This study examined whether insects can alter relationships between plant species diversity and ecosystem function in grassland communities, by (i) altering biomass across a plant diversity gradient, (ii) altering relative abundances of plant species, or (iii) altering ecosystem function directly. We measured herbivore damage on seminatural grassland plots planted with 1, 2, 4, 8, or 12 plant species, and compared plant biomass in a subset of these plots with replicates in which insect levels were reduced. Plant biomass and herbivore damage increased with species richness. Reducing insect populations resulted in greater evenness of relative plant species abundances and revealed a strong positive relationship between plant species richness and above‐ground biomass. Reducing insects also changed the relationship between plant species richness and decomposition. Plant species mixtures and their relative abundances partially explained plant biomass results, but not decomposition results. These results suggest that insects can alter relationships between plant diversity and ecosystem processes through all three mechanisms.

We formulated a mathematical model to study the evolution of biodiversity. Our model describes a collection of sites and incorporates a simple but explicit description of the competitive processes within a site. In our model the characteristics of component species evolve towards an evolutionarily stable state and in this way an evolutionarily stable assemblage of species is formed. We show that the number of species in these assemblages matches two well‐documented patterns in biodiversity: the increase in the number of species towards the equator and the dependence of the number of species on the productivity of habitat: the average number of species rises to a maximum and then falls when plotted against increasing productivity of that habitat. Our results show that population dynamical and evolutionary processes can underlie patterns in biodiversity.

In our study group of 13 adult refractory coeliac disease patients, cyclosporin in therapeutic doses induced a histological improvement in eight patients (61%), in five of whom (38%) normalization of villi was demonstrated. Thus, we believe that cyclosporin is a therapeutic option in refractory coeliac disease, although we could not confirm earlier reports of unconditional successful treatment.

Controversy exists among anthropologists, conservation biologists, and development workers as to whether the concept of the "ecologically noble savage" is a myth. Central to this debate are the problem of how to identify conservationist behavior and the issue of whether sound management of common property is likely to evolve. While social scientists have documented instances of restraint in the use of resources, those who adopt an evolutionary perspective are challenged to identify the selective mechanisms whereby such altruistic conservation acts might be maintained in a population. Here a game-theoretical approach is used to analyze the case of pastoralist grazing reserves. We demonstrate that under some conditions conservation can be the result of narrow self-interest and there is no collective-action problem. However, the range of these conditions is much broader for wealthy individuals, and thus the wealthy may also find it advantageous to coerce others into conserving. In conclusion, we propose an extension of the definition of conservation that is of greater generality for use in nonforaging populations and incorporates the essential political element of how conflicts over resource use are resolved.l o r e m . ru t t a n is a postdoctoral researcher with the "Sea Around Us" project of the Fisheries Centre, University of British Columbia (2204 Main Mall, Vancouver, B.C., Canada V6T 1Z4). Born in 1961, she was educated at the University of Chicago (A.B., 1984) and the University of Minnesota (M.S., 1988). Her research interests are human behavioral ecology and commonproperty resource management. She has published (with C.