[R-sig-eco] question about appropriate model for abundance studies

[Sacha Viquerat]

hello! I did a count survey on a tropical fish species! Well, I didnt do 
it, Im just helping at the statistics-stage. We recorded some water 
parameters alogside each catch, such as no3, no2, po4 etc. as the data 
are count data (and require error terms due to spatial 
pseudoreplication), the glm with poisson error structure should be the 
method of choice. however, I do fear that in doing so, I will not be 
able to model fish abundance correctly. In my opinion (and, as far as I 
remember, in the opinion of those who gave ecology classes), the 
abundance of species should be sort of bell shaped, since there will 
always be, for example, an optimal temperature, pH-level and so forth. 
However, I have not yet seen such a discussion arise on one of the many 
forums. Am I missing the obvious??