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Plant Competition and Positive Interactions: Insights from Target Neighborhood Experiment

Explore the impact of competition on plant species and the role of positive interactions, such as facilitation and mutualism, using the Target Neighborhood Experiment as a case study. Learn about the influence of herbivory, disturbance timing, phenology, and allelopathy on plant competition. Discover the challenges in proving allelopathy and the importance of positive interactions in plant communities.

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Plant Competition and Positive Interactions: Insights from Target Neighborhood Experiment

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  1. Competition (Ch. 10) Ken Jennings: my hero! 74 wins (2004) $2.52 million

  2. Target-neighborhood experiment • Remove around “target” shrub • Target monitored (water status) • Result: • little intraspecific comp. both sp. • great Larrea-Ambrosia comp. Danger…

  3. Danger for removal experiments: Apparent competition • Herbivore effects mimic competition • Ex: Herbivore eats A and B • Remove A, herbivore leaves, • Interaction b/w A & B

  4. Other points • 1) Herbivory influences competition • Ex, chalk grassland (England) • Lab studies: grass better competitor. How forbs persist? • Rabbits (“killer rabbits?”) Plant Ecology Theatre!

  5. Other points • Rabbits prefer grass (help forbs) • Twist: Myxomatosis decimated rabbits 1950s—forbs declined • Rare butterflies (ex, marsh fritillary) declined The marsh fritillary

  6. Other points • 2) Disturbance timing on competition species 1 numbers species2 No disturbance time

  7. Other points Frequent disturbances • Can allow coexistence species 1 numbers species2 time

  8. Other points 3) Phenology can affect competition • Ex, lab study • Germinate same time: sp. 2 • Sp. 2 germinate 2 wk earlier: sp. 1

  9. Allelopathy • Allelopathy: chemical • May be • Allelopathy: chemicals added to env.

  10. Plants “leaky” • Many ways • rainwater leaches • volatiles • Root • decay

  11. Examples • Ex, Salvia (sage): coastal sage scrub (CA) • Leaves release cineole & camphor camphor

  12. Examples • Chemicals inhibit germination & growth annuals • “Bare zones” camphor

  13. Examples • Ex, Juglans nigra (black walnut) • Roots: juglone

  14. Examples • Ex, Ceratiola ericoides (beach rosemary) • Sandy soils

  15. Examples • Ex, Ceratiola ericoides (beach rosemary) • Releases ceratiolin

  16. Allelopathy: Problems with proof • Need to: • #3 hard! Allelopathy proof difficult

  17. Allelopathy: Problems with proof • Other factors: herbivory • Cages:

  18. Weeds and allelopathy • Ex, Centaurea maculosa (spotted knapweed) • Invasive exotic

  19. Weed example • Ex, Centaurea maculosa (spotted knapweed) • Releases catechin catechin

  20. Ch. 10: Positive plant-plant interactions

  21. Facilitation • Facilitation: + effect ( • Commensalism: Some epiphytes

  22. Commensalism • Nurse plant effect (+,0) Saguaro plant nurse……

  23. Commensalism • Nurse plant effect (+,0) • Ex, Saguaro cactus (Carnegiea gigantea)

  24. Commensalism • Seedlings under Palo Verde trees • Provides:

  25. Commensalism • Ex, Marsh elder (Iva frutescens: salt marsh) • Juncus roemerianus shading decreases evaporation:

  26. Commensalism • Can help exotics • Ex, chenopod shrubland

  27. Mutualism • (+,+) interaction: pollination, seed dispersal, N-fixation….

  28. Mutualism • Ex, root grafts connect

  29. Mutualism • Radioactive tracers • Roots Danger!

  30. Mutualism • Danger: Disease

  31. Lichens • Mutualism (+,+) • Lichen: fungus

  32. Lichen • Together:

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