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# Lotka-Volterra equation

Lotka-Volterra equation

Somewhere I once saw a great site that simulated this model of predator-prey interaction on your browser using cute pictures of fish! I can't find it now. I tried one site and it completely crashed my browser...

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Comment Source:You mean [this JSXGraph example](http://jsxgraph.uni-bayreuth.de/showcase/carpsandpikes.html)?
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edited May 2012

That's the one I wanted, thanks! And it didn't crash my browser. I notice they let you download the source code. Do you think this is the sort of software an idiot like me could include in This Week's Finds?

There's something really appealing about this simulation - it's like having a fishbowl... much more fun than merely watching the graph of some function. You could say it's a gimmick, but if we ever try to make stuff that appeals to ordinary folks, instead of 'scientists and engineers', I think this is the kind of gimmick that could work.

Comment Source:That's the one I wanted, thanks! And it didn't crash my browser. I notice they let you download the source code. Do you think this is the sort of software an idiot like me could include in _This Week's Finds_? There's something really appealing about this simulation - it's like having a fishbowl... much more fun than merely watching the graph of some function. You could say it's a gimmick, but if we ever try to make stuff that appeals to ordinary folks, instead of 'scientists and engineers', I think this is the kind of gimmick that could work.
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edited May 2012

FI: I set all the sliders to their minima and the program crashed on Windows7. I wonder why?

Comment Source:FI: I set all the sliders to their minima and the program crashed on Windows7. I wonder why?
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I can crash it too! The image became filled with fish, and it said carps: NaN, pikes: NaN.

Comment Source:I can crash it too! The image became filled with fish, and it said carps: NaN, pikes: NaN.
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edited May 2012

I'm temporarily at a machine powerful enough that I dare enable javascript and I've had a look at this. This is an old browser, so it's conceivable that it's misbehaving but not crashing. What I see is a lot of fish pictures bouncing around a bit too fast for me to follow, and too random for me to see anything that registers as a pattern.

I wish I could say I liked this, but it looks to me like it doesn't communicate very much. It would be better if there were (say) two cohesive "shoals", one for each species, which bobbed around a bit for "excitement" but stayed overall still and in formation enough that you could visually see the two populations increasing/decreasing. I can't see what purpose the current fish movement serves, and it makes visually seeing patterns difficult. Since they're plotting the "trajectory in state space", it might be informative to plot a dot showing position in state state space corresponding to the currently displayed fish shoals. (There's lots of other stuff that you could do: you could perhaps plot "ghost fish" to get an idea of how the current population relates to the maximum population has been so far, come up with some way of showing the linkage between the two populations, etc.)

I'm sure there's some very impressive technology behind the application, but the "output design" doesn't seem to connect the "entertaining" part of the app with the "educational" part.

Comment Source:I'm temporarily at a machine powerful enough that I dare enable javascript and I've had a look at this. This is an old browser, so it's conceivable that it's misbehaving but not crashing. What I see is a lot of fish pictures bouncing around a bit too fast for me to follow, and too random for me to see anything that registers as a pattern. I wish I could say I liked this, but it looks to me like it doesn't communicate very much. It would be better if there were (say) two cohesive "shoals", one for each species, which bobbed around a bit for "excitement" but stayed overall still and in formation enough that you could visually see the two populations increasing/decreasing. I can't see what purpose the current fish movement serves, and it makes visually seeing patterns difficult. Since they're plotting the "trajectory in state space", it might be informative to plot a dot showing position in state state space corresponding to the currently displayed fish shoals. (There's lots of other stuff that you could do: you could perhaps plot "ghost fish" to get an idea of how the current population relates to the maximum population has been so far, come up with some way of showing the linkage between the two populations, etc.) I'm sure there's some very impressive technology behind the application, but the "output design" doesn't seem to connect the "entertaining" part of the app with the "educational" part.
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The fish movement serves no purpose whatsoever but to make them look like fish. I still like it, though it's a guilty sort of pleasure because it's not scientifically justified.

I will not attempt to crash my browser by breeding too many fish!

Comment Source:The fish movement serves no purpose whatsoever but to make them look like fish. I still like it, though it's a guilty sort of pleasure because it's not scientifically justified. I will not attempt to crash my browser by breeding too many fish!
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Note that I'm not saying entertaining or attractive looking stuff is bad, just that it looks like in this case the current "entertainment" actively interferes with the understanding part and I'm sure with a little more thought they could be made to not clash, and maybe even re-inforce each other.

Comment Source:Note that I'm not saying entertaining or attractive looking stuff is bad, just that it looks like in this case the current "entertainment" actively interferes with the understanding part and I'm sure with a little more thought they could be made to not clash, and maybe even re-inforce each other.
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I added a link there, to the review of L.V. results in my dissertation. Edited as "AnonymousCoward" because I was clumsy with the interface, but it's me.
Comment Source:I added a link there, to the review of L.V. results in my dissertation. Edited as "AnonymousCoward" because I was clumsy with the interface, but it's me.
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One of the most challenging aspects of Lotka-Volterra is in applying it to real-world predator-prey observations. There is always a possibility that an underlying common-mode mechanism is controlling the population instead of non-linear feedback dynamics.

How the mechanism may have been isolated for Lemming/Arctic Fox populations:

https://geoenergymath.com/2020/03/29/lemming-fox-dynamics-not-lotka-volterra/

Comment Source:One of the most challenging aspects of Lotka-Volterra is in applying it to real-world predator-prey observations. There is always a possibility that an underlying common-mode mechanism is controlling the population instead of non-linear feedback dynamics. How the mechanism may have been isolated for Lemming/Arctic Fox populations: https://geoenergymath.com/2020/03/29/lemming-fox-dynamics-not-lotka-volterra/