The Distribution of Leafhopper Pests in Relation to Other Leafhoppers (Hemiptera; Cicadellidae)

22 Pages·2002·1.8 MB·English

by  Mckamey, Stuart H

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The Distribution of Leafhopper Pests in Relation
to Other Leafhoppers (Hemiptera; Cicadellidae)
S.H. MCKAMEY
Abstract
A species-level database with country- the N 20-30° interval and exceeded 4,000
level information was used to examine the species in the N 40-50° interval. The lat-
global distribution patterns across biogeo- ter richness estimate seems to be an arti-
graphic realms and across latitudes for
fact of using country-level data. The ratio
13,621 leafhopper species (among 2,016
of species per genus was higher in the
genera and subgenera) and 148 known
New World than in the Old World and
leafhopper vectors of phytopathogens.
was higher in the N 20-60° latitude inter-
There were only seven cosmopolitan gene-
vals, even separating data for the New and
ra: Balclutha, Cicadella, Deltocephalus,
Old Worlds. This suggests that a natural
Empoasca, Exitianus, Idiocerus, and
phenomenon driving finer, species-level
Xestocephaltis. Cicadellid generic richness
diversification may be at work on leafhop-
was highest in the Indomalaysian and
Neotropical Realms. Deltocephaline gene- pers in the northern habitats. The ratio of
ra peaked in the Nearctic and the known vectors to all species was used to
typhlocybine genera peaked in the Indo- calculate the expected number of vectors,
malaysian Realm. The generic overlap assuming random distribution, in all bio-
among most biogeographic realms was low, geographic realms and latitude intervals.
with complementarity (distinctness) The seven cosmopolitan genera and the
values over 90%. Geographical proximity
seven largest genera have fewer known
between realms generally was directly pro-
vectors than expected. The Australian,
portional to their overlap. The Nearctic
Nearctic, and Palearctic Realms, where
and Neotropical Realms were the least
most research has been conducted, have
distinct, whether the Mexican fauna was
many more known vectors than expected
classified as Nearctic, as Neotropical, or
and this is reflected in the latitudinal pat-
even excluded completely from the compa-
tern. The true number of vectors is there-
rison. The Nearctic and Palearctic Realms
fore probably much greater than known
were more distinct than many others, for
example, the Palearctic and Afrotropical and their agricultural importance has been
Realms. The leafhopper fauna of the vastly underestimated. An appendix listing
Greater Antilles was most similar to that the genera of all biogeographic realms and
of Mexico+Central America. Cicadellid the Holarctic genera is provided.
generic richness peaked in the N 0-10°
Key Words. Membracoidea, biogeogra- Denisia 04,
interval while species richness peaked in zugleich Kataloge des OÖ. Landesmuseums,
phy, distribution, vector, phytopathogen.
Neue Folge Nr. 176 (2002). 357-378
357
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Introduction thogens and later examined the taxonomic
distribution of the species (NlELSON 1979b),
Leafhoppers constitute the largest family but the geographical distribution has not been
in Hemiptera, which is the fifth largest insect examined.
order. Leafhoppers are of great agricultural
For the first time, it is possible to examine
importance because of their ability to transmit
the global distribution patterns of Cicadelli-
phytopathogens occurring in phloem or
dae. These are based on an in-progress world
xylem, although vectors of most diseases are
database on the family (McKamey, in. prep.).
unknown (e.g., less than 5% of the vectors of
Though still far from complete, country-level
phytoplasms, a group of pathogens often trans-
data are recorded for the majority of valid spe-
mitted by leafhoppers, are known [Robert
cies. Some 7,699 of these have current coun-
Davis, ARS, pers. comm.]). So many leafhop-
try names based on the localities listed in the
pers are undescribed that we are not able to
Catalogue of the Homoptera, while the rema-
estimate with any accuracy how many exist.
inder are from more recent literature: Coelidi-
Most subfamilies are cosmopolitan, and this is
inae (NlELSON 1975, 1977, 1979a, 1982);
attributable partly to dispersal, including pas-
Cicadellinae (YOUNG 1968, 1977, 1986); and
sive drift in air currents (WELLINGTON 1945,
original descriptions of species in other subfa-
WOLFENBARGER 1946) rather than vicariance.
milies. This database also indicates the vector
Despite their importance in agriculture, status of 148 valid species.
the overall distribution patterns of leafhoppers
and leafhopper pests are unknown. Examining
Materials and Methods
the distribution of known pests and other spe-
cies may enable us to predict where additio-
Because of the high subjectivity inherent
nal, as yet unknown pests or other species
in higher taxa, the incomplete knowledge of
occur, or at least direct us to productive ave-
most species distributions, and the existence
nues for further investigation.
of many undescribed species, most compari-
The most general view of species distribu-
sons are limited to genus-groups (genera and
tions up until now was provided by METCALF
subgenera). Counting subgenera also skirts
(1962a, 1962b, 1962c, 1962d, 1963a, 1963b,
disagreements regarding the most appropriate
1963c, 1963d, 1964b, 1965a, 1965b, 1966a,
status of some taxa. To look for parallels in
1966b, 1966c, 1966d, 1967a, 1967b, 1967c,
subsets of Cicadellidae, generic patterns
1968a). In each section of the Catalogue of
within the two largest subfamilies, Deltoce-
the Homoptera, Fascicle VI, METCALF cited
phalinae and Typhlocybinae (both sensu
the number of species occurring in each bio-
OMAN et al. 1990), were also examined. The
geographic region. The taxonomic and distri-
results are based on country-level data for
bution data of that catalogue fascicle are avai-
13,621 valid species, of which 5,080 are Del-
lable at http://www.sel.barc.usda.gov/selhome
tocephalinae and 4,348 are Tyhlocybinae, and
/leafhoppers/mckpaper.htm. Nevertheless, sin-
2,016 genera (including 739 deltocephalines
ce the 1955 cut-off date ofthat catalogue, the
and 481 typhlocybines). Unnaccounted for
number of species has almost doubled and
here, because at this point they lack country-
there have been many changes in specific and
level information in the database, are 3,765
generic taxonomy. LlNNAVUORI (1959) discus-
species as well as most species described after
sed the endemic elements and representative
1992. There are also 590 genera and subgene-
genera of Deltocephalinae in subregions of the
ra in the database that could not be included
Neotropical Realm. OMAN et al. (1990) provi-
because at this point we have captured no
ded biogeographic regions for the nearly 2,400
country-level information for their included
genera described through 1985, with pheno-
species.
monal accuracy given the absence of a species
database. As we shall see, however, while they The database shell is Biota (COLWELL
succeeded for most genera, many designations 1996), a relational database well suited to the
were incomplete. NlELSON (1968) provided objective of this paper. Elaborate search
distributions for known vectors of phytopa- strings can be designed, then saved for re-
358
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loading later. The lists generated from these Japan and China were assigned to the Palear-
searches can be compared in many ways (e.g., ctic Realm. Indonesia, however, was divided
shared records, unshared records), all within in the database along biogeographic realm
Biota, and the resultant lists can be exported lines, western Indonesia pertaining to the
(Appendix 1). For this investigation, search Indomalaysian Realm and eastern to the
strings consisted of lists of countries (and in Oceanian Realm (the division falling just east
some cases regions, e.g., "Europe Central and of the Philippines and Sulawesi and between
Northern") categorized by latitude in incre-
Bali and Lombok Island, corresponding to
ments of 10°, and by biogeographic realm.
Wallace's line (from MAYR 1944; Fig 1).
The country-level
nature of the data intro-
duces some artifacts, as
many countries span the
limits of the 10° latitude I M«U0
intervals and some even Wallace - Line (from Huxley) 1368
span two biogeographic
realms. Below 1 have Wallace-Line (from Mayr) 1M4
attempted to give some
measure of the influence
of these artifacts.
For breakdown by
latitudes, all species
occurring from a country
falling in an increment
were counted, regardless
of the species' distributi-
on within that country.
Species of countries
spanning more than 10°
latitude were therefore — .Maraupialia - Border
counted multiple times,
i.e., counted as present
in every increment in which their country
The biogeographic realms for the data Fig. 1
occurs. Consequently, a species with a restric- reported below were as follows. The Afrotropi- (after HEPPNER 1991). Various lines that
ted distribution within a large country would have been used as limits of biogeogra-
cal Realm (formerly known as the Ethiopian
phic realms in southeast Asia. In this
be counted as present in 10° latitude bands Realm) includes sub-Saharan Africa and the paper, Wallace's line (from MAYR 1944)
where it does not actually occur, and the over- southwest coiner of Arabia. The Australian was used to distinguish the Indoma-
lap between increments and richness within Realm is composed of Australia and the near- laysian from the Oceanian Realm.
one or more latitude intervals would be over- by Coral Sea Islands. The Indomalaysian
estimated. Realm includes India, Asia (south of Hima-
layas), and western Indonesia. The Palaearctic
Categorizing countries by biogeographic
Realm includes Europe, Asia (north of the
realm posed a different challenge. The coun-
Himalayas), very northern Africa, and most of
tries China, Japan, Mexico, and the United
Arabia. The Nearctic Realm includes North
States of America span two biogeographic
America (including Mexico) and Greenland.
realms, but the country-level data in the data-
The Neotropical Realm includes Central
base precluded dividing the fauna of the two
America, South America, West Indies, and
elements in each country. For example,
the Galapagos Islands. The Oceanian Realm
although southern Florida and southern Mexi- includes Hawaii, eastern Indonesia, Microne-
co have tropical climates (and faunas), the sia, New Guinea, New Zealand, Polynesia, and
entire United States and entire Mexico were many other islands. Countries of the Oceanian
assigned to the Nearctic Realm. Likewise, Realm include: American Samoa, Ashmore &
359
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Cartier Islands, Baker Island, Clipperton centage. Like many simple measures of over-
Island, Cook Islands, Easter Island, Fiji, lap, C is affected strongly by sample size. For
Table 1.
Cicadellid generic and specific richn- French Polynesia, Guam, Hawaii, Howland example, the comparison of two samples, one
ess, average number of species per Island, Jarvis Island, Kiribati, Mariana Islands, with 30 genera and the other with 100, will
genus, number of known vector spe- necessarily have at least 70 genera unique, and
Marshall Islands, Micronesia Federated States,
cies, and number of vectors expected thus a high complementarity, even if all 30
by chance the biogeographic realms Midway Islands, Nauru, New Caledonia, New
genera of the first sample occur in the second.
arranged generally by continuity. The Zealand, Niue, Norfolk Island, Palau, Palmyra
chance probability is based on 148 For this reason the total observed generic
Atoll, Papua New Guinea, Pitcaim Islands,
known vectors for 18,386 species, or richness is reported for each comparison, as
0.008 vectors/species. Solomon Islands, South Georgia and Sand-
well as the actual number of genera shared
between each pair of biogeographic realms.
Realm Gen. Spp. Spp./Gen. Vector spp. Expected
by chance
Results
Australian 200 500 2.5 8 3
Oceanian 168 604 3.6 5 5
Biogeographic Realms
Indomalavsian 569 2380 4.18 18 19
Afrotropical 399 1378 3.45 5 11 While many genera occur in multiple bio-
Palearctic 469 2166 4.62 31 17 geographic realms, almost none occurred in all
Nearctic 447 3802 8.51 97 30 of them. There were only seven truly cosmo-
Neotropical 730 4130 5.66 25 33 politan genera: Balclutha, Cicadella, Dekoce-
Australian 1 30 58 38 46 17 19
Oceanian 91 (338) _ 33 40 17 30 29
Indomalavsian 92(711) 95 (704) 106 33 57 54
Afrotropical 93(561) 92(527 88 (862) . 102 38 41
Palearctic 93 (623) 97 (620) 97 (1005) 87 (766) _ 90 49
Nearctic 97 (630) 95 (585) 94 (959) 96 (808) 89 (826) _ 199
Neotropical 98(911) 97 (869) 96(1245) 96 (1088) 96(1150) 80 (978) _
Australian Oceanian Indomalavsian Afrotropical Palearctic Nearctic Neotropical
Total genera: 200 168 569 399 469 447 730
wich Islands, Tokelau, Tonga, Tuvalu, Vanua- phalus, Empoasca, Exitianus, ldiocerus, and
Table 2.
Cicadellid generic complementarity tu (formerly New Hebrides), Wake Island, "Xestocephalus, and among their 1,365 species
(to the left of the diagonal) and the Wallis & Futuna Islands, and Western Samoa. there are only two known vectors of phytopa-
number of shared genera (to the right
The richnesses and affinities of the Holarctic thogens.
of the diagonal) of the biogeographic
realms arranged generally by conti- region (a combination of Nearctic and Palear- The generic and specific richness per bio-
nuity. Cell values for complementari- ctic Realms) and the Greater Antilles (sou-
geographic realm for Cicadellidae are given in
ty are % C (text equation 1) and, in
theastward to Dominica) also were examined.
parentheses, total observed generic Tab. 1 and the generic richness for Deltoce-
Generic faunas of biogeographic realms
richness (Sjk).
phalinae and Typhlocybinae are listed on the
were compared using two measures: one of
bottom of Tables 3 and 4, respectively. For
similarity, as the absolute number of shared
Cicadellidae overall, generic richness peaks in
genera, and one of difference, as the measure
the Indomalaysian and Neotropical Realms,
of complementarity (C, of COLWELL & COD-
exceeding the next most generic-rich Realm
DINGTON 1994). As a straightforward measure
(the Palearctic) by 100 and 261 genus-groups,
of the extent that two samples are comple-
respectively. The Realms with the most descri-
mentary, C is the proportion of the pooled spe-
bed species, however, are the Neotropical and
cies richness (Sjk, in samples j and k) that is
unique to either sample (fjk). That is, Nearctic. The richest realms for genera of Del-
tocephalinae and Typhlocybinae are the Near-
c = u /s (i)
jk jk ctic and Indomalaysian, respectively.
So, for example, two samples of 75 species
that each have 25 unique and 50 shared will The generic overlaps and complementari-
have a complementarity of 0.5. C varies from ties among the biogeographic realms are given
0, when samples are identical (Ujk=O), to 1, in Tables 2-4- The most apparent pattern is
when the samples are completely complemen- that all the values are high, from 65% (Nearc-
tary (Ujk=Sjk), and can be expressed as a per- tic vs. Neotropical Typhlocybinae) to
360
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(Australian vs. Neotropical Cicadellidae), The complementarity trends for Deltoce-
with the majority of values in the 90s. phalinae (Tab. 3) resembled those for Cicadel-
Table 3.
lidae regarding the importance of geographical
For Cicadellidae overall (Tab. 2), the Deltocephaline generic complementa-
proximity among realms and the lowest com-
Indomalaysian Realm generic overlap with rity (to the left of the diagonal) and
plementarity values, with three exceptions: the number of shared genera (to the
the Neotropical Realm is second only to the
(1) a comparison that resulted in one of the right of the diagonal) of the biogeo-
Nearctic. That surprise is not reflected in the lowest distinctnes values (C of 79%) was that graphic realms arranged generally by
complementarity values for the Neotropical between the Australian and Oceanian continuity. Cell values for comple-
mentarity are % C(text equation 1)
Realm, however, which gradually decrease Realms; (2) the complementarity of the Indo-
and, in parentheses, total observed
from the furthest to closest biogeographic malaysian and Oceanian faunas was lower generic richness (5jk).
Australian 11 14 14 15 7 6
Oceanian 79 (52) 17 14 16 10 6
Indomalavsian 89(123) 85(117) . 36 64 24 17
Afrotropical 89 (124) 88(121) 79(173) . 38 17 14
Palearctic 93 (223) 93 (219) 74 (245) 86(271) _ 49 16
Nearctic 97 (260) 96 (254) 92(315) 95 (322) 87 (390) _ 59
Neotropical 97 (203) 97 (200) 94 (263) 95 (267) 96 (365) 83 (351) _
Australian Oceanian Indomalavsian Afrotropical Palearctic Nearctic Neotropical
Total genera: 33 30 104 105 205 234 176
Australian 10 12 6 10 4 3
Oceanian 73 (37) . 20 6 13 8 4
Indomalavsian 95 (245) 92 (250) . 27 68 14 8
Afrotropical 95(111) 95 (124) 91 (313) . 25 8 5
Palearctic 92 (123) 90 (133) 76 (288) 87(191) . 24 9
Nearctic 95 (75) 90(84) 95 (288) 95(154) 84(154) _ 31
Neotropical 96(71) 96 (84) 97 (289) 97(152) 95 (164) 65 (88) _
Australian Oceanian Indomalavsian Afrotropical Palearctic Nearctic Neotropical
Total genera: 17 30 240 100 116 62 57
realms. Likewise, geographical proximity cor- than that found between the Afrotropical and Table 4.
responds to the complementarity values with Palearctic; and (3) the lowest complementari- Typhlocybine generic complementari-
ty (to the left of the diagonal) and
Australian and with the Nearctic Realms. The ty value was between the Indomalaysian and
the number of shared genera (to the
highest generic overlaps do correspond to the Palearctic comparison, which for all Cicadelli- right of the diagonal) of the biogeo-
lowest complementarity values, as expected dae had been one of the highest values. graphic realms arranged generally by
continuity. Cell values for comple-
for the following comparisons: between the The complementarity trends for Typhlocy-
mentarity are % C(text equation 1)
Nearctic and Neotropical Realms, the binae (Tab. 4) also resembled those for all and, in parentheses, total observed
Afrotropical and Palearctic Realms, and the leafhoppers but, as for the deltocephalines, generic richness (Sjk).
Afrotropical and Indomalaysian Realms. Alt- there was a strong affinity (high generic over-
hough the Holarctic is often treated as a bio- lap and low complementarity) between the
geographic region, in leafhoppers only 90 Australian and Oceanian Realms and between
genus-groups (Appendix 1) occur in both the the Indomalaysian and Palearctic Realms
Palearctic and Nearctic components, and The generic richness, overlap, and com-
complementarity, a measure of distinctness, is plementarity of the Greater Antilles (south-
greater than the three pairs of biogeographic ward to Dominica) with Mexico plus Central
realms just mentioned. America and with South America is given in
The influence of Mexico on the comple- Tab. 5. By all measures, the Greater Antillean
mentarity of the Nearctic and Neotropical fauna had closer ties to the Mexico plus Cen-
Realms was investigated by subtracting it from tral American fauna than to that of South
the Nearctic search string of countries and America.
adding it to the Neotropical one. This resulted Comparing the ratio of species per genus
in even less overlap between the realms (172 across biogeographic realm (Tab. 1), the ratios
genus-groups). The reclassification had no were higher in the biogeographic realms of the
effect on the list of cosmopolitan genera. New World than in those of the Old World.
361
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Latitudes
N 10-20° band for Deltocephalinae). Deltoce-
phalinae richness was distinctly higher (excee-
Looking from South to North, species
ding 1,800 species) in the three bands between
richness of Cicadellidae (Fig. 2) first exceeded
20° and 50° latitude. Typhlocybine species
2,000 species in the S 10-20° band, correspon-
richness was lower than that of deltocephali-
ding to much of Indonesia and Brazil. Generic
nes in all intervals except from N 0-20° latitu-
richness peaked in the N 0-10° band, while de. Species richness of both subfamilies peaked
species richness peaked in the N 20-30° band in the N 20-30° band, just north of the Tropic
and still exceeded 4,000 species in the N 40- of Cancer, and no doubt contributed impor-
tantly to the same peak for overall Cicadelli-
dae.
Taxon Greater Antilles Mexico & South America
Central America Comparing the ratio of species per genus
Cicadellidae 98 373 644
Oeltocephalinae 25 123 159 across latitude (Tabs 6, 7, Fig. 6) shows that
Typhlocybinae 27 42 40
the overall pattern for Cicadellidae closely
Complementarity Genera Shared
Greater Antilles Mexico South America Mexico South resembled that of Deltocephalinae, which
& C. America & C. America America
made up 37% of the genera and 37% of the
Cicadellidae 81 (396) 91 (680) 75 62
Deltocephalinae 84(128) 89(166) 20 18 species of all leafhoppers tabulated for this
Typhlocybinae 48(44) 67 (49) 23 16
paper. The ratios across latitude for Typhlocy-
binae contrasted sharply, spiking in the N 40-
Table 5: Generic richness (above) and complementarity and overlap (below) of Cicadel-
50° band.
lidae, Deltocephalinae, and Typhlocybinae faunas of the Greater Antilles (southeast-
ward to Dominica) compared to Mexico+Central America and to South America. Cell
values for complementarity are % C (text equation 1) and, in parentheses, total obser-
Vectors of Phytopathogens
ved generic richness (Sjk).
Latitudes Genus-groups Species-groups Spp./Genus Vector spp. Expected There are 148 known vectors among the
bv chance 18,386 species, or about 0.008 vectors/species.
S 50-60 181 396 2.19 9 3 This figure was used to calculate the expected
S 40-50 199 474 2.38 10 4 number of known vectors per fauna based on
S 30-40 490 1200 2.45 18 10 random distribution. The number of known
S 20-30 854 2863 3.35 19 23
phytopathogen vectors per biogeographic
S 10-20 898 3431 3.82 17 27
realm (Tab. 1) was higher than expected by
S 0-10 906 3710 4.09 12 30
chance in the Australian, Palearctic, and
N0-10 1181 5321 4.51 28 43
Nearctic Realms, and equal to or less than the
N 10-20 983 4327 4.4 52 35
N 20-30 957 5876 6.14 114 47 number expected by chance in the rest of the
N 30-40 666 4203 6.31 105 34 world. The number of known phytopathogen
N 40-50 656 4496 6.85 107 36 vectors per 10° latitude band (Tab. 6) was hig-
N 50-60 340 1518 4.46 56 12 her than expected by chance in most non-
N 60-70 294 1152 3.92 56 9 equatorial latitudes, with the highest numbers
N 70-80 283 967 3.42 52 8 (all more than double the number expected by
chance) in the N 20-50° bands.
Table 6. 50° band. Species overlap also peaked in the
Cicadellid generic and specific richn-
N 40-50° band, whether measured in absolu-
ess, average number of species per
Discussion
genus, and number of known vector te numbers (Fig. 3) or as the proportion of the
species of the 10° latitudinal bands combined total species in the latitude bands As discussed in Materials and Methods,
arranged by continuity. The chance
the patterns above are distorted by a number
probability is based on 148 known being compared (Fig. 4), exceeding 80%. Spe-
vectors for 18,386 species, or 0.008 cies overlap also exceeded 80% in the nort- of factors because they were based on country-
vectors/species. level data. Other factors also affect the accu-
hern and southern extremes.
racy of the results. Of foremost importance is
The patterns for Deltocephalinae and
that perhaps the majority of leafhopper species
Typhlocybinae (Fig. 5) differed from that of are undescribed, and the vector status of most
total Cicadellidae in that species richness did described species is unknown. The geographic
not increase markedly until further north (in spread of the undercounts resulting from all
the N 0-10° band for Typhlocybinae and the these factors are probably far from even, being
362
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7000
6000
5000
4000
E
300C
2000
Fig. 2.
Overall generic and species richness of
1000 Cicadellidae across latitude.
«P J^ >ö rt^ f&
O' 0' *O' r& rS>'
* * *
Latitude Band
Fig. 3.
4 500 Cicadellid species overlap among adja-
cent latitudinal bands expressed as
4000
absolute numbers. Higher values indi-
3500 cate count redundancy, in many cases
probably an artifact of the country-
300C level information used to generate the
2500 data rather than reflecting the actual
distribution of species.
2000
1500
1000
50o
C
Latitude Bands Compared
Fig. 4.
Cicadellid species overlap among adja-
cent latitudinal bands expressed as a
percentage of the combined total spe-
cies for compared latutude bands. Hig-
her values indicate count redundancy,
in many cases probably an artifact of
the country-level information used to
generate the data rather than reflec-
ting the actual distribution of species.
Latitude Bands Compared
363
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Fig. 5.
Generic and species richness of Delto- 2400
cephalinae and Typhlocybinae across
2200
latitude.
2000 Dell Gen
- - De« Spp
1800
— -Typti Gen I
1600 Typh Spp
i 1400
£ 1200
Z 1000
800
600
400
200
0
Latitude Band
Fig. 6.
1 2
Average ratio of species per genus
across latitude for Cicadellidae, Delto-
cephalinae, and Typhlocybinae. tn —"Cicadellidae spp per Genus
3
C 10 — Delt. Spp./Genus
0)
- -Typh Spp./Genus
O
8.
(0
0)
'5
8.
0)
2
Latitude Band
364
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concentrated in the equatorial and southern Among the equatorial biogeographic
latitudes except Australia. Also, there was no realms, the Afrotropical Realm was the least
account for elevation, topography, and other speciose. While this may be an artifact of
such variation that can drive diversification; undercollecting, the finding is consistent with
species of known agricultural importance are other organisms, from plants to mammals,
likely to have more complete distribution birds, and Lepidoptera (HEPPNER 1991, 1998).
information than other species; and despite
As expected, the Nearctic fauna, in terms
the attempts to reduce effects of relatedness
of all Cicadellidae, Deltocephaline, or
(phylogenetic effects) on patterns by looking
Typhlocybinae, had greatest affinity to the
for parallels with Cicadellidae in Deltocepha-
linae and Typhlocybinae, it was impossible to Deltocephalinae Tvphlocvbinae
eliminate this artifact. Latitudes Gen. Spp. Spp./Genus Gen. Spp. SppVGenus
Aside from these caveats, quite a bit can S 50-60 77 137 1.8 10 45 4.5
be gleaned from the results. S 40-50 84 156 1.9 14 52 3.7
S 30-40 158 319 2.0 40 129 3.2
S 20-30 218 569 2.6 74 228 3.1
Biogeographic Realms
S 10-20 188 498 2.6 92 304 3.3
Despite the strong influence of sample S0-10 153 408 2.7 151 425 2.8
size, the complementarity measure was found N0-10 180 635 3.5 304 1039 3.4
to be useful. In at least two instances (the N 10-20 199 824 4.1 263 1088 4.1
Neotropical/Indomalysian comparison and N 20-30 344 2188 6.4 270 1856 6.9
the Australian/lndomalysian comparison) the N 30-40 321 1899 5.9 140 1243 8.9
N 40-50 326 2044 6.3 129 1347 10.4
generic overlap gave the surprising result that
N 50-60 190 719 3.8 61 411 6.7
distant faunas had higher affinities than some
N 60-70 164 566 3.5 53 314 5.9
closer faunas, but those surprises were not mir-
N 70-80 158 505 3.2 50 230 4.6
rored by the complementarity values, which
supported a larger role of geographical proxi- Neotropical and Palearctic faunas, and in all Table 7.
mity in determining degree of distinctness. three cases it also shared more genera and had Deltocephaline and typhlocybine
generic and specific richness and aver-
Among all the realms, the Australian and a lower complementarity with the Neotropical
age number of species per genus of
Oceanian were the least speciose and their fauna. This was why Mexico was reclassified as the 10° latitudinal bands arranged by
complementarity with each other was lower described above. The result, that fewer genera continuity.
than either had to any other biogeographic were shared between the Nearctic and
realm. Curiously, the Oceanian leafhopper Neotropical Realms when Mexico was defined
fauna was less distinct from and shared more as Neotropical, can only be interpreted to
genera with the Nearctic than to the Palearc- mean that, overall, the Mexican leafhopper
tic in terms of overall Cicadellidae (Tab. 2), fauna has more affinity to the Neotropical fau-
though this situation was reversed in Deltoce- na than to the Nearctic fauna. While unsur-
phalinae (Tab. 3), and about equal to those prising to many, LlNNAVUORl (1959) struggled
two realms in Typhlocybinae (Tab. 4). Other with this issue in his revision of Deltocephalinae
patterns emerging from Tabs 3-5 are that most and related subfamilies and decided to define
biogeographic realms have distinct generic the Neotropical limit as "approximately in
faunas, with the highest affinities being bet- Costa Rica". Mexico has strong elements of
ween the Nearctic and Neotropical Realms, both faunas, and its long-term presence has
and between the Palearctic and both the allowed many genera to cross from one to the
Indomalaysan and the Afrotropical Realms. other realm: leaving Mexico entirely out of
Indeed, the Palearctic fauna had more in com- the comparison, the Nearctic and Neotropical
mon with that of sub-Saharan Africa than Realms still shared 129 genera and had a com-
with North America, suggesting that the cold plementarity of 86%, which is still lower than
northern temperatures have been a strong bar- any other comparison in Tab. 2.
rier to dispersal. The Afrotropical deltocepha- The Greater Antilles are well known for
line fauna was least distinct from the Indoma- their long isolation and high rates of ende-
laysian fauna while the latter was least mism (see LlEBHERR 1988). The high comple-
distinct from the Palearctic. mentarity values in the Greater Antilles corn-
365
© Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at
parisons (Tab. 5) bely high generic overlap countries which span two biogeographic
between the island leafhopper genera and the realms, could be assigned to the appropriate
western continental fauna, from 77-85% realm based on state or provincial distribution
depending on the group. Thus, the high com- to get a more accurate measure of realm over-
plementarity values result less from the ende- lap and affinities. For example, in Mexico the
mism and more from the great disparity in transverse volcanic range north of Veracruz
richness between the Greater Antilles and the and Chiapas states generally marks the
mainland faunas, because there were unavoid- Nearctic-Neotropical divide.
ably many genera that were unshared. Still, by
any measure the leafhoppers of the Greater
Latitudes
Antilles showed greater affinity with Mexico
and Central America than with South Ameri-
For cicadellids overall, both generic and
ca. This finding is consistent with data from
specific richness were highest in the tropics, as
many other organisms (see LlEBHERR 1988)
expected, except for a decline in the N 10-20°
and is likely due to the tectonic history of the
band. This decline cannot be explained simp-
Greater Antilles as a partial bridge between
ly as an artifact of low species overlap (Figs. 3,
North and South America in the late Creta-
4), so perhaps it reflects a species-area rela-
ceus and later, in the Paleocene, having
tionship in that there is less land mass in that
contact with the Yucatan and each other
latitude in the New World (Costa Rica
(WOODS 1989).
through mid Mexico). The lack of a decline in
The detailed examination of biogeogra- the more northern latitudes, however, appears
phic realm composition brings forth a cautio- to be an artifact. The presence of a few large
nary note regarding the biogeographic regions countries (USA, Canada, and Russia) in the
provided by OMAN et al. (1990) in their gene- northern latitudes caused a high species over-
ric check list. For example, among deltoce- lap there (Figs. 3, 4). This overlap is a
phalines, they reported that Parabolocratus measure of count redundancy, an artifactual
and Hecalus are cosmopolitan genera, but the boost in richness as discussed under Materials
former does not occur in the Australian Realm and Methods. This count redundancy peaked
and the latter does not occur in the Neotropi- in the 30-40°/40-50° comparison, at over
cal Realm. They indicate that Deltocephalus is 4,000 species (Fig. 3), representing over 80%
Holarctic, which is indeed where most species of the combined fauna (Fig. 4). In this con-
occur, but 5-32 species occur in each of the text, the supposed high richness from N 30-
other biogeographic realms. There are many 50° is not so surprising. The high species over-
other differences also, and even the species laps at the northern and southern extremes
database is far from complete. As our know- result from the almost identical country sets in
ledge of leafhoppers increases, additional these bands (e.g., S 40-50°: Argentina, Chile,
genera will undoubtedly show up in biogeo- and New Zealand; S 50-60°: Argentina, Chi-
graphic realms from which they are presently le, and Falkland Islands). Because the faunas
unrecorded and thus a later reassessment of are so depauperate at the extreme latitudes,
the composition and overlap of the biogeogra- however, the count redundancy did not trans-
phic realms is fully warranted once more data late into high species overlap (Fig. 3) or richn-
is captured. Until then, the generic lists in ess (Fig. 2).
Appendix 1 are offerred. More up-to-date lists
While count redundacy partially accounts
are available for Australia (M. Fletcher, at
for the high values of deltocephaline and
URL
typhlocybine species and generic richness in
http://www.agric.nsw.gov.au/Hort/ascu/start.ht the N 30-60° range (Fig. 5), the lower values,
m) and for many leafhopper subfamilies in the especially from S 20° -N 10° (Fig. 5), cannot
Neotropical Realm (M.A. Gaiani and P.W. be ignored and seem to indicate that these
Freytag, at URLhttp://cicadellidae.miza-fpo- taxa are, indeed, more common in the North.
lar.info.ve/). To what extent this represents a collecting
Certainly the species of China, Japan, bias will be revealed only when the faunas are
Mexico, and the United States of America, more completely known.
366