Estimating Abundance

Estimating Abundance

Today I am going to investigate how various

species and their population density can

determine the health of an ecosystem.

As of now (if you’ve done your work) you know…

• Estimating Abundance….– Impossible to study every organism…so you need

limitations on how many plants & animals you study– You take a sample to analyze as a representation of the

ecosystem. – Trapping methods help to take these limited samples

• Pitfall traps (species falls into trap)• Small mammal traps (bait & trap/catch)• Light traps (UV on white attracts some bugs)• Tullgren Funnels (cloth funnels with light at one end to lure

and trap invertebrates as they move away from the heat)

Quadrats

• Used to limit sampling area when you measure the population size of non-mobile organisms. – If they move, you’ll sample the more than once and

have invalid results• Know when to use and what random samples are• Stratified random sampling– Transects

• Systematic sampling– Continuous sampling

Tullgren Funnel

Determining Abundance

• One way to determine the number or abundance of organisms is Percent Coverage

• Rather than counting each individual• You can give an approximate percent coverage

of the number of (species with limited movement) in the area

• In 1980’s Terry Erwin, a scientist at the Smithsonian Institution collected insects from the canopy of tropical forest trees in Panama.

• He sampled 19 trees and collected 955 species of beetle.

Using extrapolation methods, he estimated there could be 30 million species of arthropod worldwide.

*We now believe that to be an overestimate, this study started the race to calculate the total number of species on Earth before many of them become extinct

Determining Abundance

• To calculate species that are able to move easily, you can determine the number indirection.

• Do to this you use a specific formula• The Lincoln Index!

Lincoln Index

• Allows you to estimate the total population size of an animal in your study area

• It is a mathematical method to calculate the total numbers

• Requires you to collect a sample from the population and mark them; tag them, make the identifiable

• Release back into the wild• Then later you resample the same area, and

determine how many of them are being caught a second time.

Lincoln Index

It is the Capture-Mark-Release-Recapture Technique• Must be non-invasive. • Can’t harm the species.• Must be non-conspicuous – Can’t make it easier for them to be seen by their

predators

Has nothing to do with this

guy!

Lincoln Index

• If all the marked animals are recaptured then the number of marked animals is assumed to be the total population size.

• If half the marked animals are recaptured then the total population size is assumed to be twice as big as the first sample

• There is a formula!

Lincoln Index Formula

N = n1 x n2

mN= total Population.n1= number of animals captured on the first dayn2 = number of animals recapturedm= number of marked animals recaptured

Lincoln Index Assumptions• …we all know what happens when you assume something…

• An individual caught and tagged in the first capture must be neither more nor less likely than other members of the population to be caught on the second capture. – This means that tagged individuals must not have a higher mortality rate,

tagged individuals mingle freely with other members of the population when released, sufficient time has elapsed between captures to allow dispersal of tagged individuals, and tagged individuals must not become "trap-happy" or "trap-shy".

• Tags do not become lost or unrecognizable. • There is no emigration or death of tagged individuals.

– Emigration and death rates for unmarked members of the population must be equal to immigration and birth rates.

Lets Try It

Population Density

Population Density

• Number of individuals of each species per unit area

• Calculated by dividing the number of organisms sampled by the total area covered by the quadrants

• Population Density Case Study for you to evaluate

Percent Cover & Frequency

• Percent Frequency: The percentage of the total quadrat number that the species was found in

• Percent Cover: The percentage of the area within the quadrat covered by one particular species. – Calculated for each species found

What is diversity

• Diversity just means the amount of differences within a system or more illustrative it to think of it as how non-uniformed something is.

• The ethnic mix of the population of say a village in the Papua New Guinea highland is much less diverse than say the ethnic mix in a mega city such as New York.

Diversity

• Diversity is considered as a function of 2 components: – the number of different species – the relative numbers of individuals of each species

• It is different from simply counting the number of species (species richness) because the relative abundance is accounted for

When we consider ecosystems

• Diversity is sometimes used to mean how many different species there are in a community. – However this is a very simple idea about what

diversity is. • Take two forest areas as an example of this. – The first forest has 15 different species with 100

individuals of 1 species and 1 individual of each of the other 14 species.

– The second forest area also has 15 species, but this one has 7 individuals of each of the 15 species.

Take two forest areas as an example …

• The first forest has more individuals than the second one, BUT it is less diverse.

• In the second forest, the total number of individuals is spread more evenly between each species.

• If we think about diversity to include not just the number of species but relative number of individuals in each species as well, then spread of individuals between species is more important than the total number of individuals in a habitat.

• Low diversity Atlantic maritime woodland in Les Landes, France dominated by Pinus pinaster, the maritime pine with little field layer.

• Oak and Hornbeam woodland in the Caucasus mountains, with a diverse mix of tree species and a complex understory

Habitat: A B C

Think About It…

• Ecological sampling can at times involved the killing of wild organism.

• For example, to help assess species diversity of poorly understood organism (identification involving taking dead specimens back to the lab for identification), or to assess biomass.

• An ecocentric worldview, which promotes the preservation of all life, may lead you to question the value of such approaches.

• Does the end justify the means, and what alternatives (if any) exist?

Simpsons diversity index

• As long ago as 1878 Alfred Russel Wallace recognised that the biota of the tropics was more abundant and more varied than of the temperate regions of Europe.

• The problem for ecologists is how to compare the differences between regions or even single ecosystems.

• The simplest measure of diversity is just to count the number of species and this is often referred to as species richness.

• However species richness takes no account of differences between populations of the species encountered.