Things To Do Objectives Pick up notes and handouts Learn about populations Discuss how a population is limited Go over carrying capacity

Population Ecology Notes 1

Terms: Species: Organisms that can interbreed and create fertile offspring Population: A group of interacting individuals Exponential Growth: Growth pattern where a population grows faster as it increases in size Carrying Capacity: The number of individuals of a species that an environment can support Density - Dependent Factor: Factor such as disease, parasites or food supply that has an increasing effect as populations increase Density - Independent Factor: Factors such as temperature, storms, floods, drought or habitat that disrupt the affects all populations, regardless of their density

What is a Population? It consists of all the individuals of a species that live together in one place at one time. Every population tends to grow because individuals tend to have multiple offspring Eventually limited resources in an environment limit the growth of a population The statistical study of all populations is called demography Demographers study and predict the composition of a population and how it will change 4 Key Features of Populations Population Size Population Density Dispersion Growth Rate

Size and Density Population Size Population Density Can affect the populations ability to survive Studies have shown that very small populations are among the most likely to become extinct Small populations are prone to interbreeding Large populations will run out of resources Population Density The number of individuals that live in a given area If the individuals of a population are few and are spaced widely apart, they may seldom encounter one another, making reproduction rare.

Dispersion and Growth Rate The way the individuals of the population are arranged in space Three Ways Random Distribution Even (Uniform) Distribution Clumped Distribution Growth Rate Number of Births - Number of Deaths = Growth Rate Positive Growth Rate: More births than deaths, population grows Negative Growth Rate: Less births than deaths, population declines Zero Growth Rate: Number of births and deaths are about the same, population remains the same

How Fast does a Population Grow? Reproductive Potential: The maximum number of offspring each individual of a population can produce Varies for each species Examples 750 years for elephants to produce 19 million offspring 2 weeks for bacteria to produce 19 million offspring

Population Models Hypothetical population that attempts to exhibit the key characteristics of a real population They use models to predict and simulate growth, dispersion, size and density Populations don't grow in a linear fashion but exponentially Example: 1 bacteria becomes 2 2 bacteria become 4 4 bacteria become 16 16 bacteria become 256

Limiting Factors These are biotic or abiotic factors that limit the existence, reproduction, growth, numbers, and distribution of an organism Think about this: A female sea turtle can lay about 2,ooo eggs in her lifetime If all of the eggs survived, there would be huge increases in numbers every year Why doesn't the population of sea turtles increase rapidly each year?

Limiting Factors Populations rarely grow to their capacity Carrying Capacity The maximum population of a specific species that the ecosystem can support indefinitely There are many factors that can limit growth: Resources Competition Disease Natural Disaster

Resources and Competition Resource availability is going to be the biggest limiting factor Example: Plants need 8 1/2 hours of sunlight, 1/4 gallon of water, and 10 different mineral nutrients a day The ecosystem can provide 12 hours of sunlight, 1/2 gallon of water and 9 mineral nutrients a day What is the limiting factor: sunlight, water or minerals? Competition There can be competition within a population Competition can exist among species as well

Population Regulation Causes of death in a population Density - Dependent Death occurs more rapidly in a dense population rather than a sparse one This can come from resource depletion as well Density Dependent Factors: Competition Predation Disease Parasitism Crowding Stress Example: 14th Century saw the Bubonic Plague Cities were more affected than rural communities

Population Regulation Density - Independent Death occurs regardless of the density of the population It usually includes environmental conditions like weather Density Independent Factors: Natural Disasters Temperature Sunlight Human Activities Physical Characteristics Behaviors