Population Ecology Population ecology is the study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size

Population Ecology Key Terms: populationA population is a group of individuals of a single species living in the same general area DensityDensity is the number of individuals per unit area or volume DispersionDispersion is the pattern of spacing among individuals within the boundaries of the population

Population size Emigration Deaths Immigration Births Population

3 Patterns of Dispersion Environmental and social factors influence spacing of individuals in a population 1.Clumped 2.Uniform 3.Random

Clumped. Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

Uniform. Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

Random Random. Dandelions grow from windblown seeds that land at random and later germinate.

Survivorship Curves A survivorship curve is a graphic way of representing the data in a life table Survivorship curves can be classified into 3 general types: Type I: Type II Type III

Type I characterized by high survival in early and middle life, followed by a rapid decline in survivorship in later life. – Example: Humans

Type II These curves are an intermediate between Types I and III, where a roughly constant mortality rate is experienced regardless of age. – Example: Birds and Lizards

Type III The greatest mortality is experienced early in life, with relatively low rates of death for those surviving. This type of curve is characteristic of species that produce a large number of offspring. – Example: most marine invertebrates like an Oyster

III II 100 Percentage of maximum life span Number of survivors (log scale) , I

Males Females 10 Age (years) Number of survivors (log scale) ,

The Exponential Growth Model It is useful to study population growth in an idealized situation that may facilitate this growth – In animals, parental care of smaller broods may facilitate survival of offspring Exponential population growth results in a J- shaped curve

Number of generations Population size (N) 2,000 = 1.0N 1,000 1, dN dt = 0.5N dN dt

The logistic growth model Exponential growth cannot be sustained for long in any population A more realistic population model limits growth by incorporating carrying capacity Carrying capacity (K) is the maximum population size the environment can support In the logistic population growth model, the per capita rate of increase declines as carrying capacity is reached The logistic model of population growth produces a sigmoid (S-shaped) curve

Population size (N) Per capita rate of increase (r) Maximum Positive Negative N = K 0

Number of generations Population size (N) K = 1,500 1,500 2,000 1, Logistic growth Exponential growth = 1.0N dN dt = 1.0N dN dt 1,500 – N 1,500

Time (days) Number of Paramecium/mL 1, A Paramecium population in the lab

Time (days) Number of Daphnia/50 mL A Daphnia population in the lab

Time (years) Number of females A song sparrow population in its natural habitat

Health, Predation and Toxic Wastes Population density can influence the health and survival of organisms In dense populations, pathogens can spread more rapidly As a prey population builds up, predators may feed preferentially on that species Accumulation of toxic wastes can contribute to density-dependent regulation of population size

1960 Year Moose population size 2,500 Steady decline probably caused largely by wolf predation 2,000 1,500 1, Dramatic collapse caused by severe winter weather and food shortage, leading to starvation of more than 75% of the population

1960 Year Commercial catch (kg) of male crabs (log scale) 730, ,000 10,

Year Hare population size (thousands) 1850 Snowshoe hare Lynx population size (thousands) Lynx

Regional Patterns of Population Change No population can grow indefinitely, and humans are no exception To maintain population stability, a regional human population can exist in one of two configurations: – Zero population growth = High birth rate – High death rate – Zero population growth = Low birth rate – Low death rate The demographic transition is the move from the first state toward the second state The demographic transition is associated with various factors in developed and developing countries

Birth or death rate per 1,000 people Sweden 2050 Year Birth rate Death rate Mexico Birth rate Death rate

Age Structure One important demographic factor in present and future growth trends is a country’s age structure Age structure is the relative number of individuals at each age It is commonly represented in pyramids Age structure diagrams can predict a population’s growth trends They can illuminate social conditions and help us plan for the future

Rapid growth Afghanistan Age Male Percent of population Female –49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0– –84 75–79 70–74 65–69 60–64 55–59 50–54 Slow growth United States Age Male Percent of population Female –49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0– –84 75–79 70–74 65–69 60–64 55–59 50–54 8 Decrease Italy Male Percent of population Female

Infant Mortality and Life Expectancy Infant mortality and life expectancy at birth vary greatly among developed and developing countries but do not capture the wide range of the human condition

Infant mortality (deaths per 1,000 births) Developed countries 60 Developing countries Life expectancy (years) Developed countries 60 Developing countries