mark-recapture equation
N/M = n/R
- N = unknown population size
- M = number of individuals marked
- n = number of individuals recaptured
- R = number of recaptured individuals that are marked
range (distribution)
area over which a specific population occurs
two ways to estimate abundance
- quadrats: splitting a range up into quadrats (square frames)
- mark-recapture: animals are captured, marked, and then recaptured
examples of organisms that demonstrate clumped distribution
- social animals (e.g. wolves, lions)
- animals that eat unevenly distributed food (i.e. seedlings can clump around parent plants if gravity-dispersed)
- plants that are dispersed by small scatter-hoarder animals
four conditions necessary for stable metapopulations, following Levins’ Classic Model
- suitable habitats occur in patches
- all populations must have a substantial risk of local extinction
- habitat patches can’t be too isolated, to allow for recolonization after local extinction
- the dynamics of the subpopulations aren’t synchronized (or the entire metapopulation could go extinct at once)
population size
the number of individuals in the total population; density × range
geographic range
area over which all populations of a species reside
the importance of corridors between subpopulation habitat patches
- when patches are isolated, more species become extinct
- when patches are connected by corridors, fewer species become extinct
three types of individual distribution
- random: the position of each individual is independent of the position of the other individuals in the population
- uniform: individuals are evenly spaced out, often due to negative interactions (i.e. competition, territoriality)
- clumped: individuals occur in groups, due to location of resources, suitable habitats, or protection from predators (social units)
subpopulation vs. metapopulation
- subpopulation: a subset of a larger population
- metapopulation: a collection of subpopulations that are exchanging genetic information (connected by gene flow)
Richard Levins’ definition of metapopulations
- a set of local subpopulations that persist in balance between individuals that reproduce and die within local patches, and their offspring disperse into other patches
- emigration/immigration is rare
examples of organisms that demonstrate uniform distribution
nesting birds (e.g. penguins on breeding grouns)
three ways individuals move within a population
- dispersal: permanent movement of individuals/genes into a certain space
- emigration: movement of individuals/genes out of a subpopulation
- immigration: movement of individuals/genes into a subpopulation
two things population abundance is influenced by
population density and population range
reasons why population abundance has to be estimated
- hard to see microscopic/dull-coloured organisms
- some organisms are only present during reproduction
- to measure size (especially for plants; trees)
examples of organisms that demonstrate random distribution
- trees
- wind-dispersed seeds
- animal-dispersed seeds, and the animals that eat them
the importance of empty patches in a metapopulation
a certain number of empty patches is necessary for a stable metapopulation, to allow for offspring dispersal to patches
population density
the number of individuals per unit area
population abundance
the number of individuals in a given area (can vary across the range)
