Topic 10 – Population Ecology

Population ecology

groups of individuals of the same species living together, examining how their numbers and distribution change over time

divided into spatial attributes (size, range, dispersion) and temporal attributes (demography, life history, population dynamics)

Abundance

Total number of individuals (absolute or relative)

Density

Number of individuals per unit area/volume

Quadrat

Defined survey area used to count sessile organisms

Mark-recapture

Method estimating mobile population size using N = RM/m

Population index

Indirect evidence (tracks, scat, eDNA) used to estimate population size

Dispersion

Spatial pattern of individuals: clumped, uniform, or random

Demography

Study of population age/stage structure over time

Survivorship

Proportion of individuals surviving to a given age

Type I survivorship

Low early mortality, high late mortality (e.g. humans, elephants)

Type II survivorship

Constant mortality throughout life (e.g. songbirds)

Type III survivorship

Very high early mortality, few survive to reproduce (e.g. fish, frogs)

Fecundity

Average number of female offspring produced per female per lifetime

Life history trade-off

Resources invested in reproduction reduce investment in survival, and vice versa

Semelparous

Reproducing once then dying (e.g. salmon, century plant)

Iteroparous

Reproducing multiple times over a lifetime (e.g. elephants, trees)

Per capita growth rate (r)

Rate of population change per individual; r = (B−D)/N

Exponential growth

Accelerating growth when r is constant and resources are unlimited (J-curve)

Logistic growth

Growth that slows as population nears carrying capacity (S-curve)

Carrying capacity (K)

Maximum population size a habitat can sustainably support

Density-dependent factors

Factors whose impact scales with population size (competition, disease, predation)

Density-independent factors

Factors that affect populations regardless of size (weather, disasters, habitat loss

Age structure

Distribution of individuals across age classes; predicts future population growth