Ecosystems and Evolutionary Change

Environmental Sciences: Towards a Sustainable Future Chapter 4 Part 2

This Lesson Discusses Those Factors That Contribute to Ecosystem Change Change is inevitable. Adaptations, natural selection and

sexual reproduction are the tools of change.

Differential vulnerability of each species to environmental change.

Change on a geological time scale.

Selection of Traits and Genes: Definitions DNA: molecule that carries the

genetic code of an organism Chromosome: structure on which

DNA of an organism is arranged

Selection of Traits and Genes: Definitions Gene: segment of DNA that codes for

a particular protein Allele: form of a gene. Each person

carries 2 alleles for each gene Trait: certain characteristic of an

organism; e.g., hair color, disease resistance, intelligence

The Link Between DNA and Traits

Selection by the Environment Genetic variation: genetic differences

that exist among individuals Gene pool: sum total of all the genes

that exist among individuals of a species

Selection by the Environment is “Natural Selection”

Differential reproductive success (or “fitness” in Darwinian terms): some individuals in the population survive to reproduce more than others

Change Through Selected Breedingis “Artificial Selection”

Selected breeding: artificial selection e.g., selection for

dogs with shorter legs

Corn for higher yeilds even with overcrowding

Process is repeated in subsequent generations

Change Through Natural Selection Factors of environmental resistance act as

selective pressures Natural selection: the process by which

evolution occurs Individuals which possess certain traits

can produce more viable offspring than individuals lacking those traits and continue their gene line, while others who are less adapted die off

Recipe for Change

GENES ENVIRONMENT

ADAPTATIONS

NATURAL SELECTION:For? or Against?

Adaptations

Adaptations

Selective Pressure

Genetic Variation Generated by sexual reproduction Each gamete (sperm and egg) carries

one set of alleles Fertilization or the union of sperm and

egg results in the combination of both sets of alleles = unique individual

Genetic Variation in Eye Color

Genetic Variation in Eye Color

Genetic Variation Mutation: any inheritable change in

the DNA molecule. Lethal mutation: results in death of

organism.

Genetic Variation Neutral mutation: neither harms nor

benefits organism. Mutations are rare and random events.

Spontaneous Induced

Speciation (Evolution) Process by which separate populations

of a single species develop into distinct species.

Must have geographic separation (to prevent interbreeding) and have different selective pressures in the new environment.

Speciation Populations of a given species become

isolated from each other. No interbreeding between populations

occurs.

Speciation: Foxes

Speciation: Galapagos Finches

Developing Ecosystems All ecosystems have the same

functional “parts”. Only the “actors” who play these parts are different across ecosystems.

Example: Buffalo vs. Kangaroo

Developing Ecosystems Why have species evolved so

differently across ecosystems with similar environmental conditions? (Hint: remember the recipe for change.)

The Limits of Change New selective pressures require

species to: adapt migrate or go extinct.

The Limits of Change Factors affecting species’ adaptation

to environmental change: Geographical distribution. Habitat specialization. Genetic variation. Size of individual. Reproductive rate.

Will The Panda Survive In A Changing Environment?

Evolution Natural selection occurs slowly vs. Punctuated equilibrium theory: model of

evolution in which there is little change in a balanced ecosystem. A shift in the environmental conditions will alter selective pressures, thereby causing rapid changes in the species until balance is restored.

Geological Time Scale

Drifting Continents

250 million years ago

Today

Plate Tectonics

Plate Tectonics Tectonic plates: slabs of rock that

make up the earth’s surface; 14 major plates

Tectonic plates move approximately 6cm per year

4 basic tectonic plate interactions

Divergent Boundaries Rising convection currents of hot less

dense magma force apart plates Result: mid-ocean ridges, rift valleys

Transform Boundaries Two plates slide

past each other Result: fault lines

marking major earthquake activity; San Andreas fault in California

Convergent Boundaries Ocean-Continental Plates moving toward each other Result: dense oceanic plate moves under a

continental plate creating subduction zone, oceanic trench and volcanic activity; like Cascade mountains of California

Convergent Boundaries Continental-Continental Collision

Formation of mountain ranges like Himilayas, Alps etc.

http://www.hcrhs.hunterdon.k12.nj.us/science/helen.html

What happened when Mount St.Helens erupted?

Convergent Boundaries Ocean-Ocean Collision Create subduction zones, oceanic trenches and

underwater volcanoes, often resulting is island chains (island arcs)

Tectonic Movement has dramatic Climatic Effects Changing position on earth’s surface

isolates or connect new communities Movements alter ocean currents Mountain formation alters air currents Geological Activity along boundary

lines like volcanoes and earthquakes

Evidence Of Evolution Fossil record Species evolution DNA nucleotide similarities and

differences

Fifth Principle of Ecosystem Sustainability

Ecosystems depend on biodiversity.

Stewardship of Life: A Question Revisited

Why is the fifth principle of sustainability (biodiversity) important in understanding the following issues? Endangered species Agriculture Biotechnology Medicine