Yellow crazy ants supercolonies on Christmas Island

I haven’t been an active blogger so far. After one year of PhD research I came to the conclusion that I’ve spent most of my time getting my head around an interesting PhD question instead of an interesting blog post. But last year in December fellow students Darren, Yi and I went on an amazing trip to Christmas Island. We were very lucky to be there during the annual red crab migration, which is one of the most amazing nature wonders I have ever seen! I definitely wanted to share that with you and post a blog about! (Or blog a post…?)

We visited the island to get a better understanding of the ecosystem and discuss our PhD projects with the park managers there. Christmas Island’s ecosystem is under high pressure at the moment. One major problem is caused by yellow crazy ants (Anoplolepis gracilipes). These introduced ants didn’t cause any problem for decades, until in the early 1980’s a scale insect was introduced. This insect provides honeydew to the ants, which results in the ants becoming very abundant and forming supercolonies. These supercolonies can become extremely large and attack and kill the endemic red crabs (Gecarcoidea natalis) on the island. This resulted in a severe decline in the red crab population, which is catastrophic for the entire island ecosystem since red crabs are a keystone species in the forest. Their diet is based on leaf litter and seedlings and in absence of the crabs the forest develops an extremely dense understory.

In order to control this problem, Christmas Island National Park (together with Peter Green and Dennis O’Dowd from La Trobe University) set up an island wide survey to keep track of where supercolonies form.  Every other year they survey the entire island, which is a very time consuming and exhausting process.  It would be very useful if they got a better understanding of what causes supercolony formation. One of the aims of our projects is to get a better understanding of the habitat requirements and spread of supercolonies. If we know more about the habitat these supercolonies prefer and how they spread, it might be possible to do the survey in a more cost-effective way.

Our work is still in progress so I won’t show any results here but I do want to show you some pictures (taken by Darren, Yi and myself) of the island and its inhabitants.

Enjoy!

More than 60 % of the island is national park.

More than 60 % of the island is national park

Red crabs are endemic on the island.

Red crabs are endemic to the island

Red crabs are very important in the forest ecosystem because they forage on leaf litter and their burrows provide oxygen to the soil.

They are a keystone species of the tropical forest since their diet is based on leaf litter and seedlings

During the annual red crab migration millions of crabs are migrating from the forest to the shore

When the wet season starts millions of crabs are migrating from the forest to the coast to spawn

Temporary fences are placed to keep the red crabs out of the yellow crazy ants supercolonies.

Temporary fences are placed to keep the red crabs out of the yellow crazy ants supercolonies

Unfortunately that doesn't always work and crabs like to 'explore' what's on the other side of the fence...

Unfortunately many crabs like to ‘explore’ what’s on the other side of the fence…

Park rangers show us how they do the intensive yellow crazy ants survey

Park rangers show us how they do the intensive yellow crazy ants survey

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Welcome!

This will be updated soon with more details about my project.

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