Population Growth and Regulation

Question 1

Human Population Growth: A Case Study

Answer 1

Humans have a large impact on the global environment
Our population has grown explosively
Along with our use of energy and resources
Human population reached 7.7 billion in 2019 more than doubled since 1960
Our use of energy and resources has grown even more rapidly
From 1860 to 1991, the human population quadrupled in size
Energy consumption increased 93-fold
For thousands of years, our population grew relatively slowly
reaching 1 billion for the first time in 1825
Now we are adding 1 billion people every 13 years
Growth rate has slowed to about 1.18%/ year (even though the population is still growing)

Question 2

Ecological Footprint:

Answer 2

Total area of productive ecosystems required to support a population
Data used on agricultural productivity, production goods, resource use, population size, and pollution
Area required to support these activities is then estimated
In 2007:
11.9 billion hectares of productive land available globally
Average ecological footprint: 2.7 hectares
Suggests a carrying capacity of 4.4 billion
Population: 6.7 billion, a 50% overshoot of carrying capacity
Using resources in the same rate as:
U.S. citizens in 2006, carrying capacity would be 1.3 billion people
Indian citizens in 2006, carrying capacity would be 14 billion people

Question 3

Introduction:

Answer 3

“ No population can increase in size forever”
The limits imposed by a finite planet restrict a feature of all species: A growth capacity for rapid population growth
Ecologists try yo understand the factors that limit or promote population growth

Question 4

Population Dynamics:

Answer 4

The ways in which populations change in abundance over time
Population Size Changes as a Result of:
1. Birth
2. Death
3. Immigration
4. Emigration

Question 5

Population Dynamics Formula

Answer 5

LOOK AT LECTURE NOTES

Question 6

Geometric Growth

Answer 6

If a population reproduces in synchrony at discrete time periods and growth rate doesn’t change
Geometric and exponential growth can lead to rapid increases in population size
Population increase by constant proportion:
The number of individuals added is larger with each time period
Growth Rate (λ): ratio of population size in year t+1 (Nt+1) to population size in year t (Nt )
λ(landa): geometric growth rate or per capita finite rate of increase
Graph:
The blue point is exponential growth

Question 7

Geometric Growth Formula

Answer 7

LOOK AT LECTURE NOTES

Question 8

Exponential Growth

Answer 8

When individuals reproduce continuously, generations can overlap.
If a population is growing geometrically or exponentially
a plot of the natural logarithm of population size versus time will result in a straight line
dN/ dt: rate of change in population size at each instant in time
R: exponential population growth rate or per capita intrinsic rate of increase

Question 9

Exponential Growth Formula

Answer 9

LOOK AT LECTURE NOTES

Question 10

Exponential Growth pt.2

Answer 10

Much higher growth rates have been observed in many species
Western grey kangaroos (λ = 1.9)
Field voles (λ = 24),
Rice weevils (λ = 10^17)
Some bacteria double in number every 30 minutes, resulting in an annual growth rate of λ = 10^5,274.
In natural populations, favourable conditions result in exponential growth, but it CAN NOT continue indefinitely
There are limits to population growth

Question 11

Effects of Density

Answer 11

Population size can be determined by density-dependent and density-independent factors
Under ideal conditions, λ > 1 for all populations
But conditions rarely remain ideal
λ fluctuates over time

Question 12

Density-Dependent Factors

Answer 12

Decrease population size at higher population
1. Birth
2. Death
3. dispersal rates change as the density of the population changes
As density increases, birth rates often decrease, death rates increase, and dispersal (emigration) increases, all of which tend to decrease population size

Question 13

Population Regulation

Answer 13

Density-dependent factors cause population to increase when density is low and decrease when density is high.
Food, space, or other resources are in short supply and population size decreases
Density-independent factors can have larger effects on population size
Do not regulate population size
Density-dependent mortality has been observed in many populations
Ex. Egg density affects mortality in flour beetles
Ex. Population growth rates decline at high densities for grasses and water fleas

Question 14

Density-Independent Factors

Answer 14

Effects on birth and death rates are independent of the number of individuals in the population:
Temperature and precipitation, catastrophes such as floords or hurricans
Warming drys up soil and extends growing seasons and leads to less snowfall
Illegal poaching the primary cause of a decline in elephant population growth rate in Africa
Growth rate must remain above 1 to avoid extinction

Question 15

Logistic Growth

Answer 15

Population increases rapidly, then stabilizes the carrying capacity
Growth rate decreases as population nears carrying capacity
Because resources begin to run short
At carrying capacity: the growth rate is 0… the population does not change

Question 16

The Logistic Equation

Answer 16

Assumes that r declines as N increases
When densities are low, logistic growth is similar to exponential growth
As density increases, growth rate approaches 0 as population nears K
A population can be characterized by its age structure—the proportion of the population in each age class
Age structure influences how fast a population will grow
If there are many people of reproductive age (15 to 30), it will grow rapidly
A population with many people older than 55 will grow more slowly
Ex. Rapid Growth: Nigeria
Ex. Negative Growth: Japan

Question 17

The Logistic Growth Formula

Answer 17

LOOK AT LECTURE NOTES

Question 18

Survivorship Curve

Answer 18

Plot of the number of individuals from a hypothetical cohort that will survive to reach different ages.
Can be classified into three general types:
Type I: most individuals survive to old age (Dall sheep, humans)
Type II: the chance of surviving remains constant throughout the lifetime (some birds)
Type III: High death rates for young, those that reach adulthood survive well (species that produce a lot of offspring)- most organisms
Birth and death rates can vary greatly between individuals of different populations of the same species
Ex; Gambians’ survivorship depends on the season of birth
For any given species curves can differentiate a bit depending on resources given

Question 19

Life Tables

Answer 19

Can be used to predict age structure and population size
- can also be based on size or life cycle stage
Ix (survivorship): number of survivors divided by the original number of individuals
Fx (fecundity): average number of offspring a female will have at age x
If survival or fecundity rates change, the population growth rate, and age distribution will change
In some species, age is not important, reproduction is more dependent on size (related to growth conditions) than age
Ex. many plants