Transcript Keystone species

Chapter 3
Lecture
Outline
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Learning Outcomes
After studying this chapter, you should be able to answer the following
questions:
• How does species diversity arise?
• Why do species live in different locations?
• How do interactions among species affect their fates and
that of communities?
• If a species has unlimited growth potential, why doesn’t it fi
ll the earth?
• What special properties does a community of species have,
and why are they
important?
• What is the relationship between species diversity and
community stability?
• What is disturbance, and how does it affect communities?
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3.1 Evolution Leads to Diversity
• Natural selection and adaptation modify
species
– Adaptation, the acquisition of traits that allow a
species to survive in its environment, is one of the
most important concepts in biology.
– The process of better-selected individuals passing
their traits to the next generation is called natural
selection.
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The ecological niche is a species’ role
and environment
• Habitat describes the
place or set of
environmental conditions
in which a particular
organism lives.
• Ecological niche,
describes both the role
played by a species in a
biological community and
the total set of
environmental factors
that determine a species
distribution.
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Niches: generalists & specialists
• Generalists have a
broad niche, like
cockroaches.
• Specialists have
narrow niches, like
giant pandas.
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Competitive exclusion principle &
Resource partitioning
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The competitive exclusion principle
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Speciation
• The development of a new species is called
speciation.
• Geographic isolation results in allopatric
speciation—species arise in non-overlapping
geographic locations.
• Behavioral isolation results in sympatric
speciation—species arise in the same location as the
ancestor species.
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Directional, stabilizing, and
disruptive selection
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Geographic
isolation is a
mechanism in
allopatric
speciation.
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Taxonomy
• Taxonomy is the study of types of organisms and their
relationships.
• Genus and species compose binomials, Also called scientific
or Latin names.
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Taxonomy describes relationships
among species
• With taxonomy you
can trace how
organisms have
descended from
common ancestors.
• Taxonomic
relationships among
species are displayed
like a family tree.
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3.2 Species Interactions Shape
Communities of Species
• Competition is a type of
antagonistic
relationship within a
biological community.
• Organisms compete for
resources that are in
limited supply.
• Competition among
members of the same
species is called
intraspecific
competition.
• Competition between
members of different
species is called
interspecific
competition.
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Predation affects species relationships
• Consumers include herbivores, carnivores, omnivores,
scavengers, detritivores, and decomposers.
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Some adaptations help avoid predation
• Toxic chemicals, body armor, extraordinary speed,
and the ability to hide are a few strategies organisms
use to protect themselves.
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Coevolution
• The response of predator to prey and vice versa, over
tens of thousands of years, produces physical and
behavioral changes in a process known as
coevolution.
• Coevolution can be mutually beneficial: many plants
and pollinators have forms and behaviors that benefit
each other.
• A classic case is that of fruit bats, which pollinate and
disperse seeds of fruit-bearing tropical plants.
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Prey Defense Mechanisms:
Batesian & Mullerian mimicry
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Prey Defense Mechanisms:
Camouflage
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Types of Symbiosis: Intimate relations
among species
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Types of Symbiosis:
Intimate relations among species
• Commensalism is a type of symbiosis in which one member clearly
benefits and the other apparently is neither benefited nor harmed.
• Mutualism is a type of symbiosis in which both members clearly benefit.
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Keystone species
• A keystone species plays a critical role in a
biological community
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3.3 The Growth of Species Populations
• Biotic potential— the amount of potential growth
of a population with unrestrained biological
reproduction.
• Exponential (r) growth is population growth with
no limits; it results in a “J” growth curve when
graphed.
• Logistic growth curves result from carrying capacity
(K) limiting population growth; it results in a “S”
shaped growth curve when graphed.
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J curve of exponential growth
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Population cycles
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S curve of logistic growth
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Limits to population size
• Density-dependent, meaning as population size
increases, the effect intensifies. With a larger
population, there is an increased risk that disease
or parasites will spread, or that predators will be
attracted to the area.
• Density-independent limits to population are often
nonbiological, capricious acts of nature. A
population is affected no matter what its size.
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Species respond to limits differently:
r- and K-selected species
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Survivorship curves
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3.4 Properties of Communities Depend
on Species Diversity
• Diversity and abundance
– Diversity is the number of different species per unit
area.
– Abundance refers to the number of individuals of a
species in an area.
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Species patterns create community
structure
• Boundaries of species populations and
communities form patterns that fit together:
– (1) individuals and species are spaced throughout
communities in different ways;
– (2) the communities themselves are arranged over a
large geographic area or landscape
– (3) communities have relatively uniform interiors
(“cores”) and also “edges” that meet.
• Community (or ecological) structure refers to these
patterns of spatial distribution of individuals,
species, and communities.
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Individuals in communities
are distributed in various ways
• Random patterns arise from random distribution of
resources.
• Uniform patterns usually arise from competition.
• Cluster patterns help a species protect themselves.
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Communities are distributed
in patterns across a landscape
• Core habitat-a mostly uniform environment big
enough to support nearly all the plants and animals
that are typically found in that community.
• Ecotone-or border between two communities, rich
in species.
• Edge effects-where communities meet, the
environmental conditions blend and the species and
microclimate of one community can penetrate the
other. .
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3.5 Communities Are Dynamic and
Change Over Time
• Climax community-The community that developed last and
lasted the longest.
• Primary succession- land that is bare of soil—a sandbar,
mudslide, rock face, volcanic flow—is colonized by living
organisms where none lived before.
• Secondary succession-after a disturbance, if left undisturbed, a
community will mature to a characteristic set of organisms.
• Pioneer species-the first species to colonize a community in
primary succession on land.
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Practice Quiz
1. Explain how tolerance limits to environmental factors determine
distribution of a highly specialized species such as the saguaro cactus.
2. Productivity, diversity, complexity, resilience, and structure are exhibited to
some extent by all communities and ecosystems. Describe how these
characteristics apply to the ecosystem in which you live.
3. Define selective pressure and describe one example that has
affected species where you live.
4. Define keystone species and explain their importance in community
structure and function.
5. The most intense interactions often occur between individuals
of the same species. What concept discussed in this chapter
can be used to explain this phenomenon?
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Practice Quiz continued
6. Explain how predators affect the adaptations of their prey.
7. Competition for a limited quantity of resources occurs in all
ecosystems. This competition can be interspecific or intraspecific.
Explain some of the ways an organism might deal with
these different types of competition.
8. Describe the process of succession that occurs after a forest
fire destroys an existing biological community. Why may
periodic fire be beneficial to a community?
9. Which world ecosystems are most productive in terms of biomass
( fig. 3.31 )? Which are least productive? What units are
used in this figure to quantify biomass accumulation?
10. Discuss the dangers posed to existing community members
when new species are introduced into ecosystems.
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