De la RosaA/elez et al.: Genetic strLicture of Penaeus califomtensts and P. stylirostns 



679 



mouth of the Gulf, subtropical conditions prevail; abun- 

 dant fringing vegetation, dominated by four species of 

 mangroves, contributes a huge amount of organic matter 

 that triggers a complementary source of organic produc- 

 tion within the detritus chain. Biodiversity indices rise 

 and trophic resources become diversified (Gonzalez-Farias 

 and Mee, 1988; Flores-Verdugo, 1990). Hence, it is plausi- 



ble to assume that complexity of ecological webs increases 

 from the northern to the southern coastal zone of the Gulf 

 of California. A parallel gradual increment in heterozygos- 

 ity in the populations of P. stylirostns may be related to 

 that ecological feature. However, Burton (1983) has stated 

 that a direct relation between high heterozygosity and 

 high ecological complexity is very difficult to demonstrate, 



