Populations Chapter 16 How Populations Grow Change in

Populations Chapter 16

How Populations Grow • Change in one population causes change in another – Population: • All the individuals of a species that live together in 1 place at 1 time. • Balance must occur for life to be supported.

Three Key Features of Populations • Population Size: – The number of individuals in a population can affect the populations ability to survive. • Small populations are likely to go extinct • Population Density: – The number of individuals that live in a given area. • Ex. Los Banos Human Populations- 36, 211 • Dispersion: – The way the individuals of the population are arranged in the space.

Models to Explain Population Growth • Growth rate affects population size – Exponential Growth Curve: • The rate of the population growth stays the same, as a result the population size increases steadily. • Ex. J-shaped curve- Single celled bacteria • Resources affect population size – Logistic Model: • Exponential growth is limited by a densitydependent factor • Ex. S-shaped curve- 6 billion humans

Population Growth Model K is the carrying capacity

Rapidly Growing Populations • R-Strategists: – Grow exponentially when environmental conditions allow them to reproduce. • Density-independent • Ex. Bacteria, some plants, and many insects – – – Short life span Usually reproduce early in life Have many offspring Offspring mature rapidly Have no parental care

Slowly Growing Populations • K-Strategists: – Populations that grow slowly and have small population sizes. • Ex. Whales and Redwood Trees – Long life span – Few offspring – Slow maturing process – Reproduce late in life

How Populations Evolve • Hardy-Weinberg Principle: – The frequency of alleles in a population do not change unless evolutionary forces act on the populations. • Equation to predict genotype frequencies: – p² + 2 pq + q² = 1 – AA Aa aa

5 Principle Evolutionary Forces • 1. Mutation • 2. Gene Flow: – The movement of alleles into or out of a population. • 3. Nonrandom Mating: – Individuals that prefer to mate with others that live nearby or are their own phenotype • Ex. Male widowbirds • 4. Genetic Drift: – Random change in the allele frequency. • Ex. Cheetahs • 5. Natural Selection – Acts only on the phenotype

Natural Selection Changes Trait Distribution a) Normal distribution b) Directional Selection c) Stabilizing Selection