Population Ecology Items that are BOLD, underlined, or a different color are MOST important to write down

Population Characteristics Population Ecology: Population Characteristics Population Characteristics Population Density: The number of organisms per unit area Spatial Distribution: Dispersion: The pattern of spacing a population within an area 3 main types of dispersion Clumped Uniform Random The primary cause of dispersion is resource availability

Measuring density of populations is a difficult task. We can count individuals; we can estimate population numbers. Unfortunately, it is usually impractical to attempt to count individuals in a population. One sampling technique that researchers use is known as the mark-recapture method. Individuals are trapped, captured, tagged, recorded, and then released. After a period of time individuals are recaptured. This information allows estimates of population changes to be made Fig. 52.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Population Limiting Factors Population Ecology: Population Characteristics Population Limiting Factors Population growth rate How fast a given population grows Factors that influence this are: Natality (____ rate) Mortality (_____ rate) Emigration (the number of individuals moving _________ a population) Immigration (the number of individuals _________ a population) birth death away from moving to

How they effect size or density of a population: Immigration Birth Population (N) Death Emigration Figure 1. The size of a population is determined by a balance between births, immigration, deaths and emigration

Review What is an… Organism Population Community Ecosystem Biome What do we know so far that affects populations?

Lets say we constructed a table with data about the lives of ground squirrels. Looks confusing… Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A graphic way of representing the data is a survivorship curve. A Type I curve shows a low death rate early in life (humans). The Type II curve shows death rate constant over lifespan(squirrels). Type III curve shows a high death rate early in life (oysters).

Survivorship Curve This is a plot of the number of individuals in an area still alive at each age.

Population Limiting Factors Population Ecology: Density-independent factors Population Limiting Factors Density-independent factors Factors that limit population size, regardless of population density. These are usually abiotic factors They include natural phenomena, such as weather events Drought, flooding, extreme heat or cold, tornadoes, hurricanes, fires, etc.

Population Limiting Factors Population Ecology: Density-dependent factors Population Limiting Factors Density-dependent factors Any factor in the environment that depends on the number of members in a population per unit area Usually biotic factors These include Predation Disease Parasites Competition

Review Look at your scales… What is a… Survivorship Curve Are you a 1 or a 2? means you can list factors the influence population growth, know what exponential and logistic growth is, and can state types of succession Can classify factors as density dependent or independent/ predict affect of resources on carrying capacity What is a… Survivorship Curve Density-Independent factor Density-Dependent factor

Understanding Exponentials Population Ecology: Population Growth Rate Understanding Exponentials Put your pens down (DO NOT WRITE) for a minute & think about this: An employer offers you two equal jobs for one hour each day for fourteen days. The first pays $10 an hour. The second pays only 1 cent a day, but the rate doubles each day. Which job will you accept? 13

Understanding Exponentials Population Ecology: Population Growth Rate Understanding Exponentials Dollars an hour Now, how much would your employer owe you if you stayed at this job for another 2 weeks? Job 2 lags for a long time before exponential growth kicks in! What would happen if this type of growth took place within a population? Days at work

Population growth models Exponential growth model Also called geometric growth or J-shaped growth. First growth phase is slow and called the lag phase Second growth phase is rapid and called the exponential growth phase Bacteria can grow at this rate, so why aren’t we up to our ears in bacterial cells?

Limits to exponential growth Competition - as nutrients and resources are used up The limit to population size that a particular environment can support is called carrying capacity (k) When you’re done writing, put your pens down…

Population Ecology: Population Growth Rate What population do you think this is? Look at the dates and number of individuals Plants? Animals? Insects? Humans?

So, what do you think is going to happen to the human population? We will probably reach our carrying capacity. Our growth rate will start to look like most organisms, which is the Logistic Growth Model Carrying Capacity (k) What letter does this curve kind of look like?

Logistic Growth Model S-shaped growth curve population’s growth slows or stops following exponential growth stops at the population’s carrying capacity Populations stop increasing when: Birth rate is less than death rate (Birth rate < Death rate) Emigration exceeds Immigration (Emigration > Immigration)

Ecological Succession The change in an ecosystem that happens when one community replaces another as a result of changing biotic and abiotic factors

Ecological Succession Community Ecology: Ecological Succession Ecological Succession Consists of 2 types: Primary Succession Secondary Succession

Ecological Succession: Primary Community Ecology: Ecological Succession: Primary Succession Ecological Succession: Primary The establishment of a community in an area of exposed rock that does not have topsoil is called Primary Succession. It occurs very slowly at first

Community Ecology: Ecological Succession: Primary Succession The first organisms to arrive are usually lichens or mosses, which are called pioneer species. They secrete acids that can break down rock Their dead, decaying organic materials, along with bits of sediment from the rock make up soil.

Community Ecology: Ecological Succession: Primary Succession Small weedy plants and other organisms become established. As these organisms die, additional soil is created

Community Ecology: Ecological Succession: Primary Succession Seeds brought in by animals, water and wind begin to grow in the soil. Eventually enough soil is present for shrubs and trees to grow.

Ecological Succession: Secondary Community Ecology: Ecological Succession: Secondary Succession Ecological Succession: Secondary Disturbances (fire, flood, windstorms) can disrupt a community. After a disturbance, new species of plants and animals might occupy the habitat. Think Lion King 

Community Ecology: Ecological Succession: Secondary Succession Pioneer species in secondary succession are usually plants that begin to grow in the disturbed area. This is much faster than primary succession