Transcript community - lynchscience

Anu Singh-Cundy • Gary Shin
Discover Biology
SIXTH EDITION
CHAPTER 23
Ecological Communities
© 2015 W. W. Norton & Company, Inc.
CHAPTER 23
Ecological Communities, Part 1
FATAL FELINE ATTRACTION
Mutualistic relationships benefit both species involved
23.1 Species Interactions
Mutualistic relationships benefit both species involved
Only one partner benefits in commensalism
In exploitation, one member benefits while another is harmed
In competition, both species are negatively affected
23.2 How Species Interactions Shape Communities
Keystone species have profound effects on communities
Invasive species can overtake communities
23.3 How Communities Change over Time
Succession establishes new communities and replaces disturbed communities
Communities change as climate changes
CHAPTER 23
Ecological Communities, Part 2
23.4 Human Impacts on Community Structure
Communities can reassemble after some human-caused disturbances
People can cause long-term damage to communities
BIOLOGY MATTERS: Introduced Species: Taking Island Communities by
Stealth
APPLYING WHAT WE LEARNED: HOW A PARASITE CAN HIJACK YOUR BRAIN
Fatal Feline Attraction
Imagine an alien that
enters people’s brains
and changes their
behavior, sometimes
even driving them
crazy.
•
•
Toxoplasma gondii is a single-celled parasite, most often contracted from raw meat, that
alters the brain activity of rodents.
The species that make up a community interact in all kinds of ways.
An Association of Different Species
• An ecological community is an association of different species that
live in the same area.
• Communities vary greatly in size and complexity and can be
characterized by their species composition, or diversity.
The Two Components
of Community
Diversity
• Species richness refers to the
total number of different
species that live in the
community.
• Relative species abundance
describes how common
individuals of a species are
compared with individuals of
other species in the
community.
• Interactions among organisms
have huge effects on natural
communities.
Species Interactions
• Coevolution occurs when two species that interact trigger
evolutionary change in each other as a consequence of their
interactions.
• Interactions among organisms can be divided into four categories:
– Mutualism (+/+): interactions in which both species benefit
– Commensalism (+/-): interactions in which one species benefits
at no cost to the other
– Exploitation (+/-): interactions in which one species benefits and
the other is harmed
– Competition (-/-): interactions in which both species may be
harmed
Species Interactions: Mutualism
Mutualism evolves when the
benefits of the interaction
outweigh the costs for both
species.
• Mutualism is an association between two species in which both species benefit
more than it costs them to interact with each other.
• Two or more organisms of different species living together is symbiosis.
• Although both species in a mutualism benefit from the relationship, what is good
for one species may come at a cost to the other. For example, a species may use
energy or increase its exposure to predators when it acts to benefit its mutualistic
partner.
• From an evolutionary perspective, mutualism evolves when the benefits of the
interaction outweigh the costs for both species.
There Are Many Types of Mutualism
Gut inhabitant mutualism in
deer gut: microbes that live
in digestive tract receive food
from their host and benefit
the host by digesting foods
that the host otherwise could
not use.
Examples of mutualisms include
- Gut inhabitant mutualism
- Protection mutualism
- Behavioral mutualism
- Seed dispersal mutualism
- Pollinator mutualism
An example of
seed dispersal mutualism
An Example of Behavioral Mutualism
The goby acts as a “seeing eye” fish for the shrimp, which has poor vision. In return, the
shrimp shares its burrow with the goby, thereby providing the fish with a safe haven in an
environment with few options for sheltering from predators.
Mutualism Can Determine the Distribution
and Abundance of Species
In this pollinator mutualism, the
plant gets pollinated and the moth
larvae eats some of its seeds.
The plant and pollinator are
completely interdependent: the
yucca is the moth’s only source of
food, and this moth is the only
species that pollinates the yucca.
•
•
•
Mutualism can affect species distribution, the geographic area over which a species is
found.
Species abundance, the number of individuals of a species in a defined habitat, can also
be affected by mutualism.
Mutualism can have indirect effects on the distribution and abundance of species that
are not part of the mutualism.
Only One Partner Benefits in
Commensalism
• A relationship in which one partner benefits while the other is
neither helped nor harmed is called commensalism.
• Barnacles that attach themselves to whales are an example of
commensalism.
In Exploitation, One Member Benefits
While Another Is Harmed
• Exploitation encompasses a variety of interactions in which one
species benefits and the other is harmed.
• Exploiters are generally consumers falling into three main
categories:
– Herbivores are consumers that eat plants or plant parts
– Predators are animals that kill other animals for food
– Parasites are consumers that live in or on the organisms they
eat
A marine crustacean, Cymothoa exigua enters
through fish gills and attaches to the base of the fish’s
tongue to draw blood from it. Starved of oxygen, the
tongue will eventually atrophy and die. The fish,
however, will not. It will continue to live with C.
exigua, still attached, acting as a surrogate tongue.
Consumes Can
Strongly Affect the
Abundance of
Their Food
Organisms
• Sometimes a consumer exerts
such a significant impact on a
prey species that the
population sizes of two species
change together in a tightly
linked cycle, known as a
population cycle.
Lynx populations increase when
hare populations increase, but the
increased number of lynx drive the
hare populations down, which then
turn drives down lynx populations.
Consumers and Their Food Organisms Can Exert
Strong Selection Pressure on Each Other
• The presence of consumers in
an environment has caused
many species to evolve
elaborate strategies to avoid
being consumed.
• An evolutionary arms race can
develop as prey or host evolve
a powerful defense and their
consumers in turn experience
strong selection pressure to
overcome that defense.
Avoiding Predation: Induced Defense
• Induced defenses are
responses from certain
plants that are directly
stimulated by an attack
from herbivores.
Avoiding Predation: Warning Coloration
• Warning coloration
is used by prey
organisms to warn
potential predators
that they are heavily
defended, for
example, with
toxins.
Avoiding Predation: Mimicry
• Mimicry is a type of adaptation arising from predator-prey
interactions in which a species evolves to imitate the appearance of
something unappealing to its would-be predator.
In Competition, Both Species Are
Negatively Affected
• Interspecific (interspecies) competition is most likely
when two species share an important resource that
is limited.
• An ecological niche is the sum total of the conditions
and resources a species or population needs in order
to survive and reproduce successfully in its particular
habitat.
• When two or more species compete, each has a
negative effect on the other because each uses
resources needed by its competitor.
Competitors May Exclude Each
Other from Their Own Special Niche
• Competitive exclusion
occurs when one species
uses all the resources
needed by another and that
species becomes extinct.
• There are two main types of
competition:
– Interference
competition: one
organism directly
excludes another from
the use of a resource
– Exploitative competition
Competition Can Limit the
Distribution and Abundance
of Species That Share
Resources or Space
•
Exploitative competition:
species compete indirectly for
a shared resource, each
reducing the amount of the
resource available to the other
Exploitative competition
between an introduced
and native wasp caused
the extinction of the native
in most localities. Both
feed on the same insect,
the citrus mealybug.
Competition Is Reduced
When Niches Are Used in
Different Ways
• Niche partitioning occurs when
natural selection leads
competing organisms to use
their common niche in different
ways as a method of reducing
competition.
These birds can coexist on the
same shore because they
dig for crustaceans in
waters of different depths.
Keystone
Species Have
Profound Effects
on Communities
• Keystone species have a
disproportionately large effect,
relative to their own
abundance, on the types and
abundances of the other
species in a community.
• Keystone species can include
any producer or consumer of
relatively low abundance that
has a large influence on its
community, and they are
usually noticed only when they
are removed or disappear from
an ecosystem.
Invasive Species Can Overtake
Communities
• Nonnative species
introduced by people to
new regions sometimes
disrupt the ecological
communities there.
• Some species multiply
rapidly when introduced
to new areas due to lack
of predation and fewer
parasites than in their
original home.
How Species Interactions Shape
Communities
• Interactions among organisms can impact the
communities and ecosystems in which those organisms
live.
• Human actions, such as urbanization and natural causes,
such as fire, affect a species’ chances of survival.
• Any changes in species diversity in a community will have
a ripple effect throughout the community.
How Communities Change over Time
• The number of individuals of different species in a community
often changes as the seasons or the years change.
• Communities also undergo broad directional changes in species
composition over longer periods of time.
• The process by which species in a community are replaced over
time is called succession.
• Primary succession occurs in newly created habitat when a few
species that are able to grow and reproduce under the challenging
conditions begin to colonize the area.
• Secondary succession is the process by which communities regain
the successional state that existed before a disturbance.
Succession Establishes New
Communities
• The first species to colonize the area may alter the habitat in ways that cause
later-arriving species to thrive or fail.
• The process of succession ends when the species composition of a community
remains stable over a long period of time, resulting in a mature community.
• Most ecological communities never reach maturity because of frequent
disturbances such as fires or windstorms.
Succession Replaces Disturbed
Communities
• Secondary succession is the process by which communities regain the
successional state that existed before a disturbance.
Communities Change as Climate Changes
• The climate at a
given location can
change over time as
a result of either
global climate
change or
continental drift.
• The change in the global climate causes slow but dramatic changes in the location
and diversity of plant and animal species in an ecosystem.
• Human activities are now accelerating the natural changes in the global climate.
• As the continents move slowly over time, their climates change, causing large
changes in their communities.
People Can Cause Long-Term Damage
to Communities
• Some communities, such as cleared farmland, can recover from a human
disturbance.
• The sizes and abundances of species in a community are different after a
disturbance, and there may be fewer species.
• Ecological interactions brought about by humans, such as logging or overgrazing
by cattle, can permanently affect natural communities for example by causing
desertification.
• Some communities may take hundreds to thousands of years to recover; others
may never recover.
Overgrazing can
lead to desertification
BIOLOGY MATTERS:
Introduced Species: Taking
Island Communities by
Stealth
• The Hawaiian Islands are the most isolated
chain of islands on Earth.
• Entire groups of organisms that live in most
other communities have never reached these
islands (no native ants or snakes; only one
mammal, a bat).
• The few species that did reach the islands
evolved in isolation to form unique
communities, without many types of predators
and competitors found elsewhere.
• As a result, these communities are ill equipped
to cope with invasives, such as rats and beard
grass, introduced by people.
Hawaiian silverswords are found only in Hawaii. This
diverse species evolved from a single ancestor (a
tarweed from California). The three species in these
photos have very different form because they’re
adapted to live in very different habitats.
APPLYING WHAT WE LEARNED:
HOW A PARASITE CAN HIJACK YOUR BRAIN
T. gondii improves its chances
of spreading to cats by
changing the behavior of
infected rats.
• Male rats infected with Toxoplasma gondii find the smell of cat urine irresistible;
they’re eaten by the feline, the only host group in which T. gondii can sexually
reproduce, which then excretes the parasite.
• The parasite forms cysts in the brain and releases dopamine, a “feel good”
neurotransmitter.
• T. gondii infections in humans alters behavior differently in men versus women
• The parasite is contracted from cleaning cat litter boxes, but also from handling
raw meat or from consuming undercooked meat, unpasteurized milk, and
unwashed fruits and vegetables.
List of Key Terms: Chapter 23
character displacement (p. 534)
coevolution (p. 527)
commensalism (p. 529)
community (p. 526)
competition (p. 532)
competitive exclusion (p. 533)
desertification (p. 540)
diversity (p. 526)
exploitation (p. 530)
exploitative competition (p. 533)
herbivore (p. 530)
host (p. 530)
induced defense (p. 530)
interference competition (p. 533)
keystone species (p. 535)
mimicry (p. 530)
mutualism (p. 527)
niche (p. 532)
niche partitioning (p. 533)
parasite (p. 530)
pathogen (p. 530)
pollinator (p. 528)
population cycle (p. 531)
predator (p. 530)
prey (p. 530)
primary succession (p. 537)
relative species abundance (p. 526)
secondary succession (p. 537)
species richness (p. 526)
succession (p. 537)
symbiosis (p. 537)
warning coloration (p. 530)
Class Quiz, Part 1
Which of the following is not a major type of
exploitation?
A. herbivores
B. parasites
C. induced defenses
Class Quiz, Part 2
Two species of bumblebees coexist in the same
meadow, but one has a long feeding tube
(proboscis) and sips nectar from columbines, and
the other has a short proboscis and sips nectar
from asters. This is an example of
A. pollinator mutualism.
B. behavioral mutualism.
C. exploitative competition.
D. niche partitioning.
Class Quiz, Part 3
As this glacier retreats, the barren land that is
exposed comes to be colonized by
herbaceous plants, sedges, low shrubs, then
alders, and finally, subalpine fir. This pattern
of change is an example of
A. primary succession.
B. secondary succession.
C. niche partitioning.
D. commensalism.
Relevant Art from Other
Chapters
All art files from the book are available in
JPEG and PPT formats online
Producers and Consumers
23.1 Concept Check, Part 1
1. The yucca moth pollinates the yucca plant and
depends on it for food. How would you classify this
type of interaction? Is it cost-free for both moth and
plant? Explain.
ANSWER: It is a mutualism. There are costs for both:
the moth’s reproduction is limited because the plant
restricts the number of eggs the moth can lay
successfully, and the plant in turn loses some of its
seeds to the moth larvae.
23.1 Concept Check, Part 2
2. Cattle egrets trail livestock—sometimes perching on
their backs—to pick up insects stirred up by the grazing
animals. How would you classify this type of
interaction? Who benefits in this type of interaction?
ANSWER: This is commensalism. The birds benefit
because they get better access to their insect prey. The
grazers are neither harmed nor benefited.
23.1 Concept Check, Part 3
3. Chthamalus (a barnacle that lives high on the shoreline)
and Semibalanus (a barnacle that lives in the low intertidal
zone) exhibit interference competition. How would the
survival and reproduction of a Chthamalus colony be affected
if it were relocated to the low intertidal zone either in the
absence of Semibalanus or intermixed with Semibalanus?
ANSWER: Chthamalus would thrive low on the
shoreline as long as Semibalanus was absent.
23.2 Concept Check, Part 1
1. What is a keystone species?
ANSWER: Any organism of relatively low abundance
that has a disproportionately large influence on the
diversity of a community is a keystone species.
23.2 Concept Check, Part 2
2. Why are invasive species such a significant
problem?
ANSWER: Because they lack biological controls on
their population growth, such as predators or parasites,
invasive species can potentially grow rapidly and
displace, outcompete, or prey on native species.
23.3 Concept Check, Part 1
1. Describe the distinctive characteristics of
species that tend to be the first to colonize a new
habitat.
ANSWER: They disperse more rapidly than other
species, and/or they are better able to survive and
reproduce in challenging environments.
23.3 Concept Check, Part 2
2. Compare primary succession with
secondary succession.
ANSWER: Primary succession is the order in which
species replace others in a new habitat (one that
contains no species). Secondary succession is the
sequence of species that appear in a preexisting
community disturbed by natural processes (such as
fire) or human actions (such as deforestation).
23.4 Concept Check, Part 1
1. What kinds of human activities influence
community structure?
ANSWER: Logging, fire, agriculture, and grazing are
among the many human activities that affect
communities.
23.4 Concept Check, Part 2
2. Can human activity ever induce primary
succession?
ANSWER: Not likely. Human activity may damage or
degrade communities, but it does not remove all
species and soil.