Infectious diseases of humans, wildlife, and domesticated species are increasing worldwide, driving the need to understand the mechanisms that shape outbreaks. These concurrent patterns have prompted suggestions that biodiversity and the spread of diseases may be causally linked.
According to Prof Francois Durand a Paleontologist at the University of Johannesburg (UJ), "Researchers have long sought to better understand the evolutionary importance of parasites, as Global change could facilitate the spread of invasive parasites, and alter the existing dynamics between parasites, communities, and ecosystems."
Although parasites are common in modern ecosystems, we actually know little about parasitism in the distant past. And when parasites first evolved remains a mystery.
"But our research brings us one step closer to an answer, as we document that Parasitism, in common with competition, facilitation, and predation, could regulate biodiversity-ecosystems relationships. These different mechanisms by which parasites might affect ecosystem function pose challenges in predicting their net effects," said Prof Durand.
"It is gradually becoming clear how important parasites are on many levels of existence, including the individual, the population and the ecosystem level. Parasites have an impact on the immune systems of their hosts and play an important role in natural selection.
Parasites are an important factor for the maintenance of population dynamics which is one of the controlling mechanisms of the composition of ecological communities. This in turn modifies trophic interactions which has an impact on the whole food web from the rate of predation to the recycling and availability of nutrients," explains Prof Durand who has challenged this perception of evolution, suggesting that parasites rule the world.
Prof Durand pointed out that if an organism does not eat dead organic matter which is what certain bacteria, saprophytic fungi and scavenging animals do, if it is not a predator which kills and consumes its prey and if it does not generate its own food by means of photosynthesis, then the chances are that it is a parasite. "The natural world is full of examples where parasites are harmful under some conditions and helpful under others."
"Parasites are not necessarily always detrimental to an organism's health. In most cases, organisms co-evolved over millions of years with parasites and can tolerate moderate numbers and diversity of parasites. This study shows that the adaptations of parasites and their overwhelmingly important role in food webs indicate that they have been around for millions of years, long before humans existed. The fossil record of Ophiocordyceps for instance could be traced back to 48 million years ago. The evolutionary adaptations and feeding strategies of predators pale in comparison with the intricate adaptations and strategies of parasites. A few examples to prove this point are Ophiocordyceps, Dicrocoelium and Sacculina,"clarifies Prof Durand.
Prof Durand added: "Parasites have a very important role in the ecology and that life as it exists would not have been possible without them. Humans are parasites too, because their behavior matches the exact behavior of other identified parasitic organisms. Humans are organisms that benefit from depriving nutrients from their host. In this case, our host is the organism known as Earth. This implies that our romanticised ideas of ecology, biodiversity, the morality of nature and the purpose of life should be reviewed."
Prof Durand concludes: "One could argue that in order to save biodiversity, one should try and save all species and not the one that you are culturally programmed to revere more than others. Clearly, every species has a role in the ecology, and in order to save biodiversity one should attempt to save all species and not only those that are attractive," says Prof Durand. "The emotional connection between humans and nature, although flawed in some respects, and often not very objective, could be the last chance to conserve nature in the face of the growing ecological catastrophe."