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Ecosystems
Introduction
• Many ecosystems around the world are
currently experiencing significant changes in
species composition, abundance, and diversity
due to the influence of human activity.
– These changes have, more often than not, led to a
reduction in species diversity.
• The issue is whether the biogeochemical
functioning of an ecosystem will be impaired
by a loss of species or the introduction of a
new species.
Misconceptions about Ecosystems
• Ecosystems are not an organized whole, but a
collection of organisms.
• Forest fires are harmful to terrestrial
ecosystems and should not be allowed to
burn.
• An organism cannot change trophic levels.
Misconceptions about Ecosystems
• An animal that is high on the food web preys
on all populations below it.
• The top of the web has the most energy.
• Characteristics of a population are created
according to the needs of the individual or
according to a predetermined grand plan.
Misconceptions about Ecosystems
• Characteristics are passed on by the bigger,
stronger organisms.
• Species live together in an ecosystem because
they have compatible needs and behaviors.
• A change in the prey population has no effect
on the predator.
What is an Ecosystem?
What is Ecology?
• physiological ecology - relationships between
organisms and their physical environments
• population ecology - between organisms of
the same species
• community ecology - between organisms of
different species
• ecosystem ecology - between organisms and
the fluxes of matter and energy through
biological systems
Major Terrestrial & Aquatic Biomes
• The most important factors are temperature
ranges, moisture availability, light, and
nutrient availability, which together determine
what types of life are most likely to flourish in
specific regions and what environmental
challenges they will face.
What are biomes?
• Biomes are regions of the world with similar
climate (weather, temperature) animals and
plants. There are terrestrial biomes (land)
and aquatic biomes, both freshwater and
marine.
How many biomes are there?
• Some say there are only 5 major types of
biomes: aquatic, desert, forest, grassland, and
tundra.
• Others split biomes further. Forests are
separated into rainforest, temperate forest,
chaparral, and taiga; grasslands are divided
into savanna and temperate grasslands; and
the aquatic biome is split into freshwater and
marine.
Additional Info
AQUATIC
BIOMES
•Freshwater
•Freshwater
wetlands
•Marine
•Coral reef
•Estuaries
TERRESTRIAL
BIOMES:
•Tundra
•Rainforest
•Savanna
•Taiga
•Temperate forest
•Temperate
grassland
•Alpine
•Chaparral
•Desert
Biodiversity Gradient
• Biodiversity varies with
change in latitude or
altitude. The diversity
increases as we move
from high to low
latitudes (i.e., from
poles of equator). In
the temperate region,
the climate is severe
with short growing
period for plants while
in tropical rain forests
the conditions are
favorable for growth
throughout the year.
Here’s a thought …
Life is an improbable occurrence. The
conditions for life are a rare, if not unique, event
in the universe. Both the evolution and
maintenance of life depends on an unusual
blend of the rare and the common, which allow
an organism to survive. One of the most
important of these conditions is climate –
predictable ranges of temperature and
humidity; another is the availability and flow of
certain organic and non-organic nutrients.
Energy Flow Through Ecosystems
• Without autotrophs, there would be no
energy available to all other organisms that
lack the capability of fixing light energy.
• However, the continual loss of energy due to
metabolic activity puts limits on how much
energy is available to higher trophic levels
(this is explained by the Second Law of
Thermodynamics).
Energy Flow Through Ecosystems
Trophic levels
are simply a
feeding level,
as often
represented
in a food
chain or food
web.
Energy Flow Through Ecosystems
• Only a fraction of the energy available at one
trophic level is transferred to the next trophic
level. The rule of thumb is 10%, but this is very
approximate.
• Typically the numbers and biomass of
organisms decrease as one ascends the food
chain.
Energy Flow Through Ecosystems
• A rabbit eats or ingests plant matter;
we'll call this ingestion.
• Part of this material is processed by
the digestive system and used to make
new cells or tissues, and this part is
called assimilation.
• What cannot be assimilated exits the
rabbit’s body and this is called
excretion.
• Assimilation = Ingestion - Excretion.
Energy Flow Through Ecosystems
secondary production maintaining a high, constant
body temperature,
synthesizing proteins, and
hopping about. This energy
used (lost) is attributed to
cellular respiration. The
remainder goes into making
more rabbit biomass by
growth and reproduction.
Energy Flow Through Ecosystems
• The efficiency with which an organism converts
assimilated energy into primary or secondary
production varies because of the differing
metabolic requirements of the organism.
• Some organisms have such low net production
efficiencies because they are homeotherms, or
they maintain a constant internal body
temperature.
• Poikilotherms, organisms that do not regulate
their temperatures internally, have a greater net
production efficiency.
Energy Flow Through Ecosystems
• Other processes that reduce the energy transferred
between trophic levels include respiration, growth and
reproduction, defecation, and nonpredatory death
(organisms that die but are not eaten by consumers).
• The low rate of energy transfer between trophic levels
makes decomposers generally more important than
producers in terms of energy flow.
– Decomposers process large amounts of organic material
and return nutrients to the ecosystem in inorganic form,
which are then taken up again by primary producers.
– Energy is not recycled during decomposition, but rather is
released
Energy Flow Through Ecosystems
• An ecosystem's gross primary productivity
(GPP) is the total amount of organic matter
that it produces through photosynthesis.
• Net primary productivity (NPP) describes the
amount of energy that remains available for
plant growth after subtracting the fraction
that plants use for respiration.
• In equation form, we have net production
efficiency = (production / assimilation), or for
plants = (NPP / GPP).
Energy Flow Through Ecosystems
• Many factors influence primary productivity rates, but the most
important on land are temperature and water availability.
Energy Flow Through Ecosystems
• In contrast to land, where vascular plants carry out most primary
production, most primary production in the oceans is done by microscopic
algae.
Energy Flow Through Ecosystems
• How many trophic levels can an ecosystem
support?
• The amount of energy entering the ecosystem
• Energy loss between trophic levels
• The form, structure, and physiology of organisms
at each level.
– At higher trophic levels, predators generally are
physically larger and are able to utilize a fraction of
the energy that was produced at the level beneath
them, so they have to forage over increasingly large
areas to meet their caloric needs.
Energy Flow Through Ecosystems
• An important consequence of the loss of energy
between trophic levels is that contaminants
collect in animal tissues—a process called
bioaccumulation.
• Bioaccumulation is the gradual build up
over time of a chemical in a living organism.
– This occurs either because the chemical is taken up
faster than it can be used, or because the chemical
cannot be broken down for use by the organism (that
is, the chemical cannot be metabolized).
Energy Flow Through Ecosystems
Biogeochemical Cycling in Ecosystems
• Along with energy, water and several other
chemical elements cycle through ecosystems
and influence the rates at which organisms
grow and reproduce.
• About 10 major nutrients and six trace
nutrients are essential to all animals and
plants.
• The most important biogeochemical cycles
affecting ecosystem health are the water,
carbon, nitrogen, and phosphorus cycles.
Biogeochemical Cycling in Ecosystems
• Earth's water is always in movement, and the
natural water cycle, also known as the
hydrologic cycle, describes the continuous
movement of water on, above, and below the
surface of the Earth.
• Water is always changing states between
liquid, vapor, and ice, with these processes
happening in the blink of an eye and over
millions of years.
Biogeochemical Cycling in Ecosystems
Atmosphere · Condensation · Evaporation · Evapotranspiration · Freshwater storage
Groundwater discharge · Groundwater storage · Ice and snow · Infiltration · Oceans
Precipitation · Runoff · Snowmelt · Springs · Streamflow · Sublimation
Biogeochemical Cycling in Ecosystems
Biogeochemical Cycling in Ecosystems
Carbon exists in the nonliving
environment as:
• carbon dioxide (CO2) in the
atmosphere and dissolved in
water (forming HCO3−)
• carbonate rocks (limestone
and coral = CaCO3)
• deposits of coal, petroleum,
and natural gas derived from
once-living things
• dead organic matter,
e.g., humus in the soil
Biogeochemical Cycling in Ecosystems
• While CO2 is only a very small part of the
atmosphere (0.04%), it plays a large role in
the energy balance of the planet.
• CO2 in the atmosphere acts like a blanket over
the planet by trapping long wave radiation,
which would otherwise radiate heat away
from the planet.
Biogeochemical Cycling in Ecosystems
The NOAA global
cooperative air
sampling network
used to determine
the AGGI. Red dots
are weekly flask
sampling sites and
blue circles are
continuous
measurement sites.
Biogeochemical Cycling in Ecosystems
The nitrogen cycle
represents one of the
most important nutrient
cycles found in terrestrial
ecosystems. Nitrogen is
used by living organisms
to produce a number of
complex organic molecules like amino acids,
proteins, and nucleic
acids.
Despite its abundance in the atmosphere,
nitrogen is often the most limiting nutrient
for plant growth. This problem occurs
because most plants can only take up
nitrogen in two solid
forms: ammonium ion (NH4+ ) and the
ion nitrate (NO3- ).
Biogeochemical Cycling in Ecosystems
Biogeochemical Cycling in Ecosystems
• Phosphorus is an essential nutrient for plants and
animals in the form of ions PO43- and HPO42-.
• It is a part of DNA-molecules, of molecules that
store energy (ATP and ADP) and of fats of cell
membranes.
• Phosphorus is also a building block of certain
parts of the human and animal body, such as the
bones and teeth.
Biogeochemical Cycling in Ecosystems
• The amount of phosphate available to plants
depends on soil pH.
• As a result, the highest concentrations of
available phosphate occur at soil pH values
between 6 and 7.
• Excessive phosphorus can also contribute to
over-fertilization and eutrophication of rivers
and lakes.
Population Dynamics
• Every organism in an ecosystem divides its
energy among three competing goals:
growing, surviving, and reproducing.
• Ecologists refer to an organism's allocation of
energy among these three ends throughout its
lifetime as its life history strategy.
Population Dynamics
• Organisms at the first of the two extremes
(those adapted to unstable environments) as
r-selected.
• The other extreme, organisms adapted to
stable environments, are termed K-selected
because they live in environments in which
the number of individuals is at or near the
environment's carrying capacity (often
abbreviated as K).
Population Dynamics
Feature
Reaches sexual or
reproductive
maturity
Norway rat (rselected)
African elephant (Kselected)
3-4 months
10-12 years
Average gestation
period
Time to weaning
Breeding interval
(female)
22-24 days
22 months
3-4 weeks
Up to 7 times per
year
48-108 months
Offspring per litter
2-14 (average 8)
Every 4 to 9 years
1 average, 2 high
Population Dynamics
• In a growing population, survival and
reproduction rates will not stay constant over
time.
• Eventually resource limitations will reduce one or
both of these variables.
• Populations grow fastest when they are near zero
and the species is uncrowded.
• A simple mathematical model of population
growth implies that the maximum population
growth rate occurs when the population size (N)
is at one-half of the environment's carrying
capacity, K (i.e., at N = K/2).
Regulation of Ecosystem Functions
• What factors limits the activity within an
ecosystem?
• Resources influence ecosystem activity
differently depending on whether they are
essential, substitutable, or complementary.
• Essential resources limit growth
independently of other levels.
Regulation of Ecosystem Functions
• If two resources are substitutable, then
population growth is limited by an
appropriately weighted sum of the two
resources in the environment (replacement).
• Resources may also be complementary, which
means that a small amount of one resource
can substitute for a relatively large amount of
another, or can be complementary over a
specific range of conditions (range).
Regulation of Ecosystem Functions
Regulation of Ecosystem Functions
• A keystone species is a plant or animal that
plays a unique and crucial role in the way
an ecosystem functions.
• Without keystone species, the ecosystem
would be dramatically different or cease to
exist altogether.
Regulation of Ecosystem Functions
• Foundation species play a major role in
creating or maintaining a habitat that
supports other species.
• An umbrella species is a large animal or other
organism on which many other species
depend.
– Umbrella species are very similar to keystone
species, but umbrella species are usually
migratory and need a large habitat.
Regulation of Ecosystem Functions
• An indicator species is a plant or animal that is
very sensitive to environmental changes in its
ecosystem.
• This means it is affected
almost immediately by damage to the
ecosystem and can give early warning that a
habitat is suffering.
Ecological Niches
Type of interaction
Effect of interaction
Symbols
Competition
Both species are harmed
(population growth rates
are reduced).
--
Predation
Parasitism
One species benefits, one
is harmed.
Mutualism
Both species benefit.
Relationship may not be
essential for either.
Commensalism
One species benefits, one
is not affected.
+++
+0
Amensalism
One species harms another
(typically by releasing a
toxic substance), but is not
affected itself.
0-
Ecological Niches
• Each species in an ecosystem occupies a niche,
which comprises the sum total of its
relationships with the biotic and abiotic
elements of its environment—more simply,
what it needs to survive.
Ecological Niches
• The full range of habitat types in which a species
can exist and reproduce without any competition
from other species is called its fundamental
niche.
• A species' realized niche can be thought of as its
niche in practice—the range of habitat types from
which it is not excluded by competing species.
– Realized niches are usually smaller than fundamental
niches.
– Species may occupy different realized niches in
various locations if some conditions, such as a certain
predator, is present in one area but not in another.
Ecological Niches
• Many key questions about how species
function in ecosystems can be answered by
looking at their niches.
• Species with narrow niches tend to be
specialists, relying on comparatively few food
sources.
• In contrast, species with broad niches are
generalists that can adapt to wider ranges of
environmental conditions within their own
lifetimes and survive on diverse types of prey.
Ecological Niches
Evolution and Natural Selection in
Ecosystems
• But natural selection doesn't lead to the
development of a new species. In most cases,
the process simply allows a species to better
adapt to its environment by changing the
genetic make up from one generation to the
next.
• If a species lacks a certain trait that will allow
it to survive, there are two options: Either the
species dies out or it develops the missing
trait
Evolution and Natural Selection in
Ecosystems
• Most people think of biologist and naturalist
Charles Darwin as the father of the theory of
evolution, but the truth is that the concept of
evolution is much older.
Evolution and Natural Selection in
Ecosystems
• As species interact, their relationships with
competitors, predators, and prey contribute to
natural selection and thus influence their
evolution over many generations.
• Predators - to find, catch, and kill prey
• Prey - avoid detection and make organisms
harder to handle or less biologically profitable
to eat.
Evolution and Natural Selection in
Ecosystems
• Mimicry - Evolving to appear similar to
another successful species or to the
environment in order to dupe predators into
avoiding the mimic, or dupe prey into
approaching the mimic.
Evolution and Natural Selection in
Ecosystems
• Predators are more likely to survive and
reproduce if they restrict their diets to prey
that provide the most energy per unit of
handling time and focus on areas that are rich
with prey or that are close together.
• This tends to suggest herding/pack behavior
among some species of animals.
Evolution and Natural Selection in
Ecosystems
• Avoidance/escape
features help prey elude
predators.
• These attributes may be
behavioral patterns, such
as animal herding or fish
schooling to make
individual organisms
harder to pick out.
• Markings can confuse
and disorient predators
When the Automeris moth perceives
a threat, it moves its forewings to
reveal false eye spots on its
hindwings and to frighten predators
away.
Evolution and Natural Selection in
Ecosystems
.
– Spines serve this function for many plants and
animals.
– Shells make crustaceans and mollusks harder to eat.
:
– Squid and octopus emit clouds of ink that distract and
confuse attackers
– Hedgehogs and porcupines increase the effectiveness
of their protective spines by rolling up in a ball to
conceal their vulnerable underbellies.
Evolution and Natural Selection in
Ecosystems
• Some plants and animals emit noxious
chemical substances to make themselves less
profitable as prey.
Evolution and Natural Selection in
Ecosystems
• Coevolution - Simultaneous evolution of two
or more species of organisms that interact in
significant ways.
• These ecological relationships where
coevolution may occur include:
– Predator/prey and parasite/host
– Competitive species
– Mutualistic species
A case study of coevolution:
squirrels, birds, and the pinecones they love
The plot:
In most of the Rocky Mountains, red squirrels are an
important predator of lodgepole pine seeds. They harvest pinecones
from the trees and store them through the winter. However, the pine
trees are not defenseless: squirrels have a difficult time with wide
pinecones that weigh a lot but have fewer seeds. Crossbill birds live in
these places and also eat pine seeds, but the squirrels get to the
seeds first, so those birds don't get as many seeds.
However, in a few isolated places, there are no red squirrels,
and crossbills are the most important seed predator for lodgepoles.
Again, the trees are not defenseless: crossbills have more difficulty
getting seeds from cones with large, thick scales. But the birds have a
mode of counterattack: crossbills with deeper, shorter, less curved bills
are better able to extract seeds from tough cones.
The stage is set, but the question remains: has coevolution
happened? In order to show coevolution, we need evidence that
suggests that the prey (the trees) have evolved in response to the
predator (squirrels or birds) and that the predator has evolved in
response to the prey.
A case study of coevolution
• There should be geographic differences in the
pinecones.
If the trees have evolved in response to their seed
predators, we should observe geographic
differences in pinecones:
• Where there are squirrels, the pinecones are
heavier with fewer seeds, but have thinner scales,
like the pinecone on the left.
• Where there are only crossbills, pinecones are
lighter with more seeds, but have thick scales,
like the one on the right.
A case study of coevolution
Lodgepole pine
cones adapted to
squirrels — easier
for crossbills to eat.
Lodgepole pine
cones adapted to
crossbills — easier
for squirrels to eat.
A case study of coevolution
Where the pinecones have thick scales, birds have deeper, less
curved bills (below left) than where the pinecones have thin scales
(below right).
The bill is less
curved on this
female red crossbill
The bill is more
deeply curved on
this male red
crossbill
Evolution and Natural Selection in
Ecosystems
• Competition is an interaction between
organisms or species, in which the fitness of
one is lowered by the presence of another.
• Limited supply of at least one resource (such
as food, water, and territory) used by both is
required.
– Competition among members of the same species
is known as intraspecific competition.
– Competition between individuals of different
species is known as interspecific competition.
Natural Ecosystem Change
• Just as relationships between individual
species are dynamic, so too is the overall
makeup of ecosystems.
• The process by which one
changes into another
years to centuries is
Natural Ecosystem Change
• In the early 20th century, plant biologist
Frederic Clements described two types of
succession: primary (referring to colonization
of a newly exposed landform, such as sand
dunes or lava flows after a volcanic eruption)
and secondary (describing the return of an
area to its natural vegetation following a
disturbance such as fire, treefall, or forest
harvesting).
Natural Ecosystem Change
• British ecologist Arthur Tansley distinguished
succession based on biotic and abiotic causes.
• Autogenic succession—change driven by the
inhabitants of an ecosystem (biotic), such as
forests regrowing on abandoned agricultural
fields.
• Allogenic succession - change driven by new
external geophysical conditions (abiotic) such
as rising average temperatures resulting from
global climate change.
Natural Ecosystem Change
Ecosystem attributes
Developmental stages
Mature stages
Energetics:
Production/respiration
More or less than 1
Approaching 1
Production/biomass
High
Low
Food chains
Linear
Web-like
Community structure:
Niches
Broad
Narrow
Species diversity
Low
High
Nutrient conservation
Poor; detritus unimportant
Good; detritus important
Nutrient exchange rates
Rapid
Slow
Stability
Low
High
Natural Ecosystem Change
• Many natural disturbances have interrupted
the process of ecosystem succession
throughout Earth's history, including natural
climate fluctuations, the expansion and
retreat of glaciers, and local factors such as
fires and storms.
• An understanding of succession is central for
conserving and restoring ecosystems because
it identifies conditions that managers must
create to bring an ecosystem back into its
natural state.
Resources
• http://kids.nceas.ucsb.edu/biomes/index.html general information
• http://www.globalchange.umich.edu/globalchan
ge1/current/lectures/kling/energyflow/highertro
phic/trophic2.html - trophic levels
• Bioaccumulation - Food, Pollutant, Toxic, and Fish
- JRank
Articles http://science.jrank.org/pages/854/Bioac
cumulation.html#ixzz2LmYt9VUo – biological
magnification
Resources
• http://ga.water.usgs.gov/edu/watercycle.html
- water cycle
• http://www.lenntech.com/phosphoruscycle.htm#ixzz2LqdTCC00 – phosphorus cycle
• http://www.globalchange.umich.edu/globalch
ange1/current/lectures/kling/ecosystem/ecos
ystem.html - global change
• http://www.sustainablescale.org/areasofconc
ern/Biodiversity/BiodiversityandScale/QuickFa
cts.aspx - fast facts
Resources
• http://www.pbs.org/nationalparks/watchvideo/#914 – the story of the National Parks
• http://education.nationalgeographic.com/edu
cation/encyclopedia/keystonespecies/?ar_a=1 – keystone species
information
• http://evolution.berkeley.edu/evolibrary/articl
e/evo_33 - coevolution notes
Resources
• http://en.wikipedia.org/wiki/Competition_(bi
ology)