Population Dynamics Part 2

Population Characteristics 1.Population Density: – The number of organisms per unit area 2.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 Population Ecology: Population Characteristics

Population Limiting Factors 3.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) Population Ecology: Population Characteristics birth death away from moving to

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 Ecology: Density-independent 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 Population Ecology: Density-dependent factors

Understanding Exponentials Put your pens down 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? Population Ecology: Population Growth Rate

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

Population growth models – Exponential growth model Also called geometric growth or J-curve. 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? Population Limiting Factors Population Ecology: Population Growth Rate

Population Limiting Factors Population Ecology: Population Growth Rate Population growth models – Limits to exponential growth Population Density (the number of individuals per unit of land area or water volume) increases as well Competition follows 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…

What population do you think this is? Population Ecology: Population Growth Rate

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?

Population Limiting Factors Population Ecology: Population Growth Models Population growth models – Logistic Growth Model Often called the S-shaped growth curve Occurs when a population’s growth slows or stops following exponential growth. 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)

Population Limiting Factors Population growth models – Logistic Growth Model The S-curve is not as pretty as the image looks 1.Carrying capacity can be raised or lowered. How? Example 1: Artificial fertilizers have raised k Example 2: Decreased habitat can lower k 2.Populations don’t reach k as smoothly as in the logistic graph. Boom-and-Bust Cycles Predator-Prey Cycles Population Ecology: Population Growth Models

Species that follow this pattern usually 1.Have a Boom-and-Bust Life Cycle 2.Have short life spans 3.Produce many offspring 4.Smaller organisms i.e., fruit flies, mice, locusts 5.Don’t maintain a population near carrying capacity 6.Controlled by density- independent factors They are called r-strategists (for rate of increase) Population Limiting Factors Population Ecology: Reproductive Strategies

Species that follow this pattern usually 1.Have long life spans 2.Produce few offspring that have a better chance of living to a reproductive age 3.Are larger organisms i.e., elephants 4.Maintain a population at or near k 5.Controlled by density- dependent factors They are called k- strategists (for karrying kapacity) Population Limiting Factors Population Ecology: Reproductive Strategies