[LS 7B] week 8- population ecology
The carrying capacity for this population represents only the abiotic factors that limit population growth past a certain number of individuals. t or f
f
The carrying capacity for this population will be the same for all populations of the same species.
f
why is the shape of a logistic curve S?
Logistic growth curves are S-shaped because they actually reflect two sets of processes, each related to population size. At first, growth reflects only the rate at which individuals can reproduce themselves (when N is very small relative to K), so the curve rises steeply. The second part of the curve, where it starts to level off, reflects the onset of additional factors that become important above a certain population size, such as decreasing availability of food and space.
Consider five human populations that differ demographically only in their age structures. The population that will grow the most in the next 30 years is the one with the greatest fraction of people in which age group(s): Question 3 choices Choice A., the oldest age group Choice B., the middle of the reproductive age groups Choice C., the late-reproductive and post-reproductive age groups Choice D., the middle of the age structure Choice E., the pre-reproductive age groups
e
what factors can keep a population below K?
Predation and parasitism can reduce the population size below K, but they do not change K itself.
Most populations demonstrate _____ growth, in which the population size increases exponentially until it levels off near the K value of the habitat for that species. intrinsic exponential logarithmic extrinsic logistic
e
Two islands lie off the coast of Florida. One is larger and the other is closer to the mainland. What determines which one will have more species?
The closer island will initially receive more colonists than the farther one, but the larger island can eventually support more kinds of species.
life-history tradeoffs
negative relationship btwn growth, reproduction and survival reproduction a lot really fast >< surviving alone => live fast die young or long hold determining factor: environment => These kinds of trade-off evolve through natural selection and are the rule in ecology, explaining in part why species tend to produce either many small offspring or a few larger ones.
a low population density of fish in a pond increases the likelihood of infection by viruses, bacteria, and fungi because these agents are transmitted from fish to fish
f high
exponential growth
growth rate (r) does not change over time during exponential growth dN/dt=rN r const N increase -> dN increase
what happen when the number of young produced at birth exceeds the number of adults that can be supported by available resources?
individuals within the population compete to obtain the resources needed for growth and reproduction. This intraspecific (within-species) competition results in natural selection
what is the major cause of density dependence on population growth and its significance?
intra-specific competition =? key driver for nat sel
fundamental unit of evolution
it is populations, not individuals, that evolve
population growth rate r<0 r=0 r>0
r=0 => b=d its still producing offsprings r<0 => d>b
How do ecologists determine population size? Depends on motility of organism
*Transect-quadrat* method Used for site-attached organisms *Capture, Mark, Recapture* Used for mobile organisms *assumptions* Population is randomly distributed Capture is random Marking is not fatal Marks are not lost
ppltn vary in space and time
*abundance varies on spatial scale* -geographic range -> habitat -> habitat patches (islands of suitable habitats separated by unsuitable habitats) --> abiotic factor *densities are dynamic ~ change over time* -due to environmental fluctuations --> abiotic factor or other species ppltn --> biotic factor
ecology describes system at a hierarchy of level
*organism*: the basic unit of ecology ex: an individual plant, animal or microbe that exhibits behavior, physiology and life history *ppltn*: group of individuals of the same species that interact *community*: assemblage of interacting ppltn of dif species in a particular area *ecosystem*:community+abiotic environment *biosphere*: all organisms and envr of the planet
The maximum number of individuals that a habitat can support decreases as resources increase. T or F
F
why study ppltn?
-increase ppltns of beneficial species -decrease ppltns of pest,pathogen.. -conserve species for ethical rsn -study whats driving human ppltn levels
If a population triples in size in a year, what is the per capita growth rate?
2
r and K strategists reflect an evolutionary trade-off
A reproductive individual has access to a finite amount of resources and can invest either in many inexpensive young or few well-provisioned offspring. Depending on the combination of physiology and environment, natural selection in a given set of circumstances may favor one strategy over the other.
as long as some local populations remain—if they do not all become extinct at the same time—these populations can recolonize old habitats or find new habitat patches, thus ensuring survival of the metapopulation.
As expected, isolated patches showed decreases in species diversity, up to 40% in 1 year; some species became extinct. However, when nearly isolated moss patches were left with a narrow corridor of moss connecting them, the rate of extinction was lower. Even narrow corridors of suitable habitat can allow species to move between patches of habitat and prevent extinction, or serve to reintroduce species that become locally extinct.
Why must a plant or animal make trade-offs among growth, reproduction, defenses, and other adaptive traits?
Every organism invests all available energy in the ways that are most useful in the current environment. Increase in one area means decrease in another. To increase investments in all these areas, more resources in terms of food or energy would have to be acquired.
how abiotic and biotic interactions drive pattern and process at different organizational levels
Interactions between biotic and abiotic factors determine *distribution* and *abundance* of organisms => through population the condition for the struggle for existence => drive natural selection
*abundance* why do ppltn sizes grow or shrink? or stay constant? or go through cycle?
It is the traits evolved under natural selection that determine whether a population will grow or shrink under a given set of physical and biological conditions
an initial population of 80 individuals increased by 20 per year over 2 years, for a per capita rate of increase of 0.25 per year. If this per capita rate of increase were to continue, how large would the population be after 10 years?
Nt = N0 (1 + r)^t 745
ppltn ecology
Studies how and why the size, range, and density of a population changes over time
Density-Independent Factors
Temperature Flood Drought
density-independent or dependent factor?
The number of territories then plummets, regardless of territory numbers the previous year.
patterns of survivorship
Type I, Type II, and Type III— which correspond to the pattern of mortality: whether most mortality occurs late in life, is even throughout life, or is concentrated early in life, respectively.
A few of the turtles in the population really love lettuce, the bait you were using to lure them into the trap, and come back on Day 2 for more lettuce (this phenomenon is called 'trap happiness'). How will this affect your estimation of the population ? A. Underestimate B. Overestimate C. No change
a
K-strategists tend to inhabit "unpredictable" environments and also have population densities near the carrying capacity of an environment. False True
a
The common mud turtle experiences relatively uniform mortality rates throughout its life. It exhibits Type _____ survivorship. II III I
a
The intrinsic growth rate, r, of a population is measured as 0.05. When not limited by resources, the size of this population should: Question 3 choices Choice A., increase exponentially over time. Choice B., decrease slowly over time. Choice C., stay the same.
a
When the number of young produced at birth exceeds the number of adults that can be supported by available resources, it leads to natural selection. A. True B. False C. Need more information
a
Which line on this graph is representative of a density-independent population? A. LineA B. Line B C. Need more information
a
_____ describes the number of individuals in a species that survive from one life-cycle stage to the next. Survivorship A population pyramid A cohort The intrinsic growth rate of a population
a
principle of allocation
abiotic condition can determine where and when the organism can have a happy thriving ppltn => affect distribution
habitat island
an area of habitat surrounded by inhospitable habitat ex: island surrounded by ocean, or body of water surrounded by land
A population of pocket gophers shows logistic growth. As the population approaches carrying capacity (K), the number of individuals added to the population per unit of time will: Question 4 choices Choice A., increase. Choice B., decrease. Choice C., stay the same.
b
A population that is decreasing in size will have an age-structure histogram shaped like a(n): pyramid, with a wide base at the bottom representing a large number of young individuals. inverted pyramid, with a narrow base representing a small number of young individuals. diamond, with a wide center depicting a large number of individuals that have reached reproductive maturity. rectangle, with an (roughly) equal number of individuals in each age group.
b
According to MacArthur and Wilson's theory of island biogeography, both the land area (size) of an island and the _____ contribute to species diversity. climate of the island distance of the island from neighboring land masses depth of the water surrounding the island rock composition of the island proximity of the island to the equator
b
As a population approaches its carrying capacity, its growth rate: A. increases B. decreases C. stays the same D. stops
b
In another population, turtles that have been captured once become terrified of traps and avoid them at all cost (this phenomenon is called 'trap shyness'). What will this behavior do to your population estimate? A. Underestimate B. Overestimate C. No change
b
Large, even distances typically separate individual panda bears from each other. What type of population distribution do pandas exhibit? sinusoidal distribution uniform distribution logistic distribution random distribution clustered distribution
b
The greatest rate of population growth is represented by which point on the graph? A. Point A B. Point B C. Point C
b
What are the units of r? individuals per unit time change in individuals per unit time/individuals at starting time individuals
b
Which of the following results from a mark-recapture study done on mice would reflect a larger population size? Both of these scenarios would result in the same population estimate. When taking the second sample, 200 individuals are caught and 20 are marked from the first sample. When taking the second sample, 200 individuals are caught and 80 are marked from the first sample.
b
Why are biologists interested in age structures of populations? Question 5 choices Choice A., because age structures provide information about current reproductive rates in the population Choice B., because age structures provide information that allows the estimation of a population's potential for future growth , Choice C., because age structures provide information about the number of individuals in a population that are of a reproductive age
b
_____ allows populations to adapt to the abiotic and biotic conditions where they live. Reproduction Natural selection Competition Predation
b
The population starts with 80 individuals and grows to 100 after 1 year. What is the per capita growth rate? A. 0.20 B. 0.25 C. 0.40 D. 0.60 E. Need more info
b r = (ΔN/Δt)/Ni
interaction in ecology
biotic: among organisms abiotic: btwn organisms and their non-living environment
force that shape organism's life history
budgeting of resources among maintaining *homeostasis*, growth, defense, reproduction
A large population made up of smaller populations linked by migration is a: colonization. habitat patch. metapopulation. island founder event.
c
Imagine that a lizard inhabits a desert where it has very few natural predators. During a year when resources are scarce, the lizard produces a handful of large eggs rather than several small eggs. This is an example of: mortality. survivorship. a trade-off. a life history. a life table.
c
logistic growth
carrying capacity (K): Maximum number of individuals a habitat can support => Competition for limited resources increases as N approaches K
Density-Dependent Factors
competition for resources, diseases, predation, territoriality, intrinsic factor, (*toxic waste*) ??
A researcher is comparing the species diversity of two islands. Both islands are roughly equal in size. However, one island is much closer to the mainland. She determines that the S value for the island closer to the mainland is _____ the S value for the island located farther from the mainland. In addition, she finds that the closer island's extinction rate is _____ the extinction rate on the farther island. the same as; higher than the same as: lower than lower than; the same as higher than; lower than higher than; the same as lower than; higher than
d
The carrying capacity for a population of birds limited to a specific forest area should increase if you increase: Question 5 choices Choice A., food availability alone. Choice B., nesting site availability alone. Choice C., disease or predators alone. Choice D., both food availability and nesting sites. Choice E., food availability, nesting sites, and disease or predators.
d
The expanding base of a population pyramid over time indicates which of the following? Question 4 choices Choice A., The average age of the population is increasing. Choice B., The number of older people in the population is increasing. Choice C., The number of people of reproductive age in the population is increasing. Choice D., The number of younger individuals in the population is increasing.
d
When a population is small relative to its carrying capacity, its growth will be: geometric. both geometric and logistic. both geometric and exponential. exponential. logistic.
d
factors affecting ppltn size
dN= (B-D)+(I-E)
age structure of a population reflects
death rates as well as birth rates
edge effect
decrease biomass and biodiversity
k-strategist
evolve in stable, unchanging, and predictable environments, where there tends to be more crowding and larger populations. Here, there is intense competition for limited resources, so traits such as increased parental care and few offspring are favored.
r-strategist
evolve in unstable, changing, and unpredictable environments. In such an environment, there is an advantage to reproducing quickly and producing many offspring when conditions are favorable.
the link between environmental (biotic+abiotic) conditions and per capita growth rate
ex: abiotic -> stress of weather biotic: more foraging -> more resources -> more plants around
what is the growth curve of a small ppltn w unlimited resources?
exponential curve
Carrying capacity for this population will keep the population at the same size for the entire time the population exists.
f
The carrying capacity for this population represents only the abiotic factors that limit population growth past a certain number of individuals.
f
Crowding only affects death rate, not birth rate
f For example, as the fish population of a pond increases, there is less food available for each individual, and oxygen may be used up by microbes that proliferate because of nutrients in the fish waste.
what are the key features of a ppltn?
size(abundance) range biomass density (size/range)
in metapopulation, why does small populations become extinct more often than large populations?
small populations become extinct more often than large populations because they are more susceptible to random factors that increase mortality, such as weather, natural disasters, or predation.
how are r and K related to ppltn growth?
species like most fish as r-strategists because they reproduce at rates approaching r, the intrinsic rate of growth => parents produce many offspring and invest relatively little in any of them due to unpredictable environment(predators, limited patchy resources,..) Animals like eagles and bears are called K-strategists because their population densities commonly lie near the carrying capacity K due to predictable environment (better protected from predators, able to compete with others when they are young, and more likely to survive periods of bad weather)
type of age structures
stable growing
what is ecology?
study of relationships among organism and their environment
density dependence can decrease per capita growth rate via
survivorship or fecundity
At its earliest stages, a logistic growth curve closely resembles an exponential growth curve. True False
t
In other words, birth and death rates are themselves affected by population density,
t
Ppln has the potential to increase exponentially over time
t
The size of a population of frogs is significantly below the population size that the environment can support. This could be the result of frog parasites and/or predators. False True
t
The slope of the line at any point on the curve represents the rate of population growth at that time.
t
What information do you need to determine the distribution pattern of individuals in a population of Big Horn Sheep?
the amount of resources, predators or intracompetition
range
the range of climates a population can tolerate and determines how many other species the population encounters