Chapter 53- AP Biology

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: 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

5 moose in a township (24,000 square miles)

10,000 Oak trees in 25 square miles

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

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.

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

Population   Births Deaths

during a          =      and -      and

time interval        immigrants emigrants

simplified:    Δ N/ Δ t  = B-D

“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

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

ΔN/ Δ t  = rN

Under “perfect conditions,” with abundant resources, a population will grow “without limit”

ΔN/ Δ t  = rmaxN Result is a “J” curve

Greater ( r) means faster growth

Grew exponentially for 60 years when they were first protected from hunting

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)?

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

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

“as N increases, r decreases”

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

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

Density-dependent: trait or growth rate that is affected by population densityEx: death rate may rise due to overpopulation

Density-independent: trait or growth rate that is NOT affected by population densityEx: death rate may rise due to forest fires

CompetitionTerritorialityDiseasePredationToxic wastesIntrinsic factors (stress hormones)

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

ZGP (Stable population)High birth rate – high death rate ORLow birth rate – low death rate

Demographic transition = movement towards low birth rate and low death rateSanitationBetter Health CareImproved Education access

Relative number of individuals of each age group in a population

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.

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