Lecture 21 - Geographic Distributions and Patterns

Question 1

Define biogeography

Answer 1

The study of historical changes in distributions of organisms across the land/seascape.

“the search for patterns of plant and animal life that can be put on a map”

Question 2

Define species distribution. What are three characteristics that can describe it?

Answer 2

Describes the area occupied by a population or species → can be described at different scales (global, regional, local)

Characteristics: By size, shape and location.

Different factors are important for the different scales of distribution. For example, when you look at the global distribution, you’re gonna be thinking about this broad scale pattern that changes with latitude, that’s probably gonna drive that broad distribution. When you zoom in all the way down to local distribution, you’re gonna be thinking about what is it about one side of the tree that’s better than the other side.

Question 3

Explain The Global Scale of species distribution

Answer 3

Idea: range is dynamic and you can think of ways to show how the range can change through the seasons.

Question 4

What’s the main driver for regional and local scale of species distribution?

Answer 4

One of the drivers will be predation or species interaction.

Question 5

What’s the most common species distribution range?

How does this relate to species abundance?

Answer 5

Most species have a small global geographic range.

Relating it to species abundance (saw in earlier chapters), most species are rare.

Question 6

Define Hanski’s Rule.

Answer 6

Hanski’s Rule: Relationship between range size and population abundance are positively correlated

• Species that are more abundant, then to have larger ranges (more dense).

Question 7

Name two species that defy Hanski’s Rule.

Answer 7

2 examples where small ranging species are more abundant (Dabra species and Erigeron species pair)

Question 8

What is the central tenet of ecology and biogeography regarding species global distributions?

Answer 8

A central tenet of ecology and biogeography is that temperature and moisture influences continental-scale distributions of species

Question 9

What makes people hold the central tenet?

Answer 9

Biomes : large geographic regions that experience similar climatic conditions contain similar communities of organisms.

It’s been said that you can go out and you can look at what the temperature is of a place on earth and look at what it’s annual precipitation is. Then you can put your finger down on a part of this plot and guess what the biome should be.

Question 10

What distinguishes biomes?

Answer 10

The predominant vegetation type, e.g. tropical rain forest biome, grassland biome.

Question 11

Draw the Solar driven air circulation diagram and explain the 4 different components. Where is the Hadley cell?

Answer 11

See slides p13.

Question 12

Define 2 things that limit species distribution

Answer 12

1. Dispersal: species have different ways to disperse across the landscape
2. Abiotic (temperature, precipitation) and biotic factors (predation, competition) : Once a species (could be a propagule) has reached a new location, the factors that will allow it to grow and establish itself.

Question 13

What are two measures of temperature (abiotic) tolerance?

Answer 13

1. Critical cold and heat limits: loss of motor function as temperature ramped up and down.
2. Lethal cold and heat limits: static temperature at which 50% of individuals die.

Question 14

How can an organism change its thermal tolerance range?

Answer 14

by acclimation

Question 15

For what estimation of parameters do the patterns of distribution hold

Answer 15

Patterns hold when simultaneously estimating the effects of elevation, ramping rate, duration, & acclimation temperature

Question 16

Why doesn’t the max thermal tolerance of terrestrial species not decline with latitude in terrestrial species whereas in aquatic species, heat tolerance does decline with latitude?

Answer 16

At high latitudes, even though on average is cooler, they still get really warm summer, so they need to have a high maximum temperature just to get through that day even though the annual average temperature is lower. That’s because the temperature is more variable on land.

Question 17

What’s the relation between thermal limits vs absolute latitude in Marine, Freshwater, and Terrestrial organisms?

Answer 17

All max and min thresholds decrease at higher latitude, except the max of terrestrial doesn’t decrease because of more variable temperature (summer).

Question 18

Define Shelfords law of tolerance

Answer 18

The distribution of a species will be controlled by that environmental factor for which the organism has the narrowest range of tolerance.

Question 19

Can evolutionary adaptation lead changes in tolerances? Give examples/experiments.

Answer 19

Tolerances can also change by evolutionary adaptation. For example, serpentine soils contain high concentration of metals that are toxic to many plants. Unhealthy soil limits many species

Experiment: Reciprocal Transplant. Strains from serpentine-soil planted. Species from serpentine-soil grow in both normal and serpentine soil. Species from normal soil only grows in normal soil.

Question 20

Describe the Transplant experiment to decipher mechanism of Dispersal limitation vs abiotic tolerance.
Interpret the outcome of:
1. Transplant successful
2. Transplant unsuccessful

Answer 20

Transplant successful
Distribution limited either because the area is inaccessible, time has been too short to reach the area, or because the species fails to recognize the area as suitable living space.

Transplant unsuccessful
Distribution limited either by other species or by physical and chemical factors.

Question 21

Define the 3 main modes of dispersal, and examples.

Answer 21

1. Diffusion
2. Jump dispersal (more common) : movement of individuals across large distances (usually inhospitable terrain)
   ex: (most to least)
   …….Wind dispersed are fastest
   …….Animal (bird) dispersed
   …….Sea dispersed
3. Secular dispersal: diffusion over evolutionary time scales.
   Ex: the llamas and vicunas of South America are descended from now extinct North American members of the camel family that migrated during the Pliocene over the Isthmus of Panama.

Question 22

Explain how jump dispersal can be accelerated by humans

Answer 22

Dispersal accelerated by humans: shipping routes as invasive species vectors.

Question 23

Are Colonization rates often driven by mean dispersal distances or by extreme events?

Answer 23

extreme events

Question 24

Explain Reid’s paradox

Answer 24

Observation that dispersal distances of most herbs and trees are too limited to account for their recolonization
of northern latitudes following glacial recession

Question 25

What explains species differential range edge responses to climate change (traits associated with range extension rate)? (3)

Answer 25

1. Extrinsic driver: Climate expectations
2. Arrival: adult mobility
3. Establishment: trophic position, latitudinal range size.

Question 26

Why do latitudinal range size might matter to a species’ ability to shift its range?

Answer 26

Species with greater ranges likely have !greater local abundance or are more ecologically versatile

Question 27

Broad-ranging species were more responsive to… (climate change)

Answer 27

warming.

Question 28

Explain the relationship between island size and species count/habitat count

Answer 28

The larger the island, the more species, more habitats

Question 29

Give the formula for Species-area curve

Answer 29

Species-area curve: S = C * A^Z → linear on a log scale log(S) = log(C) + Z*log(A)
S: # of species
A: island area
C: constant measuring the # of species per unit area
Z = slope (avg 0.3, range 0.15-0.35)

Question 30

Define the Equilibrium Theory of Island Biogeography

Answer 30

When a lot of species are present, high chance that the species is already there, so few new species and high chances of extinction
On larger islands, there is a lower per-species rate of extinction.
Island far from mainland → lower max rate of immigration

Draw the graph representing this relationship. (see slides).