the double life of a squirrel: seed disperser and predator 12.05.2012 jakob nalley, liz schultheis...
TRANSCRIPT
The double life of a squirrel:seed disperser and predator
12.05.2012
Jakob Nalley, Liz Schultheis and Tomomi Suwa
Today’s Outline
• Background on dispersal and predation• Field Experiment• Project Squirrel (citizen science project)
Seeds
Why is there so much diversity in
seed shape and size?
Seeds evolved many strategies to interact with other species
Seeds encounter …• Dispersers• Predators
DispersalOrganism moves away
from parent or current population
Stickiness
Bright color & fruits
Mass Production
Air & Wind
Water
DispersalWhy is it important to disperse?
Seed Predators
Post-dispersal seed predators: larger, mobile and generalist. e.g. rodents, birds, ants
Pre-dispersal seed predators: small, sedentary, specialist feederse.g. insect larvae
Seed’s dilemma: Attractive for dispersers
Defensive against predatorsvs.
Squirrel as disperser and predator
Advantages of caching (from seed perspective):• Disperse seeds• Predators do not eat all the seeds they cache
(some are lost)• Death rates are lower for buried seeds than
seeds exposed on the surface.
Caching – a food storing behavior of animals (hoarding)
e.g. birds, rodents, ants,
Chocolate-chip cookie study
Steven Lima, Thomas Valone, and Thomas Caraco. 1985. Foraging-efficiency -- predation-risk trade-off in the grey squirrel. Animal Behaviour 33:155-165.
Squirrels are more likely to carrycookies over shorter distances
Chocolate-chip cookie studySquirrels are more likely to carry
larger cookies
Size of Cookie
If you give a squirrel a cookiesunflower seed
Today’s Experiment
Forest
Open Lawn
Experimental Design
Open Lawn
ForestWhat are the differences between these habitats from the perspective of a squirrel?
Do you think a squirrel will behave more like a predator or a disperser depending on the habitat?
Hypothesis
What are the differences between these habitats from the perspective of a squirrel?
Do you think a squirrel will behave more like a predator or a disperser depending on the habitat?
I predict that squirrels will behave more like a ___________ in the forest, compared to the open field. This is because _______________________.
predator/disperser
give a reason you might predict this
Fox Squirrel Gray Squirrel Chipmunkblack
morph
Data to collect:Data on seed consumption:• Number of seed coats remaining (divide by 2 to
get a number of seeds consumed at the tray)• Number of full seeds remaining• Number of seeds without coats remaining• Difference between number of seeds placed into
tray (100, or 50g) and number remaining
Data on squirrel visitation:• Number of footprints in the sand• Squirrel observations when collecting trays• Squirrel behaviors in each habitat type
Open Lawn
Forest
Experimental Data
Open Lawn Forest
observations?
Data to collect:
Data Analysis and Interpretation
http://www.youtube.com/watch?v=Dxhn4W9NKnY
Citizen Scientists Unite!
Extra slides
PredatorsOrganism that kills and feeds on its prey
Pathogen• is a microorganism that causes
disease in its hoste.g. virus, bacteria, fungi,
• Pathogen do not necessarily kill the host animal/plant
Need more pictures here
II. Scientific Method
Steven Lima, Thomas Valone, and Thomas Caraco. 1985. Foraging-efficiency -- predation-risk trade-off in the grey squirrel. Animal Behaviour 33:155-165.
Predict that tendency to carry a food item should decrease with distance of food from cover (predation risk) and increase with item size (food reward). Both risk and reward should influence behavior
Experiments were conducted in Highland Park in Rochester, New York. The reward was chocolate-chip cookies, cut to weigh 1, 2, or 3 g. More “natural” foods were buried rather than eaten and cookies may be a “natural” food for a park squirrel anyway. Food was placed at different distances from trees.
II. Scientific Method
Steven Lima, Thomas Valone, and Thomas Caraco. 1985.
II. Scientific Method
Steven Lima, Thomas Valone, and Thomas Caraco. 1985. Foraging-efficiency -- predation-risk trade-off in the grey squirrel. Animal Behaviour 33:155-165.
The authors conclude that the results support their hypothesis. Simple models that only incorporate foraging rate or only exposure to predators are insufficient, as both are important.