Biological Sciences
Population in Ecosystems
Population in ecosystems refers to the group of organisms of the same species that live in a particular area and interact with each other. It is a fundamental unit of ecological study and is influenced by factors such as birth rates, death rates, immigration, and emigration. Understanding population dynamics is crucial for assessing the health and sustainability of ecosystems.
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11 Key excerpts on "Population in Ecosystems"
eBook - PDF- Kimon Hadjibiros(Author)
- 2013(Publication Date)
- CRC Press(Publisher)
15 © 2010 Taylor & Francis Group, LLC Chapter 3 Organisation at Population Level 3.1 POPULATION AND ECOSYSTEM The study of the living elements of an ecosystem could theoretically mean the examination of the actions of all organisms, which are extremely numerous. Therefore, for practical reasons, organisms should be grouped, and individu-als of the same species that live in the same space should be examined as a whole. Thus the concept of population results, which constitutes a basic ecological unit. A significant part of the phenomena observed at a population or ecosystem level can be explained through the interactions of populations. Populations are formed by groups of individuals of the same species that live in a certain place so that they can breed with one another. The total of populations living in one place is called biological community . Important issues concerning population ecology are the prediction of: • Population change over time • Population distribution in space • The abundance of each population within the biological community • The distribution of the individuals of a population by age and sex Population is a characteristic case of a system. Even though population is nothing more than the total of individuals comprising it, it can be described by parameters and variables, such as population size, natality, mortality, immigration, age distribution etc. that have no meaning for each one of the individuals but only for the population itself. These parameters determine in any given moment the state of the population, its temporal change and the manner in which external circumstances affect it. The ecological niche is an important concept of theoretical ecology. It represents the space of a population’s ecological activity, i.e.
eBook - PDFStream Ecology and Self Purification
An Introduction, Second Edition
- Frank R. Spellman, Joanne Drinan(Authors)
- 2001(Publication Date)
- CRC Press(Publisher)
CHAPTER 5 Population Ecology The Earth is one but the world is not. We all depend on one biosphere for sustaining our lives. Yet each community, each country, strives for survival and prosperity with little regard for its impact on others. Some consume the Earth's resourcesat a rate that would leave little for future generations. Oth- ers, many more in number, consume far too little and live with the prospects of hunger, squalor, disease, and early death.65 5.1 THE 411 ON POPULATION ECOLOGY L ET'S begin with the basics. 5.1 .l POPULATION Webster's Third New International Dictionary defines population as fol- lows: The total number or amount of things especially within a given area. The organisms inhabiting a particular area or biotype. A group of interbreeding biotypes that represents the level of organiza- tion at which speciation begins. 5.1.2 POPULATION SYSTEM Population system, or life system, is a population with its effective environ- ment.66 6 5 ~ ~ ~ ~ , World Commission on Environment and Development. Our Common Future. New York: Oxford Uni- versity Press, p. 27, 1987. clark, L. R., Geier, P. W., Hughes, R. D., and Morris, R. F., The Ecology of Insect Populations. New York: Methuen, p. 73, 1967; Berryman, A. A., Population Systems: A General Introduction. New York: Plenum, p. 89; Sharov, A. A., Life-system approach: A systems paradigm in population ecology. Oikos, 63: 485-494, 1992. 48 POPULATION ECOLOGY Major components of a population system are as follows: (1) The Population: organisms in the population can be subdivided into groups according to their age, stage, sex, and other characteristics. (2) Resources: food, shelters, nesting places, space, etc. (3) Enemies: predators, parasites, pathogens, etc. (4) Environment: air, water, soil, temperature, composition, variability of these characteristics in time and space.67 5.1.3 POPULATION ECOLOGY~~ Population ecology is the branch of ecology that studies the structure and dynamics of populations.
eBook - PDFMicrobial Ecology
An Evolutionary Approach
- J Vaun McArthur(Author)
- 2006(Publication Date)
- Academic Press(Publisher)
Living Together in Populations III Fundamentals of Microbial Population Ecology 7 Populations in Ecology Populations in ecology are often defined as groups of interbreeding individuals. This definition is not satisfactory for most of the world’s biota. All asexual and parthenogenic organisms, regardless of their densities, would not be populations based on that definition. A more general definition of an ecological population might be a group of like organisms living in a defined area in a specific period of time. Whether the number of organisms is 2 or 10 million does not matter. The boundaries of populations vary both in space and time. They are difficult to determine and are usually defined by the specific investigator. For example, a researcher may define the population of interest to be the enteric bacteria found in the gut of a single human host. The spatial bounds of this popula-tion may appear to be set. However, enteric bacteria from other humans and animals may enter the specific human host, and the real population includes all potential col-onizers and the resident members. The strains of enteric bacteria of a single human host may change over time. The structure of a population at time T 0 may be very dif-ferent from the population found at time T 1 . The physical boundaries of some pop-ulations are ridiculous to consider but still may have important ecological impacts. One such example might be considering the population of a specific species of bac-teria found in the oceans. Properties of Populations Populations have properties (primarily statistical) that cannot be applied to indi-viduals. They have meaning only in populations. These include measures such as density or size of the population. Density refers to the number of individuals per unit area. We do not speak of the density of an individual. There are four characteristics that affect the size of a population: births, deaths, immigration, and emigration.
eBook - PDFPopulation Ecology
A Unified Study of Animals and Plants
- Michael Begon, Martin Mortimer, David J. Thompson(Authors)
- 2009(Publication Date)
- Wiley-Blackwell(Publisher)
Population ecology is, to us, the study of the sizes (and to a lesser extent the distributions) of plant and animal populations, and of the processes, particularly the biological processes, which determine these sizes. As such, it must inevitably be a numerical and quantitative subject. Nevertheless, \'ve have avoided complex mathematics, and we have, wherever poss- ihle. relegated the mathematical aspects of a topic to the final parts of the section in which that topic is examined. This will, we hope, make population eco- logy more generally accessible. and more palatable. But this is not to say that the mathematics have been played down. Rather, we have tried to play up the importance of real data from the real world: it is thes{\ and not some mathematical abstraction, which must always be the major and ultimate concern of the population ecologist. Developing the subject in this way. however. em- phasizes that mathematical models do have an essen- tial role to play. Time and again they crystallize our understanding of a topic. or actually tell us more about the real world than we can learn directly from the real world itself. Nature may be the ultimate concern of population ecology, but mathematical models. laboratory experiments and field experiments and observations can all help to further our under- standing. \'\Ie have also tried to establish the point implied by the subtitle: that population ecology is a unified study of animals and plants. VVe are. of course, aware of the differences between the two. We feel, however. that plant and animal populations have had their own. independent ecologists for too long, and that, since the same fundamental principles apply to both, there is most to be gained at present from a concentration on similarities rather than differences.
eBook - PDFThe Environment
Science, Issues, and Solutions
- Mohan K. Wali, Fatih Evrendilek, M. Siobhan Fennessy(Authors)
- 2009(Publication Date)
- CRC Press(Publisher)
137 Topics Populations—the Central Units in Ecology and Evolution Population Growth Regulation of Population Size Spatial Patterns of Population Abundance Life Histories of Organisms Interspecific Interactions and Population Dynamics 8 Population Ecology Populations—the Central Units in Ecology and Evolution As we know from the fossil record and direct observation, living organ-isms can (and do) change over time. Some groups have become extinct, while others have become more diverse. Population changes do not come about because an individual changes genetically in response to its environment. Rather, it is a population that changes as the rela-tive frequency of different genes (or different forms of genes, alleles) changes within the population. Any genetic change that confers an advantage in survival and reproduction is more likely to be passed on. If, over generations, this leads to a change in gene frequency, then evolution has occurred. However, environmental factors often act randomly and do not necessarily lead to change. A rodent that has a greater range of diet and is capable of producing healthier off-spring might just as easily be killed by a predator or a storm as her littermate that lacks these characteristics. The environment is com-posed of a complex interplay of factors that may confer advantages and disadvantages to a species and to individual organisms. For centuries, humans have used their knowledge of “selection” to select for certain desirable traits in countless domestic plants and animals. However, despite a long history of breeding by humans into endless variations from original forms, we can still recognize all dogs, all apples, and all horses as such. Biologists refer to these as species. The branch of biology that covers the study and naming of different kinds of species is called systematics.
eBook - PDFSurvey of Biological Progress
Volume 1
- George S. Avery, E. C. Auchter, G. W. Beadle, George S. Avery, E. C. Auchter, G. W. Beadle(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
It is one of these more abstract aspects, namely biodemography or the ecology of homogeneous populations, and its extension to very simple cases of interaction of two species, with which this contribution is concerned. To present a review of all significant advances in ecology in a single article, produced in collaboration by a finite number of writers, is obviously impossible. It has therefore seemed best to plan a series of articles to appear over a number of years that will finally cover the significant modern advances in those sciences that consider organisms in relation to their environments and to one another. When the whole field has thus been surveyed the present article will be sufficiently out of date to justify return-ing to its subject matter. This subject matter has been chosen for several reasons. Firstly, it occupies a central place in modern ecological thought, and has a considerable bearing on other aspects of biology, notably evolution theory. Secondly, though demographic concepts have primarily been evolved in the study of animal ecology, there is no reason why they should not be applicable to plant ecology and might indeed play a part in the current rejuvenation of that science, which has in the past shown an arthritic ECOLOGICAL STUDIES ON POPULATIONS 327 tendency. Thirdly, the kind of matter that is presented below is the only part of biology other than genetics to have developed an autonomous quantitative theory independent of the physico-chemical sciences. Fourthly, though the heroic period in the development of that theory reached its peak rather more than a decade before the publication of most of the material to be considered, the years since 1934 have shown an interesting and significant cooperation involving the field naturalist, taxonomist, experi-mentalist and mathematician, which has of course also affected genetics and evolutionary studies.
eBook - PDF- G. Miller, Scott Spoolman(Authors)
- 2014(Publication Date)
- Cengage Learning EMEA(Publisher)
CONCEPT 4-4 75 or ecosystem. Rather, succession reflects the ongoing struggle by different species for enough light, water, nutrients, food, and space. Most ecologists now recog-nize that mature, late-successional ecosystems are not in a state of permanent equilibrium. Rather, they are in a state of continual disturbance and change. 4-4 What Limits the Growth of Populations? CONCEPT 4-4 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources. ▲ Populations Can Grow, Shrink, or Remain Stable Four variables— births , deaths , immigration , and emigration — govern changes in population size. A population increases by birth and immigration (arrival of individu-als from outside the population) and decreases by death and emigration (departure of individuals from the population): Populationchange = (Births + Immigration) – (Deaths + Emigration) Species vary in their biotic potential or capacity for population growth under ideal conditions. In gen-eral, populations of large species, such as elephants and blue whales, have a low biotic potential, whereas those of small species, such as bacteria and insects, have a high biotic potential. The intrinsic rate of increase ( r ) is the rate at which the population of a species would grow if it had unlimited resources. Individuals in populations with a high intrinsic rate of growth typically reproduce early in life , have short generation times (the time between suc-cessive generations), can reproduce many times , and have many offspring each time they reproduce. Some species have an astounding biotic potential. For example, in some species of bacteria, one bacterium can reproduce itself every 20 minutes.
eBook - PDF- Julianne Zedalis, John Eggebrecht(Authors)
- 2018(Publication Date)
- Openstax(Publisher)
In most cases, numerous species share a habitat. The interactions between these populations play a major role in regulating population growth and abundance. All populations occupying the same habitat form a community: populations inhabiting a specific area at the same time. The number of species occupying the same habitat and their relative abundance is known as species diversity. Areas with low diversity, such as the glaciers of Antarctica, still contain a wide variety of living things, whereas the diversity of tropical rainforests is so great that it cannot be counted. Ecology is studied at the community level to understand how species interact with each other and compete for the same resources. Predation and Herbivory Perhaps the classical example of species interaction is predation: the hunting of prey by its predator. Nature shows on television highlight the drama of one living organism killing another. Populations of predators and prey in a community are not constant over time: in most cases, they vary in cycles that appear to be related. The most often cited example of predator-prey dynamics is seen in the cycling of the lynx (predator) and the snowshoe hare (prey), using nearly 200 year-old trapping data from North American forests (Figure 36.19). This cycle of predator and prey lasts approximately 10 years, with the predator population lagging 1–2 years behind that of the prey population. As the hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, however, they kill so many hares that hare population begins to decline, followed by a decline in the lynx population because of scarcity of food. When the lynx population is low, the hare population size begins to increase due, at least in part, to low predation pressure, starting the cycle anew.
eBook - PDF- Jonathan Roughgarden, Robert M May, Simon A. Levin, Jonathan Roughgarden, Robert M May, Simon A. Levin, Jonathan Roughgarden, Robert May, Simon Levin(Authors)
- 2014(Publication Date)
- Princeton University Press(Publisher)
1, pp. 357-77. Pennsylvania State Univer- sity Press, Philadelphia. Tilman, D. 1977. Resource competition between planktonic algae: An experimental and theoretical approach. Ecology 58:338-48. Tilman, D. 1982. Resource Competition and Community Structure. Princeton Univer- sity Press, Princeton, NJ. Utida, S. 1953. Interspecific competition between two species of bean weevil. Ecology 34:301-307. Utida, S. 1957. Population fluctuation: An experimental and theoretical approach. In Cold Spring Harbor Symp. Quant. Biol. 22:139-51. Vol terra, V. 1931. Leqons sur la theorie mathematique de la lutte pour h vie. Marcel Brelot, Paris. Volterra, V., and U. D'Ancona. 1935. Les associations biologiques au point de vue mathematique. Hermann, Paris. Chapter 6 Discussion: Population Dynamics and Species Interactions DAVID T I L M A N Ecology is the scientific discipline that attempts to determine the causes of patterns in the distribution, abundance, and dynamics of the earth's biota. The earth's ecosystems are complex. In any given habitat, there are tens to hundreds or even thousands of different species. These influence each other both through direct pairwise interactions and through indirect interactions mediated by inter- mediate species, processes, or substances (Levine 1976; Holt 1977; Vandemeer 1980; Schaffer 1981). Because it is impractical, if not impossible, to observe all the potential interactions among all species and processes, ecological research in- volves the simplifying assumption that much of the complexity of nature is either unimportant or can be subsumed within a few summary variables. Schaffer (1981, p. 383) defined such simplification as the process of ecological abstraction: "Accordingly, when the empiricist fits data to equations describing the growth rates of particular species, he has, in a sense, 'abstracted' these species from a more complex matrix of interactions in which they are embedded.
eBook - PDF- William W. Murdoch, Cheryl J. Briggs, Roger M. Nisbet(Authors)
- 2013(Publication Date)
- Princeton University Press(Publisher)
C H A P T E R T W O Population Dynamics: Observations and Basic Concepts This chapter has two parts. The first discusses the various types of population dynamics observed in nature. The second looks at basic concepts that relate these observations to mathematical theory. A brief appendix introduces local stability analysis, illustrated by the logistic model. TYPES OF POPULATION DYNAMICS: PHENOMENA TO BE EXPLAINED In this section we present a range of observed dynamics seen in popula-tions. By “dynamics” we mainly mean temporal changes in density or abundance. Average density of a population, and the relative densities of different populations, are of course also of interest. For example, we care greatly about average density in pest control and in populations we harvest, and we would like to be able to explain why some species are rare, others common, and why the general pattern of relative abundance of different species in an area is often maintained over ecologically long periods. Interestingly, particular types of dynamics do not appear to be restricted to any particular group of organisms or environments. Cyclic populations, for example, occur in terrestrial, freshwater, and marine habitats. They are found in birds, mammals, insects, fish, marine crabs, etc. (Kendall et al. 1998). Only in plants do cycles appear to be rare, per-haps because they often compete with other plant species for non-living resources. P O P U L AT I O N D Y N A M I C S 7 Biological Control of California Red Scale by Aphytis melinus We first introduce a particular system, California red scale and its “nat-ural enemies,” since we use it to illustrate various phenomena we wish to explain. This system also motivated many of the models discussed later in the book, so we briefly summarize its natural history here. California red scale, a plant-sucking insect (Homoptera), was acci-dentally introduced to southern California, probably from China via Australia, more than 100 years ago.
eBook - PDFBiology
Concepts and Applications
- Cecie Starr, Christine Evers, Lisa Starr, , Cecie Starr, Christine Evers, Lisa Starr(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
DeMatteo says, “The goal is to expand our knowledge of how these species move through the landscape so we can determine locations for biological corridors/wildlife crossings that maximize animal movement and minimize human–wildlife conflict.” E N G A G E : P R O C E S S O F S C I E N C E Dr. Karen DeMatteo 715 C H A P T E R 4 0 POPULATION ECOLOGY Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 IMMIGRATION AND EMIGRATION In nature, populations continually change in size. Individu- als are added to a population by births and immigration, the arrival of new residents that previously belonged to another population. Individuals are removed from it by deaths and emigration, the departure of individuals who take up perma- nent residence elsewhere. In many animal species, young of one or both sexes leave the area where they were born to breed elsewhere. For example, young freshwater turtles typically emigrate from their parental population and become immigrants at another pond some distance away. By contrast, seabirds typically breed where they were born. However, some individuals may emigrate and end up at breeding sites more than a thousand kilometers away. In most species, the tendency of individu- als to emigrate to a new breeding site is related to resource availability and crowding. As resources decline and crowding increases, the likelihood of emigration rises. ZERO TO EXPONENTIAL GROWTH If we set aside the effects of immigration and emigration, we can define zero population growth as an interval during which the number of births is balanced by an equal number of deaths. As a result, population size remains unchanged, with no net increase or decrease in the number of individuals. We can measure births and deaths in terms of rates per individual, or per capita.
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