1. Possible Interactions Species 1  Species 2 Species 2  Species 1 +0- + 0 - Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease

3. Herbivory as a Tool Invasive Opuntia in Australia Impact of biocontrol insect Cactoblastis

4. Defenses against Herbivory Physical structures Trichomes Spines Non-digestible tissues Secondary chemical compounds Toxins Hard to digest chemicals (e.g., tannins)

5. Inducible Defenses

8. Possible Interactions Species 1  Species 2 Species 2  Species 1 +0- + 0 - Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease

9. Seymeria cassioides Mistletoe Dodder Plant Parasites

10. Strangler Figs

11. Possible Interactions Species 1  Species 2 Species 2  Species 1 +0- + 0 - Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease

12. Possible Interactions Species 1  Species 2 Species 2  Species 1 +0- + 0 - Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease ?

13. Possible Interactions Species 1  Species 2 Species 2  Species 1 +0- + 0 - Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease Ammensalism/ Allelopathy

14. Allelopathy: A controversial topic

16. Possible Interactions Species 1  Species 2 Species 2  Species 1 +0- + 0 - Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease ? Ammensalism/ Allelopathy

17. Possible Interactions Species 1  Species 2 Species 2  Species 1 +0- + 0 - Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease Ammensalism/ Allelopathy Competition

18. Competition between different species Potentially assymetrical! Light Space H20 Nutrients Space

19. Possible Interactions Species 1  Species 2 Species 2  Species 1 +0- + 0 - Mutualism Commensalism Herbivory/ Parasitism/ Disease Neutral Ammensalism/ Allelopathy Competition

20. Experimental Studies of Competitive Interactoins

21. The Design Matrix Density of species i Density of species j

22. The Design Matrix Treatment combination indicating densities of both species i and j

23. The Design Matrix

24. Commonly Used Designs Partial AdditiveReplacement Series AdditiveComplete Additive

25. The Partial Additive Design Target species Competitor

26. The Partial Additive Design Commonly used design to study the impact of weeds on a crop plant

27. The Partial Additive Design Yield drops as density of competitor increases

28. The Partial Additive Design

29. Problems with the Partial Additive Design Target species only studied at one density Effects of density confounded with a change in the ratio between the two species 100 50 0 Species 1 Species 2 Density Ratio 200 1:1 150 1:2 50 0:1

30. The Replacement Series Design Density is fixed Ratio of two species systematically altered

31. The Replacement Series Design Species 1 Species 2 Treatment 1 Treatment 3 Treatment 2 Treatment 6 Treatment 5 Treatment 4 Density = 5

32. Monoculture Experiments as a Control

33. Monoculture treatment Replacement Series Experiment

34. Monoculture treatment Replacement Series Experiment Competition treatment Impact of Competition

35. Monoculture treatment Replacement Series Experiment Competition treatment Impact of Competition

36. Monoculture treatment Replacement Series Experiment Competition treatment Avena fatua has a large competitive effect A. barbata has little competitive effect

37. Monoculture treatment Replacement Series Experiment Competition treatment Assessing the interaction Total yield in treatment

38. Additive Competitive Effects I = J

39. Additive Competitive Effects I = J I > J

40. Additive Competitive Effects I = J I > J I < J

41. Non-Additive Competitive Effects Combined effects of competition have a greater negative effect than when plants are grown alone Species i has a bigger effect on species j than it has on itself Species j has a bigger effect on species i than it has on itself

42. Non-Additive Competitive Effects Combined effects of competition are less in combination than when plants are grown alone Both species impact themselves more than their competitor does

43. A Non-Additive Example Relative yield total = Sum of yields in competition Sum of yields in monoculture

44. A Non-Additive Example