Pre IB Bio Chapter 52

Population Ecology

Population

Group of single species in a given area.

Population density

Number of individuals per unit area/volume.

Population density is the result of…

Immigration, Emigration, Births (Natality), and Death

Mortality

Death

Morbidity

What’s causing

Quadrat method other known as…

Capture, mark, release, recapture (CMRR)

The Lincoln Index

N=(n1*n2)/m

N

Total population size of animal interest in the study site

n1

Number of animals captured on the first day

n2

Number of animals recaptured on the second day

m

Number of marked animals in the sample recaptured on the second day

Population dispersion

Patterns of spacing within a boundary

Clumped

A dispersion pattern where individuals are aggregated in patterns, generally around resources

Most common dispersion pattern

Clumped

Example of uniform dispersion

King penguins on South Georgia Island

Uniform

Dispersion pattern in which individuals are evenly distributed (influenced by social interactions such a as territoriality)

Random

Dispersion pattern in which the position of each individual is independent of other individuals

Example of random dispersion

Seeds being dispersed by animals randomly

Demography

The study of vital statistics and how they change over time

Growth rate =

birth rate - death rate, r=b-d

Life table

Age-specific summary of the survival pattern of a population

Life tables are best constructed by following the fate of a

Cohort

Semalparity

“Big-bang” reproduction, reproduce a single time and die — common in insects.

Iteroparity

Repeated reproduction, produce offspring repeatedly over time (Iteroparity sounds like reitorate) common in humans.

Reasoning for small and many seeds

Ensuring that some of them will grow and eventually reproduce

Reasoning for large and few seeds

They provide a large store of energy — will help seeds become established.

It is useful to study population growth in an

Idealized situation

r

Growth rate

b

Birth rate

d

Death rate

Exponential population growth

dN/dt=rN

dN

Change in population

dt

Change in time

rN

Population size

Exponential model is

population under idealized conditions

The rate of reproduction in the exponential model is at its

Maximum

The exponential model isn’t realistic because

Resources become limited as the population grows

Shape of the exponential curve

J

Can exponential growth be sustained for long periods at a time?

No, it reaches carrying capacity — humans cheat by using natural resources

Logistic model

Population growth model that levels off as population size approaches carrying capacity

The death rate in the logistic model increases when

Resources become limited

Carrying capacity

When the environment can’t support any more individuals

K

Carrying capacity

Shape of logistic model curve

S

Logistic equation

dN/dt=rN(K-N/K)

r-selected populations

High reproductive rate is the chief determinant of life history

Characteristics of r-selected populations

High fecundity (ability to reproduce), small body size, early maturity onset, short generation time, ability to disperse offspring widely, little/no parental care

Example of r-selected organisms

Bacteria

Way to remember r-selected

r=reproduction

K-selected populations

Producing few offspring that have a good chance of survival

Characteristics of K-selected populations

Large body size, long life expectancy, production of fewer offspring, lots of parental care

Example of K-selected organism

Humans

Density independent factors

Abiotic factors that equally effect birth and death rates no matter how many individuals — doesn’t care about the population size

Examples of density independent factors

Weather, temperatures, natural disasters, etc.

Density dependent factors

Factor that varies on population density

Examples of density dependent factors

Competition for resources (food, water, nutrients, mates, etc.), territoriality, health, predation, toxic wastes, intrinsic factors

Example of difference between dependent and independent

Independent — Millions of people moving to California won’t cause an earthquake

Dependent — Millions of people moving to California will cause a food shortage

Metapopulation

Spatially separated population that interacts through immigration and emigration

Example of metapopulation

Mountain sheep

High levels of genetic diversity combined with higher species diversity can result in

Greater stability in populations

Population cycle

Number of individuals in a species predictably rises and falls over time

Boom-bust cycles

Influenced by complex interactions (biotic and abiotic)

Time lag

An increase in prey will cause an increase in predator a short time later. A decrease in prey will cause a decrease in predator a short time later

No population can grow

Indefinitely (including humans)

The human population

Increased relatively slowly until about 1650 and then began to grow exponentially

2 possibilities for zero population growth

High birth rate - High death rate

Low birth rate - Low death rate

Ecological footprint

The aggregate land and water area needed to sustain the people of a nation