Invasion by the amphipod Gammarus pulex alters community composition of native freshwater macroinvertebrates

Assessing the effects of invading species on native community structure is often confounded by environmental factors and weakened by lack of replicated, long-term pre- and post-invasion monitoring. Here, we uncouple the community effects of a freshwater amphipod invader from environmental differences. In Irish rivers, the introduced Gammarus pulex replaces the native Gammarus duebeni celticus. However, the River Lissan in Northern Ireland is dissected by a weir that has slowed the upstream invasion by G. pulex. This allowed us in 2000 to sample three contiguous 150-m reaches that were (1) G. pulex dominated; (2) mixed Gammarus spp.; and (3) G. duebeni celticus only. In 2003, we resampled these reaches and one additional of mixed Gammarus species and one with only G. duebeni celticus further upstream. In temperature, conductivity, and pH, there were statistically significant but no biologically relevant differences among the five reaches of 2003, and between the three reaches surveyed in both years. Although there was evidence of recovery in macroinvertebrate diversity and richness in invaded reaches between years, continued upstream invasion was associated with sustained reductions in these community metrics as compared to un-invaded sites. Community ordination indicated (1) different associations of community composition attributed to the distribution, abundance, and biomass of the invader; and (2) increasing similarity of invaded communities over time. The impact mechanisms of G. pulex on macroinvertebrate community composition may include predation and competition. The consequences of the observed community changes for ecosystem functioning require further investigation.

Predatory interactions between the invasive amphipod Gammarus tigrinus and the native opossum shrimp Mysis relicta

The invasive North American amphipod Gammarus tigrinus is successfully established in Lough Neagh, Northern Ireland. Gammarus tigrinus is increasingly recognized as having significant predatory impacts on macroinverebrates, contrary to the accepted functional feeding group status of Gammarus species. The native opossum shrimp Mysis relicta overlaps in habitat use with G. tigrinus. However, its interaction with benthic macroinvertebrates is rarely appreciated. Mutual predatory interactions between G. tigrinus and M. relicta were assessed in a series of laboratory experiments. Gammarus tigrinus actively preyed on adult and juvenile M. relicta at a range of spatial scales. Females and recently molted M. relicta were particularly vulnerable to predation. Mysis relicta did not prey on adult G. tigrinus, but rapidly eliminated juvenile G. tigrinus in microcosms. Changes in dissolved 02 saturation did not alter the predatory interaction between these species. Microhabitat use by M. relicta was altered in the presence of G. tigrinus, and the presence of G. tigrinus facilitated fish predation on M. relicta. A balance of mutual predatory pressure between these invasive and native species may explain their coexistence. Both species are likely to be strongly interactive with other macroinvertebrates in both native and invasive ranges.

Coexistence among native and introduced freshwater amphipods (Crustacea); habitat utilization patterns in littoral habitats

Studies of biological invasions predominantly stress threats to biodiversity through the elimination and replacement of native species. However, we must realise that resident communities may often be capable of integrating invaders, leading to patterns of coexistence. Within the past ninety years, three freshwater amphipod species have invaded Northern Ireland the North American Gammarus tigrinus and Crangonyx pseudogracilis, plus the European G. pulex. These species have come into contact with the ubiquitous native species, G. duebeni celticus. This study examined spatiotemporal patterns of stability of single and mixed species assemblages in an invaded lake. Lough Beg and its associated rivers were surveyed in summer 1994 and winter 1995, and a selection of stations re-sampled in summer one and five years later. All possible combinations of the four amphipod species were found. Although species presence/absence was stable between seasons at the scale of the whole lough, it was extremely fluid at the scale of individual sites, 82% of which changed in species composition between seasons. Overall mean amphipod abundance was similar across 5 distinguishable habitat types, but there were differences in species compositions among these habitats. In addition, although co-occurrences of Gammarus species did not differ from random, there was a strong negative association between Gammarus spp. and C. pseudogracilis. This latter pattern was at least in part generated by the better tolerance of C. pseudogracilis to lower water quality. A review of previous studies indicates that the exclusion of C. pseudogracilis by Gammarus species from high water quality areas is likely to involve biotic interaction. Thus, overall, co-existence of the four species, which is clearly dynamic and scale-dependent, appears promoted by spatial and temporal habitat heterogeneity. However, biotic interactions may also play a role in local exclusions. Since the three introduced species have not eliminated the native species, and each successive invasion has not replaced the previous invader, this study demonstrates that freshwater invaders may integrate with native communities leading to coexistence and increased species diversity.

Factors influencing the distribution of native and introduced Gammarus spp. in Irish river systems

Populations of Gammarus duebeni celticus, previously the only amphipod species resident in the rivers of the Lough Neagh catchment, N. Ireland, have been subjected to invasion by G. pulex from the British mainland. Numerous previous studies have investigated the potential behavioural mechanisms, principally differential mutual predation, underlying the replacement of G. d. celticus by G. pulex in Irish waters, and the mutually exclusive distributions of these species in Britain and mainland Europe. However, the relative degree of influence of abiotic versus biotic factors in structuring these amphipod communities remains unresolved. This study used principal component analysis (PCA) to distinguish physico-chemical parameters that have significant roles in determining the current distribution of G. pulex relative to G. d. celticus in L. Neagh rivers. We show that the original domination of rivers by the native G. d, celticus has changed radically, with many sites in several rivers containing either both species or only G. pulex. G. pulex was more abundant than the G. d. celticus in sites with low dissolved oxygen levels. This was reflected in the macroinvertebrate assemblages associated with G. pulex in these sites, which tended to be those tolerant of low biological water quality. The present study thus emphasizes the importance of the habitat template, particularly water quality, for Gammarus spp. interactions. If rivers become increasingly stressed by organic pollution, it is probable the range expansion of G. pulex will continue. Because these two species are not ecological equivalents, the outcomes of G. pulex incursions into G. d. celticus sites may ultimately depend on the prevailing physico-chemical regimes in each site.

Degradation, receptor binding, insulin secreting and antihyperglycaemic actions of palmitate-derivatised native and Ala(8)-substituted GLP-1 analogues

The hormone glucagonlike peptide-1(736)amide (GLP-1) is released in response to ingested nutrients and acts to promote glucosedependent insulin secretion ensuring efficient postprandial glucose homeostasis. Unfortunately, the beneficial actions of GLP-1 which give this hormone many of the desirable properties of an antidiabetic drug are short lived due to degradation by dipeptidylpeptidase IV (DPP IV) and rapid clearance by renal filtration. In this study we have attempted to extend GLP-1 action through the attachment of palmitoyl moieties to the epsilon-amino group in the side chain of the Lys(26) residue and to combine this modification with substitutions of the Ala(8) residue, namely Val or aminobutyric acid (Abu). In contrast to native GLP-1, which was rapidly degraded, [Lys(pal)(26)]GLP-1, [Abu(8),Lys(pal)(26)]GLP-1 and [Val(8),Lys(pal)(26)]GLP-1 all exhibited profound stability during 12 h incubations with DPP IV and human plasma. Receptor binding affinity and the ability to increase cyclic AMP in the clonal beta-cell line BRIN-BD11 were decreased by 86- to 167-fold and 15- to 62-fold, respectively compared with native GLP-1. However, insulin secretory potency tested using BRIN-BD11 cells was similar, or in the case of [Val(8),Lys(pal)(26)]GLP-1 enhanced. Furthermore, when administered in vivo together with glucose to diabetic (ob/ob) mice, [Lys(pal)(26)]GLP-1, [Abu(8),Lys(pal)(26)]GLP-1 and [Val8,Lys(pal)26]GLP-1 did not demonstrate acute glucoselowering or insulinotropic activity as observed with native GLP-1. These studies support the potential usefulness of fatty acid linked analogues of GLP-1 but indicate the importance of chain length for peptide kinetics and bioavailability.

Comparison of the functional responses of invasive and native amphipods

While we can usually understand the impacts of invasive species on recipient communities, invasion biology lacks methodologies that are potentially more predictive. Such tools should ideally be straightforward and widely applicable. Here, we explore an approach that compares the functional responses (FRs) of invader and native amphipod crustaceans. Dikerogammarus villosus is a Ponto-Caspian amphipod currently invading Europe and poised to invade North America. Compared with other amphipods that it actively replaces in fresh-waters, D. villosus exhibited significantly greater predation, consuming significantly more prey with a higher type II FR. This corroborates the known dramatic field impacts of D. villosus on invaded communities. In another species, FRs were nearly identical in invasive and native ranges. We thus propose that if FRs of other taxa and trophic groups follow such general patterns, this methodology has potential in predicting future invasive species impacts.

Differences in composition of macroinvertebrate communities with invasive and native Gammarus spp. (Crustacea : Amphipoda)

1. Assessing the effects on communities of invasive species is often confounded by environmental factors. In Irish rivers, the introduced amphipod Gammarus pulex replaces the native G. duebeni celticus in lowland stretches. The two amphipods are associated with different macroinvertebrate communities, which may in part be the result of natural longitudinal physicochemical change. However, this hinders assessment of any direct community impacts of the invasive as compared with the native species. Here, we report on a fortuitous circumstance that allowed us to uncouple the community effects of Gammarus species from environmental differences.

Non-indigenous marine macroalgae in native communities: a case study in the British Isles

It has traditionally been considered that areas with high natural species richness are likely to be more resistant to non-indigenous species than those with lower numbers of species. However, this theory has been the subject of a debate over the last decade, since some studies have shown the opposite trend. In the present study, a macroalgal survey was carried out at 24 localities in Northern Ireland and southern England, using a quadrat approach in the lower littoral. The two opposing hypotheses were tested (negative versus positive relationship between native and non-indigenous species richness) in this marine environment. The effect of the presence of 'impacts', potential sources of disturbance and species introduction (e.g. marina, harbour or aquaculture), was also tested. A positive relationship was found between the number of non-indigenous species and the native species richness at the three different scales tested (quadrats, sites and localities). At no scale did a richer native assemblage appear to restrict the establishment of introduced species. The analyses revealed greater species richness and different community composition, as well as more non-indigenous species, in southern England relative to Northern Ireland. The presence of the considered impacts had an effect on the community composition and species richness in southern England but not in Northern Ireland. Such impacts had no effect on the non-indigenous species richness in either area.

'The Adorning of My Native Tongue: Linguistic Metamorphosis in Milton'

This chapter, in a prize-winnng volume, examines Milton's bilingual practices in relation to his translation of Horace, Odes 1, 5 and the 1645 volume as a whole. Drawing upon seventeenth-century pedagogical practice and methodology it examines the potential importance of his schooling and university exercises to the methodology of Paradise Lost.

Do non-native invasive fish support elevated lamprey populations?

Summary
1: Managing populations of predators and their prey to achieve conservation or resource management goals is usually technically challenging and frequently socially controversial. This is true even in the simplest ecosystems but can be made much worse when predator–prey relationships are in?uenced by complex interactions, such as biological invasions, population trends or animal movements.
2: Lough Neagh in Northern Ireland is a European stronghold for pollan Coregonus autumnalis, a coregonine ?sh and for river lampreyLampetra ?uviatilis, which feeds parasitically as an adult. Both species are of high conservation importance. Lampreys are known to consume pollan but detailed knowledge of their interactions is scant. While pollan is well known to be a landlocked species in Ireland, the life cycle of normally anadromous river lamprey in Lough Neagh has been unclear. The Lough is also a highly perturbed ecosystem, supporting several invasive, non-native ?sh species that have the potential to in?uence lamprey–pollan interactions.
3: We applied stable isotope techniques to resolve both the movement patterns of lamprey and trophic interactions in this complex community. Recognizing that stable isotope studies are often hampered by high-levels of variability and uncertainty in the systems of interest, we employed novel Bayesian mixing models, which incorporate variability and uncertainty.
4: Stable isotope analyses identi?ed troutSalmo trutta and non-native breamAbramis brama as the main items in lamprey diet. Pollan only represented a major food source for lamprey between May and July.
5: Stable isotope ratios of carbon in tissues from 71 adult lamprey showed no evidence of marine carbon sources, strongly suggesting that Lough Neagh is host to a highly unusual, nonanadromous freshwater population. This ?nding marks out the Lough’s lamprey population as of particular scienti?c interest and enhances the conservation signi?cance of this feature of the Lough.
6: Synthesis and applications.Our Bayesian isotopic mixing models illustrate an unusual pattern of animal movement, enhancing conservation interest in an already threatened population. We have also revealed a complex relationship between lamprey and their food species that is suggestive of hyperpredation, whereby non-native species may sustain high lamprey populations that may in turn be detrimental to native pollan.Long-term conservation of lamprey and pollan in this system is likely to require management intervention, but in light of this exceptional complexity, no simple management options are currently supported. Conservation plans will require better characterization ofpopulation-level interactions and simulation modelling of interventions. More generally, our study demonstrates the importance of considering a full range of possible trophic interactions, particularly in complex ecosystems, and highlights Bayesian isotopic mixing models as powerful tools in resolving trophic relationships.
Key-words: Bayesian, conservation dilemma, Coregonus autumnalis, hyperpredation, Lampetra ?uviatilis, pollan, potamodromous, River lamprey, stable isotope analysis in R, stable isotope

Environmental mediation of intraguild predation between the freshwater invader Gammarus pulex and the native G. duebeni celticus

Invasive species and environmental change often occur simultaneously across a habitat and therefore our understanding of their relative roles in the decline of native species is often poor. Here, the environmental mediation of a critical interspecific interaction, intraguild predation (IGP), was examined between invasive (Gammarus pulex) and native (G. d. celticus) freshwater amphipods. In the laboratory, IGP asymmetries (males preying on congeneric females) were examined in river water sourced from zones where: (1) the invader has completely displaced the native; (2) the two species currently co-exist, and (3) the native currently persists uninvaded. The invader was always a more effective IG predator, but this asymmetry was significantly weaker moving from 'invader-only water' through 'co-existence water' to 'native-only water'. The constituent of the water that drives this mediation of IGP was not identified. However, balancing the rigour of laboratory experiments with field derived 'environment' has advanced understanding of known patterns in a native species decline, and its co-existence and persistence in the face of an invader.

Role of behaviour in biological invasions and species distributions; lessons from interactions between the invasive Gammarus pulex and the native G-duebeni (Crustacea : Amphipoda)

In attempting to understand the distributions of both introduced species and the native species on which they impact, there is a growing trend to integrate studies of behaviour with more traditional life history/ecological approaches. The question of what mechanisms drive the displacement of the freshwater amphipod Gammarus duebeni by the often introduced G pulex is presented as a case study Patterns of displacement are well documented throughout Europe, but the speed and direction of displacement between these species can be varied. From early studies proposing interspecific competition as causal in these patterns, I review research progress to date. I show there has been no evidence for interspecific competition operating, other than the field patterns themselves, a somewhat tautological argument. Rather, the increased recognition of behavioural attributes with respect to the cannibalistic and predatory nature of these species gave rise to a series of studies unravelling the processes driving field patterns. Both species engage in 'intraguild predation' (IGP), with moulting females particularly vulnerable to predation by congeneric males. G pulex is more able both to engage in and avoid this interaction with G duebeni. However, several factors mediate the strength and asymmetry of this IGP, some biotic (e.g. parasitism) and others abiotic (e.g. water chemistry). Further, a number of alternative hypotheses that may account for the displacement (hybridization; parasite transmission) have been tested and rejected. While interspecific competition has been modelled mathematically and found to be a weak interaction relative to IGP, mechanisms of competition between these Gammarus species remain largely untested empirically. Since IGP may be finely balanced in some circumstances, I conclude that the challenge to detect interspecific competition remains and we require assessment of its role, if any, in the interaction between these species. Appreciation of behavioural attributes and their mediation should allow us to more fully understand, and perhaps predict, species introductions and resultant distributions.

The replacement of a native freshwater amphipod by an invader: roles for environmental degradation and intraguild predation

We assessed the extent to which an invader, Gammarus pulex (Crustacea: Amphipoda), has replaced a native, Gammarus duebeni celticus, over a 13-year period in a European river system and some of the abiotic and biotic factors that could account for this. Between 1988 and 2001, 56% of mixed-species sites had become invader-only sites, whereas no mixed sites had become native only again. The native dominated areas of higher dissolved oxygen and water quality, with the reciprocal true for the invader. Field transplant experiments revealed that native survivorship was lower in areas where it had been replaced than in areas where the invader does not yet occur. In invader-only areas, native survivorship was lower than that of the invader when kept separately and lowest when both species were kept together. We also observed predation of the native by the invader. Laboratory oxygen manipulation experiments revealed that at 30% saturation, the native's survivorship was two thirds that of the invader. We conclude that decreasing water quality favours replacement of the native by the invader.

Lethal and sublethal toxicity of ammonia to native, invasive, and parasitised freshwater amphipods

In lethal and sublethal ammonia toxicity tests, we examined differences in tolerance of three species of freshwater amphipods, one native and two invasive in Ireland. The native Gammarus duebeni celticus was slightly less tolerant to ammonia than the invasive G. pulex (96h LC50 = 1.155 and 1.544 mg l(-1), respectively), while another invader, Crangonyx pseudograeilis, had the lowest tolerance (LC50 = 0.36 mg l(-1)). Parasitism of G. pulex by the acanthocephalan Echinorhynchus truttae greatly reduced the tolerance of the invader to ammonia (LC50 = 0.381 mg l(-1)). Further, precopula pair disruption tests indicated that G. d. celticus was more sensitive to ammonia than G. pulex at sublethal levels. We discuss these results in the context of the ecological replacements of native by invader amphipods. (C) 2004 Elsevier Ltd. All rights reserved.

Differential drift and parasitism in invading and native Gammarus spp. (Crustacea : Amphipoda)

Invading and native species often interact directly, such as by predation, producing patterns of exclusion and coexistence. Less direct factors, such as interactions with the broader abiotic and biotic environment, may also contribute to such patterns, but these have received less recognition. In Northern Ireland, the North American Gammarus tigrinus has invaded freshwaters populated with the native Gammarus duebeni celticus, with intraguild predation between the two implicated in their relative success. However, these species also engage in day and night