Facilitation

Mutualism (+/+)

Both species benefit

has Degree of specificity and Duration of intimacy

Degree of specificity

Specialists and generalists

Specialists

species-specific interactions

Generalist

association with a wide diversity of mutualistic partners

Duration of intimacy

Nonsymbiotic mutualists and Symbiotic mutualism

Nonsymbiotic mutualists

are free living

Symbiotic mutualism

involves much more dependence of species for one another (obligatory)

Obligate mutualists

cannot survive or reproduce without the mutualistic interaction

Facultative mutualists

can survive without the interaction

Dispersive Mutualisms

Involve dispersal of pollen and seed

Plants with heavy seeds depend on animals for dispersal away from the parent plant

Seed dispersal mechanisms are not as obligatory as plant-pollinator systems

Attracting pollinators: bees

◎ ~65% of angiosperm species pollinated by bees

◎ Have conspicuous colors (nectar guides)

◎ Don’t see red

◎ Sometimes only visible in UV range

• Mostly blue, purple and yellow flowers

Attracting pollinators: bees characteristics

◎ Flowers often have landing pads

◎ Visual cues

◎ Delicate, sweet scents

◎ Small, narrow tube

◎ Sturdy flowers

Attracting pollinators: moths characteristics

◎ More visual than olfactory

◎ White flowers

◎ Long floral tubes

◎ Flat petals or bent back

◎ Hover-feeders

◎ Night blooming

Attracting pollinators: butterflies characteristics

◎ Visual, not olfactory

◎ Perching feeders

◎ Blue, yellow, red, showy flowers

◎ Deep floral tubes

Attracting pollinators: moth examples

Madagascar orchid

30 cm to the nectar!

Attracting pollinators: flies characteristics

◎ Bad odors, Coloration of rotting flesh

◎ Attract beetles and carrion flies because they will try to lay eggs

Attracting pollinators: flies example

Voodoo Lily, corpse flowers

Attracting pollinators: birds

◎ Often red and odorless

◎ Flower shape

◎ Sturdy structure

◎ Recurved petals

◎ Hover-feeders

Attracting pollinators: bats

◎ Night blooming

◎ White flowers

◎ Robust

◎ Strong smells

Attracting pollinators: other mammals

possoms

Pollination of Magnolias

trap beetles in the flowers

Frugivores

fruit-eating animals and eat only the tissue around the seed

Attracting frugivores

Plants must attract frugivores at the right time, when seeds are mature and ready for dispersal

○ Attractive odors, softened texture, increasing sugar/oil content, bright fruit coloration

Benefits of frugivores to the plant

Competition Avoidance

Predator Escape

Colonization

Directed Dispersal

Competition Avoidance

Competition with the parent plant is avoided, but there is no guarantee that the seed will fall into an optimal habitat.

Predator Escape

Seed predators congregate under parent trees to feed on the fallen seeds, so well-dispersed seeds suffer less predation.

colonization

Constantly shifting environmental conditions for seed germination means that parental location is not always a good predictor of seedling success.

Directed Dispersal

Some dispersers distribute seeds into optimal

sites.

Myrmecochores

plants that produce seeds with an ant-attracting food body on the seed coat (elaisome)

Defensive Mutualisms

Involves one species defending another in return for a reward

Defensive Mutualism examples

aphids and ants

ants in hallowed thorns of acacia tree

ants get food and protection, tree gets protection from predators and competition

Resource-based Mutualisms

Involve species that can obtain resources better together than alone

The human microbiome

The microbial communities that live in and on our bodies (NIH)

○ ∼1013–10 14 microbial cells (Sender et al. 2016)

○ 1 : 1 bacterial: human cells (Sender et al. 2016)

Breakdown and digest food to obtain nutrients and energy

Stimulate and shape our immune system

Produce vitamins

Protect from pathogens

changes w/ age and diet

Bacteroides thetaiotamicron

Synthesizes carbohydrates, vitamins, nutrients.

Signals genes to build a network of intestinal blood vessels

Signals genes to produce antimicrobial compounds

Resource-based Mutualisms examples

legumes, mycorrhiza, oxpeckers and ticks(questionable)

Mutualism and Population Dynamics

Mutualisms can occur indirectly: through a third species or by altering the local environment

At the population level: Mutualism occurs if the growth rate of species A increases with increasing density of species B (and vice versa)

○ Not easily modeled

Modeling Mutualistic Interactions equations

Species 1: dN1 /dt = r1N1((K 1 – N1 + αN2)/K1)

○ α = per capita effect of an individual of species 2 on species 1

◎ Species 2: dN2/dt = r2N2((K2 – N2 + βN1/K2)

○ β = per capita effect of an individual of species 1 on species

hwo to solve zero-growth isoclines

set numerator = 0

then N1/N2 =0

Game Theory

the study of conflict and cooperation between intelligent, rational decision makers

Prisoner’s Dilemma

if prisoners both turn each other in they get 0, if both prisoners cooperate they get 5 mil each, if one defects they get 10 mil and the other 0

average payoff twice as high if they defect

Flood & Dresher

applied prisoner’s dilemma to evolutionary biology in the 1980s

Prisoner’s Dilemma species

bee that bites out nectar(carpenter bees), plant mimics bee(bee orchid), plant that mimics other plant

Iterative Prisoner’s Dilemma

less deception than expected

Multiple opportunities to interact

Players adapt their behaviors according to the other player’s actions

If both cooperate, minor initial reward, but adds up over time (reciprocal altruism)

Economic Model of Trade

Specifically account for variation in rewards

Assumes two independent groups differ in their ability to access resources in ways that makes it advantageous to trade resources

Commensalism (+/0)

One species benefits and the other is unaffected

Commensalism example

eyelash mites, mites on white fly larvae, hooked part of plants and bears, cattle egrets(cattle stir up bugs)

Associational resistance

plant that chills by myrica which wards of beetles

Metabiosis

using organisms parts after death(hermit crabs)

inquilinism

using anotehr organism for housing(epiphytes)

phoresy

use for transport(mites on insects)