Population ecology: r- vs. k- strategists

Many r-selected species tend to be opportunists, meaning that they reproduce and disperse rapidly when conditions are favorable or when a disturbance opens up a new habitat or niche for invasion. This could occur in the early stages of ecological succession. Once their populations are established, their populations may crash due to changing or unfavorable environmental conditions or invasion by more competitive species. Because of this, most r-selected species go through irregular and unstable boom-burst cycles in their population size. In order to survive, these r-selected species must continually invade new areas to compensate for being displaced by more competitive species.

K-selected species tend to do well in competitive conditions when their population size is near the carrying capacity of their environment. These populations typically follow a logistic growth curve. Most K-selected species thrive in ecosystems with fairly constant environmental conditions

Comprehensive Review: www.youtube.com/watch?v=Bu6ouKt9zhs

Population ecology: r- vs. k-strategists

By: Danielle Lewis

Differences between R- and K-selected species:

An interesting difference between the two strategies is the shape of the survivorship curve. By plotting the log of the fraction of organisms surviving versus the age of the organism, a survivorship curve can be generated. To compare species, the age axis is normalized by stretching or shrinking the curve in the horizontal direction so that all curves end at the same point, the maximum life span for the individuals of that particular species.

Survivorship curves are important because...

It is valuable when studying the ecology of various organims.s There are two components that are involved in reproduction: 1) How many females survive to each age and 2) the average number of female offspringe produced by females at each age. By using this data, the intrinsic rate of reproduction can be computed. This is necessary in order to create accurate models of population growth

• http://www.bio.miami.edu/tom/courses/bil160/bil160goods/16_rKselection.html
• http://faculty.plattsburgh.edu/meiyin.wu/304/Homework%20assignment/HW7-r%20and%20k%20species.htm
• Pearson Baccalaureate Higher Level Biology
• https://notes.utk.edu/bio/greenberg.nsf/0/14f2db31736becfa852571fe004f3765?OpenDocument
• http://www.britannica.com/EBchecked/topic/309092/K-selected-species

K-strategists

Examples of Extreme R-strategists

-- Man: most individuals live to old age, relative to the specie's maximum life expectancy.

-- oysters: lose most of the individuals very quickly, relative to the specie's maximum life span; however, there are a few individuals who survive much longer than the rest.

-- Elephants

-- dandelions

-- rats

-- Oak trees

-- algae

K-Strategists:

Strategy of nurturing

r- strategists:

Strategy of Disposable Offspring

-- voles

-- Horses

-- Saguaro Cacti

Environmental Conditions

- includes most invertebrates like insects and spiders

- short life span

- many offspring

- early maturity

- small body size

- reproduce once during lifetime

- no parental care

- unstable environment

- generalist niche

- type III survivorship pattern, meaning that most of the individuals dies within a short time, but few live much longer

Environmental Conditions

- includes most larger animals

- have fewer young

- spend considerable time and energy caring for the few

young that they do produce

- most mammals are k-strategists

- long life span

- few offspring

- late onset of maturity- after a long period of parental care

- large body size

- reproduce more than once during lifetime

- very likely to have parental care

- stable environment

- specialist niche

- type I or II survivorship pattern, meaning that most individuals live near to the maximum life span

K-strategists flourish in stable environments. When a habitat becomes diverse and is filled with a large collection of species, they will be K-strategists.

An extreme K-strategist lives in a stable environment that is not seriously affected by sudden, unpredictable effects; therefore, the population is close to carrying capacity for extreme K-strategists

In unstable environmental conditions, it is better to produce many offspring as quickly as possible. In an unstable environment, lots of offspring are lost to unpredictable forces. The few that remain can reproduce and carry on the genes or the organism.

Ecological disruption favors r-strategists, such as pathogens and pests. Most likely, if you call something a pest, it is an r-strategist.

r-strategists

k-strategists