species

How are these terms related?

population community

What they have in common:

How will you remember?

What makes them unique

5-1 How Populations Grow

Objectives:1. List the characteristics used to describe a

population2. Identify factors that affect population size3. Differentiate between exponential and logistic

growth

Characteristics of Populations

• Four Characteristics:1. Geographic range2. Density and distribution3. Growth rate4. Age structure

Geographic Range• Area covered by a population– Size depends on organism and other limiting

factors

Distribution of long-tailed salamanders Eurycea longicauda

Population Density• Refers to the number of individuals per unit

areaA B

• Can vary greatly among species in the same ecosystem

What is the population density?

1 m

5 m 10 butterflies/5 m2

= 2/m 2

Distribution• Distribution refers to

how members of a populations are spaced out across the range of that population

• Can be described in one of 3 ways:– Random– Uniform– Clumped

Ways to Determine Population Size

1. Direct Observation- counting one by one2. Indirect Observation- relies on signs like tracks,

empty nests– Useful when organisms are difficult to observe

3. Sampling- uses an estimate (an approximation of a number based on reasonable assumptions)

4) Mark and Recapture- another way of estimating the population

Mark and Recapture• Scientists capture and mark members of a species and

then release them• Later the species is captured again and the marked

members are counted to estimate the populationTotal population = number marked x number captured = 5 x 4 = 20

number captured with marks 1

Marked Species = 5Captured Species =4

Number with marks = 1

Population Growth

Population size is affected by:1. Births and deaths

Births>Deaths= population grows

2. Immigration and emigration– Organisms immigrate into and emigrate out of

populations to find mates, food, establish new territories, etc.

Immigration>emigration=population grows

3. Limiting Factors- Space, food, predators, disease, etc.

Patterns of Population Growth

• Exponential growth- occurs when the number of organisms rises at an ever-increasing rate – Occurs when conditions are ideal • no limiting factors affecting population

– Population reproduces at a constant rate• i.e. binary fission (reproduction) in bacteria occurs

every 20 minutes

– Can result in a population explosion

J-shaped Curve

• Shows exponential growth (unchecked growth)

• Initial increase in number of organisms is slow because the number of reproducing organisms is small

• Rate increases rapidly because the total number of potential reproducers increases

Patterns of Population Growth

• Logistic growth- occurs when a population’s growth slows or stops following a period of exponential growth– Growth pattern of natural populations– Due to limited availability of resources when

populations increase in size

S-shaped Curve• Shows logistic growth

A= lag phase-small # of reproducing individuals

B= exponential growthC= population growth

levels off• carrying capacity (K)- number

of organisms of a population that a particular environment can support over an indefinite period of time– Determined by limiting factors

A

B

C

Logistic Growth

5-2 Limits to Population Growth

• Limiting factors- factors that controls the growth of a population– Determine the carrying capacity of an

environment• Two types:– Density dependent- affect increases as population

density increases– Density independent- affect is the same

regardless of population size

Types of Limiting Factors

• Density-dependent• competition• predation• herbivory• parasitism• disease

• Density-independent• temperature• floods• drought• habitat disruption

Competition• Constant competition for resources within

the same population (intraspecific) or between populations (interspecific)

• Can lead to evolution (speciation)

Predation• Cyclical in nature which increases and

decreases over time• Important for the health of natural

population

Parasitism and Disease• Also limit population growth

5-3 Human Population Growth

• Objectives:1. Discuss the trend of human population

growth2. Explain why population growth rates differ

from country to country

History of Human Population Growth

Industrial Revolution and Human Population

• Living conditions improved and more reached reproductive age– Food supplies became more reliable – Improved nutrition– Sanitation– Medicine– Healthcare

• Led to exponential growth of population

Thomas Malthus

• Suggested that populations would be regulated by war, famine, an disease– Limiting factors:• Competition (war)• Limited resources (famine)• Parasitism (disease)

Malthus’ ideas influenced Charles Darwin

Patterns of Population Growth

• Demography- scientific study of human population–examines characteristics of human

populations and attempts to explain how those populations will change over time–Characteristics examined:• Birth rates• Death rates• Age structure

Demographic Transition

• Population growth in developed countries like US, Europe, and Japan has slowed dramatically

• these countries have completed the demographic transition, a dramatic change in birth and death rates

• Birth rate falls to meet the death rate and population stops growing

Demographic TransitionSTAGE IReproduction and death rates are high throughout most of history

STAGE II Death rates fall, but birth rates remain high for some time; births exceed deaths and population grows exponentially

STAGE III Standard of living and education level rises and birthrate falls causing population to level off

World Population Growth

Age Structure

• Population growth depends, in part, on how many people of different ages make up a given population.

• Demographers can predict future growth using models called age-structure diagrams

• Age-structure diagrams show the population of a country broken down by gender and age group.

Age Structure Diagrams

Future Population Growth

• Considerations for predicting world population growth:– Age structure of each country– Prevalence of life-threatening disease

• Prediction for 2050 is slowing growth, but still 9 billion – Increasing population, regardless of rate, could have

negative impact on environment and global economy

– Or, will be offset by science, technology and changes in society