MathBench > Statistical Tests

Goodness of Fit Tests

Example 2: Habitat selection (ecology)

You have just returned from a 3 year stint in the jungles western Africa, where you studied the habitat selected by the native bee eaters (a family of birds that specialize in catching bees and wasps on the wing, taking them to a perch, bashing their stingers out, and devouring them. In a pinch, they will eat other flying or hopping insects, such as grasshoppers). Three habitats were available to the bee eaters:

habitat Jungle Grassland Fields
% of area 75% 10% 15%
bee eater

Here's where you observed birds:

habitat Jungle Grassland Fields
# of birds 86 3 11

Is there evidence that birds prefer jungle habitat over grassland or fields? See if you can set this test up and interpret it on your own. Below is an excerpt from the chi-square table:

bee eaterexcerpt from chi-square table

Click below for hints if you need them.


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I think I have the answer: The null hypothesis is random distribution,
so the expected values are 75, 10, and 15. Your chi-square-calc should be
121/75 + 49/10 + 16/15, which is approximately 7.5, which is definitely
bigger than 5.99 (chi-square-crit for 2 df), so the birds do NOT fit
the null hypothesis of random distribution -- they do prefer some
habitats over others.