Flashcards in Population Ecology Deck (79):
describes where individuals of a species might potentially be located.
(In the United states, most species have a range of 4-24 states.)
These species are an extreme, they are worldwide in distribution.
species found in only a small, restricted area, they represent the other side of the spectrum.
Factors Determining the Geographic Range of a Species
A combination of the above
Why can't palm trees present where winter temperatures regularly go below freezing?
The meristems are at the top of the trunk, not tolerant of freezing
What other reasons explain why palm trees are near beaches and in micronenvironments?
They compete well in moist environments. Seeds are water dispersed.
Many species have what is called a “Gondwanan” distribution. They occur in the Southern continents of Australia, South Africa, South America, and sometimes India.
These places are far away from each other now, but 150 million years ago, they were all linked together in a massive continent.
What is this an example of?
Historical Factors Determining Geographic Range
Populations arise when....
Discontinuities in suitable habit for a species restricts the movement of individuals
consequences of the way an organism interacts with the environment, and with other organisms, and influence its evolution
Simply the number of individuals in the population at any given time. Sometimes called abundance.
The number of individuals in the population per unit area or unit volume.
For many organisms this measure, rather than its actual numbers, exerts a real effect on the organism.
Patterns of Dispersion
The most common pattern of dispersion, occurs because some areas of habitat are more suitable than others
ex:salamanders in numbers under fallen logs
Why do plants often clump?
Because seeds fall close to parent plant
What are other reasons why a species may clump?
Safety of social reasons
This pattern occurs in the absence of strong attraction or repulsion among individuals.
It is uncommon.
This generally happens because of interactions between individuals in the population, like competition, territoriality, and human intervention
Creosote bushes in the Mojave desert are uniformly distributed because competition for water among the root systems of different plants prohibits the establishment of individuals that are too close to others.
The desert lizard Uta sp. maintains somewhat regular distribution via fighting and territorial behavior
I.e. ., the spacing of crops
This is the relative number of individuals at different ages
is the proportion of individuals of each sex. The number of females is more important in the overall growth rate of populations
Examples: elk; fewer males of reproductive age than females; males breed with more than one female.
differences among individuals in the population
Most populations show differences among individuals.
Some variation has a genetic basis.
Other variation is largely environmental.
In many cases, variability is caused by both genes and the environment
Variability that occurs when the two sexes differ greatly in appearance
Variability that occurs when individuals differ in appearnace because of a dramatic transformation as they age
Many organisms that exist as interwoven collections of subpopulations
exhibit their own dynamics, with localized extinction, and recolonization of unoccupied areas of suitable habitat, determining their dynamics.
This is probably the best, simple, model of population growth…it predicts the rate of growth, or decay, of any population where the per capita rates of growth and death are constant over time
Formula for exponential growth
Nf = Ni(e^rt)
Can a population continue growing forever?
No, they would outstrip their resources
this is the maximum number of individuals a given environment can sustain.
Resources that are rare enough to inhibit a species' reproduction so that the population no longer grows.
ex) light, water, nesting sites, prey, nutrients
Factor limiting populations that intensifies as the size of a population increases
Examples of this factor that limits populations includes suitable nesting sites for birds, competition for light and water amongst prairie grasses
Density Dependent Factor
Factors limiting populations that are independent of population size
Examples of this factor that limits populations includes winter temperatures
growth model that accounts for carrying capacity
Logistic growth model
Formula for logistical growth model
NOTE: when k =n, dN/dT is equal to zero
When it is small, growth rate is approximately rmax
When N>K, population declines
Does logistical growth model fit actual populations?
Only lab populations, not actual populations due to other factors like lag time.
The time it takes between reaching carrying capacity and the slowdown in reproduction
Rapidly growing populations, or populations with lag time often overshoot K, and exhibit population cycles, or chaotic behavior
the study of the age structure and growth of populations. It is, essentially, the study of birth, reproduction, and death, as it relates to populations.
was a famous early demographer/economist.
In his Essay on the Principal of population, 1798, he was the first to reach the conclusion that human populations tended to grow until they outstripped their available food supply.
count every individual in the population
count individuals in many small portions of the area (e.g., quadrats) then calculate density
mark and recapture
index of relative abundance (e.g., pheremone baited insect traps, camera traps)
Sample the population
A person’s chance of death
a group of organisms born at the same time.
The variable that can estimate population growth or decline using life tables
the sum of l(x)m(x) for the entire lifespan, estimates the number of female offspring produced per female.
R0>1, R0<0, R0=1
Increase, decline, stable
traces the decline of a group of newborns over time.
plot the probability of surviving to a certain age for a representative member of the population.
They sometimes differ from male vs. female.
Different populations might have different
A convex curve. Most individuals live to adulthood with most mortality occurring during old age. I.e., humans, red deer, elephants.
A straight line. An individual’s chance of dying is independent of its age. I.e., small birds and mammals.
A concave curve, few individuals live to adulthood, with the chance of dying decreasing with age. I.e., oysters, redwood trees, snapping turtles.
is the proportion of individuals at different ages.
It has a significant impact on future population growth.
Populations that have remained constant for a long time have what type of age distributions?
Rapidly growing populations have a disproportionate number of young individuals.
many older people, fewer young people. Populations of some countries will decrease in the future.
Europeans and Japanese
many young people, fewer old people populations will increase in the future.
Africa, Near east
When is m(x), or age specific fecundity highest in humans?
20 yr olds.
When are death rates highest?
Babies and old age.
Are death rates in U.S. higher or lower than guatemala, mexico, and most of developing world?
the timing of an organisms reproduction and death
how many offspring an organism produces that are ultimately able to produce their own offspring.
Why is there a trade-off between survivorship and reproduction?
Reproduction is dangerous, involves resources for growth/maintenance
Life histories have evolved to maximize an organisms expected fitness
is one large reproductive effort (most insects, annual plants). Examples, grasshoppers, mayflies, octupi and squids Agave.
is fewer offspring and many reproductive episodes. Example, perennial plants, most large mammals, sharks, most birds such as gulls and terns.
the number of offspring produced per reproductive episode.
expend all their resources on a single clutch.
must save some resources for growth and survival.
Clutch size varies depending on...
As an organism ages, it has more resources available to it. So more resources later means?
Reproduce earlier means?
Larger organisms reach reproductive age faster or slower?
an adaptation by which an organism may potentially increase the survivorship of its offspring.
It comes at a cost to the parents, however, and results in fewer offspring because resources must be conserved
Birds providing varying or similar amounts of parental care?
hatch and are able to fend for themselves immediately. Eggs are often laid in warm environments, and parents do not incubate them. In theory, this means more time to forage .