Question for Thought How would you describe the population of elephants below to a classmate? What kinds of information would you use?

Population ecology is the study of how and why populations change A population is a group of individuals of a single species that occupy the same general area. Individuals in a population rely on the same resources, are influenced by the same environmental factors, and are likely to interact and breed with one another. © 2012 Pearson Education, Inc. 2

What do population ecologist look at? Population ecology is concerned with the changes in population size and factors that regulate populations over time. Populations increase through birth and immigration to an area and decrease through death and emigration out of an area. © 2012 Pearson Education, Inc. 3

Population Density and Dispersion Population density is the number of individuals of a species per unit area or volume. Examples of population density include the number of oak trees per square kilometer in a forest or number of earthworms per cubic meter in forest soil. The dispersion pattern of a population refers to the way individuals are spaced within their area. © 2012 Pearson Education, Inc. 4

3 Different Dispersion Patterns In a clumped pattern resources are often unequally distributed and individuals are grouped in patches. In a uniform pattern, individuals are most likely interacting and equally spaced in the environment. In a random pattern of dispersion, the individuals in a population are spaced in an unpredictable way. © 2012 Pearson Education, Inc. 5

3 Different Dispersion Patterns Clumped Uniform Random Figure 36.UN05 Testing Your Knowledge, question 12 6

Population size (N) Time (months) 500 450 400 350 300 250 200 150 100 Figure 36.4A 500 450 400 350 Population size (N) 300 250 200 Figure 36.4A Exponential growth of rabbits 150 100 50 1 2 3 4 5 6 7 8 9 10 11 12 Time (months) 7

Breeding male fur seals Figure 36.4B 10 8 Breeding male fur seals (thousands) Figure 36.4B Growth of a population of fur seals 6 4 2 1915 1925 1935 1945 Year 8

Carrying Capacity Most populations follow the logistic curve because eventually the carrying capacity is reached. The carrying capacity is the largest size of a population that the environment can sustain. Carrying capacity is represented by K. Once reached, it will usually stay there. © 2012 Pearson Education, Inc. 9

Most species fall between these two extremes. R vs K Selection Theory r-selected species produce many offspring and have little or no parental care grow rapidly in unpredictable environments. K-selected species raise fewer offspring and a lot of parental care maintain relatively stable populations. Most species fall between these two extremes. © 2012 Pearson Education, Inc. 10

Some populations have “boom-and-bust” cycles Some populations fluctuate in density with regularity. Boom-and-bust cycles may be due to food shortages or predator-prey interactions. © 2012 Pearson Education, Inc. 11

There are three main types of survivorship curves. Survivorship curves plot survivorship as the proportion of individuals from an initial population that are alive at each age. There are three main types of survivorship curves. Type I Type II Type III © 2012 Pearson Education, Inc. 12

Percentage of survivors (log scale) Figure 36.3 100 I 10 Percentage of survivors (log scale) II 1 III Figure 36.3 Three types of survivorship curves 0.1 50 100 Percentage of maximum life span 13

Analyzing the Age of Individuals in a Population The age structure of a population is the proportion of individuals in different age groups and affects the future growth of the population. © 2012 Pearson Education, Inc. 14

Analyzing the Age of Individuals in a Population