Terrestrial subsidies in the diets of fishes: A comparison across climate regions

Background/Question/Methods

The importance of the linkage between land and water systems has long been recognized by ecologists.  While terrestrial leaf litter provides energy basis for some stream systems, terrestrial arthropods can also subsidize aquatic consumers, especially for fishes.  The main objective of this study is to compare the diets of fishes from different climate regions.  We sampled a total of 36 references that contain diet data on 77 fish species to detect if some environmental factors may influence the contribution of terrestrial food items to the diets of fishes.  A database was constructed for each diet reference where we recorded fish species, fish family, aquatic habitat sampled (lotic vs. lentic), major climate conditions, elevation of sampling area, mean annual temperature and precipitation (taken for nearest major city for which data was available), percent of terrestrial subsidy in overall food intake by fish, diet analysis method (percent of terrestrial food items by abundance, or by mass, or by volume), and notes on the temporal scale from which samples were taken.  We used principal components analysis (PCA) to determine whether or not the consumption of terrestrial food items by fishes is more important in certain climate zones than others.  By adding coded variables that indicate mouth morphology, we also analyzed terrestrial food consumption by mouth morphology.

Results/Conclusions

The results suggest that tropical fishes consume more terrestrial food items, especially terrestrial plant material.  Our PCA results indicate that terrestrial food consumption (%) by fishes was negatively associated with both distance from equator (in decimal degrees) and elevation (meters above sea level).  Jaw position also plays a role; fishes with terminal and superior jaw morphologies tended to consume more terrestrial food items.  Our results suggest that the importance of terrestrial subsidies for many fish taxa is ubiquitous across different climate regions.  The information from this type of study supports the notion that across-ecosystem trophic subsidies should be considered when developing ecosystem level conservation plans.