Life History and Competition

life history

the pattern and timing of demographic events in the life of an organism from birth through reproduction and death

life history parameters

lifespan, age/size of first reproduction, number of reproductive episodes, number of offspring produced per episode, size of offspring

cost of reproduction

the reduction in growth or survival that occurs as a result of allocation resources to reproduction rather than to growth

gonadosomatic index (GSI)

mass of anatomical structures related to reproduction / total body mass - measures reproductive effort

relationship between reproductive effort and adult mortality rate

positive relationship

species with higher adult survival rates reach sexual maturity at _____ age

later

species with lower adult survival rates reach sexual maturity at _____ age

earlier

r-selection

short lifespan, early age of reproduction, production of many small offspring, semelparity

k-selection

long lifespan, late age of reproduction, production of few large offspring, iteroparity

semelparity

single reproductive episode over lifespan

iteroparity

multiple reproductive episodes over lifespan

environments in which k-selection operates

highly competitive, climatically stable, small individuals susceptible to predation/abiotic factors

environments in which r-selection operates

mortality occurs regardless of size, competition-free, large individuals especially prone to mortality

disturbance

an event that removes biomass from an ecosystem

stress

external constraints that limit the rate at which plants can produce biomass

Grime’s plant life-history categories

ruderals, stress-tolerant plant, competitive plants

ruderals

mature at young age, small body size, invest in reproduction, many small offspring (high disturbance, low stress)

stress-tolerant plants

grow slowly, late maturation, protected against herbivory (low disturbance, high stress)

competitive plants

late maturing, rapid growth when resources available, few large offspring (low disturbance, low stress)

competition

an interaction that reduces the fitness of both organisms involved because they draw upon the same limited resource pool

intraspecific competition

competition amongst the same species

interspecific competition

competition between different species

interference competition

an individual physically prevents access to resources by other individuals

exploitation competition

no direct physical interaction, but one deprives the other resources by using them first or more efficiently

competitive exclusion principle (Gause’s principle)

two species that use the same limited resource in the same way cannot coexist; one of the species will inevitably be better at exploiting the shared, limited resources and exclude the other from the community

implication of competitive exclusion principle

communities will not contain similar species, and resource diversity places an upper limit on the number of species that can coexist in the community

character displacement

morphological differences that may enhance differentiation in resource use in the presence of competitors