. Bulletins of American paleontology. Cheilostome Bryozoa: Cheetham etal. 171 PPP 150 100 50 (/) c U o o 150 o o 100 »*- o 50 0) ^ 0 fc 3 Encrusting v^ Erect 05. 100 50 0 Free-living 50 Free-living 05 A Zs- 02 Abundance per collection (thousands) Text-figure 10.âFrequency distributions ol abundance per collec- tion of three growth forms in the PPP and DR. Abundance and Occurrence of Species Largely but not entirely because of its superabun- dance in the PPP collections, free-living growth char- acterizes the 5 most abundant species in the combined PPP-DR database, and 13 of the 25 mos
. Bulletins of American paleontology. Cheilostome Bryozoa: Cheetham etal. 171 PPP 150 100 50 (/) c U o o 150 o o 100 »*- o 50 0) ^ 0 fc 3 Encrusting v^ Erect 05. 100 50 0 Free-living 50 Free-living 05 A Zs- 02 Abundance per collection (thousands) Text-figure 10.âFrequency distributions ol abundance per collec- tion of three growth forms in the PPP and DR. Abundance and Occurrence of Species Largely but not entirely because of its superabun- dance in the PPP collections, free-living growth char- acterizes the 5 most abundant species in the combined PPP-DR database, and 13 of the 25 most abundant species (Table 3). The same free-living species, Cii- pidadrici biporosa, ranks first or second in abundance and number of occurrences in both the PPP and the DR, and is one of only two species to rank in the top 10 in both areas. (The other, Mamillopora tuberosa, is also classed as free-living on the basis of morphology illustrated in Cheetham and Jackson, 1999.) The 19 free living species have a median rank in abundance of 14 among the 250 cheilostome species, compared to 79 for the 64 erect species and for the 167 encrusting ones. Four free-living species occur in 100 or more collections, in contrast to only two erect and two encrusting ones (Text-fig. 11). Further differences in the patterns of distribution of the three growth forms are evident in the relationship between the abundance of a species and the number of collections in which it occurs (occurrences; Text- fig. 11). Although abundance is highly significantly correlated with occurrences for all three growth forms (Spearman rank-order correlation , P < in all cases), the rate at which abundance in- creases with occurrences for free-living species is about 50% greater than the rate of increase for erect species and 100% greater than for encrusting ones (Text-fig. 11). Unsurprisingly, the most frequently oc- curring and abundant species in each group are those that occur in both t
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