© 2015 Pearson Education, Inc. PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE TAYLOR SIMON DICKEY HOGAN Chapter 36 Lecture by Edward J. Zalisko Population Ecology

© 2015 Pearson Education, Inc. Introduction Has parental care evolved by natural selection? Consider parental investment, the time and energy expended on offspring. The females of some species carry the embryos internally and give birth after they have hatched. Some fish do not provide any form of parental care and instead invest in quantity, producing millions of eggs at a time.

© 2015 Pearson Education, Inc. Introduction In a small Mediterranean species known as the peacock wrasse, the largest males build seaweed nests, where they court and mate with females, fertilize a nest full of eggs, and then lose interest in mating and guard the nest from predators. Females must search for a large nesting male, spending time and energy, to increase her chances of reproductive success.

© 2015 Pearson Education, Inc. Figure

© 2015 Pearson Education, Inc. Figure Chapter 36: Big Ideas Male Female 1989 The Human Population Population Structure and Dynamics

© 2015 Pearson Education, Inc. P OPULATION S TRUCTURE AND D YNAMICS

© 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. 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.

© 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 of population density include the number of oak trees per square kilometer in a forest or the 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.

© 2015 Pearson Education, Inc Density and dispersion patterns are important population variables Dispersion patterns can be clumped, uniform, or random. In a clumped dispersion pattern, resources are often unequally distributed and individuals are grouped in patches.

© 2015 Pearson Education, Inc Density and dispersion patterns are important population variables In a uniform dispersion pattern, individuals are most likely interacting and equally spaced in the environment.

© 2015 Pearson Education, Inc Density and dispersion patterns are important population variables In a random dispersion pattern of dispersion, the individuals in a population are spaced in an unpredictable way, without a pattern, perhaps resulting from the random dispersal of windblown seeds.

© 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. 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

© 2015 Pearson Education, Inc. Table 36.3

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

© 2015 Pearson Education, Inc. Figure 36.3b I II III Percentage of maximum life span Percentage of survivors (log scale)

© 2015 Pearson Education, Inc Idealized models predict patterns of population growth The rate of population increase under ideal conditions is called exponential growth. It can be calculated using the exponential growth model equation, G = rN, in which G is the growth rate of the population, N is the population size, and r is the per capita rate of increase (the average contribution of each individual to population growth, i.e. offspring). Eventually, one or more limiting factors will restrict population growth.

© 2015 Pearson Education, Inc. Figure 36.4a-0 Time (months) Population size (N)

© 2015 Pearson Education, Inc. Table 36.4a

© 2015 Pearson Education, Inc Idealized models predict patterns of population growth The logistic growth model is a description of idealized population growth that is slowed by limiting factors as the population size increases. The growth curve is usually S shaped. K is the carrying capacity, the maximum population size a particular environment can sustain.

© 2015 Pearson Education, Inc. Figure 36.4b-0 Year Breeding male fur seals (thousands) Data from K. W. Kenyon et al., A population study of the Alaska fur-seal herd, Federal Government Series: Special Scientific Report—Wildlife 12 (1954).

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

© 2015 Pearson Education, Inc Multiple factors may limit population growth The logistic growth model predicts that population growth will slow and eventually stop as population density increases. At higher population densities, density-dependent rates result in declining births and/or increases in deaths. The following example shows how, the more female birds there are, the fewer offspring each female will have. Fecundity is the number of live births per female in a population

© 2015 Pearson Education, Inc. Figure 36.5a-0 Density of females Data from P. Arcese et al., Stability, Regulation, and the Determination of Abundance in an Insular Song Sparrow Population. Ecology 73: 805–882 (1992) Mean number of offspring per female

© 2015 Pearson Education, Inc Multiple factors may limit population growth Intraspecific competition is competition between individuals of the same species for limited resources and is a density-dependent factor that limits growth in natural populations. Limiting factors may include food, nutrients, or nesting sites.

© 2015 Pearson Education, Inc Multiple factors may limit population growth In many natural populations, abiotic factors such as weather may affect population size well before density-dependent factors become important. Density-independent factors are unrelated to population density. These may include fires, storms, habitat destruction by human activity, or seasonal changes in weather (for example, in aphids).

© 2015 Pearson Education, Inc SCIENTIFIC THINKING: 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. A striking example is shown in Figure 36.6, which shows estimated populations of the snowshoe hare and the lynx based on the number of pelts sold by trappers in northern Canada to the Hudson Bay Company over a period of nearly 100 years.

© 2015 Pearson Education, Inc. Figure Snowshoe hare Lynx population size (thousands) Lynx Hare population size (thousands) Year Data from C. Elton and M. Nicholson, The ten-year cycle in numbers of the lynx in Canada, Journal of Animal Ecology 11 : 215–244 (1942).

© 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 life history 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 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 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. Most species fall between these two extremes.

© 2015 Pearson Education, Inc CONNECTION: Principles of population ecology have practical applications Sustainable resource management involves harvesting crops without damaging the resource. In terms of population growth, this means maintaining a high population growth rate to replenish the population. According to the logistic growth model, the fastest growth rate occurs when the population size is at roughly half the carrying capacity, K, of the habitat.

© 2015 Pearson Education, Inc CONNECTION: Principles of population ecology have practical applications Fish are hunted on a large scale and are particularly vulnerable to overharvesting. The northern Atlantic cod fishery was overfished, collapsed in 1992, and still has not recovered. Resource managers may try to provide additional habitat or improve the quality of existing habitat to raise the carrying capacity and thus increase population growth.

© 2015 Pearson Education, Inc. T HE H UMAN P OPULATION

© 2015 Pearson Education, Inc The human population continues to increase, but the growth rate is slowing The human population grew rapidly during the 20th century and currently stands at about 7 billion. An imbalance between births and deaths is the cause of population growth (or decline). The human population is expected to continue increasing for at least the next several decades.

© 2015 Pearson Education, Inc. Figure 36.9a Adapted from The World at Six Billion, United Nations Publications (1999) Population increase Total population size Annual increase (in millions) Total population (in billions) Year Notice the Y-axis is population increase, not population.

© 2015 Pearson Education, Inc The human population continues to increase, but the growth rate is slowing The demographic transition is a shift from zero population growth, in which birth rates and death rates are high but roughly equal, to zero population growth, characterized by low but roughly equal birth and death rates. Figure 36.9B (slide 39) shows the demographic transition of Mexico, which is projected to approach zero population growth with low birth and death rates in the next few decades.

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

© 2015 Pearson Education, Inc. Figure 36.9b Birth or death rate per 1,000 population Rate of increase Birth rate Death rate Year Adapted from Transitions in World Population, Population Bulletin 59: 1 (2004). What happened between 1900 and 1925!?

© 2015 Pearson Education, Inc The human population continues to increase, but the growth rate is slowing In the developing world death rates have dropped, but high birth rates persist, and these populations are growing rapidly.

© 2015 Pearson Education, Inc. Table 36.9 What does this mean for the populations of more developed vs less developed nations?

© 2015 Pearson Education, Inc The human population continues to increase, but the growth rate is slowing The age structure of a population is the number of individuals in different age-groups and affects the future growth of the population.

© 2015 Pearson Education, Inc The human population continues to increase, but the growth rate is slowing The fertility rate is the average number of children produced by a woman over her lifetime. Population momentum is the continued growth that occurs despite reduction of the fertility rate to replacement level and is a result of girls in the 0–14 age-group of a previously expanding population reaching their childbearing years.

© 2015 Pearson Education, Inc. Figure 36.9c-1 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 Adapted from International Data Base, U.S. Census Bureau (2013).

© 2015 Pearson Education, Inc. Figure 36.9c-2 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 Estimated population in millions Total population size = 114,975,406 Female Adapted from International Data Base, U.S. Census Bureau (2013).

© 2015 Pearson Education, Inc. Figure 36.9c-3 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– Projected population in millions Total population size = 139,457,070 Male Female 2035 Adapted from International Data Base, U.S. Census Bureau (2013).

© 2015 Pearson Education, Inc CONNECTION: Age structures reveal social and economic trends Age-structure diagrams reveal a population’s growth trends and social conditions. For instance, an expanding population has an increasing need for schools, employment, and infrastructure, and a large elderly population requires that extensive resources be allotted to health care.

© 2015 Pearson Education, Inc. Figure Male Female 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– Population in millions Total population size = 246,819,230 80–84 Birth years Data from International Data Base, U.S. Census Bureau website, (2013) Male Female Birth years 2035 MaleFemale Birth years Estimated population in millions Total population size = 313,847,465 Projected population in millions Total population size = 389,531, before – – – – – – – – – – – – – – – – –89 before – – – – – – – – – – – – – – – – –2012 before – – – – – – – – – – – – – – – – –10 Age structure for the US, 1989, 1912, Notice where you are in each structure

© 2015 Pearson Education, Inc CONNECTION: An ecological footprint is a measure of resource consumption The U.S. Census Bureau projects a global population of 8 billion people within the next 20 years and 9.5 billion by the mid-21st century. Do we have sufficient resources to sustain 8 or 9 billion people? To accommodate all the people expected to live on our planet by 2025, the world will have to double food production.

© 2015 Pearson Education, Inc CONNECTION: An ecological footprint is a measure of resource consumption An ecological footprint is an estimate of the amount of land required to provide the raw materials an individual or a nation consumes, including food, fuel, and housing.

© 2015 Pearson Education, Inc CONNECTION: An ecological footprint is a measure of resource consumption Comparing our demand for resources with Earth’s capacity to renew these resources, or biocapacity, gives us a broad view of the sustainability of human activities. When the total area of ecologically productive land on Earth is divided by the global population, we each have a share of about 1.8 global hectares (1 hectare, or ha, = 2.47 acres; a global hectare, or gha, is a hectare with world-average ability to produce resources and absorb wastes).

© 2015 Pearson Education, Inc CONNECTION: An ecological footprint is a measure of resource consumption Figure compares the ecological footprints of several countries to the world average footprint (orange line) and Earth’s biocapacity.

© 2015 Pearson Education, Inc. Figure 36.11a Key World biocapacity Year Built-up land Carbon Footprint Data from B Ewing et al., The Ecological Footprint Atlas, Oakland: Global Footprint Network (2010). Ecological Footprint (number of Earths)

© 2015 Pearson Education, Inc. Figure 36.11b World average Earth’s biocapacity Afghanistan Haiti India Colombia Uzbekistan China South Africa Argentina Mexico United Kingdom Australia United States Adapted from Living Planet Report 2012: Biodiversity, Biocapacity, and Better Choices, World Wildlife Fund (2012). Ecological Footprint (global hectares per person)

© 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.UN05