Ecosystems

Part 2

Edge effects

How the local environment changes along the boundary or edge in a habitat

Caused by: natural events (tree fall) humans (deforestation)

Results: Changes in species composition and

diversity

Vocabulary

Interior species: can only live in the undisturbed core of a habitat

Edge species: can live in edge habitats Open community: edge is gradual or

has indistinct boundaries which many species cross over

Closed community: community is sharply devided from its neighbors

U.S. Roads

3.9 million miles of public roads in the United States.

Wildlife and highways

Road kill – animals that are killed by being run over by cars each year

Millions of animals die each year Have a significant

impact on populations

Costs $8 billion per year

Wildlife crossings:bridges and tunnels

Ecosystem diversity

Involves: Biodiversity Natural selection Evolution Ecosystem services

Biodiversity

Attempts to describe diversity of life at three levels: Genetic – range of all genetic traits in a

population Species – number of different species

that inhabit a different area Estimated between 10 and 30 million

species on Earth Named around 1.5 million

Ecosystem – the range of habitats that can be found in a defined area

Biodiversity

Increases Diverse habitats Moderate disturbance

in the habitat Environmental

conditions with low variation

Trophic levels with high diversity

Middle states of succession

Evolution

Decreases Extreme stress Extreme

environments Extreme limitations in

the supply of a fundamental resource

Extreme amounts of disturbance

Introduction of species from other areas

Geographic isolation

Natural Selection

The mechanism of how organisms evolve

Works on the individual level by determining which organisms survive and reproduce

The range of genetic variation in a population determines if the species

Natural Selection

“Survival of the fittest” Fittest = how many babies you have

who go on to have babies New genes enter the population

through mutation

Natural selection

Types of selection Stabilizing Directional Disruptive

Stabilizing Selection

Selects against the extremes of a population

Most common form of natural selection

Results: Decreased

diversity Maintenance of a

stable gene pool No evolution

Directional Selection

Affects one extreme of a population

Gives an advantage to other extreme

Results Change in

population characteristics

Can lead to evolution of a new species

Disruptive Selection

Acts against the individuals in the middle

Favors both extremes

Results: Splitting of

population into two smaller populations

Results in evolution of two new species

Evolution

Change in the genetic composition of a population over successive generations

Supported by evidence from: Fossil record Genetics Homologous traits Embryological similarities Computer models

Speciation

Results when segments of a population becomes isolated so gene flow stops

The isolated populations eventually become new species

Maintaining gene flow

Some species of spiders balloon to disperse through the environment

They let out a long strand of silk which is caught by air currents and transports them over long distances

Patterns in Evolution (A) Divergent (adaptive radiation) – similar species

become less similar (B) Convergent – Unlike species evolve similar

(analogous) traits while evolving in separate ecosystems

(C) Parallel – Two independent species evolve at the same time, in the same ecosystem, and acquire similar traits

Convergent Evolution

Adaptive Radiation

Parallel Evolution

Gradualism vs. Punctuated Equilibrium

Gradualism Views evolution as

slow, stepwise development of species over a long period of time

Punctuated Equilibrium Proposes some

species arose suddenly in a short period of time after long periods of stability

Ecosystem services

Things the environment does for us for free.

Includes but not limited to: Moderate weather extremes and their

impacts Disperse seeds Mitigate droughts and floods Cycle and move nutrients Detoxify and decompose waste Purify air and water