Null model in Ecology

[Gusha]

Hi, I have an exam in Ecology on Tuesday morning. But I have dificulties with the null model. For example, how can I make up a null model to see if birds forage at different heights in a wood habitat by chance or by competition.

 

• What observations should I make ?
• Which values should I nullify?

Does anybody has an example or an explanation?

 

Thanks in advance

[studiot]

You need to observe forraging bird counts at different height intervals, by species.

 

The null model is clearly going to be that there is no stratification of species so any differences you observe will occur randomly.

 

You then test to see if the observed level of stratification could have occured randomly, within the chosen confidence interval.

[overtone]

You might want to mention that eliminating random foraging height is not enough by itself to establish competition as the alternative. You would need to observe a change in foraging habit with the presence/absence of the competition, and consider scale in time - one fair null hypothesis for that on a short time scale would be: no differences in foraging height of a given species correlated with presence/absence of any other bird species or combination thereof.

 

It's only fair because it overlooks predation and habitat correlations.

 

On an evolutionary time scale you would have a serious problem. I doubt the question on an exam would include that.

Edited June 9, 2015 by overtone