Spatial patterning

Question 1

More organisms are dispersal limited. What does this mean?

Answer 1

They can only disperse by a certain amount.

Question 2

Give an example of a factor that limits dispersal.

Answer 2

Size: large organisms do not disperse as uniformly as small ones. Small is classed as <1mm, as these organisms are hugely affected by the environment, e.g. blown in the wind.

Question 3

Nearly all ecological interactions are local ones. Give 3 examples.

Answer 3

1. Predator-prey (+,-)
2. Competition (-,-)
3. Mutualism (+,+)

Question 4

There are 2 types of spatial heterogeneity. What are they?

Answer 4

1. Externally generated: created by the abiotic environment.

2. Internally generated: created by biotic interactions

Question 5

What generates spatial pattern?

Answer 5

Local dispersal

Question 6

What does spatial patterning determine?

Answer 6

Local neighbourhood.

Question 7

There is a link between spatial patterning and mortality rate. True or false?

Answer 7

True: if organisms are aggregated into high densities they will suffer.

Question 8

Ecological neighbourhoods are defined where the focal individual sits in a circle. The circle represents a boundary. What does this boundary signify?

Answer 8

The distance at which neighbours no longer have an effect on the growth/mortality/fecundity rate etc. of the focal individual.

Question 9

There are 3 main spatial patterns. What are they?

Answer 9

1. Aggregated
2. Segregated
3. Random

Question 10

Explain aggregated patterning.

Answer 10

Small groups of individuals clustered together.

Question 11

What kind of a) dispersal and b) interaction is involved in aggregated spacing?

Answer 11

a) short range - organisms stay close to parent/family group

b) short range - organisms thrive on close interaction, sociality

Question 12

What are other names for segregated spacing?

Answer 12

Over-dispersed or even-spaced.

Question 13

Describe segregated spacing.

Answer 13

Individuals are evenly spaced - there are exclusion zones around each organism as competition is intense.

Question 14

What kind of a) dispersal and b) interaction is involved in aggregated spacing?

Answer 14

a) long range - organisms travel far from their original location
c) short range - close competition between neighbours

Question 15

Describe random spacing.

Answer 15

The distribution of each individual is independent of its closest neighbours.

Question 16

In random spacing, organisms neither inhibit each other, as in segregated spacing, or promote each other as in aggregated spacing. True or false?

Answer 16

True.

Question 17

What kind of a) dispersal and b) interaction is involved in aggregated spacing?

Answer 17

a) long range

b) long range - organisms rarely interact

Question 18

What 2 things do we assume about a population if it is randomly spaced?

Answer 18

1. There is a high birth rate

2. There are high levels of post-birth movement

Question 19

Aggregated spacing is the most common pattern and serves as the null hypothesis in dispersal experiments. True or false?

Answer 19

False - aggregated is the most common pattern, but random distribution serves as the null hypothesis as it assumes there is no interaction between individuals.

Question 20

Individuals in densely aggregated populations do not often survive. Why?

Answer 20

Due to competition, there are not enough resources to sustain that many organisms in one space.

Question 21

What is ballistic dispersal mode?

Answer 21

Seeds in a pod are thrown out.

Question 22

What are the 3 main dispersal mechanisms for seeds?

Answer 22

1. Ballistic
2. Wind
3. Animal

Question 23

Which type of seed dispersal results in the least clumped spacing?

Answer 23

Wind

Question 24

What does the Logistic equation of dN/dt = rN(1-N/K) where N pop size, r births-deaths, K carrying capacity assume about spatial patterning?

Answer 24

It is random and the population is well mixed.

Question 25

What can be said about a) growth rate and b) size in segregated populations and why?

Answer 25

a) Faster growth
b) larger size

because space is used more efficiently.

Question 26

What can be said about a) growth rate, b) size and c) carrying capacity in aggregated populations and why?

Answer 26

a) slower growth
b) smaller size
c) reduced K

because space is used less efficiently.

Question 27

Which population is faster to reach equilibrium, segregated or aggregated?

Answer 27

Segregated. Equilibrium is when K is reached.

Question 28

Generally what kind of competition is seen in aggregated populations?

Answer 28

Intraspecific

Question 29

Dispersal causes clustering under what condition?

Answer 29

Conspecific interaction.

Question 30

Aggregated and segregated distribution can be observed together between 2 species. The aggregation is conspecific and the segregation is heterospecific. True or false?

Answer 30

True - members of the same species are clustered together, but members of different species are segregated.

Question 31

What does it result in if conspecific competition is strong and heterospecific competition is weak?

Answer 31

Strong niche differentiation.

Question 32

What is the classical theory of effective competition?

Answer 32

The most effective competition is between the most similar competitors. Conspecific competition limits pop. growth but heterospecific competition causes niche differentiation.

Question 33

What is the segregation hypothesis?

Answer 33

Competition over space is fiercest between ecologically similar species.

Question 34

Under the segregation hypothesis ecological resilience increases in smaller spatial scales. What does this lead to?

Answer 34

Coexistence. Organisms are forced to exist in smaller areas. This leads to the elimination of efficient interspecific competition.

Question 35

List 3 problems with the segregation hypothesis.

Answer 35

1. Only slows the exclusion of weakest competitors
2. At cluster boundaries the strongest competitor still wins
3. The rate of exclusion depends on the shape of the cluster

Question 36

Even under the segregation hypothesis where organisms are forced to coexist, is coexistence not stable. Why?

Answer 36

Because interspecific competition is limited (by exclusion zones), not prevented, thus eventually the stronger competitor will encroach it the other’s territory.

Question 37

What happens in stable coexistence?

Answer 37

All species are expected to increase when rare.

Question 38

What happens in unstable coexistence?

Answer 38

There is ecological drift, i.e. the loss of some species.

Question 39

There are 2 theories for the outcome of species dominance in an area. What are they?

Answer 39

1. Non special theory: if neither species can invade the other, then that which dominates will be by founder control, i.e. it arrived first or has a larger population.
2. Spatial theory: if neither species can invade the other, that with the smaller population wins because it is less aggregated so there is less intraspecific competition, promoting growth.

Question 40

What is the theory of asymmetric dispersal?

Answer 40

Long range dispersal is hugely advantageous, for example it escapes kin competition and allows a higher density at equilibrium.

Question 41

What is the competition-disperser trade-off?

Answer 41

Better dispersers prove weaker competitors.

Question 42

If organisms are similar competitors it makes coexistence easier. True or false?

Answer 42

False - it makes it harder as they are more equally matched.

Question 43

Give evidence for the asymmetric theory of dispersal.

Answer 43

Ozinga in 2009 conducted a meta-analysis and found plants with mammal and water seed dispersal were declining, bird and wind dispersers were doing well. The former display short range dispersal and the latter long range dispersal.

Question 44

Why are evenly spaced rows of crops the best for producing maximum yield?

Answer 44

There is space for weeds to grow between the rows. This reduces competition between crops (conspecific) as they are not aggregated and increases heterospecific competition, with crops outcompeting weeds.