Population ecology Chapter 53- AP Biology

Population Ecology The study of populations in relation to their environment Explores how biotic and abiotic factors influence the density, distribution, size and age structure of populations What is a population?

Density and Dispersion Density: number of individuals per unit area or volume Ex: number of oak trees per square kilometer in the Minnesota country Dispersion: Random Clumped- most common pattern of dispersion (plants, fungi) Uniform – often seen with territoriality

Population Density is DYNAMIC

Guess the dispersion Pattern…. Calculate Density of…. 5 moose in a township (24,000 square miles) 10,000 Oak trees in 25 square miles Guess the dispersion Pattern….

Demographics Demography: study of the vital statistics of populations and how they change over time Life Tables (Usually follow certain “cohorts”): death rate, birthrate, etc. Survivorship curves Reproductive Rates

Life Table: “age specific summaries of survival pattern of a population”

Survivorship Curves Type I: few offspring but provided with good care; low infant death rate Type II: Intermediate; death rate remains constant over time Type III: many offspring with a high infant mortality; fish, oysters, etc.

Reproductive Table

Natural Selection & Life History Natural selection favors traits that improve an organism’s chances of survival and reproductive success. “Life history traits are evolutionary outcomes reflected in their development, physiology, and behavior” Semelparity: “beget once,” organism produces once in its lifetime (salmon, agave) Iteroparity: “repeted,” reproducing many times in a lifetime (humans, dogs) Two critical factors Survival rate of the offspring Likelihood that the adult will survive to reproduce once again

Exponential Growth Population Births Deaths during a = and - and time interval        immigrants emigrants simplified:    Δ N/ Δ t  = B-D

Per capita rate of increase “Average births or deaths per unit of time in average population” Example: 34 births per year in a population of 1,000 (or 34/1,000) annual per capita birth rate  b = .034 50 deaths per year in a population of 1,000 annual per capita death rate  d = .05 In the equation Δ N/ Δ t  = B-D B = bN and D = dN

Rate of Increase (r) if (r > 0 ), then population is growing r = b – d if (r > 0 ), then population is growing if (r < 0 ), then population is declining Zero growth population (ZGP) is when r = 0

Revised equation Δ N/ Δ t  = rN

Exponential growth Δ N/ Δ t = rmaxN Under “perfect conditions,” with abundant resources, a population will grow “without limit” Δ N/ Δ t  = rmaxN Result is a “J” curve Greater ( r) means faster growth

African elephant, Kruger National Park, South Africa Grew exponentially for 60 years when they were first protected from hunting

Practice In 2006, the United States had a population of about 300 million people. If there were 14 births and 8 deaths per 1,000 people, what was the country’s net population growth that year (ignoring immigration and emigration)?

Practice In 2006, the United States had a population of about 300 million people. If there were 14 births and 8 deaths per 1,000 people, what was the country’s net population growth that year (ignoring immigration and emigration)? 14/1000 = .014 = annual per capita birth rate  b 8/1000 = .008 = annual per capita death rate  d b – d = .006 annual per capita growth rate .006 x 300 million = 1,800,000 net growth in 1 year

Logistical Growth- The “real world” Carrying Capacity (k): the maximum population size that a particular environment can sustain Varies over time Depends on limiting factors Result = change in r Logistic growth: per capita rate of increase (r ) approaches zero as carrying capacity (k) is reached

Logistic Growth “as N increases, r decreases”

Example of Logistic growth in Lab

Life History Trait Selection k-selection: density-dependent selection, select for traits that are sensitive to population density; (when organisms are near carrying capacity). r-selection: density-independent selection, select traits that maximize reproductive success at LOW densities

Question When a farmer abandons his field, it is quickly colonized by rapidly-growing weeds. Is this a k-selected or r-selected species?

Density and population growth Density-dependent: trait or growth rate that is affected by population density Ex: death rate may rise due to overpopulation Density-independent: trait or growth rate that is NOT affected by population density Ex: death rate may rise due to forest fires

Density-Dependent population regulation Competition Territoriality Disease Predation Toxic wastes Intrinsic factors (stress  hormones)

Population dynamics Complex interactions between biotic and abiotic factors that cause variation in the size of populations

Human Populations

Trends ZGP (Stable population) High birth rate – high death rate OR Low birth rate – low death rate Demographic transition = movement towards low birth rate and low death rate Sanitation Better Health Care Improved Education access

Age Structure Relative number of individuals of each age group in a population

Infant mortality and life expectancy

Global Carrying capacity? . . Estimated at 7.8 – 10.8 billion Ecological footprint: sum of aggregate land and water area required by each person, city, or nation to produce all the resources it consumes and absorb all the waste it generates.

You should be able to… Find the density and dispersion of a given species Interpret life tables, survivorship curves, and age structure tables Identify and describe “r” strategists and “k” strategists Interpret logistic and exponential population growth models Identify and describe density-dependent and density-independent factors