What is an Ecosystem?

• • Ecosystem(s)
• – Interacting biological & physical components in a particular place
• – Comprise interacting environmental components along with
• – Organisms living within them
• – Have definable boundaries & are open to movement in & out
• – Ecosystems are dynamic • Conditions within them change continuously
• Environment & Organisms
• • Physical environment
• – Limits where organisms live
• • Physical & other factors
• – Nutrients, organism size, food item size, diet requirements, food availability can be limiting
• – Organism cannot live where it cannot finds things it needs

Nutrient Cycling & Energy Flow

• • Physical environment
• – Supports life through cycling of water & nutrients & is their source
• • Water & nutrients cycle through ecosystems
• – Nutrient cycles involve more than organisms
• – Also involve physical environment
• Nutrient Cycling & Energy Flow
• • For living things, 4 of most important cycles are
• • Water
• • Nitrogen
• • Carbon
• • Phosphorus

Four Major Nutrient Cycles

• • The Carbon Cycle
• – Diffusion
• – Volcanic emissions
• – Decomposition
• – Organic respiration
• – Industrial pollution
• – Burning
• – Runoff/erosion
• – Photosynthesis
• – Consumption
• – Mining

• • The Water Cycle
• – Evaporation
• – Precipitation
• – Runoff
• – Ground water

• • The Nitrogen Cycle
• – Denitrification
• – Biological fixation
• – Industrial fixation
• – Runoff/erosion
• – Fixation

• • The Phosphorous Cycle
• – Organic decay
• – Consumption
• – Biological uptake
• – Mining
• – Erosion
• – Runoff
• – Sediment settling
• – Tectonic shifts

 The Physical Environment  - How does it Affect Organisms?

• • Light
• – Differences in light in 24-hour period
• • Amount of light varies with season, latitude, local topography
• • Temperature
• – Effects of light & temperature hard to separate
• • Available water
• – Varies widely from place to place
• • Wind
• – Many plants depend on wind for reproduction
• • Speeds up evaporation
• • Climate
• – Sum total of weather events in region
• – Light, temperature, wind, available water all interact in climate

Food Chains & Food Webs

• • Biological communities are organized in trophic levels
• • Most obvious interrelatedness in ecosystems is – “Who eats whom?” – food chain (with trophic levels)
• • Biological communities
• – A set of linked food chains, each of which links plants to herbivores to carnivores
• • Primary producers
• – Plants & other species that produce food of food chain
• • Primary consumers (herbivores)
• – Organisms that eat plants
• – Feed directly on primary producers of food chain
• • Secondary consumers (carnivores)
• – Animals that eat other animals
• Food Chains & Food Webs
• • Stable community is like pyramid
• – Usually more producers than primary consumers
• – More primary consumers than secondary consumers
• • These groups are measured by biomass

Human Activities - How do they Affect the Environment?
•

• • Humans are dominant in today’s ecosystems
• – We are generalists & opportunists
• • Science plays limited role
• – On environmental problems, many solutions to such problems require changing human behavior

The Growth of Human Population - Can We Control It?

• • Humans’ unique feature – Ability to control environments
• • People are not evenly distributed worldwide
• • Increased mortality for most species results in population stability

• Increased human mortality would control population, but...

• • Encouraging war, disease epidemics, starvation go against human nature
• • What we could control is ability to reproduce & it is available option

• The Growth of Human Population - Can We Control It?
• • Birth rate has decreased in some countries (Europe, China)
• – For it to happen in other countries - Changes in education, economic opportunities, female empowerment, availability of birth control methods are needed

Are Human Activities Poisoning the Earth?

Water & air pollution are serious problems

• • Example in which pollution reversal may be underway
• – Air conditioning & chlorofluorocarbons (CFCs)

• • Government of the world
• – Called for world congress in 1987 to discuss CFCs’ effect on ozone layer
• – 27 countries signed Montreal Protocol
• • Restrict use & production of CFCs

Global Warming & Earth’s Climate

• • Light constantly strikes Earth , transforms into heat (temperature)
• • 30% incoming light never becomes heat, – reflects, mainly off clouds
• • 20% is absorbed by upper atmosphere gases
• – Only about 50% of light affects Earth’s temperature
• • If more energy is absorbed or less is lost, Earth’s temperature rises
• • If less absorbed than lost, Earth cools
• • Key factors in this are atmospheric gases
• – Called greenhouse gases (water vapor, CO2, methane, etc.)
• • Water vapor in atmosphere– Is beyond human control & is self-regulated
• • Amount of other greenhouse gases maybe more under human control

• • Calculations suggest – Earth’s average temperature could increase several degrees by 2050

Return to Syllabus