3.3.1 The Effect of Biotic and Abiotic Factors on Populations Flashcards Preview

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Flashcards in 3.3.1 The Effect of Biotic and Abiotic Factors on Populations Deck (61)
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Define Habitat

Place where an organism lives


Define Population

All the organisms of one species in a habitat


Define Community 

All populations of different species in a habitat = community


Define Ecosystem

A community + all abiotic & biotic factors in the area


Define Abiotic conditions

Non-living features of ecosystem

e.g. temperature, availability of water


Define Biotic conditions

Living features of ecosystem

e.g. predators, food


Define Niche

Role of a species within its habitat

e.g. what it eats, where and when it feeds


Define Adaptation

Feature that member of a species have that increases their chance of survival and reproduction


The niche of a species occupies within its habitat includes...

  • Its biotic interactions 
    • e.g. the organisms it eats, and those it's eaten by
  • Its abiotic interactions 
    • e.g. oxygen an organism breathes in & CO2 it breathes out


If 2 species try to occupy same niche, there'll be ______


(One species will be more successful & it'll be one its own)


Organisms are adapted to both ____ conditions (e.g. water availability) and _____ conditions (e.g. predators) in their ecosystem 

Organisms are adapted to both abiotic conditions (e.g. water availability) and biotic conditions (e.g. predators) in their ecosystem 


What is meant by carrying capacity?

Maximum stable population size of a species that an ecosystem can support


What does population size vary due to? (2x)

  • Abiotic Factors 
  • Biotic Factors 


Name 3 examples of abiotic factors 

light, water, space available, temperature, chemical composition of surroundings, pH, etc.


Explain how when a mammal's surroundings is the ideal temperature (e.g. abiotic factor), it can lead variations in population size

  • e.g. when temperature of a mammal's surroundings is the ideal temp. for metabolic reactions to take place = don't have to use up as much energy maintaining their body temperature 
  • ∴ more energy can be used for growth and reproduction & population size will increase


Name 3 biotic factors that affect population size

  • Intraspecific Competition 
  • Interspecific Competition 
  • Predation 


What is interspecific competition?

When organisms of different species compete for same resources


Explain how interspecific competition can cause a change in population size 

  • Results in reducing the resources available to both populations
    • e.g. if share same food source = less available for both of them
    • Both populations limited by lower amount of food
    • Less energy for growth and reproduction
    • ∴ populations sizes lower for both species


What happens when 2 species are competing but one is better adapted to surroundings?

Less adapted species = out-competed (won't exist with other species)


Define Intraspecific Competition

When organisms of the same species compete for same resources


Explain how intraspecific competition leads to variation in population size

  1. Population of species increases when resources plentiful
    • Population ↑ = more organisms competing for same amount of space + food
  2.  Resources become limiting (not enough for all organisms)
    • Population ↓
  3. Smaller population = less competition = better for growth and reproduction
    • Population ↑


Explain how predation leads to variation in population size

  1. Predator population peaks after prey population
  2. Prey population ↑ (due to less preadators/more food available)
  3. More food available = predator population ↑
  4. As predator population ↑, ↑ predation ∴ prey population ↓
  5. Less food for predators = predator population ↓


Predator and Prey Population Cycle

Why does the prey population initially decline?

∵ there's too many of them for amount of food available

(This is then accelerated by predation)


Describe how to take a random sample from an area you're investigating

  1. Choose an area to sample
  2. Samples should be random to avoid bias
    • e.g. divide field into grid and use random number generator to select coordinates
  3. Use appropriate technique to take sample
  4. Repeat processes many times to reduce likelihood that results are due to chance
  5. No. of individuals for whole area can be estimated by taking mean of data collected in each sample & multiplying it by size of whole area


Name 2 methods of investigating non-motile organisms

  • Transects 
  • Quadrats


What is recorded in each quadrat?

Species frequency or no. of individuals of each species 


How can the percentage cover of a species be measured?

By counting how much of quadrat is covered by species

Count a square if it's more than half-covered


What is the benefit of measuring percentage cover?

Quick way of investigating populations & don't have to count all individual organisms


What are transects used for?

Used to find out how organisms (e.g. plants) are distributed across an area


Describe how you would conduct a belt transect

Place quadrats are next to each other along a transect to work out the species frequency & percentage cover along transect

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