© 2015 Pearson Education, Inc. POPULATION STRUCTURE AND DYNAMICS

© 2015 Pearson Education, Inc 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. rely on the same resources, influenced by the same environmental factors, interact and breed with one another.

© 2015 Pearson Education, Inc Population ecology is the study of how and why populations change 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.

© 2015 Pearson Education, Inc Density and dispersion patterns are important population variables Population density is the number of individuals of a species per unit area or volume. Examples: the number of oak trees per square kilometer in a forest or the number of earthworms per cubic meter in forest soil.

© 2015 Pearson Education, Inc Density and dispersion patterns are important population variables The dispersion pattern of a population refers to the way individuals are spaced within their area. Clumped: unequal distribution of resources Uniform: individuals are interacting and equally spaced Random: population spaced in without a pattern

© 2015 Pearson Education, Inc Life tables track survivorship in populations Life tables track survivorship, the chance of an individual in a given population surviving to various ages.

© 2015 Pearson Education, Inc Survivorship Curves Survivorship curves plot survivorship as the proportion of individuals from an initial population that are alive at each age. Type I Type II Type III

© 2015 Pearson Education, Inc Population Growth Models The rate of population increase under ideal conditions is called exponential growth. G = population growth rate N = population size r = per capita rate of increase (the average contribution of each individual to population growth). Eventually, limiting factors will restrict population growth.

© 2015 Pearson Education, Inc Population Growth Models The logistic growth model is a description of idealized population growth that is slowed by limiting factors as the population size increases. K = carrying capacity, the maximum population size a particular environment can sustain.

© 2015 Pearson Education, Inc. Figure 36.4c Time Number of individuals (N) G = rN (K − N) K K 0

© 2015 Pearson Education, Inc Limits to population growth At higher population densities, density-dependent limiting factors result in declining births and/or increases in deaths. Limiting factors may include food, nutrients, or nesting sites.

© 2015 Pearson Education, Inc Limits to population growth Density-independent factors are unrelated to population density. These may include fires, storms, habitat destruction by human activity, or seasonal changes in weather

© 2015 Pearson Education, Inc “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.

© 2015 Pearson Education, Inc EVOLUTION CONNECTION: Evolution shapes life histories The traits that affect an organism’s schedule of reproduction and death make up its life history. Key traits include: age of first reproduction, frequency of reproduction, number of offspring, and amount of parental care.

© 2015 Pearson Education, Inc EVOLUTION CONNECTION: Evolution shapes life histories Populations with r-selected life history traits (maximize reproductive success) grow rapidly in unpredictable environments, where resources are abundant, have a large number of offspring that develop and reach sexual maturity rapidly, and offer little or no parental care.

© 2015 Pearson Education, Inc EVOLUTION CONNECTION: Evolution shapes life histories Populations with K-selected traits (density dependent) tend to be long-lived animals (such as bears and elephants) that develop slowly and produce few, but well-cared-for, offspring and maintain relatively stable populations near carrying capacity.

© 2015 Pearson Education, Inc EVOLUTION CONNECTION: Evolution shapes life histories Life strategies & survivorship curves Most species fall between these two extremes.

© 2015 Pearson Education, Inc.

You should now be able to 1.Define a population and population ecology. 2.Define population density and describe different types of dispersion patterns. 3.Explain how life tables are used to track mortality and survivorship in populations. 4.Compare Type I, Type II, and Type III survivorship curves. 5.Describe and compare the exponential and logistic population growth models, illustrating both with examples.

© 2015 Pearson Education, Inc. You should now be able to 6.Explain the concept of carrying capacity. 7.Describe the factors that regulate growth in natural populations. 8.Define boom-and-bust cycles, explain why they occur, and provide examples. 9.Explain how life history traits vary with environmental conditions and with population density. 10.Compare r-selection and K-selection and indicate examples of each.

© 2015 Pearson Education, Inc. You should now be able to 11.Describe the major challenges inherent in managing populations. 12.Explain how the structure of the world’s human population has changed and continues to change. 13.Explain how the age structure of a population can be used to predict changes in population size and social conditions. 14.Explain the concept of an ecological footprint. Describe the uneven reliance upon natural resources in the world.

© 2015 Pearson Education, Inc. Figure 36.UN01 Percentage of maximum life span Percentage of survivors I II III

© 2015 Pearson Education, Inc. Figure 36.UN02 Age –79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0– Male Female Population in millions Total population size = 83,366,836 Estimated population in millions 2012 Total population size = 114,975,406 Male Female

© 2015 Pearson Education, Inc. Figure 36.UN03 G = rN (K − N) K

© 2015 Pearson Education, Inc. Figure 36.UN04 Time I IIIIIIV Birth or death rate

© 2015 Pearson Education, Inc. Figure 36.UN05