1.3 Populations

1990’s Number of sea otters living near the Aleutian Islands (near Alaska) sharply fell by 90%. Killer whales started eating sea otters Killer whales normally eat seals and sea lions not smaller otters. Study the next slide to find out why the whales changed their feeding habits.

Figure 1.15 page 18

Carrying Capacity It’s the largest population of a species that an environment can support. Food supply, competition, and predators can affect population size. Seychelles Paradise Flycatcher requiring about one hectare of mixed woodland per breeding pair. Lives on small island north-east of Madagascar.

4 factors determine the carrying capacity 1) MATERIALS AND ENERGY Limited by amount of energy from the Sun Supply of water, carbon and other materials adventures.com/costarica_nature.asp

4 factors that determine the carrying capacity of an ecosystem 2) FOOD CHAINS Biomass in all levels affects the length of the chain. Limited by amount food supply (so trophic level below) Limited by predators (so trophic level above)

4 factors that determine the carrying capacity of an ecosystem 3. COMPETITION Competition for food, water, mate and space. Intraspecific competition: among members of the same species Interspecific competition: between species.

4 factors that determine the carrying capacity of an ecosystem 4) Population density : How many individuals that can live in an area at one time.

Density-dependent factors When density increases beyond suitable level: Overcrowding may : –increase stress and spread of diseases or parasites –Increase aggression and neglect of offspring Therefore decreases population

Density-independent factors Limit a population regardless of its size. -Forest fire -Earthquake -Volcanic eruption -Tornado

Lets Correct p. 24 # 1 to 6