Ecology Part 4 Populations Part 5 Communities Part

Ecology Part 4. Populations Part 5. Communities Part 6. Biodiversity and Conservation

Population Ecology: 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: • • birthrate) Natality (____ death rate) Mortality (_____ Emigration (the number of individuals moving _____ away from a population) moving to Immigration (the number of individuals _____ a population)

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 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

Population Ecology: Population Growth Rate 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 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?

Population Ecology: Population Growth Rate Population Limiting Factors • 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?

Population Ecology: Population Growth Rate Population Limiting Factors • 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…

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

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 Ecology: Population Growth Models Population Limiting Factors • 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 Ecology: Population Growth Models 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

Community Ecology: Communities • Review: – A community is a group of interacting populations that occupy the same area at the same time.

Community Ecology: Communities • Limiting Factors – Any abiotic or biotic factor that restricts the numbers, reproduction, or distribution of organisms.

Community Ecology: Communities • Range of Tolerance – The limits within which an organism can exist.

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

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

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

Community Ecology: Ecological Succession: Primary Succession Ecological Succession • Ecological Succession: Primary – 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.

Community Ecology: Ecological Succession: Primary Succession Ecological Succession • Ecological Succession: Primary – The stable, mature community that eventually develops from bare rock is called a climax community.

Community Ecology: Ecological Succession: Secondary Succession Ecological 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.

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

Community Ecology: Ecological Succession • Ecological Succession: End point? – Cannot be predicted – Different rates of growth & human involvement make it impossible to know if a true climax community has been reached.

Biodiversity and Conservation: Introduction On the left side of your Int. NB, address the following: • What would happen if all of the jackrabbits in a food web died suddenly? • Is the disappearance of one species from Earth important, or will another species fill its niche?

Biodiversity and Conservation: What is biodiversity? Biodiversity • What is Biodiversity? The variety of life in an area that is determined by the number of different species in that area. • There are 2 main types: Genetic Diversity Species Diversity

Biodiversity and Conservation: Why is biodiversity important? Biodiversity Penicillin: Derived from bread mold Teosinte: A distant relative of corn Domestic corn plant Madagascar Periwinkle: Used to treat childhood forms of leukemia

Biodiversity and Conservation: Extinctions Extinction Rates • The gradual process of becoming extinct is known as background extinction. • Mass extinctions: When a large percentage of all living species become extinct in a relatively short period of time. • 250 MYA: Over 90% of species died

Biodiversity and Conservation: Extinctions Estimated number of Extinctions since 1600 Group Mainland Island Ocean Total Approximate Percent of Number of Species Group Extinct Mammals 30 51 4 85 4000 2. 1 Birds 21 92 0 113 9000 1. 3 Reptiles 1 20 0 21 6300 0. 3 Amphibians 2 0 0 2 4200 0. 05 Fish 22 1 0 23 19, 100 0. 1 Invertebrates 49 48 1 98 1, 000+ 0. 01 Flowering Plants 245 139 0 384 250, 000 0. 2

Biodiversity and Conservation: Extinctions Five Most Recent Mass Extinctions Cretaceous Period (65 MYA) Triassic Period (200 MYA) Permian Period (250 MYA) Devonian Period (360 MYA) Ordovician Period (444 MYA)