Option G.1: Community Ecology

1. Option G.1: Community Ecology Page 418

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 • Temperatureand 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?

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 • Fundamental 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.