Chapter 9: Population Distribution and Abundance Flashcards
Distribution
geographic area where individuals of a species occur
Abundance
number of individuals in a given area
Population
a group of individuals of the same species that live in a particular area and interact with each other
Population Size
number of individuals
Population Density
Number of individuals per unit area
What are some problems that are had in population density studies?
-The total area occupied may not be known
-It is often difficult to know how far organisms or their gametes travel
How do they determine an area for population density studies?
An area is delimited based on best available knowledge of the species
Why can it be hard to determine what an individual is?
-Aspen trees produce clones (genetically identical copies) when new plants grow from root buds. A grove of Aspens may all be from the same individual
-Other organisms can do this too
How is an individual defined?
-Product of a Single Fertilization
Name of single genetic individual
Genet
Members of a genet that are independent physiologically, each member is called a….
ramet
Absolute Population Size
actual population abundance
Relative Population Size
number of individuals in one time period or place relative to the number in another
What are relative population size estimates based on?
-estimates are based on data presumed to be correlated with absolute population size
-Ex: number of cougar tracks in an area or number of fish caught per unit of effort
Methods for estimating abundance
- Area-based counts
- Distance Methods
- Mark and Recapture Studies
Methods for estimating abundance: Area Based Counts
individuals in a given area or volume are counted
-used most often to estimate abundance of plants
-Quadrants: sampling areas of specific size; must be a good representation of the entire area and are chosen at random or placed on a grid
-Individuals are counted in several quadrants; counts are averaged to estimate population size
Methods for Estimating Abundance: distance methods
Distance of individuals from a line or point are converted into estimates of abundance
-Line Transects: observer travels along a randomly place line, counts individuals and determines distance from the line
-A detection function converts distance measurements into an estimate of the absolute population size
Methods for Estimating Abundance: Mark and Recapture Studies
are used for mobile organisms
-a subset of individuals are captured again and the ratio of marked to unmarked individuals is used to estimate population size
Example of Mark and Recapture Study
-23 butterflies are captured and marked
-Later, 15 butterflies are captured, 4 of them marked
-Population is estimated
Dispersal
movement of individuals into (immigration) or out of (emigration) an existing population
Metapopulation
group of geographically isolated populations linked by dispersal
Geographic Range
species might consist of one or multiple metapopulations
Dispersion
spatial arrangement of individuals in a population
Regular Dispersion
individuals are evenly spaced throughout their habitat
Random Dispersion
individuals are randomly spaced
Clumped Dispersion
more common in natural populations
How many locations do endemic species occur in?
one location only, no where else on earth
What all does geographic range include?
all the areas a species occupies during all life stages
What may be the cause of patchy distribution?
abiotic factors
Species Distribution Models
useful if the geographic range of a species is unknown or to predict spread of a pest species, or shifts in ranges due to climate change
Example of a species distribution model
distributions of chameleons in Madagascar. a model used mapped environmental data along with “habitat rules” for each species to accurately predict the distribution of 11 species
What determines distribution and abundance?
habitat suitability
Abiotic factors
moisture, temperature, pH, light, nutrients, etc.
What influences habitat suitability?
food availability
What organisms affect species distribution?
Herbivores, predators, competitors, parasites, and pathogens
What can interact to determine species distribution and abundance?
Abiotic and biotic factors
Disturbance
events that kill or damage some individuals, creating opportunities for other individuals to grow and respond
Continental Drift
Wallace 1860 observed very different animal species on the Philippines and New Guinea , even though they are very close together
What caused continental drift?
discovery that two islands were on different tectonic plates, and have been close together for a relatively short amount of time
Migration
type of dispersal in response to seasonal variation in resources; involves round-trip movement of whole population
Dispersal Limitation
a species’ limited capacity for dispersal can prevent it from reaching areas of suitable habitat
Van der Veken et al. 2007
-27 populations of English Bluebells were established experimentally in suitable habitat in 1960
-After 45 years, 11 populations persisted, hundreds or thousands of individuals
-suggests that dispersal limitation prevented the bluebells from reaching habitats where they could thrive
Metapopulation
a set of spatially isolated populations linked to one another by dispersal
How are metapopulations formed?
-some populations are sources of individuals that disperse to other populations
-other populations are sinks that receive more immigrants than the number of emigrants they produce
-individual populations may be prone to extinction but the meta population persists
Levins (1969,1970)
represented meta population dynamics in terms of extinction and colonization of patches
Model Assumptions of Levins 1969-1970
-a very large (infinite) number of identical habitat patches
-all patches have an equal change of getting colonists (spatial arrangement of patches doesn’t matter)
-all patches have an equal chance of extinction
Habitat Fragmentation…
can result in metapopulations
-patches become smaller and more isolated; colonization rate may decrease and extinction rates increase
Isolation By Distance
patches located far from other patches were less likely to be colonized; few patches separated by more than 2 km from an occupied patch were colonized during that period
Why is patch size important to metapopulations?
larger patches were more likely to be colonized; small patches had highest rate of extinction
Rescue Effect
high rates of immigration from a nearby patch that protects a small population from extinction
