12 Population Ecology

Question 1

Given a description of a species and its distribution, be able to list reasonable biotic and abiotic factors that could limit its distribution to the area described.

Answer 1

• Biotic Factor: living components of an ecosystem (ex: predation, food resources)
• Abiotic Factor: nonliving components of an ecosystem (ex: temperature, sunlight, soil)

Question 1

Define a population

Answer 1

group of organisms of the same species living in the same area and can interbreed

Question 2

Define Population Density. Describe one method other than mark/recapture that is used to estimate population density/size

Answer 2

• Population Density: number of individuals per unit area

Methods to estimate Population Density:
- Count Samples counting sample of individuals using standardized methods and extrapolate
- Count a Proxy: counting indirect indicators like nests, feeding damage, or tracks
- Mark/Recapture: capture first sample of animals, mark those animals and release, capture second sample of animals, count how many of those are marked

Question 3

Calculate an estimate of population size based on mark/recapture data.

Answer 3

1) Capture sample of organisms within population, mark those organisms, release those organisms back into population
2) Capture another sample of organisms within population, count how many recaptured (n) and

N = (Mn)/m
N = Population Size
M = Total # originally marked & released
n = Total # recaptured
m = Total # individuals marked in new sample

Question 4

Given a description of a population’s life history, be able to roughly sketch the
survivorship curve of that population

Answer 4

• Flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups (large mammals)
• Drops sharply at the start, reflecting very high death rates of the young, but flattens out as death rates decline for those few individuals that survive (fish)
• Immediate, constant death rate over the organism’s life span (rodents)

Question 5

Draw the 3 main types of survivorship curves (and know what goes on the horizontal
and vertical axis of the graph). Compare and contrast each type with regards to life
history strategy, and give an example of the types of organisms that show each type of
curve.

Answer 5

• Flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups (large mammals)
• Drops sharply at the start, reflecting very high death rates of the young, but flattens out as death rates decline for those few individuals that survive (fish)
• Immediate, constant death rate over the organism’s life span (rodents)
• X axis: % of max life span
• Y axis: # of survivors (log scale)