Supplementary Online Material s2

1 SUPPLEMENTARY ONLINE MATERIAL

3 Assessing trophic position from nitrogen isotope ratios: effective

4 calibration against spatially varying baselines

1 1 2 1 6 Paul Woodcock , David P. Edwards , Rob J. Newton , Felicity A. Edwards ,

3 2 1 7 Chey Vun Khen , Simon H. Bottrell , Keith C. Hamer

9 1Institute of Integrative and Comparative Biology, University of Leeds, Leeds, LS2 9JT, UK

10 2School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.

11 3Sepilok Forest Research Centre, Sandakan, Sabah, Malaysia

13 Corresponding author: Paul Woodcock; email: [email protected]

15 Table S1: Details of approaches to baseline correction in 34 recent stable isotope studies

16 conducted in terrestrial ecosystems.

17 Table S2: Mean and standard deviation for repeated isotope analyses of ant and plant

18 samples.

19 Table S3: Standard deviations of random effects in linear mixed models.

20 Figure S1: Variation in plant δ15N values between transects, with and without samples of

21 the Fabaceae. 2 22 Table S1: Approaches to baseline correction in recent stable isotope studies conducted in terrestrial ecosystems Study # distinct consumer # spatially Max. distance between Baseline # Question, study taxa and sampling sites distinct baselines sampling locations material Sa ecosystem recognised used to interpret assumed to have a mp data constant baselinea les pe r ba seli ne Duyck et al. ? - but total sampling area is N/ Examine effects of cover crops on N 4 0 and 2b N/A (2011) 920m2 A arthropod food web structure o Pisanu et al. N/ Determine trophic positions of 2 b 4km N/A (2011) 0 and 1 A rats on a Subantarctic island δ15N used as a trait to assess B Bihn et al. N/ 12 0 ? – Not given N/A changes in ant functional diversity (2010) A a along a successional gradient O’Grady et ? – but sampling area is 4 x N/ Trophic ecology of ants in s 1 0 N/A al. (2010) 2km A temperate grassland. e Compare trophic positions of 4 Prochazka et N/ l 1 0 120m N/A understorey bird species across a al. (2010) A i forest-savannah ecotone Divergence in resource use Vidal and N/ n 5 0 and 2b 100km N/A amongst mainland and island Sabat (2010) A e lizard populations Investigate intra- and inter- Smith et al. N/ 4 0 c N/A colonial variation in diet of (2008) Several km A harvester ant castes Tillberg et al. N/ Inter and intra-colonial variation 2 0 ? – Not given N/A (2006) A in trophic position of ants Yi et al. N/ Describe food web in alpine 1 0 and 1b ? – Not given N/A (2006) A meadow 23

1 a No baseline means that the study effectively assumes that all sampling locations have a constant baseline of zero. 2 b A combination of uncorrected and corrected data were presented/analysed 3 c Principal conclusions on caste determination unaffected, because all castes are collected from all nests (thereby averaging out baseline variation), but cannot be 4 confident on whether intercolonial variation is genuine. Study # distinct # spatially Max. distance between Baseline # Question, study taxa and consumer distinct baselines sampling locations material Sam ecosystem sampling sites used to interpret assumed to have a ples recognised data constant baselinea per base line Pisanu et al. Leaf litter, grass Determine trophic positions of S 2 0 and 1b 4km ? (2011) and top soil rats on a Subantarctic island i Describe tropical forest food Hyodo et al. Leaves, litter, dead 1 1 ?- Not given ? web, including birds, mammals n (2010) wood and soil g and invertebrates Pollierer et ? – Not given, but sampling area Leaf litter and Describe soil food web in 6 1 15 l al. (2009) is 2000m2 roots temperate forest Traugott et Trophic positions of wireworm e 29 1 Several km Soil, plants 382 al. (2008) species in European farmland Sanders and Intraguild interactions between Moss, herbs and B Platner 5 1 ? – Not given 18 predatory arthropods in grass a (2007) grassland and meadow. Kupfer et al. Describe tropical forest food 1 1 < 50m Termites 11 s (2006) web. Yi et al. Describe alpine meadow food e 1 0 and 1b ? - Not given Herbivores ? l (2006) web. Describe soil invertebrate food Halaj et al. Plants, litter and i 5 1 ? - Not given 10 web in coniferous forest and (2005) soil n examine effects of thinning Schmidt et ? – Not given, but sampling area e 4 1 Plants and stubble 19 Soil food web in arable field al. (2004) is 2000m2 Tooker and Investigate trophic position of 15- Hanks 10 d >50 km Plants flower beetle on 2 plant species 1 29 (2004) in Illinois and Indiana prairies Omnivory and food web Blüthgen et ≈3km. Within-site sampling area 2 1 Leaves 37 structure in arboreal rainforest al. (2003) not givene ants 24

5 d Study presents data separately for beetles on 2 different plant species, with each plant species used as a separate baseline 6 e Models investigating interspecific variation in ant δ15N values included the δ15N value of the plant from which the ant was collected as a covariate. Study # distinct # spatially Max. distance between Baseline # Question, study taxa and consumer distinct baselines sampling locations material Sam ecosystem sampling sites used to interpret assumed to have a ples recognised data constant baselinea per base line Duyck et al. ? - but each baseline applies Examine effects of cover crops M 4 b Plants ? (2011) 0 and 2 to an area of 460m2 on arthropod food web structure u 3 hom l Gibb and Leaf litter, grass, ogeni Comparing ant community t Cunningham 12 12 <6m top soil sed across regenerating pastures (2011) i samp p les Hom l ogeni e sed samp Hawke and le Describe arthropod food web in 2 2 <5m Soil B Clark (2010) analy penguin burrows a sed in s dupli e cate 4-5 l Examine spatial variation in Menke et al. ? – Not given, but may be plant 4 4 Plants trophic position of i (2010) >100m speci chaparral/scrub ants n es e 1 hom s Smith and ogeni Trophic position of harvester ant 8 8 0m Seeds Suarez (2010) sed castes samp le Divergence in resource use Vidal and Sabat 5 0 and 2f 50km Seeds & fruits ? amongst mainland and island (2010) lizard populations El-Wakeil 2 2 30m Plants, soil and 25 Description of soil food web in (2009) litter coniferous forest 7 f 2 mainland sites and 3 island sites examined, each separated by ≈50-100km. Correction carried out at mainland and island levels. Within site distances not given. Kozhu et al. 5m in some analyses, 60- Description of arthropod and 10 g Plants ? (2009) 2 and 10 1000m in other analyses mammal food web on grasslands 3 repli cates of 3 McGlynn et al. Determining predictors of ant 7 7 <10m? Leaf litter hom (2009) d15n values ogeni sed samp les 1-7 per York and samp Compare trophic level within 5 5 ? – Not given Plants Billings (2009) ling and between fruit bat species locati on 25

8 g Data sometimes interpreted at the site level (= 2 distinct baselines) and sometimes at each of 5 sampling locations within each site (= 10 distinct baselines) Study # distinct # spatially distinct Max. Baseline # Samples Question, study taxa and consumer baselines used to distance material per ecosystem sampling sites interpret data between baseline recognised sampling locations assumed to have a constant baselinea Effect of humification on termite M Hyodo et al. Soil, leaf litter 6 2 1kmh 4-5 & earthworm δ15N values in (2008) & grass u forest & savannah Effect of disturbance on food l Takimoto et al. 36 36 <20m Leaves 5-10 chain length, focusing on lizards t (2008) & spiders i Daugherty and Trophic structure of arthropod 4 4 0m Leaves 10-31 p Briggs (2007) community in pear orchards Spatial variation in trophic Tillberg et al. l 6 6 ? – Not given Plants 6-21 position of invasive ant species (2007) e in woodland/pasture ? – Not Plants, leaf Effect on arthropod food web of Gratton and 36 4 given, but litter & soil 5-10 removing an invasive plant from Denno (2006) B >10m core salt marshes Mooney and a Spatial variation in ant omnivory Tillberg 6 6 0m Pine needles 5 s in pine forest (2005) e Schneider et Leaf litter and Niche differentiation in orbatid 4 4 5m 8 l al. (2004) bark mites in temperate forest. Davidson et al. 3 3 ? – Not given Leaves ? Herbivory and food web i (2003) structure in arboreal ant food n web of rainforests e s ( c o

9 h Within vegetation types, δ15N values differ by ≈1.5‰ n t d . ) 26 27 28 REFERENCES 29 30 31 Bihn JH, Gebauer G, Brandl R (2010) Loss of functional diversity of ant assemblages in secondary tropical forest. Ecology 91:782-792 32 Blüthgen, N, Gebauer G, Fiedler K (2003) Disentangling a rainforest food web using stable isotopes: dietary diversity in a species-rich ant 33 community. Oecologia 137:426-435 34 Daugherty MP, Briggs CJ (2007) Multiple sources of isotopic variation in a terrestrial arthropod community: challenges for disentangling food 35 webs. Environ Entomol 36:776-791 36 Davidson DW, Cook SC, Snelling RR, Chua TH (2003) Explaining the abundance of ants in lowland tropical rainforest. Science 300:969-972 37 Duyck P-F, Lavigne A, Vinatier F, Achard R, Okolle JN, Tixier P (2011) Addition of a new resource in agroecosystems: Do cover crops alter 38 the trophic positions of generalist predators? 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New Zeal J Zool 37:317-321 47 Hyodo F, Tayasu I, Konate S, Tondoh JE, Lavelle P, Wada E (2008) Gradual enrichment of 15N with humification of diets in a below-ground 48 food web: relationship between 15N and diet age determined using 14C. Funct Ecol 22:516-522 49 Hyodo F, Matsumoto T, Takematsu Y, Kamoi T, Fukuda D, Nakagawa M, Itioka T (2010) The structure of a food web in a tropical rain forest in 50 Malaysia based on carbon and nitrogen stable isotope ratios. J Trop Ecol 26:205-214 51 Kohzu A, Iwata T, Kato M, Nishikawa J, Wada E, Amartuvshin N, Namkhaidorj B, Fujita N (2009) Food webs in Mongolian grasslands: the 52 analysis of 13C and 15N natural abundances. Isot Environ Healt S 45:209-219 53 Kupfer A, Langel R, Scheu S, Himstedt, W, Maraun M (2006) Trophic ecology of a tropical aquatic and terrestrial food web: insights from 54 stable isotopes (15N). 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J Mammal, 90 90:1469-1477 15 91 Table S2: Mean and standard deviation (SD) of δ Nair values for repeated isotope analyses of

92 ants collected from within single sampling points: Lophomyrmex bedoti (Ant1),

93 Pachycondyla obscurans (Ant2 and Ant3), Paratrechina sp3 (Ant4) and Pseudolasius sp1

94 (Ant5) and sp2 (Ant6). The standard deviation for repeats of a homogeneous leaf sample

95 (EUP) run in several columns is also shown. Numbers of repeats analysed per sample are

96 shown in brackets.

Ants Plant

Sample Sample Sample Sample Sample Sample EUP

1 (5) 2 (3) 3 (3) 4 (3) 5 (3) 6 (3) (38) Mea n 5.77 6.89 7.54 6.03 5.64 5.46 0.00 (‰) SD 0.18 0.20 0.21 0.07 0.36 0.36 0.25 (‰)

98 99 Table S3: Standard deviation of random effects in linear mixed models of corrected ant δ15N

100 values versus local baseline for overall ant community, ant subfamily, and ant species

101 analyses within unlogged and logged forests. The greater the standard deviation, the more

102 variation is attributable to the random effect.

Overall Subfamily Species Unlogged Logged Unlogged Logged Unlogged Logged subfamily 1.85 1.58 - - 0.20 0.32 species (within subfamily) 0.96 0.86 - - - - species - - 1.01 0.87 - - 104 Figure S1: Mean plant δ15N values (‰) + for the entire dataset (n=160 plants; ALL) and for

105 each transect (n = 20 plants per transect) in (a) unlogged forest and (b) logged forest. Shaded

106 columns have Fabaceae samples removed for comparison. Transects are presented in rank

107 order, from highest plant δ15N value to lowest.

(a) 3.5 All leaf samples 3 Excluding Fabaceae samples 2.5 N 5 1

l 1.5 p

n 1 a e

0 ALL 1 2 3 4 5 6 7 8 -0.5 Sampling location in rank order 108

(b) Sampling location in rank order ALL 1 2 3 4 5 6 7 8

-0.5 N 5 1 δ

t -1 n a l p -1.5 n a e M -2 All leaf samples

Excluding Fabaceae samples 109 -2.5