Classification by the Method of Reproduction
Asexual vs. sexual
Organisms can reproduce either asexually or sexually. Some organisms can alternate between the two, such as jellyfish.
| Asexual reproduction | Sexual reproduction |
| Involves one parent | Involves two organisms |
| Gametes not produced | Gametes produced |
| Offspring are genetically identical to parent (clones) | Offspring have genetic variation |
| Cell division is mitotic | Gametes produced by meiosis |
| Larger number of offspring produced | Smaller number of offspring produced |
r vs. k strategists
We can then further classify sexually reproducing organisms, broadly splitting them into r-strategists and K-strategists.
“r” stands for “rate” {growth rate}.
In German, the word for capacity is “Kapazität” and K stands for the “Kapazitätsgrenze” (capacity limit, now called carrying capacity).
- r-strategists have a high r value and a low K value.
- They grow fast but have minimum life expectancy.
- Have many small offspring with little parental care.
- Tend to be pioneers/colonisers and niche generalists, positioned at lower trophic levels.
- The population is controlled by density independent factors such as climatic events or fires, etc.
- K strategists have a low r and a high K.
- They grow slower but more survive.
- Have fewer larger offspring and invest in parental care.
- Tend to appear in the later stages of succession and are niche specialists, positioned at higher trophic levels.
- The population is controlled by density dependent factors such as competition or predation, etc.
K-strategist species exhibit which characteristic?
a. Produces many offspring
b. Late age of maturity
c. Relatively short life expectancies
d. Little time spent by parents raising offspring
The tapeworm Diphyllobothrium dendriticum can produce millions of eggs a day. This reproductive strategy is most similar to which of the following:
a. A r-strategist, because it aims to produce a large abundance of offspring to ensure survival
b. A K-strategist, because it aims to produce a large abundance of offspring to ensure survival
c. An r-strategist, because it is best suited to thrive in stable environments and over a long life-span.
d. A K-strategist, because it is best suited to thrive in stable environments and over a long life-span
K-strategist populations are often regulated by ____________ limiting factors, and r-strategist populations are often regulated by ___________ limiting factors.
a. density-independent, density-dependent
b. density-independent, density-independent
c. density-dependent, density-independent
d. density-dependent, density-dependent