Date post: | 22-Dec-2015 |
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Species Interactions• Competition: (-,-) interaction• Mutualism: (+, +) interaction• Commensalism: (+, 0) interaction• Exploitation: (+, -) interaction
Competition• Def’n: Mutually adverse interaction between organisms that use a shared resource that is in limiting supply
• Interaction: ( -,- )Effect on Sp. 1
Effect on Sp. 2
Competition: (-,-) interaction• Interference Competition:
– Individuals interact directly to limit one another’s access to resource
• Resource Competition: – Individuals interact with resource in effort to obtain more. Once gained, resource unavailable to competitor.
Interference Competition: Allelopathy• Allelopathy: chemical released by one plant species negatively impacts another
• Differs from resource competition, where resources removed from environment
• In allelopathy chemicals are added to environment
Examples• Some of these chemicals inhibit other plants
• Example, Salvia (sage) in coastal sage scrub (California)
Examples• Releases cineole and camphor from leaves
• Inhibit germination & growth of annual plants
• In grassland, “bare zones” around shrub borders
camphor
Weeds and allelopathy• Example, Centaurea
maculosa (spotted knapweed)
• Major invasive nonnative weed
Weed example• Example, Centaurea maculosa (spotted knapweed)
• Releases catechin into soil• When absorbed by roots of other plant species, causes wave of cell death to move up roots into stems
• Aids invasiveness
catechin
Pattern• Pattern: placement of individuals of a species relative to each other or members of another species
• Important for sessile organisms (ex, plants)
• May reveal species interactions– Positive may result in clumping– Negative may result in wide spacing
Pattern• Patterns:
– Clumped distribution (positive interaction)
– Distances less than expected compared to random
Pattern• Patterns:
– Uniform distribution (negative interaction)
– Distances greater than expected compared to random
Pattern• Patterns:
– Random (no association)– Individuals dispersed without influence by another’s location
Species Interactions• Competition: (-,-) interaction• Mutualism: (+, +) interaction• Commensalism: (+, 0) interaction• Exploitation: (+, -) interaction
Mutualism: (+, +) interaction
• Example:• Lichens: partnership between fungi and unicellular photosynthesizer (green alga or cyanobacteria)
Lichen• Fungus forms body, obtains photosynthate from partner
• Together, can colonize harsh environments.
Mycorrhizae• Mycorrhizae: Association of fungus with plant root
• Common: 90% of plants do this!• Exceptions:
– Aquatic vascular plants– Cabbage family
Mycorrhizae• Fungus extends into soil (up to 8m away!) and aids in uptake of nutrients (P, Zn, Cu in particular) and possibly water for plant
• Fungus obtains sugars from plant
Mycorrhizae• Important in revegetation/reclamation of disturbed areas: if fungi not present, plants don’t do well!.
Plant on left grownwithout mycorrhizal fungi
Revegetating a mine
Nitrogen Fixation• Nitrogen: lots in atmosphere (79% N2)• But plants can’t use that• Nitrogen fixation: bacteria use N2 to form NH3 (ammonia) or NO3- (nitrate)
Nitrogen Fixation• Special ways to get N:
– Symbiotic bacteria: many legume plants form nodules on roots.
– Rhizobium (N-fixing bacterium) inhabit, obtain sugars, provide plant with N
Defensive mutualisms• Typically between plants and insects• Insect gets home/food, plant gets protection from herbivory/competitors/hazards
Defensive mutualisms• Example, Acacia and acacia ants• Acacia, trees/shrubs in legume family. Some of those in Central America have large hollow stipular spines
• Ants nest in spines
Defensive mutualisms• Example, Acacia and acacia ants• Leaves have extrafloral nectary at base (makes nectar but not produced on a flower)
• Young leaflets have Beltian Bodies (protein rich) at tips
Defensive mutualisms• Benefits to plant:• Ants eat insect herbivores• Ants are territorial and defensive and attack herbivores not useful for food (even humans)
• Ants clear area below shrub: removes competitors, protects shrub (and ants!) from fire
Species Interactions• Competition: (-,-) interaction• Mutualism: (+, +) interaction• Commensalism: (+, 0) interaction• Exploitation: (+, -) interaction
Commensalism: (+, 0) interaction• Interaction that benefits one
species but has no effect on other• Plant/plant examples:
– some epiphytes– “nurse plant effect”
Example: some epiphytes• Epiphyte: Plant that grows on surface of other plants
• Example:– Spanish moss
Example: some epiphytes• Epiphyte: Plant that grows on surface of other plants
• Example:– Lots in wet tropics
Commensalism• Nurse plant effect (+, 0)• Larger plant provides favorable microhabitat for seedlings of another species (+)
• Seedling so small it has no effect on larger plant (0)
Commensalism• Example,• Saguaro cactus (Carnegiea gigantea)
• Large individuals hundreds of years old