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ECOLOGY
Energy in an Ecosystem
Species Interactions
Population Dynamics
From: Kristal Schneider - Germany
ENERGY AND THE ECOSYSTEM
Food Chains and Food Webs

Energy in the Ecosystem is transferred through the
different trophic (feeding) levels.
 Food
Chain – a sequence of organisms, each of which
serves as a source of food or energy for the next.
 Food Webs – a series of interconnected Food chains.
 Chemical energy and nutrients travel through trophic
levels primarily through photosynthesis, feeding, and
decomposition.
Food Chains and Food Webs

Each trophic level contains a certain amount of biomass
where chemical energy is stored
 Biomass

is the dry weight of all organic matter in organisms
As chemical energy travels through trophic levels:
 Decrease
in amount of high-quality energy available at
each succeeding energy level (10%)
 Some useful chemical energy is lost to the environment as
low-quality heat (90%).
Producers and Consumers

Producers
Land – Plants
 Water – Phytoplankton, aquatic plants, algae


Consumers

Herbivores
Eats plants
 Zooplankton, grazing animals such as cows, goats, and sheep


Carnivores
Consume other animals such as herbivores
 Sharks, Lions, Tigers, Crocodiles


Omnivores
Eat both plants and animals
 Turtles, Bears, Skunks, some lizards

Food Web
Food Chain
Energy Efficiency Question

Assuming 10% ecological efficiency, if green plants
capture 10,000 units of energy, how much chemical
energy will be available to support herbivores and
carnivores?
Energy Efficiency
The Importance of Producers

The amount of living
organic material that a
particular ecosystem can
support is determined by
how much solar energy its
producers can capture
and store as chemical
energy.
Global oceanic and terrestrial photoautotroph abundance, from
September 1997 to August 2000. As an estimate of autotroph
biomass, it is only a rough indicator of primary production potential,
and not an actual estimate of it. Provided by the SeaWiFS Project,
NASA/Goddard Space Flight Center and ORBIMAGE.
The Importance of Producers

Different areas in the planet, both terrestrial and
aquatic, have variable primary productivity due to
the amount of sun and nutrients available.
http://marine.rutgers.edu/opp/Production/html_files/Annu_Glb_T_noCld_Inh1.html
SPECIES INTERACTION
Species Interact in Three Ways

There are three basic types of species interactions:
Competition
 Predation
 Symbiosis


These interactions help influence survival techniques
which make them agents of Natural Selection.
Competition
•
The most common interaction between species is
competition.


One species will eventually become more efficient in
acquiring resources and food.
2 types of competition
 Interspecific
competition
 Occurs
between 2 or more individuals from two
different species
 Intraspecific
 Occurs
species
competition
between 2 or more individuals of the same
Competition - Niches

Niche – a species’ way of life or role in
the community
 Includes
everything that affects its survival
and reproduction

When two species compete for food in
the same niche, their niches overlap
 Remember
only one species can occupy a
niche at a time.
 Competitive
exclusion principle.
Predation

All organisms need food to survive
 Plants
make their own
 All others must eat
Predation is the interaction between a
feeder (predator) and what it eats (prey).
 Herbivores, Carnivores and Omnivores
are all predators.

Prey

To evade predators, many prey species have
developed ways to defend themselves.
 Physical
barriers and strengths
 Spines,
shells, thick bark
 Faster escape and strong senses
 Camouflage
Cuttlefish
 Chemical
Warfare
 Poisonous
to eat or create poison that they excrete when
aggravated.
 Taste Bad
Benefit of Predator-Prey Relationships

Predation plays a major role in Natural
Selection
 Predators
weed out the weak, sick, and dying
species.
 Increases biodiversity

Help keep grazing animals down and preserve
the balance of an ecosystem.
Symbiosis
Symbiosis is when two species live
together in some form.
 Three Types of Symbiosis:

Parasitism
Commensalism
Mutualism
Parasitism
Parasitism occurs when one species (the
parasite) feeds on the body of, or the
energy used by, another organism (the
host), usually by living on or in the host.
 Common Characteristics of Parasites:

 Smaller
than the host
 Rarely Kill the Host
 Live directly on or in the Host
Parasitism: Tree with Parasitic Mistletoe,
Trout with Blood-Sucking Sea Lampreys
Commensalism

Two species interact so that one
species benefits and the other is not
harmed or benefits lightly.
Commensalism: Barnacles live on whales and filter food as
the whale swims. Doesn’t harm or benefit whale
Mutualism

An Interaction where both species
benefit from living together.
Nutrition
Protection
Hygiene
Health
Mutualism: Oxpeckers Clean Rhinoceros; Anemones
Protect and Feed Clownfish
Checkpoint #1
A tapeworm, which may reach a length of 20 feet,
inhabits the intestines of a human. The worm
absorbs the nutrients digested by the human.
What type of relationship does this illustrate?
How is each organism affected by this relationship?
Checkpoint #2
In Texas, cattle egrets (large white birds) are often found near
cattle. Sometimes they are seen riding on the backs of
these cattle where they are believed to feed on insects
within the cattle’s fur. They can also be seen feeding on
insects that the cattle stir up in the grass as they walk.
What kind of relationship is this?
How is each animal affected by this relationship?
Food Web
1. How much of the Earth’s
surface is covered by
oceans?
2. Consider the food web here.
What would happen if we
removed the krill?
3. Is the squid a primary or
secondary consumer?
4. Which of the following is an
example of an autotroph?
1. Whale
2. Squid
3. Phytoplankton
Native vs. Non-native

Niches can be divided into the roles species play in
their community:
 Native
 Non-native
 Indicator
 Keystone
 Foundation
Native vs. Non-native


Native species are those individuals that normally
live and thrive in a particular ecosystem.
Non-native species are those individuals that
migrate or are accidentally or deliberately
introduced to a particular ecosystem.
 Invasive,
alien, or exotic
Native vs. Non-native

Non-native species can be good or bad.
 Good
NN
 Cows,
 Bad
chickens, and other domesticated animals
NN
 Kudzu
Vine, Water Hyacinth, Hydrilla, and Killer Bees
Indicator Species


When an ecosystem or community starts to collapse,
ecologist look at indicator species for the first
warning signs.
Indicator species are, generally, specialist species
that are affected by a change in one or more key
abiotic factors in the environment.
Indicator Species

Examples of Indicator Species:
 Trout
for water quality
 Walleye spawning for climate change
 Frogs a general measure of productivity in a
region.
 Tropical
Regions
Keystone Species

Keystone species have a large effect on the
types and abundances of other species in an
ecosystem.
 Ex:

Mangrove Crab and Sea Otters
Two major roles of Keystone Species
 Pollinator/Life
 Top

support
Predator
Loss of Keystone Species usually lead to a
population crash and other extinctions
Keystone and Foundation Species

Foundation species play a major role in shaping
communities by creating and enhancing their
habitats in ways that benefit other species.
 Elephants
push over trees and uproot plants to help new
plants take root.
 Beavers create dams and cut down trees.
HUMAN IMPACTS
Invasive Species:
 Species introduced by man, deliberately or
accidentally, into a local ecosystem where the
new species have caused a dramatic change
in the roles of other species within the original
ecosystem.
 Biggest cause of animal and plant
extinctions
 About 50,000 nonnative species now live in
the US and about 1 and 7 of them are
harmful

INVASIVE SPECIES


Silver Carp (Asian Carp)
Asian carp were
introduced to the United
States in the early '70s to
control algae in catfish
farms in the South. Floods
washed them into the
Mississippi River in the
1980s. They've worked
their way upriver ever
since.
INVASIVE SPECIES

Many invasive species have been introduced
intentionally.
Figure 11-11
Accidentally Introduced Species
Sea lamprey
(attached to lake trout)
Formosan termite
Argentina
fire ant
Zebra mussel
Brown tree
snake
Eurasian ruffe
Common pigeon
(Rock dove)
Gypsy moth larvae
Asian long-horned Asian tiger mosquito
beetle
Fig. 11-11b, p. 234
Characteristics of
Successful
Invader Species
• High reproductive rate,
short generation time
(r-selected species)
• Pioneer species
• Long lived
Characteristics of
Ecosystems Vulnerable
to Invader Species
• Climate similar to habitat
of invader
• Absence of predators on
invading species
• Early successional
systems
• High dispersal rate
• Release growth-inhibiting
chemicals into soil
• Low diversity of native
species
• Absence of fire
• Generalists
• High genetic variability
• Disturbed by human
activities
Fig. 11-13, p. 236
INVASIVE SPECIES

Prevention is the best
way to reduce threats
from invasive species,
because once they
arrive it is almost
impossible to slow their
spread.
Figure 11-13
Biomagnification in Populations


A chemical increases in
concentration as it moves
up the food web
Each year pesticides:
 Kill
Example of biomagnification of DDT in an
aquatic food chain.
6 -14 million fish.
 Threaten 1/5th of the
U.S.’s endangered and
threatened species.
Figure 11-15
Eutrophication



Caused by runoff of nutrients or fertilizers that
speed the growth of marine autotrophs
Causes red tides, yellow foams, and thick green
slimes of plankton blooms.
Toxic substances released from the algae can sicken
or kill other species
Case Study:
The U.S. Endangered Species Act



Endangered species: so few individual survivors that it could
soon become extinct.
Threatened species: still abundant in its natural range but is
likely to become endangered in the near future.
One of the world’s most far-reaching and controversial
environmental laws is the 1973 U.S. Endangered Species Act
(ESA).
ESA forbids federal agencies (besides defense department) to carry
out / fund projects that would jeopardize an endangered species.
 ESA makes it illegal for Americans to engage in commerce
associated with or hunt / kill / collect endangered or threatened
species.

Endangered Aquatic Species





Mottled Eagle Ray
Michoacan Stream
Salamander
Tasmanian Giant
Freshwater Lobster
Blue Whale
South Asian River Dolphin
POPULATION DYNAMICS
Exponential Vs. Logistic Growth


Biotic Potential is the capacity for population growth
under IDEAL conditions.
Intrinsic Rate of Increase (r) is the rate at which the
population of a species would grow if it had
unlimited resources.

Individuals that have a high intrinsic rate:




Reproduce early
Short Generation Time (time between successive generations)
Reproduce Many Times
Many offspring in each generation
Reproductive Patterns

Species have different Reproductive Patterns that
can help enhance their chance for survival:
species *note that the r is not capitalized
 K-selected species
 r-selected
r-selected species

These species are those that have a high intrinsic rate
of increase.

What are the common traits had by those that have a high
intrinsic rate of increase?




Examples of r-selected species:


Many offspring
Usually small offspring
Little or no parental care
Algae, bacteria, rodents, frogs, turtles, annual plants, and most insects
r-selected species are opportunists

When conditions are right they have a boom in reproduction.
K-selected species

K-selected species are also called competitor species.
Reproduce later in life with small number of offspring
 Develop inside their mother and are rather large at birth
and mature slowly.
 They are cared for by the parent species.
 Called K-selected because they live well when the
population is near the Carrying Capacity.
 Examples of K-selected species:


Large Mammals, birds of prey, large-long lived plants.
Exponential vs. Logistic Growth

No population can grow indefinitely
 Limiting

factors
Environmental Resistance is the combination of all
factors that act to limit the growth of a population.
Biotic Potential + Environment Resistance = CARRYING
CAPACITY
Exponential vs. Logistic Growth


Carrying Capacity (K) is the maximum
population of a given species that a
particular habitat can sustain
indefinitely without being degraded.
A population with few limitations can
grow exponentially

Exponential growth starts slowly but then
accelerates as the population increases.

J-Shaped Curve
Exponential Vs. Logistic Growth

Logistic Growth involves rapid exponential
growth followed by a steady decrease in
population growth until the population size levels
off.


Yields an S shaped or sigmoid curve
Logistic Growth occurs because of environmental
resistance.

What happens if that resistance disappears?
Population Changes

The are four general patterns of variation in
population size:
 Stable
 Irruptive
 Cyclic
 Irregular
Population Changes

Stable
 Very
little fluctuation around the carrying capacity of
the area
 Species
found in the tropical rainforest exhibit stable
population changes because the weather and climate
changes very little from year to year

Irrupt
 When
population growth occasionally explodes to a
high peak then crash to a more stable lower level.
 Algae
and insects
Population Changes

Cyclic Fluctuations
 Similar
to irruptive but the cycle is drawn out much
longer.
 Lemmings
populations rise and fall every 3-4 years
 Lynx and hare populations rise and fall on a ten year cycle.
 Predator-prey relationships have cyclic fluctuations

Irregular Patterns
 No
discernable pattern in population change