Is there an ecological name to describe a population of organisms where most of the newborns die after birth without reproducing? The population as a whole keeps growing, however, because there are enough individuals that manage to reproduce.


Yes, we talk about r/K selection theory:

In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus upon either increased quantity of offspring at the expense of individual parental investment of r-strategists, or reduced quantity of offspring with a corresponding increased parental investment of K-strategists, varies widely, seemingly to promote success in particular environments.

The type of species you describe are the r type.

Please note the following potential confusions:

A species can vary its strategy through time and space

Species can change from K to r (and vice-versa) depending on the environment and number of individuals. Consider humans as an example.

The expression r/K selection theory can be misleading

The term "selection" in "r/K selection theory" can be a bit misleading as it refers more to a demographic reality (which has come to be due to selection pressures) but not to the selection process behind it.

Alternative meaning of 'r/K selection theory'

The terms r and K are sometimes used to mean whether a species has reached carrying capacity (K) or whether they are growing in number (r) which is not exactly the same as the interpretation of whether there is much parental investment in the species presented in the wikipedia article.

This second interpretation is actually closer to the origin of the terms r and K. The most common (and one of the simplest) equation of population growth through time is the logistic equation (see here for an easy explanation and also wiki > Population ecology )

$$\frac{dN}{dt} = rN \left( 1 - \frac{K}{N}\right) $$

enter image description here

, where $N$ is the population size, $t$ is time in generation, $r$ is the maximal growth rate and $K$ is the carrying capacity. On the graph above, $r$ represent the maximal slope (that is the maximal growth rate).

r selected species are those that have a growth rate as indicated at the center of the graph. K selected species are those that have a growth rate of 1 (no increase in $N$) as the ones that are at carrying capacity $K$.

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    $\begingroup$ Thanks, very good answer. That's the term I was looking for. On the other hand, is there a synonymous name for it, that is just a word, in use, instead of this name that involves an $r$ from an equation? $\endgroup$ – becko Oct 22 '17 at 19:46
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    $\begingroup$ You can just talk about an r-selected (or r-strategy) species. I don't think there is another term. If it is not intuitive enough when you talk to lay people, you can talk about species that favour quantity over quality of offspring. $\endgroup$ – Remi.b Oct 22 '17 at 20:05
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    $\begingroup$ Remi is right the closest you get to a term is r-strategist or K-strategist. Also keep in mind these are ends of spectrum not discrete categories. $\endgroup$ – John Oct 23 '17 at 4:02
  • $\begingroup$ @becko They are also said to have a fast life history as described in life history theory which is a theory built upon r/K-selection theory. $\endgroup$ – Eff Mar 15 '18 at 9:38
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    $\begingroup$ @becko I would simply start with the wikipedia article on life history theory. I may be able to find some good references later (I'm not with my computer at the moment). Remember that both r/K-selection and Life history theory are concerned with many traits other than number of surviving offspring. In fact, a whole suite of life history traits are correlated: maturation time, lifespan, number of offspring, size of offspring, amount of parental investment, etc. Fast life history is roughly equal to r-selected, and slow is K-selected. $\endgroup$ – Eff Mar 15 '18 at 13:35

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