Juvenile Epilobocera Sinuatifrons Growth Rates and Ontogenetic
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JUVENILE EPILOBOCERA SINUATIFRONS GROWTH RATES AND ONTOGENETIC SHIFTS IN FEEDING IN WILD POPULATIONS by KAUAOA MATTHEW SAM FRAIOLA (Under the direction of Alan P. Covich) Abstract Freshwater amphibious crabs are understudied and found in tropical streams of many parts of the world and have the potential to influence stream and terrestrial communities. In this thesis I investigate basic biology and ecology aspects of the freshwater amphibious crab Epilobocera sinuatifrons in headwater streams of the Luquillo Experimental Forest, Puerto Rico. I measured growth rates of juvenile crabs given high and low quality food resources, and investigated ontogenetic shifts in feeding using natural abundances of stable isotopes δ13C and δ15N in crab tissue from two streams. Crabs are slow growing, with no differences in growth rates on different quality foods. Stable carbon and nitrogen stable isotopes suggest that crabs are increasing their trophic position as they grow larger in the wild, possibly the result of foraging on land as adults. These studies suggest that E. sinuatifrons are long lived and may require a range of foods to survive. INDEX WORDS: Food webs, Growth, Ontogenetic shift, Life-history omnivory, Tropical streams, Freshwater crabs, Epilobocera sinuatifrons, Puerto Rico, Stable isotopes JUVENILE EPILOBOCERA SINUATIFRONS GROWTH RATES AND ONTOGENETIC SHIFTS IN FEEDING IN WILD POPULATIONS By KAUAOA MATTHEW SAM FRAIOLA B.S., The University of Hawaii at Manoa, 2004 A thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirement for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2006 © 2006 Kauaoa M.S. Fraiola All Rights Reserved JUVENILE EPILOBOCERA SINUATIFRONS GROWTH RATES AND ONTOGENETIC SHIFTS IN FEEDING IN WILD POPULATIONS by KAUAOA MATTHEW SAM FRAIOLA Major Professor: Alan P. Covich Committee: J. Bruce Wallace Amy D. Rosemond Electronically Approved Version: Maureen Grasso Dean of the Graduate School The University of Georgia August 2006 DEDICATION This thesis is dedicated to my family, friends, Puerto Rico, and La Buruquena. iv ACKNOWLEDGEMENTS I would like to first of thank my family and friends for all their support through to the completion of this thesis. This research was supported by grant DEB-9411973 from the National Science Foundation through the University of Puerto Rico and the International Institute of Tropical Forestry (US Department of Agriculture), as part of the LTER Program in the Luquillo Experimental Forest. Additional support was provided by the Forest Service (US Department of Agriculture), Species at Risk Program of the Biotic Resources Division (US Geological Survey), the University of Puerto Rico, the University of Georgia, and Utah State University. This study would not have been possible without the dedicated efforts of A. P. Covich, J. B. Wallace, A.D. Rosemond, W.F. Cross, K.L. Jones, A. Ramirez, C. Prather, D. Kikkert, R. Kikkert, T. Heartsill- Scalley, A. Santana, M. Ocasio-Torres, C. Del Mar-Ortiz, E. Marrero, the Luquillo LTER researchers and staff, and my family and friends. The manuscript benefited from comments from A. P. Covich, A. D. Rosemond, J.B. Wallace, A. Fisk, and W.F. Cross. Ua Mau Ke Ea O Ka Aina i Ka Pono. v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS………………………………………………………………………v LIST OF TABLES…………………………………………………………………………...…..vii LIST OF FIGURES………………………………………………………………………………ix CHAPTER 1 INTRODUCTION………………………………………………………………...1 2 EVIDENCE OF ONTOGENETIC SHIFTS IN FEEDING OF A FRESHWATER CRAB, EPILOBOCERA SINUATIFRONS, PUERTO RICO…………………….3 3 THE EFFECT OF FOOD QUALITY ON THE GROWTH RATE OF JUVENILE FRESHWATER CRAB (EPILOBOCERA SINUATIFRONS)………………..…32 4. CONCLUSION………………………………………………………………….53 REFERENCES…………………………………………………………………………………..56 APPENDICES……………………………………………………………………………….…..59 A. RAW DATA ON CRABS CAPTURED………………………………………...60 B. RAW ISOTOPE DATA ON CAPTURED CRABS….………………………….63 vi LIST OF TABLES Table 2.1. Table 2.1. Catch statistics from field surveys, with number of crabs observed in stream (within wetted perimeter) and forest habitat (outside of wetted perimeter), there size range in mm carapace width (CW), and the number (No.) of crabs caught feeding. n = number of samples.…………………………………………...……………………………………………25 Table 2.2. Summary of the 10 crabs observed feeding by food type, stream, and size class. There were two food categories: 1) Seeds from Dacryodes excelsa, Prestoea montana, Guarea spp, and a Liana; 2) Animal and detritus, Atya lenipes, Epilobocera sinuatifrons, and Fine particles. * = same crab; φ = unidentified taxa; and γ = material of unknown particles, picked off substrate. -- = no crabs observed feeding on that food type………………………………….…26 Table 2.3. Table of the mean δ13C and δ15N values for all 4 size classes I (< 25mm), II (26 – 50mm), III (51-75mm), and IV(>76mm), mayfly larvae, conditioned leaves from the stream, biofilm, and seeds from each stream plus or minus the standard error (se). N = number of samples. δ13C values with the same superscript letter are not statistically different (P>0.05)….27 Table 2.4. Table of the mean trophic elevation values for all 4 size classes I (< 25mm), II (26 – 50mm), III (51-75mm), and IV(>76mm) for each size class from each stream plus or minus the standard error (se). n = number of samples. Size classes with the same superscript letter are not significantly different (P>0.05)……….……………………………………...……………..……28 Table 2.5. Results of the Post-ANOVA least squared means comparison test testing for differences in trophic elevation between size classes (I, II, III, and IV) in Stream A and B. Showing the P values…………………………………………………………………………….29 Table 2.6. Results of the Post-ANOVA least squared means comparison test testing for differences in δ13C between size classes (I, II, III, and IV) in Stream A and B. Showing the P values…………………………………………………………………………………………….30 Table 3.1. Minimum (min) and maximum (max) initial crab carapace width (CW). Mean carapace width (standard error). N = number of replicate per treatment. Means with the same letter are not statistically significant different (P>0.05)…...…………………………………….47 Table 3.2. Minimum (min) and maximum (max) initial crab carapace width (CW). Mean carapace width (standard error). N = number of replicate per treatment, leaves (Dacryodes excelsa), mayfly larvae, and combination (leaves + mayfly larvae). Means with the same letter are not statistically significant different (P>0.05)...……………………………………………..48 Table 3.3. Molt frequency of crabs. Initial carapace width (CW) in mm, change in carapace width (ΔCW) per molt, and the crab growth (CG) in ΔCW·day-1 calculated as ΔCW/MF. n = number of replicates.……………………………………………………………………………..49 vii Table 3.4. Published individual instantaneous growth rates of different stream decapods including this thesis. All growth rates are presented in units mass per day and were calculated based on the equation ln(Mf – M0)/t, where Mf = final mass, M0 = initial mass, and t = time grown. AFDM = ash free dry mass and d = days……………………………………………….50 viii LIST OF FIGURES Figure 2.1. Relationship between trophic elevation and δ13C of Epilobocera sinuatifrons for stream A (open squares) and Stream B (closed squres) based on equation 1 using the mean δ15N values of mayflies from each stream and standard error bars. For each size class: I (< 25 mm) = 12.5 mm; II (25-50 mm) = 37.5 mm; III (50-75 mm) = 62.5 mm; and IV (> 76mm) = 87.5 mm...…………………………….……………..…………..….31 Figure 3.1. Mean juvenile crab daily growth rates when feeding on different leaf species: Dacryodes excelsa (native), Cecropia scheberiana (native), Spathodea campanulata (non-native), Syzygium jambos (non-native), and crab food. With standard error bars for leaf treatments. Means with the same letter are not statistically significant different (P>0.05).…..…………………………………………….…………………….…………51 Figure 3.2. Graph of the mean juvenile crab daily growth rates when feeding on leaves (Dacryodes excelsa), mayfly larvae, combination (D. excelsa leaves and mayfly larvae), and crab food with standard error bars. Bars with the same letter are not statistically significant different (P>0.05)…………………………………………………….…....…52 ix Chapter 1 INTRODUCTION In many insular tropical streams decapods play a major role in processing terrestrially derived carbon and can attain high biomass (Crowl et al. 2001; Smith et al. 2003). Macroconsumers in tropical streams, such as omnivorous shrimp, have also been shown to affect multiple trophic levels from basal food resources such as leaf detritus to secondary consumers, such as aquatic insect abundances (Rosemond et al. 1998; Wright and Covich 2005). Of the common decapod crustaceans found in tropical headwater streams, we know very little about the ecology of freshwater crabs and their roles in these food webs (Covich and McDowell 1996; Dobson 2004). However, freshwater crabs have the potential to be important seed predators, and predators of other animals, as well as important processors of terrestrial plant material in streams. Freshwater crabs are found in tropical lotic systems all around the world. The strong influence of marine and land crab species in other ecosystems (Gutiérrez et al. 2006; Lindquist and Carroll 2004; Green et al. 1997) suggests that freshwater crabs may be strong interactors in their own environments. Dobson (2004) suggested that freshwater crabs in Africa can be important processors of leaf litter. This role for freshwater decapods contrasts with the temperate view of stream food webs, in which aquatic insects