1. Species Interactions Competition: (-,-) interaction Mutualism: (+, +) interaction Commensalism: (+, 0) interaction Exploitation: (+, -) interaction

2. Competition Def’n: Mutually adverse interaction between organisms that use a shared resource that is in limiting supply Interaction: ( -,- ) Effect on Sp. 1Effect on Sp. 2

3. Plant Competition Light very important: explains trees!

4. 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.

5. Resource competition Example: creosote bush (Larrea tridentata) Important desert shrub

6. Resource competition Avoidance of root overlap

7. 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

8. Examples Some of these chemicals inhibit other plants Example, Salvia (sage) in coastal sage scrub (California)

9. Examples Releases cineole and camphor from leaves Inhibit germination & growth of annual plants In grassland, “bare zones” around shrub borders camphor

10. Weeds and allelopathy Example, Centaurea maculosa (spotted knapweed) Major invasive nonnative weed

11. 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

12. 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

13. Pattern Patterns: –Clumped distribution (positive interaction) –Distances less than expected compared to random

14. Pattern Patterns: –Uniform distribution (negative interaction) –Distances greater than expected compared to random

15. Pattern Patterns: –Random (no association) –Individuals dispersed without influence by another’s location

16. Prediction? What pattern predicted for creosote bushes? Clumped, uniform, random?

17. Species Interactions Competition: (-,-) interaction Mutualism: (+, +) interaction Commensalism: (+, 0) interaction Exploitation: (+, -) interaction

18. Mutualism: (+, +) interaction Example: Lichens: partnership between fungi and unicellular photosynthesizer (green alga or cyanobacteria)

19. Lichen Fungus forms body, obtains photosynthate from partner Together, can colonize harsh environments.

20. Mycorrhizae Mycorrhizae: Association of fungus with plant root Common: 90% of plants do this! Exceptions: –Aquatic vascular plants –Cabbage family

21. 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

22. Mycorrhizae Important in revegetation/reclamation of disturbed areas: if fungi not present, plants don’t do well!. Plant on left grown without mycorrhizal fungi Revegetating a mine

23. Nitrogen Fixation Nitrogen: lots in atmosphere (79% N 2 ) But plants can’t use that Nitrogen fixation: bacteria use N 2 to form NH 3 (ammonia) or NO 3 - (nitrate)

24. 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

25. Defensive mutualisms Typically between plants and insects Insect gets home/food, plant gets protection from herbivory/competitors/hazards

26. 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

27. 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

28. 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

29. Species Interactions Competition: (-,-) interaction Mutualism: (+, +) interaction Commensalism: (+, 0) interaction Exploitation: (+, -) interaction

30. Commensalism: (+, 0) interaction Interaction that benefits one species but has no effect on other Plant/plant examples: –some epiphytes –“nurse plant effect”

31. Example: some epiphytes Epiphyte: Plant that grows on surface of other plants Example: –Spanish moss

32. Example: some epiphytes Epiphyte: Plant that grows on surface of other plants Example: –Lots in wet tropics

33. 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)

34. Commensalism Example, Saguaro cactus (Carnegiea gigantea) Large individuals hundreds of years old

35. Commensalism Seedlings found only under shrubs/trees Particularly Palo Verde trees

36. Species Interactions Competition: (-,-) interaction Mutualism: (+, +) interaction Commensalism: (+, 0) interaction Exploitation: (+, -) interaction