Ecosystem Ecology
I. Ecosystems
A. Definition
1. An ecosystem is an association of
organisms and their physical environment,
2. Linked by a flow of energy and a
cycling of materials.
B. Structure of Ecosystems
1. Physiognomic structure
a. Physical size & shape of organisms & their
relation to each other & the physical environment
b. Relative abundance of trees, shrubs, herbs,
mosses, etc.
c. Phenotypes, physical characteristics
d. Vertical & horizontal stratification
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2. Temporal Structure
a. Ecosystems change over time (succession)
b. Diurnal (Daily) patterns
c. Seasonal changes
3. Species Structure (Composition)
a. Diversity, relative abundance
b. Determined by soil resources, climate tolerance
ranges, stresses (ex. Competitive interactions,
herbivory)
II. Trophic levels
A. Feeding levels
1. Autotrophs
a. Plants, algae, cyanobacteria, phytoplankton
b. Bring energy into the ecosystem by PSN
c. First level of all food webs ---- primary
producers
2. Heterotrophs
a. consumers - depend directly or indirectly
on energy stored in tissues of primary producers.
b. Types of Heterotrophs
i. Herbivores eat plants – primary consumers
ii. Parasites reside in or on living hosts
iii. Detritivores consume dead or decomposing organic matter.
iv. Carnivores – eat herbivores & other carnivores – secondary
consumers
v. Omnivores partake of a variety of edibles
vi. Decomposers - extract energy and recycle nutrients from
organic matter.
Fig 55.4
Decomposition intertwines
all trophic levels.
c. Complications
i. Some organisms like man extract energy from more
than one trophic level so it is hard to assign them to a
specific trophic level.
ii. Actual feeding relationships in an ecosystem are
complex – more accurately described by food webs.
Fig 54.12
III. Bioenergetics
A. Primary Production (PP)
1. Conditions
a. Light = Amount of light energy converted to
chemical energy (organic compounds) by an
ecosystem’s autotrophs’ during a certain amount of
time
b. Efficiency = How much energy actually get
stored depends on
i. How many plants are present?
ii. The balance between photosynthesis and
aerobic respiration.
2. Ecosystems differ in their PP:
a. Tropical rain forest – most per area
b. Oceans – most overall
Fig 54.4
Fig 54.5
B. Gross primary productivity (GPP)
1. total amount of light energy converted to
chemical energy per unit time
C. Net primary productivity
1. NPP = GPP – R
2. R = energy used by the primary
producers for respiration. Energy released as
heat.
3. Availability = The amount of stored
chemical energy that will be available to the
other trophic levels.
4. Net primary productivity
a. Only a small part of the energy from
sunlight becomes fixed in plants (1%).
b. The plants themselves use as much as
half of what they fix (respiration).
c. Other organisms tap into the energy that
is conserved in plant tissues, remains, or
wastes.
d. They lose heat to the environment.
e. All of these heat losses represent a oneway flow of energy out of the ecosystem.
D. Secondary Production
1. Amount of chemical energy from a consumer’s
food that is converted into new biomass in their body.
2. Example Caterpillar eating a plant:
a. 50% loss to feces (energy transfer to detritus)
b. 34% to respiration (heat loss)
c. 16% to growth
Fig 55.9
IV. Trophic efficiency
A. Percentage of production transferred
from one trophic level to the next.
B. 5-20% depending on ecosystem.
C. Thus 85-90% of available energy at
one level is not transferred to the next.
Instead lost as heat, not consumed, or
transferred to detritus
Fig 55.11
Fig 55.11
Fig. 54.13
V. Biogeochemical Cycles
A. Characteristics
1. Availability of inorganic material as well as
energy profoundly influences the structure of
ecosystems.
2. Cycling of nutrients involves biotic & abiotic
components: “biogeochemical”
3. These are transferred from the environment to
organisms and back again
4. Generally, these move slowly through the
environmental reservoir, compared to its rapid
exchange between organisms and the environment.
B. Reservoirs of Material
1. Available vs. Unavailable Organic
a. Living & dead organisms – available through
decomposition & consumption
b. Fossil fuels: coal, oil, peat
2. Available vs. Unavailable Inorganic
a. Molecules in air, soil, & dissolved in water
b. Elements in solid rock
Fig 55.13
3. Characteristics of Material Reservoirs
a. Elements used usually become available to
producers as mineral ions, such as ammonium (NH4+).
b. Inputs from the physical environment and the
cycling activities of decomposers and detritivores
maintain an ecosystem’s reserves.
c. The amount being cycled through most major
ecosystems is greater than the amount entering or
leaving in a given year.
d. Inputs to the reserves occur by rainfall or snowfall,
metabolism, and weathering of rocks.
e. Outputs for land ecosystems include losses by
runoff.
Figure 55.14
Figure 55.14
Figure 55.14
Always move forward by building on the past.