What are the contrasting conditions that favor the evolution of semelparous versus iteroparous reproduction?

Question

What are the contrasting conditions that favor the evolution of semelparous versus iteroparous reproduction?

Answer 1

Semelparity is when a species reproduces only once in its lifetime, often saving up energy for a big event.  Iteroparity, on the other hand, is when a species reproduces many times.

If a species lives in a very unpredictable environment where its chances of survival to the next year are low, then semelparity makes no sense.  It is better for a species to invest energy each year in reproduction (i.e., iteroparity) because, even though the organism might be small and not able to produce many offspring, at least they had a chance whereas if they wait until they're bigger, they might not make it.

However, if your chances of survival are good for the next year, then it may be better for you to invest your energy into growth this year so that when you finally do reproduce, you can really make it count both in numbers and quality of your offspring (i.e., semelparity) (By the way, this means your chances of making it to the next year once you've become an adult.  Larvae of almost all species have very poor survivorship.)

Another reason why some species may be semelparous is that they are optimizing the conditions for offspring survival.  An example of this is Agave.  The desert is a harsh place for new seedlings, so these plants save up their reproductive effort for a good year and then put everything they have into it.

Overall, species that are iteroparous make lots of offspring in their lifetime, but are generally of poorer quality.  Semelparous species make up for quantity with quality.  Their offspring are fewer, but have more nutrition for their start to live.  This big investment of energy just wipes out the parents.