Chapter 4 Population Ecology 4.1 Population Dynamics

Population Characteristics Population Density: number of organisms per unit area Spatial distribution: the dispersion or pattern of spacing of organisms RANDOM UNIFORM CLUMPED

Principles of Population Growth Population growth rate: explains how fast a given population grows. Population growth measured in different ways

How Fast Do Populations Grow Usually not linear

How Fast Do Populations Grow Usually slow at first Called a “J”-shaped curve Slow at first because number of reproducing organisms is small Called exponential growth: as a population gets larger it grows faster

Limits of the Environment Population growth usually stops due to lack of resources Food Water Shelter Space Population growth usually stops due to build up of waste products which poison the organisms

Carrying Capacity Number of organisms of one species that an environment can support “S”-shaped growth

Carrying Capacity Fluctuations above and below carrying capacity are normal

“J”-shaped population growth pattern Mosquito, bacteria Rapid Life-history pattern Reproduce very rapidly, produce many off spring in short period of time Environment unpredictable and change rapidly Small body size, mature rapidly, reproduce early, short life span Populations increase rapidly then decline

”S”-shaped population growth pattern Slow Life-history pattern Slow rate of reproduction, produce few offspring Elephants, bears, whales, redwood trees, cacti Live in stable environment Large, reproduce and mature slowly, long-lived Maintain population size near carrying capacity

Environmental Limits to Population Growth Limiting Factors: biotic or abiotic factors that regulate size of a population Two types of limiting factors Density dependent factors Density independent factors

Density Dependent Factors Increasing effect as population size increases Disease Competition Parasites Food The more dense the population the faster disease can spread Big problem in agricultural crops

Density Independent Factors Affect all populations regardless of their density Most are abiotic factors Temperature Floods Storms Drought Habitat destruction Pollution

Organisms Interactions Limit Their Population Size Predation affects population size Predator prey relationships often show a cycle of population increases and decreases over time

Predator Prey Relationships Hare Lynx

Predator Prey Relationships Important for health of natural population Usually young, old or injured are caught

Effects of Competition Competition for food, water, territory are density dependent factors Only the best suited to the environment survive

Chapter 4 Population Biology 4.2 Human Population

Human Population Demography: study of human population growth characteristics: size, density, distribution, movements, birthrates, and death rates. People live longer and they’re able to produce more children, causing the population to grow.

Humans can control limiting factors by: eliminating competing organisms increasing food production controlling disease organisms

Effects of Birth and Death Rates Birthrate : the number of live births per 1000 people in a given year. Death rate: the number of death per 1000 people in a given year

How to determine the growth rate of a population? Population growth rate( PGR)= birth rate – death rate When is PGR = 0 ? Zero population growth exists when birthrate equals death rate.

Zero population growth It means that new people are entering the population (through birth) at the same rate that people are leaving the population (through death) The population is changing but it is stable.

When PGR is above zero or positive More people are entering the population Less people are leaving the population Population is growing More births than deaths in the population When PGR is less than zero or negative Less people are entering the population More people are leaving the population More deaths than births in the population

Doubling time: is the time needed for population to double in size Happen with growing population ( positive PGR) Slow growth rate means it will take longer for population to double

What is the age structure of a population? Age structure: refers to the number of people at each different age level. (ex: 10- 14, 15-19) Male or female Is population is stable , growing , or becoming smaller?

Age Structure Graph: shows the age of the largest group in the population. When a large amount of population is made up of children, then the population experiencing rapid growth. When there are more adults than children, then the population is declining. When the amount of population in the different age levels is about equal, then the population is stable.

Age Structure Graph

Does environment affect population growth? Not enough food, water, or space for everyone Population creates more waste than can be handled Conditions of the environment cause disease to spread, or pollution affects the water

Homework: pages : 15-18 Due date: Monday October 10, 2016 Test on Monday October 10, 2016 Chapters 3.1 + chapter 4 Section 3.2 Biomes will NOT be on the test Review on Friday