The double life of a squirrel seed disperser

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

Dispersal Organism moves away from parent or current population

Stickiness

Bright color & fruits

Mass Production

Air & Wind

Water

Dispersal Why is it important to disperse?

Seed Predators Pre-dispersal seed predators: small, sedentary, specialist feeders e. g. insect larvae Post-dispersal seed predators: larger, mobile and generalist. e. g. rodents, birds, ants

Seed’s dilemma: Attractive for dispersers Defensive against vs. predators

Squirrel as disperser and predator Caching – a food storing behavior of animals (hoarding) e. g. birds, rodents, ants, 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.

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.

Chocolate-chip cookie study Squirrels are more likely to carry larger cookies Size of Cookie Squirrels are more likely to carry cookies over shorter distances

Today’s Experiment If you give a squirrel a sunflower cookie seed

Experimental Design Forest Open Lawn

What are the differences between these habitats from the perspective of a squirrel? Forest Do you think a squirrel will behave more like a predator or a disperser depending on the habitat? Open Lawn

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 predator/disperser in the forest, compared to a ______ the open field. This is because give a reason you might predict this ____________.

Fox Squirrel Gray Squirrel black morph Chipmunk

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 50 g) and number remaining Data on squirrel visitation: • Number of footprints in the sand • Squirrel observations when collecting trays • Squirrel behaviors in each habitat type

Experimental Data Forest Open Lawn

Open Lawn Forest observations?

Data to collect:

Data Analysis and Interpretation

Citizen Scientists Unite! http: //www. youtube. com/watch? v=Dxhn 4 W 9 NKn. Y

Extra slides

Predators Organism that kills and feeds on its prey

Pathogen • is a microorganism that causes disease in its host e. 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. Foragingefficiency -- 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. Foragingefficiency -- 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.