Kato, Kimberly M., Biological Sciences, California State Polytechnic University, Pomona, 91768
The effects of flooding on riverine food webs in southern California
Flooding occurs seasonally after the winter rains in Southern California. It is a major natural disturbance of rivers. Food webs can play an important part in forming the assemblages of these rivers. This study examined food webs including the fish, speckled dace Rhynichthyes osculum and its prey, macroinvertebrates (insect larvae such as blackflies, caddisflies, beetles and mayflies). Three rivers were examined: the San Gabriel, Santa Clara and Santa Ana. I evaluated the different assemblages formed before and after flooding occurred and determined how flooding affected them by examining where they were located before and after flooding and how their diets changed after flooding. Three microhabitats were identified for each river: rocky bottom, sandy bottom with pebbles and large boulder substrates. This was coupled with a medium and low current. I wanted to examine the six combinations of microhabitats to the variable of the currents. The study was done over a 2-year period to examine two seasons of before and after affects of flooding. Habitats and diets were compared to species composition in all three rivers and their 3 microhabitats to determine the affects of flooding on the food webs. Data analysis included Principal Component Analysis (PCA), niche breadth (B) and niche overlap (S) and frequency distribution. Species compositions were consistent within each habitat and changed after flooding in each of the 3 microhabitats of the rivers. Differences in species composition among the sections were due to physical characteristics of each species. Most species were segregated by habitat, microhabitat and/or diet.