Modelling different gene drive scenarios on snails to prevent schistosomiasis

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Yujean Kim

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Aug 3, 2021, 10:46:24 AM8/3/21
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Dear Tristan,

I am currently in the process of modeling different gene drive scenarios on snails to prevent schistosomiasis. 

For my model, I ensured the fecundity of snails depends on the population density and carrying capacity to ensure that the snail population does not go over the carrying capacity. I accomplished this by using the equation that I have attached to this document. I have derived this equation through the following website:


However, from my research, the intrinsic growth rate of snails are all below the value 1. This ultimately produces a negative value, causing an error in my code. I was wondering whether this methodology is correct and whether there is an alternative method to ensure the fecundity of snails depend on carrying capacity.

As shown in the equation, I must find the intrinsic growth rate of snails. Currently all the intrinsic growth rate I have identified of snails are below 1, which ultimately produces a negative value in the result of the equation. 

Thank you for your time!

Kind regards,
Yujean Kim
Screen Shot 2021-08-03 at 3.45.48 PM.png

Jackson Champer

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Aug 9, 2021, 11:22:47 PM8/9/21
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The "intrinsic growth rate" for a discrete generation model should not be below 1, or else the population cannot replenish itself. It seems that you referring to the "low density growth rate" in the equation (beta). This actually has to be above 1, or else the population can't replenish itself or grow more rapidly when competition is low.
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