Ecology: Concepts, Ecosystems & Organization

Basic Concepts of Ecology

• The habitat is the place where organisms live.
• Ecology studies the relationships between organisms and their environment.

Levels of Organization in Ecological Studies

• Species are the lowest level of classification, consisting of organisms that can interbreed to produce fertile offspring.
• A population is a group of organisms of the same species living in the same habitat.
• A community includes all the populations of different species living in the same habitat.
• An ecosystem is a natural unit composed of living and non-living components.
• Ecosystem interactions make the unit self-supporting, stable, and dynamic
• A biome is a complex of communities in a large geographical area with a dominant vegetation type.
• The biosphere is the entire space on Earth where organisms exist.

Basic Features of an Ecosystem

• Ecosystems are self-supporting, stable, and dynamic.
• Useful elements (e.g., carbon and nitrogen) are recycled, not lost.
• These elements cycle through the ecosystem during various processes like photosynthesis and respiration.
• Ecosystems do not need extra materials supplied.
• Interactions between organisms and the environment make an ecosystem dynamic.
• Feeding transfers materials from one organism to another as sustenance.
• Inorganic materials can be absorbed by organisms and converted to organic matter through autotrophic nutrition.
• Materials return to the environment through processes like respiration.
• Organisms adapt to live in specific environments, affecting their physical environment.
• Ecosystems require an ongoing energy input, typically from the sun.
• After plants absorb solar energy to produce organic matter, the energy transfers through the food chain.
• Energy, in the form of sustenance, is eventually lost as heat.

Major Types of Ecosystems in Hong Kong

• Freshwater streams (淡水河流)are a major type of ecosystem
• Mangroves (紅樹林) with salty + fresh mixed water are a major type of ecosystem
• Woodland (林地)is a major type of ecosystem
• Grassland (草地)is a major type of ecosystem
• Rocky shores (岩岸)are a major type of ecosystem

Components of an Ecosystem: Abiotic Factors

• Ecosystems consist of abiotic (non-living) and biotic (living) components.
• Abiotic factors include temperature, light, rainfall, humidity, wind speed, water current, oxygen level, salinity, and the nature of the substratum.

Common Abiotic Factors

• Temperature greatly affects the distribution and behavior of organisms due to its influence on metabolic reactions.
• Light intensity affects photosynthesis rates in plants, and the duration of light affects plant growth.
• Light influences animal behavior, dictating when certain animals are active
• The amount of water available affects habitats, leading organisms in water-limited areas to develop mechanisms to retain water and reduce water loss.
• Adaptations develop in organisms exposed to strong wind and waves to help hold on to the substratum.
• Streamlined body forms reduce water resistance.
• Factors affecting oxygen levels in aquatic habitats include temperature, water current, and organic matter decomposition.
• Oxygen solubility decreases as temperature increases.
• Splashes by water currents increase contact with water.
• The decomposition of organic matter uses oxygen
• Salinity directly impacts the availability of water and minerals.
• Soil particle size affects air spaces and oxygen concentration, while soil type influences pH, oxygen, water, nutrient, and humus content.

Key Abiotic Factors in Different Ecosystems

• In woodlands, the canopy layer prevents the soil from eroding and reduces runoff.
• Tree roots hold soil particles, preventing soil erosion and reducing runoff.
• Humus maintains soil fertility.
• Rocky shores are exposed to strong waves and divided into zones based on exposure.
• Rocky shore organisms develop adaptations to attach to rocks and protective shells.
• Tidal actions affect mangroves in sheltered bays.
• Salinity in mangrove mud fluctuates throughout the day.
• Organic matter accumulates in soft mud, resulting in low oxygen levels in the mud.
• Mangrove trees have specialized roots to obtain oxygen, while others excrete salt.
• Organic matter in mangrove substratum provides food for various animals.
• In freshwater ecosystems, oxygen levels are typically higher in the upper course
• Substratum particles are larger in the upper course.
• Plants along stream banks provide food, regulate water temperature, purify water, reduce flooding, and prevent erosion.

Describing the Biotic Community

• The biotic community is the living component of an ecosystem.

Niche and Habitat

• A habitat is where an organism lives.
• A niche defines the role an organism plays in its environment, including its temperature range, diet, and space.

Species Diversity

• Species diversity refers to the variety of organisms and is determined by the number of species (species richness) and the proportion of different species (relative abundance).
• Communities can have the same species richness but different species diversity if the proportions of species present vary.

Dominant Species

• Dominant species have the greatest influence on the composition and diversity of a community.
• The most common terrestrial plants are dominant species

Interactions Among Organisms in a Community

• Organisms in a community interact in ways that can benefit, harm, or not affect one another.

Predation (+/-)

• In predation, the predator benefits while the prey is harmed.
• Predator population changes lag behind those of the prey.
  • Initially, prey have plenty of food and increase in numbers.
  • The predator population increases as prey becomes more available.
  • As predator numbers increase, the prey population decreases.
  • When food becomes scarce, the predator population decreases.
  • The prey population recovers and the cycle repeats.

Competition (-/-)

• All organisms involved in competition are harmed.
• Two types of competition are interspecific (between different species) and intraspecific (within the same species).
• Intraspecific competition is more intense because individuals of the same species share the same niche and resources.

Commensalism (+/0)

• In commensalism, one organism benefits while the other is unaffected.
• Egrets benefit from insect feeding stirred up by livestock who are unaffected.

Mutualism (+/+)

• Mutualism is when two organisms live interdependently, such that they both benefit
• Algae produce food while the fungi hold water for it

Parasitism (+/-)

• Parasitism is when an organism lives inside (endoparasite) or outside host who is obtaining benefits causing harm
  • Tapeworms live in the intestines of mammals and absorb digested foods.

Ecological Succession

• Ecological succession is the sequence of community composition changes over time.
• Organisms modify their environment, facilitating the arrival of other species repeatedly leading to species diversity
• Progressively leading to a maximum when a climax community is formed

Primary Succession

• Primary succession starts during colonisation of a bare area
• Barren rocks get smaller via weathering
• This forms organic matter, which forms the - pioneer community
• Which gradually forms together with rock particles
• Dead, decaying plants and animals enriches with minerals which attracts growth, creating a woodland

Characteristics of a climax community

• There is usually a greater number of species, organism
• The energy input is at a maximum

Secondary Succession

• Secondary succession occurs on barren hillsides where there was a previous disturbance
• Different communities include pioneer communities
  • There is usually present of soil
  • Secondary succession occurs faster if there are seed roots
  • or underground crops present