1. Ecosystem: all the organisms living in a particular area and all the non-living (abiotic) factors
2. Habitat: the place where an organism lives, e.g., a rocky shore or a field
3. Population: all the organisms of one species in a habitat
4. Population size: the number of individuals of one species in a particular area
5. Community: all of the organisms of different species that live in the same habitat and interact with each other
6. Abiotic factors: the non-living features of the ecosystem, e.g., temperature and the availability of water
7. Biotic factors: the living features of the ecosystem, e.g., the presence of predators or food
8. Abundance: the number of individuals of one species in a particular area (it’s the same as population size)
9. Distribution: where a species is within a particular area
Factors affecting population size / abundance
1. Abiotic factors
e.g., amount of light, water, space available, surrounding temperatures, chemical composition of their surroundings, etc...
• When abiotic conditions are IDEAL for a species --- organisms can grow fast and reproduce successfully (& vice versa)
2. Biotic factors
a) Interspecific competition
= competition between members of DIFFERENT SPECIES
What does this mean?
: Resources available to both populations are reduced, e.g., if they share the same source of food, there will be less available to both of them
• Both populations will be limited by a lower amount of food
(they’ll have less energy for growth and reproduction → population sizes will be lower)
b) Intrapecific competition
= competition between members of the SAME SPECIES
• If the population of a species is too large
: resources become limiting, population begins to decline
• The maximum stable population size of a species that an ecosystem can support = the CARRYING CAPACITY
c) Predation
= where an organism (the predator) kills and eats another organism (the prey)
• As the population of one changes, it causes the other population to change as well
Factors affecting distribution
1. Abiotic factors
e.g., some plants can only grow on south-facing slopes in the northern hemisphere → that’s where light intensity is greatest
some plants don’t grow near the shoreline → the soil is too saline
2. Biotic factors
e.g., INTERSPECIFIC COMPETITION → if two species are competing but one is better adapted to the environment, the less well adapted
species is likely to be out-competed
2
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The role of a species within its habitat
• Its BIOTIC interactions: e.g., the organisms it eats, and those its eaten by
• Its ABIOTIC interactions: e.g., the oxygen an organism breathes in, and the CO2 it breathes out
Investigating populations & abiotic factors
Sampling
PROCESS:
1. Choose an area to sample – a small area within the habitat being studied
2. Count the number of individuals of each species
3. Repeat the process – take as many samples as possible (at least 10)
4. Use the results to estimate the total number of individuals or the total number of different species in the habitat being studied
5. When sampling different habitats and comparing them, always use the same same sampling technique
Random vs non-random sampling
• To avoid BIAS – sampling should be random
However, sometimes a non-random sample is needed (e.g., in habitats where there is a lot of variety in the abiotic factors and/or distribution
of species in the habitat and you want to make sure all the areas are sampled) → SYSTEMATIC SAMPLING – a type of non-random sampling
Investigating populations
1. Immobile populations
= using a FRAME QUADRAT
1. Frame quadrat placed on the ground (by selecting random coordinates with a random number
generator)
2. The number of each species can be recorded in each quadrat
3. The percentage cover can then be calculated
4. Repeat the same for different coordinates and calculate a result using a test such as
Simpson’s Diversity Index
2. Plant populations
= using a POINT QUADRAT
1. Placed on the ground at random points
2. Pins are dropped through the holes in the frame and every plant that the pin touches is
recorde
3. Number of individuals of each species is recorded in each quadrat
(line transects for distribution)
Investigating abiotic factors
1. Climate – temp: thermometer
- rainfall: rain gauge
- humidity: hygrometer
2. Oxygen availability (in aquatic habitats): oxygen sensor
3. Light intensity: light sensor
4. Soil – pH: pH monitor / indicator liquid
- moisture: difference in mass before and after drying the soil
3
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