53 Flashcards
population
is a group of individuals of the same species that occupy the same general area
populations are affected by
– Density
– Dispersion
– Structure
– GrowthRate
population ecology
is the study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size
density
is the number of individuals per unit area or volume
dispersion
is the pattern of spacing among individuals within the boundaries of the population
what increases density
births, migration into population
what decreases density
deaths, migration out of populations
In a _____ dispersion, individuals aggregate in patches
clumped
A _____ dispersion is one in which individuals are evenly distributed
uniform
It may be influenced by social interactions such as territoriality
In a ______ dispersion, the position of each individual is independent of other individuals
random
demographics
is the study of the vital statistics of a population and how they change over time
• Death rates and birth rates are of particular interest to demographers, but also consider
– Population Size
– Density and Distribution
– Age Structure, Sex Ratio
– Birth, Death, Immigration and Emigration
type I
species that invest much energy caring for young have low death rates early in life. Most individuals survive to reproduce.
mammals and large vertebrates, humans
type II species
have an approximately equal probability of dying at any age.
birds, small mammals
type III
Species that invest little energy raising their young have high death rates among offspring. Few individuals survive to reproductive age.
fishes, invertebrates, plants
3 types of growth patterns:
constant growth
exponentials growth
logistic growth
j shaped curve is
exponential growth
Exponential growth cannot continue indefinitely, why?
carrying capacity
Two outcomes:
– 1. population crash
– 2. slow population growth and level off at K
carrying capacity
(K) is the upper limit to the population of any given species that an ecosystem can support
s shaped curve is
logistic growth
The S-curve of logistic growth describes
a population’s changing number over time in response to feedback from the environment or its own population density
The effects of density- dependent factors ______ as the population density rises.
increase
density-dependent factors
• These flamingoes might be competing among each other for space, nutrients, food, or mates • Disease spreads easily among them, and the risk of predation might increase with population density.
Density-independent factors
exert effects that are unrelated to population density.
examples:
Natural disasters, such as this fire, might eliminate half of the deer population in the area without regard to population density.
Mechanisms of Density-Dependent Regulation
competition for resources disease predation territoriality intrinsic factors toxic wastes
life histories fall into two patterns shaped by natural selection:
- Opportunistic species (r-selected)
* Equilibrium species (K-selected)
Opportunistic species tend to:
r- selected
be short-lived, reproduce at an early age, and have many offspring that receive little care.
Weeds, insects, and many species with type III survivorship curves have opportunistic life histories.
Equilibrium species tend to:
k-selected
be long-lived, mature late, and receive extended parental care.
The large fruits of this coconut tree are evidence of a high investment in each offspring.
Birds, large mammals, and species with type I or type II survivorship curves are often equilibrium species.
reproductive strategies for r selected species
- short life
- rapid growth
- early maturity
- many small offspring
- little parental care or protection
- prey
- low tropic level
reproductive strategies for k- selected species
- long life
- slower growth
- late maturity
- few, large offspring
- high parental care and protection
- high investment in offspring
- predators
- high trophic level
How do you estimate population size?
• Total counts – usually unfeasible in wildlife • Incomplete counts – counting a portion and
extrapolating
• Indirect counts - using indirect signs of the presence as indices of relative abundance
– Eg. Fecal counts, nest counts • Mark-recapture techniques
The ______ concept summarizes the aggregate land and water area needed to sustain the people of a nation
ecological footprint
population ecologists follow the fate of same age cohorts to:
determine the birth rate and death rate of each group in a population
a populations carrying capacity:
may change as environmental conditions change
scientific study of the population cycles of the snowshoe hare and its predator, the lynx has revealed that
predation is the dominant factor affecting prey population cycling
analyzing ecological footprints reveals that
the ecological footprint of the US is large because per capita resource use is high
based on the current growth rates, earths human population in 2019 will be closest to
7.5 billion
the observation that members of a population are uniformly distributed suggests that
the members of the population are competing for access to a resource
according to the logistic growth equation
dN/dt = rN (K-N)/K
population growth is zero when N equals K
during exponential growth, a population always
has a constant per capita population growth rate
which of the following statements about human populations in industrialized countries is incorrect?
birth rates and death rates are high
To figure out the human population density of your community, you would need to know the number of people living there and _____.
the size of the area in which they live
A biologist wants to use the mark-recapture method for a population census of desert mice. This will work if _____.
none of the above
When needed resources are unevenly distributed, organisms often show a _______ dispersion pattern.
clumped
Herring gulls fiercely defend the areas around their nests in cliff-top breeding colonies. Within the colony they would show a _______ dispersion pattern.
uniform
Pine trees in a forest tend to shade and kill pine seedlings that sprout nearby. This causes the pine trees to _____.
grow in a uniform pattern
The dispersion pattern of a population is _____.
the spatial distribution of individuals
An example of population density is _____.
the number of Paramecium caudatum in a 250-milliliter solution within a glass flask
An ecologist used the mark-recapture method to estimate the size of a coyote population in eastern Oregon. He trapped and marked 20 coyotes. One month later, 50 coyotes were trapped, and 5 of these animals had marks. The population size was estimated at _____.
200 coyotes
Organisms that live in a homogenous abiotic environment but that cooperate to avoid being eaten by predators would likely show a(n) _____ pattern of dispersion.
clumped
Chimpanzees have a relatively low birth rate. They take good care of their young, and most chimps live a long life. The chimp survivorship curve would look like _____.
a relatively flat line that drops steeply at the end
Which of the following describes the distribution of survivorship or mortality for a population that has a Type II survivorship curve?
The chance of death is roughly constant over all ages.
When the per capita birth rate equals the per capita death rate, _____.
the size of a population remains constant
A population will always grow exponentially _____.
if there are no limiting factors
r _____.
is an organism”s inherent capacity to leave offspring
Which of the following populations probably exhibits exponential growth?
a fruit fly population that recently arrived on a lush mid-oceanic island previously inhabited only by plants
Kingfish, Louisiana, had a population of 1,100 individuals. They had a birth rate of 12/100, a death rate of 8/100, and an emigration (individuals leaving the population) rate of 2/100. How many people were added to Kingfish’s population in one year?
22
A population that grows rapidly at first and then levels off at carrying capacity can be modeled _____.
by a logistic equation
A population that is growing logistically _____.
grows fastest at an intermediate population density
In the logistic model, a smaller r will cause _____.
a slower increase in the size of a population to the same carrying capacity (K).
No population can grow indefinitely. The ultimate size of any population is limited by _____.
the carrying capacity of its environment
In an equilibrium population (at its carrying capacity), thousands of eggs and hundreds of tadpoles are produced by a single pair of frogs. On average, about how many offspring per pair will live to reproduce the next year?
2
At carrying capacity, a population __________.
fluctuates around a median number
Assuming that r has a positive value, in the formula dN/dt = rN(K — N)/K, the factor rN tends to cause the population to __________.
grow increasingly rapidly
A newly mated queen ant founds a nest in an unoccupied patch of suitable habitat. Assuming that no disasters strike the nest, which one of the following types of equation is likely to best describe its population growth?
logistic
Chimpanzees tend to have few offspring and will tend their young very carefully for an extended period of time before having additional young. Chimpanzees display characteristics suggesting that they __________.
are K-selected
A population of mice has grown so rapidly that there are 2,400 individuals in an ecosystem that will support about 1,800 mice. The mouse population is most likely to __________.
undergo a dramatic decline in size, possibly to a stable level at or below 1,800 individuals
Which one of the following would most likely be an example of a density-independent factor limiting population growth?
daily temperature extremes
Which one of the following is most likely a density-dependent growth regulator of animal populations?
a decrease in clutch size
Which one of the following is most clearly a case of density-dependent population regulation?
a dangerous new flu strain transmitted among humans by sneezing
A particular environmental change causes the deaths of 25 individuals in a herd of 100 wild horses, and it kills 50 individuals in a herd of 200 horses. In this case, the growth of a wild horse population is most likely limited by _____. (Assume that the two herds are found in territories of equal size.)
a density-independent factor
The cyclic growth exhibited by populations of snowshoe hares in the North American taiga most likely results from _____.
predation by lynx and fluctuations in the hare”s food resources
If you wanted to see what percentage of the population of Thailand is under 10 years old, you could look at _____.
the population”s age structure
An ecologist would suspect a population to be growing rapidly if it _____.
contains many more prereproductive than reproductive individuals
In developing countries, continued population growth occurs primarily because _____.
the birth rate exceeds the death rate
The logistic growth model differs from the exponential growth model in that it _____.
expresses the effects of population-limiting factors on exponential growth
What are life tables and survivorship curve?
Life table- summarizes the survival and reproductive rates of individuals in specific age groups within a population
Survivorship curve- a plot of the proportion or numbers in a cohort still alive at each age
What does r stand for?
Intrinsic rate of increase- the per capita rate at which an exponentially growing population increases in size at each instant time
What is the difference between density-dependent and density-independent factors? Give examples of each.
Density dependent- a death rate that increases with the population density or birth rate falls with rising density
Factors: competition, predation, disease
Density independent- a birth rate or death rate that does NOT change with population density
example: weather or climate
