英语听力：自然百科 为生而死的生物

Hi, it’s Kasey-Dee Gardner, in this weekend Why Tell Me Why will answer an interesting viewer question. The viewer wants to know why certain species die after they reproduce. So, we're here to find out the answer.

Urn, so there are a bunch of species, both plant and animal that once have babies they just die. Is that correct?

Yes, that’s true. The viewer that asked the question asked about salmon in particular. There are also plant species in particular annual plants(一年生植物), there are some a lot of annual plants that grow and reproduce in one summer and then die. There is actually a plant called “the century plant(龙舌兰)”, it’s called “the century plant” because it can live up to a hundred years without reproducing. And then reproduce one big event one time and then die.

Insects do it too, right?

Yes, yes, there is, there is a lot of organisms that do it. Things that have really high rates of predation or death due to environmental factors are competition. Those are the organisms that reproduce once and just die.

And what they are trying to do is maximize how many offspring they have at one point in order to ensure that at least one survives. Now in order to reproduce, an organism has to put resources into it. Resources can either go to current reproduction or it can store them up for future reproduction, or it can just put them toward maintenance of, urn, current survival basically.

And so, in order to produce as many offspring as possible, organisms put fewer resources towards survival and toward maintenance than they put into offspring. So they put all their resources in the offspring and basically at the end of that reproductive event they don’t have any energy left to survive, they put every effort possibly they can into producing just one more offspring. Because the probability of any one offspring surviving iss very very low.

And what’s really important in evolution of species is how many offspring you produce, but not just how many you produce but how many of those make it to reproduce some cells because that’s what keeps a species going.

It seems that it wouldn’t make sense to put all of your eggs in one basket. Why would you have all of them at once?

But actually, mathematically, it turns out if you can produce just one more, if an organism can produce one more offspring in one year than another organism will produce in multiple years. That, that’s actually beneficial to the organism because then, its offspring will reproduce the next year and have an equal number of offspring.