A biologically explicit simulation model of resource competition between two species of seed-eating heteromyid rodent indicates that stable coexistence is possible on a homogeneous resource if harvested food is stored and consumers steal each other's caches. Here we explore the coexistence mechanisms involved by analyzing how consumer phenotypes and presence of a noncaching consumer affect the competitive outcome. Without cache exchange, the winning consumer is better at harvesting seeds and produces more offspring per gram of stored food. With cache exchange, coexistence is promoted by interspecific trade-offs between harvest ability, metabolic efficiency, and ability to pilfer defended caches of heterospecifics or scavenge undefended caches of dead conspecifics or heterospecifics. Cache exchange via pilferage can equalize competitor fitnesses but has little stabilizing effect and leads to stable coexistence only in the presence of a noncaching consumer. In contrast, scavenging is both equalizing and stabilizing and promotes coexistence without a third consumer. Because body size affects a heteromyid rodent's metabolic rate, seed harvest rate, caching strategy, and ability to steal caches, interspecific differences in body size should produce the trade-offs necessary for coexistence. The observation that coexisting heteromyids differ in body size therefore indicates that cache exchange may promote diversity in heteromyid communities.

In this paper, partnerships between parents/carers, children and professionals within child protection social work are critically assessed in relation to Beck’s (1992) concept of the ‘risk society’. Partnerships within core groups provide the specific focus for this paper, as in the authors’ view these groups provide particular opportunities for the development of partnerships between professionals, parents/carers and children. In the risk society new dangers and risks are constantly being created and (re)discovered, the status of professional and lay expertise is questioned and professional judgement is often mediated through discourses of risk. In this environment reflexivity becomes an essential element of professional practice. Two case studies of child protection are used to link theory and practice, and to raise questions for professional practice in core groups.

Macrophages are capable of destroying T cells with which they form cellular conjugates. The deletion can be prevented by the simultaneous transmission of costimulatory signals. We show here that T cells with elevated major histocompatibility complex (MHC) class I expression are resistant against macrophage-mediated cytotoxicity. T cells that express the CD45RO isotype, considered memory T cells, exhibit MHC class I antigen at higher density than naive CD45RA T cells and upregulate MHC class I expression promptly when they form cellular conjugates with macrophages. We confirm previous observations that CD45RA T cells are more susceptible to antibody- and macrophage-mediated deletion than memory CD45RO T cells. When MHC class I molecules are masked by specific monoclonal antibody or antibody Fab fragments, CD45RA T cells and CD45RO T cells exhibit equal susceptibility to macrophage cytotoxicity, demonstrating that the difference between CD45RA and CD45RO T cells in their sensitivity to macrophage cytotoxicity is determined by their MHC I expression. Separation of CD4 T cells from CD8 T cells deprives memory CD4 T cells of their resistance against macrophage cytotoxicity, suggesting that memory T cells' resistance against destruction by macrophages is controlled by regulatory T cells.