Mutualisms - Chap. 15
I. Terms and concepts
A. Symbiosis vs. Mutualism
B. Degree of dependence: Obligate vs. facultative
C. Degree of specialization: Specialists vs.
generalists
D. What types of "currency“?
E. Coevolution
F. Effects on realized niche
II. Examples
A. Mycorrhizae - fungi and plants
Ectomycorrhizae
Endomycorrhizae (Arbuscular)
B. Nitrogen fixation
C. Corals- zooxanthellae, anthozoans
Questions to focus on
1. What is the difference between symbiosis and mutualism?
2. What do the terms “obligate” and “facultative” mean with respect to
mutualisms? How do the mutualisms discussed in the book and
powerpoint differ in their degree of dependence?
3. What are specialists and generalists? If one species in a mutualism
is a specialist, does that mean the other must be as well?
4. What are the different types of “currency” exchanged in
mutualisms? Which ones are important for the different examples
in the book and powerpoint?
5. What is co-evolution and how does it differ from convergent
evolution? How might mutualisms affect the realized niche of
the species involved?
6. For the different examples of mutualisms in the book and
powerpoint, know what the different currencies are, the relative
degrees of dependence and specificity, and how those mutualisms
are important in community and/or ecosystem processes.
A. Symbiosis vs. Mutualism
Symbiosis: “sym” = together, “biosis”=
living; close physical association (e.g.,
host and internal symbiont). Could be
beneficial or parasitic.
Mutualism: +/+ interaction, both species
benefit. Could be symbiotic or freeliving
B. Degree of dependence
Obligate: at least on species could not
grow and reproduce without the other
Facultative: both organisms do better
with their mutualist, but can survive
and reproduce without it.
Ant-Acacia Mutualism
Ant-Acacia Mutualisms
Facultative or Obligate?
15.8
15.9
Leafcutter ants: a complex mutualism
http://bio.kuleuven.be/ento/photo_gallery.htm http://www.wildernessclassroom.com
Currie et al. 2006 Science
Leaf cutter ants
C. Degree of specialization
Specialists: reliant on only one other
species
Generalists: multiple species can
perform the function
Degree of specialization? Pollination
Hawk moth pollinated
Hummingbird pollinated
http://www.geocities.com/pennypoint9/hawkmoth.html
Hawk moth
www.naturephoto.ru
Generalist pollinators
http://en.wikipedia.org/wiki/Pollination
D. The “currency”
Nutrition – energy and nutrients
Protection – biotic and abiotic
Fertilization/gamete dispersal (e.g., pollination)
Seed dispersal
E. Co-evolution
Co-evolution occurs when two species interact so
strongly with one another that they are dominant
evolutionary forces on one another.
Examples:
- Obligate, specialist mutualisms
- Specialist predator/prey interactions (the term
was first coined in describing the “evolutionary
arms race” between plant chemical defenses and
insect herbivores that evolve resistance to those
defenses).
F. Effects on realized niche
fundamental
niche
realized niche
Competition, exploitation often
reduce the realized niche of an
organism compared to it’s
fundamental niche.
Mutalisms can increase
the size of the realized
niche compared to the
fundamental niche.
II. Examples of important
mutualisms
A. Mycorrhizae
“mycor” = fungi, “rhizae” = roots
- In almost all families of vascular plants
Ectomycorrhizae
Endomycorrhizae
4
2
1
B. N-fixation
3
Importance to N-cycle
C. Corals
www.scubaventure.net/photos%202.html
Zooxanthellae + Anthozoan
1
http://www.barrierreefaustralia.com/wdm
-enterprises/leather-coral.jpg
2
Anthozoans provide protection and nutrients to
the zooxanthellae, in exchange for fixed
carbon from algal photosynthesis