5

Evolution and Community Ecology

CHAPTER

Black and White, and Spread �All Over

• Zebra mussels and quagga mussels were accidentally introduced into Lake St. Clair in the late 1980s.
• They have since spread throughout the Great Lakes system and connecting rivers.
• The invasive mussels have a high economic and ecological cost.

Other invasive species in our area of the world:

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Japanese honeysuckle

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Japanese kudzu

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Asian carp

Examples of Invasive Species

Lesson 5.1 Evolution

Scientists have identified and described �over 1.5 million species. Millions more �have yet to be discovered.

Evolution and Natural Selection

Evolution is simply change over time

Gene: A sequence of DNA that codes for a particular trait

Gene pool: All the genes present in a population

Biological evolution: The change in a population’s gene pool over time

Lesson 5.1 Evolution

4 primary mechanisms of evolution!!

• Mutation
• Migration
• Genetic drift
• Natural Selection

Lesson 5.1 Evolution

Mechanisms of Biological Evolution: Mutation and Migration

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1. Mutation

Lesson 5.1 Evolution

Accidental change in DNA that can give rise to variation among individuals. Can be passed on to new generation

2. Migration (gene flow)

Movement of individuals into (immigration) or out of (emigration) a population

Mechanisms of Biological Evolution: Genetic Drift and Natural Selection

Lesson 5.1 Evolution

3. Genetic Drift

4. Natural Selection

Evolution that occurs by chance (luck)

Ex: fishing net kills or separates fish, bugs get squashed.

Process by which traits useful for survival and reproduction are passed on more frequently than those that are not

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Conditions of Natural Selection

Lesson 5.1 Evolution

1. Organisms produce more offspring than can survive. “struggle for existence”

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2. Individuals vary in characteristics, some of which are heritable.

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3. Individuals vary in fitness, or reproductive

Success.

SURVIVAL OF THE FITTEST!

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Video - Natural Selection stated clearly.

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• http://biologyinmotion.com/evol/index.html

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http://evolution.berkeley.edu/evolibrary/article/evo_30

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http://science.discovery.com/games-and-interactives/charles-darwin-game.htm

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Artificial Selection

Lesson 5.1 Evolution

Selection under human direction

Throughout history, humans have chosen and bred animals and plants with beneficial traits.

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Speciation

Lesson 5.1 Evolution

• Process by which new species are generated

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• Can occur in a number of different ways; the most important way is called allopatric speciation :geographic separation

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• Has resulted in every form of life on Earth— today and in the past

Allopatric Speciation

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Extinction

Lesson 5.1 Evolution

The disappearance of species from Earth

Generally occurs gradually, one species at a time, when environmental conditions change more rapidly than the species can adapt

There are five known mass extinction events, each of which wiped out a large proportion of Earth’s species.

Did You Know? During the Permo-Triassic extinction 250 million years ago, 70% of all land species and 90% of all marine species went extinct.

Trilobites

Marine arthropods that went extinct at the end of the Permian period.

Lesson 5.2 Species Interactions

The zebra mussel has completely displaced 20 native mussel species in Lake St. Clair.

The Niche

Lesson 5.2 Species Interactions

• Describes an organism’s use of resources and functional role in a community
• Affected by an organism’s tolerance—its ability to survive and reproduce under changing environmental conditions
• Often restricted by competition

Competition

• Organisms compete when they seek the same limited resource.
• In rare cases, one species can entirely exclude another from using resources.
• To reduce competition, species often partition resources, which can lead to character displacement.

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Lesson 5.2 Species Interactions

Competition

• Competitive exclusion: one species can entirely exclude another from using resources.
• Ex: zebra mussels out compete mussels in lake Erie
• Resource Partitioning: Species divide common resources by specializing Ex: eat different types of seeds, becoming more active in the morning or night

Lesson 5.2 Species Interactions

Competition

• Realized niche: niche restricted by competition. Species adjust to one another
• Fundamental niche: full niche of a species

Lesson 5.2 Species Interactions

Competition

• Character displacement: result of resource partitioning. Evolution of physical characteristics among competing species reflect new roles (natural selection)

Lesson 5.2 Species Interactions

Symbiotic relationship: essential for organisms and ecosystems to maintain balance

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Close interactions between 2 or more different species.

Predation (+/–)

• The process by which a predator hunts, kills, and consumes prey
• Causes cycles in predatory and prey population sizes
• Defensive traits such as camouflage, mimicry, and warning coloration have evolved in response to predator-prey interactions.
• Some predator-prey relationships are examples of coevolution, the process by which two species evolve in response to changes in each other.

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Lesson 5.2 Species Interactions

Did You Know? A single rough-skinned newt contains enough poison to kill 100 people. Unfortunately for the newt, its predator, the common garter snake, has coevolved resistance to the toxin.

Rough-Skinned Newt

Parasitism and Herbivory (+/–)

Lesson 5.2 Species Interactions

Did You Know? One study of Pacific estuaries suggests that parasites play an important role in keeping these ecosystems healthy by controlling host populations.

Hookworm (a parasite)

• Parasitism: One organism (the parasite) relies on another (the host) for nourishment or for some other benefit

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• Herbivory: An animal feeding on a plant

Mutualism (+/+) and Commensalism (+/0)

Lesson 5.2 Species Interactions

Did You Know? Symbiosis describes a long-lasting and physically close relationship between species in which at least one species benefits.

• Mutualism: a relationship in which two or more species benefit
• Ex: bee and flower, bacteria and human

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Commensalism: a relationship in which one species benefits while the other is unaffected ex:Remora Fish and Sharks, barnacles and whales

Lichen: a symbiotic relationship between a fungus and a photosynthetic partner, such as an alga

Competition is a -/- relationship.

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Species Interactions National Geographic Website

Lesson 5.3 Ecological Communities

The sun provides the energy for almost all of the ecological communities and species interactions on Earth.

Primary Producers (Autotrophs)

• Capture energy from the sun or from chemicals and store it in the bonds of sugars, making it available to the rest of the community
• Energy from the sun is captured by plants, algae, or bacteria through photosynthesis.
• Energy from chemicals is captured by some bacteria through chemosynthesis.

Lesson 5.3 Ecological Communities

Did You Know? Deep-sea vents, far from sunlight, support entire communities of fish, clams, and other sea animals, which depend on energy converted through chemosynthesis.

Consumers (Heterotrophs)

• Rely on other organisms for energy and nutrients
• Herbivores: plant-eaters
• Carnivores: meat-eaters
• Omnivores: combination-eaters
• Detritivores and decomposers: recycle nutrients within the ecosystem by breaking down nonliving organic matter
• Use oxygen to break bonds in sugar and release its energy through cellular respiration (primary producers do this, too)

Lesson 5.3 Ecological Communities

California Condor

--The decomposers can either be classified into two group: fungi and detritivores.

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Energy in Communities

• An organism’s rank in a feeding hierarchy is its trophic level.
• Primary producers always occupy the first trophic level of any community.
• In general, only about�10% of the energy available at any trophic level is passed to the next; most of the rest is lost to the environment as heat.

Lesson 5.3 Ecological Communities

Pyramid of Energy

Numbers and Biomass in Communities

• A trophic levels biomass is the mass of living tissue it contains.

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• In general, there are more organisms and greater biomass at lower trophic levels than at higher ones.

Lesson 5.3 Ecological Communities

Food Chains� and Webs

• Food chain: Linear series of feeding relationships
• Food web: Shows the overlapping and interconnected food chains present in a community

Lesson 5.3 Ecological Communities

• Species that have strong and/or wide-reaching effects on a community
• Removal of a keystone species can significantly alter the structure of a community.

Beavers as engineers video

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Keystone Species

Lesson 5.3 Ecological Communities

Wolves of Yellowstone Activity. Use the handout to guide you through the Wolves of Yellowstone activity.

Video link

Lesson 5.4 Community Stability

A 2010 report on invasive species suggests that they cost the U.S. $120 billion a year in environmental losses and damages.

Invasive kudzu

VIDEO

Ecological Disturbances

Lesson 5.4 Community Stability

• A community in equilibrium is generally stable and balanced, with most populations at or around carrying capacity.
• Disturbances or changes in the environment can throw a community into disequilibrium.
• Severe disturbances can cause permanent changes to a community and initiate a predictable series of changes called succession.

Forest fire

Primary Succession

Lesson 5.4 Community Stability

• Occurs when there are no traces of the original community remaining, including vegetation and soil
• Pioneer species, such as lichens, are the first to colonize.
• The environment changes as new species move in, adding nutrients and generating habitat.

Secondary Succession

Lesson 5.4 Community Stability

• Occurs when a disturbance dramatically alters a community but does not completely destroy it
• Common after disturbances such as fire, logging, or farming
• Occurs significantly faster than primary succession video

Succession in Water

Lesson 5.4 Community Stability

• Primary aquatic succession occurs when an area fills with water for the first time.
• Disturbances such as floods or excess nutrient runoff can lead to secondary aquatic succession.

Climax Communities

Lesson 5.4 Community Stability

• Ecologists once thought succession leads to stable “climax” communities.
• Today, ecologists see communities as temporary, ever-changing associations of species.
• Communities are influenced by many factors and constant disturbances.

Beech-maple forest, a classic “climax community”

Invasive Species

Lesson 5.4 Community Stability

• Nonnative organisms that spread widely in a community
• A lack of limiting factors such as predators, parasites, or competitors enables their population to grow unchecked.
• Not all invasive species are harmful.

Video

Video

Did You Know? Although the European honeybee is invasive to North America, it is beneficial because it pollinates our agricultural crops.