Fruit Avian Choice & Mixed Displays
Fruit-bird interactions
Plants encase seeds in fleshy fruits Birds eat fruit and disperse seeds away from parent plant A mutualistic relationship that is important to many local plants and birds
Eva Lewandowski January 22, 2008
Fruit-bird Visual Communication
What visual signals are plants using to attract birds to their fruits?
Bird Vision
Tetrachromatic
Can see UV through red
What visual characteristics are birds looking for or considering when foraging for fruit?
Oil droplets increase ability to discriminate colors
Schaefer et al. 2007
3 Parts of a Visual Signal
What can fruit displays say?
Presence
Were here! Hey, eat me!
Light Environment
Surface Reflectance
Visual System Sensitivity
Intensity (counts)
120
M aster G autol(lf)1008.M aster.R eflection G autol(red)1008.M aster.R eflection H poke(blk)1008.M aster.R eflection
110
100
90
Content/Quality
Im ripe and fresh!
400 500 600 700
80
70
60
50
40
30
20
Im full of anthocyanins!
10
0
Wavelength (nm )
Announcing Presence
Contrast more impt than fruit color Contrast btw fruit and leaves increases consumption
Birds locate fruit faster when it contrasts strongly with the background (Schaefer et al. 2006) Birds preferentially choose more contrasting fruit in choice trials (Giles & Lill 1999; Schmidt et al. 2004)
Red & Black Fruits Contrast the Most Against Green Leaves
Innity on) tes (cuts
Intensity
Itesycuts nnit (on)
Intensity
1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0
Ites (cuts nnity on)
Intensity
1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0 3 0 0
1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0
4 0 0 5 0 0 6 0 0 400 500 600 Wenthn) a leg (m v wavelength(nm) 7 0 0 700
300 400 500(nm 600 Wenth ) a leg v wavelength(nm)
4 0 0
5 0 0
6 0 0
700
7 0 0
0 3 0 0 300
0 3 0 0 300
4 0 0 5 0 0 6 0 0 400 500 600 Wenth m a leg (n) v wavelength(nm)
7 0 0 700
Most Fruits Are Red Or Black
Regional and worldwide trend
Mixed Displays
Traditionally fruit displays were considered only ripe fruit, or sometimes ripe fruit with leafy background But many species have complex displays with ripe fruit, leaves, and at least one other color
Two Types of Mixed Displays
Structural: plant has stems, bracts, pedicels etc. that add color
What Is the Role of Mixed Displays? Do temporal and structural
components have different effects? Do they increase conspicuousness to birds? Do they signal content or quality? Does the plant benefit from ripening?
asynchronous Spreading seeds between groups of birds Decreasing bacterial and fungal attacks
Temporal: unripe fruit coincide with ripe fruit and add an additional color
Mixed Displays Increase Contrast
More contrast between sec. structure and background than ripe fruit and background Didnt distinguish between structural and temporal components
My Research- Temporal vs. Structural
Prediction 1: Structural components will add more contrast to a display than temporal Prediction 2: Plants with small fruit-leaf contrast will be more likely to have mixed displays Recording presence, length, and color and contrast measurements of local fruiting plants with mixed displays
Schaefer et al. 2007
My Research- Mixed Displays and Fruit Removal
Recording fruit removal on local plants
Looking for correlation between removal and mixed displays
My Research- Mixed Displays and Fruit Removal
Previous research had mixed results
Didnt quantify contrast or color Didnt consider background
Looking within and between species
I hope to clear up some of the questions about mixed displays
Experimental and observational studies My experiments test fruit removal rates between mixed and non-mixed displays
Experiments with Pokeweed
Temporal & structural mixed displays Common, easily manipulated Frogs!
Preference vs. Detection Bias
Looking at foraging on mixed and non-mixed displays If there is a difference, is it due to:
preference (birds see fruits equally well, but p...