Populations

Bell Ringer

A nearby high school is closing, and all their students will be coming to your high school. What will be different about your school with the addition of all these new students?

Growing Populations

Increases in general populations can put stresses on resources

Which resources do we protect and consume?Abundance or scarcity of food sources?Disruption of ecological systems?

Florida School Project

1. What does the problem at Central High have to do with the environment?

2. Do you think it is important to protect the gopher tortoise?

3. What are some ways that building the school will affect the gopher tortoise?

4. Do you think any living organisms were affected when (your school) was built?

What are gopher tortoises?

Gopher Tortoise

Keystone species - alter the habitat by constructing and maintaining their burrows

Indicator species - used as an indicator of ecosystem health.

Burrow Details

Protect from temperature extremes and predators

Max. length 13 m (40 feet), depth 3m (10 feet)

Burrow has ledge at end where tortoise rests

http://www.youtube.com/watch?v=ioOTnXSf4u0

Population Ecology

A population is a group of members of the same species defined by geographic boundaries

Population dynamics help ecologists understand how a population may grow or decline.

Population Dynamics

Size - # of organisms

Density - # of individuals with a population per unit area

1. High population density = easier for organisms to find mates, may lead to conflict in competing for resources

2. Low population density = organisms benefit from space & resources, difficult to locate mates.

Population Distribution/Dispersion

Spatial arrangement of organisms within an area.

1. Random = no pattern.2. Uniform = Evenly spaced3. Clumped = In groups

Sex Ratios – Proportion of males to females

Age Structure – relative numbers of organisms of each age within a population

a. Pre-reproductiveb. Reproductivec. Post-reproductive

Age Pyramids

Visual tools used to show the age structure

What limits population growth?

BirthsDeathsImmigrationEmigration

Population change = (b + i) – (d + e)

Survivorship Graphs

Identify biotic/abiotic factors that limit population size

Abiotic Factors Abiotic Factors

Biotic Factors Biotic Factors

Growth Factors Decrease Factors

High reproductive rateAdequate food supplySuitable habitatAbility to compete for resourcesAbility to hide from or defend against predatorsAbility to resist diseases and parasites

Low reproductive rateInadequate food supplyUnsuitable or destroyed habitatToo many competitorsInsufficient ability to hide from or defend against predatorsInability to resist diseases and parasites

Favorable lightFavorable temperatureFavorable chemical environment (optimal level of critical nutrients)

Too much or too little lightTemperature too high or too lowUnfavorable chemical environment (too much or too little of critical nutrients)

Abiotic

Biotic

Abiotic

Biotic

Growth factors Decrease factors

POPULATION SIZE

Populations (r) = growth rate

Population change = (b + i) – (d + e)

2 models of population growth:

1) Exponential growth: assumes ‘r’ stays constant

2) Logistic growth: as popns grow, resources diminish

Exponential population growth

Under ideal conditions, a population grows rapidly(J-shaped curve)

Logistic Population Growth

Unlimited resources are rare, so populations tend to level out.

S-shaped curve

3 Phases in Logistic Growth

Carrying Capacity • The maximum stable population size a particular environment can support • Occurs when Birth rate = Death rate

Bell Ringer

1. Describe the 2 models of population growth.

2. What is carrying capacity?

3. Identify factors that can limit carrying capacity factors.

Carrying Capacity

Limited by density-dependent factors

1. Competition for limited resources (food, water, territory)

2. Health (overcrowded plants produce less seeds)

3. Physiological factors (overcrowding in field mice causes stress)

2 Types of Life Histories Strategies

1. K-strategists: organisms live and reproduce around K, and are sensitive to population density

2. R-strategists: organisms exhibit high rates of reproduction and live in unstable environments in which population densities fluctuate

K Selected - EquilibrialR Selected - Opportunistic

Long life span Long maturation time Low death rate Few offspring Several reproductions per

lifetime Extensive parental care Usually in stable,

predictable environments Good competitors Ex: tigers, whales,

elephants

Short lifespanShort maturation timeHigh death rateUsually one reproduction/lifetimeMany offspringNo parental careTemporary large populations followed by crashesUnpredictable changing environmentsEx: insects, bacteria

2 Types of Life Histories Strategies

Humans: R or K?

From beginning to 1350 AD, humans experienced logistic growth

But agriculture (food surplus), medicine, and technology expanded carrying capacity

Eventually, damage to planet will decrease carrying capacity and slow human growth leading to environmental, health, food & social changes.

Human Population Growth