Lecture 8: Fluctuating Resource Availability Hypothesis (FRA)

Question 1

What’s the role of vectors?

Answer 1

• they determine what types of species are likely to be delivered to a new region
• vectors are related to movement of people or merchandise

Question 2

What did Levine and D’Antonio find?

Answer 2

• rate of invasions increases with trade volume but not linearly bc the probability of imports bringing in new exotic sp declines as more invaders become established

Question 3

Where do most insect invaders in NA come from?

Answer 3

66% Western Palearctic (Europe)
- not equal in distribution
BUT the climate is similar btwn NA and europe which i why they can establish

Question 4

Explain the asymmetry in insect exchange between continents.

Answer 4

• more went to NA vs Europe

- asymmetry characterizes most if not all biotic exchanges between biogeographic regions.

Question 5

Explain the hypotheses to explain asymmetric biotic exchange (Vermeij 1991)

Answer 5

1. Dispersal opportunities. The number of species going in any direction is proportional to the propagule pressure (trade and human dispersal) in that direction
2. Relative sizes of donor pools. Numbers of invaders reflect differences in the species available in each donor region.
3. Ecological opportunities for invaders. Numbers of invaders are determined by the opportunities (resources) avail upon arrival.
4. Intrinsic superiority of a donor pool. Numbers of invaders are determined by competitive ability of species in each donor region.

Question 6

List reasons for host availability for Euro insects in NA.

Answer 6

1. Similar Hosts
2. More hosts in NA
3. More abundant and less fragmented forests in NA

Question 7

Explain: Similar hosts for european insects.

Answer 7

• potential hosts are budnant and closely related to ancestral hosts in Europe

Question 8

Explain: More hosts in NA for euro insect

Answer 8

• NA has twice as many plant species and genera bc many genre went extinct in europe during the Pleistocene glaciation

Question 9

Explain: host availability for european insects via more abundant and less fragmented forests in NA

Answer 9

• NA tree abundance is twice that of europe bc europe has higher human population densities

Question 10

List the factors that influence invasion success that we have covered so far.

Answer 10

1. Propagule pressure
2. Attributes of the invader
3. Invasibility of the environment (abiotic and biotic)

Question 11

What factors make some communities more invisible than others?

Answer 11

1. Fluctuating Resource Availability
2. Disturbance
3. Vacant Niches
4. Enemy Release
5. Biotic Resistance

Question 12

Explain what the theory of fluctuating resource availability is and it’s assumptions

Answer 12

• a plant community becomes more susceptible to invasion whenever there is an increase in the amount of unused resources either via removal of competitors or increase in resources
• *by fluctuating the resources, naive sp cannot get a strong hold on the resources, we inhibit comp which is often the main source of why invasion happens

Assumptions

• an invader must have access to limiting resources ( e.g. light, nutrients, water)
• the invader will have greater success if it does not encounter intense competition for these resources

Question 13

How can the availability of resources be increased and this the invasibility of the community ?

Answer 13

1. The use of resources by resident sp declines. Can result from any factor that removes competitors (e.g. disturbance, herbivory, disease)
2. Resource supply increases at a rate faster than the resident sp can use it. This can result from organic pollution (nutrient addition), a wet season (increased water supply), or removal of tree canopy (increased light)

OR BOTH

** these must occur with propagule pressure

Question 14

describe the effect of shading on the biomass of an invasive grass (para grass).

Answer 14

• removed supply of solar radiation (limiting nutrient)
• less extreme for areas that are the uppor portion of the plant bc they are adapted to the sun
• biomass decreased

Question 15

Explain the canary grass ex

Answer 15

• disturbance promotes success of it by removing shading by native dominants

Question 16

Explain the effect of simulated grazing and nutrient addition on biomass of Phalaris arundinacea

Answer 16

• grazing should reduce shade
• removal of shade alone did not help the invader much
• adding nutrients alone didn’t have a big impact either
  BUT nutrient + grazer = highest biomass
  *so neither disturbance on their own but together they did

**where disturbance is highest and resources are highest = greatest cover of invasive sp

Question 17

Explain the predictions of the theory of fluctuating resource availability

Answer 17

1. Areas subject to pronounced fluctuations in resource supply are more susceptible to invasion than areas with stable supply
2. Community invisibility will fluctuate over time
3. invisibility will increase following disturbance
4. invisibility will increase following the introduction of herbivores into nutrient rich areas

Question 18

Explain the influence of grazers on sp richness in nutrient-rich vs nutrient-poor communities

Answer 18

• in nutrient rich areas with high disturbance = greater plant species richness
• if poor nutrient, as grazing intensity goes up, species richness goes down

Question 19

What are the implications of the FRA theory

Answer 19

• invisibility of a system varies over time
• biological disturbance agents (including other invaders) can facilitate invasions
• a general theory of invasion will be elusive due to numerous resource release mechanisms