Showing papers in "American Midland Naturalist in 1979"

Age Structure and Successional Dynamics of a Colorado Subalpine Forest

Abstract: Population age structures of old-growth Engelmann spruce, subalpine fir and lodgepole pine are described in the Colorado Front Range subalpine forest (2850 and 3500 m). Among the populations of these three species, five types of age structures can be recognized; up to four different types of age structures were found in one species under different environmental or historical conditions and no species showed the same type of age structure throughout its entire range of occurrence. The age structures of populations are used to infer their climax or successional (selfreplacing or not self-replacing) status. From the combination of climax or successional populations in a stand and the distributions of these combinations on environmental gradients, three types of forest are recognized: (1) climax lodgepole; (2) climax sprucefir, which is pioneered after disturbance by lodgppole; and (3) climax spruce-fir which is pioneered primarily by spruce. The changes from one forest type to another follow a unidimensional gradient which begins with climax lodgepole at low elevation, dry sites, followed by a forest mosaic of successional lodgepole and climax spruce-fir at both higher elevations and intermediate moisture sites, and ends with climax spruce-fir in which lodgepole is not pioneer, at both high elevations and on the most mesic sites. INTRODUCTION Studies of the seral status of species are commonly based on size distributions and differences in sizes between species in a stand. However, significant errors may be introduced into these studies by differences in growth rates between species. In addition, the seral status of a species may not be reflected in its size distribution because of a tendency for gaps in the distribution to be filled by differential growth of individuals (Schmelz and Lindsey, 1965; Johnson and Bell, 1975). The result may be that the shape of the size distribution does not reflect whether a population is reproducing, i.e., successional or climax. Ideally, succession should be studied by observing an area over a period of time. In the case of long-lived species, such as trees, this is not practical. However, the age structures of tree populations may indicate whether they are successional -or climax, and successional pathways may be inferred from this information (Leak, 1975). Climax types and advanced seral sequences were investigated in the Colorado Front Range subalpine forest using tree population age structures of the three dominant species: Engelmann spruce (Picea engelmannii Parry), subalpine fir IAbies lasiocarpa (Hook.) Nutt.] and lodgepole pine (Pinus contorta Engem.) The objectives of this study are: (1) to describe the age structures of Engelmann spruce, subalpine fir and lodgepole pine; and (2) to infer seral and climax status from tree age distributions. The study area was the Fraser Experimental Forest (39?50'N, 105050'W), located 8 km (5 miles) SW of Fraser, Colorado. This area is in the southern part of the W flank of the Colorado Front Range, and was chosen because of its accessibility and undisturbed condition. LITERATURE There has been considerable debate over the boundaries of a subalpine zone in the Colorado Front Range and other nearby portions of the Rocky Mountains (Ramaley, 1907; Young, 1907; Ramaley and Robbins, 1909; Bruderlin, 1911; Present address: Department of Botany, Louisiana State University, Baton Rouge 70803.

Comparative Biomass and Growth of Cypress in Florida Wetlands1

Abstract: Tree biomass and increase in biomass were determined for cypress (Taxodium distichum) in different systems in Florida. Ten trees were harvested to de- termine biomass regressions. Lowest biomass and tree growth rates were found in cypress-pine associations indicative of low water, in monospecific stands of cypress which are indicative of high water levels, and in a poorly drained cypress dome. Increases in individual tree growth ranged from 1.0 to 3.5 kg/y-1 in these groupings. Highest cypress tree growth rates were found in cypress-tupelo systems and cypress-hardwood systems. The latter are less dominated by cypress, however, so individual tree growth is greater (7.7 kg/y vs. 4.0 kg/y). Cypress-hardwood associations are known to be generally better drained than cypress-tupelo systems. Two experimental cypress domes currently receiv- ing treated sewage effluent and groundwater showed high individual tree growth (5.0 and 4.2 kg/y, respectively), but little difference was noted between the two domes. Tree diameter increase showed normal cypress tree growth to be 1.0-2.0 mm/y with higher values of 2.8-3.3 in cypress-hardwood associations and the experimental cypress dome. Cypress in the poorly drained dome increased by only 2.0 mm/y.

A severe drought: impact on tree growth, phenology, net photosynthetic rate and water relations.

Abstract: An unusually severe drought occurred in central Missouri during the summer of 1976. The drought resulted in an average soil water potential of ?26.1 bars in the upper 45 cm of soil profile in spite of the addition of 4.9 cm of irrigation water. It enabled us to examine its effects on phenology, growth and physiological processes, as well as the water relations of white oak (Quercus alba L. ), and eight other species found in this oak-hickory forest. The drought had a dramatic impact on base (presunrise) xylem pressure potential of white oak in both irrigated ( ? 19.6 to ?34.3 bars) and nonirrigated specimens ( ? 27.8 to ?45.2 bars). Growth was reduced, die-back increased, net photosynthetic rate was depressed to near the compensation point and phenological patterns in the following year (1977) were altered. An estimation of the number of days on which stornata were closed for most of the photoperiod was compared to the number of days when mature leaves were present. The following ranking of species based on this index of stomatal control was possible (from most to least time spent with stornata closed) : sunflower > flowering dogwood = hlack walnut > sugar maple > northern red oak > white oak =? eastern red cedar = black oak. Various drought avoidance mechanisms are also presented and discussed in regard to these eight species. The long periods of low soil water potentials and base xylem pressure potentials experienced during the drought of 1976 did not prevent the recovery of the growth processes that autumn or the subsequent spring. All study species seemed well-adapted to survival and to continued functioning during this severe drought.

Aspects of mating frequency and reproductive maturity in Papilio zelicaon

Abstract: Female Papilio zelicaon in different populations show a mean frequency of 1.2-1.9 matings, with a maximum of three. Mating frequency increases with female age. No seasonal or latitudinal mating frequency differences were discovered but mating frequency was significantly greater in females from montane populations compared to lowland females. This difference was interpreted as resulting from increased mating frequency of selected males in "hilltop" areas leading to sperm/accessory gland depletion and rapid return of sexual receptivity in females mated to such males. Use of sperm from the last male in a mating sequence (sperm displacement) occurred in a doublemated female using a red-eyed mutant as a genetic marker. Females mated to mature males laid more ova than those paired with immature males, while no differences were noted between the latter group and virgin females. Oviposition appears to be influenced more by sperm quantity and/or accessory gland secretion than by physical presence of the spermatophore. Rapid multiple mating by males leads to smaller spermatophores deficient in sperm. Sperm is produced continuously at a uniform rate during the male's life whereas production rate of accessory gland secretions decreases with male age. At least 40-50% of males less than 12 hr old are incapable of insemination of females. Male mating ability (related to variance and duration of copulation) is low from 0-12 hr, peaks at age 2-8 days, then gradually declines. Extended copulation occurred in immature and old males and in second matings of rapid mating sequences. This was regarded as permitting sperm/accessory fluids to be produced and transferred in copulo while allowing depleted or immature males to exploit mating opportunities.

Sexual Size Dimorphism in Vespertilionid Bats

Abstract: Sexual size dimorphism was investigated in 18 species of vespertilionid bats (Chiroptera: Vespertilionidae). The characters representing size were length of head and body (HBL), length of forearm (FAL), condylocanine length (CCL) and length of maxillary toothrow ( MTL ). From these variables, two proportional characters were calculated, HBL/FAL and CCL/MTL. Student's t-tests were used to determine significant differences (P ^ 0.05). Females averaged larger than males in two or more size dimensions for all 18 species, with significant differences being noted in 15 of the species. In no cases were males significantly larger than females. Proportional differences were fewer, with significant differences being found in only five species. Mean lengths of forearm and maxillary toothrow were adjusted by covariance analysis in order to negate the differences in absolute size between the sexes. Using this procedure, females of six species had significantly longer forearms than males, and males of one species had significantly longer forearms than females. There were no significant correlations between the number of young per pregnancy and the degree of dimorphism exhibited by the species tested. The general patterns in these data, when coupled with life history information, suggest that increased energy demands during pregnancy may be the primary factor in the selection for larger size in females. Larger females can maintain homeothermy, and hence the timing of birth, more efficiently, can store more fat, and have a greater size array of prey available to them. Increased weight loading of pregnant females is probably also important in the selection of larger size in females, but this hypothesis is not supported by these data.

Deer Mouse Reproduction and Its Relationship to the Tree Seed Crop

Abstract: Deer mice {Peromyscus maniculatus rubidus) averaged 57% males in a sample of 3833 collected in the Douglas fir (Pseudotsuga menziesii) belt in western Oregon from 1952-1966. The percentage of mice captured in autumn and recaptured in spring was significantly greater in good (2.66 kg/ha or more) than in poor (0.45 kg/ha or less) Douglas fir and western hemlock (Tsuga heterophylla) seed years. However, the autumn-spring population estimates for good and poor seed years were not significantly different, but by the following autumn the good seed years had significantly greater populations. There was a significantly larger number of young female (and, by inference, male) deer mice in the population during the good seed years. Individuals of both sexes were fecund each month of the year; however, yearly fecundity periods varied and the longest were 11 months. Males were most active sexually from February through November and females from March through October. Males reached peak fecundity in May, 1-2 months earlier than the females. The average male and female fecundity percentage from September-March, when tree seed was most abundant, was significantly greater for good seed years. Average yearlong fecundity for both sexes was not significantly larger in the good seed years, but for the females there was a significant difference. The percentage of pregnancies from September-March was significantly greater (eight times) in good years, but during April-August was only one-half of those for the poor, a significant difference. However, on a seed year basis, the average percentage of pregnancies was 2.9% greater for good years but was not significantly different. Average litter size was not significantly affected by the size of the seed fall, being 4.6 for corpora lutea and 4.4 for both the embryos and placental scars. Smallest average embryo litters were found in winter and spring and larger ones were tallied in summer and autumn. Calculated average number of litters per year was 2.9 for good seed years and 2.5 for poor, a significant difference. The positive factors contributed variously to higher populations during and/or following a good seed crop, at least by the following autumn.

The longitudinal distribution of fishes in an East Texas stream

Abstract: The fish populations of Big Sandy Creek were investigated from June 1974 to January 1976 to evaluate longitudinal changes. A total of 46 fish species were collected by seining, electrofishing and gillnetting. The number of species per station from seven stations increased regularly?by addition of species?from 22 in the headwaters to 33 at the downstream limits of the study area. Relative abundance for individual species increased in some cases, decreased in others or remained roughly constant in relation to longitudinal position. Among the 24 abundant species, longitudinal change in size composition was detected by length-frequency analysis only in Erimyzon oblongus, which had high percentages of_small individuals in headwater streams. Diversity per individual (H) was generally greater at downstream stations, but the relationship between fish diversity and longitudinal position was not precise. An unusually diverse headwater assemblage may have been related to soil characteristics of the watershed. Diversity in general seemed to be more highly correlated with depth than with longitudinal position. Calculated heterogeneity (IH) showed that changes in community structure were gradual along a longitudinal continuum. These changes were not related to increase in stream order.

The Origin of Populus deltoides and Salix interior zones on Point Bars along the Minnesota River

Abstract: An investigation was made to ascertain the nature and origin of the separate and distinctive zones of Populus deltoides Marsh, and Salix interior Rowlee commonly occurring on point bars along the Minnesota River. These vegetation zones are primarily monospecific, have high stem densities, possess well-defined boundaries and are restricted to specific contour intervals on the point bars. A method was devised to determine past river elevations at ungauged locations between two gauging stations along the lower Minnesota River. Comparisons of calculated river elevations with sur- veyed vegetation-zone elevations have illustrated two mechanisms by which the zones originate. During years of zone establishment the river elevation remained fixed for periods ranging from 13-22 days near the contour line marking the lower boundary of the zones, thereby limiting the area available for colonization during the dispersal period of a pioneer species. The second and less common mechanism involves the stunt- ing, by a constant river elevation, of the lower portion of a zone previously established by the above mechanism. The plants in the upper portion of the zone initiate normal spring growth but the lower, submerged plants must await a drop in river elevation be- fore growth can begin. Thus the development of what appears to be two vegetation zones from one previously established zone may occur. Both mechanisms require the maintenance of an appropriate river elevation during the waning period of general flooding.

Succession of small mammals on pine plantations in the Georgia Piedmont

Abstract: Populations of small mammals were sampled by removal trapping on 32 pine plantations, 1-15 years old. Twelve species were captured. One-year-old planta- tions supported dense stands of annual plants and primarily seed-eating forms of small mammals (Peromyscus leucopus and Mus musculus). By the 3rd year lesser vegetation consisted mostly of perennial grasses, and an herbivore (Sigmodon hispidus) predom- inated. Herbivores continued to be most abundant in 5-year-old plantations, but total catch of all forms declined sharply. The pine canopy closed at age 7 and total catch declined further, despite increased capture of woodland species. Fifteen-year-old stands supported very few animals. Comparison of trapping records with estimates of cover density at each trap site showed that P. leucopus and S. hispidus were associated with different densities of cover. Ground cover increased with plantation age, and this may have caused the succession of small mammals observed.

Food Habits of Stream Benthos at Sites of Differing Food Availability

Abstract: The food habits of 17 species of macroinvertebrates were examined and compared with the potential foods present in a small stream in northwestern Colorado. The majority of common species were small-particle herbivore-detritivores, but Hesperophylax consimilis and T?pula commiscibilis were large-particle detritivores. Isoperla patricia was the most common invertebrate predator. Hydropsyche oslari was eclectic in food habits, but was primarily a large-particle herbivore-detritivore with carnivory exhibited only by late instars. Only Hydropsyche and Isoperla showed significant size class differences in the composition of food ingested. No aquatic vascular plant material was identified in the gut contents of the species examined. Filamentous algae, although abundant at one location, were extensively utilized only as new growths or as decomposing fragments; however, epiphytic diatoms which extensively colonized algal filaments and vascular plant surfaces were an important food item. The use of t-tests following conversion of percentages to arcsin values showed that proportions of diatoms in the habitat and in the diets of macroinvertebrates were not significantly different. Nor did major dietary components differ significantly between sites despite considerable differences in food availability. Food ingested by herbivore-detritivores averaged 73% detritus, 22% diatoms and 5% filamentous algae. The similarity of food habits of herbivore-detritivores at different sites indicates that particle size, and possibly nutritive values, were the primary criteria determining food composition.

Behavioral Ecology of the Dragonfly Libellula pulchella Drury (Odonata:Anisoptera)

Abstract: The behavioral ecology of the dragonfly Libellula pulchella Drury was studied at four ponds in Minnesota. Males of this species are highly aggressive and defend a particular portion of the breeding site from all other males. Territories are established only in areas of the pond which have water free of surface vegetation, a sunny exposure and perch sites offering an unobstructed view of the territory. Males normally remain in the same territory throughout the day and are rarely displaced by other males. They are, however, seldom present at the site for more than 1 day. Ter- ritorial defense consists of patrol, pursuit and circle flights and physical attacks. The response of a territorial male to an intruder depends largely on its behavior. Non- territorial males are more likely to evoke intense aggression. A number of other odonate species, particularly those similar to L. pulchella in size and behavior, are also the objects of aggression. At high population densities the frequency of aggressive interactions in- creases and territory size decreases. High densities also result in increased interference with mating. Interference is reduced to some extent by the brevity of copulation and by male guarding and female avoidance behavior. Certain areas of the breeding site are more attractive to females, and males with territories there achieve the most matings. A number of abiotic factors including time of year, time of day, light intensity and tem- perature have a strong influence on the pattern of male and female occurrence at the pond. Peaks in abundance of both sexes occur within similar ranges of temperature and light intensity. The temporal peak in female abundance is shorter than that of males. Time of day and light intensity have a significant effect on abundance only within the range of temperature favorable for breeding activity. Beyond this range few dragonflies appear at the pond. Even when temperatures are favorable, a large proportion of a male's time is spent thermoregulating. By varying its perching posture in relation to the sun, this dragonfly is able to maintain thoracic temperatures within the range necessary for reproductive behavior and thus achieves a certain degree of independence from fluctuation in the ambient temperature.

Comparative carbohydate storage and utilization patterns in the submersed macrophytes, Myriophyllum spicatum and Vallisneria americana

Abstract: A prolonged dormant period for Vallisneria americana is one of the conspicuous differences between it and Myriophyllum spicatum, another submersed macrophyte with which it co-occurs in the littoral zones of lakes of Madison, Wisconsin. To test the hypothesis that ample storage of total nonstructural carbohydrates (TNG) by V. americana could support a growth to compensate for its shorter growing season, plant tissues were collected over two annual cycles and analyzed for TNC. Both species exhibited marked seasonal patterns in % TNC in above- and below-sediment plant parts. Mean TNC values in M. spicatum tissues ranged from 1.6 to 19.0% for roots and 2.0 to 20.0% for shoots. The low values were associated with the spring growth flush. Analysis of variance revealed significant differences in these TNC storage and utilization patterns for roots and shoots, plants collected at different sites and plants collected at different times. Vallisneria americana tissues ranged from 4% to 28% TNC during the growing season, while winter bud TNC values were ca. 45%. By virtue of low winter biomass, however, the total reserves in the Vallisneria community were inadequate to permit compensation for a late start in the spring, prompting us to reject our hypothesis.

Secondary Production of Epilithic Fauna in a Woodland Stream

Abstract: Epilithic fauna were sampled by placing three sets of 40 cobbles in transects across a riffle in Factory Brook, Massachusetts. One set was sampled monthly from September 1973 to August 1975, allowing 3 months for recolonization. Three Surber samples were collected concurrently during the last 12 months to provide biomass estimates of infauna. Length-wet weight regression equations and dry weight conversion factors were computed for genera; caloric equivalents were obtained from the literature. Surface area of cobbles was determined by a foil-areagraph technique. Secondary production on cobbles was calculated mainly by genus with the modified Hynes method. Mean standing stock in dry weight (DW) was 0.65 gDW/m2 of cobble surface in 1974 and 0.61 gDW/m2 in 1975. Insect production on cobbles in 1974 was 4.80 gDW/m2-year and 4.32 gDW/m2-year in 1975, or between 22.3-24.7 kcal/m2-year. Approximately half of the mean biomass and production on cobbles was attributed to four genera, Epeorus, Ephemerella, Hydropsyche and Acroneuria. Dipterans constituted 56% of the organisms collected but less than 20% of production; mayflies represented 53% of epilithic production. Annual turnover ratios were 7.4 and 7.1 in 1974 and 1975, respectively, and are a first estimate of community-based P/B for stream benthos in New England. Trophic level production efficiency between primary and secondary consumer groups agreed closely with previous studies on benthic communities in streams and may provide a simplified method for estimating secondary production. Total benthic production on the riffle, based on Surber and cobble sampling, was approximately 12.2 gDW/m2-year.

The Effects of Flooding on Floodplain Arthropod Distribution, Abundance and Community Structure

Abstract: Distribution, abundance and species diversity of selected arthropod groups were sampled by pitfall trapping over a flooding gradient in a Midwestern river bottomland forest. Species richness increased with elevation above the floodplain, and was inversely related to flooding frequency. Areas exposed to more frequent flooding also had greater variation in species richness. Abundance of all arthropods increased with elevation over the gradient, although individual groups showed some variation in distribution patterns. Seasonality of flooding was found to influence seasonal abundance of some groups differentially. Changes in arthropod abundance and diversity (owing to reservoir construction downstream) were predicted, using data on modified flooding regimes and subsequent changes in litter habitats. Consequences of reservoir impact on arthropod communities are discussed.

Movements of Larval and Adult Pycnopsyche guttifer (Walker) (Trichoptera: Limnephilidae) along Factory Brook, Massachusetts

Abstract: Drift distances of larval Pycnopsyche guttifer were determined from May through July 1975, on the basis of recoveries from 4100 larval cases marked with an acrylic pigment-epoxy mixture in a sequence of pools 1.5 km above the mouth of Factory Brook. Average drift distances for larvae released in May and early June ranged from 400-700 m before case attachment began in late June. Catastrophic drift after a rainstorm washed most larvae a considerable distance downstream. Three marked larvae, retrieved below the mouth of the stream, had traveled the 1.5 km in less than 25 days. No marked larvae were found upstream from their release pool. Directional movements of adults were determined by spreading a nondrying adhesive on nine house screens (three rows of three screens each} suspended over midstream and on six screens placed in trees adjacent to the stream. Captures on the midstream screens showed the number of females flying upstream to be significantly greater (p < .05) than the number flying downstream; directional movements of males were not significantly different. Adults collected on screens in the adjacent woodland exhibited no directional flight preference.

Microhabitat Utilization and Species Distribution of Sympatric Small Mammals in Southwestern Ontario

Abstract: To examine predictable patterns of small mammal species distribution several habitat measures were taken, and small mammal species recorded, in six major habitat types in southwestern Ontario. Peromyscus leucopus, P. maniculatus, Microtus pennsylvanicus, Tamias striatus, Zapus hudsonius and Blarina brevicauda were captured in large enough numbers for multivariate analysis. All species pairs except Blarina-Zapus were found to be significantly different in habitat utilization due to a combination of tree basal area, amount of vegetation between 0.25 m and 1 m, number ot trees, depth of dead grasses, leaves and other debris on the soil surface, and proportion of trees with first branches between 2 m and 3 m. Individual species predictably selected significantly different microhabitats. Species density of small mammals in southwestern Ontario was significantly correlated with the depth of dead grasses, leaves and other debris on the soil surface, a probable indicator of runway suitability and available productivity. Mean foliage height diversity was correlated with species density, whereas most measures of horizontal habitat heterogeneity were not good predictors of species number.

Nectar Production and Flower Visitors of Asclepias verticillata

Abstract: Asclepias verticillata is self-incompatible and can propagate vegetatively. Nectar is produced mainly between 1800 and 2200 hr, throughout the 4-5 day life of the flower. Insect visitations at this time were infrequent on all four study sites, a seemingly anomalous situation ; most pollinia vectors visited the flowers during the day. The most frequent vectors were Hymenoptera, especially wasps and honeybees, and Lepidoptera, especially moths and the introduced cabbage white butterfly. Most flower-visiting insects were nectar thieves, carrying no pollinia. None of the potential pollinators seem to be closely coevolved, morphologically or seasonally, with the flowering of A. verticillata. The probability of an individual flower being visited by a potential vector is very low, corresponding to the observed low percentage of pod set, but between-site differences in composition of the vector fauna (proportional similarities less than 36%) and rates of visitation were not correlated with differences in levels of fruit production. Our earlier studies of the floral display and fruit production of Asclepias (Willson and Rathcke, 1974; Willson and Price, 1977) showed that fruit set varied considerably within and between conspecific populations. Furthermore, casual observations indicated marked spatial variation in insect visitors to A. verticillata. Roadside populations could often be spotted at a distance by the clouds of pierid butterflies clustered over the flowers, whereas flowers in other areas were seldom visited by pierids. These observations suggested that different populations of A. verticillata might encounter such different pollinator faunas that differences in timing and success of fruit production might result. We examined both temporal and spatial variation of the insect visitors and potential pollinators of A. verticillata and monitored temporal patterns of nectar production. Specifically, we here address the following questions: (1) Which insect visitors carry pollinia and are potential pollinators, and which visit the flowers for nectar but do not carry pollinia, and hence function as thieves? (2) Does the rate of visitation, the composition of the fauna of potential pollinators, and the proportion of visits made by thieves vary between sites or seasonally? Can these factors be related to fruit production? (3) Can the temporal pattern of nectar production be related to daily patterns of flower visits by potential pollinators?

Pollination of three species of euphorbia subgenus chamaesyce, with special reference to bees

Abstract: Euphorbia albomarginata, E. capitellata and E. hyssopifolia together attract over 200 species of insect visitors to their cyathia; bees that are oligolectic on Euphorbia figure prominently among these in both number of species and abundance of individuals. Euphorbia albomarginata, a mat-forming plant, attracts three times as many species as the erect species E. capitellata and E. hyssopifolia. All insects pollinate the plants by "mess and soil" behavior. Bees are more effective pollinators than other in- sects by virtue of their frequent movement on cyathia and their ability to carry pollen. Bees are abundant on the large, conspicuous cyathia of E. albomarginata and E. capitel- lata, but are less common on the small, inconspicuous cyathia of E. hyssopifolia. Plant growth form (mat vs. erect) probably exerts a major influence on the number of insect visitors, but cyathial size determines the abundance of effective pollinators. The evidence suggests that these species of Euphorbia have not evolved in response to their associated bees, despite the important role of the bees in the pollination ecology of the plants. I NTRODUCTION In this paper I describe the insect fauna responsible for pollinating three species of Euphorbia subgenus Chamaesyce (Euphorbiaceae), and evaluate the amount of coevolution that apparently has resulted from the interactions of the plants and the pollinators. Euphorbia albomarginata T. & G. cannot set seed without insect visitors; E. capitellata Engelm. can produce only a small fraction of its normal seed set with- out insects, and E. hyssopifolia L. sets abundant seed in the absence of insects. All three species are self-compatible (Ehrenfeld, 1976). The cyathia of all three species are flat and radially symmetric, their nectar and pollen are readily accessible, and they are visited by a diverse group of insects, of which many are solitary bees that are obligately dependent on these plants for food. I hypothesized that if selection for coadaptation of plants and pollinators were occur- ring, it would involve the bees, which furnish reliable pollination. (Coadaptation is- here taken to mean the result of an evolutionary process in which interdependent selection pressures are exerted by two (or more) groups of organisms on each other, resulting in a reciprocating pattern of evolutionary change in both groups (Baker and Hurd, 1968; Ehrlich and Raven, 1964).) Coadaptation in this system might be manifested in the two insect-pollinated species of plants through special adapta- tions for promoting bee visits and discouraging other insects, and for increasing the efficacy with which bees pollinate the plants. Selection for coadaptation could also be demonstrated by differences in the plant-insect interactions between the insect- pollinated species and the self-pollinated species. In the course of testing these hypotheses, I have recorded the diversity of insects visiting these plants, and have assessed the effectiveness of the various kinds of insects as pollinators. The plants.-Euphorbia is characterized by a unique floral device, a cyathium, which is an inflorescence composed of many male flowers and one terminal female flower. Each flower consists simply of the sexual parts (in the case of the male flowers, a single stamen), and lacks calyx and corolla. They are tightly clustered within an involucre of five united bracts, each of which bears a nectar gland with an expanded petal-like appendage. Thus, the cyathium resembles a flat, simple

Stonefly (Plecoptera) Food Habits and Prey Preference in the Dolores River, Colorado

Abstract: Gut contents of 1013 stonefly nymphs, comprising nine species, from the Dolores River, Colorado, were analyzed from December 1974-October 1975 and compared with food availability. Pteryonarcyids ingested large quantities of detritus and some moss, moss being a substantial food item in later instar Pternarcella badia nymphs. Perlodids fed primarily on chironomids and simuliids, although Isoperla fulva also ingested mayflies in June. Claassenia sabulosa remained carnivorous throughout development: young nymphs ingested chironomids and small mayflies and larger nymphs ingested caddisflies and mayflies. Horn's Coefficient of Dietary Overlap indicated significant overlap between all perlodids and chloroperlids. It also showed significant overlap between small and large C. sabulosa nymphs, yet selection of different prey sizes indicated resource partitioning. A comparison of food habits with the Gunnison River stoneflies indicated differences between the diets of large and small Claassenia sabulosa, with chironomids comprising large percentages of the diet for both size classes in the Gunnison River and smaller nymphs in the Dolores. Mayflies were important prey for larger individuals in the Dolores River. These differences could be attributed to different prey populations in each river and/or to availability of prey in the particular size that each predator preferred. In both rivers, Chironomidae and Simuliidae larvae were the major prey in the guts of Cultus aestivalis and Isoperla fulva. This prey specificity may have been due to decreased availability of smaller individuals in the other major prey groups or a difficulty in capture of larger prey organisms. INTRODUCTION Fuller and Stewart (1977) discussed stonefly food habits and showed that seasonal-developmental shifts occurred in nymphal diets and food preferences among 10 species in the Gunnison River, Colorado. They also addressed dietary overlap, prey size electivity, resource partitioning and diel periodicity in feeding. Earlier studies by Muttkowski and Smith (1929), Hynes (1941), Brinck (1949), Jones (1950), Mackereth (1957) and Richardson and Gaufin (1971) dealt only with gut analyses and descriptive aspects of feeding. More recent studies have reported seasonal fluctuations in diets (Tarter and Krumholz, 1971; Sheldon, 1972; Vaught and Stewart, 1974; Cather and Gaufin, 1975), yet only one (Siegfried and Knight, 1976) contains information on prey availability. When feeding habits of specific taxa are compared between river systems, prey availability data are essential before any conclusions can be drawn about a predator's preference or selection for particular prey taxa. This article describes a study made of food habits and prey selection by nine stonefly species in the Dolores River, Colo. The research was done concurrently with that reported by Fuller and Stewart (1977) on the Gunnison River, Colo., and comparisons will be made for the eight species encountered in both rivers December 1974 October 1975. STUDY RIVER AND METHODS Headwaters of the Dolores River originate on the S slope of the San Miguel mountains in southwestern Colorado. The West and East Forks converge about 13 miles above Dolores, and the river flows southwestward to Dolores, thence north' Study supported in part by U.S. Environmental Protection Agency Traineeship #T900115 and North Texas State University Faculty Research Fund Grants # 34866 and 34905. 2 Present address: Department of Zoology, University of Toronto, Toronto, M5S, lAl, Ontario, Canada.

Vegetation and Soil Patterns on a Chihuahuan Desert Bajada

Abstract: Vegetation and soils were sampled along a 1100-m transect on a bajada in southern New Mexico to determine if present vegetation patterns can be interpreted from soil patterns. Species cover was measured in 66 plots, each 50.3 M2. Of these, 22 were randomly chosen as sites for soil pits, which were described and analyses conducted on the top (Al) horizon. The plots were clustered into four communities: Erioneuron pulchellum desert grassland transition, Larrea tridentata desert shrub, Bouteloua curtipendula semidesert grassland and Bouteloua eriopoda desert grassland. Soils of these communities differ significantly in pH, Mg, organic carbon and total nitrogen. These soil chemistry differences could be due to relatively recent changes from Bouteloua grassland to Larrea shrubland, as indicated by our dead shrub data and as documented for many bajadas in southern New Mexico. However, soil series and geomorphic surface patterns, which are not readily affected by recent vegetation changes, suggest that Larrea may always have been an important shrub on shallow calcareous soils (of erosional surfaces) in southern New Mexico. Its importance as a mosaic type in the once extensive desert grasslands has probably been underestimated.

Estimating coyote food intake from undigested residues in scats

Abstract: Average dry weights per occurrence in a coyote (Canis latrans) scat were determined for undigested fractions of mammals, birds, reptiles, arthropods, plants and seeds. Dry weights of these items are useful for estimating biomass originally ingested. Normalizing data produce an estimate of the coyote dietary. If coyote population densities and food intake rates were known, estimates of relative biomass taken from each prey population could be obtained.

Vegetation and Soil Pattern in a Mesophytic Forest at Ithaca, New York

Abstract: Vegetation and soil were sampled intensively in a 2-ha area of Mc- Gowan's woods, a rich, mixed deciduous forest at Ithaca, New York. The main vegeta- tation gradient was caused by moisture differences associated with a variation of 3 m in elevation, and Tsuga canadensis abundance caused a secondary gradient. The moisture gradient was accompanied by gradients in soil nutrients, pH and texture ; also the vegeta- tion gradient caused the mineral content of leaf litter to change. Hence, the "mois- ture" gradient is a complex gradient, with numerous variables changing together. Ordina- tion, particularly reciprocal averaging, was effective for analyzing these data. Correlation coefficients and canonical correlation analysis were less useful. McGowan's woods is exceptionally rich in species, probably because of disturbances. Its preponderance of phanerophytes and hemicryptophytes resembles southern or mid-temperate mesophytic forests.

Diversity of Small Mammals in a Powerline Right-of-way and Adjacent Forest in East Tennessee

Abstract: One year of trapping along a powerline right-of-way (ROW) in E Tennessee showed that diversity (H') of small mammals was highest in edge and ROW communities. Diversity was almost identical for ROW communities bordered by either pine or hardwood forest, suggesting that the composition of the adjacent forest has little or no effect on the diversity of small mammals inhabiting the ROW. Diversity in hardwood forest and edge was lower than in pine forest and edge.

Litter Accumulation in Four Plant Communities in the Dismal Swamp, Virginia

Abstract: Marshes and swamps are reported to exhibit the largest accumulation of litter among world ecosystems. The objective of the present study was to quantify litter accumulations in four plant communities in the Great Dismal Swamp, Virginia. The four communities differed by species composition and extent of flooding. Woody litter ranged from a minimum of 8428 kg ha-1 in the mixed hardwood community to a maxi- mum of 50,147 kg ha-1 in the Atlantic white cedar (Chamaecyparis thyoides (L.) BSP.) community. The ranking of communities based on quantity of 01 leaf litter in December was reversed with 4028 kg ha-1 in the cedar community and 5484 kg ha-1 in the mixed hardwood community. Intermediate values were obtained for the red maple-gum {Acer rubrum L. ? Nyssa spp.) and cypress (Taxodium distichum (L.) Richard) communities. Leaf litter pools decreased from December to August in all four communities. The gen- eral trend for community totals and most species was leaf biomass > maximum leaf litter standing pools > peak leaf fall. The dynamics of the Dismal Swamp litter layer are only partially defined presently but a study of decomposition rates and litter fall is in progress and should clarify the picture.