Lecture 15: Impacts on Ecosystems

Question 1

How did an aquatic plant invasion cause bald eagle deaths?

Answer 1

• Hydrilla-cyanobacterial mats spread, which mallard ducks are highly exposed to. The mats produce a neurotoxin causing degenerative brian disease in the ducks. Bald eagles die via eating the duck.
• Hydrilla on it’s own does not produce this…needs the cyano
• removal of a top predator like the eagle will have ripple effects in the ecosystem

Question 2

What is an ecosystem?

Answer 2

a set of organisms the interact with each other and their physical environment
*energy flow

Question 3

What was the ecosystem impact of the gypsy moth?

Answer 3

• defoliation of oak and pine forests brought down net carbon uptake by 40-55%

Question 4

How do invaders alter ecosystem processes?

Answer 4

1. when they alter a limiting resource
2. When they alter the flow of energy within the system
3. When they alter the frequency / intensity of disturbance

**such invaders tend to differ greatly from resident species in how they acquire and use resources

Question 5

Alterations of Ecosystem ex via limiting resource:

- Myrica faya

Answer 5

• nitrogen fixing tree
• native to azores, introduce in Hawaii
• facilitates invasions by other exotics
• in lava fields which are nutrient poor
• altered soil chemistry

Question 6

Explain the primary succession in the lava fields after Myrica entered it.

Answer 6

• increased N
• plants were able to take advantage of this change i availability
• For this to be true:
  1. N must be a limiting nutrient
  2. N-fixation by Myrna must alter the ecosystem’s N budget
  3. N fixed by Myrica must become available to other organisms
• *experiment found that addition of N to young lava field promoted native plant growth where as it didn’t in old fields

Question 7

Alterations of Ecosystem ex via limiting resource:

- Saltceder trees

Answer 7

• deeply rooted in groundwater
• have high transpiration rate
• desiccate streams and marshes
• threaten stream pool habitats of endangered pupfish

Question 8

Alterations of Ecosystem ex via limiting resource:

- Pine and Eucalyptus in South Africa

Answer 8

• heavy water uptake

- caused many rivers to dry up or flow infrequently

Question 9

Alterations of Ecosystem ex via Alter the flow of energy within ecosystems?

Answer 9

• introduction of piscivores to small lakes

- filter feeders introduced to isolated systems

Question 10

Explain alteration in energy flow via zebra mussels?

Answer 10

• they clear the water
• deposit feces and pseudofeces on sidemoits
• pseudofeces are material not digested, wrapped in mucous. The sheath has some carbon in it, so it is an energy deposit for others
• take materials from the water column and release these
• so they provide food
• they also provide shelter, interstitial space providing refuge for small invertebrates

*density of invertebrates increased with zebra

Question 11

Alterations of Ecosystem ex via alter the frequency or intensity of disturbance?

Answer 11

1. Broomsedge (invasive grass)
2. European earthworms
3. Feral pigs

Question 12

Alterations of Ecosystem ex via alter the frequency or intensity of disturbance:
1. Broomsedge

Answer 12

• perennial weed
• invaded slopes in wet mountain forest areas
• dring winter, the weed is dormant and transpires very little water
• soils on mountain slopes become saturated with water , resulting in landslides

Question 13

Alterations of Ecosystem ex via alter the frequency or intensity of disturbance:
2. Earthworms?

Answer 13

• exotic earthworms (night crawlers) effect on deciduous forest floors
• chew up leaf litter which normally takes 3-5 years to decay
• they speed up decomp
• causes habitat to change bc they remove understory which needs leaf litter

Question 14

Alterations of Ecosystem ex via alter the frequency or intensity of disturbance:
3. Feral pigs?

Answer 14

• native to Eurasia
• introduced for farms and game
• disturb soil through their digging activities
• remove litter
• trample soil
• disturbance causes erosion, releasing nitrogen, change soil chemistry and water
• changes understory veg
• pits they create fill up with water which is a great place for mosquitos
  L> enhance malaria which can infect birds

Question 15

Explain the invasion of the mediterranean sea by the green alga Caulerpa taxifolia

Answer 15

• used in aquaria
• grows in many temp regimes
• it spread like crazy
• spreading via cuttings from boats
• genetically all the same strain , spreading colonially
• homogenizing the habitat
• algal also has toxins to resist grazers

Question 16

What are the effects of introducing goldfish to a pond?

Answer 16

stir up fine sediment, suspending them, increasing turbidity
- gold fish are shiny which attracts attention of birds
- more gold fish = more turbidity, their activity can reduce visibility to predators = niche construction
- increased turbidity hurts macrophytes bc it lowers illumination
- epiphytic inverts tha live on plants, will be harmed as well
L> spotted newts feed on these inverts, it’s a visual predator, so turbidity reduces it’s sight and foraging success
L> newts pop will lower
**doesn’t always need to be a predator causing a change

Question 17

Impact of common carp on rooted aquatic plants?

Answer 17

• ## uproots plants, eat plants, increases turbidity which reduces light, which reduces plant biomass

Question 18

What four things do we know so far about ecosystem impacts?

Answer 18

1. many invasions cause no detectable ecosystem impacts
2. Invasions can alter a varied of ecosystem properties: productivity, nutrient cycling, hydrology etc
3. To cause ecosystem level impacts, invaders must be able to acquire and use resources differently than native species (e.g. by altering energy flow or disturbance regimes)
4. Some keystone invaders can cause cascading impacts that affect multiple components of the ecosystem

Question 19

Explain the root rot fungus

wrt death of threes and shrubs

Answer 19

• soil fungus
• attacks roots of shrubs and trees
• antive to SE Asia
• introduced to Aus with orange trees from Indonesia
• caused dieback of plants
• spread widely in Australia via soil on wheels
• caused death of threes and shrubs
• understory increases
• loss of nesting sites and refuges –> therefore reduction in pollinators and seed disposals -> loss of prey for predators
• loss of nectar insects and birds, therefore reduced food for predators
• loss of transpiration -> increase water table
• reduced plant biomass -> reduced nutrient cycling

Question 20

Explain the root rot fungus

wrt increase in herb cover

Answer 20

• increased food for marsupials (increase dung beetles )
• increased food for some insects –> increase in certain predators
• suppressed germination of wood plants -> reduction in associated animals-> reduction of certain predators

Question 21

What are the three ways zebra mussels impact the ecosystem

Answer 21

1. Removal of suspended particles
2. Biodeposition
3. Biofouling

Question 22

Zebra mussel invasion:

1. Removal of Suspended particles?

Answer 22

1 loss of phytoplankton

• reduced food source for zooplankton
• reduced food for planktivores
• reduced food for piscivores
  2. Increased light penetration
• increase in benthic algae and plants
• increased food and habitat for consumers
  3. Altered nutrient and contaminant cycles

Question 23

Zebra mussel invasion:

2. Biodeposition

Answer 23

1. Increased sedimentation
   - lower dissolved oxygen
   - habitat for burrowing fauna
2. increased food source for detritivores
   - increased food for predators

Question 24

Zebra mussel invasion:

3. Biofouling

Answer 24

1. Habitat for interstitial fauna
   - increased food for predators
2. Mortality of native mussels
   - reduced sediment mixing
   - lower dissolved oxygen

Question 25

Cascading ecosystem impacts are caused by?

Answer 25

• species that create or disrupt energy pathways
  i. e. those that cut or build links between species from different trophic groups or ecosystem compartments
• solid lines = transfer of organic
• Dashed= pathways of inorganic

*ex = zebra mussels
altered links from carnivore all the way to detritus

• Ex: mnemiopsis jelly fish altered the link btwn herbivore and carnivore via feeding on anchovy
• Ex: goats on islands and chestnut blight both alter links between plants and herbivores + detritus

Question 26

Explain the cascade in Hawaii upon the intro of goats and pigs

Answer 26

• took out nectar producing plants
• which lowered levels of nectivorous birds
• which lowered hawaiian hawk

Question 27

Invasiveness vs impact of exotic sp?

Answer 27

• high impact = higher rate of spread

- higher prob of establishment success too

Question 28

Summarize key points of this chapter.

Answer 28

1. An important determinant of an invaders impact or native species i the naivete of the recipient community
2. The greatest ecological impacts are caused by uncontrolled generalist consumers
3. Ecosystem level impacts tend to be caused by invaders that acquire and use resource differently from resident species.
4. Cascading ecosystem impacts are caused by invaders that create or disrupt energy pathways
5. The potential impact of an exotic species is not correlated with its ability to spread

Question 29

Explain the zebra mussel impact one more timeee.

Answer 29

• overgrow on other mussels
• facilitate other inverts via providing interstitial spaces
• stimulate success of grazing inverts which can also leave and go to other areas
• can cause benthic algal to increase via increasing light and water clarity
• submerged macrophytes do well with zebra
• phytoplankton will reduce bc of the filtrations, zooplankton which feed on them will decrease and larval fish that feed o zooplankton will decrease primary production, habitat structure, nutrient cycling all effected.