Invasive species suck.
Humans intentionally or unintentionally introduce some organism into a new environment… and shit hits the fan. Whether its zebra mussels in the Great Lakes or rabbits in Australia, invasive species wreak havoc on their ‘new homes’.
There are lots of reasons for this, but there are only three reasons Im interested in:
1. The organism escapes from a pathogen in its native environment. No more pathogen, more reproduction.
2. The organism introduces a pathogen into its new environment. Organism has coevolved with this pathogen for ages, native organisms cant deal with it, invasive species kills off its new competitors.
3. Everyone is infected with the same pathogen, but get different diseases.
I never ever thought of #3 before I read this paper (been out for ages, but this is the first Ive heard of it!)
Native California grasses are perennials . Since Europeans colonized Cali, the native perennial grasses have been wiped out by European annual grasses.
Well, okay, so the European annuals are ‘more fit’, so they can reproduce more, and thats why their kickin perennial butt, right? Survival of the fittest, *yawn*
Except apparently, the European annuals arent more fit. Experimentally, the native perennials are better suited for the California ecosystem.
What?? The ‘most fit’ grasses arent dominating the landscape?? They arent out-competing the invading European grass??? Evilution is wrong! The Designer changed His mind and doesnt want native grasses growing in Cali anymore! Crumbling! Darwinism is CRUMBLING!!!!
Well, no. There is one thing in nature that can explain why the ‘less fit’ species are out-competing the ‘more fit’: viruses.
What if both the native and invasive grasses are infected with a virus, everybody is sick… but the ‘more fit’ grasses get so sick, they turn ‘less fit’?
So researchers just tried something:
If Cali and Euro grasses were left ‘pathogen free’, Cali grasses out-competed Euro grasses. Totally what we would have expected, more fit grass out-competes less fit. Hurray.
HOWEVER, if you introduce a virus into the system, in this case, barley yellow dwarf virus, the European annuals take over!
Annual grass invasion combined with aphid preferences for annual grasses alters disease dynamics by increasing transmission rates and disease prevalence in perennial grasses. Before annual grass invasion, some perennial grasses remained uninfected each season, whereas in a mixed annual-perennial community, all perennials become infected in the first year, such that virtually no healthy perennials are seen at the end of any growing season…
… BYDV infection has several compounding negative effects on perennials that have survived their first year. First, infection halves the lifespan of adult perennials. Reduced survival to the subsequent year (σPI), compounded by reduced fecundity (εp), depresses the lifetime net seed production of an adult perennial (e.g., from 330 to 75 seeds per plant) to a level insufficient for an infected adult perennial to replace itself if all of its offspring were to be infected at germination. Finally, because perennial adults are superior to annuals in competition for light and nutrients, loss of perennial biomass reduces interspecific competitive pressure on annuals. Thus, the disease is more detrimental to the long-lived perennial life history than to the annual grass life history; this permits annuals to increase in relative abundance, which further amplifies viral incidence.
This virus has a detrimental effect on European annuals, but its not the end of the world. But ‘no big whoop’ problems for annuals turn into Big Problems for perennials, and THATS why these ‘more fit’ grasses arent taking care of the invasive species problem themselves!