Effect * of species 1 on species 2
Effect of
species 2
on species 1
* On per capita growth rate
Two ways to Classify Mutualisms
I. By Function:
• Trophic Mutualisms
• Protective Mutualisms
• Dispersive Mutualisms
Two ways to Classify Mutualisms
II. By relationship of mutualists for one another:
Obligate: species are so dependent on their mutualistic
relationship that cannot live in its absence.
e.g., symbionts
leaf-cutter ants & fungus
termites and gut fauna
Facultative: species can live without their mutualistic partner
e.g., oxpeckers
many diffuse mutualists
Diffuse Mutualisms: Mutualistic interactions that where the
“partner” can be one of any species, e.g., pollinators, seed
Trophic Mutualisms – involve a mutual exchange of
energy/nutrients – specialized to the point of obligates
Mycorrhizal fungi
Nitrification processes carried out only by specialized bacteria
NH3  NO2-
NO2-  NO3-
Nitrosomonas (soil)
Nitrosoccus (marine)
Nitrobacter (soil)
Nitrococcus (marine)
Denitrification processes carried out only by specialized bacteria,
such as Pseudomonas denitificans
NO3-  NO2-  NO
Nitrogen fixation offsets
Denitification and is
accomplished by free-living
bacteria, such as Azotobacter,
symbiotic bacteria, such as
Rhizobium occurring in roots
of legumes, and cyanobacteria.
Nitrogen-fixing bacteria in root nodules of soybeans
Protective Mutualisms – involve an exchange of protection
from predators/parasites often for an exchange of resources
Ant-leafhopper-goldenrod interactions
#alarm signals before
and after predator
Alarm Calling
• prey-2 predator
Tree hopper-ant mutualisms
More ants
Fewer LB
Mechanically mimicking the tactile alarm call
Dispersive Mutualisms – involve an exchange of a reproductive
service often for an exchange of resources
Magnificent Hummingbird
Seed Dispersal
Friendly Relations Between
Clark’s Nutcracker and
Whitebark Pine
Seed dispersal
American robin and Viburnum
Experimental tests of
Beltian bodies
Janzen’s study of Psuedomyrmex
and the bullshorn acacia.
A comparison of acacia with ants and those with ants removed
Growth (cm) by
bullshorn acacia
Survival (%) by
bullshorn acacia
The benefit to the plant is fewer
herbivorous insects
• 2000 interactions/day w/queue
• Eat parasites (coop) & mucosal
tissue/scales (defect)
• The latter leads to client “jolt”
so an observable cue
Jolts are predictors:
• 12-18/min among biting cleaners
• 2-3/min among coop cleaners
Do clients image score?
• If previous client ends w/conflict
100% bystanders (queue) depart
• w/o conflict 100% approach
Audience effects?
• 17 vs. 6 cleaners spp showed (-)
relationship between jolts and
bystander presence
And also observed in Sergeant major
More ants
Fewer LB
Mechanically mimicking the tactile alarm call
Keystone Mutualists (Eco Eng, Foundation Spp)
Plant species
Virola surinamensis
Tetragastris panamensis
Virola sebifera
Caesearia corymbosa **
Gurarea glabra
Didymopanax morototoni
Miconia argentea
Avian frugivores
** Considered a Keystone species by Howe (1977) because
it bears a fruit crop for 10 week period including December, the
time of lowest fruit production in La Selva forest
Casearia corymbosa
Red-lored Amazon eats the arils
and drops the fruit w/o dispersing
Eats huge quantities of seeds, but a
poor disperser. Toucans however depend
on Casearia seeds in December when
all their preferred foods are gone.
The only known dependable disperser
for Casearia seeds. Like the toucan, it
appears to have no alternative food to
eat in December.
Disappearance of key fruit would push the tityra, the toucan, and other
species to local extinction. Without its main disperser, Casearia, Virola
(primarily dispersed by the Chestnut-mandibled toucan), and other trees
dependent on these birds for dispersal would slowly lose their competitive
position and diversity would slowly erode away in the tropical rain forest in
La Selva.
Alternative *forms* of mutualisms
(1) Physical Ecosystem Engineers (after Jones et al. 1997)
What does a tree do in the forest?
- living and dead tissues are eaten by animals (+,-)
- competes with other plants for water and nutrients (-,-)
- branches, bark, roots, and leaf surfaces make shelter, resting locations,
and living space
- small pools for organisms are created where water gets channeled into
- soil cavities that from when roots grow provide places to live and cache food
- leaves and branches cast shade, reduce the impact of rain and wind, moderate
temperature extremes, and increase humidity in the under story and soil
- root growth aerates the soil, alters its texture, and affects the infiltration of
And more…..
Jones et al. called these modifications ecosystem engineering
And there are many, many, many examples.
Some almost trivial, such as plants creating shade??
Others are very obvious….
And EE have both
positive and negative
effects on individual
Species or the
Sometimes it’s the non-living
structure left behind that provides
the benefit, other times it may be
new structures created as a result
of an animal’s activity.
Coral reefs
Kelp forest
Sometimes Eco. Engineers are called Foundation species
when they form the base from which a whole community
of species is built
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