Evolution and Ecology

Like all of biology’s sub-disciplines, ecology makes sense in light of evolutionary theory.

Evolutionary change leads to adaptation, and is central in ecology.

So what is Evolution?

Evolution (outcome) ≠ Nat Selection (mechanism)

Evolution is change over time

Natural Selection is the mechanism…. Works because

-          Variation exists!

-         Every population of organisms produces an excess of offspring

-         Not all individuals will survive and reproduce

-         Competition for limited resources occurs, some inds have an advantage in obtaining resources à more survival and repro.

-         If characteristics are inherited, favored traits will be more frequent in next generation

A simple example of natural selection is shown in the peppered moth, Biston.

Selection acts on phenotypes (observable attributes of inds.)

Different types of selection can act on these phenotypes.

Directional-  phenotypes at one extreme are selected against

Finch beaks

Pesticide resistance

Stabilizing- phenotypes near the mean are fitter.

The mean does not change, but distribution is tighter.

Human birth weight/infant mortality

Canadian snow geese

Disruptive selection, where extremes are favored over mean. 

Examples hard to find in natural settings (often extreme forms interbreed), but can be shown in the lab.

Drosophila is selected for having a small or large # of abdominal bristles.  After 35 generations, the new pops no longer overlap with the original population.

What is fitness? 

-         A measure of the contribution of an individual to future generations

-         a.k.a. adaptive value

-         Includes reproduction rates and survival

-         A “relative” term: applies only to individual organisms within same species

FITNESS IS NOT ABSOLUTE- specific for a certain environment

Cost-Benefit / Optimality model

And these evolutionary changes lead to adaptation and speciation-

Only occurs under appropriate conditions, which will lead to reproductive isolating mechanisms.  Isolation may be:

-         Behavioral (mating rituals)

-         Temporal (breeding times, etc.)

-         Mechanical (structure, size)

-         Ecological (lions and tigers)

-         Gametes may be prevented from fusing

Adaptation does not produce “optimal” phenotypes.

Adaptation is constrained in real populations by:

Genetic forces:  Mutation and Gene Flow (immigration)

Environmental forces: Environments are continuously changing

Limitation forces: Especially of resources, time and energy

(trade-offs between adaptations)