B4.2 Ecological niches

Define the term niche

A niche is the role of a species within its habitat.

What are some examples of factors that make up an organism's niche

What it eats, which other species depend on it for food, what time of day it is active, exactly where in a habitat it lives, exactly where in a habitat it feeds.

True or False? Two species can occupy exactly the same niche within a habitat

False. No two species can fill the same niche; one will out-compete the other.

True or False? Species can only survive in habitats in which they are well adapted to their niche

True. Species must be well adapted to their niche to survive.

What are examples of biotic interactions that influence an organism's ability to fill its niche

Contact with pathogens and parasites, competition for food, avoiding predators, finding food.

True or False? All organisms can switch between aerobic and anaerobic respiration

False. Some can switch, many survive using only one type.

Where can obligate anaerobes be found

In oxygen-free environments such as lower layers of soil, deep water, and inside other organisms.

What are facultative anaerobes

Organisms that mainly respire aerobically but can switch to anaerobic respiration without negative effects.

What are obligate aerobes

Organisms that cannot survive without oxygen and rely on aerobic respiration.

What happens if obligate aerobes perform anaerobic respiration

They must switch back to aerobic respiration quickly due to cellular damage.

What is meant by the phrase mode of nutrition

The way an organism acquires organic molecules for respiration.

How does photosynthesis function as a mode of nutrition

It transfers light energy into a usable chemical form.

What are the main types of photosynthetic organisms

Plants, algae, and photosynthetic bacteria such as cyanobacteria.

Define the term holozoic nutrition

A form of heterotrophy where organisms ingest and internally digest organic molecules.

True or False? All animals are heterotrophic

True. All animals obtain organic molecules from other organisms.

What is a mixotroph

An organism that uses both autotrophic and heterotrophic nutrition methods.

Give an example of a mixotrophic organism

Euglena, which photosynthesises and digests bacterial cells.

What distinguishes obligate mixotrophs from facultative mixotrophs

Obligate mixotrophs must use both methods; facultative mixotrophs can use just one and supplement with the other.

What are saprotrophs

Heterotrophs that digest food externally and absorb the products.

Name two examples of saprotrophic organisms

Fungi and bacteria.

What are the archaea

A group of single-celled organisms forming one of the three domains.

What are some of the ways that archaea provide energy for ATP production

From light (phototrophic), inorganic chemicals (chemotrophic), or carbon compounds (heterotrophic).

What does the jaw muscle size difference between chimps and gorillas suggest about their diets

Chimps have smaller jaw muscles for softer foods; gorillas have larger ones for tougher plant material.

True or False? The dentition of extinct hominids can provide clues about their diet

True.

Why do teeth not provide a perfect indication of the diets of extinct hominids

Teeth may also have been used for purposes like defence.

What does the presence of large molars in Paranthropus robustus suggest about its diet

It suggests a diet of tough plant material.

What kinds of fossil evidence from Homo floresiensis might suggest that they were primarily plant eaters, but that they may have eaten some meat

Large grinding teeth, large jaw, and tooth abrasions suggest plant eating; skull shape suggests possible meat eating.

Define the term herbivore

A heterotroph that feeds on plants.

How are some insect mouthparts adapted for herbivory

Stylets pierce plant tissue (e.g. aphids); mandibles chew plant tissue (e.g. caterpillars).

What is an example of a mechanical defence against herbivory in plants

Sharp spines (e.g. cacti), stinging hairs (e.g. nettles), thick bark, hairy leaves.

How do plants use secondary compounds as a defence against herbivory

They may be toxic (e.g. caffeine), or taste bitter (e.g. tannins).

How do some mammals avoid being harmed by toxins in the plants that they consume

Neutralising proteins or cautious sampling of plants.

What are examples of chemical adaptations in predators

Production of venom, chemical mimicry, and scent camouflage.

What are examples of physical adaptations that help predators to catch prey

Long-distance vision, forward-facing eyes, strong sense of smell, echolocation, speed, and large canine teeth.

What type of predator adaptation is lying in wait

It is a behavioural adaptation.

What are examples of chemical adaptations found in prey animals

Toxins (e.g. poison dart frogs), scent camouflage.

What type of prey adaptation is having eyes on the sides of the head

It is a physical adaptation.

What are examples of behavioural adaptations found in prey animals

Hiding, fleeing, group living, playing dead, and mimicry of larger size.

What are some examples of plant adaptations for harvesting light

Growing tall, climbing other plants (lianas), living in the canopy (epiphytes), being shade-tolerant.

How do strangler epiphytes differ from lianas

Strangler epiphytes start life in the canopy and grow in both directions; lianas grow from the forest floor.

True or False? Shade-tolerant plants contain the same photosynthetic pigments as plants in the canopy

False. They contain different pigments to absorb low-light wavelengths.

Why do ground-dwelling forest plants often have large leaves

To maximise surface area for light absorption.

What is the difference between a species' fundamental niche and its realised niche

The fundamental niche is the potential niche; the realised niche is what it actually occupies in competition.

Define the term competitive exclusion in the context of ecological niches

The elimination of one species from a niche due to competition.

True or False? When two species compete for the same niche, one of the two species will always become locally extinct

False. Extinction is one outcome, but not the only one.

What are the possible outcomes of competitive exclusion for species

One species becomes extinct, one shifts to a different niche, or both use smaller parts of their niche.