Population DynamicsChapter 15

Learning Objectives

Factors that determine the size of a population

Carrying capacity

population rate of growth Mortality Biotic/abiotic

factorspredation & competition

• Abundance and Population• Age Structure• Rate of Growth• Distribution• Birth and Death Rate

Characterising Species

distribution

Population: Abundance and SamplingAbundance: The number of individuals of a species

per unit area (Density)

Sampling Techniques:1. Mark-recapture technique

1. Total number= (# marked x total caught)/ # marked ones caught

2. Sampling through quadrats.3. Transects (changes in environment)DynamicScience – Population sampling information

Distribution: Uniform, Random, Clumped

Sampling allows us to map distribution and density of organisms

Population distributionAbundance assists us with

determining distribution.What factors affect

Distribution?Food sourcePredation/ hunting/ habitat

destructionClimate, temp, environmentReproductive factors

What factors Abiotic/Biotic might be affecting the distribution of the elephant population (Questions from internet)

Population: Age StructureAge

StructurePre-

reproductive age

Reproductive age

Post-reproductive

age

Population Growth CurvesUsually there are 3

phases:1. Slow growth as

numbers are built up2. Rapid growth3. Population growth

decreases, population is approximately stable.

Slow growth

Rapid growth

Stable, no growth

Population Growth PatternsJ Shaped Curves: Exponential growth

Lag phaseAcceleration phasePopulation (next generation)= Rate of increase x Population (previous

gen.)

Population Growth PatternsS Shaped Curves: Logistic Growth

Deceleration phase: growth slows due to environmental resistance, competition, organism death

Growth rate is stopped by the Carrying Capacity of the environmentCarrying Capacity: maximum population that can be sustained by the

environment- Affected by Biotic and abiotic factors

Birth rate Vs. Death Rate

Population explosions• Reproduction (many new offspring) & lower death rate• Abiotic environment (lots of food)• Predator control (lack of predators)• Dispersal (spreading into new areas)

Factors affecting growth ratesDensity- dependent factors (Intraspecific): (food/ resources) Increased

influence in higher populationsDensity- Independent factors: floods, drought. Interspecific Factors: (Competition with other species)Predation & Habitat DestructionGrowth Rate (intrinsic)- K-selected/ R-selected strategy (pg 493)

Feature R-selected Strategy

K-selected strategy

Life span Shorter-lived Longer-lived

No. offspring Many few

Energy req. for reproduction

Small energy Large energy

Survival Rate Low High

Sexual maturity Earlier in life Later in life

Incubation period Short/ none Extensive (mths)

Parental care Little/none Extensive

Population InteractionsCompetition: Food, resources (nests, sunlight)Predator + Prey relationships

• Which population peaks first?

• In the absence of adequate predators what happens?

• Without predators, how is prey population regulated?

• How many ‘boom-bust’ cycles can we see?

• What other factors not visible on this graph could be influencing populations

Application QuestionsComplete questions online at

http://rasozbiologyresources.weebly.com

Population Evaluations & Changes in Ecosystems

Chapter 15 & 16

Population EvaluationsPopulation growth = (births + immigration) – (deaths +

emigration)

Percentage population growth rate in a given period = (pop. change during the period/ pop. At start of the period) x 100 Example

100 dolphins in 2012. 3 years later they found 143 dolpins. What is the population growth per year?

Pop. Change= 143-100 = 43. % Growth Rate = (43/100) x 100 (remember this is over 3 yr period)Per year = 43/3 (gives us the % per year) = 14.3% growth per year

Population Elements

Birth Rate

• Birth rate = (number of births per year/ tot. pop in the same year) x 1000

Death Rate

• Death rate= (no. of deaths per year/ total. Pop. In the same year) x 1000

Factors affecting Birth rate in Humans Factors affecting Death Rate In humans

Political policies & economic conditions War and natural disasters

Cultural & Religious background Food supply

Birth control Safe Drinking water & sanitation

Education level Life expectancy and Age profile (more oldies = higher death rate)

Social elements and pressures Disease and access to medical care

Population Analysis

Relate the changes to population:- Death rate- Birth rate- Overall growth

Changes in EcosystemsIs the change environmentalRegular (tides, seasons)Sporadically / Irregular (floods in tropical areas)One-off events (100 year flood or fire, volcanic eruption)Disease or a flow on from population change in another interacting organism.

Is the change the result of humans Oil spill De-forestation Habitat Destruction Global Warming Introduction of new species (deliberate, accidental or ‘classical biocontrol’)

Examples and effects. Management: Biocontrol (biopesticides- bacteria, fungi), Immunocontraception.

Human Impact on Ecosystems