Ecosystem
Ecology
Energy Powers
Ecosystems
Sustainable Practices
 Ecologists
and economists characterize
practices that can be continued
indefinitely as sustainable.
Ecological Footprint

The area of land
required to
sustainably provide
all resources a
population uses
and assimilate all
the waste it
generates, given
the prevailing
current technology.
Energy Powers Ecosystems
 All
life requires energy—energy that is
used to maintain tissues, grow, move,
reproduce, and keep warm.


Energy flows through ecosystems
Nutrients cycle within ecosystems
What is an Ecosystem?
 Ecosystem
– the community of organisms
plus their physical environment.

How well a tree grows is affected by the
organisms it interacts with and the physical
environment it lives in.
 Biotic
and abiotic factors
Scale of Ecosystems
 The
spatial scale of
an ecosystem varies
widely:



The “lake” within a
rain-filled pitcher
plant
A New Hampshire
forest
The whole Earth
Photosynthesis Powers
Ecosystems
 Energy
arrives as sunlight.
 Captured by autotrophs during the
process of photosynthesis.

Primary production
Other Autotrophs

Some autotrophs, primarily bacteria, can use
the energy stored in methane or in inorganic
chemicals like ferrous iron (Fe2+), manganese
(Mn2+) and hydrogen sulfide (H2S) to power
the synthesis of organic molecules through a
process known as chemosynthesis.
Primary Producers
 Primary
producers burn up half the energy
they capture during photosynthesis.


Respiration
The rest is stored.
Primary Producers
 Gross
primary production – the rate at
which energy is captured by
photosynthesis.
 Net primary production – the difference
between the rate at which energy is
captured by photosynthesis and the rate
at which energy is lost as heat.

GPP - Ra = NPP
Energy Moves up Food Chain
 Producers
are
eaten by
herbivores, or by
decomposers after
they die.

Energy is passed
along to predators
when they eat the
herbivores.
Aquatic Ecosystems
 Light
is important
for photosynthesis.


Light penetration is
reduced with
depth.
Photosynthesis is
reduced as well.
Aquatic Ecosystems
 The
transition between these two regions
occurs at the compensation depth—the
point at which GPP = Re and NEP = 0.

 In
NEP = net ecosystem production
highly productive systems with dense
populations of phytoplankton, light
decreases quickly with depth, and the
compensation depth is close to the
surface.
What limits primary production
in aquatic ecosystems?
 In
order to grow,
phytoplankton must
obtain sufficient
quantities of
nutrients from their
environment, and
primary production
can be slowed if any
required nutrient is in
short supply.
 N,P, Fe, Si
What limits primary production
in terrestrial ecosystems?
 Light
and nutrients are important in
terrestrial ecosystems, too.


Length of the growing season
N, P, K
What limits primary production
in terrestrial ecosystems?
 Most
important in
limiting production
in terrestrial
ecosystems are
temperature and
precipitation.
What Happens to NPP
 Much
of a plants
NPP gets eaten by
herbivores.
 Trophic levels




Primary producers
Herbivores
Primary carnivores
Secondary
carnivores
Secondary Production
 Collectively,
the
biomass that
accumulates in
heterotrophs is
called secondary
production.
 Primary production
fuels secondary
productions.

Other factors
involved too.
Energy Transfers are Inefficient
 Going
from plant to
animal appears to
be very inefficient.
Food Quality Matters
 The
quality of food,
and not just its
energy content,
affects production
efficiency.
 Clover is N fixer –
lowers C:N ratio in
plant, herbivore
can build more
proteins.
The Cost of Thermoregulation


Endotherms have lower production efficiency
than ectotherms, which suggests that an
organism's thermal physiology affects how
efficiently it is able to grow.
In order to keep warm, endothermic
organisms must devote more of the energy
they assimilate to maintaining their energy
budget than ectotherms, and consequently
will have less energy available for growth.
Energy Availability Declines
along Food Chains
 As
the diagram
indicates, energy is
lost at every step
along the grazer
food chain, which is
why the trophic
efficiencies of
herbivores and
carnivores are low.
Ecosystem
Energetics
Detrital Food Chain
 Plants
that don’t
get eaten
eventually die and
become detritus.
 An ecosystem’s
secondary
production includes
the growth and
reproduction of
decomposers as
well as grazers.
Eltonian Pyramids
 Without
imports,
substantially less
energy flows through
higher trophic levels
than through primary
producers.
 Ecologists often
illustrate this pattern
with energy
pyramids.
Ecosystem
Services
Our Growing Footprint


The collapse of the Atlantic
cod fishery helps illustrate the
enormous and increasing
pressure people place on
global ecosystems.
Demand for goods and
services provided by Earth's
ecosystems is increasing
rapidly as human
populations increase in size
and affluence.
Ecological Footprint


The Ecological Footprint is the area of land
required to sustainably provide all the
resources a population uses and to assimilate
all the wastes it generates, given the
prevailing technology.
It includes the area of biologically productive
land and water required to meet demands
for human infrastructure, timber and fuel
woods, fishing, livestock, food, and fiber, and
for assimilating carbon dioxide released
during fossil fuel combustion.
http://footprintnetwork.org/en/index.php/GFN/page/calculators/
Our Growing Footprint


Between 1965 and
2007 humanity's
Ecological Footprint
grew from about 0.6
Earths to nearly 1.5
Earths.
In other words,
humanity's current
annual demand is
one-and-a-half-times
that of Earth's annual
productivity.
Our Growing Footprint
 To
make up the difference, people
consume the standing crop rather than
just what was produced in a given year.
 This suggests that, as a whole, humanity is
not living sustainably but instead is
depleting the natural capital needed to
support future generations.
Our Growing Footprint


The growing carbon footprint is the principal
reason humanity's total Ecological Footprint
has nearly doubled since 1961.
This carbon footprint represents the area of
forest land needed to assimilate the
CO2 people release into the atmosphere
each year—primarily as a result of fossil fuel
combustion and land use change—after
accounting for CO2 that is absorbed by the
world's oceans.
Ecological Services
 The
Ecological Footprint makes it clear
that we rely on ecosystems for a wide
variety of goods and services,
or ecosystem services, that directly or
indirectly contribute to our welfare and
without which our existence would be
impossible.
Ecosystem Services

Supportive


Provisioning


Directly consumed by
people.
Regulating


fundamental processes like
primary production,
necessary for producing all
other ecosystem services.
benefits that result from the
regulation of ecosystem
processes including Earth's
climate, water purification,
and flood control.
Cultural

various nonmaterial
cultural and recreational
benefits people gain from
ecosystems.
Ecosystem Services
 To
meet the demands of a growing
global Ecological Footprint, people have
taken more and more of a critical
supporting service, net primary
production.

What we take is not available for other
species or to support other ecosystem
services.
Ecosystem Services
 Clearly,
people are critically dependent
on ecosystem services like primary
production for their welfare.
 Ecosystem services are often ignored in
policy decisions.

As a result of this oversight, ecosystems are
increasingly stressed and their ability to
sustainably provide critical services is
compromised.
Service Valuation
Forest Preserve
Cropland Ecosystem
Restored Cropland
Tragedy of the Commons


Even when ecosystems are valued, they can be
hard to protect.
The Atlantic cod fishery collapsed because
harvest rates were higher than secondary
production over a long time period.


The overharvest was due in part to the fact that
fish in the open ocean are a common resource
and fishermen benefit by catching more fish.
Unfortunately, with enough fishermen, rational
individual choices to catch more led to overfishing
and the potential demise of the entire fishery, a
phenomenon often called the tragedy of the
commons.
The Tragedy of the Commons
 Part
1: http://youtu.be/KZDjPnzoge0
 Part 2: http://youtu.be/IVwk6VIxBXg
 A managed commons, though it may
have other defects, is not automatically
subject to the tragic fate of the
unmanaged commons. - Garrett Hardin
 http://youtu.be/fNhr2RNhw5w