aposematism

The theory of warning signals dates back to Wallace but is still confusing, controversial and complex. Because predator avoidance of warningly coloured prey (aposematism) is based upon learning and reinforcement, it is difficult to understand how initially rare conspicuous forms subsequently become common. Here, we discuss several possible resolutions to this apparent paradox. Many of these ideas have been largely ignored as a result of implicit assumptions about predator behaviour and assumed lack of variation in the predators, prey and the predation process. Considering the spatial and temporal variation in and mechanisms of behaviour of both predators and prey will make it easier to understand the process and evolution of aposematism.

Zotero.org and Mendeley.

The lack of an adequate method for retrieving metadata has led to proposals such as the Life Sciences Identifier (LSID) [138],[139] and BioGUID [140] (Biological Globally Unique IDentifier)

Figure 4. A typical workflow for using a digital library representing a subset of the literature.

Google Scholar [95] (e.g., [96]–[99]) is a service provided by Google (see also [100]), which indexes traditional scientific literature, as well as preprints and “grey” self-archived publications [19] from selected institutional Web site

Scopus [88] is a service provided by Reed Elsevier and seems to be the Digital Library with individually the most comprehensive coverage, claiming (June 2008) >33,000,000 records (leaving aside Web pages). As far as linking is concerned, Scopus allows links <1?show=[to]?>to its content using OpenURL [89], which provides a standard syntax for creating URIs. For example, the URI

ubMed [75] is a service provided by the National Center for Biotechnology Information (NCBI). The PubMed database includes more than 17 million citations from more than 19,600 life science journals [76],[77]. The primary mechanism for identifying publications in PubMed is the PubMed identifier (PMID);

URIs for granted, but these humble strings are fundamental to the way the Web works [58] and how libraries can exploit it, so they are a crucial part of the cyberinfrastructure [59] required for e-science on the Web. It is easy to underestimate the value of simple URIs, which can be cited in publications, bookmarked, cut-and-pasted, e-mailed, posted in blogs, added to Web pages and wikis [60]–[62], and indexed by search engines. Simple URIs are a key part of the current Web (version 1.0) and one of the reasons for the Web's phenomenal success since appearing in 1990 [63]. As we shall demonstrate with examples, each digital library has its own style of URI for being linked to (inbound links) and alternative styles of URI for linking out (outbound links) to publisher sites. Some of these links are simple, others more complex, and this has important consequences for both human and programmatic access to the resources these URIs identify.

Where available, DOIs can be used to retrieve metadata for a given publication using a DOI resolver such as CrossRef [57], a linking system developed by a consortium of publishers.

DOIs are a specific type of URI and similar to the International Standard Book Numbers (ISBN), allowing persistent and unique identification of a publication (or indeed part of a publication), independently of its location

These applications allow users to add personal metadata, notes, and keywords (simple labels or “tags” [27],[28]) to help manage, navigate, and share their personal collections

Table 1. A summary of some of the digital libraries described in this Review. https://doi.org/10.1371/journal.pcbi.1000204.t001

digital library more broadly as a database of scientific and technical articles, conference publications, and books that can be searched and browsed using a Web browser

digital library [2]–[4] denotes a collection of literature and its attendant metadata (data about data) stored electronically.