Galapagos Land Iguana

It has developed both a resilient digestive system and a careful feeding technique for handling prickly pear cactus, a dominant food source on many of the arid islands it inhabits. Rather than avoiding the sharp spines, it often rolls a cactus pad around in its mouth first to help break or dull some of the spines before swallowing, and its tough mouth lining and digestive tract can tolerate the swallowing of some spine material without serious injury. This ability gives it reliable access to both food and moisture in an environment where standing fresh water can be scarce for much of the year, since cactus pads and fruit contain a useful amount of water.

This behaviour is a well-documented example of mutualism, a relationship in which both species benefit from an interaction that costs neither species very much. Certain Galapagos finches will hop directly onto a resting iguana's back, head, or limbs and pick off ticks and other external parasites, gaining an easy meal in the process, while the iguana benefits from having irritating parasites removed from parts of its body it cannot easily reach or clean itself. Some iguanas appear to actively encourage this cleaning behaviour, remaining unusually still or even raising a leg to give a finch clearer access to a particular area.

Species introduced to the Galapagos Islands by human settlers, particularly goats, pigs, cats, and dogs, caused severe damage through several different mechanisms at once. Goats and pigs degraded and altered the native vegetation the iguanas depend on for food, while cats and dogs directly preyed on iguana eggs and young, vulnerable hatchlings, which have little natural defence against mammalian predators the species never evolved alongside. On some islands, this combination of habitat degradation and direct predation drove land iguana populations to complete local extinction, while others survived only in severely reduced numbers.

Conservation programmes, primarily led by Ecuadorian park authorities and international conservation organisations, have focused on two main strategies with considerable success in several locations. Sustained efforts to fully eradicate introduced goats, pigs, cats, and other invasive predators from specific islands removed the core threats driving decline, while a captive breeding programme raised iguanas in a controlled setting before releasing them back onto islands where the wild population had previously been eliminated entirely, most notably restoring a breeding population to the island of Baltra decades after the original population there had disappeared.