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?