Limitations

Parts of the database, particularly for Coleoptera and Lepidoptera, have been updated recently (2007-08) from the most up-to-date monographs available. These groups may still not have been updated with individual species’ observations published in the amateur journals. For example, numerous Lepidoptera monographs are now more than 10 years out of date, so new information is likely to have appeared. Although corrections were made, beware that certain updated files may still contain old nomenclature, so that more than one name refers to the same invertebrate. This may cause species lists to appear longer than they actually are.

For groups without recent updating, the invertebrate checklists, nomenclature and interactions will reflect the state of knowledge as at the last source. This is more than 20 years ago for many groups, especially the poorly studied ones. The Family backgrounds [hyperlink to families.aspx] show when each invertebrate family was last updated. Some backgrounds have recent expert assessments of the condition of the data.

Coverage of host plants

There are two related issues:

• Host plants are not sampled evenly for herbivores. The data in the published literature are not the result of systamatic sampling of host plants. Rather, they reflect what has been recorded. Consequently, around 432 native and 223 alien plant names are missing from DBIF. Scarce native plants tend to be absent, as do species in relatively inaccessible habitats, such as the uplands and aquatic environments.

• Host plant information is reported at different taxonomic resolutions. Host plant records are mostly made by entomologists, who tend not to be expert botanists. DBIF accommodates the various taxonomic resolutions at which observations are reported, either on plant species, genera, or families. For example, ‘on oak(s)’ and ‘on an unidentified species of oak’ would be both be entered as Quercus. Numerous sources that give a list of host species, e.g. oaks, then state ‘and on other oak species’ are entered in the database as ‘Quercus other species’.

Broader host plant categories are also included in DBIF, such as ‘deciduous shrubs and trees’, ‘grasses’ or ‘mosses’ and ‘lichens’. There is bias in the level of detail for different plant groups, e.g. grasses and sedges are reported less specifically.

Sources

DBIF contains the interactions reported in primary (i.e. the original) and secondary sources, although the type of source is not identified in the database. Both types of source have advantages and disadvantages in terms of interpreting host records:

• Primary sources (such as observations published in amateur journals) should make an accurate statement about a relationship, although the information may only apply to a particular locality. Unless stated, it may not describe the relationship throughout the distribution of the herbivore.

• Secondary sources (such as monographs on a taxon of herbivores) serve as compilations of knowledge, and thus may provide both a broader picture and an assessment of older data (both accurate and erroneous). However, secondary sources may also perpetuate errors. When the original database was created (see PIDB it was anticipated that the credibility of an interaction would be enhanced through repeated reporting by different observers. Obviously, secondary reports of an original observation will obscure this effect, and repeated errors will accrue a false authority.

Similarly, British and continental European sources may report each others information, without stating as much. Again, this could give a false picture of where interactions occur.

Geographical ranges of herbivores in Great Britain

The original PIDB database contained information on the geographical distribution of the invertebrate, if given in a source. This may have been incomplete at the time, and is now likely to be out-of-date. For many invertebrates, distribution maps are now available on the National Biodiversity Network, so geographical information was not entered in the 2007-08 update. Nevertheless, for poorly studied taxa, the geographical information included in DBIF may still be the best available (see Attributes related to Interactions).