POPULATION ECOLOGY ORIGINAL RESEARCHDoes abigger mouth make you fatter Linking intraspecic gape variability tobody condition ofatropical predatory shOsmarJLuiz DavidACrook MarkJKennard JulianDOlden T ID: 863821
Download Pdf The PPT/PDF document "Oecologia httpsdoiorg101007s004420190452..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
1 Oecologia https://doi.org/10.1007/s00442
Oecologia https://doi.org/10.1007/s00442-019-04522-w POPULATION ECOLOGY ORIGINAL RESEARCHDoes a bigger mouth make you fatter? Linking intraspeci c gape variability to body condition of a tropical predatory shOsmar J. Luiz · David A. Crook · Mark J. Kennard · Julian D. Olden · Thor M. SaundersMichael M. Douglas · Dion Wedd · Alison J. King Received: 20 May 2019 / Accepted: 30 September 2019© Springer-Verlag GmbH Germany, part of Springer Nature 2019AbstractIn gape-limited predators, gape size restricts the maximum prey size a predator is capable to ingest. However, studies investigating the energetic consequences of this relationship remain scarce. In this study, we tested the hypothesis that gape-size variability in uences individual body condition (a common proxy for tness) in one of the largest freshwater teleost predators, the barramundi. We found that individual barramundi with larger gapes relative to body size had higher body condition values compared to conspeci cs with smaller gapes. Body condition was highest soon after the wet season, a period of high feeding activity on productive inundated oodplains, and body condition decreased as the dry season progressed when sh were restricted to dry season remnant habitats. The increased condition obtained during the wet season apparently o sets weight loss through the dry season, as individuals with large gapes were still in better condition than sh with small gapes Communicated by Joel Trexler.Electronic supplementary materialThe online version of this article (://doi.org/10.1007/s0044) contains supplementary material, which is available to authorized users.Osmar J. Luiz osmarjluiz@gmail.comResearch Institute for the Environment and Livelihoods, Charles Darwin University, Ellengowan Dr, Darwin, NT 0810, AustraliaAustralian Rivers Institute, Grith University, Nathan, QLD, AustraliaSchool of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USADepartment of Primary Industry and Fisheries, Darwin, NT, AustraliaSchool of Biological Sciences, School of Agriculture and Environment, The University of Western Australia, Perth, WA, Australia Oecologia size (Schmitt and Holbrook ; Persson et al. ; Scharf et al. ; Magnhagen and Heino ). The importance of gape limitation in sh predatorprey relationships is also demonstrated by the prevalence of prey defense mechanisms designed to constrain passage through a predators oral gape; for example, long dorsal and pectoral spines, body in ation and extreme lateral compression of body shape (Hobson 1979; Nilsson and Brönmark 2000). Conversely, prey exposed to nongape-limited predators are often small, lack defenses, or exhibit reduced morphological defense (e.g., Kristjánsson et al. ). This has led to evidence for directional selection on prey traits based on gape limitation of predators (e.g., Miehls et al. Interspeci c variability in gape- to body-size ratio is a commonly used trait in studies of sh functional ecology (Villéger et al. ). Species with larger size-speci c gape sizes are assumed to be able to forage on a wider range of prey sizes than species with relatively smaller mouths (Gatz ). Comparative trait analyses have found that variability in gape size among species in uence feeding mode, trophic guild position and diet overlap (Gerking ; Karpouzi and Stergiou ; Albouy et al. ). For example, ambush sh piscivores tend to have large gape sizes, allowing them to better engulf large individual prey (Juanes et al. ). In contrast, sh that feed on zooplankton or small benthic invertebrates tend to have small gapes relative to body size, as small gapes help increase suction power when associated with long snouts (Gerking ; Norton ; Cooper et al. Within species, maximum swallowing capacity often de nes the amount of food available to an individual to consume (Forsman ). Gape size and swallowing capacity increase with body length, but there is often natural residual variation in gape size among individuals of the same body size (Forsman 1996; Forsman and Shine 1997). The extent to which intraspeci c variability in relative gape size (i.e. gape size adjusted for the individual body length) in uences foraging success and tness of individuals has not been widely tested. A theoretical model, which is supported by data from snake-feeding experiments, predicts a positive relationship between net energy gain and relative gape size (Forsman ). Howeve
2 r, the relationship between relative gap
r, the relationship between relative gape size and individual tness in shes remains unexplored.Body condition is generically described as the well being or robustness of an individual (Pope and Kruse ), and is an indicator of foraging success and, ultimately, tness (Jakob et al. ). Body condition has typically been estimated by (1) comparing an individual weight to a standard weight for a given length and assuming that larger ratios (condition index) re ect a better physiological state or (2) by directly measuring physiological parameters related to energy stores, such as tissue lipid content (Bolger and Connolly 1989; Peig and Green 2009). Measures of condition are commonly used as an indicator of tissue energy reserves, with the expectation that individuals in good condition should demonstrate relatively high growth rates, reproductive potential, and survival (Sutton et al. ). Furthermore, at a population level, body condition is used to measure the overall health or tness of a population, particularly re ecting the abundance and quality of food resources available.In the wetdry tropics of northern Australia, rivers are characterized by strong seasonality in their ow regimes (Warfe et al. ), which is thought to drive signi cant uctuations in food resources and individual sh condition (Bishop et al. ). In the wet season, oodplains and associated riparian zones become inundated, allowing the lateral movement of sh for feeding (Jardine et al. ). In the dry season, ows either cease or low ows are maintained by sub-surface and local groundwater ow (Kennard et al. ). The reduction or loss of aquatic connectivity during the dry season potentially imposes limitations on food availability, consequently inducing seasonal variability in sh body condition and growth rate (Balcombe et al. ; Xiao Here, we use a large predatory riverine sh as a model organism to test the widely held though poorly validated hypothesis that gape size variability in uences individual tness. Furthermore, while we expect antecedent conditions (particularly ow) to in uence body condition (Hoeinghaus et al. ), we also hypothesize that sh with larger relative gapes will be better able to capitalize on wet season periods of high food availability when compared to sh with smaller gapes. It was demonstrated that it is energetically advantageous for individuals to select large prey (Norin and Clark ). Therefore, our expectation is that large-gaped individuals will have better body condition (a common proxy for tness), at the end of the wet season and o set condition decay over the dry season, thus resulting in a positive relationship between relative gape size and body condition.Materials and methodsThe barramundi, or Asian sea bass, Lates calcarifer (family Latidae), is a large (~180 cm maximum total length) iconic teleost predator inhabiting tropical and semi-tropical coastal seas, estuaries, and river waters of the IndoWest Paci c region (Pusey et al. ). It is highly regarded as a trophy and food sh in recreational and commercial sheries, resulting in signi cant economic importance in some parts of Australia (Ebner et al. ; Saunders et al. ). Barramundi are sequential, protandrous hermaphrodites with complex biology and life-history characteristics showing much variability at individual and population levels (Crook et al. 2017). It exhibits an ontogenetic shift in diet, preying predominantly on macro-crustaceans as juveniles and Oecologia becoming increasingly piscivorous as adults (Pusey et al. ). Prey are swallowed whole, drawn into the mouth by an extremely powerful sucking action e ected by the rapid expansion of the buccal cavity (Davis ). Gape size in barramundi, therefore, imposes physical limitations on the potential maximum size of prey that can be consumed (Davis ; Mihalitsis and Bellwood ) and, consequently, a ects sh energy budgets by constraining feeding opportunities.Field collection of wild barramundi was performed on four sampling occasions across 1 year, encompassing a range of river ow conditions (Fig. ) from the 2016 late-dry season (OctoberNovember 2016), to the next early-dry season (MayJune 2017), mid-dry (August 2017) and the late-dry season (late SeptemberNovember 2017). Using boat electro shing and gill net shing, 197 barramundi individuals with sizes ranging from 310 to 872 mm (standard length, SL) were collected from 11 sites in 7 rivers in the
3 Australias northern territory (Fig. b;
Australias northern territory (Fig. b; Table ). Barramundi of similar sizes were collected on each sampling season (Fig. ; ANOVA193, 0.16). Fish were euthanized using an overdose of Aqui-S, placed on ice and transported to the laboratory and stored in a freezer at20 °C prior to measurement. All sh caught was measured (SL) to the nearest mm and weighed on an electronic scale to the nearest mg. In addition, the mouth depth (Md) and mouth width (Mw) were measured to the nearest mm using Vernier calipers. Relative gape (RG) was calculated by the product of Md and Mw standardized by SL (Karpouzi and Stergiou The relative condition factor index () was calculated for individual samples using the following equation: Fig. Mean daily discharge in the Adelaide river during the study period. The timing of sh sampling periods is indicated with black bars. Location of sh sampling sites (green circles) in the four study rivers. Inset map shows the location of the study region in northern Australia. Discharge data shown in was sourced from stream gage located at the Adelaide river sh sampling with crossed green circle (a)(b) Table Number of individual barramundi collected per site and sea Sites Late dry16Early dry17Mid dry17Late dry17COAR 5.86.06.26.46. 66 .8 7.7.8.8.9.9. Ln Length (mm Ln Weight (g Late dry16Early dry17 Mid dry17 Late dry17 (n= 62(n= 36(n= 55(n= 46 Fig. Scatter plot of the lengthweight relationship of the sh collected for each sampling season Oecologia where is individual sh weight and is the predicted length-speci c weight based on ln transformed pooled data of all individuals collected for this study (Pope and Kruse We tested the e ect of RG and season on using a linear mixed-e ect (lme) model. Because variation in sh condition may re ect multiple environmental and ecological factors (e.g. habitat, prey availability, parasites and competition), we included the sampling site as a random factor to account for these potential spatially varying e ects. The lme model was tted using the packages lme4 (Bates et al. 2018) and lmerTest (Kuznetsova et al. 2018) in the statistical programming language R 3.6.0 (R Development Core Relative mouth gape of barramundi varied substantially among individuals, showing a 2.74-fold increase from the lower to the higher range endpoints. The condition factor also varied considerably among barramundi individuals and across seasons, increasing 2.12-fold across its range and peaking in the early-dry season and reaching its lower values in the late-dry season (Fig. cated both relative gape size and season as signi cant factors predicting barramundi condition factor (Table ). Gape size was positively related to condition factor (Fig. b) and the slope of this relationship in the early-dry season was signi cantly higher than in all other seasons (Table ). No statistically signi cant interaction was detected between RG and season. The relationship between gape size and condition factor is robust regardless of whether condition factor is estimated from all individuals pooled across all seasons (present analysis; Fig. b; Table ) or estimated separately for each season only from individuals captured in that season (Fig. S1; Table S3). DiscussionAssociation between variability of relative mouth gape size and individual tness remain relatively unexplored. We found that barramundi, a high-order aquatic predator of rivers in tropical Australia, with larger gape relative to body length exhibited higher body condition values than conspeci cs with smaller gapes. In gape-limited predators, gape size is widely correlated with the maximum prey size a predator is capable of ingesting (Schmitt and Holbrook ; Hambright ; Scharf et al. ). However, studies investigating the energetic consequences of this relationship are very scarce. Forsman () has shown that snakes with similar body sizes but higher relative gape size bene t from a higher rate of net energy gain, and therefore, tness. Our nding broadens the taxonomic coverage of this relationship, lling an important gap in understanding the potential outcomes of intraspeci c morphological variability on the tness of gape-limited sh predators.We found that barramundi body condition peaked soon after the wet season and that body condition decreased as the dry season progressed. The e ect of seasonality on body Relative gape Seasonlate
4 -dry 16early-dry1mid-dry1late-dry 17
-dry 16early-dry1mid-dry1late-dry 17 0.1.1.late-dry '16early-dry17mid-dry17 late-dry '1SeasonLn condition factor (Kn) (a) (b)Ln condition factor (Kn) 0.1.1.1. 0.0150.0200.0250.030 Fig. Seasonal variation in barramundi condition factors (Vertical lines, gray bars, black horizontal lines and black dots represent, respectively, data upper and lower extremes, interquartile range, Relationship among barramundi condition factor () and relative gape for each sampling season. Lines are the predicted values of the lme model for each season plus the 95% CI Oecologia condition has been previously reported for some species inhabiting Australian rivers (Balcombe et al. ), including barramundi (Bishop et al. ). In northern Australia, peak feeding activity by barramundi occurs during the wet season when sh often move onto temporarily inundated and highly productive oodplains (Crook et al. Pettit et al. ) and declines during the dry season when sh are restricted to river channels and o -channel waterholes (Davis ; Bishop et al. ). Consequently, the relatively high body condition of barramundi observed during the early-dry season is likely the result of elevated food availability and high feeding activity during the wet season. It is perhaps not unexpected, therefore, that the relationship between gape size and body condition was stronger in the early-dry than in the mid- and late-dry seasons (Table Fig. a), because that is the time of year when feeding opportunities are at the greatest and barramundi can reap the predatory bene ts of having a large gape. Migration of sh onto oodplain habitats to access rich food resources during the tropical wet season has been widely reported (Arrington et al. ; Anderson et al. ), with the pulsed input of energy and nutrients during such periods considered a key driver of ecosystem productivity (Winemiller and Jepsen ). Further research on the relationships between food resource availability, gape size and body condition in other systems, and across functional feeding groups, would shed light on the generality of our ndings for shes and other taxa.Gape size also plays a role in mediating the e ects of resource uctuations on sh condition. For example, individuals with large relative gape size in the late-dry season have equal or better body condition than small gaped individuals in the early-dry season. To cope with variable food resource levels, sh store energy as fat during productivity booms, enabling them to survive through extended periods of limited food resources and allocate energy for reproduction (Balcombe et al. ). Our results suggest that individuals with large gapes may be able to capitalize on the many feeding opportunities provided by rivers and their wetlands during oods, gaining more weight than conspeci cs with similar length but smaller gapes. The good condition obtained in the late-wet/early-dry period apparently o sets weight loss through the dry season, as individuals with large gapes were still in better condition than sh with relatively small gapes in the late-dry season.Given the intimate associations between food intake and nutritional gain, we suggest a likely causal relationship between relative gape size and body condition. Nonetheless, other factors can potentially in uence variability in relative gape size and body condition. First, piscivores may frequently consume prey much smaller than their maximum gape limitation (Juanes ). Second, rapid changes in prey availability such as invasion of a novel prey (Cattau et al. ), di erent prey densities and types (Magnhagen and ) and foraging in multiple habitats (Ehlinger and Wilson ) are thought to produce intraspeci c morphological variability through phenotypic plasticity. Further studies on gape size plasticity under di erent conditions should generate fruitful insights into the role of individual variation in driving ecomorphological responses to a rapidly changing environment.Species traits, rather than taxonomic species, are increasingly acknowledged as providing new opportunities to enhance our understanding of ecological patterns and processes operating in nature (McGill et al. ). Traits have now become the central component of the growing area of functional or trait-based ecology, where functional traits relate to the performance (growth rate, survival, reproduction) of an organism and/or its contribution to ecological processes (Violle et
5 al. ). However, trait-based studies in
al. ). However, trait-based studies in sh ecology typically use phenotypic traits as proxies for functions and most of these relationships have been tested only for a few sh families. This study provides empirical support for a mechanistic link between gape size and individual performance in a gape-limited predatory sh. We caution, however, that this result may not apply to shes that feed at other trophic levels. Species that do not swallow their food whole, like browsing herbivores or detritivores, for example, are not gape limited and, therefore, gape size may not in uence their rate of energy acquisition and condition. Further tests investigating correlations between gape size and body condition across a range of species with distinct diet strategies are needed to assess the generality of our ndings.Elucidating the links between intraspeci c variability in traits and performance is a key challenge for sh ecologists and in functional ecology more generally (Violle et al. Villéger et al. 2017). Recent meta-analysis points to comparable ecological importance of variation within species versus variation among species (Des Roches et al. ). Table Parameters of the linear mixed-e ect model predicting variation in barramundi condition factor () as a function of relative gape size and season of sampling ( xed e ects), with site as a random Presented are parameter estimates (±standard error), degrees of free), test statistic ( value) and probability ( value). Reference levels for the season category were set as Early dry17 VariableEstimate value valueInterceptRelative gapeMid dry17Late dry 16Late dry 17 Oecologia Plasticity in species functional traits can occur at a range of spatial scales in response to varying biotic and abiotic conditions (e.g. Blanck and Lamouroux 2007; Messier et al. 2010Hall et al. ). In practice, however, values for most traits are recorded for a set of individuals and these values are averaged at the species level assuming that intraspeci c variability is weak compared to interspeci c variability (known as the mean eld approach). This study emphasizes that even small intraspeci c variability in trait values can result in marked di erences in individual performance over a portion of species distribution.AcknowledgementsWe thank B. Adair, K. Keller, D. Lowensteiner, Q. Allsop, W. Baldwin, C. Errity, N. Croft for assistance with eld sampling, R. Morais and three anonymous reviews for comments that improved the manuscript, and B. Adair and D. Lowensteiner for assistance with sh measurement in the laboratory.Author contribution statementAJK, DAC, JDO, MJK, MMD and TMS conceived the study. AJK, DW and OJL collected the data. OJL analyzed the data and wrote the rst draft of the manuscript and all authors contributed to revisions.FundingFinancial support was provided by the Australian Research Council (LP150100388) and the Department of Primary Industry and Fisheries, Northern Territory Government.ReferencesAlbouy C, Guilhaumon F, Villéger S, Mouchet M, Mercier L, Culioli J, Tomasini J, Le Loch F, Mouillot D (2011) Predicting trophic guild and diet overlap from functional traits: statistics, opportunities and limitations for marine ecology. Mar Ecol Prog Ser Anderson JT, Saldaña-Rojas J, Flecker AS (2009) High-quality seed dispersal by fruit-eating shes in Amazonian oodplain habitats. Oecologia 161:279290Arrington DA, Winemiller KO, Layman CA (2005) Community assembly at the patch scale in a species rich tropical river. Oecologia Balcombe SR, Lobegeiger JS, Marshall SM, Marshall JC, Ly D, Jones DN (2012) Fish body condition and recruitment success re ect antecedent ows in an Australian dryland river. Fish Sci Balcombe SR, Arthington AH, Sternberg D (2014) Fish body condition and recruitment responses to antecedent ows in dryland rivers are species and river speci c. River Res Appl 30:12571268Bates D, Maechler M, Bolker B, Walker S, Christensen RHB, Singmann H, Dai B, Scheipl F, Grothendieck G, Green P, Fox J (2018) Linear mixed-e ects models using Eigen and S4. R Package lme4.://cran.r-project.org/web/packages/lme4/. Accessed 26 Nov 2018Bishop KA, Allen SA, Pollard DA, Cook MG (2001) Ecological studies on the freshwater shes of the Alligator rivers region, northern territory: autecology. supervising scientist report 145, Supervising scientist, DarwinBlanck A, Lamouroux N (2007) Large scale intraspeci c variation in l
6 ife history traits of European freshwate
ife history traits of European freshwater sh. J Biogeogr Bolger T, Connolly PL (1989) The selection of suitable indices for the measurement and analysis of fish condition. J Fish Biol Cattau CE, Fletcher RJ Jr, Kimball RT, Miller CW, Kitchens WM (2018) Rapid morphological change of a top predator with the invasion of a novel prey. Nat Ecol Evol 2:108115Cooper WJ, Carter CB, Conith AJ, Rice AN, Westneat MW (2017) The evolution of jaw protrusion mechanics is tightly coupled to bentho-pelagic divergence in damsel shes (Pomacentridae). J Exp Biol 220:652666Crook DA, Buckle DJ, Allsop Q, Baldwin W, Saunders TM, Kyne PM, Woodhead JD, Maas R, Roberts B, Douglas MM (2017) Use of otolith chemistry and acoustic telemetry to elucidate migratory contingents in barramundi Lates calcarifer. Mar Freshw Res 68:15541566Davis TLO (1985) The food of barramundi, Lates calcarifer (Bloch), in coastal and inland waters of Van Diemen Gulf and the Gulf of Carpentaria, Australia. J Fish Biol 26:669682Des Roches S, Post DM, Turley NE, Bailey JK, Hendry AP, Kinnison MT, Schweitzer JA, Palkovacs EP (2018) The ecological importance of intraspeci c variation. Nat Ecol Evol 2:5764Detmer TM, Einfalt LM, Parkos JJ, Wahl DH (2018) Comparison of mouth morphology and prey size selection among three esocid taxa. Environ Biol Fish 101:110Ebner BC, Morgan DL, Kerezsy A, Hardie S, Beatty SJ, Seymour JE, Donaldson JA, Linke S, Peverell S, Roberts D, Espinoza T (2016) Enhancing conservation of Australian freshwater ecosystems: identi cation of freshwater agship shes and relevant target audiences. Fish Fish 17:11341151Ehlinger TJ, Wilson D (1988) Complex foraging polymorhphism in bluegill sun sh. Proc Natl Acad Sci 85:18781882Forsman A (1996) Body size and net energy gain in gape-limited predators: a model. J Herpetol 30:307319Forsman A, Shine R (1997) Rejection of non-adaptive hypotheses for intraspeci c variation in trophic morphology in gape-limited predators. Biol J Linn Soc 62:209223Gatz AJ (1979) Ecological morphology of freshwater stream shes. Tulane Stud Zool Bot 21:91124Gerking SD (1994) Feeding ecology of fish. Academic Press, CaliforniaHall ES, Martin BE, Brubaker K, Grant CJ (2018) Latitudinal variation in the geometric morphology of the largemouth bass, Micropterus . Mar Freshw Res 69:14801485Hambright KD (1991) Experimental analysis of prey selection by largemouth bass: role of predator mouth width and prey body depth. Trans Am Fish Soc 120:500508Hobson ES (1979) Interactions between piscivorous shes and their prey. In: Clepper H, Stroud RH (eds) PredatorPrey systems in sheries management. Sport Fishing Institute, DC, pp 231242Hoeinghaus DJ, Winemiller KO, Layman CA, Arrington DA, Jepsen DB (2006) E ects of seasonality and migratory prey on body Cichla species in a tropical oodplain river. Ecol Freshw Fish 15:398407Jakob EM, Marshall SD, Uetz GW (1996) Estimating tness: a comparison of body condition indices. Oikos 77:6167Jardine TD, Pettit NE, Warfe DM, Pusey BJ, Ward DP, Douglas MM, Davies PM, Bunn SE (2012) Consumerresource coupling in wetdry tropical rivers. J Anim Ecol 81:310322Juanes F (1994) What determines prey size selectivity in piscivorous shes? In: Stouder DJ, Fresh KL, Feller R (eds) Theory and application in sh feeding ecology. University of South Carolina Press, South Carolina, pp 77100Juanes F, Buckel JA, Scharf FS (2002) Feeding ecology of piscivorous shes. In: Hart P, Reynolds JD (eds) Handbook of sh biology and sheries: sh biology, 1st edn. Blackwell Scienti c, Oxford, pp 267283 Oecologia Karpouzi VS, Stergiou KI (2003) The relationships between mouth size and shape and body length for 18 species of marine shes and their trophic implications. J Fish Biol 62:13531365Kennard MJ, Pusey BJ, Olden JD, Mackay SJ, Stein JL, Marsh N (2010) Classi cation of natural ow regimes in Australia to support environmental ow management. Freshw Biol 55:171193Kristjánsson B, Skúlason S, Noakes DLG (2002) Rapid divergence in a recently isolated population of threespine stickleback (Gasterosteus aculeatus L.). Evol Ecol Res 4:659672Kuznetsova A, Brockho PB, Christensen RHB (2018) Tests in linear mixed e ects models. R package lmerTest. ://cran.r-project.org/web/packages/lmerTest/. Accessed 26 Nov 2018Magnhagen C, Heino E (2001) Gape size allometry in pike re ects variation between lakes in prey availability and relative body depth. Funct Ecol 15:7547
7 62Maret TJ, Collins JP (1996) E ect of p
62Maret TJ, Collins JP (1996) E ect of prey vulnerability on population size structure of a gape-limited predator. Ecology 77:320324McGill BJ, Enquist BJ, Weiher E, Westoby M (2006) Rebuilding community ecology from functional traits. Trends Ecol Evol Messier J, McGill BJ, Lechowicz MJ (2010) How do traits vary across ecological scales? A case for trait-based ecology. Ecol Lett Miehls AL, Peacor SD, McAdam AG (2014) Gape-limited predators as agents of selection on the defensive morphology of an invasive invertebrate. Evolution 68:26332643Mihalitsis M, Bellwood DR (2017) A morphological and functional basis for maximum prey size in piscivorous shes. PLoS One Nilsson PA, Brönmark C (2000) Prey vulnerability to a gape-size limited predator: behavioural and morphological impacts on northern pike piscivory. Oikos 88:39546Norin T, Clark TD (2017) Fish face a trade-o between eating big for growth eciency and eating small to retain aerobic capacity. Biol Lett 13:20170298Norton SF (1995) A functional approach to ecomorphological patterns of feeding in cottid shes. Environ Biol Fish 44:6178Peig J, Green AJ (2009) New perspectives for estimating body condition from mass/length data: the scaled mass index as an alternative method. Oikos 118:18831891Persson L, Andersson J, Wahlstrom E, Eklov P (1996) Size-speci c interactions in lake systems: predator gape limitation and prey growth rate and mortality. Ecology 77:900911Pettit NE, Naiman RJ, Warfe DM, Jardine TD, Douglas MM, Bunn SE, Davies PM (2017) Productivity and connectivity in tropical riverscapes of northern Australia: ecological insights for management. Ecosystems 20:492514Phillips B, Shine R (2004) Adapting to an invasive species: toxic cane toads induce morphological change in Australian snakes. Proc Natl Acad Sci 101:1715017155Pope KL, Kruse CG (2007) Condition. In: Guy CS, Brown ML (eds) Analysis and interpretation of freshwater sheries data. American Fisheries Society, Maryland, pp 423471Pusey B, Kennard M, Arthington A (2004) Freshwater shes of northeastern Australia. CSIRO publishing, AustraliaR Development Core Team (2019) R: a language and environment for statistical computing. See http://www.r-project.org. Accessed 26 Nov 2018Saunders T, Whybird O, Newman S (2018) Status of key northern territory sh stocks report 2016. Northern territory government. Department of primary industry and resources. http://www. sh.gov.au/report/7-Barra. Accessed 30 Nov 2018Scharf FS, Juanes F, Rountree RA (2000) Predator sizeprey size relationships of marine sh predators: interspeci c variation and e ects of ontogeny and body size on trophic niche breadth. Mar Ecol Prog Ser 208:229248Schmitt RJ, Holbrook SJ (1984) Gape-limitation, foraging tactics and prey size selectivity of two microcarnivorous species of sh. Oecologia 63:612Sutton SG, Bult TP, Haedrich RL (2000) Relationships among fat weight, body weight, water weight, and condition factors in wild Atlantic salmon parr. Trans Am Fish Soc 129:527538Urban MC (2007) The growthpredation risk trade-o under a growing gape-limited predation threat. Ecology 88:25872597Vatland S, Budy P (2007) Predicting the invasion success of an introduced omnivore in a large, heterogeneous reservoir. Can J Fish Aquat Sci 64:13291345Villéger S, Brosse S, Mouchet M, Mouillot D, Vanni MJ (2017) Functional ecology of sh: current approaches and future challenges. Aquat Sci 79:783801Violle C, Navas ML, Vile D, Kazakou E, Fortunel C, Hummel I, Garnier E (2007) Let the concept of trait be functional! Oikos Violle C, Enquist BJ, McGill BJ, Jiang LIN, Albert CH, Hulshof C, Jung V, Messier J (2012) The return of the variance: intraspeci c variability in community ecology. Trends Ecol Evol 27:244252Voshikawa T, Higuchi H (2018) Invasion of the loquat Eriobotrya into urban areas of central Tokyo facilitated by crows. Ornithol Sci 17:165172Warfe DM, Pettit NE, Davies PM, Pusey BJ, Hamilton SK, Kennard MJ, Towsend SA, Bayliss P, Ward DP, Douglas MM, Burford MA, Finn M, Bunn SE, Halliday IA (2011) The wetdry in the wetdry tropics drives river ecosystem structure and processes in northern Australia. Freshw Biol 56:21692195Winemiller KO, Jepsen DB (1998) E ects of seasonality and sh movement on tropical river food webs. J Fish Biol 53:267296Xiao Y (2000) Use of the original von Bertalan y growth model to describe the growth of barramundi, Lates calcarifer (Bloch). Fish Bull