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 2nd 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 180o 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?