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Population Ecology Chapter: 52 What you need to know! 1. 2. 3. How density, dispersion, and demographics can describe a population. The differences between exponential and logistic growth models. How density-dependent and density independent factors can control population growth. Levels of Organization From small to large: Organism (individual) Population – group of organisms of the same species that interact with one another Community Ecosystem/Biome Biosphere Population Characteristics Size* (N) = total number of individuals Density* = number of individuals per area or volume (100 buffalo/km2) *Dynamic – births/deaths & migration Dispersion = grouping of individuals in area Clumped (humans in cities) Uniform (nesting penguins) Random (trees in a forest) Demographics – Life Tables Demographics is the study of vital population statistics Life Tables are age-specific summaries of survival patterns of a population Demographics - Survivorship Curves Graph of Life Table Idealized survivorship curves show 3 common patterns of the relationship between age and death: Type I = Long Life Type II = intermediate; little to no relationship between age and death Type III = Infanticide with longevity after adolescence Demographics – Reproductive Table A fertility schedule that includes the relationship between age and reproductive success Life History Traits that impact reproduction and survival 1. 2. 3. Maturation Frequency of reproduction Clutch size Fecundity is the combination of 2 & 3 Two evolutionary patterns: 1. Semelparity (big-bang reproduction) 2. One massive reproductive event followed by death Iteroparity (repeated reproduction) Several reproductive events throughout lifetime Exponential Growth Maximum growth in ideal conditions Logistic Growth Realistic Model of Growth Carrying capacity (K) is the maximum amount of life an ecosystem can support Usually density dependent and/or limiting factors Fluctuations common Logistic Model & Life Histories r-selected species: Quick reproduction time leads to rapid increase in number (semelparity) Widespread death when K is reached K-selected species: Steady population around K Small number of large offspring needing intensive parenting Multiple reproductive events in lifetime (iteroparity) Limiting Factors Anything that reduces population growth Density-dependent factors apply as populations increase in density: Competition: food, water, territory, etc. Health (disease, waste) Predation Intrinsic factors Density-independent (abiotic) factors apply to all populations, regardless of size Weather Climate change Natural disasters Population Dynamics Complex interactions between biotic and abiotic factors that cause variation in the size of a population Population are not stable; they fluctuate Metapopulation includes the migration between more than one population Human Population Age Structure