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(This question is aimed at animals that take care of their young, e.g. dolphins.)

As I understand it, most animals reproduce if possible. The only way they don't is because they run out of resources. I'm wondering how this shows up in practice:

  1. Do they simply not have sex? If so, does this mean they don't have sex drive?
  2. Do they conceive and then let their children starve to death?
  3. Do they fail to conceive (that is, are there biological changes to a mother who's not getting enough food such that she is no longer fertile)?

Option #2 seems the least likely to me because presumably pregnancy involves a cost to the parent, and with resources already scarce this would be a waste; however the plot of White Fang does indeed involve this situation (I have no idea how scientifically accurate that book is however).

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  • $\begingroup$ Rabbits reproduce when resources are scarce. They then eat their young. There are many more options than the three you present. Consider, for example, that nutritionally challenged females might not have an estrus cycle, which would prevent pregnancy. Humans reproduce when resources are scarce as well, and it does indeed take a great toll on mothers and children. But it happens anyway. $\endgroup$ – anongoodnurse Apr 24 at 2:47
  • $\begingroup$ @anongoodnurse by the second law of thermodynamics, wouldn't it be more resource-intensive to produce children and then eat them? Not having an estrus cycle would be similar to option #3. As for humans ... I'd say that's out of the scope of the question. $\endgroup$ – Allure Apr 24 at 3:18
  • $\begingroup$ Humans are animals, too, and where sex is concerned, dolphins are like us. So, not outside of scope imo. $\endgroup$ – anongoodnurse Apr 24 at 3:22
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    $\begingroup$ Different animals use different strategies and all the three mechanisms are valid and there possibly are even more. Moreover, the laws of thermodynamics are applicable to particles and not organismal behaviour. Organisms need to choose the "theoretically most optimal" strategy for different reasons. $\endgroup$ – WYSIWYG Apr 24 at 13:41
  • $\begingroup$ I think this is probably too broad to be answerable, for the reasons pointed out in the comments. From a selection standpoint, you have to consider that resource scarcity can fluctuate, and an organism that fails to mate today does not have an opportunity to take advantage of an increase in resources in some future months. There are also a limited number of opportunities to ever reproduce: for some animals, even those that raise their young to some extent, there is only one chance ever. Consider that, on average, a given individual will produce ~2 offspring that grow up to successfully breed. $\endgroup$ – Bryan Krause Apr 24 at 16:21
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This is actually a comment, but was not allowed to comment.

I think what you're interested is more in population dynamics and I think what you're really asking about is more in line with what system of differential equations explains a network of animals and how their populations grow and decrease with the amount of resources and the species population.

I think the problem is that, there's actually no good model, because there are so many factors which seem to contribute to shifts.

@ MIT this year, they had a visiting prof from Tufts give a talk on this, and they're working on models, to try and describe this, and even HE- the prof said, yeah, it gets complicated even for two species.

I would recommend, that if you have time to read up on this?

https://sites.tufts.edu/hening/publications/ <--- a link to his publications

https://arxiv.org/abs/1710.01220

Also, this is probably more a question for the mathematics stack.

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  • $\begingroup$ I'm not more interested in population dynamics unfortunately. This is a biology question, not one about differential equations. $\endgroup$ – Allure Apr 25 at 12:51
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    $\begingroup$ @Allure - It's kinda sad that you don't recognize a good and helpful answer when given one. You think the user who answered isn't giving you a "biology" answer? $\endgroup$ – anongoodnurse May 1 at 3:00
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    $\begingroup$ ThermoRestart, thank you for this insightful and helpful answer. I hope we get more answers from you. $\endgroup$ – anongoodnurse May 1 at 3:01
  • $\begingroup$ @anongoodnurse considering I asked the question you'd think I'd know what kind of answers I'm looking for. They are of the kind that "so-and-so species adopts strategy #1, this one does #3, nobody does #2, and there's #4 which you haven't considered". This answer is inapplicable to what I had in mind. I'm not going to downvote it, but I'm not going to accept it either. $\endgroup$ – Allure May 1 at 3:06

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