Populations

Define: populations

A group of individuals of the same species living in the same area.

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Give an example of exponential growth. What problems has this caused?

1890: 120 Starlings released in New York's central Park. Today= over 100 million starlings spread over N.America. Outcompeted local species. Damage crops by eating most nutritious grains.

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How has the human population changed over time?

Very small + little growth until 2000 BC. Then birth of agriculture=surplus food=small population increase, still

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What is happening to human population growth now?

Slowing- fastest growth rate was in 1968 (2.09% growth). This has been slowly decreasing since. May decline to 1% in 2020. 2050-0.5%?

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Why can most populations not grow exponentially forever?

Environmental limits are usually reached (density-dependent factors) i.e. space, potable water, food, available mates. Not enough capacity to deal with waste products. Higher risk of disease and predation.

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What is K?

The carrying capacity for the environment, The number of individuals that can be supported.

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Give an example of discontinous growth?

Plants in temperate regions- grow in Summer and die back over Winter - stepped.

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Why are Paramecium so useful for laboratory experiments?

High growth rates even in lab. In lab other variables can be controlled e.g. no predation.

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How are Paramecium able to divide daily?

Protists/protozoa - single celled organisms- use asexual reproduction (mitosis).

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What caused such a massive die back of hooved animals in East Africa in the early 20th C?

Rinderpest

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How did Wildebeest populations change over the 20th C in East Africa?

Huge decline due to Rinderpest- below 20 animals km-2 in. Vaccine developed in 1950. Exponential growth. K reached 1977/8. Back to usual fluctuations.

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How were willow trees in the UK affected by Myxomatosis?

Decrease in rabbits= less saplings eaten=exponential growth in willow trees with K reached by 1980.

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Is the graph of numbers of Heron nests in the UK evidence of a carrying capacity?

Maybe not...Herons dip to find food. During harsher winters if lakes and rivers ice over- cannot access enough food- big die backs in heron numbers=dip. Then numbers may recover slightly after breeding season. Density-independent factor.

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Can graphs of biomass of Herring caught in the North sea provide evidence for K?

Good records of biomass caught since 1900. Can compare biomass caught pre-1950's (passive fishing with drift nets) and post 1950's.

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How has biomass of Herring caught in the North Sea changed over the 20th C?

Steady quantity caught pre-1950's. Lower biomass caught during periods of WW1 and WW2 due to lower fishing effort. 1950 onwards - increase to peak in 1975. Then decrease to 1995 when fishery was closed. Resource was over-exploited. Above MSY.

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What factors increased the biomass of North sea Herring caught post-1950?

More vessels with higher capacity. Larger nets e.g modern drift nets up to 5500ft long. Echo-sounders to locate shoals. Purse-seine nets=no escape.

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Why might the decline in Skylarks in the UK be hard to identify?

Population follows an unstable pattern due to being so dependent upon food availability etc.

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Give examples to show how some species follow population cycles with "boom" and "bust" periods.

Any example. But 1= Snowshoe Hare and Lynx. Each with a population cycle of 10 years including a rapid increase, then decline. Lag time between the 2 but are very much linked in a predator-prey relationship. Size of one affects the other.

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Is the logistic growth model applicable to patterns seen in Nature?

Some populations have dynamics similar to the model e.g. sheep, herring. Some=cyclical e.g. snowshoe hare + lynx. Some=random e.g. skylark. But all can be predicted to some extent with the model as long as K is known.

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What does "r" represent in the logistic growth model?

The growth rate of the population (per capita growth rate)

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What happens when "r" of a population is

Population usually dies out

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When r= 3-3.4 what happens to the population according to Bob May?

Oscillates between 2 fixed values.

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As r increases above 3.4 what happens to the population?

Oscillates between more and more values- dynamics appear more chaotic

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What other factors might be needed to effectively predict a population change?

Internal birth + death. Also- immigration+emigration.

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Populations

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