Spatial patterning Flashcards
More organisms are dispersal limited. What does this mean?
They can only disperse by a certain amount.
Give an example of a factor that limits dispersal.
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.
Nearly all ecological interactions are local ones. Give 3 examples.
- Predator-prey (+,-)
- Competition (-,-)
- Mutualism (+,+)
There are 2 types of spatial heterogeneity. What are they?
- Externally generated: created by the abiotic environment.
2. Internally generated: created by biotic interactions
What generates spatial pattern?
Local dispersal
What does spatial patterning determine?
Local neighbourhood.
There is a link between spatial patterning and mortality rate. True or false?
True: if organisms are aggregated into high densities they will suffer.
Ecological neighbourhoods are defined where the focal individual sits in a circle. The circle represents a boundary. What does this boundary signify?
The distance at which neighbours no longer have an effect on the growth/mortality/fecundity rate etc. of the focal individual.
There are 3 main spatial patterns. What are they?
- Aggregated
- Segregated
- Random
Explain aggregated patterning.
Small groups of individuals clustered together.
What kind of a) dispersal and b) interaction is involved in aggregated spacing?
a) short range - organisms stay close to parent/family group
b) short range - organisms thrive on close interaction, sociality
What are other names for segregated spacing?
Over-dispersed or even-spaced.
Describe segregated spacing.
Individuals are evenly spaced - there are exclusion zones around each organism as competition is intense.
What kind of a) dispersal and b) interaction is involved in aggregated spacing?
a) long range - organisms travel far from their original location
c) short range - close competition between neighbours
Describe random spacing.
The distribution of each individual is independent of its closest neighbours.
In random spacing, organisms neither inhibit each other, as in segregated spacing, or promote each other as in aggregated spacing. True or false?
True.
What kind of a) dispersal and b) interaction is involved in aggregated spacing?
a) long range
b) long range - organisms rarely interact
What 2 things do we assume about a population if it is randomly spaced?
- There is a high birth rate
2. There are high levels of post-birth movement
Aggregated spacing is the most common pattern and serves as the null hypothesis in dispersal experiments. True or false?
False - aggregated is the most common pattern, but random distribution serves as the null hypothesis as it assumes there is no interaction between individuals.
Individuals in densely aggregated populations do not often survive. Why?
Due to competition, there are not enough resources to sustain that many organisms in one space.
What is ballistic dispersal mode?
Seeds in a pod are thrown out.
What are the 3 main dispersal mechanisms for seeds?
- Ballistic
- Wind
- Animal
Which type of seed dispersal results in the least clumped spacing?
Wind
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?
It is random and the population is well mixed.
What can be said about a) growth rate and b) size in segregated populations and why?
a) Faster growth
b) larger size
because space is used more efficiently.
What can be said about a) growth rate, b) size and c) carrying capacity in aggregated populations and why?
a) slower growth
b) smaller size
c) reduced K
because space is used less efficiently.
Which population is faster to reach equilibrium, segregated or aggregated?
Segregated. Equilibrium is when K is reached.
Generally what kind of competition is seen in aggregated populations?
Intraspecific
Dispersal causes clustering under what condition?
Conspecific interaction.
Aggregated and segregated distribution can be observed together between 2 species. The aggregation is conspecific and the segregation is heterospecific. True or false?
True - members of the same species are clustered together, but members of different species are segregated.
What does it result in if conspecific competition is strong and heterospecific competition is weak?
Strong niche differentiation.
What is the classical theory of effective competition?
The most effective competition is between the most similar competitors. Conspecific competition limits pop. growth but heterospecific competition causes niche differentiation.
What is the segregation hypothesis?
Competition over space is fiercest between ecologically similar species.
Under the segregation hypothesis ecological resilience increases in smaller spatial scales. What does this lead to?
Coexistence. Organisms are forced to exist in smaller areas. This leads to the elimination of efficient interspecific competition.
List 3 problems with the segregation hypothesis.
- Only slows the exclusion of weakest competitors
- At cluster boundaries the strongest competitor still wins
- The rate of exclusion depends on the shape of the cluster
Even under the segregation hypothesis where organisms are forced to coexist, is coexistence not stable. Why?
Because interspecific competition is limited (by exclusion zones), not prevented, thus eventually the stronger competitor will encroach it the other’s territory.
What happens in stable coexistence?
All species are expected to increase when rare.
What happens in unstable coexistence?
There is ecological drift, i.e. the loss of some species.
There are 2 theories for the outcome of species dominance in an area. What are they?
- 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.
- 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.
What is the theory of asymmetric dispersal?
Long range dispersal is hugely advantageous, for example it escapes kin competition and allows a higher density at equilibrium.
What is the competition-disperser trade-off?
Better dispersers prove weaker competitors.
If organisms are similar competitors it makes coexistence easier. True or false?
False - it makes it harder as they are more equally matched.
Give evidence for the asymmetric theory of dispersal.
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.
Why are evenly spaced rows of crops the best for producing maximum yield?
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.
