Are there "speciation" events?

There have been several mass extinction events such as the K-T event, but does there exist the opposite, as it were, a “speciation” event or period? That is, are there periods in history where we see a lot of speciation compared to other periods? If so, what are some examples of what lead to this? I was watching something on youtube which, if I understood it correctly, stated that most of the major orders of placental mammals had differentiated within 200000 years of the big bang. Is this a period of speciation?

Thanks,
Rob

The Cambrian explosion comes to mind.

If you think about, there’s sort of a Newton’s Third Law going on here-- the mass extinctions generally present conditions for a newer, different set of species to develop. The analogy isn’t perfect (none ever are), but it’s pretty good unless the mass extinction was caused by something really nasty that created conditions hostile to all life (like breaking the planet into tiny bits flying thru space).

Not merely speciation, but diversification into many new niches. It wasn’t just the generation of minor variations on a theme, but the expansion into entirely new adaptive zones (at least as far as mammals were concerned).

The extinction of the dinosaurs made many new kinds of ecological niches available to mammals from which they had previously been excluded by competition from dinosaurs.

This graph shows generic diversity over time. You can see that that mass extinction events are generally followed by a period of accelerated diversification, so that diversity soon comes back to (or exceeds) its previous level.

Speciation events generally follow extinction events.

According to “punctuated equilibrium,” ecologies tend to be stable and speciation is rare, when the environment is stable and has been stable for long enough: evolution leads to relatively stable solutions, where each ecological niche is filled by a species, and any significant variation tends to make individuals less fit rather than moreso.

But when the wrench is thrown into the mix, due to climate or geological change, things are in flux, so experiments can succeed. Ecological niches aren’t stable, and new species (as well as taxons higher up the scale) emerge.

I’m assuming you’re using “big bang” here as a shorthand for the KT asteroid impact, rather than in its conventional sense. Stars hadn’t even formed within 200000 years of the Big Bang. Earth didn’t even form until ten billion years after.

Yes, I meant KT, not big bang. I was distracted when I wrote that.

It’s not quite what you’re speaking of, but islands tend to have really explosive speciation. Galapagos, Hawaii, Madagascar, etc.: examples of places with riotous, runaway species diversity. Isolated areas like mountaintops surrounded by deserts can also act as “islands” in this way, and produce more species per square mile than is average for a comparable environment that is square in the middle of migration routes.

(Per David Quammen, Song of the Dodo, a very good – and depressing – book about speciation and extinction.)

The asteroid impact opened up a lot of ecological niches.
Overall rate of mutation may not have changed, but there were more opportunities.
So mutations that were beneficial had a disproportionate impact relative to times of more biodiversity.

Is my guess. I’m not a speciationologist.

Yeah, one general thought is that KT killed pretty much anything over 5lbs. This gave a lot of opportunity for new species to emerge.

A species occupies an ecological niche - a particular environment, food source, etc. If the niche is already occupied, a usurper needs a lot of advantage to displace the existing species, already well-adpated. Coyotes, for example, seem to have filled the spot vacated because we shot almost all of the wolves. Several invader species benefit from lack of predators, or local food that has not had time to generate a defence. Rabbits in Australia are a classic, as is a species of poisoned toad imported for pest control and now running wild. Feral cats in New Zealand are decimating the flightless bird population that did not evolve to hide their nests from sneaky little purrballs. Rats have done the same to a lot of bird islands when modern sailing vessels visited.

Similarly, the niches can open up because geology has kept the competition out. Presumably a small starter kit of lemurs made it to Madagascar. Since nobody was occupying the place, they expanded to take advantage of every food source. As a protospecies becomes better at exploiting a food source, or other means of beating their neighbours at the game of life, they (presumably) tend to prefer similarly developed mates, thus emphasizing the selection. Eventually, the two goups are so different that cross-breeding becomes less viable (and of course, the cross-product is less adapted than the pure-bred to either environment.)

nm