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					Biodiversity and Evolution
Asim Zia Introduction to Environmental Issues EnvS 001, Spring 2007 Department of Environmental Studies San Jose State University

Chapter 4 Overview Questions
do scientists account for the development of life on earth?  What is biological evolution by natural selection, and how can it account for the current diversity of organisms on the earth?  How can geologic processes, climate change and catastrophes affect biological evolution?  What is an ecological niche, and how does it help a population adapt to changing the environmental conditions?
 How

Chapter Overview Questions (cont’d)
do extinction of species and formation of new species affect biodiversity?  What is the future of evolution, and what role should humans play in this future?  How did we become such a powerful species in a short time?
 How

Core Case Study Earth: The Just-Right, Adaptable Planet
 During

the 3.7 billion years since life arose, the average surface temperature of the earth has remained within the range of 10-20oC.
Figure 4-1


billion years of chemical change to form the first cells, followed by about 3.7 billion years of biological change.

Figure 4-2

Biological Evolution
 This

has led to the variety of species we find on the earth today.

Figure 4-2

How Do We Know Which Organisms Lived in the Past?
 Our

knowledge about past life comes from fossils, chemical analysis, cores drilled out of buried ice, and DNA analysis.
Figure 4-4

 Biological

evolution by natural selection involves the change in a population’s genetic makeup through successive generations.
 

genetic variability Mutations: random changes in the structure or number of DNA molecules in a cell that can be inherited by offspring.

Natural Selection and Adaptation: Leaving More Offspring With Beneficial Traits
 Three

conditions are necessary for biological evolution:
Genetic variability, traits must be heritable, trait must lead to differential reproduction.

 An

adaptive trait is any heritable trait that enables an organism to survive through natural selection and reproduce better under prevailing environmental conditions.

Coevolution: A Biological Arms Race
 Interacting

species can engage in a back and forth genetic contest in which each gains a temporary genetic advantage over the other.

This often happens between predators and prey species.

Hybridization and Gene Swapping: other Ways to Exchange Genes
 New

species can arise through hybridization.

Occurs when individuals to two distinct species crossbreed to produce an fertile offspring.

 Some

species (mostly microorganisms) can exchange genes without sexual reproduction.
Horizontal gene transfer

Limits on Adaptation through Natural Selection

population’s ability to adapt to new environmental conditions through natural selection is limited by its gene pool and how fast it can reproduce.

Humans have a relatively slow generation time (decades) and output (# of young) versus some other species.

Common Myths about Evolution through Natural Selection
 Evolution

through natural selection is about the most descendants.
Organisms do not develop certain traits because they need them. There is no such thing as genetic perfection.


 The

movement of solid (tectonic) plates making up the earth’s surface, volcanic eruptions, and earthquakes can wipe out existing species and help form new ones.


The locations of continents and oceanic basins influence climate. The movement of continents have allowed species to move.

225 million years ago

135 million years ago

65 million years ago

Fig. 4-5, p. 88

Climate Change and Natural Selection
 Changes

in climate throughout the earth’s history have shifted where plants and animals can live.

Figure 4-6

Catastrophes and Natural Selection
 Asteroids

and meteorites hitting the earth and upheavals of the earth from geologic processes have wiped out large numbers of species and created evolutionary opportunities by natural selection of new species.

 Each

species in an ecosystem has a specific role or way of life.
Fundamental niche: the full potential range of physical, chemical, and biological conditions and resources a species could theoretically use. Realized niche: to survive and avoid competition, a species usually occupies only part of its fundamental niche.


Generalist and Specialist Species: Broad and Narrow Niches
 Generalist

species tolerate a wide range of conditions.  Specialist species can only tolerate a narrow range of conditions.
Figure 4-7

SPOTLIGHT Cockroaches: Nature’s Ultimate Survivors
 350

million years old  3,500 different species  Ultimate generalist
 


Can eat almost anything. Can live and breed almost anywhere. Can withstand massive radiation.
Figure 4-A

Specialized Feeding Niches

 Resource

partitioning reduces competition and allows sharing of limited resources.

Figure 4-8

Avocet sweeps bill through mud and surface water in search of small crustaceans, insects, and seeds Brown pelican dives for fish, which it locates from the air

Black skimmer seizes small fish at water surface

Ruddy turnstone Herring gull is a searches tireless scavenger under shells and pebbles for small Dowitcher probes deeply into mud in search of invertebrates snails, marine worms, and small crustaceans

Louisiana heron wades into water to seize small fish

Flamingo feeds on minute organisms in mud

Scaup and other diving ducks feed on mollusks, crustaceans,and aquatic vegetation

Oystercatcher feeds on clams, mussels, and other shellfish into which it pries its narrow beak

Piping plover feeds on insects and tiny crustaceans on sandy beaches

Knot (a sandpiper) picks up worms and small crustaceans left by receding tide
Fig. 4-8, pp. 90-91

(Birds not drawn to scale)

Evolutionary Divergence

 Each

species has a beak specialized to take advantage of certain types of food resource.

Figure 4-9

 Speciation:

A new species can arise when member of a population become isolated for a long period of time.

Genetic makeup changes, preventing them from producing fertile offspring with the original population if reunited.

Geographic Isolation

 …can

lead to reproductive isolation, divergence of gene pools and speciation.
Figure 4-10

Extinction: Lights Out
 Extinction


when the population cannot adapt to changing environmental conditions.
golden toad of Costa Rica’s Monteverde cloud forest has become extinct because of changes in climate.
Figure 4-11


Era Cenozoic

Period Quaternary Tertiary

Millions of years ago Today

Bar width represents relative number of living species


Mesozoic Jurassic 180 Triassic 250

Species and families experiencing mass extinction Extinction Current extinction crisis caused by human activities. Many species are expected to become extinct Extinction within the next 50–100 years. Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including many foraminiferans and mollusks. Extinction Triassic: 35% of animal families, including many reptiles and marine mollusks. Extinction Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites. Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites.

Permian Carboniferous
345 Paleozoic Devonian Silurian Ordovician Cambrian Extinction



Ordovician: 50% of animal families, including many trilobites. Fig. 4-12, p. 93

Effects of Humans on Biodiversity

 The

scientific consensus is that human activities are decreasing the earth’s biodiversity.
Figure 4-13

 We have

used artificial selection to change the genetic characteristics of populations with similar genes through selective breeding. used genetic engineering to transfer genes from one species to another.
Figure 4-15

 We have

Genetic Engineering:
Genetically Modified Organisms (GMO)
 GMOs

use recombinant DNA

genes or portions of genes from different organisms.

Figure 4-14

How Would You Vote?
Should we legalize the production of human clones if a reasonably safe technology for doing so becomes available?


a. No. Human cloning will lead to widespread human rights abuses and further overpopulation. b. Yes. People would benefit with longer and healthier lives.

 Biologists

are learning to rebuild organisms from their cell components and to clone organisms.

Cloning has lead to high miscarriage rates, rapid aging, organ defects.

 Genetic

engineering can help improve human condition, but results are not always predictable.

Do not know where the new gene will be located in the DNA molecule’s structure and how that will affect the organism.

Controversy Over Genetic Engineering
are a number of privacy, ethical, legal and environmental issues.  Should genetic engineering and development be regulated?  What are the long-term environmental consequences?
 There

Case Study:
How Did We Become Such a Powerful Species so Quickly?
 We lack:
  

strength, speed, agility. weapons (claws, fangs), protection (shell). poor hearing and vision.

 We have

thrived as a species because of


opposable thumbs, ability to walk upright, complex brains (problem solving).