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POPULATIONS Ch 5.1 Ecology Population Review • What is a population? • Groups of individuals that belong to the same species and live in the same area • Give an example from a biome. Population Characteristics 1) 2) 3) 4) Geographic Distribution Population Density Growth Rate Age Structure* Each factor listed above is equally important in determining the future of a population. (ex: endangered vs. overpopulated) Geographic Distribution • Also called “range” • Area (size) inhabited by a population • Ex: Migrating Blue Whales vs. Bacteria on a rotting apple Bacteria vs. Blue Whale Range VS. Population Density • Number of individuals per unit area • Main characteristic to describe a population • Varies greatly depending on species and quality of ecosystem • Ex 1: Cacti vs. Rainforest Fig Trees….Which is more dense? • Ex 2: Science Daily (Dec. 7, 2000) — Nov. 22, 2000 -- Zoologists from the University of Toronto have cracked the ecological puzzle of how animals - in this case the arctic ground squirrel - manage to control their own population in the northern boreal forest of Canada. Growth Rates • Natural populations can grow, decline, or stay the same • Depends on 3 factors: • Birth Rate • Death Rate • Individuals entering or leaving population • Immigration (in) and Emigration (out) • Give an example for the terms above! Examples • What will happen to the following population (grow, decline, stay the same) immediately and later. 1. The EPA protects sea otters from hunting. 2. Killer whales prey on sea otters. Exponential Growth • With abundant space and food, protection from disease and predators, a population will increase in size exponentially 1. Reproduce at constant rate 2. Unlimited Resources 3. Begins slowly, then takes off! Ex: Doubling effect of bacteria Consider this… • Bacteria have the fastest rates of reproduction among living things • Assume “binary fission” (doubling) occurs every 20 minutes • 20 min= 2 bacteria • 40 min= 4 bacteria • 60 min=8 bacteria • 120 min = 64 bacteria • 3 hrs = 512 bacteria • 24 hrs = 4,720,000,000,000,000,000,000 bacteria Charting Exponential Growth • J-shaped curve = unlimited resources and growth *This graph displays actual results showing cell death as a result of toxicity from build up of detritus. Logistic Growth • As shown prior, exponential growth only lasts for a short while • Logistic growth occurs when growth slows or stops after exponential growth occurs • Results from: • Birthrate drops/Death rate increases • Immigration slows/Emigration increases • Both can result from lack of space and resources Charting Logistic Growth • “S” shaped curve • Shows “carrying capacity” of an ecosystem (maximum # of organisms based on available resources) • Why does the population remain constant towards the end of the curve?