2023-08-19 01:09:00
For many years, biologists have argued that top predators such as lions, wolves or cheetahs can benefit prey herds by targeting weaker and slower-moving animals, and thus providing better opportunities for healthy animals. and strong to reproduce – a hypothesis formalized in 2003 as the “healthy herd hypothesis.” »
Although this hypothesis has often been used to suggest that manipulating predator numbers to protect prey might be a useful conservation strategy, supporting hard evidence is scarce, and recently many of its hypotheses and predictions have been questioned.
To test the healthy flock hypothesis, a team of researchers led by the University of Michigan (UM) conducted an experiment on a predator-prey-parasite system made up of predatory fly larvae that feed on the flea. ‘water. Daphnia dentiferawhich harbors a virulent fungal parasite (Metschnikowia bicuspidé).
According to the healthy herd hypothesis, increasing predator density in this three-organism study would help eliminate the fungal pathogen and improve the overall health of flea populations.
However, the experiment found that although at the highest levels predation was successful in completely eliminating the fungal pathogen, it also significantly reduced the size of daphnid populations – a finding that does not support the theory. hypothesis of a healthy herd.
“The appeal of the healthy herd hypothesis lies in the alignment of multiple conservation goals – simultaneous conservation of predators, reduction of parasitism and protection of vulnerable populations – as well as the potential for reducing the risk of spread to others. populations, including humans,” said lead author Meghan Duffy, an aquatic and disease ecologist at UM. “But even when predators reduce disease in their prey populations, this does not necessarily lead to an increase in prey population size, as our study shows. »
Other well-known historical examples of attempts to apply the healthy herd hypothesis gone awry include the culling of badgers in the UK to reduce the incidence of bovine tuberculosis in cattle or culling of bats to reduce the spread of rabies in domestic dogs or wild animals (badgers and bats being wild reservoirs of bovine tuberculosis and rabies, respectively). In both cases, these strategies failed and the diseases continued to spread to other animal populations.
“Unless we develop a more complete understanding of when and how predators influence disease, management strategies that propose to reintroduce or increase predator populations might backfire,” explained the author. The study’s lead author, Laura Lopez, a former postdoctoral researcher in Professor Duffy’s lab, who now works as a vaccine safety research officer at the National Center for Immunization Research and Surveillance in Australia.
“If your primary concern is the overall population size of a vulnerable animal species, adding high levels of predation that eliminate disease might be detrimental. Interestingly, intermediate predation levels reduced parasitism in our study without incurring a cost in terms of overall prey density. Any management decision should weigh the potential costs and benefits associated with increased predation,” Duffy concluded.
The study is published in the journal Ecology.
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Par Andrei Ionescu, Terre.com Personal editor
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