Ecology Flashcards
Population ecology:
- the study of population in relation to their
environment. - How biotic and abiotic factors influence the abundance,
dispersion and age structure of populations.
population
a group of individuals of a single species living in the same area that can interbreed and produce fertile offspring
Density:
the number of individuals (of a pop) per unit area or volume
Changes as individuals are added or removed from a population via births and deaths (natality and mortality) and emigration and immigration
Dispersion:
pattern of spacing among individuals within the boundaries of the pop.
Clumped:
- Individuals aggregate in patches because the resources are
rife there and they are better able to survive - May also be due to mating behaviour
- Where they can breed effectively
- Increases the predation or defence of the group
Uniform:
- Evenly spaced pattern or dispersion
- May be because organisms are territorial and need space from other individuals
Random:
The position of everyone is independent of
other individuals
demographic
how the abiotic and biotic factors influence pop density and dispersion as well as
immigration, emigration, natality and mortality
- Statistics of a pop and how they change over time
Life table
summaries the survival and reproductive rates of individuals in specific age groups
Survivorship curves
- made from life tables
- useful when there is not a lot of emigration or immigration as it
shows how a population changes over time. - Reproductive rates can also be used insuch a population.
R- type survivorship curve
type 3
- low parental care -> fewer offspring survive into adulthood
- high number of offspring produced
e. g. trees, barnacle, fish
K-type survivorship curve
type 1
- > more offspring survive into adulthood
- few offspring
- high prenatal care
e. g. humans, elephants etc.
Type 2
constant death rate in the organism’s life
e.g. birds, rodents, lizards
reproductive rates
proportion of females weaning a litter x mean number of females in a litter = average number of female offspring
exponential growth model
Populations expand greatly when resources are abundant, and the resources start
reducing compared to population size
change in population size = births + immigrants entering the population - deaths - immigrants leaving the population
(LOOK AT EQUATIONS ON PRINTED NOTES)
Exponential growth:
The population increases at a constant rate per individual = J shaped
growth curve
Logistic model growth
population grows more slowly as it nears carrying capacity
LOOK AT PRINTED NOTES
A S-shaped graph is produced
The pop increases exponentially and then levels out at carrying
capacity
Assumptions of the logistic growth model:
-Populations don’t just adjust to a new environment and grow according the
model
-There is a lag effect
Life history traits are produced by natural selection
There are trade-offs between survival and reproductive traits (frequency of
reproduction, number of offspring, investment in parental care)
life history
Traits that affect an organism’s schedule of reproduction and survival make up its
Diversity of life histories:
Organisms also differ in:
- How many offspring they produce (one or many)
- How often they reproduce
Semelparity:
- Reproduce once off with lots of offspring and then
dies - Organisms that live in environments that are
unpredictable
iteroparity
- Repeated reproduction
- Environment is predictable, and they can depend on it
Trade-offs and life histories:
Organisms need to choose between conserving their energy to grow
themselves or to produce offspring
There is a trade-off between offspring number and the amount of resources
a parent can devote to each offspring
Number of offspring:
Large number of offspring with no parental care = many individuals
survive even if some are lost
Size:
- Smaller organisms are formed = less energy to give each offspring
therefore many small are formed - Smaller organisms are formed so that they can be cared for by
parents and they can grow - Organisms with high levels of being predated produces large amounts of
offspring to increase the survival likelihood - Increased parental care increases the change of offspring survival
Logistic model and life history:
Look at printed notes
- K - selected species
Density dependent
Produce and live in areas with limited resources
Organisms can extract resources better when the resources are low
There population size doesn’t fluctuate as much
E.g.: humans, mammals with parental care - R- selected species
Density independent
Live and produce in areas with maximum resources
These organisms produce lots of offspring
Resources aren’t limited
Organisms overshoot carrying capacity and fluctuate there
E.g.: trees, barnacles, fish
Population change and population density:
Population grows when birth rate > death rate
Density independent regulation:
A birth rate or death rate that doesn’t change with population
density
E.g.: climate, temperature, salinity, precipitation
Density dependent regulation:
Birth rate that decreases with a rising density or a death rate that
increases with an increase in population density
E.g.: predation, disease, competition for resources, waste,
competition for waste, space (territoriality)
Positive feedback
- between population density and the rates of births and
death - Helps stabilise a population
Negative feedback
between density dependent factors and population
density
Population dynamics:
Fluctuation of size of a population from place to place or time to time
Predator prey relationship:
Predator population never reaches the highs of the prey and they lag
behind the prey’s fluctuations