Community Dynamics Through Time

Question 1

Biotic drivers of change

Answer 1

Interspecific interactions (selection)
Demographic stochasticity (drift)
Invasive species (dispersal and selection)

Question 2

Abiotic drivers of change

Answer 2

Global change: habitat loss, fragmentation, climatic change
Eutrophication
Pollutants
Disturbance: floods, wildfires

Question 3

Eutrophication

Answer 3

Chnage in nutrient salt concentrations of water

Changes ecosystem = increased algae levels, depleted fish species, deteriorating water quality

Question 4

Why would there be equilibrium/ stationary change in community dynamics

Answer 4

This is normal

Likely to vary around equilibrium due to intrinsic dynamics or extrinsic disturbance e.g flood, fire

Question 5

Why would there be long term, directional change in community dynamics

Answer 5

• decline, increase or turnover
• can be natural or anthropogenic chnage
• primary or secondary successional
• often moves towards a climax with directional pattern of colonisation and extinctions

Question 6

E.g. of long term directional change

Answer 6

Vegetative successions 
- volcano erupts and creates new land type 
- lichen colonise 
-soil forms 
-vascular plants created
Climax vegetation achieved

Question 7

Describe alternative states

Answer 7

Small environmental changes can cause dramatic community structure shit
Often needs disproportional large change to drive system, back

Question 8

Describe eutrophic shallow lakes

Answer 8

Nutrient level increase caused large change
1. Clear macrophage growth, zooplankton suppress phytoplankton
2. Turbid abundant phytoplankton as fish suppress zooplankton due to reduced shelters and resuspended sediment
Tried to revert back to original state but often unsuccessful e.g. buffer strips on farms
Elements maintain state e.g. fish stir up sediments and keep nutrients present in water

Question 9

List the types of change

Answer 9

Equilibrium/stability
Long term, directional
Alternative stable states
Collapse

Question 10

E.g. of collapse

Answer 10

Australian megafauna after human colonisation = 60 spp lost, 45-50,000 YA
Caused dietary shifts emu and wombat
- mix of C3 and C4 pants
- pre humans = variable diet, lots of C4. Abundant nutritious grasses
- post mans = restricted trees and shrubs; C3
Vegetation changed due to land management and burning regime so more resitant to fires

Question 11

How to detect community change

Answer 11

changes in a combination of:
- abundance
- evenness 
- richness
- composition 
quality assurance scheme (QA) may look at percentage of samples to ensure accuracy over time 
Citizen science

Question 12

Name the disturbance types

Answer 12

Pulse
Press
Ramp

Question 13

Pulse disturbance

Answer 13

Short time frame
Discrete events
- can easily mark when started and stopped

Question 14

Press distrubance

Answer 14

• may be rapid

- reaches a level thats maintained

Question 15

Ramp disturbance

Answer 15

• steadily increasing
• no set endpoint
  E.g. climate change

Question 16

What can stability be broken down into

Answer 16

Variability
Resilience
Resistance
Ecological resilience

Question 17

How variability affects stability

Answer 17

Large variability = lower stability and vice versa

Question 18

How resilience affects stability

Answer 18

Speed community returns to original state after disturbance

Often linked to pulse disturbance

Question 19

Disturbance half life

Answer 19

Disturbance decays exponentially

E.g. Vaughan and Gotelli (2019) climate change distrubance on UK rivers = 2.5-5 years

Question 20

How Ecological resilience affects stability

Answer 20

Magnitude of disturbance to shift community between states
In ramp disturbances low ecological disturbance is better as dont want to adapt and then be unable to live in original state

Question 21

How resitance affects stability

Answer 21

The change in a community following disturbance

Communities ability to maintain itself during disturbance

Question 22

How does community research affect structure? Evolution of thought

Answer 22

1. 1950s
complex communities more stable. Qualitative reasoning 
- more routes for energy flow
- more natural 
- pest outbreaks simplified 
2. 1970s
More complex communities less stable; mathematical reasoning 
- more routes for disturbance 
- stronger coupling between species 
3. Modern 1990s+
- population level less stable 
-community level more stable

Question 23

Cedar creek grassland experiment

Answer 23

13 years measured overall biomass

• increased diversity. Stable community, unstable populations
• main mechanism = asynchrony among species in community
  
  • different niches, populations respond differently at different rates
  • averages out at community level

Question 24

Asynchronous community

Answer 24

Stable community that levels over time

Question 25

Synchronous community

Answer 25

If there are smaller species diversity

Each species has broadly similar ecology leading to similar extremes so less stable