Emigration and Pop Decline

[fuzzybuttons]

I don't understand how emigration works with pop decline.

I see that immigration/emigration affects the pop growth rate on a planet. This seems to abstract the idea of pops moving around from planet to planet, and even empire to empire. So pops emigrating just means that the current pop is taking longer to grow, and vice versa.

But sometimes I see a pop actually declining in the "Pop Decline" window. This seems to be related to emigration. But if the effect of pops emigrating is already figured into a reduced growth rate, then why is there sometimes an additional pop decline? In addition, the emigration rate is usually -1.6 to -2.0, but the pop decline rate is always exactly -5.0.

In addition, this pop decline only happens sometimes. I have planets where I've forced emigration rates up to -2.1 and not seen any pops declining. I have other planets with an emigration rate of -0.7 that start a pop declining immediately when they go negative. It always seems to be my primary species, but that could just be chance. It seems to be fairly rare.

Finally, I don't know how the game decides WHICH pop is declining. I can find them in the pop display window because they have a little green bag on their picture. But when I pulled up one to find out why he was leaving, the pop details didn't indicate why. His happiness was 77% and he was employed. The habitability for him was 60%, but there were other species on that planet with 20% habitability. I checked my population totals when he completed his decline, and they dropped by 1. So he didn't move to another planet in my empire - he either died or moved to another empire. But if that's what it means to decline, that you are emigrating to another empire, then why the -5.0 growth rate on top of the already reduced growth from emigration?

I've been through the wiki section on population several times, but haven't been able to figure this out. I'd appreciate any insights anyone might have. Thanks!

 

[Stars_and_Bars]

I don't think emigration is related to pop decline at all, though I may be wrong. As far as I can tell, pop decline happens in three scenarios. 1. A species has been selected for purging. , 2. The housing of the planet can only afford to house half the population of the planet, I think this is equivalent to the population being twice the housing limit, and 3. Two species have a pop growth selection ratio higher than 3, the lower growth species declines.

I don't really see why emigration would affect pop decline, since that's already taken into consideration in pop growth. The only way that it would make sense for emigration to affect pop decline is if pop growth is somehow negative as a result of emigration, which isn't possible in game.

 

[fuzzybuttons]

Thank you for the detailed reply. Can you explain what you mean by "pop growth selection ratio"?

 

[Stars_and_Bars]

Thank you for the detailed reply. Can you explain what you mean by "pop growth selection ratio"?

I can't define it, or rather it's used in the defines files.

POP_DECLINE_THRESHOLD = 3.0 # A species will decline when there is another species with a growth priority this many times higher

I think this is self-evident, each species (& subspecies ?) is given a pop growth priority. The highest one is the one that gets grown next, and then I assume there's a way to vary which one gets grown next (probably using random variables). So, for any pair of species, if the ratio between their growth priority is 3 or higher, the lower priority one will decline. I don't know if that's the only necessary condition for declining this way, but the normal way of pop decline requires that the population exceed it's housing capacity by double, while pop growth will already cease if they exceed the housing capacity by 1.5, so how would it ever reach 2.0 if growth already stopped at 1.5 (immigration maybe?). There's probably a lot more that needs explaining and I don't know everything about this new system.

 

[Theter]

Pop decline can be linked to emigration under certains conditions.

Everything that increases your emigration push will reduce you pop growth by an absolute amount depending emig push strength itself, among other things. If that absolute value is higher than your total pop growth, growth will stop and your pop will start declining. The only exception I have seen this far is emig push from Newly Founded Colonies, which cannot make you lose pop this way)

 

[Stars_and_Bars]

Pop decline can be linked to emigration under certains conditions.

Everything that increases your emigration push will reduce you pop growth by an absolute amount depending emig push strength itself, among other things. If that absolute value is higher than your total pop growth, growth will stop and your pop will start declining. The only exception I have seen this far is emig push from Newly Founded Colonies, which cannot make you lose pop this way)

But is it actually possible for pop growth to become negative? If you look in the defines file.

MAX_GROWTH_PENALTY_FROM_EMIGRATION = 0.95 # Fraction of base monthly growth

You see that not only is the growth penalty scaled to the base monthly growth, it is capped at a 5% reduction.

 

[fuzzybuttons]

I can't define it, or rather it's used in the defines files.

POP_DECLINE_THRESHOLD = 3.0 # A species will decline when there is another species with a growth priority this many times higher

Thank you, I understand now. To test this, I changed that value in my defines file to 9.0 and then restarted a saved game with several pops declining. All were my main species and all were declining on worlds where a new species was growing. Everyone stopped declining once the current pop was finished. So I'm guessing it checks this value when it makes the decision to start the decline.

I'm guessing this is all about getting your species to reach the ideal mix specified by the parameters more quickly, but it does seem a bit odd. If I had a single species empire, I'd never see decline from this. But because the pop growing is a newly arrived species, then one of mine has to die.

Regardless, I can set the value to whatever I want now that I know what it does. Thanks again!

 

[beckermt]

Identically -5 pop growth as declining sounds like Displacement. Mouse-over the declining Pop to see the reasons for the decline.

 

[fuzzybuttons]

Identically -5 pop growth as declining sounds like Displacement. Mouse-over the declining Pop to see the reasons for the decline.

If I mouse over the "Declining" window where the pop shows, it just says "Decline Progress" and "Base Decline 5.0". No reason given. If I look at the individual pop details, it doesn't say anything about it declining. The only indication is the green bag.

 

[AmpsterMan]

-snip-
...so how would it ever reach 2.0 if growth already stopped at 1.5 (immigration maybe?).

In my current game, I'm at 2400 and robots have the plurality of population in my empire. They aren't affected by migration, even as synthetics, so they keep growing and I feel I'm either going to have to start dismantling some robot factories, or build a ring world to keep all my pops.

 

[beckermt]

If I mouse over the "Declining" window where the pop shows, it just says "Decline Progress" and "Base Decline 5.0". No reason given. If I look at the individual pop details, it doesn't say anything about it declining. The only indication is the green bag.

You certain you don't have that species set to Undesirable and Displacement? That's the only thing that I can think of...

Share a screenshot maybe?

 

[beckermt]

In my current game, I'm at 2400 and robots have the plurality of population in my empire. They aren't affected by migration, even as synthetics, so they keep growing and I feel I'm either going to have to start dismantling some robot factories, or build a ring world to keep all my pops.

You can simply disable the factories instead of dismantling them.

 

[fuzzybuttons]

You certain you don't have that species set to Undesirable and Displacement? That's the only thing that I can think of...

Share a screenshot maybe?

I'm certain they are not Undesirable - they are my primary species. In fact, they were my only species until a few years before. Unable to share a screenshot at this time.

At any rate, I'm quite certain Stars_and_Bars explained how this is caused by the pop growth settings, as I mentioned in my earlier post. Once I changed that setting from 3.0 to 9.0 the decline stopped. When I changed it back to 3.0 to look at the tool-tip, the pop decline resumed right away.

 

[beckermt]

I'm certain they are not Undesirable - they are my primary species. In fact, they were my only species until a few years before. Unable to share a screenshot at this time.

At any rate, I'm quite certain Stars_and_Bars explained how this is caused by the pop growth settings, as I mentioned in my earlier post. Once I changed that setting from 3.0 to 9.0 the decline stopped. When I changed it back to 3.0 to look at the tool-tip, the pop decline resumed right away.

Fascinating.

 

[Urza1234]

I'm certain they are not Undesirable - they are my primary species. In fact, they were my only species until a few years before. Unable to share a screenshot at this time.

At any rate, I'm quite certain Stars_and_Bars explained how this is caused by the pop growth settings, as I mentioned in my earlier post. Once I changed that setting from 3.0 to 9.0 the decline stopped. When I changed it back to 3.0 to look at the tool-tip, the pop decline resumed right away.

Fascinating.

imo this part of their pop system is operating exactly as described and designed.

 

[AlanC9]

You can simply disable the factories instead of dismantling them.

OTOH, no sense wasting the building slot if you really don't want any more robots.

 

[beckermt]

OTOH, no sense wasting the building slot if you really don't want any more robots.

True! I suppose the pertinent question would be if you think you want to build more robits in the near future. e.g. after a new housing tech is researched.

 

[Urza1234]

True! I suppose the pertinent question would be if you think you want to build more robits in the near future. e.g. after a new housing tech is researched.

Agree, and I likely also want to ship those robots to other planets.