IB ESS Topic 2.5

What should we investigate to better understand the health of an ecosystem?

• Number of animals per species, number of species, lifespan of species

• Abiotic factors: sun, water, pH, temperature, O2, possible toxins within the soil

• Population growth, food chain or food web

How do you figure out what the biotic factors are? 

• Identity based on specific physical characteristics

• COUNT.

• Compare and contrast with organisms to narrow down what it isn’t

• Dichotomous keys

• Genetic testing

• Beware of using color, presence or absence of features, specific measurements

Dichotomous Keys & Benefits/Drawbacks

• Series of yes or no questions based on physical characteristics of an organism to figure out what species it is

• Benefits: Provide an easy way to identity, not difficult to make

• Drawbacks: Each individual organism may not match the overall description of a species, subjectivity involved when identifying traits, changing in color/trait depending on time, parts of organisms may be lost somehow

Ways to estimate population of motile organisms (benefits and drawbacks)

• Capture mark recapture method 

  • Use some sort of sampling method to measure a small area, capture the creatures, then mark them, then put them back into the wild and allow them to remix. Then recapture them and calculate the population within the quadrat then multiply up

  • Benefits: you don’t need to measure every single organism, the estimation is relatively accurate

  • Drawbacks: the mark may cause the remixing to be affected, the mark may kill them, other sources of error. The organisms may have moved in the time

• Pit trap 

  • Dig a hole and then wait for organisms to fall into it. Then, count the number of organisms within the bucket. 

  • Generally for very small organisms 

• Drones – look from above and count how many organisms are within an area, then multiply to expand outward

  • Benefits: good for large animals

  • Drawbacks: may hide animals from above

• Suck up the spiders in a straw (pooters)

Lincoln Index

Used with the capture mark recapture method to calculate the size of the population

(N1 * N2)/N3

N1 = total caught and marked first time

N2 = total second time recapture

N3/NM = marked caught 2nd time during recapture

Types of Sampling

• Random – completely with no order to get an entirely random sample

• Stratified – divide the population into groups, then sample from those (strata)

• Systematic – pick every n organisms (have some sort of system) 

Ways to estimate the abundance of nonmotile organisms

Count how many of the plant/non motile organisms in a quadrat then multiply by how many quadrats there are

Population density

how much of a population (number of organisms) per piece of land

Percent frequency

squares with flower / total of squares

Percentage cover

count pieces to make full squares → covered / total squares * 100%

Quadrats

square section (1x1 m, 1x1 feet) of land that can be used to divide up an ecosystem. Measure how much of something is within the ecosystem)

Transects

• line, often useful to observe if there’s some sort of gradient within conditions

  • Belt - uses line of transect to form quadrats → more data

• Replication is important to increase confidence. More data, better the confidence interval.

Biodiversity (what is it, why is it important, how to measure, and how to improve it)

• The different types of species within an ecosystem 

• Why is this important? The more divers, the more strength there is in case an organism dies out—the food chain will therefore not collapse. 

  • Also supports our use of resources

  • Generally more aesthetically pleasing

  • Ensures stability

  • Disease resistance

• How to measure: count the number and quantity of species

• How to improve it

  • Usually it is best to stay hands off

  • Preserve keystone species

  • Reintroduce species that died off (the wolves!)

  • Get rid of invasive species

  • Increase green spaces

Species richness

how many different species there were

Species evenness

how many individuals per species were there

Simpson’s Biodiversity Index

• Allows to quantify the amount of biodiversity within an ecosystem

• The higher, the more biodiverse

• D = N(N-1)/ SUM(n(n-1))

• N being the series abundance aka the number of organisms

• n being the number of individuals per species 

• High D – stable, ancient, more diversity, healthy habitat

• Low D — dominance by 1 species, environmental stress, pollution, colonization, agriculture

Estimating Biomass

• Measurement of dry mass

• Combustion/extrapolation from samples

• Used to create ecological pyramids 

• Samples → dry mass → repeat weighing until stable for 3 years → extrapolar

• Limigations: combustion → co2, biomass of the roots