Lecture 9 Flashcards
1
Q
Human Pipulation Growth
A
- Humans have a large impact on the global environment
- Our population has grown explosively
- Along with our use of energy and resources
- 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
2
Q
Ecological Fooptprint
A
- 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
3
Q
Introduction
A
- “no population can increase in size forever”
4
Q
A Growth Capacity for Rapid Population Growth
A
- The limits imposed by a finite planet restrict a feature of all species
5
Q
What do Ecologists try to Understand
A
- try to understand the factors that limit or promote population growth
6
Q
Population Dynamics
A
- The ways in which populations change in abundance over time
7
Q
Population Size Changes as a Result of
A
- Birth
- Death
- Immigration
- Emigration
8
Q
Equations:
A
- see notes
9
Q
Geometric Growth
A
- 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
10
Q
Population Increase by Constant Proportion
A
- The number of individuals added is larger with each time period
11
Q
Growth Rate (λ)
A
- ratio of population size in year t+1 (Nt+1) to population size in year t (Nt )
12
Q
Lamda (λ)
A
- geometric growth rate or per capita finite rate of increase
13
Q
Exponential Growth
A
- 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
14
Q
dN/ dt
A
- rate of change in population size at each instant in time
15
Q
R
A
- exponential population growth rate or per capita intrinsic rate of increase
16
Q
In Natural Populations
A
- favourable conditions result in exponential growth, but it CAN NOT continue indefinitely
- There are limits to population growth
17
Q
Effects of Density
A
- Population size can be determined by density-dependent and density-independent factors
18
Q
Effects of Density Under Ideal Conditions
A
- λ > 1 for all populations
- But conditions rarely remain ideal
- λ fluctuates over time
19
Q
Density-Dependent Factors
A
- Decrease population size at higher population
- Birth
- Death
- dispersal rates change as the density of the population changes
20
Q
As density increases
A
- birth rates often decrease
- death rates increase
- dispersal (emigration) increases
- all of which tend to decrease population size
21
Q
Population Regulation
A
- 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
22
Q
Density- Independent Factors
A
- 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
- Temperature and precipitation, catastrophes such as floords or hurricans
- Illegal poaching the primary cause of a decline in elephant population growth rate in Africa
23
Q
Logistic Growth
A
- Population increases rapidly, then stabilizes the carrying capacity
- Growth rate decreases as population nears carrying capacity ( since resources begin to run short)
24
Q
At Carrying Capacity
A
- the growth rate is 0
- the population does not change
25
The Logistic Equation
- 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
26
Age Structure
- characterizes a population
- the proportion of the population in each age class
27
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
- Rapid Growth: Nigeria
- Negative Growth: Japan
28
Survivorship Curve
- Plot of the number of individuals from a hypothetical cohort that will survive to reach different ages
29
Survivorship Curve can be Classified into 3 General Types
1. Type I
2. Type II
3. Type III
- Birth and death rates can vary greatly between individuals of different populations of the same species
30
Type I
- most individuals survive to old age - Ex. Dall sheep, humans
31
Type II
- the chance of surviving remains constant throughout the lifetime
Ex. some birds
32
Type III
- High death rates for young, those that reach adulthood survive well (species that produce a lot of offspring)
Ex. most organisms
33
Life Tables
- Can be used to predict age structure and population size
- can also be based on size or life cycle stage
34
Ix (survivorship)
- number of survivors divided by the original number of individuals
35
Fx (fecundity)
- average number of offspring a female will have at age x
36
If Survival or fecundity Rates Change
- the population growth rate, and age distribution will change
37
In some Species, Age is not Important
- reproduction is more dependent on size (related to growth conditions) than age
Ex. many plants
