Transposons don’t stop if they have one copy per individual in a species. They continuously increase their copies per chromosome.
Most species have evolved ways to suppress transposon activity for the transposons that are native to that species. If you add a new transposon for which you don’t have any suppression systems that can plausibly make the species extinct.
The abstract of the paper does discuss this:
These results provide new insight into the process of a transposon’s invasion into a new species and the potential risk of extinction such an invasion might entail.
Generally, it’s quite surprising that we see a newly inserted transposon family in a species with 50 transposon families in one of our core model organisms if you assume that species survive a majority of insertions of new transposons.
Transposons don’t stop if they have one copy per individual in a species. They continuously increase their copies per chromosome.
Most species have evolved ways to suppress transposon activity for the transposons that are native to that species. If you add a new transposon for which you don’t have any suppression systems that can plausibly make the species extinct.
The abstract of the paper does discuss this:
Generally, it’s quite surprising that we see a newly inserted transposon family in a species with 50 transposon families in one of our core model organisms if you assume that species survive a majority of insertions of new transposons.