Population Ecology

Population Ecology Chapter 4

Population Density Population density: # of organisms per unit area • Example: 5 deer per square mile of forest • If 10 people are in a 100 square foot room, what is their population density?

Spatial Distribution Dispersion: pattern of spacing of a population • Uniform – spread out evenly throughout an area • Clumped – found in clumped groups • Random – spaced out randomly and unpredictable • What does dispersion pattern tell you about an organism?

Population Range Where on earth do you find a specific population? • Some organisms are found throughout the world = large population range • Other organisms only found in a few places = limited population range • Why might an organism such as the Kiwi bird have a limited population range?

Population Limiting Factors Remember limiting factors keep a population from continuing to grow • These factors may be biotic (ex. predators) or abiotic (ex. temperature) • Decreasing a limiting factor often changes the number of individuals that can survive in an area • Two types of limiting factors on populations • Density-independent limiting factors • Density-dependent limiting factors

Density-independent factors • Does not depend on the size of the population • Affects all populations equally no matter how big or small the population is • Usually are abiotic • Often includes natural phenomena such as floods, fires, etc. • Can sometimes be beneficial to some members of the community

Density-dependent factors • Effect depends on the size of the population • Often biotic • such as predation, disease, parasites, & competition • disease: transmitted easier when population is larger competition: occurs more often when pop. is larger parasites: more common when population is larger

Population Growth Rate • How fast a population grows • Four factors affect growth rate 1. Natality = birthrate 2. Mortality = death rate 3. Emigration = moving out of a population 4. Immigration = moving into a population

Exponential Growth • Growth begins slowly but then takes off quickly • Creates a J-shaped curve on a graph Exponential phase = growth is quick Lag phase = growth is slow

Logistic Growth • Population grows exponentially until some limiting factors slows its growth • Forms an S-shaped curve on a graph • Carrying capacity = max number of individuals an ecosystem can support

Reproductive patterns • Reproductive patterns of different species vary • may have different # of births per cycle • May begin reproducing at different ages • May have different life spans • R-strategist and k-strategists

r-strategists • Also called the rate strategy • Used by organisms that live in environments where biotic and abiotic factors often fluctuate • characteristics 1. Usually are small organisms 2. Usually have short life spans 3. Usually produce many offspring at once

k-strategists • k refers to carrying capacity • Used by species living in areas with predictable and fluctuations in the environment • Characteristics 1. usually larger organisms 2. usually have long life span 3. only produce a few offspring at a time

Human Population Growth • Demography: study of the human population • Includes size, density, distribution, movement, birthrate and deathrate

Human Population cont. • Has grown rapidly as humans have learned to alter their environment. • Better agriculture, domestication of animals, technological advances, and discoveries in medicine

Zero Population Growth (ZPG) & Age Structure • ZPG occurs when births + immigration = deaths + emigration • Age structure: # of people in each age group in a population • Pre-reproductive, reproductive, & post-reproductive

Population Ecology