Populations

Populations

• Population - a group of organisms of the same species which have the potential to interbreed – or a population is a group of organisms occupying a particular place at a particular time

• Populations have a number of properties which are not possessed by individual organisms - this is because a population is the sum of many organisms interacting

Prairie Dog Distributions

Properties dealing with changes in population size

• Natality - may think of this as births, but includes more than just birth - hatching, germination, fission

• Natality includes idea of fecundity - number of offspring produced per unit time - we are most concerned with realized fecundity - actual number of survivors

• Mortality - death rate - its converse is survivorship - mortality looks at how many die per unit time, survivorship at how many don't die per unit time

• Longevity examines life-span of individuals - again we are most interested in realized longevity, not potential longevity

• Immigration - individuals moving into a population• Emigration - individuals leaving a population

What is an individual?• unitary organism - individuals are highly

determinate in form and while growing pass through predictable (innately determined) sequences of life history stages

• modular organisms - zygote develops into unit, or module, which produces more modules thus producing an organism with a variable number of modules, whose development is unpredictable and strongly influenced by environmental factors

A classic unitary organism

A classic modular organism

Bryozoan colony

More classic modular organisms

Genets and Ramets

• ramet - a module with the potential for a separate existence

• genet - the "genetic individual"; the collection of all modules derived from a single zygote

A single Aspen clone

Posidonia oceanica – Neptune grass

Sampling to collect population data Census - most basic sampling - count and determine age of all

individuals in population, count again later • Several ways to subsample:1. Determine total area in which population occurs, count all

individuals in small plots, multiply average number in plots to get total, repeat at later dates - works best for sessile organisms

2. Mark-recapture methods 3. Catch per unit effort 4. Miscellaneous methods – traps, counts of fecal pellets,

counts of vocalizations, feeding damage on plants, roadside sightings, fur or pelt records, roadkill

Quadrat Sampling

Mark recapture of Cicadas

Catch per unit effort – Pacific Threadfin

Beetles feeding on Viburnum

Beetle damage on Viburnum

Bird migration data – typical altitude – from radar

Bird migration radar map

Skylark

Metapopulations

• A metapopulation is a series of small, separate populations united together by dispersal

Metapopulation Dynamics

Metapopulations of Bay Checkerspot Butterfly

Aphids and Epilobium

Habitat fragmentation in Amazonia

Demography

Demography

• Demography is the study of processes that influence population size - it is the way we study changes brought about by births, deaths and dispersal

For Northwest Montana, Greater Yellowstone, Central Idaho

The Fundamental Equation of Ecology – Harper 1977

Δ N = B – D + I – E

Change in Number = Births – Deaths + Immigration - Emigration

John L. Harper – 1925-2009

Rearrange Fundamental Equation

Δ N = B – D + I – E

Nfuture = Nnow + B – D + I – E

Common Field Grasshopper