Interactions Within Ecosystems

Populations

• Made up of a group of organisms of the same species that live together in one place at one time and interbreed. (produce offspring)

• Understanding population growth is important– Populations of different species interact– Interactions can affect the number of individuals

in a population

Population Growth• How do populations grow and shrink?– Immigration

• Movement of individuals into a population

– Emigration• Movement of individuals out of a population

• Growth Rate– Affected when more individuals are born than die

• Population grows

– Exponential growth• Numbers increase by a certain factor over a period of time• J-shaped curve graph (pg 104 in text)

Exponential Growth

• Logistic Growth– Exponential Growth illustrates what the

population would look like if there were no outside influences

– Populations are affected by certain factors like availability of habitat, predators, and disease

– Populations slow and stabilize– Carrying capacity• Largest population that an environment can support

• Logistic Growth– Population growth that starts with a minimum

number of individuals and reaches a maximum depending on the carrying capacity of the habitat

– S – shaped curve graph (pg 105) • Population starts off small • Growth rate increases due to the abundance of

resources • Population reaches carrying capacity as resources

become scarce• Competition for resources slows the growth rate of the

population • birthrate = deathrate, no growth in population

Logistical Growth

Factors that Affect Population Size

• Abiotic Factors• Biotic Factors• Human Activities• Science and Technology• Predator – Prey Interactions– Predation– Coevolution

• Predator – Prey Interactions– Predation• Act of one organism killing another for food

– Coevolution• Back and forth evolutionary adaptations as a result of

interactions

– Parasitism• One organism feeds on the other (host)

– Herbivory• Plants adapt to protect themselves from being eaten

• Herbivory– Monarch caterpillar and

milkweed– Milkweed is toxic to deter

herbivores but does not harm caterpillar instead it stores toxin to keep from getting eaten itself

• Predation/Coevolution– Zebra has stripes to confuse predator, also long

legs, stays in herds– Lion hunts in packs, camouflage with landscape

• Symbiosis• Species live in close association with each other

– Mutualism • both species benefit

– Commensalism• one species benefits other is neither harmed or helped

• Parasitism– Tapeworm

• Mutualism– Clownfish and Sea

Anemone

• Commensalism– Orchid gets closer to the sun

Competition

• Competition determines the organism’s niche– Role that the organism plays in the community

• Carving a Niche– Affects other organisms in the community– Niche vs Habitat• Habitat is where an organism lives• Niche is the role that the organism plays in that habitat

Ecosystem Resiliency• Interactions between organisms and the number

of species (biodiversity) in an ecosystem add to the resiliency of an ecosystem.

• Resiliency– to withstand, resistant, tough, hardy, durable

• Keystone species– Species that is critical to an ecosystem because the

species affects the survival and number of other species in its community

– Examples (wolves in Yellowstone, Sea Otters off the Pacific Coast)