Native vs. introduced species – the discussion continues

I was asked earlier today to comment on the Garden Rant blog regarding the issue of nonnative plants and insect survival, specifically in reference to Dr. Tallamy’s research.  Though I haven’t read his popular book (Bringing Nature Home), I did read one of his most recent papers (DW Tallamy and KJ Shropshire, 2009.  Ranking lepidopteran use of native versus introduced plants, Conservation Biology 23(4): 941-947).  The authors argue that lepidopterans prefer native to alien species for egg laying.  A serious problem I see in this paper is that the authors are literally comparing apples to oranges.  They do not compare effects among species in the same genus (the reasoning is there aren’t enough publications to look at), but among genera.  Thus, they lump at least 179 “alien” woody species into “native” woody genera and compare those to woody genera that are completely alien.  There are only 112 species in the latter.

I would bet that if he separated out these 179 woody species and added them to the alien genera list his findings would be quite different.

Comments?

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Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and an Associate Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

16 thoughts on “Native vs. introduced species – the discussion continues”

  1. I don’t have access to the article and am wondering what are some of the “alien” species that that you think are incorrectly lumped in with the “native” woody species?

  2. These are the authors’ own designations, not mine. They have a supplementary spreadsheet that summarizes all the articles they looked at.

  3. There are several pages – the only two I looked at were the woody natives and woody alien sheets. Haven’t had a chance yet to look at the others.

  4. I’ve wondered this many times! Could it really be less useful to plant domesticated versions of wild species (eg cherries) especially when domesicated plants generally have lower levels of anti-feedant chemicals

  5. It’s a great question, Matt! Many crop species have been bred for increased palatability – which benefits all herbivores, not just us. There’s not a simple answer to this puzzle, which is why us Garden Professor types get frustrated when the topic is boiled down to “native = good, nonnative = evil.”

  6. Do you mean that the author has compared between genera, and not within genera? And also, they’ve combined indigenous and non-indigenous natives together, and then compared them to all other exotics?

  7. Yes, Jimbo, that’s correct. For example, the authors consider the genus Rubus to be native, even though there are nonnative Rubus species in the US. (This of course includes Rubus armeniacus (syn. R. discolor), or Himalayan blackberry, a nonnative, aggressive invader in the Paci
    fic Northwest.) All of them are combined together. The only species considered alien are those whose genus is not native to the US.

  8. That was a FAST reply, Linda!
    Well there’s the problem, isn’t it? What a strange method of comparison. Don’t universities in the USA teach research design and analysis!?

  9. @how it grows, no I haven’t yet. This whole thing just erupted yesterday and kind of took me by surprise. I’m trying to get some feedback from one of my colleagues in this field first to make sure I’m not somehow missing something, and if I get the all clear I thought I’d invite him to respond.

  10. I was also going to mention that I read another of Tallamy’s papers. I’ve posted my comments on it yesterday on Garden Rant’s site (Feb. 1 posting on natives.) Here’s what I said there: “You might be interested in some of Dr. Tallamy’s research findings (Zuefle, ME, WP Brown and DW Tallamy. 2008. Effects of non-native plants on the native insect community of Delaware. Biological Invasions 10(7): 1159-1169.) Here are some direct quotes from this article:

    1) Our data did not support the hypothesis that phytophagous insects are predominantly specialists.
    2) Based on Chi-square tests, there was no difference in the ratio of specialist to generalist insects found on Native, Non-native Congener, and Alien plant species groupings

  11. The Tallamy & Shropshire paper seems a reasonable first approximation to answering the question posed. As they note in the M&M “Our early attempts to compare host use of introduced and native plants in the same genus were thwarted by a lack of information at the species level.”

    My takeaway message from this paper would be to favour an exotic with local congeners over one without, not to avoid exotics altogether.

    My impression is that Tallamy’s main interest is in maintaining functioning ecosystems, not in policing aliens.

  12. Dave, the title of the paper states they are comparing native to introduced plants. So the blanket labeling of genera (which contain nonnatives) as “native” is illogical. In their own analysis, they include the genera Rubus, Berberis, Clematis, and Lonicera as “natives.” Each of these genera contain aggressively invasive nonnative species. Their “alien” list includes genera that have species which are native at least in parts of the US (such as Philadelphus and Pseudotsuga). It’s just not a clean analysis and I don’t see how it serves to answer the question of whether introduced species have a negative effect on insect diversity.

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