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The Complexity and stability of ecosystems.

by on October 29, 2011

Stuart L. Pimm article “The Complexity and stability of ecosystem” argues that there has been confusion regarding the relationship between stability and complexity. People have posed a different question regarding their relationship but the question to the answer varies with people. Pimm states that human have the interpretation that if the ecosystem becomes less stable then it becomes simple but they do not know the consequences that increasing instability leads to the extinction of the resources of the ecosystem and more instability. Early theoretical studies proposes that complex system are more stable but the studies done after that proves opposite and field studies by field workers are ambigious. He argues through Elton theoretical argument that orders are characterized by oscillation, more complex model fluctuates less. He also gives his evidence that increased change of pest outbreaks in agriculture systems, another absence of pest outbreaks in tropical forests.  Earlier theoretical arguments and field studies are incomplete because they have not answered to the complex relationship between stability and complexity. That’s why he tries to relate through different definition of stability of complexity. One of them is that if the system is not stable, we will observe it except in transition to a new equilibrium. The variable of interest is hierarchical in nature. He sues the theoretical and field studies of some of the combination of measures of complexity and variables of interest and measures of stability.

He argues that if there are greater amount of different species then they need to less connected because they compete for their resources in the ecosystem.

He also argues that majority of studies have examine the local stability of species abundances. To measure the stability, one can ask the existing systems were more resilient, resistant, persistent or variable. There are many kinds of perturbation to natural system. To get the answers of complexity and stability question, may depend on what is perturbed, or change in the species abundances. He also states that the biomass of all of the species in an ecosystem may correlate with the notions of what defines an ecosystem than the abundance of species. finally, he uses the resilience as the measure of stability.

In this way, Pimm states the more species are present in a community; they need to less connect to be stable. If there is greater number of species and they are removed from the community, then there will be change in the composition and the biomass and the community will be more likely to lose other species. The more resilient the population, the more persistent will be its composition and the more resistant.

Questions

Why do species need to be less connected to be stable, isn’t it connection between the species make a community?

Why there is a domination between species in nature?

Can we get the specific answer to the relationship between complexity and stability of the nature?

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11 Comments
  1. janellekramer permalink

    To answer the first question, I think that Pimm is taking an ecosystem being stable to mean that it doesn’t change. The relationships, interactions, and species in the ecosystem are basically constant. With this definition of stable, the more species there are, the greater the likelihood that species are changing niches, changing which predator each which prey, etc. The less species in an ecosystem, the less likely that species will trade jobs, essentially. I see what he means, if this is in fact what he means, but I am not sure I agree with him that the less species there are, the more stable an ecosystem becomes.

  2. 242colleencarey permalink

    Pimm argues that the less species there are the more stable an ecosystem is. I can see how this would make sense, but there are also some downfalls in this argument. Yes, the less species there are, there is less competition for food, cycles will continue and less species will become extinct. But the downfall is, there will continuously be cycles. With less species, the greater reproduction will be and this initself will disrupt equillibrium and up competition for food.
    There will always be a domination in species within nature. That’s just how it’s always been and always will be.
    I think that is makes sense that there is stability when equillibrium is occuring. But that isn’t always the case. There are constantly disruptions in ecological systems, and that’s were complexity comes into play.

  3. When Pimm’s says the less species in an environment the more stable, more connected the ecosystem is because those species have to less to work with for survival. They become co-dependent on each forcing species to interact productively for survival – creating a stable ecosystem. If more perturbations persist and one of more of those species is removed from that ecosystem, the more likely others will to go extinct becoming detrimental to the already small ecosystem.

  4. I agree that too few species in an ecosystem will make it unstable. I also agree that the interaction of several species in an environment help to keep it stable. An example that I thought of when reading this is a problem that is here in Colorado. I recently saw something about how there are too many Elk here. There should be around 150,000; however, with the removal of predators, their numbers have almost doubled this. It is so bad that if you go to Rocky Mountain National Park, there are fenced off areas. If you look into the purpose of these, it’s to allow a safe place for native plant species to grow back as the Elk are eating them all. This huge number is an example of how only a few species isn’t always a good thing. They are removing large numbers of plants for other species to eat as well which will cause damage to the environment in the future which is the opposite of being stable. So I do think that a larger variety of species in an environment will lead to a more stable one. At least with more species, even if a few are removed, the impact on the environment wont be as bad as if there were only a few species to begin with. One other thing is that I do think that in some cases an environment with a smaller amount of species can be stable, it all depends on the environment and what is available. Though the impact of losing a species would be far worse in this kind of environment than one with a wider range of species.

  5. In his paper Pimm defines local stability as “the constraint that species densities, when slightly perturbed from equilibrium, will return to that equilibrium.” In this way local stability measures the “constancy” or “robustness” of a species and therein its resilience to a ‘normal’ state once its environment has been disturbed. In this way, I would not agree with Pimm because I would think that a larger population would create more individualistic communities, whereas a smaller more tight-knit community would build a dependent community, very susceptible to fluctuation and instabilities as a whole. I also think that a community with less species would result in a lazy community due to the lack of competition, and thereafter, if another stronger species did happen to find this community, it could easily take advantage of its weakness.

  6. I disagree with Pimm’s article when he claims that simpler ecosystems are more stable than more complex ecosystems. Even though there is less competition for food for example, if for some reason one species goes extinct or dramatically decreases in population, the whole system collapses. It does not matter how many organisms or species are involved in an ecosystem because no matter what, they all rely on one another in some way; if one point in the cycle starts wobbling, everyone else is wither going to have to learn to adapt or will not be resistant to the change. Also, i find it hard to understand that any ecosystem can be “resilient” enough to return back to it’s natural state. When an ecosystem undergoes change, there will be adaptations involved in order to survive, and because that change is taking place, everyone has been impacted in some way and therefore the system can never truly go back to its original state.

  7. Summer Rose W permalink

    When Pimm is talking about a more connected community, he explains that there should be fewer species to be stable. This is not something I can agree with because it is natural for species to survive and others to live, new ones to come. If there are only a few species in a connected community, it is very difficult to change after one species has become extinct. In a community where there are more species, perhaps the species that was dependent on the one that went extinct can find something else to be dependent on; new species may come into that community and take the place of the one that has gone extinct.

  8. what I am confused with this model in the first place is the definition of “stability”. Is there truly such a thing, or is it an unobtainable form? I feel like there’s actual context when relating ‘stable’ to the an atom, a bridge, a number system, but what about to the actual physical world; and nature above all. Pimm is describing a system that goes about finding ‘stability’ and is completely geared toward that describing it. But is there really such a thing? Do we even know when a species, let alone an entire ecosystem, is ‘stable’. I’m very interested in seeing how this resilience method addresses ‘stability’.

  9. Less of a connection between species will allow for them to rebuilt their groups and support themselves without depending on another species interaction.

  10. Benjamin N. permalink

    In response to the first question, I think species need to be connected to be stable. If prey goes unchecked by predators, it can lead to overpopulation and domination of one species. This isn’t stable. When species are interacting with each other, populations and ecological effects are being kept in balance, because species are naturally made to wax and wane.

  11. After looking back on the semester, it is interesting to reflect on the concept of resilience. It is now very easy to notice how big of a role and how of an impact resilience has on a society. It is also easy to recognize how many aspects come into play to determine a society’s resilience, assuming they have some resilience. After learning about identity, it is definitely easier to grasp a better idea of resilience. With that said, I am also not a fan of Pimm’s definition. Pimm’s idea is based around the fact that resilience is how long, or return time to equilibrium. This implies there is a certain point to get to and a balance. I do not like this assumption because it doesn’t really seem to account for actual change as a result of an outside force. In other words, I prefer to very things and resilience in more of Holling’s view.

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