Chapter 36 Population Ecology Lecture by Brian R. Shmaefsky 1

Introduction: A Tale of Two Fishes Population ecology is concerned with Changes in population size Factors that regulate populations over time It helps explain the biodiversity of an environment

Introduction: A Tale of Two Fishes Ecologists learn the structure and dynamics of natural populations With this information they are better equipped to Develop sustainable food sources Assess the impact of human activities Balance human needs with the conservation of biodiversity and resources

POPULATION STRUCTURE AND DYNAMICS

36.1 Population ecology is the study of how and why populations change 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 Are likely to interact and breed with one another

Population dynamics is the interactions between A population can be described by the number and distribution of individuals Population dynamics is the interactions between Biotic and abiotic factors It is the cause of variation in population sizes A population increases through birth and immigration Death and emigration out of an area decrease the population

Examples of population density 36.2 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 The number of oak trees per square kilometer in a forest The number of earthworms per cubic meter in forest soil Ecologists use a variety of sampling techniques to estimate population densities

Within a population’s geographic range, local densities may vary greatly The dispersion pattern of a population refers to the way individuals are spaced within their area

Dispersion patterns can be The dispersion pattern of a population refers to the way individuals are spaced within their area Dispersion patterns can be Clumped Uniform Random

In a clumped pattern individuals are grouped in patches

In a uniform pattern individuals are equally spaced in the environment

In a random pattern of dispersion, the individuals in a population are spaced in an unpredictable way

36. 3 Life tables track survivorship in populations Life tables track survivorship over the life span of individuals in a population Survivorship curves plot the proportion of individuals alive at each age Type I Type II Type III

100 I 10 II Percentage of survivors (log scale) 1 III 0.1 50 100 Percentage of maximum life span

36.4 Idealized models predict patterns of population growth Exponential growth model The rate of population increases under ideal conditions Calculated using the equation G = rN G is the growth rate of the population N is the population size r is the per capita rate of increase

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

Logistic growth model This growth model takes into account limiting factors Limiting factors are environmental factors that restrict population growth Formula

Breeding male fur seals 10 8 Breeding male fur seals (thousands) 6 4 2 1915 1925 1935 1945 Year

Breeding male fur seals 10 8 Breeding male fur seals (thousands) 6 4 2 1915 1925 1935 1945 Year

Idealized models describe two kinds of population growth Exponential growth Logistic growth

G = rN (K – N) K G = rN Number of individuals (N) K Time

36.5 Multiple factors may limit population growth The logistic growth model Population growth slows and ceases as population density increases Increasing population density results in a decrease in birth rate, an increase in death rate, or both

4.0 3.8 3.6 Clutch size 3.4 3.2 3.0 2.8 10 20 30 40 50 60 70 80 Density of females

Abiotic factors may reduce population size before other limiting factors become important Most populations fluctuate in numbers

Exponential growth Sudden decline Number of aphids Apr May Jun Jul Aug Sep Oct Nov Dec

80 60 40 Number of females 20 1975 1980 1985 1990 1995 2000 Time (years)

36.6 Some populations have “boom-and-bust” cycles Some populations fluctuate in density with regularity Boom-and-bust cycles Food shortages Predator-prey interactions

Snowshoe hare 160 120 9 Lynx Hare population size (thousands) Lynx population size (thousands) 80 6 40 3 1850 1875 1900 1925 Year

36.7 EVOLUTION CONNECTION: Evolution shapes life histories Life history Series of events from birth to death r/K selection r-selective traits K-selective traits

Predator: Killifish; preys mainly on small guppies Experimental transplant of guppies Predator: Killifish; preys mainly on small guppies Pools with killifish, but no guppies prior to transplant Guppies: Larger at sexual maturity than those in pike-cichlid pools Predator: Pike-cichlid preys mainly on large guppies Guppies: Smaller at sexual maturity than those in killifish pools 11 years later 200 185.6 100 Control: Guppies from pools with pike-cichlids as predators 85.7 92.3 161.5 160 80 120 Age of guppies at maturity (days) 60 58.2 48.5 Mass of guppies at maturity (mg) 80 67.5 76.1 40 Experimental: Guppies transplanted to pools with killifish as predators 40 20 Males Females Males Females

Experimental transplant of guppies Predator: Killifish; preys mainly on small guppies Pools with killifish, but no guppies prior to transplant Guppies: Larger at sexual maturity than those in pike-cichlid pools Predator: Pike-cichlid preys mainly on large guppies Guppies: Smaller at sexual maturity than those in killifish pools

11 years later Control: Guppies from pools with pike-cichlids as predators 200 185.6 100 92.3 85.7 161.5 160 80 Mass of guppies at maturity (mg) Age of guppies at maturity (days) 120 58.2 60 48.5 80 76.1 67.5 40 Experimental: Guppies transplanted to pools with killifish as predators 40 20 Males Females Males Females

Sustainable resource management 36.8 CONNECTION: Principles of population ecology have practical applications Sustainable resource management Maximum sustained yield

900 800 700 600 Yield (thousands of metric tons) 500 400 300 200 100 1960 1970 1980 1990 2000

THE HUMAN POPULATION

36.9 The human population continues to increase, but the growth rate is slowing Human population is expected to continue increasing for several decades 95% of the increase is in developing nations

100 10 Population increase 80 8 60 6 Annual increase (in millions) Total population (in billions) 40 4 Total population size 20 2 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 2050 Year

per 1,000 population Birth or death rate 50 40 30 per 1,000 population Birth or death rate Rate of increase (r) 20 Birth rate Death rate 10 1900 1925 1950 1975 2000 2025 2050 Year

36.9 The human population continues to increase, but the growth rate is slowing Population momentum of Mexico

Age 80+ 1980 75-79 70-74 Male Female 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 0-4 5 4 3 2 1 1 2 3 4 5 Population in millions Total population size = 68,347,479

Age 80+ 2005 75-79 70-74 Male Female 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 0-4 5 4 3 2 1 1 2 3 4 5 Population in millions Total population size = 106,202,903

Age 80+ 2030 75-79 70-74 Male Female 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 0-4 5 4 3 2 1 1 2 3 4 5 Population in millions Total population size = 135,172,155

36.10 CONNECTION: Age structures reveal social and economic trends Age structure diagram Reveals a population’s growth trends

1980 Age Birth years Male Female 80+ before 1900 75-79 1901-1905 70-74 1906-10 65-69 1911-15 60-64 1916-20 55-59 1921-25 50-54 1926-30 45-49 1931-35 40-44 1936-40 35-39 1941-45 30-34 1946-50 25-29 1951-55 20-24 1956-60 15-19 1961-65 10-14 1966-70 5-9 1971-75 0-4 1976-80 12 10 8 6 4 2 2 4 6 8 10 12 Population in millions Total population size = 227,726,463

2005 Age Birth years Male Female 80+ before 1926 75-79 1926-30 70-74 1931-35 65-69 1936-40 60-64 1941-45 55-59 1946-50 50-54 1951-55 45-49 1956-60 40-44 1961-65 35-39 1966-70 30-34 1971-75 25-29 1976-80 20-24 1981-85 15-19 1986-90 10-14 1991-95 5-9 1996-2000 0-4 2001-2005 12 10 8 6 4 2 2 4 6 8 10 12 Population in millions Total population size = 295,734,134

2030 Age Birth years Male Female 80+ before 1951 75-79 1951-55 70-74 1956-60 65-69 1961-65 60-64 1966-70 55-59 1971-75 50-54 1976-80 45-49 1981-85 40-44 1986-90 35-39 1991-95 30-34 1996-2000 25-29 2001-05 20-24 2006-10 15-19 2011-15 10-14 2016-20 5-9 2021-25 0-4 2026-30 12 10 8 6 4 2 2 4 6 8 10 12 Population in millions Total population size = 363,811,435

36.11 CONNECTION: An ecological footprint is a measure of resource consumption U.S. Census Bureau projection 8 billion people within the next 20 years 9.5 billion by mid-21st century

36.11 CONNECTION: An ecological footprint is a measure of resource consumption Ecological footprint helps understand resource availability and usage The United States has a Big ecological footprint Large ecological deficit

North America Europe Asia Africa > 5.4 global ha per person 3.6–5.4 global ha per person 1.8–3.6 global ha per person South America 0.9–1.8 global ha per person Australia < 0.9 global ha per person Insufficient data

Few large offspring, low mortality until old age I Percentage of survivors Many small offspring, high mortality II III Percentage of maximum life span

(K − N) G = rN K

I II III IV Birth or death rate Time