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Population density is the number of individuals that live in a defined area.
5.1 How Populations Grow
Four factors affect the size of a population.
– immigration– births– emigration– deaths
5.1 How Populations Grow
Exponential Growth vs. Logistic Growth
• Exponential growth is a rapid population increase due to an abundance of resources.
• Shown as a “J‐shaped” curve
5.1 How Populations Grow
Exponential Growth vs. Logistic Growth
• Exponential growth is a rapid population increase due to an abundance of resources.
Lag Phase = initial period of slow growth
Exponential Growth Phase= period of rapid growth when
population repeatedly increasesin size; does not continue forever
5.1 How Populations Grow
• Logistic growth is due to a population facing limited resources. • Shown as a “S‐shaped” curve
5.1 How Populations Grow
• Carrying capacity is the maximum number of individuals in a population that the environment can support.
1) Lag Phase
2) Exponential Growth Phase
3) Reaching CarryingCapacity
4) Leveling Off
5.1 How Populations Grow
• humans are in the exponential phase of growth• Projections for the future estimate 8.9 billion people by
2050
Human Population Growth
5.1 How Populations Grow
Ecological factors limit population growth.
• A limiting factor is something that keeps the size of a population down. 1) Density-dependent limiting factors
- affected by the number of individuals in a given area- ex: predation, competition, parasitism and disease
5.2 Limits of Growth
2) Density‐independent limiting factors ‐ limit a population’s growth regardless of the density.– ex: unusual weather, natural disasters, human activities
5.2 Limits of Growth
Importance of Biodiversity
• Every organism has its own niche (ex: producers, decomposers)
• All organisms depend on each other (ex: symbiosis, food chain/food web)
• Provide a variety of resources:‐ food‐ clean water‐medicine‐ recycled nutrients
6.3 Biodiversity
Loss of Biodiversity Causes:1) Habitat loss2) Pollution3) Overharvesting4) Global climate change5) Introduced or Invasive new species
(non‐native species)
6.3 Biodiversity
Introduced species can disrupt stable relationships in an ecosystem.
• An introduced species is one that is brought to an ecosystem by humans.– accidental– purposeful
• Invasive speciescan have anenvironmentaland economicimpact.
6.3 Biodiversity
Introduced species can disrupt stable relationships in an ecosystem.
• Non‐native species may introduce parasites, plants, and animal species that are not native to a particular area.
• Many non‐native species compete against native species for the resources (food, shelter) and disruptthe balance of the environment.
• Non‐native species flourish because they have few natural predators or parasites to slow down their population growth.
6.3 Biodiversity
• Invasive species often push out native species.– Burmese python
Origin: Southeast AsiaCurrent Habitat: Florida EvergladesMethod of Arrival: came to U.S. as a pet speciesProblem: threats to endangered bird species in the Everglades
6.3 Biodiversity
• Invasive species often push out native species.– mice
Origin: EuropeCurrent Habitat: AustraliaMethod of Arrival: British Cargo ship in late 1700sProblem: major pest species and caused economic
damage of crops
6.3 Biodiversity
• Invasive species often push out native species.– Kudzu plant
Origin: Southeast AsiaCurrent Habitat: Eastern United StatesMethod of Arrival: came to U.S. as an ornamental
house plant in 1876Problem: classified as a problematic weed species
because of its rapid growth
6.3 Biodiversity