APES Module 15-16: K-selected vs. R-selected Species, Survivorship Curves, Carrying Capacity, Population Growth

Niche generalists

can live under a wide variety of abiotic and biotic conditions

Niche specialists

can live under a narrow temperature range and display a very narrow curve

• persist well when environmental conditions remain relatively constant

Intrinsic growth rate (population growth rate)

the number of offspring an individual can produce in a given time period, minus the deaths of the individual or its offspring during the same period

Biotic potential

under ideal conditions with unlimited resources available, every population has a maximum potential for growth.

K-selected species

species with low intrinsic growth rate that causes the population to increase slowly until it reaches the carrying capacity of the environment

Carrying capacity

the limit of the number of individuals that can be supported by an existing habitat or ecosystem, and as denoted as k.

Traits of K-selected species

• large size

• reach reproductive maturity late

• produce few, large offspring

• expend significant energy providing parental care

Examples of K-selected species

Elephants, large mammals, most birds, and humans

R-selected species

species that has a high intrinsic growth rate, and their population typically increases rapidly.

• reproduce quickly and in large numbers

• high growth rate allows r-selected species to rapidly surpass their carrying capacity

Process of overshoot & dieback

an increase and then a rapid decline in a population to due to death / die off

Overshoot

when a population becomes larger than the environment’s carrying capacity

Dieback

a rapid decline in a population due to death

Traits of R-selected species

• reach maturity quickly

• tend to reproduce frequently

• provide little to no parental care

Examples of r-selected species

House mice, small fish, insects, certain plant species

Survivorship curves

a graph that represents the distinct patterns of species survival as a function of age

Type 1 survivorship curve

a pattern of survival over time in which there is high survival throughout most of the life span, but then individuals start to die in large numbers as they approach old age.

• include k-selected species such as whales, elephants, and humans

Type 2 survivorship curve

a pattern of survival over time in which there is a relatively constant decline in survivorship throughout most of the life span

• include k-selected species such as raptors and birds of prey that have equal chance of survivorship throughout their life span but provide parental support

Type 3 survivorship curve

a pattern of survival over time in which there is low survivorship early in life with few individuals reaching adulthood

• include r-selected species such as mosquitoes, many fish, dandelions, and many frog species

Success and survival of a species depends on

the type of species and reproductive strategy

Density-dependent factors

a factor that influences an individual’s probability of survival and reproduction in a manner that depends on the size of the population

Density-independent factors

a factor that has the same effect on an individual’s probability of survival and the amount of reproduction at any population size

Population growth models

mathematical equations that can be used to predict population size at any moment in time

Fecundity

the ability to produce an abundance of offspring

• when food is abundant, individuals have high fecundity

Exponential growth model

estimates a population’s future size after a period of time based on the biotic potential and the number of reproducing individuals currently in the population

J-shaped curve

the curve of the exponential growth model when graphed

Logistic growth model

describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment

• used to predict the growth of populations that are subject to density-dependent factors as the population grows, such as increased competition for food, water, or nest sites

S-shaped curve

the shape of the logistic growth model when graphed

Why does the logistic model not account for density independent factors

hurricanes and floods are often unpredictable

Limiting resource

a resource that a population cannot live without and that occurs in quantiles lower than the population would require to increase in size

Population oscillation

when a population experiences a cycle of overshoot and dieback that causes it to oscillate around the carrying capacity

Overpopulation can lead to

fluctuations in carrying capacity