Desert plant associations

1
Desert plant associations
2
Announcements
we will leave in 1h from the start of the lab
(22) and in 15 minutes (24) the assignment
for this lab is a report -same format (I expect
to see typed tables, graphs,..) -points
distribution in the last slide -no revision
Matthew Lopez will present next lab.
period. there is a handout of the final project
example titles. -prospectus of the final
project is due next week(5 points) -simple
out line of an experiment -number of
samples -names of the group members
-analysis proposed to test the hypothesis
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Desert plants
dry environment evolved adaptation -nurse
plants (cactus) -evade drought -fleshy water
storing leaves -leaves only when water is
abundant -small size leaves -cacti have
spines rather than typical leaves -root system
adaptation -fewer stomata and less evaporation

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Association between plants
Nursing plant hypothesis(HA) seedling cacti
survive only in the shade of trees and
shrubs. predator hypothesis(HA) mutualism
hypothesis(HA) random distribution (null
hypothesis or H0)
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Target plants
1- Carnegiea gigantea Saguaro
cactus Straight spines
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Target plants
2- Ferocactus wislizenii Barrel
cactus Hook end spines (curved)
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Target plants
3- Ambrosia deltoidea Triangle Leaf Bursage,
(Rabbit Bush)
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Criteria for association
1-height of the target plant 28cm (height of data
sheet) i.e. juvenile plant 2-base of the
target plant lie below the branches of tree
or shrub. each group of 3 must count 15
individuals for each target and determine
whether associated or not
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Test your hypothesis
Chi square X2 X2? (O-E)2 E 45
represent nonrandom distribution degree or
freedom 1 Compare your results with table 1
appendix C is it significant or not due accept
or reject the null hypothesis
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Test your hypothesis
Example Saguaro cactus
associated non associated
total observed 70
25
95 Expected 4595 43 5595
52
100 100 X2..
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Important
-watch out for rattlesnakes -dont put your hands
under rocks -look carefully under plants
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• Lab. Reports point distribution
• Title 1 point
• Abstract 4 points
• Introduction 3 points
• Materials and methods 1point
• Results 3 points
• Discussion 3 points