General Ecology

1
General Ecology

• Optimality and Tolerance Limits

2
Tolerance Limits

• We need to think in terms of the niche
• A niche can be defined as
• where an organism lives, and what an organism
  does.
• Note this definition is vague, but for the
  moment, it will have to do.

3
Tolerance Limits

• As an example, lets consider the southern flying
  squirrel, Glaucomys volans.
• Lives in hard-wood deciduous forests from Canada
  to Florida, and from the east coast to the
  midwest. There are also several populations in
  Mexico and Guatemala.

4
Tolerance Limits

• How did the populations in Mexico and Guatemala
  get there? These populations are completely
  allopatric with any other G. volans populations.
  Furthermore, they are genetically distinct, in
  that they are recognizable subspecies.

5
Tolerance Limits

• Why does G. volans live in hardwood deciduous
  forests?
• They eat hard mast (Acorns and Hickory nuts,
  walnuts, pecans).
• They nest in cavities in snags.
• They glide from tree to tree.

6
Tolerance Limits

• In order to reproduce, the animals must have a
  nest cavity.
• To make it through the winter, they must be able
  to store an adequate supply of nuts.
• They have a high energy lifestyle, and require a
  high energy food source.
• They are not capable of hibernation, but can
  enter a very mild torpor.

7
Tolerance Limits

• We know that flying squirrels in North America
  are derived from the genus Eoglaucomys in Asia.
  Also, we know that both G. volans and G. sabrinus
  got here abou 30,000 years ago.
• So, how did they get to Mexico?
• They are restricted to forests.
• They rarely enter open areas (but see Findley)

8
Tolerance Limits

• The answer can be found if we understand the
  historical distribution of deciduous forests.
• In the Pleistocene, a glacier extended south to
  the Missouri River.
• Hardwood deciduous forests extended into Mexico
  and Central America.
• As the glacier retreated, HWDF followed northward.

9
Tolerance Limits

• Now, what happens as you move up in altitude?
• What happens as you move north?
• The pattern is revealed in Merriams life zones.

10
Tolerance Limits

• So, segments of hardwood deciduous forest were
  trapped, along with their fauna, on mountaintops
  in Mexico and Guatemala, surrounded by desert and
  scrub habitats.

11
Tolerance Limits

• Consider another example the collared lizard
  Crotaphytus collaris.