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The plant that helps you slim (if you’re a bluegill)

Utricularia vulgaris isn't a slimming aid as such. It's just hard for a fish to grow when someone else has eaten all the fleas.

A paper in the Journal of Animal Ecology might seem a bit outside our remit here, but an interesting paper has popped up with relevance to quite a few botanists: Complex Inter-Kingdom interactions: Carnivorous plants affect growth of an aquatic vertebrate by Davenport and Riley. The starting point for the study is peculiar. Typically, coexistence of organisms is more likely the more different they are. Nature has problems when two very similar creatures are competing for the same resources. However, what happens when the species are very different and competing for similar resources? The authors point out that you can’t get much more different than a fish and a plant, so is there competition between the bluegill, Lepomis macrochirus, and the bladderwort, in this case Utricularia vulgaris? They both eat zooplankton, despite being very different. Does U. vulgaris reduce the survival or growth of L. macrochirus?

Utricularia vulgaris
Utricularia vulgaris. Photo: Patchy / Wikipedia

If I were running the experiment, I’d make it simple and run one experiment with bluegills in one tank and bluegills and bladderworts in another to see how they fared – and this is why it’s a good thing that I didn’t do the experiment. What Davenport and Riley were looking at was whether predation of zooplankton by the bladderworts affected the bluegills. Simply removing the plants would change other factors as well as the predation. So what they did was crush the bladders on some of the plants to stop them from working. Until those plants grew new traps, they’d be there but not catching anything. They then filled sixteen tanks with water and exposed them to gather zooplankton. After preparing the tanks, they had 4×4 experiments. One had nothing in it. That was to observe the zooplankton levels without predation. Another had just the bluegill fish in it. That would be the comparison for the fish in the two other experiments. Finally the other two tanks had either functional or non-functional bladderworts, but everything else was similar.

What they found was that the bluegills gained most mass in the tank with the crushed bladderworts. What Davenport and Riley think was going on is that the bladderworts made it easier for the fish to have territories and avoid running into each other. Effectively the complexity that the plants added stopped the thank from being one place and made it lots of smaller places. That reduced between-fish competition for the same food. However in the tank with the fully-functional bladderworts, there wasn’t an increase in size – so the positive effect of the habitat was countered by the negative effect of the competition.

What caught my eye is that I couldn’t think of any similar studies. There is lots and lots on mutualism. There are whole careers built on it, but I can’t remember seeing anything about this kind of competition. Davenport and Riley have found three papers. Evidence for competition between carnivorous plants and spiders by Jennings et al. is one. They found that spiders tended to avoid areas with sundews when there was relatively little prey. It Takes 30 blogged on this in 2010.

Jennings et al. returned to the topic in the more complex Foraging modality and plasticity in foraging traits determine the strength of competitive interactions among carnivorous plants, spiders and toads. This is an interesting step up, as it contrasted the various hunting strategies for the same food source.

The final study the paper mentions is a model analysed by Crowley et al. You might think it a bit simpler as it only spiders and plants. However, it does have both web-making spiders and wandering spiders generating ideas for testing in the field, and the the authors of this paper find that the different foraging techniques make quite a difference in what to expect.

By my count, that’s just four papers. If that doesn’t scream UNDERSTUDIED, I don’t know what does. If you know of another similar paper, then let me know in the comment box below.

References

Davenport, J. M., & Riley, A. W. (2017). Complex Inter-Kingdom interactions: Carnivorous plants affect growth of an aquatic vertebrate. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.12652

Jennings, D. E., Krupa, J. J., Raffel, T. R., & Rohr, J. R. (2010). Evidence for competition between carnivorous plants and spiders. Proceedings of the Royal Society B: Biological Sciences, 277(1696), 3001–3008. https://doi.org/10.1098/rspb.2010.0465

Jennings, D. E., Krupa, J. J., & Rohr, J. R. (2016). Foraging modality and plasticity in foraging traits determine the strength of competitive interactions among carnivorous plants, spiders and toads. Journal of Animal Ecology, 85(4), 973–981. https://doi.org/10.1111/1365-2656.12526

Crowley, P. H., Hopper, K. R., & Krupa, J. J. (2013). An Insect-Feeding Guild of Carnivorous Plants and Spiders: Does Optimal Foraging Lead to Competition or Facilitation? The American Naturalist, 182(6), 801–819. https://doi.org/10.1086/673477

Crowley, P. H., Hopper, K. R., & Krupa, J. J. (2013). An Insect-Feeding Guild of Carnivorous Plants and Spiders: Does Optimal Foraging Lead to Competition or Facilitation? The American Naturalist, 182(6), 801–819. https://doi.org/10.1086/673477

About the author

Alun Salt

When he's not the web developer for AoB Blog, Alun Salt researches something that could be mistaken for the archaeology of science. His current research is about whether there's such a thing as scientific heritage and if there is how would you recognise it?

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