Unit 3– Populations
Module 15: Generalist and specialist species, K and r-selected species, and survivorship curves
Generalists exist under a broad range of conditions while specialists exist under a narrow range
Species have different reproductive strategies
Population/ intrinsic growth rates are the number of offspring an individual can produce in a given time period minus the deaths
Biotic potential: maximum potential for growth with unlimited resources
K-selected species: with low intrinsic growth rates, usually longer gestational periods and longer lifespans living in stabler environments (elephants, humans)
Carrying capacity: the amount of individuals that can be supported by the ecosystem
Population overshoot/ dieback— some go over the carrying capacity and then die back
r-selected species: high intrinsic growth rates, often overshoot populations (overshoot and dieback), smaller animals with more offspring that have relatively low competition and smaller lifespans (rats, flies)
Species exhibit three distinctly different survivorship curves
Survivorship curve: graph that represents patterns of survival as a function of age
Type 1: pattern where there is high survival throughout most of the life span, but individuals die in large numbers as they approach old age (K-selected)
Type 2: patterns where there is a relatively constant decline in survivorship
Type 3: patterns where where there is low survivorship with few individuals reaching adulthood (r-selected)
Module 16: Carrying capacity, population growth, and resource availability
Density dependent factors: factors that depend on the size of the population that influence an individual’s probability of survival and reproduction
Density independent factors: factors that have the same effect on an individual’s probability of survival and reproduction at any population size
The exponential growth model describes populations that continuously increase, and is the first step in explaining carrying capacity
Fecundity: ability to produce offspring
Exponential growth model: a growth model that estimates a population’s future size after a period of time based on the biotic potential and number of reproductions individuals (produces a J-shaped curve)
The logistic growth model describes populations that are limited by the carrying capacity
S-shaped curve
Slows as the population approaches the carrying capacity
Growth early is exponential, begins to slow, and then eventually falls to 0 as it reaches carrying capacity
Density-dependent factors: competition over limiting resources impact the size of a population
Density independent factors: disasters, ice ages, etc.
Carrying capacity can impact ecosystem diebacks
After things like food supply are exhausted, there are diebacks and populations experience oscillations between overshoot and diebacks
Higher predator populations mean low prey, and low prey means less prey to feed predators
Isle royale case: wolves died of a virus, their moose prey increased— and then experienced dieback
Populations change when a resource base shrinks
Resources sustain animals
Module 17– Age structure diagrams and total fertility rates
The total number of people the earth can support is not known
We can innovate to our challenges but a lot of resources are exhaustible
Many factors drive human population change
Social and cultural factors in population change
Impacted by births, deaths, and migration
Help determine crude birth and death rates
Life expectancy (depends on country, industrialization)
Infant and child mortality rates
Depends on socioeconomic status and access to nutrition and healthcare (environmental justice addresses these inequities)
Aging and disease also regulate populations
Age structure diagrams describe how populations are distributed across age ranges and provide insights into future population changes
A population pyramid illustrates a rapidly growing population
A column shaped diagram indicates population stability
In some developed countries, the population is declining (the bottom is less than the top)
When largest part is in the middle, it suggests that population decline will happen
Population momentum: continued population growth after growth reduction measures have been implemented, like in China
Age when having the first child and access to family planning the total fertility rate
Places where young moms give birth have a higher total fertility rate
Many factors influence it, women who are more educated usually learn about birth control and have a smaller tfr
Replacement level fertility is the TFR that leads to a stable population
Replacement level= the total amount of fertility that offsets the average number of deaths to maintain the current population size
Usually replacement levels of greater than 2.1 replace the population
Help indicate/ are also indicated by age structure diagrams
Module 18– Human population dynamics and the demo-graphic transition
Social, political, and economic factors contribute to population growth and decline
Limiting population growth in china: the one-child policy has decreased population size And slowed tfr
Factors of global population change: crude birth rate, tfr, infant mortality, marriage, family planning, nutrition, death rate
Some are density-dependent factors
Largest cities in the world: more people are projected to live in urban areas
The rule of 70 allows you to calculate doubling time
Doubling time= the number of years it takes a population to double
Doubling time (years) = 70/ growth rate (percent)
The demographic transition is a model that predicts population changes as countries develop
Theory of demographic transition: a country moves from high to lover birth and death rates as development occurs
Stage 1: preindustrial (slow) population growth, birth and death rates are high
Stage 2: industrializing (rapid) growth where death rates sink
Stage 3: industrialized (stable) growth, where birth rates sink alongside death rates
Stage 4: postindustrial (declining) population growth, where birth rates sink alongside death rates
Population and consumption influence the environment different, depending on the country
Many countries with high populations use a lot of resources
IPAT equation: impact= population affluence technology