Survivorship curve

[Adz795]

Here,
http://upper.usm.k12.wi.us/academics/fa ... orship.gif

I understood all the curves except the 2nd one.
What does the 2nd curve mean? What organisms have it? How can the survival rate increase suddenly at some age?

[plasmodesmata11]

Not terribly conclusive, but hopefully I can spark an idea...
It's close to curve 1 with the difference of that spike. I think that may indicate maturity. Their ability to survive increases as they mature (larger mass etc.). It seems to be a rapid event. After the organism matures sexually, it reproduces and dies (indicated by the steep drop off afterwards). So it appears to be an animal that mates late in life. It could be semelparous. However, I am unsure of what organism would do his since semelparity usually indicates mass spawning and therefore low parental investment, which wouldn't explain the high survivorship young in life. The seeming semelparity could be explained though by perhaps a low availability of mates.

[Adz795]

I appreciate your expert interpretation of the graph.

Will you please elaborate on this statement of yours. I am not able to relate it.
"The seeming semelparity could be explained though by perhaps a low availability of mates."

Thank you so much.

[plasmodesmata11]

It would be unusual for something to mate only once if it produces few offspring and can do it again. A harsh environment, however, may only allow the organism to reproduce once. A competitive environment may also only allow it to reproduce once. So despite it having the capacity to mate multiple times, it may be the norm for only one mating per lifetime. The difficulty of mating again (which may be deferred to the few dominant individuals) makes it seem as though the organism reproduces once per lifetime then dies. This all goes off the assumption that the spike is indicative of maturity. I can't get more specific though because of the individual's varying ecology and biology. Does that help?

[Adz795]

Oh, so you want to say that normally iteroparous individuals may be forced to be semelparous due to conditions you mentioned, like competition or harsh environment. But such an apparently semelparous individual wounld not produce in a big-bang way right?.. or would it? I mean to say that it should produce normal no. of offspring (characteristic of iteroparity) even though it reproduces only once.

Thanks so much for the explanation. It fascinated me.