Population Sampling

Measures the amount of population per unit

area

Population Density

Understanding the population size in an area

allows ecologist to know if a population is healthy or not Review terms: carrying capacity and critical

number Many factors affect population density of a

species Review limiting factors

Why Study population density?

Scientists use different sampling techniques to

estimate the number of organisms in a given population

Population Sampling

1. Direct Count- actually

counting every organism; only works with certain organisms

Examples:People- censusBacteria- colonies on a petri dish

Sampling Techniques

2. Indirect Counting- look for signs of an

organisms presenceExample- bird’s nest, burrows, scat (droppings)

Bird’s nest with eggs

Deer Scat

3. Quadrat Sampling- mapping out a grid of specific size and counting the organisms within that grid - Very common method

4. Mark and Recapture- involves marking a number of individuals in a natural population, returning them to that population, and subsequently recapturing some of them as a basis for estimating the size of the population at the time of marking and release

Population sampling allows for estimates of a

population in a region Using statistical analysis, scientists are able to

get an idea of the amount of organisms for a specific species.

The Horseshoe Crab

Scientific Name: Limulus polyphemus

Horseshoe crab blood is

extremely important in the medical field Every single intravenous

drug is tested for contaminants using horseshoe crab blood

One quart of horseshoe crab blood costs around fifteen thousand dollars

Uses

There is concern over the horseshoe crab

population due to its over use as bait for eel and whelk

Population Decline

Besides its use in the medical community,

horseshoe crabs play a key role in migratory bird patterns

When the horseshoe crabs spawn, its eggs provide a major food source for incoming shorebirds and other fish

If there are not enough eggs, the bird populations will begin to decline

Why is this a problem?

Horseshoe crab spawning

Horseshoe crab eggs

Shorebirds eating the eggs*first meal in 3-4weeks*

Citizen Science

Project Limulus- uses everyday citizens to do population counts of horseshoe crabs along the Eastern Coast to determine population rate Has led to laws in DE and NJ protecting and

restricting the catching of horseshoe crabs for bait

Uses quadrat sampling technique