Characteristics of Populations SBI4U Miss Richardson

Population Size and Density Populations are constantly in flux. They move, change and are influenced by their environment Various ecosystems and their abiotic components make up a biome Together, biomes make up the biosphere

Ecology Terminology

Biomes of the World

Population Size & Density World Population Density Map

Population Size, N Population size is the total number of organisms of the same species It is determined by actual counting (census) or by estimation

Population Density, Dp Is the number of individuals per unit of volume or area It can be calculated by: Dp = N/A

Crude vs. Ecological Density Crude density refers to the total number of organisms per total area Ecological density refers to the number of organisms in the actual space used by the population

Example If 22 fox live in a small national park which is 300 hectares and 250 hectares without the lake, calculate the crude and ecological density.

Example Crude Density D = N S D = 22 foxes 300 ha = 0.07 foxes /ha Ecological Density D =  N         S D =  22 foxes          250 ha     = 0.08 foxes /ha

Determining Population Size There are three main techniques for determining population size: Transects Quadrats Mark-Recapture

Transects Samples populations along a long rectangular area/line of specific length The species being monitored are counted and recorded Useful when density of a species is low or when individual organisms are very large (ie: trees)

Quadrats A small square area is measured in which individuals are counted and extrapolated for the whole area Most effective for stationary populations

Mark-Recapture A number of organisms are caught and marked (or tagged with technological devices) and returned to the environment They are later recaptured and the numbers are compared to the original capture: Total #marked = #marked recaptured total population size of recapture

Example You are part of a summer research team and in trying to count the number of catfish in a lake you capture 29 fish and tag them.  Then a week later you catch 35 fish and of those only 10 are tagged.  Estimate the population size.

Example Total # of Marked (M) =   #marked recaptured (m) Total population (N)             size of recapture (n) M = 29 m = 10 n = 35 29  =  10 N        35 N = 101.5 is approximately 102 fish.

Population Distribution There are 3 recognized distribution patterns Uniform Random Clumped

Clumped Distribution Occurs due to uneven distribution of resources – populations gather around them Common among species that travel in groups

Uniform Distribution Occurs when resources are scarce, but evenly distributed Usually a result of negative interactions among population members

Random Distribution Occurs when resources are plentiful and uniformly distributed Results from neutral interactions amongst individuals

Life Histories and Populations Ecologists rely on survivorship and reproductive patterns to help them understand populations – these patterns are referred to as life histories Life histories vary between species They are described based on: Fecundity – average number of offspring produced by a female over her lifetime Survivorship - #/% of organisms that typically live to a given age