BIOL205Ecology Lab 5

Estimating Population AbundanceDr. Erik D. Davenport

Ecological measurements

A number of basic measurements are used in describing populations and communities.

– Density– Abundance– Biomass

density

Density: in the ecological population studies, density (D) is the number of individuals expressed per unit area or per unit of volume.

Abundance (N) is the number of individuals in a given area.

For example, a species may have an abundance of 100 individuals in a particular area. If the total area is 2.5 hectares, then the density of this species would be 40 per hectare (40/ha).

Biomass

Biomass (B) is the weight of the individuals of a population or group of populations and often is expressed per unit area or volume.

For example, the grams of chlorophyll per liter in a lake.

However, what is the difference between density and biomass???

Capture-recapture sampling

Useful to estimate the population size of a single species of highly mobile animal.

It is called capture-recapture, or mark-recapture.

It is also referred as Lincoln-Peterson method.

Capture-recapture sampling

First sample: A number of individuals from a population of interest are captured, marked by some identifiable means, and then released within a short period of time.

At a later date ( perhaps after a week or two), a second sample of individuals is taken from the population.

Some of the individuals in the second sample might be also captured and then released in the first sample.

Like the first sample was diluted within the populations.

Removal Sampling

Removal methods of population estimation involve successive trapping of members of the population.

Assumption: the number of caught and removed from the population at a given time of trapping will be greater than the number of caught at a later trapping using the same sampling effort.

That is, as one reduce the population size, the size of the catch will decrease.

Transect sampling

There are several transect sampling techniques, however, here we are going to cover the Line transect sampling

Line transect sampling involves a walking a line established through an area and recording the distance of individuals observed from that line.

This method can be quantified to yield density estimates useful in studies where the animals are highly mobile, yet often difficult to see until flashed.

Assumptions to use the capture-recapture procedure:– All individuals in the population have an equal and

independent chance of being captured.– There is no change in the ratio of marked to

unmarked animals.– Marked animals distribute themselves

homogenously.

Capture-recapture sampling

Capture-recapture sampling

Assume the total population size in certain area contains N individuals, and from this population, take a sample of M individuals. Then mark and release these M individuals.

In the second sample, if you catch n individuals, which contains m marked individuals from first sample

Then M/N = m/n Then you can estimate the population size

N = (M*n)/m

Regression method

Involves taking a series of samples (at least 3 samples) from a population.

Each sample involves the same amount of effort. Number of individuals from each collection is plotted

against the cumulative OR previous number captured.

Population estimation then extrapolated. It is also called regression method:

Y = aX + b and then N=-b/a