UNIT ____: Communities and Ecosystems            Name:______________________

Essential Idea(s):

The continued survival of living organisms including humans depends on sustainable communities

A community of organisms is a group of organisms comprising the populations of all the different

species that coexist and interact with each other in the same ecosystem due to having overlapping

habitats and niches.

• Define community, population, species and habitat and niche.
• Give an example of a community of organisms.

Community interactions include mutualistic, competition, predation, herbivory, parasitic and pathogenic interactions, commensalism, amensalism and no overall effect.

• Define mutualism, competition, predation, herbivory, parasite, pathogen, commensalism, amensalism and neutralism.
• Outline an example of each type of ecological interaction.

The population size of a species can be estimated using random sampling.

• Outline why sampling must be random.
• Explain methods of random sampling, including the use of a quadrat.
• Compare sampling sessile species to motile species.

Testing for association between two species using the chi-squared test with data obtained from quadrat sampling.

• State the null and alternative hypothesis of the chi-square test of association.
• Use a contingency table to complete a chi-square test of association.

A community forms an ecosystem by its interactions with the abiotic environment.

• Define abiotic and ecosystem.
• List biotic and abiotic factors of an ecosystem.

Ecosystems have the potential to be sustainable over long periods of time.  

• Define sustainable ecosystem.
• Outline three requirements of a sustainable ecosystem.

Mesocosms can be used to study the effect of variables on ecosystem sustainability.

• Define mesocosm.
• List three example mesocosms.
• Outline requirements of setting up a mesocosm.

Flowering plants depend on pollinators for reproduction. This knowledge has led to protecting entire ecosystems rather than individual species.

• Contrast traditional conservation efforts with newer strategies of conservation.

Definition of Biological Community:

Community:

Organism:

Population:

Species:

Coexist:

Ecosystem:

Habitat:

Niche:

Community Interactions

Random Sampling

The aim is to select a sample, without bias, so it is representative of the population. From the sample, inferences can be made about the whole population.

Why sample populations?

How to sample populations:

Chi-square (x2) Test of Association

The chi-squared test is a statistical tool used to determine whether there is an association between two sets of categorical data. The test involves calculating the probability (p) of an association by comparing observed values to values expected if there was no association. It is important that the data used is categorical, not continuous.

The chi-squared test of association is used to determine if the presence of one species is associated with the presence of another.

NULL hypothesis:  There is no association between the two species.

ALTERNATIVE hypothesis:  There is an association between the two species.

1.  X2 tests use a contingency table in which the quadrats with each species present and/or absent are recorded.
2. Calculate the expected value for each cell of the contingency table if the null hypothesis were true, using this formula:

3. Finally, calculate the chi-square (X2) value for each cell in the contingency table by using the formula →
4. Compare the chi-square value to a table of critical values to see if the result is significant at p = 0.05.

Table of critical values for the chi-square test

If the calculated value is lower than the 0.05 level of significance, accept the null hypothesis and conclude that there is NO significant association between the variables.   If the calculated value is higher than the 0.05 level of significance, reject the null hypothesis and conclude that there IS a significant association between the variables.  ​

You may check your work by using an online chi-square calculation tool , the TI calculator, or the ‘CHITEST’ function on Excel and Sheets to compare the expected to observed values.

Chi-Square NOTES

OBSERVED 

EXPECTED 

X2 Calculations 

Calculated X2 = _________________________________ 

Degrees of Freedom: ________ 

Critical X2 Value: _________

Chi-Square Practice Problem #1  

OBSERVED 

EXPECTED 

X2 Calculations 

Calculated X2 = _________________________________ 

Degrees of Freedom: ________ 

Critical X2 Value: _________

Chi-Square Practice Problem #2  

OBSERVED 

EXPECTED 

X2 Calculations 

Calculated X2 = _________________________________ 

Degrees of Freedom: ________ 

Critical X2 Value: _________

A community forms an ECOSYSTEM by its interactions with the abiotic environment

Sustainability

Definition:

Requirements of a Sustainable Ecosystem:

Mesocosm

Definition:

Conservation

• Traditional

• New Approach