BIO 420
Evolution ‘requires’ genetic variation, 1 by mutation (gene flow matters)
Natural selection acts on individuals with different combinations of genes, enduring the most fit a survival advantage
Ensures individuals are well suited to their environment
Fitness = proportionate contribution of individuals to future generations. Individuals leaving the greatest number of descendants relative to others are the fittest individuals in the population.
Evolution occurs when the effects of selection on a heritable trait in 1 generation is transmitted to the next generation.
Best evidence for natural selection involves:
Variable traits
Demonstration that the trait confers a fitness advantage
Evidence that the trait is heritable
Ecological time: circa 10 generations, period over which population could reach a state VS
Evolutionary time - circa 500,000 years, long enough period to disrupt ecological steady states (rapid evolution)
4 Categories:
Category I. Evolution of trophic links via specialization ( influence of climate evolution in contemporary time) (evolution unpredictable due to unpredictable environment changes)
Changes in climate can drive natural selection
Example: Environment changes (El Nino) created differences in the abundance of seed resources causing directional selection in break size ( Grant and Grant 1993)
Category 2. Evolution of Defense ( cryptic coloration in peppered (biston) moths in response to changes in color of habitat - bird predation was agent of selection ) (occurs over mant generations)
Category 3. Rapid loss of traits in absence of interaction - loss of traits in guppies when predation diminished (Endler 1995) In stream pool habitats in trinidad
Category 4. Change in outcome of interaction
Niche - organism’s place in environment, defined by physiological tolerances and resource requirements is fundamental niche
Realized Niche - constrained by biological interaction among species “Post interactice Niche”
Lecture #2
Answer: How many species are alive on planet Earth?
Force imposed on a structure by a water velocity of 2 m s^-1 is roughly equivalent to that exerted by a wind of 130 mph
No Slip condition: low velocity layer
Fluids in immediate contact with a solid surface does not slip (move) relative to the surface
Boundary layer - mainstream velocity to 99% of velocity to 0
Biological and ecological processes occur within boundary layers at all scales
DRAG (pressure): due to the difference between the high pressure on the high stream side and the low pressure on the downstream side.
Due to upstream - downstream difference in pressure
Skin friction drag: more surface or skin objects presents to flow, higher SKFD
DRAG: Fd = .5 Pu^bAcCd (density fluid) (fluid velocity) (characteristic area perpendicular to flow) (drag coefficient shape dependent paramount)
DRAG “Strategies”
Flexibility: reduce area exposed to flow
Drag minimizing strategy
Palm trees, seaweed and kelp are flexible in their environment when is comes of flow and drag resistance.
Drag Resistance - Large tropical trees have wide bases (buttresses)
Helps resist drag from high winds & uprooting
Reduce Cd - evolve or develop streamlined body to reduce drag
Pregnancy is a drag from bottlenose dolphins
Small body size
Pressure - Flow Relations:
Pressure drag: arises due to upstream - downstream pressure differences
Skin friction drag - more surface (skin) - exposed to flow, the higher skin friction drag - due to no slip conditions.
Principle of Continuity: velocity inversely proportional to cross sectional area - reduce area of aperture increase excurrent velocity
“Biological nozzle” in sponges, other filter feeders (bivalves)
Minimizes chances of re-filtering food laden water
Bernoulli Principle - pressure is inversely proportional to velocity
Creates biological phenomenon of induced flow (blk board)
Is the coupling of external to internal flow, results in fluid being drawn out of the structure or organism
Pressure - Flow Relations
Pressure along Ridge
Pressure along Side
Lift - arises due to same mechanism as pressure drag but at approx right angles to oncoming flow
Lift maximizing = flight
Lift minimizing = cone shaped limpets