intermittent streams having the highest persistence; (iii) species common to ...... Norman: University of Oklahoma Press:111-120. ...... Schwarzkopf 2012).
STREAM FISH RESPONSE TO INTERMITTENCY AND DRYING IN THE ICHAWAYNOCHAWAY CREEK BASIN by JESSICA L. DAVIS (Under the Direction of Mary C. Freeman and Stephen W. Golladay) ABSTRACT Streamflow alteration from the combined effects of water extraction and climate change is recognized as a major threat to aquatic ecosystems. The Ichawaynochaway Creek Basin is a Gulf Coastal Plain stream system in southwestern Georgia, where streamflows are strongly influenced by agricultural water withdrawals and recent droughts. This study explores effects of stream intermittency and drying on the composition of biologically diverse fish communities, and life history traits that may influence persistence of four closely related cyprinid species. Intermittent stream communities were found to be a subset of perennial stream communities, with the highest persistence rates among adults and juveniles of species that commonly occur in intermittent streams. My results identify life history traits that may be useful for understanding differences in how closely related species respond to changing environments, with smaller body size at maturity along with appropriate reproductive timing promoting greater persistence given more frequent and intense disturbances.
INDEX WORDS:
Warmwater Streams, Fish Community Structure, Drought, Persistence, Colonization, Life History Traits
STREAM FISH RESPONSE TO INTERMITTENCY AND DRYING IN THE ICHAWAYNOCHAWAY CREEK BASIN
by
JESSICA DAVIS B.S., University of North Carolina, Asheville, 2015
A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree
MASTERS OF SCIENCE
ATHENS, GEORGIA 2017
© 2017 Jessica L. Davis All Rights Reserved
STREAM FISH RESPONSE TO INTERMITTENCY AND DRYING IN THE ICHAWAYNOCHAWAY CREEK BASIN
by
JESSICA L. DAVIS
Major Professor:
Mary C. Freeman Stephen W. Golladay
Committee: Seth J. Wenger Robert B. Bringolf
Electronic Version Approved: Suzanne Barbour Dean of the Graduate School The University of Georgia December 20017
DEDICATION For pop, the best dad a kiddo could ever have asked for.
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ACKNOWLEDGEMENTS I couldn't have made it through this project without the support from my colleagues, family, and friends. My project would have been little compared to what it is without the help of Mary Freeman at every turn. From helping write code, to always making herself available for questions big and small, I couldn't have found a more caring and supportive advisor. Special thanks to Steve Golladay, my co-advisor, for his support of both me and my husband, d.w., during our time at the Jones Center. To my committee members, Seth Wenger and Robert Bringolf, thank you for helping develop my understanding of statistics and fishes. I would also like to thank the Odum School of Ecology and the Joseph W. Jones Ecological Research Center for funding me through this endeavor. The opportunity to live and work in such a magical part of the world is something I will always look back on fondly. I would also like to thank those at the Jones Center who helped make this project possible. Especially, Denzell Cross, Meg Hederman, and Robert Ritger we made it through the heat, the gnats, the mosquitoes, and the snakes, all while singing songs and dancing the electrofish dance! Denzell, you were with me from day one, and words can’t describe how happy I am to see you at Odum in pursuit of your PhD. Chelsea Smith, you are my live version of stackexchange, thank you for always being there to bounce ideas off and help me with statistics. Camille Herteux and Cara McElroy, thank you for all of the laughs and little distractions that helped keep me sane.
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A final thanks to d.w. giddens, my husband and partner in all else, without whom I would rarely have taken a step back to appreciate all that is wonderful in the Universe. I give my deepest love and appreciation for the encouragement and sacrifices you gave and made throughout this project.
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TABLE OF CONTENTS Page ACKNOWLEDGEMENTS .................................................................................................v LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES .......................................................................................................... xii CHAPTER 1
LITERATURE REVIEW AND SUMMARY OF OBJECTIVES ...................1
2
STREAM DRYING AND FISH OCCUPANCY DYNAMICS IN THE ICHAWAYNOCHAWAY CREEK BASIN ..................................................10
3
IDENTIFYING LIFE HISTORY TRAITS THAT PROMOTE FISH SPECIES PERSISTENCE IN INTERMITTENT STREAMS ......................73
4
CONCLUSIONS AND SUMMARY ...........................................................140
APPENDICES A
SPECIES OCCURRENCE OF TAXA FOUND FOR CHAPTER 2 ..........146
B
DETAILED DESCRIPTION OF OCCUPANCY MODEL ........................157
C
SPECIES AND AGE CLASS OCCURRENCES OF TAXA FOUND AT INTERMITTENT STREAMS FOR CHAPTER 2 .....................................163
D
R CODE USED FOR DYNAMIC OCCUPANCY MODEL ......................165
E
INDICATOR ANALYSIS AND CLASSIFICATION FOR SPECIES STRATEGISTS ENDPOINTS.....................................................................169
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LIST OF TABLES Page Table 2.1: Summary statistics of water quality data obtained in 90 isolated pools monitored in 12 stream sites in the Ichawaynochaway Creek basin, June through September 2015 and 2016, followed by their values centered and scaled around zero by subtracting the mean and dividing by the standard deviation. Scaled values were used as covariate effects on observed fish occurrence in isolated pools. Numbers of isolated pools (n), and mean covariate value are shown along with standard deviation (SD), standard error (SE), minimum (Min) and Maximum. ..............................................................................................................43 Table 2.2: Effects of covariates on regression coefficients for persistence, colonization, and detection from multi-taxa, dynamic occupancy models using a time-series (2015-2017) of detection for adults of 21 species and juveniles of 25 species in the Ichawaynochway Creek basin. Stream state, sampling method and cool season use binary coding. Distance is the distance of the study site from the nearest downstream perennial stream, standardized by subtracting the mean and dividing by the standard deviation. Effects of indicator-species covariates (Intermittent Nonindicative species and Perennial species, with Intermittent species as the baseline) on regression coefficients are shown for persistence during the number of weeks a site was isolated (Weeks Slack) and for colonization after resumption of flow (Weeks Flowing). Variance terms are for random effects of site and date
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(“surveys”) on intercepts for persistence, colonization, and detection, and on species-slopes for relations between persistence and Weeks Slack, and between colonization and Weeks Flowing. All values are on the logit scale, and show the posterior means and 95% credible intervals (in parentheses) ................................44 Table 2.3: Modeled effects of environmental covariates on probability of observed occurrence of adult fishes in 90 isolated stream pools in the Ichawaynochway Creek basin, 2015-2016. Values are the estimated effects on the log-odds of occurrence (95% confidence intervals) for predictor variables (values were centered and scaled around zero by subtracting the mean and dividing by the standard deviation) and the estimated random variance in intercepts attributable to species, surveys, and pools (nested within repeated survey of a pool), and in slopes attributable to species ..................................................................................45 Table 2.4: Modeled effects of environmental covariates on probability of observed occurrence of juvenile fishes in 90 isolated stream pools in the Ichawaynochway Creek basin, 2015-2017. Values are the estimated effects on the log-odds of occurrence (95% confidence intervals) for predictor variables (values were centered and scaled around zero by subtracting the mean and dividing by the standard deviation) and the estimated random variance in intercepts attributable to species, surveys, and pools (nested within repeated survey of a pool), and in slopes attributable to species ..................................................................................46 Table 3.1: Ovary and oocyte stages and descriptions of development based on oocyte size, coloration, yolk condition, and physical location within the ovum modified from Heins and Rabito (1986) and Heins and Baker (1987) ...............................106
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Table 3.2: Standard lengths of males and females of four species assessed for reproductive development (>25mm) from seven study sites in the Ichawaynochaway Creek Basin from May 2016- April 2017. Numbers of individuals (n), and mean lengths are shown along with standard deviation (SD), standard error (SE), minimum (Min) and maximum (Max) ................................107 Table 3.3: Results from Chi-square tests of significance, which were performed separately on sexually mature individuals and non-reproductive individuals. Significant differences are marked with an * (p>.05) between the expected sex ratio of 1:1 and the observed sex ratio for males and females of a given species ..................................................................................................................108 Table 3.4: Standard lengths of mature males and females (Mature, Mature Ripening, or Ripe) of four species assessed for reproductive development from seven study sites in the Ichawaynochaway Creek Basin from May 2016- April 2017. Numbers of individuals (n), and mean lengths are shown along with standard deviation (SD), standard error (SE), minimum (Min) and maximum (Max) ......................109 Table 3.5: Standard lengths of all individuals captured during survey periods for length distributions at thirteen study sites in the Ichawaynochaway Creek Basin from May 2016- April 2017. Individuals within the genus Notropis that were not identifiable in the field were categorized as Notropis sp. Numbers of individuals (n), and mean lengths are shown along with standard deviation (SD), standard error (SE), minimum (Min) and maximum (Max)...............................................110 Table 3.6: Summary statistics for egg size (mm) of mature, mature ripening, and ripe females assessed for reproductive investment. Each individual had twenty eggs
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measured, where n is the number of individuals assessed per species. Numbers of individuals (n), and mean lengths are shown along with standard deviation (SD), standard error (SE), minimum (Min) and maximum (Max) ................................111 Table 3.7: Species strategy weight and assignment for Soft Classification for opportunistic strategist (OS), periodic strategist (PS), and equilibrium strategist (ES) strategist end points calculated following Mims et al. (2010) for species identified in the Ichawaynochaway Creek Basin (June 2015-January 2017). Species strategy weight was assessed using only the life history traits of the four cyprinid species....................................................................................................112
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LIST OF FIGURES Page Figure 2.1: Locations of intermittent streams study sites (marked with squares) that were surveyed to assess shifts in community assemblages, species-specific rates of persistence and colonization in dynamic occupancy models, and probability of persistence in isolated pools within the Ichawaynochaway Creek Basin during 2015-2017. Perennial sites (marked with triangles) indicate streams where published and unpublished data were obtained using similar survey methods, and were used to assess differences in community assemblages between intermittent and perennial streams .............................................................................................47 Figure 2.2: Discharge, water temperature, and air temperature at Spring Creek near Leary, GA (USGS gage 02354475). Periods where discharge is at or near zero represent timing of intermittency, during which isolation or complete drying occurred..................................................................................................................48 Figure 2.3: Changes in stream state used as covariates to estimate persistence and colonization in intermittent streams, where “flowing” represents stream state where discharge is >0, “isolated” represents a pool that is isolated from upstream or downstream movement of fishes (e.g. a small pool), and “isolated-open” represents an isolated pool that is open to upstream or downstream movement of fishes (e.g. a big pool) ............................................................................................49
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Figure 2.4(a-c): Non-metric multi-dimensional scaling (NMDS) ordination of stream samples based on Brays-Curtis dissimilarities in species occurrences. Ellipses represent centroids and 95% confidence intervals for mean scores for samples from perennial and intermittent streams. Each graphic represents 2 of the 3 dimensions in two-dimensional space ...................................................................50 Figure 2.5: Time series of changes in stream state for 12 intermittent study sites in the Ichawaynochaway Creek Basin, June 2015 to January of 2017 ............................52 Figure 2.6: Posterior mean probabilities of taxa-specific detection and 95% confidence intervals for adults of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 21 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species ................................53 Figure 2.7: Posterior mean probabilities of taxa-specific detection and 95% confidence intervals for juveniles of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 25 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species ................................54 Figure 2.8: Posterior mean probabilities of taxa-specific persistence and 95% confidence intervals for adults of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 21 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species ................................55
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Figure 2.9: Posterior mean probabilities of taxa-specific persistence and 95% confidence intervals for juveniles of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 25 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species ................................56 Figure 2.10: Posterior mean probabilities of taxa-specific colonization and 95% confidence intervals for adults of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 21 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species ................................57 Figure 2.11: Posterior mean probabilities of taxa-specific colonization and 95% confidence intervals for juveniles of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 25 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species .....58 Figure 2.12: Average mean of probability of persistence for adult fish in isolated pools, plotted in relation to duration of pool isolation. Probabilities are plotted for 21 species estimated using a multi-taxa, dynamic occupancy model applied to 26 periods of continuous isolation at 12 study sites in the Ichawaynochaway Creek Basin. Black lines indicate the species-specific means of persistence and red lines indicate the means for each of the three species types...........................................59 Figure 2.13: Average mean of probability of persistence for juvenile fish in isolated pools, plotted in relation to duration of pool isolation. Probabilities are plotted for
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25 species estimated using a multi-taxa, dynamic occupancy model applied to 26 periods of continuous isolation at 12 study sites in the Ichawaynochaway Creek Basin. Black lines indicate the species-specific means of persistence and red lines indicate the means for each of the three species types...........................................60 Figure 2.14: Average mean of probability of colonization for adult fish, plotted in relation to duration of flow since isolation or complete drying. Probabilities are plotted for 21 species estimated using a multi-taxa, dynamic occupancy model applied to 26 periods of continuous isolation at 12 study sites in the Ichawaynochaway Creek Basin. Black lines indicate the species-specific means of persistence and red lines indicate the means for each of the three species types...........................................61 Figure 2.15: Average mean of probability of colonization for juvenile fish, plotted in relation to duration of flow since isolation or complete drying. Probabilities are plotted for 25 species estimated using a multi-taxa, dynamic occupancy model applied to 26 periods of continuous isolation at 12 study sites in the Ichawaynochaway Creek Basin. Black lines indicate the species-specific means of persistence and red lines indicate the means for each of the three species types ..62 Figure 2.16: Modeled probability of observed occurrence of adults in relation to maximum total ammonia (ug/L) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plot shows mean and 95% confidence intervals ...............................................................................................63 Figure 2.17: Modeled observed occurrence of adults in relation to maximum depth (m) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plot shows mean and 95% confidence intervals ...........................................................64
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Figure 2.18: Modeled observed occurrence of juveniles in relation to maximum depth (m) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plot shows mean and 95% confidence intervals ....................................................65 Figure 2.19: Modeled observed occurrence of juveniles in relation to maximum ammonia (u/gL) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 20152016. Plot shows mean and 95% confidence intervals ..........................................66 Figure 2.20: Modeled observed occurrence of juveniles in relation to dissolved oxygen (mg/L) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 20152016. Plot shows mean and 95% confidence intervals ..........................................67 Figure 2.21: Species-specific random effects on the intercept and slope of modeled observed occurrence of juveniles in relation to maximum depth in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals .....................................................................68 Figure 2.22: Species-specific random effects on the intercept and slope of modeled observed occurrence of juveniles in relation to maximum ammonia in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals .....................................................................69 Figure 2.23: Species-specific random effects on the intercept and slope of a modeled observed occurrence of juveniles in relation to dissolved oxygen in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals .....................................................................70 Figure 2.24: Species-specific random effects on the intercept and slope of modeled observed occurrence of adults in relation to maximum depth in 90 isolated pools
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samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals. ......................................................................................71 Figure 2.25: Species-specific random effects on the intercept and slope of modeled observed occurrence of adults in relation to maximum ammonia in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals .....................................................................72 Figure 3.1: Mean probabilities of species-specific persistence for four adult cyprinid species found intermittent streams using a multi-taxa, dynamic occupancy model over the weekly duration of isolation. Species-specific rates of persistence were averaged for each species over 12 study sites and 14 weeks of continuous isolation in the Ichawaynochaway Creek Basin from 2015-2017 (Chapter 2). Species-specific persistence rates were used to develop hypotheses for life history trait differences among N. harperi, N. petersoni, N. texanus, and P. grandipinnis .........................................................................................................113 Figure 3.2: Locations of thirteen study sites within the Ichawaynochaway Creek Basin that were used to measure length distributions for four cyprinid species and to obtain individuals for analyzing diet and reproductive characteristics, May 2016April 2017. Apart from Brantley Creek (the most north easterly circle) all survey streams are intermittent and experienced isolation or complete drying during the survey period ........................................................................................................114 Figure 3.3: Standard length distribution to the nearest millimeter for all P. grandipinnis individuals found at thirteen study sites within the Ichawaynochaway Creek Basin
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from May 2016- April 2017, plotted by Julian date. The horizontal line represents the minimum reported length at maturity (34.82 mm standard length) ...............115 Figure 3.4: Observed GSI for P. grandipinnis females (upper left) and males (upper right) and standard length for females (bottom left) and males (bottom right) of individuals assessed for reproductive state from within the Ichawaynochaway Creek Basin from May 2016- April 2017, plotted by Julian date. For females, the black symbols for MA, MR, and RE represent reproductively mature individuals and the grey symbols for LA, EM, and LM represent reproductively latent or immature individuals. For males, black symbols indicate mature males and the grey symbols indicate latent or immature individuals. The horizontal line for standard length represents minimum observed length of reproductively mature females (34.82) and males (39.32)………………………………………… 116 Figure 3.5: Standard length distribution to the nearest millimeter for all N. harperi collected at thirteen study sites within the Ichawaynochaway Creek Basin from May 2016- April 2017, plotted by Julian date. The horizontal line represents the minimum reported length at maturity (34.82mm standard length) ......................117 Figure 3.6: Observed GSI for N. harperi females (upper left) and males (upper right) and standard length for females (bottom left) and males (bottom right) of individuals assessed for reproductive state from within the Ichawaynochaway Creek Basin from May 2016- April 2017, plotted by Julian date. For females, the black symbols for MA, MR, and RE represent reproductively mature individuals and the grey symbols for LA, EM, and LM represent reproductively latent or immature individuals. For males, black symbols indicate mature males and the
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grey symbols indicate latent or immature individuals. The horizontal line for standard length represents minimum observed length of reproductively mature females (38.26) and males (32.35) .......................................................................118 Figure 3.7: Standard length distribution to the nearest millimeter for all N. petersoni collected at thirteen study sites within the Ichawaynochaway Creek Basin from May 2016- April 2017, plotted by Julian date. The horizontal line represents the minimum reported length at maturity (46.84mm standard length) ......................119 Figure 3.8: Observed GSI for N. petersoni females (upper left) and males (upper right) and standard length for females (bottom left) and males (bottom right) of individuals assessed for reproductive state from within the Ichawaynochaway Creek Basin from May 2016- April 2017, plotted by Julian date. For females, the black symbols for MA, MR, and RE represent reproductively mature individuals and the grey symbols for LA, EM, and LM represent reproductively latent or immature individuals. For males, black symbols indicate mature males and the grey symbols indicate latent or immature individuals. The horizontal line for standard length represents minimum observed length of reproductively mature females (46.84) and males (49.20) .......................................................................120 Figure 3.9: Standard length distribution to the nearest millimeter for all N. texanus collected at thirteen study sites within the Ichawaynochaway Creek Basin from May 2016- April 2017, plotted by Julian date. The horizontal line represents the minimum reported length at maturity (49.2mm standard length) ........................121 Figure 3.10: Observed GSI for N. texanus females (upper left) and males (upper right) and standard length for females (bottom left) and males (bottom right) of
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individuals assessed for reproductive state from within the Ichawaynochaway Creek Basin from May 2016- April 2017, plotted by Julian date. For females, the black symbols for MA, MR, and RE represent reproductively mature individuals and the grey symbols for LA, EM, and LM represent reproductively latent or immature individuals. For males, black symbols indicate mature males and the grey symbols indicate latent or immature individuals. The horizontal line for standard length represents minimum observed length reproductively mature females (49.47) and males (49.26) .......................................................................122 Figure 3.11: Discharge at USGS 02354475 Spring Creek near Leary, GA (left y-axis) during the survey period. Light gray regions indicate the Palmer Drought Index for the region (National Integrated Drought Information System, NIDIS; www.drought.gov). While drought index values were exceptional from October to December of 2016, values were not exceptional for summer and early fall moths (July-September) ..................................................................................................123 Figure 3.12: The Tukey adjusted comparison of trends of slopes for reproductive timing of individuals of four cyprinid species using a ANCOVA. Points indicate the slope of the probability curves for a given species with error bars indicating the 95% confidence intervals. Results are given on the response scale (the natural log of a given date), where date 1is January 1st. Means sharing a letter are not significantly different by Tukey-adjusted mean separations ...............................124 Figure 3.13: Probability curves of presence of mature individuals of a given species over a year time span. Normal confidence intervals are constructed on the link scale,
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and then back-transformed to the response scale. The numeric date of 1 represents the first day of the calendar year (January 1st) .....................................................125 Figure 3.14: The least square means of the standard length for mature individuals of four cyprinid species using ANOVA. Points indicate the least square mean of the standard length by species; error bars indicate the 95% confidence intervals using Tukey-adjusted comparisons. Means sharing a letter are not significantly different by Tukey-adjusted mean separations ...................................................................126 Figure 3.15: The simple linear regression of the natural log of eviscerated mass and the natural log of standard length for all fishes of an individual species combined were: P. grandipinnis, log(mass)= -12.55+3.40*log(length), F1,150=5846, p=0, “isolated” represents a pool that is isolated from upstream or downstream movement of fishes (e.g., a small pool), and “isolated-open” represents an isolated pool that is open to upstream or downstream movement of fishes (e.g., a big pool).
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(a)
(b)
50
(c)
Figure 2.4(a-c): Non-metric multi-dimensional scaling (NMDS) ordination of stream samples based on Brays-Curtis dissimilarities in species occurrences. Ellipses represent centroids and 95% confidence intervals for mean scores for samples from perennial and intermittent streams. Each graphic represents 2 of the 3 dimensions in two-dimensional space.
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Figure 2.5: Time series of changes in stream state for 12 intermittent study sites in the Ichawaynochaway Creek Basin, June 2015 to January of 2017.
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Figure 2.6: Posterior mean probabilities of taxa-specific detection and 95% confidence intervals for adults of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 21 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species.
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Figure 2.7: Posterior mean probabilities of taxa-specific detection and 95% confidence intervals for juveniles of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 25 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species.
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Figure 2.8: Posterior mean probabilities of taxa-specific persistence and 95% confidence intervals for adults of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 21 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species.
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Figure 2.9: Posterior mean probabilities of taxa-specific persistence and 95% confidence intervals for juveniles of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 25 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species.
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Figure 2.10: Posterior mean probabilities of taxa-specific colonization and 95% confidence intervals for adults of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 21 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species.
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Figure 2.11: Posterior mean probabilities of taxa-specific colonization and 95% confidence intervals for juveniles of species found in >5% of surveys averaged over 12 study sites in the Ichawaynochaway Creek Basin. Values plotted are estimates for each of the 25 species using a multi-taxa, dynamic occupancy model. Taxa are identified by the first three letters of their genus and species.
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Figure 2.12: Average mean of probability of persistence for adult fish in isolated pools, plotted in relation to duration of pool isolation. Probabilities are plotted for 21 species estimated using a multi-taxa, dynamic occupancy model applied to 26 periods of continuous isolation at 12 study sites in the Ichawaynochaway Creek Basin. Black lines indicate the species-specific means of persistence and red lines indicate the means for each of the three species types. 59
Figure 2.13: Average mean of probability of persistence for juvenile fish in isolated pools, plotted in relation to duration of pool isolation. Probabilities are plotted for 25 species estimated using a multi-taxa, dynamic occupancy model applied to 26 periods of continuous isolation at 12 study sites in the Ichawaynochaway Creek Basin. Black lines indicate the species-specific means of persistence and red lines indicate the means for each of the three species types. 60
Figure 2.14: Average mean of probability of colonization for adult fish, plotted in relation to duration of flow since isolation or complete drying. Probabilities are plotted for 21 species estimated using a multi-taxa, dynamic occupancy model applied to 26 periods of continuous isolation at 12 study sites in the Ichawaynochaway Creek Basin. Black lines indicate the species-specific means of persistence and red lines indicate the means for each of the three species types. 61
Figure 2.15: Average mean of probability of colonization for juvenile fish, plotted in relation to duration of flow since isolation or complete drying. Probabilities are plotted for 25 species estimated using a multi-taxa, dynamic occupancy model applied to 26 periods of continuous isolation at 12 study sites in the Ichawaynochaway Creek Basin. Black lines indicate the species-specific means of persistence and red lines indicate the means for each of the three species types. 62
Figure 2.16: Modeled probability of observed occurrence of adults in relation to maximum total ammonia (ug/L) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plot shows mean and 95% confidence intervals.
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Figure 2.17: Modeled observed occurrence of adults in relation to maximum depth (m) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plot shows mean and 95% confidence intervals.
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Figure 2.18: Modeled observed occurrence of juveniles in relation to maximum depth (m) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plot shows mean and 95% confidence intervals.
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Figure 2.19: Modeled observed occurrence of juveniles in relation to maximum ammonia (u/gL) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plot shows mean and 95% confidence intervals.
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Figure 2.20: Modeled observed occurrence of juveniles in relation to dissolved oxygen (mg/L) in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plot shows mean and 95% confidence intervals.
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Figure 2.21: Species-specific random effects on the intercept and slope of modeled observed occurrence of juveniles in relation to maximum depth in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals.
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Figure 2.22: Species-specific random effects on the intercept and slope of modeled observed occurrence of juveniles in relation to maximum ammonia in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals.
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Figure 2.23: Species-specific random effects on the intercept and slope of a modeled observed occurrence of juveniles in relation to dissolved oxygen in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals.
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Figure 2.24: Species-specific random effects on the intercept and slope of modeled observed occurrence of adults in relation to maximum depth in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals.
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Figure 2.25: Species-specific random effects on the intercept and slope of modeled observed occurrence of adults in relation to maximum ammonia in 90 isolated pools samples in the Ichawaynochaway Creek Basin, 2015-2016. Plots show means and 95% confidence intervals.
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CHAPTER 3
IDENTIFYING LIFE HISTORY TRAITS THAT PROMOTE FISH SPECIES PERSISTENCE IN INTERMITTENT STREAMS1
1
Davis, J. L., M. C. Freeman, S. W. Golladay. To be submitted to Freshwater Biology
Abstract
Life history traits of stream fishes partly reflect adaptations to natural flow regimes, which in turn shape assemblage composition via environmental filtering on species persistence. Thus, trait-based approaches, including the trilateral life history model, have been useful for understanding species responses to streamflow alteration. In this study, I focused on life history traits of four cyprinid species in a Coastal Plain stream system of southwestern GA that is shifting from historically perennial streamflow to intermittency. Native fishes, including these four species, vary in occurrence, and tolerance to intermittency. I evaluated differences among the four cyprinids in reproductive timing (based on ovary and oocyte development), sex ratio, body size at maturity, and reproductive investment (gonadosomatic index (GSI), gonad weight and egg diameter), traits hypothesized to influence the ability of species to persist in intermittent streams. I periodically sampled individuals in 14 streams over the duration of a year (May 2016April 2017). I found that for Notropis harperi, a species with high persistence rates, reproductive timing did not overlap with typical seasonal stream drying. N. harperi also had the significantly smallest minimum length at maturation, greatest GSI and gonad weight, and a tendency towards larger average egg diameter. Species with low persistence rates in isolated pools (Notropis petersoni, Notropis texanus, and Pteronotropis grandipinnis), had at least a portion of their reproductive timing overlapping with times when streams were likely to dry, and had significantly lower GSI and relative gonad weight than N. harperi. All four species would be considered opportunistic, rather than periodic or equilibrium, strategists. Our results suggest however, that some life history traits used to define the trilateral life history model may be useful for understanding differences in how even closely related species respond to changing
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environments, with smaller body size at maturity along with appropriate reproductive timing promoting greater persistence given more frequent and intense periods of drying.
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Introduction Streamflow defines the physical template of river ecosystems (Poff 1997) and acts as a selective force and an ecological filter for survival strategies of aquatic organisms (Townsend and Hildrew 1994, Lytle and Poff 2004). It shapes the distribution and character of riverine habitats and, in turn, the distribution and abundance of lotic organisms (Power et al. 1995, Bunn and Arthington 2002). Species adaptations to flow regime occur as a response to the interaction between frequency, magnitude, and predictability of mortality-causing events (Lytle and Poff 2004). Streamflow in lotic systems has been altered by humans for many reasons, including extraction for water supply, impoundments for flood control and hydropower, and to support irrigated agriculture. Human freshwater needs and actions have altered historical hydrologic regimes, reducing effectiveness of some biotic adaptations, and decreasing stream suitability for native fauna (Pringle et al. 2000). Increasingly, species traits are being used to study flow-ecology relationships across diverse species-assemblages and broad geographic scales (Poff et al. 2006, Frimpong and Angermeier 2010). Life-history theory predicts that the magnitude, frequency, and predictability of hydrologic events, such as floods or droughts, can affect evolutionary processes (Iwasa and Levin 1995, Lytle and Poff 2004). Convergence in the suites of traits characterizing dominant species along hydrologic gradients has been demonstrated for freshwater fishes (Lamouroux et al. 2002, Logez et al. 2010), and studies testing predictions from life-history theory support these relationships (Tedesco et al. 2008, Kennard et al. 2010, Carlisle et al. 2011). This developing body of work has provided insights into environmental influences on community assemblages in fresh waters (Poff and Allan 1995, McManamay and Frimpong 2015) and provides useful
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frameworks for developing flow-ecology hypotheses and environmental flow standards (McManamay et al. 2015). Environmental variability is a natural part of aquatic ecosystems and influences the structure of aquatic communities (Resh et al. 1988, Poff and Allan 1995). From an evolutionary perspective, floods and droughts that are relatively predictable in their frequency, duration, and intensity can exert selective pressures that filter certain life history traits, while on ecological time scales, flow regime shapes assemblage composition by altering population numbers and species persistence (Poff 1997, Naiman et al. 2008). In systems with a high degree of flow variability (i.e., hydrologically ‘flashy’) including intermittence, fish assemblages are controlled by abiotic factors (Echelle et al. 1972, Taylor 1997, Matthews and Marsh-Matthews 2003). As a result, the predominant fish species in these systems are especially tolerant of variable environmental conditions ( Winemiller 1989, Fausch and Bramblett 1991). While drought and stream intermittency are normal processes, low-flow and no-flow events are increasing in frequency in many areas due to anthropogenic alterations of streamflow regimes through dams, water diversion, and climate shifts (Brown et al. 2013). The ecological effects of low-flows are expected to accumulate with increasing frequency and duration (Lake 2003). Evidence suggests that climate-driven streamflow intermittence has increased in the southeastern US (Palmer et al. 2008b, Falke et al. 2011), including the Coastal Plain of Georgia, where trends in declining seasonal flows are projected to continue (Larned et al. 2010, Golladay and Hicks 2013). Natural resource managers face the challenge of understanding the effects of both water withdrawals, and projected increases in intermittency, when working towards conserving biological integrity of freshwater systems. Management can be improved through models of fish responses to low-flow or isolated events that account for life history traits.
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Life history theory proposes that populations are regulated by trade-offs along demographic axes of age at maturity, juvenile survival, and fecundity (Stearns 1977). The trilateral life history model proposed by Winemiller and Rose (1992) identifies three life history strategies for fishes using tradeoffs among basic demographic parameters. The endpoints of the trilateral life history model represent strategies that are optimal under certain environmental conditions (Winemiller and Rose 1992, Winemiller 2005). Opportunistic Strategists (OS) are predicted to be associated with habitats defined by frequent and intense disturbances. OS have short generation time, high fecundity, and low juvenile survivorship. Periodic Strategists (PS) are favored under predictable yet seasonally fluctuating environments. PS maximize fecundity via delayed reproduction and have larger maturation size. Equilibrium Strategists (ES) are favored under stable environmental conditions. ES maximize juvenile survival through low fecundity per spawning event, have larger eggs, and prolonged parental care. Studies have found utility in fish life-history trait ordination along these three axes across North America (Kennard et al. 2010, Mims et al. 2010, Mims and Olden 2013, Perkin et al. 2017) for predicting responses to natural and altered flow regimes on fish assemblages. For example, a study of two cyprinid and one percid species shows PS traits (high fecundity) favored at sites with greater flow seasonality and low variability, while ES traits (large eggs) were prevalent in stable flow conditions (Bennett et al. 2016). Nevertheless, intraspecific trait variation may contradict the trilateral life history model (Bennett et al. 2016). Additionally, species placement within the trilateral life history model is largely dependent on the species assessed within an assemblage. This study focused on four commonly occurring, yet relatively understudied cyprinid species, Pteronotropis grandipinnis, Notropis harperi, Notropis petersoni, and Notropis texanus, in a southeastern Coastal Plain system. I previously found that mature individuals of these
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cyprinid taxa vary substantially in rates of persistence during periods of flow intermittence, when fishes are restricted to isolated pools, yet the underlying life history mechanisms remain unknown (Chapter two of this thesis, Figure 3.1). Regional streamflows in my study area are strongly influenced by agricultural water withdrawals and climate variability, resulting in increases in the duration and intensity of intermittency. The primary objective of this study was to explore life history strategies that enable cyprinid species to persist within intermittent streams and to determine if those life history traits actually coincide with high persistence rates. I explored differences in reproductive timing, sex ratio, reproductive size, reproductive investment (via gonadosomatic index (GSI), gonad weight, egg diameter), and food habits during flowing and intermittent periods. A secondary objective was to determine if predictions of the trilateral life history model apply to morphologically similar species belonging to a single family. I hypothesized that (i) species with low persistence probabilities reproduce during summer months (e.g., when periods of stream drying to isolated pools occur); (ii) species with high persistence probabilities have increased reproductive investment as assessed via GSI, gonad weight, and egg diameter; (iii) higher probabilities of persistence (N. harperi) coincides with OS, low probabilities of persistence (N. texanus and P. grandipinnis) coincides with ES, and intermediate probabilities of persistence (N. petersoni) coincides with PS; and (iv) species with higher persistence will have a greater shift in diet items between flowing and intermittent periods, reflecting intentional feeding patterns while streams flow and more opportunistic feeding patterns during intermittence.
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Methods
Study sites I collected and used data on four cyprinid species found in the Ichawaynochaway Creek basin (ICB), a major tributary of the lower Flint River Basin (FRB), southwestern GA, to study life history patterns in intermittent streams (Figure 3.2). The channels of major tributary streams within the lower Flint River and the Ichawaynochaway Creek are incised into the Upper Floridian aquifer and tend to be perennial. Small streams in the northwestern portion of the ICB are in the Fall Line Hills physiographic district, and also tend to be perennial. Small streams in the remainder of the basin, within the Dougherty Plain physiographic district, have channels perched above the aquifer, and tend to have periods of intermittence The study area has low topographic relief, and porous, sandy soils, which results in low stream drainage density. During typical winters streamflow increases in response to extended storms (Hicks et al. 1987, Albanese et al. 2007), and lower temperature and evapotranspiration rates (Torak and Painter 2006). Rainfall is evenly distributed throughout the year, but during the summer most precipitation is lost through evapotranspiration, causing water table declines as groundwater recharge is minimal. This results in riparian areas drying and streams decreasing to seasonal low-flows (Golladay and Battle 2001) or periods of intermittency. The FRB has experienced an increased demand on water resources resulting from population expansion in the upper basin, and irrigation expansion in the lower basin (Golladay and Hicks 2013). Over the last four decades, the FRB has experienced warming temperatures, more frequent growing season and multiyear droughts, and increased water withdrawal from groundwater and surface waters for agriculture. As a result, some streams are shifting from
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perennial to intermittent. Streams crossing the Dougherty Plain in the southern portion of the ICB are increasingly likely to dry during periods of low rainfall and high groundwater use, during which the upper Floridan aquifer levels drop below stream channels (Opsahl et al. 2007). Flow in the smaller streams of ICB is typically lowest (and most likely to cease) during summer and early fall, usually June through October, then recovers from November through May. The shift from historically perennial to intermittency in the ICB, combined with the predictable timing of intermittency, provides a useful framework for assessing fish life history patterns.
Survey and Collection Methods To study cyprinid life-history patterns, I collected individuals of the four target species from thirteen study sites in the ICB over a period of one year (May 2016-April 2017). Initial surveys included twelve sites, all experiencing periods of flow cessation to isolated pools (“isolation”) or complete drying, with some target species becoming locally extirpated when isolation occurred. Mills Creek was the only site that maintained inundated habitat and was thus sampled for the duration of the study period. One perennial stream, Brantley Creek, within the upper ICB in the Fall Line Hills district, was sampled from October of 2016 to April of 2017 to continue collection after target individuals became locally extirpated at the original twelve survey sites within the Dougherty Plain (Figure 3.2). Target species were collected using a combination of backpack electrofishing and seining (2.4 m X 1.8 m; 3 mm mesh) at study sites on a three week to monthly basis, with some targets not found on each date. Streams were surveyed to collect ten individuals of four cyprinid species, Pteronotropis grandipinnis, Notropis harperi, Notropis petersoni, and Notropis texanus. When streams were flowing, surveys comprised multiple seine-sets in a minimum of a 50-meter reach,
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where two persons held the seine in flowing water, with the lead-line on the substrate, while one person disturbed water and bed sediment while backpack electrofishing. In isolated pools, I collected with only a seine using multiple passes until no additional target species were found. On every survey date, fish were identified to species, counted, and up to 50 individuals of each species were measured for standard length to the nearest millimeter. A total of 2725 individuals were assessed for length at the thirteen survey sites, but 177 were too small to confidently identify to species. A target of ten individuals were collected during each survey and euthanized using an overdose (100 mg/L) of buffered MS-222, immediately preserved in 10% formalin, and transported back to the laboratory for dissection (Heins and Baker 1999). Individuals occurring at seven study sites were used for reproductive assessment, and individuals occurring at four study sites were used for diet assessment.
Laboratory Methods and Gonad Assessment Prior to dissection, all specimens were measured for standard length (SL) with digital calipers to the nearest 0.01mm, blotted dry, and weighed to the nearest 0.0001g. Specimens were then cut longitudinally and their gonadal tissue and GI tract removed (esophagus to anus) with the aid of a stereo microscope (Olympus SZX7). Gonads were blotted dry and weighed to the nearest 0.0001g using an analytical balance (Mettler AE240). Sex was determined at the time of excision. Individuals
