Midterm 2 Study Guide

Question 1

How has the movement of continents contributed to the distribution pattern of organisms?

Answer 1

• Movement of continents has been the most important factor in long term changes in organism distribution
• Movement along latitude bands= different land masses lying in different climatic regions
• Formation of mountain chains and volcanic islands
• *formation/ destruction of epeiric/ epicontinental seas
  –> Acted as barriers to terrestrial organisms (land subdivided into smaller pieces)
  –> Diverse marine life could thrive

Question 2

Briefly outline the major changes in the positions of the continents over time.

Answer 2

• At first: 1 supercontinent called Rodinia (formed over a billion years ago)
• Early Cambrian: 3 fragments broke away from Rodinia
• During Carboniferous & Permian periods (Paleozoic era): consolidation of the ancient continents → formed mountain ranges
• Eventually, supercontinent Pangaea formed & the global Panthalassic Ocean
  –> Supercontinent + global ocean= great connectivity
• Mesozoic Era: Laurasian and Gondwanan continents separated (began as a rift valley & expansion of the Atlantic Sea
  –> This separation led to opening of the circum-equatorial seaway
• Early Cenozoic: chicxulub asteroid + mass extinctions
  –> Continents continued to drift apart, sometimes colliding with once isolated landmasses
  =rapid northward drifting of india→ eventually it hit Asia which resulted in the uplift of Himalayas

Neogene & Quaternary periods: continents continued drifting, most landmasses ended up north of the equator = climatic instability + glacial cycle in pleistocene

Question 3

Explain how continental drift occurs.

Answer 3

Mechanism of continental drift= plate tectonics
- New sea floor created at mid-ocean ridges, where it moves outward by seafloor spreading & gets destroyed by subduction into ocean trenches
- Ocean floor= “conveyor belt” being continuously formed at mid-ocean ridges & then destroyed at trenches → continents passively ride along the conveyor belt

Question 4

Provide evidence for the following events: first prokaryotic cells, increase in atmospheric oxygen, Cambrian explosion.

Answer 4

1st Prokaryotic Cells Evidence:
- Resemble modern photosynthetic algae?
- Stromatolites in limestone built by photosynthetic cyanobacteria

Increase in Atmospheric Oxygen Evidence:
- Deposition of iron oxide sediments on marine continental shelves
- Stromatolites in limestone built by photosynthetic cyanobacteria
- Extensive banded iron formations

Cambrian Explosion Evidence:
Burgess Shale! In Field, BC: very rich fossil record of the Cambrian Explosion

Question 5

List the drivers of change (9).

Answer 5

Changing solar output
Evolving atmosphere
Tectonic/ volcanic activity
Asteroid impacts
Methane clathrate releases
Orbital patterns (Milankovitch cycles)
Changing ocean circulation
Changing sea levels
Humans!

Question 6

Explain the three concepts of change.

Answer 6

1. Predictable rules govern climate change and results in gradual change
   Eg solar luminosity, continental drift, CO2/ O2 concentrations
   - High CO2 associated with warmer conditions → found on multiple timescales (El Nino oscillations to geological timescales)
2. Random, abrupt, catastrophic events cause climate change
   Eg asteroid impacts, volcanic eruptions, methane clathrate releases
3. The Climate alternates between alternate stable states
   Eg glacial/ interglacial periods (ice-house vs hot-house)
   - Called “metastable models”

Question 7

Describe what life was like in the Phanerozoic eon.

Answer 7

Showed all 3 patterns of change (gradual, abrupt, periodic)

Both catastrophe and recovery
–> Mass extinctions and rebounds (adaptive radiation)

Diversity gradually increased during phanerozoic, but was punctuated by major extinctions

Question 8

Explain the concept of extinction.

Answer 8

= the permanent loss of a species, population, etc

Often followed by adaptive radiation

Question 9

Explain the cause behind many of the mass extinctions.

Answer 9

Tectonically-driven cycles of regression and transgression of marine waters across continental inland seas
- Regression → vast decreases in area of shallow water enviros

• Transgressions → brings masses of anoxic waters across expanses of shallow seas
• Each of these events could = mass extinctions (could have also been in conjunction with other factors like asteroids)

Question 10

Describe the Permian-Triassic extinction event.

Answer 10

The most disastrous extinction ever!
Occurred 250 mya, and spanned 60,000 years

Massive scale and scope. Extinctions:
90%+ of marine invertebrates
75%+ of land tetrapods (mostly amphibians)
Majority of land plants

Question 11

Explain the cause of the P-T extinction event.

Answer 11

There was likely more than one cause over the massive time span. Possibilities:

• Continental drift
• Ocean salinity changes
• Anoxic, acidic, and sulfidic oceanic conditions
• Possible meteorite impact
• Extensive volcanism, causing cooling
  –> Sulfur dioxide from eruption goes into atmosphere, combines with water → forms sulfuric acid aerosols which reflect incoming solar radiation (cooling effect)

Question 12

Describe the Cretaceous-Tertiary extinction event.

Answer 12

The mass extinction between the cretaceous and tertiary
~65 mya

Well-known because it caused the dinosaurs to go extinct

Question 13

Explain the cause of the K-T extinction event.

Answer 13

Most likely cause= meteorite impact

Initial evidence= Italy: thin clay layer with very high iridium concentrations at the K-T boundary (later found around the world)

*Note Iridium suggests extraterrestrial origin

Additional evidence: Yucatan impact crater in Mexico (10km wide!)

Question 14

What are the mechanisms for species formation (5)?

Answer 14

• Mutations (changes in DNA sequences) → substitution, insertion, deletion, or inversion of at least 1 nucleotide
• Genetic drift: occurrence of random changes in allele frequency b/w generations
• Natural Selection: change in a population b/c individuals express genetic traits that alter their interactions w/ their environment so that their survival & reproduction are enhanced relative to other individuals in the population
• Gene flow: movement of alleles within or between populations b/c of the dispersal of gametes or offspring
• Endosymbiosis: a symbiotic relationship where one organism lives inside the other

Question 15

What is the difference between allopatric and sympatric speciation?

Answer 15

Allopatric:
Geographic isolation cuts off gene flow
Vicariance due to enviro barriers
Peripheral isolates due to founder events/ jump dispersal

Sympatric:
No geographic isolation
Includes sympatric and parapatric

Question 16

Describe the two processes under which allopatric speciation occurs.

Answer 16

1. Allopatric speciation due to vicariance
   Each species arises from an isolation event (geographic barrier) → populations diverge into separate species (can happen again and again)
2. Allopatric speciation due to peripheral isolates and founder events
   Random dispersal= new, geographically isolated populations that diverge into separate species (also can happen again and again- many levels)

Question 17

What is the difference between sympatric and parapatric speciation?

Answer 17

• In sympatric, the populations are overlapping extensively and maintain contact throughout the speciation process
• In parapatric, there is only slight overlap in populations (narrow zone of contact b/w ancestral population and new population)

Question 18

How does sympatric speciation arise?

Answer 18

There are a few causes of sympatric speciation:
- Strong selective pressures within a population
Eg the appearance of a new host in the cause of herbivorous insects or animal parasites, or new mutualistic associations
- Disruptions along an environmental gradient
- Resource partitioning and behavioral isolation (eg niche partitioning)
- Abrupt chromosomal changes (eg polyploidy common in plants)

Question 19

Describe the Cenozoic radiation of mammals in terms of extinction and evolution.

Answer 19

Cenozoic radiation of mammals:

Ancestors of modern mammals developed key innovations like jaws, teeth, large brain, etc during the Mesozoic

K-T mass extinction brought about an abrupt change allowing terrestrial vertebrates to become dominant by extinguishing dinosaurs

Eliminates competitive rivals and opened new ecological niches

Question 20

Describe the rise of angiosperms in terms of extinction and evolution.

Answer 20

Angiosperms evolved during cretaceous

Innovations in reproductive biology: allowed them to evolve mutualistic associations w/ animals that pollinate their flowers + disperse their seeds

Despite these advantages, rise to dominance took 100 million years to replace dominant gymnosperms like conifers and ferns

Question 21

Describe the replacement of brachiopods in terms of extinction and evolution

Answer 21

Eg clams

• Over 600 million years, clams replaced ancient brachiopods
  –> Groups have superficially similar morphology, feeding habits and habitat needs
• Shift in dominance= due to competition, but mass extinctions played a role
• Brachiopods more susceptible to extinctions b/c they don’t have planktotrophic larvae (which can disperse easily)

Question 22

What three observations did early biogeographers notice about islands?

Answer 22

1. Islands are species-poor relative to mainlands (Georg Forster)
2. Larger or ecologically diverse islands have more species (Georg Forster)
3. Age and degree of isolation affects island species number (de Candolle)

Question 23

What are the 3 themes in island biogeography?

Answer 23

Dispersal
Extinction
Diversity

Question 24

Explain how islands become inhabited.

Answer 24

Steps:
1. Initial dispersal event to previously unoccupied land
- natural (swim or fly) or
- Artificial introduction (accidental or on purpose)

2. Subsequent adaptive radiation because they don’t have any natural predators
3. As more species are introduced, the original species will decline

*reverse selection can occur
*radiation is very common on island archipelagos → adapts into niches

Question 25

What is meant by the term “ecological release”? Provide an example to support your answer.

Answer 25

Ecological release= relaxation of selective pressures. Resources might be abundant and competition reduced when a species disperses to an uninhabited island, so they can experience ecological release (even reverse selection)

result= population in a species-poor enviro with little competition will occupy a broader range of their fundamental niche

Example: Voles and shrews

Shrew density is much higher in a habitat where voles are not present: they experience ecological release when voles aren’t present
- Niche shift in presence or absence of another species

Question 26

List and briefly explain three phenomena observed on islands.

Answer 26

1. Endemism: species are unique to that location (not found anywhere else)
   - The more isolated the island, the higher number of endemic species
2. Reduced dispersal: for example, flightless species: a bird might disperse to an island, then experience no competition, so lose the ability to fly because there is no need to. This prevents further dispersal
   - Also, plants on an island can usually only disperse WITHIN that island
3. Gigantism and Dwarfism:

Island Rule: trend towards medium size (dwarfism in large species and gigantism in small species)

Bergmann’s Rule: body mass increases with latitude

Cope’s Rule: trend towards larger body size (and range of sizes) during the evolutionary diversification of a lineage

Question 27

What is the relationship between endemism and isolation?

Answer 27

The more isolated the island, the higher number of endemic species

Question 28

Where do we expect to see more endemic species?

Answer 28

On very isolated islands nearest to the equator

• Because increase in isolation= increase in endemic species
• And islands are biodiversity hotspots, & the highest biodiversity is near the equator

Question 29

What organisms experience reduced dispersal after colonizing an island? Explain how and why their dispersal is reduced.

Answer 29

Lots of birds
- The ancestral population can fly, which is how they originally disperse
- They experience several generations with no predators on the new island, so have no need to fly → lose ability to fly
Eventually, dispersal is reduced because they can no longer fly

Also plants:
Can only disperse within the island they’re on, unless a vector brings their seeds somewhere else (likely how they dispersed in the first place)

Question 30

Compare the Island Rule, Bergmann’s Rule, and Cope’s Rule.

Answer 30

Island Rule= trend towards medium-sized organisms (dwarfism in large species and gigantism in smaller species)
Little things get bigger (because of ecological release)
Big things get smaller (because of ecological release from competitors and resource limitation)

Bergmann’s Rule= body mass increases with latitude

Cope’s Rule= trend towards larger body size (& range of sizes) during the evolutionary diversification of a lineage

Question 31

In biogeography, why is the term “island” an abstraction? Provide an example to illustrate your point.

Answer 31

Because the theory behind actual islands also applies to any isolated area (that acts as an island). For example, chains of lakes and forest fragments are isolated similarly to an actual island, and the phenomena observed are the same

Example: If there is a chain of lakes that aren’t connected, the aquatic organisms cannot move from one lake to another. This has the exact same implications as a typical island

Question 32

How can a fragmented piece of land act as an island?

Answer 32

A fragmented piece of land (a forest, for example) acts as an island, especially to smaller organisms, because it may be impossible for that organism to get from one forest patch to another.

Question 33

Describe the two general patterns of species richness on islands.

Answer 33

1. Bigger islands have more species
2. The greater the distance to the island (from mainland) = fewer species

Question 34

Why are more species able to populate a larger island compared to a smaller one?

Answer 34

There are usually more species on a bigger island simply because there is more land, so more potential niches to fill

Question 35

Why do isolated islands have fewer species?

Answer 35

More isolated islands are a further distance from the mainland, creating physical barriers to dispersal.

For example, having to swim or fly 1000 km to an isolated island may be impossible for many species, but possible for only a couple. If it was only 500 km, more species would be able to make the trek, so the nearer island would be able to have more species

Question 36

Explain in detail the Equilibrium Theory of Island Biogeography. Draw and label the graphical model in your answer.

Answer 36

be able to draw graph on the exam
- Proposed in 1967 by MacArthur and Wilson
- Proposed the # of species inhabiting an island represents a dynamic equilibrium b/w opposing rates of immigration and extinction
- Dynamic b/c immigration and extinction are recurrent, opposing processes, maintaining a relatively stable species # despite ongoing changes in species composition
- Simply:
–> Distance of an island from a source pool will affect immigration rate
–> Area of an island will affect extinction rate
–> A near island should return to equilibrium more rapidly than a distant island of = size b/c it should have a higher immigration rate but the same extinction rate

Question 37

Describe the three phenomena that are taken into account by the Equilibrium Theory.

Answer 37

They simply stated 3 phenomena exhibited by islands:
- Species-area relationship: species richness increases with increasing area
- Species-isolation relationship: species richness decreases with increasing isolation
- Species turnover: the rate of replacement as colonizing species replace those that have gone extinct

Question 38

What are the limitations of the Equilibrium Theory of Island Biogeography?

Answer 38

Does not account for:
- Interspecific differences and interactions (species differences- this model is species-neutral)
- Succession or disturbance (time)
- Shape and other habitat complexity (such as edge effects)

• Equilibrium state is rarely attained in nature (succession and disturbance)

Question 39

Draw and explain the model proposed by Simberloff and Wilson.

Answer 39

be able to draw graph on exam

Proposed there are 3 equilibriums for species number on an island

During each phase, something different is happening

More complex than the original theory of island biogeography

Question 40

Explain the model proposed by Whittaker.

Answer 40

Understand the graph, but don’t need to draw it

This model accounts for geophysical effects that might drive immigration and extinction (like land bridges, volcanoes, etc)

Question 41

Compare and contrast the three proposed models of island biogeography.

Answer 41

The original equilibrium theory was the first to explain how islands were colonized, but it did not account for many complexities that the other 2 models did (eg. edge effects, interspecies differences, etc)

Wilson and Simberloff’s model proposed 3 equilibriums, which was a unique idea
- More complex: accounted for interactions b/w species

Robert Whittaker’s model accounts for geophysical effects that drive immigration/ extinction, suggests a maximum topographic complexity (carrying capacity)

Question 42

Explain the challenges biogeographers have faced studying marine environments.

Answer 42

Challenging to survey and sample marine environments

Difficult to determine barriers b/w areas or distribution

Oceans are massive

Marine species are often morphologically similar → differences have to be determined by genetics, which is expensive (hard to determine if they’re related by just looking at them)

Question 43

Which zone do a majority of marine organisms live? Provide three advantages and three disadvantages of residing in this zone.

Answer 43

Most organisms live in the pelagic zone (open ocean)

Advantages to living in pelagic zone:
- Access to light still (important for photosynthetic organisms)
- High primary productivity (= food for consumers)
- Warmer temps= don’t need to be adapted to live in cold-water environments

Disadvantages to living in pelagic zone:
You don’t get the stability that comes with living in the benthic zone!
- Little shelter from storms
- Benthic has more supply of organic matter (falls through column)
- Pelagic has less habitat than benthic zone