Change Dropdown jQuery to show/hide but with default place holder that shows all

How to set the jQuery so if default Department is selected show all, and only hide all else one other section made.

for example, if non selected will be Department, if Department 1 selected only show Department 1 and same with other options.

code

     script
        jQuery(document).ready(function ($) {
            $(select).change(function () {
                $(this).find(option:selected).each(function () {
                    var optionValue = $(this).attr(value);
                    if (optionValue) {
                        $(.box).not(. + optionValue).hide();
                        $(. + optionValue).show();
                    } else {
                        $(.box).hide();
                    }
                });
            }).change();
        });
    /script

    div
        label
            select
!--                option value=starter selectedDepartment (--?php //echo $total; ?!--)/option--
                ?php
                $tax_terms = get_terms('department', array('hide_empty' = '0'));
                foreach ($tax_terms as $tax_term):
                    ?
                ?php
                    echo 'option value=' . $tax_term-name . '' . $tax_term-name, 'span (' . $tax_term-count . ')/span' . '/option';
                endforeach;
                ?
            /select
        /label
    /div