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• 61. [Article] Exploring, Exploiting and Evolving Diversity of Aquatic Ecosystem Models: a Community Perspective

  Here, we present a community perspective on how to explore, exploit and evolve the diversity in aquatic ecosystem models. These models play an important role in understanding the functioning of aquatic ...

  Citation × Citation Citation Abstract Copy Title: Exploring, Exploiting and Evolving Diversity of Aquatic Ecosystem Models: a Community Perspective Author: Janssen, Annette B.G., Arhonditsis, George B., Beusen, Arthur, Bolding, Karsten, Bruce, Louise, Bruggeman, Jorn, Couture, Raoul-Marie, Downing, Andrea S., Elliott, J. Alex, Frassl, Marieke A., Gal, Gideon, Gerla, Daan J., Hipsey, Matthew R., Hu, Fenjuan, Ives, Stephen C., Janse, Jan H., Jeppesen, Erik, Jöhnk, Klaus D., Kneis, David, Kong, Xiangzhen, Kuiper, Jan J., Lehmann, Moritz K., Lemmen, Carsten, Özkundakci, Deniz, Petzoldt, Thomas, Rinke, Karsten, Robson, Barbara J., Sachse, René, Schep, Sebastiaan A., Schmid, Martin, Scholten, Huub, Teurlincx, Sven, Trolle, Dennis, Troost, Tineke A., Van Dam, Anne A., Van Gerven, Luuk P.A., Weijerman, Mariska, Wells, Scott A., Mooij, Wolf M. Year: 2015 Here, we present a community perspective on how to explore, exploit and evolve the diversity in aquatic ecosystem models. These models play an important role in understanding the functioning of aquatic ecosystems, filling in observation gaps and developing effective strategies for water quality management. In this spirit, numerous models have been developed since the 1970s. We set off to explore model diversity by making an inventory among 42 aquatic ecosystem modellers, by categorizing the resulting set of models and by analysing them for diversity. We then focus on how to exploit model diversity by comparing and combining different aspects of existing models. Finally, we discuss how model diversity came about in the past and could evolve in the future. Throughout our study, we use analogies from biodiversity research to analyse and interpret model diversity. We recommend to make models publicly available through open-source policies, to standardize documentation and technical implementation of models, and to compare models through ensemble modelling and interdisciplinary approaches. We end with our perspective on how the field of aquatic ecosystem modelling might develop in the next 5–10 years. To strive for clarity and to improve readability for non-modellers, we include a glossary. Title: Exploring, Exploiting and Evolving Diversity of Aquatic Ecosystem Models: a Community Perspective Author: Janssen, Annette B.G., Arhonditsis, George B., Beusen, Arthur, Bolding, Karsten, Bruce, Louise, Bruggeman, Jorn, Couture, Raoul-Marie, Downing, Andrea S., Elliott, J. Alex, Frassl, Marieke A., Gal, Gideon, Gerla, Daan J., Hipsey, Matthew R., Hu, Fenjuan, Ives, Stephen C., Janse, Jan H., Jeppesen, Erik, Jöhnk, Klaus D., Kneis, David, Kong, Xiangzhen, Kuiper, Jan J., Lehmann, Moritz K., Lemmen, Carsten, Özkundakci, Deniz, Petzoldt, Thomas, Rinke, Karsten, Robson, Barbara J., Sachse, René, Schep, Sebastiaan A., Schmid, Martin, Scholten, Huub, Teurlincx, Sven, Trolle, Dennis, Troost, Tineke A., Van Dam, Anne A., Van Gerven, Luuk P.A., Weijerman, Mariska, Wells, Scott A., Mooij, Wolf M. Year: 2015 Here, we present a community perspective on how to explore, exploit and evolve the diversity in aquatic ecosystem models. These models play an important role in understanding the functioning of aquatic ecosystems, filling in observation gaps and developing effective strategies for water quality management. In this spirit, numerous models have been developed since the 1970s. We set off to explore model diversity by making an inventory among 42 aquatic ecosystem modellers, by categorizing the resulting set of models and by analysing them for diversity. We then focus on how to exploit model diversity by comparing and combining different aspects of existing models. Finally, we discuss how model diversity came about in the past and could evolve in the future. Throughout our study, we use analogies from biodiversity research to analyse and interpret model diversity. We recommend to make models publicly available through open-source policies, to standardize documentation and technical implementation of models, and to compare models through ensemble modelling and interdisciplinary approaches. We end with our perspective on how the field of aquatic ecosystem modelling might develop in the next 5–10 years. To strive for clarity and to improve readability for non-modellers, we include a glossary. Close

• 62. [Article] Increased Taxonomic and Functional Similarity Does Not Increase the Trophic Similarity of Communities

  Aim: Despite a long-standing research interest in the association between the biodiversity (i.e. taxonomic and functional composition) and trophic structure of communities, our understanding of the relationship ...

  Citation × Citation Citation Abstract Copy Title: Increased Taxonomic and Functional Similarity Does Not Increase the Trophic Similarity of Communities Author: Pool, Thomas K., Cucherousset, Julien, Boulêtreau, Stéphanie, Villéger, Sébastien, Strecker, Angela L., Grenouillet, Gaël Year: 2015 Aim: Despite a long-standing research interest in the association between the biodiversity (i.e. taxonomic and functional composition) and trophic structure of communities, our understanding of the relationship remains limited. Community assembly theory predicts that niche partitioning will result in communities with a diverse array of functional traits, which in turn may facilitate a correspondingly diverse array of trophic interactions that define the trophic niche of those communities. The aim of our study is to test this prediction. Methods: We built a database composed of functional traits and stable isotope values (δ13C and δ15N) for 63 freshwater fish communities containing 109 species in 34 lentic and 29 lotic ecosystems. First, using linear mixed models (i.e. an alpha-diversity approach), we tested whether the taxonomic diversity of communities was positively associated with their functional diversity and if their functional diversity was positively associated with their trophic diversity. Second, we assessed the taxonomic, functional and trophic similarity of communities using multiple regression on distance matrices (MRM) and their respective ‘turnover’ and ‘nestedness-resultant’ components to test if the taxonomic similarity of communities was positively correlated with their functional similarity and if their functional similarity was positively associated with their trophic similarity (i.e. a beta-diversity approach). Results: We found that the functional diversity of communities increased as their taxonomic diversity increased. Similarly, the trophic diversity of communities increased as their functional diversity increased. The pairwise taxonomic and functional similarity of communities were also positively associated, but there was a weak relationship between the functional and trophic similarities of communities. Main conclusions: Our study demonstrates that communities with similar functional characteristics can have disparate food web structures, suggesting that additional site-specific factors influence community variation in trophic niche geometry. Determining the relative importance of functional characteristics and site-specific factors in shaping trophic interactions is crucial for a better understanding of how future species loss and species introductions will affect food web structure and ecosystem functioning. Title: Increased Taxonomic and Functional Similarity Does Not Increase the Trophic Similarity of Communities Author: Pool, Thomas K., Cucherousset, Julien, Boulêtreau, Stéphanie, Villéger, Sébastien, Strecker, Angela L., Grenouillet, Gaël Year: 2015 Aim: Despite a long-standing research interest in the association between the biodiversity (i.e. taxonomic and functional composition) and trophic structure of communities, our understanding of the relationship remains limited. Community assembly theory predicts that niche partitioning will result in communities with a diverse array of functional traits, which in turn may facilitate a correspondingly diverse array of trophic interactions that define the trophic niche of those communities. The aim of our study is to test this prediction. Methods: We built a database composed of functional traits and stable isotope values (δ13C and δ15N) for 63 freshwater fish communities containing 109 species in 34 lentic and 29 lotic ecosystems. First, using linear mixed models (i.e. an alpha-diversity approach), we tested whether the taxonomic diversity of communities was positively associated with their functional diversity and if their functional diversity was positively associated with their trophic diversity. Second, we assessed the taxonomic, functional and trophic similarity of communities using multiple regression on distance matrices (MRM) and their respective ‘turnover’ and ‘nestedness-resultant’ components to test if the taxonomic similarity of communities was positively correlated with their functional similarity and if their functional similarity was positively associated with their trophic similarity (i.e. a beta-diversity approach). Results: We found that the functional diversity of communities increased as their taxonomic diversity increased. Similarly, the trophic diversity of communities increased as their functional diversity increased. The pairwise taxonomic and functional similarity of communities were also positively associated, but there was a weak relationship between the functional and trophic similarities of communities. Main conclusions: Our study demonstrates that communities with similar functional characteristics can have disparate food web structures, suggesting that additional site-specific factors influence community variation in trophic niche geometry. Determining the relative importance of functional characteristics and site-specific factors in shaping trophic interactions is crucial for a better understanding of how future species loss and species introductions will affect food web structure and ecosystem functioning. Close

• 63. [Article] Glacial Ecosystems

  There is now compelling evidence that microbially mediated reactions impart a significant effect upon the dynamics, composition, and abundance of nutrients in glacial melt water. Consequently, we must ...

  Citation × Citation Citation Abstract Copy Title: Glacial Ecosystems Author: Hodson, Amy, Anesio, Alexandre M., Tranter, Martyn, Fountain, Andrew G., Osborn, Mark, Priscu, John Charles, Laybourn-Perry, Johanna, Sattler, Birgit Year: 2008 There is now compelling evidence that microbially mediated reactions impart a significant effect upon the dynamics, composition, and abundance of nutrients in glacial melt water. Consequently, we must now consider ice masses as ecosystem habitats in their own right and address their diversity, functional potential, and activity as part of alpine and polar environments. Although such research is already underway, its fragmentary nature provides little basis for developing modern concepts of glacier ecology. This paper therefore provides a much-needed framework for development by reviewing the physical, biogeochemical, and microbiological characteristics of microbial habitats that have been identified within glaciers and ice sheets. Two key glacial ecosystems emerge, one inhabiting the glacier surface (the supraglacial ecosystem) and one at the ice-bed interface (the subglacial ecosystem). The supraglacial ecosystem is characterized by a diverse consortium of microbes (usually bacteria, algae, phytoflagellates, fungi, viruses and occasional rotifers, tardigrades, and diatoms) within the snowpack, supraglacial streams, and melt pools (cryoconite holes). The subglacial system is dominated by aerobic/anaerobic bacteria and most probably viruses in basal ice/till mixtures and subglacial lakes. A third, so-called englacial ecosystem is also described, but it is demonstrated that conditions within glacier ice are sufficient to make metabolic activity and its impact upon nutrient dynamics negligible at the glacier scale. Consideration of the surface and internal heat balances of the glacier show that all glacial ecosystems are sensitive to climate change, although at different timescales. Thus, while rapid, melt-driven habitat changes lead to melt-out, resuscitation, and redistribution of microorganisms in many supraglacial ecosystems, much slower climatic and glacial mass-balance processes effect such changes in the subglacial ecosystem. Paradoxically, it is shown that these forces have brought about net refreezing and the onset of cryostasis in the subglacial ecosystems of many Arctic glaciers subject to thinning in recent decades. Title: Glacial Ecosystems Author: Hodson, Amy, Anesio, Alexandre M., Tranter, Martyn, Fountain, Andrew G., Osborn, Mark, Priscu, John Charles, Laybourn-Perry, Johanna, Sattler, Birgit Year: 2008 There is now compelling evidence that microbially mediated reactions impart a significant effect upon the dynamics, composition, and abundance of nutrients in glacial melt water. Consequently, we must now consider ice masses as ecosystem habitats in their own right and address their diversity, functional potential, and activity as part of alpine and polar environments. Although such research is already underway, its fragmentary nature provides little basis for developing modern concepts of glacier ecology. This paper therefore provides a much-needed framework for development by reviewing the physical, biogeochemical, and microbiological characteristics of microbial habitats that have been identified within glaciers and ice sheets. Two key glacial ecosystems emerge, one inhabiting the glacier surface (the supraglacial ecosystem) and one at the ice-bed interface (the subglacial ecosystem). The supraglacial ecosystem is characterized by a diverse consortium of microbes (usually bacteria, algae, phytoflagellates, fungi, viruses and occasional rotifers, tardigrades, and diatoms) within the snowpack, supraglacial streams, and melt pools (cryoconite holes). The subglacial system is dominated by aerobic/anaerobic bacteria and most probably viruses in basal ice/till mixtures and subglacial lakes. A third, so-called englacial ecosystem is also described, but it is demonstrated that conditions within glacier ice are sufficient to make metabolic activity and its impact upon nutrient dynamics negligible at the glacier scale. Consideration of the surface and internal heat balances of the glacier show that all glacial ecosystems are sensitive to climate change, although at different timescales. Thus, while rapid, melt-driven habitat changes lead to melt-out, resuscitation, and redistribution of microorganisms in many supraglacial ecosystems, much slower climatic and glacial mass-balance processes effect such changes in the subglacial ecosystem. Paradoxically, it is shown that these forces have brought about net refreezing and the onset of cryostasis in the subglacial ecosystems of many Arctic glaciers subject to thinning in recent decades. Close

• 64. [Image] Klamath Falls Resource Area resource management plan and environmental impact statement : final : Volume 1

  	Proposed resource management plan/final environmental impact statement for the Klamath Falls Resource Area
  	Citation × Citation Citation Abstract Copy Title: Klamath Falls Resource Area resource management plan and environmental impact statement : final : Volume 1 Author: United States. Bureau of Land Management. Klamath Falls Resource Area Office Year: 1994, 2005, 2004 Proposed resource management plan/final environmental impact statement for the Klamath Falls Resource Area Title: Klamath Falls Resource Area resource management plan and environmental impact statement : final : Volume 1 Author: United States. Bureau of Land Management. Klamath Falls Resource Area Office Year: 1994, 2005, 2004 Proposed resource management plan/final environmental impact statement for the Klamath Falls Resource Area Close

• 65. [Article] Hydrology shapes taxonomic and functional structure of desert stream invertebrate communities

  This is an author's peer-reviewed final manuscript, as accepted by the publisher. The article is copyrighted by The Society for Freshwater Science and published by The University of Chicago Press. It can ...

  Citation × Citation Citation Abstract Copy Title: Hydrology shapes taxonomic and functional structure of desert stream invertebrate communities Author: Lytle, David A., Olden, Julian D., Jaeger, Kristin L., Bogan, Michael T., Schriever, Tiffany A., Cañedo-Argüelles, Miguel, Boersma, Kate S. This is an author's peer-reviewed final manuscript, as accepted by the publisher. The article is copyrighted by The Society for Freshwater Science and published by The University of Chicago Press. It can be found at: http://www.press.uchicago.edu/ucp/journals/journal/fws.html Title: Hydrology shapes taxonomic and functional structure of desert stream invertebrate communities Author: Lytle, David A., Olden, Julian D., Jaeger, Kristin L., Bogan, Michael T., Schriever, Tiffany A., Cañedo-Argüelles, Miguel, Boersma, Kate S. This is an author's peer-reviewed final manuscript, as accepted by the publisher. The article is copyrighted by The Society for Freshwater Science and published by The University of Chicago Press. It can be found at: http://www.press.uchicago.edu/ucp/journals/journal/fws.html Close

• 66. [Article] Comparative Composition, Diversity and Trophic Ecology of Sediment Macrofauna at Vents, Seeps and Organic Falls

  This is the publisher’s final pdf. The published article is copyrighted by the Public Library of Science and can be found at: http://www.plosone.org/home.action.

  Citation × Citation Citation Abstract Copy Title: Comparative Composition, Diversity and Trophic Ecology of Sediment Macrofauna at Vents, Seeps and Organic Falls Author: Smith, Craig R., Thurber, Andrew R., Levin, Lisa A., Bernardino, Angelo F. This is the publisher’s final pdf. The published article is copyrighted by the Public Library of Science and can be found at: http://www.plosone.org/home.action. Title: Comparative Composition, Diversity and Trophic Ecology of Sediment Macrofauna at Vents, Seeps and Organic Falls Author: Smith, Craig R., Thurber, Andrew R., Levin, Lisa A., Bernardino, Angelo F. This is the publisher’s final pdf. The published article is copyrighted by the Public Library of Science and can be found at: http://www.plosone.org/home.action. Close

• 67. [Article] Hydroclimatic and hydrochemical controls on Plecoptera diversity and distribution in northern freshwater ecosystems

  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 published article is copyrighted by Springer ...

  Citation × Citation Citation Abstract Copy Title: Hydroclimatic and hydrochemical controls on Plecoptera diversity and distribution in northern freshwater ecosystems Author: Soulsby, Chris, Laudon, Hjalmar, Cunjak, Richard, Carey, Sean K., Shanley, Jamie, Buttle, Jim, Seibert, Jan, Kruitbos, Laura M., McGuire, Kevin, McDonnell, Jeffrey J., Tetzlaff, Doerthe 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 published article is copyrighted by Springer and can be found at: http://www.springer.com/?SGWID=0-102-0-0-0. Title: Hydroclimatic and hydrochemical controls on Plecoptera diversity and distribution in northern freshwater ecosystems Author: Soulsby, Chris, Laudon, Hjalmar, Cunjak, Richard, Carey, Sean K., Shanley, Jamie, Buttle, Jim, Seibert, Jan, Kruitbos, Laura M., McGuire, Kevin, McDonnell, Jeffrey J., Tetzlaff, Doerthe 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 published article is copyrighted by Springer and can be found at: http://www.springer.com/?SGWID=0-102-0-0-0. Close

• 68. [Article] Obligations to Protect Marine Ecosystems Under International Conventions and other Legal Instruments

  Research Paper

  Citation × Citation Citation Abstract Copy Title: Obligations to Protect Marine Ecosystems Under International Conventions and other Legal Instruments Author: Aqorau, Transform Research Paper Title: Obligations to Protect Marine Ecosystems Under International Conventions and other Legal Instruments Author: Aqorau, Transform Research Paper Close

• 69. [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

• 70. [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