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• 41. [Article] Laboratory studies of successional patterns in assemblages of attached estuarine diatoms

  Successional patterns of attached estuarine diatoms were investigated using laboratory model ecosystems. Artificial substrates of acrylic plastic were exposed to 0, 4, and 10 hours of desiccation per day. ...

  Citation × Citation Citation Abstract Copy Title: Laboratory studies of successional patterns in assemblages of attached estuarine diatoms Author: Berglund, Lisette Aline Successional patterns of attached estuarine diatoms were investigated using laboratory model ecosystems. Artificial substrates of acrylic plastic were exposed to 0, 4, and 10 hours of desiccation per day. Diatom assemblages that developed under temperatures normal for Yaquina Bay, Oregon (control ecosystem) were compared to assemblages that developed at temperatures elevated 10 C (heated ecosystem). Continuously submerged substrates were quickly invaded by solitary, motile and attached diatoms. By the end of the experiment, filamentous and tube dwelling colonial diatoms had become established with many motile and epiphytic diatoms interspersed among the colonies. However, planktonic taxa were the first to settle on the substrates exposed to 4 and 10 hours of desiccation. These taxa were gradually replaced in prominence by solitary, motile and attached taxa that had previously colonized the continuously submerged substrates and by several species that were tolerant of desiccation and high air temperatures. Again, filamentous and tube dwelling forms began to establish colonies at the end of the experiment. A total of 21,569 diatoms was counted in 42 samples, and 136 species were identified. The most abundant diatoms found in the control ecosystem included Navicula directa, Thalassiosira no. 1, Thalassionema nitzschioides, Nitzschia no. 2, and Navicula diserta. Thalassiosira no. 1, Thalassionema nitzschioides, Nitzschia aerophila, Nitzschia sigma, and Navicula no. 2 were the most abundant species in the heated ecosystem. Of these taxa, Navicula directa and Thalassionema nitzschioides were the most evenly distributed over the samples. Species diversity was higher in the heated ecosystem than in the control ecosystem. Title: Laboratory studies of successional patterns in assemblages of attached estuarine diatoms Author: Berglund, Lisette Aline Successional patterns of attached estuarine diatoms were investigated using laboratory model ecosystems. Artificial substrates of acrylic plastic were exposed to 0, 4, and 10 hours of desiccation per day. Diatom assemblages that developed under temperatures normal for Yaquina Bay, Oregon (control ecosystem) were compared to assemblages that developed at temperatures elevated 10 C (heated ecosystem). Continuously submerged substrates were quickly invaded by solitary, motile and attached diatoms. By the end of the experiment, filamentous and tube dwelling colonial diatoms had become established with many motile and epiphytic diatoms interspersed among the colonies. However, planktonic taxa were the first to settle on the substrates exposed to 4 and 10 hours of desiccation. These taxa were gradually replaced in prominence by solitary, motile and attached taxa that had previously colonized the continuously submerged substrates and by several species that were tolerant of desiccation and high air temperatures. Again, filamentous and tube dwelling forms began to establish colonies at the end of the experiment. A total of 21,569 diatoms was counted in 42 samples, and 136 species were identified. The most abundant diatoms found in the control ecosystem included Navicula directa, Thalassiosira no. 1, Thalassionema nitzschioides, Nitzschia no. 2, and Navicula diserta. Thalassiosira no. 1, Thalassionema nitzschioides, Nitzschia aerophila, Nitzschia sigma, and Navicula no. 2 were the most abundant species in the heated ecosystem. Of these taxa, Navicula directa and Thalassionema nitzschioides were the most evenly distributed over the samples. Species diversity was higher in the heated ecosystem than in the control ecosystem. Close

• 42. [Article] Environmental variability and system heterogeneity in terrestrial biogeochemical models

  Ecosystems are highly heterogeneous systems subjected to important levels of environmental variability; however, it is common in terrestrial biogeochemical models to assume homogeneous properties of the ...

  Citation × Citation Citation Abstract Copy Title: Environmental variability and system heterogeneity in terrestrial biogeochemical models Author: Sierra, Carlos Alberto Ecosystems are highly heterogeneous systems subjected to important levels of environmental variability; however, it is common in terrestrial biogeochemical models to assume homogeneous properties of the elements of the system or constant environmental conditions. For some processes, heterogeneity in these models is treated very simplistically, but there is not much information about the advantages of including more complex representations in these models. By environmental variability I refer to the continuous changes of abiotic drivers in ecosystems, mainly climatic conditions. System heterogeneity is treated here as the diversity of elements that compose an ecosystem and respond differently to biotic and abiotic drivers. In this dissertation I performed a theoretical analysis to evaluate the consequences of ignoring heterogeneity and variability on the representation of carbon and nitrogen cycling in terrestrial biogeochemical models. For this purpose I used tools from probability theory and simulation models to test the hypothesis that ignoring heterogeneity and variability excludes a variety of system properties and behaviors that cannot be obtained with simpler models. Explicit treatments of climatic variability showed that changes in temperature variance alone can modify the amounts of respiration and carbon storage in ecosystems. Additionally, changes in temperature variance can modify predictions solely based on changes in temperature averages. This behavior is strongly dependent on the degree and nature of nonlinearity in ecosystems. Effects of system heterogeneity on carbon and nitrogen cycling are also strongly influenced by nonlinearities. Extrapolations of average system behavior are only valid when the system is linear and the elements of the system are distributed homogeneously or symmetrically around an average value. In all other cases, the nonlinearity of the system and the distribution of its elements produce complex behaviors that are impossible to predict with simple models. Title: Environmental variability and system heterogeneity in terrestrial biogeochemical models Author: Sierra, Carlos Alberto Ecosystems are highly heterogeneous systems subjected to important levels of environmental variability; however, it is common in terrestrial biogeochemical models to assume homogeneous properties of the elements of the system or constant environmental conditions. For some processes, heterogeneity in these models is treated very simplistically, but there is not much information about the advantages of including more complex representations in these models. By environmental variability I refer to the continuous changes of abiotic drivers in ecosystems, mainly climatic conditions. System heterogeneity is treated here as the diversity of elements that compose an ecosystem and respond differently to biotic and abiotic drivers. In this dissertation I performed a theoretical analysis to evaluate the consequences of ignoring heterogeneity and variability on the representation of carbon and nitrogen cycling in terrestrial biogeochemical models. For this purpose I used tools from probability theory and simulation models to test the hypothesis that ignoring heterogeneity and variability excludes a variety of system properties and behaviors that cannot be obtained with simpler models. Explicit treatments of climatic variability showed that changes in temperature variance alone can modify the amounts of respiration and carbon storage in ecosystems. Additionally, changes in temperature variance can modify predictions solely based on changes in temperature averages. This behavior is strongly dependent on the degree and nature of nonlinearity in ecosystems. Effects of system heterogeneity on carbon and nitrogen cycling are also strongly influenced by nonlinearities. Extrapolations of average system behavior are only valid when the system is linear and the elements of the system are distributed homogeneously or symmetrically around an average value. In all other cases, the nonlinearity of the system and the distribution of its elements produce complex behaviors that are impossible to predict with simple models. Close

• 43. [Article] Climate Change Impacts on Marine Ecosystems

  This is the publisher’s final pdf. The published article is copyrighted by Annual Reviews and can be found at: http://www.annualreviews.org/.

  Citation × Citation Citation Abstract Copy Title: Climate Change Impacts on Marine Ecosystems Author: Ruckelshaus, Mary, English, Chad A., Chan, Francis, Grebmeier, Jacqueline M., Hollowed, Anne B., Galindo, Heather M., Barry, James P., Duffy, J. Emmett, Sydeman, William J., Knowlton, Nancy, Talley, Lynne D., Doney, Scott C., Polovina, Jeffrey, Rabalais, Nancy N. This is the publisher’s final pdf. The published article is copyrighted by Annual Reviews and can be found at: http://www.annualreviews.org/. Title: Climate Change Impacts on Marine Ecosystems Author: Ruckelshaus, Mary, English, Chad A., Chan, Francis, Grebmeier, Jacqueline M., Hollowed, Anne B., Galindo, Heather M., Barry, James P., Duffy, J. Emmett, Sydeman, William J., Knowlton, Nancy, Talley, Lynne D., Doney, Scott C., Polovina, Jeffrey, Rabalais, Nancy N. This is the publisher’s final pdf. The published article is copyrighted by Annual Reviews and can be found at: http://www.annualreviews.org/. Close

• 44. [Article] Resource waves: phenological diversity enhances foraging opportunities for mobile consumers

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The article is copyrighted by the Ecological Society ...

  Citation × Citation Citation Abstract Copy Title: Resource waves: phenological diversity enhances foraging opportunities for mobile consumers Author: Takimoto, Gaku, Hayes, Matthew M., Schindler, Daniel E., Kauffman, Matthew J., Armstrong, Jonathan B. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The article is copyrighted by the Ecological Society of America and published by John Wiley & Sons, Inc. It can be found at: http://esajournals.onlinelibrary.wiley.com/hub/journal/10.1002/%28ISSN%291939-9170/ Title: Resource waves: phenological diversity enhances foraging opportunities for mobile consumers Author: Takimoto, Gaku, Hayes, Matthew M., Schindler, Daniel E., Kauffman, Matthew J., Armstrong, Jonathan B. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The article is copyrighted by the Ecological Society of America and published by John Wiley & Sons, Inc. It can be found at: http://esajournals.onlinelibrary.wiley.com/hub/journal/10.1002/%28ISSN%291939-9170/ Close

• 45. [Article] Patterns and Variation in Benthic Biodiversity in a Large Marine Ecosystem

  Supporting information can be located at: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0135135#sec014

  Citation × Citation Citation Abstract Copy Title: Patterns and Variation in Benthic Biodiversity in a Large Marine Ecosystem Author: Ingeman, Kurt E., Lindsley, Amy J., Piacenza, Susan E., Barner, Allison K., Reimer, Jessica N., Rowe, Jennifer C., Heppell, Selina S., Thompson, Kevin A., Boersma, Kate S., Kindinger, Tye L., Cerny-Chipman, Elizabeth B., Benkwitt, Cassandra E., Lee, Jonathan D., Thurman, Lindsey L., Shen, Chenchen Supporting information can be located at: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0135135#sec014 Title: Patterns and Variation in Benthic Biodiversity in a Large Marine Ecosystem Author: Ingeman, Kurt E., Lindsley, Amy J., Piacenza, Susan E., Barner, Allison K., Reimer, Jessica N., Rowe, Jennifer C., Heppell, Selina S., Thompson, Kevin A., Boersma, Kate S., Kindinger, Tye L., Cerny-Chipman, Elizabeth B., Benkwitt, Cassandra E., Lee, Jonathan D., Thurman, Lindsey L., Shen, Chenchen Supporting information can be located at: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0135135#sec014 Close

• 46. [Article] Determinants of moth diversity and community in a temperate mountain landscape: vegetation, topography, and seasonality

  This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Ecological Society of America. The published article can be found at: http://www.esajournal...

  Citation × Citation Citation Abstract Copy Title: Determinants of moth diversity and community in a temperate mountain landscape: vegetation, topography, and seasonality Author: Miller, Jeffrey C., Jones, Julia A., Highland, Steven A. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Ecological Society of America. The published article can be found at: http://www.esajournals.org/loi/ecsp. Title: Determinants of moth diversity and community in a temperate mountain landscape: vegetation, topography, and seasonality Author: Miller, Jeffrey C., Jones, Julia A., Highland, Steven A. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Ecological Society of America. The published article can be found at: http://www.esajournals.org/loi/ecsp. Close

• 47. [Article] Diversity and productivity of hypogeous fungal sporocarps in a variably thinned Douglas-fir forest

  Although ecosystem management techniques are designed to enhance species diversity in managed forests, no comprehensive study has been conducted to evaluate effects of such techniques on diversity and ...

  Citation × Citation Citation Abstract Copy Title: Diversity and productivity of hypogeous fungal sporocarps in a variably thinned Douglas-fir forest Author: Trappe, James M., Carey, Andrew B., Colgan, Wesley, Thysell, David, Molina, Randy Although ecosystem management techniques are designed to enhance species diversity in managed forests, no comprehensive study has been conducted to evaluate effects of such techniques on diversity and productivity of hypogeous fungi (truffles). During this study, truffles were collected in a 55- to 65-year-old Douglas-fir forest from March 1993 through December 1995 at approximately 6-week intervals. Half of the stands served as controls, half were assigned a variable density thinning (VDT) treatment. A VDT stand comprised a mosaic of patches thinned to different densities of standing live trees. To further evaluate the effect of harvesting impacts, this mosaic was divided into two thinning categories, lightly thinned and heavily thinned areas. Truffle standing crop varied greatly but generally was highest in spring with a smaller peak in the fall. At least some sporocarps were found year round, with winter having the lowest biomass and species richness. Overall standing crop biomass (over all seasons) was significantly lower in VDT stands compared with control stands. The abundance of Gautieria and Hysterangium species was lower in thinned stands, while Melanogaster species diversity and productivity were highest in these stands. Title: Diversity and productivity of hypogeous fungal sporocarps in a variably thinned Douglas-fir forest Author: Trappe, James M., Carey, Andrew B., Colgan, Wesley, Thysell, David, Molina, Randy Although ecosystem management techniques are designed to enhance species diversity in managed forests, no comprehensive study has been conducted to evaluate effects of such techniques on diversity and productivity of hypogeous fungi (truffles). During this study, truffles were collected in a 55- to 65-year-old Douglas-fir forest from March 1993 through December 1995 at approximately 6-week intervals. Half of the stands served as controls, half were assigned a variable density thinning (VDT) treatment. A VDT stand comprised a mosaic of patches thinned to different densities of standing live trees. To further evaluate the effect of harvesting impacts, this mosaic was divided into two thinning categories, lightly thinned and heavily thinned areas. Truffle standing crop varied greatly but generally was highest in spring with a smaller peak in the fall. At least some sporocarps were found year round, with winter having the lowest biomass and species richness. Overall standing crop biomass (over all seasons) was significantly lower in VDT stands compared with control stands. The abundance of Gautieria and Hysterangium species was lower in thinned stands, while Melanogaster species diversity and productivity were highest in these stands. Close

• 48. [Article] Multi-scale relationships between aspen and birds in the northern Yellowstone ecosystem

  I conducted a multi-scale evaluation of aspen – bird relationships in the northern ungulate winter range of the northern Yellowstone ecosystem during June 2001-03. Questions addressed were: (1) Does bird ...

  Citation × Citation Citation Abstract Copy Title: Multi-scale relationships between aspen and birds in the northern Yellowstone ecosystem Author: Hollenbeck, Jeff P., 1967- I conducted a multi-scale evaluation of aspen – bird relationships in the northern ungulate winter range of the northern Yellowstone ecosystem during June 2001-03. Questions addressed were: (1) Does bird diversity increase with conifer presence in aspen stands? (2) Given known habitat selection cues, are migrating birds passively intercepted by aspen patches oriented perpendicular to migratory direction of travel? (3) Are resident (short-distance migrant) birds passively intercepted by aspen patches? and (4) Given the dynamics of wolves, ungulates, and forage plants in the northern Yellowstone ecosystem, what is the present condition of aspen and cavity-nesting birds within Yellowstone National Park (YNP) and how will they change over the next 100+ years? Regression analyses of migratory bird diversity (species richness or Shannon-Weiner index) on measures of habitat heterogeneity (ratio of conifer to aspen canopy cover, or basal area) suggested no positive relationship with intermediate levels of conifer presence. Migratory birds were most diverse in pure aspen, and least diverse in pure conifer. I found a weak, but significant, positive relationship between most measures of habitat heterogeneity and resident bird diversity. Many residents were habitat generalists or conifer-associated species. To maximize bird diversity and aspen, managers may want to manage for pure aspen stands in a matrix that includes conifer habitat. Using model selection techniques, long-distance migratory birds did not show evidence of passive interception by aspen patches oriented against northerly or elevational direction of travel. Aspen patch area was most important for migratory birds, given the data and set of models analyzed. Resident (and short-distance migrant) birds showed a marked positive response to patch orientation relative to the elevational gradient of the northern range. Migratory birds appear not to be passively intercepted at high elevation sites such as YNP’s northern range. Short distance migrants appear to be passively intercepted. Northern range aspen stands within YNP have 10cm greater mean live and dead stem diameter, 80% more snags, and greater abundance of many cavity-nesting bird species than northern range stands outside YNP. These conditions fit a conceptual framework of interactions driven by a top-down ecosystem structure that predicts aspen and cavity-nester dynamics over several decades. Title: Multi-scale relationships between aspen and birds in the northern Yellowstone ecosystem Author: Hollenbeck, Jeff P., 1967- I conducted a multi-scale evaluation of aspen – bird relationships in the northern ungulate winter range of the northern Yellowstone ecosystem during June 2001-03. Questions addressed were: (1) Does bird diversity increase with conifer presence in aspen stands? (2) Given known habitat selection cues, are migrating birds passively intercepted by aspen patches oriented perpendicular to migratory direction of travel? (3) Are resident (short-distance migrant) birds passively intercepted by aspen patches? and (4) Given the dynamics of wolves, ungulates, and forage plants in the northern Yellowstone ecosystem, what is the present condition of aspen and cavity-nesting birds within Yellowstone National Park (YNP) and how will they change over the next 100+ years? Regression analyses of migratory bird diversity (species richness or Shannon-Weiner index) on measures of habitat heterogeneity (ratio of conifer to aspen canopy cover, or basal area) suggested no positive relationship with intermediate levels of conifer presence. Migratory birds were most diverse in pure aspen, and least diverse in pure conifer. I found a weak, but significant, positive relationship between most measures of habitat heterogeneity and resident bird diversity. Many residents were habitat generalists or conifer-associated species. To maximize bird diversity and aspen, managers may want to manage for pure aspen stands in a matrix that includes conifer habitat. Using model selection techniques, long-distance migratory birds did not show evidence of passive interception by aspen patches oriented against northerly or elevational direction of travel. Aspen patch area was most important for migratory birds, given the data and set of models analyzed. Resident (and short-distance migrant) birds showed a marked positive response to patch orientation relative to the elevational gradient of the northern range. Migratory birds appear not to be passively intercepted at high elevation sites such as YNP’s northern range. Short distance migrants appear to be passively intercepted. Northern range aspen stands within YNP have 10cm greater mean live and dead stem diameter, 80% more snags, and greater abundance of many cavity-nesting bird species than northern range stands outside YNP. These conditions fit a conceptual framework of interactions driven by a top-down ecosystem structure that predicts aspen and cavity-nester dynamics over several decades. Close

• 49. [Article] Modeling ocean ecosystems: The PARADIGM program

  THE ROLE OF THE OCEANS in Earth systems ecology, and the effects of climate variability on the ocean and its ecosystems, can be understood only by observing, describing, and ultimately predicting the state ...

  Citation × Citation Citation Abstract Copy Title: Modeling ocean ecosystems: The PARADIGM program Author: Denman, Ken, Cullen, John, Spitz, Yvette, Abbott, Mark R., Doney, Scott, Hoffman, Eileen, Chassignet, Eric, Yoder, James, Ducklow, Hugh, McGillicuddy, Dennis, Maltrud, Mathew, Karl, David, Olascoaga, M., Fennel, Katja, Rothstein, Lewis, McClain, Chuck, Haidvogel, Dale, Kindle, John, Wiggert, Jerry, Follows, Mick, Lima, Ivan THE ROLE OF THE OCEANS in Earth systems ecology, and the effects of climate variability on the ocean and its ecosystems, can be understood only by observing, describing, and ultimately predicting the state of the ocean as a physically forced ecological and biogeochemical system. This is a daunting but exciting challenge, because the ocean-atmosphere system is dynamically linked, and oceanic habitats are both diverse and complex, providing tremendous variety in environmental conditions and associated life forms. And paradoxically, as we learn more and more about ocean life, for example, through the genomics revolution (Doney et al., 2004), the number of unanswered questions increases. Models, be they conceptual, statistical, or numerical simulations, are useful and necessary tools for studying the complex interactions that influence ecosystem structure and function. Originally, a primary function of marine ecosystem models was to help in the development of understanding; also, they were applied in fisheries models to predict the abundance of specific commercial fish stocks. Now, they are being asked to do much more. On local and regional scales, there is growing recognition that management of marine resources and assessment of human perturbations must encompass the whole ecosystem, not individual species. Extending further to basin and global scales, the potential impacts of global change present an immediate challenge, nationally and globally, to define and execute responsive strategies, based to a large extent on the predictions of interdisciplinary global models that must be validated by comparison with measurements. Consequently, the ultimate objective of any comprehensive marine ecosystem modeling program must be the development and implementation of reliable forecast systems, guided by and validated with systematic observations of the sea. Title: Modeling ocean ecosystems: The PARADIGM program Author: Denman, Ken, Cullen, John, Spitz, Yvette, Abbott, Mark R., Doney, Scott, Hoffman, Eileen, Chassignet, Eric, Yoder, James, Ducklow, Hugh, McGillicuddy, Dennis, Maltrud, Mathew, Karl, David, Olascoaga, M., Fennel, Katja, Rothstein, Lewis, McClain, Chuck, Haidvogel, Dale, Kindle, John, Wiggert, Jerry, Follows, Mick, Lima, Ivan THE ROLE OF THE OCEANS in Earth systems ecology, and the effects of climate variability on the ocean and its ecosystems, can be understood only by observing, describing, and ultimately predicting the state of the ocean as a physically forced ecological and biogeochemical system. This is a daunting but exciting challenge, because the ocean-atmosphere system is dynamically linked, and oceanic habitats are both diverse and complex, providing tremendous variety in environmental conditions and associated life forms. And paradoxically, as we learn more and more about ocean life, for example, through the genomics revolution (Doney et al., 2004), the number of unanswered questions increases. Models, be they conceptual, statistical, or numerical simulations, are useful and necessary tools for studying the complex interactions that influence ecosystem structure and function. Originally, a primary function of marine ecosystem models was to help in the development of understanding; also, they were applied in fisheries models to predict the abundance of specific commercial fish stocks. Now, they are being asked to do much more. On local and regional scales, there is growing recognition that management of marine resources and assessment of human perturbations must encompass the whole ecosystem, not individual species. Extending further to basin and global scales, the potential impacts of global change present an immediate challenge, nationally and globally, to define and execute responsive strategies, based to a large extent on the predictions of interdisciplinary global models that must be validated by comparison with measurements. Consequently, the ultimate objective of any comprehensive marine ecosystem modeling program must be the development and implementation of reliable forecast systems, guided by and validated with systematic observations of the sea. Close

• 50. [Article] Grazing, nutrients, and marine benthic algae : insights into the drivers and protection of diversity

  Two of the most powerful ways in which humans have altered ecosystems are by increasing productivity and changing the densities of important consumers. The bottom-up effects of productivity and the top-down ...

  Citation × Citation Citation Abstract Copy Title: Grazing, nutrients, and marine benthic algae : insights into the drivers and protection of diversity Author: Guerry, Anne D., 1973- Two of the most powerful ways in which humans have altered ecosystems are by increasing productivity and changing the densities of important consumers. The bottom-up effects of productivity and the top-down effects of consumers have been identified as primary determinants of biological diversity, though the links between them remain unclear. Understanding how consumers and productivity act and interact to yield differences in diversity is of both conceptual and pragmatic importance. Here, I describe three experiments designed to examine the links between grazing, productivity, and diversity in rocky intertidal systems in Oregon and New Zealand. In two experiments I used fully-factorial designs in which I manipulated both grazing and nutrients. Both experiments revealed the primary importance of grazing as a structuring force of algal assemblages. In the Oregon experiment, I also document an interaction between grazing and productivity, with nutrient enrichment decreasing algal diversity at low grazer densities and increasing algal diversity at high grazer densities. This interaction was not apparent in the New Zealand experiment. In the absence of grazers, nutrient addition led to increased abundance of foliose algae at this site but had no net effect on algal diversity. In the third experiment, also conducted in New Zealand, I used natural variation in nearshore productivity as a backdrop against which I manipulated the access of grazers. In this experiment, I found that grazers had negative impacts on benthic algal diversity and abundance at sites with lower productivity and negligible impacts on benthic algal assemblages at sites with higher productivity. Overall these three studies suggest that in these intertidal grazer-dominated communities, the strong top-down effects often documented in such systems can be modified by more subtle bottom-up effects. Together, results from these experiments elucidate factors that determine algal diversity in these systems and underscore the importance of the evolutionary context in which experiments are conducted. Finally, I conclude with a synthesis of the literature in which I put these and other findings to work by exploring the ways in which basic marine ecological research can inform the management of human activities that affect the marine environment. Title: Grazing, nutrients, and marine benthic algae : insights into the drivers and protection of diversity Author: Guerry, Anne D., 1973- Two of the most powerful ways in which humans have altered ecosystems are by increasing productivity and changing the densities of important consumers. The bottom-up effects of productivity and the top-down effects of consumers have been identified as primary determinants of biological diversity, though the links between them remain unclear. Understanding how consumers and productivity act and interact to yield differences in diversity is of both conceptual and pragmatic importance. Here, I describe three experiments designed to examine the links between grazing, productivity, and diversity in rocky intertidal systems in Oregon and New Zealand. In two experiments I used fully-factorial designs in which I manipulated both grazing and nutrients. Both experiments revealed the primary importance of grazing as a structuring force of algal assemblages. In the Oregon experiment, I also document an interaction between grazing and productivity, with nutrient enrichment decreasing algal diversity at low grazer densities and increasing algal diversity at high grazer densities. This interaction was not apparent in the New Zealand experiment. In the absence of grazers, nutrient addition led to increased abundance of foliose algae at this site but had no net effect on algal diversity. In the third experiment, also conducted in New Zealand, I used natural variation in nearshore productivity as a backdrop against which I manipulated the access of grazers. In this experiment, I found that grazers had negative impacts on benthic algal diversity and abundance at sites with lower productivity and negligible impacts on benthic algal assemblages at sites with higher productivity. Overall these three studies suggest that in these intertidal grazer-dominated communities, the strong top-down effects often documented in such systems can be modified by more subtle bottom-up effects. Together, results from these experiments elucidate factors that determine algal diversity in these systems and underscore the importance of the evolutionary context in which experiments are conducted. Finally, I conclude with a synthesis of the literature in which I put these and other findings to work by exploring the ways in which basic marine ecological research can inform the management of human activities that affect the marine environment. Close