2.6 CHANGES

By Peter Stanley, International School of Tanganyika, 2008

By Peter Stanley, International School of Tanganyika, 2008

Population vocab:Natality – (births) offspring are produced and added to the population

Mortality – (deaths) individuals die and are lost from the population

Immigration – (Move in) individuals move into the area from somewhere else and add to the population

Emigration – (Move out) individuals move out of the area and are lost from the population

Click for practice with Click for practice with exponential growthexponential growth

2.6.1 Limiting factors & Carrying capacity (K)

• The environment (biotic and abiotic) limits the population growth and determines the carrying capacity (K)

• Factors that limit population growth include: • Shortage of food (prey)

• Predation or parasitism

• Disease

• Pollution

• Shortage of space (territory) factors

“Explain the concepts of limiting factors and carrying capacity in the context of population growth.” (3)

Carrying capacity (K) -The maximum number of a species that can be sustainably supported by the environment.

2.6.2 Population curves“Describe and explain S and J population curves.” (3)

This is a Sigmoid (S-shaped) population growth curve.

Includes the following:

a.Exponential growth phase

b.Transitional phase

c.Plateau phase

d.Carrying capacity (K)

What would a J-shape population growth curve look like and why?

a

b

c

d

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Time

5.3.3

Phases in the growth

• Exponential Growth Phase:

• Natality rate is higher than the mortality rate.

• disease and predators are rare.

• abundance of food

Plateau Growth Phase:• Natality and mortality are

equal so the population size stays constant.

• Limiting factors:

• shortage of food

• increase in predation

• more diseases and parasites

Transitional Growth Phase: • Natality is still higher so population

continues to grow, but at a slower rate

• Limiting factors:

• Food is no longer as abundant due to the increase in the population size.

• May also be increase predation and disease.

In groups, prepare a summary of each, comparing numbers and rates of growth. ---I’ll pick the name sticks to see who presents

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2.6.3 Regulating factors of populations

• Density-dependent factors• Operate as negative feedback mechanisms that lead to the stability of a

population• Link to... positive and negative feedback: topic 1.1.6• Competition (hare and lynx example)

• Density-independent factors• Control many species, particularly the r-strategists (lots of reproduction

and offspring)• Weather and catastrophic events

• Internal factors may include:• Density-dependent fertility• Size of breeding territory

• External factors may include:• Predation• Disease

“Describe the role of density‑dependent and density‑independent factors, and internal and external factors, in the regulation of populations.” (2)

•K-strategists share these qualities:Benefit from stable K (carrying capacity)

•Found in a stable habitatLong life spansBegin breeding later in lifeLong gestation timesProduce small numbers of offspringTake good care of their young – infant mortality lowHave evolved to become increasingly efficient at exploiting an ever-narrower slice of their environment.

•In general, r-strategists share a number of features:Benefit from huge numbers (reproduction)

•Usually found in disturbed habitatsHave short life spansBegin breeding early in lifeHave short gestation timesProduce large numbers of offspringTake little care of their offspring (infant mortality large)Have efficient means of dispersal to new habitatsK

2.6.4 K- and r- strategies“Describe the principles associated with survivorship curves including, K‑ and r‑strategists.” (2)

r

Survivorship CurvesSurvivorship Curves The graph shows 4 representative survivorship curves.The graph shows 4 representative survivorship curves.

source: unknown

Survivorship CurvesSurvivorship Curves Curve A – Curve A – characteristic of organisms that have low mortality characteristic of organisms that have low mortality

until late in life when aging takes its toll.until late in life when aging takes its toll.

Curve B – Curve B – typical of populations in which factors such as typical of populations in which factors such as starvation and disease inhibit the effects of aging and infant starvation and disease inhibit the effects of aging and infant mortality is high. mortality is high.

Curve C – Curve C – a theoretical curve for an organism whereby the a theoretical curve for an organism whereby the chance of death is equal at all stageschance of death is equal at all stages

Curve D – Curve D – typical of organisms that produce huge numbers of typical of organisms that produce huge numbers of offspring accompanied by high rates of mortality.offspring accompanied by high rates of mortality.

source: unknown

Survivorship CurvesSurvivorship Curves

KK-strategists usually have survivorship curves somewhere -strategists usually have survivorship curves somewhere between between AA and and CC..

RR-strategists usually have -strategists usually have DD survivorship curves. survivorship curves.

source: unknown

2.6.5 Succession“Describe the concept and processes of succession in a named habitat.” (2)

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Primary SuccessionChanging an area from one lacking any community (no plants, no animals, no insects, no seeds, AND NO SOIL) to one consisting of individuals, populations, communities, and ecosystems.

Starts with no organic matter (NO SOIL)

Pioneer plants include lichens and mosses

Can you think of examples where primary succession is seen...* following a volcanic eruption* Bare rock* Glacier and Glacial retreat

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Secondary Succession

Follows disturbance of an existing community that removes or damages the vegetation, but does not remove, destroy, or cover the soil.

Starts WITH SOIL

Pioneer plants are the first plants to become established after disturbance.

Faster than primary succession

Can you think of examples where secondary succession is seen:* After a forest fire* Abandon farms* After flood

Wetland Succession

• Wetland areas present a special case of ecological succession because they can develop in a variety of ways and are constantly changing.

• What is the trend is this diagram (right) and how may it evolve?

Open water

Plant invasion

Siltation and Infilling

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2.6.6 Changes in succession

• Biomass Accumulation and Successional Stage:

“Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stages of succession.” (3)

Graph of Net Productivity during succession

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Species diversity during succession

Early Stage Mid Stage Late Stage

Productivity Low GPP but High percentage NPP

Gross Productivity increases rapidly

(high level of photosynthesis )

Ratio of NPP to R is roughly equal

Biomass Little increase in biomass

Increases in biomass as plant

forms become bigger

Trees reach their max size

2.6.7 Climax communities

A relatively stable group of plants and animals that are the end result of the successional process.

Examples include:Old growth forests

Cacti in deserts

grasses in the serengetti

Factors affecting climax communities include:Climatic and edaphic (soil) factors determine the nature of a climax community.

Human factors frequently affect this process through, for example; fire, agriculture, grazing and/or habitat destruction.

“Describe factors affecting the nature of climax communities.” (2)

Questions/Discussion

1. Explain what is meant by a climax community.

2. Explain each of the following changes which occur during succession:i. Species diversity increases

ii. Gross production increases

iii. Stability of the ecosystem increases

3. Give two reasons why farmland in Morogoro does not reach a climax community.

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* negative feedback (slide 64)* survivorship curves (slide 66)* succession (slide 69)

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