Lecture 18 Flashcards
T/F the population grows fast when it is small in a logistic model
true
most of the resources are available
doesn’t happen irl
T/F the pop grows slowly when it is large in a logistic model
true
run out of resources
doesn’t happen irl
Allee Effects
when the pop decreases when the population size or density is low
- difficulty finding mates, group defence, group living = social benefits
- cooperative behaviours become ineffective when the pop size is too small
when allee effects are too high - the pop will not be able to grow past a certain lower limit
why do meerkats need a minimum population density to grow
they cooperate in groups of 6 to avoid predators - so they need a minimum number of individuals to create these groups to survive
T/F exponential and logistic models do not include allee effects and treat all individuals in a population the same
true
not realistic
not all individuals have the same probability of giving birth or dying
what is fecundity
the number of offspring an individual can produce over a given period
- reproductive capacity of an individual, of a population
- depends on age, health, environmental conditions
- it is the biological POTENTIAL for reproduction - not fertility which is the actual number of children born
what is survivorship (lx)
the probability that an individual will survive from birth to a given age
- 3 different types of survivorship curves
- age, predation, disease, resource availability = factors that affect survivorship
(older age = less survivorship)
what is the typical life history for many plants and animals
- start life = small size
- grow without reproducing, resource accumulation - gather resources
- when enough accumulation of resources + sexually mature, start spending resources on reproduction (some reproduce at once - die, some reproduce periodically)
- need to consider the age structures of the population to predict the population better
an elephant has ___ fecundity and spends ___ of investment on one offspring at a time
low fecundity
a lot of investment
becomes sexually mature later on in life
has 1 offspring –> wait –> 2 offspring
a pika has ___ fecundity and spends ___ of investment on offspring
high fecundity (1-13 offspring at a time)
medium lifespan
very fast reproduction, within the first year of living = sexually mature
invests a little in the offspring
a salmon has ____ fecundity and invests ___ of an investment in offspring
very high fecundity (thousands of eggs)
invests very little in each egg
very late reproduction maturity, waits till the end of its life to reproduce –> die
explain how a population without and with age structure would be classified
without age, the structure would be 24 individuals in a population with no in-depth classification
with age structure = categorizing based on fecundity and survivorship into babies, children, young adults, and elderly
- ecologists = women as the only reproduction because they invest in it more, men = cheap sperm
what are arbitrary units of time
chosen to give a reasonable number of age classes for an organism
- microbes = minutes
- insects = weeks
- mammals = years
what are life tables
a statistical tool used to summarize the survival and reproduction pattern of a population
- things that are expected of the average individual of a certain age
what are survivorship schedules
lx = probability of being alive at the age x
l0 = 1.0 when a child is born and is always declining
graph of lx against x = age
what are the types of survivorship curves
Type 1: high survivorship early and a steep decline later
- survive through early and middle life - the mortality increases significantly with age
- humans, live to old age, infant mortality is low, and large mammals
Type 2: straight diagonal line
- the chance of dying at any age is the same
- birds and small mammals = predation and high risk of disease
Type 3: concave up curve and flattens as the age increases
- the majority of individuals die in early ages - eggs, larvae, seedlings
- survivors in adulthood face lower mortality rates
- fish, plants - lots of eggs and seedlings but they do not all survive
fecundity schedules
tables or representations that describe the reproductive output of individuals at different ages or stages of their life
- mx or bx
- the curve of fecundity should increase around 20-35 years old = sexual maturity = more potential for more daughters
- the curves vary widely among species - usually genetically determined
fecundity-survivorship tradeoffs
refers to the balance organisms must have between investing energy and resources in reproduction and ensuring the survival of themselves and their offspring
- must learn to allocate resources efficiently
what is the net reproductive rate (R0)
the average expected number of daughters a female has in their lifetime
R0 = sigma lx * mx
mx = total number of daughters produced by a mother who doesn’t die early, multiplying it by the probability that some mothers do die early
- units of one generation, not one-time interval
Net reproductive rate (R0) in the news
R) is the average number of secondary infections that a single infection gives rise to
- every daughter that is made gives rise to another daughter
How can we model the time at which a female gives birth
T = sigma x * lx * mx / R0
* a formula you have to remember
- this formula = weighted average
x = female age
multiplying the 2 terms together = time
what are the tradeoffs to reproduction
reproduction = costly
longer pre-reproductive periods allow time to accumulate more resources
semelparous organisms
big bang
organisms that reproduce all eggs at one period of time –> die
salmon, at the end of life
plants that reproduce, annual, biennial or monocarpic perennial (all monocarpic plants = die after reproducing once)
iteroparous organisms
humans, elephants, pikas
organisms reproduce multiple times over their lifetime, producing fewer offspring per event
plants = perennial
why does natural selection favour semelparity
when reproductive output is increased by accumulating resources for longer
plants that = more fruits = more beneficial to attract pollinators or seed dispersed = preparation for reproduction
they want to produce more flowers and fruits to maximize their single reproductive period of time
*NS favours semelparity because they take the time to maximize their fitness as a strategy
what is the advantage of synchrony in semelparity
- some plants like bamboo synchronize the semelparity
- producing more seeds at once reduces the likelihood that all seeds will be eaten by predators (PREDATION SATIATION TACTIC)
- masting = sometimes no seeds, sometimes a lot of seeds
what is the K strategy
focuses on producing fewer offspring and investing heavily in their survival, maintaining populations near the carrying capacity (K) of the environment.
- slower growth
- lower reproductive rate
- poor at dispersal
- longer generation time
- iteroparity more likely - more offspring with more time
what is the r strategy
The r-strategy emphasizes rapid reproduction and high fecundity to maximize the growth rate (r) of a population
- faster growth
- shorter generation time
- higher reproductive rate
- good at dispersal
- semelparity = more likely - one reproductive
T/F selection generally selects for early reproduction but the need to accumulate resources and size-dependent mating success can override that effect = delayed reproduction or semelparity
true
T/F semelparity selects for synchrony
true
more seeds at once = less eaten by predators
what is ex
life expectancy
- the expected years of life left to live in an individual of age
what is vx
the reproductive value
- the expected number of future daughters left to an individual of age x
- this is good for breeding - males only like females with high vx = highest reproductive value offspring
- the graph = upside down parabola
- maximum vx = in late teens as they enter reproductive years
increase age = decrease reproductive success
