Representing mediating effects and species reintroductions in Ecopath with Ecosim (original) (raw)
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Conservation Biology, 2010
Recovery criteria for depleted species or populations normally are based on demographic measures, the goal being to maintain enough individuals over a sufficiently large area to assure a socially tolerable risk of future extinction. Such demographically based recovery criteria may be insufficient to restore the functional roles of strongly interacting species. We explored the idea of developing a recovery criterion for sea otters (Enhydra lutris) in the Aleutian archipelago on the basis of their keystone role in kelp forest ecosystems. We surveyed sea otters and rocky reef habitats at 34 islandtime combinations. The system nearly always existed in either a kelp-dominated or deforested phase state, which was predictable from sea otter density. We used a resampling analysis of these data to show that the phase state at any particular island can be determined at 95% probability of correct classification with information from as few as six sites. When sea otter population status (and thus the phase state of the kelp forest) was allowed to vary randomly among islands, just 15 islands had to be sampled to estimate the true proportion that were kelp-dominated (within 10%) with 90% confidence. We conclude that kelp forest phase state is a more appropriate, sensitive, and cost-effective measure of sea otter recovery than the more traditional demographically based metrics, and we suggest that similar approaches have broad potential utility in establishing recovery criteria for depleted populations of other functionally important species.
Ecological model development : Toolkit for interActive Modeling (TAM)
Ecological models provide crucial tools for informing many aspects of ecosystem restoration and management, ranging from increasing understanding of complex ecological functions to prioritizing restoration sites and quantifying benefits for project reporting. The diversity of ecosystem types and restoration objectives often precludes the use of existing models; as such, model development is commonly required to inform restoration decision-making. Index-based habitat models are a common approach for assessing ecosystem condition. These models relate habitat quality to species’ distributions. Habitat suitability (quality) typically ranges on a scale from 0 to 1. Habitat models have been developed to assess habitat suitability for specific taxa, communities, or ecosystem functions. Restoration-project timelines often require that these models be developed rapidly and in conjunction with many external stakeholders or partners. Here, the Toolkit for interActive Modeling (TAM) is proposed...
PeerJ
Recovering species are often limited to much smaller areas than they historically occupied. Conservation planning for the recovering species is often based on this limited range, which may simply be an artifact of where the surviving population persisted. Southern sea otters (Enhydra lutris nereis) were hunted nearly to extinction but recovered from a small remnant population on a remote stretch of the California outer coast, where most of their recovery has occurred. However, studies of recently-recolonized estuaries have revealed that estuaries can provide southern sea otters with high quality habitats featuring shallow waters, high production and ample food, limited predators, and protected haul-out opportunities. Moreover, sea otters can have strong effects on estuarine ecosystems, fostering seagrass resilience through their consumption of invertebrate prey. Using a combination of literature reviews, population modeling, and prey surveys we explored the former estuarine habitats...
Exploring an Ecosystem Approach to Endangered Species Conservation
2006
An ecosystem approach focuses on landscapelevel processes (natural and human) that support or affect the area, such as this wetland, as a means of conserving the species within i t (Wetland in Lower Iron River, a tributary to Lake Superior. Photo by Joan Elias.)-1 Endangered Species UPDATE Vol. I 0 Nos. 3 & 4 1993 Thinking "Ecosystems" is Learned Several of the authors remind us of the extraordinary expense in speciesby-species approaches, and offer this as Judy Tasseis the Editor of the EhgeredSpccies UPDATE. She is a Ph.D. student in the School of Natural Resources and Environment at the University of Michigan, studying mechanisms for wildlife reintroductions and movements of individuals in small release populations.
INCOFISH ecosystem models: transiting from Ecopath to Ecospace
2007
Once again a Fisheries Centre Research Report was produced which features an international cast of authors, and documenting a number of ecosystem models constructed using the Ecopath with Ecosim (EwE) suite of software. This report, however, also very nicely illustrates the increased sophistication of the users of this software, which parallels the improvements of EwE. Thus, we have here a number of models which emphasize the spatial dimension of EwE, i.e., the use of its Ecospace module. While technically not difficult to use, this module implies familiarity with the spatial dimension of an ecosystem. This is a dimension that all ecosystem modelers should be expected to master, though it may not be apparent to casual users of Ecopath, used for describing food webs, and Ecosim, used to simulate how they may change through time. This report also illustrates another aspect of ecosystem modeling based on EwE, i.e., that numerous initiatives centered on this modeling approach are emerging outside of UBC's Fisheries Centre. In this case, the initiative was the INCOFISH Project (see www.incofish.org), funded by the European Commission, and which gathered a vast number of international collaborators, only some of whom are associated with the Fisheries Centre. Still, our Villy Christensen interacted with most of the authors of contributions included herein, one of the reasons for their quality. Finally, I want to congratulate the editors and the authors of the contributions in this report for the enormous amount of contextualized ecological data that they are herewith making available to colleagues, and thus advancing ecosystem modeling everywhere.
Ecopath with Ecosim: methods, capabilities and limitations
Ecological Modelling, 2004
The Ecopath with Ecosim (EwE) modeling approach combines software for ecosystem trophic mass balance analysis (Ecopath), with a dynamic modeling capability (Ecosim) for exploring past and future impacts of fishing and environmental disturbances as well as for exploring optimal fishing policies. Ecosim models can be replicated over a spatial map grid (Ecospace) to allow exploration of policies such as marine protected areas, while accounting for spatial dispersal/advection effects.
Hydrobiologia, 2007
Trophic cascade hypotheses for biological communities, linking predation by upper trophic levels to major features of ecological structure and dynamics at lower trophic levels, are widely subscribed and may influence conservation policy. Few such hypotheses have been evaluated for temporal or spatial generality. Previous studies of sea otter (Enhydra lutris) predation along the outer coast of North America suggest a pattern, often elevated to the status of paradigm, in which sea otter presence leads to reduced sea urchin (Strongylocentrotus spp.) biomass and rapid increases in abundance and diversity of annual algal species, followed by a decline in diversity as one or a few perennial algal species become dominant. Both sea otter predation and commercial sea urchin harvest are ecologically and economically important sources of urchin mortality in nearshore benthic systems in northern Washington marine waters. We recorded changes in density of macroalgae in San Juan Channel, a marine reserve in the physically protected inland waters of northern Washington, resulting from three levels of experimental urchin harvest: (1) simulated sea otter predation (monthly complete harvest of sea urchins), (2) simulated commercial urchin harvest (annual size-selective harvest of sea urchins), and (3) no harvest (control). The two experimental urchin removal treatments did not significantly increase the density of perennial (Agarum and Laminaria) or annual (Desmarestia, Costaria, Alaria and Nereocystis) species of macroalgae after 2 years, despite significant and persistent decreases in urchin densities. Our results suggest that other factors such as grazing by other invertebrates, the presence of dense Agarum stands, and recruitment frequency of macroalgae and macroinvertebrates may play a large role in influencing community structure in San Juan Channel and other physically protected marine waters within the range of sea otters.