New paper: learning to see what is missing

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The red flowers of the invasive African tulip tree (Spathodea campanulata; Bignoniaceae) stand out in a Puerto Rican rain forest. This species may occupy a mathematical hole, having an ecological strategy unoccupied by other species in the community. Recent mathematical advances now allow detection of holes and better understandings of species invasions and extinctions.

Imagine an island populated by small and large animals. A reasonable assumption would be that the island might also have medium-sized species—but what if none are found? These empty spaces, or ‘holes,’ may represent missing components of ecological communities. Identifying these holes may help researchers predict the outcomes of invasions, extinctions, and long-term evolution. What we don’t see may matter as much as what we do. My new paper in The American Naturalist (link, PDF) now provides a new way to answer the previously unanswerable question—does a community have holes, or not?

The trouble is that holes are difficult to detect. Imagine a volleyball. This three-dimensional shape has an empty space inside of it, but from a two-dimensional photograph you would never be able to tell that it isn’t solid. Ecological strategies work the same way. Along any individual strategy axis (like body size, or temperature tolerance), species may be able to take on small, medium, and large values—but when considering all axes together, some combinations may never occur, just like the hidden interior of the volleyball. Yet these holes may be exactly where a new species could invade a community, or where another species may have recently gone extinct.

Computers have not been able to solve this problem before now. As the number of dimensions in the ecological strategy space increases, the number of possible ecological strategies grows exponentially. That means there are too many places to find a hole for a computer to easily find. But there is now a new set of free software tools that will enable researchers to efficiently discover such holes (CRAN link to hypervolume package). These holes may represent forbidden ecological strategies or available but unrealized opportunities that have never yet been identified. We don’t know how common holes are in real ecological communities, but we won’t know until we look. Now we can.

(This may also be the first paper I have ever published that includes a peace symbol!)
demo

4 Comments Add yours

  1. Aaron Hogan says:

    Nice work, Ben! It’s always a pleasure seeing what you’re working on.

    I do agree that the Spathodea does occupy a novel niche in the vegetation community of Puerto Rico, however its “invasiveness” has been debated. Some evidence, by Ariel Lugo, shows that Spathodea is a “nursery tree”, quickly colonizing abandoned lands as vegetation succession starts and providing shade as native, old-growth, k-specialists take their time in the stand intitiation phase of forest succession. There seems to be a “hole” in the community at that “nursery tree” niche role in Puerto Rico. I (and I think Lugo, as well) would argue against an invasive species classification for Spathodea, because the species does persist in this niche particularly well, and no evidence supports the claim that it has displaced other species from this niche. Good stuff! Thanks for sharing!

    All the best,
    Aaron

    1. bblonder says:

      Hi Aaron, great to hear from you, and thanks for the thought-provoking comment! I hadn’t heard the natural history of how the species takes a nurse role. However do you think a species can be both facilitative and invasive? My question is really a broader one for you: how do you define an invasive species? I suppose I am using the word more as ‘invading’, i.e. non-native and successful in establishing.

      I am going to share your comment with Cathy Hulshof, a collaborator who is now on the faculty at UPR and who will be very interested in your thoughts.

      Ben

  2. Aaron Hogan says:

    Hi Ben,

    please do. I had seen that she was a new addition to the Mayaguez campus. Please tell her that I would be interested to meet and talk about Caribbean plant ecology, if she would like.

    1. bblonder says:

      Message passed on!

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