Marissa L. Baskett

MARINE RESERVE DESIGN AND THE EVOLUTION OF SIZE AT MATURATION IN HARVESTED FISH

By significantly changing size-dependent mortality, fisheries can cause rapid evolution toward earlier maturation in harvested species. Because earlier maturation neg- atively affects biomass yield and sustainability, ignoring evolutionary changes could sig- nificantly reduce the success of fisheries management policy. With a quantitative genetic model of size at maturation that incorporates phenotype plasticity, we examine the impact of different management strategies including traditional effort control and Marine Protected Areas (MPAs). After verifying the models accuracy, using historical trajectories for size at maturation in cod (Gadus morhua), we test model predictions under different management schemes with life history parameters for red snapper (Lutjanus campechanus) and two rockfish species (Sebastes paucispinis and S. ruberrimus). The model results show that no- take MPAs can protect against strong fisheries-based selection for earlier maturation. The potential to protect against anthropogenic selection declines with increasing fragmentation of reserves to networks of small reserves. Accounting for the evolution of size at maturation increases the predicted biomass contribution from MPA populations to harvested popula- tions. Traditional management approaches, such as adjustments to harvest rate and maxi- mum size limits, can lead to equivalent protection against anthropogenic selection and equivalent or greater long-term biomass yield than establishing MPAs; however, the pro- tection and yield from establishing no-take MPAs appears more robust to uncertainty.

Symbiont diversity may help coral reefs survive moderate climate change

Given climate change, thermal stress-related mass coral-bleaching events present one of the greatest anthropogenic threats to coral reefs. While corals and their symbiotic algae may respond to future temperatures through genetic adaptation and shifts in community compositions, the climate may change too rapidly for coral response. To test this potential for response, here we develop a model of coral and symbiont ecological dynamics and symbiont evolutionary dynamics. Model results without variation in symbiont thermal tolerance predict coral reef collapse within decades under multiple future climate scenarios, consistent with previous threshold-based predictions. However, model results with genetic or community-level variation in symbiont thermal tolerance can predict coral reef persistence into the next century, provided low enough greenhouse gas emissions occur. Therefore, the level of greenhouse gas emissions will have a significant effect on the future of coral reefs, and accounting for biodiversity and biological dynamics is vital to estimating the size of this effect.

Propensity of marine reserves to reduce the evolutionary effects of fishing in a migratory species.

Evolutionary effects of fishing can have unwanted consequences diminishing a fishery’s value and sustainability. Reserves, or no‐take areas, have been proposed as a management tool for reducing fisheries‐induced selection, but their effectiveness for migratory species has remained unexplored. Here we develop an eco‐genetic model to predict the effects of marine reserves on fisheries‐induced evolution under migration. To represent a stock that undergoes an annual migration between feeding and spawning grounds, we draw model parameters from Atlantic cod (Gadus morhua) in the northern part of its range. Our analysis leads to the following conclusions: (i) a reserve in a stock’s feeding grounds, protecting immature and mature fish alike, reduces fisheries‐induced evolution, even though protected and unprotected population components mix on the spawning grounds; (ii) in contrast, a reserve in a stock’s spawning grounds, protecting only mature fish, has little mitigating effects on fisheries‐induced evolution and can sometimes even exacerbate its magnitude; (iii) evolutionary changes that are already underway may be difficult to reverse with a reserve; (iv) directly after a reserve is created or enlarged, most reserve scenarios result in yield losses; and (v) timescale is very important: short‐term yield losses immediately after a reserve’s creation can give way to long‐term gains.

Persistence and Change in Community Composition of Reef Corals through Present, Past, and Future Climates

The reduction in coral cover on many contemporary tropical reefs suggests a different set of coral community assemblages will dominate future reefs. To evaluate the capacity of reef corals to persist over various time scales, we examined coral community dynamics in contemporary, fossil, and simulated future coral reef ecosystems. Based on studies between 1987 and 2012 at two locations in the Caribbean, and between 1981 and 2013 at five locations in the Indo-Pacific, we show that many coral genera declined in abundance, some showed no change in abundance, and a few coral genera increased in abundance. Whether the abundance of a genus declined, increased, or was conserved, was independent of coral family. An analysis of fossil-reef communities in the Caribbean revealed changes in numerical dominance and relative abundances of coral genera, and demonstrated that neither dominance nor taxon was associated with persistence. As coral family was a poor predictor of performance on contemporary reefs, a trait-based, dynamic, multi-patch model was developed to explore the phenotypic basis of ecological performance in a warmer future. Sensitivity analyses revealed that upon exposure to thermal stress, thermal tolerance, growth rate, and longevity were the most important predictors of coral persistence. Together, our results underscore the high variation in the rates and direction of change in coral abundances on contemporary and fossil reefs. Given this variation, it remains possible that coral reefs will be populated by a subset of the present coral fauna in a future that is warmer than the recent past.

Evolution of dispersal and life history interact to drive accelerating spread of an invasive species.

Populations on the edge of an expanding range are subject to unique evolutionary pressures acting on their life-history and dispersal traits. Empirical evidence and theory suggest that traits there can evolve rapidly enough to interact with ecological dynamics, potentially giving rise to accelerating spread. Nevertheless, which of several evolutionary mechanisms drive this interaction between evolution and spread remains an open question. We propose an integrated theoretical framework for partitioning the contributions of different evolutionary mechanisms to accelerating spread, and we apply this model to invasive cane toads in northern Australia. In doing so, we identify a previously unrecognised evolutionary process that involves an interaction between life-history and dispersal evolution during range shift. In roughly equal parts, life-history evolution, dispersal evolution and their interaction led to a doubling of distance spread by cane toads in our model, highlighting the potential importance of multiple evolutionary processes in the dynamics of range expansion.

The evolution of dispersal in reserve networks.

The fragmentation of an environment into developed and protected areas may influence selection pressure on dispersal by increasing the chance of moving from a favorable to an unfavorable habitat. We theoretically explore this possibility through two cases: (1) marine systems in which reduced predation and/or increased feeding drive the evolution of planktonic larval duration and (2) more generally, where stochasticity in reproductive yield drives the evolution of the proportion of offspring dispersing. Model results indicate that habitat fragmentation generally shifts selection pressure toward reduced dispersal, particularly when areas outside reserves are uninhabitable. However, shifts to increased dispersal may occur when temporal heterogeneity is the primary selective force and constant‐quota harvest occurs outside reserves. In addition, model results suggest the potential for changes in the genetic variability in dispersal after habitat fragmentation. The predicted evolutionary changes in dispersal will depend on factors such as the relative genetic and environmental contributions to dispersal‐related traits and the extent of anthropogenic impacts outside reserves. If the predicted evolutionary changes are biologically attainable, they may suggest altering current guidelines for the appropriate size and spacing of marine reserves necessary to achieve conservation and fisheries goals.

Refuge‐mediated apparent competition in plant–consumer interactions

At the intersection of consumer behaviour and plant competition is the concept of refuge-mediated apparent competition: an indirect interaction whereby plants provide a refuge for a shared consumer, subsequently increasing consumer pressure on another plant species. Here, we use a simple model and empirical examples to develop and illustrate the concept of refuge-mediated apparent competition. We find that the likelihood that an inferior competitor will succeed via refuge-mediated apparent competition is greater when competitors have similar resource requirements and when consumers exhibit a strong response to the refuge and high attack rates on the superior competitor. Refuge-mediated apparent competition may create an emergent Allee effect, such that a species invades only if it is sufficiently abundant to alter consumer impact on resident species. This indirect interaction may help explain unresolved patterns observed in biological invasion, such as the different physical structure of invasive exotic plants, the lag phase, and the failure of restoration efforts. Given the ubiquity of refuge-seeking behaviour by consumers and the ability of consumers to alter the outcome of direct competition among plants, refuge-mediated apparent competition may be an underappreciated mechanism affecting the composition and diversity of plant communities.

Linking models with monitoring data for assessing performance of no-take marine reserves

No-take marine reserves are an increasingly popular conservation and management tool. Assessing reserve performance in an adaptive management framework ideally involves predicting the response of populations and communities to reserves (typically in the design process) and testing predicted outcomes against observations. Here we compare existing modeling and empirical studies on no-take marine reserves, and provide a prospectus for their future integration. Numerical models of ecological responses to reserves typically project longterm, steady-state interactions over the relatively broad spatial scales of larval dispersal, reserve configuration, fishing effort, and fish movement. Existing empirical studies focus on short-term outcomes over small scales, typically aggregated over many explanatory factors. Linking models and empirical data together for the adaptive management of marine reserves requires adjusting the spatial and temporal scales of models to match empirically feasible tests, and adjusting the metrics and scale of empirical studies to account for the interacting biological and human factors affecting reserve outcomes.

Microsatellite evolution in modern humans: a comparison of two data sets from the same populations

We genotyped 64 dinucleotide microsatellite repeats in individuals from populations that represent all inhabited continents. Microsatellite summary statistics are reported for these data, as well as for a data set that includes 28 out of 30 loci studied by Bowcock et al. (1994) in the same individuals. For both data sets, diversity statistics such as heterozygosity, number of alleles per locus, and number of private alleles per locus produced the highest values in Africans, intermediate values in Europeans and Asians, and low values in Americans. Evolutionary trees of populations based on genetic distances separated groups from different continents. Corresponding trees were topologically similar for the two data sets, with the exception that the (δμ)2 genetic distance reliably distinguished groups from different continents for the larger data set, but not for the smaller one. Consistent with our results from diversity statistics and from evolutionary trees, population growth statistics Sk and β, which seem particularly useful for indicating recent and ancient population size changes, confirm a model of human evolution in which human populations expand in size and through space following the departure of a small group from Africa.

Evaluating Alternative Strategies for Minimizing Unintended Fitness Consequences of Cultured Individuals on Wild Populations

Artificial propagation strategies often incur selection in captivity that leads to traits that are maladaptive in the wild. For propagation programs focused on production rather than demographic contribution to wild populations, effects on wild populations can occur through unintentional escapement or the need to release individuals into natural environments for part of their life cycle. In this case, 2 alternative management strategies might reduce unintended fitness consequences on natural populations: (1) reduce selection in captivity as much as possible to reduce fitness load (keep them similar), or (2) breed a separate population to reduce captive-wild interactions as much as possible (make them different). We quantitatively evaluate these 2 strategies with a coupled demographic-genetic model based on Pacific salmon hatcheries that incorporates a variety of relevant processes and dynamics: selection in the hatchery relative to the wild, assortative mating based on the trait under selection, and different life cycle arrangements in terms of hatchery release, density dependence, natural selection, and reproduction. Model results indicate that, if natural selection only occurs between reproduction and captive release, the similar strategy performs better. However, if natural selection occurs between captive release and reproduction, the different and similar strategies present viable alternatives to reducing unintended fitness consequences because of the greater opportunity to purge maladaptive individuals. In this case, the appropriate approach depends on the feasibility of each strategy and the demographic goal (e.g., increasing natural abundance, or ensuring that a high proportion of natural spawners are naturally produced). In addition, the fitness effects of hatchery release are much greater if hatchery release occurs before (vs. after) density-dependent interactions. Given the logistical challenges to achieving both the similar and different strategies, evaluation of not just the preferred strategy but also the consequences of failing to achieve the desired target is critical.