BIOS104 Interspecific interactions

What are interspecific interactions?

interactions between different species

What are the types of interspecific interactions?

• competition

• predation

• parasitism

• mutualism

• commensalism

• amensalism

What is mutualism?

a form of symbiosis where 2 or more organisms of different species live in close physical contact with each other deriving advantages from the other

What is commensalism?

where one organism benefits while the other is neither helped nor harmed

What is amensalism?

one species is inhibited or destroyed and the other is unaffected

What are saprotrophs?

organisms that make use of dead matter

What is the main difference between saprotrophs and other organisms?

Can’t control their supply of resources

→ have to wait for an animal to die

What do decomposes break down?

organic matter at the molecular level

examples of decomposers?

microorganisms

→ bacteria, fungi

What do detritivores feed on?

dead plant and animal matter → detritus

examples of detritivores

invertebrates

→ earthworms, millipedes, termites, springtails

How long can a whale fall nourish an entire ecosystem of deep-sea creatures?

up to 2 years

what happens after a whale dies?

bacteria work first → produce gasses so whale floats to surface

then sharks and fish scavenge

then will sink again

What are the stages of decomposition?

• leaching

• fragmentation

• chemical alteration

What factors affect decomposition?

• temperature

• moisture

• oxygen availability

• substrate availability

Is cellulase common in the animal kingdom?

no, it is rare

What does cellulase do?

enzymes that break down cellulose

are decomposers specialists?

most are

What does intraspecific competition mean?

competition between the same species

Who wins the game, species who exploit resources more or less?

species who exploit resources more efficiently

What is interference competition?

species directly interfere with each others access to a resource

→ i.e. allelopathy in plants

What is resource (or exploitative) competition?

species compete indirectly by reducing the availability of a shared resource

What does niche mean?

the role and position a species occupies within an ecosystem, encompassing its interactions with both biotic and abiotic factors

What is a fundamental niche?

the full range of environmental conditions and resources a species could occupy and use

What is a realized niche?

the actual range of environmental conditions and resources a species does occupy and use, after accounting for biotic interactions

→ competition, predation etc

What is the competitive exclusion principle?

two species competing for the same limiting resource can’t coexist indefinitely

→ one will outcompete the other and persist → the other will go locally extinct

What factors mediate coexistence?

• resource partitioning (niche differentiation)

• environmental variation

• disturbance

Is competition symmetric or asymmetric?

asymmetric

What is character displacement?

the evolutionary divergence of traits in sympatric species due to competition

what is a sympatric species?

species living in the same area

How does character displacement reduce niche overlap and competition?

selection for each species to utilise a different niche

What are requirements for character displacement?

• phenotypic difference have a genetic basis

• resource use is related to the trait

• competition for that resource exists

What are the key ideas of the Lotka-Volterra model for interspecific competition?

• population growth - each group can grow on its own but there is a limit to how many can live there

• competition - species compete for food, affects how fast each group can grow

• carrying capacity - max. number of animals the area can support

What are the predicted outcomes of the Lotka-Volterra model?

• competitive exclusion

• coexistence

• unstable dynamics - if competition is too intense

What is the Lotka-Volterra model used for?

• predict whether 2 species can coexists or one will dominate

• understand how competition shapes ecosystems