摘要:

A study of the reproductive cycle of three species of lizards, a forest form, Anolis limifrons, a forest edge species, A. tropidogaster, and a grassland species, A. auratus, was carried out in the Isthmus of Panama from November 1965 until September 1969. The collecting sites were: Pacific side for all three species, mid—Isthmus for A. limifrons and A. auratus and Caribbean side for A. limifrons. Females of all three species of all sites were reproductively active during the wet season (May through December). For A. tropidogaster and A. auratus egg production almost ceases during the dry season. In A. limifrons egg production essentially ceases at the drier Pacific site and is reduced at the other two wetter ones during the same January—to—April period. The testes of males of all three species have mature spermatozoa during the dry season but mean testis weight declines from wet season highs. The male changes occur before the corresponding ones in their females so that the cycles of the two sexes may be controlled by different factors. Lipid levels of adults from the mid—Isthmus site show high values in the late dry season and lower ones throughout much of the wet season. Precipitation, food level, temperature, photoperiod, soil and leaf litter, wind, and evaporation are considered as cues influencing the cycle. The most likely candidate for the female cycle is precipitation with certain limitations. The flexible reproductive system of A. limifrons enables it to reproduce at low rates in some areas where the other two species must cease reproduction during dry periods.

ISSN:0012-9658    

DOI:10.2307/1934579

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

In this paper I attempt to answer the question, What (if any) differences occur in the foraging of isolated wood warblers (Parulidae) and ones in large multispecies populations? Parula (Parula americana), Myrtle (Dendroica coronata), and Black‐throated Green (D. virens) Warblers were studied on seven small spruce‐clad islands off the coast of Maine, each island supporting one pair of one to three of these species. Data obtained were compared with earlier studies of these species in large adjacent populations. Though seasonally isolated, all individuals belonged to the large gene pools of the appropriate species on the adjoining mainland. While the insular forests resemble those of the mainland, they are in general shorter and more open. When only one species was present, it was always the Parula Warbler; when two species were present, they were always the Parula and Myrtle. Black‐throated Green Warblers only occurred in the presence of the latter two species. diversity increased as the size of forest and proportion of foliage in tree crowns grew. Parula and Myrtle Warblers experienced greater nesting success than Black‐throated Green Warblers. Black‐throated Green Warblers foraged much as they did in large populations; however, Myrtle and Parula Warblers demonstrated considerably more plasticity in foraging. When Black‐throated Green Warblers were absent, the two other species tended to modify their foraging. On the one island studied in detail where only Parula Warblers occurred, they appeared to expand their foraging range farther than where Myrtle Warblers were present. Overlap in foraging usually decreased as species compositions became more depauperate. Though variability occurred among individuals of each species, variability of an individual in two different years appeared as great. Black‐throated Green Warblers dominate the other two species socially, and the implications of this situation upon distributions in larger populations and on small islands are discussed. I hypothesize that the stereotypy of the Black‐throated Green Warbler represents an adaptation to the extremely high density it experiences in large populations, which make up the major part of the gene pool. The higher degree of plasticity seen in Parula and Myrtle Warblers may be appropriate to their subordinate roles.

ISSN:0012-9658    

DOI:10.2307/1934580

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Measurements of cores or disc samples representing slightly more than 76,000 annual rings from 336 western white pine tree were compiled to obtain a set of deviations from normal growth of healthy trees that would express the response of these trees to variation in the environment during the last 280 years. Their growth was demonstrated to be a function of temperature and available moisture for the period of climatic record from 1912 to 1958. Extrapolating the relation of growth to weather to the long tree ring record of western white pine, we find that the period 1916—40 represents the most adverse growth conditions with regard to intensity and duration in the last 280 years. This drought, superimposed on sites having severe moisture—stress characteristics, triggered the chain of events which ultimately resulted in pole blight. If the unfavorable conditions for growth during 1916—40 do not represent a shift to a new climatic mean and if western white pine is regenerated only on sites with low moisture—stress characteristics, the probability is high that pole blight will not reoccur for many centuries in stands regenerated from this date on.

ISSN:0012-9658    

DOI:10.2307/1934581

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Males of the lizard Anolis carolinensis are potentially continuous breeders but an annual testicular cycle is induced by seasonal climatic changes. Both photoperiod and temperature are involved as proximate factors in the regulation of testes activity but the importance of each varies with the phase of the cycle. The regenerative phase of spermatogenesis between late fall and spring is controlled primarily by temperature, whereas, the maintenance and eventual regression of the testis in late summer depends primarily on photoperiod. The male reproductive system shows a discrete period of photosensitivity; in nature the lizard shows photo—sexual responses only between late June and mid—October. It is the reduction in day length below about 13.5 hours (the critical day length) in August that induces gonadal regression. The onset and rate of regression is slightly retarded by high temperatures (32 degrees C). The critical day length and temperature dependence of these photoperiodic responses gradually change during the 4—month photosensitive period; and some photorefractoriness is evident early in this period. The factors that determine the onset of the photosensitive phase are poorly understood; short day lengths appear to be important for the termination of this phase. Photoperiod may also affect appetite and growth but these photoperiodic responses differ in several respects from the photo—sexual responses. The two types of photoperiodic responses have different seasonalities, critical day lengths and temperature dependencies. Analysis of the photo—thermal relations of testis activity in A. carolinensis in light of phenological and experimental data for testis cycles in other species indicates that considerable interspecific variation exists in saurian physiological adaptations.

ISSN:0012-9658    

DOI:10.2307/1934582

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Most animal and plant populations are divided into a number of local populations with some dispersal of individuals from one site to another. A theoretical investigation of the phenomenon of dispersal suggests the following consequences: Isolated and poorly accessible sites will tend to become less crowded than an average site as a result of dispersal. An episode of dispersal will result in uneven crowding at the various sites. Variation in the degree of crowding resulting from dispersal will depress the total population size of a species over its entire range. Variation in the carrying capacity with time will lead to an analogous depression of the mean population size. Spatial variation in the carrying capacities of the sites will favor a sensitive response leading to a rapid increase in the emigration rate with crowding, while variation with time will disfavor a response very sensitive to crowding. Variation in space will favor the emigration of a small fraction of the population, while variation in time will favor the emigration of a larger fraction.

ISSN:0012-9658    

DOI:10.2307/1934583

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Structural habitat data generally support the interpretation that competition for food results in habitat partitioning. In this investigation, the importance of ethological factors in determining the structural habitat of Anolis lizards is demonstrated by examining the structural habitat of Anolis polylepis during foraging and social interaction, its two major activities. “Overall” structural habitats show that intraspecific classes use perches of significantly different heights and diameters. Perch heights of adult males and females are also shown to be related to the type of activity in which they are engaged. Overall structural habitat data show a greater difference between the sexes than actually exists in their feeding locations. Ecological differences between insular and continental Anolis potentially affecting the structural habitat are also discussed.

ISSN:0012-9658    

DOI:10.2307/1934584

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

An ecosystem approach was used to assess the effects of soil contamination with an organophosphate insecticide on ecological succession in 3—acre old field on the Piedmont of New Jersey. Diazinon was applied to one—half of the field in May 1967 and again in May 1967 and again in May 1968 at a rate of 12 lbs of active ingredient per acre. A latin square experimental design was used to analyze the effects of the insecticide on the density, diversity, and production of vegetation; the density and diversity of herb—stratum arthropods; and the trophic relationships that developed on treated and untreated areas. In 1967, insecticide contamination produced a significant enrichment in both density and diversity of vegetation as well as a consistent trend toward greater plant biomass on treated areas. The vegetation changes represented a summation of small but consistent differences in major producers common to both treated and untreated areas. Plant differences were believed due to a phytotoxic effect of diazinon on Convolvulus sepium, which was significantly reduced on treated areas. Other plant species normally inhibited by Convolvulus subsequently flourished on treated areas. Herb—stratum arthropod populations were similar on treated and untreated areas in 1967, despite the vegetation differences. Only a trend toward greater insect diversity on treated areas was present. The failure of indirect arthropod differences to develop was due to the similar availability of dominant producers and thus food web bases on treated and untreated areas. Radionuclide tracer studies indicated that ragweed (Ambrosia artemisiifolia) was the major food web base for resident consumers in the latter part of the growing season. The trophic transfer from ragweed was quite similar in treated and untreated areas. The lack of arthropod differences was thus attributed to similar availability of ragweed biomass in both areas. Vegetation differences were absent in 1968 following a second treatment with diazinon. Moisture appeared to be a major factor influencing the impart of the insecticide during the two summers. Vegetation differences developed in June 1967 at a time when rainfall was almost absent. In 1968, however, considerable rainfall occurred during the same period. The increased rainfall stimulated a greater seedling development than in 1967, thus apparently overcoming the effects of the insecticide. Environmental factors such as soil moisture can therefore interact with pollutants and seriously influence the degree of ecosystem modification.

ISSN:0012-9658    

DOI:10.2307/1934585

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The effects of exploitation on growth, condition, and surplus production were measured over an 8—year period for a population of seven species of warm—water fishes in a 4.05—ha lake. The lake was shallow, fertile, and moderately productive. Population estimates of individual species were made each spring concurrently with the annual removal of 34% to 71% of the existing population. The initial stock density of all species was 48.66 g/m2in the spring of 1962. The optimum yield for this mixed population was calculated to be 14.56 g/m2per year at a stock density of 18.67 g/m2, with the bluegill producing most of this surplus weight. When species were considered separately, there was poor correlation between exploitation rate and either growth or condition. The response of the entire population to thinning was more predictable, with both growth and condition related to stock density. Best growth occurred at densities near 20 g/m2or approximately at the level for optimum yield.

ISSN:0012-9658    

DOI:10.2307/1934586

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The upstream and downstream directional responses of demes of sockeye salmon (Oncorhynchus nerka) fry from inlet and outlet streams hatched and reared under controlled, identical conditions were tested in the laboratory. The tests compared innate directional responses of fry from the two sources to variables of water source and temperature. Both variables influenced the directional responses of the fry. The direction of migration (upstream for outlet fry or downstream for inlet fry) and response to changes in the test variables differed substantially between fry from inlet or outlet streams; this response difference held for populations of sockeye salmon from different geographical locations (Canada and Alaska). The differences were concluded to be innate in origin. Single tests of fry of rainbow (Salmo gairdneri) and cutthroat (S. clarki) trout from inlet and outlet streams indicated that directional responses of fry from these species are also innately influenced. The significance of matching the innate responses of donor stocks of fish to the characteristics of a recipient environment is discussed.

ISSN:0012-9658    

DOI:10.2307/1934587

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The annual energy budgets of four small ponds in northwestern Florida were calculated from the amounts of 1) solar radiation, 2) atmospheric long—wave radiation, 3) back radiation, 4) evaporative energy, 5) conducted energy, and 6) sensible heat which entered or was lost from the wager. Long—wave radiation constituted between 62.1 and 63.9% of the total incoming radiative energy and 80.8 to 85.0% of the total energy loss. Evaporative loss was between 14.6 and 18.3% of the total. Between 370,498 and 631,970 kcal m(—2)yr(—1) (37,050 — 63,197 cal cm(—2)y(—1)) were stored. Atmospheric radiation counteracts a portion of the radiative loss from water, thus reducing loss of stored solar energy.

ISSN:0012-9658    

DOI:10.2307/1934588

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY