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Comment on Pauchard et al. on assessing biodiversity

Posted by msagoff on 17 Mar 2020 at 21:17 GMT

Pauchard et. al [1] have offered several arguments to rebut the perspective of Schlaepfer [2] that ecologists should include in their inventories of biodiversity both native and naturalized non-native species, regardless of their biogeographical origins or ecological contexts. According to Schlaepfer, the concept biodiversity should reflect “the potentially positive contributions of non-native species to biodiversity and to the long-term welfare of humans.”

Pauchard et al. replied that such an inclusive concept of biodiversity “will reduce our capacity to detect the effects of non-native species on native biodiversity.” They do not explain why. They added, “Combining native and non-native species together into a single biodiversity index would … inflate biodiversity estimates ….” This begs the question; the estimates would be “inflated” only if one assumes that they should have included only native species.

Pauchard et al. argued that to combine native and non-native within a single biodiversity index “would also ignore the fundamental ecological differences between the two groups.” What fundamental ecological differences? Simberloff [3] asked whether “a biologist blindfolded, transported to a distant location, and placed in the midst of a plant community would be unable to tell which of the species there are native and which are introduced.…” He wondered “whether something about the way the species interact with one another … or other features of community organization would reveal their introduced origin.” Simberloff [4] correctly identified as an “unexplored topic” the “question of whether novel ecosystems dominated by nonnative species characteristically differ from long-standing ones barely affected by humans.”

According to Pauchard et al., “Native species have coevolved with one another and the physical environment, often resulting in intricate coadaptations.” These authors cite an article [5] which discusses “eco-evolutionary experience in novel species interactions” but does not mention interspecific coevolution. Evolution is usually considered an intraspecific phenomenon. Janzen [6,7] argued in the 1980s that the fact that species co-exist or “fit” together over long periods of time does not imply that they have coevolved. Ecologists have not taken up this challenge.

In the context of ecological science, the decision whether to “count” introduced species may determine whether a theory is falsified or is confirmed. For example, island biogeography theory predicts that the species diversity on an island depends on its area and isolation. If one includes introduced species as “diversity,” this theory is easily and everywhere falsified, since introductions have at least doubled the species richness of most islands without affecting their geographical size or location [8,9]. If one excludes introduced species, on the other hand, one can find data to confirm this theory [10]. The decision what data to count for or against the theory depends on one’s ontology concerning the Culture-Nature divide [11]. If humanity is part of nature, introduced species falsify the theory; if humanity and with it introduced species are external to nature, these species are irrelevant or relegated to ceteris paribus conditions.



In the context of conservation, the decision whether to “count” introduced species reflects what one believes one has good reasons to protect or conserve. If the reasons are welfarist or economic, one may agree with Schlaepfer that the origin of a species is not a measure of its utility. If the reasons are aesthetic, ethical, historical, and spiritual, however, one would to agree with Pauchard et al. that the historical “isolation of continents, islands, and marine realms has produced … the natural heritage that biodiversity assessments seek to document and that global conservation policy seeks to maintain.” These authors eloquently have explained that with the continued influx of introduced species “millions of years of biological adaptation and evolutionary history would be lost.” This loss is haunting, tragic, and negligent however “biodiversity” is defined.

Over a century ago, the American resource economist Gifford Pinchot and the nature preservationist John Muir entered the same lists to joust over the question whether the conservation movement should appeal to economic or ethical arguments. This debate is still with us.



1. Pauchard A, Meyerson LA, Bacher S, Blackburn TM, Brundu G, Cadotte MW, et al. Biodiversity assessments: Origin matters. PLoS Biol 2018;16(11): e2006686. https://doi.org/ 10.1371/journal.pbio.2006686

2. Schlaepfer MA. Do non-native species contribute to biodiversity? PLoS Biol. 2018; 16(4): e2005568. https://doi.org/10.1371/j... PMID: 29664943

3. Simberloff, D. "Invasions of plant communities–more of the same, something very different, or both?." The American Midland Naturalist 2010; 163.1: 220-233.

4. Simberloff D. Nature, culture, and natureculture: the role of nonnative species in biocultures. In: From Biocultural Homogenization to Biocultural Conservation 2018 (pp. 207-218). Springer, Cham.

5. Saul WC, Jeschke JM. Eco-evolutionary experience in novel species interactions. Ecol Lett. 2015; 18: 236–245. https://doi.org/10.1111/e... PMID: 25626585

6. Janzen DH. When is it coevolution? Evolution 1980; 34:611–12.

7. Janzen DH. 1985. On ecological fitting. Oikos 1985; 45:308–10.

8. Rosenzweig, M.L. The four questions: what does the introduction of exotic species do to diversity? Evol. Ecol. Res. 2001; 3 (3), 361–367.

9. Sax, D.F., Gaines, S.D. Species invasions and extinction: the future of native biodiversity on islands. Proc. Natl. Acad. Sci. 2008; 105 (Supplement 1), 11490–11497.

10. Valente L, Phillimore AB, Melo M, Warren BH, Clegg SM, Havenstein K, Tiedemann R, Illera JC, Thébaud C, Aschenbach T, Etienne RS. A simple dynamic model explains the diversity of island birds worldwide. Nature. 2020 Feb 19:1-5.

11. Inkpen SA. Are humans disturbing conditions in ecology?. Biology & Philosophy. 2017 Jan 1;32(1):51-71.



No competing interests declared.
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