TOPIC 2: Ecosystems & Ecology

2.1 Species & Populations

2.2 Communities & Ecosystems

2.3 Flows of Energy & Matter

2.4 Biomes, Zonation, & Succession

2.5 Investigating Ecosystems

2.2 Knowledge & Understanding

• A community is a group of populations living and interacting with each other in a common habitat.
• An ecosystem is a community and the physical environment with which it interacts.
• Respiration and photosynthesis can be described as processes with inputs, outputs and transformations of energy and matter.
• Respiration is the conversion of organic matter into carbon dioxide and water in all living organisms, releasing energy. Aerobic respiration can be represented by the following word equation.
• During respiration, large amounts of energy are dissipated as heat, increasing the entropy in the ecosystem while enabling organisms to maintain relatively low entropy and so, high organization.
• Primary producers in most ecosystems convert light energy into chemical energy in the process of photosynthesis.
• The photosynthesis reaction can be represented by the word equation to the right.
• Photosynthesis produces the raw material for producing biomass.
• The trophic level is the position that an organism occupies in a food chain, or the position of a group of organisms in a community that occupy the same position in food chains.
• Producers (autotrophs) are typically plants or algae that produce their own food using photosynthesis and the form the first trophic level in a food chain. Exceptions include chemosynthetic organisms that produce food without sunlight.
• Feeding relationships involve producers, consumers and decomposers. These can be modeled using food chains, food webs and ecological pyramids.
• Ecological pyramids include pyramids of numbers, biomass and productivity and are quantitative models that are usually measured for a given area and time.
• In accordance with the second law of thermodynamics, there is a tendency for numbers and quantities of biomass and energy to decrease along food chains, therefore, the pyramids become narrower at the apex.
• Bioaccumulation is the build-up of persistent or non-biodegradable pollutants within an organism or trophic level because they cannot be broken down.
• Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants along a food chain.
• Toxins such as DDT and mercury accumulates along food chains due to the decrease of biomass and energy.
• Pyramids of numbers can sometimes display different patterns; for example, when numbers of individuals at lower trophic levels are relatively large (inverted pyramids).
• A pyramid of biomass represents the standing stock or storage of each trophic level, measured in units such as grams of biomass per square meter (g m^-2) or Joules per square meter (J m^-2) (units of biomass or energy).
• Pyramids of biomass can show greater quantities at higher trophic levels because they represent the biomass present at a fixed point in time, although seasonal variations may be marked.
• Pyramids of productivity refer to the flow of energy through a trophic level, indicating the rate at which that stock/ storage is being generated.
• Pyramids of productivity for entire ecosystems over a year always show a decrease along the food chain.

Vocabulary

• community
• ecosystem
• respiration
• photosynthesis
• primary producer
• biomass
• trophic level
• autotroph
• heterotroph
• producer
• consumer
• decomposer
• ecological pyramids (numbers, biomass, productivity)
• bioaccumulation
• biomagnification
• food chain
• food web

Biological Levels of Organization

Descending

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• Organism/species
• Organ system
• Tissue
• Cell
• Organelles
• DNA

Ecological Levels of Organization

Ascending

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• Organism/species
• Population
• Community
• Ecosystem
• Biome
• Biosphere

2.2.1 Community

A group of populations interacting in a common habitat.

2.2.2 Ecosystem

A community and the physical (abiotic) environment within which it exists.

2.2.3 Respiration & Photosynthesis

2.2.4 Cellular Respiration

The conversion of organic matter into chemical energy, CO₂, and H₂O.

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2.2.5 Respiration & Entropy

Living organisms are constantly fighting against the 2^nd law…

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… and a lot of heat is released in the process...

2.2.6 Photosynthesis

Primary producers (in most ecosystems) convert light energy into chemical energy within their chloroplasts

2.2.7 Photosynthesis

Reduced to the following equation… what is missing?

2.2.8 Biomass

The dry mass of living matter/material.

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usually measured in a given area at a given time

2.2.9 Trophic Level

The position an organism (or group of organisms) occupies in a food chain.

2.2.9 Trophic Levels

Bottom level – Primary producers/ autotrophs

obtain energy from simple inorganic substances (chemotrophs)

Photosynthesis:

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6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂

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Consumers/heterotrophs - obtain energy from other organisms

Primary, secondary, tertiary, quaternary, etc. consumer

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Uppermost level – Top carnivore (niche)

2.2.10 Producers & Consumers

• Autotrophs
• photosynthesize or chemosynthesize to provide energy to make food
• phototrophs, lithotrophs, chemotrophs
• fundamental to food chains
• Heterotrophs
• cannot "fix" carbon
• break down complex molecules (proteins, carbohydrates) into simpler compounds

2.2.10 Decomposers (saprotrophs)

• Bacteria
• one gram of soil has 52 000 000 bacterial cells
• more biomass than all other living things
• Fungi
• "roots" are called hyphae
• primary decomposers in forests
• Break down lignin (organic polymer, like cellulose, found in woody plants)
• Detritivores
• millipedes, worms, wood lice, dung flies, slugs
• often eaten by consumers
• Scavengers
• carrion-eaters
• hawks, vultures, eagles, hyenas, Tasmanian devils, maggots, Flesh-flies

2.2.11 Food Chains

Show:

Flow of energy from one organism to the next

Feeding relationships between species

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Arrows connect species

Points to the → consumer

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Almost always starts with the sun (often ignored)

2.2.11 Food Webs

Complex interrelated network of food chains

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Shows species eaten in multiple food chains

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Shows species consuming in multiple food chains

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More realistic

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Can become overwhelmingly complicated

Complex Food Webs

2.2.12 Ecological Pyramids

Quantify information at various trophic levels for easier comparison

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Size of bars are relative to one another

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3 types:

• numbers
• biomass
• productivity

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Usually narrower at the top

2.2.13 The 2^nd Law

The real law behind Raymond Lindeman’s “10% Law”

2.2.14 Bioaccumulation

The buildup of persistent (non-biodegradable) substances in an organism or trophic level.

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2.2.15 Biomagnification

The buildup of persistent (non-biodegradable) substances along a food chain

2.2.16 Methylmercury & DDT

Bioaccumulation: the buildup of persistent (non-biodegradable) substances in an organism or trophic level.

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2.2.17 Pyramids of Numbers

Shows the proportional number of organisms at each trophic level in a food chain

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Seasonal snapshot (time dependent)

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Graphically: producers → top carnivores

2.2.18_19 Pyramids of Biomass

Biomass – dry organic material (organism, population, or trophic level)

Units – mass per unit area (example: gm^-2)

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Mostly pyramidal shaped

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How do you get biomass?

(Individual biomass) x (individuals)

2.2.20_21 Pyramids of Productivity

Energy generated @ each trophic level

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Energy available to next level

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Not time-dependent

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Always pyramidal (in healthy ecosystems)

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Shows decrease over a year

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Units: energy per unit area per time (J m^-2yr^-1)

2.2.21 Ecological Pyramid Summary

2.2.21 Ecological Pyramid Summary