Class Notes (809,487)
Biology (6,677)
Hugh Henry (242)
Lecture 9

# Lecture 9 - Population Growth and Regulation

5 Pages
32 Views

School
Western University
Department
Biology
Course
Biology 2483A
Professor
Hugh Henry
Semester
Fall

Description
LECTURE 9: POPULATION GROWTH AND REGULATION Human Population Growth: A Case Study  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 6.8 billion in 2010, more than double the number of people in 1960  Our use of energy and resources has grown even more rapidly. From 1860 to 1991, human population quadrupled in size, and energy consumption increased 93-fold  For thousands of years, our population grew relatively slow, reaching 1 billion for the first time in 1825. Now we are adding 1 billion people every 13 years.  Growth rate has slowed recently, to about 1.18% per year, and continues to slow  By 2080, it is predicted there will be roughly 9-10 billion people on Earth  Is 10 billion above the carrying capacity of the human population?  Many people have tried to estimate human carrying capacity.  Researchers must make assumptions about how people would live and how technology would influence our future.  Estimates range from fewer than 1 billion to more than 1,000 billion.  Ecological footprint – total area of productive ecosystems required to support a population  Uses data on agricultural productivity, production of goods, resource use, population size, and pollution  The area required to support these activities is then estimated.  In 2006: o 11.9 billion hectares of productive land available globally o Average ecological footprint: 2.6 hectares o Suggests a carrying capacity of 4.6 billion o Population: 6.6 billion, a 40% overshoot of carrying capacity  If everyone in the world used resources at the same rate as: o U.S. citizens in 2006, carrying capacity would be 1.3 billion people o Indian citizens in 2006, carrying capacity would be 14 billion people  Ecological footprint is much lower in India, compared to that of the U.S. Introduction  One of the ecological maxims is: o “No population can increase in size forever”  The limits imposed by a finite planet restrict a feature of all species: a capacity for rapid population growth  Ecologists try to understand the factors that limit or promote population growth  Life table – summary of how survival and reproductive rates vary with age  Information about births and deaths is essential to predict future population size  Life data table for the grass Poa annua were collected by marking 843 naturally germinating seedlings and then following their fates over time  S = survival rate – chance that an individual of age x x will survive to age x + 1 o Survival rate is highest when the species is young in this case, but it decreases as they get older o Could increase in other cases  x = survivorship – proportion of individuals that survive from birth to age x  Fx= fecundity – average number of offspring a female will have at age x  Birth and death rates can vary greatly between individuals of different ages  Gambians’ survivorship depends on the season of birth  Gambians born during the “hungry season” (when food stored from the previous year is depleted) had lower survivorship than those born at other times of the year  In some species, age is not important o e.g. in many plants, reproduction is more dependent on size (related to growth conditions) than age  Life tables can also be based on size or life cycle stage  Survivorship curve – plot of the number of individuals from a hypothetical cohort that will survive to reach different ages o Cohort – group of organisms born at the same time  Survivorship curves can be classified into three general types: o Type I: most individuals survive to old age (Dall sheep, humans)  Not a linear scale, number of survivors = log scale o Type II: the chance of surviving remains constant throughout the lifetime (some birds) o Type III: high death rates for young, those that reach adulthood survive well (species that produce a lot of offspring)  Most commonly seen in nature  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  If the population starts with 100 individuals: o Age class 0 (n ) = 20 individuals 0 o Age class 1 1n ) = 30 individuals o Age class 2 2n ) = 50 individuals  To predict population size for the following year, calculate: o The number of individuals that will survive to the next time period o The number of offspring those survivors will produce in the next time period  Growth rate (λ) – ratio of population size in year t +t+1(N ) to population size
More Less

Related notes for Biology 2483A

OR

Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Join to view

OR

By registering, I agree to the Terms and Privacy Policies
Just a few more details

So we can recommend you notes for your school.