Transcript Keystone Species Concept

SPECIES INTERACTIONS OR THE ROLES
SPECIES PLAY IN AN ECOSYSTEM (SLIDES
1 – 22 NEW)
ECOLOGY PRINCIPLE
• EACH SPECIES HAS A SPECIFIC ROLE TO PLAY IN THE
ECOSYSTEM WHERE IT IS FOUND
• THAT ROLE THE SPECIES PLAYS IS ITS ECOLOGICAL
NICHE
• A SPECIES WAY OF LIFE IN A COMMUNITY OR
• ITS PATTERN OF LIVING
• INCLUDES EVERYTHING THAT AFFECTS THE SPECIES
SURVIVAL & REPRODUCTION
• THE NEEDS OF THE SPECIES SUCH AS AMOUNT OF WATER,
SUNLIGHT, SPACE, FOOD, OPTIMUM TEMPERATURE AND
WHAT FEEDS ON IT
CLASSIFYING NICHES
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GENERALISTS – BROAD NICHES,
LIVE IN MANY DIFFERENT PLACES
EAT A VARIETY OF FOODS
OFTEN TOLERATE A WIDE RANGE OF
ENVIRONMENTAL CONDITIONS
• FLIES, COCKROACHES, MICE, RATS,
WHITE-TAILED DEER, RACCOONS,
HUMANS
CLASSIFYING NICHES
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SPECIALISTS – OCCUPY NARROW NICHES
MAY BE ABLE TO LIVE IN ONLY ONE TYPE OF HABITAT
USE JUST ONE OR A FEW TYPES OF FOOD
TOLERATE A NARROW RANGE OF CLIMATIC & ENVIRONMENTAL
CONDITIONS
SHOREBIRDS OCCUPY SPECIALIZED NICHES – FEEDING ON
CRUSTACEANS, INSECTS & OTHER ORGANISMS UNIQUE TO
SANDY BEACHES & COASTAL WETLANDS
MORE PRONE TO EXTINCTION WHEN ENVIRONMENTAL
CONDITIONS CHANGE
GIANT PANDA HIGHLY ENDANGERED DUE TO HABITAT LOSS,
LOW BIRTH RATE AND SPECIALIZED DIET OF BAMBOO
5 MAJOR SPECIES ROLES WITHIN
ECOSYSTEMS
• NATIVE SPECIES – NORMALLY LIVE AND THRIVE IN A
PARTICULAR ECOSYSTEM
• NONNATIVE SPECIES – MIRGRATE INTO, DELIBERATELY
OR ACCIDENTALLY INTRODUCED INTO AN ECOSYSTEM
(INVASIVE, ALIEN, EXOTIC)
• NONNATIVE SPECIES CAN COMPETE WITH & REDUCE A
COMMUNITY’S NATIVE SPECIES, CAUSING UNINTENDED &
UNEXPECTED CONSEQUENCES
• CAN SPREAD RAPIDLY DUE TO NO PREDATORS OR
DISEASES FACED IN NATIVE NICHES
• EXAMPLES: WILD AFRICAN HONEYBEES, KUDZU
5 MAJOR SPECIES ROLES WITHIN
ECOSYSTEMS
• INDICATOR SPECIES – PROVIDE
EARLY WARNINGS OF DAMAGE TO A
COMMUNITY OR ECOSYSTEM
• EXCELLENT BIOLOGICAL
INDICATORS INCLUDE BIRDS,
BUTTERFLIES, AMPHIBIANS
• WHY?
5 MAJOR SPECIES ROLES WITHIN
ECOSYSTEMS
In ecological communities there
are little players and big players.
The biggest players of all are
referred to as keystone species.
A keystone species may be
defined as one whose presence/
absence, or increase/decrease in
abundance, strongly affects other
species in the community.
Removal of the keystone in
the arch will cause the
structure to collapse.
Evidence usually comes from the
addition or removal of species.
Starfish as Keystone Predators
Photo by Raymond Seed
In the rocky intertidal zone, mussels are
superior at occupying space, crowding
out other species. Starfish are effective
predators of mussels, and thereby make
room for other species.
http://life.bio.sunysb.edu/marine
bio/rockyshore.html
Starfish as Keystone Predators
A hoard of hungry starfish converge on
a mussel bed. A starfish curls its body
around the mussel, using its tube feet to
pry apart the valves enough to insert its
extensible stomach. Digestive enzymes
break down the mussels’ muscles, and
the starfish consumes its prey.
A starfish removal experiment
in Washington State
demonstrated that the mussels
are competitive dominants.
Starfish predation opens up
enough space for various
barnacles, echinoderms and
other marine invertebrate
species to maintain a presence.
When starfish are
experimentally removed,
mussels take over and other
species are excluded.
Fig. 5-1, p. 79
Fig. 5-1, p. 79
Fig. 5-A, p. 82
Core Case Study: Endangered Southern
Sea Otter
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Santa Cruz to Santa Barbara shallow coast
Live in kelp forests
Eat shellfish
~16,000 otters around 1900
Hunted for fur
Hunted because they were considered competition for
abalone and shellfish
• 1938-2008: otter population declined
• 1977: otters declared an endangered species
Science Focus: Sea Urchins Threaten
Kelp Forests
• Kelp forests
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Can grow two feet per day
Require cool water
Host many species – high biodiversity
Provide essential habitat for entire ecosystem
Fight beach erosion
Algin – gelatinous polysaccharide from brown
algae used as a thickener in foods (ice cream)
Science Focus: Sea Urchins Threaten
Kelp Forests
• Kelp forests threatened by
– Sea urchins
– Pollution
– Rising ocean temperatures
• Southern sea otters eat urchins
– Keystone species
Other Indirect Species
Interactions
• The keystone species effect is the bestknown example of indirect interactions. One
cannot have a keystone species effect
without the presence of indirect interactions.
– Keystone species produce strong indirect effects, out of
proportion to their abundance.
• If a predator strongly suppresses its prey
(e.g., herbivores), one expects the trophic
level below (e.g., plants) to benefit. Such
top-down trophic cascades are well-known in
lakes.
Other Indirect Species
Interactions
• Removal of one species
causes other species to be
lost from the system
•Aka “ripple effect”
• When the dodo (a 25 kg
pigeon) was exterminated
on Mauritius, the tree
Calvaria major ceased to
recruit. Its seeds needed to
be abraded in the dodo’s
gizzard to germinate.
5 MAJOR SPECIES ROLES WITHIN
ECOSYSTEMS
• FOUNDATION SPECIES – PLAY A MAJOR ROLE IN SHAPING
THEIR COMMUNITY BY CREATING AND ENCHANCING
THEIR HABITATS IN WAYS THAT BENEFIT OTHER SPECIES
• ELEPHANTS PUSH OVER, BREAK AND UPROOT TREES
WHICH CREATE OPENINGS IN GRASSLANDS AND
WOODLANDS OF AFRICA
• THIS STIMULATES THE GROWTH OF GRASSES AND OTHER
FORAGE PLANTS THAT BENEFIT SMALLER GRAZING
SPECIES SUCH AS ANTELOPE
• IT ALSO ACCELERATES NUTRIENT CYCLING RATES
• OTHER FOUNDATION SPECIES INCLUDE BEAVERS,
ALLIGATORS,
Interspecific Competition
• No two species can share vital limited
resources for long
• Resolved by:
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Migration
Shift in feeding habits or behavior
Population drop
Extinction
• Intense competition leads to resource
partitioning
Resource Partitioning of 5 species of insect eating warblers
Blackburnian
Warbler
Black-throated
Green Warbler
Cape May
Warbler
Bay-breasted
Warbler
Yellow-rumped
Warbler
Stepped Art
Fig. 5-2, p. 81
Mutualistic Interactions
• A mutualism is an
interaction where both
species benefit
• facultative mutualisms
are beneficial but not
essential to either
species’ survival
• obligate mutualisms are
essential to the survival
of one or both species
Pollination is a classic
mutualism. The plant gains
through gamete transfer.
The pollinator receives a
reward of nectar and pollen.
The Boran - Honeyguide Mutualism
• Example of a facultative
mutualism between an
African people, and a bird,
Indicator indicator.
• Borans find bee colonies
more quickly when guided
by the bird
• Honeyguides get larvae,
wax, and are in less danger
from bees
The bird informs on direction,
distance to, and arrival at bee
colony. Search time is
reduced from 8.9 to 3.2 hrs
The Ant - Acacia Mutualism
• Example of an obligate
mutualism between
ants and a thorny,
small tree of dry
tropical forests.
• Acacia provides
shelter (hollow thorns)
and food (nectar,
protein bodies) to ant.
Ants remove herbivorous
insects, vines, others plants,
and leaf litter (which
reduces risk of fire).
The Ant - Acacia Mutualism
An acacia ant (Pseudomyrmex ferruginea) sipping nectar from
the petiolar nectary of a swollen thorn acacia (Acacia collinsii)
in Costa Rica.
http://waynesword.palomar.edu/acacia.htm#antleafb.gif
The Ant - Acacia Mutualism
Plants also supply ants with protein and fat-rich food in the
form of “Beltian bodies”, shown here being harvested by ants
(arrows) from the tips of newly expanding leaflets of Acacia
cornigera (Photo by T.W. Sherry)
The Ant - Acacia Mutualism
•Newly developing bull’s
horns (evolutionarily
enlarged thorns)
•Filled with a pith that ants
easily remove, creating
hollow interiors
•Ants chew small hole into
each thorn for use as home
The Ant - Acacia Mutualism
Pseudomyrmex ants
provide two services to
Acacia trees:
•24-hour patrolling of
leaves for protection
against insects and
mammals
•Clearing of plants from
ground and from Acacia
trees themselves as
protection from
competitors and fire
Fig. 5-6, p. 85
Fig. 5-6, p. 85
Commensalism
• When one
species
benefits, and
the other
neither
benefits nor is
harmed.
• A “+/0”
interaction
Cattle egrets follow cattle, consuming the
insects disturbed by the cows’ movements.
It is unlikely that the cows benefit.
Fig. 5-7, p. 85