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Personality-dependent inter-and intraspecific foraging competition in the invasive round goby, Neogobius melanostomus
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Competition not only occurs between species, but (probably more importantly) also among individuals within species, especially, for species occurring in high densities and when resources are limiting. Fluctuating densities and dietary overlap may account for massive ecological and evolutionary changes in fish communities. We sampled a mixed juvenile (0+ stages, being younger than 1 year of age) fish community at the Lower Rhine over three consecutive years, including native and newly established species (~ 64,000 captured individuals and ~ 4200 dissected fish). Our aim was to develop a new approach in which data on density, individual consumption rates, and diet overlaps (both intra- and interspecific) solely originating from the natural environment, were used and combined to estimate species-specific competitive strengths within and between seasons and species. The juvenile fish community at the food-limited Rhine was dominated by invasive gobies. Species-specific consumption rates decreased depending on the dietary overlap with other juveniles. Two invasive gobies (Neogobius melanostomus and N. fluviatilis) showed the greatest competitive abilities, followed by a third invasive Gobiid species (Ponticola kessleri) and the native Aspius aspius, a species utilizing an exclusive food source. Both other native species (Perca fluviatilis and Sander lucioperca) had the lowest estimates of food-related competitive strength, indicating that these species are forced into a juvenile competitive bottleneck by the invasive gobies, before they finally can develop into successful predators on gobies later in life. Our new analytical approach to measure dietary competitive strength among individuals provides a powerful tool to empirically study eco-evolutionary feedback dynamics in the field.
Count data can be analyzed using generalized linear mixed models when observations are correlated in ways that require random effects. However, count data are often zero-inflated, containing more zeros than would be expected from the typical error distributions. We present a new package, glmmTMB, and compare it to other R packages that fit zero-inflated mixed models. The glmmTMB package fits many types of GLMMs and extensions, including models with continuously distributed responses, but here we focus on count responses. glmmTMB is faster than glmmADMB, MCMCglmm, and brms, and more flexible than INLA and mgcv for zero-inflated modeling. One unique feature of glmmTMB (among packages that fit zero-inflated mixed models) is its ability to estimate the Conway-Maxwell-Poisson distribution parameterized by the mean. Overall, its most appealing features for new users may be the combination of speed, flexibility, and its interface's similarity to lme4.
Few studies have systematically investigated mid- or long-term temporal changes of biological characteristics in invasive alien species considering the different phases of an invasion. We studied the invasion performance of one of the most invasive species worldwide, the round goby Neogobius melanostomus, from total absence over first occurrence until establishment from 2010 to 2015 in the upper Danube River. After an upstream movement of the invasion front of about 30 river km within four years, the pattern that round goby pioneering populations significantly differ from longer established ones has been confirmed: Pioneering populations at the invasion front comprised more females than males, and adult specimens with a larger body size compared to those at longer inhabited areas. On the population-level, the proportion of juveniles increased with time since invasion. The results of this study provide support for the previously postulated ´bigger is better´ and ´individual trait utility´ hypotheses explaining invasion success in round goby. Pioneering invaders with their greater exploratory behavior, highly adaptive phenotypic plasticity and increased competitive ability seem to act as prime emperors of new habitats, strongly following and benefiting from man-made river-bank structures.
Round goby Neogobius melanostomus is currently one of the most wide-ranging
invasive fish species in Europe and North America. The present study demonstrates how the distribution
of round goby has expanded from 2008 to 2013 at a rate of about 30 km yr−1 along the
Danish coastline in the western Baltic Sea. Further analyses showed that fish from an established
high-density round goby population were slow-growing and displayed poorer condition (weight
at age and hepatosomatic index) compared to fish sampled from recently invaded locations (i.e. at
the forefront of the distribution range). The established population revealed a broad age distribution
and a 1:1 gender ratio, while fish from a recently invaded site were primarily of intermediate
ages with a male-biased gender ratio. Otolith analyses suggested that the oldest individuals from
the recently invaded area experienced superior growth conditions only in the most recent years,
suggesting immigration into the area as adults. Our results suggest that intraspecific competition
for food may cause continued dispersal of the species and that population demographics likely
relate to invasion history
This report is based on data from the national Danish Fish Atlas projects (Atlas over danske ferskvandsfisk and Atlas over danske saltvandsfisk). It can be read as a contribution to our knowledge about the non-indigenous species (NIS) of fish and the Chinese mitten crab, Eriocheir sinensis, in Danish waters. The content can be used in a larger baseline-analysis. It is demonstrated that NIS of fish have a tendency to avoid detection by the current monitoring programs for aquatic biodiversity (NOVANA) and fisheries recourses (DTU Aqua/ICES). The main reason for this is that most of the species are (still) very rare, and that they live in shallow waters where the conventional monitoring is scarce. In the Fish Atlas database, 17 NIS of fish are included as occurring in Danish marine waters. Only the Round Goby is truly Invasive according to the criteria. It is by far the most abundant and important of the NIS of fish in Danish waters, and its biology is therefore included here in detail. The remaining 16 fish species have mostly been caught only a few times in Danish waters, and many are not able to establish populations at our latitudes. They are therefore not likely to become invasive. This is also the case for the otherwise abundant rainbow trout, which depends on continuous escapes from fish farms, in order to stay present in Danish waters. Several species are freshwater fishes that only occur in the brackish parts of our inner waters. Some of these are very common in Danish fresh water.
Different studies on the position of the non-indigenous species Neogobius melanostomus within the coastal food web of the Pomeranian Bay (western Baltic) were performed, resulting in a quantitative and qualitative species list of prey organisms found in the stomachs of the invader and an estimation concerning the importance of round goby as prey for different resident predators. It seems that the colonization process is not fully completed yet, but the results reveal that the species is already established in the food web 16 years after the first observation within the study area. The results show that N. melanostomus feed upon a wide range of different resident organisms. While a direct predation effect on native fish species appears rather unlikely, indirect effects such as competition cannot yet be excluded. In addition, our results reveal an ontogenetic diet shift and that the round goby itself already serves as an important prey for piscivorous fish and seabirds. Finally, we formulate different hypotheses based on our results which will require further research.
Animal personalities are an important factor that affects the dispersal of animals. In the context of aquatic species, dispersal modeling needs to consider that most freshwater ecosystems are highly fragmented by barriers reducing longitudinal connectivity. Previous research has incorporated such barriers into dispersal models under the neutral assumption that all migrating animals attempt to ascend at all times. Modeling dispersal of animals that do not perform trophic or reproductive migrations will be more realistic if it includes assumptions of which individuals attempt to overcome a barrier. We aimed to introduce personality into predictive modeling of whether a nonmigratory invasive freshwater fish (the round goby, Neogobius melanostomus) will disperse across an in-stream barrier. To that end, we experimentally assayed the personalities of 259 individuals from invasion fronts and established round goby populations. Based on the population differences in boldness, asociability, and activity, we defined a priori thresholds with bolder, more asocial, and more active individuals having a higher likelihood of ascent. We then combined the personality thresholds with swimming speed data from the literature and in situ measurements of flow velocities in the barrier. The resulting binary logistic regression model revealed probabilities of crossing a barrier which depended not only on water flow and fish swimming speed but also on animal personalities. We conclude that risk assessment through predictive dispersal modeling across fragmented landscapes can be advanced by including personality traits as parameters. The inclusion of behavior into modeling the spread of invasive species can help to improve the accuracy of risk assessments.
We review empirical studies on how bioinvasions alter food webs and how a food-web perspective may change their prediction and management. Predation is found to underlie the most spectacular damage in invaded systems, sometimes cascading down to primary producers. Indirect trophic effects (exploitative and apparent competition) also affect native species, but rarely provoke extinctions, while invaders often have positive bottom-up effects on higher trophic levels. As a result of these trophic interactions, and of nontrophic ones such as mutualisms or ecosystem engineering, invasions can profoundly modify the structure of the entire food web. While few studies have been undertaken at this scale, those that have highlight how network properties such as species richness, phenotypic diversity, and functional diversity, limit the likelihood and impacts of invasions by saturating niche space. Vulnerable communities have unsaturated niche space mainly because of evolutionary history in isolation (islands), dispersal limitation, or anthropogenic disturbance. Evolution also modulates the insertion of invaders into a food web. Exotics and natives are evolutionarily new to one another, and invasion tends to retain alien species that happen to have advantage over residents in trophic interactions. Resident species, therefore, often rapidly evolve traits to better tolerate or exploit invaders—a process that may eventually restore more balanced food webs and prevent extinctions. We discuss how network-based principles might guide management policies to better live with invaders, rather than to undertake the daunting (and often illusory) task of eradicating them one by one.
The invasion success of introduced species may be limited by competitive interactions with phylogenetically unrelated invaders. The round goby (Neogobius melanostomus) and spinycheek crayfish (Orconectes limosus) are invasive benthic predators that occupy and defend similar cryptic microhabitats, and thus may compete for shelter. The round goby expanded throughout the North American Great Lakes within 8 years of introduction, whereas another 6 years passed before it had spread through the upper St. Lawrence River. Here, we explore the premise that dense established populations of the invasive spinycheek crayfish slowed round goby colonization of the St. Lawrence River. We performed a series of videotaped laboratory experiments to determine if round gobies suffer from aggressive attacks or alter their behaviour (e.g. use of shelter and movement) in the presence of spinycheek crayfish. We also assessed the prolonged effects of food and shelter competition by comparing changes in the submerged mass of juvenile round gobies and spinycheek crayfish in conspecific and heterospecific pairs. Contrary to our predictions, round gobies more frequently initiated aggressive encounters with spinycheek crayfish, whereas the crayfish were more likely to flee or be evicted from their shelters. Furthermore, round gobies gained more body mass than spinycheek crayfish, regardless of conspecific or heterospecific pairing. Rather than impeding round goby colonization, spinycheek crayfish appear more likely to suffer energetic costs and an increased exposure to predation in the presence of round gobies.
The round goby Neogobius melanostomus has recently invaded several major freshwater systems in Europe and North America. Despite numerous studies predicting an impact on native fish assemblages, few have attempted to demonstrate it. In this case study, we monitored the effect of N. melanostomus colonisation on abundance and habitat utilisation of both young-of-the-year (YOY) native fish and YOY western tubenose goby Proterorhinus semilunaris in a typical, medium-sized European river. Colonisation by N. melanostomus had no apparent effect on either native fish abundance and species richness or P. semilunaris abundance. Moreover, after colonisation, both native fish and P. semilunaris occupied similar niches (i.e. microhabitats) to those occupied before colonisation. While niche use of YOY N. melanostomus and P. semilunaris overlapped significantly, YOY native fish utilised different habitats from the gobiids. We suggest that N. melanostomus did not compete for resources with YOY fish in our study area due to lack of niche overlap and/or surplus resources. As N. melanostomus rapidly dominated the fish assemblage at our site, we further suggest that utilisation of an empty niche, rather than competitive superiority, was the main factor facilitating its success.
Invasive species are one of the greatest threats to biodiversity worldwide, and to successfully manage their introductions is a major challenge for society. Knowledge on the impacts of an invasive species is essential for motivating decision makers and optimally allocating management resources. We use a prominent invasive fish species, the round goby (Neogobius melanostomus) to objectively quantify the state of scientific knowledge on its impacts. Focusing on how native fish species are affected by round goby invasions, we analyzed 113 peer-reviewed papers and found that impacts are highly ecosystem and time scale dependent. We discovered round goby impacts to be profound, but surprisingly complex. Even if identical native species were affected, the impacts remained less comparable across ecosystems than expected. Acknowledging the breadth but also limitations in scientific knowledge on round goby impacts would greatly improve scientists' ability to conduct further research and inform management measures.
Biological invasions cause major ecological and economic costs in invaded habitats. The round goby Neogobius melanostomus
is a successful invasive species and a major threat to the biodiversity and ecological function of the Baltic Sea. It is
native to the Ponto-Caspian region and has, via ballast water transport of ships, invaded the Gulf of Gdansk in Poland. Since
1990, it has spread as far north as Raahe in Northern Finland (64°41´04”N, 24°28´44”E). Over the past decade, consistent individual
differences of behavioral expressions have been shown to explain various ecological processes such as dispersal, survival
or reproduction. We have previously shown that new and old populations differ in personality trait expression. Individuals in new
populations are bolder, less sociable and more active than in old populations. Here we investigate if the behavioral differentiation
can be explained by phenotype-dependent dispersal. This was investigated by measuring activity, boldness and sociability of individually
marked gobies, and subsequently allowing them to disperse in a system composed of five consecutive tanks connected
by tubes. Individual dispersal tendency and distance was measured. Our results revealed that in newly established populations,
more active individuals disperse sooner and that latency of a group to disperse depends on the mean sociability of the group. This
indicates the presence of personality dependent dispersal in this species and that it is maintained at the invasion front but lost as
the populations get older [Current Zoology 61 (3): 529–542, 2015].
The successful establishment and expansion of invasive species may be linked to the behavior and dispersal tendency of individuals within an introduced population. To test the prediction that the boldest individuals, with the greatest dispersal tendency would be concentrated in the area of active range expansion, we compared the behavior, dispersal tendency, and metabolic rate of male round goby (Neogobius melanostomus) sampled from the expanding edge of their range with those sampled from an established area in the Trent-Severn Waterway, Ontario, Canada. Behavior and dispersal tendency were assessed in an artificial flume at 2 different water velocities using individuals caught in the spring and autumn of 2013, while resting metabolic rate (RMR) was determined using intermittent flow-through respirometry on fish collected in the autumn only. Round goby from the edge of their expanding range emerged from a shelter sooner, moved farther and faster in the flume, and had higher RMRs than individuals from established areas within the river. Neither water velocity nor season of capture was important in explaining the variation in time of emergence or movement. The higher proportion of bold individuals with high dispersal potential at invasion fronts facilitates further dispersal of round goby populations, and could help explain the rapid expansion of this species in North America and Western Europe. However, the benefits of bold phenotypes in terms of dispersal may be offset by increased energetic costs while at rest.
Fish have proven to be model organisms for the study of animal personalities, and a rich literature documents consistent interindividual behavioral differences in a variety of species. However, relatively few studies have examined the ecological consequences of such consistent interindividual differences in behaviors in fish or other organisms, especially under field conditions. In this review and perspective, we discuss the factors that may lead to the formation and maintenance of behavioral types in fish populations. We then examine what is known about the effects of personality variation on individual growth and survival, breeding behaviors and reproductive success, habitat use, diet, and ontogenetic niche shifts, migration and dispersal, as well as potential consequences for species interactions and ecosystem functioning. We focus as much as possible on studies conducted under natural or seminatural conditions, as such field studies are most relevant to elucidating the ecological consequences of behavioral variation. Finally, we discuss the potential importance of consistent individual differences in behaviors to fisheries management and conservation, specifically examining consequences for recreational and commercial fishing, hatchery rearing, and stock enhancement.
Maximum likelihood or restricted maximum likelihood (REML) estimates of the
parameters in linear mixed-effects models can be determined using the lmer
function in the lme4 package for R. As for most model-fitting functions in R,
the model is described in an lmer call by a formula, in this case including
both fixed- and random-effects terms. The formula and data together determine a
numerical representation of the model from which the profiled deviance or the
profiled REML criterion can be evaluated as a function of some of the model
parameters. The appropriate criterion is optimized, using one of the
constrained optimization functions in R, to provide the parameter estimates. We
describe the structure of the model, the steps in evaluating the profiled
deviance or REML criterion, and the structure of classes or types that
represents such a model. Sufficient detail is included to allow specialization
of these structures by users who wish to write functions to fit specialized
linear mixed models, such as models incorporating pedigrees or smoothing
splines, that are not easily expressible in the formula language used by lmer.
Environmental and biological characteristics interact in complex ways to determine ecosystem susceptibility to invasive species, and a greater understanding of their relative roles in invader spread and impact is needed. We evaluated relationships between environmental characteristics, biodiversity of indigenous species, and the abundance and ecological impact of an invasive fish, round goby (Neogobius melanostomus).
Tributaries to Lake Michigan, WI, USA.
We assessed the distribution and abundance of round gobies and native fishes in tributaries via electrofishing. We compared fish community composition and diversity in streams with (n = 30) and without (n = 52) round gobies and examined how trends in round goby abundance from 2007 to 2010 correlated with changes in abundance of five native benthic fishes. We used redundancy analysis to determine how indigenous stream communities related to environmental characteristics and round goby abundance.
Round goby abundance was best explained by environmental characteristics, with watershed area and temperature explaining 22.4% of the variation. Species richness and Shannon diversity only explained 6.9% of the variation in round goby abundance and only an additional 2.3% after considering environmental characteristics. Round goby abundance was not a significant predictor of fish community composition, which was best explained by seven environmental variables (30.3% of the variation). Invaded communities had significantly higher indigenous species richness than uninvaded communities (8.38 vs. 6.54). Round goby abundance was low compared with estimates from other studies, but showed an increasing trend in many tributaries (average 10.8-fold increase from 2007 to 2010). Surprisingly, there were no temporal trends in native benthic fish abundance despite increases in round goby abundance.
Environmental characteristics favouring high fish diversity (e.g. resource availability and warm water temperature) were positively associated with round goby abundance. However, round goby density and impact are relatively low in most tributaries at present, emphasizing the importance of considering heterogeneity in an invader's abundance when assessing invasion success.
The role of aggression as a factor promoting invasiveness remains hotly debated. Increased aggression or a lack of tolerance for conspecifics may promote population spread. Some previous research suggests that more aggressive or bold individuals are increasingly likely to disperse and as such these individuals may be overrepresented at the invasion front. In contrast, it has also been argued that individuals at the invasion front represent the least aggressive or least competitive individuals in the population, as these animals are excluded from established areas. Accordingly, the invasion front should be made up of shy, submissive individuals that exhibit reduced aggression. In this study we explore these alternative predictions by quantifying the levels of intra-specific aggression in the round goby (Neogobius melanostomus), an invasive fish that continues to spread rapidly through the Laurentian Great Lakes region in North America. We collected size matched male round goby from an invasion front as well as from an area with an established population, and we staged resource contests between them. Invasion front fish won 65% of the contests and tended to perform more aggressive acts overall. Invasion front fish were not more active or bold prior to the contest, and used the same types of aggressive displays as fish from established areas. Our results also showed that body size asymmetry was an overriding determinant of competitive outcomes, and that body size rather than individual variation in aggressiveness might be the most important contributing factor determining the composition of round goby invasion fronts throughout the Laurentian Great Lakes and its tributaries.
The objective of this research was to determine if the highly invasive round goby (Neogobius melanostomus) experiences lower predation risk during early stages of invasion. We compared round goby predation rates between a recently invaded area (occupied for ≈1 year) and a longer established area (≈7 years) of the Trent River, Ontario, Canada. Tethering trials were conducted in three habitat types, and comparable habitats in the two areas were similar in water temperature, velocity and depth. Predation rates of tethered round gobies were on average 27% lower in the recently invaded area. Reduced predation in the recently invaded area may be due to the short duration of round goby occupancy and/or differences in predator communities between the two study areas. Data before the round goby invasion suggest that predator communities were similar between the two range areas, but differences in predator abundance cannot be ruled out as a potential mechanism. Other possible mechanisms include a numerical or learned response by predators over time to a novel prey item. Reduced predation rate during the initial stages of invasion may contribute to the fitness of individuals that migrate into areas not previously occupied, and thus facilitate successful range expansion.
Few studies have systematically investigated differences in performance, morphology and parasitic load of invaders at different stages of an invasion. This study analyzed phenotype-environment correlations in a fish invasion from initial absence until establishment in the headwater reach of the second largest European river, the Danube. Here, the round goby (Neogobius melanostomus) formed 73% of the fish abundance and 58% of the fish biomass in rip-rap bank habitats after establishment. The time from invasion until establishment was only about two years, indicating rapid expansion. Founder populations from the invasion front were different from longer established round goby populations in demography, morphology, feeding behaviour, sex ratio and parasitic load, indicating that plasticity in these traits determines invasion success. Competitive ability was mostly dependent on growth/size-related traits rather than on fecundity. As revealed by stable isotope analyses, specimens at the invasion front had a higher trophic position in the food web and seem to benefit from lower food competition. Somatic performance seems to be more important than investment in reproduction during the early stages of the invasion process and upstream-directed range expansion is not caused by out-migrating weak or juvenile individuals that were forced to leave high density areas due to high competition. This mechanism might be true for downstream introductions via drift. Greater abundance and densities of acanthocephalan endoparasites were observed at the invasion front, which contradicts the expectation that invasion success is determined by lower parasitic pressure in newly invaded areas. Overall, the pronounced changes in fish and invertebrate communities with a dominance of alien species suggest invasional meltdown and a shift of the upper Danube River towards a novel ecosystem with species that have greater resistance to goby predation. This seems to contribute to overcoming biological resistance and improve rapidity of dispersal.
Examined rates of prey consumption by mottled sculpin Cottus bairdi and perlid stoneflies Agnetina capitata, separately, and together. Two types of Ephemeroptera prey (Ephemerella subvaria, Baetis tricaudatus) were used. When both types of predators were present consumption of Baetis larvae was significantly less than model predictions of combined prey consumption, indicating a negative interaction between predators. Consumption of Ephemerella was significantly higher than predicted by the model indicating a positive interaction between predators. Agnetina captured fewer Baetis larvae in the presence of sculpins, and sculpins caputred significantly more Ephemerella larvae in the presence of stoneflies. Negative effects of sculpins on the number of Baetis larvae captured by Agnetina were found even when the sculpins were unable to feed. Positive effects of Agnetina on the number of Ephemerella captured by sculpin were still found even when Agnetina density was reduced by more than half. -from Authors
The invasive round goby Apollonia melanostomus (formerly Neogobius melanostomus) has negatively affected benthic fish communities throughout the Great Lakes. In this study, we compared the sensory physiology and behavior of three native species—slimy sculpin Cottus cognatus, spoonhead sculpin C. ricei, and logperch Percina caprodes—with those of the round goby to determine the mechanisms that allow the round goby to dominate native fish. The reaction and strike distances of the four species were examined during predator-prey trials using natural amphipod prey Gammarus spp. under varying light intensities (0-130 lx) to compare input from the mechanosensory lateral line and visual systems. Trials in the dark (0 lx) indicated that the sculpins and the round goby had similar lateral line sensitivity. However, all three native species had a significant advantage in reaction and strike distance over the round goby at higher light intensities. Interspecific resource competition was assessed by pairing a round goby with a native fish in an artificial stream. Round gobies gained significantly more weight than the native fishes during all trials. Slimy sculpins were able to maintain their weight in the presence of the round goby; however, spoonhead sculpins and logperch lost a significant amount of weight during the trials. These experiments indicate that although the round goby does not possess an inherent sensory advantage, it can dominate resources and outcompete native fish. Thus, round gobies may pose risks for a wide variety of native benthic fishes.
Analysis of stomach contents of 52 cod (Gadus morhua callarias) individuals (TL 37.0-58.0 cm) caught in November 2003 in the coastal waters of the Gulf of Gdansk showed the presence of the prawn Palaemon elegans, a malacostracan species that has been recently reported as abundant in various parts of the Baltic Sea. This is the first observation of P. elegans as a cod food item in the Baltic Sea. The prawns were found in 88.5% of the stomachs analysed, accounting for 17% and almost 7% of food weight of cod 45.0 cm and epsilon 45.0 cm, respectively. The prawns consumed by the cod measured from 20 to 48 mm (average +/- SD: 31.7 +/- 5.3 mm), the prawn length increasing slightly with the cod length. Although P. elegans seems to be the most important invertebrate food item, diet in the cod was still dominated by fish. Neogobius melanostomus and Zoarces viviparus were the most important fish species found in the cod stomachs examined. In addition, the contents of some of the cod stomachs featured other malacostracan species, mainly Crangon crangon, as well as other invertebrates; however, these were of lesser importance. The significance of P. elegans as food of the cod fished commercially in the coastal waters of the Gulf of Gdansk in comparison with other species preyed upon by cod there is discussed.
The fish community of the Gulf of Puck in the Baltic Sea has changed in recent years following the successful introduction of the Round Goby (Neogobius melanostomus). The first specimen of Round Goby was caught in 1990 and now is estimated in millions of individuals. The Round Goby was a main component of the Grey Heron diet in the colony at Mosty and made up 95% of regurgitated prey items. During chick rearing period, herons mostly flew to the coast to forage in shallow waters and feed on the Round Goby. The numbers of Grey Herons at Mosty have increased recently, especially since 1999 (from 238 in 1999 to 493 nests in 2003; an increase of 107%). The indirect evidence suggests that the rapid expansion of the Round Goby has influenced the Grey Heron and affected both the diet and the numbers of birds feeding and breeding in the vicinity of the Puck Gulf.
In many animals, individual differences in behavior show remarkable consistency across situations and contexts (i.e., animal
personality and behavioral syndromes). Studies on the association between personality traits and fitness-related measures
in nature are, however, important to clarify the causes and consequences of this phenomenon. Here, we tested for correlations
between 3 behavioral axes in brown trout (Salmo trutta) parr: exploration tendency, behavioral flexibility, and aggressiveness. Next, we tested how these individual behaviors relate
to social dominance and performance under natural conditions (growth, survival, and movement). We found support for behavioral
syndromes in brown trout with less explorative individuals being less aggressive and showing more flexible behavior. In addition,
these low-explorative personality types grew faster than bolder conspecifics in the wild. Standardized aggression in the laboratory
was a poor indicator of social dominance, and neither of these 2 traits affected performance in the wild. These results challenge
the view that personality traits can be predicted by constant associations with life-history trade-offs (e.g., boldness is
linked with rapid growth). Moreover, our findings suggest that fitness predictions from laboratory measures of behavior should
be made with caution and ideally tested in nature.
Invasive species represent a challenge because the particular characteristics of a species’ invasion are often unknown before
the invasion. To provide some clarity as to how invasive species demographic structure might change as a population advances
its range, we compared the proportion of occupied sites, size structure and sex ratio of round gobies in the area where they
first invaded with more recently invaded areas at the extent of their range in a river in south-eastern Ontario. We used a
standardized angling technique to sample gobies larger than 45-mm total length in the summer and early autumn of 2007. Round
goby at the upstream and downstream extent of their range occupied a lower proportion of randomly selected sites, and contained
a wider distribution of sizes as well as significantly larger individuals. Sex ratios in all areas were male-biased and the
male-to-female ratio was significantly higher in the upstream segment of the river (2.2:1) compared to the area of first introduction
(1.4:1). The difference between the newly invaded and the established sites suggests that round goby population structure
may be affected by density. The results of this study help us further describe the demographic characteristics of biological
invasions whilst examples of population structure and behaviour in gobies and other species provide a basis for generating
hypotheses for range expansion.
KeywordsDispersal–Gobiidae–Invasive–Non-indigenous–Range expansion
During the past decade, a bottom-dwelling, aggressive, multiple-spawning fish, the round goby (Gobiidae: Neogobius melanostomus), has spread from its native region in the Ponto-Caspian throughout Europe and to the Laurentian Great Lakes in North America. An international workshop, held at the Hel Marine Station, Poland, was organized to summarize population features of the round goby. Common fish predators of round gobies in the Great Lakes and in native regions are obligate and facultative benthic fishes and occasionally, pelagic fishes. In contrast, the main predator of the round goby in the Gulf of Gdansk is the Great Cormorant (Phalacrocorax carbo). In the Great Lakes, round gobies have lead to the decline of mottled sculpin (Cottus bairdi) and logperch (Percina caprodes) and reduced the hatching success of native fishes by feeding on their eggs. In the Gulf of Gdansk, round gobies have increased in abundance, while three-spined sticklebacks (Gasterosteus aculeatus) have declined. Round gobies have a broad diet throughout their range; larger specimens are molluscivores. There are fewer species of parasites and lower infection rates of round gobies in recently colonized areas than in native areas. Overall, newly colonized round gobies in brackish waters and lakes are smaller, mature earlier, have a male biased operational sex ratio and are more short-lived compared with round gobies from marine (native) habitats.
The round goby Neogobius melanostomus is one of the most wide-ranging invasive fish on earth, with substantial introduced populations within the Laurentian Great Lakes watershed, the Baltic Sea and several major European rivers. Rapid expansion and deleterious ecosystem effects have motivated extensive research on this species; here this research is synthesized. Maps of the global distribution are provided and the invasion history of N. melanostomus, which spread more rapidly at first in North America, but has undergone substantial expansion over the past decade in the Baltic Sea, is summarized. Meta-analyses comparing their size at age, diet, competitors and predators in North American and European ecosystems are provided. Size at age is region specific, with saline habitats typically supporting larger and faster growing individuals than fresh water. Neogobius melanostomus prey differs substantially between regions, demonstrating a capacity to adapt to locally abundant food sources. Neogobius melanostomus comprise at least 50% of the diet of eight taxa in at least one site or life stage; in total, 16 predator taxa are documented from the Laurentian Great Lakes v. five from Eurasia. Invasive N. melanostomus are the only common forage fish to heavily exploit mussels in the Laurentian Great Lakes and the Baltic Sea, facilitating the transfer of energy from mussels to higher trophic levels in both systems. Neogobius melanostomus morphology, life history, reproduction, habitat preferences, environmental tolerances, parasites, environmental effects, sampling strategies and management are also discussed. Neogobius melanostomus inhabit a wide range of temperate freshwater and brackish-water ecosystems and will probably continue to spread via ballast water, accidental bait release and natural dispersal worldwide. Climate change will probably enhance N. melanostomus expansion by elevating water temperatures closer to its energetic optimum of 26° C. Future research needs are presented; most pressing are evaluating the economic effects of N. melanostomus invasion, determining long-term population level effects of egg predation on game-fish recruitment and comparing several variables (density, ecological effects morphology and life history) among invaded ecosystems. This review provides a central reference as researchers continue studying N. melanostomus, often as examples for advancing basic ecology and invasion biology.
This paper presents the reshape package for R, which provides a common framework for many types of data reshaping and aggregation. It uses a paradigm of ???melting??? and ???casting???, where the data are ???melted??? into a form which distinguishes measured and iden- tifying variables, and then ???cast??? into a new shape, whether it be a data frame, list, or high dimensional array. The paper includes an introduction to the conceptual framework, practical advice for melting and casting, and a case study.
This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as “bold”, fish that took more time to resume movement were categorized as “shy”, and those who fell in between these two categories were determined to have “intermediate” boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Hence, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus, however results also show that competition is also governed by other mechanisms which require further study.
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Differences between individuals in behavioral type (i.e. animal personality) are ecologically and evolutionarily important because they can have significant effects on fitness components such as growth and predation risk. In the present study we ere used the invasive round goby (Neogobius melanostomus) from an established population in controlled experiments to examine the relationships among personality, metabolic performance, and growth rate (inferred as size-at-age). Boldness was measured as the time to return to normal behavior after a simulated predator attack, where fish with shorter freezing times were categorized as "bold" and fish with longer times were categorized as "shy." We show that bold fish have significantly higher standard metabolic rate (SMR) than their shy conspecifics, whereas there was no difference between personality types in their maximum metabolic rate (MMR) or aerobic scope (AS). Bold fish furthermore had a smaller size-at-age as compared to shy fish. Together this provides evidence of a metabolic underpinning of personality where the high-SMR bold fish require more resources to sustain basic life functions than their low-SMR shy conspecifics, indicating that bold round goby from established populations with high densities (and high competition for food) pay a price of reduced growth rate.
When invasive species become integrated within a food web, they may have numerous direct and indirect impacts on the native community by creating novel trophic links, and modifying or disrupting existing ones. Here we discuss these impacts by drawing on examples from freshwater ecosystems, and argue that future research should quantify changes in such trophic interactions (i.e. the links in a food web), rather than simply
focusing on traditional measures of diversity or abundance (i.e. the nodes in a food web). We conceptualise the impacts of invaders on trophic links as either direct consumption, indirect trophic effects (e.g. cascading interactions, competition) or indirect nontrophic effects (e.g. behaviour mediated). We then discuss how invader impacts on trophic links are context-dependent, varying with invader traits (e.g. feeding rates), abiotic variables (e.g. temperature, pH) and the traits of the receiving community (e.g. predators or competitors). Co-occurring invasive species and other environmental stressors, such as climate change, will also influence invader impacts on trophic links. Finally, we discuss the available methods to identify new food web interactions following invasion and to quantify how invasive species disrupt existing feeding links. Methods include direct observations in the field, laboratory trials (e.g. to quantify functional responses) and controlled mesocosm experiments to elucidate impacts on food webs. Field studies which use tracer techniques, such as stable isotope analyses, allow diet characterisation of both invaders and interacting native species in the wild. We conclude that invasive species often drastically alter food webs by creating and disrupting trophic links, and
future research should be directed particularly towards disentangling the effects of invaders from other environmental stressors.
The Laurentian Great Lakes have been the site of numerous aquatic invasive species such as the sea lamprey, zebra mussel and round goby. To further understand interactions between invasive and native species in situ, competitive interactions between native logperch (Percina caprodes) and invasive round goby (Neogobius melanostomus) were examined using submerged enclosures in the Duluth-Superior Harbour. Experiments were conducted on rocky or sandy substrate throughout the spring and summer months. Trials consisted of single fish, paired conspecifics or round goby/logperch pairs with weight change determined after 28 days. The round gobies were able to outcompete and/or negatively affect logperch on rocky substrates as a direct result of round goby/logperch interactions, as logperch fared well when round gobies were excluded from the enclosures. Although there is evidence that round gobies exclude logperch from rocky substrates, the logperch population remains close to pre-invasion levels in the predominantly soft-bottomed harbour. The continued coexistence of the logperch with the round goby is attributed to the vastly greater area of soft-bottom vs. rocky substrate in the harbour, with the round gobies in the soft bottom younger and smaller than those in the rocky substrate. Recent evidence suggests that the round goby population is declining on the soft substrates indicating that the two populations will continue to coexist in the harbour.
Invasion biology research has identified two juxtaposing behavioural traits, aggressiveness and sociality, that may both increase the success of species invasions. Highly aggressive invaders can out-compete native species for resources, while social gregarious invaders can tolerate high conspecific density. In order to tease apart the effects of aggressive versus social tendencies on the success of invasive species, we studied round goby (Neogobius melanostomus), a highly successful invasive fish species now common in the Laurentian Great Lakes. While round goby are well known for being aggressive, much less is known about their tendency to affiliate with conspecifics, in spite of the fact that they thrive in extremely high densities in many of their invaded habitats. We collected round goby from Hamilton Harbour, ON, Canada and conducted three separate experiments to explore group-forming behaviour by measuring preference for conspecifics. We found that round goby have a strong preference to associate with a single conspecific, and that both males and females showed this preference. No overall preference was detected for large versus small groups of conspecifics. Females chose the safety of a shelter over associating with a conspecific but males were equally attracted to conspecifics as shelter. Our results provide new insight into how interactions between aggressive and social behaviours play a role in the rapid spread of invasive round goby.
Abstract Fish can undergo changes in their life‐history traits that correspond with local demographic conditions. Under range expansion, a population of non‐native fish might then be expected to exhibit a suite of life‐history traits that differ between the edge and the centre of the population’s geographic range. To test this hypothesis, life‐history traits of an expanding population of round goby, Neogobius melanostomus (Pallas), in early and newly established sites in the Trent River (Ontario, Canada) were compared in 2007 and 2008. Round goby in the area of first introduction exhibited a significant decrease in age at maturity, increased length at age 1 and they increased in GSI from 2007 to 2008. While individuals at the edges of the range exhibited traits that promote population growth under low intraspecific density, yearly variability in life‐history traits suggests that additional processes such as declining density and fluctuating food availability are influencing the reproductive strategy and growth of round goby during an invasion.
We examined territorial defense and behavioural interactions between two species of fish resident in Hamilton Harbour: non-indigenous round gobies (Neogobius melanostomus) and native logperch (Percina caprodes). Trials consisted of placing one fish, “the resident” (either a round goby or a logperch), in a tank with a shelter for 24 hours before adding another fish, “the intruder” (either a round goby or a logperch), and recording aggressive incidents. Overall, gobies exhibited more aggressive behavior than logperch, and in general resident status had no effect on amount of aggression displayed. Also, gobies spent more time in shelters than logperch, and overall resident status did not affect the amount of time spent under shelter. We also compared abundance data for gobies and logperch using electrofishing transects in Hamilton Harbour that were conducted in 1995 and 2001 and found a dramatic increase in round goby numbers and a non-significant decrease in logperch numbers. Our data suggest that gobies are superior space competitors and hence the range expansion coupled with an increasing population size of the round gobies in Hamilton Harbour is likely to have deleterious consequences for logperch populations.
We examined territorial behaviors and interactions between two species of benthic clingers, nonindigenous round gobies (Neogobius melanostomus) and native mottled sculpins (Cottus bairdi). Interactions were observed for 24 h using infrared video photography in the laboratory. Trials were conducted using either a round goby or mottled sculpin resident in a shelter. An intruder (either a round goby or mottled sculpin) was added at random. Fish (fasted for 24 h before each trial) were used only once. Food (Gammarus, amphipods), maintained below satiation levels (estimated from functional feeding experiments), was used to enhance interactions. Over 24 h, amount of time spent in a refuge by a resident round goby did not change when intruders were present (round gobies or mottled sculpins). Time spent in a refuge over 24 h by a resident mottled sculpin was significantly reduced in the presence of a round goby intruder, but not in the presence of a mottled sculpin intruder. Both round gobies and mottled sculpins spent more time outside a refuge during the night than during the day. Resident round gobies and mottled sculpins spent more time in a refuge at night when a conspecific was present and even more time in the refuge when a fish of another species was introduced. The mean number of approaches, chases, and bites by resident round gobies was significantly greater than those of intruders. Mottled sculpin intruders never exhibited any aggressive behaviors (approaches, chases, bites). In cases where mottled sculpins were resident, a round goby intruder exhibited a greater number of acts (approaches, chases, bites) that were more aggressive compared to the resident sculpin (approaches). In nature, the aggressive habits of round gobies will likely result in the demise of mottled sculpins.
We examine the evolving concept of what constitutes a nonnative
(or alien) freshwater fish. In an attempt to distinguish
between biogeographical and socio-political perspectives, we
review the patterns in the introduction and dispersal of nonnative
fishes in Europe and North America, and especially the
recent expansion of Ponto-Caspian gobies in Europe. We
assess patterns in the development of national policy and
legislation in response to the perceived threat of non-native
fish introductions to native species and ecosystems. We review,
and provide a glossary of, the terms and definitions associated
with non-native species. Finally, we discuss perspectives as
regards the future treatment of naturalized species.
There is increasing interest in individual differences in animal behaviour. Recent research now suggests that an individual's behaviour, once considered to be plastic, may be more predictable than previously thought. Here, we take advantage of the large number of studies that have estimated the repeatability of various behaviours to evaluate whether there is good evidence for consistent individual differences in behaviour and to answer some outstanding questions about possible factors that can influence repeat- ability. Specifically, we use meta-analysis to ask whether different types of behaviours were more repeatable than others, and if repeatability estimates depended on taxa, sex, age, field versus laboratory, the number of measures and the interval between measures. Some of the overall patterns that were revealed by this analysis were that repeatability estimates were higher in the field compared to the laboratory and repeatability was higher when the interval between observations was short. Mate pref- erence behaviour was one of the best studied but least repeatable behaviours. Our findings prompt new insights into the relative flexibility of different types of behaviour and offer suggestions for the design and analysis of future research.
Interference competition for food is difficult to measure because feeding rates altered by behavioral interactions of competitors are confounded by exploitative competition, the depletion of food over time. We quantified the magnitude of interference competition between individuals using a combination of experiments and computer simulations, which allowed us to remove the effect of exploitative competition. We used this approach to test the hypothesis that interference competition reduces feeding rates of young red drum (Sciaenops ocellatus) and that the magnitude of interference competition is related to phenotypic traits, such as the sizes of competitors and behavioral interactions between them. In laboratory experiments, we measured prey consumption and behavioral interactions between 2 fish of different sizes (7- to 25-mm standard length). We used computer simulations to remove the effects of exploitative competition and found that prey consumed by focal individuals decreased in the presence of competitors due to interference competition and that the decrease was stronger when focal individuals were smaller than competitors and when the competing individuals were generally larger. We also found greater impairment of prey consumption by focal individuals when they were more vigilant (more reactive) to the presence of competitors. A better understanding of the magnitude of asymmetry in interference competition has important implications for understanding population dynamics, spatial distribution, and reproductive strategies of many organisms. This is the first study to quantify the asymmetry in interference competition when prey density changes over time. Copyright 2010, Oxford University Press.
The Ponto-Caspian round goby (Neogobius melanostomus, Pallas 1814) most probably was established in the Gulf of Gdańsk, Baltic Sea, in the late 1980’s and has since become one
of the dominant species in the region. In this study we assess the role of round gobies as prey for two important fish species
in the Gulf of Gdańsk, cod (Gadus morhua) and perch (Perca fluviatilis). We compared their present diet with stomach analyses from the area prior the round goby establishment, as well as with
diet analysis from Baltic regions where round gobies are absent. There were large differences in the diet between cods from
the Gulf of Gdańsk 2003–2006 compared to cods in earlier studies (1977–1981) from the Southern Baltic Sea. There were also
large differences in cod and perch diets from areas with and without round goby. Presently, round goby constitutes the most
important prey for medium sized cods in Gulf of Gdańsk, and perch from the same area almost exclusively feed on gobiids. Stomach
analysis, trophic level estimates, and stable isotope analyses all indicated that cod and perch in Gulf of Gdańsk after the
round goby establishment belonged to a similar trophic level. Beside round goby, no mussel feeding fish contributed much to
the diet of cod or at all to the diet of perch. Thus, it is likely that round gobies constitute a new energetic pathway from
mussels to top predators. However, due to the short time elapsed after round goby establishment, we can only speculate on
the species future impacts on Baltic food webs.
Keywords
Neogobius melanostomus
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Gadus morhua
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Perca fluviatilis
-Diet-Trophic levels-Stable isotopes
Within populations of many species, individuals that are otherwise similar to one another in age, size or sex can differ markedly
in behaviours such as resource use, risk taking and competitive ability. There has been much research into the implications
of such variation for intraspecific interactions, yet little investigation into its role in influencing interspecific interactions
outside of a predator–prey context. In this study, we investigated the role of individual-level behavioural variation in determining
the outcomes of interactions between two ecologically similar fishes, the threespine and ninespine sticklebacks (Gasterosteus aculeatus and Pungitius pungitius). Experiment 1 asked whether individuals of both species were consistent in their expression of two behaviours: activity
in novel surroundings and latency to attack prey. For each behaviour, focal individuals were assayed twice, 10days apart.
Performances were positively correlated between exposures, suggesting behavioural consistency within individuals, at least
over this timescale. Experiment 2 revealed not only differences in habitat use described both by species-level variation,
with ninespines spending more time in vegetated areas, but also by individual differences, with more active individuals of
both species spending more time in open water than in vegetation. Experiment 3 revealed that when heterospecific pairs competed
for prey, bolder individuals consumed a greater share, irrespective of species. These findings suggest that individual-level
variation can facilitate overlap in habitat use between heterospecifics and also determine the outcomes of resource contests
when they meet. We discuss how this might vary between populations as a function of prevailing selection pressures and suggest
approaches for testing our predictions.
This study documents a local extinction of mottled sculpins, apparently due to round gobies, and presents data pertinent to the mechanism of extinction. Mottled sculpins, Cottus bairdi, were assessed using SCUBA standardized diving transects during the invasion of the round goby, Neogobius melanostomus, into Calumet Harbor, southern Lake Michigan. Laboratory stream studies were conducted in which gravid male and female mottled sculpins were allowed to nest, then were exposed to one male round goby. Diet studies were conducted to assess the potential for competition for food at small sizes of both species. The SCUBA surveys showed that mottled sculpin populations rapidly declined, after the first round gobies were found in the area in 1994, despite the presence of a well established population prior to the round goby arrival. Mottled sculpins have been almost totally extirpated from the area in 1998 due to three proposed mechanisms: competition for food resources at small sizes, for space at intermediate sizes, and for spawning space at large sizes. The laboratory stream study confirmed that round gobies interfered with nest-guarding male mottled sculpins, seized their spawning shelters, changed to spawning coloration in preparation for spawning, and caused near loss of all the mottled sculpin eggs. It is concluded that recruitment failure and subsequent demise of mottled sculpins was most likely caused by spawning interference by round gobies.
Ecology Letters (2012)
Interspecific trait variation has long served as a conceptual foundation for our understanding of ecological patterns and dynamics. In particular, ecologists recognise the important role that animal behaviour plays in shaping ecological processes. An emerging area of interest in animal behaviour, the study of behavioural syndromes (animal personalities) considers how limited behavioural plasticity, as well as behavioural correlations affects an individual’s fitness in diverse ecological contexts. In this article we explore how insights from the concept and study of behavioural syndromes provide fresh understanding of major issues in population ecology. We identify several general mechanisms for how population ecology phenomena can be influenced by a species or population’s average behavioural type, by within-species variation in behavioural type, or by behavioural correlations across time or across ecological contexts. We note, in particular, the importance of behavioural type-dependent dispersal in spatial ecology. We then review recent literature and provide new syntheses for how these general mechanisms produce novel insights on five major issues in population ecology: (1) limits to species’ distribution and abundance; (2) species interactions; (3) population dynamics; (4) relative responses to human-induced rapid environmental change; and (5) ecological invasions.
Unintentional species invasions are instigated by human-mediated dispersal of individuals beyond their native range. Although most introductions fail at the first hurdle, a select subset pass through each stage of the introduction process (i.e., transport, introduction, establishment and spread) to become successful invaders. Efforts to identify the traits associated with invasion success have predominately focused on deliberate introductions, which essentially bypass the initial introduction stage. Here, we highlight how behavior influences the success or failure of unintentional species introductions across each stage of the introduction process, with a particular focus on transportation and initial establishment. In addition, we emphasize how recent advances in understanding of animal personalities and individual-level behavioral variation can help elucidate the mechanisms underlying the success of stowaways.