Population Ecology Flashcards
What to add for more complexity in log models
Different forms of density dependence
* e.g., Allee effects (next slide)
* Time lags
* Incorporate species interactions (e.g., effects
of competitors, predators, mutualists, etc.)
Allele Effects
Allee effects are negative
effects of low density,
arising from social benefits
such as mate finding, group
living, group defence
Age-structured populations
adding in factors such as fecundity, survivorship, life history strategies
Life History
Start life at small size
* Grow for a period without reproducing
* This period is for resource accumulation
* When have enough resources, become mature,
start spending resources on reproduction
* Organisms show various lifestyles after sexual
maturity
* Some expend all resources at once, some spread them
out
* Need to consider age structure of populations to
better predict population trajectories
Age-structured population growth
Still considering a single population
* But now, fecundity and survivorship vary with
age
* Variation summarized by life tables of age-
specific rates
* Important implications for:
* Evolution of life histories
* Conservation of populations
* Understanding the changing structure of human
populations (human demography)
age-class
intervals
Arbitrary units of time chosen to give a
reasonable number of age classes for the
organism in question
* For microbes, minutes to hours;
* Most insects, weeks;
* Most mammals and birds, years;
* Humans, typically 5-year intervals, therefore
about 20 age classes
Life tables
Data that summarize the life events that are
statistically expected for the average
individual of a specified age in a population
* Age of death
* Age and timing of reproduction
* For modeling, these are treated as constants
* Usually consider females only
Survivorship schedules
Age classes denoted by subscript x
* lx = probability of being alive at age x
* l0 = 1.0 by definition
* “Survivorship curve” = a graph of lx vs. x
* lx necessarily declines with x
* Shape of lx curve is characteristic of species
Fecundity schedules
Age classes denoted by subscript x
* mx (or b x ) = # daughters born to a female of
age x during the interval x to x + 1
* Shape of m x curve characteristic of species
* Reproductive period usually preceded by
resource-accumulation phase
* Fecundity-survivorship trade-offs = cost of
reproduction
Net reproductive rate, R 0
Average (“expected”) # of daughters a
female has in her lifetime = net reproductive
rate = R 0
* R0 = Σ l x mx
* Why does it work? Σ m x would be the total #
daughters produced by a mother who doesn’t
die early; multiplying by l x discounts
expected production by the probability that
some mothers do die early
* R0 is like λ, but in time units of one generation
rather than one time interval
Generation time, T (Average age
at which a female gives birth)
T = Σ x l x mx / R0
* Why does it work? This is a formula for a
weighted average. x is a female’s age;
multiplying x by lx mx weights x by how many
offspring are produced at that age; dividing
the sum of the weighted x’s by the total
lifetime production of daughters (R0) gives a
weighted average that specifies when a
female gives birth, on average
Relationships among R 0 , λ, r
These parameters indicate the factor by
which a population changes during a discrete
interval of time, but those intervals are
different
* As you would expect, these parameters can
be related mathematically
r=ln(r0)/T = ln(lambda)
Semelparous
reproduces quick, many at once, then dies “big bang” ex. salmon
Iteroparous
Takes at least 2 years before it reproduces, does not immediately die after reproduction, no “big bang”
Plant life history categories
Seasons of
growth
1. One
2. 2
3. More than 2
Semelparous = “monocarpic”
1. annual
2. annual
3. monocarpic perennial
Iteroparous =
1. not applicable
2. not applicable
3. perennial
