Ecology is the study of the interrelationsips

Levels of organisation

  1. Species
  2. Population: group of organisms of the same spcies in the same habitat
  3. Community: groupd of organisms of different species in the same habitat
  4. Ecosystem: living components + non-living components, self-supporting, stable, dynamic
  5. Biome: complex of communities that occupy a large geographical area, dominant type of plant
  6. Bioshpere: entire space on earth surface where oranisms exist

Basic features of an ecosystem

  1. interactions of organisms with one another and the physical environment
  2. Flow of energgy
  3. Cycling of materials

Types of ecosystems in Hong Kong

  1. Freshwater stream
  2. Mangrove
  3. Rocky shores
  4. Woodland
  5. Grassland

Freshwater stream


Rocky shore



Abiotic factors of an ecosystem

1. Temperature



2. Light



Duration of light in a day afffects the flowering of the plants

3. Rainfall and humidity



4. Wind speed



5. Water current

6. Salinity

7. Oxygen concentration


Aquatic insects have specialized breathing structure that sticks out of water to obtain O2 from air


Mangrove plants: to obtain O2 from air

8. Soil Properties

e.g. soil PH, air content, nutrient content --> types of animals and plants

Biotic community of an ecosystem

Niche and habitat

Habitat = the living place of organisms
Each species occupies a specific niche
Niche: is determined by: temperature range, types of food they eat, space they occupy

Species diversity

Dominant species

Interaction of organims in a community

  1. Predation (+,-)
    Predator eats prey
  2. Competition (-,-)
    Intraspecific ~ : same species
    Interspecific ~ : different species
    Intraspecific: more intense because individuals of the same species have the same needs
  3. Symbiosis
    1. Commensalism (+,0)
      One gains benefits while the other does not
    2. Mutualism (+,+)
      Both organisms gain benefits
    3. Parasitism (+,-)
      Some organisms live on or inside organisms, obtaining nutrients for them and harming the host

Ecological succession

Primary succession Secondary succession
Starts with barren areas where no soil or organisms were present before areas where organisms were once present
Pioneer community Pioneer community of lichens is needed Not needed because soil is already present
Biodiversity at the beginning Low Low
Period of time taken to reach a climax community long More quickly because seeds/ roots of plants may survive in the soil

Energy flow in an ecosystem

graph LR;
Carnivore/Omnivore--> .......
graph LR; Sun-->Plant; Plant-->Herbivore; Herbivore-->Carnivore/Omnivore; Carnivore/Omnivore--> .......

Food chain


graph LR;
graph LR; grass-->rabbit; rabbit-->fox;
  1. Producers
  1. Consumers
  1. Decomposers

Food web
Connect food chains together

Trophic levels and energy flow

Less energy at higher trophic level

  1. Uneaten body materials
  1. Egested material
  1. Excretory products
  1. Respiration

Energy "lost"

refers to energy not transferred to the next trophic level
1,2,3 --> broken down by decomposers
Energy loss in food chain --> sledom more than fice trophic levels

Ecological pyramids

  1. Pyramid of numbers
    Predator: larger in size than prey --> require more energy to maintain life
  2. Pyramid of biomass
    energy proportional to amount of living material

limitations of the ecological pyramids