anova seminar #30 (economic value of tropical forest to coffee production) mike dedad 12/3/07...
DESCRIPTION
Purpose To “conduct pollination experiments to examine the effects of these patterns on coffee production and quality, and to estimate the resulting economic value of tropical forest fragments to coffee farms.” Previously determined that “bee species richness and visitation rate decline with distance from forest.”TRANSCRIPT
ANOVASeminar #30
(Economic Value of Tropical Forest to Coffee Production)
Mike DeDad12/3/07
Source: http://www.pnas.org/cgi/reprint/0405147101v1.pdf
Economic Value of Tropical Forest to Coffee Production
Societal benefits are immense Not a big enough motivator
Economic value pollination services to agriculture
Purpose
To “conduct pollination experiments to examine the effects of these patterns on coffee production and quality, and to estimate the resulting economic value of tropical forest fragments to coffee farms.” Previously determined that “bee species richness
and visitation rate decline with distance from forest.”
Methods
Studied a 1,065 hectare coffee farm in the Valle General, Costa Rica
Took branches from three types of sitesNear, Intermediate, and Far
Took 4 branches from each of 5 healthy plants from each site divided randomly between hand-pollination and ambient pollination
Methods
Explanatory VariablesDistance (Near, Intermediate, or Far)Pollination (By hand or ambient)
Response Variables seed massFruit setpeaberry frequency
Methods
What are some possible confounding variables? Length of the branch number of leaves relative shade
Dismissed these because r<.19 Not significantly related
What are the hypotheses?
Null Hypothesis: population means of each response variable are equal for each explanatory variable
Alternative Hypothesis: population means differ
Two-way ANOVA
DFG= product of the two degrees of freedom for each factor Distance dfg= (I-1)= 3-1= 2 Pollination dfg= (I-1)= 2-1= 1 Two-way ANOVA dfg= 2 x 1= 2
F2,24 = 8.13, P < 0.0001 F2,24 = 2.96, P = 0.0710
F2,24 = 7.28, P = 0.0034
Reject H0
Reject H0
Borderline
Conclusions
Hand pollinating increased seed mass and fruit set for far sites while decreasing peaberry frequency (higher quality)
Ambient pollination decreased seed mass and fruit set for far sites while increasing peaberry frequency (lower quality)
Conclusions
The presence of native tropical forest increased both the quantity and quality of harvested coffee (near and int. sites)
The lack of nearby forest decreases quantity and quality of harvested coffee (far sites)
What are the consequences of committing error?Type 1: Rejecting the null hypothesis even
though it is trueConvincing farmers to not expand even though the
presence of forests has no effect on coffee productionType 2: Failing to reject the null hypothesis even
though it is falseAllowing deforestation even though forests have an
effect on coffee quality and yield
Are there any questions?