Showing papers in "Ecology in 1971"

The Nonconcept of Species Diversity: A Critique and Alternative Parameters.

Abstract: The recent literature on species diversity contains many semantic, conceptual, and technical problems. It is suggested that, as a result of these problems, species diversity has become a meaningless concept, that the term be abandoned, and that ecologists take a more critical approach to species—number relations and rely less on information theoretic and other analogies. As multispecific collections of organisms possess numerous statistical properties which conform to the conventional criteria for diversity indices, such collections are not intrinsically arrangeable in linear order along some diversity scale. Several such properties or "species composition parameters" having straightforward biological interpretations are presented as alternatives to the diversity approach. The two most basic of these are simply ▵1=[n/n—1][1—Σi(N_i/_N)2] =the proportion of potential interindividual encounters which is interspecific (as opposed to intraspecific), assuming every individual in the collection can encounter all other individuals, E(Sn) = Σi [1—(N—Nin)/(Nn)] =the expected number of species in a sample of n individuals selected at random from a collection containing N individuals, S species, and Ni individuals in the ith species.

On the Measurement of Niche Breadth and Overlap

Abstract: Measures of niche breadth and overlap that depend on the distribution of individual among resource states (ecological categories) should be independent of the relative abundance of the species and of the number of resource states considered. Such measures should also take into account the degree of distinctness of the resource states from the point of view of the organisms concerned. An ecoassay of the distinctness of resource states may well be easier and more meaningful than measurements of physical and chemical factors. We propose that the species composition of communities utilizing different resource states may be used to develop weighting factors with which each state may be weighted in proportion to its degree of distinctness. The weighting factors are used in the development of indices of niche breadth and overlap that correct for variation in the range and distinctness of resource states and that suffer less from human subjectivity than do the measures used to date. The use of such indices and the relationship of niche overlap to competition are discussed.

Competition in tropical stream fishes : support for the competitive exclusion principle

Abstract: Two collections of fish were made from the same Panama lowland stream, one during the dry season, and a second during the wet season. Food overlaps among nine sympatric fish species were calculated for each collection by examining fish stomach contents. Species habitats and feeding methods were determined from field and laboratory observations. Estimates of food abundance, measured independently from food overlap, were made by direct and indirect methods, and were used to determine relative levels of competition. The results show that food overlaps among the fishes are at a minimum during the dry season. Food abundance is also lowest during the dry season, which suggests increased competition for food at this time. This seasonal coincidence of the most distinct species separations with the time of increased competition are exactly those consequences predicted by the principle of competitive exclusion. It is concluded that this study provides strong support for the validity of this principle.

Territory and Breeding Density in the Great Tit, Parus Major L.

Abstract: This paper describes an investigation into whether or not spring territorial behavior was limiting the breeding density of a population of Great Tits on Wytham Estate, near Oxford. The analysis of distances between neighboring nests showed that nest sites were more spaced out than would be expected from a random distribution; this indicated that interactions between the birds produced at least a local density—limiting effect. In 2 successive years, established territorial pairs were removed from a stable spring population in mixed woodland. The removed birds were rapidly replaced by new pairs. These newcomers were largely first—year birds; they came from territories in the hedgerows that surrounded the wood; the vacated hedgerow territories were not refilled. The hedgerows were found to be suboptimal in terms of reproductive success. Thus territory limited the breeding density in the optimal habitat. Song advertisement is probably important in maintaining territorial boundaries, hedgerow birds being able to detect the presence of individual woodland territory holders by recognizing their songs. The effect of winter food supply on the population was investigated by supplying excess food throughout one winter. This artificial food supplement appeared to have no effect on the number of Great Tits breeding in the wood, but did produce an increase in the case of a related species, the Blue Tit. The results show that territorial behavior influences density; this is not considered to be a function of territory in the evolutionary sense, but rather a consequence of spacing out that has been selected for in some other context. A possible advantage of spacing out in the Great Tit is as a defense against predators. Territory size varies considerably from year to year. These variations are the result of interactions between the birds themselves, rather than direct adjustments of territory size to fluctuations in some environmental resource. Even though territory has an effect on the number of birds breeding in the wood,it is not an important density—dependent factor acting to regulate the population.

On the Ecological Significance of Bergmann's Rule

Abstract: A positive correlation of weight with latitude in homoiotherms (Bergmann's rule) cannot normally depend upon the physics of heat exchange. Most latitudinally widespread mammals in North America do not follow this rule. Those that do are usually carnivores or granivores; a change in their body size reflects a change in the size of their prey. A latitudinal change in the size of available prey is due either to the distribution of the prey species or to the distribution of other predators utilizing the same prey species. Only the smallest species of a set of similar predators normally will conform to Bergmanns rule, and then only beyond the limits of distribution of the largest species. These changes in size seem to be another example of character displacement. See full-text article at JSTOR

Distribution on Environmental Gradients: Theory and a Preliminary Interpretation of Distributional Patterns in the Avifauna of the Cordillera Vilcabamba, Peru

Abstract: A new theoretical approach to the study of distribution is presented in this paper. The central concerns the types of interactions between organisms and their surroundings which may function to impose limits on the occurrence of species on a smooth unifactorial environmental gradient. The theory is constructed of a set of three complementary and mutually exclusive models which arbitrarily are given the power of accounting for all possible distributions. Each of the models predicts a different patter of distribution within a group of organisms and each contains two or more unique features which serve to distinguish it from the others. In their simplest form the models state that the occurrence of species is limited respectively by: (i) physical or biological conditions that vary in parallel with the measured gradient, (ii) competitive exclusion and (iii) environmental discontinuities (ecotones). Predictions of each model include (a) the shape of population density curves, (b) the shape of congruity (faunal attenuation) curves, (c) distributional patterns at the termini of gradients, and (d) the form oft he frequency distribution of ecological amplitudes. Application of the theory is demonstrated with data obtained in a study of the distribution of bird species on a uniform elevational gradient in the Eastern Andes of Peru. A series of four expeditions to the Northern Massif of the Cordillera Vilcabamba, a vast undisturbed mountain wilderness, provided information on the upper and lower limits of occurrence of over 410 species of forest birds. Faunal composition and the relative abundances of many species wee estimated at each of 15 stations through large netted samples of birds (170—604 individuals). Following a protocol described in the text, the upper and lower limits of 261 species were assigned to one or another of the three models. Certain limitations of method result in a small number of unavoidable errors in these assignments; hence the outcome of the partitioning procedure is only a first approximation. As evaluated by this preliminary analysis, the three mechanisms of distributional limitation differ appreciably in their importance in the Vilcabamba avifauna. Ecotones account for less than 20% of the distributional limits, competitive exclusion for about one—third of the limits and gradually changing conditions along the gradient for about one—half of the limits.

Dispersal: Population Consequences and Evolution

Abstract: 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.

Density-Dependent Natural Selection

Abstract: Density—dependent selective values illustrate the evolutionary effect of population—regulating processes that diminish an individual's probability of survival with increased crowding. The selective values, assumed to decrease as a linear function of density, lead in a mild environment to the evolution of phenotypes having a high carrying capacity, K, at the expense of a low intrinsic rate of increase, r. A graphical technique shows that selection causes evolution of phenotypes having a high r at the expense of a low K in harsh seasonal environments. A mathematical technique developed for analyzing evolution in coarse—grained seasonal environments reveals genetic mechanisms, including ones with full dominance, with which a moderately harsh seasonal environment causes stable polymorphism between high—r and high—K genes. The energy balance equation demonstrates the role of high—r and high—K phenotypes in the population's energy flow. A high—r phenotype makes a large expected contribution to the population's productivity under conditions of negligible crowding, and a high—K phenotype has, for a given contribution to the population's productivity under uncrowded conditions, a low sensitivity to having that contribution diminished by crowding.

Soil Respiration Studies in Tallgrass Prairie in Missouri

Abstract: Rates of carbon dioxide evolution from soil in mid—Missouri tallgrass prairie were highly correlated with temperature of the surface soil. Values increased exponentially with rising temperatures through the seasonal range under observation. Twenty—four—hour measurements employing infrared analysis were conducted periodically during all seasons from August 1968 to June 1970. Weekly averages calculated from regression for the entire year ranged from zero during the coldest period to 450 mg CO_2m(—2)hr(—1) during summer. The annual total was 1,675 g CO_2m(—2). The organic matter equivalent was 1,005 g, approximately 2.2 times the indicated biomass turnover for the root system for the same period. The difference was attributed to root respiration by determining a correlation between CO2 evolution and root biomass with KOH absorption and titration and by converting these data to infrared equivalents. It was estimated that 60% of the total respiration (surface litter excluded) was due to microbial processes in organic turnover and the balance to root metabolism.

A Short‐Term Experimental Investigation of Resource Partitioning in a New Zealand Rocky Intertidal Habitat

Abstract: The effects of single—species removals on community composition and overt appearance were examined in an exposed, rocky, intertidal habitat at Anawhata, New Zealand. Two experiments were performed. A carnivorous starfish, Stichaster australis, was removed manually and kept removed from a stretch of shore for a period of 9 months (September 1968 through May 1969). This manipulation resulted in the mussel Perna canaliculus extending its vertical distribution by 40% of the available range, and a decrease in the species richness of the invaded area from 20 to 14 species. The second manipulation involved the removal of both Stichaster and a large brown alga, Durvillea antarctica, from two areas. Results were striking. Within 15 months 68% of the available space in one area, and 78% in the other, was occupied by Perna, to the almost total exclusion of other fauna or flora. These events not only duplicated the results of the Stichaster removal experiment, but also suggested that space, as the prime limiting requ...

A multivariate statistical approach to the hutchinsonian niche: bivalve molluscs of central canada'

Abstract: A bstract. The use of multiple discriminant analysis to identify the significant and independent ecological factors separating species distributions is proposed and discussed. Such an analysis was performed on 345 samples, containing a total of 10 bivalve mollusc species, from 32 lakes in Manitoba, Ontario, and Saskatchewan. Measurements of nine ecological parameters were associated with each sample. Five discriminant functions account for 95% of the amongspecies variance, and 4 of the 5 are ecologically interpretable. Three of these, accounting for 80% of the among-species variance, are interpreted as bases of trophic, rather than physical or chemical, separation. There is separation of species on each discriminant function. The use of discriminant scores to classify lakes with maximum relevance to species distributions is demonstrated and discussed. A generally applicable measure of environmental heterogeneity based upon this type of analyisis is proposed. The value of this type of analysis in quantifying ecological concepts derived from the Hutchinsonian niche model is discussed. An example is given of a reduced available niche resulting in the loss of two species, smaller realized niches for the remaining species, and greater niche overlap.

Selection in Density‐Regulated Populations

Abstract: This paper examines the effect of natural selection on the composition of a population when the expected numbers of offspring of the different genotypes are decreasing functions of population size. It is shown that the eventual outcome of selection (whether there is a stable polymorphism or fixation of one or other allele) is determined by the genotypic K—values, but that the r—values influence the composition of equilibrium populations. With certain r—values there may be permanent oscillations in population size and gene frequency. A different model of selection, where selective differences are unrelated to differences in r and K in a regulated population, is also described and its relevance to the problem of genetic load is discussed. See full-text article at JSTOR

Population Control in Arctic Ground Squirrels

Abstract: Unlike most tundra rodents, the arctic ground squirrel, Spermophilus undulatus, maintains a relatively constant population. The squirrels exist in two types of groupings: (1) breeding colonies, which cannot expand because their members are territorial, the females reacting to the availability of burrow sites (an environmental constant), and (2) refugee populations, which cannot expand because they cannot breed and, living in habitat only periodically suitable for squirrels, are killed off twice each year. The breeding populations have two distinct types of territories: breeding territories from May to August and prehibernation territories from August to November. During each episode, surplus animals are driven from the colonies and enter the refugee populations, where they are subjected to heavy predation by foxes and bears. See full-text article at JSTOR

Time and Energy Budgets of Territorial Hummingbirds

Abstract: From laboratory data of flying and resting metabolism and field data on time budgets of territorial male Eulampis jugularis hummingbirds we were able to estimate caloric energy budgets associated with territorial behavior. The relative time and energy expenditures for territorial defense, foraging, and sitting varied in territories with different species of flowers. For example, territories centered around banana flowers had lower foraging costs than those centered around Myrtaceae or Inga—Hibiscus. The costs for flycatching, hovering,and perch changes accounted for relatively little of the time and energy budgets at any of the territorial defense and foraging were expended in sitting on perches within the territory. Territorial defense was of relatively low cost in time and energy because of the inactive defense utilized by Eulampis. Selection will optimize time and/or energy budgets, but the type of budget optimized will depend in large part on the exploitation technique of the species. For birds that do not fly to forage, but exploit food items that require a long search time per calorie, time that can be released for other activities may be more important than major shifts in energy budgeting. For hummingbirds, however, optimizing energy may be more important to insure a positive energy budget.

Mechanisms of Competitive Exclusion Between Two Species of Chipmunks

Abstract: Two species of chipmunks, Eutamias dorsalis and E. umbrinus exclude each other from certain elevations on isolated mountain ranges in the central Great Basin. Competitive success is determined by habitat; dorsalis excludes umbrinus from the sparse pinon—juniper forests at lower elevations and umbrinus excludes dorsalis from the denser forests at higher altitudes. The two species occur together only in a very narrow strip of intermediate habitat. Observation of the behavior and interactions of the two species within this overlap zone resulted in the following explanation for the mutual exclusion. E. dorsalis, the more aggressive and more terrestrial species, chases umbrinus from those areas where the trees are so widely spaced that umbrinus must flee on the ground. The competitive advantage immediately shifts to the more social and arboreal umbrinus when the trees are sufficiently large and dense that their branches interlock. In these habitats umbrinus readily escapes dorsalis by fleeing through the trees over routes that the more aggressive species cannot follow. In such situations the aggressive nature of dorsalis actually becomes competitively disadvantageous because the more social umbrinus is so numerous that dorsalis wastes a great deal of time and energy on fruitless chases. The differences between the two species in aggressive behavior apparently represent adaptations to the density of cover and food resources in their habitats. The main mechanisms of the competitive interaction between these two chipmunks (interspecific aggression, the ability of the subordinate species to utilize some feature of the habitat to escape from the dominant species, and aggressive neglect on the part of the dominant species) may frequently be important in cases of competitive exclusion between highly mobile animals.

Intraspecific Differences in Nitrate Half‐Saturation Constants for Three Species of Marine Phytoplankton

Abstract: Half—saturation constants (K) for NO_3 uptake were measured on eight clones, belonging to three species, of marine phytoplankton. The clones isolated from oceanic, low—nutrient areas had K values of below 0.75 (mu)M NO_3, while clones of the same species taken from estuarine regions had higher K values (over 1.5 (mu)M NO_3). Other isolated from shelf areas had intermediate (1.2 (mu)M NO_3) or low (0.1 (mu)M NO_3) K values. These data suggest that physiological races of marine phytoplankton are adapted to high or low nutrient levels. See full-text article at JSTOR

Oak Regeneration in the Upper Carmel Valley, California

Abstract: Acorn germination and seedling survival were studied in three species of foothill woodland oaks. Quercus douglasii and Q. lobata acorns matured in October. These nondormant acorns germinated quickly at favorable temperatures. Quercus agrifolia acorns matured later and germinated more slowly. Acorns placed on the surface of a south—aspect plot lost viability. On a north—facing plot they survived autumn heat and germinated during the winter, but rooted poorly. Acorns buried on either aspect germinated well. Burial by birds and squirrels, important in regeneration, insulates acorns from autumn heat, partially hides them from animals, and ensures rooting. Quercus douglasii seedlings had the greatest drought tolerance. In grass cover on a south—facing soil even they can survive their first summer only during wet years. On north aspects seedlings of several species can survive grass competition over a broader range of climatic conditions. Deer and pocket gophers are important in eliminating seedlings that survive the summer drought.

The Ecological Consequences of Interspecific Territorial Behavior in Birds

Abstract: When, considering cases in which territorial aggression occurs between species, we find that the relationship varies with the species' geographical and ecological distributions. If similarly sized species are narrowly sympatric or are widely sympatric but normally occupy different habitats, they both are interspecifically territorial and maintain mutually exclusive territories. If similarly sized species are widely sympatric and are common in the same hab- itats, one species is interspecifically aggressive and the other species flies away when chased. In this paper I present a model that explains these observations. I propose that interspecific territoriality can account not only for these differences in behavior and habitat but also for differences in foraging behavior and bill shape between sympatric species. The last three dif- ferences have usually been explained to be consequences of interspecific competition for food. The assumptions of the model proposed here are that (i) interspecific territoriality is misdirected intraspecific territoriality, (ii) territorial behavior prevents some individuals from breeding in optimal habitat, (iii) the individuals of one species are usually dominant over the other species in interspecific encounters, and (iv) of the habitats available to two interspe- cifically territorial species in their area of sympatry, one habitat is optimal for them both. This model is unusual in that a corollary of assumption (i) is that interspecific territoriality is not an adaptive characteristic, contrary to the assumptions of earlier writers. Nevertheless, the model is interesting and worth consideration because of the range of observable phe- nomena that are predicted. A territory is a space within which an animal is aggressive toward, and usually dominant over, cer- tain categories of intruders (Emlen 1957a). Usually aggressive displays of territory holders (territorial behavior) are directed toward members of the same species, but sometimes similar displays showing some

Interspecific territoriality in a pomacentrid reef fish, Pomacentrus flavicauda Whitley

Abstract: Field observations on territorial behavior of the fish P. flavicauda were made for a total of 200 hours at Heron Island, Great Barrier Reef. Specimens 6 cm or more in length restricted their movements to areas of approximately 2 m2 over at least a 5-month period. Distribution of the fish was highly correlated (rs = 0.89) with the amount of interface between sand and dead coral. Such areas provided algae in close proximity to shelter. Observations of agonistic behavior showed that P. flavicauda usually responded agonistically to 38 species of 12 families, but not to 16 other species of 6 families. Apparently competitors for algae elicit an agonistic response from P. flavicauda, while carnivores do not. Maps locating the positions of agosnistic encounters indicate that the entire home range is defended as a territory. The effectiveness of the agonistic behavior was indicated when, following the removal of 6 specimens of P. flavicauda, there was an increase in algal-feeding fishes seen within their territories. Implications, of these results for out understanding of interspecific territoriality are discussed.

Competitive Exclusion as a Factor Influencing the Distributions of Two Species of Terrestrial Salamanders

Abstract: The salamander Plethodon richmondi shenandoah is restricted to areas of talus on Hawksbill Mountain, Shenandoah National Park, Virginia, while P. cinereus inhabits the soil outside the talus. To test the hypothesis that the former species is excluded from the soil by the latter species, three enclosures were constructed in each of four habitats: (i) in talus consisting only of bare rocks, (ii) in talus where soil has infiltrated between but not under rocks, (iii) in isolated pockets of shallow soil within the rocky confines of the talus, and (iv) in deep soil outside the talus. In each habitat one enclosure contained an isolated sample of shenandoah, another an isolated sample of cinereus, and the third a mixture of the two species. The above testes indicated that: (i) neither species survived the extremely dry conditions of the bard rocks for more than a week, (ii) shenandoah expressed a higher survivorship than did cinereus in this relatively dry habitat, (iii) in the shallow soil shenandoah had lower survivorship in the presence of cinereus than it did in isolation, and (iv) in the deep soil shenandoah had poorer survivorship than cinereus in the mixed species enclosure and poorer survivorship than its isolated control. P. cinereus apparently inhibits the presence of shenandoah in areas of soil, while shenandoah survives better under rocky conditions. However, the talus is a suboptimal habitat for shenandoah, since its survivorship in isolated enclosures is significantly better in the presence of soil. It seems unlikely that salamanders other than cinereus could exclude shenandoah from the soil or that other animals exert a strong influence. Predation, diseases, and parasites also do not appear to exclude shenandoah from areas of deep soil. Competitive exclusion by cinereus has probably restricted the distribution of shenandoah to the suboptimal talus refugium.

Escape of Cassia grandis L. beans from predators in time and space.

Abstract: In Central American deciduous forests, most of the seeds of the caesalpinaceous legume tree Cassia grandis are killed by the larvae of two bruchid beetles, Pygiopachymerus lineola and Zabrotes interstitialis Pygiopachymerus lineola oviposits on the large pods, the first—instar larvae bore into the seeds, and the emerging adults cut large exit holes in the pod wall Moth larvae gain access through these holes and eat clean much of the sticky pulp around the seeds Simultaneously, the adults of Z interstitialis enter through the P lineola exit holes and oviposit directly on all clean seeds In heavily disturbed communities where vertebrate dispersal agents are absent, these host—specific bruchids achieve almost 100% predation on the C grandis seed crop; however, the more rapidly the dispersal agents remove the seed pods, the less seed predation there will be by Z interstitialis Since C grandis bears mature fruit every other year, the size of each seed crop is large enough to surpass the predation abi

Plant Diversity in a Chronosequence at Glacier Bay, Alaska

Abstract: Eight sites of known age were sampled in Glacier Bay National Monument, Alaska, to examine the changes in plant diversity during primary succession in that region. Four strata–trees, tall shrubs, low shrubs—herbs, and bryoid—thalloids–were sampled independently. Data suggested a sequence of wave—like invasions on sites by strata, largely in order of increasing size. Bryoid—thalloids were exceptional in demonstrating a late peak in cover values. In general, diversity of a particular stratum declined during the period in which the stratum dominated the community in terms of foliar cover. Richness (species number) of communities increased rapidly in the first 100 years, then more gradually to reach a maximum in the muskeg steady state. Equitability (evenness of distribution of foliar cover among species) was erratic, but tended to increase with age. After initial rises, three diversity indices showed nearly flat curves with two exceptions: marked decreases in the 30— to 50—year period; and a rise to maximum levels in the final steady state. Total information per unit area calculated from diversity and foliar cover increased in a sigmoid manner with peak information in the final muskeg stage.

Postglacial and Interglacial Vegetation History of Southern Georgia and Central Florida.

Abstract: From 8,500 to 5,000 radiocarbon years ago three sites in southeastern Georgia and peninsular Florida, Lake Louise, Scott Lake, and Mud Lake, had predominant sclerophyllous oak forest, scrub, or savanna, probably with patches of bluestem prairie. About 5,000 year ago pine forest came to predominate on upland sites, and there was a more diverse flora of broad-leaved trees than before. Bayhead and cypress swamp vegetation did not become significant until after 5,000 BP, when Fagus (beech) also became abundant for the first time. The sediments at both Lake Louise and Scott Lake present evidence for recent forest clearance and consequent modification of the lake ecosystem. No vegetation record is available for the earlier postglacial or the period of the main Wisconsin Glaciation. Probably most lake basins of the region were dry during this time because of depression of the regional water table in highly permeable Tertiary limestones, caused by eustatic depression of sea level during Wisconsin Glaciation. At Lake Louise, as at Mud Lake, organic deposits too old to be dated by the radiocarbon method underlie the postglacial sequence, separated from it by clastic sediments that represent a large sedimentational hiatus. The lower organic deposits have the characteristics of an interglacial cycle. They are referred to the Sangamon interglacial, thus modifying a previous opinion that the Mud Lake sediments were partly Illinoian and partly Sangamon in age. A basic interglacial cycle proceeding from dry oak forest and herbaceous communities with eutrophic lakes to pine forest with hammock, bayhead, and cypress swamp vegetation is reconstructed for the southeastern United States.

Regulation of the Annual Testis Cycle by Photoperiod and Temperature in the Lizard Anolis Carolinensis

Abstract: 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.

Structural Habitat and Time Budget of a Tropical Anolis Lizard

Abstract: 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. See full-text article at JSTOR

Some Effects of Stem Flow from Forest Canopy Trees on Chemical Properties of Soils

Abstract: The most abundant elements contained in stem flow from American beech (Fagus grandifolia), red oak (Quercus rubra), and sugar maple (Acer saccharum) were C >>> K = Ca > Na = Mg = P. Variations in leaching potential and in concentration of chemical constituents around the base of beech trees, due to non-uniform stem flow, produced considerable variation in chemical properties of soil around the stems. The presence or absence of organic litter in surface soil samples caused only slight differences in chemical properties of the samples. Systematic variations in chemical properties of Bennington and Dekalb soils were developed with radial symmetry with respect to the stems of several tree species. Generally, the greater the difference in chemical properties of these soils with respect to distance from the tree stem, the greater the quantity of stem flow from the tree. In soil under those trees with relatively large quantities of stem flow, organic C, exchangeable K, and ( 137)Cs increased, while pH decreased progressively inward toward the stems, particularly in the upper 10-20 cm of soil. The magnitude of variations was greater in Bennington soil than in the more acidic and coarser textured Dekalb soil, and greater under beech trees and red oak than under sugar maple, pignut hickory (Carya glabra), and white oak (Quercus alba). The variations under beech and red oak were attributed mainly to effects of stem-flow water, whereas those under the other species were attributed mainly to effects of organic litter or to a combination of the two effects. The content of the fallout radioisotope ( 137)Cs in soil under the trees was used as substantiating evidence of the quantity of stem flow the trees.

Altitudinal Zonation of Chipmunks (Eutamias): Interspecific Aggression

Abstract: Eutamias alpinus, E. speciosus, E. amoenus, and E. minimus are contiguously allopatric on the eastern slope of the Sierra Nevada, California. This paper is part of a study of the factors determining the lines of contact between these contiguously allopatric populations. Overlapping fundamental niches and overlapping realized niches indicate that competitive exclusion has occurred. Patterns of intra— and interspecific aggression are described for these four species. The aggressive dominance of alpinus and amoenus explain the limited realized niches of speciosus and minimus. Hypotheses regarding the evolution of the patterns of aggressive behavior observed in these species are suggested. Aggression has been selected for in alpinus and amoenus because of a seasonal, potentially limited food supply which is economically defendable. Aggression has not been selected for in minimus because it is not metabolically feasible to engage in aggressive interactions in the hot sagebrush desert. Aggressive behavior has not been selected for in speciosus probably because of predator pressure and the seasonal abundance of food in its habitat.

A Dynamic Analysis of Age in Sugar Maple Seedlings

Abstract: Age data from populations of sugar maple (Acer saccharum Marsh.) seedlings in southern Wisconsin were used to investigate two plant—population models: a negative exponential model and a power function model. A weighted death probability was calculated and compared to densities of potential germinants, and the influence of seed—crop numbers on stem density was analyzed. The power function model, implying a decreasing mortality rate as the seedling ages, is a good model for describing population dynamics of sugar maple seedlings. Seed crops and potentially viable seeds appear to have no effect on the numbers of stems remaining in the population after several years. However, the density of the initial input into the population system does affect the probability of a seedling surviving during its germination year. See full-text article at JSTOR

Quantitative Investigations of Leaf Pigments From Their Inception in Buds Through Autumn Coloration to Decomposition in Falling Leaves

Abstract: Pigments in hazel (Corylus americana), aspen (Populus tremuloides), and pin oak (Quercus ellipsoidalis) leaves were measured from their inception in buds to development of a summer maximum, and through the autumn coloration period to decomposition in dry falling leaves. Leaves contained generally high but varyingconcentrations of chlorophyll and carotenoid pigments throughout the summer months. The summer pigment variations among the three species are discussed in the light of the usefulness of chlorophyll content as an index of net primary productivity. During the autumn coloration period, preceding leaf desiccation and fall, chlorophyll decays rapidly, producing low levels of pheophytin with only occasional faint traces of pheophorbide and chlorophyllide during the period of most rapid chlorophyll breakdown. The levels of carotenoids begin declining at the same time as chlorophyll, but at a much slower rate. Violaxanthin disappears most rapidly, followed closely by neoxanthin. Lutein and Beta—carotene a...