I am in the process of forming an index for frugivore preference/avoidance of certain fruit types of differing colours. It is hypothesised that for a given fruit type of a certain colour, the frugivore will either prefer or avoid it. For simplicity purposes, let's assume the fruit types are A, B, and C. And the colours are 1, 2, and 3.
I know that for a preference index, I need to know the observed and the expected values. Observed should be the proportion of food type x in the 'gut' whereas expected should be the proportion of food type x in the environment of all available food.
I am fairly certain that Observed should then be written off as, for example:
number of Fruit Type A of Colour 1 eaten / Sum (Fruit of colour 1 eaten)
I am having a bit of trouble grasping the expected value. I am imagining it as being either:
number of Fruit Type A of Colour 1 total / Sum (Fruit of colour 1 total)
number of Fruit Type A total / Sum (all fruit total)
My data will be set-up in a spreadsheet in the following way:
Fruit Type Capsule Drupe Fig
Fruit Colour Yellow Orange Red Brown Green
Any comments or thoughts on this would be greatly appreciated!