Evolution and Community Ecology

5Evolution and Community EcologyC

HA

PT

ER

Black and White, and Spread All Over

• Zebra mussels and quagga mussels were accidentally introduced into Lake St. Clair in the late 1980s. This means they are NON-NATIVE.

• They have since spread throughout the Great Lakes system and connecting rivers. This means they are INVASIVE.

• The invasive mussels have a high economic and ecological cost.

Talk About It The Great Lakes are home to more than 20 native mussel species. Why are the zebra and quagga mussels so much more destructive than the lakes’ native mussels?

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

• 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


A starting population of fish. Genes control the color and pattern of the fish’s scales.

Mechanisms of Biological Evolution: Mutation and Migration

Mutation


Accidental change in DNA that can give rise to variation among individuals

Migration (gene flow)

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

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 and reproduction are passed on more frequently than those that are not

Conditions of Natural Selection


(1) Organisms produce more offspring than can survive.

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

(3) Individuals vary in fitness, or reproductive success.

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

Artificial Selection


• Selection under human direction

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

Speciation


• Process by which new species are generated

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

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

Extinction


• 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.

TrilobitesMarine 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 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.


Resource Partitioning

Symbiosis-describes a long lasting relationship between species, in which at least one species benefits

• 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.


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: One organism (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 two or more species benefit

• Commensalism: a relationship in which one 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 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.


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)


California Condor

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

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 about10% of the energy available at any trophic level is passed to the next; most of the rest is lost to the environment as heat.


Pyramid of Energy

Numbers and Biomass in Communities

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

• In general, there are more organisms and greater biomass at lower trophic levels than at 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 a keystone species can significantly alter the structure of a 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


• 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


• Occurs when there are no traces of the original community remaining, including vegetation and soil

• Pioneer species, such as lichens and mosses, are the first to colonize.

• The environment changes as new species move in, adding nutrients and generating habitat.

Secondary Succession


• 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

Succession in Water


• 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


• 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


• 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.

Documents

Evolution and Community Ecology