false

Class Notes
(836,147)

Canada
(509,656)

University of Toronto Scarborough
(31,491)

Biological Sciences
(3,949)

BIOB50H3
(258)

Marc Cadotte
(64)

Lecture 7

Unlock Document

Biological Sciences

BIOB50H3

Marc Cadotte

Winter

Description

Lecture 7-8: Population Growth and Regulation
Factors Affecting Human Population
▯ - you have to understand how population change over time
▯ - Very recently, human population has exploded in size
▯ - The reason for this has to do with technological innovations, industrial revolution, modern medicine, etc
▯ - However, the Bubonic plague caused a greater decrease in population
▯ - In 1975, the population was growing at an annual rate of nearly 2%. At this rate, a population will double in
▯ size every 35 years. If this growth rate were sustained, we would reach 32 billion by 2080
▯ - But growth rate has slowed recently, to about 1.21% per year. If this rate is maintained, there would be
▯ roughly 16 billion people on Earth in 2080. Could Earth support 16 billion people?
Introduction
▯ - One of the ecological maxims is: “No population can increase in size forever”
▯ - If no one can increase in size forever, what does that mean for the human population?
▯ ▯ - human population has declined
▯ ▯ - Through maybe, women waiting longer to reproduce, women getting more educated
▯ ▯ - we must understand why population grows
Life Tables
▯ - Life tables show how survival and reproductive rates vary with age, size, or life cycle ages
▯ - Information about births and deaths is essential to predict trends or future population size
▯ - Data for a life table for the grass Poa annua were collected by marking 843 naturally germinating seedlings
▯ and then following their fates over time
▯ - Sx= age-speciﬁc survival rate: chance that an individual of age x will survive to age x +1
▯ - x = survivorship: proportion of individuals that survive from birth (age 0) to age x
▯ - Fx= fecundity: average number of offspring produced by a female while she is of age x
▯ - Hereʼs the table
▯ - A cohort life table follows the fate of a group of individuals all born at the same time (a cohort). This is usually
▯ hard to do since you gave to follow individuals throughout time
▯ - In some cases, a static life table can be used- survival and reproduction of individuals of different ages during
▯ a single time period are recorded
▯ - A survivorship curve is a plot of the number of individuals from a hypothetical cohort that will survive to reach
▯ different ages
▯ ▯ - Survivor ship curves can be classiﬁed into 3 general types
▯ ▯ - Type I: high survival rate and then decline with old age
▯ ▯ - Type II: linear survival rate
▯ ▯ - Type III: rapid decline. Once you have made it through
▯ ▯ childhood, you have a higher chance of surviving
Age Structure
▯ - Life table data can be used to project the future age structure, size, and growth rate of a population
▯ - A population can be characterized by its age structure- the proportion of the population in each age class
▯ - Age structure inﬂuences whether a population will increase or decrease in size
▯ - Three types:
▯ ▯ - Rapid growth (eg. Guatemala, Nigeria, Saudi Arabia)
▯ ▯ most young people are heading to the reproductive age ▯ ▯ - Zero growth (eg. Spain, Austria, Greece)
▯ ▯ have relatively the same people dying as are
▯ ▯ being born
▯ ▯ - Negative growth (eg. Germany, Bulgaria, Italy)
▯ ▯ more old people than younger people
▯ - Life table data can be used to predict age structure and population size
▯ -
▯ - Assume the population starts with 100 individuals
▯ ▯ Age class 0 = 20 individuals
▯ ▯ Age class 1 = 30
▯ ▯ Age class 2 = 50
▯ - Two things must be calculated:
▯ ▯ 1. Number of individuals that will survive to the next time period
▯ ▯ 2. Number of newborns those survivors will produce in the next time period
▯ - Results from this shows:
▯ ▯ - there is a lot of ﬂuctuation since there is not a good age representation
▯ ▯ - the population is increasing/growing
▯ ▯ - Refer to graph above
▯ - The growth rate (⋋) can be calculated as the ration of the population size in year t + 1 (N ) to the t+1
▯ population size ▯in year t (N) t
▯ - Equation: ⋋ = N /N t+1 t
▯ ▯ - If your population is growing then the top number will always be greater then the denominator
▯ ▯ - lambda (⋋) will be greater than 1
▯ ▯ - When age-speciﬁc survival and fecundity rates are constant over time, the population ultimately grows at a
▯ ﬁxed rate
▯ - The age structure does not change from one year to the next- it has a stable age distribution
▯ - In the example, the stable age distribution is 0.73 in age class 0, 0.17 in age class 1, and 0.10 in age class 2
▯ - Any factor that alters survival or fecundity of individuals can change the population growth rate
▯ - Two things greatly affect population growth: survival and production
▯ - This can be used to develop management practices that decrease pest populations or increase an
▯ endangered population
▯ - Example: Loggerhead sea turtles are threatened by development on nesting sites and commercial ﬁshing
s t e ▯ n
▯ - Reasons for the decline on the turtle population:
▯ ▯ - ﬁsheries, development of resorts that impose on their laying space, being eaten by predators
▯ ▯ - scientist are trying to ﬁnd ways to increase survival rates. Some people have been focusing on
▯ ▯ eggs, but others are focusing on trying to get the nets to have holes so turtles can be released
▯ - Even if hatching survival were increased to 100%, loggerhead populations would continue to decline
▯ - Instead, population growth rate was most responsive to decreasing mortality of older juveniles and adults
▯ - Shrimping resulted in 5,000 to 50,000 loggerhead deaths per year!
Exponential Growth
▯ - Populations can grow exponentially when conditions are favourable, but exponential growth cannot continue
▯ indeﬁnitely ▯
▯ - In general, populations can grow rapidly whenever individuals leave an average of more than one offspring
▯ over substantial periods of time
▯ - If a population reproduces in synchrony at regular time intervals (discrete time periods), and growth rate
▯ remains the same, geometric growth occurs
▯ - The population increases by a constant proportion, so the number of individuals added to the population
▯ becomes larger with each time period
▯ - When we use a life table, we are assuming the population is increasing in intervals (Geometric growth), the
▯ population is growing by a constant amount
▯ - Geometric growth:
▯ ▯ N t+1 = ⋋N t
▯ ▯ ⋋: geometric growth rate; also known as the (per capita) ﬁnite rate of increase
f ▯ ▯ I ⋋ = 1 the population is replacing itself and not growing
▯ - Geometric growth rate predicts exponential increase in population size
t
▯ - Geometric growth can also be represented by N = ⋋N t 0
▯ ▯ - N 0ives you the starting population size today
▯ - This predicts the size of the population after any number of discrete time periods
▯ - In any species, indivi

More
Less
Related notes for BIOB50H3

Join OneClass

Access over 10 million pages of study

documents for 1.3 million courses.

Sign up

Join to view

Continue

Continue
OR

By registering, I agree to the
Terms
and
Privacy Policies

Already have an account?
Log in

Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.