1. Option G.1: Community Ecology
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2. Vocab Recap
Community is a group of interacting populations living together and interacting with each other in an area
Distribution of organisms in communities is affected by abiotic and biotic features

3. Factors affecting distribution of plant species
Temperature and water
Light
Soil pH
Salinity
Mineral nutrients
Turn and talk
Turn to your neighbor and discuss how theses factors affect plant distribution
Are these factors abiotic or biotic?

4. Factors affecting distribution of animal species
Temperature
Water
Breeding sites
Food supply
Territory
Turn and talk
Turn to your neighbor and discuss how theses factors affect animal distribution
Which of these factors are biotic and which are abiotic?

5. Random Sampling
Suppose you wanted to determine the size of a population
You could count every organism, but that would be very time consuming
Ecologists use a sampling method
They take a random sample and use it to estimate the total number of organisms
Samples must come from all around the habitat
Why?
In a truly random sample, each organism has an equal chance of being selected for the count

6. Quadrat Method A quadrat is a square of a certain size
Organisms within the quadrat are counted
These counts are used to determine the population size
How to solve:
Calculate the average number of organisms in your sample quadrats
Multiply the average by the total number of quadrats

7. Example
A scientist wants to determine how many beech trees and maple trees are growing on a dune. The scientists measures the area and divides it into 20 quadrats. Using a random sample table, five sample squares are selected and trees counted. The table on the next slide shows the data.

8. Example – continued
How many beech trees are there on the dune? How many maple trees?
Quadrat
Beech trees
Maple trees 1 5 10 2 8 12 3 4 9 6 7

9. Example – continued Take the average
Beech: 5.2
Maple: 8.4
Multiply the average by the total number of quadrats
Beech: 5.2 x 20 = 104
Maple: 8.4 x 20 = 168

10. Transect
Commonly used for studying how the distribution of plants in an ecosystem is affected by abiotic factors
Ecologists still draw quadrats and count the number of plant species of interest
They also measure the abiotic feature (e.g. temperature, pH, light …)

11. The niche concept
Every organism in an ecosystem has a particular role in that ecosystem
That’s the organism’s niche
Concept includes where the organism lives (spatial habitat), what and how it eats (feeding activities) and its interactions with other species
What’s your niche?

12. Spatial habitat Unique space in the ecosystem
Area inhabited by any particular organism
The ecosystem is changed by the presence of the organism
Habitat loss is the greatest threat to biodiversity on our planet
What’s causing this?

13. Feeding activities
Affect the ecosystem by keeping other populations in check
For example, green frogs eat aquatic larvae of mosquitoes, dragonflies, and black flies
Green frogs keep these insect populations in check

14. Interactions with other species
Competition
When two species rely on the same limited resource
One species will be better adapted than the other
Herbivory
A herbivore is a primary consumer (plant eater) feeding on a producer (plant)
The growth of the producer is critical to the well-being of the primary consumer
This is an interaction between plants and animals

15. Interactions with other species
Predation
A predator is a consumer (animal) eating another consumer (animal)
One consumer is the predator and the other is the prey
The number of prey affects the number of predators and vice versa

16. Interactions with other species
Parasitism
A parasite is an organism which lives on or in a host and depends on the host for food
The host is harmed by the parasite
Ex: plasmodium is a parasite that causes malaria in humans (reproduces in the liver and RBC); part of its life cycle take place in mosquitoes – mosquitoes are the vector

17. Interactions with other species
Mutualism
Two organisms living together where both organisms benefit from the relationship
Ex: clown fish and sea anemones
Clown fish are brightly colored and live within the area of the tentacles of the poisonous sea anemone
Clown fish are covered with mucus, which protects them
Clown fish lure other fish; sea anemone eats the fish and the clown fish eat the remains

19. Competitive Exclusion
No two species in a community can occupy the same niche
1934; Russian ecologist G.F. Gause
Experiment with two different species of paramecium (P. aurelia and P. caudatum)
When each species was grown in a separate culture they did equally well
When the two were cultured together, with a constant food supply, P. caudatum died out and P. aurelia survived
When two species have a similar need for the same resources, one will be excluded

20. Fundamental niche vs. realized niche
Potential mode of existence, given the adaptations of the species
No competition from other species
Realized niche
Actual mode of existence, which results from its adaptations and competition with other species

21. Biomass Total mass of organic matter
Organic matter = carbon compounds (carbs, lipids, proteins)
Since matter also includes water, which is not organic, it has to be dried
Biomass is measured as dry mass or organic matter of living organisms
Units = grams per meter squared per year
g m-2 yr-1

22. Measuring biomass at each trophic level
How difficult is this?
There are tables and charts available which tell you the biomass of animal according to its size or weight
Ex: trap a raccoon, weigh it, then find its biomass in a table (raccoon should be returned to ecosystem)
There are tables for plant species, but it’s not easy to determine the weight of a tall tree
What to do?

23. Measuring biomass – cont.
Measure the total area of the ecosystem
Divide the ecosystem into small areas & choose one plot to sample
Measure the size of each plant species (height and diameter)
Cut down all trees and vegetation
Dry them out
Mathematical model to show relationship between weight and height of each plant and its biomass
Sample other plots by measuring height and diameter (cutting down is not necessary)

24. Measuring biomass – cont.
If you are measuring the biomass of the ecosystem, then you would add in the animal species
Process is repeated seasonally or yearly to study changes in biomass over time

25. Issues – Turn and Talk
After measuring or counting organisms, we may fail to return them to the same ecosystem. Is there a moral principle involved here?
In order to measure biomass, destructive techniques are used – trees are cut down and plants are destroyed. Is this unethical?
Could the destructive sampling techniques described be explained as “moral relativism”?

26. Review
List three factors that affect the distribution of animal species.
Explain the competitive exclusion principle.
Describe one technique that ecologists use to estimate accurately the size of a population of animals, including any calculations that need to be done.