Sea otters, kelp forests, and the extinction of Steller’s sea cow

Estes, James A.; Burdin, Alexander M.; Doak, Daniel F.

doi:10.1073/pnas.1502552112

Cited by 64 publications

(53 citation statements)

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“…Whale densities have declined by 66-99% (3,45). To date there have been few global extinctions of marine megafauna, with the exception of some coastal aquatic species such as Steller's sea cow (46).…”

Section: Megafauna Prehistorymentioning

confidence: 99%

Megafauna and ecosystem function from the Pleistocene to the Anthropocene

Malhi

Doughty

Galetti

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

419

382

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Large herbivores and carnivores (the megafauna) have been in a state of decline and extinction since the Late Pleistocene, both on land and more recently in the oceans. Much has been written on the timing and causes of these declines, but only recently has scientific attention focused on the consequences of these declines for ecosystem function. Here, we review progress in our understanding of how megafauna affect ecosystem physical and trophic structure, species composition, biogeochemistry, and climate, drawing on special features of PNAS and Ecography that have been published as a result of an international workshop on this topic held in Oxford in 2014. Insights emerging from this work have consequences for our understanding of changes in biosphere function since the Late Pleistocene and of the functioning of contemporary ecosystems, as well as offering a rationale and framework for scientifically informed restoration of megafaunal function where possible and appropriate.For hundreds of millions of years, an abundance of large animals, the megafauna, was a prominent feature of the land and oceans. However, in the last few tens of thousands of years-a blink of an eye on many evolutionary and biogeochemical timescales-something dramatic happened to Earth's ecology; megafauna largely disappeared from vast areas, rendered either actually or functionally extinct (1, 2). Only in small parts of the world do megafauna exist at diversities anything close to their previous state, and, in many of these remaining regions, they are in a state of functional decline through population depletion and range contraction. In the oceans, a similar process has occurred over the last few hundred years: although there has been little absolute extinction, there has been a dramatic decline in the abundance of whales and large fish through overharvesting (3). Both on land and in oceans, declines continue today (4-7).Homo sapiens evolved and dispersed in a world teeming with giant creatures. Our earliest art forms, such as the haunting and mesmerizing Late Pleistocene cave paintings of Lascaux and Altamira, show that megafauna had a profound impact on the psyche and spirituality of our ancestors. To humans past and modern, they indicate resources, danger, power, and charisma, but, beyond these impacts, such large animals have profound and distinct effects on the nature and functioning of the ecosystems they inhabit.Martin (8) first posited a major human role in past megafaunal disappearances, and, since then, much has been written on their patterns and causes and the relative importance of human effects, climate change, and other factors (8)(9)(10)(11)(12)(13)(14)(15). Only recently has work begun to address the environmental consequences of this dramatic transition from a megafaunal to a nonmegafaunal world on Earth's ecology, as manifested through vegetation cover (16), plant-animal interactions (17), ecosystem structure (16, 18), trophic interactions (7), fire regimes (19), biogeochemical cycling (20), and climate (21,22).In this pap...

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Section: Megafauna Prehistorymentioning

confidence: 99%

Megafauna and ecosystem function from the Pleistocene to the Anthropocene

Malhi

Doughty

Galetti

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

419

382

View full text Add to dashboard Cite

show abstract

“…Sea otters are a keystone species in nearshore marine communities, maintaining kelp forest ecosystems by foraging on urchins and other invertebrates (Estes and Palmisano ). While humans hunted sea cows, they also exploited sea otters to near extinction (Estes et al ). Thus, the authors demonstrate that the direct extinction of a few large vertebrates in the late Pleistocene can result in a cascading series of co‐extinction of other species.…”

Section: Habitat and Ecosystem Structurementioning

confidence: 99%

Megafauna in the Earth system

et al. 2015

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Understanding the complex role of large‐bodied mammals in contemporary ecosystems and the likely consequences of their continued decline is essential for effective management of the remaining wild areas on Earth. The very largest animals are in particular peril owing to a disastrous combination of continued hunting or poaching, habitat alterations, and loss of habitat. Because these threats are ongoing, conservation biologists may not be able to wait for the results of long‐term studies before proposing potential mitigation strategies. A recent conference on ‘Megafauna and ecosystem function: from the Pleistocene to the Anthropocene’ at Oxford Univ. brought together paleontologists, conservation and environmental scientists and others who share an interest in characterizing the influence of large animals on ecosystems. Integrating historical perspectives of Late Pleistocene ecosystems when large‐bodied animals were still widespread, with modern studies of areas with varying levels of intact megafauna, the aim was to develop a more holistic understanding of the consequences of the ongoing decline of large‐bodied animals around the Earth. The conference resulted in the development of two special features – one in the Proceedings of the National Academy of Science, USA and one in Ecography synthesizing the state of our knowledge about the environmental legacies of the terminal Pleistocene megafauna extinction, the complex role of modern large‐bodied animals and what the ongoing loss of their ecological interactions might mean in terms of ecosystem function. Here, we briefly review the main themes developed during the conference and outline promising future research directions.

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“…This proposed mechanism is similar to the idea of how temporal lags in ecosystems accumulate (Essl et al, ). An example supporting this assumption is the extinction of the Steller's sea cow ( Hydrodamalis gigas ) in the Commander Islands in the mid‐1700s provided by Estes, Burdin & Doak () who argued that the extinction of this large‐bodied, marine mammal was the result of an effect cascade triggered by a population crash of sea otters ( Enhydra lutris ) due to overhunting. This reduction in sea otter numbers reduced the predation pressure on sea urchins, which are major consumers of kelp.…”

Section: The Ecological Memory–rewilding Frameworkmentioning

confidence: 98%

The importance of ecological memory for trophic rewilding as an ecosystem restoration approach

et al. 2018

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Increasing human pressure on strongly defaunated ecosystems is characteristic of the Anthropocene and calls for proactive restoration approaches that promote self-sustaining, functioning ecosystems. However, the suitability of novel restoration concepts such as trophic rewilding is still under discussion given fragmentary empirical data and limited theory development. Here, we develop a theoretical framework that integrates the concept of 'ecological memory' into trophic rewilding. The ecological memory of an ecosystem is defined as an ecosystem's accumulated abiotic and biotic material and information legacies from past dynamics. By summarising existing knowledge about the ecological effects of megafauna extinction and rewilding across a large range of spatial and temporal scales, we identify two key drivers of ecosystem responses to trophic rewilding: (i) impact potential of (re)introduced megafauna, and (ii) ecological memory characterising the focal ecosystem. The impact potential of (re)introduced megafauna species can be estimated from species properties such as lifetime per capita engineering capacity, population density, home range size and niche overlap with resident species. The importance of ecological memory characterising the focal ecosystem depends on (i) the absolute time since megafauna loss, (ii) the speed of abiotic and biotic turnover, (iii) the strength of species interactions characterising the focal ecosystem, and (iv) the compensatory capacity of surrounding source ecosystems. These properties related to the focal and surrounding ecosystems mediate material and information legacies (its ecological memory) and modulate the net ecosystem impact of (re)introduced megafauna species. We provide practical advice about how to quantify all these properties while highlighting the strong link between ecological memory and historically contingent ecosystem trajectories. With this newly established ecological memory-rewilding framework, we hope to guide future empirical studies that investigate the ecological effects of trophic rewilding and other ecosystem-restoration approaches. The proposed integrated conceptual framework should also assist managers and decision makers to anticipate the possible trajectories of ecosystem dynamics after restoration actions and to weigh plausible alternatives. This will help practitioners to develop adaptive management strategies for trophic rewilding that could facilitate sustainable management of functioning ecosystems in an increasingly human-dominated world.

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Sea otters, kelp forests, and the extinction of Steller’s sea cow

Cited by 64 publications

References 50 publications

Megafauna and ecosystem function from the Pleistocene to the Anthropocene

Megafauna and ecosystem function from the Pleistocene to the Anthropocene

Megafauna in the Earth system

The importance of ecological memory for trophic rewilding as an ecosystem restoration approach

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