Chi-Squared Test: Skills

What can be tested?

An association between species or if they co-exist independently of each other

What are the two possible hypotheses?

H0: null hypothesis

H1: alternative hypothesis

What is the null hypothesis (H0) related to interspecific competition between two species?

Two species are distributed independently with no statistical significant association in their distribution.

What is the alternative hypothesis (H1) regarding interspecific competition?

Two species are associated, indicating a statistical significant association between their distributions.

What statistical test is used to compare observed and expected frequencies in interspecific competition studies?

The chi-square test.

What is the aim of field manipulation in testing for interspecific competition?

To remove one of two species from quadrats in order to observe the effects on competition.

What is the aim of laboratory exoeriment in testing for interspecific competition?

Species could be growth together and apart to investigate whether they compete for resources

In the context of species association, what does a positive association indicate?

Species are found in the same habitat, such as predator-prey relationships.

What does a negative association imply about species distributions?

Species occur separately in differing habitats, likely due to competition.

What does no association imply about species distributions?

Species occur as frequently apart as together

Testing for Association

Define the hypothesis

Draw a contingency table of observed frequencies (the number of quadrats containing and not containing the species)

Calculate the expected values using the formula:

Expected values = (row total x column total) / grand total.

Now you can calculate the Chi2 value using the following equation

Calculate the degrees of freedom and compare the calculate Chi2 value to the critical one in the 0.05 confidence interval