Populations

Estimating Abundance

Population Size

• Estimating population size– Indices

– Density

Relative Abundance

Indices for Relative Abundance

• An index of abundance is a measure that varies directly with the abundance of the population of interest.

• Based on:• Scats, pellets, pellet groups• Point or transect counts (Bird Songs)• Tracks• Signs • Etc.

Index of Deer abundance in Nova Scotia

• Based on counting pellet groups –Pellet Group Index PGI

• Pellet groups are counted along a 1 km

transect that are within 1 m on either side of the transect.

• Counting takes place in the spring

2 m

1 km long

PGI = 7

This index can be turned into a density estimate

Deer Density

• Index can be converted to a density estimate

• Need to know how long a period the pellet groups have accumulated over

• Need to know how often deer defecate per day.

Birds

• Point count• Line transect count• Strip count• Variable distance line transect

Direct Density Estimates

Catch-effort Methods

Assumptions:1 – The population is closed2 – Probability of each individual being

caught in a trap is constant throughout the experiment

3 – All individuals have the same probability of being caught in sample i

Cat

ch p

er u

nit e

ffor

t

Accumulated catch

Number

of in

divid

uals

Leslie plot of catch-effort data

Capture-Mark-Recapture Techniques

• For Closed Populations:

• Single marking, single recapture – Petersen Method

• Multiple markings and recaptures – Schnabel Method

• For Open populations:

• Multiple capture and recapture -

Jolly-Seber method

• How do we know that a population is decreasing and in need of protection?

Long-term monitoring! Increase or decrease?

Survey Data

Important concepts

• Habitat• movement (dispersal)

Habitat

• habitat – physical condition where species live – defined specifically for individual species.

• source/sink

Movement

Movement (Dispersal) is central to population health!

- Density

- Genetics

What factors affect movement?

Habitat Reduction and Fragmentation

Corridors

Connectivity

Spatially structured populations

Spatially structured populations

High dispersal rate = homogeneous populations, low extinction

Spatially structured populations

Low dispersal rate = heterogeneous populations, high extinction

Metapopulation

• Dispersal rate intermediate where individual populations go temporarily extinct.

Concepts

• Minimum Viable Population (MVP)

• Population Viability Analysis (PVA)

PVA for Spotted Owl