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This chapter examines recent case studies of marine food webs to evaluate the applicability of food web theories for the marine environment. Classical macrodescriptors and recent network metrics are evaluated for each marine food web example. Food webs are defined as those which are non-estuarine, non-coastal, and larger in scale than food webs typically and classically studied (i.e., not a bay, not a river-ocean mixing zone, not a rocky inter-tidal zone, etc.). There are clear distinctions for marine food webs when compared to all terrestrial and other aquatic food webs, yet there are also clear distinctions among different types of marine food webs. The chapter notes that there are three categories of food web theories: (i) those factors and models which apply categorically to all food webs; (ii) those factors and models which can be split into simple, lowly connected, strongly interacting, clearly defined localized food webs versus complex, highly connected, weakly interacting, broader, more extensive food webs; and (iii) those factors and models which are uniquely and distinctly marine. Understanding the qualitative properties of food webs can provide further evaluation of which theories are appropriate, which are not, when each is true, and why. Finally, the chapter discusses the applications and implications of these theories for ecosystem-based natural resource management.

How do diverse species coexist in the complex networks of prey-predator interactions in nature? While most theoretical models predict that complex food webs do not persist, recent empirical studies have revealed the very complex structure of natural food webs. This discrepancy between theory and observation implies that essential factors stabilizing natural food webs are lacking from previous models. This chapter reviews these studies on food web complexity and its community-level consequences. It contends that the architectural flexibility arising from foraging adaptation of consumer species is key to explaining linkage patterns and persistent mechanisms of complex food webs. A novel hypothesis is presented, which relates the complexity-stability relationship to evolutionarily history of the community.

Marine conservation priorities have been established mostly on the basis of species and habitat diversity, but little attention has been paid to food web diversity. Ecologists are aware of the dynamic nature of marine food webs, and of the simplification of food web structure by anthropogenic activities, mainly fishing. Transient food web structures along gradients of fishing pressure are an analogue to stages along a successional gradient. This chapter describes regularities in food web structure along these gradients, and explores the global initial conditions (e.g., availability of species, sequence of species additions) needed to ensure that marine food webs will continue to function and adapt to environmental change in a world with increasing anthropogenic disturbance.

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.

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 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.

Studies on lakes provide some of the most complete investigations on the structure, dynamics, and energetics of food webs encompassing organisms from bacteria to vertebrates. The life cycle of organisms in temperate lakes is adapted to a highly seasonal environment. Food web interactions in these lakes depend on the seasonal overlap of the occurrence of potential prey, competitor, or predator species. This seasonal overlap (i.e., the match-mismatch of food web interactions) depends strongly on the seasonal dynamics of the physical environment of lakes, such as temperature, light availability, and mixing intensity. Consequently, climate variability influences food web interactions and hence the structure, dynamics, and energetics of lake food webs. This chapter provides examples and discusses the importance of seasonality for the understanding of various aspects of lake food webs and the impact of climate variability thereon.

This chapter examines food webs at the landscape scale by focusing on the large-scale food web architecture that is deeply constrained by space. It begins with a discussion of how variability in space, time, and food web structure, coupled with the ability of organisms to rapidly respond to variation, affect the maintenance of the food web and its functions. It then explains how individual traits such as body size and foraging behavior relate to food web structure in space and time. It also considers the role of spatial constraints on food webs and how the existence of fast–slow pathways coupled by mobile adaptive predators gives rise to spatial asynchrony in the resources. The chapter concludes with a review of some empirical examples to show that some food webs display the bird feeder effect and that resource coupling of distinct habitats appears to stabilize food webs.

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.

This chapter examines some of the potential empirical signatures of instability in complex adaptive food webs. It first considers the role of adaptive behavior on food web topology, ecosystem size, and interaction strength before discussing the implications of this behavior for ecosystem dynamics and stability. It then analyzes the results of empirical investigations of Canadian Shield lake trout food webs and how human influences and ecosystems coupled in space may drive biomass pyramids, potentially leading to species loss. It also explores the tendency of subsidies, through human impacts, to homogenize natural ecosytems and concludes by assessing some of the changing conditions that are being driven by humans and how these may change ecosystems.

This chapter considers topology, i.e. the shape and structure of networks of interacting organisms in ecological systems. Species often form the nodes of such networks, though life stages, age classes or functional groups are sometimes equally applicable. The links between nodes in ecological networks can have a variety of meanings, in particular they can represent transfer of energy or material, they can represent the net effect on fitness or population size (direct and/or indirect) of one species on another, or represent the exchange of information. These differences create at least three types of interaction networks: competition networks, mutualistic networks and food webs (consumption networks), all of which are subsets of the full network of interactions in any community.

This chapter describes ecology of the Galapagos rocky reef system and the important role of biogeographic position on biodiversity, the El Niño cycle, and the history of resource extraction on the current state of the ecosystem. The chapter presents a model of the energetic pathways in the ecosystem and its predictions for fisheries yields and the role of key species. The history of exploitation is outlined as well as the role of the current marine protected areas to develop sustainable management system.

Evolutionary dynamics may help us understand the structure and dynamics of food webs. The theoretical understanding of empirical food web patterns faces a dilemma, as it is difficult to account simultaneously for dynamical components (demography, evolution) and for the complexity of these systems (species number, connectance). Current knowledge of food web structures is dominated by many-species models that do not incorporate any dynamical aspects, and by models that detail demographic or evolutionary dynamics of species but consider communities composed of few species. Community evolution models incorporate both the dynamical components of food webs and the complexity that is necessary to understand empirical food web data.

The Eastern Bering Sea (EBS), the Gulf of Alaska (GOA), and the Barents Sea (BS) share key features: they are dominated by gadoids populations, they are heavily fished, and they are under the influence of large-scale climatic fluctuations. Previous studies have shown that climate forcing can impact the species composition and the food webs in each of these ecosystems. However, food webs and species interactions can mediate the relative impact of climatic perturbation on community. For example, a relatively small increase in SST over the western GOA region during the mid-1970s led to a spectacular change in the local species community, but a reverse in climatic conditions that occurred during the late 1980s did not result in similar biological changes. This chapter reviews the food webs of the GOA, EBS, and BS, and relates them to prevailing large-scale climatic phases. The comparative approach adopted in this review is aimed at increasing the understanding of the mechanisms linking climate change and food web dynamics in marine ecosystems.

This chapter focuses on the formal statistical analysis of community food webs. Among the issues covered are testing for hypothesized regularities (e.g., constant connectance) in a collection of food webs and fitting and testing parametric models (e.g., the cascade model). The analysis of partially observed food webs is also covered.

This chapter extends the consumer–resource theory to include simple but common three-species modules behind the construction of whole food webs, with particular emphasis on food chains and omnivory. It first considers some common simple modular food web structures and whether the dynamics of subsystems can be seen using the framework laid out in previous chapters. Specifically, it asks when common food web structure increases or weakens the relative interaction strengths and/or when a food web structure modifies flux between consumers and resources in a density-dependent manner such that the food web tends to increase flux rates in some situations and decrease the coupling in other situations. The chapter also explores how stage structure can influence food chain stability before concluding with a review of empirical evidence on the dynamical implications of omnivory for food webs.

This chapter introduces various approaches to dynamic network analyses and illustrates some of the key findings. First, classic results from dynamic analyses of simple interaction modules of few species (food chains, omnivory modules) are shortly introduced. Subsequently, the question of whether embedding such simple modules in complex food webs affects the dynamic outcome is illustrated using the example of a classic keystone module. The following section on dynamic analyses of complex food webs is organized around the classic and enduring debates on the relationships between (1) complexity and stability and (2) diversity and stability. The allometric (body size dependent) scaling of the biological rates of the populations is presented as a solution to the instability of complex food webs, and future directions of research on dynamic models of complex food webs are outlined.

Polar lakes and rivers encompass a diverse range of aquatic habitats, and many of these environments have broad global significance. This introduction to polar aquatic ecosystems presents a summary of the history of lake research in the Arctic and Antarctica, an overview of the limnological diversity within the polar regions, and descriptions of high-latitude rivers, lakes, and lake districts where there have been ecological studies. The comparative limnology of such regions, as well as detailed long-term investigations on one or more lakes or rivers within them, have yielded new perspectives on the structure, functioning, and environmental responses of aquatic ecosystems at polar latitudes and elsewhere. This review then examines the controls on biological production in high-latitude waters, the structure and organization of their food webs including microbial components, and their responses to global climate change, with emphasis on threshold effects.