Population DynamicsPopulation Dynamics Chapter 6 Populations

AP Environmental ScienceAP Environmental ScienceGNHS

4 types of Population Fluxes

• Population flux – changes in pops over

time.

Advantage: Allows vegetation and organism reproduction time to recover

Types: 1) stable 3) irregular

2) irruptive 4) cyclic

Stable Pop Flux

• Pop fluctuates around carrying capacity

either slightly above or below

• Typical of species in undisturbed tropical forests…little variation in average temp or rainfall.

Stable Pop Flux Example

Irruptive Pop Flux

• Pop is normally stable but occasionally explodes (erupts) to peak and then crashes to stable lower level.

• Ex: Racoon, house mouse

Irruptive Pop Flux

Irregular Pop Flux

• Chaotic behavior in population size

• No recurring pattern

• May be due to: chaos in ecosystem

Cyclic Pop Flux

Fluctuations in size that occur over a regular time period.

Includes predator-prey

(lynx and hare)

Population Dynamics OutlinePopulation Dynamics Outline

• Characteristics of a PopulationCharacteristics of a Population• Population Dynamics and Carrying Capacity

• Reproductive Strategies

• Conservation Biology

• Human Impacts

• Working with Nature

Characteristics of a PopulationCharacteristics of a Population

• Population - individuals inhabiting the same area at the same time and can interbreed.

• Population Dynamics: Population change due to– Population Size - number of individuals– Population Density - population size in a certain

space at a given time– Population Dispersion - spatial pattern in habitat– Age Structure - proportion of individuals in each age

group in population

Population SizePopulation Size• Natality

– Number of individuals added through reproduction– Crude Birth Rate - Births per 1000– Total Fertility Rate – Average number of children

born alive per woman in her lifetime

• Mortality– Number of individuals removed through death– Crude Death Rate Deaths per 1000

Population GrowthPopulation Growth

• Populations show two types of growth– Exponential

• J-shaped curve• Growth is independent of population density

– Logistic • S-shaped curve• Growth is not independent of population

density

Population Growth – “Mathway”

Benefits: 1.Prediction of future generations

2.Creation of population trends

3.Assists in determining type of growth:

exponential or logistics

Population Growth - Mathway

Basic variables of population growth

N=population number

r = rate of growth

t = Time in days, months, years, generations

d = ‘delta” or change in (ex. dN = change in

population)

K = carrying capacity

Population GrowthPopulation Growth• Population growth depends upon

– birth rates– death rates– immigration rates (into area)– emigration rates (exit area)

Pop = Pop0 + (b + i) - (d + e)

Zero Population Growth(b + i) = (d + e)

How is “r” determined?

r = births – deaths

Total Population (rN)

Does not include immigration or emigration!

Example: 20,000 births – 15,000 deaths

500,000 organisms

Growth Rate (r) = .01 (x 100) = 1.0%

Exponential Growth Model (J)

Growth Rate ExampleWhat type of growth is this?

Time N Rate (r) r x N

T1 2 10 20

T2 20 10 200

T3 200 10 2000

T5 2000 10 20,000

J-curve – Exponential Growth

Population Growth Rate Practice

Exponential Growth

Time N r r x N

0 10 1.5 15

1 15 1.5 23

2 23 1.5 35

3 35 1.5 53

4 53 1.5 80

5 80 1.5 120

6 120 1.5 180

Exponential Growth

Rules: If r ˂ 0, then dN is negative and

population is declining.

If r > 0, then dN is positive and

population increases over time

If r = 0, then dN is 0 → no change in

population

Logistics Growth Model (S)

Logistics Growth

• Solve for the right side of the equation.

• You must know your carrying capacity (K)

Example;

1.Look at the N/K part.

2.If K=100 wolves, the maximum pop

3.If N =100 wolves, then N/K = 100 = 1

100

Logistics (cont)

4. If 1-N/K = 1-1 = 0 and rN (0) = 0 and dN/dt = 0.

5. This means no change in population because the population = carrying capacity.

6. What if N=50 and K=100, please calculate the outcome using the formula.

Logistics (cont)

7. Then N/K = 50/100 = ½.

8. 1-N/K = 1-1/2 = ½

9. Rate of increase is ½ rN or half of the reproductive rate.

10.Try it with N=120 and K=100, what is the reproductive rate going to be?

Logistics Growth from Model

Population DensityPopulation Density

• Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area– Some species exist in high densities - Mice– Some species exist in low densities - Mountain lions

• Density depends upon– social/population structure– mating relationships– time of year

Population Doubling

Rule of 70 – used for determining how long it takes for a population to double.

If a population grows at a rate of 7%, how long would it take to double?

70%, 70 / 14..7 doubling = .7 = 10 =

r (% form) = rr (decimal form) ,.07 yrs.

THIS IS THE DOUBLING TIME OF A POPULATION!!!is. It states that to find the doubling time of a quantity growing at a given annual percentage rate, divide the

percentage number into 70 to r

Population DispersionPopulation Dispersion

Population dispersion is the spatial pattern of distribution

There are three main classifications

Clumped: individuals are lumped into groups ex. Flocking birds or herbivore herds due to resources that are clumped or social interactions most common http://www.johndarm.clara.net/galleryphots/

Population DispersionPopulation DispersionUniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals, or do to regular spacing of resources rare because resources are rarely evenly spaced

http://www.calflora.net/bloomingplants/creosotebush2.html

www.agry.purdue.edu/turf/ tips/2002/clover611.htm

Random: Individuals are randomly dispersed in the environment ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met

Age StructureAge Structure• The age structure of a population is usually

shown graphically

• The population is usually divided up into prereproductives, reproductives and postreproductives

• The age structure of a population dictates whether is will grow, shrink, or stay the same size

Age Structure DiagramsAge Structure DiagramsPositive Growth Zero Growth Negative Growth (ZPG)Pyramid Shape Vertical Edges Inverted Pyramid

Population Dynamics OutlinePopulation Dynamics Outline

• Characteristics of a Population

• Population Dynamics and Population Dynamics and Carrying CapacityCarrying Capacity

• Reproductive Strategies

• Conservation Biology

• Human Impacts

• Working with Nature

• Biotic Potential– factors allow a population to increase

under ideal conditions, potentially leading to exponential growth

• Environmental Resistance – affect the young more than the elderly

in a population, thereby affecting recruitment (survival to reproductive age)

Biotic PotentialBiotic Potential• Ability of populations of a given species to

increase in size– Abiotic Contributing Factors:

• Favorable light

• Favorable Temperatures

• Favorable chemical environment - nutrients

– Biotic Contributing Factors:• Reproductive rate

• Generalized niche

• Ability to migrate or disperse

• Adequate defense mechanisms

• Ability to cope with adverse conditions

Environmental ResistanceEnvironmental Resistance• Ability of populations of a given species to

increase in size– Abiotic Contributing Factors:

• Unfavorable light

• Unfavorable Temperatures

• Unfavorable chemical environment - nutrients

– Biotic Contributing Factors:• Low reproductive rate

• Specialized niche

• Inability to migrate or disperse

• Inadequate defense mechanisms

• Inability to cope with adverse conditions

Exponential GrowthExponential Growth• As early as Darwin, scientists have realized that

populations have the ability to grow exponentially

• All populations have this ability, although not all populations realized this type of growth

• Darwin pondered the question of exponential growth. He knew that all species had the potential to grow exponentially

• He used elephants as an example because elephants are one of the slowest breeders on the planet

Exponential GrowthExponential GrowthOne female will produce 6 young over her 100 year life span. In a population,

this amounts to a growth rate of 2%

Darwin wondered, how many elephants could result from one male and one

female in 750 years?

19,000,000 elephants!!!19,000,000 elephants!!!

Exponential Growth GraphExponential Growth Graph

Population Dynamics and Carrying Population Dynamics and Carrying CapacityCapacity

• Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)– There is a dynamic balance between

biotic potential and environmental resistance

Carrying Capacity (K)Carrying Capacity (K)

• Exponential curve is not realistic due to carrying capacity of area

• Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)

Logistic GrowthLogistic Growth• Because of Environmental Resistance,

population growth decreases as density reaches carrying capacity

• Graph of individuals vs. time yields a sigmoid or S-curved growth curve

• Reproductive time lag causes population overshoot

• Population will not be steady curve due to resources (prey) and predators

Population Dynamics OutlinePopulation Dynamics Outline

• Characteristics of a Population

• Population Dynamics and Carrying Capacity

• Reproductive StrategiesReproductive Strategies• Conservation Biology

• Human Impacts

• Working with Nature

Reproductive StrategiesReproductive Strategies• Goal of every species is to produce as many

offspring as possible• Each individual has a limited amount of

energy to put towards life and reproduction• This leads to a trade-off of long life or high

reproductive rate• Natural Selection has lead to two strategies for

species: r - strategists and K - strategists

r - Strategistsr - Strategists• Spend most of

their time in exponential growth

• Maximize reproductive life

• Minimum life

K

R StrategistsR Strategists• Many small offspring• Little or no parental care and protection of offspring• Early reproductive age• Most offspring die before reaching reproductive age• Small adults• Adapted to unstable climate and environmental

conditions• High population growth rate – (r)• Population size fluctuates wildly above and below

carrying capacity – (K)• Generalist niche• Low ability to compete• Early successional species

K - StrategistsK - Strategists

• Maintain population at carrying capacity (K)

• Maximize lifespan

K

K- StrategistK- Strategist• Fewer, larger offspring• High parental care and protection of offspring• Later reproductive age• Most offspring survive to reproductive age• Larger adults• Adapted to stable climate and environmental

conditions• Lower population growth rate (r)• Population size fairly stable and usually close to

carrying capacity (K)• Specialist niche• High ability to compete• Late successional species

Survivorship CurvesSurvivorship Curves• Late Loss: K-strategists that produce few young

and care for them until they reach reproductive age thus reducing juvenile mortality

• Constant Loss: typically intermediate reproductive strategies with fairly constant mortality throughout all age classes

• Early Loss: r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age

Population Dynamics OutlinePopulation Dynamics Outline

• Characteristics of a Population

• Population Dynamics and Carrying Capacity

• Reproductive Strategies

• Conservation BiologyConservation Biology• Human Impacts

• Working with Nature

Conservation BiologyConservation Biology

• Careful and sensible use of natural resources by humans

• Originated in 1970s to deal with problems in maintaining earth's biodiversity

• Dedicated to protecting ecosystems and to finding practical ways to prevent premature extinctions of species

Conservation BiologyConservation Biology

• Three PrinciplesThree Principles1. Biodiversity and ecological integrity are

useful and necessary to all life on earth and should not be reduced by human actions

2. Humans should not cause or hasten the premature extinction of populations and species or disrupt vital ecological processes

3. Best way to preserve earth’s biodiversity and ecological integrity is to protect intact ecosystems that provide sufficient habitat

Habitat FragmentationHabitat Fragmentation• Process by which human activity

breaks natural ecosystems into smaller and smaller pieces of land

• Greatest impact on populations of species that require large areas of continuous habitat

• Also called habitat islands

1949 1964

Habitat fragmentation

in northern Alberta

1982 1991

Population Dynamics OutlinePopulation Dynamics Outline

• Characteristics of a Population

• Population Dynamics and Carrying Capacity

• Reproductive Strategies

• Conservation Biology

• Human ImpactsHuman Impacts• Working with Nature

Human ImpactsHuman Impacts

• Fragmentation and degrading habitat

• Simplifying natural ecosystems

• Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides

• Elimination of some predators

Human ImpactsHuman Impacts• Deliberately or accidentally

introducing new species

• Overharvesting potentially renewable resources

• Interfering with the normal chemical cycling and energy flows in ecosystem

Population Dynamics OutlinePopulation Dynamics Outline

• Characteristics of a Population

• Population Dynamics and Carrying Capacity

• Reproductive Strategies

• Conservation Biology

• Human Impacts

• Working with NatureWorking with Nature

Working with NatureWorking with Nature

• Learn six features of living systems– Interdependence– Diversity– Resilience– Adaptability– Unpredictability– Limits

Basic Ecological LessonsBasic Ecological Lessons1. Sunlight is primary source of energy

2. Nutrients are replenished and wastes are disposed of by recycling materials

3. Soil, water, air, plants and animals are renewed through natural processes

4. Energy is always required to produce or maintain an energy flow or to recycle chemicals

Basic Ecological LessonsBasic Ecological Lessons5. Biodiversity takes many forms because it has

evolved over billions of years under different conditions

6. Complex networks of + and – feedback loops exist

7. Population size and growth rate are controlled by interactions with other species and with abiotic

8. Organisms generally only use what they need

Four Principles for SustainableFour Principles for Sustainable

1. We are part of, not apart from, the earth’s dynamic web of life.

2. Our lives, lifestyles, and economies are totally dependent on the sun and the earth.

3. We can never do merely one thing (first law of

human ecology – Garret Hardin).

4. Everything is connected to everything else; we are all in it together.