Populations and Communities 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 is critical 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 Science and Technology 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.