Population Dynamics Unit 4: The Biosphere Let them know about the quiz. Four day unit, three days of notes (but short). We’re going outside next class!!!

Species Occur in Groups Called Populations Population density – the number of organisms per unit area Species distribution (dispersion patterns) Based on the availability of resources (food) Population – all the members living in the same place at the same time. Pattern of spacing within an area (based on the organism’s needs). Examples Clumpted – American bison Uniform – black bears Random – White-tailed deer

Population Growth Population growth rate explains how fast a population grows Birth rate Reproductive potential – the maximum number of offspring each member of the population can produce Different generation times Death rate Emigration – moving away from a population Immigration – moving into a population

Exponential Growth – J-Shaped No limits placed on a population by its environment Numbers Time

Logistic Growth – S-shaped Most populations Growth slows when the carrying capacity is approached The maximum number of individuals that an environment can support in the long-term Limited by energy, water, oxygen, and nutrients available

Population-limiting Factors Both of these types control population numbers, but in different ways Density-independent factors – do not depend on the number of organisms per unit area Abiotic factors – weather events like drought, flooding, extreme temperature, or tornadoes Forest fires – crown v. controlled fires

Density-dependent factors Any factor that depends on the number of members per unit area Usually biotic factors Disease – outbreaks occur when population density is high Competition – increases when population density is high Parasites – can limit the population size when population density is high

Lemmings – Competition Population grows exponentially until food become limited and the population sizes decreases significantly