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Reproductive Patterns and Population Density Questions for Today: What are the different Reproductive Patterns found in Nature? How can Genetic Diversity affect the size of small Populations? Compare and Contrast Density-dependent and Density-independent Population Controls. What are the different Types of Population Changes that can occur in Nature? Review Terms: Immigration Emigration Biotic Potential Intrinsic Rate of Increase Environmental Resistance Carrying Capacity Reproductive Patterns Species have different Reproductive Patterns that can help enhance their chance for survival: r-selected species *note that the r is not capitalized K-selected species r-selected species These species are those that have a high intrinsic rate of increase. What are the common traits had by those that have a high intrinsic rate of increase? Examples of r-selected species: Algae, bacteria, rodents, frogs, turtles, annual plants, and most insects r-selected species are opportunists When conditions are right they have a boom in reproduction. K-selected species K-selected species are also called competitor species. Reproduce later in life with small number of offspring Develop inside their mother and are rather large at birth and mature slowly. They are cared for by the parent species. Called K-selected because they live will when the population is near the Carrying Capacity. Examples of K-selected species: Large Mammals, birds of prey, large-long lived plants. Genetic Diversity and Population Size The Size of a Population can affect the genetic diversity in the area. Usually in Large population, Genetic diversity is fairly constant or there is very little change. There are several factors that can play a role in the loss of genetic diversity: Founder Effect Demographic Bottleneck Genetic Drift Inbreeding Genetic Diversity and Population Size Founder effect Demographic Bottleneck When a few individuals survive after a catastrophic event. Genetic Drift Occurs when a few individuals leave the population and colonize a new area that is geographically isolated from the main population Random changes in the gene frequencies in a popuationthat can lead to unequal reproductive success. Inbreeding Can increase the frequency of defective genes. Population Density Controls Population density is the number of individuals in a population found in a particular area or volume. Two types of controls: Density-dependent Density-independent Population Controls Density-dependent controls limit population growth as density increases. Predation, parasitism, infectious disease, and competition for resources Density-independent controls limit population growth regardless of density. Mostly abiotic Weather phenomenon, geologic processes, catastrophes Population Changes The are four general patterns of variation in population size: Stable Irruptive Cyclic Irregular Population Changes Stable Very little fluctuation around the carrying capacity of the area Species found in the tropical rainforest exhibit stable population changes because the weather and climate changes very little from year to year Irrupt When population growth occasionally explode to a high peak then crash to a more stable lower level. Algae and insects Population Changes Cyclic Fluctuations Similar to irruptive but the cycle is drawn out much longer. Lemmings populations rise and fall every 3-4 years Lynx and hare populations rise and fall on a ten year cycle. Predator-prey relationships have cyclic fluctuations Irregular Patterns No discernable pattern in population change