Do all species form the same way as songbirds?

As niches are filled up by new species speciation slows down. Comes to a halt, even. This makes sense, as the niches are ways of life that organisms can have, if there are no other ways of life currently available, thing will stay the same. This is in line with a mode of speciation driven by niches, in accordance with the Ecological Species Concept by Van Valen (1976)* (which is a definition; species is the concept; it should be a criterion**). I'll even go so far as saying that most speciation events can be explained by this framework, though there are some known instances of speciation driven by weird genetic events that cause reproductive isolation, e.g., in European crows.

A recent study uses Himalayan songbirds to show that speciation rates decrease as niches are filled (Price et al., 2014).

Speciation generally involves a three-step process—range expansion, range fragmentation and the development of reproductive isolation between spatially separated populations1, 2. Speciation relies on cycling through these three steps and each may limit the rate at which new species form1, 3. We estimate phylogenetic relationships among all Himalayan songbirds to ask whether the development of reproductive isolation and ecological competition, both factors that limit range expansions4, set an ultimate limit on speciation. 

It's a nice paper - the link between niches and speciation is close to my heart (Østman et al., 2014). Grrlscientist has a nice write-up about it in The Guardian. However, I have to mention that I am taken aback by three things in the above quote from the first lines of the abstract:

1) Generalizing from songbirds to everything else: Speciation is not always about reproductive isolation, and it may certainly not generally work the way it does in Himalayan songbirds. Especially not in asexual organisms.

2) Allopatric speciation (with geographic isolation) may be prominent, but we don't know how much sympatric speciation (without geographic isolation) occurs, so we can't discount it (and theoretically it is easy).

3) Species evolve, they don't develop. So does that mean that reproductive isolation evolves rather than develops? Semantics, I realize, but I think it's important to get this right.

So, fixed:

Speciation in sexually reproducing organisms generally involves a three-step process—range expansion, range fragmentation and the evolution of reproductive isolation between spatially separated populations1, 2. Allopatric speciation relies on cycling through these three steps and each may limit the rate at which new species form1, 3. We estimate phylogenetic relationships among all Himalayan songbirds to ask whether the evolution of reproductive isolation and ecological competition, both factors that limit range expansions4, set an ultimate limit on speciation. 

That'll be $20.

* Best title ever: "Ecological Species, Multispecies, and Oaks." I never get tired of saying this.
** I will also not likely get tired of saying that: Pragmatic definitions in biology.

References

Price TD, Hooper DM, Buchanan CD, Johansson US, Tietze DT, Alström P, Olsson U, Ghosh-Harihar M, Ishtiaq F, Gupta SK, Martens J, Harr B, Singh P, and Mohan D (2014). Niche filling slows the diversification of Himalayan songbirds. Nature, 509 (7499), 222-5 PMID: 24776798.

Østman B, Lin R, and Adami C (2014). Trade-offs drive resource specialization and the gradual establishment of ecotypes. BMC evolutionary biology, 14 PMID: 24885598