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General Biology 101
Chapter Outlines
Starr & Taggert
10th edition
Chapter 48:
Ecosystems
Introduction: Antarctica – Life here consists of bacteria, lichens and mosses clinging to
exposed rock in an inhospitable environment that is very cold. Larger animals such as
penguins and seals live there but hunt offshore. The focus in the introduction is about the
tenacity of life and the interdependence of this delicate ecosystem that has experienced
some degree of disturbance by the very people studying it.
Ecosystem – An association of organisms in their physical environment.
Characteristics of an ecosystem:
 Interconnected by an ongoing flow of energy.
 Materials cycle through it.
 It is an “open” system.
 Includes inputs, transfers and outputs of Energy and Nutrients.
 Energy flow is one direction
i.e. Autotrophs (self feeders) > Food chains > Food webs
Section 48.1 Participants in Natural Ecosystems
Primary Producers – Photosynthesizing organisms that convert sunlight energy to
chemical energy and use inorganic compounds to make organic compounds (used for
basic life processes). Include the photoautotrophs (plants) and chemoautotrophs
(nitrifying bacteria).
Heterotrophs – Organisms that feed on other organisms to obtain energy. They must
feed on other things such as other consumers/animals or plants or bacteria, i.e. they are
NOT self- feeding.
Consumers – feed on the tissues of other organisms
Categories:
1) Herbivores – eat plants
2) Carnivores – consume flesh
3) Parasites – ingest tissues of living hosts but don’t usually kill them.
4) Decomposers – eat non-living remains of producers and consumers. Usually
heterotrophic fungi and bacteria, usually feeding via extra-cellular absorption.
5) Detritivores – heterotrophs that digest bits of decomposing matter e.g. worms
and crabs.
6) Omnivores – organisms that feed on a variety of organisms including animals,
plants, fungi, protistans, bacteria etc. e.g. fox.
7) Scavengers – any animal that ingests dead plants, animals or both e.g.
termites.
Ingredients of Life (organic compounds)
-
Water
CO2
Minerals
= Phosphorous
= Nitrogen
These ingredients are combined to make carbohydrates, lipids, proteins and nucleic acids.
Structure of Ecosystems:
Trophic levels – feeding relationships, a functional hierarchy.
First trophic level – autotrophs e.g. plants
Second trophic level – primary consumers e.g. herbivores such as insects,
detritivores e.g. worms.
Third trophic level – secondary consumers that eat primary consumers
Food Chain – a straight line sequence of steps by which energy is passed onto higher
trophic levels.
Food Webs – Cross connections of food chains.
Section 48.2
The Nature of Food Webs
 In most cases energy that producers initially capture passes through no more than 4-5
trophic levels.
General Observations regarding food webs:
 A bit of energy is lost at every step/transition.
 Food chains have more steps i.e. they are longer, in more stable environments.
 The most complex webs have more herbivore species, though chains tend to
be shorter.
 Simple food webs have more top carnivores.
 Most of the net primary production moves through detritivores.
Energy flow from primary sources flow in one direction.
1) Grazing food webs – flow from plants to consumers.
2) Detritus food webs – detritivores and decomposers i.e. depends on remains
and wastes of photosynthesizers and consumers to pass energy e.g. in many
aquatic systems.
Section 48.3
Biological Magnification in Food Webs
Ecosystem Modeling – researchers identify crucial data on ecosystem components and
use computers to model and predict outcomes of potential disturbances.
Biological Magnification – Occurs when a substance/chemical degrades slowly or not at
all in an ecosystem. It can be concentrated in the tissues of organisms at higher trophic
levels of a food web.
Example – DDT (a pesticide used by humans)
Banned since the 1970’s (in the U.S)
It interfered with the egg shell viability in birds and
disrupted the hatching rates in hunting birds i.e. raptors such as
eagles and falcons (top level consumers).
Section 48.4
Primary Productivity – The rate by which primary producers capture and store energy in
their tissues per a given time interval.
Energy is captured during photosynthesis (by plants), but is used during cellular
respiration (which both plants and animals and all living organisms carry out) to fuel their
biological, cellular processes such as growth.
Net ecosystem production =
Gross primary production – energy used by plants & soil organisms
This is a measure/rate at which primary producers store energy in their tissues in excess
of their rate of aerobic respiration.
Factors affecting production rates:
 Seasonal patterns
 Distribution in the habitat
 Mineral availability
 Temperature ranges
 Amount of sunlight
 Amount of rainfall.
Ecological Pyramids
I.
Biomass pyramid – depicts the weight of all of an ecosystem’s organisms
at each tier. Largest tier is the base of the pyramid (producers). This
measurement is given in g/meters2 for a given time interval.
II.
Energy pyramid – portrays how usable energy diminishes with higher
trophic levels in an ecosystem.
 Ultimate source of energy is the sun!
Rules of energy transfer
- Energy is lost out of ecosystems mainly because of metabolic heat.
- With every energy transfer between trophic levels, there is a declining
availability of energy.
Section 48.5
This section shows a quantitative representation of energy (measured in kilocalories) that
moves through an ecosystem.
Most notable is that only about 1.2% of incoming available sunlight is captured by
producers.
At each level significant energy is lost to metabolic heat from the bodies of individuals,
and much is lost as organic wastes e.g. feces.
Only about 10-11% of available energy is actually passed onto higher trophic levels with
each energy transfer.