Chapter 3 Ecosystems What Are They and How Do They Work
Chapter 3 Ecosystems What Are They and How Do They Work?
Core Cases Study
Have You Thanked the Insects Today?
· Insects have a bad reputation as pests
o Compete for food
o Disease vectors
o Invade houses, lawns, gardens and homes
· Natural services (Part of earth’s natural capital, Fig. 3.1)
o Pollination
o Pest control
· Insect attributes
o Been around for 400 my
o Many have high reproductive rate
o Rapidly evolve when faced with new environmental conditions
o Resistant to extinction
· Environmental lesson
o Although insects can thrive without newcomers such as us, we and most other land organisms would perish w/o them.
I. The Nature of Ecology
A. What is ecology?
1. Ecology – study of how organisms interact with one another and with their non-living environment.
2. Levels of organization of matter (Fig. 3.2)
B. Organisms and Species
1. Organism – any form of life and the fundamental unit of ecology.
2. Species – groups of organisms that resemble each other in appearance, behavior, chemistry, and genetic makeup
a. Classification is based common ancestry – sciences called Systematics and Taxonomy
b. How many species are their?
i. 1.4 million identified
ii. Estimated to be 4 to 100 million
C. Case Study: Which Species Run the World?
1. Microbes – bacteria, protists, fungi
2. Bad reputation justified?
a. Handful are pathogenic
b. Most play key roles in ecosystem functioning
i. Nitrogen cycle
ii. Decomposers
iii. Produce oxygen
c. Benefit humans directly
i. Help produce food – bread, yogurt, cheese, vinegar, tofu, soy sauce
ii. Intestinal bacteria
iii. Antibiotics
iv. Control plant diseases and populations of insects that attack crops.
D. Populations, Communities, and Ecosystems
1. Population – group of interacting/interbredding individuals of the same species occupying a specific area.
a. Genetic diversity – variation in genetic make-up (Fig. 3.5)
b. Habitat – place where organism or population lives and can have access to food, shelter, water, and mates.
c. Distribution, or range – area over which we can find a species
2. Community (biological) – group of interacting populations of species in an area
3. Ecosystem – community and its interaction with non-living matter and energy
a. Range from a small puddle to streams, woods, to the gut of an animal.
b. May be natural or artificial (farm, reservoir, crop field, urban area)
4. Biosphere – all of earth’s interconnected ecosystems.
II. The Earth’s Life-Support Systems
A. The Earth’s Life-Support Systems: Four Spheres
1. Biosphere consists of several spherical layers (Fig. 3.6).
a. Atmosphere
i. Troposphere – to 17 km (11 mi) above sea level; mostly N2 (78 %) and O2 (21 %)
ii. Stratosphere – 17-48 km (11-30 mi) above sea level; contains O3
b. Hydrosphere
i. Liquid water, surface and underground
ii. Ice, as ice caps, icebergs, and permafrost
iii. Water vapor
c. Lithosphere
i. Crust and upper mantle
ii. Contains nonrenewable fossil fuels and minerals
iii. Renewable soil, important for plant life
B. What Sustains Life on Earth?
1. Flow of high-quality energy
a. Sun ® ecosystem w/ much lost to heat dispersed ® radiated back into space
i. No round trips because high-quality energy can’t be recycled
2. Cycling of matter or nutrients
a. Atom, ions, or compounds needed by organisms
3. Gravity
a. Holds the atmosphere
C. What Happens to Solar Energy Reaching the Earth?
1. About 1-billionth of sun’s output reaches the Earth.
a. Either reflected or absorbed by chemicals, dust, and clouds.
b. Amount reaching the earth equals the amount reflected or radiated back to space (Fig. 3.8).
2. Some rough numbers
a. 80% that gets into the atmosphere warms the troposphere and evaporates and cycles water through the biosphere.
b. 1% generates the wind.
c. 0.1% used by green plants, algae, and bacteria for photosynthesis.
3. Most radiation making it through the atmosphere is degraded into loner-wavelength infrared radiation (IR).
a. Encounters greenhouse gases – CO2, H2O, CH4, N2O, and O3
i. Molecules vibrate and release even loner IR increase the KE of molecules in the atmosphere.
ii. Warms atmosphere causing a natural greenhouse effect.
III. Ecosystem Components
A. Biomes and Aquatic Life Zones: Where Organism Live
1. Biomes – terrestrial portions of biosphere with distinct climates and species.
a. Forests, deserts, and grasslands
2. Aquatic life zones
a. Freshwater – lakes, steams
b. Marine – coral reefs, coastal estuaries, deep ocean
B. Nonliving and Living Components of Ecosystems
1. Two types of components (Fig. 3.10):
a. Abiotic
i. Water
ii. Air
iii. Nutrients
iv. Sunlight
b. Biotic
i. Producers
ii. Consumers
iii. Decomposers
2. Different species and their populations thrive under different physical and chemical conditions.
a. Each pop. has a range of tolerance to variations in physical and chemical conditions (Fig. 3.11).
i. Individuals in a pop. have slight diff in genetic makeup allowing differences in tolerance ranges.
(a.) Optimum range
(b.) Physiological stress zone
(c.) Intolerance zone
b. A species may have a wide rang of tolerance to one factor but narrow for another.
i. Highly tolerant species can live in a wide variety of habitats w/ widely diff conditions.
c. Physical conditions can limit the distribution of a particular species (Fig. 3.12).
C. Factors That Limit Population Growth
1. Limiting factor – factor important in regulating population growth.
a. Limiting factor principle – too much or too little of any biotic factor can limit of prevent growth of a population, even if all other factors are at or near the optimum range of tolerance.
i. What types of conditions limit organisms in aquatic ecosystems? Terrestrial?
D. Producers: Basic Source of All Food
1. Producers, or autotrophs
a. Green plants, algae, types of bacteria
2. Photosynthesis
a. Light used to fix carbon into high energy chemical bonds
b. Plants, phytoplankton, cyanobacteria
c. Carbon dioxide + water + solar energy ® glucose + oxygen
3. Chemosynthesis
a. Specialized bacteria convert simple inorganic compounds from their environment into more complex nutrients compounds without sunlight.
b. Chemosynthetic bacteria near hydrothermal ocean vents, obtain energy from H2S gas, which is used to produce carbs.
E. Consumers: Eating and Recycling to Survive
1. Consumers, or heterotrophs
a. Primary consumers, herbivores
b. Secondary consumers, carnivores
c. Tertiary consumers or higher
2. Omnivores
3. Decomposers (Fig. 3.13)
4. Detritivores
5. In natural ecosystems there is little or no waste.
F. Aerobic and Anaerobic Respiration: Getting Energy for Survival
1. Aerobic respiration – energy is released from organic compounds such as glucose using oxygen.
a. Process turns organic molecules back to CO2 and water.
2. Anaerobic respiration, or fermentation – breaking down organic molecules in absence of oxygen to obtain energy.
a. Instead of CO2 and water, products may include methane, ethanol, acetic acid, lactic acid, and hydrogen sulfide.
G. Two Secrets of Survival: Energy Flow and Matter Recycling
1. Individual organisms have a one-way energy and matter flow.
2. But, ecosystems are sustained by matter recycling and one-way energy flow (Fig. 3.14).
IV. Biodiversity
A. The Diversity of Life: A Crucial Resource
1. Biological diversity, or biodiversity – one of earth’s most important renewable resources.
2. Four components (Fig. 3.15):
a. Genetic diversity
b. Species diversity
c. Ecological diversity
d. Functional diversity
B. Biodiversity Loss and Species Extinction: Remember HIPPO
1. Human impact is reducing biodiversity through habitat loss and premature extinctions at rates 100 to 10 000x higher than the world’s natural rate.
2. Five major causes, HIPPO
a. Habitat destruction and degradation
b. Invasive species
c. Pollution
d. Population growth
e. Overexploitation
C. Why Should We Care about Biodiversity?
1. Wealth of natural capital
a. Natural resources – food, wood, energy, medicines, etc.
b. Natural services – air and water purification, recycling soil, waste disposal, and pest control, etc.
2. Goals, Strategies, and Tactics for protecting biodiversity (Fig. 3.16)
V. Energy Flow in Ecosystems
A. Food Chains and Food Webs: Who Eats and Decomposes Whom?
1. There is little matter wasted in ecosystems.
2. Food Chain (Fig. 3.17)
a. Shows conceptually how energy and matter flow from one organism to another.
b. Trophic level – feeding level
i. First trophic level – producers
ii. Second trophic level – primary consumers, or herbivores
iii. Third trophic level – secondary consumers, or carnivores
iv. etc
3. Detritivores and decomposers “feed” from all levels
4. Food Web (Fig. 3.18)
a. Conceptually represents the truer network of interconnected food chains.
b. A “map of life’s interdependence.”
B. Energy Flow in and Ecosystem: Losing Energy in Food Chains and Webs
1. Each trophic level in a food web contains a certain amount of biomass – the dry mass of all organic matter contained in a trophic level.
a. Chemical energy in biomass, transferred from one trophic level to next.
i. Process not efficient, 2 – 40%, but typically 10%
ii. Ecological efficiency – percentage of usable energy transferred as biomass from one trophic level to the next.
2. Pyramid of energy flow (Fig. 3.19)
a. Explains how earth can support more people if they eat at lower energy levels.
b. Limits the number of trophic levels that can occur in an ecosystem
C. Productivity of Producers: The Rate Is Crucial
1. Gross primary production (GPP) – rate at which and ecosystem’s producers convert solar energy into biomass.
2. Net primary productivity (NPP) – rate at which producers use photosynthesis to store energy minus the rate at which they use some of this stored energy for respiration.
a. Various ecosystems and life zones differ in their NPP (Fig. 3.22).
b. Only biomass (NPP) is available as food
c. The planet’s entire NPP limits the number of consumers (including humans) that can survive on earth.
3. Humans use, waste, or destroy:
a. 27% of earth’s total potential NPP
b. 10-55% of the plant’s terrestrial NPP
c. main reason habitats and species are lost
d. Interestingly (or should I say, Disturbingly, Alarmingly, Unsustainably, etc.), humans, their livestock and pets now make up 98% of total vertebrate biomass.
i. An ecological footprint that’s crowding out the other 2% of birds, mammals, reptiles, and amphibians.
VI. Soil: A Renewable Resource
A. What Is Soil and Why Is It Important
1. Soil – thin covering over most of land, components: eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms (most microscopic decomposers).
2. Weathering – physical, chemical, and biological process that can lead to soil formation.
a. Can take long periods of time.
i. One centimeter can take 15 -100 y depending on climate.
3. Function
a. Nutrients for producers
b. Cleans water
c. Decomposes and recycles waste
d. Water recycling and storage
4. Human activities have accelerated soil erosion.
B. Layers in Mature Soils (Fig. 3.23)
1. Mature soils are arranged in to layers called horizons.
2. Soil profile – cross-sectional view of horizons.
3. The soil horizons:
a. O horizon – surface litter layer; contains mostly undecomposed or partially decomposed leaves, twigs, crop wastes, animal waste fungi and other organic material.
b. A horizon – top soil layer; a porous mixture of partially decomposed bodies of dead plants and animals, called humus, and inorganic materials such as clay, silt and sand.
i. Helps hold water and nutrients taken up by plants.
ii. As long vegetation anchors these layers, a soil stores water for use by plants.
iii. The top two layers have bacteria, fungi, earthworms, and small arthropods that interact in complex food webs.
iv. Color of topsoil suggests how useful it is for growing crops.
v. Dark brown or black, rich in nitrogen and organic matter.
vi. Gray, bright yellow, and red, are low in organic matter and nitrogen.
c. B horizon – this and the layer below contain mostly inorganic matter, broken-down rock as varying mixtures of sand, silt, clay, and gravel.
d. C horizon – lies on the base of unweathered parent material, often bedrock.
4. Spaces in the soil allow plant roots to “breath.”
a. Downward movement of water into the soil pores, called infiltration.
i. Leaching
C. Some Soil Properties
1. Soils are mixtures of different-sized particles (Fig. 3.25).
a. Sand – 0.05-2 mm
b. Silt – 0.002-0.05 mm
c. Clay – <0.002 mm
2. Soil texture
VII. Matter Cycling In Ecosystems
A. Nutrient Cycles: Global Recycling
1. Nutrients – elements and compounds that organisms need to live, grow, and reproduce.
a. They move through the air, water, soil, rock, and organisms – called biogeochemical cycles or nutrient cycles.
b. Driven directly or indirectly by the sun and gravity.
c. Include the carbon/oxygen, nitrogen, phosphorus, sulfur, and water cycles.
B. The Water Cycle
1. Properties of water
a. H-bonding
b. Liquid over a wide range of temperatures
c. High specific heat
d. High vaporization energy
e. Universal solvent
f. Filters UV
g. Cohesion
h. Expands when it freezes
2. The cycle (Fig. 3.26)
a. Precipitation may be stored in glaciers, infiltrates soil and percolates to aquifers, most becomes surface runoff back to ocean.
b. Primary sculptor of earth’s landscape and carries dissolved nutrient compounds.
c. Purification of water by evaporation, transpiration, and filtration during percolation.
d. The hydrologic cycle can be viewed as a cycle of natural renewal of water quality.
3. Only about 0.024% of earth’s water supply is available to us as liquid fresh water.
C. Effects of Human Activities on the Water Cycle
1. Withdraw fresh water from sources faster than nature replaces it.
2. Clear vegetation from land for agriculture, mining, roads and buildings.
a. Increases runoff and reduces infiltration and percolation
3. Eutrophication
4. Water cycle speeding up because of warmer temperatures.