Transcript Population Growth

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?