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Showing papers in "Ecology in 1970"


Journal ArticleDOI
01 Jul 1970-Ecology
TL;DR: The content of oak leaf tannins, which inhibit the growth of winter moth larvae, increases during the summer and may render leaves less suitable for insect growth by further reducing the availability of nitrogen and perhaps also by influencing leaf palatability.
Abstract: Concentration in the spring of feeding by caterpillars of the winter moth, Operophtera brumata L., and other species of Lepidoptera on oak trees in England is believed to be related to seasonal changes in the texture and chemical composition of the leaves. Increasing leaf toughness is a proximate, though probably not ultimate, factor preventing late larval feeding by the winter moth, the commonest spring species on oak. Early feeding coincides with maximum leaf protein content and mimum leaf sugar content, with suggests that availability of nitrogen, rather than of carbohydrate, may be a limiting factor for spring—feeding larvae. The content of oak leaf tannins, which inhibit the growth of winter moth larvae, increases during the summer and may render leaves less suitable for insect growth by further reducing the availability of nitrogen and perhaps also by influencing leaf palatability. Oak trees are extensively damaged by insect attack, and it is likely that leaf tannins have a defensive function against insects as well as against other herbivores and against pathogens.

1,885 citations


Journal ArticleDOI
01 May 1970-Ecology
TL;DR: The first observation may be related to the first in the following way: nonsynchronous spatial overlap could dictate relatively great resource overlap for species coinhabiting patchy or edge areas, requiring great differences between the species in prey size in addition to those in climatic habitat.
Abstract: Sympatric native Anolis species with similar structural habitats but contrasting climatic habitats are closer in head and body size on species—rich than on depauperate islands. In two localities, sympatric Anolis species with differential occurrences in sun or shade sought lower, more shaded perches during midday, resulting in partly nonsynchronous utilization of the vegetation by the two species. The second observation may be related to the first in the following way: nonsynchronous spatial overlap could dictate relatively great resource overlap for species coinhabiting patchy or edge areas, requiring great differences between the species in prey size in addition to those in climatic habitat. The extent of such overlap on small depauperate islands could be greater if these contained a greater proportion of patchy or edge habitats (with respect to insolation), or if climatic preferences were broader and more overlapping than on large, species—rich islands. In each locality, the relatively more shade—inhab...

1,562 citations


Journal ArticleDOI
01 May 1970-Ecology
TL;DR: The hypothesis that increased evaporation at high altitudes and in arid areas accentuates the depression of a wet- bulb thermometer may partially account for several cases of size variation in birds cited by others as disturbing exceptions to Bergmann's ecogeographic rule.
Abstract: There is a high degree of concordance among the patterns of geographic size variation in birds in the eastern and central United States. This is demonstrated for 12 species by assuming that wing length measurements are an indicator of body size on the intraspecific level, and by arranging the data in the form of a grid of means of wing lengths for sample areas. Maps giving isophenetic lines for wing length indicate gradually increasing size dines northward and westward from Florida in the Hairy Woodpecker (Dendrocopos villosus), Downy Woodpecker (Dendrocopos pubescens), Blue Jay (Cyanocitta cristata), Carolina Chickadee (Parus carolinensis), White-breasted Nuthatch (Sitta carolinensis), and Eastern Meadowlark (Sturnella magna). In each case there is a trend for larger (or longer-winged) birds to extend southward in the Appalachian Mountains and for smaller (or shorter-winged) birds to extend northward in the Mississippi River valley. Maps made by a computer and automatic plotter using contour intervals of 0.5 mm of mean wing length for the Downy Woodpecker, for male White-breasted Nuthatches, and for female Blue Jays show that, in addition to the pattern just mentioned, relatively longer-winged birds extend southward in the interior highlands of Arkansas, and relatively shorter-winged birds extend northward up other river valleys. These subtle relationships between intraspecific size variation and topo- graphic features suggest that the link between the two phenomena may be precise adaptations to even minor climatic gradients. The relationship between these findings and the subspecies concept is discussed. Correlation coefficients for the pattern of variation in the Downy Woodpecker with seasonal and annual wet-bulb temperature, vapor pressure, and absolute humidity were all either equal to or higher than correlations with dry-bulb temperature. Since these variables reflect the combined effects of temperature and humidity, the obvious indication is that size variation is more closely related to this combination than to temperature alone. Additional correlations using the mean wing length data for seven other species confirmed that wet-bulb temperature patterns are more closely related to bird size than either dry-bulb temperature patterns or latitude. These relationships can be expressed numerically as regressions of mean wing length on either annual wet-bulb temperature or mean annual total heat per pound of air. Since increased evaporation at high altitudes and in arid areas accentuates the depression of a wet- bulb thermometer, my hypothesis may partially account for several cases of size variation in birds cited by others as disturbing exceptions to Bergmann's ecogeographic rule. Sections of a translation of Bergmann's paper published in 1847 are given. The biological mechanisms by which these relationships are maintained are unknown, and the wide range of tolerance by birds to diurnal and seasonal temperature variations tends to mask them. If the well-established inverse relationship between weight and metabolic rate per gram of homeotherms is operative on the intraspecific level, the relationships can be discussed in terms of avenues of heat loss and of energy budget equations.

768 citations


Journal ArticleDOI
01 Mar 1970-Ecology
TL;DR: Calculated productivity of various calcareous algal zones indicates that these do not contribute significantly to overall reef production on atolls of the northern Marshall Islands, and island reefs are less productive than previously studied inter—island reefs.
Abstract: Primary productivity of reef—building algae was studied by putting samples from the reef in a closed system and measuring oxygen exchange in the light and in the dark Gross productivity determined for 32 samples in full sunlight had a mean value of 0048 mg O2 cm—2 hr—1 Photosynthesis was found to increase with the logarithm of light intensity up to 1,000 ft—c and was constant between 1,000 and 8,000 ft—c Rates of gas exchange in flowing water showed no correlation with water velocity but were greater than rates in still water Daily patterns of photosynthesis were calculated for populations of calcareous algae living on the submarine faces of the windward sides of atolls During most of the daylight hours light is probably not a limiting factor for photosynthesis in these populations Calculated productivity of various calcareous algal zones indicates that these do not contribute significantly to overall reef production on atolls of the northern Marshall Islands Island reefs are less productive than previously studied inter—island reefs

503 citations


Journal ArticleDOI
01 Nov 1970-Ecology
TL;DR: The authors showed that fire-dependent plant communities burn more readily than non-fire-dependent communities because natural selection has favored development of characteristics that make them more flammable, and the hypothesis was experimentally derived following laboratory combustion tests with litter of eucalyptus, pine, and hardwood leaves.
Abstract: Plant species which have survived fires for tens of thousands of years may not only have selected survival mechanisms, but also inherent flammable properties that contribute to the perpetuation of fire—dependent plant communities. This concept goes by beyond the commonly accepted fire climate—fuel moisture basis of wildland fire occurrence. Plant communities may be ignited accidentally or randomly, but the character of burning is not random. The following hypothesis treats this interaction between fire and the ecosystem: Fire—dependent plant communities burn more readily than non—fire—dependent communities because natural selection has favored development of characteristics that make them more flammable. The hypothesis was experimentally derived following laboratory combustion tests with litter of eucalyptus (Eucalyptus obliqua L'Herit), ponderosa pine (Pinus ponderosa Laws.), and tropical hardwood leaves.

487 citations


Journal ArticleDOI
01 Jan 1970-Ecology
TL;DR: The average nitrogen content of shrub leaves, stems, and roots was 1.31,.87, and.80%, respectively as mentioned in this paper, and areas between shrubs averaged 0.19% nitrogen.
Abstract: Total nitrogen incorporated in the shrubs of a low—fertility desert plant community (principally Acacia Gregii, Cassia armata, and Larrea divaricata) was estimated from the nitrogen content of plant parts, the total weight of plants and proportional weight of roots, stems, and leaves, and the number of plants per unit area. The average nitrogen content of shrub leaves, stems, and roots was 1.31%, .87%, and .80%, respectively. Shrub cover occupied 20% of the ground surface and contained an average of 29 kg nitrogen/ha. Legume shrubs were not significantly greater in nitrogen content than nonlegume shrubs. Soil nitrogen content decreased significantly as a function of radial distance from the center of the shrub canopy. Areas between shrubs averaged 0.19% nitrogen in the surface inch of soil. Soil nitrogen content decreased significantly from the surface to 90—cm depth and was closely related to shrub species and their root—distribution patterns. See full-text article at JSTOR

366 citations


Journal ArticleDOI
01 Jan 1970-Ecology
TL;DR: In this article, the authors studied the behavior of a goat-like bovid after liberation in New Zealand and determined trend of demographic stastistics across an eruptive fluctuation that spans 50 years, finding that the major influence on rate of increase was traced to variation in death rate.
Abstract: An eruptive fluctuation is defined operationally as an increase in numbers over at least two generations, followed by a marked decline. Reported eruptions in ungulates suggest that the upswing is initiated by a change in food or habitat and is terminated by over- grazing. An apparent exception-the Kaibab eruption-probably also fits this pattern. The interpretation causally linking reduction of predators on the plateau with increase of deer is an overstatement of evidence. Eruption of established populations is essentially the same process as the buildup of populations initiated by liberation, with the difference that in the second case a zone of high density migrates radially from the point of liberation. Eruption of thar (a goat-like bovid) after liberation in New Zealand was studied by sam- pling populations at different distances from the point of liberation. The aim was to determine trend of demographic stastistics across an eruptive fluctuation that spans 50 years. Although fecundity varied across the eruption, the major influence on rate of increase was traced to variation in death rate. The major component of this variation was the rate of mortality over the first year of life. Trend in death rate, and hence in rate of increase, was associated with trends in other population statistics that are easier to measure. The most useful corre- lative of rate of increase is probably the level of fat reserves. While we do not know whether trends in population statistics of thar reflect those of other ungulates during an eruptive fluctuation, the generality of the reported trends may usefully serve as a testable hypothesis.

365 citations


Journal ArticleDOI
01 May 1970-Ecology
TL;DR: In this paper, a class of models analogous to those used in the analysis of variance is discussed, and a method for computing the expected cell counts for the different models is presented.
Abstract: Ecological data often come in the form of multidimensional tables of counts, referred to as contingency tables. During the last decade several new methods of analyzing such tables have been proposed. Here, a class of models analogous to those used in the analysis of variance is discussed, and a method for computing the expected cell counts for the different models is presented. Two differenet tests for checking the goodness—of—fit of a particular model are then examined. The first is the simple generalization of the Pearson chi—square test statistic, while the second is referred to as the likelihood—ratio chi—square test statistic. Both have the same asympototic g2 distribution. The likelihood—ratio statistic can be used in the selection of a suitable model, via the technique of partitioning. All of the methods presented are illustrated using data collected by Schoener on lizards from the West Indies. See full-text article at JSTOR

359 citations


Journal ArticleDOI
01 Jul 1970-Ecology
TL;DR: The ecological challenges facing the northern populations are primarily physical, largely climatic ones, biotic interactions (particularly predation) assume relatively greater importance to southern lizards.
Abstract: I studied various aspects of the life history of Cnemidophorus tigris over much of its geographic range, from southern Idaho through southern Arizona and into northern Sonora. In the northern parts of its range, Cnemidophorus usually emerge from hibernation in May, and most adults aestivate during the midsummer months, but in the south the animals are active from April through late August. The seasonal period of activity is therefore considerably shorter in the north. Daily periods of activity are of similar duration from north to south, although the time of emergence tends to be later on northern areas. There is a significant positive correlation between estimated abundance and the total precipitation during the last 5 years, suggesting that the abundance of this species is determined by food supply. There is a latitudinal cline in the mean body temperature of active lizards, with northern populations being active at lower air and body temperature. Whereas termites constitute the major food of southern lizards, beetles and grasshoppers are the primary food of northern lizards. Some seasonal dietary trends are described. The numbers and biomass of predatory lizards, birds, and snakes increase from north to south; correlated with this is a latitudinal increase in the percentage of lizards with broken regenerated tails. Hence there is probably greater predation on southern lizards. The length of fat bodies in C. tigris is not correlated with latitude but shows an inverse correlation with the long—term average annual precipitation. It is suggested that lizards from less productive areas must allow themselves a greater margin of safety due to the more probable occurrence of drought. Northern lizards breed only once during the short northern season but lay significantly larger clutches than southern lizards, which lay at least two clutches annually. Clutch size appears to be flexible in response to feeding conditions; in one study area with a low long—term mean precipitation, females laid larger clutches during the second year, after supranormal rainfall. There is a significant correlation between mean number of eggs per clutch and the deviation of the short term (last 5 years) mean precipitation from the long—term mean precipitation. A number of facts suggest that there was a decided population "crash" on one study area during the period of study. Competition is briefly discussed and it is suggested that if there is any latitudinal trend, it is most likely in the direction of greater competition among southern lizards. In the conclusions, I suggest that the ecological challenges facing the northern populations are primarily physical, largely climatic ones, biotic interactions (particularly predation) assume relatively greater importance to southern lizards.

277 citations


Journal ArticleDOI
01 Sep 1970-Ecology
TL;DR: The results of censuses taken at the end of the second year on the four islands in the group located in the lower Keys (El, E2, E3, ST2) found the numbers of species were found to have changed little from the previous year, providing further evidence that they are in equilibrium.
Abstract: In 1966-1967 the entire arthropod faunas of six small mangrove islands in the Florida Keys were removed by methyl bromide fumigation. In earlier articles we described the process of recolonization through the first year, during which the numbers of species in five of the six faunas rose to what appear to be noninteractive equilibria and then slumped slightly to interactive equilibria. The sixth, that of island El, we believed to be climbing more slowly because of its greater distance from the source area. It had not reached the predefaunation (interactive) equilibrium by 1 year. Here we give the results of censuses taken at the end of the second year on the four islands in the group located in the lower Keys (El, E2, E3, ST2). The numbers of species were found to have changed little from the previous year, providing further evidence that they are in equilibrium. Species immigrations and extinctions have continued at a high rate, and the species compositions on three of the four islands appear to be moving slowly in the direction of the original, predefaunation states. In the first two articles of this series we de- scribed an experiment in which the entire arthro- pod faunas of six small mangrove islands in the Florida Keys were exterminated by methyl bro- mide fumigation and the process of recolonization was monitored thereafter by frequent censuses (Wilson and Simberloff 1969, Simberloff and Wilson 1969). The experiment was designed both to test and to extend certain aspects of spe- cies equilibrium theory (MacArthur and Wilson 1967, Simberloff 1969, Wilson 1969) and to ob- serve the actual processes of immigration and ex- tinction. At the end of the first year following defaunation, the numbers of species had reattained approximately the original (prefumigation) levels on five of the six islands. The most distant island (El) supported the fewest species, just as it had prior to defaunation; it alone had not approached the original species number. Intermediate islands (E3, ST2) reattained intermediate numbers of species. The time-colonization curves appeared to have assumed the logarithmic forms predicted by basic equilibrium theory. Moreover, higher levels of species numbers were reached prior to the buildup of the populations belonging to the constituent species. These numbers then dipped slightly as the densities of the constituent popula- tions approached the predefaunation levels. The

270 citations


Journal ArticleDOI
01 Mar 1970-Ecology
TL;DR: Field and experimental data suggest that the stream species, O. virilis, is excluded from ponds by summer drying and periodic low oxygen periods of those ponds, and is not as competent a burrower as O. immunis nor is its as tolerant of low oxygen levels.
Abstract: The two crayfish, Orconectes virlis and O. immunis, have similar ranges but are ecologically isolated within these ranges; the former species inhabits streams and lake margins, the latter inhabits ponds and sloughs. Field and experimental data suggest that the stream species, O. virilis, is excluded from ponds by summer drying and periodic low oxygen periods of those ponds. It is not as competent a burrower as O. immunis nor is its as tolerant of low oxygen levels. Neither current nor substratum excludes the pond species, O. immunis, from the stream. But both field and laboratory observations strongly indicate a competitive exclusion of O. immunis by O. virilis. The latter was demonstrated to be intrinsically more aggressive in interspecific contacts, and in other experiments, evicted O. immunis from crevices in the substratum.

Journal ArticleDOI
01 Sep 1970-Ecology
TL;DR: It is argued that cone production may in this way provide a vehicle through which weather affects squirrel populations was supported by a number of statistically significant negative correlations between Alberta and Saskatchewan fur returns and the preceding year's summer rainfall.
Abstract: This paper describes red squirrel population dynamics on two intensive study areas (Camp and Main) in mixed—forest types near Rochester, Alberta. It also examines local and regional population fluctuations, and their relationship to cone crops and weather factors. Adult red squirrel numbers on our study areas varied little from 1967 to 1968. Yearly differences in reproductive output were caused principally by changing ovulation and pregnancy rates. Mean litter size increased significantly from 3.4 in 1967 to 4.3 in 1968; while the per cent adult females breeding increased significantly from 67 to 88. A life—table analysis of age—ratio data estimated mean annual mortality among juveniles (postweaning) at 67%; and an adult mortality rate of 34% for yearlings and 61% for older cohorts. A time—specific estimate of adult mortality on the Camp study area during the year starting summer 1967 was 21%. Red squirrel territories appeared to be of two distinct types: (1) defended winter food caches which were subsequently abandoned during the summer, and (2) "prime" territories in which a specific area was defended year round. During the summers of 1967 and 1968, 31% and 26% of study—area adult populations occupied prime territories. The distribution of prime territories chiefly reflected the presence of mature seed—producing conifers, and hence a potential year—round food supply. Deciduous areas were particularly important in overwintering the juvenile cohort. Fur returns were used as population indices in determining synchrony and periodicity of red squirrel fluctuations. Fluctuations tend to occur synchronously over much of the Prairie Provinces. Furthermore, mean intervals between peak years in Alberta (2.6) and Saskatchewan (2.8) were significantly shorter than in random series of comparable length, while the 2.9—year mean interval in Manitoba approached significance. A statistically significant correlation was found between white spruce cone crops and red squirrel populations in Alberta as indexed by annual fur harvests. The negative correlation between cone crops in late summer and rainfall during summer of the preceding year was almost significant. This supported the widely held view that weather factors influence bud differentiation and hence determine the size of the following year's cone crop. Our contention that cone production may in this way provide a vehicle through which weather affects squirrel populations was supported by a number of statistically significant negative correlations between Alberta and Saskatchewan fur returns and the preceding year's summer rainfall. Such a mechanism would explain the observed widespread synchrony of population fluctuations, since extensive regional weather patterns could be involved.

Journal ArticleDOI
J. M. A. Swan1
01 Jan 1970-Ecology
TL;DR: In this article, a single ordination procedure was evaluated by its ability to detect the ecological information in the hypothetical models and the procedure was reasonably successful when the data were drawn from a short length of the gradient but became progressively less so as longer lengths of the environmental gradient were included in the data.
Abstract: Hypothetical vegetation models were made to simulate numerical changes in species populations along a single environmental gradient. A single ordination procedure was evaluated by its ability to detect the ecological information in the hypothetical models. The procedure was reasonably successful when the data were drawn from a short length of the gradient but became progressively less so as longer lengths of the environmental gradient were included in the data. This parallels an increase in the number of stands from which each species is absent in the total data set. Zero values appear to mask ecological information, and an intuitive method of assigning "degree of absence" values to the data is described. After this adjustment, ordination patterns were easier to interpret because ecological information was concentrated in fewer axes. See full-text article at JSTOR

Journal ArticleDOI
01 Jul 1970-Ecology
TL;DR: This paper attempts to deal with the question of aging as a byproduct of natural selection, drawing on the theories of Medawar, Williams and Hamilton, and to apply the conclusions to considerations of population and behavioral ecology.
Abstract: This paper attempts first to deal with the question of aging as a byproduct of natural selection, drawing on the theories of Medawar, Williams and Hamilton, and second, to apply the conclusions to considerations of population and behavioral ecology. It is concluded that: (1) Age—specific mortality should drop to a minimum prior to earliest reproductive age and then rise with age. (2) Age—specific fecundity should rise with age to a peak, which may occur at almost any age depending on the sort of organism considered, and then fall. (3) A sudden increase in mortality at a given age will result in natural selection favoring higher relative mortality at immediately preceding and following ages, and lowered fecundity immediately after that age. (4) A sudden increase in fecundity at a given age will result in natural selection favoring relative higher mortality in early life and immediately after that age, as well as relaxed selection for increased fecundity, especially at middle and late ages. (5) Selection acts to make increasingly steep the survivorship curve of a population declining or fluctuating due to changes in mortality. (6) Selection acts to postpone reproductive effort in populations declining or fluctuating due to changes in fecundity. (7) If mortality is very low, animals, as they age, should ideally take greater risks to secure reproductive success. (8) The nature of altruistic behavior may be age specific, with older individual more characteristically altruistic and younger individuals more characteristically pampered. (9) Intergroup hostilities should be largely directed toward certain age groups.

Journal ArticleDOI
01 Sep 1970-Ecology
TL;DR: Pinyon and juniper invade and increase in black sagebrush communities until the understory, except for a few hardy plants, is eliminated, andJuniper invades first and tends to be eventually replaced by pinyon.
Abstract: As a means of studying inter— and intrazonal invasion in black sagebrush (Artemisia nova A. Nels) communities six maturity classes were established for pinyon (Pinus monophylla Torr. and Frem.) and juniper (Juniperus osteosperma (Torr.) Little) in east—central Nevada. Pinyon and juniper invade and increase in black sagebrush communities until the understory, except for a few hardy plants, is eliminated. Juniper invades first and tends to be eventually replaced by pinyon. Accelerated invasion by both species started about 1921 and is closely related to overgrazing, fire suppression, and climatic change. See full-text article at JSTOR

Journal ArticleDOI
01 Jan 1970-Ecology
TL;DR: The defense of the territories against intrusions by other grazers permits the growth of a thick algal film on which the Lottia can effectively graze, and their response to predatory snails may be a defense mechanisms.
Abstract: Lottia gigantea, a large (up to 8 cm in length) limpet of the California and northern Mexican coast, lives in association with an approximately 1,000 cm2 area of algal film in which its grazing marks can be seen, whereas the remainder of the rock surface is usually free of any visible film. These areas of algal film represent the territories of the Lottia; within them the animals do all their grazing. They keep their territories free of other organisms by shoving off any intruders: other Lottia, grazing limpets of the genus Acmaea, predatory snails, and sessile organisms such as anemones and barnacles. Within 2—3 weeks after Lottia were removed from their territories, the density of Acmaea in these territories increases to that found outside them, and the algal film disappeared. Apparently the defense of the territories against intrusions by other grazers permits the growth of a thick algal film on which the Lottia can effectively graze. Their reaction to sessile organisms prevents these animals from encroaching on and covering the territory. Their response to predatory snails may be a defense mechanisms.

Journal ArticleDOI
01 Nov 1970-Ecology
TL;DR: The influence of meadow mouse populations on grass—land ecosystems was studied at two sites with similar densities of Microtus, but in different types of grassland–a coastal prairie and an inland valley grassland.
Abstract: The influence of meadow mouse (Microtus californicus) populations on grass—land ecosystems was studied at two sites with similar densities of Microtus, but in different types of grassland–a coastal prairie and an inland valley grassland. Height of vegetation, volume of standing crop, and percentage cover were greater at the dry inland site where the annual grass Bromus rigidus was dominant. At the milder coastal site the annual grass Lolium multiflorum and the perennial bunchgrass Danthonia californica were dominant; forbs and other perennial grasses were more important. During a year with high rainfall and moderate densities of Microtus (1967) total standing crop, average height of vegetation, and weight of seed crop at the coastal site increased. Although 1966 and 1968 were both dry years, standing crop, seed production, and volume and cover of vegetation were less in 1968, when the meadow mouse population was high, than in 1966, when it was low. Exclosure studies demonstrated that these vegetation chan...

Journal ArticleDOI
01 Mar 1970-Ecology
TL;DR: The contribution to forest regeneration of seeds stored by these small forest mammals is probably of minor significance except when bumper seed crops are produced and large numbers of caches are created.
Abstract: Typical seed caches made in the fall of the year by white—footed mice (Peromyscus leucopus) and red—backed voles (Clethrionomys gapperi) contained 20—30 pine seeds, buried beneath the litter of pine needles and in contact with mineral soil. Many caches were revisited by the mice and their contents destroyed before winter. Most caches not decimated in the fall were invaded the following spring. However, some of them escaped complete destruction and their unconsumed seeds germinated and produced seedlings. Although mice make their caches in micro—environments highly favorable to germination, their subsequent feedings on the stored seeds, both before snowfall and before and during the spring germination period, greatly deplete the number of potential germinants. Therefore, the contribution to forest regeneration of seeds stored by these small forest mammals is probably of minor significance except when bumper seed crops are produced and large numbers of caches are created. Under these circumstances, stored seeds may be of sufficient quantity to exceed food requirements of the mice. If pirating by other animals is low, then a surplus of seeds is left to help regenerate the forest.

Journal ArticleDOI
01 Mar 1970-Ecology
TL;DR: It is believed that smaller animals have a competitive advantage while husking seeds because they have a smaller metabolic drain, and resource allocation based on husking speed differences would seem of little potential importance in maintaining competing heteromyids in a state of coexistence.
Abstract: Seven species of heteromyid rodents varying in size from 8 to 114 g were studied in the laboratory. Starved rodents husked four kinds of large seeds (spinach, sunflower, squash and pumpkin) and were timed at the task. Geometric mean husking times varied from 3.1 to 70.1 seconds, depending on the seed and the rodent. Husking time was inversely proportional to an animal's body size. However, despite their slowness, smaller animals appear to be more efficient at dealing with these large seeds because they have a smaller metabolic drain. This conclusion is based on the assumption that gross caloric need increases linearly with (body weight).75. The authors defend the assumption and thus believe that smaller animals have a competitive advantage while husking seeds. These rodents might engage in a limited amount of habitat and resource selection based on their relative seed—husking abilities. However, the order in which the various species should prefer these seeds is quite similar, so resource allocation based on husking speed differences would seem of little potential importance in maintaining competing heteromyids in a state of coexistence. Previous investigators have shown that seed selection occurs in some cases, but many cases are also known in which little or no selection is practiced.

Journal ArticleDOI
01 May 1970-Ecology
TL;DR: The results suggest that in areas where root growth occurs at low temperatures and where lands are infested with B. tectorum and T. asperum, seedlings of A. desertorum would be more successful than seedlingsof A. spicatum.
Abstract: Rapidly elongating Bromus tectorum and Taeniatherum asperum roots penetrated the soil ahead of Agropyron spicatum roots and used available moisture. In contrast, Agropyron desertorum roots penetrated the soil almost as rapidly as B. tectorum and T. asperum and remained in favorable moisture. These differences in root penetration resulted in lower leaf water potentials and poorer survival in A. desertorum. The results suggest that in areas where root growth occurs at low temperatures and where lands are infested with B. tectorum and T. asperum, seedlings of A. desertorum would be more successful than seedlings of A. spicatum. See full-text article at JSTOR


Journal ArticleDOI
01 Nov 1970-Ecology
TL;DR: Plant composition and coverage and small mammal populations were compared in virgin forest (control) and clearcut areas from April 1954 to October 1965 and herbaceous species then became dominant for a 3—year period, after which woody plants gradually gained dominance.
Abstract: Plant composition and coverage and small mammal populations were compared in virgin forest (control) and clearcut (experimental) areas from April 1954 to October 1965. Changes in ground cover vegetation were modest on the control area but marked on the experimental area. A late fall burn on the experimental area may have retarded herbaceous plant establishment. Nearly half of the herbaceous species were invaders not found in the virgin Douglas—fir (Pseudotsuga menziesii) forest. Ground plant coverage was less than 23% in the virgin forest; 1 year after the clearcut area was burned, the cover was 2%; and by 10 years it was above 53%. Woody plant coverage (mostly sprouts) was slightly more abundant the first 2 years after burning. Herbaceous species then became dominant for a 3—year period, after which woody plants gradually gained dominance. Deer mice (Peromyscus maniculatus) increased on the experimental area soon after the burn. The populations varied from an estimated 0.9 to 12.8 animals per acre and fluctuated widely and irregularly. Townsend's chipmunk (Eutamias townsendii), Oregon vole (Microtus oregoni), and snowshoe hare (Lepus americanus) populations also increased on the area at different periods after the burn. Trownbridge's shrews (Sorex trowbridgii), vagrant shrews (Sorex vagrans), and ermine (Mustela erminea) were present on both areas in relatively low numbers. Redback voles (Clethrionomys occidentalis), Douglas' squirrels (Tamiasciurus douglasii), and northern flying squirrels (Glaucomys sabrinus) were not found on the clearcut. California ground squirrels (Spermophilus beecheyi) migrated to the clearcut and established a modest population. Richardson's voles (Microtus richardsoni), jumping mice (Zapus trinotatus), bushy—tailed woodrats (Neotoma cinerea), and a pika (Ochotona princeps) were visitors.

Journal ArticleDOI
01 Mar 1970-Ecology
TL;DR: Dry matter standing crop was the decisive factor determining quantities of chemical constituents per square meter in tissue concentrations of chlorophylls a and b, carotenoids and most macronutrients.
Abstract: Shoot productivity was measured for Typha latifolia and Scirpus americanus. Samples were also subjected to chemical analyses. Tissue concentrations of chlorophylls a and b, carotenoids and most macronutrients declined as the plants aged. Net accumulation of these constituents per square meter usually continued during periods of dry matter increase, even though tissue concentrations were diminishing. Dry matter standing crop was the decisive factor determining quantities of chemical constituents per square meter. Uptake rates for macronutrients were generally not proportional to productivity rates. The most rapid uptake of several nutrients occurred earlier than maximum growth rates. See full-text article at JSTOR

Journal ArticleDOI
01 Nov 1970-Ecology
TL;DR: The bioenergetics of a detritus—feeding stonefly Pteronarcys scotti, were invetigated and a 17—month energy budget for the average nymph was tabulated.
Abstract: The bioenergetics of a detritus—feeding stonefly Pteronarcys scotti, were invetigated. The nymphs were collected from a north Georgia trout stream and held under simulated field conditions of temperature and photoperiod in a laboratory stream. Rates of respiration and egestion were measured at temperatures approximating those in the field at the time of collection. An estimate of the growth rate of nymphs was made from a statistical analysis of monthly field samples. Calorimetric determinations were made of nymphs, molted exoskeletons, and feces. A 17—month energy budget for the average nymph was tabulated on the basis of the data collected. Assimilation and growth efficiencies were found to be low with mean values of 10.6%, 34.2%, and 3.6% for assimilation and net and gross growth efficiencies, respectively. An assessment was made of the rate of leaf breakdown by the nymphs, and a value of approximately 29.1% of the dry body weight per day was calculated. The functional importance of the organism to the ...

Journal ArticleDOI
01 Jan 1970-Ecology
TL;DR: Two small ponds in Bartow County, Georgia, northwest of Atlanta, originated by subsidence of unconsolidated surface deposits into solution hollows in the underlying lower Paleozoic Knox Dolomite as mentioned in this paper.
Abstract: Two small ponds in Bartow County, Georgia, northwest of Atlanta, originated by subsidence of unconsolidated surface deposits into solution hollows in the underlying lower Paleozoic Knox Dolomite. The pond sediments consist of copropelic clays 250—400 cm thick with well—preserved plant remains, covered by as much as 150 cm of colluvial deposits with moderately to poorly preserved plant fossils. The clays yield radiocarbon dates of 20,100 and 22,900 BP near their base, contemporaneous with the main Wisconsin glaciation. The full—glacial sediments are rich in pollen and plant macrofossils. The pollen assemblage is dominated by Pinus (pine), with small amounts of Picea (spruce), Quercus (oak), Ostrya type (hophornbeam), and herbaceous types. It closely resembles published full—glacial pollen assemblages from southeastern North Carolina. Pinus banksiana (jack—pine) and Picea sp. are represented by fossil needles at many levels, and the rich macroflora of aquatics shows a marked phytogeographical relationship w...

Journal ArticleDOI
01 May 1970-Ecology
TL;DR: In this article, a step-by-step derivation of the Marquardt's algorithm is given in terms that require only a knowledge of elementary calculus and matrix algebra, and the method is used to fit the logistic equation to a set of data.
Abstract: Equations describing biological phenomena frequently have parameters entering nonlinearly. A highly efficient method for determining the values of parameters in such equations that will give the best least—squares fit to a set of data is Marquardt's algorithm. A step—by—step derivation of the algorithm is given in terms that require only a knowledge of elementary calculus and matrix algebra. As an example, the method is used to fit the logistic equation to a set of data. See full-text article at JSTOR

Journal ArticleDOI
01 Jan 1970-Ecology
TL;DR: Data on two species of Microtus do not refute the hypothesis that aggressive behavior may act to regulate population size, but there is no information on what causes these behavioral changes, and the next step is to see if these changes occur in other populations of these two species and whether they are genotypic or phenotypic.
Abstract: If aggressive behavior regulates population size in small rodents (as claimed by Chitty 1967), periodic fluctuations must be associated with behavioral changes. In an attempt to test this hypothesis, exploratory activity and aggressive behavior were measured in 645 male Microtus ochrogaster and 570 M. pennsylvanicus of 7 populations in southern Indiana from August 1965 to September 1967. Exploratory activity was measured in an open—field test under daylight conditions, and aggressive behavior was measured by fighting voles in pairs in a neutral fighting arena. Exploratory activity could not be related to the individual attributes of home range size or duration of life in males of either Microtus species. On the population level, mean exploratory activity could predict the mean rate of population growth in M. ochrogaster populations, but not in M. pennsylvanicus populations. Aggressive behavior changed significantly over the population cycle in both species, and males from peak populations were most aggressive. Multiple discriminant analysis was used to characterize the behavior patterns of males from increasing, peak, and declining populations. These discriminant scores predicted the mean rate of population growth in M. pennsylvanicus populations but not in M. ochrogaster populations. Aggressive behavior types characteristic of increase, peak, and decline phases showed differential survival rates, but no association was found with body weight or transferrin genotype in either species. Home range size was related to aggressive behavior type in M. ochrogaster but not in M. pennsylvanicus. These data on two species of Microtus do not refute the hypothesis that aggressive behavior may act to regulate population size. However, there is no information on what causes these behavioral changes, and the next step is to see if these changes occur in other populations of these two species and to determine whether they are genotypic or phenotypic.

Journal ArticleDOI
01 May 1970-Ecology
TL;DR: Incoming solar, net, and reflected radiation, wind velocity, relative humidity, and temperatures at various levels above and below an open desert surface were recorded simultaneously at 30—minute intervals for a 3—day period to solve inherent problems in the estimation of contributing factors to net energy exchange and comparison of similar budgets for mesic arthropods are discussed.
Abstract: Incoming solar, net, and reflected radiation, wind velocity, relative humidity, and temperatures at various levels above and below an open desert surface were recorded simultaneously at 30—minute intervals for a 3—day period. Concurrent measurements were also made of arthropod burrow temperatures and relative humidities, scorpion body temperatures, and body and subelytral temperatures of tenebrionid beetles. The burrowing habit enabled arthropods to escape the hot, desiccating conditions recorded on the desert surface during the day. Temperatures and humidities to which scorpions were subjected while in their subterranean retreats depended upon the burrow's depth and subsequent movements in the burrow. Vertical movements between the surface and maximum burrow depths during a 24—hour period provided arthropods with a wide choice of micro— environments. Tenebrionid beetles on the surface were able to achieve a temperature equilibrium only under low temperature and radiation loads. Subelytral cavity temperatures in black Eleodes armata were generally 2—7°C warmer than body temperatures after exposure to direct sunlight. Temperature differences between subelytral cavities of black beetles and beetles with their elytra painted white were small, but suggested that a white dorsal surface was, at least, paritally effective in reducing absorption of solar radiation. The subelytral cavity, in addition to reducing transpiratory water loss, apparently provides a mechanism for increasing convective cooling, and may serve as a temperature “buffer zone” against heat conduction resulting from high intensity solar radiation. A heat exchange budget was estimated for E. armata on the desrt surface. Major contributing factors were heat gained from incoming radiation versus heat lost from convection and reradiation. Contributions from evaporation and metabolism, as determined by laboratory experiments, were very small in comparison, while the role of conduction in energy exchange was assumed to be negligible. Inherent problems in the estimation of contributing factors to net energy exchange, and comparison of similar budgets for mesic arthropods are discussed.

Journal ArticleDOI
01 Mar 1970-Ecology
TL;DR: A new approach is developed for the estimation of insect population densities which eliminates the necessity of counting every individual per sample and indicates that there is an optimal threshold level associated with every p level.
Abstract: A new approach is developed for the estimation of insect population densities which eliminates the necessity of counting every individual per sample. Although the method was developed for populations of corn rootworm eggs, it seems as applicable to other organisms featuring contagious distributions. Estimation by the proposed method is based upon the proportion (p) of samples containing at least t insects each, where t, termed threshold density, can be any positive integer specified. For example, if t is 1, counting is entirely unnecessary since the only information required is the proportion of samples in which the organism is present. The prediction equation which links mean density to the variables ° and t must be estimated beforehand from a series of samples extending over a wide range of population densities. Expressing the model in terms of logarithms premits the estimation of its parameters by linear least squares. The study indicates that there is an optimal threshold level associated with every p...

Journal ArticleDOI
01 Nov 1970-Ecology
TL;DR: Stability of oak woods after fire was greater than that of northern hardwoods as shown by the lower percentage of dead and dying trees, higher percentage of saplings sprouting, and higher average number of sprouts per sapling.
Abstract: Four plant communities–northern hardwoods, oak woods, goldenrod (Solidago sp.)—poverty grass (Danthonia spicata) fields, and little bluestem (Andropogon scoparius) fields–were studied in seventeen areas on west to southeast slopes which had been burned by wildfires in 1962, 1963, or 1964. Stability of oak woods after fire was greater than that of northern hardwoods as shown by the lower percentage of dead and dying trees (16% vs. 35%), higher percentage of saplings sprouting (87% vs. 43%), higher average number of sprouts per sapling 4.4 vs. 2.5), and higher percentage of ground—layer species remaining unchanged or increasing in frequency (87% vs. 67%). In goldenrod—poverty grass fields, fire caused goldenrods to increase and poverty grass to decrease. Average weight of dicots was 24% more and that of monocots was 50% less in burns than in unburned portions. These fields appeared to revert to poverty grass dominance after several years without fire. In little bluestem fields, red top (Agrostis alba) and l...