Interactions between Multiple Recruitment Drivers: Post-Settlement Predation Mortality and Flow-Mediated Recruitment

Dispersal is a primary driver in shaping the future distribution of species in both terrestrial and marine systems. Physical transport by advection can regulate the distance travelled and rate of propagule supply to a habitat but post-settlement processes such as predation can decouple supply from recruitment. The effect of flow-mediated recruitment and predation on the recruitment success of an intertidal species, the eastern oyster Crassostrea virginica was evaluated in two-replicated field experiments. Two key crab species were manipulated to test predator identity effects on oyster mortality.Recruitment was ∼58% higher in high flow compared to low flow, but predation masked those differences. Predation mortality was primarily attributed to the blue crab Callinectes sapidus, whilst the mud crab Panopeus herbstii had no effect on recruit mortality. Recruit mortality from predation was high when recruit densities were high, but when recruit density was low, predation effects were not seen. Under high recruitment (supply), predation determined maximum population size and in low flow environments, recruitment success is likely determined by a combination of recruitment and resource limitation but not predation.Four processes are demonstrated: (1) Increases in flow rate positively affect recruitment success; (2) In high flow (recruitment) environments, resource availability is less important than predation; (3) predation is an important source of recruit mortality, but is dependent upon recruit density; and (4) recruitment and/or resource limitation is likely a major driver of population structure and functioning, modifying the interaction between predators and prey. Simultaneous testing of flow-mediated recruitment and predation was required to differentiate between the role of each process in determining population size. Our results reinforce the importance of propagule pressure, predation and post-settlement mortality as important determinants of population growth and persistence, but demonstrate that they should not be considered mutually exclusive

8008: The measure of a competent child care social worker?

This paper reflects upon some mixed messages found in recent consultation and framework documents that have been issued as part of the debate surrounding the Government's emphasis upon education and training within its 'modernisation' agenda. It identifies the long-standing arguments about 'testing' versus 'learning' or 'contextual' paradigms and suggests that, perhaps, there is still scope to influence the future direction of social work. The author has drawn upon his research with social workers and their team managers in current post-qualification award programmes to argue for a renewed emphasis upon the inter-personal and relationship aspects of educational processes within more broadly conceived socio-cultural contexts. A focus upon reflexively defined concepts of 'engagement' and 'assessment' is used to explore constructivist arguments that locate individuals within an interplay of potential and constraints. It is argued that constructive engagements within revised conceptions of assessment can form the basis of a framework of continuing professional development that starts from and develops the unique realities of social work practice. This requires the committed involvement of more people, in the negotiation of a professional practice agenda for knowledge creation through relationships, rather than the imposition of more measures