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Chapter 3

Lecture

Outline

CASE STUDY:Darwin's Voyage of Discovery

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When I view all beings not as special creations, but as lineal descendents of some few beings which have lived long before the first bed of the Cambrian system was deposited, they seem to me to become ennobled.

–Charles Darwin

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Galápagos Islands

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3.1 Evolution Leads to Diversity– Acclimation – a non-permanent change that

occurs during an individual’s lifetime

– Adaptation, the acquisition of traits that allow a species to survive in its environment, is one of the most important concepts in biology.

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Evolution by Natural Selection

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The process of the fittest individuals passing their

traits to the next generation more successfully is

called natural selection.

Natural Selection Acts on Traits in the DNA

• Where do the traits come from that make some individuals more successful?

• Changes to the DNA of individuals, called mutations, occur and these changes are inherited by offspring.

• Some are positive and some negative.

• During the lifespan of a species, many mutations accumulate to give individuals of that species an advantage over other individuals.

• The end result is a species population that differs from those of numerous preceding generations.

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All Species Live Within Limits

• Environmental factors exert selection pressure and influence the fitness of individuals and their offspring.

• An organism’s physiology and behavior allow it to survive only in certain environments.

• Each environmental factor has both minimum and maximum levels, called tolerance limits, beyond which a particular species cannot survive or is unable to reproduce.

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Freezing Temps Limit the Northern Range of the Saguaro Cactus

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Florida Invasive Python Problem: Learn its limits and control its spread

The Ecological Niche is a Species’ Role in the 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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Species Respond to Limits Differently:r- and K-selected Species

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The Competitive Exclusion Principle

• The competitive exclusion principle states that no two species can occupy the same ecological niche for long.

– The one that is more efficient in using available resources will exclude the other.

– We call this process of niche evolution resource partitioning.

• Partitioning can allow several species to utilize different parts of the same resource or feed at different times in order to coexist within a single habitat without directly competing.

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Warblers Partition Their Resource to Reduce Competition

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Graphical Models of The Competitive Exclusion Principle & Resource Partitioning

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• The development of a new species is called speciation.

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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Three Patterns of Species Divergence

– From an original range of characteristics, the shift can be toward an extreme of the trait (directional selection),

– The shift can narrow the range of a trait (stabilizing selection),

– Or it can cause traits to diverge to the extremes (disruptive selection).

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Taxonomy Describes RelationshipsAmong Species

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• Taxonomy is the study of types of organisms and their relationships.

• Scientists communicate about species using these scientific names instead of common names (e.g., buttercup or bluebell), to avoid confusion. A common name can refer to any number of species in different places, and a single species might have many common names.

The Taxonomic Hierarchy

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Taxonomy Describes RelationshipsAmong Species

• Taxonomic relationships among species are displayed like a family tree.

• Using this display technique, one can trace how organisms have descended from common ancestors.

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3.2 Species Interactions ShapeCommunities of Species

• Competition leads to resource allocation

– 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

• Herbivores, carnivores, and omnivores, which feed on live prey, are predators.

• Even pathogens (disease-causing organisms) can be considered predator organisms.

• Predation is a powerful but complex influence on species populations in communities.

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Predatory Relationships may Change with Life Stage

• In marine ecosystems, crustaceans begin as floating plankton.

• Planktonic animals eat each other and are food for larger carnivores, including fish.

• As prey species mature, their predators change.

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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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Prey Defense Mechanisms:Batesian & Mullerian Mimicry

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Prey Defense Mechanisms: Camouflage

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Symbiosis: Intimate Relations Among Species

• Symbiosis is a process where two or more species live intimately together, with their fates linked.

• There are three major types of symbiotic relationships among species:

– Mutualism: both partners benefit

– Commensalism: one partner benefits while the other neither benefits nor is harmed

– Parasitism: one partner benefits while the other is harmed (a type of predation)

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Types of Symbiosis: Intimate Relations Among Species

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Keystone Species

• A keystone species plays a critical role in a biological community.

• They exert their influence by changing competitive relationships.

• They help maintain balance in an ecosystem.

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Monterey Bay, California

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Keystone Species

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3.4 Properties of Communities Dependon Species Diversity

• Diversity and abundance defined:

– Diversity is the number of different species per unit area. Diversity is important because it indicates the variety of ecological niches and genetic variation in a community.

– Abundance refers to the number of individuals of a species in an area.

• Diversity and abundance are often related.

– Communities with high diversity often have few individuals of any one species.

– Most communities contain a few common species and many rarer ones.

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Individuals in Communitiesare 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 Can Also Be Distributed Vertically

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3.5 Communities Are Dynamic andChange Over Time

• Primary succession-Land that is bare of soil—a sandbar, mudslide, rock face, volcanic flow—is colonized by living organisms where none lived before.

• Pioneer species-the first species to colonize a community in primary succession on land.

• Secondary succession-After a disturbance, if left undisturbed, a community will mature to a characteristic set of organisms.

• Climax community-The community that developed last and lasted the longest.

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Primary Ecological Succession

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