Chapter 5
Evolution of Biodiversity
Geologic Time Scale
Earth’s chemical and
biological history can be
described along a timelinethe geologic time scale.
To understand this timeline,
you need to think in time
units much larger than the
time units used to define
our lives.
Earth’s evolution led to our
present day life supporting
system.
Figure 5.23 Mass Extinctions
Five “recent” global mass extinctions - Over Earth’s history, individual species have
evolved and gone extinct at random intervals. But the fossil record shows periods of
global mass extinction, in which large numbers of species went extinct over relatively
short periods of time.
The sixth mass extinction Earth is experiencing a
global mass extinction of a
magnitude within range of
previous mass extinctions.
Estimates of extinction
rates vary widely, ranging
from 2% to as many as 25%
of species going extinct by
2020.
Speciation and extinction determine
biodiversity
Earth is home to a tremendous
diversity of species
•
•
•
Species diversity- the variety of
species in a given ecosystem.
Ecosystem diversity- the
variety of ecosystems within a
given region.
Genetic diversity- the variety of
genes within a given species.
•
•
Species richness- the number of species in a given
area.
Species evenness- the measure of whether a
particular ecosystem is numerically dominated by
one species or are all represented by similar numbers
of individuals.
Evolution shapes ecological niches and
determines species distributions
Range of tolerance- all
species have an
optimal environment
in which it performs
well. The limit to the
abiotic conditions they
can tolerate is known
as the range of
tolerance.
Fundamental nichethe ideal conditions for
a species.
Niches
Realized niche- the range of abiotic and biotic conditions under which a species
actually lives. This determines the species distribution, or areas of the world
where it lives.
Niche generalist- species that live under a wide range of conditions (broad realized
niche).
Niche specialist- species that live only in specific habitats (narrow realized niche).
Niche generalists - very broad realized niche, i.e. can survive in wide range of conditions
Niche specialists - can live only under a very narrow range of conditions
E. Mediohispanicum (mustard family) –
flower attracts more than 100 species of
insects
raccoon
koala bear
giant panda
coyote
B. Rockii (pua’ana) – moth with specialized
mouth parts (extinct), now pollinated by hand
www.centerforplantconservation.org
orchid mantis
biodilloversity.wordpress.com
Present day Latitudinal Biodiversity Gradient of terrestrial
species richness
Richness Centers (top 5% richest for each taxon)
Amazon, Southeast Brazil, Central Africa
Total ~7% global land, ∼50% of all species
Amphibians most geographically concentrated,
~2% global land area with entire known
ranges of 50% of world’s amphibians
Same areas also contain a portion of the ranges for
most remaining amphibians
i.e., total 96.6% of all amphibian species.
www.pnas.org (Jenkins et al. 2012. Global patterns of terrestrial vertebrate diversity and conservation)
Changes in environmental conditions have the potential to
affect species’ distributions
Figure 5.21
Predicting future species
distributions.
Based on knowledge of niche requirements of
different tree species, it can be predicted how
distributions might respond to future changes
in environmental conditions.
Response of species distribution to
environmental change based on more
than knowledge of present niche
requirements
•
•
•
There may be no favorable environment
that is geographically close enough
Favorable environment may already be
occupied by other very successful species
Change may occur so rapidly that a species
does not have time to migrate or adapt
Geologic Time Scale
Earth’s chemical and
biological history can be
described along a timelinethe geologic time scale.
To understand this timeline,
you need to think in time
units much larger than the
time units used to define
our lives.
Earth’s evolution led to our
present day life supporting
system.
Figure 5.23 Mass Extinctions
Five “recent” global mass extinctions - Over Earth’s history, individual species have
evolved and gone extinct at random intervals. But the fossil record shows periods of
global mass extinction, in which large numbers of species went extinct over relatively
short periods of time.
The sixth mass extinction Earth is experiencing a
global mass extinction of a
magnitude within range of
previous mass extinctions.
Estimates of extinction
rates vary widely, ranging
from 2% to as many as 25%
of species going extinct by
2020.