Showing papers in "Ecological Monographs in 1973"

Organization of a Plant-Arthropod Association in Simple and Diverse Habitats: The Fauna of Collards (Brassica Oleracea)

Abstract: Collards were grown at Ithaca, New York, in two experimental habitats: pure stands and single rows that were bounded on each side by diverse, meadow vegetation. The arthropods associated with these plants were sampled on 20 dates over a 3—year period. The status of the herbivore species was measured by their rank in biomass in each sample. The two most prominent species, Phyllotreta cruciferae and Pieris rapae, maintained high status throughout the investigation, but another important species, Brevicoryne brassicae, was absent for an entire season. Pit feeders usually formed the most important herbivore guild. Nevertheless, the guild spectrum, which describes the functional structure of the fauna, varied widely in time and space. The size distributions of species and of individuals were both highly skewed toward the smaller sizes. Herbivore loads, the mean biomass of herbivores per 100 g of consumable foliage, were consistently higher in the pure stands. Moreover, herbivore loads varied significantly with season in each experimental habitat. Both the number of herbivore species and the diversity of the herbivore load were greater in the diverse habitat. Biomass was more heavily concentrated among the prominent herbivores in the pure stands; increased dominance, rather than differences in species richness, appeared to be the major cause for the lower herbivore diversity in this habitat. The diversity of predators and parasitoids was higher in the pure stands. Most of the abundant species found on collards shared a similar narrow range of hosts. As a result the species in this core group of herbivores and parasitoids were regularly associated with each other. Predators and the less abundant herbivores tended to be less specialized and served to link the collard association with the surrounding community. Plant—arthropod associations are representative of component communities, well—integrated systems that form portions of larger compound communities. This distinction facilitates the analysis of community structure. Microclimates and the effectiveness of "enemies" did not appear to differ sufficiently in the two experimental habitats to account for the observed differences in the herbivore load. The results suggest a new proposition, the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments; and that, as a result, biomass tends to become concentrated in a few species, causing a decrease in the diversity of herbivores in pure stands.

Energy Flow in Bear Brook, New Hampshire: An Integrative Approach to Stream Ecosystem Metabolism

Abstract: An annual energy budget is presented for Bear Brook, a small undisturbed second-order stream in northeastern United States. The ecosystem approach, in which all input and output fluxes of potential energy as organic matter are considered, is used to describe the dynamics of energy flow in a 1,700-m segment of the stream. The annual input of energy to the system is 6,039 Kcal/m2. Over 99% of this is allochthonous, from the surrounding forested watershed or from upstream areas. Autochthonous primary production by mosses accounts for less than 1% of the total energy available to the ecosystem. Algae and vascular hydrophytes are absent from the stream. Meteorologic inputs (litter and throughfall) from the adjacent forest account for 44% of annual energy input. Most of this is in particulate form. The remaining 56% of input enters by geologic vectors (inflowing surface and subsurface waters). Eighty-three per cent of the geologic input and 47% of the total input of energy occur as dissolved organic matter. Approximately 4,730 Kcal/m2 of organic detritus, nearly equally divided between leaves and branches, is stored within the system. The size of this detritus reservoir is stable from year to year. The turnover time of the branch compartment is about 4.2 years; of the leaf compartment, about 1 year. Although much of the annual input of energy is in a dissolved state, dissolved organic matter does not tend to accumulate in the system and displays a very rapid rate of turnover. Sixty-six per cent of annual energy input is exported to downstream areas in stream water. The remaining 34% is lost as heat through consumer activity. Bear Brook is a strongly heterotrophic steady-state system in which import and export of organic matter play a significant role. A conceptual scheme is presented by which import, export, photosynthesis, and respiration may be used to describe the functional dynamics and developmental processes of ecosystems.

Nutrient Release From Decomposing Leaf and Branch Litter in the Hubbard Brook Forest, New Hampshire

Abstract: Rates of weight loss and nutrient release (N, P, S, K, Mn, Ca, Zn, Fe, Mn, Cu. Na) were measured in decomposing leaf and branch tissue from yellow birch, sugar maple, and beech, and in branch tissue from red spruce and balsam fir. Neither leaf nor branch decomposition differed significantly over an elevational range of 220 m. Decomposition rates for leaves varied with yellow birch > sugar maple > beech. The decomposition rate for hardwood branches was greater than that for conifer branches, but differences between hardwoods were not significant. Maximum decomposition rates occurred during the summer for both branch and leaf tissue. The rate of nutrient release from decomposing branch and leaf litter appears to be correlated with nutrient concentration in current litter fall, precipitation, and leaf wash. The concentration and absolute weight of N, S, and P in the leaf litter of all species increased with time. The amount of the increase as well as the initiation of nutrient release was influenced by C:element ratios in the leaf tissue. These studies also indicate that P levels can influence the mineralization or immobilization of other important nutrients. Carbon-to-element ratios in decomposing litter varied between species and elevation at different times of the year, but element:P ratios were much more uniform. In branch tissue the physical loss of N- and P-rich bark and buds offset any increase in concentration that would have occurred through decomposition. Potassium and magnesium were rapidly released from the litter by leaching. Similar minimum concentrations in leaf tissue indicate that critical C:element ratios also exist for these elements. Calcium release was similar to dry weight loss, indicating that it is a structural component primarily released by decomposition. Maximum nutrient release from current litter occurred in the autumn and summer. It was not correlated with the nutrient output from the ecosystem which occurred primarily

Ecology of a New England salt marsh

Abstract: Measurements of the abundance of major populations, their metabolism, and the seasonal patterns of total system metabolism throughout a year were used to develop energy-flow diagrams for a New England salt-marsh embayment. The annual ecological energy budget for the embayment indicates that consumption exceeds production, so that the system must depend on inputs of organic detritus from marsh grasses. Gross production ranged from almost zero in winter to about 5 g 02 m-2 day-' in summer. Respiration values were similar, but slightly higher, with the maximum difference observed in fall. Populations of shrimp and fish were largest in fall, with a much smaller peak in spring. Few animals were present in the embayment from May to July, but fall populations of shrimp ranged from 250 to 800 m-2 and fish averaged over 10 m-2. Birds were most abundant in winter and spring. In spite of high numbers, no evidence was found that the marsh embayment exported large amounts of shrimp or fish to the estuary. Production of aboveground emergent grasses on the marsh equaled 840 g m-2 for tall Spartina alterniflora, 432 g m-2 for short S. alterniflora, and 430 g mr2 for S. patens. These values are similar to those for New York marshes, but substantially lower than the southern marsh types. The efficiency of production of marsh grasses in the New England marsh was lower than reported for southern areas. A simulation model based on the laboratory and field metabolism and biomass measurements of parts of the embayment system was developed to predict diurnal patterns of dissolved oxygen in the marsh. The model was verified with field measurements of diurnal oxygen curves. The model indicated the importance of the timing of high tides in determining oxygen levels and was used to explore simulated additions of sewage BOD and increases in temperature.

Pattern and Process in Grassland Bird Communities

Abstract: Variations in abundance and distribution of bird species and avifaunal and community organization at regional, local, and within—plot levels were studied during 1969 and 1970 at a shortgrass prairie in Colorado and during 1970 at six additional International Biological Program (IBP) grassland sites. Patterns were generally not distinct at the regional level, although low rainfall sites tended to support fewer individuals and less biomass than more mesic sites. The dominant bird species were widely distributed, but 70% of all species recorded were present at only one of the seven sites. Local plot—to—plot differences, associated with grazing intensity, were considerably more important than the regional differences. Vegetational and avifaunal relationships of plots were determined by similarity—cluster analysis and by examination of vegetation structure. Variations in the number of breeding bird species, bird—species diversity, or equitability, were unrelated to the gradient of plots from tallgrass through shortgrass to desert, but standing crop biomass generally decreased along this gradient. The plots differed in the proportions of small, medium, and large—sized species. Shortgrass sites were generally dominated by omnivorous species; plots with a greater vegetation structure supported more carnivorous forms. Only carnivorous species occurred at the desert site. The effect of grazing on bird populations varied among the treatment plots at the various sites. In the Colorado shortgrass prairie, grazing season had a greater effect on community organization than grazing intensity. Patterns of variation were much more pronounced when single species rather than breeding faunas were considered. Grasshoppers, Lepidoptera larvae, beetles (especially curculionids, carabids, cerambycids, and scarabaeids), ants, and various seeds were the most important prey of the dominant bird species. Small sparrows and larks had generally similar diets. The diets of the larger meadowlarks and shorebirds differed from those of the former group and also differed from each other. The proportion of seeds and arthropods in the diets of Lark Buntings and Horned Larks varied considerably with time. Diurnal raptors, studied at only one site, were widely dispersed, occurring at densities and standing crops substantially less than those of small passerine populations. Owls preyed chiefly upon small mammals and insects, but the proportions of these food items in the diet differed significantly among the four species studied. The estimated energy intake of the breeding bird populations from April through August ranged from 1.01 to 2.33 kcal/m²; thus the energy flux through avian consumers in grasslands is apparently very small. In general, seeds decreased in importance as energy sources and arthropods increased in importance along a gradient from shortgrass through mixed grass to tallgrass plots. Secondary production estimated for six grazing—treatment plots ranged from 3.9 to 6.9 x 10— ³ g/m². The role of birds as consumers in the dynamics of grassland ecosystems is considered. It is suggested that birds may act as controllers of other elements of system function or may not be closely evolved into the functional framework of the ecosystem at all, existing on "excesses" in production.

Regulation of Numbers in an Island Population of the California Vole, A Problem in Community Dynamics

Abstract: A population of California voles, Microtus californicus, living on Brooks Island in San Francisco Bay was studied for 13 years. During the first 2 years following its establishment, the performance of the population was significantly different from that in the subsequent 11 years. The 11—year pattern that developed is characterized by: (1) annual peaks in abundance; (2) a delay of up to 5 months between the return of wet season conditions and population growth; and (3) an alternating pattern of "high" and "low" winter densities. Reproduction shows a strongly seasonal pattern, beginning 1—2 months after the start of the rainy season and ending with the desiccation of the vegetation in June. In contrast to this, reproduction started promptly with the autumn rains during the initial 2—year colonization phase, and limited summer reproduction occurred as well. Within the breeding season, litter size and number of corpora lutea produced per ovulation episode show marked seasonal changes which appear to be independent of annual variations in demographic detail and condition of the mice. Males are more vagile than females, although both show a reduction of movements during the main breeding period. The incidence of wounding was positively correlated with reproductive condition in males, but not in females. Mortality schedules were studied by means of population age structure, recruitment rates, and sex ratios. Apparent aging ceases for almost 5 months from about 1 month after the dry season begins to 60 days after it ends. This period is associated with heavy mortality, particularly among old males and young females. Consequently, late fall and early winter sex ratios favor males. In general, however, females survive longer than males, and during the breeding season the sex ratio progressively favors females. Recruits first appear 1—2 months into the wet season, but initially their numbers are very few and are insufficient to reverse population declines. Rapid population growth in late spring is largely dependent on reproduction by these early recruits. Physiological condition was measured by study of body—weight changes, particularly ratios of body weight to body length, ectoparasite loads, including scabies mite infections (mange), and molting patterns. The body—weight data reveal that wet season condition, especially in spring, is much better than dry season. Surprisingly, males begin to recover during the winter period whereas females continue their decline. Moreover, the whole pattern of weight losses is more severe in poor survival summers than in the alternate ones. A flea—mite index reveals a strong seasonal pattern which seems to be induced by vole demography; during the colonization period, ectoparasites were barely noticeable. It took 4 years for scabies to reach significant levels of infestation. Highest incidence generally occurs in winter, and an outbreak occurred in the seventh winter; subsequently, the mange mites returned to endemic levels. Molt activity showed two strongly marked seasonal peaks, one in the late spring—early summer and one in the autumn. Males molt at a slower rate than females; female molt is strongly inhibited by reproduction. The autumn molt begins before the wet season arrives suggesting a photoperiodic cue. During colonization, molts were completed more quickly than afterwards. The quasi 2—year cycle of regularly recurring peaks every year and alternating high and low winter densities which came to characterize the Brooks Island vole population is considered to be the result of a regulation process in which a multiplicity of factors interact to achieve regulation. Both density—unresponsive and responsive factors are involved: unresponsive–rainfall pattern, photoperiod and/or gonadotrophic potency of diet, heavy autumn dews, and possibly winter sex ratios favoring males; responsive–dry season resource levels, long—term physiological damages, and ectoparasite load, including scabies infections. The first two factors in each category are probably the essential ingredients. During the colonization phase, regulation involved the additional factors of emigration and possibly intraspecific strife of some sort. Finally, a model is proposed to explain the longer term cycles in abundance presumably characterizing mainland populations. It is suggested that a 2—year cycle (peak every other year) would be generated without the involvement of mammalian predation. Such a cycle would result from the action of all the essential factors proposed for Brooks Island, plus a supposedly more severe dry season and much more extensive emigration. Longer term cycles probably require the further addition of mammalian predators to this complex. Thus, changes in numbers in this species can be explained most satisfactorily in terms of the interacting effects of at least six variables.

Niche Relationships Among Six Species of Shorebirds on Their Wintering and Breeding Ranges

Abstract: The dynamics of the organization of a community of six species of migrant predatory shorebirds (Least Sandpiper, Semipalmated Sandpiper, Dunlin, Short—billed Dowitcher, Lesser Yellowlegs, and Semipalmated Plover) was appraised by studying foraging behavior and habitat utilization under winter conditions in southern Florida and under summer conditions in the eastern Canadian Arctic. Eight foraging methods, defined primarily on the basis of how the bill is used and the pattern of locomotion, constitute the behavioral repertoire of the species. Each foraging method is correlated with a particular rate of locomotion (distance/time) and rate of feeding (pecking or probing/time). Feeding and locomotion rates seem independent of air temperature, number of conspecifics, and total number of shorebirds foraging nearby. Instead, the seasonal changes in these rates are probably related to food density. On the basis of these findings and of differences in rates of feeding and locomotion between species the most reason...

Growth, Production, and Community Composition of Fishes Inhabiting a First-, Second-, and Third-Order Stream of Eastern Kentucky

Abstract: Fish populations in a first—order, a second—order, and a third—order stream were studied during the summers of 1967—68. The primary food of each fish species was determined. Available food sources included terrestrial invertebrates, aquatic primary production, aquatic invertebrates, aquatic vertebrates, and detritus. Average daily growth rates showed that age—group I fish of most species grew faster in early than in late summer. The growth rate of most age—group II fish varied little between these seasons. Total numbers, total standing crop, and gross production were estimated for each species in each order. Total production was compared among stream orders on a per linear meter basis. Production values were nearly equal in first (2.35 g dry weight per linear meter) and second order (2.36), but increased in third order (3.29). The relative importance of terrestrial invertebrates as an energy source decreased with increasing stream order. Aquatic primary production and aquatic invertebrates began to be utilized as energy sources in second order. The aquatic vertebrates and detritus began to be utilized in third order. The relative importance of aquatic primary production utilization increased in third order, but the relative importance of aquatic invertebrate utilization was approximately the same as in second order. The community structure of the fish populations of each pool was analyzed the information theory and the ratio H/Hmax. Community structure differed between third—order and second—order pools even when the same species complement was present. It is postulated that stream order in most cases represents a biological unit which can be subdivided into microhabitats based on riffle, pool, type of substrate, etc., and addition in most cases proceeds by discrete units of stream order.

Energy Allocation in the Allegheny Mountain Salamander, Desmognathus Ochrophaeus

Abstract: The reproductive cycle, energy budget, and relationships between rates and energetics of vitellogenesis, lipid deposition and depletion, and changes in lean carcass tissue were examined in Desmognathus ochrophaeus salamanders from northeastern Ohio Oviposition begins prior to emergence in mid-April, reaches a peak in mid-May, and continues in greatly reduced frequency into September Lipids in the carcass and ovarian fat bodies apparently are used for maintenance and vitellogenesis during winter dormancy (mid-October to midApril) and after emergence in the spring when food reserves are scarce Carcass lipids, lean carcass tissue, and perhaps fat body lipids are used for maintenance during brooding A typical female oviposits in mid-May, replaces depleted lipids and lean carcass tissue by late August, and produces intermediate-sized follicles before winter and full-sized follicles during April and early May Energy ingested, egested, assimilated, and lost through respiration was examined in gravid females, spent females, and males acclimated to four temperature-photoperiod regimes: (1) 50C, LD 10:14; (2) 50C, LD 14:10; (3) 15WC, LD 10:14; and (4) 15C, LD 14:10 Size, sex, reproductive condition, and temperature significantly influence energetics in D ochrophaeus Photoperiod does not affect metabolism significantly at either temperature There is an inverse exponential relationship between body weight and weightspecific rates of ingestion, egestion, assimilation, and respiration Gravid females, actively depositing yolk in follicles, show higher 02 consumption rates than recently spent females and males at 15'C, but not at 50C when yolking rates apparently are reduced Rates of 02 consumption are significantly higher at 15'C than 50C At 150C gravid females, spent females, and males lost 432, 360, and 384 cal g-1 day-' as metabolic heat; at 50C they lost 192, 192, and 168 cal g-1 day-', respectively Salamanders cease to feed at 5VC At 15'C gravid females, spent females, and males ingested 210, 378, and 238 cal g-1 day-' and egested 27, 51, and 29 cal g-1 day-', with assimilation efficiencies of 872%, 863%, and 882%, respectively The estimated annual energetics of a typical female are: ingestion = 2,940 cal; egestion = 378; assimilation= 2,562; respiration= 1,1044; and secondary production = 1,4576 Reproductive activities (vitellogenesis = 8075 and brooding maintenance = 430 cal) cost 483% of a female's annual energy flow (A = 2,562 cal)

Periphyton Dynamics in Laboratory Streams: A Simulation Model and Its Implications

Abstract: A simple and an expanded model of periphyton dynamics in lotic environments are described. The simple model includes one level variable, the biomass of the periphyton assemblage, and four rate variables: primary production, community respiration, and two export fractions. In the expanded model three level variables and eight rate variables are added to the simple model to introduce the effects of allochthonous organic matter and grazing activities by an aquatic snail. In general, computer output from the expanded model supports the hypothesis that the relatively low biomasses of periphyton observed in the small streams of western Oregon are the result of grazing activities by aquatic animals, high silt loads during the fall and winter months, and the effects of a dense canopy of terrestrial vegetation on light penetration. Furthermore, the model indicates that it is bioenergetically feasible for a periphyton biomass of about 10 g m— ² ash—free dry weight to support a consumer biomass of 150 g m— ² or more if the productive capacity of the system is sufficient. The simulation models provided an analytical way of synthesizing the results of a number of experiments with periphyton assemblages, identified weaknesses in the experimental data, and provided insights into the dynamics of periphyton assemblages that could not be obtained by intuition alone or by examining the results of individual experiments.

Consumption of Primary Production by a Population of Kangaroo Rats (Dipodomys Merriami) in the Mojave Desert

Abstract: The energy requirements for a population of kangaroo rats in the Mojave Desert were estimated indirectly. Energy expenditure for maintenance was 84.1 megacal ha—1yr—1. Total energy expenditure for growth was 1.4 megacal ha—1yr—1, half of which was secondary productivity. Secondary productivity was 0.8% of the total energy flow. This percentage of the total energy flow is lower than for nondesert rodents and may be due to the low productivity of the desert areas in which D. merriami is found. The diet of D. merriami contained an average of 75% seeds. Green herbage formed 35% of the diet during the winter quarter. Kangaroo rats showed a high preference index for Erodium cicutarium seeds, which were larger and had a higher caloric value than the seeds of other annual plants. The average assimilation efficiency was 0.87 for the natural diet. Estimates indicated that kangaroo rats consumed 97.8 megacal ha—1yr—1, 99% of which was from the primary production. Total net primary production (NPP) on the study area was only 1,400 megacal ha—1yr—1; of this, 900 megacal ha—1yr—1 was considered to be available to D. merriami. Kangaroo rats consumed 6.9% of the NPP. This is higher than for any other rodent populations that have been studied and is probably due to the large proportion of available production (AP) in the total primary production (64%). The population consumed 10.7% of AP, which is high when compared to most other rodent species. The high consumption efficiency for D. merriami may be an adaptation to areas of low production, or it may be simply the result of high densities of kangaroo rats in areas of low production. Dipodomys merriami consumed over 95% of the estimated Erodium production and 90% of the total Erodium production. It is estimated that the rats consumed a sufficient number of Erodium seeds in 1970 to reduce the density of that plant by more than 30% in 1971. The D. merriami population was on the brink of overexploitation of its food sources and was potentially food limited. It is probable that desert herbivores in general are food limited since productivity in the desert is so variable.

Late Pleistocene Palynology and Biogeography of the Western Missouri Ozarks

Abstract: Palynological investigations of spring deposits were conducted as part of an interdisciplinary research effort into late Pleistocene archaeology, geology, and paleoecology of the western Missouri Ozarks. The springs, located in the Pomme de Terre River valley in Benton and Hickory Counties, Missouri, lie 400 km south of the maximum extent of the Wisconsin ice sheet on the present Great Plains—Eastern Deciduous Forest border. The valley will soon be flooded by a government impoundment. Two springs were completely excavated and three others sampled, including a spring originally excavated by Albert Koch in 1840. The pollen record, with associated plant macrofossils, is divided into three distinct zones: a lower nonarboreal pollen (NAP) and pine zone, a middle spruce— (Picea) dominated zone, and an upper zone of spruce with deciduous elements. Radiocarbon dates show that the NAP—pine zone was established prior to 40,000 BP and existed until 20,000—25,000 BP; it was deposited during the mid—Wisconsin interstade. The mid—Wisconsin interstadial vegetation of the Ozarks is interpreted as an open pine—parkland. Plant macrofossils of Pinus banksiana in this zone indicate that jack pine was present. Spruce was probably absent as no spruce macrofossils and only traces of spruce pollen were found. The associated mid—Wisconsin fauna is dominated by mastodon (Mammut americanum) with horse (Equus) and musk—ox (Symbos). With the onset of late Wisconsin full—glacial conditions, variously dated at 20,000—25,000 BP, pollen dominance shifts from NAP—pine to spruce. This is interpreted as the replacement of the pine—parkland by boreal spruce forest. Two pollen zones are apparent within the full—glacial: an older zone with up to 92% spruce pollen occurring after the transition from NAP—pine to spruce, and a younger zone with less spruce (38%) and more thermophilous deciduous tree pollen. The change to less spruce and more deciduous tree pollen apparently reflects slightly improved climatic conditions during a late phase of the full—glacial; the zone is radiocarbon dated at 16,500 BP on spruce logs. It contains abundant spruce and larch (Larix) macrofossils associated with the remains of at least 30 mastodons plus giant beaver (Castoroides), ground sloth (Paramylodon), tapir (Tapirus), deer (Odocoileus), and horse (Equus). The western Missouri Ozarks were covered by open pine—parkland from at least 40,000 BP until the start of the full—glacial 20,000—25,000 BP, then boreal spruce forest until at least 13,500 BP. Deciduous elements became more prominent in the spruce forest in its latter phase. The present oak—hickory forest developed after the decline of the spruce and is thus no older than postglacial.

Population Biology of the Yellow-Breasted Chat (Icteria Virens L.) in Southern Indiana

Abstract: A population of color—banded Yellow—breasted Chats was studied during the breeding seasons of 1966 through 1970 on 18 ha of upland deciduous scrub habitat near Bloomington, Monroe County, Indiana. The number of breeding males varied between five in 1970 and eight in 1966, and the number of territorial, nonbreeding males ranged from two in 1968 and 1969 to five in 1967. During the spring migratory period the capture rate of unbanded males per 100 net—hours varied between 1.40 in 1970 and 3.48 in 1969 (pooled mean = 2.57); the capture rate of females varied between 0.59 in 1970 and 3.88 in 1967 (pooled mean = 1.49). Capture rates of unbanded birds were considerably lower after the end of the spring migratory period (pooled mean capture rate of unbanded males = 0.24; unbanded females = 0.24). Approximately 50% of the males and females captured during spring migration and 75% of those captured in the summer did not settle on the study area; the rest were resident there. The sex ratio of both the breeding and the transient populations did not differ significantly from 1:1. The mean size of territories varied between 1.12 ha in 1967 and 1.58 ha in 1970 (pooled mean = 1.24 ha); territory size did not differ significantly among years. When territorial males disappeared, the vacancies in most cases were filled either by the settlement of new males or by expansion of the territorial boundaries of neighbors. New males that settled usually acquired females, which attempted to reproduce. In the absence of vacancies new males were prevented from settling by the presence or behavior of the established males. The replacements on and transients through the study area of both sexes were not necessarily birds without previous breeding experience and, in the case of males, territories in the seasons involved. The males may have abandoned territories elsewhere, or they may have wandered onto the study area from territories still held. The females had bred elsewhere; they had probably experienced nest failure and some, at least, were in the process of changing mates. Only one male was polygnous; all others formed pair—bonds with a succession of females, or remained paired to one female the entire time they were on the study area, of were for a time paired to one female and for a time unpaired. Of the males that experienced nest failure and bred again, 50% did so with new mates. No females and only 11% of the breeding males returned to the study area in the years following first capture. Nest success varied between 0.0% in 1970 and 38.5% in 1966 (pooled mean = 22.4%). Nests that were begun in late June and July succeeded in significantly greater numbers than nests begun early. Approximately 94% of the nest failures were attributed to predators. The number of young produced varied between none in 1970 and 24 in 1966. If each territory on the study area had been occupied for an entire breeding season by monogamously and polygynously mated males and unmated males in the same proportions as were observed, it is estimated that the population would have produced, on the average, 1.19 young per territory per year. This estimated mean potential productivity probably would not have produced enough young to replace estimated annual losses to the population. The area was, therefore, unfavorable habitat on which the chat population had to be maintained by immigrants in excess of emigrants. The low productivity resulted from a combination of nest predation and early cessation of reproductive activities in some years.

Density, Dispersion, and Population Structure in Drosophila Pseudoobscura

Abstract: Wild D. pseudoobscura flies were captured, marked, and released in relatively low numbers at nine separate, centrally located sites in each of two Colorado, U.S.A., locations in midsummer 1970. The flies were marked by spraying with micronized dusts which fluoresce in characteristic colors under ultraviolet light. The dusts are harmless, they mark the flies well, and they are not transferred from one fly to another. The trapping design extending out from the central release points contained additional traps on eight evenly spaced radii. Data on the number of captured, unmarked flies and recaptured, marked flies in the central and outlying traps provided maximum likelihood estimates of adult density and dispersion. These data were adjusted for the presence of a sibling species, D. lowei, by means of an accurate morphological technique which permits classification of the two kinds of males. Preliminary analyses indicated that dispersal estimates made during an evening activity period 1 day after release of marked flies pertain mostly to dispersion during the intervening morning activity period, when no traps were exposed. It was necessary to base estimates of both density and dispersion on trapping days following days when only a few or no traps had been exposed in the habitat. The minimum attractive radius of a trap was approximately 46 m. The estimates of density at both locations were similar, averaging 0.38 flies/100 m2. An independent and much simpler estimate of density, based on the number of flies captured at the center trap, gave inconsistent results. This was attributed to accidental interference with normal fly activity. The mean distance (d) of marked flies from the release points after 1 day (presumably after one morning activity period) was 176 and 202 m at the two locations. The mean—squared distance (d2°) was 97 and 146, respectively, in units of 400 m2. The estimates for the first location are more reliable because those data were more homogeneous and extensive. The patterns of the observed dispersion agreed well with Brownian motion expectations on the basis of comparing first— and second—order moments of distance dispersed. This permitted the construction of graphs which depict the spread of released flies with an increasing number of activity periods. An activity parameter °, the standard deviation of dispersed flies along one direction in a two—dimensional environment, was estimated from @ under the assumption of Brownian motion (°b.m.) and without this assumption (°D.F.). These estimates refer only to the observed dispersion. At the first location the values were 141 and 139 m, respectively; at the second they were 162 and 171. Closer inspection of the observed dispersal patterns, accompanied by further analyses of the data, revealed a departure from Brownian motion and probably serious underestimates of the true dispersal rates. A certain proportion of flies dispersed rapidly to points outside the experimental area during the morning activity period following an evening release. Using an estimate of 95.3% daily survival of marked flies, 2—day dispersal data suggested that more than half the flies had moved beyond the experimental area in two morning activity periods. The earlier experiments on density and dispersion of D. pseudoobscura, conducted by Dobzhansky and Wright in California, were re—analyzed by the present methods. Midsummer density of wild flies in Colorado was one—seventeenth that on Mt. San Jacinto in southern California, and three—fifths that at Mather in the Sierra Nevada of central California. Comparison of °d.f. estimates indicated that the wild Colorado flies dispersed at a rate approximately 50% greater than the laboratory flies released in California, even though the latter probably had more opportunity for dispersion. This difference may result partly from an adaptive strategy for greater dispersion of flies in low density habitats, and partly from a fundamentally different behavior of wild and laboratory flies. The large values of °d.f. (which are underestimates due to dispersion beyond the experimental areas) in both Colorado and California suggest that natural populations of D. pseudoobscura are not broken up into a number of very small breeding units within which allelic variation could be stored by genetic drift. Wright's panmictic circle concept yielded estimates of effective population size (Ne) between 1,000 and 10,000 in both Colorado and California. According to existing theory, these values are not large enough to maintain the allelic diversity known to exist for certain enzyme loci. The need for more sophisticated experiments to determine which components of dispersion are most closely associated with distribution of emergence sites of parents and offspring is discussed.

Distribution of Major Forest Species in Southeastern Pennsylvania

Abstract: Vegetation and environment of 82 forest stands in Lancaster, York, and Lebanon Counties in southeastern Pennsylvania were studied to determine the factors controlling the location of major forest species. Plants of some species were transplanted into 12 stands in which certain environmental factors were checked each week for two growing seasons. Thirty—six per cent of the 82 stands were the oak—hickory type, in which Quercus alba, Q. velutina, Q. coccinea, Carya ovalis, and C. tomentosa were among the leading dominants. Representatives of these oak—hickory forests have very low soil moisture for extended periods of time even in a year of normal rainfall. Quercus prinus was among the main dominants in 43% of the stands, representatives of which show excellent soil—moisture conditions even in a year of severe drought. Tsuga canadensis, Quercus rubra, Fagus grandifolia, Betual lenta, and Acer saccharum were among the leading dominants in 27% of the stands; representatives of these mixed mesophytic stands sho...

Vegetation of the Big Horn Mountains, Wyoming, in relation to substrate and climate

Abstract: The vegetation of the Big Horn Mountains is typical of the Central Rocky Mountain region; a lower Juniperus osteosperma zone is followed by Pinus ponderosa, Pseudotsuga menziesii, Pinus contorta, and Picea engelmannii-A bies lasiocarpa zones. Rock or geologic substrate type has a strong influence on forest vegetation. On sedimentary areas forests cover less that 50% of the area and are composed of Pseudotsuga menziesii or Picea engelmannii-Abies lasiocarpa. On granitic substrates forests cover over 80% of the surface and are composed chiefly of Pinus contorta with Picea engelnannii-A bies lasiocarpa at higher elevations. Populus tremuloides is present but unimportant as a vegetation type. Most of the rainfall comes during March, April, and May; precipitation is less than 30 mm per month during summer. Thus soil-water relationships are important in determining vegetation pattern. Precipitation comes from the east, which allows forest vegetation to reach lower elevations on the east than on the west slope.

Ecology of Knobcone Pine in the Santa Ana Mountains, California

Abstract: Knobcone pine (Pinus attenuata) is restricted in the Santa Ana Mountains to hydrothermally modified serpentinite which supports only limited shrub growth as opposed to the surrounding dense chaparral on nonspecialized substrates. Ceanothus papillosus var. rowaenus and Ribes malvaceum var. viridifolium are also restricted locally. The pines survive on the serpentinite by tolerating the existing edaphic conditions, including nitrogen and phosphate deficiencies and low pH, and because the otherwise dense competitive growth has been minimized. The water—retaining capacity of the serpentinite is nearly double that of the chaparral soils. This soil characteristic, the frequent fogs, the location of the pines in fog gaps, the scattered growth, multiple—trunked trees, spreading crowns, and medium—length needles all contribute to the persistence of the pines by enhancing their ability to intercept marine air and produce considerable fog drip which is readily held by the soils. The controlling influences of the serpentinite diminish as soil genesis advances. This is countered by the dynamic expansion and uplifting of the serpentine body and by continuous erosion which is linked to the friable geology, typically steep slopes, thin soils, sparse cover, and repeated disturbance by fire. The life cycle of these knobcone pines is related to fire, and its periodic occurrence is a necessity for survival. The pines possess a strict closed—cone habit, with firmly attached cones accumulating throughout the life of each tree. The seed remains until heat generated by a fire opens the cones. Cones are seldom burned, and the seed is not shed until well after the fire, remaining viable for at least 3 years in opened cones. Fire creates pioneer conditions necessary for seedling establishment. Trees have a short lifespan and occur in even—aged groves that date back to known fires.

Dry Matter Production in Young Loblolly (Pinus Taeda L.) and Slash Pine (Pinus Elliottii Engelm.) Plantations

Abstract: The net primary productivity of the pine species and lesser vegetation (herbaceous ground cover) plus turnover rates between the litter layer and soil organic matter were investigated in young loblolly and slash pine plantations in Beaufort County, North Carolina. Estimations of the aboveground tree biomass and production by components were made by applying multiple regression, weight-prediction equations developed from harvest data ( 1 5 slash pine and 41 loblolly pine trees) *to tree dimensions from 28 permanent, undisturbed plots. Optimal plot size was determined by time-cost analysis. Total biomass for slash pine

Rock‐Face Populations of the Mountain Salamander, Desmognathus Ochrophaeus, In North Carolina

Abstract: The ecology and life history of Desmognathus ochrophaeus inhabiting wet rock faces at high elevations near Highlands, North Carolina, were studied. Comparisons were made with rock-face populations in Great Smoky Mountains National Park and with woodland populations at Rabun Bald, Scaly Mountain, and Blue Valley in the Blue Ridge Mountains. The reproductive cycle in rock-face populations is annual; spawning occurs mostly in July and August, and females begin to emerge from brooding as early as late August. The new spermatogenic cycle begins in May and June. Animals on rock faces average 40-45 cm in movements between successive captures and appear to have a limited range. Animals displaced to the base of the rock face and higher on the rock face can return to their home range. Population density is high (up to 25 individuals/M2), diurnal activity is nearly as high as nocturnal activity (correlated with subdued body colors), and at least a moderate level of activity occurs during warm winter periods. Animals mature at 2 years of age as in woodland populations, but at a smaller size, and grow more slowly thereafter. Small body size is not due to paucity of food on the rock faces. The high population densities on the wet rock faces indicate that they are highly favorable habitats for D. ochrophaeus. Differences between rock-face and forest-floor populations are attributable to modified selective pressures in the two different ecological settings. Variation among rock-face populations is attributed to the intensity of selection for small body size and cryptic coloration, the size of the rock face, and variation among forestfloor populations from which they were derived. Since rock-face populations are linked genetically to surrounding forest-floor populations of D. ochrophaeus, they cannot be considered examples of taxonomic variation, but rather of ecotypic variation.

Responses of continuous-series estuarine microecosystems to point-source input variations.

Abstract: Six continuous—series microecosystems, each containing five cells, were constructed to simulate hydrological factors of estuarine regions. Exchange and retention characteristics were adjusted to closely model the hydrological conditions of Trinity Bay, Texas. The metabolic and structural responses of the microecosystem communities to quantitative and qualitative changes in freshwater input were investigated. Primary production and community respiration in the first three cells of the microecosystems were dependent on both quantity and quality of freshwater input, whereas primary production and community respiration in the saltwater portions (cells 4, 5) of the microecosystems were virtually independent of the quantity and quality of freshwater input. Metabolism of the freshwater portions of the microecosystems was heterotrophic under normal flow conditions and autotrophic under drought conditions. Addition of an industrial effluent to the freshwater inputs resulted in extensive shifts towards metabolic heterotrophy of the more freshwater portions of the microecosystems. Metabolism of the saltwater cells was heterotrophic under all conditions of freshwater input. The upstream communities were adapted to a dependency on allochthonous materials input for production and respiration maintenance. Retarding freshwater input resulted in tying up larger portions of the nutrient pool within the systems in living components. Addition of industrial effluent increased the community maintenance requirements. Retarding freshwater input acted as an environmental stress on the first three cells of the microecosystems. Magnitudes of production and respiration were significantly lower, and zooplankton standing crops and species diversity decreased significantly. Addition of industrial effluent produced similar effects. Decreased freshwater input rate (primary stress) rendered the receiving communities more susceptible to the industrial effluent addition (secondary stress). The organismal composition of the microecosystems was qualitatively similar but quantitatively dissimilar to the organismal composition of Trinity Bay. Because of fundamental similarities in all living systems, the observed responses might be especially representative of those which would occur in Trinity Bay if subjected to similar hydrological alterations.

Size‐Association Analysis of Forest Successional Trends in Wisconsin

Abstract: A method for quantitatively evaluating the successional relationships which exist between species was tested on data from Menominee County, Wisconsin. The method is based upon an examination of the changes in interspecific association which occur when successively larger diameter classes of one or both species are used as the basis for the calculation of an association index. With this method it is possible in most cases to determine which species tend to replace which others. In addition, by averaging replacement tendencies in various ways, index values can be arrived at which express the degree to which a particular species may be characterized as pioneer or climax. The results of the analysis agree well with other studies on succession in these forests. This method should prove useful in elucidating successional relationships, especially in areas where these are not well understood. See full-text article at JSTOR

Structural analysis and dynamics of the plant communities of Wizard Island, Crater Lake National Park.

Abstract: Wizard Island, a ½—square—mile volcanic cinder cone located in Crater Lake, Oregon, was sampled by continuous belt transects. Separation of the one herbaceous and four forested community types, which were mapped as major vegetation units, was remarkably distinct, as 60% of the herbaceous species were found in only one or two communities. Physical factors such as the distribution and stability of substrate materials, temperature extremes, and soil—moisture availability exert the greatest control over plant community structure and development. Biotic factors have reduced effects on the generally sparsely vegetated island. The unstable cinder slope community was dominated by Polygonum newberryi Small., Eriogonum pyrolaefolium Hook. var. coryphaeum T. & G., and Arenaria pumicola Cov. & Leib. Pinus albicaulis Engelm. constituted 55% of the importance value of the crater rim community, but appears to be declining in importance. Pinus contorta is invading the crater area and may slowly replace P. albicaulis. Other characteristic crater rim species were Holodiscus microphyllus Rydb. var. glabrescens (Greenm.) Ley. and Castilleja applegatei Fern. The lower cone and north slope forests were dominated by Abies magnifica Murr. var. shastensis Lemm. and Tsuga mertensian (Bong.) Carr., with Pinus monticola Dougl. the only other important tree species. An importance value of 51% for T. mertensiana in the north slope community as compared with 25% in the lower cone reflects the cooler, moist microclimate and greater community maturity on the north slope. The more tolerant T. mertensiana increases in importance as the stands mature. Characteristic shrub and herb species were Vaccinium membranaceum Dougl. and Luzula glabrata (Hoppe) Desv. in the north slope, and Arctostaphylos nevadensis Gray and Pyrola secunda L. in the lower cone communities, respectively. The lava flow community was largely restricted to recesses between lava ridges where moisture and soil conditions are improved. Tsuga mertensiana was the dominant tree species on the lava flow at 51% importance value, with Sambucus microbotrys Rydb. and Cheilanthes gracillima D. C. Eaton as indicators of the shrub community development was and herb strata. Diversity, total plant density, and herbaceous and shrub community development was greatest in the favorable forest microclimates of the north slope. The north slope, crater rim, lower cone, cinder slope, and lava flow communities had 28, 23, 21, 12, and 10 nonarborescent species, respectively. The reported vascular flora of the island comprises 105 species and varieties. The best forest development occurred in an encircling belt at about 6,400—6,500 ft (1,950—1,980 m) elevation, but tree species characteristic of an elevational range of 2,500 ft (820 m) are telescoped onto the 760—ft—(250—m) high island. Substrate and local climatic diversity and climatic moderation due to lake effects and shielding by the caldera wall permit survival of trees above their usual elevation range. Tree invasion on the upper cone (particularly of Tsuga mertensiana) is slowed more by unstable slopes than by climatic severity. Mat—forming plants, such as Arctostaphylos nevadensis and Penstemon davidsonii Greene, anchor the substrate and serve as nurseries for tree seedlings. Ecesis of tree seedlings on the lava flow occurs only in crevices which exhibit some soil development and microclimatic amelioration. Log density—size class plots gave a straight line relationship for north slope tree species, but all other community types had marked density reductions in some size classes. As such, the north slope community is considered to be in equilibrium at the present level of substrate and microclimatic alteration.

Radionuclide Tracer Analysis of Trophic Relationships in an Old-Field Ecosystem

Abstract: Wild radish (Raphanus raphanistrum) and ragweed (Ambrosia artemisiifolia), the dominant producers during initial succession in an old field, were labeled with 32P in several trophic—transfer studies. Feeding relationships were determined by correlating the population dynamics and 32P uptake by consumer species with the phenological changes in producer components and isotope distribution in plant tissues. The relative magnitude of consumer pathways was estimated by using trophic—transfer indices. The first year of old—field succession was characterized by rapid phenological changes in plant—organ availability with related shifts in consumer trophic relationships. The food web of wild radish, the early summer dominant producer, changed rapidly over time resulting in successive pulses of leaf, pollen, and seed feeders. Grasshoppers were the major leaf feeders. Aphids consumed internal juices within stems while flea beetles were concentrated and feeding solely on nutrient—rich seed tissue. Leafhoppers and tarnished plant bugs also consumed internal fluids during wild radish development. The high densities and consumption by plant bugs and aphids, the major consumers of wild radish, resulted in a low food—web diversity for wild radish. Predator—prey relationships during early summer were governed mainly by the aphid infestation. Young ragweed plants and the litter and seed crop of wild radish were major food—web bases in midsummer. Generalized herbivores such as grasshoppers and crickets utilized radish seeds and ragweed tissue during this period. A second phase of specialized feeders entered the old field as ragweed became available. Food—web diversity was highest at this time when many species were present and at low densities. Ragweed was the dominant producer late in the growing season. Some herbivores utilized ragweed leaves while several species of plant bugs became abundant and were consuming the nutrient—rich fluids being channeled into pollen tissue. Plant bugs were the major ragweed herbivores. The importance of these plant bugs resulted in a decline in food—web diversity near the end of the growing season. Most consumers decreased in numbers and 32P activity as ragweed died back in September. Ragweed litter, however, supported crickets and other components of the detrital food web over the fall season. Wild radish and ragweed were the major food—web bases during the first year of succession. Over 90% of the arthropods sampled in the old field were food—web components of these producers. Many of these consumers were specialists and sucking forms which peaked in density and 32P activity as nutrient—rich fluids were entering their specific food sources. The synchronal occurrence of consumer population peaks and successive nutrient pulses in host—plant organs thus appears to maximize the energy utilization by these consumers while minimizing interspecific competition for sites of trophic transfer. Little foliar damage was evident for wild radish or ragweed because of the importance of herbivores with sucking mouthparts. Tracer studies were thus critical in evaluating the role of both producers as food—web bases. The similarity of results in two replicate studies confirmed the repeatability and accuracy of tracer techniques for trophic—transfer analysis. However, temporal aspects of food—web structure should be considered in future studies where rapid changes in plant phenology are present.