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History has profoundly affected the composition, distribution, and abundances of species in contemporary ecosystems. A full understanding of how ecosystems work and change must therefore take history into account. We offer four well-studied examples illustrating how a knowledge of history has strengthened interpretations of modern systems: the development of molluscan antipredatory defenses in relation to shell-breaking predators; the North Pacific kelp ecosystem with sea otters, smaller predators, sea urchins, and large herbivores; estuarine ecosystems affected by the decline in oysters and other suspension feeders; and the legacy of extinct large herbivores and frugivores in tropical American forests. Many current ecological problems would greatly benefit from a historical perspective. We highlight four of these: soil depletion and tree stunting in forests related to the disappearance of large consumers; the spread of anoxic dead zones in the ocean, which we argue could be mitigated by restoring predator and suspension-feeding guilds; ocean acidification, which would be alleviated by more nutrient recycling by consumers in the aerobic ecosystem; and the relation between species diversity and keystone predators, a foundational concept that is complicated by simplified trophic relationships in modern ecosystems., (© 2022 The Ecological Society of America.)

Competing Interests: The authors declare no conflict of interest.

Few concepts in ecology have been so influential as that of the trophic cascade. Since the 1980s, the term has been a central or major theme of more than 2000 scientific articles. Despite this importance and widespread usage, basic questions remain about what constitutes a trophic cascade. Inconsistent usage of language impedes scientific progress and the utility of scientific concepts in management and conservation. Herein, we offer a definition of trophic cascade that is designed to be both widely applicable yet explicit enough to exclude extraneous interactions. We discuss our proposed definition and its implications, and define important related terms, thereby providing a common language for scientists, policy makers, conservationists, and other stakeholders with an interest in trophic cascades., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Robert T. Paine, who passed away on 13 June 2016, is among the most influential people in the history of ecology. Paine was an experimentalist, a theoretician, a practitioner, and proponent of the "ecology of place," and a deep believer in the importance of natural history to ecological understanding. His scientific legacy grew from the discovery of a link between top-down forcing and species diversity, a breakthrough that led to the ideas of both keystone species and trophic cascades, and to our early understanding of the mosaic nature of biological communities, causes of zonation across physical gradients, and the intermediate-disturbance hypothesis of species diversity. Paine's influence as a mentor was equally important to the growth of ecological thinking, natural resource conservation, and policy. He served ecology as an Ecological Society of America president, an editor of the Society's journals, a member of and contributor to the National Academy of Sciences and the National Research Council, and an in-demand advisor to various state and federal agencies. Paine's broad interests, enthusiasm, charisma, and humor deeply affected our lives and the lives of so many others., (© 2016 by the Ecological Society of America.)

Recovery criteria for depleted species or populations normally are based on demographic measures, the goal being to maintain enough individuals over a sufficiently large area to assure a socially tolerable risk of future extinction. Such demographically based recovery criteria may be insufficient to restore the functional roles of strongly interacting species. We explored the idea of developing a recovery criterion for sea otters (Enhydra lutris) in the Aleutian archipelago on the basis of their keystone role in kelp forest ecosystems. We surveyed sea otters and rocky reef habitats at 34 island-time combinations. The system nearly always existed in either a kelp-dominated or deforested phase state, which was predictable from sea otter density. We used a resampling analysis of these data to show that the phase state at any particular island can be determined at 95% probability of correct classification with information from as few as six sites. When sea otter population status (and thus the phase state of the kelp forest) was allowed to vary randomly among islands, just 15 islands had to be sampled to estimate the true proportion that were kelp dominated (within 10%) with 90% confidence. We conclude that kelp forest phase state is a more appropriate, sensitive, and cost-effective measure of sea otter recovery than the more traditional demographically based metrics, and we suggest that similar approaches have broad potential utility in establishing recovery criteria for depleted populations of other functionally important species.

Ecological surprises, substantial and unanticipated changes in the abundance of one or more species that result from previously unsuspected processes, are a common outcome of both experiments and observations in community and population ecology. Here, we give examples of such surprises along with the results of a survey of well-established field ecologists, most of whom have encountered one or more surprises over the course of their careers. Truly surprising results are common enough to require their consideration in any reasonable effort to characterize nature and manage natural resources. We classify surprises as dynamic-, pattern-, or intervention-based, and we speculate on the common processes that cause ecological systems to so often surprise us. A long-standing and still growing concern in the ecological literature is how best to make predictions of future population and community dynamics. Although most work on this subject involves statistical aspects of data analysis and modeling, the frequency and nature of ecological surprises imply that uncertainty cannot be easily tamed through improved analytical procedures, and that prudent management of both exploited and conserved communities will require precautionary and adaptive management approaches.

For tens of thousands of years, passenger pigeons (Ectopistes migratorius) were a dominant member of eastern North American forest communities, with megaflocks comprising up to several billion individuals. The extinction of passenger pigeons in the early twentieth century undoubtedly influenced associated species and ecosystems as interactions stemming from the pigeons disappeared suddenly. Here, we strive to better understand what was probably one of the most significant of these interactions-that between passenger pigeons and seed bearing trees. Using the band-tailed pigeon (Patagioenas fasciata) and the rock dove (Columba livia) as physical and ecological proxies, we evaluated passenger pigeon dietary range and potential to disperse seeds. Our findings suggest that the passenger pigeon's dietary range, observed historically to be taxonomically broad, was constrained to certain seed sizes due to bill gape size. In addition, we conclude that the digestive process invariably destroyed consumed seeds but the potential for a nutrition/dispersal mutualism might still have existed via regurgitation and post-mortem release of crop contents. Our results highlight the range of ecological interactions that can be lost with species' extinction and the inherent challenge of understanding the consequences of those interactions.

Here, we identify the extant species of marine megafauna (>45 kg maximum reported mass), provide a conceptual template for the ways in which these species influence the structure and function of ocean ecosystems, and review the published evidence for such influences. Ecological influences of more than 90% of the 338 known species of extant ocean megafauna are unstudied and thus unknown. The most widely known effect of those few species that have been studied is direct prey limitation, which occurs through consumption and risk avoidance behavior. Consumer-prey interactions result in indirect effects that extend through marine ecosystems to other species and ecological processes. Marine megafauna transport energy, nutrients, and other materials vertically and horizontally through the oceans, often over long distances. The functional relationships between these various ecological impacts and megafauna population densities, in the few well-studied cases, are characterized by phase shifts and hysteresis.

The article informs on a study published by Gregr et al., evaluating the recovery of an apex predator, sea otters in the Canadian Pacific coast, and report that certain economies have been either negatively or positively affected by sea otter restoration, but the overall economic outcomes are positive. It mentions that inasmuch as plants are the foundation for nearly all life on Earth, this link from predator to herbivore to plant extends broadly through nature.

How best to predict the effects of perturbations to ecological communities has been a long-standing goal for both applied and basic ecology. This quest has recently been revived by new empirical data, new analysis methods, and increased computing speed, with the promise that ecologically important insights may be obtainable from a limited knowledge of community interactions. We use empirically based and simulated networks of varying size and connectance to assess two limitations to predicting perturbation responses in multispecies communities: (1) the inaccuracy by which species interaction strengths are empirically quantified and (2) the indeterminacy of species responses due to indirect effects associated with network size and structure. We find that even modest levels of species richness and connectance (~25 pairwise interactions) impose high requirements for interaction strength estimates because system indeterminacy rapidly overwhelms predictive insights. Nevertheless, even poorly estimated interaction strengths provide greater average predictive certainty than an approach that uses only the sign of each interaction. Our simulations provide guidance in dealing with the trade-offs involved in maximizing the utility of network approaches for predicting dynamics in multispecies communities. [ABSTRACT FROM AUTHOR]

Differences in diet composition among conspecifics (dietary specialization) have been documented across a broad range of taxonomic groups and habitats, and such variation at the individual level is increasingly recognized as an important component of diversity in trophic interactions. Accurate identification of individual dietary specialization, however, requires longitudinal dietary records that are labor-intensive and cost-prohibitive to obtain for many species. Here we explore the use of stable isotopes (δ13C and δ15N) as a promising technique for detecting and quantifying patterns of individual dietary specialization. Southern sea otters (Enhydra lutris nereis) offer a unique opportunity for testing this approach because (1) they consumea, wide variety of prey that span multiple trophic levels, habitats, and ecologically defined functional groups; and (2) individual diet specialization can be validated with existing observational data. We analyzed the isotopic composition of sea otter vibrissae (n = 31) in order to characterize inter- and intra-individual variation in sea otter diets at Monterey Bay, California, USA. At the population level, sea otters showed substantial variation in both δ13C and δ15N values, occupying nearly all of the "isotopic space" created by the diversity of isotopic signatures of potential prey taxa. Most of the variation in sea otter vibrissae was accounted for by differences between individuals, with much less contributed by within-individual variation. A majority of sea otters (∼80%) showed relatively little temporal variability in isotopic composition, suggesting that the proportional composition of most individuals' diets is relatively constant over time; a few individuals (∼20%) exhibited a high degree of intra-vibrissa isotopic variability, suggesting seasonal shifts in diet composition. These results and our interpretation of them were supported by long-term observational data on the diets of radio-tagged sea otters from the same population (n = 23). Our results demonstrate that stable isotopes can provide an efficient tool for measuring individual- and population-level dietary breadth and may be useful for studying populations where longitudinal data on individuals would otherwise be impossible to acquire. This will be critical for examining the causes and consequences of dietary variation within and among consumer populations, thereby improving our understanding of these important ecological and evolutionary processes at the community level. [ABSTRACT FROM AUTHOR]

The rarity or absence of highly interactive species leaves a functional void that can trigger linked changes leading to degraded or simplified ecosystems. A preliminary analysis indicates a relatively high frequency of such interactive species among endangered mammals. Rapid environmental change is likely to increase the interactivity of some species and reduce that of others over relatively short intervals. The current implementation of environmental policies and laws, such as the U.S. Endangered Species Act, generally ignores interspecific effects; recovery goals are autecological, short term, and numerically and spatially minimalistic. Moreover, by failing to account for interspecific interactions, recovery objectives are becoming indefensible in light of increasing knowledge from community ecology. Using the sea otter ( Enhydra lutris ) and wolf ( Canis lupus ) as examples, we argue that conservation plans should call for recovery or repatriation of such interactive species at ecologically effective densities in as many places as are currently realistic. It will be prudent and beneficial to estimate ecologically effective densities where there is disagreement among experts and interested parties about the desirability of restoring an interactive species to a particular region and to a particular density. [ABSTRACT FROM AUTHOR]

The article discusses the implications of concepts and reserve design theory for the design of coastal marine reserves. It explains how humans have influenced the environmental, ecological, and evolutionary processes. It identifies many of the environmental and ecological processes and design criteria necessary for consideration in the development of the analytical approaches.

After having been hunted to near-extinction in the Pacific maritime fur trade, the sea otter population at Amchitka Island, Alaska increased from very low numbers in the early 1900s to near equilibrium density by the 1940s. The population persisted at or near equilibrium through the 1980s, but declined sharply in the 1990s in apparent response to increased killer whale predation. Sea otter diet and foraging behavior were studied at Amchitka from August 1992 to March 1994 and the data compared with similar information obtained during several earlier periods. In contrast with dietary patterns in the 1960s and 1970s, when the sea otter population was at or near equilibrium density and kelp-forest fishes were the dietary mainstay, these fishes were rarely eaten in the 1990s. Benthic invertebrates, particularly sea urchins, dominated the otter’s diet from early summer to mid-winter, then decreased in importance during late winter and spring when numerous Pacific smooth lumpsuckers (a large and easily captured oceanic fish) were eaten. The occurrence of spawning lumpsuckers in coastal waters apparently is episodic on a scale of years to decades. The otters’ recent dietary shift away from kelp-forest fishes is probably a response to the increased availability of lumpsuckers and sea urchins (both high-preference prey). Additionally, increased urchin densities have reduced kelp beds, thus further reducing the availability of kelp-forest fishes. Our findings suggest that dietary patterns reflect changes in population status and show how an ecosystem normally under top-down control and limited by coastal zone processes can be significantly perturbed by exogenous events. [ABSTRACT FROM AUTHOR]

Reviews known or suspected roles played by predatory animals in the workings of their ecosystems. Presentation of two perspectives regarding predators and ecosystems; Example of the sea otter; Samples of mammals playing important roles in ecosystems; Application of the study to conservation issues.