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APES CHARACTERISTICS OF POPULATIONS Changes in population size, density, dispersion, age structure and sex ratio are known as population dynamics. The most common pattern of population dispersion found in nature is a clumped pattern. Population dispersion may be affected by Immigration Emigration Mating habits Seasonal changes Population dispersion in an ecosystem is often determined by the distribution of resources. Age structure categories include Pre-reproductive Reproductive Post-reproductive Population size is governed by births, deaths, immigration, and emigration. The biotic potential of a population is the maximum reproductive rate of the population. Biotic potential is determined by Reproductive age span Litter size How many offspring survive to reproductive age How often reproduction occurs Rapidly growing populations in nature may be limited by Light Water Space Nutrients Environmental resistance is enhanced by a specialized niche. A population will increase if the biotic potential increases. Carrying capacity refers to the maximum size of population the environment will support. The curve depicting the growth of a population that is limited by a definite carrying capacity is shaped like the letter “S”. A population crash occurs when a population overshoots its carrying capacity and environmental pressures cause effects. One reason why a population may overshoot its carrying capacity is due to a time delay. The human population of Ireland experienced a major crash as a result of a potato fungus. Humans have extended the Earth’s carrying capacity for the human species by Controlling many diseases Using energy resources at a rapid rate Using material resources at a rapid rate Increasing food production Carrying capacity is determined by Climatic changes Migration Predation Interspecific competition Density dependent population controls include Human destruction of habitat Parasitism Competition for resources Predation Studies of populations of mice indicate that overcrowding is associated with Reduced milk production in nursing females Lower sexual activity More spontaneous abortions Inhibited sexual maturity Density-independent population controls include Drought Fire Floods Unfavorable chemical changes in the environment Some general types of population curves are Stable (monkeys in a rainforest) Cyclic (muskrats after trapping has been outlawed) Irruptive (rabbits and coyotes in undisturbed habitat) REPRODUCTIVE STRATEGIES AND SURVIVAL r-strategists Are generally is small and short lived Insects, aquatic organisms (fish and invertebrates) Exhibit early-loss survivorship curves K-strategists are generally less adaptable to change than r-strategists have populations that follow an S-shaped growth curve large mammals exhibit late-loss survivorship curves Extinctions There have been (5) mass extinctions 20-60 million years apart during the past 500 million years The last mass extinction occurred about 65 million years ago Adaptive radiation usually follows mass extinctions