Lecture 7 - Human Population Ecology

why is extrapolating data beyond the range of data always dangerous

because you’re assuming that everything happening beyond the range of data is the same as everything happening within

logistic model

allows no overshoots because it gradually saturates then plateaus as you approach K and it assumes that r and K are constants

what is a very simple possible hypothesis for density dependence?

logistic growth

when does carrying capacity (K) change?

when density dependence acts on the population

what factors is growth rate dependent on?

depends on a balance of fertility rates and mortality

what societal changes causes growth rate to increase?

changes in health care regarding first vaccination and hygiene, antibiotics and insecticides

what societal changes caused carrying capacity to increase?

changes in agriculture regarding genetics, machines, fertilizers and biocides

Rt

measures time lag

what is the current trajectory of population growth?

that it is growing exponentially although growth percent is lower than it was before

high momentum

they have a broad-based age pyramid so even if the whole population growth rate goes to zero it will continue to expand because it has an excess of children

low momentum

majority of the population is in their mid to high 40s meaning fewer children are of reproductive age causing growth rate to be slower and stop if it reaches zero

population momentum toy example

there are two populations, N=20, there are 2 children per female and there is a 50-50 sex ratio

population 1 results

females ranged from 40 to 80+, so 60 - 80 would have died 20 yrs later and 40-60 will be beyond reproductive age so they will end up having the lower growth rate momentum and therefore a smaller population

population 2 results

range from 0 to 80 so most 0 to 40 will still be alive in 20 yrs and have had children and be of reproductive age so they have a higher momentum and be bigger in population size after 20 yrs

Antoni van Leewenhoek

estimated land area of globe, applied human density of crowded holland and said it capped at 13.4 billion

• first to estimate human capacity of earth

demographic transition model stage 1 pre industrial

birth and death rates are both high and growth rate is near zero

demographic transition model stage 2

death rates drop due to sanitation and vaccination but birth rates stay high so there is a bloom in population

demographic transition model stage 3

birth rates fall due to contraception, later marriage, changing values and growth rates slows

demographic transition model stage 4

birth and death rates equilibrate and r is near zero again

dependency ratios

the number of children and older people ratio to the working age population

why is retirement at age 65?

designed for when not many people lived long enough to collect retirement suggested by Otto von Bismarck, chancellor of Germany in 1880

what causes fertility to decline?

• government policy

• voluntary by parents motivated for greater survival of children, too expensive to raise children, society providing more security in old age and worry about overpopulation

how is decline in fertility made possible?

by more availability of contraception/abortion and postponement of marriage/family

how do we determine where human populations are growing the fastest?

by focusing on resource availability rather than birth rate but parts of the world consuming the most are different from parts of the world with most population growth

GDP

gross domestic product

in what event could smooth demographic transition s occur in developing countries

due to women reducing births when information and contraception becomes available

in what event will smooth demographic transitions not occur?

if social structural and health care are overwhelmed so mortality rates might not stay down cause, ex campaign against condoms so higher frequency of HIV infections

why are population issues not as relevant as they used to be?

because tradeoffs seem far in the future (benefits now, costs later)

• left: Rich countries telling poor countries to restrict reproduction is morally wrong

• right: birth control is morally wrong