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4) Populations
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Gravity
Terms in this set (28)
Factors that might limit pop density
births, deaths, immigration, emigration, limited by resources
ecology
study of the distribution and abundance of living organisms and the interactions between organisms and their environments
population
group of individuals of the same species that live in the same area
rely on the same resources
are influenced by the same environmental factors
likely to interact and interbreed with each other (intra-specific interactions-within a species)
density
number of individ's per unit area or volume
dispersion
patterns of spacing of individuals in population boundaries
demography
make up of individuals in the pop
how can individ's of a pop be distributed in space?
clumped dispersion- individ's aggregate in patches
--uneven distrib of resources, mating or other social behavior, attraction
uniform dispersion- individ's evenly spaced
--aggressive interactions, severe competition for resources, repulsion
random dispersion- no pattern seen. individ's are independ from each other
- "null model"- no special forces acting on spatial distributions
factors that influence a species' demography
demography- study of the age stucture
why may the tertiary sex ratio of a pop look different from the secondary or primary sex ratio
primary ratio= conception, about 50/50
secondary= birth/hatching, also 50/50
tertiary= later stage of life, skewed towards females
why skewed? (in non-humans)
1. Reproduction-related stresses
2. Dispersal (leaving the nest)
3. Intraspecific competition
how can age structure diagrams be used to predict future pop growth/decline
age groups based on reproductive status- see screenshot
fecundity
number of offspring/time (per female)
fecund= producing lots of offspring
generally limited by number of gametes (eggs)
generation time
time period from birth of individuals to birth of their offspring
larger body size= increased generation time
survivorship curve
plot proportion of individuals alive at each age (graphical representation)
-life table is something else, a chart
what are the life history traits typically associated with type I, type II, and type III survivorship curves
see screenshot
r:
cohort survivorship: Type III curve
age structure: pyramid shaped
pop growth rate: fast (exponential)
K:
cohort survivorship: Type I curve
age structure: column or inverse pyramid
pop growth rate: slow (logistic)
life history traits
the traits that affect an organism's schedule of reproduction and survival
r-selected populations
live fast, die young, leave lots of offspring
ex) insects
many offspring
very small offspring size
no parental care
fast growth
young age of first reproduction
K-selected populations
slow and steady, fewer offspring, longer survival times
few offspring
big offspring size
lots of parental care
slow growth
older age at first reproduction
-r and k strategists are extremes!!
exponential growth explained conceptually and mathematically
rate of population expansion under ideal conditions
G= rn
G= growth rate
r= rate= number of new individ's/time
n= number of individ's in pop at a particular time
explain r and describe situations in which r would be less than 1 (small)
r= rate of increase
r= birth rate- death rate
r= B-D
r is small (less than 1) when:
D is high (competition, limiting factors (lots of deaths), individ's not fecund or fertile
B is low (sex ratio skewed towards males, long generation time)
r smaller= growth rate slower
r is higher if:
- generation time is faster in one pop than in the other
* r varies between populations!
calculate G for a pop undergoing exponential growth
G= rn
recap of exponential growth:
rate of increase and n determine the speed at which the pop size increases
its the pop growth under idealized conditions!
--curve would eventually level off!
how does carrying capacity affect the exponential growth curve
no population can keep growing forever- limits set in
carrying capacity= the maximum population size that the environment can sustain indefinitely
when the limits set in, the pop either stabilizes or crashes
density-dependent factors affecting pop growth
Depends on population density
Higher density leads to changes in survivorship/ fecundity
competition, predation, parasitism, disease
density-independent factors affecting pop growth
Density not important
Abiotic factors
Effect on pop. size = unpredictable
-unusual weather
• natural disasters
• seasonal cycles
• certain human activities—such as damming rivers and clear-cutting forests
how can the density-dependent birth rate in a pop exemplify negative feedback
As the population grows, it reduces birth rates and increases death rates so the living population doesn't have to compete for resources
populations cycle- what are some factors that can lead to cycling?
...
how has the rate of human pop growth changed over time? predict future pop growth?
k strategists
exponential growth?
describe the typical ecological footprint of a US citizen
see pic
Ecological footprint: The
amount of land and water
needed to produce all the
resources we consume
and absorb the waste
we produce
logistic growth
see screenshot
Idealized population growth that is slowed by population
-limiting factors as population size increases -GROWTH WITH CONSTRAINT
Logistic growth model (recap)
• Population growth rate will be small when
population size is either large or small
• Population growth rate will be highest when
population is at intermediate level relative to K
•At low population levels, if resources are abundant,
the population is able to grow exponentially
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