We dedicate this paper to the memory of John P. Sutherland, a great scientist, a great human being.Abstract. The usefulness and generality of the keystone species concept has recently been questioned. We investigated variation in interaction strength between the original keystone predator, the seastar Pisaster ochraceus, and its primary prey, mussels (Mytilus ca/ifornianus and M. trossulus). The study was prompted by differences in community structure at two low zone sites along the central Oregon coast, Boiler Bay (BB) and Strawberry Hill (SH). Predators, especially seastars, were larger and more abundant at SH than at BB. Further, sessile animals were more abundant and macrophytes were less abundant at SH. Predators were more abundant at wave-exposed sites at both sites, and at SH, sessile invertebrates were more abundant at the wave-exposed location and sand cover was high at the wave-protected location. To test the hypothesis that variation in predation strength explained some of these differences, we examined the seastar-mussel interaction at locations with high and low wave exposure at both sites. Predation intensity was quantified by determining the survival of mussels in clumps (50 mussels per clump, shell length 4-7 em) transplanted to large plots (18-163 m 2 ) with or without seastars in the low intertidal zone. Predation effects were quantified by determining prey recolonization rates in marked quadrats in the same large plots. Spatial variation in interaction strength was quantified by examining predation at scales of metres (among transplants within plots), lO's of metres (between replicate plots within each exposure at each site), 1 OO's of metres (between wave exposures within locations), and 10 OOO's of metres (between sites). Temporal variation was evaluated by performing the experiments in 1990 and 1991. The relation between prey (mussel) recruitment and growth to differences in community structure was evaluated by quantifying recruitment density in plastic mesh balls (collectors) and growth of individually marked transplanted mussels, respectively, at each site x exposure x tide level combination each month for 4 yr.Predation intensity varied greatly at all spatial scales. At the two largest spatial scales ( 1 O's of kilometres, 1 OO's of metres), differences in both survival of transplanted mussels and prey recolonization depended on variation in seastar abundance with site, wave exposure, prey recruitment and growth, and at SH protected, the extent of sand burial. Variation at the two smallest scales (metres, 10's of metres) was high when seastars were scarce and low when seastars were abundant. Transplanted mussels suffered 100% mortality in 2 wk at wave-exposed SH, but took >52 wk at wave-protected BB. Seastar effects on prey recolonization were detected only at the SH wave-exposed site. Here, where prey recruitment and growth were unusually high, the mussel M. trossulus invaded and dominated space within 9 mo. After 14 mo, whelks, which increased in both size and abundance in the absence o...

Species richness has dominated our view of global biodiversity patterns for centuries. The dominance of this paradigm is reflected in the focus by ecologists and conservation managers on richness and associated occurrence-based measures for understanding drivers of broad-scale diversity patterns and as a biological basis for management. However, this is changing rapidly, as it is now recognized that not only the number of species but the species present, their phenotypes and the number of individuals of each species are critical in determining the nature and strength of the relationships between species diversity and a range of ecological functions (such as biomass production and nutrient cycling). Integrating these measures should provide a more relevant representation of global biodiversity patterns in terms of ecological functions than that provided by simple species counts. Here we provide comparisons of a traditional global biodiversity distribution measure based on richness with metrics that incorporate species abundances and functional traits. We use data from standardized quantitative surveys of 2,473 marine reef fish species at 1,844 sites, spanning 133 degrees of latitude from all ocean basins, to identify new diversity hotspots in some temperate regions and the tropical eastern Pacific Ocean. These relate to high diversity of functional traits amongst individuals in the community (calculated using Rao's Q), and differ from previously reported patterns in functional diversity and richness for terrestrial animals, which emphasize species-rich tropical regions only. There is a global trend for greater evenness in the number of individuals of each species, across the reef fish species observed at sites ('community evenness'), at higher latitudes. This contributes to the distribution of functional diversity hotspots and contrasts with well-known latitudinal gradients in richness. Our findings suggest that the contribution of species diversity to a range of ecosystem functions varies over large scales, and imply that in tropical regions, which have higher numbers of species, each species contributes proportionally less to community-level ecological processes on average than species in temperate regions. Metrics of ecological function usefully complement metrics of species diversity in conservation management, including when identifying planning priorities and when tracking changes to biodiversity values.

Organisms eating each other are only one of many types of well documented and important interactions among species. Other such types include habitat modification, predator interference and facilitation. However, ecological network research has been typically limited to either pure food webs or to networks of only a few (<3) interaction types. The great diversity of non-trophic interactions observed in nature has been poorly addressed by ecologists and largely excluded from network theory. Herein, we propose a conceptual framework that organises this diversity into three main functional classes defined by how they modify specific parameters in a dynamic food web model. This approach provides a path forward for incorporating non-trophic interactions in traditional food web models and offers a new perspective on tackling ecological complexity that should stimulate both theoretical and empirical approaches to understanding the patterns and dynamics of diverse species interactions in nature.

We conducted field surveys of rocky intertidal communities at 18 sites distributed between 29°S and 36°S on the coast of central Chile in order to document broad patterns of functional and trophic group abundance and evaluate their association with oceanographic features. Results showed that the main sessile components of the landscape throughout the region were kelps (16%) and crustose algae (48%) in the low intertidal zone, while mussels beds (30%) and corticated algae (32%) dominated the mid-intertidal zone. Geographic trends in abundance across the entire region varied from no clear regional patterns for some groups (e.g. barnacles), to smooth gradients increasing or decreasing toward higher latitudes for others (kelps and ephemeral algae) and to an abrupt switch from dominant to scarce northward of 32°S in 1 group (mussels). Significant among-site negative correlations were detected between the abundances of most algal functional groups and between mussels and barnacles. Herbivore density was negatively correlated with kelp and corticated algal cover, and positively correlated with crustose algal abundance. These correlations reinforce the notion that local biological interactions can partially account for the among-site variability in functional group abundance. We assessed the influence of mesoscale oceanographic features through satellite image analyses, by classifying the study sites as either strongly or weakly influenced by coastal upwelling. At sites strongly influenced by upwelling, we found significantly higher cover of kelps in the low intertidal zone and of corticated algae in the mid-intertidal zone. Cover of ephemeral algae in the mid-intertidal zone was significantly lower at sites strongly affected by upwelling. Contrary to predictions of bottom-up community regulation models, we found no significant differences in abundance of sessile filter feeders (mussels or barnacles), herbivores or carnivores. A significant proportion of the regional variation in abundance in some of the most abundant functional groups within each tidal level was associated with the latitudinal gradient in annual mean sea surface temperature (SST). We detected a significant correlation between SST and the abundance of kelps and crustose algae in the low intertidal zone, and mussels and ephemeral algae in the mid-intertidal zone. The abrupt change in the abundance of mussels in the mid-intertidal zone at about 32°S may indicate a similarly abrupt change in biological or environmental conditions. Lack of significant correlation between the abundance of mussels and other functional groups suggests that biological interactions may not be responsible for this geographic discontinuity. We suggest that oceanography may be largely involved in the geographic variability detected in patterns of community structure. Recent remote sensing studies documenting oceanographic discontinuities around the 32°S zone support our suggestion. Our results highlight the need for further experimental and oceanographic studies in areas ...

Large and usually unpredictable variation in species interaction strength has been a major roadblock to applying local experimental results to large-scale management and conservation issues. Recent studies explicitly considering benthic-pelagic coupling are starting to shed light on, and find regularities in, the causes of such large-scale variation in coastal ecosystems. Here, we evaluate the effects of variation in wind-driven upwelling on community regulation along 900 km of coastline of the southeastern Pacific, between 29°S and 35°S during 72 months. Variability in the intensity of upwelling occurring over tens of km produced predictable variation in recruitment of intertidal mussels, but not barnacles, and did not affect patterns of community structure. In contrast, sharp discontinuities in upwelling regimes produced abrupt and persistent breaks in the dynamics of benthic and pelagic communities over hundreds of km (regional) scales. Rates of mussel and barnacle recruitment changed sharply at Ϸ32°-33°S, determining a geographic break in adult abundance of these competitively dominant species. Analysis of satellite images demonstrates that regional-scale discontinuities in oceanographic regimes can couple benthic and pelagic systems, as evidenced by coincident breaks in dynamics and concentration of offshore surface chlorophyll-a. Field experiments showed that the paradigm of top-down control of intertidal benthic communities holds only south of the discontinuity. To the north, populations seem recruitment-limited, and predators have negligible effects, despite attaining similarly high abundances and potential predation effects across the region. Thus, geographically discontinuous oceanographic regimes set bounds to the strength of species interactions and define distinct regions for the design and implementation of sustainable management and conservation policies.coastal ecosystems ͉ upwelling ͉ community regulation ͉ Chile