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1.3. ENERGY AND EQUILIBRIA (Knowledge and Understanding (Laws of…
1.3. ENERGY AND EQUILIBRIA
Knowledge and Understanding
Laws of thermodynamics govern the flow of energy in a system and the ability to do work
First law: principle of conservation of energy - energy in an isolated system can be transformed but it can not be created or lost
Second law: entropy of a system increases overtime, entropy - measure of the amount of disorder in a system, increase in entropy arising from energy transformations reduces energy available to do work
Second law explains inefficiency and decrease in available energy along a food chain and energy generating systems
Systems can exist in alternative stable states or as equilibria between tipping points
Destabilising positive feedback mechanisms drive systems towards these tipping points
Negative feedback mechanisms resist changes
Resilience of a system, ecological or social refers to its tendency to avoid tipping points and maintain stability
Diversity and size of storages within systems can contribute to their resilience and affect speed of response to change (time lags)
Energy in systems
When energy is used to do work some is always dissipated as heat
Energy conversions are never 100% efficient
In food chain only 10% of energy moves to next trophic level
Complexity and stability
High level of complexity makes for a more stable system which can withstand stress and change better than a simple one can - another pathway can take over if one is removed
Simple systems may lack stability
Tundra - these ecosystems are simple and thus populations in them fluctuate widely
Monoculture (farming systems in which there is one major crop) are simple and more vulnerable to a sudden spread of disease or a pest through a large area e.g. Potato blight Ireland 1845-8
Equilibrium - tendency of an ecosystem to return to its original state following disturbance
Steady state equilibrium - characteristic of open systems where inputs and outputs are constant but the system as a whole remains the same e.g. a climax ecosystem
Negative feedback stabilises steady-state equillbria - it damps down, counteracts or neutralises any deviation - results in self regulation of a system
e.g. homeostasis - sweat to cool, shiver to warm up but body temp stays around 37 degrees or a climax eco system
Static equilibrium - no change overtime e.g. a stack of books - when a static equilibrium is interrupted it will adopt a new equilibrium as a result of disturbance
e.g. most non living systems such as a pile of rocks - cannot occur in a living system as life involves exchangfng energy or matter with the environment
Unstable and stable equilibria
Stable - system returns to same equilbrium after disturbance
Unstable - system adopts new equilibrium after disturbance
Feedback loops
Positive - change a system to a new state, they are destabilising as they increase change e.g. permafrost
Negative - return a system to its original state, they are stabilsing as they reduce change e.g. predator prey relations
Resilience of systems
measures how it responds to a disturbance
Factors affecting resilience of systems
diversity and complexity - more interactions between species
biodiversity - increases likelihood that there is a species that can replace another if it dies out and therefore maintain the equilibrium
genetic diversity - monoculture can be wiped out quickly as none of the organisms have resistance which is more likely in a diverse gene pool
Species that can shift their geographical ranges are more resilient
Climate - e.g. in arctic regeneration of plants is very slow - less photosynthesis
R strategists which can reproduce faster have better resilience
Tipping point
when changes tip equilibrium over a threshold - system may adopt a new equilibrium - tipping point is reaached when ecosystem experiences a shift where there are significant changes to its biodiversity and the services it provides
Characteristics of tipping points : involves positive feedback, threshold point can not be precisely predicted, changes are long lasting, changes are hard to reverse , significant time lag between the pressures driving the change and the appearance of impacts, creating difficulties in ecological management
e.g. of tipping points include - lake eutrophication, extinction of keystone species, coral reef death