Chapter 4 Biodiversity and Evolution
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What Is Biodiversity and Why Is It Important
a.
Biodiversity Is a Crucial Part of the Earth’s Natural Capital
i. Biological diversity, or biodiversity, is the variety of the earth’s species, the genes they contain, the ecosystems in which they live,
and the ecosystem processes such as energy flow and nutrient cycling that sustain all life.
1. Species diversity is the variety of species.
2. Genetic diversity is the variety of genes. It enables life on the earth to adapt to and survive dramatic environmental
changes.
3. Ecosystem diversity is the earth’s variety of deserts, grasslands, forests, mountains, oceans, lakes, rivers, and wetlands.
4. Functional diversity is the variety of processes such as matter cycling and energy flow taking place within ecosystems as
species interact with one another in food chains and webs.
Where Do Species Come From?
a.
Biological Evolution by Natural Selection Explains How Life Changes over Time
i. Biological evolution is the process whereby earth’s life changes over time through changes in the genes of populations.
ii. Darwin and Wallace concluded that survival traits would become more prevalent in future populations of the species through a
process called natural selection, which occurs when some individuals of a population have genetically based traits that enhance
their ability to survive and produce offspring with the same traits.
b. The Fossil Record Tells Much of the Story of Evolution
i. Most of what we know of the earth’s life history comes from fossils: mineralized or petrified replicas of skeletons, bones, teeth,
shells, leaves, and seeds, or impressions of such items found in rocks.
c.
The Genetic Makeup of a Population
i. Populations (not individuals) evolve by becoming genetically different.
ii. Genetic variety occurs through mutations: random changes in the structure or number of DNA molecules in a cell that can be
inherited by offspring.
1. Random mistakes that occur in coded genetic instructions.
2. Gene DNA is exposed to external agents like X-rays, chemicals (mutagens), or radioactivity.
d. Individuals in Populations with Beneficial Genetic Traits Can Leave More Offspring
i. An adaption, or adaptive trait, is any heritable trait that enables an individual organism to survive through natural selection and to
reproduce more than other individuals under prevailing environmental conditions.
ii. For natural selection to occur, a trait must:
1. Be heritable, meaning that it can be passed from one generation to another.
2. Lead to differential reproduction, which enables individuals with the trait to leave more offspring than other members of
the population leave.
e. How Did Humans Become Such a Powerful Species?
i. Strong opposable thumbs
ii. An ability to walk upright
iii. A complex brain
f.
Adaption through Natural selection Has Limits
i. A change in environmental conditions can lead to such an adaption only for genetic traits already present in a population’s gene pool
or for traits resulting from mutations.
ii. Reproductive capability. For example, populations of genetically diverse species that produce quickly often adapt to a change in
environmental conditions in a short time.
g.
The Common Myths about Evolution through Natural Selection
i. “Survival of the fittest” means “survival of the strongest.”
1. The fittest individuals are those that leave the most descendants.
ii. Organisms develop certain traits because they need or want them.
1. They develop certain traits because it gives them an advantage over other members in its population.
iii. Evolution by natural selection involves some grand plan of nature in which species become more perfectly adapted.
1. The evolutionary process appears to be a random, branching process.
How Do Geological Processes and Climate change After Evolution
a.
Geological Processes Affect Natural Selection
i. The movement of tectonic plates has had two important effects on the evolution and location of life on the earth.
1. The locations of continents and oceanic basins greatly influence the earth’s climate and thus help determine where plants
and animals live.
2. Allowed species to move, adapt to new environments, and form new species through natural selection.
ii. Earthquakes cause fissures in the earth’s crust that can separate and isolate populations of species.
iii. Volcanic eruptions destroy habitats and reduce or wipe out populations of species.
b. Climate Change and Catastrophes Affect Natural Selection
i. Determines where different types of plants and animals can survive and thrive, and it changes the locations of different types of
ecosystems.
ii. Collisions between the earth and large asteroids have caused widespread destruction of ecosystems and wiped out large numbers of
species.
How Do Speciation, Extinction, and Human Activities Affect Biodiversity?
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How Do New Species Evolve?
i. Speciation is the formation of two species from one species because of divergent natural selection in response to changes in
environmental conditions.
ii. The most common mechanisms of speciation takes place in two phases:
1. Geographic isolation occurs when different groups of the same population of a species become physically isolated from
one another for long periods.
2. In reproductive isolation, mutation and change by natural selection operate independently in the gene pools of
geographically isolated populations.
b. Extinction Is Forever
i. Another process affecting the number and types of species on the earth is extinction, in which an entire species ceases to exist.
ii. Species that are found in only one area are called endemic species and are especially vulnerable to extinction.
c.
Extinction Can Affect One Species or Many Species at a Time
i. Throughout most of history, species have disappeared at a low rate, called background extinction.
ii. Mass extinction is a significant rise in extinction rates above the background level.
What Is Species Diversity and Why Is It Important?
a.
Species Diversity Includes the Variety and Abundance of Species in a Particular Place
i. An important characteristic of a community and the ecosystem to which it belongs is its species diversity: the number of different
species it contains (species richness) combines with the relative abundance of individuals within each of those species (species
evenness).
b. Species-Rich Ecosystems Tend to Be Productive and Sustainable
What Roles Do Species Play in Ecosystems?
a.
Each Species Plays a Unique Role in Its Ecosystem
i. Ecological niche is the total way of life or role of a species in an ecosystem. It includes everything that affects its survival and
reproduction.
ii. Scientists use the niches of species to classify them broadly.
1. Generalist species have broad niches.
2. Specialist species occupy narrow niches.
b. Niches Can Be Occupied by Native and Nonnative Species.
i. Native species are those species that normally live and thrive in a particular ecosystem.
ii. Nonnative species are species that migrate into or are deliberately or accidentally introduced into an ecosystem.
c.
Indicator Species Serve as Biological Smoke Alarms
i. Indicator species are species that provide early warnings of damage to a community or an ecosystem.
d. Keystone and Foundation Species Help Determine the Structure and Functions of Their Ecosystems
i. Keystone species have a large effect on the types and abundances of other species in an ecosystem.
1. Keystone species can play several critical roles in helping to sustain an ecosystem.
a.
Pollination of flowering plant species by bees, butterflies, hummingbirds, bats, and other species.
b. Top predator keystone species feed on and help regulate the populations of other species.
ii. Foundation species play a major role in shaping communities by creating and enhancing their habitats in ways that benefit other
species.