Leah R. Gerber

POPULATION MODELS FOR MARINE RESERVE DESIGN: A RETROSPECTIVE AND PROSPECTIVE SYNTHESIS

We synthesize results from existing models of marine reserves to identify key theoretical issues that appear to be well understood, as well as issues in need of further exploration. Models of marine reserves are relatively new in the scientific literature; 32 of the 34 theoretical papers we reviewed were published after 1990. These models have focused primarily on questions concerning fishery management at the expense of other objectives such as conservation, scientific understanding, recreation, education, and tourism. Roughly one-third of the models analyze effects on cohorts while the remaining models have some form of complete population dynamics. Few models explicitly include larval dispersal. In a fisheries context, the primary conclusion drawn by many of the complete population models is that reserves increase yield when populations would otherwise be overfished. A second conclusion, resulting primarily from single-cohort models, is that reserves will provide fewer benefits for species with greater adult rates of movement. Although some models are beginning to yield information on the spatial configurations of reserves required for populations with specific dispersal distances to persist, it remains an aspect of reserve design in need of further analysis. Other outstanding issues include the effects of (1) particular forms of density dependence, (2) multispecies interactions, (3) fisher behavior, and (4) effects of concentrated fishing on habitat. Model results indicate that marine reserves could play a beneficial role in the protection of marine systems against overfishing. Additional modeling and analysis will greatly improve prospects for a better understanding of the potential of marine reserves for conserving biodiversity.

Marine Reserves as a Tool for Ecosystem-Based Management: The Potential Importance of Megafauna

Abstract Marine predators attract significant attention in ocean conservation planning and are therefore often used politically to promote reserve designation. We discuss whether their ecology and life history can help provide a rigorous ecological foundation for marine reserve design. In general, we find that reserves can benefit marine megafauna, and that megafauna can help establish target areas and boundaries for ecosystem reserves. However, the spatial nature of the interplay between potential threats and predator life histories requires careful consideration for the establishment of effective reserves. Modeling tools such as demographic sensitivity analysis will aid in establishing protection for different life stages and distributional ranges. The need for pelagic marine reserves is becoming increasingly apparent, and it is in this venue that marine predators may be most effectively used as indicator species of underlying prey distribution and ecosystem processes.

The rising tide of ocean diseases: unsolved problems and research priorities

New studies have detected a rising number of reports of diseases in marine organisms such as corals, molluscs, turtles, mammals, and echinoderms over the past three decades. Despite the increasing disease load, microbiological, molecular, and theoretical tools for managing disease in the worlds oceans are under-developed. Review of the new developments in the study of these diseases identifies five major unsolved problems and priorities for future research: (1) detecting origins and reservoirs for marine diseases and tracing the flow of some new pathogens from land to sea; (2) documenting the longevity and host range of infectious stages; (3) evaluating the effect of greater taxonomic diversity of marine relative to terrestrial hosts and pathogens; (4) pinpointing the facilitating role of anthropogenic agents as incubators and conveyors of marine pathogens; (5) adapting epidemiological models to analysis of marine disease.

Complexity in Ecology and Conservation: Mathematical, Statistical, and Computational Challenges

Abstract Creative approaches at the interface of ecology, statistics, mathematics, informatics, and computational science are essential for improving our understanding of complex ecological systems. For example, new information technologies, including powerful computers, spatially embedded sensor networks, and Semantic Web tools, are emerging as potentially revolutionary tools for studying ecological phenomena. These technologies can play an important role in developing and testing detailed models that describe real-world systems at multiple scales. Key challenges include choosing the appropriate level of model complexity necessary for understanding biological patterns across space and time, and applying this understanding to solve problems in conservation biology and resource management. Meeting these challenges requires novel statistical and mathematical techniques for distinguishing among alternative ecological theories and hypotheses. Examples from a wide array of research areas in population biology and community ecology highlight the importance of fostering synergistic ties across disciplines for current and future research and application.

Process‐based models are required to manage ecological systems in a changing world

Several modeling approaches can be used to guide management decisions. However, some approaches are better fitted than others to address the problem of prediction under global change. Process-based models, which are based on a theoretical understanding of relevant ecological processes, provide a useful framework to incorporate specific responses to altered environmental conditions. As a result, these models can offer significant advantages in predicting the effects of global change as compared to purely statistical or rule-based models based on previously collected data. Process-based models also offer more explicitly stated assumptions and easier interpretation than detailed simulation models. We provide guidelines for identifying the appropriate type of model and level of complexity for management decisions. Finally we outline some of those factors that make modeling for local and regional management under global change a particular challenge: changes to relevant scales and processes, additional sources of uncertainty, legacy effects, threshold dynamics, and socio-economic impacts.

Climate change impacts on connectivity in the ocean: Implications for conservation

Effective spatial management in the ocean requires a network of conservation areas that are connected by larval and adult dispersal. We propose a conceptual framework for including the likely impacts of a changing climate on marine connectivity, and synthesize information on the relationships between changing ocean temperature and acidification, connectivity and conservation tools. Our framework relies on concepts of functional connectivity, which depends on an organisms biological and behavioral responses to the physical environment, and structural connectivity, which describes changes in the physical and spatial structure of the environment that affect connectivity and movement. Our review confirms that ocean climate change likely reduces potential dispersal distance and therefore functional connectivity. Structural connectivity in the ocean will inevitably change with the spatial arrangement of biogenic habitats resulting from disturbance as well as enhanced growth and mortality due to climate change. Climate change will also likely reduce the spatial scale of connectivity, suggesting that we will need more closely spaced protected areas.

Including risk in stated-preference economic valuations: Experiments on choices for marine recreation

Stated-preference surveys for the economic valuation of environmental resources typically assume no uncertainty in the hypothetical valuation scenarios. However, the outcomes of environmental policies are uncertain. We explored the effects of including information on probabilities of attribute improvement and provision in choice experiments. Our results suggest that stating explicitly a high probability for the occurrence of the valuation scenario can improve the goodness of fit of choice models and the consistency of choices. As the general public becomes more aware of the uncertainty of environmental outcomes under global change, omitting information on scenario risk may contribute to hypothetical bias and impair the validity of stated-preference valuations.

Including behavioral data in demographic models improves estimates of population viability

Individual differences in behavior and social status can determine the rate of population change and thus the threat that imperiled species face in the real world. One way that behavior may be manifested in terms of an annualized population growth rate (λ) is through the effects of sex ratio biases. A populations operational sex ratio (OSR) typically deviates from the actual sex ratio (ASR), leading to pronounced sexual dimorphism in fecundity. This paper provides a framework for integrating behavioral estimates of OSR into population models used for conservation. Male and female fertility is estimated at six island study sites for California sea lions (Zalophus californianus), using population census data (ASR) and behavioral data (OSR). These estimates are used to construct alternate projection matrices to examine the impacts on. Inclusion of behavioral data in population models not only allows for explicit analysis of the effects of behaviors on viability, but may also help to identify behavioral attr...

EXPOSING EXTINCTION RISK ANALYSIS TO PATHOGENS: IS DISEASE JUST ANOTHER FORM OF DENSITY DEPENDENCE?

In the United States and several other countries, the development of popu- lation viability analyses (PVA) is a legal requirement of any species survival plan developed for threatened and endangered species. Despite the importance of pathogens in natural populations, little attention has been given to host-pathogen dynamics in PVA. To study the effect of infectious pathogens on extinction risk estimates generated from PVA, we review and synthesize the relevance of host-pathogen dynamics in analyses of extinction risk. We then develop a stochastic, density-dependent host-parasite model to investigate the effects of disease on the persistence of endangered populations. We show that this model converges on a Ricker model of density dependence under a suite of limiting assumptions, including a high probability that epidemics will arrive and occur. Using this modeling framework, we then quantify: (1) dynamic differences between time series generated by disease and Ricker processes with the same parameters; (2) observed probabilities of quasi- extinction for populations exposed to disease or self-limitation; and (3) bias in probabilities of quasi-extinction estimated by density-independent PVAs when populations experience either form of density dependence. Our results suggest two generalities about the relation- ships among disease, PVA, and the management of endangered species. First, disease more strongly increases variability in host abundance and, thus, the probability of quasi-extinc- tion, than does self-limitation. This result stems from the fact that the effects and the probability of occurrence of disease are both density dependent. Second, estimates of quasi- extinction are more often overly optimistic for populations experiencing disease than for those subject to self-limitation. Thus, although the results of density-independent PVAs may be relatively robust to some particular assumptions about density dependence, they are less robust when endangered populations are known to be susceptible to disease. If potential management actions involve manipulating pathogens, then it may be useful to model disease explicitly.

The influence of life history attributes and fishing pressure on the efficacy of marine reserves

Abstract Two key questions regarding “no-take” marine reserves are: (1) how effective are reserves likely to be, and (2) how does effectiveness vary with life history attributes and the relative size of reserves. To investigate these questions, we use a simple Ricker model that includes fishing, larval dispersal, and larval loss while in a planktonic pool, and that tracks protected and unprotected populations. We applied two different measures of reserve effectiveness to our simulation results. One metric was intended to reflect goals oriented towards conservation and the second was intended to reflect fishery enhancement goals. Both metrics compare the situation before reserves are established to after the reserve has been in place and a new equilibrium was reached. Yield effectiveness is defined as the total equilibrium annual harvest after reserves are established divided by the total annual harvest before reserves are established. Conservation effectiveness is defined as the average adult density inside the reserve divided by the average density in the same area prior to reserve establishment. A substantial fraction of the 5120 simulated parameter combinations representing different harvest rates and life history attributes went extinct in the absence of a reserve, and these scenarios leading to extinction could be predicted accurately (85% aptly classified) simply on the basis of exploitation rate and population growth rate. Of the cases that did not go extinct, we compared the performance of reserves as measured by each effectiveness metric. Few of the cases (less than 8%) produced effective reserves as measured in terms of increased harvest; whereas over half of the cases resulted in effective reserves as measured by conservation effectiveness. Moreover, the two measures of reserve effectiveness were only weakly correlated. Simple linear regression or polynomial regression could explain at most 23% of the variation in reserve effectiveness as measured by either metric. As expected, the size of the reserve area had a marked and typically negative effect on total annual yield, which suggests that while marine protected areas may do a good job of conserving protected populations, there will generally be pressure from the fishing community to keep them small because of their tendency to reduce total catch.