If only invasive species were taking their parasites in their luggage

By Forest & Kim Starr, CC BY 3.0 us, https://commons.wikimedia.org/w/index.php?curid=70489623 By Forest & Kim Starr, CC BY 3.0 us, https://commons.wikimedia.org/w/index.php?curid=70489623

Puerto Rican tree frog, Eleutherodactylus coqui.

Climate change consequences are beyond what one can imagine. Deregulating global temperatures, air and marine stream, and population dynamics have serious consequences on human societies. One of them being invasive species. Changes in ecosystems lead to fluctuations in organism movements. Where rougher climate conditions settle down, populations shift locations seeking to dwell in places with their physiological optimum, often traduced by vertical movements in latitudes. This phenomenon boosts invasive species proliferation which undoubtedly creates an imbalance in ecosystems. This rupture in the ecosystem is partially resulting from decreasing parasite populations in the new invasive species.  In fact, where parasites were once able to regulate native populations of that animal, they seem to struggle in regulating the same species that has become invasive in another location.  

I came across an article the other day https://www.nature.com/articles/nature01346.pdf that held all my attention. What role do parasites actually play in regulating and stabilising population? An interesting approach for such a question is to study invasive species and their parasites.

The success of the invasion of a non-native species dramatically relies on the host’s intrapopulation of parasites. As studies suggest, the process of invasion tends to reduce the diversity of parasite species within a host (Torchin et al. 2003) because the new environment can affects the parasite’s life cycle, nutrition, climate and even host distribution. As a general pattern, invasive species were found to have reduced parasitic infections and reduced parasite diversity. Studies have proved that on average, native hosts were infected by 16 species of parasites whereas invasive species were recorded as having as little as 3 native parasites (for this host) surviving and flourishing after the invasion, and an average of only 4 new parasites infecting the introduced species in its new environment (Torchin et al. 2003). Globally, invasive species seem, on average, to have half of the parasite richness that native populations have, and that’s where the problem stands.

Parasites regulate hosts diversity and abundance and thereby playing an integral role in an ecosystem (Scott 1989). The absence of certain parasites therefore can encourage proliferation of an invasive species and, as is well known, they may irreversibly scatter the native ecosystems to a dramatic extent. You can find detailed studies on Eleutherodactylus coqui (Marr, 2008) which will give you a broad idea of what happens when a species changes its original environment.

Having said that, it becomes clear to me that encouraging parasitologists and ecologists to work together would enhance our knowledge of the dynamic relationship between parasites and invasive species. Cooperation would synergistically improve our understanding of the cause and the results of species movements, but would also enable us to tackle the problem more thoroughly.

I am persuaded that one part of the response to this issue is to study the infra and intra populations of parasites of invasive species. Where a synergetic group of parasites stabilises the species in its native ecosystem, we could come up with a template of parasites to introduce in localised ecosystems to establish a new balance between the local ecosystem and the invasive species. Of course, this needs analysis and collection of complex data. Perhaps, science isn't ready to process this kind of data yet or is not quite interested in it. Nevertheless, it is, in my opinion, clearly a promising field of study.

Jeremy DebrulleGiel van Dooren

 - Jeremy Debrulle (ANU Undergraduate student) in collaboration with Professor Giel van Dooren


Marr, S. R., Mautz, W. J., & Hara, A. H. (2008). Parasite loss and introduced species: a comparison of the parasites of the Puerto Rican tree frog (Eleutherodactylus coqui), in its native and introduced ranges. Biological invasions, 10(8), 1289-1298.

Scott, M. E., & Dobson, A. (1989). The role of parasites in regulating host abundance. Parasitology Today, 5(6), 176-183.

Torchin, M. E., Lafferty, K. D., Dobson, A. P., McKenzie, V. J., & Kuris, A. M. (2003). Introduced species and their missing parasites. Nature, 421(6923), 628-630.

Read more about Parasites: The Good, The Bad, and The Ugly.