B4.2 Ecological niches

Niche

Niche

Includes where an organism lives, what + how it eats, and its interactions with other species (role)

Spatial habitat

Physical area inhabited by any particular organism

Biotic factors

Feeding relationships (can be complex involving many other organisms)

Provision of shelter e.g nest sites, presence of parasites

Connected to abiotic factors

Tolerance

How well a species reacts to presence of something in its environment

Obligate anaerobes

Single celled prokaryotes with no tolerance for oxygen

Live in places where oxygen can’t reach- soil, deep water, intestines of animals

Facultative anaerobes

Capable of both anaerobic and aerobic respiration

Example: bakers yeast, uses oxygen to convert sugar to energy but can do anaerobic respiration when it is not present

Obligate aerobes

Require oxygen- if it is greatly reduced (hypoxia) or not present (anoxia), they die

Example: Fish in freshwater streams need oxygen above 3mgL-1

Autotrophs

Organisms that make their own food from inorganic substances

Often referred to as producers

Heterotrophs

Organisms that rely on eating other organisms

Often referred to as consumers

Holozoic nutrition

Way of getting nutrients by ingesting all or part of an organism (ingested, digested, absorbed, then assimilated)

Examples: humans, cats, or dogs

Mixotrophic nutrition

Making food and ingesting nutrients from other organisms (useful if sun is low or food is sparse)

Example: the genus Euglena

Obligate mixotrophs

Need both nutrition systems to survive

Facultative mixotrophs

Can survive on one system, but use the other as a supplement

Saprotrophs

Live in or on non-living organic matter secreting digestive enzymes and absorbing products of digestion

Decomposers

Saprotrophic fungi and bacteria

Role is to break down waste material

Methods used in domain archaea

Photosynthesis (generating energy with sunlight)

Chemosynthesis (generating energy from reactions with organic matter)

Heterotrophic nutrition (obtaining energy through eating other organisms)

Genus Halobacterium

Able to perform a type of photosynthesis without chlorophyll, instead using bacteriorhodopsin

• Live in very salty environments (Dead Sea, Great Salt Lake)

• Not autotrophs as they receive carbon from other organisms

Chemoautotrophs

Organisms capable of producing own food using chemical reactions without sunlight (chemosynthesis)

Examples:

• Ferroplasma acidiphilium living in acidic areas, get energy from oxidising ferrous iron

• Archaea in oceans/soils use ammonia for energy, generate nitrogen compounds to be used in plants

Relationship between dentition and diet

Humans part of Hominidae family

Only evidence of extinct species in this family are bones/skulls/teeth/fossil DNA/tools they used

Knowing what a species eats tells us what niche it occupies

Incisors

Used for cutting bite sized pieces of food

Folivores (leaf eaters) and frugivores (fruit eaters) tend to have larger ones

Canines

Sharper, used for ripping or tearing tough materials like meat

Premolars and molars

Used for crushing, slicing, and grinding food into a paste

The pointer and narrower the crowns, the better adapted for meat

The rounder and blunter, better for plant material

Orangutans

Eat mostly fruit (frugivores), sometimes supplemented with insects/egg/honey

Have intimidating canines, despite being herbivores

Gorillas

Eat almost exclusively plant material (folivores) but some occasionally eat ants or termites

Have intimidating canines, despite being herbivores

Chimpanzees

Prefer fruit but also eat plants/meat e.g ants, termites, monkeys, honey, bees, birds, eggs, antelope, warthog

Dentition matches diet

Herbivores

Generally have large incisors, wide premolars/molars

Carnivores

Have sharp pointy teeth, inc. premolars/molars

Disadvantages of examining teeth

They have other purposes like intimidation so can’t always determine diet

Microwear

Small abrasions or removal of teeth surfaces

Help see diet as softer food leave different marks to harder foods, food with grit from soil scratch teeth

Adaptations for eating plants

Aphids have stylets, grasshoppers/caterpillars have mandibles to pierce the plant (and cell wall) if they don’t possess enzymes to break down cellulose

Herbivorous vertebrate adaptations

Specialised back teeth for grinding plant matter

Cows are ruminants- swallow grass then regurgitate it to continue chewing (chewing the cud)

Bacteria and archaea in digestive system to help break down cellulose

Giraffes- long necks/legs to reach acacia leaves, tough tongues resist thorns

Plant adaptations for protection

Thick bark, thorns, spikes

Common nettle (Urtica dioica) has silica hairs filled with chemical irritants which break with contact and causes swelling/stinging

Phytotoxins cause nausea, cardiac problems, hallucinations

Foxgloves produce toxins which make animals sick

Castor beans (Ricinus communis) produce toxic ricin

Adaptations for neutralising plant toxins

Ruminants have microbes that detoxify many plant poisons

Cautious sampling→ animals trying new food don’t eat too much of it

Moose (Alces alces) have proteins in saliva which neutralise tannins

If a mammal isn’t killed by a toxin, the liver neutralises it

Chemical predator adaptations

Black mamba (Dendroaspis polylepis) injects venom when biting prey containing neurotoxins to paralyse prey

Certain species of orb-weaver spiders produce chemicals which mimic sex pheromones of moths to attract prey

Physical predator adaptations

Birds of prey have excellent eyesight to detect prey, owls can see at night

Bats and dolphins use echolocation (send out ultrasonic vibrations and process how they bounce off objects)

Sharks have organs in their heads called ampullae of Lorenzini that detect electromagnetic field (fishes/seals’ nervous system sends off small electricity discharges when swimming)

Vultures have acute sense of smell to help find rotting flesh

Ability to fly/run/swim fast to catch prey

Claws/beaks/teeth to kill prey

Have brain that can rapidly make decisions if risk in catching prey is too great

Behavioural predator adaptations

Ambush predators hide and wait for prey (spiders, anglerfish)

Pack hunting helps bring down large prey (wolves have trust and know who is the leader of the pack, soldier ants use raiding parties)

Pursuit predators rely on speed and endurance to tire out prey (cheetahs, humans- persistence hunting)

Chemical prey adaptations

Produce bad-tasting or poisonous chemicals (Dart frogs produce alkaloid on skin that interferes with heart function)

Physical prey adaptations

Camouflage (moth wings, octopus species change texture/skin cells to mimic surroundings)

Aposematism: bright colours to warn predators (non-venomous king snakes use this and mimic coral snakes)

Warning vocalisations (jays, blackbirds, primates e.g monkeys)

Protective shells (grasshoppers, lobsters, clams, mussels, turtles, tortoises)

Protective spines (porcupines)

Behavioural prey adaptations

Fleeing at sight of predator

Hiding

Forming groups (elephants, wildebeest)

Tree adaptations for light

Position leaves high above competitors- dominate canopy

Canopy→ understorey→ shrub layer→ forest floor

Sturdy trunks and strong supporting branches

Liana adaptations for light

Take root on forest floor and use trees as a scaffold

Seedlings grow towards shade (tree trunks) and climb

The bigger/more tangled they get the more harm done to the tree as there is competition

Epiphytes

Attach roots to tree trunks and use moisture from tree branches/humidity, can survive on little water

Hemi-epiphytes

Example: strangler figs spending early life rooted in tree, stems push down into soil later

Interwining stems and branches can encircle a tree trunk

Shrubs on forest floor

Adapted to absorb wavelength of diffuse sunlight (longer red wavelengths)

Examples: banana, ginger

Herbaceous plants

Don’t produce woody stem e.g bananas, wildflowers, strawberries

Fundamental niche

Potential niche a species could inhabit

Realised niche

The actual niche a species inhabits (due to competition)

Red fox niche

Diet is small mammals/amphibians/insects, can survive in all seasons

Fundamental→ forest edge but over time this has become farmland and has seen competition from coyotes so niche has become narrower

Competitive exclusion

States no two species in a community can occupy the same niche, both populations would decrease and one would eventually outcompete and replace the other

Seen in 1934 experiment by G.F Cause on two types of Paramecium (P.aurelia, P. caudatum)

• Interspecific competition

• When cultured together, P. caudatum died

Competitive exclusion in natural ecosystems

Hard to see as it has usually already happened (most niches only have one species), if we introduce another than hard to know if other factors are contributing

Example: UK Grey squirrel population growing, red squirrels fading- hard to know whether human activity/disease is responsible or not