We should conserve general parasite biodiversity, because parasites play important roles in ecosystems. However, we should also do our best to control invasive or emerging parasite species that have large, negative impacts on species and ecosystems. One such parasite is Batrachochytrium dendrobatidis, a fungal parasite that causes chytridiomycosis in amphibians. There is some debate regarding how many amphibian species have been impacted by the global spread of the chytrid fungus. But no matter how you slice it, chytrid fungus has devastated amphibian communities globally, causing many declines and many extinctions. As amphibians disappeared, what happened to ecosystems?
In a recent paper, Zipkin et al. (2020) found that snake communities in Panama shifted after chyrid spread through the amphibian community. Comparing hundreds of transect surveys before and after chytrid invaded, they found that after chytrid invasion, there were fewer snake species and the snake community was more homogenous. Several snake species also had reduced body condition, on average. All of this makes sense, because many tropical snakes eat adult amphibians or amphibian eggs, and thus amphibian declines might have decreased prey availability. As a person who enjoys canned soup and using toilet paper, I feel a strong affinity for these tropical snakes and their pandemic-induced resource shortages.
We often focus on the key results of projects, without taking the time to truly appreciate the methods that yielded these results. So I just want to take a moment to appreciate the hard work and careful analyses in this study by Zipkin et al. (2020). Ecologists rarely have enough data from before parasite invasion to document how ecosystems change from before to after invasion, so the hundreds of before surveys in this project are especially valuable. Zipkin et al. (2020) also dealt with a tricky problem in their analyses; many snake species are very rare and hard to detect. For example, 12 out of 36 snake species that they observed were only observed a single time! Knowing that this uncertainty was important to incorporate, Zipkin et al. (2020) used a great Bayesian analysis to quantify not just how much the snake community changed, but also how confident they could be in their results, given snake rarity. If you want to read all about it, check out their paper, which is available as a PDF on researchgate!
E. F. Zipkin, G. V. DiRenzo, J. M. Ray, S. Rossman, K. R. Lips, Tropical snake diversity collapses after widespread amphibian loss. Science. 367, 814–816 (2020).