Biology Textbook Notes

Biology Textbook Notes - Biology Textbook Notes CHAPTER 14...

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Biology Textbook Notes CHAPTER 14- Is The Population Too Large? 14.1 A Growing Human Population Ecology - the field of biology that focuses on the interactions among organisms as well as between them and their environment. Population (from an ecological perspective)- all of the individuals of a species within a given area. Populations exhibit a structure, which includes the spacing of individuals (distribution) and their density (abundance). Population Structure # of individuals Mark-recapture method - a technique in which researchers capture many individuals, mark them in some way and release them back into the environment. At some later time, the researchers capture another group of individuals and calculate the proportion of previously marked individuals in this group. This proportion can be used to estimate the size of the total population. Dispersion- how organisms are distributed in space Clumped distribution - high densities of individuals in certain resource-rich areas and low densities elsewhere. Ex. Plants that require certain soil conditions and the animals that depend on these plants tend to be clumped. Uniform distribution - more on a local scale, species that form this are often territorial- they defend their own personal space from intruders. Random distribution - nonsocial species with the ability to tolerate a wide range of conditions typically show this, wherein no compelling factor is actively bringing individuals together or pushing them apart. Ex. Seedlings of trees with windblown seeds Conclusion A population’s distribution and abundance provides a partial snapshot of its current situation. Population Growth For most of our history, the human population has remained at very low levels, but beginning around 1750, the rate of population growth jumped to about 2% a year and has been growing rapidly since. Exponential growth - growth that occurs in proportion to the current total. J-shaped growth curve The larger a population is, the more rapidly it grows because an increase in numbers depends on individuals reproducing in the population. Annual growth rate of a population is the percent change in population size over a single year. Growth rate = birth rate – death rate. The Demographic Transition
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Demographic transition - the period when birth rates are dropping toward lowered death rates. The length of time that a human population remains in the transition has an enormous effect on the size of that population. Countries that pass through the transition swiftly remain small, while those that take longer can become extremely large. Developed countries have already passed through the demographic transition and have low population rates. Global human population growth rates have remained high because the least
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Biology Textbook Notes - Biology Textbook Notes CHAPTER 14...

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