9.1 Community and Ecosystem
In an ecosystem, organisms do not just interact with one another, but they also interact with non-living elements to establish a balanced and dynamic natural system.
Learning Objectives
- Define ecology, habitat, species, population, community, ecosystem, and niche.
- Identify and describe the biotic and abiotic components in an ecosystem.
- Classify organisms based on nutritional habits into autotrophic and heterotrophic.
- Explain energy flow through food chains and food webs across different trophic levels.
- Interpret and compare the three ecological pyramids.
- Describe the main types of interactions among biotic components.
- Investigate the effects of intraspecific and interspecific competition among organisms.
- Explain the abiotic and biotic components, adaptive features, colonisation, and succession of mangrove ecosystems.
Zonation, Colonisation, and Succession in a Mangrove Ecosystem
Pioneer mangrove species trap sediments and progressively change the soil environment, causing succession from the seaward coast to the inland zone.
Short Explanation
What is an ecosystem?
An ecosystem is an integrated network consisting of living organisms (biotic components) interacting with one another and with non-living physical elements (abiotic components) such as temperature, light, pH, and topography.
Fundamental terms in ecology
Ecology studies interactions among organisms and their surroundings. A habitat is the natural living place of an organism, while a species is a group of similar organisms able to interbreed and produce offspring.
From population to ecosystem
A population is a group of organisms of the same species in the same habitat. A community consists of populations of different species living together and interacting. An ecosystem includes communities plus non-living components such as water, air and soil.
Niche
A niche is the role of an organism in an ecosystem. The ecological niche is the role of a species in its surroundings, while the species niche is the way a species interacts with biotic and abiotic components. A niche can change during life stages involving morphological changes, such as metamorphosis in a butterfly.
Abiotic components
Abiotic components include pH value, temperature, light intensity, topography, microclimate, and air humidity.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is the main difference between an organism's habitat and its niche?
Why does an ecological pyramid of energy always have an upright shape?
What role do the prop roots of Rhizophora sp. play in mangrove succession?
Common Mistakes
- Confusing population with community: a community consists of populations of multiple different species living together in one habitat, not a single group of organisms.
- Misunderstanding the 10% energy rule: only 10% is transferred to the next trophic level, while 90% is lost as heat, respiration, and excretion — not the reverse.
- Confusing intraspecific and interspecific competition: intra- means same species, inter- means different species.
- Swapping the succession order of mangrove zones: Avicennia sp. and Sonneratia sp. are the pioneers at the seaward coastal zone, followed by Rhizophora sp. in the middle zone.
Concept Misunderstandings
A food web is simply a single straight line of who eats whom.
A single linear sequence is a food chain; a food web consists of interconnected food chains because most animals feed on more than one type of organism and occupy different trophic levels simultaneously.
All autotrophs require sunlight to produce organic compounds.
Photoautotrophs require light energy, but chemoautotrophs (such as Nitrobacter sp.) synthesise organic substances without light by oxidising inorganic substances like ammonia and hydrogen sulphide.
Commensalism means both organisms help each other survive.
That is mutualism. In commensalism, only one organism benefits while the other organism neither benefits nor suffers harm.
Summary
- An ecosystem comprises biotic components (producers, consumers, decomposers) and abiotic components (temperature, pH, light, topography, microclimate, air humidity).
- Ecological hierarchy scales from species → population → community → ecosystem.
- Trophic levels track energy flow from sunlight to producers (first level) and successive consumer levels; 90% of energy is lost at each step, leaving only 10% transferred.
- Organism interactions include saprophytism, symbiosis (mutualism, commensalism, parasitism), predation, and competition (intraspecific and interspecific).
- Mangrove ecosystems showcase extreme adaptations (succulent leaves, salt glands, pneumatophore/prop/buttress roots, vivipary) and clear ecological succession (Avicennia/Sonneratia → Rhizophora → Bruguiera → land plants).
Short Activity
Objective: test your understanding of ecological terms, energy flow, and interactions.
A. Objective Quiz
Which of the following root adaptations belongs to the pioneer species Avicennia sp. to facilitate aeration in water-submerged mud?
According to the pyramid of energy, what percentage of energy is dissipated into the environment through heat, living processes, and excretion when moving from one trophic level to the next?
B. Fill in the Blanks
Competition between individuals of different species for limited resources such as sunlight or nutrients is known as competition.
Seeds that germinate and begin growing while still attached to the parent mangrove tree are described as seeds.
C. Matching / Drag and Drop
Match each biotic interaction or role to its correct textbook description. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Ecological Term to Its Description
Write the correct ecological term next to each description.
| Description | Ecological Term |
|---|---|
| 1. An interaction that brings benefits to both interacting organisms | |
| 2. An interaction benefiting one organism without harming or benefiting the other | |
| 3. Gaining nutrients from dead and decaying organic materials via external digestion | |
| 4. Benefiting one organism while causing harm and nutrient loss to the host |
Answer choices: Mutualism • Commensalism • Saprophytism • Parasitism
