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
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.
What is mutualism?
When organisms of DIFFERENT species work together for the benefit of both.
What is pathogenicity?
When an infectious microorganism (pathogen) lives inside an organisms and causes disease
What is parasitism?
A parasite organism lives inside a host organism, causing it harm.
How do coral polyps and zooxanthellae help each other?
The corals provide shelter and protection.
The algae carry out photosynthesis, producing carbon compounds for the coral.
What are endemic species?
Found in a particular place and in no other location in the world. Especially vulnerable to invasive species (wiped out in one location = extinct).
How can a laboratory experiment be used to test for interspecific competition?
A laboratory experiment can be used to test for interspecific competition by culturing bacteria species on their own and together and measuring how this affects population size or colony distribution.
How to test for interspecific competition in a field study?
- Random sampling: quadrat samples to record the presence/absence of one or both species at different locations.
- Manipulation: removing one species and measuring the effect that this has on the second species.
What does it mean if a chi-squared test rejects the null hypothesis?
It means there is a significant difference/association between the variables being tested (eg. the species’ distributions are independent).
What is the function of antibiotics?
It is secreted by microorganisms/fungi to kill competitors.
What is the function of allelopathic agents?
Secreted by plants to inhibit growth of nearby plants.
What do antibiotics and allelopathic agents have in common?
A chemical substance is released into the environment to deter potential competitors.
