DIET OF THE CASCADES FROG (RANA CASCADAE) AS IT RELATES TO PREY AVAILABILITY IN THE KLAMATH MOUNTAINS OF NORTHWEST CALIFORNIA By Monty Daedalus Larson A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment Of the Requirements for the Degree Masters of Science In Natural Resources: Wildlife May 2012 ABSTRACT Diet of the Cascades Frog (Rana cascadae) as it relates to prey availability in the Klamath Mountains of Northwest California Monty Larson Frogs in the family Ranidae are considered generalist predators that consume prey as it is encountered in the environment. However, few studies have attempted to quantify the types and relative amounts of prey available to these frogs so a thorough understanding of their foraging ecology as it relates to prey availability is lacking. This study examined the diet of R. cascadae as it relates to prey availability in a Klamath Mountain basin in northern California during their active season of 2007. Based on the analysis of 275 stomach samples, Rana cascadae consumed 3052 prey items from 110 invertebrate taxa confirming that this species is a generalist predator. However, an Index of Relative Importance indicated that five prey categories were most important in the diet: Acrididae, Aranae, Formicidae, insect larvae, and Tipulidae. Differences in diet were detected between sexes, life stages, and seasons. Adult females consumed more Acrididae in the summer than males or Juveniles. Adult male and juvenile frogs showed selection for insect larvae and Tipulid flies during the summer. In the spring adult females and juveniles also selected Tipulid flies and adult males selected Elaterid beetles. All life-stages and both sexes appeared to avoid very small prey (<4mm3). Shifts in prey use with changes in ontogeny were documented, with frogs consuming more large prey and less small prey as they grew. iii ACKNOWLEDGMENTS This project was partially funded by a grant from the HSU Wildlife Graduate Student Society. My study would not have been possible without the inspiration of my good friend Justin Garwood. Justin and I spent many nights sitting at the little blue table in the Alps discussing research possibilities and the ecological phenomena we were observing while carrying out Justin’s masters’ research. I could not have carried out this study without the support of my advisor, Dr. Hartwell H. Welsh, Jr. who provided encouragement and direction in the writing of my thesis as well as a Forest Service vehicle so that I could travel to and from the trailhead; a car being one of many resources I lacked. I’d also like to thank Dr. Micheal A. Camann for providing me with all of the invertebrate sampling equipment I used to carry out this study and for hours of help teaching me to identify the invertebrates the frogs and I captured. I’d like to thank the fisheries group of Redwood Sciences Laboratory for allowing me to use their microscope; I’d still be measuring bugs if they hadn’t. I am tremendously indebted to the Herpetology group of Redwood Sciences Laboratory. Clara, Garth, and Karen were always there to answer whatever questions I had or just to talk to. Finally I’d like to express the greatest appreciation, and deepest love to Kasey. She has been with me from the start of this project and has provided me with the encouragement, support, and love that carried me through. iv TABLE OF CONTENTS Page ABSTRACT ........................................................................................................................... iii ACKNOWLEDGMENTS ...................................................................................................... iv LIST OF TABLES .................................................................................................................vii LIST OF FIGURES ............................................................................................................. viii LIST OF APPENDICIES ........................................................................................................ x INTRODUCTION.................................................................................................................... 1 STUDY SITE ........................................................................................................................... 4 MATERIALS AND METHODS ............................................................................................ 8 Frog Surveys ......................................................................................................................... 8 Gastric Lavage .................................................................................................................... 10 Invertebrate Sampling ........................................................................................................ 10 Invertebrate Identification.................................................................................................. 12 Statistical Analyses ............................................................................................................ 13 RESULTS ............................................................................................................................... 19 Prey use ............................................................................................................................... 19 Use versus Availability ...................................................................................................... 24 Female spring .................................................................................................................. 24 Female summer ............................................................................................................... 25 Female fall....................................................................................................................... 28 Male spring ..................................................................................................................... 31 Male summer .................................................................................................................. 31 Male Fall ......................................................................................................................... 31 Juvenile spring ................................................................................................................ 36 v Juvenile summer ............................................................................................................. 36 Juvenile fall ..................................................................................................................... 36 Frog size .............................................................................................................................. 41 DISCUSSION......................................................................................................................... 46 LITERATURE CITED .......................................................................................................... 51 APPENDICIES ...................................................................................................................... 57 vi LIST OF TABLES Table Page Table 1. Comparison of prey category volumes of stomach samples collected from Rana cascadae by season, sex, and life-stage. Statistical comparisons were made using Multi Response Permutation Procedure. Significant comparisons are shaded. The study was conducted in 2007 in the upper Deep Creek Basin Trinity Alps Wilderness, California. .............................................................................................. 21 Table 2. Seasonally important prey categories in 275 stomach samples of Rana cascadae based on Indicator Species Analysis. Only prey categories with indicator values > 20 are shown. The study was conducted in 2007 in the upper Deep Creek Basin Trinity Alps Wilderness, California. ........................................................................ 23 Table 3. Comparison of proportions of prey items collected from Rana cascadae stomach samples to proportions of prey categories from both pitfall trap samples and sweep net samples using Multi-Response Permutation Procedure analysis. The study was conducted in 2007 in the upper Deep Creek Basin Trinity Alps Wilderness, California. .............................................................................................. 25 Table 4. Comparison of female Rana cascadae stomach samples in spring, summer, and fall with availability samples using Indicator Species Analysis. Only prey categories with significant Indicator Values are shown. The study was conducted in 2007 in the upper Deep Creek Basin Trinity Alps Wilderness, California. ...... 26 Table 5. Comparison of male Rana cascadae stomach samples in spring, summer, and fall with availability samples using Indicator Species Analysis. Only prey categories with significant Indicator Values are shown. The study was conducted in 2007 in the upper Deep Creek Basin Trinity Alps Wilderness, California. ...... 32 Table 6. Comparison of juvenile Rana cascadae stomach samples in spring, summer, and fall with availability samples using Indicator Species Analysis. Only prey categories with significant Indicator Values are shown. The study was conducted in 2007 in the upper Deep Creek Basin Trinity Alps Wilderness, California. ...... 37 vii LIST OF FIGURES Figure Page Figure 2. Meadow patches where Rana cascadae stomach content and invertebrate sampling occurred