Bee Taxa and Categories

Classifications, of course, are based in large part on phy-logeny. Some specialists (cladists) base classification entirely on phylogeny; others consider also information from diverse sources in developing a classification. No one, however, should presume to make a classification without having all available phylogenetic information. For practical purposes, I present here some information on bee classification, prior to the section on phylogeny, because use of the family-group names makes explanation and understanding easier. Recent phylogenetic studies have not overturned this classification in a major way; it is therefore possible to discuss phylogeny using for the most part the taxa that have been accepted in the past by many specialists. To provide ready reference to the classification that will be elaborated later, Table 16-1 lists the taxa (family to subgenus) here accepted.

In dealing with a large group such as the bees, it is inevitable that the classification will be unsatisfactory in some areas even though quite satisfying in others. This situation arises partly because ofintrinsic differences among living bees. In some groups the taxa are well differentiated and easily organized hierarchically, whereas in other groups characters occur in diverse combinations among taxa difficult to differentiate and resistant to unambiguous classification. Another reason for differences in the usefulness of taxonomic constructs is the amount and kind of study to which each group (e.g., family) has been subjected. Some taxa have been analyzed phylogeneti-cally, others have not, and some such analyses are convincing while others are not. Thus the parts of the classification differ in their usefulness. It has not been practical to make phylogenetic studies of all groups as part of the preparation of this book. Some such studies (Roig-Alsina and Michener, 1993; Alexander and Michener, 1995), published separately partly in order to present details not appropriate here, were made specifically in the hope of clarifying the family-level classification for this book.

The tradition has been to recognize large genera of bees, like Andrena, Lasioglossum, and Megachile. I believe this is desirable, for it allows many biologists to recognize the genera and know what is meant by the names. In the same way, I find names like Culex, Aedes, and Drosophila more useful to me, and I think to biologists in general, than the many generic names that would result if the many subgenera they comprise were all raised to generic rank.

A frequent result of maintaining large genera is the development of multiple subgenera. Melittologists are sometimes criticized for extensive use of subgenera. Species-groups, named informally with specific names, could be used instead of subgenera; such a procedure would avoid burdening the literature with numerous sub-generic names and their associated formalities such as type species and problems of homonymy. For large genera, however, with hundreds or thousands of species, the choice is not between recognizing a genus with subgenera vs. a genus with species groups. It is between recognizing a genus with subgenera vs. several or many genera, because many ofthe current subgenera are quite different from one another, sometimes recognizable on flowers or even in flight, and some specialists already prefer to recognize them as genera. I prefer, nonetheless, to retain inclusive genera for the reason indicated above. In the end, however, these decisions are subjective regardless of one's views on systematic methodology.

One of the advantages of subgenera is that they need not be cited. Unlike generic names, which are required, subgeneric names are optional parts of the scientific nomenclature of organisms. Thus, Megachile (Eutri-charaea) rotundata can also be written Megachile rotun-data. Anyone can simply ignore subgeneric names. It is fortunate that much of the activity of splitters therefore can be ignored by those who wish to do so; this tactic is more difficult when the taxa are called genera.

The appropriate genus-level classification varies among groups. In Andrena, in spite of its numerous subgenera, almost no modern author proposes elevating the subgenera to generic rank. In Lasioglossum, as explained in the account of that genus, certain authors do recognize subdivisions such as Dialictus, Evylaeus, and Lasioglossum s. str. as genera, although I consider them to be subgenera. Since there is no useful definition of genus or subgenus, such differences of opinion are matters of judgment about which there is no right or wrong interpretation. The Anthidiini, a group prone to striking morphological variables like carinae and lamellae on various parts of the body, have been broken up into numerous genera; a few recent authors (Warncke, Westrich) place most of its species in Anthidium. Finally, perhaps largely for historical reasons, the Eucerini are divided into many genera rather than subgenera of one huge genus. In the systematic part of this book I have tried to reduce the diversity of treatments both by uniting some genera in much "split" taxa and by breaking up a few taxa that have usually seemed "lumped," such as the old genus Nomia. The problem, of course, is that such efforts are largely subjective, because there is no objective basis for deciding whether two taxa are distinct from one another sub-generically, generically, tribally, or whatever. This is true, moreover, whether the taxa are recognized by phenetic differences or by phylogenetic positions. See Section 30.

No bee specialist will be satisfied with all aspects of Table 16-1. It does indicate the classification that will be used in the sections of this book concerned with system-atics, i.e., Sections 36 to 121.

In Table 16-1 the authors of family-group names (su-perfamily to subtribe, or for our purposes, family to tribe) are given. Authors' names do not appear elsewhere. Traditionally less attention is given to them than for genus-group and species-group names, but details can be found in Michener (1986a), and repeated and updated in Engel (2005).

The total number of species placed to genus and subgenus, as indicated in Table 16-1, is about 17,500. As indicated elsewhere, there remain named species not placed to subgenus and not enumerated in the table. Thus in genera like Megachile, Coelioxys (especially of South America), and Eucera s. l., many species remain unplaced as to subgenus and therefore are not included in Table 161. This situation is presumably worst in the little-studied parts of the world, where many species were named in past centuries, but modern treatments of such faunas scarcely exist. The number of described species of bees (not including those relegated to synonymy) may well be over 18,000, and new species yet to be found and named will probably exceed the number of new synonyms recognized. A guess as to the total number of bee species in the world is therefore near or above the often-mentioned figure of20,000. Given the number ofcryptic species that will probably be found with the advent of molecular methods and more careful morphological analyses, the total number of species could be even higher. I am indebted to Dr. John S. Ascher for data and discussion of these matters.

Table 16-1. The Recent Bee Taxa (Family to Subgenus).

This table gives the authors' names for the higher taxa, and estimates of the approximate numbers of included species for genera and subgenera. Depending on the status of the systematics of the particular group, these numbers are based on revisions, estimates, or merely number of specific names. They relate to named species but are often uncertain because revisors were not certain about the status of some names or because of unpublished synonymies or other findings. Isolated descriptions of new species were commonly ignored. The numbers in parentheses after family-group names are those of the corresponding text sections. Subgeneric names are in italics. At the end of the table are the totals. Fossil taxa are excluded; see Section 22.

Table 16-1. The Recent Bee Taxa (Family to Subgenus).

This table gives the authors' names for the higher taxa, and estimates of the approximate numbers of included species for genera and subgenera. Depending on the status of the systematics of the particular group, these numbers are based on revisions, estimates, or merely number of specific names. They relate to named species but are often uncertain because revisors were not certain about the status of some names or because of unpublished synonymies or other findings. Isolated descriptions of new species were commonly ignored. The numbers in parentheses after family-group names are those of the corresponding text sections. Subgeneric names are in italics. At the end of the table are the totals. Fossil taxa are excluded; see Section 22.

Family Stenotritidae Cockerell(36)

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