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

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