one of three positions: dorsum-up, venter-up or defensive posture. A trial consisted of placing a chicken in an enclosure with a salamander for 3 min and noting if the salamander was eaten, contacted but not eaten, or not contacted. Each chicken was offered an equal number of Taricha and Desmogna- thus at random. Postured newts were avoided more rapidly and to a greater extent than dorsum-up newts. Intermediate avoidance was exhibited in response to venter-up Taricha. Experience with either postured or venter-up Taricha facilitated avoidance learning of dorsum- up Taricha in later trials. The defensive posture of Taricha is an apose- matic cue which elicits avoidance by birds, but the aposematic influence of the posture and that of the ventral coloration cannot be separated. Prey species have evolved several lines of defense against predators using visual cues; the most important of these are crypsis, aposematic coloration and pseudoaposematic coloration (Robinson, 1969a). Those organisms that have aposematic coloration also have some attribute that renders them undesirable to the predator and often have some

Frequency of Reflection and Absorption of Ultraviolet Light in Flowering Plants

Abstract: Flowers of 300 plant species representing 61 families were surveyed for their degree and pattern of reflection of near-ultraviolet (UV) light. Flowers were ranked in terms of four degrees of UV reflection and absorption. Yellow and violet flowers have the highest probability of reflecting UV, while white and green flowers generally reflect UV poorly. Pollination guides were generally nonreflective, independent of visible color. While independent of floral symmetry, UV reflection appears to be positively correlated with flower size. Although UV reflection probably occurs in all plant families, it appears to be more common in certain taxonomic groups. Like other floral colors, UV reflection and absorption seem to depend on both the physical structure and chemical composition of the petals.

Habitat Dimensions of White-footed Mice, Peromyscus leucopus

Abstract: Analysis of arboreal components of two habitats of white- footed mice (Peromyscus leucopus) revealed that use of the components (branch height, angle and diameter) was proportional to their occur- rence. Frequency of mouse activity, monitored in 8 m3 volumes of habi- tat, was correlated with measurements of habitat structure which described the configuration of branches in the habitat. Only two plant species (Rhus typhina and Vitis riparia) were significantly associated with P. leucopus habitat use.

Life History Phenomena in Two Populations of the Lizard Sceloporus undulatus in Southwestern New Mexico

Abstract: Fecundity, survivorship and population characteristics were determined for the lizards Sceloporus undulatus consobrinus and S. u. tristichus in southwestern New Mexico. Sceloporus u. consobrinus lays at least four clutches per year with a mean clutch size of 9.9 eggs. Sceloporus u. tristichus lays at least two clutches per year with a mean clutch size of 7.2 eggs. The deviations about the regressions of clutch size on snout-vent length were significantly different between the two subspecies. In S. u. tristichus, eggs are heavier, survivorship higher, predation (as estimated by tail loss frequency) lower, mean adult size smaller, and the population is more dense than in S. u. consobrinus. The S. u. tristichus population is probably closer to K (environmental carrying capacity) than that of S. u. consobrinus. The life history and population characteristics of other populations of the S. undulatus group were compared in light of current concepts of rand K-selection, and these concepts were evaluated. INTRODUCTION Intraspecific variability in the life history characteristics of age at maturity, juvenile survivorship, adult life expectancy, clutch size and age-specific fecundity was described for the lizard Sceloporus undulatus by Tinkle and Ballinger (1972) and Tinkle (1972). Tinkle compared population and life history phenomena in seven populations of S. undulatus to gain insight into the evolution of life history differences among lizards. The purposes of the present study were: (1) to add information concerning life history and population differences in two more populations of S. undulatus, and (2) to evaluate current theory, particularly the role of resource availability, concerning evolution of life history patterns and population phenomena in light of the empirically obtained data. MATERIALS AND METHODS The two subspecies studied were S. undulatus consobrinus and S. u. tristichus. Detailed taxonomic descriptions of these two subspecies are given in Cole (1963). Males of both subspecies have a blue patch on each side of the belly and the throat. Female S. u. consobrinus lack blue belly patches, whereas female S. u. tristichus have blue belly patches which tend to be lighter than those of the male. S. u. consobrinus is the larger of the two subspecies and males tend to be smaller than females in both. Both subspecies were studied where they seemed most abundant in southwestern New Mexico. S. u. consobrinus was studied in a desert1 Present address: Department of Environmental Health, Kettering Laboratory, University of Cincinnati Medical Center, Cincinnati, Ohio 45267.

Effect of Fire on Big Bluestem Production

Abstract: Microclimatic conditions associated with fire-induced changes in a tall-grass prairie environment were investigated, and estimates of the net photosynthetic response of Andropogon gerardi Vitm. to these changes were made by laboratory determination of the temperature dependence of net photosynthesis of A. gerardi plants collected from burned and unburned sites. Plants from both sites had temperature optima for net photosynthesis between 25 C and 30 C, and similar maximum rates. Increased production of A. gerardi in the field following burning was attributed primarily to the more favorable environmental conditions for net photosynthesis on the burned site from the time of leaf emergence through late June. Warmer soil temperatures and more light on the burned site appear to be important in initiating early season growth. Total carbon gain per unit area was greater on the burned site than on the unburned, primarily because more photosynthetic leaf and shoot area was available on the burned site earlier in the growing season. Beginning in late June and continuing for the rest of the growing season, measured environmental parameters were similar on both sites. INTRODUCTION An increase in dry matter production and flowering when tallgrass prairie is burned has been amply documented (cf., Brown, 1967; Curtis and Partch, 1948; Daubenmire, 1968; Ehrenreich and Aikman, 1963; Hadley and Kieckhefer, 1963; Kucera and Dahlman, 1968). Several factors including release from allelopathic effects and decreased competition from cool season grasses have been suggested (Robocker and Miller, 1955; Curtis and Partch, 1948; Ehrenreich, 1959; Old, 1969) as reasons for increased production after fire, but litter removal has often been cited as the primary factor (Curtis and Partch, 1950; Old, 1969). On unbumed tall-grass prairie the light-colored litter layer is often at least 10 cm deep, and quite dense. Its removal affects many microclimatic parameters and it is not clear which of these changes are responsible for increasing production. The most obvious ways in which litter removal affects the microclimate are by allowing increased light penetration and warmer temperatures near and below the soil surfaces (Hurlbert, 1969). These factors have been cited by Ehrenreich and Aikman (1963), Ehrenreich (1959) and Weaver and Rowland (1952) to account for earlier growth on burned compared to over 114 gm2 (1000 lbs acre-1) unburned areas. An additional effect of litter on microclimate was proposed by Brown (1967), who observed less net radiation in litter areas, sug1 Present address: Department of Vegetable Crops, Cornell University, Ithaca, New York 14850. 2 Department of Biology, Central State University, _Edmond, Oklahoma 73034,

Sound Communication During the Reproductive Behavior of Notropis analostanus (Pisces: Cyprinidae)

Abstract: Field and laboratory observations were made on the reproductive behavior, ecology and sounds produced by males of Notropis analostanus during reproductive behavior. Based on these observations, experiments were performed on sound communication during the repro- ductive behavior of this species. Reproductive activities began in middle to late May when the males set up territories around a suitable egg site. The males defended these territories by chasing and fighting behavior which included the lateral threat display. During this aggressive behavior, "single knocks" and "rapid series of knocks" were produced. Courtship behavior began when a female approached the territory and the male swam out to her. If the female did not swim away, the male swam in circles around her and then swam to the egg site where it would perform "solo-spawning" motions. Spawning was accomplished when the female followed the male to the egg site and assumed a spawning position with the male in a dorsolateral position to her. During the courtship behavior the male produced "single knocks" and "purrs." The functions of sounds produced by male Notropis analostanus during reproductive behavior were studied by playing back these sounds under experimental conditions designed to clarify their functions as com- municative signals. The following conclusions were reached: 1. The "single knocks" were not effective in influencing aggressive behavior of males nor did they promote courtship. 2. The "rapid series of knocks" stimulated aggressive behavior by a dominant male and inhibited the entry of a submissive male into the territory. 3. The "rapid series of knocks" inhibited the courtship behavior of the male and reduced cooperation by the female during courtship. 4. The "purrs" increased the courtship behavior of the male and pro- moted the cooperation of the female during courtship.

Litter arthropod community in a southern Appalachian hardwood forest: numbers, biomass, and mineral element content

Abstract: The biomass, numbers of individuals and mineral content of the arthropod fauna in the litter of a mixed hardwood forest were examined. The biomass values of the litter arthropods were generally higher than in other forests. Possible reasons for higher biomass values are discussed. Potassium and calcium standing crops are compared to those of a Liriodendron forest in Tennessee. With few exceptions the potassium values are comparable. However, there appear to be great differences in the calcium values. INTRODUCTION The forest constitutes an ecosystem in which organic and inorganic elements interact. The basic mineral nutrition of forest vegetation is provided by rock weathering and mineral-laden rain. The forest is charged and recharged by organic products from the vegetation (Spurr, 1964). The nutrient recharging is accomplished to a great extent by litter decomposition which releases the nutrients bound up in the dead plant structural material. Decomposition is accomplished by the activities of both the forest floor microflora and fauna. As organic materials reach the forest floor, they are attacked by the microflora and fauna, releasing nutrient substances, and 40 to 90% of the initial weight may be lost during the 1st year, the actual amount varying with species and locality (Edwards et al., 1970). Witkampl and Olson (1963) showed a nonlinear rate of weight loss by leaf litter during the 1st year, often with an initial rapid loss of weight, possibly due to leaching of soluble materials. This is followed by a slower loss rate during the winter months and subsequent acceleration during spring and summer (Crossley, 1970). Fresh leaf litter may remain unpalatable to soil fauna until the polyphenols in the stem and leaf material are removed (Edwards and Heath, 1963; Satchell and Lowe, 1966), and this may delay faunal attack on the litter for some time. Several studies on the dynamics of litter breakdown by fauna have been reported. Satchell (1967) suggested there may be extensive incorporation of litter into the mineral soils by the feeding of earthworms. 'Research supported in part by the Eastern Deciduous Forest Biome, US/IBP, funded by the National Science Foundation under Interagency Agreement AF-199, 40-193-69, with the U.S. Atomic Energy Commission Oak Ridge National Laboratory, and in part by U.S. Atomic Energy Commission Contract AT-(38-1)-641 with the University of Georgia (D. A. Crossley, Jr.). Contribution No. 147 from the Eastern Deciduous Forest Biome, US/IBP. 2 Present address: Ecology Center, Utah State University, Logan, Utah.

Fire in the Subarctic Wintering Ground of the Beverley Caribou Herd

Abstract: The study documents the timing, prevalence and importance of fires in a 105,000-sq-km area of the Northwest Territories, Canada, bounded by long 1040 and 1120, lat 600 to tree line. Lightning caused most of the fires and accounted for almost all of the area burned in a 7-year period. In this part of the subarctic, the fires appear to follow a seasonal pulse that progresses in June and July from the SW toward tree line in the NE, retreating in August. The normality of fire in this part of the northern boreal zone is beyond dispute. There is no conclusive proof that fire regime has changed substantially in recent times from what it was previously. The implication is that endemic animals, such as caribou, are adjusted to recurring fires.

Aspects of the Reproductive Biology of the Northern Diamondback Terrapin Malaclemys terrapin terrapin

Abstract: The characteristics, interrelationships and seasonal variation of the nests, eggs, clutches and plastron sizes of a population of northern diamondback terrapins (Malaclemys terrapin terrapin) nesting on a barrier beach island in southern New Jersey were studied during the 1973 breeding season. Positive correlations were obtained between (a) egg length and egg breadth; (b) clutch size and clutch weight; (c) plastron length and clutch size, and (d) plastron length and clutch weight. No significant correlations were found between (a) clutch size and any egg dimension (length, breadth, weight); (b) plastron length and any egg dimension; (c) plastron length and any nest dimension (depth, egg compartment depth, egg compartment width). The mean, median and modal clutch size of 10 eggs suggested that clutch size of northern populations may be larger than those of more southerly situated populations and subspecies. Mean egg size (length, breadth, weight) tended to decrease as the laying season advanced. Comparisons with findings from avian biology concerning eggs and egg-related phenomena were made.

Relative Growth in Two Sympatric Species of Sceloporus

Abstract: Osteological measurements on a growth series of two sympatric species of lizards, Sceloporus undulatus (maximum snout to sacrum length 59.1 mm) and S. olivaceous (maximum length 98.5 mm) were subjected to bivariate and multivariate morphometric analysis. Major identified sources of variability in the -sample are size, sex and taxonomy, the same that a paleontologist has to deal with. The two species are very similar osteologically but differ in size. Mixed bivariate plots show a separation between the two species for only one of 26 characters, but that character, as predicted, was strongly allometric. The single bivariate plot provided a more sensitive taxonomic separation than did a multivariate clustering technique, principal coordinates analysis. The latter did suggest, however, the existence of sexual dimorphism, previously unreported, which was confirmed by canonical analysis. Though the two species differ in maximum size by a factor of 1.5 to 1.7, the larger species is a geometrically scaled-up replica of the smaller one for only three of 28 relationships measured; many of the previously reported structural differences between species relate to the comparison between adults of the smaller species and juveniles of the larger. The effectiveness of jaw adduction of both species increases significantly through life, and positive allometry of limb length correlates with increased size of home range during ontogeny. INTRODUCTION This report is the second in a series of studiesi (Dodson, 1975a, b and c) designed to provide the paleontologist with a basis for understanding the kinds of variability potentially represented in a sample of fossils that spans a significant size range. The ultimate goal of the larger project is to test whether application of principles of ontogenetic allometry can demonstrate that 12 species of lambeosaurine hadrosaurs (duck-billed dinosaurs) of variable size and shape from a single formation may actually constitute a single ontogenetic series. The approach that is followed in all of the studies is explicitly morphometric, with a large number of cranial and po-stcranial variables being measured. In a study of a growth series of Alligator (Dodson, 1975a), ontogenetic changes of shape were described by means of allometric coefficients, and many of the changes were found, by bivariate and multivariate methods, to have expression in the function and ecology of the animal as it grows from hatchling to large size. In the present study data on two sympatric species of lizard, Sceloporus olivaceous and S. undulatus, are examined. The data are of considerable interest, for the two species are morphologically very similar, a growth series of each is included, and each specimen is 1 Present address: Laboratories of Anatomy, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pa. 19174.

Habitat Utilization by Four Species of Woodpeckers in a Central Illinois Woodland

Abstract: A sympatric guild consisting of the red-headed woodpecker (Melanerpes erythrocephalus), the downy woodpecker) (Dendrocopus pubescens), the red-bellied woodpecker (Centurus carolinus) and the yellow-bellied sapsucker (Sphyrapicus varius) segregated realized niches by: (1) differential foraging techniques; (2) exploiting different height classes; (3) selection of different tree species; (4) use of relative different amounts of alive and dead substrate; (5) differential selection of limb size. In downy woodpeckers, sexes separated the species' realized niche into subniches, which in the past may have caused evolution of different bill structures. Yellow-bellied sapsuckers exploited primarily a sap resource from hickory trees while in wigration. They foraged on larger limbs at lower levels. Red-headed woodpeckers had a more restricted woodland foraging pattern than did downies and red-bellied woodpeckers. Red-heads, however, spent more time out of the wooded area. Intersexual overlap values for the sexually dimorphic downies were greater than interspecific values. INTRODUCTION The principle of competitive exclusion (Hardin, 1960) implies that ecologically sirnilar, cohabiting species should exhibit various degrees of evolutionary divergence which reduce competition and thus increase fitness. The nature of divergence or niche differentiation of sympatric species of birds has been the subject of several ecological investigations, and differential foraging patterns have been found to be a major factor permitting coexistence (Dixson, 1961; Koplin, 1969; Lack, 1954; MacArthur, 1958; Root, 1966; Willson, 1970). Evolutionary divergence also occurs intersexually, presumably to reduce competition and thus allow strengthening of the pair bond. Davis (1965) and Selander and Giller (1959) have shown that sexual dimorphism in bill length exceeds that in other size characters in most species of woodpeckers. Selander (1966) discussed the role of bill dimorphism in reducing intraspecific competition and presented evidence that in Centurus striatus on Hispaniola, both bill sizes and feeding behavior of the sexes were different. Red-headed woodpeckers (Melanerpes erythrocephalus), downy woodpeckers (Dendrocopus pubescens), red-bellied woodpeckers (Centurus carolinus) and yellow-bellied sapsuckers (Sphyrapicus varius), all occur in central Illinois during the early spring. This study was initiated to quantify the behavioral and habitat use patterns which segregate these species and any intersexual differences in behavioral and habitat use patterns in the downy woodpecker. Specific questions to be answered were: (1) how does a sympatric guild of woodpeckers segregate its respective niches; (2) are the real-

The Effects of Partitions on the Growth Rates of Crowded Rana pipiens Tadpoles

Abstract: It was recognized at the outset that growth rates of tad- poles are retarded in proportion to the density of the population and that psychological stress is the major cause for retardation. This paper shows that the rate of growth is not dependent simply upon the volume of space, but also upon the shape of the space. The results support the contentions that space is psychological and that the stress of crowding is proportional to the frequency of physical encounters between tadpoles. Vision is not an important factor. Adolph's (1931) correlation of growth rates with the inverse of density can be improved by incorporating a term to represent the shape of the space or perhaps the length of the periphery.

The Blufflands: Pleistocene Pathway into the Tunica Hills

Abstract: Reinvestigation of the evidence for disjunctions of northern plant species in the Tunica Hills of southeastern Louisiana and adjacent southwestern Mississippi reveals that, rather than serving as an isolated "island refugium," these hills represent the southernmost extension of the Blufflands. This study documents the distributions in the southeastern United States of 10 plant species previously considered disjunct in the Tunica Hills by as much as 800 miles from the N. These species occur primarily in the Appalachian Mountains, the Ozarks and northward, and extend into Louisiana along the Blufflands. The Blufflands, a belt of hilly land bordering the eastern escarpment of the Mississippi River alluvial valley, coincide with the thickest accumulations of loessial sediments in the Tennessee-Mississippi-Louisiana area. The cold, glacial meltwater-fed Mississippi River and associated dense, cold air mass funneled past the Blufflands during maximum continental glaciations. We postulate that contact of cold river water and accompanying air mass with relatively warmer air produced extensive advection fogs along the Blufflands, supplying moisture and cooling the uplands bordering the Mississippi River. These conditions promoted the southward migration of numerous species of the Mixed Mesophytic Forest at least along the Bluffland pathway. Erosion of the loess into vertical ravines has maintained cool, moist habitats within the Bluffland hills suitable for the continued relict existence of many northern plant species. The causal mechanism presented here for the southward migrations of Mixed Mesophytic Forest species along all major river systems of the Southeast during the late Pleistocene adequately accounts for documented distributions of northern disjunct plant species (of those species associated with mesic deciduous woodlands) in the southern Atlantic and Gulf coastal plains. In addition, this mechanism allows for the persistence of Tertiary endemics in the Appalachians through the Pleistocene and Holocene.

Ecological and Behavioral Aspects of Coexistence in Six Crucifer-Feeding Pierid Butterflies in the Central Sierra Nevada

Abstract: Up to six species of crucifer-feeding pierids occur together at 2100 m in the central Sierra Nevada. At Boreal Ridge, a relatively pristine environment, all species maintain low densities. At Donner Pass, where disturbance allows for a great abundance of the weedy crucifer, Lepidium virginicum, the two species which breed readily on this plant, Pieris protodice and P. occidentalis, are very abundant. Due to habitat selection, P. protodice may compete with P. occidentalis for oviposition sites despite the seemingly small impact of both species on the plants; but unlike P. occidentalis it probably does not overwinter at Donner, and its ecological importance in the system probably varies from year to year as a result.

Change of Web Site in Argiope Spiders (Araneidae)

Abstract: I n t r o d u c tio n Since most animals have higher fitness in certain places, behavior has evolved which results in the selection of particular habitats (Levins, 1968). Many animals simply reduce the rate of travel in preferred localities (Sale, 1969; Klopfer, 1965; Wecker, 1963). The web of spiders serves both as the trap for food and as the spider’s living quarters. The building of the web itself has been studied (Witt et al., 1968; Reed et al., 1969), but the behavior which relates the web to the site has not. “Web-site tenacity” can be defined as the percentage probability that, once it has built a web, the spider will remain at the same web site from one day to the next '(Enders, 1973). Here I describe internal changes which affect the web-site tenacity in two species of spiders in the genus Argiope in the family Araneidae. This paper is the first formal study of web-site tenacity as it relates to selection of a place to live. O b s e r v a t i o n s in t h e F i e ld MethodsU-Argiope aurantia (Lucas) and A. trifasciata (Forskal) are large orb web spiders which are abundant in the United States. Observations of these species were made during the daytime along the edges of road-cuts in Raleigh, North Carolina. Observations were made in such a way as to1 avoid gross disturbance either to the vegetation or to the web or web site, the vegeta­ tion to which the web was actually attached, The study areas were covered with Sericea Lespedeza (Lespedeza cuneata), a tall perennial herb which dies back to the ground each winter, and a considerable admixture of other plant species (Enders, 1974). The instar of Argiope aurantia and of A. trifasciata spiders was estimated by comparison with preserved specimens of A. aurantia which had been reared in the laboratory. Second-instar spiders (Kaston, 1948) are those which emerge from the egg sac and are in the first web-building stage. One A. aurantia in the field had to be scored as the 12 th instar, but most females matured and stopped molting in instar nine or 10. While still on the webs, spiders were marked on their dorsal body surface with individual patterns of rapidly drying paint. To identify the location of of each web, the supporting vegetation was marked, using masking tape. On successive days, I searched the areas where spiders had been marked. Each day I recorded whether the spiders remained at their old sites, whether they had molted, and whether any previously marked spiders could be found at new web sites. As marked animals disappeared, additional spiders in the vicinity were marked for observation, and animals were re-marked immediately after discov­ ering that they had molted. Web-site tenacity is equal to the number of spiders remaining at old sites divided by the sum of those that (a) remained at the old site, (b) were found elsewhere than the previous site, and (c) could neither themselves nor any part of the orb section of the old web be found (Table 1). Spiders which spon­ taneously left a web site removed the orb section before leaving. Observations of the webs of spiders known to be dead support the assumption that spiders have 1975 N otes and D iscussion 4 8 5 died if their previous web can be relocated with no spider present. Thus, the denominator for the calculation of web-site tenacity is the number of spiders known to be marked the previous day less those which died (D in Table 1). In certain cases another spider was observed in a web site when the original occupant of that web site had disappeared or changed web site. Ordinarily, the new occupant was a noticeably larger animal and sometimes a marked spider. The move by the original occupant on that day was excluded from considera­ tion, because, on occasion, I have seen active intrusion onto a spider's web by another (Enders, 1974). The move by the original occupant can thus be con­ sidered to have been forced. Blanke (1972) reports similar interactions in Cyrtophora citricola Forskal (Araneidae). Since fewer than 10 of my observa­ tions are excluded for this reason, such exclusion does not materially change the calculated web-site tenacity. Most changes of web site were more than a diameter of the web and most were horizontal displacements. Criterion for change of web site was a minimum 10-cm change in the location of the hub of the web in any direction, including the vertical. Difficulty in deciding whether a change of web site had occurred was encountered only in observations made of smaller spiders, in which cases some shifts of less than 10 cm were noted, but were scored as an animal remain­ ing at same site. Tests of significance were made by the use of chi-square tests not corrected for continuity (Snedecor and Cochran, 1967), the probabil­ ity of 0.05 being used as the minimum level for reporting statistical significance. Results.— The method of marking individuals caused much mortality of the tiny second and third instars of A. aurantia. But unmarked animals (observed as discussed under laboratory results) of these instars showed a web-site tenacity of roughly 50%, lower than that of larger spiders. Because it was impossible to avoid stepping on the vegetation near the web (Lowrie, 1963), and since second instars of this species leave sparse or short vegetation (Enders, 1973), those results might be discounted, but they fit with laboratory results discussed below. Mortality was lower for larger araneids (Enders, 1974), such as 4% per day, one observation of 23 in category D (Table 1). Table 1 also shows the lower apparent mortality and movement rates of marked spiders, compared to unmarked ones, although the chi-square value is not statistically significant. Higher mortality and rate of movement had been considered possible effects of marking. A similar statistical analysis using unmarked Argiope spiders at later stages of the life history showed no significant differences between un­ marked and marked individuals in observed web-site tenacity. There were no gross differences in web-site tenacity among months and between species (Table 2). The lower web-site tenacity of second instar A. aurantia described above is reflected in Table 2 in the lower web-site tenacity for June, in which the model instar was the fifth instar. T a b l e 1.— Comparison of marked and unmarked A. aurantia observed on 4 successive days, 21-25 June 1970. Web-site tenacity = A / (A + B +C ) Record on next day No. of observations of unmarked spiders No. of observations of marked spiders A. Remained at site B. & C. Found elsewhere or neither 10 18 web nor spider found 6 4 D. Old web found, but not spider 1 1 Calculated web-site tenacity 62.5% 81.8% 4 8 6 T he American M idland N aturalist 94(2) O bser v a t io n s in t h e L aboratory M ethods.—-Web-site tenacity of early instars was observed in a 10-gal glass terrarium with a glass cover. This provided sufficient space for normal web building and for change of web site. Webs of these particular spiders were generally less than 10 cm in diam. Use of the terrarium avoided problems of gross disturbance and of disappearance of the small 1-mm-long second instar A. aurantia which had occurred in the field. Spiders were given water every day. Eye gnats {Hippelâtes sp.) were added to the terrarium once a week as food. Branches and wire had initially been placed in the terrarium for the spiders’ web building, and I did not destroy the webs during the period of observation. These unmarked individuals of A. aurantia could often be identified due to (a) size differences among caged animals, (b) the small number of individuals and (c) the failure of other individuals of a similar size to change web site. These spiders originated from two cocoons. In larger cardboard and screen wire cages in the laboratory, which were at least five times the diameter of the webs, larger spiders were similarly given a choice of changing web site or remaining at the same one. Results.— Many young spiders renewed their webs only every 2nd day. This occurred primarily in the second and third instars and was also observed in the field. In contrast, larger araneid spiders generally renewed their webs every night, as originally reported by Breed et al. (1964). There was a marked and consistent increase in web-site tenacity with instar (age and/or size) of Argiope aurantia (Fig. 1). I n f l u e n c e o f M o l t in g o n W eb -S it e T en a c ity Methods.-^Web-site: tenacity in the field seemed to be lower after the molt. To test whether this, in fact, occurred, data were assembled from control groups observed in the field, experimental groups in which no significant treatment effect had occurred, and from the field observations reported in Table 2. Little of this was useable, relative to the quantity gathered on web-site tenacity, because I only used data in which the larger spider was observed with the old, shed and marked exoskeleton in its web or immediately below the web. Results.— From field observations for the period June-September, 31 in­ stances of molting were observed in 30 individual A. aurantia, and 10 instances of molting in eight A. trifasciata. No spider left a web site for the 3 days preceding a molt. Two instances of change of web site occurred on the day of the molt, and both cases involved the spider moving onto another spider’s web, one that of another A. aurantia, T a b l e 2.— W eb-site ten ac ity of tw o species of Argiope sp id e r Month Number Number of Range of Species (No. areas per observations web-site sampled) sample per sample tenacity June (2) 16-21 2141 62-76% July (5) 6-48 26-173 75-96% August (4) 9-14 43-113 81-93% A. aurantia Sept. (1) 11 52 79% GRAND TOTAL 188 800 82% July-August (4) 4-10 2187 70-99% TOTAL 29 166 90% A. trifasciata 1975 N otes and D iscussion 4 8 7 and the other that of an A. trifasciata. [These two web invasions are notable because web invasion occurred only in a very small percentage of cases (0.6% ) of the entire set of 800 observations (En

Overland Migration of Collembola (Hypogastrura nivicola Fitch) Colonies

Abstract: Dense aggregations of Collembola (Hypogastrura nivicola Fitch) move across the surface of the forest floor in central New England in the autumn and spring for distances of 20-25 m before disappearing. Colonies 30 cm in diam have populations of 0.5-1 million individuals. Hourly movement is as much as 75 cm and daily movement as much as 6 m. Overland movement ceases at night or when colonies are covered by black plastic sheeting.