Threats to tuatara
Tuatara, close up of head and shoulders,
Stephens Island
There are three kinds of rats in New Zealand. The kiore have been here for at least 1000 years. These typially weigh about 100 grams and resemble large mice. Adult tuatara can co-exist with kiore but it seems that tuatara eventually die out where kiore are present.
Several clues suggest that the kiore may have been nest robbers - taking eggs as well as small hatchlings. Being slow breeders the tuatara cannot make up for losses. There were probably few, if any, tuarata left on the North and South Islands by the time European settlers arrived in New Zealand
The larger Norway rats weight up to 450 grams. Norway rats and ship rats (up to 200 grams) arrived in New Zealand with European visitors and settlers. These rats are nature's 'vandals', eating and destroying whatever is available, and becoming prolific breeders when food is plentiful.
Rats are considered the most serious threat to the survival of tuatara because they are easily transported as stowaways on boats and usually the first alien animals to arrive unnoticed in new places.
Islands with rats have few nocturnal invertebrates or reptiles. Even the rats have to rely on seeds, fruits and other plant material for food because there is little else. Mice are less devastating, but also damage natural communities by eating seeds and small insects that native reptiles and birds normally eat.
A less obvious, but nevertheless significant, threat to tuatara survival is the low genetic diversity of the species. Low diversity has implications for how well animals are placed to cope with future climate change and also for the viability of newly established populations. Low genetic diversity is often associated with vulnerability to new pathogens and low reproductive success for example. This low genetic diversity is now spread across small and isolated islands reducing further the ability to cope with future environmental change.
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