I live on Vancouver Island. As an island it is subject to the same island biogeographical factors as Hawai’i, albeit in a much less extreme way because it is much larger, and it is close to a continent and therefore affected by the fauna and flora there. Vancouver Island is huge compared to the Hawaiian Islands, and it is close to the North American continent. Therefore its isolation and habitat characteristics allow pretty much any organism with a decent ability to disperse to settle here. Yet, some animals have never made it, e.g., moose and skunks. In the case of moose it is likely because the coast habitat is unsuitable, so they have never even tried to come across, even though they should be perfectly capable. The skunk, however, would probably need some human assistance. The climate on Vancouver Island is benign, further allowing settlement of a broad range of organisms. Nevertheless, Vancouver Island is isolated enough that there are some
endemic animals. The Vancouver Island marmot (Marmota vancouverensis) is perhaps the best known example, but there are others, e.g., the earthworm Bimastos lawrenceae (Marshall and Fender 2007).
Along with human habitation has come a wide variety of alien species as well. In fact, some of the most common arthropods are exotic or invasive species, and among the mammals there are the usual suspects: rats (black or roof rats, Rattus rattus, as well as brown or Norway rats, Rattus norvegicus), house mouse (Mus musculus), house sparrow (Passer domesticus), rock doves (Columba livia)(pigeons), all of which now have circumpolar or worldwide distributions. All are also present (and widespread) in Hawai’i. Hawai’i is also home to a third rat species, the Pacific rat, Rattus exulans, and all three species are major threats to native species (Harper and Bunbury 2015).
These are far from all of the non-native species that one encounters when visiting these popular tourist islands, however. In fact, most visitors may never see a single native animal, at least in terrestrial environments. And as stated in my previous post, endemics like the Hawaiian honeycreepers require substantial efforts. Below, I will mention some that we encountered, with a bit more information on why they are there, and what damage they (have) cause(d). While I will not cover invasive plants, it should be obvious that Hawai’i has an invasive plant problem at similar a similar (or worse) scale given its climate.
I mentioned the cichlids in my first post in this series and provided a link to the many other freshwater fish species found in Hawaiian streams and lakes. Many of these can have profound impacts on endemic freshwater species as predators of the five species of endemic freshwater gobies (O’opu) and three species of shrimp (‘Opae). Interestingly, two of those shrimp species are anadromous, by the way. Those two species have been important to native Hawaiians as food, but invasives along with stream manipulation (de-watering and channeling) have led to both being threatened today.
Living in a wet mild climate means that you are constantly fighting snails and slugs in your garden (just ask my wife!). It is not surprising, then, that numerous terrestrial mollusks have appeared in Hawai’i, including several predatory snails which have direct impacts on native fauna (Cowie et al. 2008, Curry and Yeung 2013). If you add to the invasive macrofauna threats posed by a variety of diseases and parasites, you have a perilous situation for the native Hawaiian fauna, indeed (Font 2003).
When I was younger I had a temporary obsession with lizards as pets. My favourites were the day geckos of Madagascar. These were incredibly expensive and difficult to get hold of, so I ended up with green anoles instead. Chameleons were also fascinating to me, but completely out of reach financially, and if possible even more difficult to find. It was surprising to me, then, to run into gold dust day geckos (Phelsuma laticauda) in Manoa Valley, and not only the odd specimen, but lots of them. Supposedly there are also Jackson’s chameleon (Trioceros jacksonii) resident there as well, but we never saw one. As I mentioned earlier, there were also plenty of anoles (we saw only brown anoles (Anolis sagrei). Green anoles (A. carolinensis) are common as well, but being arboreal
they are more difficult to spot). In addition, there are a number of other gecko species (we heard house geckos (Hemidactylus frenatus) chirping at night), and a number of skink species are also established. Fortunately, the brown tree snake, which has caused devastation to native birds (Wiles et al. 2003) and lizards (Rodda and Fritts 1992), and indirectly to a number of native plants of Guam (Mortensen et al. 2008), has yet to make an appearance in Hawai’i.
It goes without saying that numerous invertebrates have established themselves. Of most concern to the native fauna is the arrival of mosquitoes. Carriers of avian malaria, they have been major contributers to the decline of the native avifauna (Jarvi et al. 2001). For humans with little interest or awareness of the ecological distress of the Hawaiian Islands, cockroaches may be of more concern (we saw three in the house where we stayed – may they rest in peace!) But there are also ants, yellowjacket wasps and other invertebrates that may affect us. Suffice it to say that Hawai’i has been, and continues to be under siege of an army of invasive and potentially injurious organisms, because unfortunately, like us humans, the benign climate is very welcoming. In the end, humans are ultimately responsible for the situation, and responsibility for the loss of unique Hawaiian fauna and flora will rest firmly on our shoulders.
Finally, here is a list of known exotics in the Hawaiian Islands. How complete it is I do not know.
Cowie, R.H., K.A. Hayes, C.T. Tran and W.M. Meyer III. 2008 The horticultural industry as a vector of alien snails and slugs: widespread invasions in Hawaii, International Journal of Pest Management 54:4, 267-276.
Curry, P.A. and N.W. Yeung. 2013. Predation on endemic Hawaiian land snails by the invasive snail Oxychilus alliarius. Biodiversity and Conservation 22 (13–14): 3165–3169.
Font, W.F. 2003. The global spread of parasites: What do Hawaiian streams tell us? BioScience 53 (11): 1061-1067.
Harper, G.A. and N. Bunbury. 2015. Invasive rats on tropical islands: Their population biology and impacts on native species. Global Ecology and Conservation 3: 607-627.
Jarvi, S.I., C.T. Atkinson, and R.C. Fleischer. 2001. Immunogenetics and resistance to avian malaria (Plasmodium relictum) in Hawaiian honeycreepers (Drepanidinae). In Studies in Avian Biology, R. J. Raitt (ed.). Cooper Ornithological Society, Lawrence, Kansas
Marshall, V.G. and W.M. Fender. 2007. Native and introduced earthworms (Oligochaeta) of British Columbia, Canada. Megadrilogica 11 (4): 29-52.
Rodda, G.H. and T.H. Fritts. 1992. The impact of the introduction of the colubrid snake Boiga irregularis on Guam’s lizards. Journal of Herpetology. 26: 166-174.
Mortensen, H.S., Y.L. Dupont and J.M. Olesen. 2008. A snake in paradise: Disturbance of plant reproduction following extirpation of bird flower-visitors on Guam. Biological Conservation. 141: 2146-2154
Wiles, G. J., J. Bart, R.E. Beck, and C.F. Aguon. 2003, Impacts of the brown tree snake: Patterns of decline and species persistence in Guam’s avifauna. Conservation Biology, 17: 1350–1360.