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There are many organisms that sometimes reproduce asexually and sometimes reproduce sexually (even snakes and sharks!).

There are also a fair number of organism that reproduce sexually but have a sex ratio of offspring that is heavily influenced by environmental conditions (e.g. water temperature with high temperatures favoring males, low temperatures favoring females and ideal temperatures favoring a mix, or vice versa, in some turtles, fish and amphibians).

Is there any scientific reason that there couldn't be an organisms that acts like K-strategists in some circumstances, and r-strategists, in others, using different reproduction modes as the circumstances merited, or that use both simultaneously? (Obviously, one way to show that this is viable would be with a real life example, if there is one.)

For example, maybe an organism would ordinarily have a K-strategy form of reproduction in good environmental conditions, but in the presence of extreme environmental stresses might reproduce by creating r-strategy spores in a manner that caused the death of the parent.

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    $\begingroup$ Humans produce lots of children when they live in poor conditions and few children when they live in good conditions. Compare the fertility rates of Nigeria and Japan. $\endgroup$ – AlexP Aug 21 '17 at 11:05
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The common side-blotched lizard, Uta stansburiana. There are 2 types of females in this species:

  1. Yellow throated, who are K-strategists and lay small clutches of big eggs.
  2. Orange throated, who are r-strategists and lay large clutches of small eggs.

The proportion of yellows to oranges fluctuates over time, as environmental conditions change and as the benefit of being the 'rare' colour waxes and wanes.

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  • $\begingroup$ I am particularly impressed that this happens in reptiles. Good catch. I feel smart today than I was yesterday. $\endgroup$ – ohwilleke Aug 21 '17 at 15:39
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This is a fine strategy. There are organisms that do this. The one that comes to my mind is physarum polycephalum, which is a slime mold.

When times are good, the slime mold is a spreading, asexual slime. yellow slime on wood

When food runs low, the slime produces fruiting bodies called sporangia, undergoes meiosis, and sets free spores. The slime dies in the effort.

from https://www2.warwick.ac.uk/fac/sci/lifesci/outreach/slimemold/facts/ yellow slime with dark blue / black fruiting bodies

From the linked wikipedia article.

As the food supply runs out, the plasmodium stops feeding and begins its reproductive phase. Stalks of sporangia form from the plasmodium; it is within these structures that meiosis occurs and spores are formed. Sporangia are usually formed in the open so that the spores they release will be spread by wind currents.

This is two different strategies as you state but represents an extreme of K-selection - rather than few expensive offspring (like elephants or humans) the asexual "offspring" of the slime mold contribute to the colonial organism that is the slime.

Stress-induced flowering is seen in a lot of plants - plants reproduce asexually by runners or the like, then flower and set seed (and die) when resources get low.

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    $\begingroup$ I m always amazed at how most of the biology world building questions already have a compelling answer in the real world. $\endgroup$ – Fred Aug 21 '17 at 6:37

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