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This research used resources of the Advanced Photon Source,
a U.S. Department of Energy (DOE) Office of Science User
Facility operated for the DOE Office of Science by Argonne
National Laboratory under Contract DE-AC02-06CH11357. This
work was supported by U.S. DOE, Basic Energy Sciences,
Materials Sciences and Engineering Division (gBCDI technique
and analysis), and by the National Science Foundation
CHE-1565945 (sample synthesis, electron microscopy). The
data reported in this paper are archived at Beamline 34-ID-C at
the Advanced Photon Source at Argonne National Lab and are
available upon request. All code, including the reconstruction
algorithm, is also available upon request. A. Y., W.C., and A.U.
designed and performed the BCDI experiment. A. Y. synthesized
the samples. All authors interpreted the results and contributed to
writing the manuscript.
Materials and Methods
Figs. S1 to S12
16 December 2016; accepted 30 March 2017
Higher predation risk for insect prey
at low latitudes and elevations
Tomas Roslin,1,2 Bess Hardwick,2 Vojtech Novotny,3,4,5 William K. Petry,6,7
Nigel R. Andrew,8 Ashley Asmus,9 Isabel C. Barrio,10,11 Yves Basset,3,4,12
Andrea Larissa Boesing,13 Timothy C. Bonebrake,14 Erin K. Cameron,15,16 Wesley Dáttilo,17
David A. Donoso,18 Pavel Drozd,19 Claudia L. Gray,20,21 David S. Hik,10 Sarah J. Hill,8
Tapani Hopkins,22 Shuyin Huang,23 Bonny Koane,5 Benita Laird-Hopkins,12
Liisa Laukkanen,24 Owen T. Lewis,21 Sol Milne,25 Isaiah Mwesige,26 Akihiro Nakamura,23
Colleen S. Nell,6 Elizabeth Nichols,13,27 Alena Prokurat,28 Katerina Sam,3,4
Niels M. Schmidt,29,30 Alison Slade,31 Victor Slade,31 Alžběta Suchanková,19 Tiit Teder,32
Saskya van Nouhuys,15 Vigdis Vandvik,33 Anita Weissflog,34
Vital Zhukovich,28 Eleanor M. Slade2,21,35
Biotic interactions underlie ecosystem structure and function, but predicting interaction
outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward
the equator, using a global experiment with model caterpillars to measure predation risk. Across
an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation
toward the equator, with a parallel pattern of increasing predation toward lower elevations.
Patterns across both latitude and elevation were driven by arthropod predators, with no systematic
trend in attack rates by birds or mammals. These matching gradients at global and regional
scales suggest consistent drivers of biotic interaction strength, a finding that needs to be
integrated into general theories of herbivory, community organization, and life-history evolution.
It is widely accepted that species diversity increases toward the tropics (1). This gradi- ent is so ubiquitous that it has been called one of the fundamental laws in ecology (2). However, whether this latitudinal variation
in diversity is paralleled by similar gradients in
the intensity of biotic interactions, both antag-
onistic and mutualistic (3–9), remains unclear.
A widespread view is that biotic interactions
become increasingly strong at lower latitudes
(10–12). However, accumulating evidence [e.g.,
(7, 8, 13, 14)] suggests that when critically ex-
amined, this pattern may be weak, absent, or even
reversed. Part of this complexity arises because
large-scale patterns are usually pieced together
from data obtained by a variety of methods and
protocols [e.g., (7, 15, 16)]. Here we use a simple,
uniform protocol to quantify ecologically impor-
tant patterns systematically at a global scale (17, 18).
Specifically, we assess predation risk using the at-
tack rate on model caterpillars (Fig. 1) for which
the identity of the attacker may be determined (19).
This method has been shown to provide accurate
estimates of predator activity at individual sites
and across local gradients (20, 21). By applying a
consistent method at a global level, our study
provides a rigorously controlled estimate of lati-
tudinal patterns in predation strength.
Building on general theory (3, 10, 11), we hypoth-
esize that overall biotic interaction strength in-
creases toward the equator. Many ecological
factors that change with latitude also change with
elevation, and thus it is important to control for
elevational variation when quantifying latitudinal
signals in predation rates. Moreover, by testing for
congruence between latitudinal and elevational
predation patterns, we can begin to identify can-
didate mechanisms underlying predation rates.
Regardless of where high predation rates are
found, depredation of herbivores is predicted to
have broad ecological and evolutionary conse-
quences across trophic levels. Stronger predation
on herbivores directly affects the abundance and
traits of herbivores (22–24), but also indirectly
affects the abundance and traits of plants through
trophic cascades (25, 26). Gradients in interaction
strength thus provide a foundation for under-
standing global patterns in ecosystem processes
742 19 MAY 2017 • VOL 356 ISSUE 6339 sciencemag.org SCIENCE
1Spatial Foodweb Ecology Group, Department of Ecology, Swedish University of Agricultural Sciences, Post Office Box 7044, SE- 750 07 Uppsala, Sweden. 2Spatial Foodweb Ecology Group, Department
of Agricultural Sciences, Post Office Box 27, FI-00014 University of Helsinki, Finland. 3Institute of Entomology, Biology Centre of the Czech Academy of Sciences (CAS), Branisovska 31, 37005 Ceske
Budejovice, Czech Republic. 4Department of Zoology, Faculty of Science, University of South Bohemia, Branisovska 1760, 37005 Ceske Budejovice, Czech Republic. 5The New Guinea Binatang
Research Center, Post Office Box 604, Madang, Papua New Guinea. 6Department of Ecology and Evolutionary Biology, University of California–Irvine, 321 Steinhaus Hall, Irvine, CA 92697-2525, USA.
7Institute of Integrative Biology, Eidgenössische Technische Hochschule (ETH) Zürich, Universitätstrasse 16, 8092 Zurich, Switzerland. 8Insect Ecology Lab, Centre of Excellence for Behavioural and
Physiological Ecology, University of New England, NSW, Australia, 2351, Australia. 9Department of Biology, The University of Texas at Arlington, Arlington, TX 76019, USA. 10Department of Biological
Sciences, University of Alberta, Edmonton, T6G 2E9 Alberta, Canada. 11Institute of Life and Environmental Sciences, University of Iceland, Sturlugata 7 IS-101 Reykjavik, Iceland. 12Smithsonian Tropical
Research Institute, Apartado 0843-03092, Panama City, Republic of Panama. 13Department of Ecology, University of São Paulo, Rua do Matão 321, T-14, CEP 05508-900, São Paulo, SP, Brazil.
14School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Rd, Hong Kong SAR, People’s Republic of China. 15Metapopulation Research Centre, Department of Biosciences, Post Office
Box 65, FI-00014, University of Helsinki, Finland. 16Center for Macroecology, Evolution and Climate Change, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15,
København, Denmark. 17Red de Ecoetología, Instituto de Ecología, CP 91070, Xalapa, Veracruz, Mexico. 18Instituto de Ciencias Biológicas, Escuela Politécnica Nacional, Ladrón de Guevara E11-253,
Quito, Ecuador. 19University of Ostrava, Faculty of Science–Department of Biology and Ecology, Chittussiho 10, 710 00 Slezská Ostrava, Czech Republic. 20Evolutionarily Distinct and Globally
Endangered (EDGE) of Existence, Conservation Programmes, Zoological Society of London, Regent’s Park, London NW1 4RY, UK. 21Department of Zoology, University of Oxford, South Parks Road,
Oxford OX1 3PS, UK. 22Zoological Museum, Biodiversity Unit, FI-20014 University of Turku, Finland. 23Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese
Academy of Sciences, Mengla, 666303 Yunnan, People’s Republic of China. 24Section of Ecology, FI-20014 University of Turku, Finland. 25University of Aberdeen, Zoology Building, Tillydrone Avenue,
Aberdeen AB24 2TZ, UK. 26Makerere University Biological Field Station, Post Office Box 409, Fort Portal, Uganda. 27Department of Biology, Swarthmore College, 500 College Avenue, Swarthmore, PA
19081, USA. 28State Institution of Education, Zditovo High School, Zditovo, Belarus. 29Arctic Research Centre, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark. 30Department of
Bioscience, Aarhus University, Frederiksborgvej 399, DK-4000 Roskilde, Denmark. 3140 Town End Lane, Lepton, Huddersfield, HD8 ONA, UK. 32Department of Zoology, Institute of Ecology and Earth
Sciences, University of Tartu, EE-51014 Tartu, Estonia. 33Department of Biology, University of Bergen, Post Office Box 7800, 5020 Bergen, Norway. 34Department of Plant Ecology, University of
Bayreuth, 95440 Bayreuth, Germany. 35Lancaster Environment Centre, University of Lancaster, Lancaster, UK.
*Corresponding author. Email: email@example.com