Researchers found that the lack of large herbivores has slowed down plant evolution for 25 million years. A team of researchers led by Washington University showed that pervasive infections caused by parasites could reduce how much wild animals eat that may negatively impact plant communities.

Amanda Koltz, the first author of the study and senior biology scientist in Arts & Sciences at Washington University, said that the study focuses on the impact brought by parasitic infections beyond the host and into broader ecosystems as it is already well known that parasites have negative impacts on both physiology and biology of their hosts.

Parasites Reduce Herbivory Behavior Among Animals That Triggers Adverse Effects on Plant Ecosystems
(Photo : Pixabay/Erik_Karits)
Parasites Reduce Herbivory Behavior Among Animals That Triggers Adverse Effects on Plant Ecosystems

Impacts of Nonlethal Parasitic Infections on Ecosystems

The international team composed of biologists, wildlife veterinarians and epidemiologists, ecosystem ecologists, and infectious disease experts have discussed in the study titled "Sublethal Effects of Parasitism on Ruminants Can Have Cascading Consequences for Ecosystems," published in the Proceedings of the National Academy of Sciences, the impacts of nonlethal parasitic infections.

According to Phys.org, deer, bison, giraffes, gazelles, and antelopes are ruminants whose eating habitats impact the ecosystem. Each of them has multitudes of parasites that occupy its gut and tissues that eventually kill its hosts and trigger cascading effects on ecosystems.

 To better understand this, the team used a mathematical model and global meta-analysis that any group of parasitic worms could cause both lethal and sublethal effects on their hosts.

Professor Vanessa Ezenwa, a senior author of the study, said that the potential for lethal infections increases the chances of host mortality and ecosystem-level effects. Similarly, the model they presented suggests that sublethal diseases can have equally important effects on ecosystems.

Assistant professor Rachel Penczykowsk, a senior author of the study, added that the models allowed them to explore how parasites harm their hosts and their food resources. The team discovered that parasites harm in three ways: survival, feeding rates, and reproduction. Therefore, parasitic infections on herbivores also matter to plants.

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Overlooked Consequences of Parasitic Infections

Aside from the models, researchers also looked into the data from more than 59 published peer-reviewed studies. According to Science Daily, the team investigated the associations between parasitic infections and key traits of free-living ruminant hosts in the wild.

Based on their analysis, these parasitic infections reduced the amount of food taken by those herbivores. However, they also found that it is not linked to the average host survival rate.

Koltz pointed out that the broader relevance of these results is that there are widespread ecological consequences of sublethal parasitic infections, although this is almost always overlooked.

The team concluded that the findings suggest the feeding rates of ruminant herbivores are lower than would be pervasive parasitic infections. 

"By reducing ruminant herbivory, these common infections may contribute to a greener world," Science Daily quoted Koltz.

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