BZ3220 - Week 7 (Rare Things)

What is the Most Consistent Pattern in Ecological Communities.

Rarity is common. This means most species are rare, few are abundant.

What Distribution often Describes Species Abundance

A log-normal distribution.

What is Preston’s Veil

The idea that rare species are often missed due to limited sampling.

How is Rarity Defined

By low abundance and/or restricted distribution relative to other species.

What are the Main Dimensions of Rarity

• Geographic range size

• Abundance/density (local or total)

• Patchiness/ubiquity

• Ecological specialization

How can Rarity be Quantitatively Defined

Using quantiles (e.g., lowest 10–25% of range size or abundance).

What is the Fundamental Niche

The full range of conditions a species could occupy.

What is the Realised Niche

Where a species actually occurs, limited by interactions and constraints.

What is the Difference between Extent of Occurrence and Area of Occupancy

Extent of occurrence: shortest continuous imaginary boundary of total distribution.

Area of occupancy: actual area occupied within that boundary.

What are the two Causes of Rarity

1. Natural

2. Imposed

Examples of Natural Causes

• Ecological

  • Narrow niche

  • High trophic level

  • Vulnerability to natural biological change

• Historical/geographic constraints

  • Recently evolved

  • Poor dispersal relative to historical limits

Examples of Imposed Causes

• Habitat loss/fragmentation/isolation

• Pollution

• Exploitation

• Climate change

What is Pseudo-Rarity

A species appears rare due to:

• Scale (e.g., locally rare but globally common)

• Detectability issues

Why are Rare Species more Vulnerable to Extinction

• Small populations

• Limited distribution (fragmentation)

• Greater sensitivity to disturbance

What is the Strongest Predictor of Extinction Risk

Small geographic range size (i.e., rarity).

Are Rare Species Functionally Unimportant

No, they can be disproportionately important.

Why are Rare Species Important for Ecosystem Function

They often occupy and perform unique functional and ecological roles.

What happens if Rare Species are Lost First

There is a disproportionate loss of:

• Functional richness (the range of functional traits in a community)

• Functional originality (how unique a species’ role is compared to others)

• Functional specialisation (how different species are from the average function)

What are Dominant Species

Highly abundant species with strong influence.

What are Rare Species

Low abundance species with potentially unique roles.

What is a Keystone Species

A species with a disproportionately large ecological impact relative to its abundance. The role of keystone species may be to create or modify habitats or to influence the interactions between other species.

What happens if a Keystone Species is Removed

Major changes in community structure and significant loss of diversity.

What is the Rivet Hypothesis

Each species contributes to ecosystem function. Therefore losing species weakens the system.

What is Redundancy

Some species can replace others functionally.

Why is this Important

Determine show much species loss affects ecosystems.

Why is Monitoring Rare Species Important

To track population trends and extinction risk.

What is the Threatened Species Index (TSX)

A tool used to measure changes in abundance of threatened species over time.

Why is TSX useful

• Tracks conservation status

• Informs policies

• Guides management decisions

Why is Rarity important for Biodiversity Patterns

Many species are rare, meaning they contribute heavily to total richness.

Why might Common Species drive Biodiversity Patterns instead

In some systems (e.g., birds), common species dominate spatial patterns.

Why are Rare Species hard to Conserve

• Limited data

• Detection difficulty

• Small populations

You are Assessing Extinction Risk, what Key Variable should I Prioritise

Geographic range size.

A Species if rare Locally, but Common Globally, what is this

Pseudo-rarity.

Why Might Losing Rare Species be more Serious than Losing Common Ones

Loss of unique ecological functions.

You suspect a species is rare due to poor sampling, what concept applies

Preston’s veil (sampling bias).

You want to map species distribution, what metrics do you use

Extent of occurrence and area of occupancy.

Why is long-term monitoring essential for rare species

To detect trends over time and evaluate conservation success.

You are managing a fragmented species, what risk is highest

Local extinction.