Chapter 11 Flashcards
the distribution of populations is limited to
ecologically suitable habitats
what are population distributions characterized by
- range
- dispersion
- density
- abundance
- dispersal
range
geographic distribution of the species
dispersion
spatial arrangement of individuals and habitats
density
number of individuals per unit of space
abundance
size of the population
dispersal
patterns of movement of individuals within and among populations
spatial structure
the pattern of density and spacing of individuals in a population
Fundamental niche
the range of abiotic conditions (e.g., temperature, humidity, salinity) under which a species can persist
what may prevent a population from persisting in an area
Competitors, predators, and pathogens
realized niche
the range of abiotic and biotic conditions under which a species can persist
geographic range
a measure of the total area covered by a population (e.g., temperature and drought define the range of sugar maple)
what do small-scale variation in the environment create
geographic ranges that are composed of small patches of suitable habitat
Ecological niche modeling
the process of determining the suitable habitat conditions for a species
Ecological envelope
the range of ecological conditions that are predicted to be suitable for a species (differs from the realized niche, which describes conditions in which a species currently exists).
when is predicting the potential geographic range of a species difficult
when only a few individuals exist
what can ecological niche modeling predict
the expansion of pest species
Geographic Distribution (Range):
all the areas that a species occupies during
their life time. This might include rivers/ocean
Endemic
species that live in a single, often isolated, location
Cosmopolitan
species with very large geographic ranges that can span several continents. Cosmopolitan species: rock doves, house sparrows, peregrine falcons, killer whales, cattle egrets
Abundance
the total number of individuals in a population that exist within a defined area (e.g., total number of lizards on a mountain).
what does the total abundance of a population provide
a measure of whether a population is thriving or on the brink of extinction
in a population, the number of individuals per unit area or volume; calculated by dividing abundance by area
density
what happens if population density is greater than what the habitat can support
some individuals must leave or the population will experience lower growth and survival
where does the largest density of individuals typically occur
near the center of a population’s geographic range
what happens near the edges of the range
conditions become less ideal and population densities decrease
the spacing of individuals with respect to one another within the geographic range of a population
dispersion
when individuals are aggregated in discrete groups (e.g., social groups or clustering around resources).
clustered (clumped) dispersion
when each individual maintains a uniform distance between itself and its neighbors (e.g., defended territories, croplands).
evenly spaced dispersion
when the position of each individual is independent of other individuals; not common due to non-random environmental heterogeneity
random dispersion
social antagonism
results in a spaced distribution
mutual attraction
leads to clumping
what happens in the absence of social antagonism or mutual attraction
individuals may distribute themselves randomly
individuals distribute themselves randomly
individuals are not influenced by the positions of others
since a random dispersion pattern implies that spacing is not related to a biological process
it is often used as the model against which an observed dispersion may be compared
probability theory
provides us with the tools to make such comparisons
poisson distribution
a probability distribution of discrete random variables (variables that can take on only a finite number of values)
expresses the probability of a number of events occuring in a fixed period of time and/or space if these events occur with a known average rate, and are independent of the time since the last event
poisson distribution
poisson distribution formula
P(x) = M^xe^-M/x!
M
the mean number of individuals per space
x!
the factorial of x
e
2.7183
when might an ecologist use the Poisson distribution
to make a quantitative determination of the pattern of dispersion
how does an ecologist use the poisson distribution to make a quantitative determination of the pattern of dispersion
by comparing the mean (M) of our distribution with the variance (V)
the variance of a random variable
a measure of the spread about the mean of the distribution of that variable
dispersal
the movement of individuals from one area to another (away from their birth place or away from centers of high population)
migration
the seasonal movement of individuals back and forth between habitats
what is the mechanism by which individuals can move between suitable habitats
dispersal
allows species to colonize areas outside of their geographic ranges
dispersal
a way to avoid areas of high competition or high predation risk
dispersal
when are barriers to dispersal revealed
when species are introduced to new areas/regions
census
counting every individual in a population
what do scientists conduct when a census is not feasible
survey
survey
count a subset of the population
area and volume based surveys
define the boundaries of an area or volume and then count all of the individuals in the space
what is the size of the defined space related to
the abundance and density of the population
what is possible by taking multiple samples
it is possible to determine how many individuals are in an average sample
line-transect surveys
surveys that count the number of individuals observed as one moves along a line
what can line-transect survey data be converted into
area estimates of a population (detection probabilities)
mark-recapture survey
a method of population estimation in which researchers capture and mark a subset of a population from an area, return it to the area, and capture a second sample of the population after time has passed
the population size is estimated by assuming that:
initially captured individiuals/population size = marked recaptured individuals/total individuals captured in 2nd sample
how can we estimate population densities
mark and recapture
mark and recapture studies
some individuals from a population are initially captured, marked, and released back into the population
M/N=
R/C
M
number initially captured and marked
N
number in population
C
total number captured on 2nd attempt
R
number of recaptures on 2nd attempt
N=
MC/R
how can dispersal be quantified
measuring how far individuals travel from a single source location, marked and recaptured, radio transmitters
lifetime disperal distance
the average distance an individual moves from where it was born to where it reproduces
what does lifetime disperal distance provide an estimate for
how fast a population can increase its geographic range
dispersal can cause a geographic range to expand rapidly if
a few individuals can disperse much farther than the average individual
Populations with high abundance also have large
geographic ranges
what may cause the relationship between population abundance and range
resource availability; species are likely to cover the area that contains the resources that they require
what may cause the large amount of variation in the abundance-range size regression
fluctuations within a geographic range
what does the regression caused by fluctuations suggest
reducing the range of a population will reduce the size of that population
how is the density of a population correlated to the body size of the species
negatively
what can we expect from the relationship between population density and body size
a given plot of habitat to support fewer large individuals than it does small individuals
what is essential to colonizing new areas
dispersal
dispersal limitation
the absence of a population from suitable habitat because of barriers to dispersal
barriers
large expanses of inhipitable habitat that an organism can’t cross
human barriers for dispersal
roads, forest clearings
habitat corridor
a strip of favorable habitat located between two large patches of habitat that facilitates dispersal (narrow band of trees that connects forests)
what habitats do individuals choose
those that provide the most energy
what happens as individuals move to a high-quality habitat
resources must be divided among more individuals (reduced per capita benefit)
per capita benefit can fall so low that
an individual would benefit by moving to the low-quality habitat
ideal free distribution
when individuals distribute themselves among different habitats in a way that allows them to have the same per capita benefit; assumes perfect knowledge of habitat variation
why do individuals in nature rarely meet the expectations required by the ideal free distribution
- they may not be aware that other habitats exist
- fitness is not solely determined by maximizing resources
- presence of predators or territory owners
what can the ideal free distribution allow
populations in low-quality habitats to persist over time
subpopulations
when a large population is broken up into smaller groups that live in isolated patches
when individuals frequently disperse among subpopulations
the whole population functions as a single structure; all subpopulations increase and decrease in abundance synchronously
when disperal is infrequent
each subpopulation fluctuates independently
basic metapopulation model
decribes a scenario in which there are patches of suitable habitat embedded within a matrix of unsitable habitat; all suitable patches are assumed to be of equal quality
source-sink metapopulation model
builds upon the basic metapopulation model and accounts for the fact that not all patches of suitable habitat are of equal quality
source subpopulation
in high-quality habitats, subpopulaitons that serve as a source of dispersers within a metapopulation
sink subpopulations
in low-quality habitats, subpopulations that rely on outside dispersers to maintain the subpopulation within a metapopulation
landscape metapopulation model
considers both differences in the quality of the suitable patches and the quality of the surrounding matrix
represents the most realistic and most complex spatial structure of populations
landscape metapopulation model
habitat patchiness has led to 3 models of population
- metapopulation model
- source-sink model
- landscape model
