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Temporal lags in the response of populations to climatic variation associated with the NAO are widespread in both terrestrial and marine environments. The existence of both immediate and lagged responses to climate presents conceptual and analytical challenges to the study of the ecological consequences of large-scale climatic variability, as well as to the ability to forecast population responses to future climatic change. This chapter discusses the influence of atmospheric processes, life history, and trophic interactions on time lags. It argues that the existence of time lags in a multitude of systems can be exploited to one obvious advantage: prediction. Hence, an empirically-derived basis for improving conceptual and analytical understanding of lagged responses to climate should prove valuable in the pursuit of scientifically robust predictions of population and community response to future climate changes.

This chapter presents a brief review and description of some of the issues in modelling and the status of modelling efforts. It attempts to link and explain changes in climate and in pelagic marine communities in the North Atlantic systems, drawing from knowledge gained from studies of all oceans. The chapter's structure is as follows. First, it briefly discusses aspects of the relationship between variability in the environment and variability in marine populations. It then presents approaches that are being taken for understanding this variability and highlights areas where progress has been made. It ends with recommendations and suggestions for new approaches necessary for further advances.

While one of the most striking features of our planet is its great variety of life, studies show that ongoing biodiversity loss could reduce the productivity of ecosystems by as much as 50%. However, evidence comes largely from experiments that have used highly simplified communities with on average seven species, all from a single trophic group. In contrast, natural communities have dozens, if not hundreds, of species spanning a variety of trophic levels. Would this additional complexity alter our conclusions about the functional consequences of diversity loss? This chapter reviews five hypotheses about how the fluxes of energy and matter through food-webs might depend on the diversity of species interacting within, as well as across trophic levels. After outlining the empirical support for or against each hypothesis, this chapter discusses several avenues of research that may prove useful as ecologists move towards a food web perspective on biodiversity and ecosystem functioning

The phytoplankton comprises a diverse array of photosynthetic organisms. The majority of polar lakes are classified as ultra-oligotrophic based on maximum chlorophyll concentrations. However, few lakes have been studied seasonally to determine the annual peak in biomass, thus trophic status is probably underestimated; intensively-studied lakes are mostly oligotrophic. The seasonal progression of primary production is initiated and ended by the large seasonal changes in solar radiation. A springtime peak occurs in most polar lakes, with subsequent enhancement or restraint by changes in light, nutrient availability or losses from grazing, disease, washout, and sedimentation. Comparisons between Arctic and Antarctic lakes imply that there may be differences in biodiversity, lake trophic status, and primary production that can improve understanding of the how polar lake phytoplankton are influenced by climate, nutrient supply, biotic interactions, and their own capacity to acclimate to their environment.

Lakes at high latitudes represent a range of biotic complexity imposed by strong abiotic limitations that are differentially ameliorated by biogeographic factors between the northern and southern latitudes. However, the communities in these lakes are simpler than those typically found in more temperate environments and represent a range of declining biocomplexity as conditions approach the limits to life in these extreme environments. This includes the relative importance of keystone predators and higher trophic levels (e.g., fish and birds) as well as the benthic-pelagic coupling in structuring the food webs. This chapter uses examples and case studies to explore food web interactions between microbial and classic food webs, the importance of autochthonous versus allochthonous carbon, and the implications of a changing climate.

Despite their minute biomass relative to other species, endophytes have the potential to have profound effects on community structure and diversity and ecosystem functions. For agronomic grasses, infection may decrease plant diversity and alter relative abundances and species richness of herbivores, predators, and parasites. In natural communities, endophyte infection has complex and often unpredictable effects on community and trophic diversity. The mechanism for these effects on higher trophic levels may be endophytic alkaloids or changes in plant physiology, morphology, or productivity that cascade upward in the community. Because natural enemies of herbivores may be more affected than herbivores, which have coevolved with alkaloids in natural grass communities, alkaloids may actually increase herbivory, counter to the long-held notion of endophytes as defensive plant mutualists. Endophytes, by altering competitive hierarchies, diversity, and productivity in communities may also render communities more invasible by non-native species as has been shown for agronomic tall fescue. Furthermore, infected tall fescue can also change successional sequences in old fields. For ecosystem functions, infected grasses may alter decomposition and nutrient cycling rates in old field communities. Much less is known about the effects of native infected grasses on community- and ecosystem-level properties and functions. Because seed-borne endophytes are maternally inherited components that dramatically alter plant phenotypes with widespread repercussions at the community and ecosystem level, they should make good models for testing recent notions of community genetics and extended phenotypes.

The chapter summarizes the history of recent scientific understanding of food webs, particularly shallow water food webs. The chapter outlines a history of key papers ranging from Elton to the most recent synthetic studies of meta-analysis of multiple food webs in many ecosystems. Changes in general organizing principles over time and conflicts with recent understanding are emphasized including an outline of the considerable progress over time and hope for an emerging discipline that takes advantage of emerging multidisciplinary tools and collaborations.

The chapter summarizes the current understanding of the kelp forest ecosystems of Alaska by focusing on the key role that otters, killer whales, and man have played in the ecological organization of this ecosystem. The role of kelp, the effect of anti-predator chemistry, and sea urchin interactions are discussed. The history of the ecosystem as well as the science is covered and includes a discussion of the debate on the role of whaling in influencing otter–killer whale interactions, which may be further changing the ecology of this ecosystem.

This chapter summarizes what the authors consider to be the key and general organizing principles of kelp forests and coral reefs along gradients of oceanography, latitude, and effects of fishing and resource use on these ecosystems. The general structure of these food webs is described as well as the effects of top-down versus bottom-up controls and the prevalence of trophic cascades. Human effects and recommendations for management are presented.

Food webs are theoretical abstractions of the complex linkages and interactions that are thought to occur in nature. Although few real food webs have actually been characterized scientifically, there is a large body of literature on the processes that contribute towards complexity and stability in webs. Food webs are generally thought of as ‘what eats what’ webs, but parasites are not usually incorporated into webs even though parasitism is a feeding strategy shared by a majority of species on earth (70%). This chapter examines major ideas on the roles of parasites in food webs, starting with Elton’s (1927) idea that parasites are analogous to predators. It describes some general patterns of parasite web structure (e.g., inverted pyramid of numbers and body size hypotheses) using both available published data and data from studies on food webs in freshwater streams in New Jersey.

GLOBEC studies focused on biological—physical interactions of target species in different study regions, emphasizing responses of organisms to varying physical forces. Population‐level processes were shown to be important, with ecological responses often being ecosystem‐specific. The timing of biological events (e.g. spring bloom, entry/exit from diapause, and fish spawning) is susceptible to environmental change. Many species can adapt their feeding modes and diets, but changes in mortality imposed by heavy fishing can disrupt biological systems, making them increasingly vulnerable to perturbations. Some organisms can move away from unfavourable conditions, changing the vertical and horizontal linkages between disparate ecosystems with unknown consequences. Trophic controls in food webs vary over time and space and food web structures also change, both over the short term and through shifts in regimes, sometimes irreversibly. There is an ongoing requirement to integrate ecological processes, from biogeochemistry to top predators, to understand potential consequences of global change.

This chapter assesses the consequences of individual nutrition for populations and the assemblages of species that comprise ecological communities. However, the ecological consequences of nutrition are not restricted to the effects of diet on individual organisms but include as well the direct and indirect interactions occurring among individuals within populations and between species. Understanding the complex network of interactions that produce food webs and structure ecosystem dynamics requires the understanding of the participants' differing nutritional requirements, priorities, and regulatory capacities. Geometric Framework analyses have shown that these features differ between species and across trophic levels. Nutritional space is one part of the fundamental niche of an organism, and there is a need to integrate nutrition with the biophysical ecology of organisms. Evolutionary processes also need to be taken into account, and agent-based models offer promise toward development of a new understanding of the evolutionary ecology of nutrition.

Biodiversity in freshwater food webs can be considered in terms of the number of species occupying unique trophic positions or the number of species within a trophic position. Either can affect energy flow or biomass partitioning, and the two aspects of diversity may feed back on one another. This chapter analyses the importance of biodiversity in aquatic food webs on three different levels. First, it asks how varying diversity within trophic groups affects the outcome of trophic interactions. It then presents a conceptual framework and contrasts this model against experimental manipulations of consumer or prey diversity. Second, it asks how consumers and resources affect biodiversity within trophic levels. This question has a long history of experimental and modeling studies, and these are reviewed. The role of biodiversity at local and regional spatial scales for freshwater food webs is examined. Dispersal among local habitats can constrain local species diversity and influence the outcome of food web interactions. The interactive effects of the regional pool versus resident diversity on the outcome of trophic interactions are discussed.

Trophic interactions, as many other relevant ecological processes, are spatially extended. Previous work has pointed out the importance of the spatial domain for understanding food webs. This chapter builds on this body of work by considering how space shapes food web structure. It considers two case studies. First, it studies whether the global structure of Doñana's food web (south-eastern Spain) is homogeneous on each habitat type, or whether different habitat types have subwebs with different structure. Second, it considers in several geographic locations in southern Spain the food web formed by the genera Turdus and the plants whose fruits they consume. It looks at how food web structure at each spatial location is related to structure at other locations.

Estuaries are excellent ecosystems for testing the veracity of the inferences of ecological network analysis for three reasons. First, more network analyses have been conducted on estuaries than any other kind of ecosystem. Second, estuarine environments are often stressed by natural and anthropogenic forcings. These conditions allow hypotheses of response to stress to be formulated and tested. Finally, sampling of estuaries has often been extensive, such that reasonable food webs can be constructed under different conditions of stress. This chapter reviews studies that incorporate these three elements, and assesses how efficacious analysis output variables are at describing the effects of stress. Output variables index a range of trophic dynamic properties from populations to entire food webs. The assessment is structured in the context of this range.

Studies on streams provide some of the most detailed and best resolved webs yet available, and provide a means to test food web theory. These systems can be used to test patterns in connectance webs and the effect of sampling on the patterns evident. The role of body-size in stream webs is reviewed. This chapter deals with attempts to quantify food webs by measures of energy flow and interaction strengths, and to characterize the circumstances leading to the presence or absence of trophic cascades in food webs. Streams are strongly linked through their food webs with surrounding systems, such as ground water and flood plains, and such cross-system subsidies is considered. The effect of natural and anthropogenic disturbances on food web attributes is addressed. Finally, the relationship between biodiversity/ecosystem functions in stream webs is addressed in the context of environmental stress.

This chapter explores three more examples that all arise in the context of fundamental ecological and evolutionary questions to further illustrate the diversifying force of frequency-dependent interactions. The first example concerns the dynamics of spatially structured populations and serves as an excellent case study for illustrating the feedback between ecological and evolutionary dynamics. The second example concerns the evolution of asymmetry in gamete size between the sexes, which sets the stage for the “paradox of sex.” Finally, the third example concerns the fundamental question of the evolution of trophic levels in food webs, that is, the evolution of complexity in ecosystems.

This chapter provides a brief historical account of the success and limitations of using chemical biomarkers in aquatic ecosystems. It also introduces the general concepts of chemical biomarkers as they relate to global biogeochemical cycling. The application of chemical biomarkers in modern and/or ancient ecosystems is largely a function of the inherent structure and stability of the molecule, as well as the physicochemical environment of the system wherein it exists. In some cases, redox changes in sediments have allowed for greater preservation of biomarker compounds; in well-defined laminated sediments; for example, a strong case can be made for paleo-reconstruction of past organic matter composition sources. However, many of the labile chemical biomarkers may be lost or transformed within minutes to hours of being released from the cell from processes such as bacterial and/or metazoan grazing, cell lysis, and photochemical breakdown. The role of trophic effects versus large-scale physiochemical gradients in preserving or destroying the integrity of chemical biomarkers varies greatly across different ecosystems. These effects are discussed as they relate to aquatic systems such as lakes, estuaries, and oceans.

This chapter describes the very prominent succession of species that characterizes the communities living in temporary waters. It examines the important biological factors that influence these communities, particularly colonization dynamics and competition. Conceptually, temporary waters are explored as islands in space and time. The chapter concludes with an in depth consideration of foodweb dynamics of communities among different habitat types and along a hydroperiod gradient, seeking to determine whether these habitats exhibit trophic continua or disjunct phases.