Ordination Flashcards
Measuring biodiversity
It is important to have species richness which is the number of different species
AND
evenness to find which species might be more abundant.
The more biodiversity would be high level of species richness and equal evenness between all species.
common measures are shannon index (proportion)
better to convert diversity index to another number that is linear (effective number of species)
shannon’s index
whats the difference between these biodiversity index
The higher the value the more biodiversity (more number of equally common species). however it is not linear so double of one won’t be the correct value.
sample species
count number of individual species
count individual of species
Find biodiversity index
then compare sites
then change number back to effective number of species so in order to convert it back you do E^(shannon’s index)
What is ordination?
When should I use it?
How do I interpret the outcome?
A way of analysing community composition (species A,B,C,D sites 1,2,3,4 and count of No. of individual species.
When you have a site-by-species table with counts of individuals of each species. make sense of this multi-dimensional data.
Points on a 2-D plot that are closer together are more ecologically similar.
ecological similar=identity of species are similar and number of species are similar.
What do you actually need to know? when you start sampling?
Ecologists often collect site-by-species data when investigating communities
For each site you can calculate basic statistics like species richness, diversity indices or effective number of species
You can measure the ecological distance between communities using measures such as Bray-Curtis similarity. This varies between 0 and 1 with 0 = sites are identical and getting larger as sites are more dissimilar
You can simplify a table of similarity between sites (or by species) by doing an ordination
On an ordination plot, sites that are ecologically similar are close together and those that are more different are farther apart.
what does Lotic mean
fast flowing (opposite to lento)
Different sampling techniques
Streams of different order
Surber sampling like kick sampling
NMDS (non-metric ….. scaling
Bray-Curtis similarity index
Examine mayfly assemblage composition across microhabitats
IndVal analysis to identify species indicative of a microhabitat type
Graph
Mayfly populations are quite similar in the majority of microhabitats including cobbles, angiosperms, sand and mosses however silt is a bit different but overall no difference
If there would be many different habitats there would be visible clusters that would be far from eachother.
constrained vs unconstrained ordination
Constrained ordination is a method to explore effects of environmental factors to the assemblage ordination by an extension of multivariate regression.
Summary of ordination
Ordination is useful technique to represent the ecological distance between communities in two or three dimensions
Look at different squares
for each year they measure 5 quadrats (different locations) so for square 1 2007 has very similar species composition however throughout the years the species composition was very different however similar in each year
second one is spacial effect so similar compositions between years however different quadrats are very different so could be environmental barriers
3rd no overall community
4th is gradual succession over time
5th intermediate time period could have active disturbance.
6th as time goes on more community assembly.
remember this is non-parametric so the x axis isn’t exactly distance however distance between points on the graph show similarity between species.
Worm field data
can make a plot with different shapes for different sampling techniques. So in ordination plot you could answer as if communities are different by habitat or sampling method. Perhaps different sampling methods draw out particular communities.
so sampling method and habitat can me compared
