Demography

Rearrange Fundamental Equation Δ N = B – D + I – E Nfuture = Nnow + B – D + I – E Often we assume that I = E, so no net dispersal

Common Field Grasshopper

R0 – Net Reproductive Rate If Ro = 1 – population is stable (constant) If Ro > 1 – population is increasing If Ro < 1 – population is decreasing

Red Deer – Stag, Hind, Fawn

Isle of Rhum, Scotland

Red deer fawn being tagged for study

Arithmetic scale Logarithmic scale

General types of survivorship curves

Human management of species may change survivorship curves A – fish mortality in typical population B – fish taken by fishing

Population Pyramid For France Jan. 1, 1967

Changes in population of Japan over time

Changes in population of Canada from 1971-2006

Population Growth Models

R0 – Net Reproductive Rate

Reproductive Rates R0 – Net Reproductive Rate – applies to populations with discrete generations and/or semelparous species r – Intrinsic Rate of Natural Increase – is calculated from R0 and is applied to populations overlapping generations and/or iteroparous species

Spruce Budworm

Spruce Budworm Budworm defoliation

Northern Elephant Seal Reduced to about 20 by 1890’s Model of exponential recovery predicted 80 seals by 1906; 40,960 seals by 1978 Real data – 125 seals in 1911; 60,000 seals in 1977

Because exponential growth is seldom seen, population growth must be constrained - two types of constraints 1) density independent constraints - growth constraints that are not effected by population size - usually abiotic - weather, storms, volcanos 2) density dependent constraints - growth constraints whose effects change as population size increases - usually biotic - competition, predation, parasitism, disease