Anole perching on a tree trunk in Ogasawara. (Photo: Naho Mitani)
The Ogasawara Islands are isolated oceanic islands with a subtropical climate located 1,000 km south of Tokyo. They are very attractive islands with many endemic plants and animals. However, those interested in nature may notice that there are few sounds of insect wings or signs of insects in the forests on Chichijima Island, an inhabited island within the Ogasawara Islands.
It is estimated that the green anole was unintentionally introduced to Chichijima Island in the late 1960s. Currently, there are several hundred to a thousand of them per hectare, depending on location. Predation by the anoles has reduced populations of mainly diurnal insects. Not only that, but disturbance of pollination systems in native flora has been noted due to the decrease in insects. The endemic skink, Cryptoblepharus nigropunctatus, was displaced where anole densities were high.
I first saw the green anole when I was involved in a project to eliminate introduced feral goats in Ogasawara. Wildlife management and conservation is my specialty. In this field, the problems of overabundant mammals such as deer and invasive introduced species are important issues. Researchers and practitioners who love animals frequently discuss the efficient capture of these animals and the eradication of invasive species at academic conferences.
When I attended conferences on reptiles, there were studies on conservation of reptiles that are affected by habitat destruction or non-native species. However, there were only a few studies that were oriented toward taking action against reptiles that cause damage to ecosystems as invasive species. Therefore, I thought I might have something to contribute, even though I am not a herpetologist.
In our first study of anoles published in 2015, we tested in the laboratory and in the field to see if we could attract them with a bait. If the bait could be seen moving, it could attract anoles up to about 2 m, even if it was in a transparent container. However, non-hungry anoles were not interested at all even if there was a bait in front of them. After this study, we wondered if it would be possible to identify their preferred location as a perching tree and capture them intensively. When we studied preference by tree species, they preferred the screw pine.
In the latest paper, I re-tabulated the data from the tree species preference study by trunk diameter. Anoles avoided tree trunks thinner than 1 cm in diameter, but had no preference by diameter for trunks larger than 2 cm. Except for very thin trunks, this means that trunks of any thickness are used according to their frequency of occurrence.
These behavioral traits may be a disadvantage when trying to capture green anoles and reduce their numbers. They are not attracted to dead, immobile baits; they are not interested in baits unless they are hungry themselves; they prefer the screw pine, but use other trees as well. Conditions for high-frequency use of sites are not clearly limited. Controlling lizard populations may be more difficult than for mammals.
On the Ogasawara Islands, where there are many endemic species, chemicals such as insecticides cannot be used easily. Also, consideration must be given to the bycatch of non-target species. We must improve our measures step by step to break through this difficult challenge.
Or perhaps we need to think differently from the way we capture mammals and insects. I assume that there would not have been many occasions in human history when we would have wished to capture a large number of reptiles in an efficient manner. It would be a great help if researchers in various fields are interested in controlling reptile numbers. In this regard, it is fortunate for those of us involved in anole control in Ogasawara to publish an article on the subject in Anole Annals, which attracts many people interested in lizards.
The latest research is available open access.