Ch. 9 Exam 3 Flashcards
Population abundances and distributions can be estimated with..
Area-based counts, distance methods, mark-recapture methods, and niche modeling
Relative population size
Number of individuals in one time period or place relative to the number in another
Relative population size
Estimates are based on data presumed to be related to absolute population size, such as..
- number of animal tracks or road kills in an area
- number of fish caught per unit of effort
Relative population example
Ride down road and count roadkill
Absolute population estimates examples
Area-based counts
Area-based counts
Counts individuals in a given area or volume
Area-based counts used to..
Estimate the abundance of immobile organisms
Belt transects
Band of area in which organisms are counted
Quadrats
- standardized sampling areas of specific size
- counts are used to estimate population size or density
Quadrat locations are selected at ___ or on a ___.
Random; regularly spaced grid
How many quadrats should be used?
Use species-area curve
Species-area curve
Helpful in determining point of diminishing returns
Distance methods
Distances of individuals from a line or point are converted into estimates of abundance
Line transects
Observer travels along line and counts individuals and their distance from the line
Mark-recapture methods
- used for mobile organisms
- a subset of individuals is captured and marked/tagged in some way, then released
- at a later date, individuals are captured again
Ratio of marked to unmarked individuals in a second sample are used to estimate what?
Population size
Lincoln-Petersen method is used for ___ populations.
Closed
Closed population
No immigration
- To estimate total population size
N = (M*C) / R
Total population size = (marked * captured) / recaptured
- Lincoln-Petersen estimate
- marked individuals behave as unmarked (random sampling)
- marking method does not affect “catchability”
- marks last throughout study period
Hantavirus study
- carried by deer mouse
- outbreak of disease in 1993
- deer mouse specimens indicated the virus had been present for 10 years
- why did outbreak occur in 1993?
- because density of species increased between 1992 and 1993
- precipitation data and satellite photos showed that high rainfall led to more plant growth, which provided seeds, nesting material and shelter for rodents
- high mouse densities increased changes of them coming in contact with humans
Ecologists often wish to predict the future distribution of a species .. why?
- pest species or disease carriers
- species distributions may also change with global warming
- Ecological niche
Abiotic and biotic conditions that a species needs to grow, survive, and reproduce
- Niche model
Predictive tool that models environmental conditions occupied by a species based on conditions at localities it is known to occupy
GARP
Genetic algorithm for rule-set prediction
___ works by changing habitat rules in a way that mimics the occurrence of genetic mutations and natural selection.
GARP
Detritus
Recently dead or partly-decomposed organisms
Test hypothesis
Sea otters control population size of urchins, and thus the distribution of kelp forests
- compare sites with and without otters
- at sites newly colonized by sea otters, urchins virtually disappeared within 2 years, and kelp densities increased
Recent sea otter decline may be due to predation by killer whales
- whaling may have reduced preferred prey
- reduced fish populations reduced seal and sea lion populations
Example of top-down control
- killer whales turned to otters as prey
- as otter density decreased, sea urchin rebounded
- with increased urchin biomass, urchin grazing on kelp increased
- increased grazing on kelp led to decrease in kelp density
