100% satisfaction guarantee Immediately available after payment Both online and in PDF No strings attached
logo-home
Summary Ecological Methods: Multivariate (visual) $6.71   Add to cart

Summary

Summary Ecological Methods: Multivariate (visual)

 5 views  0 purchase
  • Course
  • Institution

This is a summary of the second part of Ecological Methods (WEC31806), namely Multivariate analyses. The summary shows all the lectures in the Multivariate section and has been made extra visual in order to understand the material quickly and properly. In addition, with plenty of examples.

Preview 3 out of 22  pages

  • October 2, 2024
  • 22
  • 2024/2025
  • Summary
avatar-seller
12. Distance based ordination
Many response variables: more than one dependent variable
 plant/animal communities
 Microbiome studies
 Genetic studies

Multivariate analysis (MVA): simultaneously analysing multiple response variables

Community ecology: the variation in many dependent variables (e.g. species abundance) across sites
in the landscape
 may be explained by one or more environmental predictor variables
 often, we thus look for spatial gradients across sites (in species abundance and environmental
variables)

Ordination
Ordination: a way of ordering samples based on similarity
(e.g. Dutch political landscape)

Ordination is the placing of objects (= site, samples) along axes
(gradients), based on their properties (often species composition). –
Ramensky, 1929
 and relate these to environmental variables

2 main types of ordination

- Unconstrained ordination: only examines 1 dataset with response variables; the resulting
output reflects overall variation in the data, which is good for exploring data
- Constrained ordination: focussing on particular effects of interest: it attempts to explain the
variation in a set of response variables by the variation in a set of explanatory variables.


3 types of ordination plots

Scatterplot Biplot Triplot
Sites Sites + species Sites + species + predictors




 the closer the point are, the more similar they are
 triplots plots both variables, so also the predictors

,Polar ordination
Polar ordination: a foundational ordination technique

Steps of polar ordination:

1. Compute distance between sites in terms of species composition and plot in a distance
matrix
2. Select two most different sites: these are placed on opposite ends (poles) of axis 1
3. Order the remaining sites between the poles
 eventually leading to calculate an ordination score x, where x is coordinates of the site
4. Choose sites for axis 2 perpendicular to axis 1: select 2 other sies which are close together on
axis 2, but very dissimilar
5. Order all sites between these poles on axis 2


Start of dataset




Compute distances between sites (objects)
Distance: dissimilarity between objects

Euclidean distance: form of computing distances


d jk= √∑ ( y − y )
j k
2

, For a bigger dataset




Select two most different sites
Find the biggest value of difference between two sites in
the matrix
 the two sides are placed on opposite ends (poles) of
axis 1




Order remaining sites between the poles
E.g. axis score of site S2
 take the distance from S2 from both poles on the matrix and plot it
on the axis

Distance S2 – S1 = 128
Distance S2 – S5 = 74



Repeat that for every site

Can be computed by using the altered theorem of Pythagoras

2 2 2
X =( L + D1−D2 )/2 L

L = Distance between poles
D1 = Distance from pole 1
D2 = Distance from pole 2

The benefits of buying summaries with Stuvia:

Guaranteed quality through customer reviews

Guaranteed quality through customer reviews

Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.

Quick and easy check-out

Quick and easy check-out

You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.

Focus on what matters

Focus on what matters

Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!

Frequently asked questions

What do I get when I buy this document?

You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.

Satisfaction guarantee: how does it work?

Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.

Who am I buying these notes from?

Stuvia is a marketplace, so you are not buying this document from us, but from seller niekvandeven. Stuvia facilitates payment to the seller.

Will I be stuck with a subscription?

No, you only buy these notes for $6.71. You're not tied to anything after your purchase.

Can Stuvia be trusted?

4.6 stars on Google & Trustpilot (+1000 reviews)

83662 documents were sold in the last 30 days

Founded in 2010, the go-to place to buy study notes for 14 years now

Start selling
$6.71
  • (0)
  Add to cart