Depends of time and space

Very true. A few papers such as Berger et al 2001 discuss the predator-prey relationship of grizzly bears and wolf extinction within the Grand Teton National Park in Wyoming. But this did not examine wolves or bears impacts separately. The focus of the paper was on the loss of top predators and their impacts had upon moose and the whole system. It showed that these predators had significant affect on the population of moose which cause the change in the environment. However because of the grouping with wolves we cannot say that it is grizzlies that are a key stone species in this occasion. Especially when we consider how the reintroduction of wolves has had within Yellowstone. Aspen recruitment has increased. Woody plants and herbaceous forage overall has increase as well due to their impact upon elk. The more research I look into, it seems that grizzly bears are an important species but not any more than any other top predator within an habitat. I haven't actually found many papers showing the impact that grizzly bears have upon the environment as a predator. Probably has something to do with when one large predator was remove from the environment often the other ones were remove as well causing an imbalance in the entire ecosystem from the lack of top predators not a keystone species.

Good question. I think the theme of keystone species is controversial because there are conceptual (related to the ambiguity of the definition) and practical (due to the difficulty in identifying these species without deleting them from ecosystems) problems.

The biggest problem about the keystone species is their dependence on context: a species may be keystone in one place but not in another. Power et al (1996) in their article emphasize this aspect and do many examples of context-dependence. Moreover, as pointed out by Kotliar (2000), a species may be keystone only to a specific populational density (also adds a criterion to the definition: a keystone species is a species ecologically non-redundant).

Furthermore, it is difficult to control all the variables related to a species. The question then becomes: if we eliminate this species, what type of change should occur in order to consider this species as keystone? loss of biodiversity? loss of ecological processes? I think we have to choose a priori which variables we are interested in and check their evolution.

I also believe that the term "disproportionately large effect on its environment relative to its abundance" causes problems. If we take into account the limits of energy transfer between subsequent trophic levels (around 10%) and considers that predators generally have larger size of their prey and have more energy-consuming functional solutions. It follows that the number of individuals to populations located in successive levels in the food web must necessarily decrease. This series of events produces the phenomenon of reduction in population size with increasing position in the trophic chain, known as the pyramid of Elton (1927) or pyramid of numbers. Then the predators will always have lower abundances than their prey. This can create a bias that prevents to evaluate the real impact of abundant species. In fact, these species, can have a strong impact due to their ecological role and not to their abundance (e.g. insects, parasites, etc.)

So I guess the answer to your question is: grizzly bears could be a keystone species only in some areas. You should also evaluate the actual changes that have occurred in areas where it has been extinguished. The context-dependence requires us to evaluate the species, area by area.

However, the lack of an objective protocol that allows the a priori identification of key species makes many times subjective the discussion.

I'm working on practical and conceptual problemas about keystone species for a year. These days will submit an article and, if accepted, I promise to send it.

In the meantime you can read the following documentation on the subject:

- Barua, M., 2011. Mobilizing metaphors: the popular use of keystone, flagship and umbrella species concepts. Biodiversity and Conservation, 20: 1427-1440.

- Bond, W. J., 1993. Keystone species. In: Biodiversity and Ecosystem Function: 237-253 (E. – D. Schulze & H. A. Mooney, Eds.). Springer-Verlag, Berlin.

- Christianou, M. & Ebenman, B., 2005. Keystone species and vulnerable species in ecological communities: string and weak interactors? Journal of Theoretical Biology, 235: 95-103.

- Cottee-Jones, H. E. W. & Whittaker, R. J., 2012. The keystone species concept: a critical appraisal. Frontiers of Biogeography, 4(3): 117-127.

- Davic, R. D., 2000. Ecological dominants vs. keystone species: a call for reason. Conservation Ecology, 4(1): r2. Available from: http://www.consecol.org/vol4/iss1/resp2.

- Davic, R. D., 2002. Herbivores as keystone predators. Conservation Ecology, 6(2): r8. Available from: http://www.consecol.org/vol6/iss2/resp8.

- Davic, R. D., 2003. Linking keystone species and functional groups: a new operational definition of the keystone species concept. Conservation Ecology, 7(1): r11. Available from: http://www.consecol.org/vol7/iss1/resp11.

- Ebenman, B. & Jonsson, T., 2005. Using community viability analysis to identify fragile systems and keystone species. Trends in Ecology & Evolution, 20(10): 568-575.

- Estrada, E., 2007. Characterization of topological keystone species: local, global and “meso-scale” centralities in food webs. Ecological Complexity, 4: 48-57.

- Fauth, J. E., 1999. Identifying potential keystone species from field data – an example from temporary ponds. Ecology Letters, 2: 36-43.

- Garibaldi, A. & Turner, N., 2004. Cultural keystone species: implications for ecological conservation and restoration. Ecology and Society, 9(3):1. Available from: http://www.ecologyandsociety.org/vol9/iss3/art1.

- Higdon, J. W., 2002. Functionally dominant herbivores as keystone species. Conservation Ecology, 6(2): r4. Available from: http://www.consecol.org/Journal/vol6/iss2/resp4.

- Hurlbert, S. H., 1997. Functional importance vs. keystoneness: Reformulating some questions in theoretical biocenology. Australian Journal of Ecology, 22: 369-382.

- Jordán, F., 2009. Keystone species and food webs. Philosophical Transactions of the Royal Society B, 364: 1733-1741.

- Jordán, F., Liu, W. – C. & Davis, A. J., 2006. Topological keystone species: measures of positional important in food webs. Oikos, 112: 535-546.

- Jordán, F. & Scheuring, I., 2002. Searching for keystones in ecological networks. Oikos, 99: 607-612.

- Jordán, F., Takács-Sánta, A. & Molnár, I., 1999. A reliability for theoretical quest for keystones. Oikos, 86: 453-462.

- Khanina, L., 1998. Determining keystone species. Conservation Ecology, 2(2): r2. Available from http://www.consecol.org/Journal/vol2/iss2/resp2.

- Kotliar, N. B., 2000. Application of the new keystone-species concept to Prairie Dogs: how well does it work? Conservation Biology, 14(6): 1715-1721.

- Libralato, S., Christensen, V. & Pauly, D., 2006. A method for identifying keystone species in food web models. Ecological Modelling, 195: 153-171.

- Mills, L. S., Soulé, M. E. & Doak, D. F., 1993. The keystone-species concept in ecology and conservation. BioScience, 43: 219-224.

- Paine, R. T., 1966. Food web complexity and species diversity. The American Naturalist, 100: 65-75.

- Paine, R. T., 1969a. A note on trophic complexity and community stability. The American Naturalist, 103: 91-93.

- Paine, R. T., 1969b. The Pisaster-Tegula interaction: prey patches, predator food preference, and intertidal community structure. Ecology, 50: 950-961.

- Paine, R. T., 1995. A conversation on refining the concept of keystone species. Conservation Biology, 9: 962-964.

- Piraino, S. & Fanelli, G., 1999. Keystone species: what are we talking about? Conservation Ecology, 3(1): r4. Available from: http://www.consecol.org/vol3/iss1/resp4.

- Power, M. E., Tilman, D., Estes, J. A., Menge, B. A., Bond, W. J., Mills, L. S., Daily, G., Castilla, J. C., Lubchenco, J. & Paine, R. T., 1996. Challenges in the quest for keystone. Bioscience, 46: 609-620.

- Simberloff, D., 1998. Flagships, umbrellas, and keystones: is single-species management passé in the landscape era? Biological Conservation, 83(3): 247-257.

- Vanclay, J., 1999. On the nature of keystone species. Conservation Ecology, 3(1): r3. Available from: http://www.consecol.org/vol3/iss1/resp3.

Hope this helps

With best regards

Mattia

An interesting and fun question. My guess would be that as large, sometimes top-predatory species it is likely that bears do have a top-down effect on ecosystem structure and function. However, the omnivorous nature of their diet and lack of specialism means that their effects on overall ecosystem function are diffuse and therefore difficult to detect; they'll have a small but significant effect on a large number of species and processes. The salmon effect may be the strongest of these- large quantities of nutrients that would have been part of the freshwater system will be deposited into terrestrial environment where the bears are present, and this will effect overall community structure, e.g. shifts towards nitrophilous plants. Its quite possible that there are some papers on this, I know there are stable isotope studies that show that significant amounts of marine nutrients reach terrestrial systems via this pathway.

I am not specialized in keystone species, but I feel that this point of view could lead to misleading conclusions because the effects of a "keystone" species could be "hidden" to the human perception or it could be detectable only after a certain time period. May be you can look at extincted species examples to explain your present question.

I agree it's an issue of scale (for example, Tasmanian devils are the sole host of a unique array of gut flora, so their extinction would be felt by an entire community), but also about our knowledge of a system (above example; but also large carnivores in Africa were once thought to be generalist predators, but work on their prey preferences has shown that they each have unique preferred prey species, so the loss of one member of the predator community isn't adequately compensated by other members).

I'm also working with my Polish colleagues on the prey preferences of grizzly/brown bears, and it seems that they are the only predator the routinely kills bison (calves) and they seem to prefer moose. This unique element suggests they may have disproportionate impacts on other taxa depending on our understanding and the scale we look at.

According to your approach, I think that grizzly bears are not keystone species sensu stricto.

It is true that they are involved in many ecosystem services such as seed dispersal, nutrient cycling, and herbivore control, but just as a bunch of other different species. That is probably why there were no drastic changes in habitats where grizzlies were extirpated. This has been the same case in Spain, with the Cantabrian brown bear (Ursus arctos cantabricus).

Nonetheless I think that, as you pointed out, they might have a synergic effect when they coexist with wolves. My guess is that, as they consume or even steal carcasses previously hunted by wolves, they might force wolves to hunt more frequently, increasing their control of prey populations.

Finally, I agree with many comments in the context and scale-dependency of your question. For example, grizzlies might disperse the seeds of a plant that is only consumed by them. Then, the extinction of grizzlies will lead to the extinction of that particular plant.

Summing up, evidences point that grizzly bears provide a lot of ecosystem services, helping to maintain healthy, functional ecosystems, and therefore they should be conserved. However, I will not consider them as keystone species following Paine’s definition.

I say no. In most cases removing bears from the ecosystem will have little change in the overall structure of the food web. The discussion about scale and definitions are important, but when Paine and other authors were developing these terms they were not thinking about species specific microbial organisms nor that the species could be a keystone in one area but not another. Grizzly bears fall much better under the umbrella species concept. If some type of classification is necessary for bears, than this should be pushed. Leave the Keystone species concepts for species like wolves and beavers, and if the species falls in the grey area, explicitly state it.

I am presently living in the Sacramento valley/delta. Worked on the Interagency Grizzly Bear Study team for a while. Grizzly bears used to be super abundant in this delta area, possibly this was the most productive grizzly habitat in North America. Salmon used to occur here by the millions and other food sources for grizzly bears were beyond what we can now imagine. Waterfowl occurred in such numbers that early settlers used to complain about the noise (now we complain about other noises). Large cetaceans often were stranded in the delta and provided a very good food source for the bears. Berries and roots and tubers as well. If you recall, the state seal and flag of CA is the golden/grizzly bear. Of course, grizzly bears no longer occur in CA and the state refuses to take any surplus bears from other states for reintroduction. Go figure. Point is, there is absolutely no way to know whether grizzly bear extirpation from CA had an impact on the ecology of the delta because it is so far gone from pre- white conditions. We conducted salmon stable isotope analyses in the delta and found that other salmon predators; coyotes, racoons, etc. hauled up salmon carcasses onto vineyards and their marine isotope signature was detectable in the grapes that the vineyards produced. I would not consider griz to be a keystone species as much as I would consider it an 'umbrella' species. If the griz are present, the 'wilderness' characteristic is still there.

I feel the reply of Mattia has clear a lot but Grizzly bear may be considered as keystone species for a particular ecozone after a careful study only.

I really think the keystone species concept is rather a dead end - it is almost impossible to demonstrate or test in the wild anyway - and it is so abused in conservation and popular media as to have almost no meaning any more. I much prefer the idea of "strongly interactive species" - and there is no doubt that grizzly bears are very strongly interacting with many ecosystem components and trophic levels!

Hi, Dear researcher,

I think the answer of JohnD C Linnell is so nice, because I read some important conservation book like key topic in conservation and it pay attention to his answer.

good luck

I agree that John Linnell pretty much nailed it. However, Rebecca, you mentioned that part of bears' impact is their import of nutrients from salmon. Why, then, are not salmon considered at least as much a keystone or strongly interacting species? After all, there are numerous other predators and scavengers of salmon that also import these nutrients from headwaters streams into forests, and they could potentially (at least partly) replace grizzly bears in the latter's absence. But. as the mechanism for import of marine nutrients into inland terrestrial systems, there is no replacement for salmon.

Salmon are almost always considered a keystone species. They are the archetypical keystone species

I brought up the nutrients from salmon because I read a paper by Helfield and Naiman that was proposing that Grizzly bears and salmon are a keystone species because they have a significant impact on how much nitrogen was being transferred into the environment based on their model. The salmon I could see kind of sort of as a keystone species because there isn't other species that can replace them. But grizzly bears I wasn't sold on especially given how many assumptions within the model was making.

John Linnell makes an excellent point. I agree the concept has been misused and abused. But I don't think it is a dead end. The keystone species concept isn't going to go away either even if we switch to another more scientific and accurate term. The concept of a keystone species is one I think plays well to the media and general public so its going to be continued to be used. Unfortunately this will continue to cause it to be misused as well. If you want to protect a species call it a keystone species! Maybe it needs to have a stricter definition or perhaps it needs to be more policed by the scientific community to help prevent the misuse of the term.

Germane to this point, the following article models how reduced salmon harvest in low productivity years can have outsized benefits to threatened bear populations:

Levi T, Darimont CT, MacDuffee M, Mangel M, Paquet P, et al. (2012) Using Grizzly Bears to Assess Harvest-Ecosystem Tradeoffs in Salmon Fisheries. PLoS

Biol 10(4): e1001303. doi:10.1371/journal.pbio.1001303

Hello, all species may be a keystone species, that it is part of the processes occurring in ecososistema and interactions at the species level is essential. 'I know the brown bear but what if this species died out within a given area?, The effects could be the same as presented in other species, as if within his power (example) is a consumer of dominant species, frequent or heavy regulatory process at the ecosystem could be tracedental and then would come to qe is called trophic cascades (subject of study of sharks and other marine life)

Saludos

Jesus..

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Hello, as far as I am concerned brown bears are characterized as both umbrella and keystone species. Umbrella is most used in collateral conservation benefit terms; keystone is most used in ecological dependency terms.

The website below may help in this matter.

https://www.differencebetween.com/difference-between-umbrella-species-and-keystone-species/