unit 3.2-3.3 - K-selected & r-selected species & survivorship curves

reproductive strategies/patterns

species have different reproductive strategies that increase chances of survial

K-selected

r-selected

K-selected species

species with LOW intrinsic growth rate, causes pop. to increase slowly until it reaches CARRYING capacity

population is largely determined by carrying capacity, pop fluctuations are small

large mammals, birds of prey, long-lived plants like oaks

carrying capacity

(K) maximum number of individuals that can exist in poplation in given environment

K-selected species

• large organisms, reach maturity late

• few offspring / reproduction event

• substantial parent care

K-selected species

• mature after many years of parent care

• long life span and life expectancy

• reproduce few times in lifetime

K-selected species

• live in stable, predictive environments

• competition for resources in K-selected habitats is usually high

• more likely to be affected by invasive species (r-selected)

r-selected species

species with high intrinsic growth rate, leads to population overshoots and die-offs

algae, bacteria, rodents, frogs, annual plants, most insects

intrinsic growth rate- r

maximum potential for growth of population under ideal conditions with unlimited resources

overshoot

population becomes larger than environments carrying capacity

die-off

rapid decline in population due to death

r-selected species

• tend to be small

• have many off-spring

• invest minimal energy for each offspring

r-selected species

• mature quickly

• have short life span

• may reproduce many times in lifetime

r-selected species

• competition in r-selected species habitat is low

• minimally affected by invasive species

• r-selected species are opportunist

opportunist

reproduce rapidly when conditions are favorable

biotic potential

maximum reproductive rate of population in ideal conditions

• large individuals = low biotic potential

• small individuals = high biotic potential

intrinsic rate of increase - r

rate at which a population would grow if it had unlimited resources

individuals with high intrinsic rate:

• reproduce early

• short generation times

• reproduce many times

• many offspring in each generation

environmental resistance

environmental factors (limited resources/competition) restrict the biotic potential of an organism & impose limit on # of individuals in population

carrying capacity is reached

sea turtle

although large with long life-spans, they produce many, un-nutured offspring

reproductive strategies that are neither r-selected or K-selected

wind pollinated trees

long life spans & highly competitive

produce thousands of widely dispersed offspring

survivorship curves

graph that represents distinct pattern of species survival as function of age

• type I

• type II

• type III

most populations are mix of 3 types

type I survivorship curve

high survival throughout most of life span

individuals begin to die in large numbers as they approach old age- late loss pop m

lot of energy/parental care invested in individuals, result in high survivorship throughout life cycle

K-selected - humans, elephants

late loss population

high mortality at old age

type II survivorship curve

relatively constant decline in survivorship throughout most of life span

constant loss pop - mortality of individual does not depend on age

some rodents, some birds

constant loss population

individuals die at all ages

type III survivorship curve

low survivorship early in life with few individuals reaching adulthood

early loss pop - produce many thousands of individuals, most die after birth, few individuals survive to maturity

r-selected

ex. oysters, redwood trees, some fishes, marine larvae