Distribution in communities and ecosystems

In Chapter 3, the distribution of enviromnental chemicals through compartments of the gross environment was related to the chemical factors and processes involved, and models for describing or predicting environmental fate were considered. In the early sections of the present chapter, the discnssion moves on to the more complex question of movement and distribntion in the living environment— within individuals, communities, and ecosystems—where biological as well as physical and chemical factors come into play. The movement of chemicals along food chains and the fate of chemicals in the complex communities of sediments and soils are basic issues here. 

Many herbivorous fishes are found on coral reefs (Horn 1989 Choat 1991) and their grazing activities are commonly the dominant factor affecting the distribution and abundance of macroalgae (e.g., Morrison 1988 Hixon and Brostoff 1996 Marques et al. 2006) as well as the structure and function of marine communities and ecosystems in general (Duffy and Hay 2001). For example, the exclusion of... 

The next step is to combine the spatial and temporal distributions of both the ecological component and the stressor to evaluate exposure. In the case of physical alterations of communities and ecosystems, exposure can be expressed broadly as co-occurrence. Exposure analyses of individuals often focus on actual contact with the stressor because organisms may not contact all of the stressors present in an area. For chemical stressors, the analyses may focus further on the amount of chemical that is bioavailable, that is, available for uptake by the organism. Some chemical exposure analyses also follow the chemical within the organism s body and estimate the amount that reaches the target organ. The focus of the analyses will depend on the stressors being evaluated and the assessment and measurement endpoints. 

---