Science Friday: Adapted Ecosystems or Dynamic Assemblages: Two Views of Critters’n’Plants on Landscapes

Emily’s comment about barred owls reminded me of something I’ve been working on more broadly: when is it OK for humans to manipulate organisms, and when isn’t it, and who decides?  It seems like it’s OK to kill one species to protect another species in the name of “retaining a species.” Perhaps it would matter (?) if the barred owl migration was “natural” or not.. but how would you tell, since colonization, climate change, introduced or not diseases, and a variety of other changes happen through time and are correlated.  I don’t think we’ll ever tease the potential causes apart.  And when each species declines, the ESA response seems to be to  “protect more habitat”, which as we see, won’t always work.

So we’re trying to stop a possibly natural process (competition among species) in order to recreate past “naturalness”, or to keep going a maximum number of species, or because it’s the law of the land. This seems like something we’ll only be able to do in a limited number of cases.  I wonder what principles will or should guide our choices?  These are certainly not scientific questions, although the choices could be informed by science, including economics.   It almost seems like the same action (say thinning trees) is considered to be “good” when its for restoration, but “bad” when it’s for protecting communities.  Killing birds is “good” when it’s about protecting endangered species, and potentially “bad” when wind turbines do it.  So if some purposes are better than others, then that’s not a science question at all. When does the end justify the means and perhaps more importantly, how does our system of governance deal with different points of view on the subject? Has their been a public comment period on the practice of killing barred owls?

Underpinning all this may be the idea of  “keeping all the species where they used to be is necessary for ecosystem (integrity? health? function?).”  But that’s not actually “natural” in any practical sense as Stephens, Millar and … (2009) say here.

Paleorecords in areas where abundant information exists can be used as a test of what has been sustained naturally overtime. When Quaternary vegetation records from the Sierra Nevada were assessed, Millar and Woolfenden (1999b) found that only a few conditions often associated with ecological sustainability concepts pertained. These included: (1) relative stability of the Sierra Nevada ecoregion, i.e., persistence of a distinct ecoregion over time, and, (2) persistence of overall species diversity at the scale of the entire Sierra Nevada ecoregion, with only one species, a spruce (Picea spp.), disappearing from the region about 500 000 years ago. Beyond these two features, however, other conditions commonly associated with ecological sustainability did not occur. At sub-regional scales within the Sierra Nevada, species diversity changed considerably at timescales of centuries to millennia. Movement of individual species meant that vegetation assemblages changed over time and/or shifted locations as species followed climate gradients individualistically (Woolfenden1996). Vegetation communities appeared sometimes to shift locations, when individual species tracked climate coincidentally, and in other cases, changed composition and dominance relations as species responded differently. Non-analog communities occurred transiently, such as the co-occurrence 20–30 thousand years ago in the southern Sierra Nevada of yucca (Yucca brevifolia) and Utah juniper (Juniperus osteosperma) with an understory of Artemesia tridentata, Purshia tridentata, and Atriplex concertifolia (Koehler andAnderson1995). Finally, historic fire regimes reconstructed from the Sierra Nevada have changed over time at multiple scales (Swetnam1993); however we recognize that the largest change in Sierra Nevada fire regimes occurred with the onset of fire suppression in the early 20th-century.These and similar records challenge interpretations of ecological sustainability that emphasize persistence of population sizes and species abundances, stability of native distribution ranges, and continuity of vegetation and wildlife community compositions. By contrast, we find that, of the diverse concepts commonly associated with ecological sustainability, only native species persistence within large ecoregional boundaries, such as the Sierra Nevada, pertains. Our goal here is not to imply that any combination of species would be acceptable in Sierra Nevada forests but that managers should not attempt to maintain all species at their present locations, as climate continue to change this will probably not be possible or desirable.

Of course, they’re not talking about a species being completely gone from everywhere. At some point, though, I think we may cross from seeking the “natural” to something sublimely unnatural.. the Disneyland equivalent of Nature.

10 thoughts on “Science Friday: Adapted Ecosystems or Dynamic Assemblages: Two Views of Critters’n’Plants on Landscapes”

  1. Thanks for highlighting my comment, Sharon; this topic has always fascinated me! Actually, when I was still on the wildlife track in college I studied the conundrum of killing one species to save another. I focused on case studies that included raven vs. sage grouse, seal vs. salmon, and of course, the barred owl vs. the NSO.

    I would not call the barred owl invasion “natural” per say…the theory goes they were able to migrate West due to fire suppression and the settlement of the Great Plains (more trees = easier to move across the continent).

    The gray area of morality aside, I’m just not sure if this is a viable conservation method in the long term. Are we going to have to kill invasive barred owl ad infinitum? Is it possible to eradicate the entire Western population? I’d love to hear from a wildlife biologist on this.

    As for the public comment period, I have not heard of such a thing. It’s not exactly a secret, since AP covered this story in 2019:

  2. When barred owls breed with spotted owls do they produce viable young? This is not a matter of favoring one species over another, such as sage grouse vs. ravens or seals over salmon. This has always seemed more an exercise in racial purity than people choosing favorites during the evolutionary process. In any instance, the massive costs for attempts to manage this species in the wild have been enormous — apocalyptic wildfires, widespread rural unemployment, degraded landscapes, billions of tax dollars, etc. For what? Commercialized barred owl hunting?

    • Bob, first off I’ve been reading In A Dark Wood, and I want to commend you for your excellent and free thinking scientific work. I feel that we’ve become too accustomed to the issues of rural unemployment and catastrophic wildfire in the west and that many today accept these as facts without realizing the policy decisions that gave them root to grow. I didn’t fully understand the root causes until reading that excellent book. The common narrative is that these issues are a foregone conclusion; their real roots are rarely addressed in popular media.

    • I’ve seen a barred owl on my place in the Oregon Cascades, and we heard it at night. I hope no one shoots it.

    • The common name for barred owls — the most common brown-eyed owl in North America — is “hoot owl.” I think spotted owls used to be called the same thing until someone determined that they were a separate species with special needs. When hoot owls breed with spotted owls do they produce viable young?

      • Since no one else has answered who knows more, here is my take from the paper

        “Our use of whole-genome sequencing also allowed us to classify potential SO versus BO hybrid individuals. In contrast to a general lack of hybridization between NSO and WBO across much of their range (Hanna et al. 2018), hybridization appears to be a more significant phenomenon at the leading edge of the WBO expansion into regions such as the Northern Sierras where WBO are still rare (Kelly and Forsman 2004). However, as with our previous work (Hanna et al. 2018), we found that hybrid individuals are difficult to identify with certainty from physical appearance and morphological characteristics alone. Out of 15 potential hybrids in our sample, we identified four WBO, eight F1 hybrids, and three F1 × BO backcross individuals. In addition, we still have little understanding of the overall fitness and ultimate fates of hybrid individuals. In line with previous studies (Hamer and Forsman 1994; Kelly and Forsman 2004), we confirmed that there is a slight mating bias toward male SO × female BO. We also observed that the SO contribution to these hybrid individuals included NSO and F1 CSO × NSO individuals. Our results, however, cannot directly address the apparent absence of later-generation hybrids between SO and BO. We observed only three backcrosses, and all of them are backcrosses with WBO and are carrying BO mtDNA. Since we did not observe parent-offspring pair between F1 and a backcross in our samples (Supplementary Materials and supplementary fig. S15, Supplementary Material online), they could be either from matings between male F1 × female BO or between female F1 with BO mtDNA × male BO. According to Haldane’s rule, if only one sex is inviable or sterile in a species hybrid, that sex is more likely to be the heterogametic sex (in the case of birds, female). We could not conclude whether female hybrids can make the next generation or not from this data. It is also unclear at this time whether these later-generation hybrids are not found due to hybrid incompatibilities, or whether further sampling of potentially hybrid individuals would uncover a deeper collection of multigeneration hybrids. Additional in-depth studies of potential SO versus BO hybrids, along with a fully contiguous genome assembly, will be necessary to answer this question.”

        So in genetic -ese this means
        eight F1 hybrids, and three F1 × BO backcross individuals

        that F1s (first generation hybrids, that is the offspring of the two species) were in fact able to reproduce (through a mating, in this case, to one of the species). A backcross is a cross of a hybrid back to the original species.

        They didn’t find any hybrids that were further on than F1 backcrosses.. (but they only had 3 backcrosses in their sample).

        So yes, they can have fertile offspring.

  3. The idea that these authors seem to be challenging is: “interpretations of ecological sustainability that emphasize persistence of population sizes and species abundances, stability of native distribution ranges, and continuity of vegetation and wildlife community compositions.” It’s an interesting question about the extent to which the ideas of “stability” and “continuity” have been adopted as policy through law or regulation. The diversity requirements of NFMA, codified as the “ecological integrity” requirements of the Forest Service Planning Rule, don’t do this; they emphasize sustainability, which requires resiliency, and recognize that forest plans may adopt a natural range of variation that is not necessarily the same as historic.

    The species viability requirements of the Planning Rule do seek to maintain “a viable population of the species within its range.” This is intended to dovetail with requirements of ESA that seek to prevent species extinction (principally by providing ” a means whereby the ecosystems upon which endangered species and threatened species may be conserved”). However, even ESA has a bailout provision, where a political decision could be made to allow extinction to occur as a result of federal actions (such as logging). ESA does not allow the government to write off a species by not listing it, or to not develop a recovery plan (unless it “would not promote the conservation of the species”).

    It’s not as easy to make the government take actions to prevent extinction, like killing competing species. Killing barred owls should arguably be part of an ESA recovery plan if it is necessary for the spotted owl to recovery. And the Forest Service should arguably take steps to follow the recovery plan. One recent example comes to mind where litigation was successful in forcing the Fish and Wildlife Service to promote recovery of the red wolf by resuming reintroductions:

    As for public involvement in barred owl management, a permit is required to kill them under the Migratory Bird Treaty Act, which requires NEPA procedures. Plaintiffs attempting to stop the killing of barred owls lost a case in court filed under the MBTA (the FWS had prepared an EIS and established a “Barred Owl Stakeholder Group”):

    • Thanks for these links, Jon! It looks to me like the latter case was about killing them for “scientific study” of whether killing them would work for SOs. But I think that’s a different question than programmatic killing over the long term. So it’s curious that the plaintiffs didn’t come back when the non-experimental process started.


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