Population growth rates for races in D&D question

[huginn]

Has anyone worked out population growth rates for races such as Elves and Orcs? Given Orcs short life span how fast can they bred and overrun a region or would elves and dwarves be in danger of extinction

[Satinavian]

Short lifespan doesn't mean growth. What you want is number of children per adult and chance of a child to reach adulthood. That is what dictates if a population is growing or shrinking. Only if there is some lasting long inequality, it could be worth looking at generaion length.

[Recherché]

Honestly I'd be more worried about elves overpopulating the world. Assuming that an elven pregnancy doesn't take more than 5 years and that there's no biological reason why a given elven couple can't have a kid at least once a decade that's something like 40 children from one breeding pair of elves over their reproductive lifespan. Not including twins! So for the Elven population not to expand rapidly either elves need to have seriously low fertility rates, they have lots of mortality before reaching breeding age or large portion of the Elven population needs to not be reproducing for some reason.

[CharonsHelper]

So for the Elven population not to expand rapidly either elves need to have seriously low fertility rates, they have lots of mortality before reaching breeding age or large portion of the Elven population needs to not be reproducing for some reason.

I think the fluff has them with low fertility rates.

ALso - since Vulcans are basically space elves, Star Trek's solution was that women were only fertile once every seven years.

[huginn]

Short lifespan doesn't mean growth. What you want is number of children per adult and chance of a child to reach adulthood. That is what dictates if a population is growing or shrinking. Only if there is some lasting long inequality, it could be worth looking at generaion length.

Short lifespan goes hand in hand with quickly maturing. After a forest fire weeds, insects , rodents recover their loses a lot faster then Oak trees, elephants or other large animals
A rat can start breeding 5 weeks after birth and a gestation period of 24 days an elephant is has to wait 10-14 years ans gestation period of about 22 months

How long is the gestation period of an orc vs that of an elf and how old are they when they can get pregnant.

[Recherché]

I'm not sure how far down you can cut the gestation period of a humanoid. We're all pretty big creatures and that takes some time and resources. Maybe if you had the babies born more underdeveloped but even then you'd have to make it up with more care and resources after birth. Alternatively if orcs have more than one young in each pregnancy it might help make up numbers but that's pretty hard on a humanoid mother.

[Balyano]

I'm not sure how far down you can cut the gestation period of a humanoid. We're all pretty big creatures and that takes some time and resources. Maybe if you had the babies born more underdeveloped but even then you'd have to make it up with more care and resources after birth. Alternatively if orcs have more than one young in each pregnancy it might help make up numbers but that's pretty hard on a humanoid mother.

Rate of twinning varies widely within humans, between ethnic groups, races, and different families, and it varies by age of the mother, with older women having a greater chance of producing twins, especially if she has had children before. In some countries you get less than 1% twins, in the USA in the 1980's it was about 2%, and in the most recent decade it is 3%, there is a town in south america where about a fifth of all pregnancies are twins.

So having orcs have an unusually high rate of twinning would easily make for high population growth. Go ahead and take them beyond the human variance, after all they are a different species. Make it where orcs always ovulate from both ovaries each time, so nearly all their pregnancies are fraternal twins. A singleton is considered to have slain their twin in utero, and therefor destined to be a great warrior. And the orcs see triplets the way we see twins. Make them highly fertile, have them have a shorter gestation period, and have them hit puberty a few years earlier, and their population growth would be even greater. All in all they would have more than twice the human population growth potential, more than enough to offset their high death rate.

And a possibility for elves, though this changes other things. Is to have elven longevity be the result of a lethal recessive gene. One copy and you live for several centuries, two copies and you are never born. This results in a quarter of elves being stillborn, half being long lived, and a quarter not having the normal elven lifespan. Could be an alternative origin for half elves. They are not half human, instead they are just looked down on as having a birth defect and are only considered ''half a person''. Or as another alternative the alleles in question are BOTH lethal recessives and only the heterozygote makes it to full term. Humans have a different allele entirely and thus a half elf carries either one of the elven variants and gets an extra century of life, just not the full 700 years or so that elves get.

[Draconi Redfir]

All i know is that Goblins reproduce in litters. i refuse to believe otherwise.

and apparently due to an in-joke among some friends and i, Gnomes reproduce by budding.

[Satinavian]

Short lifespan goes hand in hand with quickly maturing. After a forest fire weeds, insects , rodents recover their loses a lot faster then Oak trees, elephants or other large animals
A rat can start breeding 5 weeks after birth and a gestation period of 24 days an elephant is has to wait 10-14 years ans gestation period of about 22 months

How long is the gestation period of an orc vs that of an elf and how old are they when they can get pregnant.

And ? Has that led to uncontrolled growth of the rat population so that they drowned any other mammals millions of years ago ?
No, it didn't. Because most rat babies don't procreate. On average the rat population stays the same. Yes, rats can adapt faster to catastropic mass casualty events, but that doesn't even get them a higher average number as the others still simply catch up.

[Mike_G]

An easy sociological reason for low elven birth rate can be found by looking at human populations.

As societies get better at reducing infant mortality, and as women gain more education and opportunity to do things other than reproduce, birth rates go down.

In fact, the biggest factor in the drop of number of births per capita is higher average female education.

So, if Elves have high levels of gender equality, and female elves have other things they'd rather do, like research spells or become Rangers, or craft Mithral armor or whatever rather than take five years off from their chosen occupation breastfeeding, then fewer of them will want to be mothers as a primary job, and those who do might not want to lose a few decades of each century childrearing.

Orcs could be a polygamous society, where the strongest warriors have more wives, and produce more strong orc warriors. The higher loss rates for male orcs from warfare would support this, as the extra females become second and third wives to the greatest warriors.

As others have said, once you have humanoid size and anatomy, breeding like mice or rabbits becomes unrealistic.

[Max_Killjoy]

An easy sociological reason for low elven birth rate can be found by looking at human populations.

As societies get better at reducing infant mortality, and as women gain more education and opportunity to do things other than reproduce, birth rates go down.

In fact, the biggest factor in the drop of number of births per capita is higher average female education.

So, if Elves have high levels of gender equality, and female elves have other things they'd rather do, like research spells or become Rangers, or craft Mithral armor or whatever rather than take five years off from their chosen occupation breastfeeding, then fewer of them will want to be mothers as a primary job, and those who do might not want to lose a few decades of each century childrearing.

Orcs could be a polygamous society, where the strongest warriors have more wives, and produce more strong orc warriors. The higher loss rates for male orcs from warfare would support this, as the extra females become second and third wives to the greatest warriors.

As others have said, once you have humanoid size and anatomy, breeding like mice or rabbits becomes unrealistic.

Indeed, in these discussions, something to keep in mind is that just because an intelligent species CAN breed at a certain rate, doesn't mean they WILL. One only need to look at all the reasons humans might have for not pumping out children continuously, to see what might give other intelligent species a reason to hold back.

Another factor that can affect this in even fairly low-magic or "gritty" fantasy settings is the presence of more-effective contraceptives -- herbal, magical, whatever.

[huginn]

And ? Has that led to uncontrolled growth of the rat population so that they drowned any other mammals millions of years ago ?
No, it didn't. Because most rat babies don't procreate. On average the rat population stays the same. Yes, rats can adapt faster to catastropic mass casualty events, but that doesn't even get them a higher average number as the others still simply catch up.

Is makes rats extremely difficult if not impossible to exterminate. The rat population can go from just 1 pair to thousands in a year and in a couple of years that 1 pair can have millions of descendants and yes other species can catch up but the rats are well entrenched by then. BTW Rat populations are actually getting bigger in cities

Looking at population growths of rats and other species can help explain the conflicts between Orcs and longer lived species. In addition to alignment difference Orcs can adapt as fast or faster then other species where elves probably take the slowest to adapt to any major reduction in their population.
Natural disasters and wars favor Orcs

[Mechalich]

In general, pre-industrial societies were stuck in a Malthusian equilibrium - the population was generally very close to the carrying capacity of the available agricultural land and the population fluctuated around this in cycles dependent upon climate events, plague, and warfare. Very gradual improvements in agricultural technologies and the development of additional land over time through factors such as wetland drainage, terracing, and so forth allowed for slow growth. Population growth would only occur rapidly if there was some major technological change that allowed for increased agricultural production - for instance bringing potatoes back from the Americas to Europe. Since most fantasy RPG settings are in a state of long-term technological stasis populations can be assumed to be generally either stable and at or near capacity or recovering back to capacity following some calamity.

Orcs, however, likely undergo significant boom-and-bust population cycles. Since orcs are traditionally presented as poor or non-farmers they have to survive by hunting and raiding. This allows their population to grow and their hordes to pillage until they run out of resources at which point it crashes. Elves, by contrast, are likely limited in population size by their cultural taboo against clearing woodland. This severely limits the cropland available to elves and probably forces them to practice a particular form of integrated woodland agriculture that is stable over the long term but does not easily increase. Elven populations could therefore recover rapidly from disaster so long as their forests remain intact, but suffer terribly otherwise.