'National Antiquities' and the Law

National museums, housing â??national antiquities', were a nineteenth-century cultural phenomenon throughout Europe. In the United Kingdom, they afforded the Treasury a means of preserving relics of antiquity claimed as treasure trove. While satisfying the desire of the scientific community for the preservation of archaeological finds, and national sentiment in Scotland and Ireland, Treasury practice undermined the British Museum's eponymous mission. This paper traces the development and legal consequences of the Treasury policy of national allocation of treasure trove, including the discussion in the Museums Committee of 1898â??99 of the â??nationality' of objects and artefacts, and considers the potential wider significance of â??national antiquity' in the context of changing constitutional arrangements in the United Kingdom in the 1920s, and in the future.

Parasite mediated predation between native and invasive amphipods.

Parasites can structure biological communities directly through population regulation and indirectly by processes such as apparent competition. However, the role of parasites in the process of biological invasion is less well understood and mechanisms of parasite mediation of predation among hosts are unclear. Mutual predation between native and invading species is an important factor in determining the outcome of invasions in freshwater amphipod communities. Here, we show that parasites mediate mutual intraguild predation among native and invading species and may thereby facilitate the invasion process. We find that the native amphipod Gammarus duebeni celticus is host to a microsporidian parasite, Pleistophora sp. (new species), with a frequency of infection of 0-90%. However, the parasite does not infect three invading species, G. tigrinus, G. pulex and Crangonyx pseudogracilis. In field and laboratory manipulations, we show that the parasite exhibits cryptic virulence: the parasite does not affect host fitness in single-species populations, but virulence becomes apparent when the native and invading species interact. That is, infection has no direct effect on G. d. celticus survivorship, size or fecundity; however, in mixed-species experiments, parasitized natives show a reduced capacity to prey on the smaller invading species and are more likely to be preyed upon by the largest invading species. Thus, by altering dominance relationships and hierarchies of mutual predation, parasitism strongly influences, and has the potential to change, the outcome of biological invasions.

A species invasion mediated through habitat structure, intraguild predation and parasitism.

With field, laboratory, and modeling approaches, we examined the interplay among habitat structure, intraguild predation (IGP), and parasitism in an ongoing species invasion. Native Gammarus duebeni celticus (Crustacea: Amphipoda) are often, but not always, replaced by the invader Gammarus pulex through differential IGP. The muscle-wasting microsporidian parasite Pleistophora mulleri infects the native but not the invader. We found a highly variable prevalence of P. mulleri in uninvaded rivers, with 0–91% of hosts parasitized per sample. In addition, unparasitized natives dominated fast-flowing riffle patches of river, whereas parasitized individuals dominated slower- flowing, pooled patches. We examined the survivorship of invader and native in single and mixed-species microcosms with high, intermediate, and zero parasite prevalence. G. pulex survivorship was high in all treatments, whereas G. duebeni subsp. celticus survivorship was significantly lower in the presence of the invader. Further, parasitized G. duebeni subsp. celticus experienced near-total elimination. Models of the species replacement process implied that parasite-enhanced IGP would make invasion by G. pulex more likely, regardless of habitat and parasite spatial structure. However, where heterogeneity in parasite prevalence creates a landscape of patches with different susceptibilities to invasion, G. pulex may succeed in cases where invasion would not be possible if patches were equivalent. The different responses of parasitized and unparasitized G. duebeni subsp. celticus to environmental heterogeneity potentially link landscape patterns to the success or failure of the invasion process.

Parasite transmission and cannibalism in an amphipod (Crustacea).

In its freshwater amphipod host Gammarus duebeni celticus, the microsporidian parasite Pleistophora mulleri showed 23% transmission efficiency when uninfected individuals were fed infected tissue, but 0% transmission by water-borne and coprophagous routes. Cannibalism between unparasitised and parasitised individuals was significantly in favour of the former (37% compared to 0%). In addition, cannibalism between parasitised individuals was significantly higher than between unparasitised individuals (27% compared to 0%). Thus, parasitised individuals were more likely to be cannibalised by both unparasitised and parasitised individuals. We discuss the conflicting selective forces within this host/parasite relationship, the implications of parasite mediated cannibalism for host population structure and the impacts this may have on the wider aquatic community.

How parasites affect interactions between competitors and predators

We present a synthesis of empirical and theoretical work investigating how parasites influence competitive and predatory interactions between other species. We examine the direct and indirect effects of parasitism and discuss examples of density and parasite-induced trait-mediated effects. Recent work reveals previously unrecognized complexity in parasite-mediated interactions. In addition to parasite-modified and apparent competition leading to species exclusion or enabling coexistence, parasites and predators interact in different ways to regulate or destablize the population dynamics of their joint prey. An emerging area is the impact of parasites on intraguild predation (IGP). Parasites can increase vulnerability of infected individuals to cannibalism or predation resulting in reversed species dominance in IGP hierarchies. We discuss the potential significance of parasites for community structure and biodiversity, in particular their role in promoting species exclusion or coexistence and the impact of emerging diseases. Ongoing invasions provide examples where parasites mediate native/invader interactions and play a key role in determining the outcome of invasions. We highlight the need for more quantitative data to assess the impact of parasites on communities, and the combination of theoretical and empirical studies to examine how the effects of parasitism scale up to community-level processes.

The less amorous Gammarus: predation risk affects mating decisions in Gammarus duebeni (Amphipoda)

We examined the trade-off between the behaviours associated with predator avoidance and mate acquisition in the mate-guarding amphipod crustacean Gammarus duebeni. We used laboratory experiments to investigate the impact of olfactory predator cues on activity, mate choice and mate-guarding behaviour of males and females. Pair formation declined under perceived risk of predation, reflecting reduced activity of both males and females and hence a reduced likelihood of encountering a mate. We also observed a reduction in the choosiness of both males and females. Under increased perceived predation risk, assessment of the female by the male was more likely to be followed by pair formation, and males showed a nonsignificant trend towards reduced discrimination in favour of large females and were less tenacious in their pair bond when they paired during exposure to predator cues. Females also showed less resistance behaviour, suggesting that both males and females trade off the costs of maximizing current reproductive success against the benefits of predator avoidance for survival and reproduction in the future. We discuss the implications of such context-dependent mating behaviours for ecological interactions between species and suggest that predators, via the effects of perceived predation risk on mate choice and mate guarding in the prey species, induce trait-mediated indirect effects with the potential to influence population dynamics and community structure. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

A keystone effect for parasites in intraguild predation?

Intraguild predation (IGP) is common in communities, yet theory suggests it should not often persist and coexistence of participating species should be rare. As parasitism can play keystone roles in interactions between competitors, and between predators and prey, here we examine the role of parasites in maintaining IGP. We used numerical exploration of population dynamic equations to determine coexistence and exclusion zones for two species engaged in IGP with shared parasitism. We demonstrate that parasitism increases the range of conditions leading to coexistence when the parasite exerts a greater deleterious effect on the 'stronger' species in terms of the combined effects of competition and predation. Such a parasite can enable an inferior competitor that is also the less predatory to persist, and may actually lead to numerical dominance of this species.

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.

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

Differential physico-chemical tolerances and intraguild predation among native and invasive amphipods (Crustacea); a field study

We used field surveys and transplant experiments to elucidate the relative roles of physico-chemical regime and intraguild predation in determining the generally mutually exclusive distributions of native and invader freshwater amphipod species. Field surveys showed that the native Gammarus duebeni celticus dominates the shoreline of Lough Neagh, N. Ireland, with some co-occurrence with the N. American invader G. tigrinus. However, the latter species dominates the deeper areas of the mid-Lough. Transplant experiments showed no difference in survival of the native and invader in single species 'bioassay tubes' placed along the shoreline. However, there was significantly higher survival of the invader compared with the native in single species tubes placed in the mid-Lough. In mixed species tubes on the shoreline, the native killed and ate the invader, with no reciprocal interaction, leading to significant reductions of the invader. However, the invader had significantly higher survival than the native in mixed species tubes in the mid-Lough, with no evidence. of predation between the two species. These results indicate that, whereas differential intraguild predation may determine domination of the shoreline by the native, differential physico-chemical tolerances may be major determinants of the domination of the mid-Lough by the invader. This study emphasises the need to consider the habitat template in conjunction with biotic interactions before attempting to draw conclusions about mechanisms determining relative distribution patterns of native and invasive species.

Temporal changes in the distribution of native and introduced freshwater amphipods in Lough Neagh, Northern Ireland

Studies of invasion scenarios over long time periods are important to refine explanations and predictions of invasion success and impact. We used data from surveys in 1958 and 1999 of the macroinvertebrates of Lough Neagh, Northern Ireland, to assess changes in the distribution of native and introduced amphipods in relation to the wider assemblage. In 1958, the invader G. tigrinus dominated the shoreline fauna, with the native G. d. celticus present in very low numbers, whereas in 1999 the reverse was evident. In both surveys, G. tigrinus was the only amphipod present in the mid-Lough. G. tigrinus thus seems to have become established within L. Neagh, perhaps overshot and then senesced, with the native species re-establishing on the shoreline, with the invader mostly restricted to the deep mid-Lough. The non-amphipod macroinvertebrate assemblage was similar between the two surveys, in terms of Bray-Curtis community similarity, assemblage diversity, dominance and the taxa based ASPT water quality index. However, the mean density of macroinvertebrates (all taxa combined) was lower in 1999 compared to 1958, largely accounted for by a decline in oligochaete numbers. Since Gammarus species may be predators of other macroinvertebrates and influence their distribution and abundance, we investigated this trophic link in staged laboratory encounters. Both G. tigrinus and G. d. celticus preyed on isopods, alderflies, mayflies, chironomids and mysids, however, the native G. d. celticus had a significantly greater predatory impact on isopods and chironomids than did the invader G. tigrinus. While we cannot definitively ascribe cause and effect in the present scenario, we discuss how replacement of one amphipod species by another may have impacts on the wider macroinvertebrate assemblage.

An acanthocephalan parasite mediates intraguild predation between invasive and native freshwater amphipods (Crustacea)

1. The balance of predation between closely related invasive and native species can be an important determinant of the success or failure of biological invasions. In Irish freshwaters, the introduced amphipod Gammarus pulex has replaced the native G. duebeni celticus, possibly through differential mutual intraguild predation (IGP). Theoretically, parasitism could mediate such predation and hence the invasion outcome. However, this idea remains poorly studied.

Parasitism may enhance rather than reduce the predatory impact of an invader

Invasive species can have profound impacts on communities and it is increasingly recognized that such effects may be mediated by parasitism. The 'enemy release' hypothesis posits that invaders may be successful and have high impacts owing to escape from parasitism. Alternatively, we hypothesize that parasites may increase host feeding rates and hence parasitized invaders may have increased community impacts. Here, we investigate the influence of parasitism on the predatory impact of the invasive freshwater amphipod Gammarus pulex. Up to 70 per cent of individuals are infected with the acanthoce- phalan parasite Echinorhynchus truttae, but parasitized individuals were no different in body condition to those unparasitized. Parasitized individuals consumed significantly more prey (Asellus aquaticus; Isopoda) than did unparasitized individuals. Both parasitized and unparasitized individuals displayed Type-II functional responses (FRs), with the FR for parasitized individuals rising more steeply, with a higher asymptote, compared with unparasi- tized individuals. While the parasite reduced the fitness of individual females, we predict a minor effect on population recruitment because of low parasite prevalence in the peak reproductive period. The parasite thus has a large per capita effect on predatory rate but a low population fitness effect, and thus may enhance rather than reduce the impact of this invader.