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January-October 2014 temperatures highest on record
November 29, 2014
The global average temperature over land and ocean surfaces for January to
October 2014 was the highest on record, according to NOAA. October was the
hottest since records began in 1880.
© Cengage Learning 2015
Politics, not severe weather, drive global-warming views
December 1, 2014
Scientists have presented the most comprehensive evidence to date that climate
extremes such as droughts and record temperatures are failing to change people's
minds about global warming.
"Our results show that politics has the most important effect on perceptions of
climate change."
Some previous studies suggested temperature patterns do, in fact, influence
perceptions about global warming, but none measured climatic conditions as
comprehensively as the current investigation. Past research often considers a two-day
window or a particular community and a single measure of temperature, not an
expansive sweep of multiple climate measures as the authors of this study do.
The study analyzed climatic storm-severity measures used by NOAA -- temperature,
drought, precipitation and wind velocity -- from all 50 states in combination with the 11
years of public opinion data. "This gives us the pulse of the nation," said MarquartPyatt.
While advocates of global warming reduction efforts hope that experience with a
changing climate will eventually convince the public of the reality and seriousness of the
problem, the current findings do not bode well for that scenario.
Given this expansive treatment of the issue, there is "little grounds for optimism," the
study says, "that public concern about climate change will be driven by future climatic
conditions."
© Cengage Learning 2015
Age structure for the males in a
population of large cactus
finches on one of the
Galápagos Islands in 1987.
11
10
9
Age (years)
8
7
6
5
4
3
2
1
0
10
20
30
40
50
Percent of population
© Cengage Learning 2015
Figure 19.3
Biology
Concepts and Applications | 9e
Starr | Evers | Starr
Chapter 41
Community Ecology
© Cengage Learning 2015
© Cengage Learning 2015
41.1 What Factors Affect Community
Structure?
• The type of place where a species
normally lives is its habitat, and all species
living in a habitat constitute a community
• Communities often are nested one inside
another
© Cengage Learning 2015
What Factors Affect Community Structure?
• Community structure can change:
– As the community forms and ages
– As a result of natural or human-induced
disturbances
– With changes in physical factors such as
climate and resource availability
– Due to various types of species interactions
© Cengage Learning 2015
What Factors Affect Community Structure?
• Species interactions can be mutually
beneficial, mutually harmful, or benefit one
species while harming the other
– Example: Commensal ferns attached to the
trunk of a tree; the fern benefits from the light,
and the tree is unaffected
© Cengage Learning 2015
What Factors Affect Community Structure?
• Symbiosis
– “Living together”
– A relationship in which two species have a
prolonged close association
– Two species that interact closely for
generations can coevolve – each species acts
as a selective agent on the other
– Can be a commensal, mutualistic, or parasitic
relationship
© Cengage Learning 2015
41.2 How Do Species Cooperate?
• In a mutualistic interaction, two species
benefit by taking advantage of one another
– Example: pollinators eat nectar and pollen,
and plants receive pollen from other plants of
the same species
+/+
© Cengage Learning 2015
How Do Species Cooperate?
• For some mutualists, the main benefit is
defense
– Example: Sea anemone and anemone fish
• An anemone fish has a mucus layer that shields it
from stinging cells (nematocysts) of a sea
anemone
• Tentacles of the anemone protect the fish from
predators
• The anemone fish chases away the few fishes that
are able to eat sea anemone tentacles
© Cengage Learning 2015
How Do Species Cooperate?
© Cengage Learning 2015
• Mutualistic relationship
• Commensal relationship
• Parasitic relationship
© Cengage Learning 2015
+/+
+/0
+/-
41.3 How Do Species Compete?
• Resources are limited and individuals of
different species often compete for access
to them (interspecific competition)
• Competition adversely affects both
species
© Cengage Learning 2015
How Do Species Compete?
• Each species has an ecological niche
defined by physical and biological factors;
the more similar the niches of two species
are, the more intensely they will compete
– An animal’s niches include the temperature
range it can tolerate, species it eats, and
places it can breed
– A flowering plant’s niche would include its soil,
water, light, and pollinator requirements
© Cengage Learning 2015
How Do Species Compete?
• Two Paramecium species compete for the
same food (bacteria)
• Each species thrives when grown alone
• When grown together, P. aurelia drove P.
caudatum to extinction
© Cengage Learning 2015
LM
Relative population density
Separate
cultures
Paramecium aurelia
Combined
cultures
2
P. aurelia
4
6
8
10
Days
12
14
16
LM
0
P. caudatum
Paramecium caudatum
© Cengage Learning 2015
Figure 20.8
41.4 How Do Predators and Their Prey
Interact?
• Predation
– One species (the predator) captures, kills, and
eats another species (the prey)
© Cengage Learning 2015
How Do Predators and Their Prey
Interact?
• Predator and prey exert selection pressure
on one another
– Predators exert selection pressure that favors
improved prey defenses
– Improved prey defenses in turn exert
selection pressure on predators to improve
capture skills, and so on
© Cengage Learning 2015
How Do Predators and Their Prey
Interact?
© Cengage Learning 2015
How Do Predators and Their Prey
Interact?
• Defensive adaptations of prey
– Hard or sharp parts that make prey difficult to
eat
– Chemicals that taste bad or sicken predators
– Tricking or startling an attacking predator
– Warning coloration that predators learn to
avoid, such as the black and yellow stripes of
stinging wasps and bees
© Cengage Learning 2015
How Do Predators and Their Prey
Interact?
• In a type of mimicry, prey masquerade as
a species that has a defense that they lack
– Example: some flies that can’t sting resemble
stinging bees or wasps
• Mimicry
– A species evolves traits that make it more
similar in appearance to another species
© Cengage Learning 2015
How Do Predators and Their Prey
Interact?
A Wasp that can inflict a painful
sting. Like many stinging bees and
wasps, it has a yellow and black
pattern.
B Fly, which lacks a stinger, mimics
the color pattern of stinging insects.
© Cengage Learning 2015
Milk Snake
© Cengage Learning 2015
Coral Snake
Figure 20.12
How Do Predators and Their Prey
Interact?
• Predator adaptations include sharp teeth
and claws
– Predators and prey may be coevolved for
speed
• Example: cheetah and gazelle
– Both predators and prey use camouflage (a
form, patterning, color, or behavior that allows
them to blend into their surroundings) to avoid
detection
© Cengage Learning 2015
How Do Predators and Their Prey
Interact?
A
© Cengage Learning 2015
B
How Do Predators and Their Prey
Interact?
• Herbivory
– An animal feeds on plant parts
– The number and type of plants in a
community can influence the number and type
of herbivores present
© Cengage Learning 2015
How Do Predators and Their Prey
Interact?
• Two types of defenses against herbivory
– Withstand and recover quickly
– Traits such as spines, tough leaves, or toxins
that deter herbivory
• Plant defenses favor adaptations in
herbivores
– Example: Koalas have special enzymes to
break down toxins in eucalyptus
© Cengage Learning 2015
41.5 How Do Parasites and Their Hosts
Interact?
• Parasitism
– One species (the parasite) feeds on another
(the host), without immediately killing it
• Endoparasites live and feed inside their host
• Ectoparasites feed while attached to a host’s
external surface
© Cengage Learning 2015
How Do Parasites and Their Hosts
Interact?
A
B
© Cengage Learning 2015
C
How Do Parasites and Their Hosts
Interact?
• Parasitoids
– An insect that lays eggs in another insect, and
whose young devour their host from the inside
– Reduce a host population in two ways:
• Parasitoid larvae withdraw nutrients and prevent
the host from reproducing
• Presence of larvae leads to death of the host
– As many as 15% of all insects may be
parasitoids
© Cengage Learning 2015
How Do Parasites and Their Hosts
Interact?
• Biological pest control
– Parasites and parasitoids are commercially
raised and released in target areas as
biological control agents – an environmentally
friendly alternative to pesticides
– A biological control agent must be adapted to
a specific host species
– Introducing a biological control species into a
community is risky – they sometimes go after
nontargeted species
© Cengage Learning 2015
How Do Parasites and Their Hosts
Interact?
© Cengage Learning 2015
41.6 How Do Communities Change Over
Time?
• Pioneer species
– Species that can colonize a new habitat
• Mosses, lichens, and some flowering annuals
– Species often alter the habitat in ways that
allow other species to replace them
(ecological succession)
– First, opportunistic colonizers of new or newly
vacated habitats are pioneer species, which
have high dispersal rates, grow and mature
fast, and produce many offspring
© Cengage Learning 2015
How Do Communities Change Over Time?
• Seeds of later species grow in mats of
pioneers
• Organic wastes and remains accumulate
and help other species take hold
• Later successional species often shade
and eventually displace earlier ones
© Cengage Learning 2015
© Cengage Learning 2015
Figure 20.23
© Cengage Learning 2015
How Do Communities Change Over Time?
• Secondary succession
– A new community develops in a site where
the soil that supported an old community
remains
– In secondary succession, a disturbed area
within a community recovers.
– Occurs in abandoned agricultural fields and
burned forests
© Cengage Learning 2015
How Do Communities Change Over Time?
• Species composition of a community
changes frequently, and unpredictably
– Random events can determine the order in
which species arrive, and affect the course of
succession
– Example: 1980 eruption of Mount Saint
Helens
• Presence of some pioneers helped later-arriving
plants become established
• Other pioneers kept the same late arrivals out
© Cengage Learning 2015
How Do Communities Change Over Time?
• Indicator species are the first to do poorly
when conditions change, so they can
provide an early warning of environmental
degradation
– Example: trout are highly sensitive to
pollutants and cannot tolerate low oxygen
levels
© Cengage Learning 2015
41.7 How Can A Single Species Alter
Community Structure?
• Keystone species
– A species that has a disproportionately large
effect on community structure
– Loss or addition of even one species
(keystone species) may destabilize the
number and abundances of species in a
community
© Cengage Learning 2015
How Can A Single Species Alter
Community Structure?
• Experiment: sea stars in a rocky intertidal
zone in California
– Sea stars prey mainly on mussels and were
removed from experimental plots
– Mussels then crowded out seven other
species of invertebrates
– Conclusion: sea stars are a keystone species
• Normally keep number of prey species high by
preventing competitive exclusion by mussels
© Cengage Learning 2015
How Can A Single Species Alter
Community Structure? (cont’d.)
© Cengage Learning 2015
• Keystone species – Grey Wolf
• 1995: reintroduced; 2009: 116 wolves in park
• Prey on elk and push them to a higher
elevation
– Regrowth of aspen, cottonwoods, and willows
– More beaver dams, more wetlands, more aspens
• Reduced the number of coyotes
– Fewer attacks on cattle
– More smaller mammals
© Cengage Learning 2015
How Can A Single Species Alter
Community Structure?
• Exotic species
– A species that evolved in one community and
later became established in a different one
– Can dramatically alter a natural community
– More than 4,500 50,000 exotic species have
become established in the United States
– Visit the National Invasive Species
Information Center at
www.invasivespeciesinfo.gov
© Cengage Learning 2015
How Can A Single Species Alter Community
Structure?
© Cengage Learning 2015
How Can A Single Species Alter
Community Structure?
• Kudzu native to Asia: overgrowing trees
across the southeastern United States
• Gypsy moths native to Europe and Asia:
feed on oaks through much of the United
States
• Nutrias native to South America: abundant
in freshwater marshes of the Gulf States
© Cengage Learning 2015
41.9 Fighting Foreign Fire Ants
• Red imported fire ants, Solenopsis invicta,
have a venomous sting and disrupt native
wildlife communities
– Pesticides do not control spread
– Biological control involves phorid flies – the
larvae eats its way through the fire ant and
undergoes metamorphosis in its head
– Global climate change is expected to help
RIFAs extend their range in the U.S.
© Cengage Learning 2015
© Cengage Learning 2015
Figure 19.6a
Breeding male fur seals
(thousands)
10
8
6
4
2
0
1915
1925
1935
1945
Year
© Cengage Learning 2015
Figure 19.6
100
Survivors (%)
80
60
40
20
0
20
40
60
80
100
120
Density (beetles/0.5 g flour)
(b) Decreasing survival rates with increasing density in a
population of flour beetles
© Cengage Learning 2015
Figure 19.8b
Average clutch size
12
11
10
9
8
0
10
20
30
40
50
60
70
80
90
Number of breeding pairs
(a) Decreasing birth rate with increasing density in a
population of great tits
© Cengage Learning 2015
Figure 19.8a
41.8 How Many Species Will A Community
Hold?
• Equilibrium model of island biogeography
– The number of species living on any island
reflects a balance between immigration rates
for new species and extinction rates for
established ones
– Colonization rates depend on the distance
between an island and a mainland source of
colonists (distance effect)
– An island’s size affects species richness (area
effect)
© Cengage Learning 2015
How Many Species Will A Community
Hold?
© Cengage Learning 2015
11/26 Friday Schedule
Populations
40
11/28
No Class
12/3
41
12/5
Trophic Levels
Ecology
Succession
Lab Review
12/10 Biomes & Human 43&44 12/12
Effect
Lecture Review
Lab Final Exam
12/17
Make up class if
needed
Final Exam
© Cengage Learning 2015
12/19
42