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Unit 10 .docx

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University of Guelph
BIOL 1500
Marie Therese Rush

Unit 10 Population Ecology and Human Population Growth Population Ecology Ecology- field of biology that focuses on the interactions between organisms and their environment population ecology-the study of the interaction of a particular species or genus population with its environment -combines theory (including lots and lots of mathematical modeling) with laboratory and field work to explore a population’s growth, survivorship, structure, and reproduction -studies in population ecology can help determine: -population density of deer under different management plans -yield from a population of corn plants when planted at a particular density -limits that should be placed on fish catches -when to take action on the emergence of a pest species in a forest or on farms -whether wolf hunting should be allowed in Alaska to increase the caribou herd -causes of declines in reptile and amphibian populations throughout the world Population Structure Population structure- provides picture of a population at a given moment in time and includes the abundance or number of individuals in the population, the density of individuals, the distribution or spacing of individuals, and the proportions of individuals in each age class -usually measured by going out into the field, sampling a portion of individuals in the population, and using that information to make inferences about the population as a whole Ways to sample a population but the general techniques include the following: -Distance and area sampling (counting individuals along a transect line or in a quadrat (square area)) -Random-walk techniques (walking along a random route and counting the individuals you encounter) -Removal sampling ( trapping individuals, counting, and removing them (primarily used for pest species where their removal is advantageous!) -mark-recapture method- technique that estimates population size by capturing, marking, releasing, and recapturing individuals random distribution- dispersion of individuals in a population without pattern uniform distribution- occurs when individuals in a population are disbursed in a uniform manner across a habitat Abundance-total number of individuals in a population Population density-number of individuals per unit area Distribution pattern-spacing of individuals, and some typical kinds of distributions are clumped distribution, random distribution, and uniform distribution -often corresponds with suitable habitat areas containing abundant resources; this can lead to a clumped distribution pattern with high densities of individuals in resource-rich areas, and low densities in resource-poor areas Clumped distribution-a spatial arrangement of individuals with densely populated areas interspersed with sparsely populated areas Population Ecology Age Structure -proportions of individuals in each age class, i.e., age structure, adds more detail to the understanding of a population’s structure and is used to more accurately predict changes in the population size -Knowing the number of individuals in each age class can be helpful in devising management strategies -Data collected about individuals in each age class is put into a graph called a population pyramid and into a life table which can then be analyzed using mathematical models population pyramid- visual representation of the number of individuals in different age categories in a population Mating System mating system -describes the mating patterns between males and females in a population (number of mates, whether they are simultaneous or sequential, and how long the bond between the male and female lasts) -there are three main kinds of mating systems 1. Promiscuity: “Males that mate with as many females as they can locate often provides their offspring with nothing more than sets of genes. Such males are said to be promiscuous. Promiscuity usually precludes a lasting pair bond.” -most common mating system among animals and is standard in out-crossing plants. 2. Polygamy: when one individual forms long-term bonds with more than one individual from the opposite sex -when one female is mated to multiple males 3. Monogamy: when a single male and a single female form a bond that lasts throughout the rearing of offspring and sometimes for their entire life -occurs when parental care provided by both sexes is essential for the survival of the offspring -relatively common among birds because eggs need to be incubated almost continuously, and both sexes are able to do this task *Generally, a male’s fitness (genetic contribution to future generations) depends on his number of matings, thus favouring promiscuity *Generally, afemale’s fitness depends on ability to make eggs and provide for her young, thus favouring monogamy Life-history Strategy -ecologists have recognized there is a kind of continuum of approaches to the problem of survival and reproduction -some species adopt r-strategy-produce large numbers of offspring, start reproducing at an early age, and are relatively short-lived (algae, bacteria, rodents, annual plants and most insects) (reproduce early, have lots of offspring and die young) -some species adopt a K-strategy-produce small numbers of offspring, have a high degree of parental care (often involving both the males and femalesbegin reproduction later in life, and are long-lived (most large mammals and birds and large, long-lived plant(e saguaro cactus, oak trees, redwood trees, and most tropical rain forest trees) Attributes of r-selected and K-selected species. r-stategy K-strategy Mortality High, more variable and unpredictable Low, more constant and predictable Population size Variable, typically below carrying capacity Constant, close to carrying capacity Intraspecific and interspecific competition Variable, often weak Usually strong Selection favors Rapid development Slow development Early reproduction Delayed reproduction Small body size Large body size Reproduces once (or very few times) Reproduces many times during life during life Length of life Usually shorter Usually longer Leads to High productivity High efficiency Population Growth Patterns of Population Growth p
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