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); K-selected species

Population limiting factors

• Density-dependent factors •competition •predation

•stress/crowding •waste accumulation

• Density-dependent factors regulate population size

• Density-independent factors (abiotic)

• •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

• 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?