Biodiversity Biodiversity refers to the number and variety of species on Earth The number of known species is about 1.6 million, most of which are insects. However, the estimated number is around 13 million species.

How are Humans Causing Extinctions? Population increasing at a rate of 220,000 people each day! More space is required for homes and cropland to feed them.

Requiring more space means taking away the habitats of other species. THE MOST COMMON CAUSE OF EXTINCTION TODAY IS THE DESTRUCTION OF HABITATS

2. Unregulated Hunting leads to extinction. For ex 2. Unregulated Hunting leads to extinction. For ex., the American buffalo once numbered over 60 million; however, after Europeans settled in America the numbers were reduced to only 300.

3. Exotic species threaten native species because they do not have natural defenses against them.

Ch 5 “Populations” Population density is the number of individuals in an area

Population Growth Three factors that affect population size: (1) number of births (2) number of deaths (3) number of individuals that enter or leave the population Immigration- movement of individuals into an area Emigration- movement of individuals out of an area

Exponential Growth If a population has enough space, food and is protected from predators and disease, then the population will increase. A J-shaped curve indicates that a population is undergoing exponential growth. Under ideal conditions with unlimited Resources, a population will grow Exponentially.

Logistic Growth As resources become less available, the growth of a population slows or stops. S-shaped curve of this growth pattern is called logistic growth. How does population growth slow or stop?

Carrying Capacity The carrying capacity is the largest number of individuals that an environment can support.

Limits To Growth Limiting factors cause population growth to decrease.

Density-Dependent Factors When SIZE matters! Density-Dependent Factors is a limiting factor that depends on population size. When a population reaches a certain size, especially large, dense populations Density-dependent factors that limit a population include: Competition Predation Parasitism disease

Density-Independent Factors Size DOES NOT matter! Density-independent factors affect ALL populations in similar ways, regardless of the size of population Examples include: Unusual weather Natural disasters Human activities like damming rivers & clear-cutting forests