1. associations in an ecosystem
CLS 416

2. Types of interactions Type of interaction Effect on Populations
Pop. A Pop. B
Neutralism No effect No effect
Commensalism Beneficial No effect
Synergism Beneficial Beneficial
Mutualism Beneficial Beneficial
Competition Detrimental Detrimental
Amensalism(antagonism) Detrimental No effect
Parasitism Beneficial Detrimental
Predation Beneficial Detrimental

3. Positive associations:
1- Mutualism:
An obligatory association between two organisms of different species where both populations benefit, and can not survive without each other.
Examples:
 lichen is formed when fungi belonging to the Ascomycota or Basidiomycota  live in close proximity with photosynthetic cyanobateria. The algae provide fungi with carbon and energy while the fungi supplies minerals and protection to the algae.
Lactobacilli & vagina.

4. Types of Lichens
(a) Crust like
(b) Root like
(c) Leaf like

5. Positive associations:
2- Synergism:
An association between two organisms of different species where both populations benefit from each other. Each can survive without the other.
Examples: Cross-feeding,where metabolic end products of one
pop. enhance the growth of the other pop.
a-Ectomycorrhizas: A synergistic association between 10% of vascular trees,(as pine, eucalyptus, aok & rose trees) and fungi (Zygomycetes, Baasidiomycetes & Ascomycetes).
Vascular plants provide food & protection for the fungus

6. Mycorrhizae

7. Synergism-----cont
Fungi grow their mycelium into the rhizosphere that anchors the roots of trees and increase surface area to gain more water & minerals from the soil. (Specially poor nutrional, dry soil)
Fungi secrete toxins that kills weeds & other crops that compete
with the trees.

8. 2- Synergism:----cont. b- Cross feeding between
Lactobacillus arabinosus & Streptococcus fecalis,
when grown together, will have an exagerated &faster
growth rate.
Strep. fecalis > Phenylalanine(a.a)
L. arabinosus > folic acid

9. 3- Commensalism: (unaffected) (benefits)
A positive association between two organisms where one population benefits while the other is unaffected.
Examples:
a- Cyanobacteria & rice fields.
(unaffected) (benefits)
b- S.aureus & H.influezae
c- Yeasts & bacteria
d- humans & Entamoeba coli

10. Negative associations:
1- Competition: One pop. Induces a reduction in the size of the other population, by competing with available nutrients, place or other physical environmental factors.(due to changes in the environment). Both pop. Are affected.

11. Negative associations---cont.
2- Antagonism- Amensalism:
One pop. greatly affects the environment of the other pop. mostly by secreting inhibitory agents.
Examples:
a- S.aureus & Aspergillus terreus.
Staph. prevents formation of hyphae
b- Pseudomonas sp. & Aspergillus terreus.
Pigment prevents fungal sporulation.

12. Negative associations---cont.
c- E.coli secreting Bacteriocins destroys other bacteria. d- Algae producing antibacterial fatty acids. e- Penicillium inhibiting the growth of bacteria.

13. Negative associations---cont.
Predation:
The bigger pop.(predator) Kills & consumes the smaller one(prey).
Examples:
a- Didinium feeds on Paramecium.
b- Ameba feeds on bacteria.

14. Negative associations---cont.
Predation:
C- bigger animals consume smaller animals

15. Negative associations---cont.
4- Parasitism:
The smaller organism benefits & consumes the
bigger one.
Examples:
a- Bacteriophage infects bacteria.
b- Fungi feeding on algae.
c- Microorganisms infecting man.