Temporal clumping of prey and coexistence of unequal interferers: experiments on social forager groups of brown trout feeding on invertebrate drift

Environmental fluctuations have been proposed to enhance the coexistence of competing phenotypes. Evaluations are here presented on the effects of prey density and short‐term temporal clumping of prey availability on the relative foraging success of unequal interferers in social forager groups of juvenile brown trout Salmo trutta feeding on drifting invertebrate prey (frozen chironomids). Groups of three trout with established linear dominance hierarchies (dominant, intermediate and subordinate) were subjected to three different total numbers of prey, combined with three different levels of temporal clumping of prey arrival, resulting in nine treatment combinations. Higher total number of prey increased the consumption for all dominance ranks, while higher temporal clumping decreased the consumption for the dominant individuals and increased the consumption for the subordinate individuals. The proportion of prey eaten was smaller at high prey numbers. Similarly, there was a trend that increased temporal clumping also decreased the proportion of prey eaten. We conclude that density and temporal clumping of prey contribute to the coexistence of unequal interferers, and that there is a potential positive feedback between prey behaviour and phenotypic coexistence through decreased per capita predation risk for prey that drift synchronously in high densities.     

The Causes of Resource Monopolization: Interaction Between Resource Dispersion and Mode of Competition

The degree of monopolization of resources is thought to be higher in groups that compete by interference than by exploitation. However, the monopolization of resources will presumably depend on (1) whether the dispersion of resources is economically defendable, and (2) whether some competitors have the ability to defend these resource distributions and hence capitalize on this potential. We tested for an interaction between the effects of temporal resource dispersion and aggressiveness on the degree of resource monopolization in a foraging system. Two species of fish differing markedly in aggressiveness (high: convict cichlids, Archocentrus nigrofasciatus; low: goldfish, Carrasius auratus) were allowed to compete intra‐specifically in groups of four for food that was either potentially defendable (arrived asynchronously) or not (arrived synchronously). As predicted, the monopolization of food, measured as the coefficient of variation of food eaten within groups, was significantly higher in the defendable than in the undefendable treatment for convict cichlids but not for goldfish. However, the monopolization of food was higher in the non‐aggressive goldfish than in the aggressive convict cichlids. Future studies should quantify and compare the monopolization in species that compete primarily via scramble competition to those that use primarily resource defence.     

The caudal appendage of the cladoceran Bythotrephes cederstroemi as defense against young fish

Rainbow trout (Onchorhynchus mykiss), 40–80 mm in length,were fed the cladoceran Bythotrephes cederstroemi with and withoutits caudal appendage (spined or despined) to determine if theappendage makes ingestion of the zooplankter difficult for smallfish. Handling time was measured as the period of opercularand buccal activity as fish ingested prey. In 980 observationsfor 13 trout, fish spent 8 s longer or 800% more time handlingspined Bythotrephes than despined. Fish ultimately rejectedsignificantly more spined prey than despined prey. Average handlingtimes of spined prey were negatively correlated with fork lengthand smaller fish rejected spined prey more often. All fish handleddespined prey equally well. Eight of 13 fish changed their handlingefficiency over time. However, only two fish decreased handlingtime on spined prey, while two fish increased handling timeon spined prey. Four fish decreased their handling time on despineditems. Bythotrephes' caudal appendage increases the likelihoodthat it will be rejected after capture by fish and decreasesfish predation rate by increasing handling time. This is newevidence of a freshwater zooplankter having a structural defenseeffective against young fish. Present address: Department of Biological Sciences, Lake SuperiorEcosystems Research Center, Michigan Technological University,Houghton, Ml 49931, USA     

The effects of turbidity and an invasive species on foraging success of rosyside dace (Clinostomus funduloides)

1.  Habitat degradation and biological invasions are important threats to fish diversity worldwide. We experimentally examined the effects of turbidity, velocity and intra- and interspecific competition on prey capture location, reactive distance and prey capture success of native rosyside dace ( Clinostomus funduloides ) and invasive yellowfin shiners ( Notropis lutipinnis ) in Coweeta Creek, North Carolina, U.S.A.
2.  Increased turbidity and velocity produced significant decreases in the number of prey captured forward of the fish's location. It is possible that this represents an increase in the amount of energy expended per prey captured.
3.  We used Akaike's Information Criterion (AIC) to evaluate competing explanatory models for reactive distance (10 generalised linear models, GLM) and prey capture success (9 generalised linear mixed models, GLMM).
4.  Reactive distance decreased by 12% with an increase from 2 to 4 conspecifics, whereas a 10 NTU increase in turbidity reduced reactive distance by 9%. Capture success was affected by velocity, dominance and competition, and varied among species. A 6 cm s⁻¹ increase in velocity produced a 28% decline in capture probability; however, dominant fish were 3.2 times more likely to capture a prey item than non-dominant fish. Yellowfin shiners only were 0.62 times as likely to capture a prey item as rosyside dace. Both intra- and interspecific competition reduced capture probability, and fish in high density intraspecific or interspecific trials were 0.46 times and 0.44 times as likely to capture prey, respectively, as fish in two fish intraspecific trials.
5.  These results suggest behavioural variables are as important as physical factors in determining reactive distance and capture probability by these minnows.     

Visual isolation furthers access to drift‐feeding positions for subordinate juvenile brown trout (Salmo trutta) in dominance hierarchies

Juvenile salmonids are visual predators that primarily feed on drifting invertebrates and compete for suitable feeding positions in swift water. We used an outdoor experimental stream to test the effect of visual isolation on agonistic interactions and habitat use by age‐1 brown trout ( Salmo trutta ) in riffle‐pool sections. We hypothesized that dominant fish defend suitable feeding positions in riffle and that visual obstruction between individuals enhance access to riffle for subordinates. Groups of juveniles, caught in the wild, were stocked in high and low visibility treatments. Visual isolation was manipulated by placing dark plastic ribbons or opaque Plexiglas boards onto the substrate of riffles. As expected, dominant fish held profitable positions in riffle and the proportion of fish in riffle significantly increased in presence of artificial structures. In high visibility treatment, the dominant fish despotically excluded subordinates from the riffle. In low visibility treatment, the proportion of fish that foraged on benthic prey in the pool and the number of major aggressive acts (chase, nip) decreased. Our results support the hypothesis that screening effect of physical structures in the water column loosen resource monopolization in dominance hierarchies of juvenile salmonids.     

Diel activity and home range size in relation to food supply in a drift-feeding stream fish

Individuals within a species often compete for resources inboth space and time. In dominance hierarchies individuals withthe greatest competitive ability will occupy prime locationsduring optimal periods. We compared spatial and temporal useof habitat, aggression, and feeding success among giant kokopu(Galaxias argenteus) in dominance hierarchies under normal andreduced food supply. Under normal food supply conditions dominantfish were predominantly nocturnal and maintained large homeranges at night. Conversely, subdominant fish were diurnal andoccupied large home ranges by day but were generally not observedat night. When the food supply was limited, the utilizationof pools was determined by social rank. Dominant fish from eachpool increased diurnal activity, home range size, aggressiveness,and the capture of food items offered by day while simultaneouslyreducing the spatial and temporal activity and habitat use ofsubdominant fish. These results indicate that behavioral changesin large dominant fish influence and reduce the amount of resourcesavailable to subdominant fish.     

Superfluous killing in spiders: a consequence of adaptation to food-limited environments?

The hypothesis that superfluous killing, partial consumption,and abandonment of prey is a consequence of adaptation to food-limited environments was tested in two feeding trials on a desert spider, Agelenopsis aperta. First, we made comparisons among populations inhabiting sites of high prey (HP) or low prey (LP) availabilitythat differed in their degree of genetic isolation. Typically,A. aperta entirely consumed one or two of the prey items itcaptured in a feeding bout. Additional prey were partiallyconsumed or abandoned without eating. Spiders from the geneticallyisolated HP population, however, captured fewer prey and showeda higher incidence of full feeding on prey than did individualsfrom the other populations. Only one spider from this populationcaptured a prey item that it failed to feed on, whereas spidersfrom LP populations failed to feed on high numbers of capturedprey. The greatest variability in feeding behavior was exhibitedin the HP population that experienced gene flow. The secondtest was based on the finding that aggressiveness is largelya sex-linked trait in A. aperta: the aggressiveness of thefemale parent only is inherited by male offspring, whereasboth parents contribute to this trait in female offspring.All female F₁ hybrids between LP and HP parental types exhibitedhigh levels of superfluous killing, as did male F₁ hybridsderived from LP females. F₁ hybrid males derived from HP femalesexhibited extremely low levels of superfluous killing. Superfluouskilling thus has its basis in the genetic control of levelsof aggression.     

Velocity and dominance affect prey capture and microhabitat selection in juvenile Chinook (<Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>)

Habitat selection is an important phenomenon that may greatly affect individual fitness. Using an artificial stream, we examined the relationship between the percentage of prey captured, reactive distance, dominance, and water velocity for juvenile Chinook Salmon (Oncorhynchus tshawytscha) from the Chena River, Alaska, and tested the fitness-based microhabitat selection model of Grossman et al. (Ecol Freshw Fish 11:2–10, 2002). Recent declines in the abundance of Chinook accentuate our need for habitat selection studies on this species. We conducted three experiments: two with single fish (1st N?=?27, fish SL 58–84 mm, 2nd N?=?14, fish SL 49–56 mm) and one with pairs of dominant and subordinate fish (N?=?10 pairs, 64–96 mm, mean difference in SL?=?7 mm). We placed individual or pairs of fish in an artificial flume and recorded reactive distance and the percent prey capture with individual dead brine shrimp (Artemia spp.) as prey. Prey were presented at 10 cm/s velocity intervals ranging from 10 to 60 cm/s; velocities found in the natural habitat. Mean reactive distance in single fish experiments (henceforth SFE) averaged 33 and 29 cm respectively, and was not related to velocity. We detected a negative, curvilinear relationship between velocity and percent prey capture. Holding velocities for juvenile Chinook were significantly lower than prey capture velocities. The Grossman et al. (Ecol Freshw Fish 11:2–10, 2002) model yielded an optimal focal-point velocity prediction of 35 cm/s for juvenile Chinook, however focal-point velocities occupied by juveniles in the Chena River averaged 12 cm/s. Predicted optimal velocities were present in the Chena River; hence, this discrepancy suggests that other factors such as distraction from drifting debris or predation risk influenced habitat selection. There were no differences in reactive distances or holding velocity/capture velocity relationships for dominant and subordinate fish; however, dominants captured significantly more prey than subordinates. Being subordinate resulted in a decrease of 61% in mean percent prey capture (the difference between what was captured by the fish alone versus the difference with a dominant), whereas the mean cost to fish with dominant rank was a 21% decline between the percentage captured alone versus that with a subordinate.     

Fish-induced sediment resuspension: effects on phytoplankton biomass and community structure in a shallow hypereutrophic lake

An in situ mesocosm experiment was performed at Old Woman CreekEstuary, OH, to assess the importance of fish-induced sedimentresuspension in regulating phytoplankton biomass and communitystructure Six polyethylene tubes (1 m diameter x 2 m long) wereplaced into the lake, enclosing portions of the water columnand sediments Three duplicated treatments were established:(i) control, no fish, (ii) fish, stocked with small fish fromthe lake; and (iii) fish/net, stocked with fish, but into tubeswith coarse nets suspended above the sediments to prevent resuspension.Total P concentrations and algal biomass in the fish tubes becamemarkedly higher than the fish/net and control tubes. Centricdiatoms and small cryptomonads were the initial dominants. Inthe lake and fish tubes, this community was replaced by nanochlorophytes.In the fish/ net and control tubes, a very different successionoccurred, where large cryptomonads became dominant These resultsindicate that sediment nutrient resuspensions by fish activitiescan maintain a phytoplankton community in an immature state,with small r-selected dominants. When sediment nutrient resuspensionwas prevented (in the fish/net and control tubes), larger algalspecies increased in relative biovolume, regardless of whetherfish were present.     

Warning coloration associated with nematocyst-based defences in aeolidiodean nudibranchs

This study examines the mechanisms of aposematism (unprofitabilityof prey combined with a conspicuous signal) in the aeolidioideanCratena peregrina (Gmelin, 1791). We investigated if marinefish avoid attacking aeolidioidean nudibranchs, which are anunprofitable group of prey for most predators. We analysed theinteraction between aeolids and predatory fish in laboratoryand field assays, with both live aeolids and artificial models.In the first experiment, we offered normal and blue-dyed C.peregrina to fish in the field. The number of attacks by fishwas independent of the density of the prey, albeit the normalaeolids were attacked less frequently than the blue ones. Thefact that all normal C. peregrina survived, whereas 12–20%of the blue aeolids died after fish attacks, suggests that aposematiccoloration provides a selective advantage against fish predators.Field and laboratory assays with artificial aeolids were employedto test the effects of different factors (number of cerata,colour pattern, nematocysts), or a combination of factors, onfish learning. Fish learned to avoid unpalatable models withthe colour pattern of C. peregrina. After three to four trainingsessions with unprofitable models, fish avoided profitable modelswith the same colour pattern. Our results suggest that the colourpattern of C. peregrina combined with the presence of dorsalappendages and nematocysts make fish avoid aeolids. (Received 22 January 2004; accepted 18 August 2006)     

Predation impact of age-0 fish on a copepod population in a Baltic Sea inlet as estimated by two bioenergetics models

Decreasing spring abundances of the copepod Eurytemora affinis,in a shallow brackish inlet of the Baltic Sea, were comparedwith calculated consumption of age-0 fish [dominant speciesherring (Clupea harengus) and perch (Perca fluviatihs)] as determinedby two bioenergetics models. Fish and zooplankton populationswere sampled at three stations along a salinity gradient of0.3-8.1% maximum range. Larvae and juveniles of both fish speciespreferred to prey on adults and developmental stages of E.affinis.Although there were substantial variations in fish density andcopepod production across the salinity range, consumption ofzooplankton by age-0 fish was never high enough to be a majorsource of copepod mortality.This finding is an independent confirmationof previous results obtained by direct food-intake measurementsin the same region. The low impact of fish predation may bea function of the low individual fish biomass in spring, theincreased copepod production and the dominance of the less planktivorousperch, rather than herring, in the less saline waters of theBarther Strom inlet.     

Ontogenetic and gender-related variation in the isotopic niche within and between three species of fur seals (genus <Emphasis Type="Italic">Arctocephalus</Emphasis>)

Differences in aggressiveness when competing for environmental resources are the main factor leading to social hierarchy in group living fish. Social status acquired is related to changes in physiological parameters, as metabolic rate. Habitat variation can interfere with aggressive behaviour and promote changes in physiological parameters associated with social status. The primary goal of our study was to investigate how differences in habitat complexity affect the relationship between resting metabolic rate (RMR) and social status in the Amazonian dwarf cichlid Apistogramma agassizii. We compared agonistic interactions between pairs of males in aquaria with different habitat enrichment levels, manipulated by adding shelters. RMR was measured before and after hierarchy establishment. Habitat enrichment promotes changes in aggressive behaviour and influences differences in metabolic rate between dominant and subordinate fish. We observed an increase in biting by dominant fish at high enrichment habitat, which could be related to the increase in territory value. We observed an increase in metabolic rate in dominant fish after hierarchy establishment. However, it occurs only in enriched habitats. We concluded that habitat structure interfere with behavioural characteristics in social hierarchies, as aggressiveness, and changes in aggressive interactions affect metabolic rate in different social ranks in the dwarf cichlid Apistogramma agassizii.     

Scaling of the variance and the quantification of resource monopolization

Behavioral and evolutionary ecologists often attempt to quantifymonopolization of mates or food items using indices such asthe variance, the coefficient of variation (CV), the coefficientof dispersion (CD), or the opportunity for selection (I). Becauseof the tendency for the variance to increase with the mean andbecause of the relationship between variance and the numberof competitors, such indices are of limited value for comparisonsbetween systems that differ in the mean number of resourcesper competitor or in the number of competitors. Here we examinean alternative index of relative monopolization, Q in whichthe observed variance in resource distribution is expressedas a fraction of the maximum possible variance (assuming discreteresource items) for a given resource abundance, both correctedby an estimate of the variance expected under a random distributionof resources. Q = 1 when the variance in resource distributionis maximum, and Q = 0 when resources are randomly distributed.We demonstrate analytically that (1) on average, Q is independentof mean resource abundance for overdispersed systems and, (2)Q can be used to compare systems with different numbers of competitorsas long as the total number of resource units is not largerthan the number that can be monopolized by a single individual.We illustrate the advantages of this method using data fromstudies on feeding competition in fish and on mating competitionin crickets.     

Characteristics of reaction field and the reactive distance of a planktivore, Pseudorasbora parva (Cyprinidae), in various environmental conditions

The characteristics of the reaction field and the reactive distance of the Stone moroko (Pseudorasbora parva) were studied under three environmental conditions (structural complexity, light intensity and turbidity) and three prey sizes. In optimal experimental conditions, under no structural complexity, light intensity of 200 lux and turbidity less than 1 NTU (Nephelometric Turbidity Units), the cross-section of the reaction field was found to be elliptic with a bearing angle larger than the elevation angle, but both angles changed slightly depending on environmental conditions. The reactive distance was large, and the fish frequently attacked prey that was located within 15–60 degrees to each side from the frontal direction of a fish (i.e., ± 15 degrees from the axis of the fish body) horizontally. In the light intensity below 50 lux or turbidity above 10 NTU, however, the attack frequency and the reactive distance in the frontal direction of a fish did not differ from other horizontal directions in the reaction field. The average reactive distance increased proportionally with increasing strand distance, but it gradually reached a constant value for strand distances greater than about 3.6 times the fish body length. The average reactive distance increased in the light intensity range of 10–200 lux and decreased negatively with turbidity increasing. The average reactive distance increased with larger prey size, but the rate of increase of the reactive distance gradually decreased.     

The use of territorial gardening versus kleptoparasitism by a subtropical reef fish (Kyphosus cornelii) is influenced by territory defendability

Many territorial herbivorous animals increase the productivityor quality of the prey community on their territory. However,this gardening tactic may be vulnerable to kleptoparasitismunless gardeners can exclude others from the patch. We investigatedthe influence of territory defendability on the decision ofwestern buffalo bream (Kyphosus cornelii) to defend an algalgarden or to leave their territories and invade those of conspecifics.Fish monitored while away from their territories did kleptoparasitizethe gardens of conspecifics. We manipulated the structural complexityof territories through the addition of short or tall simulatedvegetation. Increasing the height of simulated vegetation onthe territory decreased the defendability of territories butincreased their safety for fish; territories with tall vegetationwere more easily invaded by conspecifics, but fish returnedmore rapidly to these territories after being disturbed. Ina paired experiment, fish spent more time away from their territories(roving) when tall vegetation was added than when short vegetationwas added. However, this effect was influenced by depth, witha greater difference between treatments on deeper territories,and by body size, with a greater difference for larger fish.These results support the prediction that territory-holdingindividuals faced with a trade-off between defending their owngarden or kleptoparasitizing from others adjust their use ofthese tactics based on the defendability of resources.     

Kleptoparasitic prey competition in shoaling fish: effects of familiarity and prey distribution

Familiarity is thought to stabilize dominance hierarchies andreduce aggressive interactions within groups of socially livinganimals. Though familiarity has been widely studied in shoalingfish, few studies have investigated changes in prey competitionas a function of time spent together within groups of initiallyunfamiliar individuals. In this study, we created shoals ofthree-spined stickleback (Gasterosteus aculeatus) and monitoredchanges in foraging rates and related competitive behaviorswithin shoals over a 4-week period in experimental series whereprey was spatially and temporally concentrated or dispersed.Prey share was unequal under both prey distribution modes, anddisparity in prey share was not seen to change as trials progressed.Interestingly, the contest rate for prey items fell over timewhen individuals were competing for dispersed prey but not whenprey were concentrated. We found no evidence that fish showedassociation preferences for either group members that had consumeda greater or lesser proportion of prey during trials. Thoughthe intensity of competition may be reduced by increased groupstability in nature, this is likely to be strongly dependenton the way prey resources are distributed through space andtime.     

Shadow competition in wild juvenile sea-trout

Shadow competition occurs in a group of sit-and-wait predators when those closer to a source of mobile prey reduce the feeding success of those further from the prey source. It was examined in territorial juvenile sea trout Salmo trutta in a small stream. The fry formed groups of two to six fish with adjacent territories and a social hierarchy within each group. It was hypothesized that: (i) as group size increased, the mean number of prey eaten per fish within a group decreased and the variability in prey consumption between fish increased; (ii) prey consumption by individual fish decreased with increasing distance from the food source; (iii) group size increased as the mean water velocity immediately upstream from a group, and hence potential drifting food, increased. Five groups of fry were fed on small shrimps released upstream from each group at a rate of one every 15 s over a 10 min period, this procedure being repeated over 5 days to provide five replicates per group. Experiments were performed three times in 1967, 1969 and 1974 to provide information on 45 groups of fry. The first and third hypotheses were supported, but the second was only partially supported. In 1967 and 1969, territory size and shrimp consumption by individual fry decreased with increasing distance from the food source. This also occurred in 1974, except during a critical period for survival when fry density was exceptionally high with large numbers of sea trout lacking territories. This resulted in sea trout fry with the largest territories eating fewer shrimps than those with medium-sized territories because they spent more time defending their territories against sea trout lacking territories. This study is the first to demonstrate shadow competition in a vertebrate species, but has also shown that territorial defence may modify the consequences of shadow competition when densities are high and there is strong competition for the acquisition of a territory.     

Effects of the temporal predictability and spatial clumping of food on the intensity of competitive aggression in the Zenaida dove

The spatial and temporal clumping of food influence an animal's aggressiveness during competition. No studies, however, haveinvestigated the effects of the temporal predictability offood and few studies have tested for interactions between theeffects of two components of resource distribution on the ratesof competitive aggression. We simultaneously manipulated the temporal predictability and the spatial clumping of food totest whether aggression increases as food becomes more predictablein time and more clumped in space. We tested these predictionsusing wild Zenaida doves (Zenaida aurita) in Barbados becauseprevious work showed marked differences in social behaviorbetween two populations, apparently related to differences in the distribution of food in space and time. There was a significant interaction between the effects of the temporal predictabilityand spatial clumping of food. As predicted, the rate of aggressionincreased as the temporal predictability of food increased,but only significantly in the spatially clumped condition.Similarly, as predicted, aggression increased as the spatialclumping of food increased, but only significantly in the temporallypredictable condition. In addition, the per capita rate of aggression peaked at intermediate competitor densities in thespatially clumped condition. Differences in rates of aggressionobserved during experimental manipulations and between thetwo populations during baseline observations were generallyconsistent with predictions of resource defense theory.     

Behavioural aspects of predation by juvenile Atlantic salmon (Salmo salar L.) on particulate,drifting prey

A recirculatory flume tank simulating a simplified stream environment was used to study the feeding behaviour of juvenile Atlantic salmon (Salmo salar L.), 5.1 to 9.4 cm in fork length (from tip of snout to fork of tail), on artificial particulate prey passively drifting in the water current. Changes in feeding behaviour at two different times of the year and when fish were presented with prey of different sizes are described and quantified. Responsiveness to food was greatly reduced in autumn as compared to summer. The maximum distances at which prey elicited a response decreased in autumn to 40% of the summer value, and the maximum distances which fish traversed in order to capture prey decreased by 80% over the same period. During the peak growing season, the response to a range of prey sizes from 0.013 to 0.102 × fish fork length was directly related to prey size and could be accounted for on the basis of visual theory alone. Capture distances were closely related to fixation distances. Maximum capture distance increased to a peak value for prey of between 0.025 and 0.069 × fork length, while larger prey were never captured and the smallest prey rarely evoked a response. Prey size selectivity also operated after capture, through rejection versus retention of the prey.     

Novel species interactions and environmental conditions reduce foraging competency at the temperate range edge of a range-extending coral reef fish

Poleward range extensions of coral reef species can reshuffle temperate communities by generating competitive interactions that did not exist previously. However, novel environmental conditions and locally adapted native temperate species may slow tropical invasions by reducing the ability of invaders to access local resources (e.g. food and shelter). We test this hypothesis on wild marine fish in a climate warming hotspot using a field experiment encompassing artificial prey release. We evaluated seven behaviours associated with foraging and aggressive interactions in a common range-extending coral reef fish (Abudefduf vaigiensis) and a co-shoaling temperate fish (Microcanthus strigatus) along a latitudinal temperature gradient (730 km) in SE Australia. We found that the coral reef fish had reduced foraging performance (i.e. slower prey perception, slower prey inspection, decreased prey intake, increased distance to prey) in their novel temperate range than in their subtropical range. Furthermore, higher abundance of temperate fishes was associated with increased retreat behaviour by coral reef fish (i.e. withdrawal from foraging on released prey), independent of latitude. Where their ranges overlapped, temperate fish showed higher foraging and aggression than coral reef fish. Our findings suggest that lower foraging performance of tropical fish at their leading range edge is driven by the combined effect of environmental factors (e.g. lower seawater temperature and/or unfamiliarity with novel conditions in their extended temperate ranges) and biological factors (e.g. increased abundance and larger body sizes of local temperate fishes). Whilst a future increase in ocean warming is expected to alleviate current foraging limitations in coral reef fishes at leading range edges, under current warming native temperate fishes at their trailing edges appear able to slow the range extension of coral reef fishes into temperate ecosystems by limiting their access to resources.