摘要:

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.

ISSN:0012-9658    

DOI:10.2307/1934037

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

This paper describes a method for separating plant morality due to heat from mortality caused by herbage removal; squirreltail (Sitanion hystrix (Nutt.) J. G. Smith) and needle—and—thread (Stipa comata Trin. and Ruper.) are used as examples. After plants are burned in the field under controlled conditions, ratios are calculated between field—measured durations of temperatures in plants and laboratory—measured thermal death times for plant tissue. If the sum of the ratios for the various temperatures is 1.0 (designated 1 necrotherm) or greater, mortality is attributed to heat; if the sum is less than 1.0, to herbage removal. Further testing of the "predictor" on more species, sites, years, etc., is needed, but the method appears very promising. For the two bunchgrasses tested, heat alone accounted for all mortality by fire, except during July. The time required for a specific temperature to kill plants varied with season. To predict thermal death times for bunchgrasses and thus simplify the laboratory determinations, an empirical equation was developed.

ISSN:0012-9658    

DOI:10.2307/1934038

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

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.

ISSN:0012-9658    

DOI:10.2307/1934039

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Single—species populations of flour beetles, Tribolium confusum and T. castaneum, were experimentally manipulated to demonstrate that both predation by adults on pupae and predation by larvae on eggs are effective mechanisms for regulating the abundance of adult beetles. It was shown that predation by adults on pupae is the more effective of the two mechanisms, since experimental interference with the first kind of predation produces a larger increase in adult populations than does interference with the second kind. The same generalization holds for both species.

ISSN:0012-9658    

DOI:10.2307/1934040

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

The 36 least disturbed hardwood stands in Indiana were selected for analysis of the characteristics and interrelationships of the five forest types. The types were defined by the species importance sums for the four species—groups: oak—hickory, beech—maple, other upland mesophytic species, and lowland—depressional species. From the matrix of stand similarities derived by applying Motyka's coefficient to species importance values, relationships among the five forest types were indicated by cluster and ordination analyses. Both methods grouped stands of three types as extremes (oak—hickory, beech—maple, and lowland—depressional) and two mixed types as intermediates (western mesophytic and mixed woods). Within each extreme type some variant stands represented gradations toward another type. Edaphic controls of the forest types in Indiana are indicated by the patterns of the ordination distribution of substrate factors: drainage profiles, available moisture, permeability, texture of the A horizon, source of the parent material, pH of the B horizon, and degree of development of the soil.

ISSN:0012-9658    

DOI:10.2307/1934041

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Vegetation and soil systems in two beechwoods were examined by measurements of variables at the same sites. Principal components analysis was used to generate hypotheses about the relationship between vegetation and soil which were tested by simple correlation of components and variables. Further information explaining the variation of the vegetation system was obtained by simple correlation with environmental data. Canonical correlation was used to relate the variables of the two systems directly and all together. The primary relationship between vegetation and soil was found to be in terms of soil—moisture variation. However, light variation associated with changing canopy quantity and slope variation were found also to affect both systems particularly through their effect on soil moisture.

ISSN:0012-9658    

DOI:10.2307/1934042

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

The dry—weight composition of the diets of richardson ground squirrels (Citellus richardsonii), mormon crickets (Anabrus simplex), and six species of grasshoppers (Xanthippus corallipes, Circotettix rabula, Aeropedellus clavatus, Melanoplus infantalis, Melanoplus bruneri, and Melanoplus alpinus), collected at Prairie Divide, Colorado, was determined. Many food plants were shared by these herbivores. Vetch (Astragalus spp.), sandwort (Arenaria fendleri), fungi, parry oatgrass (Danthonia parryi), bluegrass (Poa spp.), fringed sagebrush (Artemisia frigida), dandelion (Taraxacum officinale), and sedge (Carex spp.) were major foods. Bluegrasses, vetch, and sandwort would probably become limiting if population peaks of several of these herbivores coincided. The ranking of the food niches of these herbivores from specialized to generalized based on mean indices of dietary similarities is X. corallipes, A. clavatus, C. rabula, M. alpinus, A. simplex, M. bruneri, C. richardsonii, and M. infantalis. Males ate fewer species of food plants than females of the same orthopteran species, and the diets of males and females of the same orthopteran species were occasionally less similar than were the overall diets of different species on the same date.

ISSN:0012-9658    

DOI:10.2307/1934043

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Plants of Thlaspi alpestre L. (Cruciferae) from a high elevation population in the Medicine Bow Range of Wyoming were genetically dwarfed. These plants broke dormancy and entered dormancy more rapidly than a subalpine population from the same area. The overwintering of seed of T. alpestre before germination in the field may be caused by properties of the seed coat. The distribution of T. alpestre at high elevations is limited in part by a low reproductive ability; at low elevations, competition and infection by pathogens may shorten the life span of T. alpestre and limit its distribution.

ISSN:0012-9658    

DOI:10.2307/1934044

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

In 1966—67 in the eastern part of Hokkaido, where severe cold weather and a dry state prevailed throughout the winter, most young conifers, especially those wintering on the southern slopes, were seriously damaged. Minimum temperature was about —30°C, and soil temperature at 10—cm depth even on the southern slopes remained below zero for 3.5 months. Soil was frozen down to about 40 cm. Temperatures of stems and leaves of young conifers wintering on the southern and northern slopes rose to about 17° and 9°C, respectively, in midday and remained unfrozen for about 6 and 2 hr, respectively, in the daytime. Under these conditions, the conifers wintering on the southern slopes were intensely dehydrated towards the end of February. In most damaged trees, browning was observed on the stem bark. Trees in which desiccation damage was artificially induced exhibited nearly the same browning as that observed in trees suffering damage under natural conditions. Stems and leaves of young Sakhalin fir and Ezo spruce could stand freezing in winter below —50C, and white pine and American arborvitate which sustained damage seriously under natural conditions also survived freezing below —120°C. Young conifers wintering in frozen soil were damaged by dehydration resulting from a combination of freezing of soil and exposure to sunshine.

ISSN:0012-9658    

DOI:10.2307/1934045

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

During the growing season alpine plants on Mt. Kurodake (1,984 m) in the Taisetsu mountain range in Hokkaido, Japan, survived freezing to only —5° to —7°C. Even after exposure to 0° and —3°C for 2 weeks, the resistance to freezing of these plants increased only slightly. During the winter, however, most alpine plants studied survived freezing at temperatures below —30°. Salix pauciflora, Diapensia lapponica, mosses, an lichens resisted freezing down to —70°C. They also retained viability after immersion in liquid nitrogen following prefreezing at —30°C. Furthermore, there did not appear to be an essential difference in the hardening effect between willows growing in high mountains and in low altitudes in Hookaido. Alpine plants may be characterized by their dwarf form, short growth period, and high freezing resistance of subterranean stems, crowns, and roots.

ISSN:0012-9658    

DOI:10.2307/1934046

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY