Well, thanks, but that is a kind of buggy and does not work as wanted.
found the solution myself…
@media only screen and (max-width: 500px) {
div#layer_slider_2 {
display:none!important;
}
}
@media only screen and (min-width: 501px) {
div#layer_slider_1 {
display:none!important;
}
}