Integration of several environmental signals
What you are looking for sounds like the mechanism for a fold-change detector. I would recommend looking at these two papers: 

The incoherent feedforward loop can provide fold-change detection in gene regulation

As an example of this working in a real system, I recommend looking at the NFkB pathway, as recently detailed by Suzanne Gaudet:

Fold Change of Nuclear NF-κB Determines TNF-Induced Transcription in Single Cells

Here are a few others that I found just by searching for "Fold change detection"

Comparing Apples and Oranges: Fold-Change Detection of Multiple Simultaneous Inputs 

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0057455

Efficient fold-change detection based on protein-protein interactions

I'm sure by looking at the referenced papers in the above you can find more examples as well.