ch. 53 Flashcards
what does population ecology explore
abundance, dispersion, and age structure of populations
population
group of individuals of a single species living in the same general area
what are populations described by
their boundaries and size
population size
number of individuals
density
number of individuals per unit area or volume
dispersion
pattern of spacing among individuals within the boundaries of the population
how are population sizes estimated?
- extrapolation from small samples
- index of population size (number of nests)
- mark-recapture method
what are sampling techniques used for
estimating densities and total population sizes
mark-recapture method
- scientists capture, tag, and release a random sample of ind. in pop
- marked ind. given time to mix back into pop
- scientists capture a second sample of ind. and note how many are marked
- N = sn/x
immigration
influx of new ind. from other areas
emigration
movement of ind. out of a population
what increases the size of a population
births and immigration
what decreases the size of a population
deaths and emigration
what influencers the spacing of ind. in a population
environmental and social factors
most common pattern of dispersion
clumped
clumped dispersion
ind. aggregate in patches
- influenced by resource availability
- mating behavior and group defense against predators
patterns of dispersion
- clumped
- uniform
- random
uniform dispersion
ind. evenly distributed
- influenced by social interactions (territoriality)
territoriality
defense of a bounded space against other ind.
random dispersion
position of each. ind. is independent of others
- occurs in absence of strong interactions or repulsions among individuals
demography
study of vital statistics of a population and how they change over time
life table
age-specific summary of the survival and reproductive rates within a population
how are life tables often made
by following the fate of a cohort
cohort
group of ind. of same age
why are males often ignored when studying sexually reproducing species
only females produce offspring
survivorship curve
graphic way of representing the data in a life table
types of survivorship curves
type 1, type 2, type 3
type 1 survivorship curve
low death rates during early/middle life, increase in death rates among older age groups
type 2 survivorship curve
constant death rate over organism’s life span
type 3 survivorship curve
high death rates for the young and a lower death ate for survivors
where do ecologists often study population growth
ideal, unlimited conditions
what do idealized situations help us understand
capacity of species to increase and the conditions that may facilitate this growth
if immigration/emigration are ignored, the change in population equals what?
births - deaths
how can populations growth be expressed mathematically
delta N / delta t = B - D
delta N
change in population size
delta t
time interval
B - D =
R - difference between number of births/deaths in time interval
exponential population growth
population increase under idealized conditions
shape of exponential population growth
J-shaped curve
carrying capacity (K)
maximum population size the environment can support
- varies with abundance of limiting resources
logistic population growth model
per capita rate of population growth approaches 0 as the population size nears carrying capacity
curve of laboratory populations of paramecium
fits S-shaped curve
- organisms grown in constant environment lacking predators and competitors
what is the logistic model useful for
- thinking about how populations grow
- predict rates of population recovery
- estimate sustainable harvest rates
- estimate size which populations may become extinct
3 key components of an organism’s life history
- age at first reproduction (maturity)
- how often organism reproduces
- how many offspring are produced per reproductive episode (clutch size)
semelparity
big-bang reproduction, reproduce once and die
iteroparity
repeated reproduction, produce offspring repeatedly
what can having finite resources lead to?
trade-offs
ex. of trade-offs
- large number of small seeds to ensure some grow/reproduce
- moderate number of large seeds that provide large store of energy to help seedlings establish
r - unstable environment, density independent ex.
- small size of organism
- energy used to make each ind. is low
- many offspring produced
- early maturity
- short life expectancy
- each ind. reproduces only once
- type III survivorship
K - stable environment, density dependent ex.
- large size of organism
- energy used to make each ind. is high
- few offspring produced
- late maturity
- long life expectancy
- ind. can reproduce more than once
- type I or II survivorship
2 important questions about regulation of population growth
- what environmental factors stop a population from growing indefinitely?
- why are some populations fairly stable in size, while others not?
density-independent populations
birth and death rate don’t change with population density
density-dependent population
birth rates fall and death increase with rising population density
what are density-dependent birth and death rates an example of
negative feedback ack that regulates population growth
what are density-dependent birth and death rates affected by
- competition for resources
- disease
- predation
- territoriality
- toxic wastes
- intrinsic factors
in crowded populations, what does increasing population density intensify
competition for resources, results in a lower birth rate
pathogen spread in dense populations
pathogens spread more rapidly
what happens to predator prey interactions with a dense population
as prey population builds up, predators, may feed preferentially on that species
territoriality and population density
individuals compete for limited space
what are intrinsic factors that regulate population size
physical factors
what can accumulation of toxic wastes contribute to
density-dependent regulation of population size
what do lynx populations follow
10-year boom and bust cycle of hare populations
hypothesis of hare’s population following cycle of winter food supply
- if correct: cycles should stop if food supply increased
- additional food provided experimentally, whole pop increased in size but continued to cycle
hypothesis of hare’s population cycle driven by pressure from other predators
- 95% of hares killed by predators
- data supports hypothesis
what can increase when a population becomes crowded and resource competition increases?
emigration often increases
metapopulations
groups of populations linked by immigration and emigration
what do local populations in a metapopulation occupy
suitable habitat surrounded by unsuitable habitat
growth of human population
increased relatively slowly until 1650, then began to grow exponentially, but began to slow during 1960s
current global human population
more than 7.2 billion people
age structure
relative number of individuals of each age in a population
- affects population growth
age-structure diagrams (pyramids)
help predict population’s growth trends and illuminate social conditions to help us plan for the future
what global population of humans do ecologists predict for 2050
8.1-10.6 billion
what is the carrying capacity of earth
it is uncertain
- but there are estimates on logistic growth models, area of habitable land, and food availability
what can our carrying capacity be limited by
- food
- sapce
- nonrenewable resources
- buildup of wastes
