FROM Mr Lapenas' 6th grade Science class:
You mentioned an extremely large population of alien insect species on the
island of Nihoa. The students have several hypotheses as to how they arrived there.
1)- Swam or caught a ride on some marine debris
2) hitched a ride in the feathers of a migratory bird
3) got sucked up in a
storm and blew over Nihoa then landed.
The one thing we can't figure out is
since there are so many birds on Nihoa - why don't the birds just feed on
the alien insects and keep their numbers down? Don't the alien bugs taste good or don't the birds recognize them as real food? We would like to know
what can be done about "alien species" before they eat all the plants and fruits and vegetables and there's nothing left for the native insects to
eat.
Dear Mr. Lapenas and 6th Grade Science Class:
Nihoa, although a small rocky island has had a total of 199 species of insects recorded. Some of those species have probably died out, but a
surprising number remain. The number of plant species are limited, but as the images from Nihoa are posted to the web site, you may be able to see
there is good plant cover, indicating that adequate soil is available to foster plant growth. Necker is actually a smaller island, perhaps even more
vertical than Nihoa. Although soil seems more extensive on Necker, only a small percentage of the island is horizontal enough to allow plant growth
and there are only 4 plant species known from Necker (although 79 insects have been recorded from there). There is a theory that the number of
species expected on an island correlate to the size of the island and some
published data seem to confirm this.
The "overpopulation" mentioned is one species in particular,
Schistocerca nitens. It is a large grasshopper and it may be that the native Millerbirds have not yet learned to take
advantage of this resource, or they may not like the taste of the grasshopper, or the grasshopper, other than the
smallest stages, are out of the size range preferred by the bird. This question obviously requires some research. Lack of predators and parasites
for the grasshopper may be allowing it to expand its population beyond carrying capacity. If that happens, will the population crash? The
insertion of a totally new species into a closed ecosystem may cause a few
problems until the system is able to accommodate the newcomer, if it is able.
The alien species could have arrived in many ways, probably all have been used. Dr. Flint's response above is quite apt. I might add another way,
self dispersal. The large grasshopper is an extremely strong flier and could likely have made the flight by itself. This grasshopper is related to
the Desert Locusts of Africa, which on occasion have been known to fly as far as India during their swarming periods. Another potential way is on
bird's feet. Many insects either live in the ground or lay their eggs there. If some mud with eggs is picked up by birds, they could be
transported long distances. Many of the species that have arrived on these
isolated islands are those that are often associated with human involvement
(like the listed American cockroach). Natural dispersal events are a lot more rare.
The problem with alien species entering is difficult. Often we are surprised at their impact (and sometimes with their lack of impact). For
example, on Necker, I found a non-native cricket hiding in the rocks. However, I also saw one of the large native spiders,
Nihoa hawaiiensis (the genus name is Nihoa even though it occurs on Necker!), hunting these
crickets. They probably will have a positive effect on the spider populations, increasing their numbers. If the numbers of spiders increase,
will that put pressure on some of the other species there until balance returns to the system? This is one of the exciting things about science and
especially in working with living animals and ecosystems.
There are usually more questions than answers and the answers are often multifaceted. What
will happen to the terrestrial food webs on Nihoa and Necker? Perhaps only
time will tell. Now that the species are here, we can watch and monitor the
situation. If the system becomes too unbalanced, we might be able to insert
specialized predators and parasites. One of the worst aliens found on these
islands and atolls are ants. Some species of ants are particularly good at
extirpating native species of insects. Their populations should be monitored and controlled at the very least. We are hoping that the baiting
program on Midway will be successful and be able to be used on the rest of
the Northwest Hawaiian Islands.
I agree with Dr. Flint (see other Q and A) and am totally amazed at your probing
questions. Congratulations for teaching and learning your lessons well so your questions are so insightful.
Aloha nui loa,
Gordon Nishida
Gordon Nishida
Click for full size
Gordon Nishida (above) is an entomologist and the Collections Manager of the Entomology Collection at the Bishop Museum.
The picture above was taken on Necker Island September 22nd and e-mailed back via satellite phone.Click here to go back to the main questions page
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