Class Notes (808,145)
Canada (493,092)
Biology (6,677)
Hugh Henry (242)
Lecture 9

Lecture 9: "Population Growth & Reproduction"

4 Pages
Unlock Document

Western University
Biology 2483A
Hugh Henry

Ecology Lecture No. 9: Population Growth & Reproduction Tuesday October 9 , 2012 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 slowly, 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: -An ecological footprint is the total area of productive ecosystems required to support a population. It 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: 11.9 billion hectares of productive land was available globally, the average ecological footprint was 2.6 hectares. This suggests a carrying capacity of 4.6 billion and as we are a population with over 6.6 billion, a 40% overshoot of carrying capacity is thereby estimate for humanity. Introduction To Population Growth: -Recall that one of the ecological maxims is “No population can increase in size forever.” The limits imposed by a finite planet restrict a feature of all species – the capacity for rapid population growth. Ecologists try to understand the factors that limit or promote population growth. Life Tables: -A life table is a summary of how survival and reproductive rates vary with age. Information about births and deaths is essential to predict future population size. Life table data for the grass Poa annua were collected by marking 843 naturally germinating seedlings and then following their fates over time (relatively simple with immobile organisms). -As the generations progressed, four key patterns were noted in the population: the species declined in number (N), a decrease in survival rate S (xhance that an individual of age x will survive to age x + 1), a decrease in survivorship I xproportion of individuals that survive from birth to age x), and an eventual decrease in fecundity F (average number of offspring a female will have at age x). 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 is stored from the previous year is depleted) had lower survivorship than those born at other times of the year (when this drought situation was not present). In some species, age is not important. For example, 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 (when age is a weak indicator of actual growth). Survivorship Curves: -A survivorship curve is the plot of the number of individuals from a hypothetical cohort that will survive to reach different ages. Survivorship curves can be classified into three general types: Type I (most individuals survive to reach old age), Type II (the chance of surviving remains constant throughout a lifetime and Type III (young have high death rates, but those that reach adulthood survive well). Age Structure: -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 (around 15 to 30), it will grow rapidly. For example, a population with many people older than 55 will grow more slowly. -There are three primary population pyramids present when examining age structures: Rapid growth (a population with youths in excess and a lack of elderly individuals), zero growth (a population where youths and the elderly have relatively the same proportion) and negative growth (a population where there is an excess of elder individuals and a lack of youths). -Life table data can be used to predict age structure and population size for future generations. To predict population size for the following year, calculate: the number of individuals that will survive to the next time period and the # of offspring those survivors will produce in the next time period. Growth Rate (λ): -Growth rate (λ) is the ratio of population size in year t + 1 (N t+1o population size in year t (N ).tThe equation is listed as follows: λ = N t+1/ Nt -If survival or fecundity rates change, the population growth rate will change. Fo
More Less

Related notes for Biology 2483A

Log In


Don't have an account?

Join OneClass

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

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
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.

Add your courses

Get notes from the top students in your class.