Lizards and their positive footprint on oceanic islands

17 October 2013
Comments: 0
17 October 2013, Comments: 0

Today sees the inauguration of a new section in our Mirlo blog: Natural cooperation. Beatriz Rumeu, who has a PhD in Biology and is the author of the investigation into the mirlo capiblanco – the little bird known in English as the Ring Ouzel and which is the inspiration behind the name of our company, will be using this section to tell us all manner of interesting stories about positive footprint and biodiversity. We’ll be seeing how in the world of nature that surrounds us, all sorts of different species relate and cooperatewith each other in the purest “Mirlo style”. This section will grow in the months to come, and we’ll also be benefitting from input from the Grupo de Ecología y Evolución en Islas del IPNA-CSIC, the Island Ecology and Evolution Group of the IPNA-CSIC.

One of the most singular characteristics of oceanic islands is the fact that they once rose from the seabed as the result of volcanic activity. Such islands come to the surface barren of any life, and they are gradually colonised by whichever living creatures are able to establish themselves on them –once they have managed to overcome the marine barrier that separates them from other inhabited areas.

One of the phenomena that certain species encounter when they colonise an insular environment is that of density compensation. Generally speaking, this phenomenon arises because there are fewer species living on the islands than on the continents (given that not all of the continental species are capable of colonising the islands). As a result, there is often less competition between insular species and fewer predators, which means that they can expand their habitats, find more food to eat and consequently, increase their population density.

As a rule, the different species of lizards that live in island environments have undergone this density compensation process. The diet of continental lizards consists mainly of arthropods; however, on islands where such creatures may well be less abundant than on the continent, lizards tend to broaden their diet by consuming nectar and fruit. As a result, this turns them into important agents for pollinating and dispersing the seeds of a wide variety of island plants.

gallotia

In the Canary Islands, lizards of the endemicGallotia genus (found in great abundance on all the islands) actively disseminate a great number of plants. For example, the role they play as pollinators has been ascertained in the case of species such as the Cockscomb, the Canary Island Bellflower or the Castor Oil plant. As lizards are not to be found in great numbers in humid, wooded habitats such as laurel or pine forests (which are not very suitable for these ectothermic or “cold-blooded” reptiles), they are also important dispersers of seeds throughout all the open habitats of the archipelago. For example, they spread the seeds of fleshy fruit species such as the Baloor the Sea Buckthorn, the Most Scented Jasmine, the Tala, the Savin, the Canary Island Juniper or Rhamnus Integrifolia, (“Moralito”, in Spanish).

So we can see therefore how important lizards are in pollinating and dispersing seeds throughout the islands due to the fact that here, as opposed to what happens on the continent, they consume the nectar of the flowers and the pulp of the fleshy fruit of a wide variety of plants. In this way, as well as the benefit that they themselves gain from such a healthy diet, they also take an active part in the reproductive cycle of the plants with which they interact, allowing many new plants to spring up and undoubtedly leaving a positive footprint on the natural world they live in.

Beatriz Rumeu

Recommended reading:
Olesen JM & Valido A (2003): Lizards as pollinators and seed dispersers: an island phenomenon. Trends in Ecology and Evolution 18: 177-181.

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