Download Keystone Species

BIOLOGY
A GUIDE TO THE NATURAL WORLD
FOURTH EDITION
DAVID KROGH
An Interactive Living World 2:
Communities in Ecology
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
34.1 Structure in Communities
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Structure in Communities
• An ecological community is all the populations
of all species that inhabit a given area.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Structure in Communities
• Many communities are dominated by only a
few species.
• The few species that are abundant in a given
area are called ecological dominants.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Ecological Dominants
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.1
Keystone Species
• A keystone species is a species whose absence
from a community would bring about
significant change in that community.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Keystone Species
• Some keystone species are top predators in a
community, meaning species that prey on other
species but that are not preyed on themselves.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Keystone Species
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.2
Keystone Species
• Keystone species need not be top predators,
however, and every community does not have a
keystone species.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Biodiversity
• Biodiversity, defined as variety among living
things, takes three primary forms:
– A diversity of species in a given area.
– A geographic distribution of species populations.
– Genetic diversity within species populations.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Biodiversity
High biodiversity
Low biodiversity
many different species
few species
broad distribution of species
narrow distribution of species
high genetic diversity
within population
low genetic diversity
within population
Species
diversity
Geographic
diversity
Genetic
diversity
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.3
Biodiversity
• Recent research indicates that species diversity
tends to enhance a community’s productivity.
• Productivity is defined as the amount of solar
energy that photosynthesizing organisms are
able to capture and transform into living
material or biomass.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Biodiversity
• There is disagreement about whether species
diversity also enhances community stability,
meaning the ability of a community to retain its
characteristics in the face of environmental
disruption.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
34.2 Types of Interaction Among
Community Members
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Modes of Interaction
• There are four primary types of interaction
among community members:
–
–
–
–
competition
predation (and a special variety of it, parasitism)
mutualism
commensalism
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Habitat
• Habitat can be thought of as the physical
surroundings in which a species normally can
be found.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Niche
• Niche can be defined metaphorically as an
organism’s occupation, meaning what the
organism does to obtain the resources it needs
to live.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Competition for Resources Among
Species
• The competitive exclusion principle states that
when two populations compete for the same
limited, vital resource, one always outcompetes
the other and thus brings about the latter’s local
extinction.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Competition for Resources Among
Species
• There are numerous instances in nature in
which two related species use the same kinds of
resources from the same habitat over an
extended period of time but will divide the
resources up such that neither of the species
undergoes local extinction.
• This phenomenon is called coexistence through
resource partitioning.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Competition for Resources Among
Species
Competitive exclusion
When two species
compete for the same
limited, vital resource,
one will always drive
the other to local
extinction—as the
paramecium P. aurelia
did to the paramecium
P. caudatum. This is the
competitive exclusion
principle at work.
Resource
partitioning
Conversely, when
Gause put P. aurelia
together with another
paramecium,
P. bursaria, the
two species divided
up the habitat, and
both survived. This is
a demonstration of
resource partitioning.
P. aurelia
P. caudatum
P. aurelia
P. bursaria
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.4
Resource Partitioning
Cape May
warbler
Bay-breasted
warbler
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Myrtle
warbler
Figure 34.6
Predation
• Predation is defined as one free-standing
organism feeding on parts or all of a second
organism.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Parasitism
• Parasitism is a variety of predation in which the
predator feeds on prey but does not kill it
immediately and may not kill it ever.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Parasitism
• The prey of a parasite is known as the host.
• A parasite can use a host not only as a food
source but as a vehicle to facilitate its
reproduction.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Plants Parasitizing Plants
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.7
Predator-Prey Dynamics
• Predator and prey population sizes can move up
and down together in a fairly tight linkage, but
predator-prey interaction generally is only one
of several factors that control the population
level of either predators or prey.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Predator-Prey Dynamics
Lemming
population
Stoat
population
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.8
Predator-Prey Dynamics
• Over evolutionary time, predator-prey
interactions have spurred physical
modifications in both predator and prey species.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Avoiding Predation Through
Camouflage
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.10
Mimicry
• One form that such modifications take is
mimicry: a phenomenon in which one species
has evolved to assume the appearance of
another.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Mimicry
• One form of mimicry, Batesian mimicry, occurs
when one species evolves to resemble a species
that has superior protective capability.
• Batesian mimicry always includes three
players: a mimic, a model, and a dupe.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Mimicry
• The mimic species evolves to match the
appearance of the model species, which has
superior protective ability.
• The dupe species is then deceived into
believing the mimic species is the model
species.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Batesian Mimicry
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.11
Mimicry
• In a second form of mimicry, Müllerian
mimicry, several species that have protection
against predators come to resemble each other.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Müllerian Mimicry
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.12
Mutualism
• Mutualism is an interaction between individuals
of two species that is beneficial to both
individuals.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Mutualism
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.13
Commensalism
• Commensalism is an interaction in which an
individual from one species benefits while an
individual from another species is neither
harmed nor helped.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Coevolution
• Coevolution is the interdependent evolution of
two or more species.
• Flowers have evolved colors and fragrances
that attract bees, for example, while bees have
evolved vision that is most sensitive to the
colors of the flowers they pollinate.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Coevolution
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.14
Community Interactions
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Table 34.1
34.3 Succession in Communities
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Succession
• Parcels of land or water that have been
abandoned by humans or devastated by
physical forces will almost always be reclaimed
by nature to some degree.
• This process is called succession: a series of
replacements of community members at a given
location until a relatively stable final state is
reached.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Succession
• Primary succession proceeds from an original
state of little or no life and soil that lacks
nutrients.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Primary Succession
ponds and bogs
eventually?
spruce
exposed
till
pioneer
species:
lichens, bacteria,
horsetails, and
liverworts
Dryas
shrub
spruce-hemlock
alder bush
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.16
Succession
• Secondary succession occurs when a final state
of habitat is first disturbed by some outside
force, but life remains, and the soil has
nutrients.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Succession
• The final community in any process of
succession is known as the climax community.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Succession
• A common set of developments occurs in most
instances of primary succession.
• These include the arrival of “pioneer”
photosynthesizers, facilitation of the growth of
some later species through the actions of earlier
species, and the competitive driving out of
some earlier species by the actions of later
species.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Succession
• As succession proceeds, species diversity tends
to increase within communities and smaller,
shorter-lived species tend to be replaced by
larger, longer-lived species.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Succession
• The rejuvenation of the Mount St. Helens area
that has occurred since 1980 has provided
ecologists with a wealth of information
regarding both primary and secondary
succession.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Mount St. Helens
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.15
Succession
• One of the chief lessons learned concerns the
degree to which succession can be facilitated by
biological legacies, defined as living things, or
products of living things, that survive a major
ecological disturbance.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Survivor on Mount St. Helens
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 34.17