Transcript Populations and Humans in the Biosphere

Populations and Humans in the
Biosphere
Population Density
• What can cause a population to grow?
– Births, immigration
• What can cause a population to
decline?
– Deaths, emigration
Population Growth Models
• Exponential model (red)
• idealized population in an
unlimited environment (J-curve);
r-selected species (r=per capita
growth rate)
• Logistic model (blue)
•carrying capacity (K): maximum
population size that a particular
environment can support (S-curve); Kselected species
Population limiting factors
• Density-dependent factors
•competition
•predation
•stress/crowding
•waste accumulation
• Density-dependent factors
regulate population size
• Density-independent factors
(abiotic)
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•weather/climate
•periodic disturbances
Question
• No matter where you live, would you
say that the total human population is
growing faster today or that it grew
faster 50 years ago?
Answer
• The rate of growth was faster 50 years
ago, but the total number of people
being added to the population each day
is greater today.
Demography: factors that affect growth & decline of (human) populations
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Birthrate (natality, fecundity)~ # of offspring produced
Death rate (mortality)
Age structure~ relative number of individuals of each age
Survivorship curve~ plot of numbers still alive at each age
Human Populations
• Not all countries have the same growth rate
– Highly developed countries (US, Germany, Japan,
etc.)
• Low birth rates and infant mortality rates and longer life
expectancies
– Developing countries
• Moderately developing countries (Mexico, Thailand, etc.):
birth and infant mortality rates high, but declining
• Less developed countries (Bangladesh, Niger, Ethiopia,
Laos, Cambodia, etc.): highest birth and infant mortality rates
and lowest life expectancies
Biodiversity
• What is it? The genetically-based variety
of all organisms in the biosphere
• Species diversity – the number of different
species in the biosphere
• The greater the biodiversity, the more
stable (able to rebound from disturbance)
an ecosystem is
Word Clue
• From the words used, what do you think
these words mean?
– habitat fragmentation
– invasive species
– biological magnification
Word Clue
• From the words used, what do you think
these words mean?
– habitat fragmentation – when a habitat is split
into pieces, usually due to development
– invasive species – non-native species
– biological magnification – concentrations of a
harmful substance increase in organisms at
higher trophic levels
Threats to Biodiversity
• What are some threats to biodiversity?
– Invasive species,
– Overexploitation,
– destruction of habitat,
– disruption of habitat,
– fragmentation of habitat,
– pollution
Pollution and Biodiversity
• What three kinds of pollution affect
biodiversity?
• Biological magnification (DDT),
• Acid rain (plants),
• Eutrophication from fertilizers, sewage,
etc. that lead to algae growth
Endangered and Extinction
• What is the difference between background
extinction and mass extinction?
– Background extinction is a gradual process; mass
extinction is a large percentage of species gone
extinct
• Which one is going on now?
– Mass Extinction
• What is its cause?
– People
• What is extinction? Endangered?
How can we help?
• Conservation and preservation the two
main ways of slowing the decrease of
biodiversity. What is the difference?
– Conservation involves maintaining species
and habitats as resources for use;
preservation involves complete protection
• What is a renewable resource?
Nonrenewable resource?
Human Impact
• Biological magnification: trophic
process in which retained substances
become more concentrated at higher levels
• Greenhouse effect: warming of planet
due to atmospheric accumulation of carbon
dioxide and other gases
• Ozone depletion:
effect of
chlorofluorocarbons (CFC’s) released into the
atmosphere
• Rainforest destruction
• Cause: Overpopulation?