An in-depth summary of CCEA A21 Physiology and Ecosystems, these particular notes cover the Ecosystems module, including populations; communities; ecological energetics; and nutrient cycling.
POPULATION AND COMMUNITY
Population: Number of individuals of a specific species in a particular area.
Community: All the species in a particular area
Ecosystem: Interaction between the biotic and abiotic factors in a particular area.
Biotic Factors: Any factor linked to the living community (e.g., Predators)
Abiotic Factors: Any factor linked to the non-living physical/chemical environment (e.g., soil/climate)
Interspecific – between two species
Intraspecific – within same species
Why do animals live in populations?
- Increases chance of survival, more food, avoid predators, building nest, find a mate.
Phases of a population growth
Lag
- Low birth rate
- Small population with little/no growth,
- Due to taking time to adapt to new habitat
Exponential
- High birth rate (max rate of reproduction) (r)*
- Rapid population rises
- Due to optimum conditions/unlimited resources
Stationary
- Birth rate = death rate
- Resources are limited (competition)
- Population reaches its max (carrying capacity*)
Decline
- Death rate higher than birth rate
- Population declines
- Due to loss of resources/accumulation of waste
*Carrying capacity is the max no. in a population that an environment can support.
* Biotic potential – (r) – max rate of reproduction when resources are unlimited
Factors affecting population growth
Renewable: long term
Non-renewable: temporary – ‘boom and bust’
Abiotic Biotic
-Temperature -Food sources
-Rainfall/water -Predators
-Sunlight/ length of day -Competition
-Soil mineral content -Disease
-Soil pH -Parasites
, Temperature is not a resource, but has a major influence, why?
It affects the rate of enzyme activity. (Higher metabolism = higher growth)
Population Dynamics
Population growth = (birth rate + immigration) – (death rate + emigration)
*If a population is in equilibrium, it is stable in stationary phase*
r selected species K selected species
Short life span Long life span
Short generational time Long generational time
Very high no. of offspring Lower no. of offspring
High population density Low population density
Very fast dispersal – good colonisers Slower dispersal – need to adapt
No adapting Long lag phase
Temporary/unstable habitat Stable/long-term habitat
Population Interactions
Mutualism (+/+) Both species benefit from the interaction
Predator-Prey Interaction (+/-) One species benefits to the detriment of the other
Interspecific competition (-/-) Detrimental affect on both species
COMPETITIVE EXCLUSION PRINCIPAL: Two species cannot occupy the same niche. There is too much
competition. The winner is the best adapted. The loser is eliminated.
Pest Control
Pest: Any organism that causes economic damage to a crop species.
Why is pest control important in farming?
-Crops would have to compete/crops would be fed on/crops would be diseases
-Loss of growth = loss of profit
Characteristics of a successful control agent:
1. Specific – only targets pest species
2. Does not negatively affect the ecosystem
3. Must not economically damage crop
4. Must be able to survive/reproduce in the habitat (long-term)
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