Understanding the long-term effects of species invasions

We describe here the ecological and evolutionary processes that modulate the effects of invasive species over time, and argue that such processes are so widespread and important that ecologists should adopt a long-term perspective on the effects of invasive species. These processes (including evolution, shifts in species composition, accumulation of materials and interactions with abiotic variables) can increase, decrease, or qualitatively change the impacts of an invader through time. However, most studies of the effects of invasive species have been brief and lack a temporal context; 40% of recent studies did not even state the amount of time that had passed since the invasion. Ecologists need theory and empirical data to enable prediction, understanding and management of the acute and chronic effects of species invasions.     

Eco-immunology of fish invasions: the role of MHC variation

The relationship between invaders and the pathogens encountered in their new environment can have a large effect on invasion success. Invaders can become free from their natural pathogens and reallocate costly immune resources to growth and reproduction, thereby increasing invasion success. Release from enemies and relaxation of selective pressures could render newly founded populations more variable at immune-related genes, such as the major histocompatibility complex (MHC), particularly when they have different origins. Using rainbow and brown trout, two of the world’s most successful fish invaders, we tested the general hypothesis that invaders should display high intrapopulation immunogenetic diversity and interpopulation divergence, due to the interplay between genetic drift and successive waves of genetically divergent introductions. We analysed genetic diversity and signatures of selection at the MHC class II β immune-related locus. In both species, MHC diversity (allelic richness and heterozygosity) for southern hemisphere populations was similar to values reported for populations at their native range. However, MHC functional diversity was limited, and population immunogenetic structuring weaker than that observed using neutral markers. Depleted MHC functional diversity could reflect a decrease in immune response, immune-related assortative mating or selection for resistance to newly encountered parasites. Given that the role of MHC diversity in the survival of these populations remains unclear, depleted functional diversity of invasive salmonids could compromise their long-term persistence. A better understanding of the eco-immunology of invaders may help in managing and preventing the impact of biological invasions, a major cause of loss of biodiversity worldwide.     

Paradox lost: genetic diversity and the success of aquatic invasions

There is mounting evidence that reduced genetic diversity in invasive populations is not as commonplace as expected. Recent studies indicate that high propagule vectors, such as ballast water and shellfish transplantations, and multiple introductions contribute to the elimination of founder effects in the majority of successful aquatic invasions. Multiple introductions, in particular, can promote range expansion of introduced populations through both genetic and demographic mechanisms. Closely related to vectors and corridors of introduction, propagule pressure can play an important role in determining the genetic outcome of introduction events. Even low-diversity introductions have numerous means of avoiding the negative impact of diversity loss. The interaction of high propagule vectors and multiple introductions reveal important patterns associated with invasion success and deserve closer scrutiny.     

Importance of fungi in the diet of Gammarus pulex and Asellus aquaticus I: feeding strategies

The importance of fungi in the trophic biology of the freshwater detritivores Gammarus pulex and Asellus aquaticus was investigated. Inspection of leaves used in feeding trials indicated that whereas A. aquaticus scrapes at the leaf surface, G. pulex bites through the leaf material. Both species discriminated between fungal mycelia, fungally colonized and uncolonized leaf material but, although A. aquaticus selectively consumed fungal mycelia, G. pulex fed preferentially on leaf material. Fungi appear to be an important food source for A. aquaticus and selection of food material was positively correlated with fungal biomass. In contrast, for G. pulex, fungi appear to be more important as modifiers of leaf material. However, no significant correlations were found between food preference and any of the leaf modifications measured.     

Tackling aquatic invasions: risks and opportunities for the aquarium fish industry

The aquarium trade is an important and rapidly growing vector for introduced species in the United States. We examined this vector by surveying pet stores in the San Francisco Bay–Delta region to compile a list of aquarium fish species commonly stocked. We identified which of these species might be able to survive in the Bay–Delta, and investigated store representatives’ knowledge and attitudes about biological invasions. A restrictive analysis using conservative estimates of fish temperature tolerances and environmental conditions found that the local aquarium trade includes 5 fish species that can survive in a temperate system such as the Bay–Delta. Under more inclusive parameters, up to 27 fish species met the criteria for survival in the Bay–Delta. We further explored these results by comparing potential invader incidence between different types of stores. In the more restrictive analysis, three national retail chains stocked significantly more potentially invasive species than independent aquarium stores, but there was no difference in the more inclusive analysis. A significantly higher percentage of fish taxa were easily identifiable and well-labeled in chain stores than in independent stores. Most aquarium store representatives indicated willingness to take action to reduce the threat of trade-related introductions, although chain store employees were more willing to assign responsibility for reducing this threat to the aquarium industry than were independent store employees. Management efforts for this vector should focus on (a) improving labeling and identification of fish species in stores, (b) expanding the often spotty data on fish physiological tolerances, especially for saltwater species, (c) educating customers and store employees about the risks posed by pet release, and (d) providing better options for responsible disposal of unwanted fish. Electronic Supplementary Material   The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Monitoring the feeding activity of individual fish with a demand feeding system

Feeding activity of individual Arctic charr ( Salvelinus alpinus ) was recorded automatically for 29 days using a demand feeding system. Each of three groups of 15 fish was kept in 1 m³ tanks, containing brackish water at 10° C. Individual biting activity was continuously monitored using a PIT-tag (Passive Integrated Transponders) system with unique individual codes. The accuracies of the bite detection system were 91, 93.1 and 99.5% respectively, in the three tanks. In all tanks, most of the individuals (12–14) bit on the releasing trigger a few times during the first 3 days. Thereafter, one or two individuals per tank accounted for almost all of the biting activity. This pronounced shift in bite-number distribution among individuals was probably due to the development of a dominance hierarchy, in which the dominant individuals monopolized the trigger. Growth rates appeared to be highest among high ranking fish. The implications of using demand feeding and PIT-tag devices in feeding studies are discussed.     

Different feeding strategies in Antarctic scavenging amphipods and their implications for colonisation success in times of retreating glaciers

Background

Scavenger guilds are composed of a variety of species, co-existing in the same habitat and sharing the same niche in the food web. Niche partitioning among them can manifest in different feeding strategies, e.g. during carcass feeding. In the bentho-pelagic realm of the Southern Ocean, scavenging amphipods (Lysianassoidea) are ubiquitous and occupy a central role in decomposition processes. Here we address the question whether scavenging lysianassoid amphipods employ different feeding strategies during carcass feeding, and whether synergistic feeding activities may influence carcass decomposition. To this end, we compared the relatively large species Waldeckia obesa with the small species Cheirimedon femoratus, Hippomedon kergueleni, and Orchomenella rotundifrons during fish carcass feeding (Notothenia spp.). The experimental approach combined ex situ feeding experiments, behavioural observations, and scanning electron microscopic analyses of mandibles. Furthermore, we aimed to detect ecological drivers for distribution patterns of scavenging amphipods in the Antarctic coastal ecosystems of Potter Cove. In Potter Cove, the climate-driven rapid retreat of the Fourcade Glacier is causing various environmental changes including the provision of new marine habitats to colonise. While in the newly ice-free areas fish are rare, macroalgae have already colonised hard substrates. Assuming that a temporal dietary switch may increase the colonisation success of the most abundant lysianassoids C. femoratus and H. kergueleni, we aimed to determine their consumption rates (g food x g amphipods^?1 x day^?1) and preferences of macroalgae and fish.

Results

We detected two functional groups with different feeding strategies among scavenging amphipods during carcass feeding: carcass ‘opener’ and ‘squeezer’. Synergistic effects between these groups were not statistically verified under the conditions tested. C. femoratus switched its diet when fish was not available by consuming macroalgae (about 0.2 day^?1) but preferred fish by feeding up to 80% of its own mass daily. Contrary, H. kergueleni rejected macroalgae entirely and consumed fish with a maximal rate of 0.8 day^?1.

Conclusion

This study reveals functional groups in scavenging shallow-water amphipods and provides new information on coastal intraguild niche partitioning. We conclude that the dietary flexibility of C. femoratus is a potential ecological driver and central to its success in the colonisation of newly available ice-free Antarctic coastal habitats.

     

Effect of saline water on early success of amphidromous fish

Organisms that migrate between rivers and the sea inevitably pass through estuarine habitats. Despite the potential importance of salinity and temperature fluctuations for metabolic adaptation, little is known about the impact of environmental changes in estuaries on the survival of residents. Ayu (Plecoglossus altivelis) is a migratory fish that inhabits estuarine brackish water in its early life stages. The recent decline in the abundance of populations ascending into rivers is of concern for local biodiversity. The present study aims to elucidate the ecological processes that determine the early success of Ayu larvae under variable environmental conditions. The effects of salinity and water temperature on the endogenous growth of newly hatched larvae from the same brood were examined experimentally based on morphological and metabolic characteristics. High salinity and high water temperature together appeared to require more energy for larval osmoregulation, resulting in the acceleration of yolk depletion and reduced growth of the notochord. Increasing the osmoregulative cost during the yolk-sac stage resulted in the faster induction of a state of starvation. Seawater is considered to have an adverse effect on the survival of newly hatched larvae, as it lowers the efficiency of foraging and predator avoidance due to an energetic tradeoff. More attention should be paid to the significance of estuarine environments involving brackish waters to ensure the early survival of amphidromous fish such as Ayu.     

The genetics and genomics of marine fish invasions: a global review

Reviews in Fish Biology and Fisheries - We present a comprehensive review of the available global literature on the genetics and genomics of marine fish invasions. Overall this review provides data...     

Effects of bottom trawling on fish foraging and feeding

The effects of bottom trawling on benthic invertebrates include reductions of biomass, diversity and body size. These changes may negatively affect prey availability for demersal fishes, potentially leading to reduced food intake, body condition and yield of fishes in chronically trawled areas. Here, the effect of trawling on the prey availability and diet of two commercially important flatfish species, plaice (Pleuronectes platessa) and dab (Limanda limanda), was investigated over a trawling intensity gradient in the Irish Sea. Previous work in this area has shown that trawling negatively affects the condition of plaice but not of dab. This study showed that reductions in local prey availability did not result in reduced feeding of fish. As trawling frequency increased, both fish and prey biomass declined, such that the ratio of fish to prey remained unchanged. Consequently, even at frequently trawled sites with low prey biomass, both plaice and dab maintained constant levels of stomach fullness and gut energy contents. However, dietary shifts in plaice towards energy-poor prey items were evident when prey species were analysed individually. This, together with a potential decrease in foraging efficiency due to low prey densities, was seen as the most plausible cause for the reduced body condition observed. Understanding the relationship between trawling, benthic impacts, fish foraging and resultant body condition is an important step in designing successful mitigation measures for future management strategies in bottom trawl fisheries.     

Modeling the long-term effect of PCBs on Everglades fish communities

Fish communities are regularly exposed to a large number of natural and synthetic toxic chemicals, whose harmful effects, both short-term and long-term, need to be studied. Mathematical simulation models are known to be useful tools in the assessment of both acute and chronic effects. A time-concentration-effect model has been developed to assess the long-term effect of PCBs on multi generations of fish communities in the Florida Everglades. The term fish is used here generically to refer to five functional fish groups (FGs), two having small and two having large adult size, and a crustacean (crayfish), each of which are further composed of several age classes. Several contaminant concentration scenarios are analyzed in the simulations, subject to mortality and hatchability failure. The model predicts the population response time series for each FG, based upon exposure concentration and duration. Model results indicate that a concentration of 0.1 gl^–1 could have adverse effects on survival and reproduction success for Everglades fish communities. For comparison, the USEPA has stipulated a standard of 0.014 gl^–1 for the protection of freshwater fish from chronic effects and a standard of 1.0 gl^–1 from acute effects. Hopefully, the model may be further developed to assist in the formulation of policy or regulations concerning aquatic ecological risk to protect the aquatic ecosystem of the Everglades.     

Evaluating the use of spawning success to estimate reproductive success in a Caribbean reef fish

Observations on egg batch production by known female Stegastes partitus and the fates of those egg batches within the nests of known males revealed that spawning success was not a reliable predictor of hatching success and, hence, reproductive success because of high egg batch mortality. Moreover, while numbers of eggs per batch increased with increasing female length, both inter- and intra-individual variation in batch size was considerable, demonstrating that spawning events cannot be considered equivalent. These two findings indicate that spawning success cannot be assumed to provide a direct quantitative substitute for a measure of reproductive success in this benthic spawning reef fish.     

The feeding success of cattle egrets in flocks

The feeding rates of grouped (<1.5 m from conspecifics) and solo (>5 m from conspecifics) cattle egrets (Bubulcus ibis) in loose flocks away from cows were compared, to test the hypothesis that grouped cattle egrets benefit from feeding on prey flushed inadvertently by nearby conspecifics. The flock feeding rates were also compared to those of grouped and solo egrets near cows, to determine the effects of flock membership on feeding rates. Birds in flocks captured prey faster than those with cows, and tended to capture larger prey, but field observations and captive experiments failed to show that the feeding success of flock members was enhanced by the hypothesized ‘beater’ effect. Increases in prey density, however, always resulted in higher feeding rates, so some cattle egret groups may form in response to local concentrations of prey. Prey size may also play a role in group formation, because birds in the field tended to feed at greater distances from their neighbours when larger prey were captured, regardless of prey density. When small groups did form among cattle egrets feeding on relatively large prey, group members occasionally captured prey items that had been discovered by nearby conspecifics. This behaviour was not observed among birds in dense aggregations, which fed on small, highly abundant prey. These data indicate that there is a potential cost associated with feeding too near others unless the prey are relatively small and abundant.     

Mechanics of the feeding action of a cyprinid fish

The pressures in the buccal cavities of Golden orfe (Idus idus) have been recorded as the fish took food from a tube connected to a pressure transducer. Pressures 50–105 cm water below the pressure of the surrounding water were recorded as the buccal cavity expanded to suck the food in. Calculations based on the dimensions of the muscles lead to the conclusion that the levatores hyoidei, sternohyoideus, rectus abdominis, epaxial trunk muscles and obliquus internus probably all had to exert almost their maximum isometric tensions, to produce the largest reductions of pressure. These muscles seem nicely balanced in strength for their functions in feeding.     

Zooplankton feeding in the fish Trichogaster pectoralis Regan

The traditional culture method of Trichogaster pectoralis, using zooplankton produced from fermenting aquatic weeds as a source of food for the fry, leads to productions of ca 1 000 kg ha^–1 a^–1. If chicken manure is applied at a rate of ca 450 kg ha^–1 month^–1 instead, much more zooplankton is produced more rapidly, and fish production increases to ca 2 000 kg ha^–1 a^–1. This results from a higher survival rate of the fry, which feeds on rotifers, ciliates, copepods and cladocera until a size of ca 15.0 mm, when plant material also becomes important in the diet.     

Proteinases of hydrobionts--potential objects of fish feeding

The review analyzes data on activities and characteristics of proteinases of digestive system and of cathepsins of various tissues in potential preys of fish differing by the character of feeding. There are presented data on multiple forms and molecular mass of proteinases, species-related differences, dependence of proteinase activities on the life cycle stages, type of nutrition, and biochemical food composition as well as on temperature and pH optima. Role of cathepsin in evolution of enzymatic systems providing degradation of food protein components in fish is discussed.     

Comparing climate change and species invasions as drivers of coldwater fish population extirpations

Species are influenced by multiple environmental stressors acting simultaneously. Our objective was to compare the expected effects of climate change and invasion of non-indigenous rainbow smelt (Osmerus mordax) on cisco (Coregonus artedii) population extirpations at a regional level. We assembled a database of over 13,000 lakes in Wisconsin, USA, summarising fish occurrence, lake morphology, water chemistry, and climate. We used A1, A2, and B1 scenarios from the Intergovernmental Panel on Climate Change (IPCC) of future temperature conditions for 15 general circulation models in 2046-2065 and 2081-2100 totalling 78 projections. Logistic regression indicated that cisco tended to occur in cooler, larger, and deeper lakes. Depending upon the amount of warming, 25-70% of cisco populations are predicted to be extirpated by 2100. In addition, cisco are influenced by the invasion of rainbow smelt, which prey on young cisco. Projecting current estimates of rainbow smelt spread and impact into the future will result in the extirpation of about 1% of cisco populations by 2100 in Wisconsin. Overall, the effect of climate change is expected to overshadow that of species invasion as a driver of coldwater fish population extirpations. Our results highlight the potentially dominant role of climate change as a driver of biotic change.     

Taxonomy-based differences in feeding guilds of fish

It has been taken for granted that feeding guilds and behavior in animals are linked to the taxonomic relatedness of species,but empirical evidence supporting such relationship is virtually missing.To examine the importance of taxonomy on trophic ecology,I here present the first well-resolved dietary taxonomy analysis based on feeding guilds(predation,herbivory,and filtering)among families and genera within the fish order Perciformes.Taxonomic relatedness in feeding did not vary with ecosystem dimension(marine vs.freshwater).Although predation dominates among Perciformes fishes,this study shows that in most cases taxonomic units(family or genus)are composed by species with several feeding guilds.Related species are more similar in feeding compared with species that are taxonomically more distant demonstrating that there is a greater variation of feeding guilds within families than genera.Thus,there is no consistency in feeding guilds between family-and genus-level taxonomy.This study provides empirical support for the notion that genera are more informative than families,underlining that family-level taxonomy should be avoided to infer feeding habits of fish species at finer taxonomic resolution.Thus,the choice of taxonomic resolution(family or genus level)in ecological studies is key to avoid information loss and misleading results.I conclude that high-rank taxonomic units(i.e.,above the generic level)are not appropriate to test research hypotheses about the feeding of fish.     

Antipredator behavior promotes diversification of feeding strategies

Animals often facultatively engage in less risky behavior when predators are present. Few studies, however, have investigated whether, or how, such predator-mediated behavior promotes diversification. Here, we ask whether tadpoles of the spadefoot toad Scaphiopus couchii have a diminished ability to utilize a potentially valuable resource--anostracan fairy shrimp--because of behavioral responses to predation risk imposed by carnivorous tadpoles of the genus Spea. Observations of a congener of Sc. couchii that occurs in allopatry with Spea, coupled with an ancestral character state reconstruction, revealed that Sc. couchii's ancestors likely consumed shrimp. By experimentally manipulating the presence of Spea carnivore-morph tadpoles in microcosms, we found that Sc. couchii reduce feeding and avoid areas where both Spea carnivores and shrimp occur. We hypothesize that the recurrent expression of such behaviors in sympatric populations of Sc. couchii led to the evolutionary fixation of a detritivorous feeding strategy, which is associated with a reduced risk of predation from Spea carnivores. Generally, predator-mediated behavior might play a key role in promoting diversification of feeding strategies.