The diversity, frequency, and scale of human impacts on coral reefs are increasing to the extent that reefs are threatened globally. Projected increases in carbon dioxide and temperature over the next 50 years exceed the conditions under which coral reefs have flourished over the past half-million years. However, reefs will change rather than disappear entirely, with some species already showing far greater tolerance to climate change and coral bleaching than others. International integration of management strategies that support reef resilience need to be vigorously implemented, and complemented by strong policy decisions to reduce the rate of global warming.

On the eve of the World Summit on Sustainable Development, it is timely to assess progress over the 10 years since its predecessor in Rio de Janeiro. Loss and degradation of remaining natural habitats has continued largely unabated. However, evidence has been accumulating that such systems generate marked economic benefits, which the available data suggest exceed those obtained from continued habitat conversion. We estimate that the overall benefit:cost ratio of an effective global program for the conservation of remaining wild nature is at least 100:1.

Field studies demonstrate that the population structure of the barnacle Balanus glandula differs between locations of high and low larval settlement rate. These observations, together with results from a model for the demography of an open, space-limited population, suggest that the settlement rate may be a more important determinant of rocky intertidal community structure than is presently realized. Locations with a low larval settlement rate exhibit a generally low abundance of barnacles that varies slightly within years and greatly between years, reflecting yearly differences in settlement. Locations with a high-settlement rate exhibit a generally high abudance of barnacles. However, the abundance varies greatly within years with a significant oscillatory component (period, 30 weeks) and only slightly between years regardless of yearly differences in settlement. At the low-settlement location mortality of barnacles is independent ofthe area occupied by barnacles. At the high-settlement location mortality is cover-dependent due to increased predation by starfish on areas of high barnacle cover. In both locations the coverindependent component of mortality does not vary with age during the first 60 weeks. As assumed in the demographic model, the kinetics of larval settlement can be described as a process in which the rate of settlement to a quadrat is proportional to the fraction of vacant space within the quadrat. Generalizations that the highest species diversity in a rocky intertidal community is found at locations of intermediate disturbance, and that competition causes zonation between species of the barnacle genera Balanus and Chthamalus, seem to apply only to locations with high-settlement rates.Many members of ecological communities in the marine intertidal zone have a life history consisting of pelagically dispersed larvae and sessile, space-limited adults. Familiar examples include barnacles and mussels (1-5). Larval phases as short as 2-3 weeks may lead to transport oflarvae in excess of 100 km (6-10). As a result, recruitment to a local section of the shore is from larvae that likely originated at other sites. Hence, a local section of shore is an open population that is not satisfactorily treated by the models of primarily closed populations applied to terrestrial ecological communities over the last decade (11)(12)(13) This study also confirms a key assumption of the openpopulation demographic model, that settlement to vacant space can be treated as a process in which the rate of settlement in a quadrat is proportional to the fraction of vacant space in it, with a constant of proportionality specific to location and time (including season). Further, this study reveals that disturbance (mortality that removes space-occupying organisms) is a cover-dependent process for barnacles subject to predation by the starfish Pisaster ochraceus and that the cover-independent component of survivorship is independent of age for at least the first 60 weeks of life.Finally, we note that the importance of t...

Rates of propagule supply can be important determinants of spatial and temporal patterns in community structure. In the northeast Pacific Ocean, large‐scale differences in the structure of intertidal invertebrate communities have been attributed to a latitudinal gradient in recruitment in this region. To determine whether such a gradient exists, recruitment of intertidal barnacles and mussels was monitored at 17 sites across this region in 1996 and 1997. A latitudinal gradient in recruitment was detected in this study. This gradient was approximately a stepcline: annual recruitment, on average, was 1–2 orders of magnitude higher in central and northern Oregon than in central and northern California. In contrast to the regional differences, large‐scale gradients in recruitment within California were small; correlations of recruitment with latitude were weak, and in all but one case, statistically insignificant. Nonetheless, trends in the data suggest that recruitment within central and northern California was highest between San Francisco and Monterey Bay, where larvae may be retained more nearshore than to the north or south. If so, apparently conflicting claims about latitudinal gradients in recruitment within California can be reconciled. The large‐scale transition in recruitment rates supports the hypothesis that a marked shift in the intensity of upwelling near Cape Blanco in southern Oregon is a major cause of a coincident transition in community structure. Stronger upwelling (and thus offshore flow) to the south has been hypothesized to transport larvae further offshore and thereby reduce larval supply to nearshore benthic communities. This study confirms that the predicted differences in recruitment exist, and that these differences are large. Preliminary calculations indicate that regional differences in offshore flow are likely to make a larger contribution to the recruitment transitions than several other plausible causes. In addition, recruitment transitions are larger, more abrupt, and more consistent across species than corresponding shifts in percentage cover, which favor competitive dominants. This supports model predictions that competition for space is more intense where recruitment is high. However, the absence of strong, large‐scale recruitment gradients within California suggests that mesoscale processes are relatively more important than latitudinal trends in upwelling as determinants of community structure patterns at smaller scales.

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Although much previous work describes evolutionary mechanisms that promote or stabilize different social behaviors, we still have little understanding of the factors that drive animal behavior proximately. Here we present a modeling approach to answer this question. Our model rests on motivations to achieve objectives as the proximate determinants of behavior. We develop a two-tiered framework by first modeling the dynamics of a social interaction at the behavioral time scale and then find the evolutionarily stable objectives that result from the outcomes these dynamics produce. We use this framework to ask whether "other-regarding" motivations, which result from a kind of nonselfish objective, can evolve when individuals are engaged in a social interaction that entails a conflict between their material payoffs. We find that, at the evolutionarily stable state, individuals can be other-regarding in that they are motivated to increase their partners' payoff as well as their own. In contrast to previous theories, we find that such motivations can evolve because of their direct effect on fitness and do not require kin selection or a special group structure. We also derive general conditions for the evolutionary stability of other-regarding motivations. Our conditions indicate that other-regarding motivations are more likely to evolve when social interactions and behavioral objectives are both synergistic.A nimal behavior is determined both by proximate mechanisms that dictate an animal's actions in real time and by evolutionary forces that shape these proximate mechanisms. Even though the evolutionary dynamics of social behavior have been extensively studied (1-4), proximate mechanisms of behavior and how they interface with evolutionary forces remain poorly understood (4). In recent years, some models have integrated a proximate mechanism with an evolutionary analysis (5, 6). Furthermore, an explicitly two-tiered approach with potentially cooperative behavioral dynamics embedded in an evolutionary dynamic has been proposed (7) as necessary to understand the evolution of social behavior. We contribute to this literature by developing a unified framework for modeling the evolution of a specific type of behavioral interaction based on a well-defined proximate mechanism.Our proximate mechanism is based on the notion that animals are motivated to achieve certain objectives. Goal-seeking behavior has been a recurring theme in animal behavior and has been an integral part of earlier ethological thinking (e.g. 8, 9). However, this idea lost its prominence after the emergence of modern behavioral ecology, which focuses mainly on the fitness consequences of behavior (see, for example, page 6 of ref. 10). In addition, proximate models of behavior based on goal-seeking have focused mostly on nonsocial behaviors such as foraging (9) and have rarely considered social interactions. Here, we study goal-seeking behavior in the context of a social interaction by developing a model of a pair of interacting animals whose motivations ...

Of the marine animals that spend their adult lives inhabiting benthic communities, most have a planktonic larval phase. In this paper, we derive the relationship between the physical oceanographic processes that transport these larvae and the strength of species interactions in the benthic habitat. We review a model of hierarchical competition for space between two species with planktonic larvae and develop a model for predatorprey dynamics in which prey are space-limited. Lotka-Volterra approximations to these models are developed. The approximations provide per capita interaction strength (the effect of an individual of one species on the per capita growth rate of another) and population interaction strength (the effect of a population of one species on the per capita growth rate of another) as functions of parameters in the original model. Per capita and population interaction strengths of dominant competitors on subordinates decrease in magnitude as offshore advection of larvae increases. The per capita effect of prey on predators also decreases as offshore advection increases, but population interaction strength is independent of offshore advection rate. Conversely, the per capita effect of predators on prey is independent of offshore larval advection rate, but the population effect decreases as offshore advection increases. We also develop submodels that simulate experimental removals of competitors and predators. Measurements of interaction strength derived from these simulations decrease as offshore advection of larvae increases. These results predict that a latitudinal gradient in upwelling intensity in the northeast Pacific produces a gradient in the intensity of species interactions in rocky intertidal communities.