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 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 –

Rearrange Fundamental Equation Δ N = B – D + I – E N future = N now + B – D + I – E

Common Field Grasshopper