Multispecies Context Research Articles

Impact of Growth Conditions on Susceptibility of Five Microbial Species to Alkaline Stress

The effects of different growth conditions on the susceptibility of five taxa to alkaline stress were investigated. Enterococcus faecalis ATCC 29212, Streptococcus sobrinus OMZ 176, Candida albicans ATCC 90028, Actinomyces naeslundii ATCC 12104, and Fusobacterium nucleatum ATCC 10953 were grown as planktonic cells, allowed to adhere to dentin for 24 hours, grown as monospecies or multispecies biofilms on dentin under anaerobic conditions with a serum-enriched nutrient supply at 37°C for 5 days. In addition, suspended biofilm microorganisms and 5-day old planktonic multispecies cultures were used. Microbial recovery upon direct exposure to saturated calcium hydroxide solution (pH 12.5) for 10 and 100 minutes was compared with control exposure to physiologic saline. Planktonic microorganisms were most susceptible; only E. faecalis and C. albicans survived in saturated solution for 10 minutes, the latter also for 100 minutes. Dentin adhesion was the major factor in improving the resistance of E. faecalis and A. naeslundii to calcium hydroxide, whereas the multispecies context in a biofilm was the major factor in promoting resistance of S. sobrinus to the disinfectant. In contrast, the C. albicans response to calcium hydroxide was not influenced by the growth condition. Adherence to dentin and interspecies interactions in a biofilm appear to differentially affect the sensitivity of microbial species to calcium hydroxide.

A computational approach to ecological and economic sustainable harvest management strategies in a multi-species context, with implications for cod recovery plans

Multi-species models consider interactions, particularly predation, between and within species. Traditional harvest management strategies, such as maximum sustainable yield do not account for these interactions. The exploitation of a single species can be maximised, but this does not mean that the entire ecosystem is being harvested sustainably or at its economic maximum. I present a computational technique (evolutionary algorithms) that can simultaneously optimise harvest management strategies of many species and can easily be modified to allow for factors such as stock recovery, sustainable yields or maximum levels of economic sustainable exploitation. I demonstrate that in an ecologically sustainably managed system where a stock is recovering, maximum economic yield is identical to the maximisation of yield by mass. These findings may have important implications for long term conservation aims and long term profits by fishers.

A stock rebuilding algorithm featuring risk assessment and an optimization strategy of single or multispecies fisheries

Abstract Gröger, J. P., Rountree, R. A., Missong, M., and Rätz, H-J. 2007. A stock rebuilding algorithm featuring risk assessment and an optimization strategy of single or multispecies fisheries. – ICES Journal of Marine Science, 64: 1101–1115. We present a simple but flexible stock-rebuilding algorithm model that features ideas of risk assessment, with all constraints set up explicitly, and with clear optimality for controlling fishing effort (or fishing mortality) and maximizing landings (or economic value). In contrast to the conventional approach, our approach does not predict future stock development from historical stock dynamics, but provides directly optimal annual F values and associated optimum catch quotas for a given planning horizon. Hence, the F values are not estimated retrospectively, but are realizations of a control variable created through the optimization process. The optimal solution is based on maximization of a non-linearly constrained objective function for catch or yield, whereas the constraints inter alia include biomass targets, F limits, and stable catch. We present the basic theory together with selected model variants, such as inclusion of biological interactions and integration of elements of risk assessment. The optimization procedure outlined here is not only “risk averse” but a risk minimization procedure in itself. It can be applied in a deterministic or stochastic decision-making process as well as within a single or multispecies context. We illustrate the approach with a simplified (deterministic) multispecies fisheries management and a (stochastic) single-species risk assessment example.

Incorporating cannibalism into an age-structured model for the Chilean hake

We incorporated predation equations from the multispecies virtual population analysis model MSVPA into an age-structured model for the Chilean hake ( Merluccius gayi gayi) to estimate cannibalism. Two models, model I with constant natural mortality and the MSM, were fitted to the total annual catch, spawning biomass from acoustic surveys and length composition data from fishery and acoustic surveys. Model I fitted the data better than MSM. The majority of the MSM estimates of adult population and spawning biomass were larger than the model I estimates; probably due to the choice of residual mortality M1. High estimates of predation mortality were observed for age-0 hake. In spite of a decreasing fishing mortality, the spawning biomass decreased in the last years. Preliminary MSM results suggest that this might be due to an increase in cannibalism. A sensitivity analysis suggested all response variables were not sensible to the “other food” parameter but sensible to M1 and the predator annual ration. MSM is a promising approach that introduces the predation mortality equations into a statistical framework, allowing the incorporation of the uncertainty in the estimation of the parameters and the use of standard statistical tools in a multispecies context. This approach will contribute to provide useful information on the indirect effects of fishing on non-target species to fisheries managers.

EVOLVING METACOMMUNITIES: TOWARD AN EVOLUTIONARY PERSPECTIVE ON METACOMMUNITIES

The metacommunity framework predicts that local coexistence depends on the outcome of local species interactions and regional migration. In analogous fashion, spatial structure among populations can shape species interactions through evolutionary mechanisms. Yet, most metacommunity theories assume that populations do not evolve. Here, we evaluate how evolution shapes local species coexistence and exclusion within the multiscale and multispecies context embodied by the metacommunity framework. In general, coexistence in joint ecological-evolutionary models requires low to intermediate dispersal rates that can promote maintenance of both regional species and genetic diversity. These conditions support a set of key mechanisms that modify patterns of species coexistence including local adaptation, gene storage effects, genetic rescue effects, spatial genetic subsidies, and metacommunity evolution. Multispecies extensions indicate that correlated selection can further alter the outcome of interspecific interactions depending on the magnitude and direction of correlations and shape of fitness trade-offs. We suggest that an evolving metacommunity perspective has the potential to generate novel predictions about community structure and function by incorporating the genetic and species diversity that characterize natural communities. In adopting such a perspective, we seek to facilitate understanding about the interactions between evolutionary and metacommunity dynamics.

Incorporating predation interactions in a statistical catch-at-age model for a predator-prey system in the eastern Bering Sea

Virtual population analysis and the statistical catch-at-age methods are common stock assessment models used for management advice. The difference between them is the statistical assumptions allowing the fitting of parameters by considering how errors enter into the models and the data sources for the estimation. Fishery managers are being asked to consider multispecies interactions in their decisions. One option to achieve this goal is the multispecies virtual population analysis (MSVPA); however, its lack of statistical assumptions does not allow the use of tools used in single-species stock assessment. We chose to use a two-species system, walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus), to incorporate the predation equations from MSVPA into an age-structured multispecies statistical model (MSM). Results suggest that both models produced similar estimates of suitability coefficients and predation mortalities. The adult population estimates from the single-species stock assessment and MSM were also comparable. MSM provides a measure of parameter uncertainty, which is not available with the MSVPA technologies. MSM is an important advancement in providing advice to fisheries managers because it incorporates the standard tools such as Bayesian methods and decision analysis into a multispecies context, helping to establish useful scenarios for management in the Bering Sea.

Testing the stability of the suitability coefficients from an eastern Bering Sea multispecies virtual population analysis

Abstract Suitability coefficients are important for the estimation of predation mortality in a multispecies virtual population analysis (MSVPA) and subsequent use in the multispecies forecasting model (MSFOR). Testing the assumption of the stability of the suitability coefficients is important in assessing the robustness of the predictions made with MSFOR. We used different statistical methods to partially test this assumption for the eastern Bering Sea MSVPA model with eight species, using stomach content data for the years 1985–1989. Comparison of the estimates from two different sets of stomach content data (set one with all data and set two mainly with data from 1985) suggested that the differences between the two types of estimates were much reduced when the number of predator stomachs sampled increased. In a second approach, we contrasted the residual variances of partial data sets with the results from the fit of the total data set. Results suggested a small increase (∼10.8%) in the variation of the suitability coefficients. Comparison of the means of the suitability coefficients associated with each predator species suggests that only 13 of the 50 possible pairwise contrasts were significantly different (α = 0.05). In general, results suggested that the predator preferences and prey vulnerabilities remained stable over the time period studied. Therefore, MSFOR could be considered as a tool to advise fisheries managers within a multispecies context.

Dynamics of a mutualism in a multi-species context.

Despite recent findings that mutualistic interactions between two species may be greatly affected by species external to the mutualism, the implications of such multi-species interactions for the population dynamics of the mutualists are virtually unexplored. In this paper, we ask how the mutualism between the shoot-base boring weevil Apion onopordi and the rust fungus Puccinia punctiformis is influenced by the dynamics of their shared host plant Cirsium arvense, and vice versa. In particular, we hypothesized that the distribution of the weevil's egg load between healthy and rust-infected thistles may regulate the abundance of the mutualists and their host plant. In contrast to our expectations we found that the dynamics of the mutualists are largely determined by the dynamics of their host. This is, to our knowledge, the first demonstration that the dynamics of a mutualism are driven by a third, non-mutualistic species.

Biological reference points for fish stocks in a multispecies context

Biological reference points (BRPs) are widely used to define safe levels of harvesting for marine fish populations. Most BRPs are either minimum acceptable biomass levels or maximum fishing mortality rates. The values of BRPs are determined from historical abundance data and the life-history parameters of the fish species. However, when the life-history parameters change over time, the BRPs become moving targets. In particular, the natural mortality rate of prey species depends on predator levels; conversely, predator growth rates depend on prey availability. We tested a suite of BRPs for their robustness to observed changes in natural mortality and growth rates. We used the relatively simple Baltic Sea fish community for this sensitivity test, with cod as predator and sprat and herring as prey. In general, the BRPs were much more sensitive to the changes in natural mortality rates than to growth variation. For a prey species like sprat, fishing mortality reference levels should be conditioned on the level of predation mortality. For a predator species, a conservative level of fishing mortality can be identified that will prevent growth overfishing and ensure stock replacement. These first-order multispecies interactions should be considered when defining BRPs for medium-term (5–10 year) management decisions.

Biological reference points for fish stocks in a multispecies context

Biological reference points (BRPs) are widely used to define safe levels of harvesting for marine fish populations. Most BRPs are either minimum acceptable biomass levels or maximum fishing mortality rates. The values of BRPs are determined from historical abundance data and the life-history parameters of the fish species. However, when the life-history parameters change over time, the BRPs become moving targets. In particular, the natural mortality rate of prey species depends on predator levels; conversely, predator growth rates depend on prey availability. We tested a suite of BRPs for their robustness to observed changes in natural mortality and growth rates. We used the relatively simple Baltic Sea fish community for this sensitivity test, with cod as predator and sprat and herring as prey. In general, the BRPs were much more sensitive to the changes in natural mortality rates than to growth variation. For a prey species like sprat, fishing mortality reference levels should be conditioned on the level of predation mortality. For a predator species, a conservative level of fishing mortality can be identified that will prevent growth overfishing and ensure stock replacement. These first-order multispecies interactions should be considered when defining BRPs for medium-term (5–10 year) management decisions.

Utilization of the Icelandic Cod Stock in a Multispecies Context

The purpose of this paper is to discuss rules for deciding Total Allowable Catch (TAC) for Icelandic cod. For this purpose, a bioeconomic model describing harvesting and processing of cod, capelin, and shrimp in the Icelandic marine ecosystem is constructed and estimated. The model is used to analyze the probable effects of harvesting strategies on biomass, catch, and economic benefits from the exploitation of these species. Simulations are used to investigate probability profiles of biological and economic variables, taking into account inaccuracies in assessments and uncertainties in predictions. Optimal harvesting strategies are also investigated using a deterministic version of the model and taking into account problems of unemployment, overcapacity, and aversion to fluctuations in consumption. The analysis shows that it is beneficial to reduce fishing from the cod stock in order to allow the stock to recover to its optimum size. This increase in the cod stock will result in big decreases in the catch of capelin and shrimp.

Extinction and market forces: two case studies

Extinction defines a loss in biodiversity. An established economic model suggests that extinction can be avoided, even in common property settings, if the initial stock is sufficiently large that price and cost evolve to a non-extinction equilibrium. Alternatively, privatization has been suggested as a means to avoid extinction. The empirical validity of these conclusions are investigated by studying the collapse of two species that signaled the end of the United States frontier-the passenger pigeon and the buffalo. The historical studies suggest that the theoretical possibility of a non-extinction equilibrium is unlikely to hold in practice. Similarly, while privatization in a single species context may appear feasible, in a multi-species context the apparent profitability of privatization may be superseded and the species driven to extinction. The latter conclusion also depends on species-specific characteristics of minimum viable population size and habitat requirements.

The theoretical basis of vegetation science

There are two distinct research approaches to a theoretical framework for vegetation science. One involves critical analysis of observed patterns of multi-species community composition; the other entails experimental examination, at the population level, of processes in a multi-species context. Each approach is currently incomplete, but has questions in common with the other. Light, nitrogen and disturbance have been identified as critical factors determining vegetation composition by researchers using different theoretical frameworks. The increasing communication between vegetation analysts concerned with community pattern and experimental ecologists concerned with community processes may lead to a convergence in their theoretical concepts.