How can the carrying capacity of an ecosystem change?
If a competitor dissappear or appear in an ecosystem, the remaining species will have more or less ressources for theme and that will allow the possible number of member of that species to live in that ecosystem to increase or decrease.
For instance a rock covered of barnacle will have a carring capacity most likely deppending on the surface avaible for theme. If a new species of barnacle colonise the rock there will be competition for the surface and the ecosysteme "rock" will see it's carrying capacity for the first baracle deacreas.
An other example, if a species big herbivorous dissapear from a habitats, it will make all the vegetation they were used to eat avaible for other species who will be able to feed more offspring making the carrying capacity of the ecosystem go's up.