Section 5.2Limits to Growth

I Can…

• LS 2.1 I can analyze a representative ecosystem to predict the effects of a disturbance on population size.

• LS 2.1 I can use the quantitative evidence to explain factors that affect population size and carrying capacity within an ecosystem.

Key Questions

1. What factors determine carrying capacity?

2. What limiting factors depend on population density?

3. What limiting factors do not typically depend on population density?

4. What is the relationship between limiting factors and extinction?

Vocabulary

• Limiting factor

• Density-dependent limiting factor

• density-independent limiting factor

Limiting Factors

• Limiting factor- any factor that controls the growth of a population • May be biotic or abiotic external factors

• Interact, directly or indirectly, with the population

• Acting separately or together, limiting factors determine the carrying capacity of an environment for a species.

Density-Dependent Limiting Factors

• Density-dependent limiting factors- limiting factors that operate strongly when the number of organisms per unit area (population density) reaches a certain level • Do not strongly affect small, scattered populations

• Competition• Predation• Herbivory• Parasitism• Disease• Stress from overcrowding

Competition

• When populations become crowded, individuals compete for food, water, space, sunlight, etc.

• Density-dependent limiting factor because the more individuals in an area, the sooner they use up available resources.

• Competition can also occur between members of different species.

Parasitism and Disease

• Weaken their hosts and cause stress or death

• Density-dependent factors because the denser the host population, the more easily parasites and diseases can spread.

ticks feeding on the blood of a deer

Stress from Overcrowding

• Some species fight amongst themselves if overcrowded.

• Fights can kill or weaken the body.

• Overcrowding can also cause females to neglect or kill their own offspring.

Predator-Prey Relationships

• Populations of predator and prey may rise and fall over time.

• Isle Royale Example: • moose population increases wolves have

plenty to eat so they increasemoose population then decreases wolves begin to starve (decrease) …cycle repeats

Predator-Prey Relationships

Herbivory Effects

• Herbivores and plants cycle up and down (just like populations of predators and prey).

Humans as Predators

• Ex.- Eighteenth century fur hunters killing otters

Density-Independent Limiting Factors

• Affect all populations regardless of population size and density

• A population may “crash”.

• Environmental extremes, including weather extremes such as hurricanes, droughts, or floods, and natural disasters, such as wildfires, can act as density-independent limiting factors.

True Density Independence?

• Sometimes, effects of so-called density-independent factors actually vary with population density.

• Isle Royale Example:• Bitterly cold winter with heavy snowfall making it

difficult for moose to find food (density-independent)

• Effects were greater on a larger population (smaller population would have had less competition)

Controlling Introduced Species

• Artificial density-independent measures—such as hunting—offer only temporary solutions and are very expensive.

Limiting Factors and Extinction

• Limiting factors do not always stay the same over time.

• Temperature and rainfall are liming factors for some organisms in certain environments, but can change if climate changes.

• When human activities chop natural environments into smaller pieces, the carrying capacity of those habitats for those species can be much smaller.

• If carrying capacity falls low enough, populations can be wiped out, leading to species extinction.

Section 5.2 Exit Ticket

1. How do populations of organisms interact with one another?

2. How does a change in one population of organisms affect the population of other organisms in the surrounding ecosystem?

3. What factors of growth can limit the growth of a population?

The End