geography unit 3

Macroecology

subfield of ecology that aims to understand patterns of where species live at large scales of space and time + how relationships between species and environmental factors change across those scales

Focuses on large-scale spatial/temporal patterns

Macroevolution

subfield of evolutionary biology that aims to understand evolutionary patterns and processes at the level of species and clades

(evolutionary processes above or at the species level)

Phenotype

An organism's observable traits, including its anatomy, internal functions, and behavior

All observable physical and behavioral characteristics.

Reproductive Isolation

A situation where different populations can no longer interbreed and produce viable, fertile offspring

Prevents gene flow between populations.

Polyploidy

Having more than the usual two copies of each chromosome, often leading to instant reproductive isolation and speciation

Common mechanism for plant speciation via chromosome duplication.

Four necessary conditions for natural selection

1. High reproduction rate to overproduce offspring.

2. Variation in phenotypic traits.

3. Traits are heritable.

4. Differential survival and reproduction linked to those traits

Allopatric Speciation

Speciation that occurs when populations become geographically separated, preventing gene flow and allowing genetic differences to accumulate

Speciation driven by geographic separation.

Sympatric Speciation

Speciation that occurs without geographic separation, often driven by polyploidy or behavioral isolation

Speciation taking place in the same geographic area.

Vicariance

An allopatric speciation mechanism where a new physical barrier appears and splits an existing continuous population

Founder-Event Speciation

A form of allopatric speciation where a small subset of a population is separated by chance events like a storm or rafting

Also known as jump dispersal

Extirpation

The local death of all individuals in a specific population

Loss from a particular region, but not global extinction.

Extinction

The global death of all individuals across every population of a species

Permanent disappearance worldwide.

Mass Extinction

An explosive, widespread extinction event where a large percentage (greater than 40% of genera) go extinct simultaneously

Caused by global catastrophes.

Background Extinction

The standard, continuous rate of extinction occurring outside of mass extinction events

The Big 5 Mass Extinctions

Late Ordovician, Late Devonian, Late Permian, Late Triassic, and Late Cretaceous (K-pg)

Extinction Selectivity

Differential extinction rates among taxa based on specific biological traits like body size, geographic range, or specialization

Certain traits make taxa more vulnerable than others. (depending on extinction event/factors/kill mechanism)

Extinction Severity

The overall magnitude of biodiversity loss during an extinction event, regardless of trait selectivity

Total percentage of taxa wiped out.

Kill Mechanism

The specific environmental process hypothesized to cause mortality during a mass extinction, such as impact winters or oxygen drops

The direct cause of death in a catastrophe— meteor > cloud cover > death of vegetation (lack of sun) > herbivore death > carnivore/omnivore death (starvation)

Clade

A monophyletic group containing a common ancestor and all of its descendants

Synapomorphy

A shared derived trait possessed by all members of a clade because it was inherited from their common ancestor

Corresponds to a homologous trait.

ex: mammals all have hair/mammary glands, hand bone organization, etc

Autapomorphy

A derived trait that is unique to a single given taxon

Convergent Evolution

The independent evolution of similar traits in organisms whose last common ancestor lacked that trait

Results in homoplastic traits due to similar habitats.

ex wings in birds/bats

Outgroup

A more distantly related taxon used as a reference point to root and define the ingroup on a phylogenetic tree

Parsimony in Phylogenetics

The principle of selecting the simplest evolutionary tree that requires the fewest trait changes

The most straightforward explanation, least gains/losses of traits

Three processes determining species richness

1. Origination (speciation in place).

2. Extinction/extirpation.

3. Dispersal (moving in or out of the area)

tetrapod tree/relationships

geographical area theory

more land area at equators than poles, so species can have larger geographic ranges

promotes allopatric speciation→ higher speciation rate at the equator

criticisms: tropics not considered single biome, larger area may not be associated w/ more speciation

evolutionary speed theory

higher avg temp means faster growth + shorter generation times, mutation rate might be higher near equator → higher speciation rate at equator (natural selection depends on mutations)

criticisms: no evidence for significant difference in molecular evolution rate in equator species + elsewhere

“tropics are a cradle” theory

climate is stable near equator, specialist species can survive better, more species can coexist bc of niche separation → higher speciation rate at equator

criticisms: there are habitats where environment is stable but diversity is low (eg tropical mountaintops); there are habitats where environment varies but diversity is high (precipitationally seasonal tropical places)

“tropics are a museum” theory

fluctuating/harsh conditions near poles present more kill mechanisms → lower extinction rates near equator

“out of the tropics” theory

studies on fossil bivalves found that clades originated in tropics expanded into higher latitudes

species w/ narrow temp niches can be widespread near equator bc large geographic areas similarly warm

tropics are both cradle and museum → speciation rate higher at equator AND species’ geographic ranges expand to include equator + surrounding areas (“bridge species”)

also lower extinction rates near equator

criticisms: hypothesis based on clams, might not explain terrestrial species as well

paleogeography

configuration of continents throughout geologic past

continent shape/distribution has changed a lot bc of sea level rise/fall + tectonic drift

sea level much lower during ice ages, rises when earth warms

plate tectonics

continents + ocean floor made of tectonic plates that float on the mantle

maps of ocean ridges + earthquakes/volcanic activity match

fossils of same species in different continents prove past connectivity

great american biotic interchange (GABI)

3mya: formation of isthmus of panama, created new land bridge bw the americas

raccoons, skunks, cats, horses, bears, camels moved from north to south

armadillos, opossums, marmosets moved from south to north

same proportion of species moved both ways BUT more species that went north went extinct (end of ice age, less competitive)

beringia land bridge

sea level dropped 300+ ft during ice ages, land bridge formed across bering strait

adaptive radiation

explosive pattern of species originations, new species diverge in ecological function + morphology

innovation or opportunity

ex: diversification of mammals after dinosaur extinction, took advantage of newly available resources