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.

How optimal life history changes with the community size-spectrum

This paper derives optimal life histories for fishes or other animals in relation to the size spectrum of the ecological community in which they are both predators and prey. Assuming log-linear size-spectra and well known scaling laws for feeding and mortality, we first construct the energetics of the individual. From these we find, using dynamic programming, the optimal allocation of energy between growth and reproduction as well as the trade-off between offspring size and numbers. Optimal strategies were found to be strongly dependent on size spectrum slope. For steep size spectra (numbers declining rapidly with size), determinate growth was optimal and allocation to somatic growth increased rapidly with increasing slope. However, restricting reproduction to a fixed mating season changed optimal allocations to give indeterminate growth approximating a von Bertalanffy trajectory. The optimal offspring size was as small as possible given other restrictions such as newborn starvation mortality. For shallow size spectra, finite optimal maturity size required a decline in fitness for large size or age. All the results are compared with observed size spectra of fish communities to show their consistency and relevance.

'Chocolate makes you autism': impairment, disability and childhood identities

This paper discusses perceptions and experiences of impairment and disability from the perspectives of learning disabled children, their parents and their social workers. The author reports on findings from her doctoral study that adults often fail to take into account the views and experiences of learning disabled chidren. As a result, these children developed their own interpretations of impairment and disability based on their experiences and interactions with others. Whilst this indicates that they are active social interpreters, it also suggests that adults should make greater efforts to inform and consult learning disabled children. The author concludes by reflecting on the relevance of these findings to contemporary theories of disability and childhood.

Exclusion and Marginalisation in Adolescence: The Experience of School Exclusion on Drug Use and Antisocial Behaviour

Young people excluded from school are a group at an increased risk to drug use and antisocial behaviour during adolescence and later marginalisation and exclusion from society in adulthood (Blyth and Milner, 1993). As part of the Belfast Youth Development Study, a longitudinal study of the onset and development of adolescent drug use, young people who entered post primary school in 2000 (aged 11/12 years) were surveyed annually on four occasions. This paper reports on findings from this survey in relation to a supplementary group of young people who were surveyed because they had been excluded from school. The findings show higher levels of drug use and antisocial behaviour among school excludees, lower levels of communication with their parents/guardians, higher levels of contact with the criminal justice system and increased likelihood of living in communities characterised with neighbourhood disorganisation. This lifestyle perhaps suggests these young people are leading a life that is already taking them towards the margins of society.

Methodological issues for qualitative research with learning disabled children

This paper discusses key methodological issues for qualitative research with learning disabled children, based on the author's experience of involving learning disabled children in her doctoral study. The study was founded on the social model of disability and a sociological understanding of childhood that recognizes the abilities of disabled children as competent research participants. Issues that arose throughout the research process, from the early stages of gaining access to children, to communication challenges for interviewing learning disabled children, and the analysis and dissemination of data, are discussed. Within this context, this paper explores key methodological issues for researchers with regard to interviewing learning disabled children and actively involving them in qualitative research.

Marine04 marine radiocarbon age calibration, 0-26 cal kyr BP

New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally ratified to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0–26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0–10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-resolution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5–26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).