Comments on: Picky eaters shouldn’t be surprised when they go extinct

By: David

David — Fri, 16 Jan 2009 22:27:42 +0000

Holmes, Jachmann and Bell (1985) studied the kinds of trees African elephants push over and noted some important distinctions they make. Elephants don’t destroy trees randomly. Unpalatable trees tend to be pushed over regardless of their size, while palatable ones aren’t pushed down until they grow out of reach of the elephants. Many palatable species respond to trunk breakage by growing multiple stems from the base (i.e. coppicing) so the elephants’ actions, in addition to encouraging surrounding new growth by opening the forest canopy and admitting sunlight, tend to kill unpalatable trees selectively and maintain palatable ones in a form that maximizes forage for thems elves and other browsers—a vivid example of the keystone role megaherbivores play in habitat creation and maintenance. The enhanced ability mega-browsers like elephants, and mastodons and Megalonyx had to survive on high fiber diets means they played a constant role in recycling the nutrients locked up in mature woody plants, and making way for younger more palatable plants to flourish for the benefit of the entire animal community. Reference Jachmann, H. and Bell, R.H.V. 1985. Utilization by elephants of the Brachystegia woodlands of the Kasungu National Park, Malawi. African Journal of Ecology 23: 245-258.

By: Holmes Semken

Holmes Semken — Mon, 29 Dec 2008 23:36:46 +0000

Dave, Your comment on megamammals (mammoths, mastodons, sloths, etc.) creating a ‘woodland disturbance’ community brought back memories of elephant watching outside of Kruger National Park in South Africa. We observed a single elephant, probably a male recently outed by its family matriarch, pulling trees (3-6 inches in diameter) out of the ground, rotating them to a horizontal position on its tusks, and then stripping the bark as we would eat an ear of corn. I was impressed that the animal would only ingest two to three feet of bark, discard the 20-30foot tree and then pull another to extract bite or two. This process certainly created hunting ground for taxa such as the ivory bill and habitat for a variety of smaller animals. I wondered then, as now, if this behavior created the parkland (lots of grass on the substrata) or if a preexisting parkland environment permitted sufficient space between trees for the giant to enter and feed. Either way, you have to give the elephant a gold star for parkland maintenance. Megamammals do modify the landscape.

By: Pete

Pete — Mon, 22 Dec 2008 22:13:20 +0000

Could be, but they seem to be scattered in lots of places. My guess is that these are just mutant trees that survived the seedling stage and are now too big for any serious threat from herbivores (ie: no mastadons around to chomp them)

By: David

David — Mon, 22 Dec 2008 21:17:29 +0000

Pete, I’m just finishing a post about the honey locust, but this is news to me. I understand a lot of the thornless trees are clones of one tree in Wisconsin. The experts have expressed some concern about the lack of genetic diversity in the cities as it gets planted everywhere, but I hadn’t picked up on any problems with it showing unusual vigor. I understand it breeds true and its seedlings are thornless–could you be seeing the progeny of one early escapee?

By: Pete

Pete — Fri, 19 Dec 2008 17:05:08 +0000

Interesting point Dave. I’d always heard the idea that hurricanes (and their tree killing power) were needed for ivory bill foraging. Never thought of megafauna in the equation…

On a similar note – has anybody noticed that a good percentage of thornless honey locust trees are thriving these days? Not the sunburst cultivar planted in towns, but the wild ones out in the woods.