Populations and ecosystems Flashcards
Define a Population
A group of interbreeding organisms of one species in a habitat.
Define a Community
All the populations of different organisms living and interacting in a particular place at the same time.
Define a Habitat
The place where a community of organisms live.
Define a Niche
A niche describes how an organism fits into the environment.
Define Abundance
Number of organisms in a given space.
What are the three factors to consider when using quadrats?
- The size of the quadrat
- The number of sample quadrats to record within the study area
- The position of each quadrat within the study area
What is a good method of random sampling?
- Lay out two long tape measures at right angles along two sides of the study area
- Obtain a series of coordinates by using random numbers taken from a table or generated by a computer
- Place a quadrat at the intersection of each pair of coordinates and record the species with it
When is it better to use systematic sampling along transects?
Where some form of transition in the communities of plants and animals takes place.
What is the difference between a line transect an a belt transect?
A line transect comprises a string or tape stretched across the ground in a straight line. A belt transect is a strip, usually a metre wide, marked by putting a second line parallel to the first.
What is the frequency of abundance?
The likelihood of a particular species occurring in a quadrat.
What is the percentage cover of abundance?
An estimate of the area within a quadrat that a particular plant species covers.
Estimated population size =
(Total number of individuals in first sample x total number of individuals in second sample)/ number of marked individuals recaptured
What are the 5 assumptions mark, release recapture relies on?
- The proportion of marked to unmarked in second sample is the same as the proportion of marked to unmarked individuals in the population as a whole
- Marked individuals released distribute themselves evenly amongst the remainder of the population and have sufficient time to do so
- No deaths, births, immigration, emigration
- Method of marking is not toxic nor does it make the individual more conspicuous to predators
- Mark or label is not rubbed off during investigation
Why is there an initial period of slow growth in a population growth curve?
The initially small number of individuals reproduce to slowly build up their population size.
Why is there a period of rapid growth in a population growth curve?
The ever-increasing number of individuals continue to reproduce.
Why is there a period when the population growth declines until it remains stable in a population growth curve?
The decline may be due to food supply shortage, increased predation or competition.
What are the abiotic conditions that influence the size of a population?
Temperature, light, pH, water and humidity
What is intraspecific competition?
Individuals of the same species compete with one another for resources such as food, water, breeding sites, etc.
What is interspecific competition?
Individuals of different species compete for resources
What is the competitive exclusion principle?
Where 2 species occupy the same niche, one will normally have a competitive advantage over the other. If conditions remain the same, this will lead to complete removal of one species.
What kind of fluctuations are seen in predator-prey relationships?
Cyclic
How are periodic population crashes important in evolution?
They create a selection pressure whereby only those individuals who are able to escape predators, or withstand disease or an adverse climate, will survive to reproduce.
Two major events that led to exponential growth in human population
- Development of agriculture
2. Development of manufacturing and trade which led to industrial revolution
Population growth =
(Births + Immigration) - ( deaths + emigration)
Percentage population growth =
(Population change during period / population at start of period) x 100
Birth rates are affected by :
- economic conditions
- cultural and religious backgrounds
- social pressures and conditions
- birth control
- political factors
Birth rate =
(Number of births per year / total population in the same year) x 1000
Death rates are affected by :
- age profile
- life expectancy at birth
- food supply
- safe drinking water and effective sanitation
- medical care
- war
- natural disasters
Death rate =
( Number of deaths per year/ total population in same year) x 1000
Define Demographic Transition
A change from where life expectancy is short and birth rates are high to where life expectancy is long and birth rates are low
What is the average life expectancy in a survival curve?
The age at which 50% of the individuals in a particular population are still alive.
