Ecology of Populations Chapter 46

Chapter Outline Scope of Ecology Population Density and Distribution Population Growth Models Survivorship Curves Age Distributions Regulation of Population Size Life History Patterns Human Population Growth Environmental Impact

Scope of Ecology Ecology – what is it? Definitions: Habitat - Place where an organism lives. Population - All the organisms within an area belonging to the same species. Community - All various populations interacting at same locale. Ecosystem – A collection of communities

Ecological Levels

Density and Distribution of Populations Population Density - Number of individuals per unit area or volume. Population Distribution - Pattern of dispersal of individuals within the area of interest.

Uniform Distribution EXAMPLE

Random Distribution EXAMPLE

Clumped Distribution EXAMPLE

Characteristics of Populations They tend to grow Intrinsic Rate of Natural Increase (r)

Population Growth Models Exponential Growth Biotic Potential Environmental Resistance

Exponential Growth Curve

Logistic Growth Logistic growth—indicated by an S-shaped curve Difference between logistic and exponential due to environmental resistance

Logistic Growth

Carrying Capacity Carrying Capacity is the maximum number of individuals of a given species the environment can support. The closer the population to the carrying capacity, the greater the environmental resistance. Biotic potential is having full effect and birthrate is a maximum during exponential growth.

St. Paul Island Reindeer Population

Mortality Patterns Cohort --- all the members of a population born at the same time. Survivorship---the probability of newborn individuals of a cohort surviving to particular ages. Illustrated by Survivorship Curves A cohort is composed of all the members of a population born at the same time. Survivorship is the probability of newborn individuals of a cohort surviving to particular ages. Survivorship Curves

Survivorship Curves NOTE: Looks at life expectancy as a percentage of maximum life span. Type I---long lived, die older, later in reproductive cycle EX? Type II—die at a constant rate Type III—Die young

Survivorship Curves Some examples

Age Distributions What proportion of population is in each cohort? Age Structure Diagrams Populations differ according to what proportion of the population falls in each age category. At least three structures possible. Increasing Stable Decreasing

U.S. Age Distributions The United States –note the Baby Boomers

Regulation of Population Size Density - Dependent Factors Density - Independent Factors

Factors That Affect Population Size Density Dependent Factors 1. Competition Intraspecific Interspecific Predation Parasitism 4. Disease

Factors That Affect Population Size Density Independent Factors Abiotic factors 2. Unpredictable, catastrophic events

Life History Patterns r - Strategists (Opportunistic) Remember r=reproduction

Life History Patterns k - Strategists (Equilibrium) Remember k=Karrying kapacity

Human Population Growth Human population has had an exponential growth pattern. Doubling time currently estimated at 53 years. Population Size 1800 1 Billion 1930 2 Billion 1960 3 Billion 2000 6 Billion

World Population Growth

Country Development More-Developed Countries (MDCs) GR=0.1% Less-Developed Countries (LDCs) GR= 1.6% LDC population expected to increase from 5-8b by 2050

Age Distributions Age Structure Diagrams divide populations into three age groups. Pre-Reproductive Reproductive Post-Reproductive

The Demographic Transition Stage I: high birthrates and death rates Stage II: continued high birthrates, declining death rates Stage III: falling birthrates and death rates, eventually stabilizing

More-Developed Countries

Less-Developed Countries

Age Distribution of the World’s Population Population Structures by Age and Sex, 2005 Millions Less Developed Regions More Developed Regions Age 80+ 75-79 70-74 65-69 60-64 55-59 50-54 45-49 40-44 35-39 30-34 25-29 20-24 17-19 10-16 5-9 0-4 Male Female Male Female Source: United Nations, World Population Prospects: The 2002 Revision (medium scenario), 2003.

Figure 7.2 World Population Distribution by Region, 1998 and 2050

Environmental Impact Measured in terms of: Population Size Resource Consumption Per Capita Resultant Pollution

Environmental Impact

Review Scope of Ecology Population Density and Distribution Population Growth Models Survivorship Curves Age Distributions Regulation of Population Size Life History Patterns Human Population Growth Environmental Impact