population Number of members of a single species in a particular area

Demography Demography – study of (human) populations, make-up and distribution Demo = people Graph = picture/diagram Ex: Commercials during cartoon programs are often for toys because their target demographic is children Term is expanded to suit all species’ populations

3 characteristics of all populations Density The number of organisms of the same species per unit area (25 people per classroom) Dispersion The pattern of population distribution Ranges Limited by biotic and abiotic factors

Population density The number of organisms per unit area. High population density = crowded So cities have… High people population density, but low… Trees and other organisms that got displaced

Dispersion often dictated by availability of food. Uniform dispersion Evenly spaced Territorial animals protect their hunting grounds, creating this. Clumped dispersion Social animals that live in herds or colonies Examples? Buffalo, ants, bees, wildebeast, schools of fish

Dispersion continued Random dispersion Neither territorial nor colonizing Unpredictable Examples: Deer, many birds (except when they group together to migrate)

Range Can be very small, like… limited to an island Or vast, like … almost everywhere on the planet Mosquitos Range is determined by both biotic and abiotic factors

Population Limiting Factors Density independent factors Factors that do/don’t (pick one) depend on the population density Don’t So abiotic factors, such as weather events, including Drought, flood, fire, tornados

Population Limiting Factors Density dependent factors Biotic factors limit the population Amount of food (plants or prey) Amount of predators Amount of competition for same resource The higher the population, the more competition Disease (higher rate with higher population density)

Population growth rate Emigration: Leaving the population Immigration Coming in to the population Pop. by: emigration and mortality (death) Pop. by: Immigration and birth

Population growth rate If population increase and decrease are equal, then population growth rate is … Zero If immigration and birth exceed (are greater than, >) emigration and death, then population growth rate is Positive What are the factors that make population growth negative? More deaths and emigration than births and immigration.

Growth models Exponential and logistical growth models Exponential All pop’s. would do this if not limited Happens when a population arrives in a new area with no competition and plenty of food

Exponential growth

Growth Models Logistical S curve Exponential growth until limiting factors bring under control Then stable

Carrying capacity The maximum number of individuals of a species an area can support over the long term Limited by biotic (predation, food availability) and abiotic (land, space for nesting, etc) factors

Survivorship survivorship – % of members of a group likely to survive to any given age Type I –Most members of the species survive into old age Type II – steady decline Type III – high infant mortality (many offspring; many die young)

Survivorship & Life Histories Limited energy Can’t both put energy into lots of offspring AND lots of care Many factors determine which it will be Semelparity Semelparity: “big bang” reproduction. All energy is focused into producing many offspring before dying Iteropartiy Iteropartiy: (iterations) cyclical reproductive pattern. Only a few offspring per cycle, usually cared for.

Reproductive patterns r-strategists and k-strategists r-strategists Produce many offspring Don’t spend much energy caring for young most offspring die, best adapted survive Typical for fluctuating environment Examples Dandelions, sponges, sea turtles

Reproductive patterns k-strategist Tend to be larger animals Produce few offspring Care for their young Most offspring survive Environmental conditions generally stable Controlled by density dependent factors Examples Most mammals, large birds,

R-strategist or k-strategist?

Modeling Populations 1-models-representations N = population size now B = # births b = # births per capita = birth RATE D or M = deaths or mortality d or m = deaths per capita = death RATE T = time, usually 1 generation r = b – r = population rate of change ∆N = change in population

Exponential Growth ∆N = rN New N = ∆N + N

Logistic Growth ∆N = rN(K-N)/K Takes into account the carrying capacity

Shows gender and age distribution at a fixed time Shape below shows many children born (high total birth rate), but also high infant mortality This is a developing country age structure Population is increasing rapidly Population Pyramid, AKA: Age Structure Diagram

Population Pyramids AKA Age Structure Diagram Here you see the US vs. Nigeria US birth rate is approximately equal to death rate and population has stabilized

Ecological Footprint Populations use resources at different rates Ecological capactiy: Different lands have differing amounts of resources to offer. Ecological footprint: the aggregate land and water area appropriated by each nation (or individual) to produce all the resources it consumes and absorb all the waste it generates.

Ecological creditors and debtors Countries that use more than their biocapacity are creditors. Countries using less are debtors.