Tetrapod Zoology

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The interconnectedness of ecosystems and their components is, today, a familiar concept. Top predators eat herbivores, herbivores eat plants, and top predators keep so-called meso-predators in check too. But perhaps it isn’t appreciated enough just how interconnected things can be. Cristina Eisenberg’s excellent 2010 book The Wolf’s Tooth: Keystone Predators, Trophic Cascades and Biodiversity draws on decades of ecological research to paint a complex picture of ecosystem interactions and cascades, of the crucial role of top predators, and of human impact on communities in the natural world. Fully referenced, meticulously researched and beautifully written, The Wolf’s Tooth is an absorbing read for anyone interested in biodiversity, ecology, conservation or wildlife management.

While Eisenberg’s case studies, and expertise, mostly centre around the wooded habitats of the United States, she devotes chapters to ecosystem change and community ecology in terrestrial, freshwater and marine habitats around the world. Discussion of Pleistocene extinctions, of deep time, re-wilding and the future should make this book, and her approach, interesting to archaeologists and palaeontologists as well.

In this review I hope not only to bring attention to a book that I rate very highly, but also to help promote and emphasise the concept of trophic cascades and the consequences of the anthropogenic removal of top predators.

Trophic cascades, keystones, and the ‘ecology of fear’

ResearchBlogging.org

The focus of the book is a discussion of trophic cascades research and on what it means for community structure, conservation and management. The term ‘trophic cascades’ – coined by Robert Paine in his 1980 work on marine ecosystems – refers to the dynamic flow of energy through an ecosystem whereby keystones (a term originally applied specifically to top predators) assert a ‘top down’ influence. If there are more wolves, there are more songbirds and more butterflies because wolves keep deer in check; if deer are kept in check, vegetation is not over-browsed and floral communities are rich and luxuriant. A healthy flora not only means successful recruitment of seedlings and saplings into a multi-tiered woodland community, it also has such knock-on effects as the stability of riverbanks, the quality of groundwater, and the health of the deer themselves. [Yellowstone wolf pack image from wikipedia].

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Good observational evidence indicates that the presence of keystone predators (like the wolf) results in an ‘ecology of fear’ (Brown et al. 1999) among local herbivores. If deer have to remain alert and on the lookout for predators, they rarely get the opportunity to over-browse: eating is done sparingly while the animal is on the move, constantly on the lookout. Contrary to what you might have read – or what you might have encountered should your experiences be (like mine) based on areas where large herbivores roam unchecked by predators – features such as browse lines are not necessarily a natural and ubiquitous feature of wooded environments. Rather, they occur where herbivores do not operate under an ecology of fear but subject foliage to too much browsing [adjacent image of deer feeding at a browse line from Blog of an Ancient Gardener].

Top-down vs bottom-up and the prevalence of trophic cascades

The concept of trophic cascades is not new. As Eisenberg notes, Darwin documented several cases in his writings. One example: more domestic cats meant less mice and therefore more bees, as mice plundered the bee’s hives. Both Charles Elton and Aldo Leopold drew attention to cascading ecological phenomenon in their pioneering works of the 1920s and onwards.

Nevertheless the importance of predators in controlling ecosystem health from the top down was largely unappreciated for much of the 20th century. Management practises that involved the planned and very much deliberate removal of wolves and others predators were applied, creating a legacy of mis-management where herbivores (deer) irrupted (that is, boomed in numbers) to form dense populations far exceeding ideal carrying capacities. This was then manifested in the affected forests by the obvious absence of saplings – they’d literally been eaten to death. A lack of sapling recruitment to the tree population means that those forests will be empty when the big, old trees die. [Image below by Doug Smith, from wikipedia].

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In 1960, Nelson G. Hairston, Frederick E. Smith and Lawrence B. Slobodkin published their important paper on the ‘green world hypothesis': a discussion of the idea that predation on herbivores controls the loss of vegetation in a top-down cascade (Hairston et al. 1960). Eisenberg shows that this crucial piece of research marked a turning point in our attitude to and understanding of ecosystem structure. While debates over the importance of ‘top-down’ versus ‘bottom-up’ processes would (and do) continue, the importance of trophic cascades have been increasingly recognised, with management and conservation strategies changing accordingly.

Among the many case studies involving trophic cascades discussed by Eisenberg are those pioneering works carried out in the H. J. Andrews Experimental Forest in Oregon and Wind River Experimental Forest in Washington. Here and elsewhere, cascading relationships involving wolves, wapiti, hemlocks, dwarf mistletoe, butterflies and other species have been documented. Eisenberg also discusses examples from freshwater habitats, and from rockpools and various other marine environments. One of the best known ecosystems affected by trophic cascades is the marine community around the Alaskan Aleutian Islands.

Sequential megafaunal collapse and ecosystem degradation

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In those Alaskan waters, the recovery of sea otters Enhydra lutris resulted in a decline in Strongylocentrotus sea urchins and a recovery of the kelps that the urchins browse upon (Estes et al. 1978). Incidentally, it’s been suggested that the decline of Steller’s sea cow Hydrodamalis gigas was linked to harvesting of sea otters and a resulting increase in urchins and loss of kelp (Anderson 1995). However, study has shown that massive over-exploitation of the sea cows themselves better explains their rapid extinction (Turvey & Risley 2006). Anyway, when killer whales Orcinus orca began feeding on sea otters, the system flipped from top-down control to bottom-up: urchins surged in numbers again, and kelp became over-grazed (Springer et al. 2003). [The adjacent photo – showing a killer whale skull to scale with that of a sea otter – is from Williams et al. (2004)].

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It seems that orcas were ‘fishing down’ the food chain. Historically, they’d predated on great whales, and then on seals and sea lions when the whales were gone, but a crash in the numbers of Common/Harbour seals Phoca vitulina and Steller’s sea lions* Eumetopias jubatus now meant that the orcas had switched to sea otters (Estes et al. 1998, Springer et al. 2003, Williams et al. 2004). The larger phenomenon at work here – termed sequential megafaunal collapse – resulted in substantial debate in the literature, with some workers questioning whether the collapse really was sequential, and whether killer whale predation was responsible for the observed otter decline. If sequential megafaunal collapse really was affecting killer whale behaviour and hence sea otter numbers, management strategies related to sea otter conservation would have to incorporate several species (rather than just the otters alone) and “reach across multiple geographic areas and food webs” (Eisenberg 2010, p. 65).

* Everyone still uses the term ‘sea lion’ but it should really be ‘sealion’, since they’re not actually lions (similar changes have been made elsewhere in zoological etymology).

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Nevertheless the sequential megafaunal collapse hypothesis has generally been supported and mirrors our own over-exploitation of marine ecosystems: as humans have removed large, apex predators like shark, tuna and cod, the affected ecosystems have simplified. Species at lower trophic levels have boomed in numbers through release from predation. While this looks great if you want to exploit those ‘newly released’, now super-abundant species, another tier in the system becomes depleted as they become exploited too. This continues until all you’re left with is vast quantities of algae and nematodes (we previously covered sequential ecosystem collapse in my review of the movie The End of the Line) [and see The End of the Line‘s site. Extrapolated collapse of global fisheries shown below from Andrew’s ENVR 2000 Blog].

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This is why the removal of top predators (and other large animals) is so insidious. Car-loving moron Jeremy Clarkson’s claim that the extinction of the tiger is a good thing for people who want to go on back-packing holidays to tropical Asia looks blissfully naïve in view of the fact that sequential deterioration of ecosystems results from the removal of apex predators. When we kill all the wolves, tigers, sharks or bears, we don’t just lose charismatic, viscerally thrilling species – we fundamentally alter the makeup and health of the community. The knock-on effects both weaken the system’s resilience to change, and eventually result in forests composed of ‘living dead’ tree species, “[destined] to die without replacement” (Eisenberg 2010, p. 114). Eisenberg points to Amazonian regions where the forests appear ok at superficial glance, but which turn out on examination to prove empty and degraded in ecological terms. Similarly, those 20th century management policies in North America and elsewhere that led to the removal of wolves proved disastrous in the long term, resulting in depleted landscapes.

What’s more, the complexity and interconnectedness of ecosystems mean that collapse in one part of a system can result in a surprising effect elsewhere. Sea otter decline in Alaskan waters resulted, predictably enough, in a surge in urchins and a deforestation of kelp. But it also led to Bald eagles switching to a diet dominated (c. 80%) by seabirds, since the fish the eagles had previously preyed on had declined or disappeared due to loss of sheltering kelp (Anthony et al. 2008) [diagram below, from Anthony et al. (2008), shows changing Alaskan Bald eagle diet at four Aleutian sites between 1993-1994 and 2000-2002. In the sample diets for 2000-2002, note the stronger association with bird prey such as ptarmigan, pintail, gull and puffin].

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Despite the focus here on top-down control, Eisenberg explains that ‘bottom-up’ effects are important too, and in some ecosystem the two processes occur in synergy. The world might sometimes be green because some or much of that greenery is inedible, not because herbivores have been prevented from running riot by their controlling predators. It might be that the dominance of one system over the over is controlled by overall environmental productivity: in the exploitation ecosystems hypothesis developed by Oksanen et al. (1981), only habitats with a high plant biomass allow the presence of top predators that then exert a top-down influence. Predators fail to have a major influence on herbivores in such unproductive habitats as semideserts, alpine regions, steppes and tundra regions.

Deep time and re-wilding

As mentioned earlier, there’s also much here of interest to palaeontologists and archaeologists, given that the loss of the Pleistocene megafauna across much of the world has very likely resulted in substantially simplified ecosystems. Megafaunal loss seems to have resulted in more powerful keystone roles for the large predators that remained, and plant communities seem to be restructured versions of what existed before. As Eisenberg says, “Ecosystems have been truncated or decapitated by the loss of larger animals. Beyond evolutionary entanglements, when one views these extinctions through trophic cascades glasses, the profound ecological wreckage humans have inadvertently wrought on this planet begins to become apparent” (p. 48).

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These days the concept of re-wilding – of somehow reconstructing communities by restoring or reintroducing lost components – is popular and increasingly discussed as a feasibility, but I think that proper reconstruction of the ecosystems concerned is far more complex than has sometimes been intimated. You can’t just release Asian elephants and camels onto the North American plains and wait to see what happens [the photo above is from a re-wilding project currently underway: Chinese tigers have been taught to live a wild life in Africa before being released in China. So, yes, you’re seeing a tiger chasing Blesbuck Damaliscus pygargus phillipsi. See Save China’s Tigers].

As if it isn’t already clear from what I’ve said, everyone with a serious interest in ecology, conservation, ecosystem management and/or biodiversity should read Eisenberg’s book. I loved it, and developed an enhanced understanding of trophic cascades research and ecosystem change. In a world where habitats and communities are changing fast due to human action, such concepts as sequential faunal collapse and ecosystem degradation are going to become all too familiar.

Eisenberg, C. 2010. The Wolf’s Tooth: Keystone Predators, Trophic Cascades and Biodiversity. Island Press, Washington, pp. 254. ISBN 13: 978-1-59726-397-9.

The Island Press page is here. Buy it at amazon: The Wolf’s Tooth: Keystone Predators, Trophic Cascades, and Biodiversity. Cristina herself blogs at Island Press’s Eco-Compass Blog.

For previous Tet Zoo articles relevant to ecosystem degradation, trophic cascades and the loss of biodiversity, see…

Refs – –

Anderson, P. 1995. Competition, predation and the evolution and extinction of Steller’s sea cow, Hydrodamalis gigas. Marine Mammal Science 11, 391-394.

Anthony, R. G., Estes, J. A., Ricca, M. A., Miles A. K., Forsman, E. D. 2008. Bald eagles and sea otters in the Aleutian Archipelago: indirect effects of trophic cascades. Ecology 89, 2725-2735.

Brown, J., Laundré, J., Gurung, M., & Laundre, J. (1999). The Ecology of Fear: Optimal Foraging, Game Theory, and Trophic Interactions Journal of Mammalogy, 80 (2) DOI: 10.2307/1383287.

Estes, J. A., Smith, N. S. & Palmisano, J. F. 1978. Sea otter predation and community organization in the western Aleutian Islands, Alaska. Ecology 59, 822-833.

– ., Tinker, M. T., Williams, T. M. & Doak, D. F. 1998. Killer whale predation on sea otters linking oceanic and nearshore ecosystems. Science 282, 473-476.

Hairston, N. G., Smith, F. E. & Slobodkin, L. B. 1960. Community structure, population control, and competion. American Naturalist 94, 421-425.

Oksanen, L., Fretwell, S. D., Arruda, J. & Niemelä, P. 1981. Exploitation ecosystems in gradients of primary productivity. American Naturalist 118, 240-261.

Springer, A. M., Estes, J. A., van Vliet, G. B., Williams, T. M., Doak, D. F., Danner, E. M., Forney, K. A. & Pfister, B. 2003. Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling? Proceedings of the National Academy of Sciences 100, 12223-12228.

Turvey, S. & Risley, C. 2006. Modelling the extinction of Steller’s sea cow. Biology Letters 2, 94-97.

Williams, T. M., Estes, J. A., Doak, D. F. & Springer, A. M. 2004. Killer appetites: assessing the role of predators in ecological communities. Ecology 85, 3373-3384.

Comments

  1. #1 Jerzy
    May 7, 2011

    Interesting thing. Some points:

    – Important piece is intra-guild predation, where big predators kill smaller predators purely as compatitors. Wolves kill foxes and coyotes (but don’t eat them), foxes kill martens etc. It is so common that one might imagine Tyrannosaurus killing and raiding nesting mounds of some smaller carnivorous dinosaurs.

    – Hunters who kill all wolves and foxes are simply mimicking instintive killing drive of carnivore predators.

    – Modern so-called natural ecosystems may themselves be modifed by loss of Pleistocene megafauna. If sabertooths and cave lions still roamed North America, they likely would keep wolves in check and the balance of trophic cascade would be different still.

    – Alternatively, one can claim that it is impossible to know what precisely natural balance would be, after 10,000 years of intervention of megafauna hunters, pre-industrial hunters and farmers and European settlers. One should simply conserve all the pieces – species from wolves to plants – because they can fit together into vastly different ecosystems.

    – Indeed, landscape protection is very influenced by what cultural memory exists of “natural landscape”. This generally means landscape 100 years ago or so, no matter whether it was truly natural or rich in biodiversity. In Britain conservationists “restore natural environment” of orchards and grazing meadows, while East European conservationists in the same climate “restore natural environment” of old-growth woods.

  2. #2 Allen Hazen
    May 7, 2011

    Jerzy (#!)– Nitpick. American “lion” (Panthera atrox, not same as European Cave Lion) maybe, but the sabertooth tiger (Smilodon sp) is usually reconstructed as an ambush predator, not a fast or distance runner: would it have been able to catch many wolves?

  3. #3 Darren Naish
    May 7, 2011

    Thanks for thoughts. Some quick responses for Jerzy…

    — Meso-predator release (where species such as foxes and coyotes benefit from elimination of apex predators) is mentioned in the article, and (in many areas and ecosystems) has been a problem for ecosystem stability and function. As you note, intraguild predation is normal and prevalent in animal communities. For previous discussion on Tet Zoo, there’s this article. I agree that it may well make sense for human hunters to want to eliminate such animals as wolves and big cats: the problem is just that we’re too good at it, and that this elimination was still/is still practised by technologically advanced nations with tiny macropredator populations.

    — I think everything you say about ‘saving the pieces’ is valid (Eisenberg covers this), as is the observation that Pleistocene systems were more complex. You say that wolves would have been affected (and perhaps controlled) by bigger predators like American lions – well, note the comment above that “Megafaunal loss seems to have resulted in more powerful keystone roles for the large predators that remained”. Furthermore, the species that have survived were different in those now-lost ecosystems. Pleistocene wolves, spotted hyenas, jaguars etc. were bigger and more robust than living forms, and different morphs existed: Leonard et al. (2007) reported a big-toothed, robust-skulled ecomorph of Canis lupus that inhabited Beringia in the Pleistocene.

    — On ‘cultural memory of the natural landscape’ – excellent point. I’ve noticed that conservationists are increasingly talking about ‘shifting baseline syndrome': the fact that we tend to compare the modern situation to whatever existed a few decades before (viz, within the scale of our own lifetimes), not to the genuine ‘original’ condition (arguably something difficult to reconstruct anyway, given the change inherent to most systems). Indeed one criticism of some re-wilding efforts is that they strive for recreation of the pre-industrial condition without appreciating that aboriginal people had already created a fundamentally artificial ecosystem. On the other hand, there are genuine efforts underway to reconstruct Pleistocene-type ecosystems.

    — Finally – Allen.. whether P. leo and P. atrox are conspecific remains the topic of disagreement. It’s now well known that P. atrox might be a jaguar and not a lion at all, but the study concerned (based on morphology) didn’t include data on P. spelaea, and ignored data indicating that P. atrox is part of the P. spelaea lineage.

  4. #4 Tsu Dho Nimh
    May 7, 2011

    Interesting … and the “ecology of fear” explains why hunting success rate goes way down when wolves reappear. It goes down out of proportion to the decrease in numbers of elk and deer.

    Hunters scream to get rid of the wolves because they can’t bring home a carcass like they used to. The elk and deer are more alert and move more and are harder to sneak up on (not that most hunters know how to sneak).

  5. #5 William Miller
    May 7, 2011

    Indeed, the Pleistocene bit raises serious questions on whether there is really any ‘natural’ to aim for: the gap between the Pleistocene extinctions and major human alteration probably isn’t long enough for an equilibrium really to have reestablished.

    I agree that fullest scale rewilding is very problematic. I doubt if modern elephants could necessarily fill the same niches as Columbian mammoths (or whatever) anyway… even if those niches still existed. Recovery of some of the preindustrial condition might still be possible though… the population of much of the central US is actually dropping – while some of that is due to modern agriculture needing fewer workers for the same amount of land, land prices may drop to the point where really huge-scale restorations can happen.

    “Conserving the pieces”, yes, is probably the way to go. Also protecting those areas of functional ecosystem still intact

  6. #6 metridia
    May 7, 2011

    The concept that there doesn’t exist a ‘natural’ anymore, due to the anthropogenic end-Pleistocene extinctions, is an important one, but doesn’t negate Darren’s point about the importance of those large predators that remain, nor does it release us of any responsibility towards preserving what’s left.

    Of course, the face of the planet has been changed dramatically, even where there are now few humans- because the keystone species that once occupied the forests and savannahs and steppes are gone. But once you recognize how complete the human-mediated extinctions were, and accept their dramatic impact on ecologies, minor differences between the ecology of current Asian elephants and e.g. mammoths become less important- as far as rewilding goes, what’s important is just to get SOME large animals back into the ecosystem, as long as they’re generally analogous, and hopefully even related to those that they replace (not that Asian elephants and potentially grass-grazing mammoths are analogous…but perhaps the Asian elephants could replace the forest browsing mastodon. And at least the Asian elephants are related to a native.)

  7. #7 heteromeles
    May 7, 2011

    I was going add in the issue of the presence of the long-term presence of humans in many areas, but #5 already beat me to it.

    The idea that humans aren’t keystone predators is, of course, ludicrous. We are, ideas about humans being “outside nature” notwithstanding. Personally, I’d be happier if ecologists reserved “natural” for discussions involving non-ecologists.

    We’re always part of the system, and when we remove wolves or whatever, we aren’t disturbing natural patterns, we’re removing a potential competitor. We deal with the ecology of fear all the time. We both cause fear and feel it.

    This may sound like hairsplitting, but the solution to any of these problems must involve human ecology and human politics.

    As scientists, we hamstring ourselves if we assume that we’re outside nature. The idea of nature vs. humanity has some rhetorical appeal in a culture based on a dualistic Christian mythology, but it is actively misleading when it comes to doing conservation science. We’re part of the system, period.

  8. #8 Vladimir Dinets
    May 8, 2011

    Allen (#2): tigers are ambush hunters, yet they effectively suppress both wolf and dhole populations in northern parts of their range.

  9. #9 David Marjanović
    May 8, 2011

    So… how much DNA of Steller’s seacow do we have left?

  10. #10 Jennifer Deland
    May 8, 2011

    The world is complex, chaotic and ever-changing. The inter-relationships of populations described here are beautiful, as cloud and wave formations are beautiful. There is something about the human mind that wants to reduce everything to a stable, simple, controllable result. Even those of us who admire the beauty of natural interactions can help but wish that what is was otherwise – “If only,” we sigh “there were more wolves! Then there wouldn’t be so many deer to eat my garden.” But out of this, will come more. The over-browsed trees will become clothed in poison-ivy, or inhabited by defending ants, like the acacias of africa.

  11. #11 Jennifer Deland
    May 8, 2011

    I meant the acacia trees. http://en.wikipedia.org/wiki/Acacia_cornigera.
    There is no such thing as a stable, permanent, unchanging, self-stabilizing “ecosystem.” Everything is a result of what went before.
    Still, it would be nice if there were more wolves. Maybe, if there were more wolves, there would be less poison ivy.

  12. #12 Dartian
    May 9, 2011

    Darren:

    Car-loving moron Jeremy Clarkson’s claim that the extinction of the tiger is a good thing for people who want to go on back-packing holidays to tropical Asia

    Fuck! That ruined Top Gear for me…

    only habitats with a high plant biomass allow the presence of top predators that then exert a top-down influence. Predators fail to have a major influence on herbivores in such unproductive habitats as semideserts, alpine regions, steppes and tundra regions.

    Could you elaborate a bit on that? Is Eisenberg (or rather, her sources) saying that wolves, for example, don’t have a major influence on caribou and musk ox populations on the arctic tundra?

  13. #13 DMA
    May 9, 2011

    Australia wasn’t the only place with an artificial ecosystem. It’s not well known, but bison were only so common because Native Americans used fire to increase the plains size. Before bison only lived in the north and in smaller numbers. Not all changes were human related though. The Siberian plains were transformed into tundra,

  14. #14 David Marjanović
    May 9, 2011

    Not all changes were human related though. The Siberian plains were transformed into tundra,

    because the mammoths died out, which may well have been human-related.

  15. #15 Zach Miller
    May 9, 2011

    I have a hard time believing that humans methologically hunted mammoths to extinction. I just attended a very interesting talk by Dr. David Yesner (of UAA) who said that for all the hoopla of mammoths dying at the hands of humans in Arctic North America, there’s actually very little, if any, evidence of humans actually hunting mammoths. Now, there’s certainly evidence of humans butchering mammoths and using their body parts for various things, but actual evidence of hunting? Very scarce.

    In Alaska, we hear about arial predator control all the time. Wolves get a short shrift here.

  16. #16 Jerzy
    May 9, 2011

    [from Darren: sorry, delayed by spam filter]

    @mertidia
    Rather surprisingly, it is not well known what vegetation types were in N America in climate similar to today but before humans arrived. Nor it is especially studied. So there is no baseline information what was the impact of mastodons and other megafauna.

    However, in Europe and Siberia there is much interest in natural vegetation type in the climatic conditions of today (last interglacial).

    About North American re-wilding. There are many examples when introduced species closely related to native ones (eg the same genus) had very negative impact on ecosystems. One example is introduced American mink in Europe which has European mink and several other native mustelids. So it is doubtful whether possible Asian elephants would re-create ancient situation instead of bringing new disturbance. Where to draw border in “similar species equals similar ecological impact” is difficult. I guess the same subspecies or sbling species is the border.

    @Zach Miller
    This is a bit of poor science/fallacious thinking/untestable hypothesis there. Proponents ask for spear points or similar weapons embedded in intact animal skeleton to prove human hunting rather than scavenging. This means that animal must have run away with hand-sized Clovis spear-point inside the body, and live long enough not be refound by hunters. Nothing surprising that such finds are very rare and only of the biggest species: mammoths and mastodons.

  17. #17 Jerzy
    May 9, 2011

    I think I commented about this before.

    Most of extinct species were chunky, thick-legged, often with big horns, tusks, claws or shells. I think, they were adapted for defense rather than escape. And that is why humans wiped them out with projectile weapons and/or fire. More slender and fast species survived.

    Of course, this “monstrous” quality also makes extinct megafauna interesting to study.

    I wonder if somebody made a comparative study of body proportions and armor of living and extinct megafauna?

  18. #18 metridia
    May 9, 2011

    I have a hard time believing that humans methologically hunted mammoths to extinction. I just attended a very interesting talk by Dr. David Yesner (of UAA) who said that for all the hoopla of mammoths dying at the hands of humans in Arctic North America, there’s actually very little, if any, evidence of humans actually hunting mammoths. Now, there’s certainly evidence of humans butchering mammoths and using their body parts for various things, but actual evidence of hunting? Very scarce.

    Absence of evidence is not evidence of absence. Where do we have ANY fully quantitative record of Pleistocene or early Holocene hunting pressure? There is some evidence in terms of butcher marks, bone houses (!), etc.; to expect smoking guns of tons bone pits or whatever is perhaps desirable, but not necessary for the anthropogenic overkill hypothesis to be supported. Besides, we can approach the problem using simulations and models, in much the way we study evolutionary theory or climate change. E.g.,
    sciencemag.org/content/292/5523/1893.abstract
    For a rather spectacular example of smoking-gun evidence collection,
    sciencemag.org/content/326/5956/1100.abstract
    Of course, these aren’t the only papers supporting this idea.

    It’s important to note that for species that typically experience low adult predation and moderate young predation, and/or have long generation times, human hunting pressure can easily drive reproductive rates below replacement. Especially in places like N. America, where there are fewer native diseases to act as population control. Finally, as evidenced by the bison cliff jumps known from the Great Plains, used before modern horses were (re-)introduced to the Americas ~1500 AD, hunting techniques could be quite wasteful.

    Anyway, one has to leave aside the non-sequitur of there being evidence of butchering, but none of ‘hunting’. You are expecting video footage?

  19. #19 metridia
    May 9, 2011

    whoops, that should be

    I have a hard time believing that humans methologically hunted mammoths to extinction. I just attended a very interesting talk by Dr. David Yesner (of UAA) who said that for all the hoopla of mammoths dying at the hands of humans in Arctic North America, there’s actually very little, if any, evidence of humans actually hunting mammoths. Now, there’s certainly evidence of humans butchering mammoths and using their body parts for various things, but actual evidence of hunting? Very scarce

  20. #20 heteromeles
    May 9, 2011

    @15: One thing that’s interesting is that there’s a rough line for megafaunal extinctions. Beyond that line, there are massive megafaunal extinctions. Within the line, there seem to be fewer megafaunal extinctions, and often later ones.

    The line? The range of Homo erectus. Apparently, H. erectus never developed clothes, so they were shut out of northern Europe, northern Asia, and the Americas. Similarly, they apparently never made it very far across the Wallace Line.

    My guess is that human style long-range hunting (humans are among the best marathoners on the planet) evolved with H. erectus, but our ancestor existed long enough for the large mammals within its range to evolve countermeasures. That’s the theory anyway.

    Aside from comprehensive evidence, the major problem I’m having is trying to remember who came up with this idea so I can cite their reference. My bad.

  21. #21 BlueFrackle
    May 9, 2011

    Everyone still uses the term ‘sea lion’ but it should really be ‘sealion’, since they’re not actually lions (similar changes have been made elsewhere in zoological etymology).

    So… should we start using “mountainbeaver” instead of mountain beaver, “slowworm” instead of slow worm and “marsupialmole” instead of marsupial mole? ;- )

  22. #22 Adam F
    May 10, 2011

    I think conserving natural environments is very important, and returning some to a prehuman state is an interesting idea. However, I think we need a theoretical and practical framework for dealing with human-dominated ecosystems. A farm or a city will never be anything like the original ecosystem. But if we want to keep humans on this planet healthy and happy we have to have farms and cities. What we need is a goal for making these ecosystems “good”, where good doesn’t just mean “like it was before humans”.

    Also, seal ion = [seal]+2 (naturally, they are cat ions)

  23. #23 herky stubby
    May 11, 2011

    Wolves are that great that they scare away most of the hunters. They are more scarier than lions?

    [from Darren: peculiar and irrelevant url deleted]

  24. #24 David Houston
    May 11, 2011

    @Adam
    No, no, no!

    Seals are definitely not cats, as they seem to be a sister group to the panda/raccoon/weasel group in the ‘dog’ lineage.

    However, a seal ion must be an ion of some sort. So anion. QED.

  25. #25 Wilbert Friesen
    May 12, 2011

    Everywhere where homo sapiens arrived, the megafauna died out. Still there are some believers out there which refuse that simple fact.
    Why did the megafauna of the Caribbean isles died out later than the megafauna in the America’s ?
    Because Homo sapiens arrived later.
    Why did the megafauna of australia die out at an earlier age ?
    Because the Aboriginals arrived in Australia at an earlier age.

    Why was the megafauna of New Zealand the last to die out ?
    Because man landed late.

    Why people deny this blatant facts is beyond me.

  26. #26 Wilbert Friesen
    May 12, 2011

    The American ‘lion’ Panthera (leo) atrox a huge version of a jaguar ?

    I find that very hard to believe.
    This species roamed the steppes, inhabited even Alaska but was absent in Florida, jaguar territory par excellence.

  27. #27 David Marjanović
    May 12, 2011

    This species roamed the steppes, inhabited even Alaska but was absent in Florida, jaguar territory par excellence.

    You’re not going to find two very similar species in the same ecosystem. The American lion would be the steppe jaguar, and the surviving jaguar would be the forest jaguar.

    Disclaimer: I have no opinion on the relationships of the American lion.

  28. #28 DMA
    May 12, 2011

    Comment 14. I don’t think that humans hunted mammoths to extinction in Siberia or that their dissapearance somehow caused the dramatic climate change the destroyed the grasslands.

  29. #29 William Miller
    May 12, 2011

    Wasn’t the Australian megafaunal extinction tens of thousands of years after the appearance of humans there? Or is there new evidence suggesting otherwise?

    And didn’t humans live alongside megafauna in Europe for tens of thousands of years also?

  30. #30 Wilbert Friesen
    May 13, 2011

    @ William Miller
    “Wasn’t the Australian megafaunal extinction tens of thousands of years after the appearance of humans there?”

    No

    And didn’t humans live alongside megafauna in Europe for tens of thousands of years also?

    Yes (the same as in Africa)

    But the wildlife of Africa and Eurasia had aeons to adapt to this threat. America and Australia were like Mauritius and the dodo.

  31. #31 metridia
    May 13, 2011

    [from Darren: sorry, delayed by spam filter]

    @DMA-I don’t think the ‘plains’ or steppes turned into tundra, actually. Tundra is simply grassland where cold temperatures and wind maintain grassland habitat, as opposed to dryness or herbivores. Tundra would actually have receded northwards with the end of the last glaciation, exposing more or new potential ‘steppe’ habitat. I think what you may be thinking of as ‘replacing’ the steppes is taiga or boreal pineforest- since that would be a non-grassland habitat that might be inhibited by large ecosystem remodelers like mammoths.

  32. #32 Woody Benson
    May 16, 2011

    Just a historical note:
    German biologist Ernst Haeckel (English translation of the 1873 edition of The History of Creation, pp. 260-1) also called attention to trophic cascades and their importance to community dynamics. Like Darwin, he incorporated human benefits, possibly for didatic ends. Darwin’s hypothetical example linked pet cats (and the widows who owned them)to beef production via the pollination services of bees. Haeckel, after recognizing the priority of Darwin, devised an ecologically diversified thought model that started with bird mites and their parasitic fungi (thus going beyond the idea of a purely predatory food chain), passing through predatory and insectivorous birds to insect pollinators and fruit production of palms. He called attention to the alternating positive and negative end effects of interventions at successive trophic links. Fifty years passed before anyone revisited this concept and more than 100 before it received a name!

  33. #33 Anne Post
    July 24, 2011

    Hope you all participate in the WILD READ blog discussion at http://wildread.blogspot.com. Beginning August 1 Cristina Eisenberg will lead a month long discussion about her book The Wolf’s Tooth!

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