What is population? Group of individuals of the same species that live in the same area

Does population change? Sea otters, kelp, and sea urchins

4 important characteristics of Population Geographic Range Density & Distribution Growth Rate –Birthrate, death rate, individuals entering/leaving Age Structure –# of males and females of each age

Geographic Distribution AKA Range Describes an area inhabited by a population Can vary –Few cubic centimeters –Kilometers of the ocean

Density & Distribution Density  # of individuals per unit area Distribution  individuals in population are spaced out across the range Random UniformClumped

Math Time Formula for calculating population density Population density=Number of individuals units area Problem: Suppose there are 150 bullfrogs living in a pond that covers an area of 3 square kilometers. What is the density of the bullfrog population? 50 bullfrogs per square kilometer

3 Factors that affect population size # of births # of deaths # of individuals that enter or leave population Population will increase or decrease depending on # of individuals added or removed Growth Rate

Immigration “im”= in Migrate= to move from one place to another Immigration is the individual movement into an area Animals in search of mates and food in new areas

Emigration “E”  means ‘out’ Migrate  means to move from one place to another Emigrate means individuals moving out of one place and into another Young wolves and bears leaving as they mature Shortage of food

Two types of growth Exponential growth –Individuals reproduce at a constant rate –Population multiplies by constant FACTOR over constant time interval Logistic growth –Occurs when a populations growth slows or stops after a period of exponential growth –As population approaches carrying capacity, BR may decrease, DR may increase or both, until equal

Exponential Growth Occurs under ideal conditions with unlimited resources Think about exponents in math…. Starts slowly then sky rockets to infinity Our graph will look like a J Bacteria

Lets look at bacteria… Bacteria reproduce by splitting in half Bacteria have a doubling time of 30 minutes If you start will one bacterium, how many bacteria will there be after the first 30 minutes? –2–2 After an hour? –4–4 After an hour and a half? –8–8 After two hours? –16 After 15 hours? –Over a billion

Logistic Growth As resources become less available, the growth of the population slows or stops S-shape curve No net increase or decrease in population What we usually see in nature

Carrying Capacity The largest number of individuals that a given environment can support The part of the logistic graph after the exponential growth…the flattening out The point at which this flat line reaches the y- axis is the size of the population when the growth rate reaches zero This doesn’t mean the population stops growing Many factors slow the growth of plants and animals…

Limiting Factor Condition that can restrict a population’s growth..create the CARRYING CAPCITY Could be: –Space –Disease –Availability of food

Factors Affecting Population Growth Density-dependent Factors Factor that limits population as population density increases –Competition –Predation –Disease –Parasitism –Crowding and Stress Density-Independent Factors Factors that affect population but are unrelated to population density; affect population regardless of size Insects vulnerable to this –Weather /Natural disasters –Human activities –Fires –deforestation

Boom and Bust Growth Cycles Increase rapidly for a period of time followed by a sharp decrease in population for a brief period of time Still not completely understood Hypothesis: –Changes in food supply –Stress from overcrowding –Other organisms influence on population

-Involves more than one population -Rapid increase and decrease in populations