October 27, 2006

Which species should we preserve?

Earlier this year I asked my students to write a short essay to answer the question, which species should we preserve? I explicitly told them not to argue that we should preserve all species, as many species as possible, or no species at all, and we later discussed why any of those answers would lead nowhere. A few weeks ago George M. Woodwell argued that we should preserve all species. Now Bradley J. Cardinale and collaborators state "that a precautionary approach to preserving as much biodiversity as possible is warranted." And they do that after finding evidence that biomass production in local ecosystems does not decrease when all but the single most productive species disappear. I will keep my eyes open to see who argues that we should preserve no species.


  1. I would be interested in what background reading you gave your students: I am embarking on an investigation of this question, to see if (1) evolutionary distinctiveness has traction as one (of several) currencies and (2) how these currencies can be made fungible. This necessitates a discussion of 'value' more generally.

  2. I'd be interested in that reading set too, as I'm not sure where Marcelino gets his conclusion that Cardinale stated the NPP doesn't decrease in lower-biodiversity ecosystems.

    Rather, the Journ Animal Ecol stated that biodiversity is both a cause and an effect of resource density.

    Surely Marcelino doesn't think that lowering biodiversity via extinctions has no effect on resilience.



  3. In the summary of the paper I linked to in my post Bradley J. Cardinale and coauthors state that "the standing stock of, and resource depletion by, the most species-rich polyculture tends to be no different from that of the single most productive species used in an experiment." In the discussion they say that "theory predicts that diverse polycultures will produce more biomass and capture a greater fraction of limited resources than even the 'best' species monoculture. The balance of evidence from experiments does not seem to support this."

    I don't know whether their results and conclusions are correct or not. But I do know that arguing that we should preserve "as much biodiversity as possible" is useless. What is "possible?"

  4. Hmmm...your HTML tags don't show in blogger beta...

    Nonetheless, what you thought as being their conclusion isn't part of their results and conclusions.

    Rather, their conclusions are:

    We show that the average effect of decreasing species richness is to decrease the abundance or biomass of the focal trophic group, leading to less complete depletion of resources used by that group. At the same time, analyses reveal that the standing stock of, and resource depletion by, the most species-rich polyculture tends to be no different from that of the single most productive species used in an experiment.

    (the hint that the conclusion starts is the 'we show').

    I don't think you understand the paper (altho it's possible I don't).

    My sub is annoying and I can't read the arty yet, but it is obvious that the abstract says that when you decrease spp richness, then you decrease the NPP of the studied trophic group.

    So, since I'm a plant guy (producer group), this letter says to me that you have less producer NPP with less spp richness. This means that there is less depletion of nutrients because there is lower NPP. And even if you look at any hi-biodiverse sample, there is no difference between population in toto and the most numerous spp [meaning you can take the most numerous spp as an indicator for the population].


    They reinforce this by saying (contra your assertion): Collectively, our analyses suggest that the average species loss does indeed affect the functioning of a wide variety of organisms and ecosystems, but the magnitude of these effects is ultimately determined by the identity of species that are going extinct .

    Their conclusions are nulling the hypothesis that ecosystems tend to converge to a species-unrich equilibrium - ecosystems sometimes tend to become dominated by most productive spp. The undertone is that, because this is population dynamics and hence statistics, this might be an effect of sampling bias due to the paucity of numbers out there.

    Are you sure you teach students?

    I suspect it's in econ and not ecology if you do, and thus you should be careful when shaping young minds with your conclusions, as it is your responsibility to teach them well. Our atomistic, reductionist science requires that we specialize, and these days we are quickly overwhelmed when going outside our discipline. Of course, this para could be negated as soon as I read the paper, but that is how it looks from here, since both of us have read the same thing and you have not quoted from the body.

    Lastly, a conclusion is not logically invalid because you don't like the word 'possible'.



  5. "Your HTML tags don't show in blogger beta." Oops, I have no clue about that. Should I fix anything?

  6. Dunno. Not sure the functionality is there - I know its there in regular Blogger, but I don't know anything about beta, sorry.