Transcript 2.4.4 Energy Limitations in an ecosystem

…~ 1 hawk
A Red hawk
in km2
Common Garter snake
7 breeding pairs km2 ~
…~ 14 snakes
…~ 2000 mice
…~ 14 snakes
Approx 400 field mice and on average 5
different species in a km2
Lots of grass in a km2 of Canadian grassland
1.25 kg
per hawk
Garter snake 0.225 kg x
14 = 3.15 kg
Mouse weighs 0.02 kg x 2000 mice = 40 kg
33 000 Kg of grass in km2
1.25 x 10% =
0.125 kg of
carbon
3.15 kg x 10% = 0.315 kg
40 kg x 10% = 4 kg of carbon
33 000 kg x 10% = 3300 kg of carbon
•This explains why there is only 4 trophic levels in an
ecosystem
•0.125 kg of carbon is not enough material or energy to
sustain the existence of an active predatory carnivore.
•Lets assume that the organism that might be in a 5th trophic
level is half as big as a hawk…what are the odds of a 0.65
kg predator catching and killing a Red hawk.
•Even evolution might be hard pressed to create a
physiological weapon that could allow this predator to
succeed…not enough mass or energy!