G1: Community Ecology

Audrey Elliott and Tanner Oracheski

G.1.1 Outline the factors that affect the distribution

of plant species Temperature Water Light Soil pH Salinity Mineral nutrients

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

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

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

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

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

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)

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)

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

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

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

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.

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

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

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

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

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