POPULATION = a group of interbreeding organisms (same species) that live in the same place at the same time and compete for the same resources. Resources = food, water, shelter, mates, and so on... resources  pop. size

The population size of a species in a given space at a given time is determined by the interplay between BIOTIC POTENTIAL and ENVIRONMENTAL RESISTANCE. Biotic potential = growth rate with unlimited resources. Environmental resistance = all the factors acting jointly to limit population growth.

Four variables change population size: 1.NATALITY = birth rate 2.MORTALITY = death rate 3.IMMIGRATION = rate of organisms moving in 4.EMIGRATION = rate of organisms moving out

DENSITY DEPENDENT FACTORS = affect a populations’ size depending on its population density. 1.Predation 2.Disease 3.Availability of food and water 4.Space Negative Feedback!!

Populations change in response to environmental stress or changes in environmental conditions. 1.In size = # of individuals 2.Density = # of individual / specific space 3.Age distribution = proportions / age group 4.Dispersion = Clumped (elephants) Uniform (creosote bush) Random (dandelions)

DENSITY INDEPENDENT FACTORS = affect a populations’ size regardless of its population density. 1.Weather 2.Earthquakes 3.Floods 4.Fires... Natural disasters R-strategists populations are most affected by these.

No population can grow indefinitely! Every environment has a CARRYING CAPACITY = the maximum number of individuals of a given species that can be sustained indefinitely in a given space Number of sheep (millions) Year

Factors that affect carrying capacity: 1.Competition with/in and between species. 2.Natural and human caused catastrophes. 3.Immigration and emigration. 4.Seasonal fluctuations in food, water, shelter, and nesting sites.

A population that has few if any resource limitations grows exponentially. EXPONENTIAL GROWTH starts out slowly and then proceeds faster and faster as the population increases. Time (t) Population size (N) “J” population growth curve

LOGISTIC GROWTH involves initial exponential growth and then there is a steady decrease in growth as the population encounters environmental resistance and approaches carrying capacity and levels off. “S or sigmoid” population growth curve Time (t) Population size (N) K

Time (t) Population size (N) K Exponential phase Transitional phase Plateau phase

Opportunistic or r-Selected Species cockroachdandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species

Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species elephantsaguaro Competitor or K-Selected Species

Number of individuals Time Carrying capacity K species; experience K selection r species; experience r selection K REPRODUCTIVE STRATEGIES

SURVIVORSHIP CURVES

Reindeer on St. Paul Island 41 mi 2 Started with 25 Reindeer (4 males and 21females) No predators 200 mi from mainland so no on or off No hunting

End Result Start with = 2046 deer 1950= 8 deer Growth Rate of 16% Did bounce back to a steady 250 deer

Birth and Death Calculations Crude Birth Rate (CBR)= # of births per 1000 individuals/yr CBR=(Births/Pop. Size)x1000 The world CBR is 20.3 Crude Death Rate (CDR) = # of deaths per 1000 individuals/yr CDR= (Deaths/Pop. Size)x1000 The world CDR is 9.6

More Calculations Natural Increase Rate in % (NIR) NIR = (CBR-CDR)/10 Doubling Rate = how many years it will take to double the population DR= 70/NIR Density= # of individuals in a given area D= Pop./ Area

IB Acronyms for Countries MEDC= More Economically Developed Country LEDC= Less Economically Developed Country NIC= Newly Industrialized Country