There are many biological and ecological measures that can be chosen as an assessment endpoint and/or representative species but regardless of the final choice it must adequately satisfy some of the criteria that the choice must fulfil such as

• Their relevance to the protection goals;
• A well-defined ecological function;
• Accessibility to measurement; and
• Level of potential exposure to the LMO.

Assessment endpoints or species representative of important ecological functions or roles should be selected on a case-by-case basis. The complexity of ecosystems and the large number of potential candidates add to the challenges in selecting the appropriate assessment endpoints in ecological systems. Some important criteria for the selection of assessment endpoints to be used in the risk assessment of LMOs may include, for example:

1. their relevance to the protection goals,
2. a well-defined ecological function,
3. accessibility to measurement, and
4. level of potential exposure to the LMO.

Identifying assessment endpoints or representative species that are relevant within the context of the likely potential receiving environment allows the risk assessor(s) to focus on interactions that are likely to occur. Moreover, risk scenarios may be also formulated to include assessment endpoints or representative species that are not present in the likely potential receiving environment but may, nevertheless, be indirectly exposed to the LMOs. This could occur, for example, if a third species, which is sexually compatible with the LMO and the representative species, has a distribution area that overlaps with the distribution areas of the former two providing an indirect exposure pathway between them.