Do Wolves Change Rivers?

A great discussion started up in the last few days on wolves in Yellowstone (more below). Not wanting to fill all 350+ EFN member’s inboxes with too many emails, we are experimenting with the blog and moving the discussion here. We think the blog may be a way to have more in depth discussions in the future without worrying about flooding inboxes. It can also engage others outside of the EFN group.

Below, Mike summarized the wolf discussion so far. It has been edited to remove the last names of those involved in the discussion since this is a more public venue.

 Summary by Mike:

I tried to narrow this down a bit, however, the question remains, what is the best vector for such discussions: email, blog IWC…

Yesterday, June initiated an in depth discussion on the benefit of wolves in Yellowstone, in the form of trophic cascade with the video: How Wolves Change the River:

This was predicted by some, and has been studied by William Ripple, Robert Beschta Trophic Cascades in Yellowstone: The first fifteen years after wolf reintroduction

Shannon, Roger, and Mike, voiced caution that the verdict was still out.

I would like to caution that many of the reported “positive” impacts wolves have had on the environment after coming back to Yellowstone remain unproven or are at least controversial. This is still a hotly debated topic in science but in the popular media the idea that wolves can create a Utopian environment all too often appears to be readily accepted. If anyone is interested, I think Dave Mech wrote a very interesting article about this (attached). As he puts it “the wolf is neither a saint nor a sinner except to those who want to make it so”.

Mech: Is Science in Danger of Sanctifying Wolves

Roger added

I see 2 points of caution regarding reports of wolves having “positive” impacts in Yellowstone. One is that understanding cause and effect is always hard, nigh onto impossible, when faced with changes that occur in one place at one time. We know that conditions along rivers and streams have changed in Yellowstone but how much “cause” can be attributed to wolves is impossible to determine.

Perhaps even more important is that evaluations of whether changes are “positive” or “negative” are completely human value judgements and have no basis in science, in this case in the science of ecology. Changes simply are. The world changes constantly. Some people like some of the changes and some people dislike some of the changes but science, ecology, gives us no objective way to make such evaluations. Ecological studies simply show us that changes occur. If we, as humans, decide that having Yellowstone more like it was before humans of European descent starting causing changes, then the changes that have occurred in the last 20 years, if we actually understand them, might be considered positive. That evaluation, however, is based purely on values that certain people believe to be good. Nothing in ecology tells us that what has happened in Yellowstone is good or bad. It just is.

I think the changes are cool but I acknowledge that that is simply my opinion and should be taken as no more than that — my incompletely informed opinion.

Eric then wrote:

Actually, reintroduction of wolves into Yellowstone provided an ideal controlled experiment. In adjacent areas of Idaho and Montana, where wolves were notintroduced, the effects were not observed. Moreover, the geography of the “trophic cascade” — which was hypothesized before reintroduction and subsequently validated by evidence — matches the area where elk behavior changed as a result of the reintroduction.

Wolves are responsible for only the first part of the trophic cascade, changing the behavior of elk. One small change begat several others, and those secondary changes led to still many others.

I am all in favor of skepticism when it comes to broad claims of cause and effect, but the reintroduction of wolves to Yellowstone is perhaps the most thoroughly documented such project in (at least) US history.

On your second point, about the normative value of various ecosystems, I should hope that naturalists consider as “good” ecosysytems which are more diverse and complex. Clearly, if your livelihood depends on preserving livestock introduced to the area, your values may differ.

This was followed by Shannon’s “rebuttal” of sorts.

Hi – Actually, Yellowstone was not an “ideal controlled experiment”. Many other (confounding) factors also changed during wolf restoration. As Kauffman et al. (2013) detail, important changes in moose (Alces alces) abundance, grizzly bear abundance, grizzly bear predation on elk calves, drought conditions and winter snow packs were all occurring while wolves were being restored to YNP. Mech (2012) also notes changing elk harvests and the increased growing season in YNP.

Regarding wolves causing behavioral changes in elk – that is where at least some of the controversy rests – wolves have reduced elk numerically through predation – but the science isn’t settled (is it ever? hah hah! but in this case it is still vigorously being debated) on the degree to which wolves have actually altered elk behavior in terms of it making a difference on other trophic levels. A great article about that is attached (can be found in the Google Group) (Western Confluence).

Similarly, if you’re looking for a controlled experiment – Banff is a little closer to that and so can inform what we’re seeing in YNP – but even that situation has its “issues” because the areas where the wolves recolonized in lower densities were functionally different than the areas where wolves recolonized in higher densities (so not a true control – but at least closer to a BACI design – Before After Impact Control – than YNP). I’ve attached (can be found in the Google Group) a great chapter highlighting the differences in these two study areas by Hebblewhite and Smith. The chapter is a few years old now so we’ve learned a few more things since then – but the main ideas are still relevant.

I (Mike) added to the discussion with the positive and negative feed-back cycles of the deer, moose and wolf populations, and how one is impacted by the other, as well as forage for said ungulates.

Please continue to add to the discussion below in the comment section! Are there any pertinent points that were made outside the Google Group Listserv or points that were missed?

Categories: Discussions | Tags: , , , , , , | 7 Comments

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7 thoughts on “Do Wolves Change Rivers?

  1. Someone also brought up a great point in the blog that we could continue this discussion on the blog AND in a seminar type event at like the IWC. 🙂 – Becca

  2. Mike

    Well, let’s test the waters and see if this catches on. The wolf, needless to say is controversial. So much so, that even someone like David Mech is vilified by the extremes on either pole. One item I continue to run across by anti-wolf factions is the claim of some sort that Mech coined the term balance of nature during his seminal days on Isle Royale. I’m currently in the process of writing a book review, and I’ve come across this accusation again that he (Mech) used the term stable equilibrium in regard to wolf/moose relationship on Isle Royale. He did not. He used the term dynamic equilibrium and then explained it. Anyone know of any Mech comments about balance of nature earlier in his career?

    • Lori Schmidt

      Hello Mike;
      Lori Schmidt from the International Wolf Center. We like your idea of a panel discussion on this issue and the broader idea that there are no simple solutions in nature. We are proposing a September session, would you like to be on the panel? The invitation is out to Roger and Eric of well, and of course… we would make sure Shannon was here too. Not sure if you are checking this blog, but let me know what you think

      • Mike


        Absolutely! Please keep me informed. Guilty of not checking the blog often enough… But I believe a panel discussion/seminar would be informative and important as another wolf season approaches. I’ll not play my cards now, but the extremes on either side of the issue provide no helpful insight.


  3. Lori Schmidt

    I think we will probably run it as a seminar to provide the information about the research published and the opinions on both sides. Panel discussions can sometimes be overwhelming for audiences that don’t know all the details. At this time, I believe Dave will be here as well as Shannon, who can likely broaden the discussion to Grizzlies. I am working on a list of citations that can be available for people to increase awareness. It might be helpful to query people who have been involved in this discussion for a list of questions or issues so we can do a good job of finding and representing sources.

  4. Pingback: Complexity should be the default assumption - MetaSD

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