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Unformatted text preview: 1.0 Squirrel Foraging - 1 Fox Squirrel Foraging and the Landscape of Fear Animals (and plants) must forage for food and other resources that are scattered around a heterogeneous environment. Food availability varies from site to site, but so too do environmental conditions that foragers experience (e.g. temperature, wind) and the risks to which they are exposed. Foraging by any organism involves trading off the gains to be made by collecting food against the costs of doing so, including costs of energy spent moving and coping with stressful environments, and their exposure to injury or death from enemies. Many animals can be considered central place foragers. These animals venture out from a relatively safe place (a burrow for a rabbit, gopher, or crayfish; a tree for a squirrel or a bird) into a more hazardous place to find food. We can sometimes estimate short-term food availability from the density of food or the ease with which a forager can extract it from the local environment. It is more difficult to evaluate how a forager very different than ourselves perceives risk in different types of environments. Joel Brown, a behavioral evolutionary ecologist at the University of Illinois, Chicago, came up with a way to measure the landscape of fear for various animals. He reasoned that foragers might deplete patches more thoroughly in areas they considered safe, where they could spend a lot of time. In patches they perceived as more dangerous, they might give up earlier, leaving behind a higher density of remaining food. If food densities at various sites were initially similar before foraging occurred, the Giving Up Density (GUD) of food at a site after an animal quits foraging there might indicate how risky it considered that particular landscape position to be. The fox squirrel ( Sciurus niger rufiventer ), native to the US Midwest, was introduced to the Berkeley campus around 1926, and has adapted very successfully to this environment (Boulware 1941). It currently nests in campus blue gum trees ( Eucalyptus globules , also non-natives) imported from Australia, and eats their nuts (Boulware 1941). Squirrels often collect gum nuts and then retreat to safe perches, where they peel husks off and eat the seeds. Have you seen campus squirrels foraging in this way? Class lab exercise: Central place foraging under different threat levels We will attempt to map how a foraging squirrel perceives risk in the Berkeley campus environment by measuring giving up densities in standardized groups of almonds placed at various locations. Our squirrels are very accustomed to humans, so we will need to have a threat treatment to try to install a little fear into some of them. Other students will study unthreatened, control squirrels. will study unthreatened, control squirrels....
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This note was uploaded on 11/24/2009 for the course IB 1B taught by Professor Carlson during the Spring '09 term at University of California, Berkeley.
- Spring '09