Non-native species threaten endemic iguana populations

Researchers of Wageningen University and Research have identi­fied a recent incursion of non-native iguanas on Saba which form a major threat to the endemic iguana pop­ulation. A promising study shows a new methodology with which non-native igua­nas can be recognised and removed at an early stage for more effective protec­tion of native populations.

Local governments and non-governmental organisa­tions need to act immedi­ately to remove non-native iguanas once these are iden­tified to be present, said ma­rine researcher Dolfi Debrot on Wageningen University’s website.

Lateral view of a native (left) and a non-native (right) female iguana captured on Saba. (Wageningen University photo)

In the Caribbean Lesser Antilles, iguanas are among the most important native keystone herbivores. Al­though several native species and subspecies occur here, hybridisation with non-na­tive iguanas introduced by people or through ship and container traffic from the Central and South-American mainland is a major threat. Throughout the region na­tive iguana populations are under extreme pressure from hybridisation and replace­ment by these non-native iguanas.

Iguanas non-native to the Caribbean islands are larger and more competi­tive than native Caribbean iguanas and lay many more eggs. As soon as non-native iguanas become established, the process of hybridisation and competitive replacement will lead to the eventual ex­tinction of the local native population. During this process, the overall iguana population size often also in creases rapidly and becomes a local pest, as can be seen in the Cayman Islands, for example.

Non-native iguanas need to be recognised as fast as possible in order to be cap­tured and removed from na­tive populations. However, as iguanas are morphologically extremely variable, coloura­tion and scale differences are not always useful for dis­tinguishing native specimens from non-native ones. Dif­ferences in morphometric characteristics have not been assessed until now.

Research led by Wa­geningen University, in col­laboration with the Durrell Wildlife Conservation Trust and the Montserrat National Trust, shows that the charac­teristic scale on the lower jaw is remarkably larger for non-­native iguanas compared to native iguanas.

Because only few non-­native iguanas occur on Saba, additional diagnostic characteristics might yet be discovered, but this initial study provides at least one approach for rapid recogni­tion in the field.

The involved scientists call on their regional col­leagues to conduct intensive research into morphometrics in local native iguana popu­lations as soon as possible. Through such efforts, new data sets can be built that al­low rapid non-native identifi­cation.

A healthy native iguana population is considered a measure of the vitality and resilience of the insular ter­restrial ecosystem, in which the iguana plays a key role as a herbivore in the endangered Caribbean dry forest on the Windward Islands.

Female iguanas also mix soil and nutrients when nest­ing, while hatchling iguanas form an important nutrition­al source for many (migrat­ing) bird species. Further­more, iguanas stimulate leaf and flower growth of native plant species. Finally, con­sumption of fruits by iguanas distributes seeds and pro­motes their germination, as well as the survival of young plants.

Saba is home to one of the last remaining native iguana populations in the Lesser Antilles that, until recently, was not directly threatened by non-native iguanas. Saba’s iguana population was found to be larger than initially ex­pected and occurred island-wide, even though feral cats through predation and goats, which cause erosion and habitat degradation, are major threats. Partly because of this, there appeared to be very few juvenile iguanas in the Saba population. The most urgent threat, however, is the presence of alien igua­nas.

Research indicates that non-native iguanas are pres­ent in small numbers in at least two areas on Saba. DNA analysis shows that these animals originate from Curacao and Central Amer­ica and probably ended up on Saba indirectly via the port of St. Maarten. There is a large invasive and non­-native iguana population in St. Maarten and almost all freight traffic to Saba trav­els via St. Maarten, allowing iguanas to hitch a ride among the freight.

Therefore, controlling the iguana population in the port of St. Maarten and fu­migation of container ship­ments would be a valuable step towards protecting the remaining native iguana pop­ulations of the Lesser Antil­les, the researchers said.

The Daily Herald.

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