6: Population ecology: age-structured populations and life histories

what are Allee effects

Difficulty in survival and reproduction at low population densities due to reduced cooperation or assistance among individuals, hindering essential activities like finding food, mating, and defending against predators.

Net reproductive rate, R0

Average (“expected”) # of daughters a female has in her lifetime = net reproductive rate = R0

• R0 = Σ lx m x

• x = age class

• mx (or bx) = # daughters born to a female

  of age x during the interval x to x + 1

• lx = probability of being alive at age x

• “Survivorship curve” = a graph of lx vs. x

• lx necessarily declines with x

compare R0 with λ,

time units of one generation

rather than one time interval

Generation time, T (Average age at which a female gives birth)

T = Σ x lx m x / R0

Relationships among R0 , λ, r

parameters indicate the factor by

which a population changes during a discrete

interval of time, but those intervals are

different

what are semelparous organisms

Species that reproduce only once in their lifetime, investing most of their energy in a single, intense reproductive event.

what are iteroparous organisms

Species that have the ability to reproduce multiple times during their lifetime, allocating resources for reproduction over several reproductive events

Plant life history categories

(iteroparous and semelparous)

When does natural selection favour

semelparity?

When reproductive output is increased by

accumulating resources for longer

In plants, if:

• Massive flower/fruit displays attract more beneficial animals

what is the Advantage of synchrony? (organisms within a population reproducing or releasing offspring at the same time)

having infrequent, synchronized reproductive pulses is a tactic used by certain organisms when they produce a large number of offspring all at once (a pulse) to potentially overwhelm predators. increases the chances of a portion of the offspring surviving to adulthood, as predators may not be able to consume all the offspring

K and r strategies

K-selected (K strategy): The "K" in K-selected refers to the carrying capacity of an environment for a particular species, representing the maximum population size that the environment can sustain over the long term. K-selected species have evolved to adapt to stable, predictable environments near their carrying capacity.

r-selected (r strategy): The "r" in r-selected refers to the intrinsic rate of population growth. r-selected species have a high intrinsic growth rate and are adapted to unstable or unpredictable environments. They tend to produce a large number of offspring, but with less investment in each individual.

Reproductive value, v x

expected number

of future daughters left to an individual of

age x

Life History

Comprehensive pattern of an organism's life, encompassing its growth, development, reproduction, and survival.

Age-Structured Populations

Populations categorized and analyzed based on the distribution and characteristics of individuals in different age groups.

Life Tables

Tabular summaries providing insights into the survival and reproductive patterns of a population, usually organized by age or life stage.

Survivorship Curves

Graphical representations illustrating the proportion of individuals surviving in a population over various age groups.

Fecundity Schedules

Data or charts detailing the reproductive output (fecundity) of a population at different ages or stages.

Net Reproductive Rate

Average number of offspring produced per individual in a population over its lifetime.

Generation Time

Average time it takes for individuals in a population to reach the age at which they reproduce.

Costs of Reproduction

Reduction in an individual's future reproductive potential due to allocating resources and energy towards current reproduction.

Semelparity vs. Iteroparity

Semelparity involves organisms that reproduce once in their lifetime, while iteroparity involves multiple reproductive events.

Masting

Synchronized and intermittent production of a large number of offspring or seeds by a population or community.

Reproductive Value

Measure estimating the expected contribution of an individual of a certain age to the future population, considering its remaining lifespan and potential offspring.