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Impact of Exotic Invertebrate Invaders on Food Web Structure and Function in the Great Lakes: a Network Analysis ApproachThis project is no longer current. Please see the Research Programs page for a list of current research projects. Collaborators EcoNetwrk development team: Sponsor: Great Lakes Fishery Commission (GLFC web site) PROJECT RATIONALE: The Great Lakes have recently undergone a second wave of species invasions dominated by exotic invertebrates- zebra mussels (Dreissena polymorpha), quagga mussels (D . bugensis), Bythotrephes cederstroemi and Cercopagis pengoi. Unlike previous fish invasions (e.g., sea lamprey and alewife), these invertebrates inserted themselves in the lower trophic levels and thus disruption percolates up through the food web with potential serious consequences to fish communities. This bottom-up effect on the food web eliminates the potential application and modification of traditional fisheries models to quantify and predict direction and magnitude of disruption. What is required is an ecosystem level approach to quantify the disruption and magnitude of disruption on food webs, and the differential effect on various regions of a lake and between lakes. Early in the 20th century, the fish communities of the Laurentian Great Lakes were profoundly disrupted, and permanently changed, by a wave of vertebrate invaders: sea lamprey, alewife, and rainbow smelt (Eshenroder and Burnham-Curtis 1999). These disruptions were largely focused at the upper end of food webs, and, hence, traditional fishery models could be adapted to quantify the associated impacts. During the last 15 years, the Great Lakes have suffered a second wave of invasions featuring invertebrates: two species of dreissenids-zebra mussels (Dreissena polymorpha) and quagga mussels (D. bugensis) -and two predatory cladocerans - Bythotrephes cederstroemi and Cercopagis pengoi (MacIsaac 1999; MacIsaac et al. 1999). These four invertebrates are expected to disrupt, or have already disrupted, the fish communities in the Great Lakes in ways quite different from the earlier wave of vertebrate invaders. In contrast to the vertebrate invasion, invertebrate disruptions start at lower trophic levels and percolate up through the food web with potentially serious consequences for fisheries (Dermott et al. 1999; Ryan et al. 1999; Johannsson et al. 2000; Vanderploeg et al., 2002). The bottom-up effect on the food web eliminates the potential application and modification of traditional fisheries models to quantify and predict direction and magnitude of disruption. Shuter and Mason (2000) argue that an ecosystem level approach, which incorporates field studies and modeling, is necessary to quantify and eventually predict the impacts of these recent invertebrate invaders. Moreover, factors such as lake morphology, trophic status and the temporal sequencing of invasions, all of which differ among lakes, likely modify the magnitude of the invertebrate impact and the current state of food web change. There are many areas of research currently underway that emphasize field and dynamic modeling approaches. However, many of these studies focus only on a subset of the system and none of them evaluates and quantifies the current state of the entire food web before and after invertebrate invasion. What is required are techniques that synoptically evaluate and quantify the structure and flows in food webs across temporal (seasons and years) and spatial (trophic status, nearshore-offshore) gradients, and how changes in the food web, from invasive invertebrates, disrupt and change these structures and flows. Network analysis is a technique that allows one to quantify the structure and function of ecosystems by evaluating biomasses and energy flow in a food web. Efficiency with which energy and material is transferred, assimilated, and dissipated conveys significant information about the structure and function of food webs (Ulanowicz and Platt 1985; Baird and Ulanowicz 1989 and 1993; Baird et al. 1991; Ulanowicz and Wulff 1991). Network analysis evaluates these components within a food web context using input/output analysis, trophic and cycle analysis, and information theory to calculate ecosystem properties (see below for details). Thus, changes in fish communities can be linked directly to changes occurring within an ecosystem. Network analysis has been used to compare ecosystems of different size, geographical location, hydrological characteristics, and trophic status (Baird et al. 1991; Ulanowicz and Wulff 1991; Baird and Ulanowicz 1993; Monaco and Ulanowicz 1997). Most recently, arguments have been made for the use of network analysis for quantifying the health and integrity of ecosystems (Ulanowicz 2000) and evaluating the magnitude of stress imposed on an ecosystem (Ulanowicz 1995; Mageau et al. 1998). Related to all of these examples, but absent from the list of applications, is quantifying the ecosystem level impact of exotic invaders and how this impact manifests itself in fish communities. We propose to construct network models of food webs for the Bay of Quinte Lake Ontario, Oneida Lake, and Lake Michigan across seasons (when data are available), years (pre-invertebrate invasion and post invasion), and trophic status (e.g., Bay of Quinte - western, central, eastern basins; Lake Michigan- nearshore, offshore) to quantify how these invertebrate invasions disrupted lake wide and regional food webs. In additional, our analysis and comparisons within and among seasons, years, regions and lakes should also allow us: (1) to explore various operating hypotheses, acknowledged throughout the Great Lakes Basin, concerning how invaders have changed the ecosystem (e.g., zebra mussels changing systems to benthic dominated systems), (2) to potential tease apart the effects of nutrient reduction (indirectly determined through changes in primary productivity) and invertebrate invasions on ecosystem structure and function, and (3) to provide a synthesis that may easily be extended to other lakes to understand changes in the ecosystem or to predict potential future changes in other Great Lakes (e.g., Lake Superior). To achieve our goals and objectives we must upgrade the old DOS code used for network analysis. NETWRK was developed by R.E. Ulanowicz (Ulanowicz and Kay 1991) in the late 1980s (some algorithms where updated in 1999) and is a DOS-based package written in ANSI Standard FORTRAN IV. NETWRK has non-intuitive input structures, data are tedious to enter, programs are command line driven, and results are output as a large report text file. Much of the analysis then comes from extracting the information from the output file, manipulating and finally summarizing the information. The complicated procedures for using the program have restricted its use by others. Heymans and Baird (2000) comment that upgrading NETWRK would ′"…...be of enormous value to ecosystem analysis′". Thus, as part of this project, we will upgrade and enhance the NETWRK software to include a graphical user interface, easy and intuitive data input, graphics and analysis, and formatted output. In addition, we will add new features to the program to extend it capabilities and applications. These capabilities may include: uncertainty analysis, improved food web balancing algorithms, system dynamics for evolving systems and potential future states, etc. The product will be a software package available to researchers and resource managers for quantifying the flows and structures in food webs. Our overall objective is to quantify the change in food web structures and flows on fish communities in Great Lakes because of invasions by invertebrate species (e.g., zebra mussels, quagga mussels, Bythotrephes, and Cercopagis). Specifically, our objectives are:
Lake Michigan Food Web diagram 2005 Plans
2004 AccomplishmentsObjective 1: To develop the windows version of the network analysis
program. Objective 2: To construct networks for the three basins of Bay
of Quinte, and for Oneida Lake, before and after zebra mussel invasion. Objective 3: To construct a network for nearshore and offshore
Lake Michigan as a comparison to the Bay of Quinte and Oneida Lake network. Overall, we have about 200 taxa in our network with approximately 3,000 interactions, where an interaction is defined as a predator taxon consuming a prey taxon. Both the taxa and the interactions are weighted. The taxa are weighted by their relative biomass (mg dry weight/m2) for each time period. The interactions are weighted using an index based on the general selectivity of the predator taxon on the prey taxon (high, medium, low), the general overlap in horizontal distribution of the two interacting taxa for both spring and summer, and the general overlap in vertical distribution of the two interacting taxa for both spring and summer and day and night. This index is also weighted by the seasonal presence of each taxon as well. This weighting scheme is a balance between weighting by energy flow, which requires an immense amount of information that is often not available for most taxa, and not using weights at all, which would provide little information on the changes that have occurred in the network structure between the two time periods. The analysis of this network consists of two components. First, the network will be tested for compartments as demonstrated in the second chapter of Ann Krause’s dissertation (Krause et al. Nature 426:282-285). If we find the network to be significantly compartmentalized, we will then test for the impact that Bythotrephes and zebra mussels have on the network with the help of Dr. Ken Frank, MSU. Second, we will be assessing the sensitivity of the evenness of the weights on the interactions and taxa before and after the two invasions. We expect to find that the weights on interactions and taxa are sensitive to the addition of these two species and the compartments that contain these two species should show more sensitivity than those that do not contain these species. In addition, we expect that evenness in interactions and taxa will decrease which indicates that a few taxa have become more dominant within the network in the second time period. While we cannot say that the changes in evenness in biomass are directly a result of these invasions, we can at least say what the changes in evenness are relative to the invasions. Since sensitivity is a measure of resistance, we can also examine the patterns of resistance in the network structure relative to the disturbance of these invasions. Finally, we will have quantitative measures of how the network structure has changed over time. A preliminary analysis of the network was present at the Quantitative Ecosystem Indicators for Fisheries Management International Symposium in Paris, France, March 31-April 3, 2004. In this analysis, the sensitivity of the evenness in interactions was simulated with the hypothetical removal of lake trout, chinook, lake whitefish, and yellow perch. As expected, the compartment that each species was a member was more sensitive to its removal than the other compartments. In addition, it was found that the two species, lake whitefish and yellow perch, that were more central taxa within their compartment (i.e. strongly interacting with many others within their compartment) had a larger impact on the network than the two species, lake trout and chinook, that were more peripheral (not as connected) within their compartment. This analysis was presented as a poster and was nominated for one of the best poster awards at the symposium. Objective 4. To quantify and contrast trends in ecosystem structure
and function in the Bay of Quinte, Oneida Lake, and Lake Michigan with
respect to the various phases of invasion from expansion to accommodation.
Objective 5. To determine the differential impact of exotic invertebrate
invasion on fish communities relative to the trophic status and nearshore/offshore
processes of an ecosystem. 2003 AccomplishmentsWe participated in the fall 2002 workshop of the Bay of Quinte and Oneida Lake group (also funded by the GLFC) held at the Cornell Biological Field Station to determine the availability of data for constructing the food webs. A second workshop was held this past spring (2003) at the Canadian Center for Inland Waters (Burlington, ONT), but we were unable to attend due to the SARS outbreak in Toronto and the corresponding government travel restrictions. A full-scale effort on this objective will likely begin in the fall of 2003 when the graduate student on this project starts at Michigan State University. The development and parameterization of the two preliminary food webs for Lake Michigan, pre and post-zebra mussel invasion, have been constructed using the tools available through ECOPATH (www.ecopath.org). We presented our preliminary results at two scientific conferences last summer (2002). The first presentation was entitled, "Disruption of an Ecosystem: Changes in ecosystem properties following the establishment of an exotic mussel in Lake Michigan," and was presented at the American Society of Limnology and Oceanography, Victoria, BC. The second one entitled, "Disruption of Lake Michigan's ecosystem processes by the invertebrate community: implications for the fish community," was presented at the American Fisheries Society Conference, Baltimore, MD. In addition, DMM was invited to give a seminar on invasive species and food web disruption at the University of Florida. In preparing the material for these presentations, we identified inherent biases in the food web balancing algorithm that estimates respiration rates for species. (Note that in ECOPATH, respiration can only be estimated from the balancing algorithm and not manually entered). For example, the ratio of respiration to consumption (R/C) cannot exceed the value of 1.0 based on the principles of thermodynamics (i.e., you cannot respire more energy than you can consume in a balanced food web). However, on several occasions the balancing algorithm estimated the R/C > 1.0. Because estimates of respiration are critical to the analysis and that the estimates derived from ECOPATH are suspect, we consider the two Lake Michigan food webs preliminary. The problem associated with ECOPATH is rectified in the new software that we are developing to perform the network analysis . Despite the prerequisites of having the food webs developed from objectives 1 and 2 prior to working on this objective, we have made theoretical progress. We have used a new technique from the social sciences towards understanding community structure in complex food webs. The technique "Cohesion Analysis" identifies compartments (communities) where interactions within compartments are stronger than interactions between compartments. The technique has four properties that are crucial towards us achieving our objectives of quantifying structural changes in the food web. First, taxa are assigned to non-overlapping compartments that maximize the concentration of interactions within all of the compartments of the food web. Second, the algorithm generally requires no a priori specification of subjective parameters (including number of compartments) and thus removing arbitrary decisions of who belongs where. Third, the algorithm has been applied to extensive simulated data with known compartment assignments allowing one to calibrate the performance of algorithm. Fourth, compartment boundaries can be embedded in a graphical representation of the food web, thus facilitating interpretation. We will use this new technique on the various food webs to explore and quantify how invasive invertebrates have restructured community dynamics within complex food webs of the Great Lakes. PublicationsKrause, A.E, K.A. Frank, D.M. Mason, R.E. Ulanowicz, and W.W. Taylor. 2003. Compartments revealed in food web structure. Nature 426:282-285. http://www.glerl.noaa.gov/pubs/fulltext/2003/20030014.pdf Mason, D.M. 2003. Quantifying the impact of exotic invertebrate invaders on food web structure and function in the Great Lakes: A network analysis approach. Interim Progress Report to the Great Lakes Fisheries Commission- yr 1. 3pp. Lake Michigan Food Web poster http://www.glerl.noaa.gov/pubs/brochures/foodweb/LMfoodweb.pdf Software ProductsA release of the first phase of the software "EcoNetwrk: A Windows-compatible tool to analyze ecological flow networks" can be found at: http://www.glerl.noaa.gov/EcoNetwrk/. EcoNetwrk is based on the text-based application 'Netwrk 4.2' by Robert E. Ulanowicz (http://www.cbl.umces.edu/~ulan/ntwk/network.html). EcoNetwrk performs all of the analysis of Netwrk 4.2 but in a windows friendly environment. Netwrk 4.2 is copyrighted (1982, 1987, 1998, 1999) and was used with the author's permission and guidance. PresentationsMason, D.M., A. Jaeger, A.E. Krause. Food web disruption: Comparison
of Lakes Michigan and Huron. Salmonid Communities in the Great Lakes:
Special session- “What does the Future Hold for the Laurentian Great
Lakes”. 134th Annual Meeting of the American Fisheries Society.
Madison WI. August 21-26, 2004. Mason, D.M. Application of network analysis to the Great Lakes. National Science Foundation Long Term Ecological Research (LTER)-All Scientist Meeting. Seattle, WA. September 19-21, 2003. (Invited) Krause, A.E., and D.M. Mason. Invasive species and food web disruption: Example from the Laurentian Great Lakes. 17th Biannual conference of the Estuarine Research Federation. Seattle, WA. September 14-18, 2003. (Invited) Mason, D.M. Invasive species and food web disruption. University of Florida. February 29, 2003. (Invited) Krause, A.E., D.M. Mason, K. Franks, and R.E. Ulanowicz. Intuitive compartments: the other half of trophic structure in food webs. 88th Annual Meeting of the Ecological Society of American. Savannah, GA., August 3-8, 2003. Mason, D.M., and A.E. Krause. Food web structure and energy flow: implications for lake whitefish production in Lake Michigan. Great Lakes Whitefish-Diporeia Workshop. Ann Arbor, MI February 26-27, 2002. Mason, D.M. Disruption of Food Webs in the Great Lakes. The Great Lakes: Current Issues and Future Challenges. Annual Great Lakes Conference, Agriculture and Natural Resources Week, Michigan State University. March 7, 2002. Krause, A.E., and D.M. Mason. Disruption of an ecosystem: Changes in ecosystem properties following the establishment of an exotic mussel in Lake Michigan. 2002 summer meeting of the American Association of Limnology and Oceanography, June 10-14, 2002 · Victoria, British Columbia, Canada. Krause, A.E. and D.M. Mason. Disruption of Lake Michigan's ecosystem processes by the invertebrate community: implications for the fish community. 132nd AFS Annual Meeting, Baltimore, MD, August 18-22, 2002. ReferencesBaird, D., J.M. Glade, and R.E. Ulanowicz. 1991. The comparative ecology of six marine ecosystems. Philos. Trans. R. Soc. Lond. 333:15-29. Baird, D., and R.E. Ulanowicz. 1989. The seasonal dynamics of the Chesapeake Bay ecosystem. Ecol. Monographs 59:329-364. Baird, D., and R.E. Ulanowicz. 1993. Comparative study on the trophic structure, cycling and ecosystem properties of four tidal estuaries. Mar. Ecol. Prog. Ser. 99:221-237. Dermott, R,M., M. Munawar, L.Witzel, and P. Ryan. 1999. An assessment of food-web changes in eastern: impact of Dreissena spp. and phosphorous management on rainbow smelt, Osmerus mordax. Pages 367-386 In: State of Lake Erie - Past, Present and Future. M. Munawar, T. Edsall, and I.F. Munawar (eds.) Backhuys, Leiden. Eshenroder, R.L., and M.K. Burnham-Curtis. 1999. Species succession and sustainability of the Great Lakes fish community. Pages 145-184 In: Great Lakes Fisheries Policy and Management, W.W. Taylor and C.P. Ferreri, eds. Michigan State University Press, East Lansing, Michigan. Heymans, J.J., and D. Baird. 2000. Network anlaysis of the northern Benguela ecosystem by means of NETWRK and ECOPATH. Ecol. Mod. 131:97-119. Johannsson, O.E., R. Dermott, D.M. Graham, J.A. Dahl, E.S. Millard, D.D. Myles, and J. LeBlanc. 2000. Benthic and pelagic secondary production in Lake Erie after the Invasion of Dreissena spp. with implications for fish production. J. Great Lakes Res. 26:31-54. MacIsaac, H.J. 1999. Biological invasions in Lake Erie: past, present and future. Pages 305-322 In: State of Lake Erie - Past, Present and Future. M. Munawar, T. Edsall, and I.F. Munawar (eds.) Backhuys, Leiden. MacIsaac, H.J., I.A. Grigorovich, J.A. Hoyle, N.S. Yan and V.E. Panov. 1999. Invasion of Lake Ontario by the Ponto-Caspian predatory cladoceran Cercopagis pengoi. Can. J. Fish. Aquat. Sci. 56:1-5. Mageau, M.T., R. Constanza, and R.E. Ulanowicz. 1998. Quantifying the trends expected in developing ecosystems. Ecol. Modelling 112:1-22. Monaco, M.E., and R.E. Ulanowicz. 1997. Comparative ecosystem trophic structure of three U.S. mid-Atlantic estuaries. Mar. Ecol. Prog. Ser. 161:239-254. Ryan, P.A., L.D. Witzel, J.R. Paine, M.J. Freeman, M. Hardy, and K.L. Sztramko. 1999. Recent trends in eastern Lake Erie fish stocks within a changing trophic state and food web (1980-1994). Pages 241-290 In: State of Lake Erie - Past, Present and Future. M. Munawar, T. Edsall, and I.F. Munawar (eds.) Backhuys, Leiden. Shuter, B., and D.M. Mason. 2001. Exotic invertebrates, food-web disruption, and lost fish production: understanding impacts of dreissenid and cladocerans invaders on lower-lakes fish community and forecasting invasion impacts on upper-lakes fish communities. Report to the Great Lakes Fishery Commission. 16pp. (http://www.glfc.org/staff/fweb_whitepaper.pdf) Ulanowicz, R.R. 1995. Trophic flow networks as indicators of ecosystem stress. Pp. 358-368. In: G.A. Polis and K.O. Winemiller (eds), Food webs: integration of patterns and dynamics. Chapman and Hall, NY. Ulanowicz, R.E. 2000. Toward the measurement of ecological integrity. In: Pimentel, D., L. Westra, and R.F. Noss (eds.) Ecological Integrity. Island Press, Washington:102-113. Ulanowicz, R.E., and J.J. Kay. 1991. A package for the analysis of ecosystem flow networks. Env Software 6:131-142. Ulanowicz, R.E., and Platt. 1985. Ecosystem theory for biological oceanography. Can Bull. Fish. Aquatic Sci. 213:1-260. Ulanowicz, R.E., and Wulff. 1991. Comparing ecosystem structures: the Chesapeake Bay and the Baltic Sea. In: J. Cole, G. Lovett, and S. Findlay (eds.) Comparative analysis of ecosystems, pattern, mechanism, and theories. Springer-Verlag, New York. Vanderploeg, H.A., T.F. Nalepa, D.J. Jude, E.L. Mills, K.T. Holeck, J.R. Liebig, I.A. Grigorovich,and H. Ojaveer. 2002. Dispersal and emerging ecological impacts of Ponto-Caspian species in the Laurentian Great Lakes. Can. J. Fish. Aquat. Sci 59:1209-1228. |
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