Macroecological trends in nestedness and modularity of seed-dispersal networks: human impact matters
Aim: We aim to characterize the macroecological patterns in the structure of mutualistic seed-dispersal networks. Tropical areas hold more species than temperate ones. This difference in species number may favour ecological processes that minimize interspecific competition in species-rich areas. The...
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Published in | Global ecology and biogeography Vol. 24; no. 3; pp. 293 - 303 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Oxford
Blackwell Publishing Ltd
01.03.2015
John Wiley & Sons Ltd Wiley Subscription Services, Inc |
Subjects | |
Online Access | Get full text |
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Summary: | Aim: We aim to characterize the macroecological patterns in the structure of mutualistic seed-dispersal networks. Tropical areas hold more species than temperate ones. This difference in species number may favour ecological processes that minimize interspecific competition in species-rich areas. There is theoretical evidence that both modularity (i.e. the presence of semi-independent groups of highly interacting species) and nestedness (i.e. specialists interact with a subset of the species interacting with generalists) reduce the effects of competition. Thus, we expect high degrees of modularity or nestedness at low latitudes in seed-dispersal networks. Moreover, we test whether climate, topography and human impact influence network structure. Location: Thirty-four qualitative and 21 weighted seed-dispersal interaction networks located world-wide. Methods: We related the degree of modularity and nestedness of seed-dispersal interaction networks with latitude. To disentangle the macroecological drivers of network structure, we also associated modularity/nestedness with species richness, altitudinal range, human impact and an array of climate predictors: precipitation, temperature, precipitation/temperature seasonality and historical climate-change velocity and anomaly. Results: Binary networks showed stronger macroecological patterns than weighted networks. Latitude was unrelated to the structure of seed-dispersal networks, but more nested assemblages were species rich and were located in areas with a high degree of human impact, high temperature seasonality, low precipitation, and, especially on the mainland, high stability in precipitation. Modular networks were species rich and found in areas with low human impact. For both nestedness and modularity, the effects of species richness and human impact were especially strong and consistent. Main conclusions: As for previous macroecological studies of mutualistic networks, we found that the structure of seed-dispersal assemblages was related to current and historical climate. The largest influences on nestedness and modularity, however, were the number of competing species and the degree of human impact. This suggests that human disturbance, not just climate, is an important factor determining the structure of a seed-dispersal network. |
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Bibliography: | Appendix S1 List of papers used for the analyses and network characteristics of the studied dataset. Table S1 GLM relating the nestedness and modularity of the networks with latitude. Table S2 Results of the model averaging for the spatial eigenvector mapping (SEVM) analyses including climate anomaly variables for all the study sites. Table S3 Results of the model averaging for the SEVM analyses including climate velocity variables for all the study sites. Table S4 Results of the model averaging for the analyses including climate anomaly variables for the continental sites. Table S5 Results of the model averaging for the analyses including climate change velocity variables for the continental sites. Table S6 Results of the model averaging for the analyses including climate anomaly variables for the sites that presented only avian species. Table S7 Results of the model averaging for the analyses including climate change velocity variables for the sites that presented only avian species. FAPESP Research Foundation - No. 2011/17968-2; No. 2009/054422-8 ArticleID:GEB12270 Danish National Research Foundation istex:6DAD91CC06B90C2BF44506D5757716417C1FAAE5 ark:/67375/WNG-V87LVCVT-H ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1466-822X 1466-8238 |
DOI: | 10.1111/geb.12270 |