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Chapter 3

Chapter 3.docx

Environmental Studies
Course Code
ENV 1101
Sonia Wesche

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Chapter 3: Evolution, Biodiversity and Population Ecology
The Process of Natural Selection:
- Because organisms produce excess young, individuals vary in their traits, and many traits
are inherited, some individuals will prove better at surviving and reproducing. Their genes
will come more prominent in future generations.
- Mutations and recombination provide the genetic variation for natural selection
- We have produced our pets, farm animals, and crop plants through natural selection
How evolution results in biodiversity:
- Natural selection can act as a diversifying force as organisms adapt to their environment in
myriad ways.
- Speciation (by geographic isolation and other means) produces new species
- Once they have diverged, lineages continue diverging, a process represented in a
phylogenetic tree
Species Extinction and Mass Extinction:
- Extinction often occur when species that are highly specialized or that have small
populations encounter rapid environmental change
- Earths life has experienced five known episodes of mass extinction, because of an asteroid
impact and possible volcanism and other factors
Levels of Ecological Organization:
- Ecologists study phenomena on the organismal population, community, and ecosystem
levels and increasingly, on the biosphere level.
Characteristics that help predict population growth:
- Populations are characterized by population size, population density, population
distribution, sex ratio, age structure, and birth and death rates
- Immigration and emigration, as well as birth and death rates, determine how a population
will grow or decline
Logistic Growth, Carrying Capacity, Limiting factors, and other Fundamental concepts of
population ecology:
- Population unrestrained by limiting factors will undergo exponential growth until they meet
environmental resistance
- Logistic growth describes the effects of density dependence; exponential growth slows as
population size increases, and population size levels off at a carrying capacity
- K-selection and r-selection describe theoretical extremes in how organisms can allocate
growth and reproduction
Directional Selection: Mode of natural selection in which selection drives a feature in one direction
rather than another for example, toward larger or smaller, faster or slower.
Stabilizing Selection: mode of natural selection in which selection produces intermediate traits, in
essence preserving the status quo
Disruptive Selection: Mode of natural selection in which a trait diverges from its starting condition
in two or more directions
Speciation: the process by which new species are created
Allopatric Speciation: species formation due to the physical separation of populations over some
geographic distance
Divergent Evolution: two species with a common genetic ancestor evolve different traits over time,
generally as a result of adaptation to selective pressures from different environment. May become so
different they are no longer considered the same species
Community Ecology: The study of interactions among species, from one-to-one interactions to
complex interrelationships involving entire communities
Ecosystem Ecology: The study of how the living and nonliving components of ecosystems interact
and transfer energy among themselves
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