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Unformatted text preview: Ecology Ecology: study of the relationship of living things and their environments. population is a group of organisms of the same species in the same area or are interbreeding and sharing genetic information. I. Population Dynamics. A. Properties of Populations The individual of a population is transitory, but the population endures. Properties of populations include growth patterns, morality patterns, age structure, density and dispersion. In the absence of net immigration or emigration, the growth rate increase is equal to the birth rate minus the death rate. The growth rate can be positive can be positive or negative. This property of a population per capita rate of increase is symbolized by the letter r. if the population increases at a constant rate, it shows an exponential curve. This can be described by the differential equation. DN/dt= rN R= per capita increase N=# of individuals present, t= time period. This type of growth is sometimes called logarithmic or log growth, presumably because the graph of log N vs. t is a straight line. The exponential growth curve is shown by microorganisms in the lab, and also by the initial stages of an algal bloom. In nature, short term exponential growth occurs when opportunistic species invade an area and use abundant local resources. Weeds and some insects are examples of opportunists. c. Limiting factors: carrying capacity For many populations, the number of individuals in an area is determined by the environment. A given environment can support only a limited number of individuals. Population size hovers around this number which is known as the caryin capacity. In the environment it may vary seasonally. A simple way of showing the effect of the carrying capacity is through the following equation often called the logistic equation. Dn/dt= rN (kn) R=capita increase and it is multiplied by the number of individuals present N at any one time. K=carrying capacity, the number of individuals the environment can support over a specified amount of time. The (kn)/ K is a negative feedback term. If N is small, (kn)/K and the curve, if graphed, is almost an exponential curve. As N increases, then the value of (kn)/k decreases and the growth curve slows. When n=K, growth stops. If the number of organisms, N, becomes grater than K, growth is negative. Eventually the population stabilizes. The model of population growth, represented by the sshaped or sigmoid curve is called the logistic. 2. Survivorship Patterns Mortality also affects population size. There are three basic survivorship patterns. These patterns often show up in combination in a population. d. type I Most organisms die at the later stages in life e. type II Mortality rate is the same for all ages .c. type III Most organisms die in the early stages of life 3. Age structure Mortality patterns affect age structure of a population. Age structure is the number of individuals of different ages in the population. A cohort is the individuals in a population of the same age. A plot of cohort survivorship for the population yields the age4 of the population. age4 of the population....
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- Spring '11