Population Growth Chapter 5

How do ecologists study populations? Geographic range: where are they distributed? Density and distribution: in what manner are they distributed? Growth rate: how is the population increasing or declining? Age structure: males and females? number at reproductive age?

Geographic range: manatees and dugongs

Patterns of distribution: why???

Clumped distribution Food – clumped around food source Protection or shelter Small differences in habitat: shade, soil, wind, water Patchy resources!

Uniform distribution Can be caused by competition for resources Some organisms have specialized mechanisms… Creosote bushes release terpines, chemicals which inhibit growth of other plants around Tree planting Farming

Random distribution Happens when none of these factors exist Least common in nature because biotic factors usually cause other type Homogeneous habitats (same all over) Wind dispersal of seeds Water dispersal of larvae

Population growth Birth rate, death rate, immigration, emigration Resources are often the driver: food, water abundance or shortage, overcrowding

Exponential population growth

What caused human population expansion?

Logistic population growth Stages: exponential growth, growth slows down, growth stops Carrying capacity: number of organisms the area can support

Limiting factors Any factor that slows or stops the growth of a population Determine the carrying capacity Can be biotic or abiotic: availability of food or water, parasitism or disease, competition and predation, natural disasters such as floods or droughts

Density dependent limiting factors Act strongly when population density reaches a certain level Competition, predation, parasitism and disease, hunting, overcrowding stress Tend to be the BIOTIC limiting factors

Density independent limiting factors Affect all populations equally, regardless of population size or density Drought, floods, unusual weather such as hurricanes, wildfires Tend to be ABIOTIC limiting factors

Invasive species Any non-native species that is introduced to an ecosystem Accidental in intentional introductions Don’t have the usual limiting factors because the species didn’t evolve there: –No natural predators –No biological controls –Often short life-history species (rapid growth, lots of reproduction

Examples: Brazilian pepper trees outcompete our mangroves Brown hoplo “armored catfish” in St. Johns River are outcompeting native fish we eat Jellyfish brought in ballast water of ships Invertebrates attached to oil rigs moving from ocean to ocean

Demography: study of human populations When you refer to “demographics” it usually means: ages, genders, ethnicities, socioeconomics Age structure very important: how many members of the population are reproducing?

The Demographic Transition Stage 1: high birth rate and high death rate Stage 2: high birth rate, but death rate begins to fall Stage 3: birth rate falls to meet the death rate Factors that influence human birth and death rates: nutrition, sanitation, medical treatment, education, higher standard of living

Countries by population

Top 400 urban areas in 2006: 1 million + Humans have a clumped distribution Notice that Florida has 3 dots!

Fertility rate by country: number of children (0-8)

More people = less resources Food competition: shortages, prices Other resources: fuels, water, space, trees Impact on the environment: –Deforestation –Air pollution –Water pollution –Overcrowding

What can we do? What should we do? Write a 1 page essay about human population growth Should we address population as a society, or leave it up to individuals? What are some of the things that we can do?