Wabash River Freshwater Drum Aplodinotus grunniens Diet: Effects of Body Size, Sex, and River Gradient

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1 Notes Wabash River Freshwater Drum Aplodinotus grunniens Diet: Effects of Body Size, Sex, and River Gradient Stephen J. Jacquemin,* Mark Pyron, Michael Allen, Lucas Etchison S.J. Jacquemin Department of Biological Sciences, Wright State University Lake Campus, Celina, Ohio M. Pyron, M. Allen, L. Etchison Aquatic Biology and Fisheries Center, Department of Biology, Ball State University, Muncie, Indiana Abstract The objectives of this study were to describe the diets of freshwater drum Aplodinotus grunniens in the Wabash River in the Midwestern United States. We used a multivariate ordination approach (nonmetric multidimensional scaling) to describe drum diets combined with a generalized linear model to test for covariation of diet with body size, sex, and longitudinal river gradient. Hydropsychidae (trichoptera, caddisfly larvae), pleuroceridae (gastropoda), and heptageniidae (ephemeroptera, mayfly larvae) were the most consumed prey items (,75% of overall diets). Among all freshwater drum, hydropsychidae, pleuroceridae, and heptageniidae were present in 69%, 23%, and 38% of stomachs, respectively. Freshwater drum diets were similar along an upstream downstream river gradient spanning 350 river km, but varied with body size and sex. Small- and medium-sized fish tended to consume more diptera and annelids compared with the largest individuals, which fed on mollusks and crayfish. With control for body size, the diets of male individuals were composed of more diptera (chironomidae) and annelid prey items compared with female individuals, whose diets included more molluscs and crayfish. Overall, we interpret the lack of diet diversity in freshwater drum with Wabash River longitudinal gradient as evidence of diet specialization. Alternatively, we propose that a potential dietary river-gradient signal may be diluted as a function of increased freshwater drum longitudinal movements. Keywords: fish diet; large river ecology; multivariate analysis; Wabash River Received: March 15, 2013; Accepted: October 23, 2013; Published Online Early: December 2013; Published: June 2014 Citation: Jacquemin SJ, Pyron M, Allen M, Etchison L Wabash River freshwater drum Aplodinotus grunniens diet: effects of body size, sex, and river gradient. Journal of Fish and Wildlife Management 5(1): ; e x. doi: / JFWM-027R Copyright: All material appearing in the Journal of Fish and Wildlife Management is in the public domain and may be reproduced or copied without permission unless specifically noted with the copyright symbol ß. Citation of the source, as given above, is requested. The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service. * Corresponding author: stephen.jacquemin@wright.edu Introduction Descriptive diet studies contribute to understanding the ecology of freshwater fishes. Diet studies can indicate evolutionary and environmental processes by eliciting individual, niche, community (e.g., competition), and ecosystem roles or processes (MacArthur and Pianka 1966). Diet within fish taxa varies with individual condition, ontogeny, local habitat, local fish assemblage, guild competition, and prey assemblage (Keast 1980; Wahl et al. 1988; Winemiller 1989; Roberts and Taylor 2008; Strongin et al. 2011). Furthermore, the results of dietary studies have management and conservation implications (Hyslop 1980; Magnan et al. 1994). For example, dietary information can be used to identify suitable habitat for conservation efforts, species of concern (Grohs et al. 2009), or broadly categorize taxa as generalist or specialist relative to prey availability (Godinho et al. 1997; Araújo et al. 2011). However, the majority of nongame taxa have little dietary information available, limiting inferences regarding evolutionary and environmental factors driving variation in diet and what potential community or ecosystem processes are related. The purpose of this study was to provide a dietary description of a large river fish species, the freshwater Journal of Fish and Wildlife Management June 2014 Volume 5 Issue 1 133

2 drum. Freshwater drum exhibit the largest geographic range of North American freshwater fishes (Barney 1926; Page and Burr 2011), are long-lived ($30 y), sexually dimorphic (Rypel et al. 2006), and are locally abundant in large river systems where they occur (Gammon 1998). Although freshwater drum are not typically preferred by anglers over other popular game species, their large body size (.600-mm length) and prevalence (Gammon 1998) result in frequent commercial and sport angler harvests (Becker 1983; Clark-Kolaks et al. 2011). Freshwater drum are considered to be benthivore dietary generalists (Daiber 1952; Wrenn 1969; Bur 1982; Pereira et al. 1995). Diets of freshwater drum have been welldescribed for lake populations (Daiber 1952; Bur 1982; Becker 1983; French and Bur 1996; Morrison et al. 1997), but less well-described for rivers (Hoopes 1960; Wahl et al. 1988; Timmerman et al. 2011). Further elucidation of freshwater drum dietary niche can facilitate management and conservation efforts, and improve ecological understanding of large river longitudinal patterns, which are poorly understood (Pyron and Lauer 2004). Our study objectives were to describe the diets of freshwater drum in the Wabash River (in the Midwestern United States) and to test for variation with body size, sex, and longitudinal river gradient. We hypothesized that drum diets would vary with these components as a function of ontogeny (Schael et al. 1991), sexual selection (Rypel 2007), and turnover in the invertebrate community with river gradient (Vannote et al. 1980; Tomanova et al. 2007; Yates and Bailey 2010). Methods We collected freshwater drum along a continuous river reach of the Wabash River spanning river km in summer 2010 (late June August) using boat and barge electrofishing (Figure 1). Collection efforts were continuous along the river gradient rather than at specific sites. We employed similar collection effort during sampling. To avoid seasonal variation in invertebrate communities along the river gradient, we haphazardly selected fish sampling dates (summer river temperature ranged 15 25uC) and locations from throughout the study reach. Upon collection, we weighed (g), measured (total length [TL], mm), and sexed individual fish using visual observation of internal gonads, and we assigned fish as either male or female when gonads were diagnosable or immature when gonads were undeveloped. We excised stomachs (intestinal tract excluded) following sex determination and preserved them in 10% formalin. Stomach contents were separated in the laboratory, identified to the lowest taxonomic level (all insects to family), and counted. We omitted individuals with empty stomachs from analyses. We first assessed the importance of various prey items using overall prey-percent abundance and prey-percent occurrence in individual drum stomachs (Costello 1990; Amundsen et al. 1996). We visualized prey-specific abundances and percent occurrence data using an Amundsen-style scatterplot (Amundsen et al. 1996). We then used the resulting scatter plot to roughly visualize Figure 1. Wabash River map, including river km locations at extremes of continuous collection area, where we collected freshwater drum in summer 2010 for purposes of dietary analyses. prey items as dominant (high prey-specific abundance and high percent occurrence), opportunistic (high preyspecific abundance and low percent occurrence), generalized (low prey-specific abundance and high percent occurrence), or rare (low prey-specific abundance and low percent occurrence) following Costello (1990), Amundsen et al. (1996), Chipps and Garvey (2007), and Grohs et al. (2009). In addition to calculated prey-specific abundance and prey occurrence data, we summarized drum diets using nonmetric multidimensional scaling (NMS). We compared resulting NMS ordination axes by sex, body size, and river km in a Generalized Linear Model (GLM). We treated drum diet NMS axes as response variables while we treated sex, body size, and river km as independent response variables. In addition, we included significant interactions among response variables, including sex 6 body size and sex 6 river km. This resulted in the following GLM model configuration: Diet NMS Axis, Sex + Body size + River km + Sex 6Body size + Sex 6River km. We used software programs PC-ORD (version 5) and R (R Core Development Team 2011, version ) for analyses. Settings in PC-ORD to calculate the NMS ordination incorporated a random starting configuration, Sorensen (Bray Curtis) distance measure, 50 runs with real data, and three axes to minimize stress (e.g.,,20; McCune and Grace 2002). Alpha was 0.05 for all significance tests. Journal of Fish and Wildlife Management June 2014 Volume 5 Issue 1 134

3 Table 1. Total prey abundances, % of stomachs observed, and nonmetric multidimensional scaling (NMS) axis loadings (correlation coefficients with axis loadings) of freshwater drum Aplodinotus grunniens diets from Wabash River (Midwestern United States) 2010 collections. A total of 6,694 invertebrates were collected. Order or Class Family or Genus Abundance Frequency of dietary occurrence NMS1 NMS2 NMS3 Bivalvia Corbiculidae Bivalvia Unionidae Coleoptera Dytiscidae Coleoptera Elmidae Coleoptera Psephenidae Cypriniformes Cyprinidae Decapoda Cambaridae Diptera Ceratopogonidae Diptera Chironomidae Diptera Simuliidae Diptera Tipulidae Ephemeroptera Baetidae Ephemeroptera Caenidae Ephemeroptera Ephemeridae Ephemeroptera Heptageniidae Ephemeroptera Polymitarcyidae Ephemeroptera Potamanthidae Gastropoda Elimia 1, Gastropoda Pleurocera Hemiptera Hemiptera Corixidae Hemiptera Gerridae Hirudinea Isopoda Megaloptera Corydalidae Neuroptera Sisyridae Odonata Aeshnidae Odonata Gomphidae Odonata Misc. Zygoptera Oligochaeta Phylum Nematoda Plecoptera Perlidae Trichoptera Hydropsychidae 2, Trichoptera Leptoceridae Trichoptera Polycentropodidae Results We collected 249 freshwater drum between river km 300 and 650 (Figure 1). Individuals ranged in TL from 50 to 600 mm. River km was not significantly correlated with collection abundances of male, female, or immature individuals. Five individuals were found with empty stomachs and were excluded from subsequent analyses. Stomach contents (n = 244 individuals) resulted in 6,694 invertebrate individuals in 36 families. Hydropsychidae (trichoptera), pleuroceridae (gastropoda), and heptageniidae (ephemeroptera) comprised the most abundant prey items (.500 specimens) and constituted 38%, 29%, and 8% of all individual dietary items, respectively (Table 1; Figure 2). Hydropsychidae, pleuroceridae, heptageniidae, chironomidae (diptera), and polymitarcyidae (ephemeroptera) were present in.15% of stomachs (Table 1; Figure 2). Raw data files can be found in Supplemental Material (Table S1). The freshwater drum diet NMS ordination resulted in three axes (stress = 15). The first NMS axis distinguished positive loadings of larger sized dietary items including molluscs (pleuroceridae, Corbicula) and crayfish from negative loadings of smaller dietary items including heptageniidae and hydropsychidae (Table 1; Figure 3). The GLM for NMS1 was significant (Table 2; NMS1, F 4,221 = 9.4, R 2 = 0.15, P, 0.001) and indicated that larger sized drum tended to consume larger sized dietary items, Journal of Fish and Wildlife Management June 2014 Volume 5 Issue 1 135

4 Figure 2. Scatterplot of freshwater drum Aplodinotus grunniens dietary items by prey-specific abundance (overall percentage of prey taxa) and percent occurrence (percent of stomachs prey items found in). Scatterplot is arranged following Amundsen et al. (1996). Data are from summer 2010 Wabash River collections. Only the most abundant (prey-specific or occurrence) are labeled. All unlabeled prey items are considered rare (low in prey-specific abundance and percent occurrence). such as molluscs and crayfish, consistent with positive loadings along NMS1 (Figure 3). The second NMS axis distinguished positive loadings of molluscs (pleuroceridae, Corbicula, unionidae) from negative loadings of chironomidae and oligochaeta (Table 1; Figure 3). The GLM of NMS2 was significant (Table 2; NMS2, F 6,219 = 20.4, R 2 = 0.36, P, 0.001) and indicated that larger sized drum consumed dietary items with positive loadings on NMS2 (Figure 3). Further, the GLM of NMS2 indicated that male drum tended to consume fewer dietary items that loaded positively, such as molluscs, compared with female drum per given length (Figures 3, 4). The third NMS axis distinguished positive loadings of molluscs (pleuroceridae, Corbicula, unionidae) and crayfish from negative loadings of hydropsychidae, elmidae, and tipulidae (Table 1; Figure 3). The GLM of NMS3 was significant (Table 2; NMS3, F 4,221 = 20.3, R 2 = 0.27, P, 0.001) and indicated that larger sized drum consumed dietary items with positive loadings on NMS3 (Figure 3). Further, the GLM of NMS3 also indicated presence of sexual selection in diets similar to trends delineated along NMS2 (Figure 3). No significant relationship with river km was detected on any dietary axis, irrespective of body size (see NMS2 residuals in Figure 4). Discussion Freshwater drum in the Wabash River exhibited dietary variation that covaried with body size and sex but not longitudinal river gradient. Our description of Wabash River freshwater drum diets differs from other published drum diet studies, which found high variation in diets among collection locales and largely considered drum to be generalist feeders (Daiber 1952; Wrenn 1969; Bur 1982; Pereira et al. 1995). For example, Bur (1982) described freshwater drum diets in Lake Erie that were dominated by cladocera, diptera, and crayfish. Later, French and Bur (1996) identified a shift in Lake Erie drum diets from these prey items (Bur 1982) to primarily zebra mussels Dreissena polymorpha following their introduction to Lake Erie. In the Mississippi River, freshwater drum diets have been found to contain primarily corixidae (hemiptera), chironomidae (diptera), and fishes (Timmerman et al. 2011). Wahl et al. (1988) compared the diets and growth rates among lentic and lotic populations and discerned higher growth rates in lotic environments (also see Rypel et al. 2006). Differences in drum growth rates have been attributed to prey availability, selectivity, and energetic return (Wahl et al. 1988; French and Bur 1996). Combined, these studies coupled with this current work demonstrate that freshwater drum exhibit high dietary variation across their range but local populations may not clearly fit this dietary generalist pattern. We identified two invertebrate families (hydropsychidae and pleuroceridae) that composed.65% of the total diets of Wabash River drum independent of river location. In addition to this specificity, we only identified five individuals with empty stomachs. The a priori expectation was that drum would exhibit a generalist feeding style that would coincide with prey availability. Invertebrate communities (prey base) are expected to covary with longitudinal gradient according to numerous theoretical and empirical studies, such as the River Continuum Concept (Vannote et al. 1980; Tomanova et al. 2007; Yates and Bailey 2010). Given the upstream downstream variation in geomorphology, tributary inputs, water volume and substrate changes (upstream gravel to downstream sand silt; Gammon 1998), we are confident the Wabash River Journal of Fish and Wildlife Management June 2014 Volume 5 Issue 1 136

5 Figure 3. Scatterplot of freshwater drum Aplodinotus grunniens total length (mm) and diets based on nonmetric multidimensional scaling (NMS) 1, 2, and 3 scores (positive and negative dietary taxon loadings). Closed circles denote females, open squares denote males, and closed diamonds denote immature individuals. Solid regression line represents best-fit line for female data points, light dashed line represents best-fit line for male data points, and heavy dashed line represents best-fit line for immature data points. Data are from summer 2010 Wabash River (Midwestern United States) collections. invertebrate community (prey base) also varies with river gradient (Vannote et al. 1980; Tomanova et al. 2007; Yates and Bailey 2010). We interpret the similarity in diets with river distance as suggesting dietary specialization. A potential alternative hypothesis is that longitudinal river signal may actually have been diluted as a result of largescale drum movements. Freshwater drum are considered a motile species; however, relatively few studies have quantified actual drum movement potential (A.L. Rypel, Wisconsin Department of Natural Resources, personal communication). One of the few tagging studies to directly quantify movement did find that Missouri River drum populations were documented to move up to several hundred kilometers over the course of less than a year (Funk 1957). Similarly, studies incorporating drum when testing fish tissue for concentrations of polychlorinated biphenyl have suggested that polychlorinated biphenyl concentrations reflect increased movements as well as differences in movement among male and female individuals (Bayne et al. 2002; Rypel 2004). Increased drum movements are possible through this study reach, given the lack of physical impoundments (one mainstem dam is upstream of study area, river km 662). Additional details for Wabash River invertebrates and drum movement behavior are necessary to formally test these hypotheses. Ultimately, identification of mechanisms underlying dietary variation can improve our understanding of drum ecology. Dietary variation is expected to vary primarily with body size as a function of ontogenic variability in gape size (Schael et al. 1991), life history (Garcia-Berthou and Moreno-Amich 2000), ecomorphology (Mittelbach et al. 1992), and interspecific and intraspecific competition (Winemiller 1989; Svänback and Bolnick 2007). Larger drum (.500 mm) tended to prey on mollusks and crayfish while small and medium drum (,500 mm) tended to consume more diptera, trichoptera, ephemeroptera and segmented worms. This was expected because ontogenetic diet changes are well-documented with increased body size (Keast 1980) and coincide with shifts to higher trophic levels (Winemiller 1989). The described ontogenic pattern also has clear implications for dietary differences between sexes. Given the well-documented pattern of sexual size dimorphism in drum (females larger than males; Rypel 2007), older females beyond the maximum size range of males ultimately utilize a different invertebrate prey base than males. However, even after removing the effect of body size, female diets were still consistently different from males. Dietary differences associated with sex and independent of body size may be due to physiological demands associated with varying energetic requirements needed to accommodate gonadal growth (Parker 1992). For example, if females exhibit different movement patterns than do males, then they are likely to be exposed to a greater variety of dietary items. Furthermore, increased growth rates in females (Rypel 2007) may result in the observed sexual differences in prey selection. In addition to the potential for intraspecific competition, dietary variation in freshwater drum populations may also result from intraspecific (e.g., sexual; Svänback and Bolnick 2007) and interspecific competition (Svänback and Persson 2004). The degree of interspecific competition can vary based on 1) abundances of preferred dietary resources, 2) population densities of drum, or 3) the Journal of Fish and Wildlife Management June 2014 Volume 5 Issue 1 137

6 Table 2. Independent variables and coefficients for generalized linear model equations used to determine relationship among multivariate dietary nonmetric multidimensional scaling (NMS) axes and Wabash River freshwater drum Aplodinotus grunniens sex (M = male, F = female, I = immature), length, collection locale, and specific interactions. Data are from summer 2010 Wabash River (Midwestern United States) collections. Only significant interaction terms were retained for the final model and reported here. Dependent variable Independent variable Coefficient SE t-value P-value Model (R 2 ) Model (P-value) NMS1 Intercept ,0.001 Sex (M vs. F) Sex (I vs. F) Length ,0.001 River km NMS2 Intercept , ,0.001 Sex (M vs. F) Sex (I vs. F) Length ,0.001 River km Sex M 6 length ,0.001 Sex I 6 length NMS3 Intercept ,0.001 Sex (M vs. F) Sex (I vs. F) ,0.001 Length ,0.001 River km presence and abundance of other benthivores with similar diet preferences. Given the well-documented Wabash River longitudinal patterns in habitat, fish assemblage, and hydrology (Gammon 1998; Pyron and Lauer 2004; Pyron and Neumann 2008), prey abundances likely fluctuate with river location in accordance with the River Continuum Concept (Vannote et al. 1980; Tomanova et al. 2007; Yates and Bailey 2010). Freshwater drum is a numerically dominant member of the Wabash River fish assemblage; however, the Wabash River contains numerous other benthivores with dietary niches similar to those of freshwater drum (Gammon 1998). Other native benthivore species include blue sucker Cycleptus elongatus, carpsucker Carpiodes spp., buffalo Ictiobus spp., redhorse Moxostoma spp., shovelnose sturgeon Scaphirhynchus platorynchus, and exotic common carp Cyprinus carpio. The presence of multiple benthivores, particularly among certain size classes, in the Wabash River may contribute to interspecific competition, which results in the observed dietary niche of Wabash River freshwater drum. The diverse Wabash River fish assemblage provides a contrast to other diet studies that find higher dietary variation where fewer potential competitors co-occur. Our conclusion is that the freshwater drum is a dietary generalist at larger spatial scales and becomes increasingly selective at local scales. Ultimately, confirmation of dietary plasticity with multiple habitat and prey availability may improve understanding distribution and persistence in widespread taxa (Ribeiro et al. 2007; Strongin et al. 2011). Supplemental Material Please note: The Journal of Fish and Wildlife Management is not responsible for the content or functionality of any supplemental material. Queries should be directed to the corresponding author for the article. Table S1. Wabash River Drum Diet Data File. Found at DOI: S1 Acknowledgments We are grateful to Andrew Rypel, the Journal of Fish and Wildlife Management Subject Editor, and two anonymous reviewers for their insightful reviews of this manuscript. In addition, we thank Brittany Ross, Matthew Pyron and Daniel Lopez for field and laboratory assistance. Fishes were collected under Indiana scientific permit IN Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. References Amundsen PA, Gabler HM, Staldvik FJ A new approach to graphical analysis of feeding strategy from stomach contents data-modification of the Costello (1990) method. Journal of Fish Biology 48: Araújo MS, Bolnick DI, Layman CA The ecological causes of individual specialization. Ecology Letters 14: Barney RL The distribution of the freshwater sheepshead, Aplodinotus grunniens Rafinesque, in respect to the glacial history of North America. Ecology 7: Bayne DR, Reutebuch E, Seesock WC Relative motility of fishes in a southeastern reservoir based on Journal of Fish and Wildlife Management June 2014 Volume 5 Issue 1 138

7 Figure 4. Scatterplot of river km and freshwater drum Aplodinotus grunniens diets based on nonmetric multidimensional scaling (NMS) Axis 2 scores (positive and negative invertebrate axis loadings on top panel), freshwater drum total length (middle panel), and NMS2 total length residuals (bottom panel). Closed circles denote females, open squares denote males, and closed diamonds denote immature individuals. Solid regression line represents best-fit line for female data points, light dashed line represents best-fit line for male data points, and heavy dashed line represents best-fit line for immature data points. Data are from summer 2010 Wabash River (Midwestern United States) collections. tissue polychlorinated biphenyl residues. North American Journal of Fisheries Management 22: Becker GC The fishes of Wisconsin. Madison: The University of Wisconsin Press. Bur MT Food of freshwater drum in western Lake Erie. Journal of Great Lakes Research 8: Chipps SR, Garvey JE Assessment of diets and feeding patterns. Pages in Guy CS, Brown ML, editors. Analysis and interpretation of freshwater fisheries. Bethesda, Maryland: American Fisheries Society. Clark-Kolaks S, Carnahan D, Ball RL Wabash River angler, recreational, and commercial fisher activity survey of 2005 to Indianapolis, Indiana: Indiana Division of Fish and Wildlife Report. Available: (March 2013). Costello MJ Predator feeding strategy and prey importance: a new graphical analysis. Journal of Fish Biology 36: Daiber FC The food and feeding relationships of the freshwater drum Aplodinotus grunniens Rafinesque in western Lake Erie. Ohio Journal of Science 52: French JRP III, Bur MT The effect of zebra mussel consumption on growth of freshwater drum in Lake Erie. Journal of Freshwater Ecology 11: Funk JL Movements of stream fishes in Missouri. Transactions of the American Fisheries Society 85: Gammon JR The Wabash River ecosystem. Bloomington: Indiana University Press. Garcia-Berthou E, Moreno-Amich R Food of introduced pumpkinseed sunfish: ontogenetic diet shift and seasonal variation. Journal of Fish Biology 57: Godinho FN, Ferrerira MT, Cortes RV The environmental basis of diet variation in pumpkinseed sunfish, Lepomis gibbosus, and largemouth bass, Micropterus salmoides, along an Iberian river basin. Environmental Biology of Fishes 50: Grohs KL, Klumb RA, Chipps SR, Wanner GA Ontogenic patterns in prey use by pallid sturgeon in the Missouri River, South Dakota and Nebraska. Journal of Applied Ichthyology 25 (Supplement 2): Hoopes DT Utilization of mayflies and caddisflies by some Mississippi River fishes. Transactions of the American Fisheries Society 89: Hyslop EJ Stomach contents analysis a review of methods and their application. Journal of Fish Biology 17: Keast A Food and feeding relationships of young fish in the first weeks after the beginning of exogenous feeding in Lake Opinicon, Ontario. Environmental Biology of Fishes 5: MacArthur RH, Pianka ER On optimal use of a patchy environment. American Naturalist 100: Magnan P, Rodrigues MA, Legendre P, Lacasse S Dietary variation in a freshwater fish species: relative contributions of biotic interactions, abiotic factors, and spatial structure. Canadian Journal of Fisheries and Aquatic Sciences 51: McCune B, Grace JB Analysis of ecological communities. Gleneden Beach, Oregon: MjM Software Design. Journal of Fish and Wildlife Management June 2014 Volume 5 Issue 1 139

8 Mittelbach GG, Osenberg CW, Wainwright PC Variation in resource abundance affects diet and feeding morphology in the pumpkinseed sunfish (Lepomis gibbosus). Oecologia 90:8 13. Morrison TW, Lynch WE Jr, Dabrowski K Predation on zebra mussels by freshwater drum and yellow perch in western Lake Erie. Journal of Great Lakes Research 23: Page LM, Burr BM Peterson field guide to freshwater fishes of North America north of Mexico. New York: Houghton Mifflin. Parker G The evolution of sexual size dimorphism in fish. Journal of Fish Biology 41 (Supplement B):1 20. Pereira DL, Bingham C, Spangler GR, Conner DJ, Cunningham PK Construction of a 110-year biochronology from sagittae of freshwater drum (Aplodinotus grunniens). Pages in Secor DH, Dean JM, Campana SE, editors. New developments in fish otolith research. Columbia: University of South Carolina Press. Pyron M, Lauer TE Hydrological variation and fish assemblage structure in the middle Wabash River. Hydrobiologia 525: Pyron M, Neumann K Hydrologic alterations in the Wabash River watershed. River Research and Applications 24: R Core Development Team R: a language and environment for statistical computing. Vienna: R Foundation for Statistical Computing. Available: (March 2013). Ribeiro F, Orjuela RL, Magalhães MF, Collares-Pereira MJ Variability in feeding ecology of a South American cichlid: a reason for successful invasion in Mediterranean-type rivers. Ecology of Freshwater Fish 16: Roberts ME, Taylor CM Using community-level analyses to identify dietary patterns for species in space and time. Journal of Freshwater Ecology 23: Rypel AL Polychlorinated biphenyl differences between sexes of six fish species in Lake Logan Martin, Alabama. Masters thesis. Auburn, AL: Auburn University. Available: (March 2013). Rypel AL Sexual dimorphism in growth of freshwater drum. Southeastern Naturalist 6: Rypel AL, Bayne DR, Mitchell JB Growth of freshwater drum from lotic and lentic habitats in Alabama. Transactions of the American Fisheries Society 135: Schael DM, Rudstam LG, Post JR Gape limitation and prey selection in larval yellow perch (Perca flavescens), freshwater drum (Aplodinotus grunniens), and black crappie (Pomoxis nigromaculatus). Canadian Journal of Fisheries and Aquatic Sciences 48: Strongin K, Taylor CM, Roberts ME, Neill WH, Gelwick F Food habits and dietary overlap of two silversides in the Tennessee Tombigbee Waterway: the invasive Menidia audens versus the native Labidesthes sicculus. American Midland Naturalist 166: Svänback R, Bolnick DI Intraspecific competition drives increased resource use diversity within a natural population. Proceedings of the Royal Society of London B 274: Svänback R, Persson L Individual diet specialization, niche width and population dynamics: implications for trophic polymorphisms. Journal of Animal Ecology 73: Timmerman TR, Dolan CR, Chick JH Assessment of backwater lake management strategies based on the diets of five riverine fishes. Journal of Freshwater Ecology 26: Tomanova S, Tedesco PA, Campero M, Van Damme PA, Moya N, Oberdorff T Longitudinal and altitudinal changes of macro-invertebrate functional feeding groups in Neotropical streams: a test of the river continuum concept. Fundamental and Applied Limnology 170: Vannote RL, Minshall GW, Cummins KW, Sedell JR, Cushing CE The river continuum concept. Canadian Journal of Fisheries and Aquatic Sciences 37: Wahl DH, Bruner K, Nielsen LA Trophic ecology of freshwater drum in large rivers. Journal of Freshwater Ecology 4: Winemiller KO Ontogenetic diet shifts and resource partitioning among piscivorous fishes in the Venezuelan Llanos. Environmental Biology of Fishes 26: Wrenn WB Life history aspects of smallmouth buffalo and freshwater drum in Wheeler Reservoir, Alabama. Proceedings of Southeast Association of Game and Fish Commissioners 22: Yates AG, Bailey RC Covarying patterns of macroinvertebrate and fish assemblages along natural and human activity gradients: implications for bioassessment. Hydrobiologia 637: Journal of Fish and Wildlife Management June 2014 Volume 5 Issue 1 140