Population Ecology - Pt II Basic Characteristics of Population

Population Ecology

A subdiscipline that studies the abundance. distribution and dynamics of population

Population

Group of organism from same species that exist in particular location and period.

Basic Population Characteristics

• Geographic Range/Distribution

• Abundance (ex: population size, population density, occurrence, etc.)

• Dispersion Pattern

• Population descriptors (population structure, age pyramids, sex ratios, life tables, fecundity, etc.) 

• Population growth, dynamics (increase/decline of population over time) 

Geographic Range 

Area or extent of geographical space within a particular species can be found 

• can vary from big to tiny. 

• Influenced by biotic/abiotic factors. 

Species Distribution

Pattern of arrangement where species is found across entire geographic range

Species Distribution includes

Density if individuals within range variation in species distribution due to different factors (eg; cougars in Argentina to Canada) 

Species with small range/geographic

Devils Hole Pupfish 

• Single dessert pool 

• population varys 

Tropical Andes 

• discovered in 1978, 90 new species on single mountain ridge (Ecuador). 

Species with large geographic range

• Blue Whale, brown bear, house mouse, many exotic species. 

• Coyote in PEI 

Spatial scale (types)

Small scale (local)

• ex: seed dispersal, competition among plants in meadow. 

Medium Scale (regional) 

• ex: Forest composition across PEI or the Maritimes 

Large scale (global) 

• Climate change, species migration, biodiversity loss.

Metapopulations

Local populations exist in patches that are spatially isolated. but still linked by dispersal 

• dispersal is a very important link between metapopulations. 

Dispersion

Arrangements of individuals within each one of these populations. 

The movement is called dispersal. 

Dispersion influences

Location/distribution of essential: 

• resources 

• individual dispersal ability

Abiotic conditions 

Behavioral interactions 

Dispersion types

• Regular/Uniform - More territorial and resources (ex, birds)

• Random - No territorial, resources are random

• Clumped/clustered - (most common) resources clustered/clumped.

Social Behavior

Individuals within a population may attract, repel, or ignore one another.

• Mutual attraction

• Avoid each other

• Natural Response

Formula to remember

Mean (x) = (sum of x)/n

Variance (s²) = (sum(xi-x)²)/(n-1)

Index of dispersion = (variance)/(Mean)

Determine dispersion type

Value >1: Dispersion is clustered

Value <1: Dispersion is uniform

Value =1: Dispersion is random