G1: Community Ecology

1. G1: Community Ecology Audrey Elliott and Tanner Oracheski

2. G.1.1 Outline the factors that affect the distribution of plant species • Temperature • Water • Light • Soil pH • Salinity • Mineral nutrients

3. G.1.2 Explain the factors that affect animal species distribution • Temperature: extremes of temperature require special adaptations, so only some species can survive them • Water: animals vary in the amount of water they require • Breeding sites: many species need a special type of site and can only live in areas where these sites are available • Food supply: many animal species are adapted to feed on specific foods • Territory: some species of animal establish and defend territories

4. G.1.3 Describe one method of random sampling to compare the population size of species • Random sampling using quadrats • A sample is a part of a population chosen to illustrate what the whole population is like • In a random sample, every individual in a population has an equal chance of being selected

5. G.1.3 (continued) • Steps to using quadrats • 1. Mark out gridlines along two edges of the area • 2. Use a calculator or tables to generate two random quadrats • 3. Count how many individuals there are inside the quadrat. Repeat these steps • 4. Measure the total size of the area occupied by the population • 5. Calculate the mean number of plants per quadrat. Then calculate the estimated population size using this equation: Population size = mean number per quadrat x total area area of each quadrat

6. G.1.4 Outline the use of a transect • Transect: an alternative to random sampling • Measure distributions along a line marked out across a site • Useful when there is a gradient in an abiotic variable • Used to correlate the distribution of plant or animal species with an abiotic variable

7. G.1.5 Explain what is mean by the niche concept • An organism’s niche includes: • Habitat: where the species lives in the ecosystem • Nutrition: how the species obtains its food • Relationships: the interactions with other species in the ecosystem • The niche that a species could occupy is often smaller than the niche that the species actually occupies

8. G.1.6 Outline interactions between species: competition, herbivory, predation, parasitism and mutualism • Herbivory: a primary consumer feeding on a plant or other producer; the producer’s growth affects food availability for the herbivore • Example 1: the beetle Epitrix atropae feeds only on leaves of Atropa belladonna (to other organisms the leaves are highly toxic) • Example 2: Algae growing on rocks in shallow seas are often heavily grazed (a snail feeds on brown seaweed)

9. G.1.6 (continued) • Predation: a consumer feeding on another consumer; the numbers and behavior of the prey affect the predator • Example 1: lynx are predators of hares; changes in the numbers of hares are followed by similar changes in lynx numbers • Example 2: Bonitos (predatory fish) feed on achovetas (smaller fish)

10. G.1.6 (continued) • Parasitism: a parasite is an organism that lives on or in a host and obtains food from it; the host is always harmed by the parasite • Example 1: ticks are parasites of deer; they feed by sucking blood from their hosts which therefore weakens them • Example 2: organisms that cause infectious diseases are parasites; Sphinogomonas bacteria cause a disease in elliptical star corals

11. G.1.6 (continued) • Competition: two species using the same resource to compete if the amount of the resource used by each species reduces the amount available to the other species • Example 1: Fir and hemlock trees grow together in mixed forests; therefore they compete with each other for light, water, and minerals • Example 2: species of coral compete with each other on coral reefs

12. G.1.6 (continued) • Mutualism: mutualists are members of different species that live together in a close relationship, from which both benefit • Example 1: Fungus and algae can grow mutualistically because the alga supplies food made by photosynthesis and the fungus absorbs mineral ions • Example 2: cleaner wrasse (small fish) that cleans parasites from the gills and body of larger fish; the cleaner benefits because the parasites that it removes are its food

13. G.1.7 Explain the Principle of Competitive Exclusion • Competitive Exclusion Principle: Only one species can occupy the same niche in an ecosystem • This occurs when a species is unable to occupy any part of its fundamental niche in an area, so it has no realized niche in that area • If two species in an ecosystem have the same niche they will compete in all aspects of life and one will be superior. This will cause the disappearance of the other species from the ecosystem.

14. G.1.8 Distinguish between fundamental and realized niche • Fundamental niche: its potential mode of existence, given the adaptations of the species • Realized niche: its actual mode of existence, which results from its adaptations and competition from other species

15. G.1.9 Define biomass • Biomass is the total dry mass of organic matter in organisms or ecosystems • Used to compare the amounts of organisms in each trophic level in an ecosystem • However, it’s a destructive technique so samples must be small as possible

16. G.1.10 Describe one method for the measure of biomass and some difficulties • Method • 1. Samples of all living organisms in the ecosystem are collected • 2. Organisms are sorted into trophic level • 3. Organisms are dried in an oven • 4. The mass of the organisms in each trophic level is measured • 5. Drying and measuring the mass may be repeated to check that samples were completely dry

17. G.1.10 (continued) • Some organisms are part of multiple trophic levels and this can cause problems while sorting organisms • Collecting the samples can be very destructive as organisms must be killed in order to dry them and measure their biomass

18. Sources • Mr. Steffens’ PowerPoint • IB Study Guide • Images: • http://www.mooseyscountrygarden.com/hampton-court-flower-show-water-gardens/water-garden-plant.jpg • http://grove.ufl.edu/~turf/weedscience/quad2.jpg • http://projects.exeter.ac.uk/devonclp/1sample_core.jpg • http://www.globalchange.umich.edu/globalchange1/current/lectures/predation/lynx_hare.jpg • http://www.sustainabilityninja.com/wp-content/uploads/2008/12/coralreef.jpg • http://www.physicalgeography.net/fundamentals/images/niche.gif