Wolf spider population size doubles.
Since beetle larvae are preyed by wolf spiders, if the population of wolf spiders increases, that of beetle larvae will decrease.
The wolf spider population size is cut by 40% because of a virus.
Conversly, if the wolf spider population decreases, the population of beetle larvae will increase.
The sanil and woodlouse population sizes increase.
In this case we can expect and increase of the beetle larva population because there are more resources for them.
The woodlouse population size is wiped out by chemical pesticides.
Snails and woodlouse are displaced by a fire in the ecosystem.
In the above example the aviability of resources for beetle larvae decreases, therefore, we will expect a decline in such population.