Gary W. Allison

MARINE RESERVES ARE NECESSARY BUT NOT SUFFICIENT FOR MARINE CONSERVATION

The intensity of human pressure on marine systems has led to a push for stronger marine conservation efforts. Recently, marine reserves have become one highly advocated form of marine conservation, and the number of newly designated reserves has increased dramatically. Reserves will be essential for conservation efforts because they can provide unique protection for critical areas, they can provide a spatial escape for intensely exploited species, and they can potentially act as buffers against some management miscalculations and unforeseen or unusual conditions. Reserve design and effectiveness can be dramatically improved by better use of existing scientific understanding. Reserves are insufficient protection alone, however, because they are not isolated from all critical impacts. Communities residing within marine reserves are strongly influenced by the highly variable conditions of the water masses that continuously flow through them. To a much greater degree than in terrestrial systems, the scales of fundamental processes, such as population replenishment, are often much larger than reserves can encompass. Further, they offer no protection from some important threats, such as contamination by chemicals. Therefore, without adequate protection of species and ecosystems outside reserves, effectiveness of reserves will be severely compromised. We outline conditions under which reserves are likely to be effective, provide some guidelines for increasing their conservation potential, and suggest some research priorities to fill critical information gaps. We strongly support vastly increasing the number and size of marine reserves; at the same time, strong conservation efforts outside reserves must complement this effort. To date, most reserve design and site selection have involved little scientific justification. They must begin to do so to increase the likelihood of attaining conservation objectives.

The influence of species diversity and stress intensity on community resistance and resilience

Recent theory, such as the insurance hypothesis, suggests that higher species diversity may dampen perturbation dynamics within a community. The dynamics of a rocky intertidal macroalgal community were evaluated using an experimentally induced heat stress applied at the end of a 15-mo manipulation of diversity. This pulse event produced a gradient of thermal stress within plots and, consequently, different degrees of perturbation. In gen- eral, the resistance of the community to the thermal stress was forecast by the pre-stress cover of dominant species, total algal cover, and standing biomass. Because higher diversity treatments, especially those containing the dominant algal group, fucoids, had higher overall abundance, highest diversity treatments were the most severely affected. The stress was also relatively nonselective, in that species were reduced in roughly equivalent proportions, suggesting an important distinction for predicting when diversity will not influence dis- turbance dynamics. The resilience of the community was strongly dependent on which species were initially present in the plots and the degree of disturbance. In highly disturbed areas, although the recovery trajectory was similar in early successional stages, differences emerged later; these differences appear to be attributable to the composition of the sur- rounding regeneration pool. For treatments not receiving the thermal stress, low-diversity plots without fucoids remained in states unlike the reference condition for most of the monitored resilience period. But plots in high-diversity treatments, even areas within plots that had experienced moderate disturbance, returned to states similar to the reference quick- ly. Thus, resilience (but not resistance) results are consistent with the insurance hypothesis. Overall, diversitys influence on community dynamics is complex and will depend on the characteristics of the stress as well as the characteristics of the species present in the

Mussel Disturbance Dynamics: Signatures of Oceanographic Forcing from Local Interactions

Local interactions, biotic and abiotic, can have a strong influence on the large‐scale properties of ecosystems. However, ecological models often explore the influence of local biotic interactions where physical disturbance is included as a large‐scale and imposed source of variability but is not allowed to interact with biotic processes at the local scale. In marine intertidal communities dominated by mussels, wave disturbances create gaps in the mussel bed that recover through a successional sequence. We present a lattice model of mussel disturbance dynamics that allows local interactions between wave disturbance and mussel recolonization, in which each cell of the lattice can be empty, occupied by a mussel bed element, or disturbed (which corresponds to a newly disturbed cell that has unstable edges). As in natural ecosystems, wave disturbance can also spread from disturbed to adjacent occupied cells, and recolonization can also spread from occupied to adjacent empty cells. We first validate the local rules from artificial gap experiments and from natural gap monitoring along the Oregon coast. We analyze the properties of the model system as a function of different oceanographic forcings of productivity and disturbance. We show that the mussel bed can go through phase transitions characterized by a large sensitivity of mussel cover and patterns to oceanographic forcings but also that criticality (scale invariance) is observed over wide ranges of parameters, which suggests self‐organization. We also show that spatial patterns in the intertidal can provide a robust signature of local processes and can inform about oceanographic regimes. We do so by comparing the large‐scale patterns of the simulation (scaling exponents) with field data, which suggest that some experimental sites are close to criticality. Our results suggest that regional patterns in disturbed populations can be explained by local biotic and abiotic processes submitted to oceanographic forcing.

The Implications of Experimental Design for Biodiversity Manipulations

I report a simulation study that tested the ability of a variety of experimental designs to achieve two fundamental goals: (1) to determine the association between loss of biological diversity and responses such as ecosystem functioning and (2) to determine which components of biodiversity, such as number of species, functional diversity, or a keystone species, were most responsible for that association. For the goal of reliably detecting an overall association, all designs I tested performed well and were unlikely to misidentify predominant patterns. Thus, this study affirms the common conclusion of many published biodiversity experiments that loss of biological diversity is often associated with a reduction in ecosystem functioning. However, for the goal of identifying the components of biodiversity that are most responsible for the effects, designs differed markedly. Some designs performed well in detecting number‐of‐species effects but poorly in detecting effects of unique species or functional groups. No design tested was able to discriminate both numeric effects and compositional effects in all situations. Thus, this study demonstrates that interpreting results about mechanisms from biodiversity experiments will be critically dependent on an experiments design.

Scale, Environment, and Trophic Status: The Context Dependency of Community Saturation in Rocky Intertidal Communities

Our understanding of the relative influence of different ecological drivers on the number of species in a place remains limited. Assessing the relative influence of local ecological interactions versus regional species pools on local species richness should help bridge this conceptual gap. Plots of local species richness versus regional species pools have been used to address this question, yet after an active quarter‐century of research on the relative influence of local interactions versus regional species pools, consensus remains elusive. We propose a conceptual framework that incorporates spatial scale and ecological interaction strength to reconcile current disparities. We then test this framework using a survey of marine rocky intertidal algal and invertebrate communities from the northeast Pacific. We reach two main conclusions. First, these data show that the power of regional species pools to predict local richness disintegrates at small spatial scales coincident with the scale of biological interactions, when studying ecologically interactive groups of species, and in generally more abiotically stressful habitats (e.g., the high intertidal). Second, conclusions of past studies asserting that the regional species pool is the primary driver of local species richness may be artifacts of large spatial scales or ecologically noninteractive groups of species.

Migration delays caused by anthropogenic barriers: modeling dams, temperature, and success of migrating salmon smolts

Disruption to migration is a growing problem for conservation and restoration of animal populations. Anthropogenic barriers along migration paths can delay or prolong migrations, which may result in a mismatch with migration-timing adaptations. To understand the interaction of dams (as barriers along a migration path), seasonally changing environmental conditions, timing of Atlantic salmon (Salmo salar) downstream migration, and ultimate migration success, we used 10 years of river temperature and discharge data as a template upon which we simulated downstream movement of salmon. Atlantic salmon is a cool-water species whose downstream migrating smolts must complete migration before river temperatures become too warm. We found that dams had a local effect on survival as well as a survival effect that was spatially and temporally removed from the encounter with the dam. While smolts are delayed by dams, temperatures downstream can reach lethal or near-lethal temperatures; as a result, the match between com...