C4.1 Population and communities Flashcards
Population definition
A group of organisms of the same species living in the same area at one time.
What is reproductive isolation?
When two populations live in different areas, so they don’t interbreed. This distinguishes populations.
Why is sampling used when aiming to estimate the size of a population?
Because it isn’t possible to count every individual.
What is a sampling error?
The difference between an estimated population size and the true size.
Does random sampling always lead to sampling error?
Yes, because it relies on the assumption that individuals are evenly distributed
What are two common sampling methods for immobile/sessile organisms?
Quadrat sampling and line transects
What is carrying capacity?
The maximum size of a population that an environment can support.
What factors can limit carrying capacity?
- Resources: water, food, space, oxygen
- Competition
- Predation
- Disease
What is the purpose of the capture-mark-release-recapture method?
To estimate population size for motile organisms
What is the equation for the Lincoln Index?
Population size = M x (N/R)
M= marked individuals in first sample
N= total captured in second sample
R= marked individuals captured in second sample
What are some assumptions made when using the Lincoln Index?
- Marked individuals mix fully with population
- The marking doesn’t affect survival rate of individuals
- The marking remains visible throughout and doesn’t rub off.
Define population density
Number of individuals present per unit area of habitat.
Examples of density-dependent factors
Disease, predation, competition (affects populations differently at different population densities).
Examples of density-independent factors
Droughts, wildfires, hurricanes
What are the 3 pieces a sigmoid graph is split into?
- The exponential phase, where the population increases rapidly as there are no limiting factors.
- The transitional phase, where the population growth slows as limiting factors have increasing effects.
- The plateau phase, where a population remains close to carrying capacity.
What is top-down control of population size?
When population size is limited by other species feeding on it.
What is bottom-down control of population size?
When size of population is limited by the availability of resources.
True or False?
One of either top-down or bottom-up control is likely to be dominant in any given ecosystem.
True.
Define a community
A group of populations living together in an area and interacting with each other.
What are intraspecific relationships?
Interactions between individuals of the same species (cooperation or competition).
What are interspecific relationships?
Interactions between DIFFERENT species within a community (eg. herbivory).
What is interspecific competition?
When organisms of different species compete for the same resources.
Explain why there is COMPETITION between members of the SAME species. (intraspecific)
Because organisms that occupy the same ecological niche require the same resources. Some individuals will be more successful and gain more of the resource.
What is mutualism?
When organisms of DIFFERENT species work together for the benefit of both.
