Seeddispersal Networks on the Canaries and the Galpagos

Global Ecology and Biogeography, (Global Ecol. Biogeogr.) (2015)

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SPECIAL Seed-dispersal networks on the Canaries ISSUE and the Galápagos archipelagos: interaction modules as biogeographical entities

M. Nogales1*, R. Heleno2, B. Rumeu1,3, A. González-Castro1,4, A. Traveset5, P. Vargas3 and J. M. Olesen6

1Island Ecology and Evolution Research Group ABSTRACT (CSIC-IPNA), La Laguna, Spain, 2Centre for Aim Mutualistic network parameters, such as modularity and nestedness, show Functional Ecology, Department of Life Sciences, University of Coimbra, Coimbra, non-random linkage patterns. Both increase network stability in different ways. Portugal, 3Real Jardín Botánico (CSIC-RJB), Modularity hampers extinction cascades, whereas nestedness resists network dis- Madrid, Spain, 4Departamento de Ciencias de assembly. We explore these parameters in seed-dispersal networks in two archipela- la Tierra, Universidad Estatal Amazónica, gos and the significance of life history, habitat, geography and phylogeny as drivers Puyo, Ecuador, 5Institut Mediterrani d’Estudis of linkage patterns and the applicability of modules as biogeographical entities. Avançats (CSIC-UIB), Palma de Mallorca, Location Canaries (Atlantic Ocean) and Galápagos (Pacific Ocean). Spain, 6Department of Bioscience, Aarhus University, Aarhus, Denmark Methods We compiled data on plant–seed disperser interactions from own observations and the literature, estimated network parameters describing interaction patterns (connectance, nestedness and modularity) and constructed a backbone phylogeny for the analyses. Results The Canarian network was highly nested but weakly modular, whereas the Galápagos network showed the opposite characteristics. Most key network species are native and have a favourable conservation status. Modularity in the Canaries is correlated with habitats (indirectly affected by altitude and orientation), whereas in the Galápagos it mainly reflects the functional roles of species. Main conclusions The divergent link patterns for the archipelagos imply that the highly nested Canarian network is stable against disassembly, whereas the modular Galápagos network may show strong resistance against extinction cascades. This *Correspondence: M. Nogales, Island Ecology difference may be driven by the specific evolutionary dynamics on the archipelagos. and Evolution Research Group (IPNA-CSIC), Keywords C/Astrofísico Fco. Sánchez no. 3, 38206 La Laguna, Tenerife, Canary Islands, Spain. Animal–plant interaction, fleshy fruit, food web, frugivory, insular network, E-mail: [email protected] modularity.

and modularity (Olesen et al., 2007). Their applicability in the INTRODUCTION context of biogeography and system stability is the focus of Biodiversity is much more than mere species lists, particularly this paper. as it also includes the myriad of ways in which species interact If a network has a highly heterogeneous structure of species (Pocock et al., 2012) and form spatio-temporally dynamic net- and their interactions, it is most often both nested and modular. works (e.g. Rasmussen et al., 2013). During the last two In a nested link pattern, a core of generalist species interact with decades, this upscaling in focus from species to networks each other and with specialists (Bascompte et al., 2003). In a has contributed signiﬁcantly to our comprehension of the modular link pattern, each module is a group of highly inter- complexity of biodiversity (Bascompte & Jordano, 2013). connected species, often sparsely linked together into a larger There are plenty of important milestones along this route, network (Olesen et al., 2007). In ecology, modules are extremely especially the concepts of nestedness (Bascompte et al., 2003) useful for our understanding of mutualistic systems such as

Table 1 General characteristics of the Canarian and Galápagos archipelagos and potential consequences for biodiversity.

Characteristics Canaries Galápagos Biodiversity consequences

Abiotic characteristics Land area (km2) c. 7900 c. 7500 Large area for immigration Number of islands (> 10 km2) 9 13 Large area for allopatric speciation Highest peak (m asl) 3718 1707 Large topographic area for immigration and speciation Maximum age of current islands (Ma) 21 4–6 Wide span of geological age Current minimum distance between archipelago c.98 c. 1000 Very different level of isolation and mainland (km) Volcanic activity in the last centuries High High Recurrent extinction events Climate Subtropical Equatorial Hotspots of diversity Mediterranean Biotic characteristics Main biomes 5 3 High habitat diversity Biodiversity (no. of species) High Medium High interaction potentiality No. of seed-plant endemic species (%) with respect to natives 537 (40.3%) 168 (38%) Strong signal for unique interactions No. of fleshy fruited species (%) with respect to natives 76 (5.7%) 34 (7.6%) Important plant component for ecological networks No. of vertebrate disperser species (%) with respect 30 (35.7%) 28 (65%) Important animal component for to native land vertebrates ecological networks plant–pollinator (Traveset et al., 2013) and plant–seed-disperser Here we integrate network theory and biogeography in a study networks (Donatti et al., 2011), but also in antagonistic systems of seed-dispersal networks on two oceanic archipelagos, the such as food webs (Dunne et al., 2002) and host–parasite net- Canaries (Atlantic Ocean) and the Galápagos (Pacific Ocean). works (Anderson & Sukhdeo, 2011). Within a module, species These archipelagos differ in geographical position and isolation, operate in dynamic ecological–evolutionary synchrony because age, elevation and mainland species source, but have quite a simi- of their high interconnectivity. Thus if modularity is strong, a lar land surface area and high interaction potentiality (Table 1). more relevant scale of analysis might be the module and not the We focused upon seed-dispersal modules in order to show their individual species or the whole network. A module may be seen value as functional entities in biogeographical analyses. as a coevolving niche (Gómez et al., 2015), a concept with wide The aims of our study were to: (1) estimate levels of implications for the study of coevolution, ecological conver- nestedness and modularity, identify modules and quantify gence, local co-occurrence, system stability, invasion/extinction, intermodule distances; (2) compare species and link composi- migration/dispersal, geography and phenological uncoupling/ tion of modules from the two archipelagos; and (3) identify local climate change (Thébault & Fontaine, 2010; Stouffer & and regional drivers of modularity. Finally, we discuss the results Bascompte, 2011; Aizen et al., 2012; Høye et al., 2013; for a in relation to system stability and the applicability of the module review of modularity, see Bascompte & Olesen, in press). Thus, concept as a biogeographical entity in studies of the ecology and insight into the link structure allows a deeper understanding of evolution of island interactions. biodiversity, for example with respect to regional/geographical patterns (e.g. Carstensen & Olesen, 2009; Dalsgaard et al., METHODS 2013), the impact of alien species (Valdovinos et al., 2009; Rodriguez-Cabal et al., 2013; Traveset et al., 2013) and system Study sites stability (Stouffer & Bascompte, 2011; Bascompte & Jordano, The archipelagos of the Canaries and the Galápagos (Appendi- 2013; Rodriguez-Cabal et al., 2013). ces S1 & S2 in Supporting Information) differ in several Seed dispersal is an essential phase in the process of regenera- respects, but also show important similarities (Table 1), for tion of plant communities and a strong driver of local biodiver- example in total land surface (7900 vs. 7500 km2, respectively) sity (Bascompte & Jordano, 2007). At the network level, most and number of islands (9 vs. 13 islands > 10 km2) and studies of seed dispersal have been carried out in mainland palaeoislands (6 vs. 7); however, the Canaries are older and communities (Jordano et al., 2003), and only a few on oceanic richer in plant species and main biomes (see Heleno et al., islands (Heleno et al., 2011a, 2013; González-Castro et al., 2011b; Padilla et al., 2012) (Appendix S3). 2012). This retards rigorous island–mainland comparisons (Schleuning et al., 2014), although as a general pattern we know Interaction matrices and network parameters birds and mammals are major mainland biotic dispersers (Herrera, 1995) whereas birds and reptiles often play this role on We compiled data about interactions from own field observa- oceanic islands (Nogales et al., 2005). tion of frugivory (over a time span of 10 years in the Canaries

2 Global Ecology and Biogeography, © 2015 John Wiley & Sons Ltd Modularity of seed–dispersal networks on oceanic islands and 6 years in Galápagos) and also included all records from an for network cohesion by gluing modules together; (3) module exhaustive literature review (Heleno et al., 2011b and references hubs (z ≥ 2.5, c < 0.62) have many links to other species in their therein). We also included all interactions involving non-native own module, and are important for module cohesion, and (4) species, with the exception of captive/cultivated species. A seed- network hubs or super-generalists (z ≥ 2.5, c ≥ 0.62) are both dispersal interaction was recorded if fruit was swallowed or connectors and module hubs (Olesen et al., 2007). removed from a plant by an animal, if undamaged seeds were Networks were visualized using the software Pajek v.2.05 found in droppings or pellets or if gut samples with intact seeds (Batagelj & Mrvar, 1998). The basic principle behind Pajek were obtained. In the Canaries, predatory birds such as the visualization is that distance between species expresses their kestrel and the meridional shrike indirectly disperse more than number of links to other species. 60 species by their predation of frugivorous lizards (Padilla et al., 2012). Such records of seeds in regurgitation pellets were Testing for phylogenetic signal in also included in the network. On both archipelagos, interactions network composition were gathered all year round with a greater effort during the main fruiting seasons. The phylogenetic signal of a trait in a sample of species expresses Interactions were compiled into two-mode binary adjacency the extent to which the phylogenetic structure of the community matrices of A animal species (matrix columns) interacting with accounts for morphological characters of the species. In order to P fleshy fruited plant species (matrix rows) (Tables S1 & S2). If estimate the importance of the phylogeny in explaining the vari- an interaction I between a plant and an animal species is rec- ation of trait values of our four communities (plants and dis- orded, its presence in the matrix cell is scored as ‘1’, if not as ‘0’. persers in the Canaries and in the Galápagos), we constructed a We estimated three network parameters: connectance, backbone phylogeny for each community. Plant phylogenies nestedness and modularity. Connectance C = 100I/AP is the were based on the supertree from APG III (Angiosperm percentage of realized interactions out of the total possible inter- Phylogeny Group, III, 2009), bird phylogenies from http:// actions in the network. Level of nestedness was measured with birdtree.org/ and Gallotia lizard phylogenies from Cox et al. the NODF algorithm (Almeida-Neto et al., 2008), and the (2010). As information on branch length was not available for all NODF value belongs to the interval [0 (not-nested); 1 (perfectly taxa and phylogenies, we used a taxonomic proxy, equalizing nested)]. Empirical NODF values were compared with distribu- branch lengths between species, genera and families. In order to tions of NODF values from 1000 random networks of similar run the R scripts, a few polytomies were resolved taxonomically size (Almeida-Neto et al., 2008). To test for modularity we used into dichotomies using branch lengths << 1. the software netcarto (Guimerà & Amaral, 2005), which We used two measures of phylogenetic signal, K and λ. assigns all plants and seed dispersers to modules. The level of Blomberg’s K compares the observed trait signal with a signal modularity M of a network expresses how strongly the network under a Brownian motion (BM) evolutionary model (Blomberg is partitioned into modules. As M approaches 0 or 1, the level of et al., 2003). If K ≈ 1, the trait is phylogenetically clustered in the modularity becomes weaker or stronger, respectively. Empirical sample of species. K ≈ 0 indicates a convergent or random M-values were compared with distributions of M-values from pattern, whereas K > 1 indicates a strong phylogenetic signal. 100 random networks of similar size (Olesen et al., 2007). The The significance of K is tested by comparing the observed signal null model assumes that the ranking of the species linkage levels with the mean of the signal from randomizations based on a null L (i.e. the number of links of each species) is like that of the model, which shuffles species randomly across the phylogeny. empirical network. We also recorded the size and composition of K was calculated using the package picante inR(Kembelet al., each module and the number of links between and within 2010). modules. We calculated the distance between each pair of Pagel’s λ measures how much trait correlations among modules (intermodule distance), defined as the number of species tell us about their shared evolutionary history. The value shared links between a pair of modules divided by the sum of all of λ ranges between 0 and 1; if λ≈0, the trait structure is not their links. If a module, on average, has a short distance to all influenced by phylogeny, whereas λ≈1 implies that the trait other modules, it has a high module centrality. follows a BM model. The lower and upper bounds of K and λ In addition, netcarto also assigns topological network roles (Table S3) indicate which of the two scenarios is the most likely. to all species based on their pattern of intra- and intermodule This analysis was performed using the packages picante and links (Guimerà & Amaral, 2005). The assignment of a role to geiger inR(Harmonet al., 2008). a species is determined by relative within-module degree or We tested for phylogenetic signal in each of the four commu- hubability (z), quantifying how well connected a species is to nities with respect to the distribution of a set of five network other species in its module, and among-module connectivity (c), traits (module affinity, module centrality, linkage level L,con- which quantifies how well distributed the links of a species are nectivity c and relative within-module degree or hubability z) among modules. We sorted all species into four categories: (1) and five species traits [body weight, fruit size, preferred habitat, peripherals (z < 2.5, c < 0.62) have few links inside their own origin (i.e. native or alien) and geographic distribution (i.e. module and rarely any to other modules; (2) connectors number of islands on which the species was present); see (z < 2.5, c ≥ 0.62) have a few links both to species in their own Table S3]. Species of the same module show module affinity, module and to species in other modules, i.e. they are important whereas species of different modules do not. A phylogenetic

Table 2 Descriptive parameters of seed-dispersal networks in the Table 3 Intermodule distance. Distance between modules i and j Canaries and Galápagos. calculated as their shared number of links ×100/(their total number of links). The module “Geospiza conirostris-Opuntia Canary Galápagos helleri” is an unconnected satellite module to the main network Islands Islands and therefore is not possible to calculate “intermodule distance” with the rest of modules. Number of seed-disperser species, A 30 28 Number of ﬂeshy fruited plant species, P 65 34 Canarian modules 1 23456 Animals to plants ratio (A/P) 0.46 0.82 Network size (S = AP) 1950 952 1 Laurel forest and large birds 6.3 5.2 5.5 1.1 7.0 Number of recorded interactions, I 325 153 2 Medium–large lizards 8.8 9.7 1.7 12 Modularity, M 0.31** 0.39** 3 Coastal shrubland 9.5 1.0 6.5

Number of modules, NM 66 4 Secondary seed dispersal 1.1 8.9 Connectance, c (100I/AP) 16.7 16.1 5 High mountain 1.7 Nestedness NODF 27.8** 12.6** 6 Thermophilous forest Average distance 5.7 Modularity (based on 100 randomizations) and nestedness (1000 randomizations); significance indicated by **P < 0.01 (Almeida-Neto Galápagos modules 1 2 3 4 5 6 et al., 2008). 1 Geospiza conirostris–Opuntia ––––– helleri signal with respect to module affinity tells us that taxonomically 2 Small–medium dispersers/ 21 14 13 23 related species tend to be in the same module. San Cristóbal As a measure of the phylogenetic signal for plant origin, 3 Western islands 3.0 12 15 we used Fritz and Purvis’ D (Fritz & Purvis, 2010), which 4 Tortoise–large mammals 5.0 7.8 was calculated using the R package caper (Orme, 2013): 5 Large finches/endemic rodent 8.6 6 Small finches/passerines D = (dobs – mean db)/(mean dr – mean db), where dobs is the number of character state changes needed to get the observed Average distance 12.24 character state distribution in our phylogeny, db is the expected distribution of d under a BM model (1000 runs) and dr is the expected distribution of d if character states are randomly dis- ‘laurel forest and large birds’ module was the most isolated. A tributed among species. We scaled dobs by dr and db in order make high proportion (49%) of all links were between modules comparisons possible across communities and archipelagos. (Table 4), i.e. intermodule distance was low. The network was D = 1 if the distribution of a trait in a community is independ- formed by two network hubs or super-generalists (the lizard ent of the phylogeny of the species; D > 1 if the trait is Gallotia galloti and the kestrel Falco tinnunculus), two module phylogenetically overdispersed; D = 0 if the trait is distributed hubs (the pigeons Columba bollii and Columba junoniae) and 30 according to a BM model; and D < 0, if the trait is more connectors (six seed dispersers and 24 fleshy fruited plants) phylogenetically clustered than expected according to a BM (Figs 1a & 2, Appendix S5). Besides, four of the six modules model (Nunn, 2011). were habitat-specific, namely high mountain, laurel forest, We also tested for any correlations between traits using thermophilous forest and coastal shrubland. Thus, an extensive phylogenetically independent contrasts (PIC), by means of the elevational habitat zonation enforced modularity (Appen- ape package in R (Paradis et al., 2004). dix S3). The other two modules were dominated by lizards and secondary seed dispersers (shrikes and kestrels; Appendix S5). The Galápagos network also consisted of six modules (Fig. 1b; RESULTS see Table S5 for information about modules and Appendix S6 for The Canarian and Galápagos networks had similar connectance information about species included in Fig. 1b).Only the modules (Table 2). However, species richness and nestedness were higher ‘small–medium dispersers/San Cristóbal Island’ and ‘western in the Canaries, whereas modularity and intermodule distance islands’ and ‘small-medium dispersers/San Cristóbal’ and ‘small were higher in the Galápagos (Tables 2 & 3; see also Appen- finches/passerines’ were strongly connected to each other. By dix S4). In other words, the different modules operated more contrast, the modules ‘western islands’ and ‘tortoise/large independently in the Galápagos. We also confirm the value of mammals’, and the ‘tortoise/large mammals’ and ‘large finches/ the seed-dispersal modules as study entities in biogeographical endemic rodent and large-seeded plants’ modules were poorly analyses. connected. The cactus Opuntia helleri and the finch Geospiza The Canarian network consisted of six interconnected conirostris made an independent small satellite module, uncon- modules (Fig. 1a; see Table S4 for information about modules nected to the main network. Only 37% of all links were between and Appendix S5 for information about species included in modules (Table 4). The giant tortoise Chelonoidis nigra was the Fig. 1a). The ‘medium–large-sized lizards’ and ‘thermophilous only network hub, the plant Miconia robinsoniana was the only forest and passerines’ modules were closely connected, while the module hub, and 10 species were connectors (four dispersers and

(A) * * * *

* MODULES Medium-large lizards

* High mountain * * * Thermophilous forest & passerines * * Coastal xerophytic shrubland * & bird/mammal

* Laurel forest & large birds * Secondary seed dispersal * * (B) *

* MODULES

Figure 1 Modular structure of the Tortoise/large mammals seed-dispersal network in the Canary * * Islands (A) and the Galápagos (B). The * Geospiza conirostris- * Opuntia helleri (satellite) outer ring of nodes represent ﬂeshy * * fruited plant species that are connected to * Small-medium dispersers/ seed-disperser species (inner ring) by S. Cristóbal Island links, representing frugivorous Large finches/endemic interactions. Modules are shown in rodent & large-seeded plants different colours/shades and species roles Western islands are labelled by different symbols. *

Asterisks indicate introduced species. For Small finches/passerines a list of the species included in the & small-seeded plants interaction networks see Appendices S5 & S6 for the Canary Islands and the * Galápagos, respectively. peripherals connectors module hubs network hubs six plants) (Figs 1b & 2, Appendix S6). One module was domi- Other traits showed phylogenetic signals, e.g. fruit size (‘fruit nated by the giant tortoise, together with cattle, pigs and goats, dm’). Phylogeny also influenced geographic distribution (‘no. of while the other modules were characterized by bird and reptile islands’) of Canarian seed dispersers and Galápagos fruiting seed dispersers. Thus, in contrast to the Canaries, functional plants. group affinity in the Galápagos disperser guild was a stronger In the phylogenies of Canarian plants and dispersers, and driver than habitat specificity. Galápagos dispersers, the trait ‘native versus alien’ was distrib- With regard to the drivers of modularity, K and λ gave quali- uted according to a Brownian motion model of evolution tatively similar results; network traits only showed some signifi- (D ≤ 0), indicating a phylogenetic signal. However, native and cant phylogenetic signals (Table S3). Canarian plants showed alien Galápagos plant species were distributed independently of phylogenetic clustering with respect to their ability to link dif- their phylogeny (D was closer to 1 than to 0). ferent modules (related plant taxa were important connectors), Several traits were correlated after correcting for phylogenetic and related taxa (e.g. species of finches) in Galápagos had a high dependency (Table 5), but the pattern differed strongly between linkage level. Body weight was a trait that was affected by phy- communities and between archipelagos. In the Galápagos, dis- logeny among both Canarian and Galápagos dispersers; the perser species sharing a module (‘module affinity’) had a more ‘tortoise/large mammals’ module from Galápagos strongly con- similar extent of geographical distribution (‘no. of islands’) than tributed to this. Habitat specificity (‘main habitat’) was influ- a random species set; by contrast, the other communities (Galá- enced by phylogeny in the Canarian disperser community and pagos plants and Canarian plants and dispersers) did not show both the plant and the disperser communities on the Galápagos. this correlation. The Canarian modules were more associated

Table 4 Number of species and links in modules of seed-dispersal networks of the Canary Islands and the Galápagos. Module connectance

CM is the proportion of realized links inside the module (i.e. number of observed links/number of possible links in the module, excluding links to other modules).

No. of No. of No. of No. of within- between- plant disperser module module

Module species species links links CM

Canary Islands Medium-large lizard 20 3 34 76 0.57 High-mountain 2 1 2 7 1.00 Thermophilous forest and passerines 11 4 37 70 0.84 Coastal xerophytic shrubland and bird/mammals 8 12 36 58 0.38 Laurel forest and large birds 14 7 35 44 0.36 Secondary seed dispersal 10 3 22 63 0.73 Total 65 30 166 318* − Galápagos Islands Tortoise–large mammal dispersers 8 4 13 11 0.41 Geospiza conirostris–Opuntia helleri 1 1 1 0 1.00 Small–medium dispersers/San Cristóbal Island 9 4 27 36 0.75 Large finches/endemic rodent and large-seeded plants 2 3 4 13 0.67 Especially two passerines (Geospiza scandens and Mimus parvulus), one dove 8 6 26 25 0.54 (Zenaida galapagoensis), the iguana Conolophus subcristatus and rich flora Especially five small passerines (Certhidea olivacea, Certhidea fusca, Camarhynchus parvulus, 6 10 26 27 0.43 Geospiza fuliginosa, Dendroica petechia) and endemic tree-like Miconia robinsoniana Total 34 28 97 112* −

*Number of between-module links is equal to the half of these values, because each between-module link is counted twice, i.e. from modules A to B, and from B to A.

Canaries Galápagos 8 Module hubs Network hubs Module hubs Network hubs ) z 6 Figure 2 Distribution of seed dispersers and ﬂeshy fruited plants according to 4 their network role (symbols as in Fig. 1)

2 in the Canarian and Galápagos archipelagos. Cut-off values (2.5 for z and

0 0.62 for c, see Material and Methods); Within-module degree ( each dot represents a species; white dots Peripherals Connectors Peripherals Connectors -2 are ﬂeshy fruited plants and grey dots 0 0.2 0.4 0.6 0.8 1 00.20.40.6 0.8 1 Among-module connectivity (C) Among-module connectivity (C) frugivores.

with habitats within islands. Large Canarian dispersers (‘body DISCUSSION weight’) had a central position in their modules (high z), whereas those speciﬁc large Galápagos dispersers had a high Although both oceanic archipelagos harbour rich communities habitat preference (‘main habitat’) and were dominated by with similar diversity of dispersers, connectance level, and the invasive alien mammals. The three main network parameters same number of modules, they differed considerably on overall (l, c and z) were positively correlated in all communities except plant diversity and on network topology. The robustness against c and z for the Galápagos plants. The most widespread Canarian disturbances of a network is inﬂuenced by levels of nestedness, fruiting plants (‘no. of islands’) had more links (L) and showed modularity and connectance. High nestedness (Thébault & more connectivity (c). Thus we see relationships between Fontaine, 2010), and also high modularity, may add stability to modular structure and body weight, habitat preference and a mutualistic network, but they do it in different ways native/alien status, and also between network characteristics and (Sebastián-González et al., 2015). The Canarian network was geographical distribution. highly nested and thus strongly coherent, resisting community

Table 5 Coefﬁcient of determination between traits (continuous/categorical) in communities of seed dispersers and their fruiting plants in the Canary Islands and the Galápagos after correcting for the inﬂuence of phylogeny (including introduced species).

Module log(body Main Native/ log(linkage Connectivity, Hubability, No. of centrality weight) habitat invasive level, L) c z islands

Canary Islands Seed dispersers Module affinity – n.s. n.s. n.s. 0.16* 0.27** n.s. n.s. Module centrality n.s. (−)0.46*** n.s. 0.14* 0.20** n.s. n.s. log(body weight) n.s. n.s. n.s. n.s. 0.19* n.s. Main habitat n.s. n.s. (−)0.11* n.s. n.s. Native/invasive n.s. n.s. n.s. n.s. log(linkage level, L) 0.87*** 0.75*** n.s. Connectivity c 0.48*** n.s. Hubability, z n.s. Galápagos Islands Seed dispersers Module affinity – n.s. n.s. n.s. n.s. n.s. n.s. 0.30** Module centrality (−)0.40*** n.s. (−)0.18* 0.14* 0.21** n.s. 0.14* log(body weight) 0.34*** 0.31** n.s. n.s. n.s. n.s. Main habitat 0.36*** n.s. n.s. n.s. n.s. Native/invasive (−)0.34*** (−)0.37*** (−)0.17* n.s. log(linkage level, L) 0.82*** 0.82*** n.s. Connectivity, c 0.63*** n.s. Hubability, z n.s. Canary Islands Fruiting plants Module affinity – (−)0.07* n.s. n.s. 0.16*** 0.17*** n.s. n.s. Module centrality n.s. (−)0.12** n.s. (−)0.28*** (−)0.21*** n.s. (−)0.05* Fruit dm n.s. 0.12** n.s. n.s. n.s. n.s. Main habitat n.s. n.s. n.s. (−)0.10** n.s. Native/invasive n.s. (−)0.08* n.s. n.s. log(linkage level, L) 0.80*** 0.22*** 0.30*** Connectivity, c n.s. 0.15** Hubability, z n.s. Galápagos Islands Fruiting plants Module affinity – n.s. n.s. n.s. n.s. n.s. n.s. n.s. Module centrality (−)0.11* n.s. n.s. 0.16* n.s. n.s. n.s. Fruit dm n.s. 0.13* n.s. (−)0.13* n.s. (−)0.48*** Main habitat 0.14* n.s. n.s. n.s. n.s. Native/invasive n.s. n.s. n.s. n.s. log(linkage level, L) 0.64*** 0.45*** n.s. Connectivity, c n.s. n.s. Hubability, z (–)0.09*

Significance level: *P < 0.05; **P < 0.01; ***P < 0.001; n.s., not significant. Module affinity is a binary variable, indicating if a species is member of the same module or not; module centrality is the number of between links of a module/(total number of links in a module), i.e. links from a given module to all other modules, divided by the total number of links of the module (no. links to other modules + no. links within the module). Minus signs in bracket indicate the direction of the correlation. disassembly, especially the extinction of rare species (Bascompte press). The strong coherence of the Canarian network is due to et al., 2003; Rodriguez-Cabal et al., 2013), whereas the Galápa- its many connectors (three times as many as in the Galápagos); gos network consisted of well-separated modules (intermodule these are animals moving between habitats, and plants with a distance was twice as large as the Canarian and the proportion of wide elevational range. In general, the Galápagos network is between-module links was considerably lower). According to functionally structured (assemblages of birds, lizards, tortoises that, the different modules operate more independently in the and their plants, and one introduced mammal module), whereas Galápagos. This pattern reduces the risk of coextinction cas- the Canarian network mainly reflects the underlying habitat cades (Rodriguez-Cabal et al., 2013; Bascompte & Olesen, in diversity (elevational zones: mountains, forests, coastland). Both

Global Ecology and Biogeography, © 2015 John Wiley & Sons Ltd 7 M. Nogales et al. are geographically well structured, and each module was often fortunately still mostly intact, with the exception of local extinc- located on one or a few islands. tions of giant tortoises on Galápagos. However, a closer look at the influence of differences in network structure, as observed on the Canaries and the Galápagos, upon extinction dynamics, Seed-dispersal networks and modules might be a fruitful future research programme that may expose The general trend that more diverse networks have more different colonization–extinction dynamics. modules (Olesen et al., 2007) was not observed in our study, even though the Canarian network had twice as many plant species as the Galápagos one. The reasons for this are: (1) the The drivers of modularity large intermodule distance and thus high modularity level of the Galápagos network; and (2) the higher topological rank (con- The drivers of modularity appear to be quite different on the nectors, module and network hubs) of Canarian species in par- two archipelagos. Habitat diversity and number of biomes are ticular – Canarian connectors were more frequent. Both features higher on the Canaries, perhaps due to a considerably higher tend to reduce the number of modules. If we regard a module as elevation coupled with a much wider geological age span. Fleshy a kind of niche shared by a set of strongly interacting species fruited plants were well represented in all habitats, except in the (Gómez et al., 2015), then our results demonstrate that the pine forest. Birds were more important in forest environments, Galápagos have a more clearly delimited and fine-grained niche while lizards were more so in the open habitat modules, in both structure than the Canaries. Finally, the stronger Galápagos coastal and high-mountain habitats (Valido et al., 2003; Rumeu modularity was further enhanced by invasive alien mammals, et al., 2011). The two modules differed because they were organ- which formed their own module. ized around lizards and secondary seed dispersers, confirming In the Canaries, the kestrel and the lizard G. galloti were the role of these animals in mutualistic insular systems (Olesen network hubs. The wide foraging range of the kestrel and the & Valido, 2003; Nogales et al., 2007; Padilla et al., 2012). wide elevational range of the lizard (Padilla et al., 2012) circum- In the Galápagos, each module was formed by species with vent the habitat specificity of their modules, in contrast to the somewhat similar traits, selecting similar functional groups of other four modules. A key role was also played by the two species, especially birds and lizards (but see the ‘tortoise/large endemic laurel forest pigeons, both being hubs in the ‘laurel mammals’ module). Most modules included sauropsid repre- forest and large birds’ module. Their central role (10–15 fruit sentatives and the importance of seed dispersal by birds, lizards plants) emphasizes the importance of these birds to this unique and tortoises is well known from islands (e.g. Guerrero & Tye, forest. Furthermore, the pigeons were responsible for two-thirds 2009; Heleno et al., 2011b, 2013; Blake et al., 2012). of all dispersal links in the forest and such a modular structure In general, the paucity of well-resolved studies of seed disper- could perhaps be said to have the signature of both the consid- sal modularity (two exceptions from mainland environments erable age of the forest and the strong elevational zonation of the being Donatti et al., 2011; and Schleuning et al., 2011) still islands. Fortunately, both species of pigeon have healthy popu- hampers comparisons of island and mainland networks. lations and no immediate threats are known. However, we hypothesize that modularity could be higher in In the Galápagos, the tortoise C. nigra constituted the sole continents, where rich species assemblages tend to have been network hub, while the plant Miconia robinsoniana was the only interacting for longer evolutionary periods, forcing species to module hub, and both are endemic. The role played as seed specialize and occupy smaller realized niches. In contrast, the disperser by C. nigra (see Blake et al., 2013) is due to its large poorer biodiversity of oceanic islands allows some species to body size, home range and capacity to disperse both small seeds become very common (density compensation), broadening and the largest fleshy fruited plants such as Hippomane their trophic niche (interaction release; Traveset et al., 2015) to mancinella (Euphorbiaceae) (Blake et al., 2012; Heleno et al., become super-generalists, and thus to make the network more 2013). Populations of this tortoise are, in general, recovering coherent. In spite of this reasoning, the number of modules was their former size with the eradication of competing feral rather similar between our two oceanic archipelagos and the two mammals occupying the same module. Modularity would cer- mainland sites (Donatti et al., 2011; Schleuning et al., 2011), tainly increase further if the populations of tortoise were treated though the island networks were smaller. Detailed studies are taxonomically as distinct species (Jiménez-Uzcátegui et al., needed in order to delve deeper into the interpretation of modu- 2014). Following the recent release of tortoises to new islands, larity between insular and continental environments. for example Pinta and Santa Fe, we can expect strong network Irrespective of the two main causes of modularity in the changes, particularly with the reintroduction of an ‘extinct func- Canaries (environmental heterogeneity) and Galápagos (species tion’ within these communities. Miconia robinsoniana is the functional roles), the six modules detected on each archipelago dominant plant throughout the highland Miconia zone. Here, it may produce strong isolation over time. On the other hand, it is is one of the few species producing fleshy fruits (Heleno et al., possible that islands have high modularity due to the important 2013) and is a key resource for most dispersers in its module habitat diversity in the different archipelagos and the strong (Table S5). temporal dynamics (e.g. vulcanism). These two factors are prob- Although human-induced extinction is relatively common on ably the basic drivers of fast speciation occurring within remote oceanic islands, the frugivore assemblage of both archipelagos is territories isolated in the middle of the two largest oceans.

Indeed, we suggest that island studies focusing upon the impor- Bascompte, J. & Jordano, P. (2013) Mutualistic networks. Prince- tance of modularity for speciation rate could be a most prom- ton University Press, Princeton. ising research avenue. Bascompte, J. & Olesen, J.M. (in press) Mutualistic networks. Mutualism (ed. by J.L. Bronstein). Oxford University Press, Oxford. CONCLUDING REMARKS Bascompte, J., Jordano, P., Melián, C.J. & Olesen, J.M. (2003) This is the first detailed study of the modularity of seed- The nested assembly of plant–animal mutualistic networks. dispersal networks on oceanic islands. We demonstrate that Proceedings of the National Academy of Sciences USA, 100, insular seed-dispersal networks may differ profoundly in their 9383–9387. linkage structure among oceanic archipelagos. In this sense, Batagelj, V. & Mrvar, A. (1998) Pajek: a program for large modules form promising biogeographical entities for exploring network analysis. Connections, 21, 47–57. the interplay between ecology and evolution on islands and Blake, S., Wikelski, M., Cabrera, F., Guezou, A., Silva, M., elsewhere. Thus the evolutionary history of insular networks Sadeghayobi, E., Yackulic, C.B. & Jaramillo, P. (2012) Seed might also differ with important consequences for our general dispersal by Galápagos tortoises. Journal of Biogeography, 39, understanding of island biogeography, colonization/extinction 1961–1972. dynamics and speciation patterns. Blake, S., Yackulic, C.B., Cabrera, F., Tapia, W., Gibbs, J.P., Kümmeth, F. & Wikelski, M. (2013) Vegetation dynamics drive segregation by body size in Galapagos tortoises migrat- ACKNOWLEDGEMENTS ing across altitudinal gradients. Journal of Animal Ecology, 82, Many colleagues in the Canaries shared with us their observa- 310–321. tions on interactions between dispersers and fruiting plants, but Blomberg, S.P., Garland, T. & Ives, A.R. (2003) Testing for especially Alfredo Valido, Félix M. Medina, Juan D. Delgado, phylogenetic signal in comparative data: behavioral traits are David P. Padilla, Patricia Marrero, Airam Rodríguez and Marta more labile. Evolution, 57, 717–745. López. In the Canaries, we also express our gratitude to public Carstensen, D.W. & Olesen, J.M. (2009) Wallacea and its institutions at national (Parques Nacionales) and autonomic nectarivorous birds: nestedness and modules. Journal of Bio- level (Gobierno de Canarias and Cabildos insulares). In the geography, 36, 1540–1550. Galápagos, we thank the Charles Darwin Foundation and the Cox, S.C., Carranza, S. & Brown, R.P. (2010) Divergence Parque Nacional de Galápagos for offering us much information times and colonization of the Canary Islands by Gallotia and logistic support. The editors and two anonymous referees lizards. Molecular Phylogenetics and Evolution, 56, 747– provided useful comments and suggestions to improve this 757. manuscript. 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Traveset, A., Olesen, J., Nogales, M., Vargas, P., Jaramillo, P., Table S1 Seed-dispersal interactions recorded in the Canary Antolin, E., Trigo, M. & Heleno, R. (2015) Bird-ﬂower visita- Islands. tion networks in the Galápagos unveil a widespread interac- Table S2 Seed-dispersal interactions recorded in the Galápagos tion release. Nature Communication, 6, 6376, doi: 10.1038/ archipelago. ncomms7376 Table S3 Phylogenetic signal for a set of traits in seed-dispersal Valdovinos, F.S., Ramos-Jiliberto, R., Flores, J.D., Espinoza, C. & communities in the Canary Islands and the Galápagos. López, G. (2009) Structure and dynamics of pollination net- Table S4 Modular structure of the seed-dispersal network of the works: the role of alien plants. Oikos, 118, 1190–1200. Canary Islands Valido, A., Nogales, M. & Medina, F.M. (2003) Fleshy fruits in Table S5 Modular structure of the seed-dispersal network of the the diet of Canarian lizards Gallotia galloti (Lacertidae) in a Galápagos. xeric habitat of the island of Tenerife. Journal of Herpetology, 37, 741–747. BIOSKETCH SUPPORTING INFORMATION Manuel Nogales works on the evolutionary ecology Additional supporting information may be found in the online of island organisms, with a special interest in version of this article at the publisher’s web-site. animal–plant mutualistic interactions. All the team has a wide experience in the ecology, evolution and Appendix S1 Map of the Canarian archipelago. biogeography of oceanic islands. Appendix S2 Map of the Galápagos archipelago. Appendix S3 Main habitats along the elevation gradient repre- Author contributions: M.N., R.H., B.R. and J.O. con- sented in Canary Islands and the Galápagos. ceived the ideas; All authors contributed to the network Appendix S4 Modular seed-dispersal networks in the archipela- database; B.R. and J.O. analysed the data; M.N. and J.O. gos of the Canaries and Galápagos. led the writing but all authors contributed to interpre- Appendix S5 Detailed interaction network of the Canary tation and writing. Islands. Appendix S6 Detailed interaction network of the Galápagos. Editor: Richard Field

M. Nogales, R. Heleno, B. Rumeu, A. González-Castro, A. Traveset, P. Vargas & J. M. Olesen

Appendix S1 Map of the Canary archipelago, showing its global location (inset) and the main islands.

1 Appendix S2 Map of the Galápagos archipelago, showing its global location (inset) and the main islands.

2 Appendix S3 Main habitats along the altitude gradient represented in the Canary Islands (A) and Galápagos (B). Note the relative scales for real altitude of each archipelago.

3 Appendix S4 Modular seed dispersal networks in the archipelagos of Canaries and Galápagos.

Canary seed-dispersal module network - incl. invaders

4 Appendix S5 Interaction network of seed dispersal in the Canary Islands and list of species included (see Table below). Outer ring of nodes represents fleshy-fruited plants that are connected to seed dispersers (inner ring of nodes). Modules are shown in different colours and species roles are shown with different symbols. Codes in the Table correspond to those in the Figure. Asterisks both in the network and after codes in the Table indicate introduced species.

* 60* 89 39 71 91 * 46 59 78 Canary Islands 45 69* 68 87 55 33 85 82 90 18 14 88 54 16 16 79 86 15 22 80 72 1 43 36 3 * 73 75 27 58 51 26 19 35 12 44 29 34 21 64 8 MODULES * 65 2 61 * 28 * 38 Medium-large lizards 20 48 * 24 41 95 High mountain 92 40 9 23* 56 Thermophilous forest 32 13 & passerines 25 84 * 67 *10 5 62 Coastal xerophytic shrubland 83 7 11 30 66 & bird/mammal 63 4 6 49 37 * Laurel forest & large birds 57 94 31 42 47 53 * 50 77 Secondary seed dispersal * 70 76 93 74 81 52 * peripherals connectors module hubs network hubs

Code Seed dispersers Code Fleshy-fruited plants Code Fleshy-fruited plants

1* Atelerix algirus 31 Apollonias barbujana 64 Olea cerasiformis 2* Atlantoxerus getulus 32 Arbutus canariensis 65* Opuntia dillenii 3 Chlamydotis undulata 33 Asparagus arborescens 66* Opuntia maxima 4 Columba bollii 34 Asparagus nesiotes 67 Persea indica 5 Columba junoniae 35 Asparagus pastorianus 68 Phoenix canariensis 6 Corvus corax 36 Asparagus plocamoides 69* Phoenix dactylifera 7 Cyanistes teneriffae 37 Asparagus umbellatus 70 Picconia excelsa 8 Erithacus rubecula 38* Atriplex semibaccata 71 Pistacia atlantica 9 Falco tinnunculus 39 Bencomia caudata 72 Pistacia lentiscus 10* Felis catus 40 Bencomia exstipulata 73 Plocama pendula 11 Fringilla coelebs 41 Bosea yervamora 74* Prunus cerasus 12 Gallotia atlantica 42 Canarina canariensis 75 Rhamnus crenulata 13 Gallotia caesaris 43 Daphne gnidium 76 Rhamnus glandulosa 14 Gallotia galloti 44 Dracaena draco 77 Rhamnus integrifolia 15 Gallotia gomerana 45 Dracunculus canariensis 78 Rosa canina 16 Gallotia intermedia 46* Einadia nutans 79 Rubia agostinhoi 17 Gallotia simonyi 47* Ficus carica 80 Rubia fruticosa 18 Gallotia stehlini 48 Heberdenia excelsa 81 Rubus ulmifolius 19 Lanius meridionalis 49 Ilex canariensis 82 Ruta pinnata 20 Larus michahellis 50 Ilex platyphylla 83 Sambucus palmensis 21* Oryctolagus cuniculus 51 Jasminum odoratissimum 84 Scilla haemorrhoidalis 22 Phyrrocorax phyrrocorax 52 Juniperus cedrus 85 Scilla latifolia 23* Rattus rattus 53 Juniperus turbinata 86 Semele androgyna 24 Saxicola dacotiae 54 Kunkeliella retamoides 87 Semele gayae 25 Serinus canarius 55 Kunkeliella subsucculenta 88 Smilax aspera 26 Sylvia atricapilla 56* Lantana camara 89 Solanum nigrum 27 Sylvia conspicillata 57 Laurus azorica 90 Solanum vespertilio 28 Sylvia melanocephala 58 Lycium intricatum 91 Tamus edulis 29 Turdus merula 59* Lycopersicon esculentum 92 Viburnum rigidum 30 Turdus torquatus 60* Morus nigra 93 Visnea mocanera 61 Myrica faya 94* Vitis vinifera 62 Neochamaelea pulverulenta 95 Withania aristata 63 Ocotea foetens

6 Appendix S6 Interaction network of seed dispersal in the Galápagos and list of species included (see Table below). Outer ring of nodes represents fleshy-fruited plants that are connected to seed dispersers (inner ring of nodes). Modules are shown in different colours and species roles are shown with different symbols. Codes in the Table correspond to those in the Figure. Asterisks both in the network and after codes in the Table indicate introduced species.

55 31 39 35 60 40 43 42* Galápagos

44 10 17 19 20 28 22 61 * 52 13 46 32 45 59 18 5 33 62 21 * 27 * 34 38 * 1 * 23 37 * 54 * 11 MODULES 51 8 * 47

50 30 Tortoise-large mammals 24 48 Geospiza conirostris- 16 Opuntia helleri (satellite) 36 9 2 Small-medium dispersers/ 6 29 S. Cristóbal Island 12 26* 7 Large finches/endemic 3 15 rodent & large-seeded plants 4 25 14 58 Western islands 49 41 56 53 57 Small finches/passerines * & small-seeded plants

peripherals connectors module hubs network hubs

Code Seed dispersers Code Fleshy-fruited plants

1* Bos taurus 29 Bursera graveolens 2 Camarhynchus pallidus 30 Capsicum frutescens 3 Camarhynchus parvulus 31 Castela galapageia 4 Camarhynchus psittacula 32 Chiococca alba 5* Capra hircus 33* Citrus sp. 6 Certhidea fusca 34 Clerodendrum molle 7 Certhidea olivacea 35 Cordia leucophlyctis 8 Chelonoidis nigra 36 Cordia lutea 9 Coccyzus melacoryphus 37 Hippomane mancinella 10 Conolophus subcristatus 38* Lantana camara 11* Crotophaga ani 39 Lantana peduncularis 12 Dendroica petechia 40 Maytenus octogona 13 Geospiza conirostris 41 Miconia robinsoniana 14 Geospiza fortis 42* Momordica charantia 15 Geospiza fuliginosa 43 Opuntia echios 16 Geospiza magnirostris 44 Opuntia helleri 17 Geospiza scandens 45 Opuntia megasperma 18 Microlophus bivattatus 46 Passiflora edulis 19 Microlophus pacificus 47 Passiflora foetida 20 Microlophus albemarlensis 48 Passiflora suberosa 21 Mimus melanotis 49 Physalis galapagoensis 22 Mimus parvulus 50 Physalis pubescens 23 Myarchus magnirostris 51 Psidium galapageium 24 Oryzomis galapagoensis 52* Psidium guajava 25 Platyspiza crassirostris 53 Psychotria rufipes 26* Rattus rattus 54* Rubus niveus 27* Sus scrofa 55 Scutia spicata 28 Zenaida galapagoensis 56* Solanum americanum 57 Solanum pimpinelifolium 58 Tournefortia psilostachya 59 Tournefortia pubescens 60 Tournefortia rufo-sericea 61 Vallesia glabra 62 Zanthoxylum fagara

8 Seed-dispersal networks on the Canaries and the Galápagos archipelagos: interaction modules as biogeographical entities M. Nogales, R. Heleno, B. Rumeu, A. González-Castro, A. Traveset, P. Vargas & J. M. Olesen

Table S1. Seed dispersal interactions recorded in the Canary Islands, with fleshy-fruited plants in rows and seed dispersers in columns. A matrix element representing a seed dispersal interaction between a plant and an animal species received the value of 1, and 0 otherwise.

lvia melanocephala Atelerix algirus Atelerix getulus Atlantoxerus undulata Chlamydotis bollii Columba junoniae Columba corax Corvus teneriffae Cyanistes rubecula Erithacus tinnunculus Falco catus Felis coelebs Fringilla atlantica Gallotia caesaris Gallotia galloti Gallotia gomerana Gallotia intermedia Gallotia simonyi Gallotia stehlini Gallotia meridionalis Lanius michahellis Larus cuniculus Oryctolagus phyrrocorax Phyrrocorax dacotiae Saxicola canarius Serinus atricapilla Sylvia Sy conspicillata Sylvia rattus Rattus merula Turdus torquatus Turdus Apollonias barbujana 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Arbutus canariensis 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 Asparagus arborescens 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 Asparagus nesiotes 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 Asparagus pastorianus 0 1 0 0 0 1 0 0 1 0 0 1 0 1 0 0 0 1 1 0 1 0 0 0 1 1 1 0 0 0 Asparagus plocamoides 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 1 0 0 0 0 0 1 1 0 0 1 0 Asparagus umbellatus 0 0 0 0 0 0 0 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 Atriplex semibaccata 0 0 1 0 0 0 0 0 1 0 0 1 1 1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 Bencomia caudata 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Bencomia exstipulata 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Bosea yervamora 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 0 Canarina canariensis 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 0 0 Daphne gnidium 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 Dracaena draco 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 Dracunculus canariensis 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Einadia nutans 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Ficus carica 0 0 0 0 1 1 1 0 1 0 1 1 1 1 0 0 1 1 1 0 0 0 0 1 1 1 0 0 1 0 Heberdenia excelsa 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 0 Ilex canariensis 0 0 0 1 1 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Ilex platyphylla 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Jasminum odoratissimum 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 0 Juniperus cedrus 0 0 0 0 0 1 0 1 1 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 1 Juniperus turbinata 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Kunkeliella retamoides 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Kunkeliella subsucculenta 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Lantana camara 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Laurus azorica 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Lycium intricatum 0 1 1 0 0 1 0 0 1 0 0 1 0 1 0 0 0 1 1 0 1 0 1 0 1 1 1 0 0 0 Lycopersicon esculentum 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 Morus nigra 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 Myrica faya 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 1 0 0 1 0 Neochamaelea pulverulenta 0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Ocotea foetens 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Olea cerasiformis 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 0 Opuntia dillenii 0 0 0 0 0 1 0 0 1 1 0 1 0 1 0 0 0 1 1 0 1 0 0 0 0 0 1 0 0 0 Opuntia maxima 0 1 0 0 0 1 0 1 1 1 0 1 1 1 0 0 1 1 0 0 1 0 0 0 1 1 0 0 1 0 Persea indica 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1

Table S1. Continued

eriffae

chahellis Atelerix algirus Atelerix getulus Atlantoxerus undulata Chlamydotis bollii Columba junoniae Columba corax Corvus ten Cyanistes rubecula Erithacus tinnunculus Falco catus Felis coelebs Fringilla atlantica Gallotia caesaris Gallotia galloti Gallotia gomerana Gallotia intermedia Gallotia simonyi Gallotia stehlini Gallotia meridionalis Lanius mi Larus cuniculus Oryctolagus phyrrocorax Phyrrocorax dacotiae Saxicola canarius Serinus atricapilla Sylvia melanocephala Sylvia conspicillata Sylvia rattus Rattus merula Turdus torquatus Turdus Phoenix canariensis 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 Phoenix dactylifera 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Picconia excelsa 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Pistacia atlantica 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 1 0 0 0 0 Pistacia lentiscus 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 0 Plocama pendula 1 0 0 0 0 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 1 0 0 0 0 1 1 0 1 0 Prunus cerasus 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Rhamnus crenulata 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 0 Rhamnus glandulosa 0 0 0 1 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Rhamnus integrifolia 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 Rosa canina 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Rubia agostinhoi 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Rubia fruticosa 0 1 0 0 1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 1 1 1 0 0 1 1 1 0 1 0 Rubus ulmifolius 0 0 0 0 1 1 1 0 1 0 0 0 1 1 0 0 0 1 0 0 0 0 0 0 1 1 1 0 1 0 Ruta pinnata 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Sambucus palmensis 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Scilla haemorrhoidalis 0 0 0 0 0 0 0 0 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Scilla latifolia 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Semele androgyna 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Semele gayae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Smilax aspera 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Solanum lycopersicum 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Solanum nigrum 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 1 1 1 0 0 0 0 0 1 1 1 0 0 0 Solanum vespertilio 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Tamus edulis 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 Viburnum rigidum 0 0 0 0 1 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 Visnea mocanera 0 0 0 1 1 1 0 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Vitis vinifera 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 Withania aristata 0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0

2 Table S2. Seed dispersal interactions recorded in the Galápagos archipelago, with fleshy-fruited plants in rows and seed dispersers in columns. A matrix element representing a seed dispersal interaction between a plant and an animal species received the value of 1, and 0 otherwise.

nirostris

phus albemarlensis phus Bos taurus Bos pallidus Camarhynchus parvulus Camarhynchus psittacula Camarhynchus hircus Capra olivacea Certhidea fusca Certhidea nigra Chelonoidis melacoryphus Coccyzus subcristatus Conolophus ani Crotophaga petechia Dendroica conirostris Geospiza fortis Geospiza fuliginosa Geospiza magnirostris Geospiza scandens Geospiza Microlo bivattatus Microlophus pacificus Microlophus melanotis Mimus parvulus Mimus mag Myiarchus galapagoensis Oryzomys crassirostris Platyspiza rattus Rattus scrofa Sus galapagoensis Zenaida Bursera graveolens 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 1 0 1 0 0 0 1 1 0 0 1 0 0 Capsicum frutescens 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Castela galapageia 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 Chiococca alba 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 1 0 1 1 0 0 0 0 0 0 Citrus sp. 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Clerodendrum molle 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cordia leucophlyctis 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 1 Cordia lutea 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 1 0 0 1 0 0 1 0 1 0 0 0 0 Hippomane mancinella 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Lantana camara 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 1 0 1 0 1 0 0 0 0 0 Lantana peduncularis 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 Maytenus octogona 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 1 0 0 0 0 0 0 0 Miconia robinsoniana 0 1 1 1 0 1 1 0 0 0 1 1 0 1 1 0 0 0 0 0 1 0 1 0 1 1 0 0 Momordica charantia 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 1 0 0 0 0 0 Opuntia echios 0 0 0 0 0 0 0 1 0 1 0 0 0 1 1 0 1 1 0 0 0 1 0 0 0 0 0 1 Opuntia helleri 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Opuntia megasperma 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Passiflora edulis 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Passiflora foetida 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 0 Passiflora suberosa 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Physalis galapagoensis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 Physalis pubescens 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 Psidium galapageium 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Psidium guajava 1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 0 Psychotria rufipes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 Rubus niveus 0 1 1 0 0 0 0 1 0 0 1 0 0 1 1 1 0 0 1 0 1 0 1 0 0 0 0 0 Scutia spicata 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 1 1 0 1 1 1 1 0 0 0 0 0 Solanum americanum 0 0 1 0 0 0 0 1 0 0 1 0 0 1 1 0 0 0 0 0 0 0 1 0 0 1 0 0 Solanum pimpinelifolium 0 0 1 1 0 0 0 1 0 0 1 0 0 1 1 0 0 0 0 0 0 1 0 0 1 1 0 0 Tournefortia psilostachya 0 0 0 0 0 0 0 0 1 0 1 1 0 1 1 0 0 1 0 0 1 1 1 0 1 0 0 0 Tournefortia pubescens 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 1 0 1 1 1 0 0 0 0 0 Tournefortia rufo-sericea 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 Vallesia glabra 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 Zanthoxylum fagara 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 1 0 1 1 1 0 0 0 0 0

3 Table S3. Pylogenetic signal (K and λ. see main text) for a set of traits in the seed-dispersal communities in the Canary Islands and the Galápagos, excluding invaders. Values in bold are significant at the 0.05 level.

P (lower bound. P (upper bound. K P λ λ = 0) λ = 1) CANARY ISLANDS Seed dispersers Module affinity 0.27 0.72 0.00 1.00 <0.001 Module centrality 0.63 0.03 0.17 0.53 <0.001 log(Body weight) 1.61 <0.001 1.00 1.00 <0.001 Main habitat 0.85 0.002 1.00 0.00 1.00 log(Linkage level L) 0.36 0.27 0.00 1.00 0.00 Connectivity c 0.33 0.4 0.00 1.00 <0.001 Hubability z 0.38 0.27 0.00 1.00 0.002 No. islands 0.88 <0.001 0.57 0.06 0.04

Plants Module affinity 0.33 0.15 0.00 1.00 <0.001 Module centrality 0.40 0.02 0.67 0.00 <0.001 Fruit dm 0.56 <0.001 0.92 0.020 0.19 Main habitat 0.33 0.32 0.39 0.12 <0.001 log(Linkage level L) 0.27 0.46 0.00 1.00 <0.001 Connectivity c 0.28 0.46 0.00 1.00 <0.001 Hubability z 0.28 0.57 0.00 1.00 <0.001 No. islands 0.27 0.55 0.00 1.00 <0.001

G ALÁPAGOS ISLANDS Seed dispersers log(Body weight) 1.81 0.01 1.00 <0.001 1.00 Main habitat 0.89 <0.001 1.00 <0.001 1.00 log(Linkage level L) 0.64 0.005 0.90 0.01 0.29 No. islands 0.45 0.08 0.44 0.21 0.007

P lants Fruit dm 1.17 <0.001 1.00 <0.001 1.00 Main habitat 0.79 0.02 1.00 0.09 1.00 log(Linkage level L) 0.55 0.30 0.00 1.00 0.01 No. islands 1.05 <0.001 1 0.002 1

4 Table S4. Modular structure of the seed-dispersal network of the Canary Islands. In bold are habitat- delimited modules and in normal font are ecological guild modules.

Module Module label Module No. species No. species per role composition Plants Animals Native Non- Native Non- Network Module Connectors Peripherals native native hubs hubs 1 Medium-large 3 ubiquitous 16 4 3 0 1 0 6 16 lizards module spp. of the endemic Gallotia lizard genus (G. galloti, G. simonyi, G. stehlini) & rich flora 2 High-mountain The wintering 2 0 1 0 0 0 1 2 module bird Turdus torquatus & the endemic plants Juniperus cedrus and Rhamnus integrifolia 3 Thermophilous 4 disperser bird 11 0 4 0 0 0 5 10 forest & spp. (Turdus passerines merula, Sylvia module atricapilla, S. melanocephala, Erithacus rubecula) & rich flora

5 Table S4. Continued

Module Module label Module No. species No. species per role composition Plants Animals Native Non- Native Non- Network Module Connectors Peripherals native native hubs hubs 4 Coastal Coastal animal- 6 2 9 3 0 0 8 12 xerophytic rich biota, shrubland & especially from bird/mammal the eastern xeric module islands 5 Laurel forest & 3 large bird spp. 12 2 6 1 0 2 4 15 large birds (Columba bollii, module C. junoniae, Corvus corax) & rich fleshy- fruited tree flora 6 Secondary seed 2 secondary 7 3 2 1 1 0 6 6 dispersal seed dispersers module or (predators Falco diplochory tinnunculus, module Felis catus), including their frugivorous lizard prey (G. caesaris) & xerophilous flora

6 Table S5. Modular structure of the seed-dispersal networks of the Galápagos Islands. All modules are based on ecological guilds.

Module Module label Module composition No. spp. No. spp. per role Plants Animals Native Non- Native Non- Network Module Connectors Peripherals native native hubs hubs 1 Tortoise- large The endemic tortoise 6 2 1 3 1 0 0 11 mammals (Chenoloidis nigra), disperser 3 introduced module mammals (Bos taurus, Sus scrofa, Capra hircus) & rich flora, incl. very invasive Psidium guajava 2 Geospiza Only composed of 1 0 1 0 0 0 0 2 conirostris- Geospiza conirostris Opuntia & Opuntia helleri helleri- satellite module 3 Small-medium 3 birds (endemic 7 2 3 1 0 0 3 10 dispersers/San Mimus melanotis, Cristóbal Myarchus Island module magnirostris, introduced Crotophaga ani) 1 endemic Microlophus bivattatus lizard & rich flora

Table S5. Continued

Module Module label Module composition No. spp. No. spp. per role Plants Animals Native Non- Native Non- Network Module Connectors Peripherals native native hubs hubs 4 Large 3 endemic dispersers 2 0 3 0 0 0 3 2 finches/ende (birds Camarhynchus mic rodent & pallidus, Geospiza large-seeded magnirostris, rodent plants Oryzomys module galapagoensis) & Bursera graveolens and Cordia lutea 5 Western Especially 2 7 1 6 0 0 0 3 11 islands passerines (Geospiza module scandens & Mimus parvulus), 1 dove (Zenaida galapagoensis), the iguana Conolophus subcristatus & rich flora 6 Small Especially 5 small 5 1 9 1 0 1 1 14 finches/passe passerines (Certhidea rines & olivacea, C. fusca, small-seeded Camarhynchus plants parvulus, Geospiza module fuliginosa, Dendroica petechia) & endemic tree-like Miconia robinsoniana