Ecological niches

The **role** a species plays in its ecosystem — its **abiotic tolerances**, its **food source** and its **interactions** with other species.

**Abiotic tolerances** (e.g. temperature, oxygen), the **food/energy source**, and **interactions** with other species.

A **habitat** is *where* an organism lives (its 'address'); a **niche** is its *role* — how it lives (its 'job').

**Yes** — e.g. two fish in the same lake that feed on different foods have the same habitat but different niches.

A **non-living** physical condition of the environment, such as temperature, oxygen, light or pH.

A **living** influence on an organism, such as predators, prey, competitors or partner species.

The range of an abiotic factor (e.g. temperature) within which a species can **survive and grow**.

The **full** range of conditions and resources a species **could** occupy if there were **no competitors**.

The **smaller** part of the fundamental niche a species **actually** occupies once **competitors** are present.

Because **competition** restricts the species to part of its potential range (the start of competitive exclusion).

**Read the data** (e.g. temperature ranges) and deduce from the numbers — do not answer from general memory of the species.

Submerged plants are part of its niche — they provide **more shelter from predators** and **more food**, so the fish survives better there.

A **non-living** physical or chemical feature of the environment (e.g. temperature, light, water, pH, oxygen, salinity).

A **living** feature of the environment — the effect of other organisms (predators, competitors, parasites, food).

Ask **is it alive?** Non-living physical/chemical = abiotic; the effect of another organism = biotic.

**Temperature, light intensity and water availability** (also pH, oxygen, salinity, soil minerals).

**Predators, competitors and parasites** (also disease and food supply).

The range of an abiotic factor over which it can **survive** — best in the optimum, absent beyond its limits.

The middle peak, where the organism's **performance / abundance is highest**.

The organism cannot survive and is **absent**.

The abiotic factor **furthest from the optimum** — the one that restricts where an organism can live.

A **large region with a characteristic climate** (abiotic conditions) and a characteristic community of organisms.

**Temperature** and **rainfall** (water availability).

**Very high temperature** and **very low rainfall** (scarce water).

Conditions are kept **near its optimum**, so the **limiting factor is removed**.

Where an organism gets its **energy** and where it gets its **carbon**.

An organism that **makes its own organic carbon** from an inorganic source (**CO₂**). 'Auto' = self-feeding.

An organism that obtains organic carbon by **taking in organic molecules** made by other organisms. 'Hetero' = feeding on others.

An organism that can use **both modes** — making its own food like an autotroph AND taking organic food like a heterotroph (e.g. Euglena).

**Carbon dioxide (CO₂)** — an inorganic carbon source.

Both fix CO₂, but a **photoautotroph** uses **light** for energy, while a **chemoautotroph** oxidises **inorganic chemicals** (e.g. H₂S).

Heterotrophic feeding in which food is **ingested and digested INTERNALLY** inside the body (most animals).

A heterotroph that feeds on **dead** organic matter, digesting it **EXTERNALLY** with secreted enzymes and absorbing the products (decomposers).

A heterotroph that feeds on a **living host** and **harms** it (e.g. a tapeworm, a head louse).

Saprotroph digests **externally** and feeds on **dead** matter; a holozoic feeder ingests food and digests it **internally**.

Some bacteria around **deep-sea vents** that oxidise chemicals such as hydrogen sulfide for energy.

It is part of the niche: an **obligate aerobe** needs O₂, an **obligate anaerobe** is poisoned by it, a **facultative anaerobe** can use it or do without.

Read the **energy source AND carbon source together** — e.g. light + CO₂ = photoautotroph; oxidising chemicals + CO₂ = chemoautotroph.

Two species **cannot occupy exactly the same niche** in the same place indefinitely — one is excluded, or they partition the resource.

An organism's **role** in its ecosystem: the abiotic conditions it tolerates, the resources it uses and its interactions with other species.

The **full range** of conditions and resources a species **could** use if there were **no competitors** present.

The **smaller part** of the fundamental niche a species **actually** uses once **competition** from other species restricts it.

The realized niche is **never larger** than the fundamental niche — competition can only restrict it.

When the species grows **alone**, with **no competitors** present.

When the species grows **alongside a competitor**, which squeezes it into a smaller range.

When competing species **divide a shared resource** (by space, time or type) so each uses a different part and they can **coexist**.

**Competitive exclusion** (one species is driven out) or **resource partitioning** (they split the resource and coexist in separate zones).

Each is the **better competitor in a different part** of the gradient and **excludes** the other from the part it loses, so each is restricted to its **realized niche**.

**Competition** between them — each has excluded the other from part of the gradient (competitive exclusion / partitioning).

An interaction where two **different species** both need the **same limited resource**, so each reduces the amount available to the other.

An interaction between **two different species** ('inter' = between, 'specific' = species).

By the **effect on each species**: **+** if it benefits, **–** if it is harmed.

One organism (the **predator**) kills and eats another (the **prey**). Predator **+**, prey **–**.

An animal eats a plant (or part of one). The herbivore **+**, the plant **–** (often not killed).

Two species use the same **limited resource**, so **both are harmed** ( **– / –** ).

Two species live closely together and **both benefit** ( **+ / +** ).

A **parasite** lives on or in a **host**, taking nutrients. Parasite **+**, host **–**.

A **pathogen** (disease-causing microbe) infects a host and causes **disease**. Pathogen **+**, host **–**.

**Mutualism** ( **+ / +** ) — e.g. a bee pollinating a flower; legume + nitrogen-fixing bacteria.

**Competition** ( **– / –** ) — it is the only – / – relationship.

By **how** the harm happens: **eaten** → predation/herbivory; **lived on / infected** → parasitism/pathogenicity.

**Name** the relationship **and** state how **each** species is affected (+ / –). Naming alone scores only half.

**Mutualism** — both the human and the bacteria benefit.

**Mutualism** — the plant gains usable nitrogen and the bacteria gain sugars and a habitat.