17.1 - Symbiosis

symbiosis

characterised by 2 or more species living purposefully in direct contact with each other

how can interactions be classified

• whether they help, harm or have no effect

• based on dependency on another organism

• resources

• physical association

3 categories of symbiosis

commensalism, mutualism and parasitism

classification by dependency on another organism

obligate and facultative symbiosis

obligate symbiosis

species that completely rely on another to the extent they couldn’t survive without the relationship e.g. lichens composed of a fungal and algal symbiont that can’t survive in other’s absence

facultative symbiosis

species that can survive independently when separated but not as well as benefits from relationship e.g. honeybees rely on pollen form flowers to survive but don’t rely on a single plant species

classification by resources

specific and diffuse

specific symbiosis

highly specialised close and often exclusive relationship usually with just 1 other species e.g. leaf cutter ants and fungal species they cultivate as food

diffuse symbiosis 

involves multiple species e.g. mycorrhizal fungi  that help extend the root systems of plants in exchange for nutrients with numerous plant species

classification by physical association

endosymbionts and ectosymbionts

endosymbionts

organisms that live within the body or cells of another organism e.g. dinoflagellate living inside corals providing energy via photosynthesis

ectosymbionts

organisms that live on the surface of another organism e.g. remora suction onto body of sharks

how do plants obtain food

autotrophy and heterotrophy

autotrophy 

synthesise food from inorganic substances via photosynthesis 

heterotrophy

rely on another organism for nourishment

haustoria

modified root projections that enable parasitic plants to invade host plant’s vascular tissue to extract nutrients and water

epiphytes

plants that grow on other plants without harming them for physical support

• specialised roots to anchor to host

• take up nutrients and water from air and environment

mixotropic

combines both autotrophy and heterotrophy

why did plants evolve these

to reduce the effects of environmental stressors

• low light = epiphyte

• nutrient availability = carnivore and parasite