Arthropod Diversity in a Tropical Forest
Yves Basset,
1,2,3
*
Lukas Cizek,
2,4
Philippe Cuénoud,
5
Raphael K. Didham,
6
François Guilhaumon,
7
Olivier Missa,
8
Vojtech Novotny,
2,4
Frode Ødegaard,
9
Tomas Roslin,
10
Jürgen Schmidl,
11
Alexey K. Tishechkin,
12
Neville N. Winchester,
13
David W. Roubik,
1
Henri-Pierre Aberlenc,
14
Johannes Bail,
11
Héctor Barrios,
3
Jon R. Bridle,
15
Gabriela Castaño-Meneses,
16
Bruno Corbara,
17
Gianfranco Curletti,
18
Wesley Duarte da Rocha,
19
Domir De Bakker,
20
JacquesH.C.Delabie,
19
Alain Dejean,
21
Laura L. Fagan,
6
Andreas Floren,
22
Roger L. Kitching,
23
Enrique Medianero,
3
Scott E. Miller,
24
Evandro Gama de Oliveira,
25
Jérôme Orivel,
26
Marc Pollet,
27
Mathieu Rapp,
28
Sérvio P. Ribeiro,
29
Yves Roisin,
30
Jesper B. Schmidt,
31
Line Sørens en,
31
Maurice Leponce
20
Most eukaryotic organisms are arthropods. Yet, their diversity in rich terrestrial ecosystems is
still unknown. Here we produce tangible estimates of the total species richness of arthropods in
a tropical rainforest. Using a comprehensive range of structured protocols, we sampled the
phylogenetic breadth of arthropod taxa from the soil to the forest canopy in the San Lorenzo forest,
Panama. We collected 6144 arthropod species from 0.48 hectare and extrapolated total species
richness to larger areas on the basis of competing models. The whole 6000-hectare forest reserve
most likely sustains 25,000 arthropod species. Notably, just 1 hectare of rainforest yields >60% of
the arthropod biodiversity held in the wider landscape. Models based on plant diversity fitted the
accumulated species richness of both herbivore and nonherbivore taxa exceptionally well. This
lends credence to global estimates of arthropod biodiversity developed from plant models.
M
ost eukaryote species are terrestrial
arthropods (1), and most terrestrial
arthropods occur in tropical rainforests
(2). However, considerably greater sampling
effort is required in tropical arthropod surveys
to yield realistic estimates of global species
richness (3–7). A basic hindrance to estimat-
ing global biodiversity lies in a lack of empir-
ical data that establish local biodiversity, which
can be scaled up to achieve a global estimate.
Although many studies reported species richness
for selected groups of well-studied insect taxa,
no satisfactory estimate of total arthropod species
richness exists for a single tropical rainforest lo-
cation to date.
The unstructured collection and small-scale
survey of tropical arthropods cannot yield con-
vincing estimates of total species richness at a
specific forest (7–9). Most studies either target
few arthropod orders or trophic guilds, or use a
limited array of sampling methods, or ignore the
diverse upper canopy regions of tropical forests
(10–15 ). Moreover , sampling protocols have
rarely been structured in such a way that, with
increased sampling, incomplete data on local
diversity (7) can be extrapolated to estimate total
species richness across multiple spatial scales
(16). Where such structured estimates are made,
it is invariably for insect herbivores on their host
plants (5). However, species accumulation rates
may differ markedly for nonherbivore guilds,
which include more than half of all described
arthropod species (1, 17). As the degree of host
specificity (effective specialization) of other guilds
can be much lower than that of insect herbivores,
or may be driven by different factors (18, 19),
global estimates based on herbivores alone are
questionable. Consequently , extensive cross-taxon
surveys with structured protocols at reference
sites may be the only effective approach toward
estimating total arthropod species richness in
tropical forests (3).
To provide a comprehensive estimate of total
arthropod species richness in a tropical rainforest,
we established a collaboration involving 102 re-
searchers with expertise encompassing the full
breadth of phylogenies and feeding modes present
among arthropods (20). This consortium invested
a total of 24,354 trap- (or person-) days sam-
pling the San Lorenzo forest (SLPA) in Panama
using structured protocols (fig. S1). We identified
129,494 arthropods representing 6144 focal spe-
cies (Fig. 1 and table S1) from 0.48 ha of inten-
sively sampled mature forest. This allowed us to
extrapolate focal arthropod species richness to
a larger forest area with unprecedented power,
through a series of best-informed species richness
estimates derived from six competing models for
each of 18 focal data sets. Using taxon ratios to
estimate the species richness of nonfocal taxa
[see “Extrapolating results to nonfocal taxa” in
materials and methods (20)], we then predicted
the total species richness of the study area. We
also evaluated differences in relative species ac-
cumulation rates among arthropod guilds, across
spatial scales.
Although individual estimators adjusting for
different aspects of sampling design offered slight-
ly different estimates (Fig. 1B), the total spe-
cies richness for the entire San Lorenzo forest
(~6000 ha) was consistently quantified at be-
tween 18,000 and 44,000 species (including focal
and nonfocal species). In particular, the most like-
ly lower bound of species richness was estimated
to be at least 21,833 species [95% confidence
level (CL) = 18,665, 29,420; model a1 in Fig.
1B], and the biologically and statistically best-
supported estimate of richness (criteria outlined
in table S2) was 25,246 species (95% CL =
19,721, 33,181, model B+S in Fig. 1B). Accord-
ing to our estimates, a single hectare of rain-
forest will be inhabited by an average of 18,439
species (95% CL = 17,234, 18,575; Fig. 2B).
A relatively large proportion of the expected
species richness of the forest was recovered for
most of our focal taxonomic groups (Fig. 2). For
example, high proportions of all ant species and
of the parasitoid species targeted in our study
were collected from our 12 sites, whereas fungal
feeders would require more intensive sampling
to achieve adequate coverage (Fig. 2). Beta di-
versity of all arthropods (in the broad sense of
species turnover among sites) increased roughly
linearly with cumulative area surveyed (F
1,3
=
2422.5, P < 0.001). With increasing sampling
effort, sample coverage [an unbiased measure of
sample completeness, see (20)] was high and ac-
cumulated at significantly different rates across
different arthropod orders and guilds, and across
the various guilds comprised by beetles (Fig. 3).
However , despite the high sample coverage val-
ues, we cannot discount the possibility that there
were some vanishingly rare species that may not
have been discovered with the sampling proto-
cols used in this study.
Despite idiosyncrasies in the rate of increase
in sample completeness across insects groups,
the high proportion of overall species richness
detected at small spatial scales (Figs. 2 and 3)
has a remarkable consequence. Based on a gen-
eral relationship between species numbers and
area,weestimatethatalmosttwo-thirds(64%)
of all species in SLPA occur in a single hectare
of rainforest (Fig. 2). Our plant models predicted
total arthropod richness in the San Lorenzo forest
to a precision of 1% (correlation between rich-
1
Smithsonian Tropical Research Institute, Panama City, Re-
public of Panama.
2
University of South Bohemia, 370 05
Ceske Budejovice, Czech Republic.
3
Universidad de Panamá,
Panama City, Republic of Panama.
4
Czech Academy of Sciences,
370 05 Ceske Budejovice, Czech Republic.
5
Muséum d’histoire
naturelle de la Ville de Genève, 1208 Genève, Switzerland.
6
The University of Western Australia and CSIRO Ecosystem Sci-
ences, 6009 Perth, Australia.
7
Catedra Rui Nabeiro, Universidade
de Évora, 7004-516 Évora, Portugal.
8
University of York,York
YO10 5DD, UK.
9
Norwegian Institute for Nature Research, 7485
Trondheim, Norway.
10
University of Helsinki, 00014 Helsinki,
Finland.
11
University of Erlangen-Nuremberg, 91058 Erlangen,
German y.
12
Santa Barbara Museum of Natural History, Santa
Barbara, CA 93105, USA.
13
University of Victoria, Victoria, BC
V8W 2Y2, Canada.
14
Cirad, 34988 Montferrier-sur-Lez, France.
15
University of Bristol, Bristol BS8 1UD, UK.
16
Universidad
Nacional Autónoma de México, México 0510 DF, México.
17
Uni-
versité Blaise Pascal, 63000 Cl ermont-Ferrand, Fran ce.
18
Museo Civico di Storia Naturale, 10022 Carmagnola, Italy.
19
Centro de Pesquisas do Cacau, 45600-000, Itabuna, and
Universidade Estadual de Santa Cruz, 45662-900 Ilhéus-Bahia,
Brazil.
20
Institut Royal des SciencesNaturelles de Belgique, 1000
Brussels, Belgium.
21
University of Toulouse III, 31062 Toulouse,
France.
22
Universität Würzburg, 97070 Würzburg, Germany.
23
Griffith University, Nathan QLD 4111, Australia.
24
National
Museum of Natural History, Washington, DC 20008, USA.
25
Centro Universitário UNA, 30350-540 Belo Horizonte-MG,
Brazil.
26
CNRS, 97379 Kourou, France.
27
Research Institute for
Nature and Forest, 1070 Brussels, Belgium.
28
Muséum d’hi stoire
naturelle, 2000 Neuchâtel, Switzerland.
29
Universidade Fed-
eral de Ouro Preto, 35400-000 Ouro Preto-MG, Brazil and
Universidade dos Açores, 9700-851 Terceira, Portuga l.
30
Uni-
versité Libre de Bruxelles, 1050 Brussels, Belgium.
31
Natural
History Museum of Denmark, 2100 Copenhagen, Denmark.
*To whom correspondence should be addressed. E-mail:
bassety@si.edu
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ness estimates provided by the plant model and
best estimates: r = 0.992, P < 0.0001, N = 18;
Fig. 1C). Notably, small discrepancies between
observed arthropod species richness and esti-
mates derived from floristic diversity appeared
not to be scale-dependent (Fig. 1D). Hence, even
for arthropod guilds other than herbivores, plant
diversity seems a powerful predictor of species
richness across areas varying in size (at least
within the limits of our study design and given
the limited heterogeneity of the study area com-
pared to larger geographical scales).
Because this study targeted the full spectrum
of arthropods, it offers a comprehensive test of
previous estimates of species richness based only
on selected guilds or taxa. Reassuringly , our well-
resolved estimates of tropical arthropod species
richness are of the same order of magnitude as
prior estimates (table S3), adding credence to
recent estimates of tropical arthropod diversity
(5, 21). Although the scope for direct compar-
ison is limited because of regional differences in
sampling effort, lowland tropical forest in Panama
seems to support 2.1 to 8.4 times as many ar-
thropod species as observed in temperate forests
(table S3). While this supports the obvious truism
that tropical arthropods are indeed more diverse
than their temperate counterparts (22), the mag-
nitude of that difference is far lower than many
previous estimates would suggest (2).
Fig. 1. Number of arthropod species estimated at SLPA (20). (A)Numberof
species (closed bars, log scale) and individuals (open bars, log scale) collected
in 0.48 ha for each data set (three-letter guild code as in table S1) and number
of species estimated in SLPA (best estimate, shaded boxes). Numbers above
bars identify the best model used for calculation (a1 to a6, fig. S2) and the
percentage of singletons. (B) Number of arthropod species estimated for SLPA
(dots: all focal taxa; shaded boxes: focal and nonfocal taxa; table S4), as
estimated by different methods: B+S: best estimates, including both biological
and statistical arguments (table S2); B+Sloc: same as B+S but estimates
calculated with local instead of global ratios (fig. S3); S: best estimates, in-
cluding only statistical arguments; and models a1 to a5. ?: optimization al-
gorithms did not converge to allow calculations of CL. Our estimates are robust
to even moderate to large shifts in taxon ratios (table S5). (C)Plotofthe
number of species estimated in SLPA with the plant model against that es-
timated with the best model, for each data set. Line denotes unity. (D)Plotof
the percentage error between all arthropod species observed and estimated by
the plant model against cumulative number of sites. Shaded boxes indicate
means and 95% CL.
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The implications of the results observed on
a local scale are clear. For every species in the
well-known vascular flora (1294 species), avifauna
(306 species), and mammalian fauna (81 species)
of SLPA, we estimate that there will be a mini-
mum of 17, 71, and 270 arthropod species, re-
spectively (based on lower bound of species
richness) and most likely as high as 20, 83, and
312 arthropod species, respectively (table S3).
Based on the dominance of arthropod species
in the tropical fauna (table S3), we may then ar-
gue that conservation planning for biodiversity
should be largely determined by the spatial scaling
of arthropod diversity . In this context, the asso-
ciation between the species richness of plants and
arthropods detected across spatial scales suggests
that conservation efforts targeted at floristically
diverse sites may also serve to conserve arthro-
pod diversity across both taxonomic lineages
and trophic guilds. As arthropods are notoriously
labor-intensive to survey, such an “umbrella” ap-
proach may be an efficient way forward.
Nonetheless, our findings also suggest that
large-scale, region-wide understanding of trop-
ical arthropod richness may actually be more
achievable than previously assumed. Our data
indicate that a thorough sampling of 1 ha of rain-
forest may reveal nearly two-thirds of all ar-
thropod species present in a much larger area
(6000 ha in our case; Fig. 2B), consistent with
Fig. 2. Accumulation of species richness with area at SLPA (20). For all
groups, a high proportion of overall species richness was detected at small
spatial scales. (A) Partitioning of species richness within arthropod guilds
at different spatial scales (a: single site of 0.04 ha; b3: three sites spaced
apart totaling 0.12 ha; b6: six sites totaling 0.24 ha; b12: 12 sites totaling
0.48 ha; bha: 1.0 ha; bSLPA: 6000 ha; means T SEM are shown for a, b3,
and b6). (B) Species-area models for the main arthropod groups and large
data sets (for all arthropods, including nonfocal species, values are indi-
cated but the curve not plotted for the sake of clarity). Each curve is
characterized by its function (Ex, Exponential; Lo, Lomolino; Po, Power; We,
cumulative Weibull), its value for 1 ha (intersection with vertical line,
shaded boxes with mean and 95% CL), and the percentage of the number
of species present in 1 ha relative to the number of species estimated to
occur in SLPA.
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reports of relatively low beta diversity of insect
herbivores in tropical rainforests (23). Hence,
to determine the species diversity of a tropical
rainforest, the total area sampled need not be
overly large—provided that the sampling design
adequately covers both microhabitats and plant
species. However, this does not imply that most
arthropod species have self-supporting popula-
tions in small forest areas or fragments.
On a global scale, our results have implica-
tions for current estimates of total species rich-
ness, which have been weakened by the lack of
knowledge regarding the strength of association
between vascular plant species and nonherbivore
guilds (5). Based on the close association ob-
served here between floristic diversity and both
herbivore and nonherbivore species richness, we
tentatively conclude that the most recent estimate
of global tropical arthropod species [6.1 million
arthropod species (24)] does not require drastic
correction to account for differential scaling rela-
tionships of nonherbivore taxa. The robust es-
timates of local arthropod diversity derived in our
study thus support previous estimates of global
species richness. They also show how stratified
sampling designs and broad scientific cooper-
ation may be developed to formulate efficient
estimates of tropical arthropod diversity. Similar
initiatives have recently been implemented in
other tropical locations around the world, using
the current template as a foundation (25).
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Acknowledgments: IBISCA-Panama is an initiative of
Pro-Natura International, Océan Vert, the universities Blaise
Pascal and of Panama, and the Smithsonian Tropical Research
Institute (STRI), with core funding from SolVin-Solvay SA, STRI,
the United Nations Environment Programme, the Smithsonian
Institution (Walcott Fund), the European Science Foundation,
and the Global Canopy Programme. J. Herrera, E. Andrade,
M. Samaniego, S. J. Wright, N. Baiben, S. Bechet, J. Belleguic,
T. Aubert, K. Jordan, G. Ebersolt, D. Cleyet-Marrel, L. Pyot,
O. Pascal, P. Basset, and E. Bauhaus helped with logistics
in the field. A. Barba, R. Cabrera, A. Cornejo, I. Díaz,
A. F. R. do Carmo, I. C. do Nascimento, E. A. dos Santos,
M. González, A. Hernandez, M. Manumbor, M. Mogia,
S. Pinzón, B. Pérez, L. S. Ramos-Lacau, and O. Valdez helped
with initial sorting of the arthropod and plant material. Data
(as of 10 May 2012) have been deposited in the Dryad
repository: http://dx.doi.org/10.5061/dryad.f 3p75.
Supplementary Materials
www.sciencemag.org/cgi/content/full/338/6113/1481/DC1
Materials and Methods
Supplementary Text
Figs. S1 to S3
Tables S1 to S5
References (26–151)
29 June 2012; accepted 1 November 2012
10.1126/science.1226727
Fig. 3. Average sample coverage [TSEM; error bars, see methods (20)] plotted against the cumulative number of sites surveyed, for the main (A)arthropod
guilds and orders and (B) beetle guilds. For the sake of clarity, SEMs are omitted in (A).
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