POPULATION ECOLOGY

HOW DO POPULATIONS CHANGE?  What is a population?  All members of a species living in the same place at the same time  They usually breed with organisms in their own population  The daisy’s in a field in Ohio won’t mate with daisy’s in a field in Maryland  Generally a person in Nutley won’t mate with someone in Brazil

PROPERTIES OF POPULATIONS  Size  Density – the number of individuals per unit area/volume  10,500 people per square mile in Washington D.C.  1.3 people per square mile in Alaska  Dispersion – the distribution or arrangement of individuals within a given space

POPULATION DYNAMICS  Birth rate – numbers of births in a population in a given period of time  Death rate – number of deaths in a population in a given period of time  Life expectancy – how long, on average, a person will live  Change in population size = births - deaths

POPULATION GROWTH  Exponential Growth – maximum growth in ideal conditions  Ideal conditions would be plenty of food, unlimited resources and no predators  What would happen if populations grew like this? Is this realistic?  This would never happen because of limiting factors – factors that prevent a population from growing (space, food, resources, predators)  What are some other limiting factors?

POPULATION GROWTH  Logistic Growth – growth that accounts for limiting factors  Populations that have limiting factors reach a carrying capacity  Carrying capacity is the max number of organisms an environment can support indefinitely.

POPULATION REGULATION  Population size can be limited in ways that may OR may not depend on the density of the population...  Density dependent – when deaths occur more quickly in a crowded population  The cause may be disease  Density independent – when a proportion of the population dies regardless of the density  The cause is usually natural disaster

HOW SPECIES INTERACT  What is the difference between lions in the zoo and lions in the wild?  Niche – the role of a species in an ecosystem  This includes: physical home, environmental factors needed for survival and all interactions

A LIONS NICHE  jkb

WAYS SPECIES INTERACT  Symbiosis – Two species live closely together in an ecosystem  There are 5 major interactions:  Competition  Predation  Parasitism  Mutualism  Commensalism

COMPETITION  When different organisms or populations try to use the same limited resource  Competition can occur within or between species  Competitive Exclusion Principal – this says that two species that compete for the exact same resources cannot stably exist together

PREDATION  When an organism feeds on another organism  Predator – hunter  Prey – hunted

PARASITISM  An organism that lives in or on another organism  Fleas, ticks etc  + -

MUTUALISM  A close relationship between two species in which each species provides a benefit to the other  Bacteria in your intestines  Shark and pilot fish  + +

COMMENSALISM  A relationship in which one species benefits and the other species is unaffected  Sea anemone and clown fish  Barnacles and whales  + 0