Introduction to Unit #5 Population Dynamics Lesson #1 Survivorship Assignment – begin part 1 of 2 today Due on Monday next week

Characteristics of Populations

Introduction Population ecology (dynamics) is concerned with numbers. For example, how many individuals are there in a population? What determines if they will increase or decrease in numbers? How would the increase or decrease of their numbers influence the environment and other species? Changes in population also tell us about how alleles (genes) change and give us clues into how populations evolve.

Population Size & Population Density Population Size: refers to the total number of organisms in a given area Population Density: refers to the number of organisms per unit area Population Density (D) = Number of Organisms (N) / Space Occupied (S)

Example The population size of Canada is 35M The density is 3.1 people/km2 Bangladesh has a density of 700 people/km2 Population size can be misleading since density tells us more about how a population is distributed. In other words, population density tells us more about the patterns within a population

Characteristics of Population Density

1) Clumped Distribution Since resources are usually unevenly distributed, populations that gather near them end up in a clumped distribution For example, animals may gather near a water source and plants may tend to cluster in locations where moisture, temperature, and soil conditions are optimum for their growth Clumped distribution is also common amongst species which gather in groups for positive interactions, such as protection from predators or to increase hunting efficiency. A clumped density also leads to greater social interaction amongst individuals.

2) Uniform Distribution Uniform distributions can result in organisms who behave territorially (this means they try to defend their food, shelter, etc.). By defending their territory, they keep other individuals out of their area. This form of distribution is often a consequence of competition between individuals.

3) Random Distribution If resources are plentiful and uniformly distributed across an area, then populations will exhibit a random distribution. Since resources are all around and well distributed, there is no need for individuals to defend their share of resources. Random distributions also require that interactions between individuals are neutral These conditions are rare in nature.

Summary Type of Population Density How are Resources Distributed? How Abundant are Resources? How do Individuals Interact? Clumped Varied Positive Uniform Not Abundant Negative Random Abundant Neutral

Survivorship Curves

Survivorship Curves Type 1: low mortality (death) rates until beyond reproductive years; high life expectancy (e.g. Human) Type 2: uniform risk of mortality throughout life (e.g. Bird) Type 3: high mortality rates when young; but, those that do reach sexual maturity have a great chance to have a high life expectancy (e.g. Plant)