Terminology
Ecology: The branch of biology that focuses on interactions between organisms and the living
(biotic) and nonliving (abiotic) components of the environment.
Population: A group of individuals of a single species that:
1. Live in the same general area
2. Rely on the same resources (e.g., food, shelter)
3. Respond to similar environmental conditions (e.g., temperature, light)
4. Have a high probability of interacting and breeding with one another
Population ecology: The branch of ecology that focuses on the dynamics of populations (e.g.,
abundance, growth, survival) and how populations interact with living and nonliving components
of the environment.
Importance:
1. Population change over space and time
2. Disease transmission and spread
3. Ecological theory
4. Managing populations
5. Conserving vulnerable species
Estimating Abundance and Density
- Abundance = total number of individuals
- Density = number of individual per unit area
- Direct = count animals themselves
- Indirect = count indices of relative abundance
Mark-Recapture
- Lincoln-Peterson model
- Imagine that we capture, mark, and release animals. Then, we capture a second
sample.
- If the probability of capture is independent of the presence/absence of marks, then…
- The proportion marked in 2nd sample = proportion marked in total population
R/C = M/N
- R = # marked in the 2nd sample (recaptures)
- C = # Caught in the 2nd sample
- M = # Marked in the first sample (population)
- N = Total Number in population (what we are solving for)
Importance Assumption of Method - Closed population (N is constant)
- All animals have equal capture probability in each sample
- Capture and marking do not affect capture probability
- Each sample is random
- Marks are not lost between sampling events
- All marks are recorded correctly and reported on capture in the second sample
Example:
- We capture and mark 105 squirrels throughout campus.
- In a second capture we catch 142 and 37 were already marked
- R = 37; C = 142; M = 105
- Therefore, N = 403
Practice Problem:
- Wildlife managers are concerned about black bear population growth. They seek to
maintain a population of 5,500 bears in MI
- Biologists captured and marked 598 bears in initial population sampling. They capture
740 bears in a second sampling event, for which the recapture rate was 10.95%
- Did the manager achieve their population goal?
- R = 81 C = 740 M = 598
- N = M* C /R = 5,463 → yes
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