Population Sampling

Population Density Measures the amount of population per unit area

Why Study 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

Population Sampling Scientists use different sampling techniques to estimate the number of organisms in a given population

Sampling Techniques Direct Count- actually counting every organism; only works with certain organisms Examples: People- census Bacteria- colonies on a petri dish

Indirect Counting- look for signs of an organisms presence Example- bird’s nest, burrows, scat (droppings) Bird’s nest with eggs Deer Scat 

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

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

Uses 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

Population Decline There is concern over the horseshoe crab population due to its over use as bait for eel and whelk

Why is this a problem? 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

Horseshoe crab eggs Horseshoe crab spawning 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