Population Ecology Flashcards
What is a population?
A group of individuals within a species living in the same area and interbreeding with fertile offspring
What is population ecology?
The study of populations in relation to their environment
What is population dynamics?
The study of relationships between abiotic and biotic factors with population size.
Describe the steps to the mark-recapture method of finding population sizes.
- Capture a sample s and mark your sample
- Release the individuals back
- Resample r individuals
- count the number of marked individuals
- the ratio between s and N, and m and r are assumed to be the same, allowing for an N value to be optained.
What are the assumptions of the mark-recapture method?
- Marked and unmarked individuals have the same probability of being captured
- The marking of individuals does not change their ability to be recaptured
- The marked individuals have mixed back into the population perfectly.
- No individuals are born/die/immigrate/emmigrate.
What is population density? How does it change mathematically?
It is the number of individuals per unit of area, and the change can be measured by the births + immigrations - deaths - emmigrations.
What are demographics?
The study of changes over time in the vital statistics of populations like birth and death rates.
What kind of figure summarizes the survival and reproduction rates of individuals in specific age groups over a population?
A life table
What sex do life tables measure?
Females
What is a cohort?
Groups of individuals born in the same time range
What is a survivorship curve?
A graph that describes the proportion of individuals of a cohort that are alive at each age. The axis are the log of number of survivors plotted against the percentage of their maximum life span.
What is a type 1 survivorship curve?
There is not a lot of death early in the lifespan, there is a strong decrease at old age groups. This includes mammals with few offspring and parental care.
What is a type 2 survivorship curve?
It is a constant death rate (straight line) that means mortality is the same throughout all age groups.
What is a type 3 survivorship curve?
It is a high infant mortality rate followed by a flattening of the death rate in adults. This includes large number of offspring with little parental care. Lots of fish have these survivorship curves.
What is the formula for exponential population growth? What do the variables mean? (add R delta T for fun)
dN/dT = rN dN is the change in numbers at a point in time, dT is the change in time at a point of time, r is the per capita change in population size at a point in time (constant), and N is the number of individuals in the population.
R delta T is the rate of change that an individual gives to the population
What is the shape of an exponential population graph?
a J-shape
What do we have to assume to draw an exponential population graph?
Infinite resources, no competition. For example a newly introduced species or a rebound from a catastrophic event.
When we introduce a resource limit what variable do we use and what do we call it?
The carrying capacity is the maximum population size an environment can sustain. It is the variable K.
How can K change over time?
There can be a different abundance of limiting resources, or a change in per capital death/birth rates.
What is the logistic population growth formula?
dN/dT = rN ((K-N)/K)
What is the formula for per capital population growth that takes into effect limiting resources on each individual?
r((K-N)/K)
How does N affect the calculations?
A small population will multiply the value by a bigger value, a large population will have a K-N value that is closer to 0, slowing growth.
When is the stationary phase of a logistic population growth curve reached?
When N = K
What is the shape of a logistic population growth curve?
It is an S with a slow start, and then the fastest point is at an intermediate stage, and then it slows down and reaches a horizontal asymptote at K.
Why is the fastest point of a logistic population growth curve at an intermediate stage?
- There are many reproducing individuals
- There are lots of resources availiable.
Where are logistic population growth curves used?
They are often typical of microorganism cultures.
Why is the logistic model limited?
It assumes that populations can adjust instantaneously to increases in density.
It also assumes the environment stays the same and no predators regulate the population size.
What is the life history of an organism?
all the traits that affect an organisms schedule of reproduction and survival.
Give some examples of life history traits
Mass at birth, frequency of sexual reproduction, number of offspring, age at death
What is sensence?
deterioration with age
Energy is allocated to different life history traits. What is the result of this?
There are trade-offs
Give the example of trade offs of life history traits in fruit flies.
They found if they made larger eggs, they lay less of them (lower fecundity).
What is the life history strategy that deals with large amounts of small offspring?
R-selection
What is the point of R-selection?
There is a high reproductive success at low densities. The organisms mature rapidly, have a short lifespan, a high mortality rate, minimal parent care investment, and low competition.
What is the point of K selection?
It is selection that favors traits at high densities near the K value. These organisms grow more slowly, have a longer lifespan, have less offspring at a time, more reproductive events, and high parental investment and competition.
What is an ecological succession?
A transition in the species composition of a community following a disturbance.
Why are K and R no longer used by ecologists?
- Evolution of life history traits can be better explained by age-specific mortality than just density dependence.
- Trade offs may not be so pronounced if individuals vary in the amount of resources they acquire.
What strategy works best after an extinction event?
R strategies work better as they are adapted for low density success by high offspring rate, rapid maturation, etc.
