Chapter 27 Community Interactions - Linn-Benton Community...

Chapter 27 Community Interactions

Learning Goals for Ch. 27

27.1 Why Are Community Interactions Important?

27.2 What Is the Relationship Between the Ecological

Niche and Competition?

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

27.4 What Is Parasitism?

27.5 What is Mutualism?

27.6 How Do Keystone Species Influence Community

Structure?

27.7 Succession: How Do Community Interactions

Cause Change Over Time?

27.1 Why Are Community Interactions Important?

An ecological community consists of all the

interacting populations within an ecosystem

– A community can encompass the entire biotic,

or living, portion of an ecosystem

– Interactions between populations in a community

help limit their size

Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e

Ecological hierarchy

Biosphere

Ecosystem

Community

Population

Organism

Table 27-1

Type of

Interaction Effect on

Species A Effect on

Species B

Competition between A and B Harms Harms

Predation by A on B Benefits Harms

Parasitism by A on B Benefits Harms

Mutualism between A and B Benefits Benefits

27.1 Why Are Community Interactions Important?

An ecological community consists of all the interacting

populations within an ecosystem (continued)

– The process by which two interacting species act as

agents of natural selection on one another is called

coevolution

Co-Evolution Bull Thorn Acacia and Ants

27.1 Why Are Community Interactions Important?

The most important community interactions are:

– Competition, which harms both species

– Predation, which benefits the predator but harms

the prey

– Parasitism, which benefits parasite but harms the

host

– Mutualism, which benefits both species

27.2 What Is the Relationship Between the

Ecological Niche and Competition?

Each species occupies a unique ecological niche that encompasses all aspects of its way of life

– These include:

– Its physical home or habitat

– The physical and chemical environmental factors necessary for its survival, such as nesting sites, climate, and the type of nutrients it needs

– The role that the species performs within an ecosystem, such as what it eats and the other species with which it competes

– Although different species share aspects of their niche with others, no two species ever occupy exactly the same ecological niche within a community

27.2 What Is the Relationship Between the

Ecological Niche and Competition?

Competition occurs whenever two organism

attempt to use the same, limited resources

– Interspecific competition occurs between

members of different species, if they feed on the

same things or require similar breeding areas

– Ex. Cattle and deer

– Ex.Wild horses and Elk

– Ex. Zebra mussels and native mussels

27.2 What Is the Relationship Between the

Ecological Niche and Competition?

Adaptations reduce the overlap of ecological

niches among coexisting species

– The competitive exclusion principle states that

if two species occupy exactly the same niche

with limited resources, one will outcompete the

other

P. aurelia P. caudatum

(a) Grown in separate flasks

(b) Grown in the same flask

Competitive Exclusion

Fig. 27-1

Resource Partitioning

Adaptations reduce the overlap of ecological

niches among coexisting species (continued)

– When species with largely similar ecological

niches coexist and compete, each species

occupies a smaller niche than it would by itself, a

phenomenon called resource partitioning

Resource Partitioning

Ecologist Robert MacArthur explored the competitive

exclusion principle by carefully observing five species

of North American warbler

– These birds all hunt for insects and nest in the same type

of eastern spruce tree

– MacArthur found that each species concentrates its

search for food in specific regions within spruce trees,

employs different hunting tactics, and nests at a slightly

different time

Resource Partitioning

Fig. 27-2

Blackburnian

warbler

Black-throated

green warbler

Cape May

warbler

Bay-breasted

warbler

Yellow-rumped

warbler

Intraspecific Competition

Competition within a species is a major factor controlling population size

– Intraspecific competition, competition between individuals of the same species, is the most intense form of competition

– If resources are limited, this is a major factor controlling population size

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

Predator–prey interactions shape evolutionary adaptations

– Predators eat other organisms; these include herbivores (animals that eat plants) as well as carnivores (animals that eat other animals)

–Predators include a grass-eating pika, a bat hunting a moth, and the more familiar example of a hawk eating a bird

– Predators tend to be less abundant than their prey

Forms of Predation

Fig. 27-3

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

– Bat and moth adaptations provide excellent examples of how body structures and behaviors are molded by competition

– Bats emit high-pitch sound pulses that bounce off their surroundings, allowing them to navigate and detect prey

– Moths (their prey) have evolved ears sensitive to the pitch of sounds the bats emit, and they take evasive actions in response

– The bats, in turn, counter by switching the frequency of their sound pulses away from the moth’s sensitivity range

Bat-Moth Coevolution

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

Camouflage conceals both predators and their

prey

– Camouflage renders animals inconspicuous

even when in plain sight

–Predators and prey have evolved colors,

patterns, and shapes that resemble their

surroundings

Camouflage by Blending In

Fig. 27-4

Camouflage

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

Camouflage conceals both predators and their

prey (continued)

– To avoid detection by predators, some animals

have evolved to resemble objects, such as

leaves, twigs, seaweed, thorns, or even bird

droppings

– Some plants have evolved to resemble rocks to

avoid detection by herbivores

Camouflage by Resembling Specific Objects

Fig. 27-5a, b

Camouflage by Resembling Specific Objects

Fig. 27-5c, d

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

Camouflage conceals both predators and their

prey (continued)

– Camouflage also helps predators ambush their

prey

–Examples include the cheetah blending with

tall grass and the frogfish resembling a rock

Camouflage Assists Predators

Fig. 27-6

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

Bright colors often warn of danger

– Some animals have evolved bright warning

coloration that attracts the attention of potential

predators

–Warning coloration advertises that the animal

is bad-tasting or poisonous before the

predator attacks

–Examples include poison arrow frogs, coral

snakes, and honey bees

Warning Coloration

Fig. 27-7

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

Some prey organisms gain protection through mimicry

– Mimicry refers to when members of one species have

evolved to resemble another species

– Two or more distasteful species may each benefit from a

shared warning coloration pattern (Müllerian mimicry)

– Predators need only experience one distasteful

species to learn to avoid all with that color pattern

– For example, toxic monarch and viceroy butterflies

have similar wing patterns; if a predator becomes ill

from eating one species, it will avoid the other

Mullerian Mimicry

Fig. 27-8

Batesian Mimicry

Fig. 27-9a, b

Batesian Mimicry

Fig. 27-9c, d

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

Some prey organisms gain protection through mimicry (continued)

– Some animals deter predators by employing startle coloration

–These animals may have spots that resemble the eyes of a larger animal

– If a predator gets close, the prey will flash its eyespots, startling the predator and allowing the prey to escape

–Examples include the peacock moth and the swallowtail caterpillar

Startle Coloration

Fig. 27-10

27.3 What Are the Results of Interactions Between

Predators and Their Prey?

Predators may use mimicry to attract prey

– In aggressive mimicry, a predator resembles a

harmless animal or part of the environment, to

lure prey within striking distance

–For example, a frogfish dangles a wriggling

lure that attracts a curious fish that is then

eaten

Aggressive Mimicry

Fig. 27-6b

Predators and prey may engage in chemical

warfare

– Predators and prey use toxins for attack and

defense

–The bombardier beetle sprays boiling-hot

chemicals from its abdomen onto its attacker

Chemical Warfare

Fig. 27-12a

Predators and prey may engage in chemical

warfare for attack and defense (continued)

– Many plants have evolved chemical adaptations

that deter their herbivore predators, such as the

milkweed

– In the case of the milkweed, however,

monarch butterfly caterpillars have evolved to

tolerate the toxins and store them in their

tissues as a defense against predation

Chemical Warfare

Fig. 27-12b

Parasites live in or on their prey, which are

called hosts, usually harming or weakening

them but not immediately killing them

– Parasites are generally much smaller and more

numerous than their hosts

–Examples include tapeworms, fleas, ticks, and

many types of disease-causing protists,

bacteria, and viruses

Social parasites!

Animals that take advantage of the social

behavior of a host to complete their life cycle.

27.5 What Is Mutualism?

Mutualism refers to interactions between

species in which both benefit

–For example, lichens form a mutualistic

relationship between a fungus and an algae

–The fungus provides support and protection

while obtaining food from the

photosynthetic alga

Not Moss but Lichen

27.5 What Is Mutualism?

Mutualism refers to interactions between

species in which both benefit (continued)

– Another example of mutualism is the clownfish

and sea anemones

–The clownfish takes shelter from predators

among the venomous tentacles of an

anemone, while in turn cleaning it, providing it

with scraps of food, and defending it from

predators

Mutualism

Fig. 27-13b

Mutualisms

Obligatory:

Yucca plants and

Yucca moths

27.6 How Do Keystone Species Influence

Community Structure?

In some communities, a keystone species plays a major role in determining community structure

– A keystone species role is out of proportion to its abundance in the community

– If a keystone species is removed from the community, normal community interactions are significantly altered and the relative abundance of other species changes dramatically

– Keystone species need to be identified and protected so that human activities do not lead to the collapse of entire communities and ecosystems

Keystone Species

Fig. 27-14a

Sea Otter as a Keystone Species