evolution and community r 5 ecologymail.faribault.k12.mn.us/~tricia_johnson/s00cf9ea7.4/chapter 5...

5 Evolution and Community Ecology C

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Lesson 5.1 Evolution

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

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Evolution (change over time) and Natural Selection

• Gene: Sequence of DNA that codes for a particular trait

• Gene pool: All the genes present in a pop

• Biological evolution: change in a pop’s gene pool over time


A starting population of fish. Genes control

the color and pattern of the fish’s scales.



Mechanisms of Biological Evolution: Mutation and Migration

Mutation


Change in DNA that can

give rise to variation among

indivs

Migration (gene flow)

Movt of individuals into

(immigration) or out of (emigration)

a pop—changes gene pool (gene

flow)



Mechanisms of Biological Evolution: Genetic Drift and

Natural Selection


Genetic Drift Natural Selection

Evolution that occurs by chance Process by which traits useful for survival & reprod are passed on more frequently than those that are not

Conditions of Natural Selection






(1) Organisms

produce more

offspring than

can survive—

struggle for

existence

(2) Indivs vary in

characteristics, some

of which are heritable.

(3) Indivs vary in

fitness, or reproductive

success. (adaptations

increase org fitness

level) Did You Know? Darwin privately researched natural selection for two decades before publishing On the Origin of Species.

Artificial Selection


• Selection under human direction

• Chosen & bred animals & plants with beneficial

traits.

Speciation Lesson 5.1 Evolution



• Process by which

new species are

generated

• Can occur in a

number of different

ways; the most

important way is

called allopatric

speciation

(geographic sep of

pops)

• Has resulted in every

form of life on Earth—

today & in the past

Allopatric Speciation

Extinction


• Disappearance of species

from Earth

• Generally occurs gradually,

1 species at a time, when

envtal conditions change

more rapidly than species

can adapt

• 5 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


• Describes org’s use of resources & functional role in a

community

• Affected by an organism’s tolerance—its ability to survive &

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.


Predation (+/–)

• Predator hunts, kills, & consumes prey

• Causes cycles in predatory & prey population sizes

• Defensive traits: camouflage, mimicry, & warning coloration have evolved in response to predator-prey interactions.

• Some predator-prey relationships are ex of coevolution, the process by which 2 species evolve in response to changes in each other.


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 (+/–)


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: 1 org (the

parasite) relies on

another (the host) for

nourishment or for some

other benefit

• Herbivory: An animal

feeding on a plant

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


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 2 or

more species benefit

• Commensalism: a

relationship in which 1

species benefits while

the other is unaffected Lichen: a symbiotic relationship

between a fungus and a photosynthetic partner, such as an alga

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 NRG from

sun/chemicals & store it in the bonds of sugars, making it available to rest of community

• NRG from the sun is captured by plants, algae, or bacteria thru photosynthesis.

• NRG from chemicals captured by some bacteria thru chemosynthesis.


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 NRG & nutrients

• Herbivores: plant-eaters

• Carnivores: meat-eaters

• Omnivores: combo-eaters

• Detritivores and decomposers: recycle nutrients w/in the ecosystem by breaking down nonliving organic matter

•Use oxygen to break bonds in sugar & release its NRG thru cellular respiration (primary producers do this, too)


California Condor

Did You Know? Scavengers, such as vultures and condors, are just large detritivores.



Energy in Communities

• Organism’s rank in a feeding hierarchy is its trophic level.

• Primary producers always occupy 1st trophic level of any community.

• In general, only about 10% of the NRG avail at any trophic level is passed to the next; most of the rest is lost to the envt as heat.


Pyramid of Energy

Numbers & Biomass in Communities

• A trophic level’s biomass = mass of living tissue it contains.

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


Food Chains

and Webs

• Food chain: Linear series of feeding relationships

• Food web: Shows the overlapping and interconnected food chains present in a community




• Species that have strong and/or wide-reaching effects on a community

• Removal of keystone species can significantly alter the structure of community.

Keystone Species


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

Ecological Disturbances


• Community in equilibrium is generally stable & balanced, w/ most populations at/or around carrying capacity.

• Disturbances/changes in envt can throw a community into disequilibrium.

• Severe disturbances cause permanent changes to a community & initiate a predictable series of changes = succession.

Forest fire

Primary Succession


• No traces of the original community remaining, including vegetation and soil

• Pioneer species (lichens):1st to colonize.

• Envt changes as new species move in, adding nutrients & generating habitat.

Secondary Succession


• Occurs when 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

Succession in Water


• Primary aquatic succession occurs when an area fills w/ water for the 1st time.

• Disturbances such as floods or excess nutrient runoff can lead to secondary aquatic succession.

Climax Communities


• Ecologists once thought succession leads to stable “climax” communities.

• Today, ecologists see communities as temporary, ever-changing associations of species.

• Communities influenced by many factors & constant disturbances.

Beech-maple forest, a classic “climax community”

Invasive Species


• 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.

Did You Know? Although the European honeybee is

invasive to North America, it is beneficial because it pollinates our agricultural crops.

evolution and community r 5 ecologymail.faribault.k12.mn.us/~tricia_johnson/s00cf9ea7.4/chapter 5...

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