Main Ideas from Ch. 23
Main Ideas from Ch. 23
Plate Tectonics & Mass Extinctions
theory that continents are part of great plates of Earth's crust that float on the hot underlying portion of the mantle
:sparkles: --> movements in the mantle cause the continents to move slowly over time
Promotes allopatric speciation
Explains geographic distribution of extinct organisms
These consequences cause extinction and thus new opportunities for organisms that survive the change
elimination of a large number of species through Earth, as a result of global environmental changes
There have been 5 mass extinctions during the past 500 million years!
Disrupts interactions within ecological community
Evolutionary lineage of extinct species (some with unique and advantageous features) is gone forever
Takes millions of years to recover levels of diversity
Promotes adaptive radiations
broad patterns of evolution above the species level
Fossil records document the rise and fall of different groups of organisms over time!
Based mostly on sequence in which fossils accumulate in sedimentary rock layers (strata)
Shows how new groups of organisms can rise through gradual modification of preexisting organisms
Helped develop a geologic record of Earth's history
What causes the rise and fall of organisms?
A group of organisms
when more new species appear than are lost (
) to extinction
Growth occurs when speciation > extinction
Processes that influence fates of organisms...
period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles (aka niches)
Promoted by 4 factors...
After mass extinction
Mass extinction --> empty spaces --> survivors adapt to fill empty species
Example: after extinction of dinosaurs, mammals expanded in diversity and size to fill roles
When a group of organisms has a major evolutionary innovation
Example: land plants fill new roles by developing adaptations such as waxy leaf coat and stem to fight gravity
When a group of organisms colonizes regions in which they face little competition
Example: ancestral tarweed landed in Hawaii --> spread to different islands --> developed different adaptations for each island with relatively little competition
After diversification of another group of organisms, which can provide new food sources
Example: plants and insects colonized land --> land plants diversified --> insects adapted to eat or pollinate plants
Changes in Morphology
How do major changes in body form (morphology) occur?
Changes to developmental genes
:sparkles: --> control the embryonic and post-embryotic development of an organism (ex. Hox genes)
Developmental genes tend to by highly conserved!
Highly conserved = important function
Change in gene sequence
aka mutation --> through duplication and divergence
Example: flies have Hox genes that regulate many important genes, humans have even more Hox genes --> different, more complex morphological structures
Change in gene regulation
--> regulating when, where, and how long a gene is expressed and allowed to function
Example: threespine stickleback fish --> marine species have spines on lower surface, lake species don't have spines --> result of different expressions of Pitx1 gene
Changes beyond developmental genes
:sparkles: --> evolutionary change in the rate or timing of developmental events
Example: salamander experiencing paedomorphosis --> organism has juvenile structures with the accelerated development of reproductive organisms