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Showing papers in "Ecological Monographs in 1969"


Journal ArticleDOI
TL;DR: From a number of experiments it was concluded that in the weak—preference case no switch would occur in nature except where there is an opportunity for predators to become trained to the abundant species, and a patchy distribution of the abundant prey could provide this opportunity.
Abstract: "Switching" in predators which attack several prey species potentially can stabilize the numbers in prey populations. In switching, the number of attacks upon a species is disproportionately large when the species is abundant relative to other prey, and disproportionately small when the species is relatively rare. The null case for two prey species can be written: P1/P2 = cN1/N2, where P1/P2 is the ratio of the two prey expected in the diet, N1/N2 is the ratio given and c is a proportionality constant. Predators were sea—shore snails and prey were mussels and barnacles. Experiments in the laboratory modelled aspects of various natural situations. When the predator had a strong preference (c) between prey the data and the "null case" model were in good agreement. Preference could not altered by subjecting predators to training regimens. When preference was weak the data did not fit the model replicates were variable. Predators could be trained easily to one or other prey species. From a number of experiments it was concluded that in the weak—preference case no switch would occur in nature except where there is an opportunity for predators to become trained to the abundant species. A patchy distribution of the abundant prey could provide this opportunity. Given one prey species, snails caused a decreasing percentage mortality as prey numbers increased. This occurred also with 2 prey species present when preference was strong. When preference was weak the form of the response was unclear. When switching occurred the percentage prey mortality increased with prey density, giving potentially stabilizing mortality. The consequences of these conclusions for prey population regulation and for diversity are discussed.

1,227 citations


Journal ArticleDOI
TL;DR: The mobility of most animals permits them to seek the environment most compatible with their physiological requirements for energy, and the microclimate around an animal is thought of as a four dimensional space in which the four independent variables are acting simultaneously and are each time dependent.
Abstract: All processes of life, all physiological events, do work and expend energy. A continuing supply of energy is necessary for an animal to live. One of the primary means by which the environment influences animals is through the exchange of energy. If the animal takes in more energy than it gives out it will get warmer, overheat and perish. If the animal loses more energy than it gains it will cool and not survive. An animal may warm or cool for a limited period of time, but on the average, over an extended period of time, an animal must be in energy balance with its environment: The mobility of most animals permits them to seek the environment most compatible with their physiological requirements for energy. The factors of the environment which are primarily responsible for energy flow to an animal are several, e.g. radiation (sunlight, skylight, and radiant heat), air temperature, wind, and humidity. There are other environmental factors, such as the gravitational, electrical, or magnetic fields, which might determine energy flow between animals and environment but may be ignored as generally not significant to the energy budget of an animal. The microclimate around an animal is thought of as a four dimensional space in which the four independent variables-radiation, wind, air temperature, and humidity-are acting simultaneously and are each time dependent. The exchange of energy between an animal and its environment affects the body temperature of the aimal. The body temperature is considered here as a dependent variable. The rate of moisture loss by the animal is in part determined by environmental

791 citations



Journal ArticleDOI
TL;DR: To compare the breeding ecology of 4 common species of Ardeids in the Gainesville, Florida, area, this is done by comparing the behaviour of the Cattle Egret and three other common species in the area.
Abstract: In spite of the large literature on various aspects of the biology of the cosmopolitan family Ardeidae, we know little about their breeding ecology. Our knowledge is especially lacking when it comes to events taking place inside the heronry, and at least one author (Valverde, 1955-56) suggests that the heronry shall remain forever a mystery. In recent years many reports documenting the remarkable range expansion of the Cattle Egret (Bubulcus ibis) have appeared, yet little information is available concerning its reproduction. The purpose of this paper is to compare the breeding ecology of 4 common species of Ardeids in the Gainesville, Florida, area. This is done by compar-

228 citations


Journal ArticleDOI
TL;DR: Decomposition and effects of fire on microclimate and plant production of a Tall Grass Prairie were studied in east—central Illinois and total flowering was proportional to duration and degree of favourable microclimatic conditions from May to mid July.
Abstract: Decomposition and effects of fire on microclimate and plant production of a Tall Grass Prairie were studied in east—central Illinois After two years simulated litter samples in contact with soil lost 64% of their initial weight Burning caused a 2—3 fold increase in production and a ten fold increase in flowering Application of mulch, lowered flowering rate; response was proportional to thickness of mulch and length of time it was in place, Artificial shading of burned areas under green—house frames lowered flowering rate Burning or clear cutting vegetation increased percent N and P in May foliage A May application of N fertilizer increased flowering and dry matter production Nutrient release from ash had no effect on flowering or production Root production was similar on burned and Burn 3 areas; a turnover rate of 045 was calculated Calcium content of roots in May increased after fire and N content decreased Temperature from —5 to +50 cm and light intensity from 0 to +50 cm were higher on burned than Burn 3 areas Maximum soil surface temperatures occurred three months earlier on Burn 0 than Burn 3 areas Soil moisture was never severely limiting to plant growth Growing season microclimate measurements at 50 and 200 cm were combined into a microclimatic index, which allowed comparison of the microenvironment of three burning regimes Total flowering was proportional to duration and degree of favourable microclimatic conditions from May to mid July

226 citations


Journal ArticleDOI
TL;DR: Mineral Nutrients .......
Abstract: Mineral Nutrients ....... 179 Light 182 Soil Moisture 183 Oxygen Levels in Soils 184 Animal Effects 185 Soil Heating 185 Laboratory Soil Heating ...... 186 Seed Heating 187 Allelopathy 188 Techniques 188

176 citations



Journal ArticleDOI
TL;DR: Flowering dogwood has been acknowledged for several decades as a nutritionallybeneficial understory species due to accumulation of calcium in its leaves and rapid decomposition of its litter, thus releasing -calcium for use by other species.
Abstract: Chemical analyses of plants and soils have helped explain agricultural productivity since the 17th century (Davies 1940) and productivity of forest trees since the 19th century (Ebermayer 1876; Rennie 1955). Because calcium is the element removed in greatest quantity when tree crops are harvested, it received much of the attention in the latter studies. The desire to understand ecosystem functioning reinforces the motivation for studies of nutrient circulation in forests. Circulation of elements within the plant-soil system is exceedingly complex. Remezov (1959) classified nutrient cycles as subannual cycles, annual cycles, and those consisting of successive annual cycles; he stated that it is impossible to list all minor cycles and that, "The biological cycle of elements in a forest is a complicated polycyclic process depending on the combination of many factors." There are inputs of elements to the plant-soil system by, e.g., precipitation, dust, and weathering of parent material, and losses due to, e.g., drainage waters and plant and animal harvests; these incomes and exports have been discussed by Ovington (1962, 1965). Auerbach (1965) summarized the needs for cycling studies and concluded that additional tracer investigations should be undertaken to measure cycles in various ecosystems. Flowering dogwood (Cornus florida L.) has been acknowledged for several decades as a nutritionallybeneficial understory species due to accumulation of calcium in its leaves and rapid decomposition of its litter, thus releasing -calcium for use by other species.

107 citations


Journal ArticleDOI
TL;DR: Breeding migrations were more strongly correlated with rainfall and temperature in early spring than in late spring and in late fall than in early fall, and for a brief period following their arrival at a pond migrants wandered back and forth between water and land, especially during rainy weather.
Abstract: The breeding migrations and wandering movements of Notophthalmus viridescens were monitored at several ponds in Dryden, Tompkins County, New York. Breeding migrations occurred in both the spring (April—May) and fall (August—October, November, or December) to all permanent ponds. The spring migrations involved both eft migrants and adult migrants, their relative numbers varying considerably from pond to pond. The fall migrations involved eft migrants almost exclusively. Eft migrants were maturing juveniles returning to the water for the first time; adult migrants were individuals which had bred before and subsequently spent some time, often an entire winter, on land. The sex ratio of eft migrants was 42 to 47% males, that of aquatic adults at least 55% males; male eft migrants had a greater future life expectancy than do female eft migrants. Male migrants arrived earlier in the spring, female migrants arrived earlier in the fall. Breeding migrants tended to use linear depressions (e.g. streambeds, slope junctions) as migration routes; their routes were conspicuously altered by seasonal changed in vegetation. About 57% of N. viridescens migrants, but only 3% of Ambystoma maculatum migrants, reached the ponds during the day; the remainder entered at night. Breeding migrations were more strongly correlated with rainfall and temperature in early spring than in late spring and in late fall than in early fall. For a brief period following their arrival at a pond migrants wandered back and forth between water and land, especially during rainy weather. Fully aquatic adults abandoned temporary ponds as or after these dried up. In July, August, and September some adults left permanent ponds, especially during rainy weather.

105 citations






Journal ArticleDOI
TL;DR: Although predation turned out to be the main factor contributing to mortality, competition and specific environmental factors could not be isolated and hence their importance remained unevaluated.
Abstract: The experimental approach to problems in insect population dynamics in the field has long been used but seldom has its full potential been exploited. Fuller (1934), in a now classic paper, reports on results of field manipulations of densities of blowfly larvae and available food, showing the importance of competition and predation. Additional mortality factors such as temperature, later shown to be of importance (Waterhouse, 1947), were not considered. Other attempts at constructing complete budgets of population mortality have been made since. One of the most notable is the work on the chrysomelid Phytodecta olivacea (Richards and Waloff, 1961). Those factors which could be measured directly from the populations, such as parasitism and egg inviability, were carefully studied. Only predation mortality was estimated independently using serological techniques. Although predation turned out to be the main factor contributing to mortality, competition and specific environmental factors could not be isolated and hence their importance remained unevaluated.

Journal ArticleDOI
TL;DR: Ninety—four species of Orthoptera occur along an altitudinal transect from 5,000 ft (1,530 m) to above 14,000ft (4,265 m) in the Front Range of the Rocky Mountains of Colorado, near 40° N. Lat.
Abstract: Ninety—four species of Orthoptera (s. lat.) occur along an altitudinal transect from 5,000 ft (1,530 m) to above 14,000 ft (4,265 m) in the Front Range of the Rocky Mountains of Colorado, near 40° N. Lat. These were sampled, with observations on life histories in relation to altitude, at a series of altitudinally spaced stations during the seasons of 1949, 1958, 1959, and 1960, the stations being selected for maximum variety of Orthoptera at each altitude. Other observations of the past 35 years were added. Sampling was by a sweeping technique designed to be qualitatively exhaustive of species and age groups; it was thus quasiquantitative. Times of hatching, times of different juvenile stages, and times of maturing were determined for species at the different altitudes at which they occurred. These data are summarized by species, the 94 species being in the following families: Mantidae, 2; Phasmidae, 1; Tetrigidae, 4; Acrididae, 73; Tettigoniidae, 8; Gryllacrididae, 3; Gryllidae, 3. Numbers of resident sp...

Journal ArticleDOI
TL;DR: An objective technique was used to identify and study related groups of chaetognath species from the Southwest Indian Ocean off the coast of the Republic of South Africa, finding the most representative groups were from the data of the N70V—nets which formed 3 groups.
Abstract: An objective technique was used to identify and study related groups of chaetognath species from the Southwest Indian Ocean off the coast of the Republic of South Africa. Groups or community—type data agreed with, corroborated, and extended the scope of data on single species, multiple species and hydrographic conditions. The most representative groups were from the data of the N70V—nets which formed 3 groups. The 1st (or main) group was composed of 9 species and was distributed as a unit almost solely in the upper 200 meters of oceanic waters, and occurred in neritic waters only when > 1 to 2 species were absent. This agrees with and corroborates individual species data as each was, according to its distribution and abundance, a resident of the general ocean and each showed, except 3 species found predominantly in deeper waters, a positive correlation with the flow—pattern of the Agulhas current. The 2nd (or associate) group of 3 species was found 61% of the time at mixed—water stations, the best of thes...