Transcript Community Processes: Species Interactions

AP Environmental Science
Community Processes:
Species Interactions and
Succession
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1. The Ecological Niche
Niche- the role that an organism plays in an ecosystem.
• Defined by the range of conditions and resources within
which an organism can live
• Conditions- physical attributes of the environment, though
not consumed, that influence biological processes and
population growth, e.g., temperature, salinity, acidity
• Resources- substances or parts of the environment used
and consumed or otherwise made unavailable to other
organisms, e.g., food, water, and nesting sites for
animals; water, nutrients, and solar radiation for plants;
Contrast with habitat, the actual place an organism lives.
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Generalists vs. Specialists
Generalists- have broad niches, whereas
Specialists- have narrow niches:
Generalists:
• Cockroaches, coyotes, dandelions,
humans
• Have advantage when environmental
conditions change
• Eat wide variety of food and tolerate wide
range of conditions: VERY ADAPTABLE
Specialists:
• Spotted owls require old–growth forests,
giant pandas eat primarily bamboo in
bamboo forests of China
• Have advantage when environmental
conditions are more constant. Prone to
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Fundamental vs. Realized Niche
Fundamental niche- full range of conditions and resources
that an organism could theoretically use in the absence of
competition with other species.
Realized niche- portion of the fundamental niche that an
organism actually occupies; actual range of conditions and
resources that an organism uses.
• Niche overlap between species leads to competition
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Community

Three characteristics to describe a biological
community
– 1. Physical appearance


Size, stratification, and distribution
Transitional edges between communities can cause
variance of community—increased edge area =
increased vulnerability
– 2. Species diversity



Combination of # of different species (richness) and
the # of individuals within each species (evenness)
Affected by latitude, pollution, habitat diversity, NPP,
etc.
Tropical rainforest at equator (low latitude) most
diverse
– 3. Niche structure

The number of niches and variety and species
interaction with one another
2. Some General Types of Species
Native species- species that normally live and
thrive in a particular ecosystem:
• Nonnative species (also called exotic species or
alien species)- originate in other ecosystems
•May enter an ecosystem by migration or by
deliberate or accidental introduction by
humans
•Example: "killer bees", wild bees from
Africa were imported to Brazil to increase
honey production, but displaced native
bees, decreased honey production, spread.
•Newly arrived nonnative species usually not
able to survive, but when they take hold they
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can be invasive.
Some General Types of Species
Indicator species- species that serve
as early warnings that a community or
ecosystem is being damaged:
• Example: decline of migratory
songbirds in North America indicates
loss and fragmentation of habitat in
meso-America and South America
• Example: presence of trout in
mountain streams is an indicator of
good water quality
• Example: spotted owls are indicator of
healthy old–growth forest.
• Example: amphibians are especially
vulnerable to environmental disruption
at several stages in their lives
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Adult frog
(3 years)
Figure 8-6
Page 147
sperm
Young frog
Tadpole
develops
Into frog
Sexual
reproduction
Tadpole
Eggs
Fertilized egg
development
Egg hatches
Organ formation
Some General Types of Species
Keystone species- species that play a
critical role in an ecosystem
• Example: sea otters because they
prevent sea urchins from depleting
kelp beds
• Example: dung beetles because
they remove, bury and recycle
animal waste
• Example: beavers are because they
build dams and create habitat for a
diverse community of species
(bluegill fish, muskrats, herons,
ducks…).
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Some General Types of Species
Foundation species- can create
and enhance habitats that
can benefit other species in a
community
 Elephants in the
savannas uprooting
trees benefits growing
grasses, smaller
grazing species,
accelerates nutrient
cycling
 Bats and birds can
distribute seeds in
waste, regenerating
deforested areas.
3. Types of Species Interactions
Major types of biotic interactions:
• Interspecific competition- 2 or more species use
same limited resources so fundamental niche
overlap.
Example: fire ants are better competitors than
native species of North America and sharply
reduce their populations up to 90%
Example: humans and many other species
• Resource partitioning- species competing for
similar scarce resources evolve more
specialized traits that allow them to use shared
resources at different times, in different ways,
or in different places
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Resource Partitioning
Species with similar
resource needs can
coexist because they use
limited resources at
different times, in different
ways, or in different
places.
• Example, specialized
feeding niches of
various birds of coastal
wetlands enable
coexistence of many
species.
Fig. 9–4a
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Resource Partitioning
Five species of insect–eating warblers are able to
coexist in spruce forest of Maine.
• Each species minimizes competition with others for
food by spending majority of feeding time in a distinct
portion of spruce trees (shaded areas)
• Each also consumes somewhat different insect
species.
Fig. 9–5
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Resource Partitioning
Fig. 9–5 (continued)
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Character Displacement
Over many years
coexisting species tend to
evolve physical and
behavioral adaptations to
minimize competition.
Example: Darwin's
finches on the same island
have evolved different bill
sizes and eat different size
prey.
Fig. 9–6.
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Principle of Competitive Exclusion
G.P. Gausse, in a
classical experiment
(1934), showed that two
species with identical
niches can not coexist
indefinitely- principle of
competitive exclusion.
Fig. 9–3
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Types of Species Interactions
– Predation- members of one
species (predator) feed on
another species (prey)
 Example: lion feeding on
zebra
 At the population level,
predation plays a role in
evolution by natural selection
 Predators often kill the sick,
weak, least fit members of a
population
 Helps successful genetic
traits to become more
dominant in the prey
population
Predation
•Predators tend to evolve
characteristics for efficient
capture of prey (keen
eyesight, speed, etc.).
•Prey tend to evolve
characteristics to avoid
being eaten (camouflage,
chemical defenses,
behaviors that startle
predators, keen sense of
smell, etc.).
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Types of Species Interactions
Major types of biotic interactions (cont’d):
• Symbiosis- a long–lasting relationship in which species
live together in intimate association:
- Parasitism- one organism (parasite) lives on part of
another organism (host)
- Mutualism- two species interacting in a way that
benefits both
- Commensalism- one organism benefits from another,
but neither helps nor harms the other organism
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4. Symbiotic Species Interactions
Parasitism can be viewed as a special type of predation
wherein the parasite:
1) is usually smaller than the prey
2) remains closely associated with the prey over time, and
3) rarely kills its host.
• Endoparasites- live inside their host, e.g., tapeworm living in the
gut; Plasmodium living inside a vertebrate and causing malaria.
• Ectoparasites- live outside their host, e.g., mosquito feeding on
the blood of mammal; lamprey attaching to outside of a host fish
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Mutualism
Mutualism is a relationship in which both species
benefit.
• Obligatory mutualism- results when two organisms can
not live without each other;
Example: in lichens an algae provides photosynthesis and a
fungi provides a home for the algae
Example: Rhizobium bacteria, in legume plant root nodules,
fix nitrogen and legume provides carbohydrates and home
Example: termites have gut organism that can digest
cellulose
• In other mutualisms the organisms can live apart, but
there is strong mutual benefit in the relationship
Example: flowering plants and their pollinators, plant gets
pollinated, pollinator gets nectar or pollen to eat © Brooks/Cole Publishing Company / ITP
Mutualism
There are many more classic
examples of mutualism.
• Oxpecker bird feeds on the parasitic
ticks of various large mammals in
Africa, such as the black rhinoceros
• Mycorrhizal fungi live in the roots of
various plants; the fungus gets
carbohydrates and the plant gets
better absorption of nutrients by the
fungal mat that extends beyond the
roots
• Clownfish in the coral reefs of
Australia; clownfish gains protection
from stinging tentacles and food when
the anemone feeds; the anemone
gains protection from various fish that
feed on sea anemones
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Commensalism
Commensalism is a relationship in
which one species benefits while
another is neither helped not harmed
to a significant degree.
• Redwood sorrel, a small herbaceous
plant, benefits from growing in the
shade of tall redwoods, but the
redwoods are not affected;
• Epiphytes (orchids and bromeliads)
grow in trees in the tropical rain forest
gain a favorable place to live; whereas
the tree is not affected
**If epiphytes become abundant to
block light, the tree can be negatively
affected, and this becomes an
example of competition.
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5. Succession
Succession- gradual and fairly predictable change in
species composition with time.
• Some species colonize and become more abundant;
• Other species decline or even disappear.
Two kinds of succession:
• Primary succession- gradual establishment of biotic
communities in an area where no life existed
beforeNO SOIL!
• Secondary succession- gradual reestablishment of
biotic communities in an area where a biotic
community was previously presentSOIL ALREADY
ESTABLISHED
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Primary Succession
Primary succession occurs with time in
lifeless areas.
• Newly formed islands and succession
after the retreat of a glacier
•Early successional speciestypically lichens and mosses first
colonize bare rock--the first species
to colonize are termed pioneer
species
•Mid: later small herbs and shrubs
colonize
•Late: finally tree species colonize
• Takes lots of time 1 inch of soil can
take 200-1000 yrs. to form.
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Primary Succession
Primary
succession
over several
hundred years
on bare rock
exposed by a
retreating
glacier on Isle
Royal in
northern Lake
Superior.
Fig. 9–19
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Primary Succession
Greatly
simplified view
of primary
succession in
a newly
created pond
in a temperate
area. Nutrient
rich bottom
sediment is
shown in dark
brown.
Fig. 9–20a
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Secondary Succession
Secondary succession occurs where the natural
community of organisms has been disturbed, removed,
or destroyed.
• Agricultural fields go through succession.
• Succession proceeds until an area is occupied by a
climax community, however recent views recognize
that a single climax is not predictable.
• Not as lengthy process as primary due to existence of
soil.
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Secondary Succession
Secondary
succession
over 150–200
years in an
abandoned
farm field in
North
Carolina.
Fig. 9–21
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Secondary Succession
Successional changes in the animal community
accompany successional changes in the plant
community.
Fig. 9–22
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Table 8-1 Ecosystem Characteristics at Immature and Mature Stages of Ecological Succession
Characteristic
Ecosystem Structure
Plant size
Species diversity
Trophic structure
Ecological niches
Community organization
(number of interconnecting
links)
Table 8-1
Page 158
Immature Ecosystem
(Early Successional Stage)
Mature Ecosystem
(Late Successional Stage)
Small
Large
Low
High
Mostly producers, few decomposers
Mixture of producers, consumers,
and decomposers
Few, mostly generalized
Many, mostly specialized
Low
High
Ecosystem Function
Biomass
Net primary productivity
Food chains and webs
Low
High
High
Low
Simple, mostly plant
with few decomposers
herbivore
Complex, dominated by
decomposers
Efficiency of nutrient recycling Low
High
Efficiency of energy use
High
Low
Disturbance
What is the role of disturbance in
succession?
• Disturbance- a discrete event that
disrupts an ecosystem or community
•Fires, hurricanes, tornadoes,
droughts and floods
•Human–caused disturbance:
deforestation, overgrazing,
plowing
•Initiates secondary succession by
eliminating part or all of the
existing community, and by
changing conditions and releasing
resources.
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Mechanisms of Succession
Both primary and secondary succession are driven by
three mechanisms:
• Facilitation- a process by which an earlier
successional species makes the environment suitable
for later successional species; e.g., legumes fixing
nitrogen can enable later successional species.
• Inhibition- a process whereby one species hinders the
establishment and growth of other species; e.g.,
shade of late successional trees inhibits the growth of
early successional trees;
• Tolerance- a process whereby later successional
species are unaffected by earlier successional
species.
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Changes During Succession
During succession species diversity and stratification
tend to increase, while growth rates and primary
productivity tend to decrease.
**See Table 8-1
Fig. 9–23
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6. Island Biogeography
In the species
equilibrium model of
island biogeography
(developed by
Robert MacArthur
and Edward O.
Wilson) the number
of species on an
island is determined
by the balance
between immigration
and extinction.
Fig. 9–24
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Island Biogeography
Small islands are
expected to have
lower immigration
rates and higher
extinction rates,
and hence fewer
species than large
islands.
Fig. 9–24
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Island Biogeography
Far islands are
expected to have
lower immigration
rates, and hence
fewer species than
near islands.
Fig. 9–24
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Case Study: Hawaii


Pre-human Hawaii had great native biodiversity before
Polynesian seafarers arrived around A.D. 400. Today it is
“synthetic.”
Island biogeography dictates that these islands far from the
mainland would have very little possibility of species naturally
immigrating. Humans did. WE were an invasive, nonnative
species here 1500 years ago.
Case Study: Hawaii

Islands have been further overrun by nonnative
species we carried, introduced accidentally or
intentionally. It was a popular stopover in Pacific
travels.
– Of the original 145 endemic birds only 35 remain, 24
of which are endangered
– Of the 1900 flowering plant species today, over 900
are alien and are dominating over the rest
– Of the 8800 insect and arthropod species, over 3000
are of alien origin
– Ants, the leading predators of insects, never used to
inhabit Hawaii, but are now wreaking havoc on their
insect populations
– Feral pigs, not on the island until they were brought
by humans, are also causing huge problems with
destroying vegetation.
Island Biogeography
The model of island biogeography has been widely
applied in conservation biology by viewing the
landscape as composed of habitat islands
separated by an ocean of degraded or unsuitable
habitat modified by human activity.
• Large habitat patches tend to have more species
• Habitat patches that are near larger intact habitat
areas tend to have more species
• These principles can be applied to land
preservation and management efforts.
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7. Stability and Sustainability
Stability has three aspects:
• Inertia (or persistence)- the ability of a system to resist
being disturbed or altered
• Constancy- the ability of a living system to maintain a
certain size or state
• Resilience- the ability of a living system to recover after a
disturbance
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Stability and Sustainability


Signs of poor health or stressed
ecosystems:
– Decrease in primary productivity
– Increased nutrient losses
– Decline or extinction of indicator
species
– Increased populations of pests or
disease organisms;
– Decline in species diversity
– Presence of contaminants.
Through an understanding of ecology we
can grapple with what it means to have
sustainable ecosystems.