5-2 Limits to Growth

Limiting Factors• Remember, primary productivity of an

ecosystem can be reduced by limiting nutrients

• Limiting factors can determine carry capacity– Density Dependent Factors– Density Independent Factors

1. Density-Dependant Factors

• Limiting factors that depend on population size

• Density-dependent factors become limiting only when population density reaches a certain level

• Does not affect small, scattered populations

1a. Competition• Occurs when populations

become crowded

• When 2 species compete for same resource, they are under pressure to change– Over time, evolve to occupy diff.

niches

1b. Predation

• Populations in nature are controlled by predation– Known as predator-prey relationship

• Isle Royale in Lake Superior

1c & 1d Parasitism & Disease• Parasites are similar to predators

– weaken and kill hosts

• Large populations can be under stress making them more susceptible to diseases

• More members = easier to pass “things” around

3. Density-Independent Factors• Factors that affect

populations regardless of their size

• Examples: – Unusual weather (Draught,

Hurricanes)– Season cycles– Human activities (damming

rivers, forest cutting)

5-3 Human Population Growth

• Like the populations of many other living organisms, the size of the human population tends to increase with time.

• For most of human existence, the population grew slowly

• Until fairly recently, only half the children in the world survived to adulthood.

• What caused human populations to suddenly grow rapidly?

• Agriculture• Industry/Medicine

• About 500 years ago, the human population began growing more rapidly because of agriculture and industry.

• With these advances, the human population experienced exponential growth

Patterns of Population Growth• English economist Thomas

Malthus observed that human populations were growing rapidly.

• Malthus predicted that such growth would not continue indefinitely.

• Malthus- war, famine, and disease would limit human population growth.

Demographic Transition• The scientific study of human

populations is called demography

• Demographic transition, a dramatic change in birth and death rates.

• Ex: U.S., Japan, Europe

What are the 4 density-dependent limiting factors?

• Predation• Disease• Competition• Parasitism

What are examples density independent limiting factors?

• Storms• Natural Disasters• Human activity

What caused the human population to grow rapidly?

• Agriculture• Industry• Medicine