Endemic to Galapagos, the Opuntia cactus is the most widely distributed and numerous plant found in the Archipelago and is a great example of adaptive radiation. The Opuntia, also known as prickly pear, has six different species on Galapagos and 300 known across the Americas. The cactuses on Galapagos divide into fourteen varieties and are found in mostly arid areas close to the coast. The tallest cactus, the size of a tree, is found in Santa Cruz, where they can grow up to 12m tall, while Santa Fe is home to the smallest cactus of the species, reaching the only 2.6m.
Prickly pears have thigmotactic anthers; when they are touched they curl over, depositing their pollen. This allows them to self-pollinate, so that they can reproduce even when there are no other cacti in the surrounding area. They can be found all over the Archipelago all year round.
In the food chain
The six species of Opuntia found in Galapagos are the main sources of food for animals occupying areas of lowland and arid areas. The fruits, seeds and pads are a major component of the diet of giant tortoises, land iguanas, mockingbirds and finches. It has been found that in arid areas, where the cactuses are usually the only available food source and grow very tall and tree-like, tortoises have evolved to have a different shape of the shell to be able to stretch up to reach the higher cactus pads. In the highlands where the tortoises’ diets are more varied, their shells have remained round as they are not required to reach up high as most of their food is found close to the ground.
Finches eat the cactus flowers, fruits and seeds, and obtain water from the succulent pads. The finches are vital to the survival of the cacti, eating the fruit and distributing the seeds across the Islands.
Fruit from the Opuntia is named tuna in Spanish and is readily available to buy and eat at markets all over Ecuador. The tasty fruit is thought to have healing properties such as aiding digestion and anti-inflammatory properties.
Loss of cacti has occurred across the Archipelago for some reasons. The main reason for the reduction in Opuntia is due to human presence. Many have been cut down to create space for development on the islands with the largest populations. Invasive species introduced by humans such as goats and pigs have also had a detrimental effect on Opuntia, as these invasive species outcompete native animals for the most accessible pads, and eat them faster than they can grow to recover.Although the cactus can self-pollinate, the reduction in pollinators such as mockingbirds and finches is also thought to have had a detrimental effect on numbers of Opuntia.
The cacti lie inside the Galapagos National Park (GNP) which covers 97% of the land area in the Archipelago and provides protection to all species within it. There have also been efforts to eradicate invasive species such as feral goats and pigs from Isabela and Floreana, which allows the cacti to recover. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) currently lists all Opuntia species under CITES Appendix II.
GCT are currently partnering with Island Conservation, among other organisations, to create and implement a never-before-seen restoration project on Floreana Island. This project will be the blueprint for invasive species eradication on an inhabited island. With the removal of invasive rats, and feral pigs and goats, Opuntia will have a chance to regrow and the native animals and birds will have a replenished food source. Click here to learn more about our Floreana restoration project.
If you would like to learn more about the prickly pear cactus of Galapagos, click here
We also have some interesting information on the Opuntia on our educational website, Discovering Galapagos