Lecture 11: Biotic Facilitation

Question 1

Discuss the invasion of christmas island by crazy ants

Answer 1

• invaded in early 20th century
• became abundant 70 yeas later (probs bc of the introduction of the scale insect)
• has a mutualism with scale insects which produce honeydew, ants provide protection to the scale insects for the honeydew.
• red crabs are the dom native omnivore/herbivore
• ants kill the crabs by spraying formic acid on them
• crabs are 40 times less abundant in ant invaded areas

Question 2

What are the primary effects of crazy ants on christmas island

Answer 2

• reduction in land crabs

- increase in scale insects

Question 3

What are the secondary effects of crazy ants on christmas island

Answer 3

• reduction in tree canopy
• increase in leaf litter
• altered understory vegetation

Question 4

Describe the trophic cascade on christmas island

Answer 4

• ants form a mutualism with scale insects
• reduce crabs
• crabs keep plants and molluscs in check
• with crabs removed, these populations go unchecked

Question 5

What can propagule pressure do to biotic resistance?

Answer 5

• overwhelm it

Question 6

What are the explanations for observed invasion trends?

Answer 6

**overal trend is increasing invasions globally:

1. sampling bias (search effort, lag times)
2. An increase in propagule supply*****
3. A reduction in environmental resistance (temperature, natural disturbance, not enough food, etc – vary over time)
4. Biotic facilitation

Question 7

List the reasons for biotic facilitation.

Answer 7

1. Animals pollinating and dispersing plants
2. Animals modifying habitats
3. Plants modifying habitat s
4. Addition of prey or host species
5. Indirect effects

Question 8

Reasons for Biotic Facilitation:

1. Animals pollinating and dispersing plants . Explain.

Answer 8

• mutualism or commensalism can occur
  ex: chinese fig has established but was not really spreading, once the fig wasp was introduced the fig tree began spreading. LAG (45 years)
  ex: non native weeds spread by foxes accidentally eating them, pigs causing disturbances by trampling

Question 9

Reasons for Biotic Facilitation:

2. Animals modifying habitats. Explain examples

Answer 9

• In Aus, the shrub M. pigra displaced native sedges after introduction of Asian water buffalo. The buffalo was trampling, creating ideal germination ground for the seedlings , this caused declines of native waterfowl and insectivores birds

Question 10

Reasons for Biotic Facilitation:

3. Plants modifying habitats. Explain examples

Answer 10

• N-fixing shrub M. faya invaded areas of nutrient poor volcanic soil in Hawaii, altered the soil chemistry (add N), and other exotic plants eventually came and introduced themselves

Question 11

Reasons for Biotic Facilitation:

4. Addition of prey or host species. Explain examples

Answer 11

1. Spread of feral cats and fox in Australia after the spread of european rabbit
2. Abundance of zebra mussels in the great lakes may have facilitated the expansion of round goby (zebra mussels natural predator)
   L> nothing was feeding on zebra mussels, so it exploited this

Question 12

Reasons for Biotic Facilitation:

5. Indirect effects

Answer 12

• can have negative effects like crowding
• say a herbivore comes around that is evolutionary adapted toe at the plant which means the plant will adapt some defence . If the exotic plant is closely related to there native plant. Say the native plant has less defence to the exotic herbivory, so the herbivore overharvasts, allowing an exotic plant to overcome comp
• coevolution decreases the intensity of interactions

Question 13

Explain the facilitation of bullfrog invasions of ponds by non indigenous fish

Answer 13

• bullfrogs invaded West coast of America
• enemy of their tadpoles = dragonfly nymph
• blue gill sunfish will go after the dragon fly nymph
• if this happens, they indirectly facilitate the tadpole by removing the resistance

Question 14

Explain the facilitation of an exotic bivalve by an exotic crab in California

Answer 14

• native sp= small clam, Nutricola which is important food source for shorebirds, crabs etc
• Gemma , an invasive clam was introduced but comp with Nutricola kept them in low numbers
• when green crabs were introduced they caused a decline in Nutricola (preferred clam), gemma which has no life history with green crabs took off in population size

Question 15

Explain the invasional meltdown model.

Answer 15

• facilitation among introduced species is common and may produce two effects:
  1. rapid accumulation of exotic species
  2. increased frequency of synergistic impacts (combined effects of multiple exotic sp)

Question 16

What is mutualism?

Answer 16

• both interacting sp benefit

Question 17

What is commensalism:

Answer 17

• one is benefited and the other is neutral

**common in predator-prey relationships when the prey reproduces a lot

Question 18

Amensalism?

Answer 18

one sp is negatively effected and the other is not

Question 19

Antagonism?

Answer 19

• both sp are negatively effected (ex competition)

Question 20

Exploitation

Answer 20

• most common direct interaction, one sp benefits from the exploitation of another

Question 21

Explain the mutualism between zebra mussels and exotic weeds.

Answer 21

• zebra mussels filter water, removing suspended solids and phytoplankton
• leads to increased water clarity, which for sp that are light limited, can benefit them. So weedy sp will adjust right away bc of the excess light
• most of these plants serve as great settling places for zebra mussels bc they can attach to the plant and reduce competition for substrate. This also facilitates attachment to boats for human vectors

Question 22

Explain changes ing great talk fish populations

Answer 22

• lake trout initially was a dom predator, reduced by humans and even more dramatically by the introduction of lamprey
• lake trout had no experience with lamprey (got in via canal)
• alewife came in via canal and could now establish bc of lower lake trout
• introduced salmon decline bc of increase in alewife
• commensalism btwn lamprey and alewife

Question 23

Explain the facilitation of the seaweed Codium fragile by bryozoans

Answer 23

• bryozoans encrust on rocks, kelp leaves and stems BUT this isn’t good for kelp bc it makes them brittle and vulnerable to storm damage. It mediates the competitiveness between kelp and sodium. It cannot attach to sodium well but does with kelp. SO kelp is damged more frequently. BIOTIC resistance. Bryozoan does not benefit at all.
• changes the environment. Kelp beds provide an open understory where as sodium does not, it shades the substrate – bad for various inverts and fish

Question 24

Explain the relationship between human activities, invasions and alteration of ecosystems.

Answer 24

Human activities like stocking and unintentional release can facilitate invasions which can then alter the ecosystem. Human activities can also directly alter the ecosystem through habitat alteration, pollution and overfishing
- there is a positive feedback between species invasions and altering ecosystems BC species invasions can facilitate more invasions through change sin the ecosystem