Assessing human-induced threats: A landscape approach

Effective large-scale management of lotic systems requires managers to assess stream condition by identifying human-induced threats affecting those systems.  By identifying threats impacting stream systems and by predicting biological condition, managers can choose appropriate suites of conservation practices for fish conservation.  Our goal was to determine how information derived from threat indices can be used in large-scale conservation planning. Hierarchically structured threat indices were developed and tested for their usefulness at predicting indicators of fish assemblage condition (e.g., Index of Biotic Integrity).  Synoptic threat indices (STI; top level in hierarchy) were constructed to summarize a stream segment’s existing suite of mappable threats.  Macroinvertebrate metrics of aquatic community health were negatively related to STI, thus indicating STI can represent overall system health.  To account for STIs lack of precision and to identify specific suites of threats, indices of specific threats (IST) were developed.  Preliminary results indicate fish guild species abundance responds primarily to urban and agricultural threats.  Reproductive guilds were most sensitive to urbanization threats and trophic guilds responded to urban and agricultural threats, although interactions were somewhat complex.  Results suggest synoptic threat indices are useful for prioritizing broad conservation strategies while ISTs allow managers to identify specific conservation actions.