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Populations What factors contribute to changes in populations? How do Populations Grow? • Describing Populations – How do ecologists study populations? • Geographic Range • Density & Distribution – Population Density • Growth Rate • Age Structure How do Populations Grow? • Population Growth – What determines whether a population grows, shrinks, or stays the same? • • • • Birthrate Death rate Immigration Emigration How do Populations Grow? • Exponential Growth • What is exponential growth? Draw a quick diagram – Rapid reproduction – Slow reproduction How do Populations Grow? • Logistic Growth – Why doesn’t exponential growth keep occurring? – Phases of growth • Phase 1 – exponential growth • Phase 2 – growth slows down. Why? • Phase 3 – growth stops and population size stabilizes. Why? – Carrying Capacity • Maximum # of individuals of a species that a particular environment can support indefinitely Limits to Growth • If populations tend to grow exponentially, why do they often follow logistic growth? • What determines the carrying capacity for a particular species? • Why would a species that’s “wellbehaved” in one environment grow out of control in another? Population Size Can Be Limited By Parasitism & Disease Natural disaster Unusual weather Competition Predation Limits to Growth • Density-Dependent Factors – Competition – Predation & Herbivory • Predator-prey relationships • Herbivore effects • Human effects – Parasitism & Disease – Stress from Overcrowding Limits to Growth • Density-Independent Limiting Factors – Unusual Weather – Droughts – Fire – Natural Disasters Human Population Growth • Historical Overview W/ a look to the future Human Population Growth Phase I Phase II Phase III • Demographic Transition Phase I Phase II Phase III – Phase 1= Death & Birth Rates are High – Phase 2 = High Birth & Low Death Rates – Phase 3 = Low birth & death rates Human Population Growth Crude Birth & Death Rates of countries in the stages of population growth. Human Population Growth • Age Structure & Population Growth Human Population Growth • Age Structure & Population Growth Human Population Growth Human Population Growth Home Work Assignment (5 pts) Due Thursday….NO EXCEPTIONS! What to do: • Create 2 exam questions from the ecology unit and e-mail them to me. • The questions should be from different sections of your ecology unit. – One of the questions should be a “deep” thinking question. – The two questions need to be different formats (multiple choice, fill-in-the-blank, short answer, essay, matching). – The ideal answer should be provided.
