Kate Bush and the mongoose: character displacement and release

A fist full of Kate.

When my sons look back on their childhoods they will likely remember many things. Lots of cricket. Great holidays in the Catlins full of boogie boards and board games. Our big old house that could hold as many friends as they cared to bring home. And too much Kate Bush.

As a tween in the late Seventies I was transfixed by Wuthering Heights when it came out.  I have snapped up every album that Kate Bush has put out, right through to her most recent in 2011. I loved the complexity of her songs, the range of her voice, the fact that the songs were about stuff, often strange stuff, with strange topics for songs (bank robbing, snowman lovers, a Viet Kong hunting a GI, the plight of the aborigines, the devil descending a lift). I’ve played her music all my life. It’s great to work to.

But it is a guilty secret. As a teenager, Kate Bush was not what boys from South Otago were supposed to listen to. Even now if a Kate song pops up on shuffle I will get comments from colleagues and friends. So I don’t tend to play Kate when others are around. My wife, Julie, tolerates Kate but has her limit (although Kate Bush featured heavily in my proposal to her! That might  be a story for another day). Through the years my sons have heard there fair share and not been huge fans (although my day was made when I discovered that one of them did have Jig of Life on their own playlist).

Should I change my behavior like this? Perhaps I should be loud and proud? Maybe, but I know that her music is challenging and not for everyone. So I continue to enjoy her in my headphones, or while hanging out the washing, or on long solo car trips. Julie is much the same about ABBA. I don’t dislike ABBA songs but one or two are fine for a day. So when I am not around my wife plays a lot of ABBA. When I am on my own I play a lot of Kate. When we are together we play a lot less of both and more of bands that we both like, say NZ bands like The Bats or Greg Johnson or international bands like The Killers and err The National. The point is that things change depending on the situation. In the world of biology this is known as character displacement, e.g. changing your music depending on who is around, or character release, e.g. playing your favorite music when no one is around.

Mongoose in cage
A mongoose captured and ready for measuring. Ariana Barun

Character displacement is usually associated with natural selection. Competition can be a powerful force in selection. If two species overlap in the resources that they use there will likely be selection that results in one or both of the species changing the traits away from the overlap (ecological character displacement). Likewise, when a species escapes from a competitor we may see character release that changes a trait to be more like that of the missing competitor.

One situation where character displacement may often occur is with invasive or introduced species. When a species arrives in a new area there may be a native species that shares a similar ecological space (or niche) and one or both of these species may show character displacement so that they can coexist. Sometimes a species arrives in a situation where there are no competitors compared to their home area and they can diversify through character release.

Although the theory is reasonably sound around character release it is fairly difficult to test. You need to have many similar discrete areas, an introduced species and areas where you find 1) only the native competitor, 2) others where you  have only the introduced species, and 3) some where you find both native and introduced species. That’s where the mongoose comes in. The mongoose is a small carnivore from southern Asia that has been introduced into various parts of the world to control local snake populations. Although they do help with controlling snakes, mongooses eat almost anything and often become a problem for local species.

Mongooses have been introduced onto several Adriatic islands of Croatia. On some of these islands is the native stone marten, a small carnivore that has a similar size and life style to the mongoose. There are islands with both mongooses and martens, some with just martens and some with just mongooses. A neat little natural experiment that has been running for about 100 years.

Croatia island
The Adriatic Islands all have human populations as well. Ariana Barun

In work published in the Journal of Biogeography, Arijana Barun, a recent postcdoc at Lincoln University, and colleagues from Croatia, Israel and the US report on character displacement of the martens and mongooses. They collected data on skull measurements  from lots of mongooses and martens from seven islands.

On islands that mongooses share with martens they had smaller skulls and canines compared to islands where they are the only small carnivore. On islands where martens are the sole carnivore they had shorter skulls compared to islands where they coexist with mongooses. These findings are consistent with the idea of character displacement/release. When the competitive species is not present you can move into their niche-space.

This type of research shows us that how a species may behave or appear is often influenced by who is present in the local habitat. This may be a key factor to understanding why some species are so successful (or otherwise) at invading some areas over others. Something to contemplate next time I am somewhere on my own listening to Kate.


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