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Pong
Post  Post subject: Animal Dispersal by Predator  |  Posted: Sat Mar 04, 2017 2:06 am
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Dispersal of plants, by animals, we're all familiar with. The holly tree attracts birds to eat its berries, they poop the seeds far and wide. Other plants may instead go for being ripped apart, scattered around, so the undigested parts take root. Animals are generally motile so they rarely need help dispersing, but there are exceptions. Parasites. I've never heard of a large vertebrate getting itself predated for sake of dispersal, besides maybe our domestic livestock.

The common garter snake, Thamnophis sirtalis, is remarkable for a reptile by bearing live young. Anecdotally, I've chopped a garter snake with a lawnmower and seen her young sliver out.

The snakes of coastal BC are predated by eagles. These snakes prefer the rocky shoreline habitat, they're often seen basking on bare boulders. The eagles - focused mostly on fishing - hang around the tops of conifers leaning over the ocean. We have many small islands unimaginatively named "Snake Island" - for besides some wild grass and stunted trees about all you'll find on these is snakes. And of course gulls, and the occasional eagle trying to fish in peace amidst the seagulls.

When a gull or eagle scores a catch, this inevitable drama unfolds where first one gull then a mob of them attempt to steal a share of the meal. The predator can't eat in that. It won't even pause to kill/dismember its prey. Instead it flies away, screeching gulls chasing after it. I've watched eagles fly out to sea while clutching their fish, vanish into the distance - presumably to land on some rock and eat their prey in peace.

That's where I think the live-bearing garter snake wins after all. I suspect that for pregnant snakes the young have a good chance of escape, as the predator rips open her body. The snakes couldn't disperse like that without the actions of predators. If I'm correct then we can say why live-birth is advantageous to the garter snake. In nasty reproductive terms we could say the pregnant garter snake wants to get caught, transported, and ripped open. So her offspring literally fly to distant or remote habitats.

This summer when the snakes are basking I'll go along the shore and sex them, also counting pregnant snakes. It's the same time of year they carry and birth young. I believe my hypothesis scores a win if I find disproportionately high numbers of swollen females, easy pickings atop bald boulders. If the ratios are insignificant, then maybe my hypothesis is still somewhat true. How do I prove it completely wrong? I think finding pregnant females avoid exposing themselves, would prove that.



I'm curious if there are other, verified cases of animal dispersal by predator.


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marnixR
Post  Post subject: Re: Animal Dispersal by Predator  |  Posted: Sat Mar 04, 2017 8:00 am
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on the other hand, snakes are usually pretty good swimmers
+ as a rule reptiles can go without food for long periods of time and could raft on vegetation, say when a river has been in flood

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Pong
Post  Post subject: Re: Animal Dispersal by Predator  |  Posted: Wed Mar 29, 2017 9:21 am
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Apples also can bob around in water. I'm wondering if some large vertebrates gain significant dispersal by getting carried off by animals that would eat them.


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paleoichneum
Post  Post subject: Re: Animal Dispersal by Predator  |  Posted: Wed Mar 29, 2017 4:41 pm
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Pong wrote:
Apples also can bob around in water. I'm wondering if some large vertebrates gain significant dispersal by getting carried off by animals that would eat them.

Most likely not, the probability of vertebrates dispersing that way is very low I think.

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marnixR
Post  Post subject: Re: Animal Dispersal by Predator  |  Posted: Wed Mar 29, 2017 6:44 pm
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especially large vertebrates
btw, what do you consider to be big ? a rabbit ? a sheep ? a human being ?

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Pong
Post  Post subject: Re: Animal Dispersal by Predator  |  Posted: Thu Mar 30, 2017 9:13 am
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Garter snake.


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paleoichneum
Post  Post subject: Re: Animal Dispersal by Predator  |  Posted: Thu Mar 30, 2017 2:35 pm
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Pong wrote:
Garter snake.

You have an odd definition of large.

And the dispersal is by rafting and swimming, not by predator

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