B4.2 Niches

What is an ecological niche?

the unique role that a species plays within an ecosystem

What does a niche include?

Includes biotic and abiotic interactions: growth, survival and reproduction including how a species obtains food.

How can organisms be classified based on their different needs for oxygen?

Obligate aerobes, obligate anaerobes, facultative anaerobes.

What are obligate aerobes?

Require continuous oxygen supply so only live in oxic envrionments

What are obligate anaerobes?

Inhibited or killed by oxygen so only live in anoxic environments

What are facultative anaerobes?

Use oxygen if available.

What is a method of nutrition?

The way in which an organism gains organic molecules to fuel respiration

What are the two main modes of nutrition?

Autotrophy and heterotrophy

What is an autotroph?

Synthesises its own organic molecules from simple inorganic substances in its environment.

What are photoautotrophs?

Use light energy to convert carbon dioxide into organic molecules such as carbohydrates. They are known as producers.

What are chemoautotrophs?

Synthesise organic carbon compounds using energy from oxidation of chemicals.

What is a heterotroph?

Obtains carbon compounds from consuming other organisms. Uses these to synthesise new carbon compounds that they use.

What is holozoic nutrition?

They are heterotrophs that gain organic molecules by ingesting, digesting, absorbing and assimilating molecules from the tissues of other organisms. It involves internal digestion.

What are mixotrophs?

Organisms that make use of more than one method of nutrition

What are obligate mixotrophs?

Must constantly have access to both methods of nutrition

What are facultative mixotrophs?

Can survive using one method of nutrition, which is supplemented by the other.

Example of mixotrophs?

Corals; carnivorous plants; euglena

How are euglena mixotrophs?

Single-celled eukaryotic organism found in fresh water that use both autotrophy and heterotrophy. They can take in bacterial cells by endocytosis and then digest them using digestive enzymes in lysosomes. Euglena cells also contain a light-sensitive spot that enables them to position themselves so that maximum light reaches their chloroplasts.

How are corals mixotrophs?

Coral polyps gain organic molecules from their symbiotic photosynthetic zooxanthellae and by filter feeding from the surrounding water

How are carnivorous plants mixotrophs?

They build organic molecules using both photosynthesis and using molecules from the tissues of digested insects.

What are saprotrophs?

Heterotrophs that ingest the tissues of dead organisms and waste material by secreting extracellular enzymes onto their food and digesting it externally

Difference between saprotrophic and holozoic nutrition?

In saprotrophic nutrition digestion takes place externally

Why are saprotrophs such an essential component of ecosystems?

The digestive enzymes allow them to hydrolyse biological molecules which release a range of products and mineral ions. Not all these minerals are absorbed by the saprotrophs which leaves them in the surrounding soil from absorption by other organisms such as plants.

Different groups of archaea (prokaryotes) vary metabolically:

Phototrophic archaea. Heterotrophic archaea (Oxidation of carbon compounds). Chemotrophic archaea (Oxidation of inorganic chemicals eg. Methanogens)

What features of teeth can be used to analyse the relationship between dentition and the diet of omnivorous and herbivorous representative members of the family Hominidae?

Gaps between teeth. Canine, incisor, premolar & molar size and shape. Strength of jaw/jaw muscles. Enamel thickness. Scratches in enamel. Isotopes in enamel.

Shape and size of teeth in carnivores?

Large pointed canines, small incisors, pointed molars and premolars, strong jaws for predators of large prey.

Shape and size of teeth in omnivores?

Medium sized blunt canines. Larger and sharper incisors. Cusps (lumps) on molars.

Shape and size of teeth in herbivores?

Small diamond shaped canines. Flattened incisors. Flat molars for grinding food. Strong jaws muscles for chewing hard foods.

Value of evidence of teeth to diet?

Teeth don’t always give a perfect indication of the diet of a species. Teeth play a role in other processes (defending territory)

Skull evidence from Paranthrapus robustus?

Suggests they had a diet of tough plant material. Their skull shape similar to modern gorillas; robust in shape, large jaw muscles for chewing tough vegetation. Large molars and premolars for grinding vegetation. Thick tooth enamel to protect the tooth from being damaged by tough plant matter.

Skull evidence from Homo floresiensis?

Suggests they were primarily plant eaters but may have eaten some meat. Large premolar teeth and small canines. Jaws were square and robust. Tooth abrasion suggests a fibrous plant-based diet. Skulls more similar in shape to humans suggesting a reduction in the biting forces used.

Skull evidence from chimpanzees?

Mainly frugivores (mainly fruits). Relatively small jaw muscles, only strong enough to chew softer fruit and animal tissues. Small incisor teeth and long canine teeth to bite and tear meat.

Which herbivore insects have sucking mouthparts?

Aphids

Sucking mouthparts of Aphids?

Modified piercing mouthparts called stylets. They secrete pectinase to digest pectin so the stylet can slide between the cell walls into the plant’s phloem to access the sucrose.

What is pectin?

A polysaccharide that sticks the cell walls of plants together

Which herbivore insects have chewing mouthparts?

Grasshoppers, crickets, ants, cockroaches, earwigs

Chewing mouthparts of insect herbivores?

Large pair of heavy jaws (mandibles) which they use to cut food. Another pair of jaw (maxillae) which they use to chew their food.

Why have plants adapted to defend against herbivores?

Herbivory causes damage to plants, reducing their leaf surface area available for photosynthesis and their ability to transport substances.

Mechanical deterrents? (Cacti, Nettles, Bark, Leaf hairs)

Cacti have sharp spines to deter herbivores that might attempt to eat their succulent stems. Nettles have tiny hairs that contain toxins which irritate the skin. Thick bark prevents insects such as aphids from piercing plant stems. Many tiny hairs on leaves may make it more difficult for insects to bite into/pierce plant tissues.

Toxic secondary compounds? (Tannins, Foxgloves, Dead nightshade)

Many plants produce chemicals called tannins which deter herbivores by their bitter taste, have negative impact on the efficiency of digestive processes. Foxgloves produce a toxic compound, digitalis, which can affect the heartbeat of humans and animals. Dead nightshade can produce a toxin known as atropine which can cause muscle paralysis by blocking the binding of neurotransmitters.

Adaptations for herbivory in mammals?

Grazing animals and ruminant mammals, neutralising toxins, cautious sampling

Grazing animals adaptations for herbivory?

Flat teeth for grinding plant matter

How are ruminant mammals adapted for herbivory?

Have digestive systems adapted to improve their digestion of tough plant material, stomachs with several compartments to regurgitate and re-chew food aiding digestion. They have specialised communities of bacteria in their digestive tracks which contain enzymes needed to break down cellulose.

Neutralising toxins as an adaptation for herbivory in mammals?

Some deer produce proteins in their saliva that bind to tannins.

Cautious sampling as an example of adaptation of herbivory in mammals?

Cautious sampling when mammals first encounter a new plant, meaning that any toxic chemicals will not be consumed in large enough quantities to be dangerous.

Types of adaptations of predators and prey?

Chemical, Physical or behavioural

Chemical adaptations of predators for Catching prey

American bolas spiders attract moths by mimicking their sex pheromones.

Chemical adaptations of predators for Killing prey

The black mamba snake kills its prey with a series of bites that inject a venom containing neurotoxins

Physical structures of predators for finding prey?

Osprey’s have acute vision

Physical structures of predators for catching prey?

Osprey have long curved claws on their feet to grasp prey such as slippery fish

Physical structures of predators for killing prey?

The lion has large canine to kill prey with a clamping bite to the throat

Behavioural adaptations of predators for finding prey?

Kestrels (falcon) hover 10-20 metres over open country waiting for signs of movement before it swoops down on ground prey

Behavioural adaptations of predators for catching and killing prey?

Lionesses often hunt in groups (prides). They are able to kill larger prey.

Chemical adaptations of prey for avoiding predators?

Texas horned lizards are able to squirt blood from their eyes which startles the predator who often drops the lizard, which can then escape

Physical structures of prey for avoiding predators?

The porcupine is covered with large protective spines

Behavioural adaptations of prey for avoiding predators?

Vervet monkeys give different warning calls depending on the predator which is attacking.

How are the Canopy layers of the forest determined?

By different amounts of sunlight required for each plant species. There is fierce competition for the sunlight.

Adaptation of canopy trees?

Trunks are branchless to heights of 30m to not waste energy on producing branches.

What percentage of light is absorbed by leaves of the canopy?

85-97%

Adaptation of topmost leaves in canopy?

Angled so that they are not fully exposed to the sun. Prevents them from being damaged by the intensity of the tropical sun

Adaptations of leaves lower down from the canopy?

Angled horizontally to capture all the rays reaching them.

Adaptations of ferns?

They are on the forest floor. Depends on sunflecks, patches of sunlight that reach parts of the forest floor for only a few seconds a day. The dark green leaves are very efficient at capturing sunlight.

What are epiphytes?

They don’t extract food from their host tree but use them to get closer to sunlight

Two types of epiphytes?

Birdsnest fern, Strangler fig

Birdnest fern structural adaptation?

Large, spoon-shaped leaves are arranged in a funnel shape:

1. Collects organic debris which decomposes over time to provide essential nutrients.

2. Retains moisture and prevents dehydration.

Strangler fig structural adaptations?

Seed dispersed by bird droppings that land in the fork of a tree. It sends roots all the way to the ground and the fig grows to the light. Roots encase and strangle the host tree. Host tree rots away leaving the strangler fig standing tall.

What is the fundamental niche?

The entire range of abiotic factors combined with the biotic factors that a species would occupy if it had no competition.

What is realised niche?

The occupied range of a species because the competitors exclude the species from parts of its fundamental niche

Example of fundamental vs realised niche in a species?

Fundamental niche of chthamalus: able to occupy high tide and low tide. In reality they only occupy high tide zone (realised niche) because they are outcompeted by Balanus in low tide regions.

What is competitive exclusion?

If there are limited resources, two organisms who exploit those resources will have to compete for them to survive. This competition could result in the extinction of one of the species.

Example of competitive exclusion?

Both Paramecium aurelia and Paramecim caudatum when grown individually in the lab thrive. When grown in the same test tube with a fixed amount of nutrients, they both grow poorly and eventually P.aurelia outcompetes P.caudatum for food leading to P.caudatum’s extinction.

What happens if extinction of one species doesn’t occur from competition?

The two species living together in the same place always have a difference between their niches.