NEWS
Madagascar : giant tortoises have returned 600 years after they were wiped out
Miguel Pedrono 1 , Andrinajoro R . Rakotoarivelo 2 , Colleen Seymour 3 and Grant Joseph 3
Current Address : 1 Cirad , 2 University of the Free State and 3 University of Cape Town Reprinted From : The Conversation
A
six-year-old project to return giant tortoises to the wild in Madagascar could result in thousands of the 350kg megaherbivores re-populating the island for the first time in 600 years .
The first group of Aldabra giant tortoises ( Aldabrachelys gigantea ) were brought in from the Seychelles in 2018 , and have been reproducing on their own since . A group of ecologists explain how reintroducing this tortoise to areas degraded by cattle grazing will help restore the island ’ s forests , grassy woodlands and shrublands of the past . It could also help prevent devastating forest fires in future .
What is the Aldabra giant tortoise and why is it important ?
The Aldabra giant is the second-largest species of land tortoise in the world , after the Galapagos giant tortoise ( Chelonoidis nigra ). It can live for 100 years and has a fascinating history .
This tortoise evolved from ancestors of Aldabrachelys abrupta , one of two giant tortoises that inhabited Madagascar for 15 million years . Four million years ago , the Aldabrachelys abrupta lineage migrated , likely via a combination of drifting with floating vegetation and assisted by their natural buoyancy and good swimming abilities , to the Seychelles .
From there it moved on to Aldabra ( an island 1,000km south-west of the Seychelles ), evolving into a third species , the Aldabra giant of today ( Aldabrachelys gigantea ). Six hundred years ago , all giant tortoises were wiped out on Madagascar by hunters . The reintroduction of the Aldabra giant is the first time giant tortoises have been released in Madagascar since the 1500s .
Aldabra giants are particularly social , coming together in large numbers to forage and sleep together . It is likely that many hundreds of thousands of giant tortoises lived historically on Madagascar .
They played a key role in maintaining the ecological balance in a now lost habitat mosaic ( a place where different habitats exist side by side ). They ate fruits of various trees and dispersed the seeds in their dung , a process known as megafauna-dependent germination . This helped foster the growth of forests , woodlands , shrublands and patchy grasslands . Today , humans have burnt most of these habitats and there is mostly treeless grassland in the areas where giant tortoises once lived .
Figure 1 . Aldabra giant tortoise spreads tree seeds through defecating , helping the seeds germinate and restore Madagascar ’ s forests . Gerard Soury / Getty Images
21 Grassroots Vol 24 No 1 March 2024