Population Ecology Model Research Articles

Consumer-Resource Dynamics. By William W. Murdoch, Cheryl J. Briggs & Roger M. Nisbet, pp. 462. Monographs in Population Biology, 36. Princeton University Press, Princeton, USA and Oxford, UK, 2003. ISBN 0 691 00658 X (hbk) and 0 691 00657 1 (pbk). £55.00 (cloth) and £24.95 (paper).

Consumer-Resource Dynamics. By William W. Murdoch, Cheryl J. Briggs & Roger M. Nisbet, pp. 462. Monographs in Population Biology, 36. Princeton University Press, Princeton, USA and Oxford, UK, 2003. ISBN 0 691 00658 X (hbk) and 0 691 00657 1 (pbk). £55.00 (cloth) and £24.95 (paper).

The dynamics of global e‐commerce: an organizational ecology perspective

PurposeA classical model of organizational ecology dynamics which is utilized to characterize an ecosystem called the internet is proposed and a parallel is drawn between the population ecology model and the current global e‐commerce environment.Design/methodology/approachSurvivorship theory is applied to global e‐commerce. The Verhulst‐Pearl logistic equation can be used to describe the inhibition of growth within an ecosystem. The approach is to apply the Verhulst‐Pearl logistic equation to describe international growth dynamics of the internet.FindingsWhen applying the Verhulst‐Pearl equation to the internet environment around the world, the number of domain names or host counts, the rate at which there is an increase or decrease in the number of domain names, and the availability of information technology infrastructure are all factors that are part of the equation. The model of population dynamics presented in our discussion lends itself to the description of the current pattern of growth within the internet environment.Practical implicationsThe application of population ecology to international growth dynamics describes the long‐term survival and differentiation strategies that impact success. The next evolution of firms on the internet, which may be the ultimate survivors, should follow the path characterized as low cost producers with a focus on meeting the needs of the consumers on the internet. An ecological approach allows managers to ascertain the effectiveness of their organizations in the internet environment and accordingly devise strategies to embrace changes and challenges of the global environment.Originality/valueThe population ecology conceptual framework offers promise for a more sophisticated and methodologically rigorous approach to future investigations by both researchers and practitioners. The operationalization of the organizational ecology model for application to the internet is an extension of the literature.

의료공급체계의 성장과정과 개혁

There is general agreement that the Korean health care delivery system has two basic structural problems. One is the limited capacity and role of public hospitals, and the other is the absence of functional differentiation and referral arrangement between the clinics and hospitals of various technological sophistication levels. This study is intended to make an empirical observation of the system's growth process from the viewpoint of the population ecology model of organizations so as to understand the background of these problems and to find out ways of approaching them. As predicted from the population ecology model of organizations, all the types of medical care facilities have expanded in response to the environmental changes for the past three decades or so, and the differences in the extent and pattern of expansion among the types are related to what have taken place in the environment. These findings suggest that the efforts for reforming the health care delivery system should be directed not only to medical care institutions but also to the environmental context under which they function. It is believed that the usefulness of the population ecology perspective on organizations for studying the health care delivery system has been demonstrated. Thus further studies along this line based upon more strict design would improve systematic understanding of the system that is needed for developing policy approaches needed to increase its effectiveness.

A Blau space primer: prolegomenon to an ecology of affiliation

This paper describes an ecological model of the behavior of social entities in a property space defined by sociodemographic dimensions. The model departs from the standard population ecology model in that it measures dimensions of the niche space, and assembles populations into a community. In this model, the time and energy of human individuals are the resource consumed by the social entities. While the model was originally developed for voluntary organizations, the paper argues that this model can be applied to a very wide variety of social phenomena, including firms, groups, associations, events, cultural artifacts, markets, social circles, collectivities, occupations, social movements, roles, identities, attitudes, beliefs, lifestyles, institutions, meanings, human cognitive structure, disease and other socially transmissible quantities. The paper concludes with some speculations based loosely on the model. Copyright 2004, Oxford University Press.

Stationary measures for some Markov chain models in ecology and economics

Let $F \equiv \{f : f : [0, \infty) \rightarrow [0, \infty), f (0) = 0, f$ continuous, $\lim\limits_{x \downarrow 0} \frac{f(x)}{x} = C$ exists in $(0, \infty), 0 < g (x) \equiv \frac{f(x)}{C x} < 1$ for x in $(0, \infty)\}$ . Let $\{f_j\}_{j \geq 1}$ be an i.i.d. sequence from F and X 0 be a nonnegative random variable independent of $\{f_j\}_{j \geq 1}$ . Let $\{X_n\}_{n \geq 0}$ be the Markov chain generated by the iteration of random maps $\{f_j\}_{j \geq 1}$ by $X_{n + 1} = f_{n + 1} (X_n), n \geq 0$ . Such Markov chains arise in population ecology and growth models in economics. This paper studies the existence of nondegenerate stationary measures for {X n }. A set of necessary conditions and two sets of sufficient conditions are provided. There are some convergence results also. The present paper is a generalization of the work on random logistics maps by Athreya and Dai (2000).

Modelling differential extinctions to understand big cat distribution on Indonesian islands

ABSTRACTAims To model differential extinction rates for island populations of tigersPanthera tigrisand leopardsP. pardus.Location Indonesia.Methods We built VORTEX population models of tiger and leopard populations on an island the size of Bali (3632 km2), using data from the literature.Results The tiger populations were less extinction prone than the leopard populations. This was unexpected as tigers had the smaller population sizes and, as such, might be assumed to be more extinction prone. We identified several aspects of tiger breeding biology that explain the result.Main conclusions Sea level reconstructions suggest that both tiger and leopard would have been present in Java, Sumatra and Bali at the end of the last glacial. Our model provides a plausible mechanism based on population ecology to explain why these leopard populations were more extinction prone than the tiger populations. In addition it illustrates the potential utility of population ecology models in understanding historical patterns in biogeography.

The Galilean turn in population ecology

The standard mathematical models in population ecology assume that a population's growth rate is a function of its environment. In this paper we investigate an alternative proposal according to which the rate of change of the growth rate is a function of the environment and of environmental change. We focus on the philosophical issues involved in such a fundamental shift in theoretical assumptions, as well as on the explanations the two theories offer for some of the key data such as cyclic populations. We also discuss the relationship between this move in population ecology and a similar move from first-order to second-order differential equations championed by Galileo and Newton in celestial mechanics.

An analysis of changing management roles in small Australian services exporters in response to the stages in industry development

Life cycle models have become important in explaining the changing size structure of firms based on the carrying capacity of regions or industries. In particular, the population ecology model predicts stages of growth, maturity and eventually decline in the number of firms in an industry. There has been criticism of such models because of their focus on external variables as pre‐determinants of the potential for enterprise development. This paper attempts to reconcile the external focus of the population ecology model with relevant internal management factors in enterprise development. A survey was conducted of Australian services exporters, and the results not only confirm the existence of four separate life cycle stages in the population ecology model, but also identify the external and internal variables that are strategically relevant at each of the stages. The findings provide potentially useful information in a range of contexts including the design of small business assistance as well a providing “guide posts” to entrepreneurs engaged in enterprise development.

Mathematical models of tumour invasion mediated by transformation-induced alteration of microenvironmental pH.

The invasive phenotype, characteristic of malignancy, is found in multiple transformed populations with widely varying genotypes. The authors hypothesize that this genetic heterogeneity and instability precludes mechanisms of tumour invasion requiring consistent, coordinated production of one or more proteins or other macromolecules. Instead, this model assumes that the genetically disordered, unstable populations found in tumours must employ a simple mechanism of invasion that arises from one common trait of all transformed cells--reversion to a phenotype more primitive (less differentiated) than the tissue of origin. Specifically, this approach focuses on primitive metabolic pathways with preferential use of glycolysis for energy production. Mathematical models of invasive cancer based on tumour-induced acidification of the microenvironment are presented. Using population ecology and diffusion-reaction models, it is shown that normal tissue adjacent to the tumour edge is subjected to an extracellular pH that is significantly lower than normal. This leads to degradation of the interstitial matrix, loss of intercellular gap junctions and cell necrosis. Tumour cells have an optimal extracellular pH less than that of normal cells and are thus able to thrive in the acidic microenvironment expanding into the space of the dying normal tissue. The model is consistent with extant data on the tumour microenvironment as well as clinical data relating increasing tumour invasiveness with elevated glucose utilization and lactate content. It predicts well-established phenomena in tumorigenesis such as the adenoma-carcinoma sequence and the critical role of angiogenesis in the invasive phenotype. An acellular gap at the tumour host interface is also predicted and can be demonstrated in pathologic specimens. Novel treatment approaches based on this model are discussed.

Products and Ecological Models: A Population Ecology Perspective

SummaryIndustrial ecology has used the systems ecology model, with its emphasis on the flows of energy and nutrients, as a tool to find ways to minimize the adverse environmental effects of industrial activity. A second ecosystem model, the population ecology model, emphasizes intra‐and inter‐specific interactions of many types. When applied to industrial systems, it suggests an increased focus on products. It therefore can provide a useful complement to the systems ecology approach. If industrial processes that are less harmful to the environment are to be successfully implemented, they will have to produce products that can successfully penetrate the marketplace. A number of historical examples are used to illustrate the many product interactions discussed.

Theoretical aspects of extinction by inbreeding depression

AbstractPopulational extinction due to inbreeding depression is analyzed with simple population genetic and population ecological models. Two alternative genetic mechanisms of inbreeding depression, i.e. recessive deleterious genes and overdominant genes, are assumed in separate analyses in order to examine their relative importance. With both mechanisms the population size and the coefficient of inbreeding are maintained at stable equilibria if there is no non‐genetic demographic disturbance or stress. With a certain amount of demographic disturbance the population declines rapidly due to interaction between the decrease of population size and the increase of inbreeding coefficient. Such rapid extinction occurs with both genetic mechanisms. However, in the case of overdominant genes extinction happens only if the equilibrium population size is small and the selection coefficient is large such that segregation load is large. In nature, extinction due to overdominant genes is considered to be much less likely than extinction due to recessive deleterious genes.

Representational Concentration and Interest Community Size: A Population Ecology Interpretation

We extend Gray and Lowery's (1996) work on interest community concentration in ways that generate novel insights about several of the empirical and theoretical controversies on interest system diversity found in the literature. This explanation, which suggests that interest community diversity is an artifact arising from the distinct growth processes of the different types of interests found in the community, is tested with highly detailed and complete data on the diversity of state interest communities, demonstrating that the empirical relationship between diversity and interest system size can be replicated solely from knowledge about the density functions of interest guilds.We use these findings both to evaluate the population ecology model's interpretation of diversity and to comment on several substantive issues raised in the larger literature on interest representation.

Understanding and managing physician restructuring through organizational theory

Physician restructuring is occurring rapidly as physicians are readily leaving solo practice and joining group practices, including multi-specialty group practices. Organizational theory provides a framework for the rationale and management of physician restructuring in this environment of managed care. Through studying Open Systems Theory, Population Ecology and Strategic Adaptation Models, Institutional Theory, Resource Dependency Theory, Group Theory, Exchange Theory, and Transaction Costs Economics, one can better understand the environment, and operational and management issues which surround physician group restructuring.

A Forager‐Resource Population Ecology Model and Implications for Indigenous Conservation

Population ecology and foraging theory can be combined to simulate the population dynamics of hunter‐gatherers and their prey resources. Such simulation study is important to issues of conservation because many of the population processes that link human foragers and their prey occur over time scales that elude both ethnographic and archaeological fieldwork. To demonstrate, we used the model to examine hunter‐gatherer population dynamics. We focused on a prey characteristic that affects its susceptibility to over‐exploitation: the intrinsic rate of increase, r. We found that forager‐prey systems can stabilize without intentional conservation behavior and that prey “switching,” fall‐back foods, and in certain circumstances, a higher r contribute to resource species persistence. Furthermore, a prey’s vulnerability to local depletion or extinction may depend on the demographic characteristics of the suite of resources harvested along with it. The model can serve as a “null hypothesis” for examining intentional resource conservation and presents points in concordance with, as well as divergent from, tenets in conservation biology. In particular, we discuss the implications of these findings for indigenous resource conservation in Amazonia (e.g., the overhunting of large primates and avifauna and the adoption of new procurement technologies) as well as the “Pleistocene Overkill Hypothesis.”Modelo de Ecología Poblacional Forraje‐Recurso y sus Implicaciones en la Conservación LocalLa ecología de poblaciones y la teoría de forraje se puede combinar para investigar la dinámica poblacional entre cazadores‐recolectores y sus especies de presa. Este tipo de investigación basada en el uso de simulaciones por computadora es importante para el tema de la conservación del medio, puesto que muchos de los procesos poblacionales entre cazadores‐recolectores y sus presas ocurren a una escala temporal que elude tanto a la etnografía como a la arqueología. Como desmostración, usamos este modelo para examinar la dinámica poblacional de cazadores‐recolectores. Nos concentramos en una característica de las presas que afecta su susceptibilidad de sobre‐explotación: el ritmo intrínseco de crecimiento, r. Comprobamos que el sistema de cazador‐recolector puede estabilizarse sin una conducta deliberada de conservación y que cambios de presa, comida de emergencia y algunas veces, un valor de r mayor, contribuyen a la persistencia de especies. La vulnerabilidad de una presa al decremento local o extinción puede depender de las características demográficas de las especies que están siendo recolectadas junto con la presa. Este modelo se puede usar como una “hipótesis nula” para una investigación sobre la conservación intensional de recursos y presenta puntos tanto en concordancia como de divergencia con principios de la biología de la conservación. En particular discutimos las consecuencias de este modelo para la conservación de recursos locales en la Amazonía (i.e., la sobre‐explotación de primates grandes y avifauna y la adopción de nuevas tecnologías) así como la “Hipótesis de la Mortandad Masiva del Pleistoceno.”

A Forager‐Resource Population Ecology Model and Implications for Indigenous Conservation

A Forager‐Resource Population Ecology Model and Implications for Indigenous Conservation

The Sequencing of Social Movements

Conventional accounts of protest cycles posit a demonstration effect-successful protests incite other constituencies to activism. The author offers an alternative theory that builds on population ecology models of organizational behavior. He argues that the expansion of social movement organizations, or organizational density, is also an essential component of protest cycles. Multivariate analyses of the effects of civil rights protest and organizational growth on feminist protest and organizational foundings between 1955 and 1985 demonstrate that organizational density promotes the diffusion of protest. Protest also engenders activism by others, but only under favorable political conditions. This implies that an enduring organizational niche and political allies in power are necessary for protest to spread beyond single movements and create protest opportunities for other challengers

Generalizations of the Lotka-Volterra Population Ecology Model: Theory, Simulation, and Applications

Social scientists have attempted in vain to explain and predict the social phenomenon and particularly the behavior of the social system, with the unsatisfactory result that they were not so successful in terms of the accuracy of the prediction that they started to look into chaos theory. Several authors presented the ability of even the most simple predator-prey models to yield damped and explosive oscillations as well as stable limit cycles. Lotka and Volterra suggested models of population dynamics incorporating interpopulation competition. In this paper, biological population ecology model, especially Lotka-Volterra model is applied to organizations and social systems at large. This paper demonstrates the power of merging system dynamics with population ecology models to assess the sensitivity to initial conditions. The dynamical properties of the generalized Lotka-Volterra model were made by simulations using the Ithink software. The implications of using simulation in the analysis of chaotic behavior are presented.

Availability of Resources and Use of Space in Eastern Chipmunks, Tamias striatus

The adaptive significance of the use of resources is a central issue in population ecology. Empirical and theoretical studies have examined the relationship between mean size of home range and environmental variables. Few studies have examined age, gender, and individual variation in these relationships. We examined the relation between patterns of variation in size of home range in eastern chipmunks, Tamias striatus , and distribution and abundance of resources in northwestern Pennsylvania. Previous research on Tamias showed that mean size of home range responded quickly to changes in abundance of resources, suggesting that individual variation in size of home range would be tied to resources. We captured 278 individuals 3,933 times. Forty individuals were studied in 1981 and 49 in 1982. Home ranges were calculated and all mast-producing trees were mapped yielding expected abundance of resources for all home ranges. Abundance of resources was an increasing function of size of home range even when corrected for competition for access to resources, contrary to predictions based upon models of use of space. When examined by age and sex of chipmunks and by different species of mast-producing trees, we noted that the distribution and abundance of white oaks influenced the distribution of age and sex groups on the study area and appeared to be a disputed resource for adults. Studies of patterns of age, sex, and individual variation in complex behaviors are logistically challenging, but they are the best way to empirically test models in population ecology dealing with the adaptive significance of access to space and resources.

Work, Resources and Population in Foraging Societies

Anthropological views on the labour effort required of hunter-gatherers have flip-flopped between stereotypic positions depicting either very limited subsistence work or long exertion. A computer simulation using evolutionary and population ecology models shows that at equilibrium foraging efficiency is a declining function of work effort, whereas population density responds to work effort by first increasing and then decreasing. This and other foraging theory models provide a framework which can explain observations of routine sharing, modest effort and limited material accumulation in hunter-gatherer societies, leads us to expect diversity in the expression of these characteristics and, is consistent with neo-Darwinian and neoclassical economic theory. Evolutionary ecology theory thus obviates the need for a Zen' economics as proposed by Sahlins. -from Author

Pilgrim’s Progress: Trends and Convergence in Research on Organizational Size and Environments

This article reviews the research conducted on organizational size and environments from 1980 through 1992. Specifically, the environmental research based on the traditional environmental contingency model is reviewed and trends over the review period are identified. The organizational size literature is reviewed in a similar fashion. Suggestions for empirical and theoretical extensions of trends identified in both research streams a represented. An especially salient finding in the review is the emerging theoretical convergence of the size and environment research streams on the topic of organizational life cycles, which seems to particularly involve the population ecology model. Possible theoretical convergence between the institutional, population ecology, interorganizational relations, and environmental enactment perspectives and other fundamental organization theory areas (e.g., culture and strategy) are then proposed. Overall, traditional organizational size and environment research continued at a steady pace over the review period, and new approaches and perspectives, especially in the area of environment research, have developed and are surpassing the traditional approaches in the volume of research they generate.