B4.2 ECOLOGICAL NICHES

Define a niche.

A niche is the role of an organism in its environment, including its habitat, feeding, and interactions with other species.

Define a habitat.

The habitat is the physical environment in which a species, population, or community normally lives.

Distinguish between habitat and niche.

A habitat is the physical space, while a niche includes the organism's role, diet, and relationships.

Define a fundamental niche.

The potential mode of existence of a species, assuming no competition.

Define a realized niche.

The actual mode of existence, considering interactions such as competition and predation.

Compare fundamental and realized niches.

Realized niches are always equal to or smaller than fundamental niches due to biotic pressures like competition.

State the competitive exclusion principle.

Two species cannot occupy the same niche indefinitely; one will eventually outcompete and exclude the other.

Explain why two species cannot share the same niche.

They would compete for the exact same resources. One would dominate, causing the other to either adapt, migrate, or go extinct.

Provide an example of competitive exclusion.

Oak vs. Birch: Both compete for sunlight and nutrients. Oaks grow taller and eventually block light, causing birch trees to die.

Define holozoic nutrition.

Ingestion of whole organisms or parts, followed by digestion and absorption (e.g., humans).

Outline saprotrophic nutrition.

Organisms secrete enzymes onto dead organic matter and absorb nutrients externally (e.g., fungi, bacteria).

Distinguish between saprotrophs and detritivores.

Saprotrophs digest outside the body; detritivores ingest first and digest internally.

State one example of a mixotroph.

Euglena: photosynthesizes and also feeds on organic matter.

Define obligate aerobes.

Require continuous oxygen for survival (e.g., most eukaryotes).

Define obligate anaerobes.

Cannot survive in oxygen-rich environments (e.g., some archaea).

Define facultative anaerobes.

Can live in both oxic and anoxic conditions (e.g., yeast).

Describe 3 physical adaptations of herbivores.

1) Dental pad (no upper incisors)

2) Broad molars for grinding

3) Chisel-like teeth for gnawing

Outline 2 digestive adaptations in herbivores.

1) Four-chambered stomach for microbial fermentation\

2) Alkaline saliva delays digestion and supports fermentation

List physical predator adaptations.

Sharp claws, good eyesight, strong jaws

Give two chemical predator adaptations.

1) Snakes and spiders produce venom/toxins

2) Use of chemical cues to locate prey

Give an example of a behavioural adaptation in predators.

Use of calls or scents to coordinate group hunting

Describe how height helps plants compete for light.

Tall plants reach the canopy, gaining better access to sunlight.

Describe the function of lianas.

Lianas climb on other plants to access light without investing in thick stems.

Explain the advantage of being an epiphyte.

Epiphytes grow on trees to reach sunlight, avoiding competition on the forest floor.

Outline adaptations of shade-tolerant plants (5)

1) Broader/thinner leaves

2) Efficient use of far-red light

3) Chloroplast movement

4) Leaf repositioning

5) Slower, efficient nutrient use

Describe the role of leaf surface area in light capture.

Large, thin leaves increase the light absorption capacity, especially in shady environments.

Define competitive exclusion

Two species can not occupy the same niche because one will come to dominate and exclude the other.

State why organisms in extreme niches face less competition.

Fewer organisms can survive in extreme conditions, so competition and predation are reduced.

Give an example of an extremophile.

Thermophilic bacteria in hot springs