Understanding PopulationsUnderstanding Populations

How Populations Change in SizeHow Populations Change in Size

Objectives1.Describe the three main properties of a

population.2.Describe exponential population growth.3.Describe how the reproductive behavior of

individuals can affect the growth rate of their population.

4.Explain how population sizes in nature are regulated.

• What is a population?

• All members of a species living in the same place at the same time

• Properties of Populations

• Density – the number of individuals per unit area or volume

•Dispersion – the relative distribution or arrangement of its individuals within a given amount of space

•Size – actual number of individuals

• How does a population grow

•More births than deaths

• Growth rate – change in pop. Over time

Change in pop. Size = births - deaths

• How fast can a population grow

• Reproductive potential – the max number of offspring that each member of a population can produce

• Most organisms have a high reproductive potential because few offspring actually survive

• Potential increases when individuals produce more offspring at a time, more often, and reproduction early (shortens generation time – ave. time it takes to reach reproductive age)

• Small animals usually have a shorter generation time than larger animals

• Exponential Growth• As a population grows, it grows faster

• Occurs in nature when populations have plenty of food and space and no competition

• What limits population growth

• Carrying capacity - max pop. That the ecosystem can support indefinitely

• Amount of resources – limited resources determines carrying capacity

• Competition within a population• Territory• Food• mates

• Types of population regulation

• Density dependent – density, of individuals affects growth’ all individuals are affected• diseases

• Density independent – certain portions of the pop. May die regardless of the pop. Density• Severe weather, natural disasters

How Species InteractHow Species Interact

Objectives1.Explain the difference between niche and

habitat.2.Give examples of parts of a niche.3.Describe the five major types of interactions

between species.4.Explain the difference between parasitism

and predation.5.Explain how symbiotic relationships may

evolve.

• Organism’s niche• Unique role of a species within an ecosystem or a pattern of use of its habitat or it’s “job”

• Includes physical home, environmental factors necessary for survival, and all interactions

• Ways species interact

• Competition – both harmful• Relationship in which different individuals or population attempt to use the same limited resource

• Within and between species

•Between different species it’s called overlap

• Indirect competition – when species do not come into contact with each other

• Competition is reduced by•Evolution – better adaptations

•Divide niche in time and space

• Predation – 1 benefits and the other is harmed• Populations of predators depend on populations of prey

• Adaptations to avoid predators•Camouflage used to lie and wait or hide

•Warning coloration•Mimicry•Protective covering

• Parasitism – 1 benefits, other is harmed or killed• Parasite (flees, ticks, tape and heartworms, leaches, mistletoe

• Host

• Mutualism – both benefit• Bees and flowers

• Commensalism – 1 benefits, the other is unaffected• “hitchhikers”, birds and trees

• Symbiosis – close relationship

• coevolution