Population Size and Ecosystems Flashcards
what is a population?
a group of interbreeding organisms of the same species, occupying a particular habitat
what four factors cause ecosystems to be dynamic and population numbers to fluctuate?
birth rate
death rate
immigration
emigration
define birth rate
the reproductive capacity of a population
define death rate
the proportion of individuals dying per unit time
define immigration
the movement of individuals into a population of the same species
define emigration
the movement of individuals out of a population of the same species
when describing population growth of bacteria and yeast, would it be correct to use the term ‘birth rate’? If not, what could be used instead?
No
we can use rate of cell division instead
how is a population of an equilibrium species controlled?
within a stable habitat through competition
what is the pattern of growth if conditions of temperature and nutrients are favourable?
sigmoidal (S-shaped)
give the 4 labels of the phases of the population growth curve and what they mean
1) lag phase - reproduction rate ≥ death rate
2) log phase - reproduction rate > death rate
3) stationary phase - reproduction rate = death rate
4) death phase - reproduction rate < death rate
what are the axis labels of the population growth curve?
number of organisms (x) and time (y)
describe lag phase
slow rate of reproduction
period of intense metabolic activity such as enzyme synthesis
in sexually reproducing organisms this represents the time for individuals to reach sexual maturity
for yeast placed in nutrient broth it represents the time it takes for them to hydrate
describe log phase
rapid increase in population numbers as more individuals available for reproduction
no factors limiting growth
bacterial cells double per unit time
rapid rate of reproduction can’t be maintained indefinitely
environmental resistance occurs at the end of log phase
what environmental resistance will occur for rabbits on a new island?
predation, parasitism and disease and competition for food/habitats
what environmental resistance will occur for bacteria in a flask?
run out of space, lack of oxygen/nutrient availability, competition for nutrients eg glucose and oxygen and toxic waste build up
describe stationary phase
birth rate or cell division is equal to death rate
factors limiting further growth
population reached carrying capacity
actual number of individuals will fluctuate around carrying capacity in response to environmental changes
yeast change from asexual to sexual reproduction as they reach stationary phase and some individuals survive as spores
define carrying capacity
the maximum number of individuals a population can sustain within a particular environment
describe death phase
environmental factors result in death rate greater than birth rate eg glucose running out in a nutrient broth or build up of ethanol when growing yeast
how to calculate population increase from a graph
when increase is very large, the range of numbers is too great to plot a graph on a linear scale
therefore a log10 scale is used so each mark on the population scale is 10x the previous mark
what are two factors that distinguish what will slow down population growth and what might cause a population crash?
density dependent factors and density independent factors
describe density dependent factors and give examples
factors that have a greater effect the larger the population size and more likely to slow down the population growth rate
eg: disease and parasitism, food availability and toxic waste build up
describe density independent factors and give examples
factors that have an effect regardless of the size of the population and is more likely to cause a population crash
eg: floods, fires and sudden temperature changes
describe predator-prey relationships
as the population density of a particular prey increases, more are eaten by the predator
as a result, the prey population decreases
when the prey population increases there is more available food for the predator
as a result, the predator population increases
describe competition and give the two types of competition
it has large impact on the potential breeding success and survival of an organism
intra-specific competition
inter-specific competition
what is the difference between intra and inter specific competition?
intra-specific is competition between members of the same species
inter-specific is competition between members of different species
define the concept of niche
the ecological role and position that an organism takes within an ecosystem, dependant on the resources it uses
only one species can occupy a particular niche within an ecosystem, one species will always outcompete another
how can the concept of niche be demonstrated?
by growing two species of the protozoan ‘Paramecium’ in flasks in a lab
both species can grow well in flasks when grown separately but when grown together ‘P-aurelia’ outcompetes ‘P-caudatum’ for food so the population of ‘P-caudatum’ falls
what is the type of competition demonstrated in the protozoan experiment?
inter-specific
what is the study of abundance and distribution called?
biogeography
what is the sampling technique in an area where abiotic variables are uniform?
1 - set up a 10m x 10m grid and use random numbers to generate coordinates to determine where to place the 1m^2 quadrat
2 - count the number of species or percentage cover in each quadrat
3 - repeat at 10 random coordinates
4 - calculate a mean for each species
why is percentage cover used instead of counting?
it is quite difficult to count individual plants such as grass or moss
using a gridded quadrat can give a better estimation
a quadrat divided into 10 x 10 squares would mean each square is represented by 1%
what is the sampling technique if you wanted to sample the change in species over time within an area?
set up a permanent area within the habitat and create a 10m x 10m grid
generate random coordinates for quadrat placement and record the number/percentage cover of plant species
review/visit periodically to gain results for comparison
what is the sampling technique in an area where there is a change in an abiotic factor?
random placement of quadrats is unsuitable if there is an environmental gradient such as altitude or light intensity
a line transect is used
describe a line transect
it would be used to describe the difference in plants as you enter a wood etc
record the species touching the transect at each point