Article

Foraging habits of invasive three-spined sticklebacks (Gasterosteus aculeatus) – impacts on fisheries yield in Upper Lake Constance

Authors:
  • Fisheries Research Station Baden-Württemberg
  • Fisheries Research Station of Baden-Württemberg
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Abstract

A massive increase in the pelagic population of non-endemic three-spined sticklebacks, Gasterosteus aculeatus L. in Lake Constance has coincided with drastic declines in fishery yields. This study assesses the possible direct and indirect impact of the mass occurrence on native fish species in the lake. Laboratory foraging experiments showed that larvae of roach Rutilus rutilus L., perch Perca fluviatilis L. and whitefish Coregonus lavaretus L. are accessible to sticklebacks as food. However, distinct species effects were apparent, with whitefish showing no effective predator avoidance strategy and therefore experiencing drastically increased mortality risk compared to the other predator adapted prey species. Furthermore, in absence of larval prey, sticklebacks were shown to feed predominantly on Daphnia in the field, indicating a strong interspecific food competition with whitefish. The results suggest that sticklebacks, acting as both an invasive species and a predator in the pelagic zone where prior no predator or neozoon existed, create a unique challenge to the unadapted autochthonous fish, and thus threaten the ecological resilience of the lake. Impacts on recruitment, e.g. through larval predation and interspecific competition for zooplankton could explain recent drastic declines in fishing yields.

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... Its adaptability, short life cycle, wide environmental tolerance, and ability to complete multiple spawning cycles per year in response to favourable conditions allow it to rapidly colonise new environments, as well as to exhibit dramatic increases in previously occupied habitats in response to altered conditions (Barber and Nettleship, 2010). In recent decades, stickleback population increases have been observed in several aquatic systems, including the White Sea (Lajus et al., 2021), Lake Constance (Germany) (Roch et al., 2018;Rösch et al., 2018) 2 A. B. Olin et al. and the above-mentioned Limfjorden (Tomczak et al., 2013). These increases have in several cases been linked to anthropogenic environmental change, such as increasing water temperatures (Lajus et al., 2021). ...
... Importantly, the stickleback not only responds rapidly to novel conditions, but may itself have substantial impacts on the ecosystem. For example, in Lake Constance, the stickleback increase is thought to explain a sharp decline of whitefish (Coregonus spp.), as the stickleback compete with whitefish for food and predate on their offspring (Roch et al., 2018;Rösch et al., 2018). As sticklebacks may via these mechanisms suppress the recruitment of their own predators, they can act to reinforce a state with low densities of predators , resulting in subsequent top-down trophic cascades (e.g. ...
... Sticklebacks along the German coastline have been found to consume substantial numbers of herring eggs, which likely results in local reductions in herring productivity (Kotterba et al., 2014). It has also been suggested that sticklebacks have a negative impact on whitefish by competing for food and predating on whitefish offspring , as observed in Lake Constance (Roch et al., 2018;Rösch et al., 2018). Finally, a strong negative relationship has been identified between juvenile abundances of stickleback and common roach along the Swedish Baltic Sea coast (U. ...
Article
Under rapid environmental change, opportunistic species may exhibit dramatic increases in response to the altered conditions, and can in turn have large impacts on the ecosystem. One such species is the three-spined stickleback (Gasterosteus aculeatus), which has shown substantial increases in several aquatic systems in recent decades. Here, we review the population development of the stickleback in the Baltic Sea, a large brackish water ecosystem subject to rapid environmental change. Current evidence points to predatory release being the central driver of the population increases observed in some areas, while both eutrophication and climate change have likely contributed to creating more favourable conditions for the stickleback. The increasing stickleback densities have had profound effects on coastal ecosystem function by impairing the recruitment of piscivorous fish and enhancing the effects of eutrophication through promoting the production of filamentous algae. The increase poses a challenge for both environmental management and fisheries, where a substantial interest from the pelagic fisheries fleet in exploiting the species calls for urgent attention. While significant knowledge gaps remain, we suggest that the case of the Baltic Sea stickleback increase provides generalisable lessons of value for understanding and managing other coastal ecosystems under rapid change.
... One such case is the invasion of one of the largest lakes in Central Europe, Lake Constance, by the three-spined stickleback (Gasterosteus aculeatus L.) (hereafter referred to as stickleback). The species first was established in the littoral zone of Upper Lake Constance (ULC) around 1958 (Muckle 1972;Roch et al. 2018). However at the end of 2012, it expanded from an exclusively shoreline habitat into the pelagic zone (Eckmann and Engesser 2019). ...
... The full ecological impact of sticklebacks on the aquatic community in ULC and its tributaries is unknown. However, the results of two recent studies (Roch et al. 2018;Rösch et al. 2018) imply significant effects of stickleback presence on pelagic whitefish Coregonus wartmanni (Bloch 1784), the previously dominant pelagic fish species and the main target of local fisheries (Baer et al. 2017). The suspected reasons include interspecific competition for food leading to reduced growth and survival, and predation by sticklebacks on whitefish larvae and probably eggs, hampering recruitment (Ros et al. 2019;Baer et al. 2021). ...
... The suspected reasons include interspecific competition for food leading to reduced growth and survival, and predation by sticklebacks on whitefish larvae and probably eggs, hampering recruitment (Ros et al. 2019;Baer et al. 2021). These observations coincide with a sharp decline in whitefish yield, from around 300-600 mt (metric tons) before stickleback invasion to less than 150 mt with stickleback presence in the pelagic zone (Roch et al. 2018). In 2019, the yield fell further, to below 60 mt (Gugele et al. 2020). ...
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Since 2012, a massive invasion of the three-spined stickleback ( Gasterosteus aculeatus ) has taken place into the pelagic area of Lake Constance. This species, which had previously been restricted to the littoral zone, is now the dominant pelagic fish and the previously dominant whitefish ( Coregonus wartmanni ) has suffered severe reductions in growth and recruitment. In this study, in total, 2871 sticklebacks were collected via monthly sessions over a 4-year period in pelagic and benthic areas of Lake Constance and examined for signs of infection with Schistocephalus solidus , a parasite known to be potentially fatal. The infection risk to sticklebacks increases throughout the course of the year and is size- and sex-dependent. Habitat has only a marginal impact. All parasite-induced harm is imparted after stickleback spawning and parental care is over. The results did not support the hypothesis that the invasion of the pelagic area might be driven by parasite-avoiding behaviour. Furthermore, the impact of the parasite is likely to be limited to post-reproductive adults, thereby ensuring stable reproduction of the hosts despite high rates of transmission and mortality. In consequence, stickleback stock development is independent of S. solidus infection, leading to secure coexistence of host and parasite even at extraordinary high host levels.
... The massive recent increase in stickleback abundance coincides with a sharp decline in pelagic whitefish (Coregonus wartmanni, Bloch, 1784) yields, both in the number of individuals caught, and their weight-at-age (Rösch et al., 2017). Previous work has speculated that the invasive stickleback population could have a negative impact on whitefish growth and abundance, and shows that stickleback will prey on whitefish larvae in laboratory foraging experiments (Roch et al., 2018;Ros et al., 2019) or following stocking (Roch et al., 2018). However, the first stickleback population expansion during the eutrophication period in Constance coincides with population size increase in whitefish (Numann, 1972), so the relationship between whitefish and stickleback abundances is either mediated by some other factors in the environment, or it is not causal. ...
... The massive recent increase in stickleback abundance coincides with a sharp decline in pelagic whitefish (Coregonus wartmanni, Bloch, 1784) yields, both in the number of individuals caught, and their weight-at-age (Rösch et al., 2017). Previous work has speculated that the invasive stickleback population could have a negative impact on whitefish growth and abundance, and shows that stickleback will prey on whitefish larvae in laboratory foraging experiments (Roch et al., 2018;Ros et al., 2019) or following stocking (Roch et al., 2018). However, the first stickleback population expansion during the eutrophication period in Constance coincides with population size increase in whitefish (Numann, 1972), so the relationship between whitefish and stickleback abundances is either mediated by some other factors in the environment, or it is not causal. ...
... However, the first stickleback population expansion during the eutrophication period in Constance coincides with population size increase in whitefish (Numann, 1972), so the relationship between whitefish and stickleback abundances is either mediated by some other factors in the environment, or it is not causal. It has been proposed that either competition for pelagic zooplankton resources such as Daphnia -that have declined in abundance with the re-oligotrophication of Lake Constance (Straile and Geller, 1998;Stich and Brinker, 2010;Rösch et al., 2017) -or direct predation on whitefish eggs and larvae (Roch et al., 2018;Ros et al., 2019) are responsible for this reduction in yield. Predation by sticklebacks on eggs and juveniles of their own species occurs frequently (Whoriskey and FitzGerald, 1985;Hyatt and Ringler, 1989;Smith and Reay, 1991;Foster and Bell, 1994;Manica, 2002;Mehlis et al., 2010) along with predation on larvae of other fish species (Hynes, 1950;Manzer, 1976;Delbeek and Williams, 1988;Kean-Howie et al., 1988;Gotceitas and Brown, 1993;Nilsson, 2006;Kotterba et al., 2014;Byström et al., 2015), while previous studies on stickleback populations in the Baltic Sea have suggested that intraguild predation on eggs and juvenile fish is responsible for the observed declines in perch (Perca fluviatilis, Linnaeus, 1758) and pike (Esox lucius, Linnaeus, 1758) recruitment (Nilsson, 2006;Bergström et al., 2015;Byström et al., 2015;Nilsson et al., 2019;Eklöf et al., 2020). ...
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Our Research Topic titled “Understanding the Impact and Invasion Success of Aquatic Non-native Species: How They Interact with Novel Environments and Native Biota,” compiled a series of research studies providing new data and approaches in assessing the invasion success and the impacts of various non-native species in the different regions of the world belonging to various groups of organisms and from various environments. A range of invasion ecology specialists endeavored to provide up-to-date information on the multifaceted issues of non-native species introductions and to map conservation priorities in terms of biological invasion. A total of 10 articles, including original pieces of research, a review, a brief research report and a hypothesis and theory, are included as part of this Research Topic. Below, an overview of these articles is provided.
... As an opportunistic species, the ability of sticklebacks to adapt to different and multiple food sources plays a significant role across the different life stages [31]. It was recently shown that the success of stickleback predation on fish larvae depends upon the size and species of prey [32,33]. Quantitative examination of predation on roach (Rutilus rutilus), perch (Perca fluviatilis) and whitefish (Coregonus wartmannii) larvae shows a particularly high toll on small-sized whitefish larvae which historically grew up in habitat without predators, in comparison to similar-sized larvae of the other two species which have co-evolved with predators in their environment [32,34]. ...
... It was recently shown that the success of stickleback predation on fish larvae depends upon the size and species of prey [32,33]. Quantitative examination of predation on roach (Rutilus rutilus), perch (Perca fluviatilis) and whitefish (Coregonus wartmannii) larvae shows a particularly high toll on small-sized whitefish larvae which historically grew up in habitat without predators, in comparison to similar-sized larvae of the other two species which have co-evolved with predators in their environment [32,34]. Sticklebacks have recently increased strongly in abundance in the pelagial of Lake Constance prompting concern that predation on whitefish larvae may be of ecological importance [34]. ...
... Sticklebacks hunting whitefish larvae which lacked previous predator experience are less successful with increasing size of the prey [32]. In a published paper based on the current experiment this prey size effect was confirmed [33], and it was postulated that the most parsimonious explanation for this effect was an increase in performance variables of the prey with increasing size, like in maximum acceleration and in swimming speed [66,67]. ...
Article
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Predator-prey interactions play a key life history role, as animals cope with changing preda-tion risk and opportunities to hunt prey. It has recently been shown that the hunting success of sticklebacks (Gasterosteus aculeatus) targeting fish larvae is dependent on both the size of the prey and the prior exposure of its species to stickleback predation. The purpose of the current study was to identify the behavioural predator-prey interactions explaining the success or failure of sticklebacks hunting larvae of three potential prey species [roach (Rutilus rutilus), perch (Perca fluviatilis) and whitefish (Coregonus wartmannii)] in a 3D environment. Trials were carried out for each prey species at four different size classes in a standardised laboratory setup and were recorded using a slow motion, stereo camera setup. 75 predator-prey interactions including both failed and successful hunts were subject to the analysis. 3D track analysis indicated that sticklebacks applied different strategies. Prey with less complex predator escape responses, i.e. whitefish larvae, were hunted using a direct but stealthy approach ending in a lunge, while the behaviourally more complex roach and perch larvae were hunted with a faster approach. A multivariate logistic regression identified that slow average speed and acceleration of the prey in the initial stages of the hunt increased the probability of stickleback success. Furthermore, predators adjusted their swimming direction more often when hunting larger whitefish compared to smaller whitefish. The results suggest that appropriate and adequately timed avoidance behaviours, which vary between prey species and ontogenetic stages, significantly increase the chances of outmanoeuvring and escaping stickleback predation. Small whitefish larvae can reach similar levels of swimming performance compared to older conspecifics, but display ineffective anti-predator behaviours, resulting in higher hunting success for sticklebacks. Thus, the development of appropriate anti-predator behaviours depending on size appears to be the crucial factor to escaping predation. PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.
... The three-spined stickleback (Gasterosteus aculeatus, hereafter referred to as stickleback) is one of several aquatic invasive species in Lake Constance, one of the largest lakes in Central Europe. Sticklebacks first established in the littoral zone of Upper Lake Constance (ULC) in the 1940s [1], but by the end of 2012 had expanded from an exclusively shoreline habitat into the pelagic zone [2]. Hydroacoustic surveys conducted twice yearly in the pelagic zone from 2009 to 2018 showed an exponentially increasing population of small fish (presumably sticklebacks) starting in 2012 and plateauing after 2014 with fluctuations between 1 280 and 7 990 individuals/ha [2]. ...
... Furthermore, hydroacoustic surveys conducted in November 2020 showed large, dense swarms of small fish that were most likely sticklebacks (around 10.000 individuals in areas less than one hectare) near larger fish that were most likely whitefish spawner stock (Baer, own observation). Since densities of zooplankton, the pelagic sticklebacks' main diet [1], are very low and sticklebacks would otherwise starving at this time of year, it is hypothesized that this winter abundance peak might represent a migration to feed on whitefish eggs [3]. The resulting egg predation pressure could then partly explain the severe declines in whitefish recruitment observed in recent years [4]. ...
... In contrast to the clear evidence of stickleback predation on whitefish larvae in Lake Constance [1], the extent and magnitude of egg predation and its implications for whitefish recruitment are still unknown. Field investigations are especially challenging because the whitefish spawning time is difficult to predict, lasts only a few days [5], and is often accompanied by strong winds that make catching enough stickleback with gillnets or trawling difficult. ...
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The three-spined stickleback Gasterosteus aculeatus invaded Lake Contance in the 1940s and expanded in large numbers from an exclusively shoreline habitat into the pelagic zone in 2012. Stickleback abundance is very high in the pelagic zone in winter near the spawning time of pelagic whitefish Coregonus wartmanni, and it is hypothesized that this is triggered by the opportunity to consume whitefish eggs. Field sampling has qualitatively confirmed predation of whitefish eggs by stickleback, but quantification has proven difficult due to stormy conditions that limit sampling. One fundamental unknown is if freshwater stickleback , known as visual feeders, can successfully find and eat whitefish eggs during twilight and night when whitefish spawn. It is also unknown how long eggs can be identified in stomachs following ingestion, which could limit efforts to quantify egg predation through stomach content analysis. To answer these questions, 144 individuals were given the opportunity to feed on whitefish roe under daylight, twilight, and darkness in controlled conditions. The results showed that stickleback can ingest as many as 100 whitefish eggs under any light conditions, and some individuals even consumed maximum numbers in complete darkness. Furthermore, eggs could be unambiguously identified in the stomach 24 hours after consumption. Whitefish eggs have 28% more energy content than the main diet of sticklebacks (zooplankton) based on bomb-calorimetric measurements, underlining the potential benefits of consuming eggs. Based on experimental results and estimates of stickleback abundance and total egg production, stickleback could potentially consume substantial proportions of the total eggs produced even if relatively few sticklebacks consume eggs. Given the evidence that stickleback can feed on eggs during nighttime spawning and may thereby hamper recruitment, future studies aimed at quantifying actual egg predation and resulting effects on the whitefish population are urgently needed.
... The massive recent increase in stickleback abundance coincides with a sharp decline in pelagic whitefish (Coregonus wartmanni, Bloch, 1784) yields, both in the number of individuals caught, and their weight-at-age (Rösch et al., 2017). Previous work has speculated that the invasive stickleback population could have a negative impact on whitefish growth and abundance, and shows that stickleback will prey on whitefish larvae in laboratory foraging experiments (Roch et al., 2018;Ros et al., 2019) or following stocking (Roch et al., 2018). However, the first stickleback population expansion during the eutrophication period in Constance coincides with population size increase in whitefish (Numann, 1972), so the relationship between whitefish and stickleback abundances is either mediated by some other factors in the environment, or it is not causal. ...
... The massive recent increase in stickleback abundance coincides with a sharp decline in pelagic whitefish (Coregonus wartmanni, Bloch, 1784) yields, both in the number of individuals caught, and their weight-at-age (Rösch et al., 2017). Previous work has speculated that the invasive stickleback population could have a negative impact on whitefish growth and abundance, and shows that stickleback will prey on whitefish larvae in laboratory foraging experiments (Roch et al., 2018;Ros et al., 2019) or following stocking (Roch et al., 2018). However, the first stickleback population expansion during the eutrophication period in Constance coincides with population size increase in whitefish (Numann, 1972), so the relationship between whitefish and stickleback abundances is either mediated by some other factors in the environment, or it is not causal. ...
... However, the first stickleback population expansion during the eutrophication period in Constance coincides with population size increase in whitefish (Numann, 1972), so the relationship between whitefish and stickleback abundances is either mediated by some other factors in the environment, or it is not causal. It has been proposed that either competition for pelagic zooplankton resources such as Daphnia -that have declined in abundance with the re-oligotrophication of Lake Constance (Straile and Geller, 1998;Stich and Brinker, 2010;Rösch et al., 2017) -or direct predation on whitefish eggs and larvae (Roch et al., 2018;Ros et al., 2019) are responsible for this reduction in yield. Predation by sticklebacks on eggs and juveniles of their own species occurs frequently (Whoriskey and FitzGerald, 1985;Hyatt and Ringler, 1989;Smith and Reay, 1991;Foster and Bell, 1994;Manica, 2002;Mehlis et al., 2010) along with predation on larvae of other fish species (Hynes, 1950;Manzer, 1976;Delbeek and Williams, 1988;Kean-Howie et al., 1988;Gotceitas and Brown, 1993;Nilsson, 2006;Kotterba et al., 2014;Byström et al., 2015), while previous studies on stickleback populations in the Baltic Sea have suggested that intraguild predation on eggs and juvenile fish is responsible for the observed declines in perch (Perca fluviatilis, Linnaeus, 1758) and pike (Esox lucius, Linnaeus, 1758) recruitment (Nilsson, 2006;Bergström et al., 2015;Byström et al., 2015;Nilsson et al., 2019;Eklöf et al., 2020). ...
Article
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Invasive species can be powerful models for studying contemporary evolution in natural environments. As invading organisms often encounter new habitats during colonization, they will experience novel selection pressures. Threespine stickleback (Gasterosteus aculeatus complex) have recently colonized large parts of Switzerland and are invasive in Lake Constance. Introduced to several watersheds roughly 150 years ago, they spread across the Swiss Plateau (400-800 m a.s.l.), bringing three divergent hitherto allopatric lineages into secondary contact. As stickleback have colonized a variety of different habitat types during this recent range expansion, the Swiss system is a useful model for studying contemporary evolution with and without secondary contact. For example, in the Lake Constance region there has been rapid phenotypic and genetic divergence between a lake population and some stream populations. There is considerable phenotypic variation within the lake population, with individuals foraging in and occupying littoral, offshore pelagic, and profundal waters, the latter of which is a very unusual habitat for stickleback. Furthermore, adults from the lake population can reach up to three times the size of adults from the surrounding stream populations, and are large by comparison to populations globally. Here, we review the historical origins of the threespine stickleback in Switzerland, and the ecomorphological variation and genomic basis of its invasion in Lake Constance. We also outline the potential ecological impacts of this invasion, and highlight the interest for contemporary evolution studies.
... The three-spined stickleback (Gasterosteus aculeatus) (hereafter referred to as stickleback) is one of several aquatic invasive species to have invaded Lake Constance, one of the largest lakes in Central Europe. Sticklebacks first established in the littoral zone of Upper Lake Constance (ULC) around 1958 (Roch et al., 2018), but by the end of 2012 they had expanded from an exclusively shoreline habitat into the pelagic zone (Eckmann and Engesser, 2019). According to a lake-wide fishing survey of ULC in September 2014, sticklebacks represented 96 % of all fish in the pelagic fish community and 28 % of total biomass (Alexander et al., 2016). ...
... The full impact of sticklebacks on the aquatic community in ULC and its tributaries is unknown. However, the results of two recent studies (Rösch et al., 2018;Roch et al., 2018) imply significant effects of stickleback presence on pelagic living and spawning whitefish Coregonus wartmanni, which previously dominated the pelagic fish community and was the main target of local fishery (Baer et al., 2016). It is suspected that interspecific competition for food has led to reduced whitefish growth and survival, while stickleback predation on whitefish eggs and larvae has hampered recruitment. ...
... It is suspected that interspecific competition for food has led to reduced whitefish growth and survival, while stickleback predation on whitefish eggs and larvae has hampered recruitment. The arrival of sticklebacks in the pelagic zone has coincided with a sharp decline in whitefish yield, from around 300− 600 mt (metric tons) before stickleback invasion to less than 150 mt (Roch et al., 2018). A better insight into the autecology of sticklebacks in ULC is needed to assess the species' ecological impact, to test the hypothesis that most of the small fish in the pelagic zone are sticklebacks (Eckmann and Engesser, 2019) and to develop appropriate fisheries management strategies. ...
Article
A combination of fishing and surveying methods (trawling, gillnetting, electrofishing and hydroacoustics) were used to obtain insight into the spatiotemporal dynamics of invasive three-spined sticklebacks (Gasterosteus aculeatus) in the pelagic zone of Upper Lake Constance. The resulting information is highly pertinent to the development of management strategies to reduce the negative impact of sticklebacks on the pelagic ecosystem of the lake, and especially on the commercially important native pelagic whitefish (Coregonus wartmanni). The results indicate that sticklebacks are very mobile and opportunistic with respect to habitat selection, making extensive shifts between benthic and pelagic habitats. The greatest abundances of sticklebacks in the pelagic zone were identified in late summer, shortly after their spawning, when densities exceeding 10,000 individuals per hectare were recorded. A second peak occurred in winter, during the spawning season of pelagic whitefish. Data from gillnetting indicate high stickleback densities in the littoral zone of the lake during the spawning season of benthic whitefish (Coregonus macrophthalmus). Thus, damaging predation of pelagic and benthic whitefish eggs and larvae by sticklebacks seems very likely. Electrofishing surveys in tributary rivers revealed that these were used irregularly as migration routes and are therefore unlikely to represent a significant habitat for stickleback reproduction. Depth distribution of sticklebacks in the pelagic zone changed throughout the year with highest densities at depths of 9–12 m in spring, summer and autumn, while in winter densities were highest at 15–18 m. The most efficient option for capturing sticklebacks is trawling during September, at depths of 9−12 m, where very large catches were recorded without significant bycatch of non-target species. This method of control would require special fishing vessels not currently deployed on the lake and its economic feasibility will require careful assessment.
... Feeding strategy can shift between opportunist and specialist depending on habitat type, season, and other environmental factors (Gill and Hard, 1994;Sánchez-Gonzáles et al., 2001;Wootton, 2012;Demchuk et al., 2015). In Lake Constance, the three-spined stickleback is an invasive species, which first became established in the littoral zone between 1940 and 1950 (Roch, 2018). Since 2012/13 however, the species has appeared in very large numbers in the pelagic zone of Upper Lake Constance (Rösch et al., 2018;Eckmann and Engesser, 2019), and in 2014 it comprised more than 95% of pelagic fish abundance and made up about 28% of total fish biomass (Alexander et al., 2016). ...
... There is indirect evidence from growth and recruitment point data that strong competition exists between sticklebacks and native whitefish, Coregonus spp. (Roch et al., 2018;Rösch et al., 2018;Gugele et al., 2020). The clear food niche overlap identified in this study points at an additional competition between stickleback and perch, potentially contributing to the creation of a novel food web structure. ...
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The fish community of Lake Constance, a large, deep, oligotrophic lake has undergone drastic changes in recent years, with the sudden rise to dominance of invasive three-spined stickleback (Gasterosteus aculeatus) in the pelagic zone, a rather atypical habitat for this species in Central Europe. The core objective of this study was to compare the feeding ecology of stickleback and young Eurasian perch (Perca fluviatilis) in this unique situation to identify reasons for this unexpected dominance, a possible food niche and feeding time overlap, and to discuss consequences for the reshaped pelagic fish community. The diel feeding patterns and prey compositions of pelagic sticklebacks and juvenile (0+) perch sampled in October 2018 and March 2019 were studied analyzing stomach contents. The diets of both species mostly comprised zooplankton, with copepods appearing in the greatest numbers. Benthic and airborne insects were consumed occasionally, mostly by sticklebacks. Both species exhibited peaks of feeding activity early in the morning, afternoon and dusk, and in both species, stomachs were fullest at dusk. Stickleback stomachs contained about 20% more prey at night than perch, and mean estimated nocturnal stomach fullness values were almost 50% greater. Night feeding in sticklebacks was confirmed by digestive states, pointing to a possible competitive advantage over perch. Dietary composition varied over a 24-h cycle and the pattern of consumption of different prey varied between the species. Perch consumed more comparatively small cladocerans (Bosmina spp.), while larger Daphnia appeared more often in stickleback stomachs. In both species, seasonal variation in diet mirrored food availability, indicating some degree of opportunism. A Morisita-Horn index value of 0.95 confirmed dietary niche overlap between species, suggesting the large population of sticklebacks may exert a competitive effect on juvenile perch when resources are limited. Both the longer feeding periods and greater intake of nutritive high quality prey like daphnids can contribute to the rapid success of stickleback in dominating the pelagic zone of Lake Constance.
... The recent invasion of sticklebacks into the pelagic zone of Lake Constance 32 has had significant negative effects on the endemic fish community and the whitefish fishery 48 . Sticklebacks display a very considerable food niche overlap with native whitefish (Coregonus sp.), feed on whitefish eggs and larvae 49 , and have been linked to whitefish declines in recent years 50 . High resolution spatial and temporal data for both species are urgently needed to better understand and manage invasion impacts, and hydroacoustic monitoring are strongly preferred given the aforementioned limitations of conventional sampling in large, deep water bodies like Lake Constance. ...
... temperature), and foraging. Information pertaining to the seasonal distribution of stickleback could help to better define spawning migration into near-shore areas 63 , and this information might be utilized to alter the timing of larval whitefish stocking in order to limit predation 49,64 . Abundance estimates for juvenile whitefish provided by hydroacoustics may also help improve estimates of natural recruitment and stocking success. ...
Article
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Monitoring fish populations in large, deep water bodies by conventional capture methodologies requires intensive fishing effort and often causes mass mortality of fish. Thus, it can be difficult to collect sufficient data using capture methods for understanding fine scale community dynamics associated with issues such as climate change or species invasion. Hydroacoustic monitoring is an alternative, less invasive technology that can collect higher resolution data over large temporal and spatial scales. Monitoring multiple species with hydroacoustics, however, usually requires conventional sampling to provide species level information. The ability to identify the species identity of similar-sized individuals using only hydroacoustic data would greatly expand monitoring capabilities and further reduce the need for conventional sampling. In this study, wideband hydroacoustic technology was used in a mesocosm experiment to differentiate between free swimming, similar-sized individuals of two swim-bladdered species: whitefish (Coregonus wartmanni) and stickleback (Gasterosteus aculeatus). Individual targets were identified in echograms and variation in wideband acoustic responses among individuals, across different orientations, and between species was quantified and visually examined. Random forest classification was then used to classify individual targets of known species identity, and had an accuracy of 73.4% for the testing dataset. The results show that species can be identified with reasonable accuracy using wideband hydroacoustics. It is expected that further mesocosm and field studies will help determine capabilities and limitations for classifying additional species and monitoring fish communities. Hydroacoustic species differentiation may offer novel possibilities for fisheries managers and scientists, marking the next crucial step in non-invasive fish monitoring.
... Due to its high tolerance of salinity and temperature and its reproductive and foraging characteristics (e.g. Roch et al. 2018;Candolin 2019), G. aculeatus can, therefore, be regarded as a high-risk species for the risk assessment area, despite its a priori non-invasive status elsewhere. ...
Article
Aquatic invasions are one of the major threats for freshwater ecosystems. However, in developing countries knowledge of biological invasions essential for the implementation of appropriate legislation is often limited if not entirely lacking. In this regard, the identification of potentially invasive non-native species by risk screening, followed by a full risk assessment of the species ranked as higher risk, enables to inform decision-makers about the extent of the threats posed to the recipient (risk assessment) area. In this study, 32 non-native extant and horizon fish species were screened for their risk of invasiveness under current and predicted climate conditions for the South Caucasus – a biodiversity and geopolitical hotspot that includes the countries of Armenia, Azerbaijan and Georgia. Overall, the number of very high-risk species increased from four (12.5%) under current climate conditions to 12 (37.5%) under predicted climate conditions. The highest-risk species under both conditions included the already established gibel carp Carassius gibelio and topmouth gudgeon Pseudorasbora parva, the locally translocated pikeperch Sander lucioperca, and the horizon North African catfish Clarias gariepinus. Under predicted climate conditions, a very high risk of invasiveness was predicted also for the translocated three-spined stickleback Gasterosteus aculeatus and Eurasian perch Perca fluviatilis, for the already established eastern mosquitofish Gambusia holbrooki, ruffe Gymnocephalus cernua, sharpbelly Hemiculter leucisculus and Nile tilapia Orechromis niloticus, and for the horizon pumpkinseed Lepomis gibbosus and largemouth bass Micropterus salmoides. Future research on the non-native species in the South Caucasus should be conducted both country- and region-wide and should account not only for the high biodiversity but also for the critical geopolitical situation affecting the study area.
... With continuing reoligotrophication since the 1980's, the relative share of copepod biomass again increased but extinct species failed to reinvade (Straile, 2015), presumably due to niche constriction by the emerged zooplankton invaders in combination with altered environmental conditions. Recently, since around 2014, Daphnia cucullata and its hybrid forms occur in the lake in high abundances, temporally coinciding with the immigration of the non-endemic three-12 spined stickleback (Gasterosteus aculeatus) in 2013 (Alexander et al., 2014;Roch et al., 2018;Rösch et al., 2018). The contemporary dominant copepod species are Eudiaptomus gracilis, Cyclops abyssorum, Cyclops vicinus, and Mesocyclops leuckarti. ...
... The whitefish yield decreased from around 300-600 t before 2012 to less than 150 t (Baer et al. 2016(Baer et al. ) in 2012 In 2019, the yield fell further to below 60 t (Gugele et al. 2020). The reasons for the decline include the decreasing nutrient load (Baer et al. 2016) and the invasion of the non-endemic three-spined stickleback (Gasterosteus aculeatus) (Roch et al. 2018, Rösch et al. 2018. As a result, already in 2012, at least 50% of all whitefish consumed at Lake Constance originated from other countries, including Italy, Finland, and Canada (Dreßler 2013). ...
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... The finding of importance of correlations between temperature and stickleback abundance is supported by their life history's capacity for responding to environmental fluctuation. The rapid and significant population fluctuations known for stickleback in different areas are facilitated by the species' quick maturation and short life cycle (Bugaev, 2007;Roch et al., 2018;Olsson et al., 2019). In the White Sea stickleback start to mature early, at age 1 year, and rarely reach 4 years . ...
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A major challenge of contemporary marine science is disentangling consequences of climate change from other impacts, and studying non-target species and using historical resources to see long-term trends can meet this need. However, such data can be fragmented, and here, we demonstrate the potential of leveraging across sources for insight. We assembled a variety of historical sources such as scientific and personal observations, anecdotal information, and archival fisheries data to create an abundance time series on threespine stickleback Gasterosteus aculeatus in the White Sea starting in the late 19th century—the longest time series for this species. Stickleback peaked during the warm period of the 1920–1940s and declined during the colder period of the 1950–1990s and now is the most numerous vertebrate in the sea. Analyses of historical and recent time series based on our own data (2007–2019) showed that stickleback abundance decreases during colder winters. It is not associated with zooplankton biomass, positively correlated with herring Clupea sp. catches and negatively with navaga Eleginus navaga catches. Large population size and food web interactions suggest that change in stickleback abundance has the potential to affect the entire White Sea ecosystem.
... Sticklebacks were already introduced to Austria in the late 19th century (Ahnelt, 1984), but were, until recently, nowhere particularly common and were not considered a major threat for other species (Wiesner et al., 2010;Zick et al., 2006). In Lake Constance, however, stickleback populations increased massively since 2012, which is assumed to have a profound impact on native species and fishery yields (Roch, von Ammon, Geist, & Brinker, 2018;Rösch, Baer, & Brinker, 2018). In the study area, the stickleback abundance is considerably lower than in Lake Constance. ...
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Non‐native fish species pose a major threat to local fish populations and aquatic ecosystems in general. Invasive gobies are a particular focus of research, but with partly inconsistent results. While some studies reported severe detrimental impacts on native species, others have concluded less serious or neutral effects. We provide results from a large‐scale, multi‐annual fish monitoring program on the occurrence and abundance of non‐native fishes in the main stem of a free‐flowing section of the Austrian Danube. Special emphasis was placed on identifying positive or negative interactions of invasive gobies with native species. Whereas most non‐native species occurred too sporadically or were too few in number to infer a direct threat on the local fish community, invasive gobies were among the most common fishes throughout all sampling years. Co‐occurrence analyses revealed species‐ and mesohabitat type‐specific associations of gobies with native species, which were primarily positive. Notably, native predators such as asp, burbot, or perch probably benefit from the ubiquitous gobies. Two characteristic fluvial fishes revealed negative associations with invasive gobies, namely barbel (Barbus barbus) and Danube whitefin gudgeon (Romanogobio vladykovi): they appear to avoid habitats occupied by gobies. Accordingly, high abundances of round and bighead goby most likely resulted in population losses of barbel and whitefin gudgeon, respectively. Overall, our results indicate a limited negative impact of non‐native species in the sampling area. This is because only two out of 51 occurring species were found to be adversely affected by gobies, the share of co‐occurrences with native species was high, and other non‐native species were generally rare. Nevertheless, invasions are highly dynamic, and new non‐native species are likely to occur in the Austrian Danube, calling for continued monitoring and awareness.
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It is a fundamental feature of evolution that natural selection acts on individuals to adapt to predation pressure via the development of anti‐predator mechanisms. As such mechanisms are costly in terms of energy and time, species living in habitats where predators are rare or absent were expected to show reduced predator responses. Such a reduction was expected for larvae of the native whitefish (Coregonus wartmanni) in Upper Lake Constance, as these pass their initial stage in a historically predator‐free pelagic habitat and only start to encounter predators in a later ontogenetic stage during which they shift to littoral habitat. However, a recent invader of the pelagic waters of the lake, the three‐spined stickleback (Gasterosteus aculeatus), is implicated in a severe decline in whitefish recruitment through larval predation. The predator‐naivety effect and its consequences on predation were experimentally tested by comparing predator defenses of different age classes of whitefish with those of roach (Rutilus rutilus) and perch (Perca fluviatilis), two species whose larvae grow up in a predator‐holding habitat. As predator, the three‐spined stickleback (Gasterosteus aculeatus) was selected. Sticklebacks actively hunted all prey species but predation was high on whitefish only. The addition of zooplankton (Daphnia) as alternative prey for sticklebacks in the experimental setup did not reduce predation on the whitefish larvae, indicating a clear preference for whitefish in this invasive predator. The escape responses of roach and perch were found to be clearly more complex and diverse to those of the predator‐naïve whitefish larvae. Particularly striking was that whitefish often did not show any apparent behavioral response to the approaching predator. Only large whitefish larvae (Table 1: length = 40.8 ± 0.6 mm) appeared capable of escaping predation, and this was correlated with a change in complexity of predator escape responses. Thus, differences in predation pressure for the different larvae species were highly related to the observed interspecific differences in predator defenses, and with the ontogenetic intraspecific change in whitefish from poor and inefficient predator escape responses to complex and more efficient predator escape responses. The evolutionary consequences of stickleback as an invasive predator on whitefish larvae behavior are discussed.
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Since 2013, the pelagic zone of Upper Lake Constance (ULC) has been subject to a massive invasion of the non-native three-spined stickleback (Gasterosteus aculeatus Linnaeus, 1758). Data from monthly monitoring of pelagic whitefish (Coregonus wartmanni Bloch, 1784) were used to compare weight-at-age and abundance of pelagic whitefish for years before (1997–2012) and after the invasion (2013–2015). Growth and abundance of pelagic whitefish is shown to be heavily influenced by stickleback presence. Mean autumn weight-at-age of whitefish decreased by 33.3% after the invasion took place and a significant decline in autumn CPUE in otherwise unfished cohorts of the population was also recorded. The results imply direct effects of stickleback presence on pelagic whitefish, including interspecific competition for food leading to reduced growth and survival, and predation of eggs and larvae, hampering recruitment. These observations coincide with a sharp decline in whitefish yield. In conclusion, this study shows that the invasion of stickleback has substantially altered the pelagic fish community of ULC, with severe consequences for commercial fisheries.
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Since 2013, the pelagic zone of Upper Lake Constance (ULC) has been subject to a massive invasion of the non-native three-spined stickleback (Gasterosteus aculeatus Linnaeus, 1758). Data from monthly monitoring of pelagic whitefish (Coregonus wartmanni Bloch, 1784) were used to compare weight-at-age and abundance of pelagic whitefish for years before (1997–2012) and after the invasion (2013–2015). Growth and abundance of pelagic whitefish is shown to be heavily influenced by stickleback presence. Mean autumn weight-at-age of whitefish decreased by 33.3% after the invasion took place and a significant decline in autumn CPUE in otherwise unfished cohorts of the population was also recorded. The results imply direct effects of stickleback presence on pelagic whitefish, including interspecific competition for food leading to reduced growth and survival, and predation of eggs and larvae, hampering recruitment. These observations coincide with a sharp decline in whitefish yield. In conclusion, this study shows that the invasion of stickleback has substantially altered the pelagic fish community of ULC, with severe consequences for commercial fisheries.
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Upper Lake Constance (ULC) is a large pre-alpine lake situated between Austria, Germany and Switzerland (9°18'E, 47°39'N). Along with the smaller, conjoined expanse of Lower Lake Constance, it forms the third largest lake in Europe. Its waters underwent pronounced eutrophication during the 20th century. Commercial fisheries benefitted strongly from the increased productivity during an initial mesotrophic phase, but these advantages were effectively neutralized when eutrophication became severe. By the turn of the 21 st century, internationally coordinated measures to reduce nutrient input to the lake had returned ULC to its historic reference state as an oligotrophic ecosystem. However, the remarkable success of the nutrient management program has been to the detriment of commercial fishers. Yields of most commercially important fish species have decreased, along with lake productivity. As a consequence, the high market demand for local fish products is nowadays met mainly by imports, the ecological footprint of which offsets the local benefits of environmental restoration. Responsibility for fisheries and environmental aspects of ULC managing is shared by the national and federal state administrations and in all cases, tourism, drinking water and environmental interests now take priority over fisheries. As a result, the number of fishers operating viably on Germany's largest inland water body continues to decline and the long-term viability of commercial capture operations is in doubt. Aquaculture of locally desired fish species may become an important factor in the future of the Lake Constance fisheries.
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Ecological speciation is the process by which reproductively isolated populations emerge as a consequence of divergent natural or ecologically-mediated sexual selection. Most genomic studies of ecological speciation have investigated allopatric populations, making it difficult to infer reproductive isolation. The few studies on sympatric ecotypes have focused on advanced stages of the speciation process after thousands of generations of divergence. As a consequence, we still do not know what genomic signatures of the early onset of ecological speciation look like. Here, we examined genomic differentiation among migratory lake and resident stream ecotypes of threespine stickleback reproducing in sympatry in one stream, and in parapatry in another stream. Importantly, these ecotypes started diverging less than 150 years ago. We obtained 34,756 SNPs with restriction-site associated DNA sequencing and identified genomic islands of differentiation using a Hidden Markov Model approach. Consistent with incipient ecological speciation, we found significant genomic differentiation between ecotypes both in sympatry and parapatry. Of 19 islands of differentiation resisting gene flow in sympatry, all were also differentiated in parapatry and were thus likely driven by divergent selection among habitats. These islands clustered in quantitative trait loci controlling divergent traits among the ecotypes, many of them concentrated in one region with low to intermediate recombination. Our findings suggest that adaptive genomic differentiation at many genetic loci can arise and persist in sympatry at the very early stage of ecotype divergence, and that the genomic architecture of adaptation may facilitate this.
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Populations occurring in similar habitats and displaying similar phenotypes are increasingly used to explore parallel evolution at the molecular level. This generally ignores the possibility that parallel evolution can be mimicked by the fragmentation of an ancestral population followed by genetic exchange with ecologically different populations. Here we demonstrate such an ecological vicariance scenario in multiple stream populations of threespine stickleback fish divergent from a single adjacent lake population. On the basis of demographic and population genomic analyses, we infer the initial spread of a stream-adapted ancestor followed by the emergence of a lake-adapted population, that selective sweeps have occurred mainly in the lake population, that adaptive lake-stream divergence is maintained in the face of gene flow from the lake into the streams, and that this divergence involves major inversion polymorphisms also important to marine-freshwater stickleback divergence. Overall, our study highlights the need for a robust understanding of the demographic and selective history in evolutionary investigations.
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The Rhine catchment in Switzerland has been transformed by a chain of hydroelectric power stations. We addressed the impact of fragmentation on the genetic structure of fish populations by focusing on the European chub (Squalius cephalus). This fish species is not stocked and copes well with altered habitats, enabling an assessment of the effects of fragmentation per se. Using microsatellites, we genotyped 2133 chub from 47 sites within the catchment fragmented by 37 hydroelectric power stations, two weirs and the Rhine Falls. The shallow genetic population structure reflected drainage topology and was affected significantly by barriers to migration. The effect of power stations equipped with fishpasses on genetic differentiation was detectable, albeit weaker than that of man-made barriers without fishpasses. The Rhine Falls as the only long-standing natural obstacle (formed 14'000 to 17'000 years ago) also had a strong effect. Man-made barriers also exacerbated the upstream decrease in allelic diversity in the catchment, particularly when lacking fishpasses. Thus, existing fishpasses do have the desired effect of mitigating fragmentation, but barriers still reduce population connectivity in a fish that traverses fishpasses better than many other species. Less mobile species are likely to be affected more severely.This article is protected by copyright. All rights reserved.
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Intraguild predation interactions make fish communities prone to exhibit alternative stable states with either piscivore or prey fish dominance. In the Baltic Sea, local declines of coastal piscivores like perch (Perca fluviatilis) have been observed to coincide with high densities of sticklebacks (Gasterosteus aculeatus). Mechanisms behind this shift between piscivore and stickleback dominance were studied both experimentally and in field. Results showed that predation by sticklebacks has a strong negative effect on perch larvae survival, but this effect rapidly decreases with increasing perch size, likely due to gape limitations and digestion constraints in sticklebacks. Large spatial and temporal variations in patterns of stickleback migration into perch spawning sites were observed. Whether or not high density of sticklebacks will cause declines in coastal piscivore populations is suggested to depend on the availability of spawning sites in which sticklebacks do not migrate into or arrive late in the reproduction season of coastal piscivores. Electronic supplementary material The online version of this article (doi:10.1007/s13280-015-0665-5) contains supplementary material, which is available to authorized users.
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Effects of temperature and group size of roach Rutilus rutilus on foraging behaviour of perch Perca fluviatilis and R. rutilus were tested in two laboratory experiments. A temperature experiment with P. fluviatilis and R. rutilus in aquaria (with either one P. fluviatilis or two R. rutilus) was tested at five temperatures: 4, 8, 12, 16 and 20° C, and showed that P. fluviatilis had a lower swimming speed and capture rate than R. rutilus, especially at 4 and 8° C. The effect of group size was tested at four R. rutilus abundances: 0, 2, 4 and 6, all at 16° C, and revealed that swimming speed and capture rate of P. fluviatilis were lowest at the highest R. rutilus abundance, whereas R. rutilus was relatively unaffected. Perca fluviatilis occupied positions closer to the bottom than R. rutilus, especially when feeding, and this tendency was reinforced at the highest roach abundance.
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We studied three-dimensional distribution patterns of temperature, phyto- and zooplankton, and fish in the large, prealpine Lake Constance during spring 2007. A strong westerly wind induced an intense eastward displacement of epilimnetic water and upwelling of hypolimnetic water in the western part of the lake. This led to the formation of an internal front separating cold, hypolimnetic water depleted of chlorophyll in the western part from epilimnetic, warm water with high chlorophyll concentrations in the eastern part. Hydroacoustic detection of zooplankton (by Acoustic Doppler Current Profiler) and juvenile fish (by echosounding) revealed both to be passively transported by the wind. Consequently, zooplankton and fish showed comparable horizontal distributions as temperature and chlorophyll. During periods of low wind velocities (< 6 m s(-1)), water temperature was more evenly distributed, whereas phytoplankton distribution was still heterogeneous, probably because of local differences in resource supply. The relative influence of biotic factors for the distribution of organisms increased when external forcing was low. At periods with weak wind forcing, phytoplankton typically showed highest concentrations in the metalimnion, where zooplankton also aggregated in thin layers. In conclusion, we found spatial distributions of temperature and organisms to be strongly controlled by wind forcing when wind velocities were sufficiently high, whereas the importance of internal biotic factors for distribution of organisms increased when wind velocities were less strong. Abiotic factors appeared to act over relatively large spatial scales and affected distributions within the entire ecosystem, whereas biotic factors affected distributions of algae, zooplankton, and fish on a more local scale.
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Time lags can be found throughout the invasion process, including in the arrival, establishment, and impacts of invaders. While we often lack the information necessary to generate quantitative expectations of invader performance, some types of lags are not surprising. For example, populations often grow exponentially in the early phases of invasion, and this will give rise to an inherent lag. More broadly, early rates of anthropogenic invasion were much slower than what we are now witnessing, but as the vectors of invasion have also increased dramatically over time, this early lag is not unexpected. Many other lags, however, appear dramatically prolonged, and can come to an end with changes to the invader or its environment. For example, exotics can exist in relatively low numbers for decades before exploding, or invaders can become more aggressive over time and increase their impacts on native species. Invasion-related lags are critical for our efforts to manage invaders, as they may lead us to make inaccurate assessments of the risks posed by invaders as well as miss critical windows for action. Recognition of the phenomenon of long lags before sudden changes in invader dynamics also suggests that we adopt a strict precautionary principle: we should assume that any invader has the potential for undesirable effects and that long periods of seemingly consistent behaviour can be poor predictors of what invaders will do in the future.
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Urpanen, O., Huuskonen, H., Marjomäki, T. J. & Karjalainen, J. 2005: Growth and size-selective mortality of vendace (Coregonus albula (L.)) and whitefish (C. lavaretus L.) larvae. Boreal Env. Res. 10: 225-238. Vendace (Coregonus albula (L.)) and whitefish (C. lavaretus L.) larvae were sampled by stratified random sampling design in four Finnish lakes. Otolith microstructure analysis was used to investigate individual age, hatching time and growth rate of newly hatched larvae to reveal possible size-selective mortality during early life. The major- ity of the larvae hatched during a short period after the ice-off. Significant differences in hatching length between the lakes were found. Growth rate decreased when larvae became larger and the growth rate was slowest in the lake with the highest density of larvae. However, larger larvae were not relatively more abundant after first weeks and thus, size-dependent mortality was not evident. Hence, we observed that mortality of these two coregonid species during the first weeks was rather random in relation to size of the larvae. Overall, the mortality of vendace larvae with smaller hatching length was higher than that of larger whitefish larvae.
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Life history divergence between populations inhabiting ecologically distinct habitats might be a potent source of reproductive isolation, but has received little attention in the context of speciation. We here test for life history divergence between threespine stickleback inhabiting Lake Constance (Central Europe) and multiple tributary streams. Otolith analysis shows that lake fish generally reproduce at two years of age, while their conspecifics in all streams have shifted to a primarily annual life cycle. This divergence is paralleled by a striking and consistent reduction in body size and fecundity in stream fish relative to lake fish. Stomach content analysis suggests that life history divergence might reflect a genetic or plastic response to pelagic versus benthic foraging modes in the lake and the streams. Microsatellite and mitochondrial markers further reveal that life history shifts in the different streams have occurred independently following the colonization by Lake Constance stickleback, and indicate the presence of strong barriers to gene flow across at least some of the lake-stream habitat transitions. Given that body size is known to strongly influence stickleback mating behavior, these barriers might well be related to life history divergence.
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Invasions of Ponto-Caspian gobiid fishes are suspected to cause regime shifts in freshwater ecosystems. This study compared the trophic niche differentiations of Neogobius melanostomus and Pon-ticola kessleri in the upper Danube River using stable isotope analyses (d 13 C and d 15 N), gut content analyses and morphometric analyses of the digestive tract. Both species were identified as predacious omnivores with high dietary overlap and a generalistic feeding strat-egy. Amphipods (especially invasive Dikerogamma-rus spp.) contributed 2/3 to the index of food importance. d 15 N-signatures of N. melanostomus revealed an ontogenetic diet shift and significantly exceeded those in P. kessleri by *1.5%, indicating a niche separation of half a trophic level. P. kessleri had shorter uncoiled intestinal tracts than N. melanosto-mus, indicating a narrower niche and adaptation to animal food. Trophic niches in both species expanded during the growth period with increasing intraguild predation and cannibalism in P. kessleri and increas-ing molluscivory in N. melanostomus. P. kessleri showed a higher degree of specialization and more stable feeding patterns across seasons, whereas N. melanostomus adapted its diet according to the natural prey availability. The feeding patterns of both species observed in the upper Danube River strongly differ from those in their native ranges, underlining their great plasticity. Both goby species consumed mainly other non-native species (*92% of gut contents) and seemed to benefit from previous inva-sions of prey species like Dikerogammarus villosus. The invasive success of gobies and their prey mirror fundamental ecological changes in large European freshwater ecosystems.
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Rapid phenotypic diversification during biological invasions can either arise by adaptation to alternative environments or by adaptive phenotypic plasticity. Where experimental evidence for adaptive plasticity is common, support for evolutionary diversification is rare. Here, we performed a controlled laboratory experiment using full-sib crosses between ecologically divergent threespine stickleback populations to test for a genetic basis of adaptation. Our populations are from two very different habitats, lake and stream, of a recently invaded range in Switzerland and differ in ecologically relevant morphological traits. We found that in a lake-like food treatment lake fish grow faster than stream fish, resembling the difference among wild type individuals. In contrast, in a stream-like food treatment individuals from both populations grow similarly. Our experimental data suggest that genetically determined diversification has occurred within less than 140 years after the arrival of stickleback in our studied region.
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The zooplankton communities of two basins of a large lake, Lake Constance, were compared during the years 2002 and 2003. The two basins differ in morphology, physical and chemical conditions. The Upper Lake basin has a surface area of 470 km 2 , a mean depth of 100 and a maximum depth of 250 m; the Lower Lake basin has a surface area of 62 km 2 , a mean depth of only 13 and a maximum depth of 40 m. Nutrient, chlorophyll-a concentrations and mean temperatures are somewhat higher in the Lower than in the Upper Lake. Total abundance of rotifers (number per m 2 lake surface) was higher and rotifer development started earlier in the year in the Lower than in the Upper Lake. Total abundance of crustaceans was higher in the Upper Lake in the year 2002; in the year 2003 no difference in abundance could be detected between the lake basins, although in summer crustacean abundance was higher in the Lower than in the Upper Lake. Crustacean communities differed significantly between lake basins while there was no apparent difference in rotifer communities. In the Lower Lake small crustaceans, like Bosmina spp., Ceriodaphnia pulchella and Thermocyclops oithonoides prevailed. Abundance (number per m 2 lake surface) of predatory cladocerans, large daphnids and large copepods was much lower in the Lower than in the Upper Lake, in particular during the summer months. Ordination with nonmetric multidimensional scaling (NMS) separated communities of both lakes along gradients that correlated with temperature and chlorophyll a concentration. Clutches of copepods were larger in the Lower than in the Upper Lake. No difference could be detected in clutch size of large daphnids between lake basins. Our results show that zooplankton communities in different basins of Lake Constance can be very different. They further suggest that the lack of large crustaceans in particular the lack of large predatory cladocerans in the Lower Lake can have negative effects on growth and reproduction of zooplanktivorous European whitefish, Coregonus lavaretus, which feeds highly selectively on large cladocerans and which is of great economic significance for the whole region. Another possibility could be that the lack of large Cladocera in the Lower Lake is a result of strong fish predation which could be a consequence of lake morphology.
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The outcome of predator-prey interactions depends on the characteristics of predators and prey as well as the structure of the environment. In a replicated field enclosure experiment, we tested the effects of quantity and quality of different prey refuges (no structure, structure forming a partial refuge, and structure forming a complete refuge) on the interaction between piscivorous perch (Perca fluviatilis) and juvenile perch and roach (Rutilus rutilus). We quantified the behaviour of the predators and the prey and predator-induced prey mortality. The piscivores stayed in or close to the prey refuge and were more dispersed in the presence than in the absence of prey refuges. Survival of juvenile perch and roach decreased in the presence of predators and was higher for juvenile roach than for juvenile perch. In addition, juvenile perch survival increased with refuge efficiency Roach formed schools which were denser in the presence of predators, had a higher swimming speed (both in the open water and in the refuge) and used a larger area than juvenile perch. Both prey species decreased their distance to the prey refuge and increased the proportion of their time spent in the refuge in the presence of predators. The number of switches between the open-water habitat and the prey refuge was higher for juvenile roach than for juvenile perch. Juvenile perch used different parts of the prey refuge in a flexible way depending both on presence of predators and refuge type whereas juvenile roach used the different parts of the prey refuge in fixed proportions over all refuge treatments. Our results suggest that juvenile roach had a overall higher capacity to avoid predation than juvenile perch. However, in the presence of qualitatively different prey refuges juvenile perch responded to predators with more flexible refuge use than juvenile roach. The differences in antipredator capacities of juvenile perch and roach when subjected to piscivorous perch predation may depend on differences in life history patterns of the two species.
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Threespine stickleback in young postglacial lakes provide a compelling example of coevolution between species that compete for resources. Coexisting pairs of stickleback species are highly divergent in habitat, diet, and body size and shape, whereas stickleback occurring alone in lakes are intermediate. We used experiments in ponds to test mechanisms of divergence between coexisting species. The results support the hypothesis of coevolution by resource competition between stickleback, but we found evidence that interactions with natural enemies also contribute to divergence. Natural selection arising from these interactions selects against intermediate phenotypes, included hybrids, and thus has contributed to the origin and persistence of stickleback species. KeywordsStickleback-Coevolution-Character displacement-Speciation-Natural selection
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Mit seiner zwischen 1952 und 1955 unter dem Leit-gedanken „Seen schreiben ihre Geschichte in die Sedi-mente“ durchgeführten und 1956 veröffentlichten Dissertation „Sedimente als Ausdruck des Zustandes eines Gewässers” hat der schweizer Limnologe Hans Züllig den Weg für eine gesamtheitliche Betrachtung eines Gewässersystems mit den engen Beziehungen zwischen Wasserkörper und seiner sedimentären „Unterlage“ nicht nur für die aktuelle Situation, son-dern auch für die Vergangenheit aufgezeigt. Damit entstand ein wichtiges Werkzeug für die Rekon-struktion der limnologischen Entwicklung eines Ge-wässers, insbesondere seines Trophiegrades, mit Hilfe der Untersuchung datierter Sedimente. Neben chemi-schen Parametern — Konzentrationen an P, N, S und waren es vor allem die in den Sedimenten ent-Corg haltenen subfossilen Kieselalgen sowie Carotinoide, Pigmente, die von Phytoplanktern aus früheren Planktonpopulationen stammten und einen Zusammenhang mit dem Eutrophierungsgrad eines Sees herstellen ließen (Züllig 1982). Die hierfür von Züllig entwickelten dünnschicht-chromatographischen Methoden wurden später auch erfolgreich auf Pigmente phototropher Bakterien eingesetzt (Züllig 1985).
Article
Fish in schools benefit from increased vigilance and, as a consequence of inspection behaviour, predator recognition and assessment is improved. Schooling behaviour and inspection behaviour may inhibit attack by predators, and, if schools are attacked a variety of tactics, ranging from the confusion effect to the flash expansion, serve to protect individual members. There are however a number of constraints on the evolution of schooling and associated anti-predator mechanisms. Conflicting selection pressures, such as the need to forage, mate and avoid predation, can operate simultaneously. Selection pressures acting on immature and adult fish may be discontinuous necessitating a period of increased vulnerability when individuals switch tactics. Schooling may not be an equally appropriate defence against all predators and the phylogenetic origins of populations or species can lead to additional genetic constraints. -from Author
Article
1. The various commonly used methods of assessing, on the basis of gut contents, the food of those fishes which have a generalized diet are listed and discussed. Both during the present investigation and by re-examination of published data it is shown that, when a large number of fish are examined, and when the results are expressed comparably, i.e. each food item is shown as a percentage of the total food eaten, all methods give substantially the same results. Reasons are, however, given for rejection of the method based on the number of organisms eaten, and also of the practice of comparing data so obtained with counts of the organisms found in samples of small areas of the substratum. Such comparisons have in the past been used to give numerical expression to the availability of food organisms; but it is suggested that this would be better accomplished by using an arbitrary method of allocation of points on the basis of estimated volume of each food item present (a) in the fish guts, and (b) in general faunal collections from the habitat. The number of points, expressed as a percentage of the total, gained by any food item in the fish guts and in the general collections could then be compared. 2. The food of Gasterosteus aculeatus is studied, and it is shown that the diet, consisting chiefly of Crustacea and insects, changes slightly with season and with increase in size of fish. During the winter the fish eat less than at other times, and both sexes feed more sporadically than usual during the breeding season. It is suggested that the two biological races, A and B of Heuts, have different diets. 3. The food of Pygosteus pungitius is shown to be similar to that of Gasterosteus aculeatus, and to vary similarly. The data for the winter are, however, incomplete, and it appears that feeding in this species is more affected during the breeding season. 4. The food relations of three species of fish (G. aculeatus, Pygosteus pungitius and Rutilus rutilus) in a a small muddy Cheshire stream are discussed. It is shown that R. rutilus does not compete with the two other species, but that the diets of the two stickleback species are almost identical. It is suggested that differences in breeding habits enable these two species to live together as they nest in different areas, and that the number of each species is regulated by the fact that during the breeding season the males defend a definite territory round their nests. There is therefore only room for a certain number of nests of each species.
Article
Throughout their circumboreal coastal distribution, the threespine stickleback (Gasterosteus aculeatus L., 1758) typically reproduce at 1 or 2 years of age (second or third summer) and die during the year of the reproductive cycle. Extending from a previous study on the Haida Gwaii archipelago, western Canada, that identified an exceptionally long life span (8 years) in a population of large-bodied threespine stickleback, we use pelvic spine annuli to examine age of the five largest adult stickleback of 12 additional populations comprising five populations with average-sized adults (45–60 mm standard length (SL)) and seven populations with large-bodied adult stickleback (>75 mm SL). Each of the small-bodied populations had a maximum age of 1 or 2 years typical for the taxon. Among the large-bodied populations, which also reached adult size in the 2nd year, adult stickleback in the populations ranged from 3 to 6 years, indicating extended longevity. Low productivity habitats and refuge against gape-limited piscivores, each of which theoretically predicts reduced rate of senescence, are associated with the greatest longevity among these populations. These data combined with the recent full genome sequence for stickleback provide opportunities for locating genetic markers for extended longevity.
Article
Predator–prey interactions play an influential role in determining the demographics of a population or species. In the Northwest Atlantic, Atlantic cod, Gadus morhua, once the basis of a lucrative commercial fishery, have not recovered despite regulations imposed on the fishery to reduce harvest rates. One possible reason for the lack of recovery is that high predation pressure on juvenile and larval stages, particularly from species such as herring and mackerel, may regulate the abundance of cod. However, traditional methods used to identify larval cod and haddock often fail when applied to partially digested remains. Here, we described a DNA-based assay to identify the presence of digested cod remains from the stomachs of predatory fish species. After development, the assay was tested on two sets of field samples. Larval and juvenile cod were successfully detected in both tests.
Article
Reviews recent literature on the responses of different types of prey (fish, benthic animals and zooplankton) to fish predation in freshwater communities. Responses include behavioural responses, predator-induced morphological or chemical defences, and alterations in life history traits. The anti-predator tactics adopted depend on the possibilities of predicting future environmental changes. The consequences of the anti-predator tactics may be evident at the individual or population level. The possible costs of the responses reflect a trade-off between survival and reproduction and/or growth, and may be evident as a lowered intrinsic growth rate of the population. In studying prey responses, account should be taken of the effects of predation on the competitive interactions among the prey. -from Authors
An investigation of the predator-evasion behaviour of minnow (Phoxinus phoxinus) shoals confronted with a pike (Esox lucius) showed that individual minnows generally chose the behaviour that minimized their chance of being eaten by the predator. As soon as the pike had been detected, minnows switched from dispersed small shoals to a single compact school. They then commenced inspection behaviour, during which individuals or groups approached the predator. This inspection served to confirm recognition of the pike and provide information on its behaviour. Avoidance and skittering behaviour took place when the pike began stalking. It was only when the predator escalated its attack and struck at the shoal that the minnows performed their most costly predator evasion tactics, such as flash expansion and fountain. After such tactics individuals often became separated from the shoal and as such were most vulnerable to capture. As a last resort, individual minnows hid among stones. Minnows from provenances with and without pike exhibited a similar repertoire of antipredator behaviour patterns, but those sympatric with the predator integrated their tactics more effectively and regained pre-exposure behaviour sooner after each encounter. Shoal size had an important effect on the execution of tactics. Minnows in shoals of 10 were more likely than minnows in shoals of 20 or 50 to abandon schooling behaviour and seek cover as individuals.
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Three-spined stickleback Gasterosteus aculeatus were given the opportunity to forage on 5-7 d old cod larvae Gadus morhua, presented alone and in the presence of alternative prey of different sizes and numbers relative to that of the larvae. In one experiment, larvae were presented with an equal munber of Artemia salina smaller, equal and larger in body size than the cod larvae. In a second experiment cod larvae were presented in the presence of a naturally co-occurring zooplankter of equal size, adult Calanus finmarchicus. Larvae were presented at ratios of larvae to Calanus of 1:1, 3:1 and 5.6:1. In both experiments, the presence of alternative prey of equal or larger size significantly increased the latency (in seconds) until a cod larva was captured and decreased the overall proportion of cod larvae captured. In the second experiment, this was true even at a ratio of larvae to copepods of 3:1. Protection to the larvae appeared to be the result of selection by the predator of the alternative prey. -from Authors
Article
European whitefish (Coregonus lavaretus) is a dominant zooplanktivorous fish in many praealpine lakes and of great commercial interest. Estimation of prey consumed by European whitefish is essential for the prediction of top down effects in the pelagic zone. Whitefish is known to feed selectively on cladocerans. Quantitative estimates of prey consumed by whitefish are often not easy to get because stomachs frequently contain only degraded fragments of already digested prey. In this study stomach contents of European whitefish which were composed of digested, degraded prey were analyzed. Daphnid prey could be quantified by the number of mandibles divided by two, the number of head capsules and abdomina present. Predatory cladocerans could be quantified by the number of mandibles divided by two and the number of tail appendages present. For stomachs which contained heavily digested fragments counting the mandibles proved to be a useful and sometimes the only applicable means to quantify prey items. Other body parts, like structured legs which were broken into many pieces, were unsuited to quantify prey items.
Article
Three-spined sticklebacks Gasterosteus aculeatus L. strongly prefer larvae of Atlantic mackerel Scomber scombrus L. over smaller wild invertebrate Zooplankton in experiments where the sticklebacks were allowed to feed ad libitum and to voluntary cessation. The relative preference for fish larvae increased as their proportion declined, a “counter-switching” behavior. In spite of this increasing preference, the presence of Zooplankton as alternative prey strongly protected the fish larvae from predation. This occurred because at high plankton abundance (or low ratio of fish larvae to zooplankton) the total number of fish larvae (and total biomass) ingested by the sticklebacks during their voluntarily limited foraging periods decreased, despite lack of satiation. The mechanism for this interaction appears to be interference by the zooplankton (nonpreferred prey) in the stickleback's search for fish larvae. We interpret the stickleback's response (cessation of feeding before satiation) as equivalent to control of total ingestion by mean prey size, which would have the effect of maximizing the rate of food intake while minimizing foraging time. This result and the counter-switching are consistent with adaptations for minimizing risk from its own predators while foraging.
Article
The horizontal and vertical distribution patterns of pelagic spawning whitefish (Coregonus lavaretus) were studied by echosounding from the end of the growing season (early November) until after spawning (late January). During early November, whitefish inhabited similar depths during day and night, but during spawning displayed vertical migrations of up to 50 m amplitude: whitefish ascended at dusk and descended at dawn. At the end of the spawning season, vertical migrations ceased. Juveniles took part in the daily migrations, but only sexually mature specimens invaded the uppermost 10 m of water, while maturing and juvenile individuals and spent females stayed deeper during the night. This vertical distribution pattern is interpreted as a means to increase encounter probability among mature specimens. Diel vertical migration of the entire population is suggested to be an aid to avoid cannibalism on freshly spawned eggs during settling to the lake bottom. Total fish density estimates increased during upward migration and decreased during downward migration; this may be the result of differences in target strength caused by both reduced swimbladder volume and positive tilt while in deep waters. Highly reproducible abundance estimates were obtained during night when whitefish were evenly distributed at the top of their vertical range.
Article
The upper basin or Obersee of the Bodensee still retains all the fish species described more than four centuries ago, though rapid changes have recently been noted in many aspects of the fish community and of the Bodensee ecosystem. Though a variety of non-native species have been introduced, including a number of European and North American salmonids, none has become a prominent part of the community. The famous Blaufelchen, a pelagic coregonine, has recently been threatened by a combination of increasingly intensive exploitation, beginning at a low minimum size, compounded by an increasing growth rate of the species due to low population density, and due to increased planktonic food as a result of eutrophication. Consequently, by the early 1960s, the fishery came to exploit large yearlings, and few Blaufelchen survived to spawn. Eutrophication has reached a stage that is marginal to a number of deeper, benthic coregonines and char. Cyprinids, usually inshore, have expanded greatly, have invaded the pelagic habitat, and are subject to periodic mass mortalities. Other of man's effects are identified as are management measures now in practice.
Article
In this paper we review recent experimental work on the effects of the parasite Schistocephalus solidus (Cestoda: Pseudophyllidea) on the feeding behaviour of three-spined sticklebacks (Gasterosteus aculeatus L.). We also discuss how increased feeding motivation and subsequent altered foraging behaviour may be a mechanism for parasite-associated changes in the shoaling behaviour of infected sticklebacks. The presence of S. solidus plerocercoids in the body cavity constricts the stomach, increases the handling time for large prey and consequently reduces the profitability of such prey for infected fish. This is reflected in a switch in dietary preference from large to small prey in the laboratory and in altered stomach contents and impaired nutrient reserves in the wild. By altering their hosts' nutritional state by direct competition for nutrients from digested food (and possibly indirectly by altering diet and reducing competitive ability) and also by altering the fishes' appearance, such parasites have the potential to alter the costs and benefits involved in joining a shoal of conspecifics. Experimental work on the shoaling decisions of S. solidus-infected sticklebacks supports this hypothesis, and such behavioural modification is discussed in the context of the manipulation hypothesis of parasite transmission.
Article
Three-spined stickleback consumed prey of one size until the stomach was full whereafter similar-sized prey were rejected, but smaller prey were consumed. This evidence leads to the prediction of a shift in prey size preference as a result of the constraint imposed by remaining stomach capacity.
Article
Between 1951 and 1979, total phosphorous concentrations in Lake Constance increased from 7 to 87 μg L−1. Following wastewater treatment, phosphorus levels were brought under control, returning to 7.6 μg L−1 by spring 2007. The biological and chemical data from 1980 to 2004 were first modelled by seasonal time series analyses and then used to create a general model. Excluding collinear variables allowed the data set to be condensed to six variables that could be fitted into a general linear model that explained ∼75% of the observed annual variation in chlorophyll a. A clear seasonal influence was apparent, with chlorophyll a tracking trends in temperature and the progress of spring. A nonseasonal influence was also observed in the interaction of two biological components, the proportion of phytoplankton biomass available to Daphnia (i.e. the percentage of ingestible size <30 μm) and the grazing intensity. In combination, these biotic variables had a negative impact on chlorophyll a levels. In contrast, the concentration of soluble reactive phosphorus (SRP) correlated positively with chlorophyll a. The effect of SRP showed a significant seasonal component, as it was more abundant in spring than at other times of year. In general, the model predicts a negative exponential response of chlorophyll a to further depletion of SRP in Lake Constance, while the temperature trends predicted by current global warming scenarios will result in a moderate increase in productivity. Data from 2005 to 2007 were used to verify the model. The modelled chlorophyll a values were nonbiased and showed a close match to the measured values (r2: 75%). Thus the applicability, reliability, and informative value of the model for pelagic Lake Constance was confirmed. The approach might easily be applied to other waters.
Article
An experiment was designed to study how gut fullness and encounter with 5-mm Asellus aquaticus influenced acceptance or rejection of less profitable 8-mm Asellus. 45-mm sticklebacks were found to always accept 5-mm prey whereas 8-mm prey were accepted with an initial probability of about 0.9. This probability decreased as the gut filled. Fish of differing sizes and sex had similar daily energy intakes per unit body size, however the acceptance of 8-mm prey was related to fish size. Whenever a fish orientated to a prey it was followed by pursuit and manipulation independently of prey size. The decision to accept or reject prey occurred after one manipulation, a criterion that was more variable for the larger prey. For one feeding session per day the total energy intake was almost constant despite the changing combination of prey sizes eaten. The fish ate prey with long handling times if the energetic contents of the stomach had not reached 450 J. Calculations were made of how many of each millimetre prey size group would satisfy the 450 J demand and how long the estimated number would take to handle. This showed that the best option is to consume 5-mm prey if given the choice.
Article
Over a number of decades the process of prey choice has been investigated using fishes as model predators. Using fishes for the model has allowed the proximate factors that determine how a mobile predator finds and chooses to eat the prey encountered within a variable 3-D environment to be estimated. During prey choice a number of constraints exist, in particular most fish predators will eat their prey whole thus their jaws and gut create functional limitations once a prey has been attacked. By considering the relationship between the size of the prey and the predator's feeding apparatus and feeding motivation this study explores the link between mechanistic studies and theoretical, optimal foraging based predictions. How the prediction of prey choices made by the fish following prey encounter can be reconciled with what is likely to be found in the fish's stomach is discussed. This study uses a progression of empirical examples to illustrate how the limits of functional constraints and prey choice at different stages of motivation to feed can be taken into account to improve predictions of predator prey choice.
Article
This study investigated changes in the feeding behaviour and prey choice of threespine stickleback, Gasterosteus aculeatus, of different body sizes, in response to increasing prey size and stomach fullness of the fish. Within the behavioural feeding sequence, a decision to attack and a decision to eat the prey were made by the fish. Smaller fish were more likely to stop in midwater during the attack and to manipulate the prey when handling it. Larger fish were more likely to attack and eat the prey. The probability of success, however, decreased with larger prey. Success also decreased with increasing stomach fullness when prey larger than the prey width:mouth width (PW:MW) ratio of 0·6 were encountered. Regardless of fish or prey size, there was a constant handling time of approximately 3 s during which the fish decided to eat. The time taken to handle and eat a prey decreased for larger fish and rose with larger prey. Spitting frequency increased with prey size and spitting was always required for prey greater than the 0·6 PW:MW ratio. This corresponded to a preference for prey oriented head first and ventral side up. Prey closest to the 0·6 PW:MW ratio were the largest prey that could be eaten with little change in the time cost over all levels of stomach fullness. These prey, therefore, gave the fish the best energy return per unit cost, except when the stomach was empty, as larger prey represented a bigger energy return for the same time cost giving them a greater effective profitability. The morphological relationship between a predator and prey determines the resulting feeding behaviour and prey choice, although this choice also depends on the predator's need to acquire food.
Article
The effect of infection with the pseudophyllidean cestode Schistocephalus solidus on the meal size of individually housed three-spined stickleback Gasterosteus aculeatus was quantified. Infected fish harboured plerocercoid loads that contributed from 1·1 to 33·9% of their total mass. Across this range of infection levels, the presence of S. solidus infection had no significant directional effect on standard length (LS) corrected meal size of host three-spined sticklebacks. Amongst multiply infected fish there was a significant negative relationship between LS-corrected meal size and the proportion of host mass contributed by S. solidus parasites. This relationship, however, did not hold for singly-infected fish. Furthermore, the data suggest that multiply-infected fish that harbour a combined mass of parasites contributing <c. 15% to host body mass might exhibit meal sizes that exceed those of length-matched uninfected fish. The results suggest that although heavy infections can significantly reduce the meal size of heavily infected three-spined sticklebacks, in the early stages of multiple S. solidus infections host food intake may increase. The probable causes of these differential effects on meal size and their consequences for the host-parasite system are discussed.
Article
Prey species may use many different behaviours to avoid predation. In this study, the antipredator behaviours of juvenile roach (Rutilus rutilus) and juvenile perch (Perca fluviatilis) were studied in wading pools with three kinds of structural complexity: no structure, structure simulating vegetation and structure simulating bottom crevices. Predation experiments with piscivorous perch and habitat choice experiments with the prey were performed, and the foraging success and prey choice of the predators were related to the type of structure. Predator foraging success was lower in the vegetation than in the other treatments. In the absence of structure and with vegetation structure, predators preferred perch over roach, while the preference was reversed in the crevice treatment. Roach and perch differed in their antipredatory behaviours. Roach responded to the presence of predators by schooling, moving fast and remaining at the surface, and escaped from attacks by jumping out of the water. In contrast, perch moved more slowly, dispersed after attacks and tried to hide at the bottom. Perch always preferred the vegetation structure to the non-structured part of the pool, while roach showed preference for the vegetation structure only when predators were present. Roach never occurred in crevices, whereas perch used crevices when predators where present. Predator pursuit speed was lower in the vegetation structure than in the non-structured treatment, but prey escape speed was unaffected. The results suggest that both the quantity and quality of structural complexity interacting with species-specific antipredator behaviours are important for predator-prey dynamics. It is also suggested that the presence of structure can have substantial effects on the structure of North Eurasian fish communities, by affecting relative and absolute predation pressures from piscivorous perch on prey species.
Article
1. Cannibalistic behaviour in fish is reviewed here for the first time. 2. Cannibalism has been recorded in 36 out of 410 teleost families according to the published literature, but is considered to be more widespread than this. Finding examples of cannibalism is not difficult, and it may be more interesting to look for taxa in which the behaviour does not take place. 3. The families that have provided the most information include the Engraulididae, Esocidae, Poeciliidae, Gasterosteidae, Percidae and Cichlidae. 4. Cannibalism has been classified into seven types, depending on life-history stage, age difference between cannibal and prey, and whether or not they are related. 5. Although in captive populations, cannibalism tends to increase with increasing density and decreasing food availability, its role in population regulation has not been unequivocally demonstrated in any wild population, and obtaining the necessary data presents a formidable challenge to fish ecologists. 6. Cannibalism is of some economic importance in aquaculture, but its impact can be reduced relatively easily, by frequent grading to reduce size variability. 7. The main proximate advantage conferred by cannibalism is assumed to be nutritional. In an ultimate sense the behaviour may have evolved as a particularly effective competitive strategy. 8. Finally, it is considered that cannibalism deserves more attention from fish biologists. Investigations, however, should recognize the different types of cannibalistic interaction, and, in particular, should explore the different implications of kin and nonkin cannibalism
Article
Phytoplankton biomass and species composition were measured with a relatively high temporal resolution (once or twice a week during the growing season) from 1979 to 1989 in Lake Constance/berlingersee. Over this period soluble reactive phosphorus (SRP) concentrations during winter mixing were reduced by ca. 50% from 104 to 47 g 1–1, which caused a prolongation and amplification of the epilimnetic P depletion during the growth period. Seasonal dynamics of phytoplankton reacted to the decrease of SRP in the following ways: (1) Algal biomass decreased at least proportionally to the winter SRP concentrations in summer, but not in spring and autumn when biomass fluctuated irregularly. (2) The peak of biomass concentration changed from summer to spring. (3) The earlier onset of epilimnetic P depletion during the season in recent years promoted a stronger growth of some pennate diatoms in spring. It caused an amplification of the silicon depletion in summer, which may cause still greater reduction of diatoms and total algal biomass in summer. (4) Reduction of algal biomass during the clear-water phase proper became shorter and less pronounced. (5) The temporal variability of algal biomass decreased in summer and autumn but not in spring. (6) Average cell sizes remained unchanged in summer and autumn but increased in spring during the beginning of oligotrophication. These results are largely in agreement with other studies on lake restoration and expectations derived from the PEG (Plankton Ecology Group) model (Sommer et al. 1986). They show that a 50% reduction of SRP concentrations during homothermy may have pronounced effects on seasonal dynamics of algal biomass in a large and deep lake. The algal response to the external change of SRP concentrations can be described by the Le Chatelier principle, implying that the internal structure of the system (e.g. species composition) changes in order to minimize the effect of the external pressure (e.g. reduction of total biomass). Suggestions are made as to how this system behaviour may emerge from local interactions.
Article
We report on two sets of experiments designed to clarify the roles of sensory ‘confusion’ and prey ‘oddity’ as they interact to influence the hunting success of a pursuit predator, the largemouth bass (Micropterus salmoides), on silvery minnows (Hybognathus nuchalis). Bass quickly captured solitary minnows, but performed many unsuccessful attacks and took much longer to make a capture as prey school size was increased. At school sizes of eight and above, bass were effectively stymied, demonstrating the ‘confusion effect’. The inclusion of one or two ‘odd’ (blue-dyed) minnows in a school of eight greatly increased the ability of bass to capture both normal and odd prey, but this effect of oddity disappeared at a school size of 15. The implications of these results for understanding the adaptive basis of mixed species flocks, herds and schools is discussed.