Population Distribution and Abundance

Question 1

Distribution

Answer 1

Geographic area where individuals of a species occur
Can map out

Question 2

Abundance

Answer 2

Number of individuals in a given area
Abundance can be reported as population size (# of individuals), or density (# of individuals per unit area)

Question 3

Population

Answer 3

Group of interacting individuals of the same species living in a particular area
Interactions within populations include sexual reproduction and competition
Sometimes the total area occupied by a population is not known
Often difficult to know how far organisms can travel
When an area is not fully known area is delimited based on the best available knowledge of the species
For some species, it’s hard to determine what an individual is

Question 4

Individuals

Answer 4

Can be defined as products of a single fertilization
The aspen grove would be a single genetic individual: genet
Genet: one unit- cluster
If members of a genet are independent physiologically: ramet
Ramet: Units within genet

Question 5

Estimating Abundance and Distribution

Answer 5

Complete counts of individual organisms in a population are often difficult or impossible
Several methods are used to estimate the actual abundance or absolute population size

Question 6

Area-based counts

Answer 6

used most often to estimate the abundance of immobile organisms

Question 7

Quadrats

Answer 7

Sampling areas of specific size, such as 1 m^2
Individuals are counted in several quadrats; the counts are averaged to estimate population size.

Question 8

Distance methods

Answer 8

distances of individuals from a line or point are converted into estimates of abundance

Question 9

Line Transects

Answer 9

The Observer travels along the line and counts individuals and their distance from the line

Question 10

Mark-recapture studies

Answer 10

Used for mobile organisms
A subset of individuals is captured and marked or tagged, then released
Tag should not affect their performance in life
At a later date, individuals are captured again, and the ratio of marked to unmarked individuals is used to estimate population size
Ratio of: marked/ total population : recaptured marked / total caught

Question 11

Relative population size

Answer 11

Number of individuals in one time period or place relative to the number in another
Estimates are based on data presumed to be related to absolute population size
Ex; number of cougar tracks in a given area, or number of fish caught per unit of effort
Weakness - hard to know how many animals are associated with the pack
Interpretation of relative population size can be tricky
Ex; number of cougar tracks is related to population density, but also activity levels of individuals

Question 12

Distribution and Abundance

Answer 12

1. The distribution and abundance patterns of species and populations vary in their spatial extent across the landscape
   Not all habitat within a range is suitable: resulting in patchy distributions
   This can operate at different spatial scales
   At large scales, climate may dictate the locations of populations
   At small scales, soils, topography, other species, etc., can determine patchiness
2. The distributions and abundances of organisms are limited by habitat suitability, historical factors, and dispersal
   Examples:
   Patchiness at different scales is illustrated by the shrub Clematis fremontii
   restricted to areas of dry, rocky soil with few trees, called barrens or glades
   The glades occur on outcrops of limestone on south- or west-facing slopes

Question 13

Dispersion

Answer 13

spatial arrangement of individuals within a population:
Regular: Individuals are evenly spaced (checkerboard)
Random: individuals scattered randomly
Clumped: the most common pattern
Often results from the distribution of resources
Random or clumped: results from short dispersal distances
Competition: results in the regular dispersion of some species
Interactions can influence dispersion- individuals may repeal or attract others

Question 14

Geographic Range

Answer 14

The entire geographic region over which a species is found
There is great variation in species ranges
the geographic ranges of many species are not well-known
Such endemic species only occur in one particular location on Earth
Many tropical plants have small ranges. In 1978, 90 new species were discovered
Other species, such as the coyote, have very large geographic ranges.
restricted to a single mountain ridge in Ecuador
Geographic range includes areas occupied during all life stages.
For some species, it is difficult to find all the life stages and the ranges they inhabit.
Ex; some species, such as monarch butterflies, migrate long distances between summer and winter habitats.
Abundance can vary throughout a species’ range
Some populations exist in isolated patches that are linked by dispersal
Can result from physical features of the environment or human activities that subdivide populations
Ex; heathlands in England have been fragmented by human development

Question 15

Species Distribution

Answer 15

Predicts a species’ distribution based on conditions at locations the species is known to occupy
“Habitat rules” for each species: describes environmental conditions where it was most likely to be found

Question 16

Biotic features

Answer 16

Organisms are affected by herbivores, predators, competitors, parasites, and pathogens

Question 17

cooperative breeding

Answer 17

Young birds postpone breeding and instead help their parents raise more offspring
In high-quality territories
Results in clumped dispersion
Advantageous when high-quality territories are scarce
If high-quality territories are abundant, cooperative breeding is not favoured

Question 18

Disturbance

Answer 18

Events that kill or damage some individuals, create opportunities for other individuals to grow and reproduce
Some species’ distribution depends on disturbance

Question 19

Historical factors

Answer 19

Evolutionary history and geologic events affect the modern distribution of species
Ex. Polar bears evolved from brown bears in the Arctic. They are not found in Antarctica because of an inability to disperse through tropical regions.

Question 20

Dispersal limitation

Answer 20

Can prevent species from reaching areas of suitable habitat
Ex. The Hawaiian Islands have only one native mammal, the hoary bat, which was able to fly there
Species vary in their ability to disperse

Question 21

Migration

Answer 21

involves round-trip movement in response to seasonal variations in resources

Question 22

Metapopulation

Answer 22

A set of spatially isolated populations linked by the dispersal of individuals or gametes
Characterized by repeated extinctions and colonizations of small individual populations
but the metapopulation persists

Question 23

Habitat Fragmentation

Answer 23

Large tracts of habitat are converted to isolated patches, resulting in a metapopulation structure
As patches get smaller and more isolated, colonization decreases and the extinction rate increases

Question 24

Isolation by Distance

Answer 24

when patches are too far apart
can affect the chance of extinction
a patch that is near an occupied patch may receive immigrants repeatedly
can affect the chance of extinction
a patch that is near an occupied patch may receive immigrants repeatedly.

Question 25

Patch size

Answer 25

small patches may be hard to find and have high extinction rates

Question 26

Rescue Effect

Answer 26

high rates of immigration that protect a population from extinction