10. Community ecology: Dispersal

Question 1

What is dispersal?

Answer 1

Individuals moving from one habitat to another

Question 2

Why is dispersal important?

Answer 2

1. Allows individuals to colonize new areas
2. Escape competition
3. Avoids inbreeding depression

Question 3

What is inbreeding depression?

Answer 3

Negative fitness consequences of mating with a relative.

Question 4

How does dispersal affect inbreeding depression?

Answer 4

Dispersal reduces inbreeding dispersal, if individuals move out they find less population of their own kind which allows them to mate with new individuals.

Question 5

How have plants evolved for better dispersal of their seeds?

Answer 5

They have fresh fleshy fruits to attract animals for seed dispersal.

Other seeds are dispersed by wind or water.

Question 6

What do plants depend on in response to the climate warming?

Answer 6

Their ability to disperse, dispersal is very important for colonization

Question 7

What are metapopulations?

Answer 7

It is a collection of spatially distinct populations that are connected via dispersal.

Question 8

Why are metapopulations important?

Answer 8

It allows populations to exist, even when individual populations are doomed. or aka in local extinction

Question 9

What is the source-sink population?

Answer 9

source: The colonists or migrant population that enter the other patches

sink: the populations of the small habitat that would go extinct if they were not saved by the source population.

Question 10

What is an unstable population?

Answer 10

Population that would go extinct

Question 11

How does archipelago of metapopulations help?

Answer 11

Even if you have a locally unstable population, it would still have a group of globally stable populations.

Question 12

How is coupling provided on islands?

Answer 12

It is provided by occasional dispersal between islands.

Question 13

What is Levin’s patch occupancy model?

Answer 13

The rate of patch occupancy over time

Question 14

What affects the colonization rate in the patches?

Answer 14

The fraction of currently occupied patches

The fraction of empty patches

Question 15

What is ‘e’ in levens patch occupancy model?

Answer 15

The constant rate ‘e’ by which patches go extinct with.

Question 16

What is ‘P’ in leven’s patch occupancy model and what happens if it’s high?

Answer 16

It the number of occupied patches, if it is high that means there are more source populations which can than go and colonize.

Question 17

What is ‘c’?

Answer 17

It is some constant, which is multiplied with the proportion of occupied patches ‘P’

Question 18

What is the hump and the straight line in the patch occupancy model?

Answer 18

The hump is the colonization rate

The straight line is ‘eP’ it is the relationship between extinction rate and patch occupancy.

The line is the constant (e), which is the extinction rate for patches.

Question 19

What is on the x, y axis of Leven’s patch occupancy model?

Answer 19

X: Patch occupancy (P) (it goes 0 -> 1, from no patches occupied to all patches occupied.)

Y: Overall rate of colonization or overall rate of extinction

Question 20

Where does equilibrium patch occupancy occur on the leven’s patch occupancy model?

Answer 20

Where both the green line and the orange line intersect, because at that point colonization rate is exactly equal to to the extinction rate.

Question 21

What are competition colonization tradeoffs?

Answer 21

It is a condition where species A is a good competitor and species B is a good colonizer. B will be an R-strategist, while specie A will be a K-strategist.

Species A will always drive species B locally extinct. But in order to be globally stable, species B will disperse. (B can also be known as weed, fugitive, tramp)

Question 22

If species A always outcompetes species B, under what conditions is global co-existence possible?

Answer 22

1. A must sometimes go locally extinct in a patch or more new patches must be created
2. B must be a better dispersal then A

3.

Question 23

What did Andy Smith’s studies show about pika’s population?

Answer 23

It was declining in southern population, while stable in both northern and middle patch network but the patch occupancy was less in the middle.

X axis: West-East distance
Y axis: North-South distance

Question 24

How were predictions modelled about the pika populations? and what were on the axes?

Answer 24

1) Y : % patch occupancy
X: Time from the present year

The models were two kinds:

1) Left hand side was connected as dispersal among pika patches in regions and within the patches.

2) Right-hand side shows that pikas can only move within their patches not in the regions. (northern pikas can only move to northern patches, southern ones can move to southern patches.

Question 25

What were the findings about the pikas population in the next 1000 years?

Answer 25

The patches in the northern region were fairly high and stable, even if it was connected via only dispersal within and outside the region

In contrast, the metapopulations in the middle and southern regions only stay high, if they have source-sink both within the same region and with other regions (northern, middle, southern) if not the patch occupancy goes to 0.

Overall the prediction was pikas will only exist in middle and southern regions, if they were connected to other regions via dispersal

Question 26

What are the ways populations can be driven to extinction?

Answer 26

1) Stochasticity
2) Competitive exclusions
3) Through prey-predator (parasites can drive hosts extinct)
4) Allee effect when populations are low. (negative effects of having low population size)

Question 27

What is stochasticity?

Answer 27

Random fluctuations in the population sizes, and just by chance a population might decline to 0 when it is low in size.

Question 28

How was the paradox of plankton resolved?

Answer 28

1) Predation keeps competitive exclusion from going to completion (as in Paine’s sea star removal)

2) Non-equilibria conditions, habitat patchiness, rescue by migration, and variation in life history strategy that happens in a meta-population (as in a competitive colonization tradeoff.

Question 29

What is metacommunity?

Answer 29

Local communities connected or linked together by one or more constituent species.

Question 30

What determines the number of species on an island?

Answer 30

1. Colonization: a species can arrive on an island from elsewhere
2. Extinction: A specie can go locally extinct on an island
3. In-situ speciation: a lineage can split in two on an island, but this is a very slow process.

Question 31

Who came up with ‘the theory of island biogeography’?

Answer 31

Robert McArthur and Edward O Wilson

Question 32

What was the goal of the theory of island biogeography?

Answer 32

Predict the number of species from islands’ location and isolation. (distance from mainland)

Question 33

What was ignored and considered in the theory of island biogeography?

Answer 33

In-situ speciation was ignored, while only colonization and extinction was considered

Question 34

What was the model for theory of island biogeography? What were on the x and y axis?

Answer 34

It was a graphical model

X aixs: Number of species
Y axis: Colonization Rate or the extinction rate

Question 35

What happens to colonization as the number of species increases in the theory of island biogeography?

Answer 35

It decreases, when there are more species.

when there are low species the colonization is high.

Because, when there are a lot of species and a new migrant arrives, the chances that there are already members of that species is high, else if there are low number of species the chances that a new migrant specie already being there is low.

Question 36

What happens to extinction rate when species increases according to the theory of island biogeography?

Answer 36

The extinction rate would increase, because more and more species will compete for resources

Question 37

Where is the equilibrium path occupancy using the theory of island biogeography?

Answer 37

Where the lines of both the extinction rate and colonization rate intersect.

Question 38

What determines the colonization rate according to the theory of island biogeography?

Answer 38

The distance from the mainland, or how isolated the island is. This is because near islands are easier to get to hence they have higher colonization rates.

Question 39

Does near islands or islands further away have more species at equilibrium?

Answer 39

The near islands have more species at equilibrium

Question 40

How does size of island depend on the number of species at equilibrium.

Answer 40

Small islands have more extinction rate, while larger islands has less extinction rate, which means it will have more species at equilibrium. ( It will intersect the colonization line further away)

Moreover, smaller islands have less population, because they are smaller.

Question 41

How was specie richness affected as studied by Prof. Luke Mahler?

Answer 41

he studies the spice richness on different-sized islands.

First graph:
X axis: Area (in sq km)
Y axis: Specie richness

He found larger islands had more specie richness, compared to smaller ones.

He also found geographically isolated species have less specie richness.

Second graph: X axis: how close to the mainland (higher values mean more geographically isolated the island is)

Y axis: Specie richess

The more isolated island was, the less species it had.

Question 42

What can the theory of island biogeography also be applied to?

Answer 42

Forests as well. Small and more isolated fragments of forests retain fewer species.