(fFom left) Dr Cynthia Froyd, of Swansea University, Dr Alistair Seddon and Dr Emily Coffey from Oxford University and Dr Froyd’s dad Stan Froyd
Swansea University researchers have been studying the fossilised droppings of giant Galapagos tortoises to better understand the link between endangered species and their habitats.
Ecologist Cynthia Froyd and her colleagues from the universities of Oxford and Bern believe the highland landscapes of Santa Cruz island in the Galapagos chain began to transform about 500 years ago as tortoise numbers dwindled and fewer remained to graze and wallow as they had done previously for thousands of years.
Dr Froyd took sediment samples from peat bogs in the highlands of Santa Cruz Island where tortoises no longer live. In the mud, the researchers found fossilised plant pollen and species of fungi that grow on the droppings of large herbivores. Adding the results of radiocarbon dating, the evidence suggests that the giant tortoise, the only large grazing herbivore on the island, lived in the highlands until about five centuries ago.
What were wetlands are today peat bogs dense enough to walk on. Dr Froyd and her colleagues believe the tortoises helped to maintain the wetlands by moving through the mud. The loss of giant tortoises from the uplands affected the ecosystems – wetland habitats are very rare in the Galapagos today.
They discovered that certain plant species that thrive in wetlands but are now rare or extinct started disappearing about the same time as the former wetlands. Charcoal layers found in the sediment suggest that fire broke out more often because the grazing tortoises weren’t there to keep down the vegetation. So man is not the only species to exert a major impact on habitat – other species can operate as “ecosystem engineers”.
Before the arrival of people in the Galapagos there were estimated to be 100,000 to 250,000 giant tortoises, dropping to fewer than 14,000 in the 1970s. Conservation efforts have increased the number of tortoises and they are currently being reintroduced to some of their former habitats.
Dr Froyd said:
“Until now we haven’t completely understood the full extent of the cascading ecological consequences as a result of the loss of large herbivores from ecosystems worldwide.
“Previously research largely focussed on extinctions. In this case tortoises still exist on this island but in much reduced numbers – and there have still been significant ecological consequences.
“Wetlands are highly specialized, limited habitats supporting specialized biodiversity. The effect of the loss of large animal species on wetlands has been largely overlooked until now. It may be that plants and animals which depend on these rare habitats are particularly vulnerable to extinction.”
Dr Froyd hopes the work of her team will help conservationists to conserve and restore ecosystems and habitats, including programmes to reintroduce species and replace ecological functions which may have been lost in the past.
