Mutualisms & Positive Interactions | Lecture 27

Mutualisms, Positive Interactions, Plant on Plant, Nurse Plants, parasitism, Commensalism, Mycoheterotrophy, Plant on Fungi, Plants & Animals/Pollination

Positive Interactions

1 species is benefitting, no one is harmed

What are the two types of positive interactions?

mutualism, commensalism

Negative interactions include…

competition, disturbance, herbivory

What is a rare example of a pollinator species and a seed disperser species being the same organism?

wild bananas, bats

Describe the mutualisms that led to the human body:

cells: cooperation between eukaryotic host and descendant of prokaryote (mitocondria)

multicellularity: cells give up reproduction to specialize in function and benefit whole organism

Microbes: more prokaryotes than eukaryotes, cooperate with each other and eukaryotic cells for digestion, immune, and excretory

Forest Mutualisms Belowground

mycorrhizal fungi transfer nutrients & carbon with trees, ++ or +0

Forest Mutualisms Aboveground

animals carry pollen from 1 flower to another and disperse seeds, ++

Forest Mutualisms Per Individual Plant

cells cooperating, microbiota

Positive Interaction (2)

interaction between organisms where at least 1 benefits and no one is harmed

Symbiosis

two organisms living in close association, not mutualism

Both competition and mutualisms can be…

asymmetric

Describe what correlates to (+,+) and (+,0)

mutualism, strong symmetric, clearly benefit like mycorrhizal fungi

commensalism, one benefits and other is not affected, like epiphytes

Why are plant-on-plant positive interactions not common?

plants living in close enough for positive interactions also likely competing for same resources

What are 3 examples of positive interactions for plant-on-plant?

nurse plants, commensalisms (epiphytes), parasitism

Nurse Plants

improve conditions for another plant species even if still engaging in competition

In what kind of habitat are nurse plants thought to be important?

arid environments

Explain how saguaro cacti use nurse plants to survive:

seedlings require shade, nurse plants Larrea and palo verde provide shade, cacti grow out

What is the cost of Saguaro cacti seedlings relying on nurse plants?

increase survival, growth rates decline by 33%

In the Juncus & Iva study, where did Iva grow best with and without neighbors?

iva grew best with neighbors in the middle zone, best without neighbors in the well-drained and low salintity soils

In the Juncus & Iva study, where did Juncus grow best with and without neighbors?

grew best with neighbors in middle zone and best without in well drained low salinity soils, but had higher biomass that iva in the waterlogged & saline soils

What determines the line between competition and facilitation in nurse plants?

stress gradients

Commensalism is _____ between plants

very common

What are two examples of commensalism in plants? (+, 0)

epiphytes, shade-dependent plants in understory

What is a less studied commensalism involving plants but not “plant on plant?”

mycorrhizal associations

Parasitic Plants

derive some or all their food from other plants or fungi

Hemiparasites

still photosynthesize to some degree, hemi-partial

Holoparasites

entirely reliant on stealing from host, holo-whole

Parasites make up ____ of angiosperm species

parasites

Parasitism evolved…

many times

Parasites can parasitize ___ and ____ of other plants

stems, roots

Haustoria

root-like projections that invade host tissues and extract water & nutrients

Mycoheterotrophy Parasite

type of plant that gives up photosynthesis to rely entirely on mycorrhizal associations

How is mycoheterotrophy indirectly plant-on-plant?

all the mycohetertroph’s biomass comes from the fungus, but all the fungi’s biomass came from a different plant

Mycorrhizae

fungi associated with plant roots

Describe the mutualistic interaction between mycorrhizae fungi and plants:

fungi gain carbon & stable environment in roots, plant gets nitrogen, phosphorus, and water

Mycorrhizae are found in _______ of plant species in most habitats

80-90%

Plants benefit _______ from interactions with animals

reproductively

What two positive interactions do animals have with plants?

pollination, seed dispersal

Generalist

interacts with a variety of species or functional types

Specialist

interacts with only 1 species or functional type

Describe how pollination and animals can be generalist:

pollination: plant welcomes many pollinators, focus on maximizing visits from most effective species and limiting ineffective pollinators

animals: visit many different species & flowers for rewards

Describe how pollination and animals can be specialists:

pollination: plant adapted for just 1 species to pollinate it

animal: only visits 1 flower/species

Most flowering plants are _____ pollinated and attract _____ pollinator(s)

animal, multiple, generalists

Animal pollination is ____ compared to wind pollination

more precise

What is an example of a generalist plant? How many pollinators visit it?

wild carrots, 334 pollinators

Most pollinators visit _____ plant species

multiple, generalists

What rewards do animals get from pollinating?

nectar/sugar/amino acids, pollen/protein, oils/fat

Pollen is both ____ and _____ by pollinators

eaten, transferred

What three things attract pollinators?

scent, pigments, pseudocopulation

What scents can attract pollinators?

sweet odor, pheromone mimics, dung/rotting meat odor

Carrion Plant/Starfish Flower:

attracts carrion flies, dead/rotting odor, covered in hairs