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17.18: Introduction to Population Ecology - Biology

17.18: Introduction to Population Ecology - Biology


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What you’ll learn to do: Discuss the scope and study of population ecology

Imagine sailing down a river in a small motorboat on a weekend afternoon; the water is smooth and you are enjoying the warm sunshine and cool breeze when suddenly you are hit in the head by a 20-pound silver carp. This is a risk now on many rivers and canal systems in Illinois and Missouri because of the presence of Asian carp.

This fish—actually a group of species including the silver, black, grass, and big head carp—has been farmed and eaten in China for over 1000 years. It is one of the most important aquaculture food resources worldwide. In the United States, however, Asian carp is considered a dangerous invasive species that disrupts community structure and composition to the point of threatening native species.


17.18: Introduction to Population Ecology - Biology

Imagine sailing down a river in a small motorboat on a weekend afternoon the water is smooth and you are enjoying the warm sunshine and cool breeze when suddenly you are hit in the head by a 20-pound silver carp. This is a risk now on many rivers and canal systems in Illinois and Missouri because of the presence of Asian carp.

Figure 1. Asian carp jump out of the water in response to electrofishing. The Asian carp in the inset photograph were harvested from the Little Calumet River in Illinois in May, 2010, using rotenone, a toxin often used as an insecticide, in an effort to learn more about the population of the species. (credit main image: modification of work by USGS credit inset: modification of work by Lt. David French, USCG)

This fish—actually a group of species including the silver, black, grass, and big head carp—has been farmed and eaten in China for over 1000 years. It is one of the most important aquaculture food resources worldwide. In the United States, however, Asian carp is considered a dangerous invasive species that disrupts community structure and composition to the point of threatening native species.


Introduction

The study of nucleic acids began with the discovery of DNA, progressed to the study of genes and small fragments, and has now exploded to the field of genomics. Genomics is the study of entire genomes, including the complete set of genes, their nucleotide sequence and organization, and their interactions within a species and with other species. DNA sequencing technology has contributed to advances in genomics. Just as information technology has led to Google maps that enable people to obtain detailed information about locations around the globe, researchers use genomic information to create similar DNA maps of different organisms. These findings have helped anthropologists to better understand human migration and have aided the medical field through mapping human genetic diseases. Genomic information can contribute to scientific understanding in various ways and knowledge in the field is quickly growing.

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    Population Ecology

    The word ‘population’ is derived from the Latin “Populus” which means people. Ecology gives the simple definition of population as a group of organisms belonging to the same species and living in the same area at the same time.

    The last and final component of the population is an individual organism that interbreeds to produce more offspring alike them. Populations are further categorized into demes and local populations.

    According to some ecologists, populations are of the following two types: Monospecific population, the one having organisms of only one species. And polyspecific population is the one having mixed populations i.e., populations are from more than one species.

    Sometimes polyspecific is regarded as a community.

    Definition of Population Ecology

    In population biology, the term population describes a group of members of a species living in the same area. The definition of population ecology is the study of how different elements impact population growth, rates of survival and reproduction, and risk of extinction.

    Population ecology has its inmost historical roots, and its wealthiest advancement, in the study of population growth, regulation, and dynamics, or demography. Human population growth functions as a crucial design for population ecologists and is one of the most essential environmental concerns of the twenty-first century.

    However, all populations, from diseased organisms to wild-harvested fish stocks and forest trees to the species in a successional series to laboratory fruit files and paramecia, have actually been the topic of standard and applied population biology.

    Characteristics of Population Ecology

    Ecologists utilize various terms when understanding and discussing populations of organisms. A population is all of one sort of species residing in a specific location.

    1.Population Size and Density

    The study of any population typically starts by figuring out the number of individuals of a particular species that exist, and how carefully associated they are with each other. Within a specific habitat, a population can be characterized by its population size (N), the overall number of individuals, and its population density, the number of individuals within a specific location or volume.

    Population size and density are the two primary characteristics used to describe and understand populations. For example, populations with more individuals might be more stable than smaller populations based on their genetic variability, and thus their perspective to adjust to the environment. Alternatively, a member of a population with low population density (more expanded in the habitat), might have more problems discovering a mate to reproduce compared to a population of greater density.

    2.Population dispersion or spatial distribution

    Dispersion is the spatial pattern of individuals in a population relative to one another. In nature, due to various biotic interactions and the influence of abiotic elements, the following three standard population circulations can be observed:

    (a) Regular dispersion:

    Here the individuals are basically spaced at an equivalent distance from one another. This is uncommon in nature but in common is cropland. Animals with territorial behavior tend towards this dispersion.

    (b) Random dispersion:

    Here the position of one individual is unrelated to the positions of its neighbors. This is also relatively uncommon in nature.

    (c) Clumped dispersion:

    The majority of populations display this dispersion to some extent, with individuals aggregated into patches interspersed with no or few individuals. Such aggregations may result from social aggregations, such as family groups or might be because of particular patches of the environment being more favorable for the population concerned.

    3.Age structure

    In a lot of kinds of populations, individuals are of different ages. The proportion of individuals in each age group is called age structure of that population. The ratio of the various age groups in a population figures out the existing reproductive status of the population, thus predicting its future. From an environmental viewpoint, there are three significant ecological ages in any population.

    Age pyramid:

    The model representing geometrically the proportions of different age groups in the population of any organism is called age pyramid. According to Bodenheimer (1938), there are following three standard kinds of age pyramids.

    (a) A pyramid with a broad base (or triangular structure):

    It shows a high percentage of young individuals. In rapidly growing young populations birth rate is high and population growth might be rapid.

    (b) Bell-Shaped Polygon:

    It shows a fixed population having an equal number of young and middle-aged individuals. As the growth rate becomes slow and steady, i.e., the pre-reproductive and reproductive age groups become basically equivalent in size, the post-reproductive group remaining as the smallest.

    (c) An urn-shaped structure:

    It suggests a low percentage of young individuals and shows a declining population. Such an un-shaped figure is obtained when the birth rate is considerably minimized the pre-reproductive group decreases in proportion to the other two ages of the population.

    Population Growth Rate

    Population growth reflects the change in the number of individuals over a time period. The population growth rate is impacted by birth and death rates, which in turn belong to resources in their environment or outdoors aspects such as climate change and disasters.

    Carrying capacity

    Due to the fact that the real world does not use endless resources, the variety of individuals in a growing population eventually will reach a point when resources become scarcer. Then the growth rate will slow and level off.

    As soon as a population reaches this leveling-off point, it is thought about the best population the environment can sustain. The term for this phenomenon is carrying capacity. The letter K represents carrying capacity.

    Population cycles

    Populations fluctuate in a cyclic way depending on the resources and competitors in the environment. An example would be harbor seals, affected by pollution and overfishing. Decreased prey for the seals causes increased death of seals. If the number of births was to increase, that population size would remain stable. However, if their deaths outpaced births, the population would decrease.

    As environment change continues to impact natural populations, using population biology designs ends up being more vital. The many elements of population ecology help researchers better understand how organisms interact and help in techniques for species management, conservation, and protection.


    Introduction

    Asian carp jump out of the water in response to electrofishing. The Asian carp in the inset photograph were harvested from the Little Calumet River in Illinois in May, 2010, using rotenone, a toxin often used as an insecticide, in an effort to learn more about the population of the species. (credit main image: modification of work by USGS credit inset: modification of work by Lt. David French, USCG)

    Imagine sailing down a river in a small motorboat on a weekend afternoon the water is smooth and you are enjoying the warm sunshine and cool breeze when suddenly you are hit in the head by a 20-pound silver carp. This is now a risk on many rivers and canal systems in Illinois and Missouri because of the presence of Asian carp.

    This fish—actually a group of species including the silver, black, grass, and big head carp—has been farmed and eaten in China for over 1000 years. It is one of the most important aquaculture food resources worldwide. In the United States, however, Asian carp is considered a dangerous invasive species that disrupts community structure and composition to the point of threatening native species.


    Population Biology

    Population biology has been investigated quantitatively for many decades, resulting in a rich body of scientific literature. Ecologists often avoid this literature, put off by its apparently formidable mathematics. This textbook provides an introduction to the biology and ecology of populations by emphasizing the roles of simple mathematical models in explaining the growth and behavior of populations. The author only assumes acquaintance with elementary calculus, and provides tutorial explanations where needed to develop mathematical concepts. Examples, problems, extensive marginal notes and numerous graphs enhance the book's value to students in classes ranging from population biology and population ecology to mathematical biology and mathematical ecology. The book will also be useful as a supplement to introductory courses in ecology.

    “This is the text of choice for mathematical population biology. It is both authoritative and pedagogical. It is the text I have been waiting for.” Simon Levin


    History

    Among others, Beissinger and McCullough 2002 and Morris and Doak 2002 (both cited under General Overviews) review the origins of PVAs in some depth. In the 1970s, four factors focused attention on the problems of small populations. These included burgeoning interest in island biogeography and its implications for extinction, especially of populations confined to small areas, which is emphasized in Simberloff 1976 increasing recognition of the importance of variability in population dynamics, which is highlighted in May 1973 a developing science of the relationship between genetics and population size, stressed in Frankel 1974 and a growing awareness of the extinction crisis, which can be seen in Myers 1979 and in the retrospective overview Simberloff 1988. Moving into the 1980s, these concerns dominated the developing field of conservation science, as seen in the treatments in Soulé and Wilcox 1980 and Soulé 1986. Questions associated with the vulnerability of small populations to extinction prompted consideration, in Shaffer 1981, of what constituted a small population and at what size a population ceased to be vulnerable. Ginzburg, et al. 1982 emphasizes the importance of stochastic modelling of quasi-extinction risk in environmental assessment. Shaffer 1983 uses such a stochastic model to estimate the risks of population extinction and, thus, the Minimum Viable Populations for grizzly bears (Ursus arctos). From these beginnings, the concept of PVA emerged (see Soulé 1987, cited under General Overviews). Early proponents, in works such as Burgman, et al. 1988, saw population-focused models of extinction probabilities, informed by high-quality autecological data, as an essential focus for larger questions about the design of reserves and the allocation of conservation resources. Subsequently, however, Caughley 1994 raised concerns about the dominant theoretical focus on small populations. Arguably, conservation biology still struggles to unite the disparate strands of research identified in Caughley 1994 and to ensure that work of academic appeal and theoretical interest contributes meaningfully to arresting rates of extinction. This remains a major challenge in the discipline.

    Burgman, M. A., H. R. Akçakaya, and S. S. Loew. 1988. The use of extinction models for species conservation. Biological Conservation 43:9–25.

    Summarizes arguments against island biogeography as a predictively useful theory on which to base conservation decisions. The authors argue that population-focused conservation is likely to be more successful than conservation focused on communities or ecosystems. Conservation based on genetic and population dynamic models is promoted.

    Caughley, G. 1994. Directions in conservation biology. Journal of Animal Ecology 63.2: 215–244.

    This seminal paper identifies two parallel approaches to conservation biology: the small population paradigm, providing theoretical insights into the problems faced by small populations and the declining population paradigm, focused on identifying and mitigating the agents of a population’s decline. Better integration of the two approaches is promoted.

    Frankel, O. H. 1974. Genetic conservation: Our evolutionary responsibility. Genetics 78.1: 53–65.

    Embodies the growing awareness, in the 1970s, of the need to conserve genetic variability within species, not just the species themselves. Frankel argues that more information is needed on the genetic processes characterizing natural populations, that we must safeguard the evolutionary potential of both wild and domesticated populations, and that genetic considerations can inform conservation practice.

    Ginzburg, L. R., L. B. Slobodkin, K. Johnson, and A. G. Bindman. 1982. Quasiextinction probabilities as a measure of impact on population growth. Risk Analysis 2.3: 171–181.

    This paper promoted stochastic modelling as a key method in environmental risk assessment. The authors proposed measures for estimating the change in quasi-extinction probabilities as the consequence of an impact and investigated the effects on time to quasi-extinction of aspects of stochasticity.

    May, R. M. 1973. Stability in randomly fluctuating versus deterministic environments. American Naturalist 107.957: 621–650.

    This paper was key to the increasing focus of conservation biologists on the importance of stochasticity in population dynamics, an important element in the developing science of conservation biology. May shows that stochastic population models can yield outcomes qualitatively different from those of their deterministic analogues.

    Myers, N. 1979. The sinking ark: A new look at the problem of disappearing species. Oxford: Pergamon.

    Influential treatment of the scale of the biodiversity crisis, focusing on explaining why so many species are doomed to extinction and what drives that fate. Focuses on tropical forests but the lessons are general, especially in regard to consumerism as the ultimate driver of extinction.

    Shaffer, M. L. 1981. Minimum population sizes for species conservation. Bioscience 31.2: 131–134.

    The development of PVA was inextricably tied to the concept of the Minimum Viable Population (MVP). Posing the question: “how much land is enough to achieve conservation objectives?” Shaffer presents the first tentative definition for the concept of the MVP and discusses methods available to derive MVPs.

    Shaffer, M. L. 1983. Determining minimum viable population sizes for the grizzly bear. Bears: Their Biology and Management 5:133–139.

    Arguably the first PVA. Presents a stochastic simulation model, with demographic structure, to estimate the minimum population of Yellowstone grizzly bears that would have a 95 percent probability of persisting for one hundred years. Uses those population size estimates to estimate the minimum area requirements of a viable population.

    Simberloff, D. 1976. Experimental zoogeography of islands: Effects of island size. Ecology 57:629–648.

    Presents empirical data from experimental manipulations of island size among mangrove islands in the Florida Keys. Data supported the principles of island biogeography, emphasizing that extinction rates will be higher in smaller areas.

    Simberloff, D. 1988. The contribution of population and community biology to conservation science. Annual Review of Ecology and Systematics 19.1: 473–511.

    Discusses the background to the developing science of conservation biology, which also prompted developments in PVA. Simberloff identifies the importance of population ecology to that science however, he also notes the complexities it introduces (for example, where it indicates that populations have very low probabilities of persistence).

    Soulé, M. E. 1986. Conservation biology: The science of scarcity and diversity. Sunderland, MA: Sinauer.

    This edited volume, including contributions from forty-five authors, helped to define the modern discipline of conservation biology. It includes important contributions on elements of the small population paradigm in Caughley 1994 and seeks to identify how those can contribute to conservation in the real world. Gilpin and Soulé’s chapter introduced the term “population viability analysis.”

    Soulé, M. E., and B. A. Wilcox. 1980. Conservation biology: An ecological-evolutionary perspective. Sunderland, MA: Sinauer.

    Perhaps the first key text in developing the small population focus of conservation biology in the 1980s, this edited volume covers a range of topics and introduces some key definitions. It was this book that introduced Franklin’s often-quoted 50/500 rule (see Minimum Viable Populations).

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    Stochastic Population Dynamics in Ecology and Conservation

    Abstract

    All populations fluctuate stochastically, creating a risk of extinction that does not exist in deterministic models, with fundamental consequences for both pure and applied ecology. This book provides an introduction to stochastic population dynamics, combining classical background material with a variety of modern approaches, including previously unpublished results by the authors, illustrated with examples from bird and mammal populations, and insect communities. Demographic and environmental stochasticity are introduced with statistical methods for estimating them from field data. The long- . More

    All populations fluctuate stochastically, creating a risk of extinction that does not exist in deterministic models, with fundamental consequences for both pure and applied ecology. This book provides an introduction to stochastic population dynamics, combining classical background material with a variety of modern approaches, including previously unpublished results by the authors, illustrated with examples from bird and mammal populations, and insect communities. Demographic and environmental stochasticity are introduced with statistical methods for estimating them from field data. The long-run growth rate of a population is explained and extended to include age structure with both demographic and environmental stochasticity. Diffusion approximations facilitate the analysis of extinction dynamics and the duration of the final decline. Methods are developed for estimating delayed density dependence from population time series using life history data. Metapopulation viability and the spatial scale of population fluctuations and extinction risk are analyzed. Stochastic dynamics and statistical uncertainty in population parameters are incorporated in Population Viability Analysis and strategies for sustainable harvesting. Statistics of species diversity measures and species abundance distributions are described, with implications for rapid assessments of biodiversity, and methods are developed for partitioning species diversity into additive components. Analysis of the stochastic dynamics of a tropical butterfly community in space and time indicates that most of the variance in the species abundance distribution is due to ecological heterogeneity among species, so that real communities are far from neutral.

    Bibliographic Information

    Print publication date: 2003 Print ISBN-13: 9780198525257
    Published to Oxford Scholarship Online: April 2010 DOI:10.1093/acprof:oso/9780198525257.001.0001

    Authors

    Affiliations are at time of print publication.

    Russell Lande, author
    Department of Biology 0116, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA

    Steinar Engen, author
    Mathematical Institute, NTNU Trondheim, Norway

    Bernt-Erik Saether, author
    Zoology Institute, NTNU Trondheim, Norway


    Introduction to Population Ecology

    Introduction to Population Ecology,قnd Edition is a comprehensive textbook covering all aspects of population ecology.  It uses a wide variety of field and laboratory examples, botanical to zoological, from the tropics to the tundra, to illustrate the fundamental laws of population ecology. Controversies in population ecology are brought fully up to date in this edition, with many brand new and revised examples and data.

    Each chapter provides an overview of how population theory has developed, followed by descriptions of laboratory and field studies that have been inspired by the theory. Topics explored include single-species population growth and self-limitation, life histories, metapopulations and a wide range of interspecific interactions including competition, mutualism, parasite-host, predator-prey and plant-herbivore. An additional final chapter, new for the second edition, considers multi-trophic and other complex interactions among species. 

    Throughout the book, the mathematics involved is explained with a step-by-step approach, and graphs and other
    visual aids are used to present a clear illustration of how the models work. Such features make this an accessible introduction to population ecology essential reading for undergraduate and graduate students taking courses in population ecology, applied ecology, conservation ecology, and conservation biology, including those with little mathematical experience.


    Watch the video: Introduction to Population Ecology (May 2022).


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