D4.2 - ecosystem stability (1h)

Question 1

what is the stability of natural ecosystems?
how long can they persist for?

Answer 1

ecosystems have the potential to be sustainable over long periods of time, without outside influence, meaning there is now an absence of changes and the ecosystem is not under stress
- there is evidence for some ecosystems persisting for millions of years

Question 2

what is a stable ecosystem?
what are some examples?

Answer 2

a stable ecosystem allows continued survival of organisms and will have high species richness and evenness ( high biodiversity)
- forest ecosystems (eg) the Amazon rainforest is thought to be 55 million years old
- desert ecosystems (eg) the Sahara desert, although there is disagreement whether this ecosystem is tens of thousands, or millions of years old

Question 3

what are the 4 requirements for a stable ecosystem?

Answer 3

for stability in ecosystems the following must remain within tolerance levels:
- ongoing supply of energy
- recycling of nutrients
- genetic diversity
- climatic variables

Question 4

why is an ongoing supply of energy needed for a stable ecosystem?

Answer 4

• energy is provided by sunlight
• this light energy is converted to chemical energy through photosynthesis, produces organic compounds
• these carbon compounds and the chemical energy they contain are transferred along food chains, when eaten by consumers
• energy is lost, when respiration releases the chemical energy as ATP, which is used to carry out life functions, or heat

Question 5

why is recycling of nutrients needed for a stable ecosystem?

Answer 5

• producers take inorganic nutrients (eg, carbon, nitrogen, phosphorous) from the environment and create organic molecules that form biomass
• the nutrients are passed along food chains with some lost as waste
• decomposers break down the waste and dead organic material to release inorganic nutrients, recycling them
• oxygen is also recycled, being released by photosynthesis and used for aerobic respiration
• supplies of water also cycle, with evaporation and transpiration adding water vapour to the atmosphere and precipitation returning water to the Earth’s surface
• if an organism is removed from the environment, the nutrient stores within the ecosystem are reduced

Question 6

why is genetic diversity needed for a stable ecosystem?

Answer 6

healthy populations have genetic diversity, which reduces the likelihood of extinction following events such as introduction of a new disease, harsh climate changes or a sudden increase in predators

Question 7

why are climatic variables needed for a stable ecosystem?

Answer 7

the genetic diversity can only protect against extinction if the changes to the climatic variables remain within tolerance levels that the species can survive

Question 8

what can be a disruption to a stable ecosystem?

Answer 8

1. changes in the number or types of species
   - impacts on food chains or webs
   - impacts of food availability
2. habitat alteration
   - biogeochemical processes, such as erosion
   - changes in abiotic environmental factors (eg, temperature, precipitation levels)
3. changes in rates biochemical processes
   - (eg, photosynthesis, respiration, decomposition)

Question 9

what is a tipping point?

Answer 9

level of disturbance causes a quick change that is difficult to reverse

Question 10

what is a rainforest?

Answer 10

a dense forest, typically found in tropical areas with heavy rainfall, which has high biodiversity

Question 11

how does the amazon rainforest influence its own weather and climate?

Answer 11

the amazon rainforest is a very large ecosystem that can influence its own weather and climate
- the vegetation produces a lot water vapour through transpiration
- condensation of the water vapour creates rainfall, and areas of low pressure that cause air to flow towards the rainforest

Question 12

how is the amazon rainforest an example of a tipping point for ecosystem stability?

Answer 12

researchers have correlated increased temperatures and lower rainfall, with the areas that are deforested
- the amazon rainforest appears able to restore itself at the edges of deforested areas, but is not capable of restoring itself near the centre of deforested areas

it is uncertain what the minimum area of rainforest is, that is sufficient to maintain the processes of transpiration, cooling, air flow and rainfall
- if the tipping point is reached, the weather and climate would change, and the ecosystem would no longer be stable

Question 13

how is human activity influencing stability of the amazon rainforest?

Answer 13

deforestation is reducing transpiration in the amazon rainforest, which acts as a coolant and creates rainfall

Question 14

what is a keystone species?

Answer 14

species have a dis-proportionally large effect of the ecosystem and community structure, relative to their abundance

Question 15

why is it important to protect keystone species?

Answer 15

some biologists think protecting keystone species helps preservation of biological diversity within an ecosystem

Question 16

how do keystone species maintain the balance of other populations in an ecosystem?

Answer 16

they preserve and stabilize biodiversity, often by preventing overpopulation and out competition by organisms in lower trophic levels; this is top-down control
- however, keystone species are not necessarily the top predator (eg, honey bees pollinate flowers, and so if they were removed plant reproduction would be reduced)
- sometimes keystone species may exert bottom-up control (eg, if a food web contains only one producer species, it may be a keystone)

Question 17

what would a loss of keystone species result in?

Answer 17

many other species are dependent on keystone species for their survival, so loss of the keystone species would mean other species in the habitat also disappear in a ‘domino effect’
- this loss leads to an imbalance in the food web and a decrease in biodiversity
- there is potential for ecosystem collapse in this situation

Question 18

what is a mesocosm?

Answer 18

model ecosystems that allow experimentation of factors affecting ecosystem stability and can be:
- open - matter and energy can be exchanged with the surroundings (eg) recreating natural ecosystems in a laboratory OR (eg) isolating areas of a natural ecosystem
- closed - only energy but not matter is exchanged with the surroundings (eg) sealed glass vessels

Question 19

what are the pros of open mesocosms?

Answer 19

this is advantageous as organisms are not harmed by removing them from their natural habitat, conditions are closer to levels experienced naturally by the organism,there is natural variation of abiotic variables, and more natural behaviour and interactions occur

Question 20

which ecosystems are the most successful?

Answer 20

aquatic or microbial ecosystems are more successful than terrestial ones

Question 21

what is needed to create a sustainable model ecosystem in a mesocosm?

Answer 21

• water
• soil nutrients e.g) mud which contains a range of bacteria, egg shells as a source of carbon and egg yolk as a source of sulfur
• light source - provides energy for photosynthesis
• producer (autotroph) - to convert the light energy into chemical energy using photosynthesis
• decomposer (sapotroph) - to recycle nutrients using decomposition

Question 22

what are pros and cons of mesocosms as ways to study ecosystems, as opposed to studies within entire natural environments?

Answer 22

advantages:
- easier to manipulate, to control variables, and are less susceptible to outside influences
- allow easier replication of experiments
- takes us up less space
- allow easier collection of continuous data

disadvantages:
- large animals cannot be included, and there are ethical concerns about enclosing any animals in mesocosms
- some variables that occur in natural ecosystems will be lacking in mesocosm
- food chains in mesocosms may be incomplete, with trophic levels missing
- difficult to mimic natural environmental conditions exactly
- conditions in natural environments are not static