A group of organisms of a single species interbreeding and occupying a particular area
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Describe environmental resistance and give some examples
Refers to all factors that may limit population growth, e.g. food availability, overcrowding, predation, disease, parasitism, competition, climate/weather change, accumulation of toxic waste
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Definition of immigration
When individuals join a population permanently
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Definition of migration
Temporary movement within a population - normally due to seasonal changes
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Definition of emigration
When individuals leave a population population
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What does a density dependent factor mean and give some examples
When there is a greater affect when the population is larger, e.g. parasites/disease,
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What does a density independent factor mean and give some examples
When all animals and plants are affected by these factors regardless of population size, e.g. forest fires, floods, drought, frost, deforestation
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What is the set point?
When a population fluctuates in size, the numbers of most species lie near an equilibrium - set point
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How does weather effect population size?
Warm weather = more reproduction = population increases, Cold weather = less reproduction = population decreases
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What resources do plants and animals compete for?
Plants - light, space, water, nutrients Animals - food, shelter, space and reproductive partners
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Definition of intraspecific competition
Competition for resources between members of the same species
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What is the driving force behind natural selection?
Intraspecific competition
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How do pests reduce crop yield?
They feed on crops and animals, compete with crop organisms for resources, can cause disease in crop organisms, can make infection by pathogens more likely, can spoil food when it's being stored or transported.
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How are chemicals applied to attack pests?
Sprayed onto the crop, applied as powders/smokes in enclosed areas, sprayed onto animals, added to animal feed
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Definition of pesticides
Poisonous chemicals used to control organisms considered harmful to agriculture or organisms involved in disease transmission
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What are the advantages of chemical control?
Chemicals can be applied on a small scale such as a single field, very effective means of control, pests are eradicated quickly and relatively cheaply, application doesn't require a high level of skill
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What are the disadvantages of chemical control?
Pests may become resistant to the pesticide, long term exposure can cause harm to humans, chemicals not specific and can eradicate beneficial insects, some pesticides may kill fish, birds or mammals by destroying their food
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What are the advantages of biological control?
Provide long term control if population equilibrium is established, usually specific to one pest, no environmental contamination, can be used in glasshouse situations, initial research costs mean it's expensive to introduce but low to maintain
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What are the disadvantages of biological control?
Little use to individual farmers - needs to be carried out on large scale, frequent input is required to attain a population balance,needs high level of skill and research, few successes, b.c. agents slow to build up, detailed knowledge needed
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Give examples of integrated pest control techniques
Minimal use of highly selective pesticides, varying cultivation techniques, pest resistant crops, biological control agents
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How can humans improve the circulation of nitrogen?
Sewage disposal boosts organic nitrogen supplies, fixing atmospheric nitrogen artificially using chemical processes that convert it to fertilisers, micro organisms can be used for making compost + silage, large amount of animal waste used as manure
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How do farming practices aid the circulation of nitrogen?
Planting fields of clover to encourage nitrogen fixation, draining land + reducing anaerobic conditions, ploughing fields in order to improve aeration of soil, plant legumes to fix N - and allow plants to die and decompose
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Why do organisms need Nitrogen?
amino acids, nitrogenous bases, proteins and nucleic acid
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What are the 4 stages of the Nitrogen cycle?
Nitrogen fixation, ammonification, nitrification and denitrification
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Other cards in this set
Card 2
Front
Describe environmental resistance and give some examples
Back
Refers to all factors that may limit population growth, e.g. food availability, overcrowding, predation, disease, parasitism, competition, climate/weather change, accumulation of toxic waste
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