Transcript lab4_leaf_size(stats).

Adaptive Leaf Size
Week Two (analysis)
Hypotheses:
H1: Plants in wet soil do not have to conserve
water, so they will be as warm as possible.
H2: Plants in dry soil must conserve water, so
they will be as cool as possible.
Predictions :
Predictions:
Wet
Dry
Sunny
In the sun, a leaf can
be warmed above the
air temp by the sun,
so this leaf should be
large to increase
photosyn.: stay hot
In the sun, the air temp
is the coolest the leaf
can be, so this leaf
should be small to reach
air temp and conserve
water: get cool
Shady
In the shade, the air
temp is as warm as the
leaf can be, so this leaf
should be the air temp
to increase photosyn.:
get hot
In the shade, the leaf can
get below air temp (due
to evaporative cooling), so
this leaf should be large
to conserve water: stay
cool
Increase photosynthesis
Decrease water loss
Assumptions:
o  Temperature :  Photosynthesis
o  Temperature :  Water loss
Fun with Statistics!
o We will do 4 t-tests
o t-test: tells us how different the averages of two groups are
o t-tests use Standard deviation (SD)
o SD: “typical” deviation from the mean
o t-tests give us a P-value
o P-value: probability that your result is due to chance alone.
o P ≥ 0.05 = the difference in averages is most likely due to chance…
o P < 0.05 = the averages are “significantly” different
o Don’t forget where you predicted the larger
vs. smaller leaf!
t-test…
t =
X1  X 2
2
1
2
s
s2

n1
n2
t = t-test value
X = group mean
s = st. dev.
n = sample size
Food for thought…
o
According to the model, what environmental factors determine leaf size?
o What other environment factors could influence leaf size?
o Why is the model applied to vine-like plants?
o What assumptions did you make to test the model?
o Do you think they were valid?
o Which lab measurements were:
o Qualitative?
o Quantitative?
Wet
Sunny
Shady
Dry
Wet
Dry
Sunny
Shady
Increase photosynthesis
Decrease water loss
Wet
Dry
Sunny
Shady
Increase photosynthesis
Decrease water loss
Wet
Dry
Sunny
Shady
Increase photosynthesis
Decrease water loss
Wet
Dry
Sunny
Shady
Increase photosynthesis
Decrease water loss
Wet
Dry
Sunny
In the sun, a leaf can
be warmed above the
air temp by the sun,
so this leaf should be
large to increase
photosyn.: stay hot
In the sun, the air temp
is the coolest the leaf
can be, so this leaf
should be small to reach
air temp and conserve
water: get cool
Shady
In the shade, the air
temp is as warm as the
leaf can be, so this leaf
should be the air temp
to increase photosyn.:
get hot
In the shade, the leaf can
get below air temp (due
to evaporative cooling), so
this leaf should be large
to conserve water: stay
cool
Increase photosynthesis
Decrease water loss