Population ecology Flashcards
A population
- All the individuals of the same species
- That occupy the same area in a particular ecosystem
- i.e. They are all potentially able to interbreed
A community
- The different populations of species
- That occupy a specific area in an ecosystem
Ecological niche
The job or role that an organism has in a particular ecosystem
Ecosystem
- A system formed by the interaction of a community of organisms with their physical environment
- Includes both biotic and abiotic factors
Population size
The number of individuals making up a particular population
Population parameters
Factors influencing population size
- Births
- Immigration
- Mortality/deaths
- Emigration
Population parameters increasing populations
- Births
- Immigration
Population parameters decreasing populations
- Mortality/deaths
- Emigration
Formula to calculate change in population size
N = (B + I) - (D + E)
B + I > D + E
Increasing population size
B + I < D + E
Decreasing population size
B + I = D + E
Stable population size
Two main approaches to finding the population size
- direct counting / census
- estimating / indirect methods
A tool often used for direct counting of organisms
Aerial photography
Two indirect methods of estimating population size
- Mark-recapture
- Quadrats
Population estimation technique for stationary or slow moving populations
- Quadrats
- direct methods
Quadrats are used for estimating…
- population size of stationary or slow moving organisms
- in which there are large numbers
- e.g. barnacles, plants
Mark-recapture methods are used for estimating…
- population size of mobile organisms
- e.g. fish, birds and insects
Population estimation formula for Mark-recapture
N = (M x C) / R
- N estimated population size
- M total captured and marked
- C total recaptured
- R total marked individuals recaptured
Population estimation formula for Quadrats
Estimated population = (Total area x number in quad) / area of quad
Precautions required when using Mark-recapture method
- do not harm organisms
- do not affect behaviour of organisms
- return marked animal where originally caught
- limit time between first and return samples to limit population parameter effects e.g. emigration
- enough time for organisms in population to mingle
- second catch should be larger than first to increase accuracy of estimate
Example ways of marking organisms in the Mark-recapture method
- Fish - metal or plastic tag on fin
- Insects - a dot of non-toxic paint
- Mammals - collared
- Birds - ring on leg
Types of interactions in a community
- Predation
- Competition
- Parasitism
- Mutualism
Predator
- Any organism that hunts a a prey species
- predators benefit by gaining food
The environment benefits from predation
- By keeping herbivore numbers down.
- Keeps carrying capacity stable.
Five examples of predators
- Spiders
- Snakes
- Lions
- Wild cats
- Wild dogs
Population cycles
- Periods where populations vary in density from high to low
- Shorter for smaller organisms e.g. mice
- Longer for larger organisms e.g. antelope
Cyclical fluctuations between predator and prey
- When a predator population relies heavily on one prey population.
- The population cycle of the predator follows the pattern of the prey population.
- When prey numbers increase, predators increase as food available.
- When prey decrease, predators soon decrease as food becomes scarce.
- time lag in predator numbers response to increasing or decreasing prey.
Individuals in a prey population most likely to be killed
Old, young or sick
- easier to catch
- lower stamina or speed
- less agile to outmaneuver
- didn’t recognize danger
Why effects of predators on prey population might be less than expected
- Old, young or sick usual targets
- These animals wouldn’t be reproducing or would have died anyway.
