Chapter 5

Populations and Communities

5-1: Populations Why is it important to study populations? What is the difference between exponential

growth and logistic growth? What factors affect population size? How have science and technology affected

human population growth?

Understanding how populations grow and shrink iscritical to managing agricultural pests and

diseases and also for knowing how to protect ecosystems.

What is a Population?

Population a group of organisms of the same species that live in a specific geographical area, at the same time and are able to interbreed Small populations

Herd of zebra Large populations

Rabbits in Australia Steady – fairly unchanging numbers Increasing – exponentially or logistically

Rabbits in Australia from 24 to 600 million in 100 years Decreasing – exponentially or logistically

Population Growth

Birth rate babies born per time Death rate deaths per time Immigration movement of individuals into a

population Emigration movement of individuals out of

a population Carrying capacity the largest population

that the environment can support at a given time

Growth Patterns Exponential growth

numbers increase by a certain factor in each successive period of time Bacteria rabbits

Logistic growth starts with a minimum number of individuals and reaches a maximum depending on the carrying capacity of the habitat Most animals are

contained by competition for food, shelter, mates and other resources

Factors Affecting Population Size

Abiotic – plants limited by amount of sunlight and soil nutrients like nitrogen

Biotic – populations can be limited by number of pollinators and predator-prey relationships

Density-Dependent – something like a disease can impact a population and be worse if there are more individuals

Density-Independent – something like a tornado can impact a forest but hits no matter how many trees there are

Human Population

Historic Hunter-gatherer societies Cities (near resources) Industrial revolution and westward expansion

Science and Technology Medicine; when ill and/or wounded Health care; especially preventative like vaccines Clean water Enough food

5-2: Interactions in Communities

How do predator-prey interactions influence both predator and prey?

What are two other types of interactions in a community?

Interactions between organisms are the basis of communities and are

shaped by changes in the environment and the evolution of organisms

Predator - Prey Interactions

Predation one organism kills another for food Lion eats zebra Shark eats fish Also at microscopic level (daphnia eat amoebas) Very few organisms have no predator (killer

whales) and most are both predator and prey

Other relationships

Coevolution two or more organims have developed responses to one another due to mutual influence Faster zebras will require faster cheetahs…. Genetic basis

occurs over many generations (of a population), evolution does not occur in the lifetime of an individual

Parasitism fleas, tick, tapeworms; host provides food and home; parasite has adaptations like the cuticle (skin) of tapeworm that keeps it from being digested

Herbivory defenses like thorns so that a plant isn’t eaten (grazed). Also includes chemical defenses…..monarch eat milkweed that is toxic to many herbivores – and then the monarch also becomes toxic!

Symbioses

Symbiosis is a relationship between two species in close association with each other. Mutualism both species benefit

Cleaner fish get meal and protection while predator is freed from potential parasites

Pollinators are a great example of this interaction Commensalism one species benefits and the

other is neither harmed or helped Orchids are epiphytes, plants that grow attached to

other plants…helps them get to sun and doesn’t hurt tree they are on.