Topic 11:

Predator-Prey Interactions

Announcements:

• Exam 1 next Tuesday!

• Life Zone Lab next week Wed. - will be taking 2 vans

• Beast in Garden discussions continue week after next...

Learning Goals for Day:

Ø      Summarize the views expressed in Leopold’s essays: Thinking Like a Mountain & Escudilla

o       Explain the “old” prevailing view of predators that Leopold was raised on

o       Explain Leopold’s “new” view after his experience in the 2^nd essay

Types of predator impact on prey species:

DIRECT impact on prey species abundance

Other types of predator impact on ecosystems & food webs:

    INDIRECT impacts...:

• Channel Islands example (Bald Eagle, DDT,  Golden Eagle, Island Fox)

• Yellowstone example (Wolves, Elk, Willows & Cottonwood)

Ø      Can predators impose any control on ecosystem structure and function? 

o       evidence from wolves in Yellowstone example - indirect influences, e.g. on vegetation health (!)

o       evidence from island fox example - removal of 1 predator allows invasion of another, which may have big impacts on the abundance of other species

o       often the main way predators influence their prey directly is by decreasing number of young that survive to maturity, & this can affect population structure

Assess – Goals:

Ø      What predators are involved in  Leopold's essays?

Ø      Why have we pushed predator control to such an extent in this culture?

Ø      Why did Leopold do such a 180^o change of opinion about predators?

Ø      What part of the prey population do predators really impact?  strong, mature adults?  old, or sick individuals?  very young individuals?

o       why is this important?

Ø      Be able to describe some potential impacts of predator removal on an ecosystem, using a real example

o       how does your example support &/or refute the old and new paradigms of predator control in ecosystems?

• What is the impact of heavy metals on food chains?  where is the impact greatest, and why?