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Indirect Interactions Between Plants Mediated by Insect Herbivores: A Study on Cholla and Prickly Pear Cacti

This research investigates the indirect interactions between the cholla cactus (Opuntia imbricata) and prickly pear cactus (Opuntia phaeacantha), focusing on the role of insect herbivores. Two hypotheses were explored: insect abundance on cholla is greater near prickly pear, and high-quality plants attract more insects. Methods included mapping plant coordinates and surveying insect populations. Observational data from 2004-2006 highlighted significant effects of distance on bug abundance. The study concludes that climate influences these indirect interactions in arid ecosystems.

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Indirect Interactions Between Plants Mediated by Insect Herbivores: A Study on Cholla and Prickly Pear Cacti

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  1. Indirect interactions between plants mediated by insect herbivores Alejandro Benhumea

  2. Direct Interactions Water Associational Susceptibility - - + + Indirect Interactions Water

  3. Overview Plants Bugs Hypothesis Methods Data conclusion Q&A

  4. Opuntia imbricata (cholla)&Opuntia phaeacantha (Prickly Pear)

  5. Cholla Cacti • Grows in cylindrical segments. • Main plant density occurs at the base of los pinos. • Structure prevents plant from being eaten by larger mammals • Cholla are much more abundant than the prickly pear

  6. Prickly Pear Cacti Cladodes Fruits

  7. Narnia pallidicornis Juveniles/Adults Reproduction Predators Insect abundance

  8. Adult Proboscis Old Fruit Juvenile

  9. Reproduction Eggs • Juveniles will depend on their host plant until they are adults. • Juveniles that have hatched

  10. Hypothesis 1 “Bug abundance on cholla cacti is greater on plants closer to the prickly pear cacti”.

  11. Method • Chose random Prickly pear and surveyed the surrounding cholla within a 15 m Radius. • Surveyed 108 Cholla plants • Took GPS coordinates for each plant with an accuracy of ~.5-1 meter to be able to measure plant distances.

  12. 4 A no significant effect of distance 3.5 3 A 2.5 A Bugs per cholla 2 1.5 1 0.5 Data 2006 Observational Data 5-10 10-15 0-5 m 0 Distance from prickly pear

  13. 2004 Observational Data. 10 significant effect of distance, P = 0.015 A 9 8 7 6 B 5 bugs per plant B 4 3 2 1 0 0-5 m 5-10 m 10-15 m Distance from prickly pear

  14. 04-06 comparison of prickly pear Fruit Production 80 70 60 50 2006 fruits # of fruits Per Plant 40 2004 fruits 30 20 10 0

  15. L Hypothesis 2 • “insects released on high quality plants will stay closer than insects released on low quality plants. H

  16. Methods Bug capture, marking and releasing. With a 24 hr wait time. 24 hr. I will be marking and releasing 30 insects per plant.

  17. Fruits Fruits were taken from nearby prickly pear and placed on the plant that would be in the experiment. 15 Or 5 Prickly pear inside the experiment Prickly pear outside of experiment

  18. Predictions • By simulating Over Population, the bugs will move out with proportion to the available food source. • Bugs will feed on fruit even though it had been cut off from the plant. • I am expecting the dispersal to be gradual over 2 or 3 days. Changed it to 24 hours • I am also expecting this experiment to follow closely with • My first hypothesis.

  19. Results of experimental release 0.12 no significant effects of treatment or distance 0.1 0.08 proportion recovered per plant low quality 0.06 high quality 0.04 0.02 0 0-5 5-10 10-15 Distance from prickly pear

  20. Predators Jumping Spider Praying Mantis Northern Mockingbird

  21. Conclusion. • The associational interaction from insects varies from one time frame to another • In a Arid ecosystem climate changes over the years influence fruit abundance and the indirect interaction of plants through a mediated insect herbivore.

  22. Questions ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

  23. A Big Thanks to… • Sevilleta LTER • Fish and Wildlife • Jennifer Johnson • Brenda Nieto • Andrew Romenger • Ashwana Fricker • Tom Miller

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