From a biological perspective, islands are special places. Their isolation from mainlands leads to more rapid evolution and results in the formation of unique forms of plants and animals that are found nowhere else on Earth. Madagascar is one such island. It is the fifth largest island in the world, and is known for its diversity of endemic and unique species. Sadly, many of these species are now threatened with extinction as they struggle to adapt to habitat loss, exploitation and climate change.
Approximately 90 percent of all Malagasy plants and animals occur on this island and nowhere else. Among the mammals there are more than 100 endemic species of lemurs, which are adapted to the many different habitats found on the island. There is also the cat-like fossa, which is a formidable predator, and in excess of 20 species of tenrecs. The remarkable diversity of unique animals and plants reflects the fact that the island has been isolated for about 88 million years after it split from the Indian landmass.
A team of biologists and paleontologists from Madagascar, Europe and the United States set out to understand the extent to which Madagasy mammals have been perturbed by human disturbance. They were concerned that so many of the mammal species are facing threats to their existence and set out to ascertain exactly what is at stake if environmental change and human pressures on the island wildlife continue.
The team, led by biologists from the University of Groningen (Netherlands), Naturalis Biodiversity Center (Netherlands) and the Association Vahatra (Madagascar), first established a new dataset describing the evolutionary relationships of all 249 species of mammals that were present on Madagascar at the time that humans settled permanently on the island, around 2,500 years ago. They established that of the 249 mammal species, 30 are now extinct, and a further 120 are listed in the IUCN’s Red List as threatened with extinction.
The experts estimated how long it took all these species to evolve from their common ancestors, and could then extrapolate how long it took this level of biodiversity to evolve. In this way the researchers predicted the length of time it would take for evolutionary processes to “replace” all the endangered mammals, if they were to go extinct.
Using a computer simulation model based on island biogeography theory, the team found that it would take approximately 3 million years to regain the number of mammal species already lost from Madagascar in the time since humans arrived. However, if currently threatened species go extinct, it would take much longer: about 23 million years of evolution would be needed to recover the same number of species.
Put simply, this is really bad news. “It’s abundantly clear that there are whole lineages of unique mammals that only occur on Madagascar and that have either gone extinct or are on the verge of extinction, and if immediate action isn’t taken, Madagascar is going to lose 23 million years of evolutionary history of mammals, which means whole lineages unique to the face of the Earth will never exist again,” said study co-author Steve Goodman, MacArthur Field Biologist at Chicago’s Field Museum and Scientific Officer at Association Vahatra in Antananarivo.
The staggering time it would take to recover this diversity surprised the scientists: “It is much longer than what previous studies have found on other islands, such as New Zealand or the Caribbean,” said lead researcher Luis Valente.
The results of this new research, published in the scientific journal Nature Communications, suggest Madagascar has reached a biodiversity tipping point and that an extinction wave with deep evolutionary impact is imminent unless immediate conservation actions are taken. However, the study finds that, with adequate conservation action, we may still preserve over 20 million years of unique evolutionary history on the island.
“It was already known that Madagascar was a hotspot of biodiversity, but this new research puts into context just how valuable this diversity is. These findings underline the potential gains of the conservation of nature on Madagascar from a novel evolutionary perspective,” said Valente.
That doesn’t mean that, if we let all of the lemur, tenrecs, fossas and other unique Malagasy mammals go extinct, evolution will recreate them if we just wait around for 23 million more years. “It would be simply impossible to recover them,” said Goodman. Instead, the model means that to achieve a similar level of evolutionary complexity, whatever those new species might look like, would take 23 million years.
This urgent conservation work is made difficult by inequality and political corruption that keeps land-use decisions out of the hands of most Malagasy people, noted Goodman. “Madagascar’s biological crisis has nothing to do with biology. It has to do with socio-economics.” But while the situation is dire, “we can’t throw in the towel. We’re obliged to advance this cause as much as we can and try to make the world understand that it’s now or never.”
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