Life History And Demography Flashcards
Asexual reproduction
Offsprings are genetic clones of the parent
Parthenogenesis
“Virgin birth”, develop from an unfertilized egg
Sexual reproduction
The product of meiosis and fertilization (two gametes produce zygote)
Alternating between sexual and asexual
Environmental cues
- declining food quality
- seasonal changes (phenology)
Asexual: pros and cons
+ high fitness under (i.e. adapted to) current conditions
+ rapid population growth
- low genetic variability; less adaptable to changing conditions
- lack of recombination; no way of getting rid of bad genes
Sexual: pros and cons
+ Portfolio effect: genetic diversity minimizes the volatility of the population’s response to changes in env. conditions
+ more raw material for natural selection to act on
- takes time and energy if the resources are scarce and the seasons are short (e.g. Arctic, Desert, etc.)
- requires reproductive organs
- courtship and mating - risky and use energy
Life history
The way that organisms allocate resources to growth, survival, and reproduction (fecundity); the sequence and timing of events in an organism’s life
- trade off between survival and fecundity
Life history trait
A heritable trait that determines some aspect of the life history of an organism (e.g; maturity, # of offspring, longevity)
Life history strategy
A pattern of life-history traits that has evolved by natural selection over time in a population in response to ecological conditions
Demography
The study of factors (i.e. birth, death, immigration, emigration) that determine the size and structure of populations through time
Random distribution
The position of each individual is independent of the others
Clumped distribution
The quality of the habitat is patchy or the organisms are social
Uniform distribution
Negative interactions occur among individuals that space them out evenly
Life table
A summary of the probability that an individual will survive and reproduce in any year during its life time
Cohort
A group of individuals of the same age that we can follow through time
Age class
A group of individuals of a specific age
Survivorship
Proportion of individuals remaining alive from one age class to the next
Survivorship curve
A plot of the logarithm of the number of survivors vs age
- helps us recognize general patters in survivorship
- helps us compare among populations or species
Type 1 survivorship curve
Survivorship throughout life is high; most individuals survive until the max. life span of individuals within the species (i.e. humans)
Type 2 survivorship curve
Most individuals experience relatively constant survivorship over their lifetimes (i.e. songbirds)
Type 3 survivorship curve
Result from high death rates early in life; high survivors ship after maturity (i.e. many plants, turtles)
Fecundity
The number of female offspring produced by each female in the population
Age specific fecundity
The average number of female offspring produced by a female in a given age class
The growth rate of a population per generation (Rknot)
Net reproductive rate
= 1 : population is stable
< 1 : population is decreasing
> 1 : population is increasing
Per-capita population growth rate
r = b - d
b > d, r is posivite; population is growing
b < d, r is negative; population is declining
r = 0, stable
PER TIME INTERVAL
Net reproductive rate
Rknot = SUM OF lx(mx)
> 1 : growing population
= 1 : stable population
< 1 : shrinking population
PER GENERATION BASED ON LIFE TABLE INFO
Generation time
G = SUM OF lx(mx) / Rknot
- age-specific fecundity : lx(mx)
- Rknot : net reproductive rate
- x : age category
Using Rknot and G to calculate r
r = ln(Rknot) / G
Population growth
Nt = Nknot e^rt
This is exponential or continuous growth
Maximum intrinsic growth rate (r max)
Birth rates per individual (b) are as high as possible and death rates per individual (d) are low as possible
delta N / delta t = r max (N)
Exponential population growth
When r does not change over time. The population growth rate does not depend on the number of individuals in the population (density independent).
Can occur when individuals found a new pop. or after a population bottleneck caused by a disaster (i.e. fire, disease etc.)
Density Independent
Population growth when increases in the size of a population do not affect (or change) r
Density dependent
When population density (the # of individuals per unit time) gets high, the population per-capita birth rate decreases, and the per-capita death rate increases, causing r to decline.
Carrying capacity (K)
The maximum number of individuals in a population that can e supported in a particular habitat over a sustained period of time
- as a population exceeds K, resource consumption moves beyond what can be regenerated; becomes unsuitable habitat
r = r max (K - N / K) so that delta N / delta t = r max (K - N / K) (N)
As N approaches K, r is approaching 0
As N approaches 0, r is approaching r max
Density independent factors
Usually abiotic; change birth rates and death rates regardless of population size
Density dependent factors
Can be biotic (i.e. resources, predation, disease/parasites); change in intensity as a function of population size
Antagonistic selection
When any components of fitness are in opposition to each other
- viability selection vs. sexual selection
- viability vs. fecundity
- sexual vs. fecundity
The principle of allocation
Any energy an organism uses for one function to reduce the amount available for another function
- age vs. fecundity : delayed sexual maturity results in higher fecundity, but increases the probability of death before reproduction (good strategy if top predator)
Strategy 1: number vs. size of offspring
Lots of offspring means little investment in each child
Strategy 1: generate a lot of offspring, invest little in each with the expectation o low survival rates
Altricial: young are born helpless
Strategy 2: number vs. offspring size
Produce few young, but invest heavily in each to maximize offspring survival
Increase the fitness of young at the expense of the fitness of the parents
Precocial: longer gestation, young are born at mor advanced developmental age
Semelparous
One breeding event/one shot to reproduce ; produce as many offspring as possible
Iteroparous
Repeated reproduction events ; can depend on environment/phylogeny
r vs. K
r strategists:
- r-selected maximize reproduction
- short lived and reproduce at a young age
- produce lots of small babies with little parental care
- tend to be precocial
- semelparous
- fast, high adult mortality rate
K strategists:
- K selected
- long lived and mature at a late age
- few babies and lots of care
- tend to be altricial
- iteroparous
- slow, low adult mortality rate
Most species are somewhere in the middle
Grime model
Competitors (C) - K (i.e. oak tree)
Ruderals (R) - r (i.e. dandelion)
Stress tolerators (S) - organisms that will survive extreme conditions (i.e. extreme high/low temps, bottom of the ocean); don’t fit R or C strategies (i.e. cactus)
Metapopulations
Populations of populations linked by immigration and emigration
- individual patches “wink” on and off
- larger pop. can save smaller pop. from going extinct
Source-sink metapopulations
One or several large sources; self-sustaining populations
- r values greater than or equal to 0
- R knot values greater than or equal to 1
They’re growing or are stable
True-sink population
Will go extinct if immigration is cut off
Pseudo-sink population
Population would persist at a lower equilibrium in the absence of immigration
Momentum
A reduction is infant mortality before the reduction in birth rate (in industrializing countries)
Ecological footprint
The aggregate and and water needed to sustain the population
