I had a question just like yours. I decided as follows: whenever the select is changed, you take the option value and use this value to filter from all the events you searched in ajax. An example would be:
$('#seleciona').change(function(){
$("#calendar").fullCalendar('removeEvents');//remove os eventos anteriores
var idEspacoFisico=$('#seleciona option:selected').val();//Pega o id do option
$.ajax({
type:"POST",
url:'eventos/getEventos.json', //Pega todos os eventos
success: function(data){
$.each(data,function(index,value){//Para cada valor do data, compara se o campo é igual ao filtro selecionado. Se for igual, renderiza.
if(value.espacoFisico==idEspacoFisico){
$("#calendar").fullCalendar('renderEvent', value, true);
}
})
}
});
});
});