CHAPTER 4 Population Ecology
Lesson 4.1 Studying Ecology Ernst Haeckel defined ecology in 1866 as the body of knowledge concerning the economy of nature the total relations of the animal to both its inorganic and organic environment.
Lesson 4.1 Studying Ecology Levels of Ecological Organization Study how organisms interact w/ each other & w/ envts Study ecology at various levels of organization.
Lesson 4.1 Studying Ecology Biotic and Abiotic Factors Biotic factors: Parts of an ecosystem that are living or used to be living Abiotic factors: Parts of an ecosystem that have never been living Did You Know? Decaying organisms are biotic factors as long as their structure remains cellular.
Lesson 4.1 Studying Ecology Habitat Specific envt in which organism lives Provides an organism w/ resources anything an organism needs to survive & reproduce, includes food, shelter, & mates.
Lesson 4.2 Describing Populations From 1900 to 2000, the white-tailed deer population of New York state grew from about 20,000 to more than 1 million. Densities of more than 100 deer per sq mi occur in some metropolitan areas.
Lesson 4.2 Describing Populations Population Size # of indivs in a pop at a given time Sudden & dramatic decreases in pop size indicates unhealthy pop headed toward extinction. Ecologists often use sampling tech to est pop size. Sample areas-mark/recapture Count animal tracks/droppings Did You Know? The passenger pigeon was once North America s most abundant bird. Hunting drove them to extinction in less than 100 years. Counting Laysan Albatross Nests
Lesson 4.2 Describing Populations Population Density Measure of how crowded a pop is Larger organisms generally have lower population densities. Low population density: More space, resources; finding mates can be difficult High population density: Finding mates easier; tends to be more competition; more infectious disease; more vulnerability to predators Northern pintail ducks
Lesson 4.2 Describing Populations Population Distribution How organisms are arranged within an area: Random distribution: Orgs arranged in no particular pattern Uniform distribution: Orgs evenly spaced QuickTime and a decompressor are needed to see this picture. Clumped distribution: Orgs grouped near resources; most common distribution in nature QuickTime and a decompressor are needed to see this picture.
Lesson 4.2 Describing Populations Relative # of orgs of each age group w/in population Age Structure Can be used to predict future pop growth QuickTime and a decompressor are needed to see this picture.
Lesson 4.2 Describing Populations Sex Ratios Proportion of males to females Age structure diagrams give info about sex ratios. For a monogamous species, the ideal sex ratio is 50:50.
Lesson 4.3 Population Growth From 1800 to today, the human population has grown from about 1 billion to more than 6.8 billion an exponential rate of increase.
Lesson 4.3 Population Growth Pop s relative birth (natality) & death rates (mortality) affect how it grows. Survivorship curves show how the likelihood of death varies with age. Birth and Death Rates Type I: Humans higher mortality @ older agelikelihood of dying w/age Type II: Steady survivorship; equal mort. @ all ages ex:birds Type III: young suffers high death rates--toads QuickTime and a decompressor are needed to see this picture.
Lesson 4.3 Population Growth Immigration and Emigration In addition to births & deaths, pop growth is affected by immigration & emigration indivls moving into & out of a pop. Migration, seasonal movt into & out of area, can temporarily affect pop size.
Lesson 4.3 Population Growth Calculating Population Growth Determined by the following equation: (birthrate + immigration rate) (death rate + emigration rate) Growing pops have positive growth rate; shrinking populations have negative growth rate. Usually expressed in terms of individuals per 1000 Did You Know? Immigration contributes more than 1 million people to the U.S. population per year.
Lesson 4.3 Population Growth Population increases by fixed % every year. Normally occurs only when small populations are introduced to an area w ideal envtal conditions Rarely lasts long Exponential Growth
Lesson 4.3 Population Growth Logistic Growth & Limiting Factors Growth almost always slows & stops due to limiting factors. Limiting factors: Envtal characteristics slow pop growth & determine carrying capacity (largest pop size in given envt) Density-dependent: Influence changes w/ pop density. Density-independent: Influence does not change w/ pop density.
Lesson 4.3 Population Growth Org s max ability to produce offspring in ideal conditions Biotic Potential Factors influence biotic potential, including gestation time & generation time. Orgs w/ high biotic potential can recover more quickly from pop declines than orgs w/ low biotic potential.