Chapter 14: Population Ecology Planet at capacity: patterns of population growth Lectures by Mark Manteuffel, St. Louis Community College

14.1–14.6 Population ecology is the study of how populations interact with their environments.

14.1 What is ecology?

Take-home message 14.1  Population ecology is the study of the interaction between populations of organisms and their environment, particularly their patterns of growth and how they are influenced by other species and by environmental factors.

14.2 A population perspective is necessary in ecology.

Take-home message 14.2  Most ecological processes cannot be observed or studied within an individual.  Rather, when studying them it is necessary to consider the entire group of individuals that regularly exchange genes in a particular locale.

14.3 Populations can grow quickly for a while, but not forever. There is no exception to the rule that every organic being naturally increases at so high a rate that, if not destroyed, the Earth would soon be covered by the progeny of a single pair. —Charles Darwin, The Origin of Species

In stable populations,  How many of the five million eggs that a female cod might lay over the course of her life will, on average, survive and grow to adulthood?  Who leaves more surviving offspring, a pair of elephants or a pair of rabbits?

Take-home message 14.3  Populations tend to grow exponentially, but this growth is eventually limited.

14.4 A population’s growth is limited by its environment.

Density-dependent Factors  The limitations on a population’s growth that are a consequence of population density  This ceiling on growth is the carrying capacity, K, of the environment.

Density-independent Forces  Factors that strike populations without regard for the size of the population  Mostly weather-based

How many people can earth support? Why does the answer keep increasing?

Take-home message 14.4  A population’s growth can be reduced both by density-dependent factors related to crowding and density-independent factors such as natural or human-caused environmental calamities.

14.5 Some populations cycle between large and small.

Do lemmings jump off cliffs committing suicide when their populations get too big?

Take-home message 14.5  Although the logistic growth pattern describes the general growth pattern of populations better than any other model, some populations cycle between periods of rapid growth and rapid shrinkage.

14.6 “Maximum sustainable yield” is a useful but impossible- to-implement concept.

Almost all natural resource managers working for the U.S. government fail to do their job exactly as mandated. Why?

What We Often Do Not Know…  Population carrying capacity  Number of individuals alive  Stability of carrying capacity from year to year  Which individuals to harvest

Take-home message 14.6  Based on models of population growth, it seems easy to efficiently and sustainably utilize natural resources.  In practice, however, difficulties such as estimating population size and carrying capacity complicate the implementation of such strategies.

14.13–14.15 The human population is growing rapidly.

What is the baby boom? Why is it bad news for young people today? Age pyramids reveal much about a population.

Describing Populations  In terms of the proportion of individuals from each age group  The population age distribution  Age groupings called cohorts

Take-home message  Age pyramids show the number of individuals in a population within any age group.  They allow us to estimate birth and death rates over multi-year periods.

14.14 As less-developed countries become more developed, a demographic transition often occurs.

Population growth is alarmingly slow in Sweden and alarmingly fast in Mexico. Why is there a difference?

Take-home message  The demographic transition tends to occur with the industrialization of countries.  It is characterized by an initial reduction in the death rate, later followed by a reduction in the birth rate.

14.15 Human population growth: How high can it go?

How high can it go?!  Very difficult to assess just how many resources each person needs.  Ecological footprints Evaluating how much land, how much food and water, and how much fuel, among other things, are necessary.

Take-home message  The world population is currently growing at a very high rate, but limited resources will eventually limit it, most likely at a population size between 7 and 11 billion.