Indirect interactions between plants mediated by insect herbivores

Alejandro Benhumea

Water

Water

+-

+

-Associational Susceptibility

Direct Interactions

Indirect Interactions

Overview

•Plants•Bugs•Hypothesis•Methods•Data•conclusion•Q&A

Opuntia imbricata (cholla) &

Opuntia phaeacantha (Prickly Pear)

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

Prickly Pear Cacti

Fruits

Cladodes

•Juveniles/Adults

•Reproduction

•Predators

•Insect abundance

Narnia pallidicornis

Adult

Old Fruit

Juvenile

Proboscis

Reproduction Eggs

•Juveniles will depend on their host plant until they are adults.

•Juveniles that have hatched

Hypothesis 1

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

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.

LegendCactus Sample Points

°0 100 20050

Meters

Data

5-100 0-5 m 10-15

0.5

1

1.5

2

2.5

3

3.5

4

Bu

gs p

er

cho

lla

no significant effect of distance

A

A

A

2006 Observational Data

Distance from prickly pear

2004 Observational Data.

0

1

2

3

4

5

6

7

8

9

10

0-5 m 5-10 m 10-15 m

bu

gs

per

pla

nt

significant effect of distance, P = 0.015A

B

B

Distance from prickly pear

04-06 comparison of prickly pear Fruit Production

0

10

20

30

40

50

60

70

80

# o

f fr

uit

s P

er

Pla

nt

2006 fruits

2004 fruits

L

Hypothesis 2

• “insects released on high quality plants will stay closer than insects released on low quality plants.

H

MethodsBug capture, marking and releasing. With a 24 hr wait time.

24 hr.

I will be marking and releasing 30 insects per plant.

Fruits

15

Or

5

Fruits were taken from nearby prickly pear and placed on the plant that would be in the experiment.

Prickly pear outside of experiment

Prickly pear inside the experiment

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.

Results of experimental release

0

0.02

0.04

0.06

0.08

0.1

0.12

0-5 5-10 10-15

pro

po

rtio

n r

eco

ver

ed p

er p

lan

t

low qualityhigh quality

no significant effects of treatment or distance

Distance from prickly pear

Predators

Jumping Spider Praying Mantis Northern Mockingbird

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.

Questions

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A Big Thanks to…

• Sevilleta LTER

• Fish and Wildlife

• Jennifer Johnson

• Brenda Nieto

• Andrew Romenger

• Ashwana Fricker

• Tom Miller