What is Rarity?

What is Rarity?

What is Rarity?

What is Rarity?

Characterizing Communities through the Relationships Among Species

Rank Abundance Curves Community #1

Rank Abundance Curves Community #1

Three Models Predicting Rank Abundance Patterns

Resources Divided Among Species

The Broken Stick Model Resources are randomly divided among species.

The Broken Stick Model

The Niche Preemption Model (Geometric series) Strong dominance with a few species acquiring most of the resources

The Broken Stick Model

The Log Normal Distribution Assumption: A large number of factors influence species abundances Veil line

Impact of Increased Sampling 1/8 yr 1 yr 4 yr

Sonoran Desert Example veil line

The Broken Stick Model

Observed Patterns Broken stick Nesting bird pairs in West Virginia Log Normal Vascular plants of Great Smokey Mountains Niche Preemption Fir forest Great Smokey Mountains

General Trends Only in select groups of higher animals Broken stick: Niche preemption: Communities with few species and one dominant Most common, particularly in communities with a large number of species Log normal:

Comparing Communities Community #1 Community #2 Subsampling Stand level sampling

How do we make sense of all of this information? Data Arrranged Listing Species in Each Sample Unit How do we make sense of all of this information?

Braun-Blanquet: An Historical Approach

Step #1: Place Similar Stands Next to One Another

Step #2: Place Species with Similar Distributions Next to One Another

Step #3: Remove Species with Little Information Content Rare Supercommon Not grouping well

Repeat Process Until Satisfied Key species have: (1) High fidelity (e.g., not in more than 20% of stands outside association) (2) High constancy (e.g., are in most of the stands within the association) Association c Association a Association b

This is a highly subjective approach Criticism: This is a highly subjective approach

Quantitative Approaches

Comparisons with Communities of One Species dab= 10 dac= 20 50 A B C 30 20 dbc= 30

Comparisons with Communities of Two Species dab= 10 dac= 20 50 A B C 30 20 dbc= 30

Comparisons with Communities of Two Species B C A

Comparisons with Communities of Three Species B C Species 3 A

Comparisons with Communities of Lots of Species?

Multivariate Approaches

Step #1: Calculation of Site Similarities

Presence/Absence Data Definitions a = number of species in both sites b = number of species only in second site c = number of species only in first site

Presence/Absence Data The Jacard Index Definitions a = number of species in both sites b = number of species only in second site c = number of species only in first site

Presence/Absence Data

Quantitative Data Bray-Curtis Index Definitions

Quantitative Data Bray-Curtis Index Definitions

Now What? Similarity matrix

Dimension Reduction through Ordination