Assuming no common structure, we could define them to all be abstract elements:

<xs:element name="b:species" type="xs:anyType" abstract="true"/>
<xs:element name="b:location" type="xs:anyType" abstract="true"/>
<xs:element name="b:areatype" type="xs:anyType" abstract="true"/>
<xs:element name="b:counts" type="xs:anyType" abstract="true"/>
<xs:element name="b:observations" type="xs:anyType" abstract="true"/>

Then we define specific kinds of species/locations/etc. and put them in the substitution group:

<xs:element name="b:latin-name" substitutionGroup="b:species">
<xs:complexType>
<xs:attribute name="genus" type="xs:string" use="required"/>
<xs:attribute name="species" type="xs:string" use="optional"/>
</xs:complexType>
</xs:element>

<xs:element name="b:gis-location" substitutionGroup="b:location">
<xs:complexType>
</xs:complexType>
</xs:element>