The Ecological and Evolutionary Implications of Interspecific Competition

HMS Beagle

The Voyage of the HMS Beagle

Admiral Robert Fitzroy

Alfred Russell Wallace

Variation & Natural Selection

1) Individual variation in organisms within a population is the norm not the exception.

2) Populations reproduce at a geometric rate that is faster than the environment can support.

3) Some organisms will survive…most will die.4) Which organisms will live and which will die?

Variation & Natural Selection

1) Variation

2) Geometric (exponential) Growth

3) Differential Reproduction

4) Natural Selection (Survival of the Fittest)

Based on A.J. Lotka(1925) and V. Voltera (1926)

Natural Selection and Adaptation: Leaving More Offspring With Beneficial Traits

Three conditions are necessary for biological evolution:

•Genetic variability, •Traits must be heritable, •Trait must lead to differential reproduction.

An adaptive trait is any heritable trait that enables an organism to survive through natural selection and reproduce better under prevailing environmental conditions.

Geographic Isolation

Allopatric Speciation

After a long period of time these changes become so great that the individuals from the different populations can no longer reproduce with one another Reproductive Isolation

Robert MacArthur (1930-1972)

• Professor at UPenn & Princeton

• Studied the diversity of insectivorous warblers in northeastern forests

• Discovered that different warbler species used different parts of the forest canopy

• Established the ecological principle of resource partitioning

Evidence for Resource Partitioning

“It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change.”

Leon C. Megginson