The Reconfiguration of Seed- Dispersal Networks After Megafaunal Extinctions Mathias M. Pires Mauro Galetti Camila Donatti Rodolfo Dirzo Marco A. Pizo Paulo R. Guimarães Jr IB - USP
Megafaunal Extinction The Pleistocene fauna was different from today s
Megafaunal Extinction South America: 3 orders entirely lost (Proboscidea, Notoungulata, Litopterna) and one was drastically reduced (Xenarthra) 80% of the South American large mammals ~50 genera Koch and Barnosky 2006 - Ann. Rev.!
Megafaunal Extinction Several extinct species possibly consumed fruits Important seed dispersers of several plant species (especially those with large seeds) Evidence Anachronisms Janzen & Martin 1982 - Science!
Seed-dispersal networks The loss of megafauna may have impacted not only megafaunadependent species, but whole plant communities Species are connected through their interactions interaction networks
Seed-dispersal networks How seed-dispersal systems were reorganised after Pleistocene extinctions?
Seed-dispersal networks Seed dispersal in the Pantanal region - Central Brazil Donatti et al. 2011 - Ecol Lett.!
Seed-dispersal networks The Pantanal region - Tropical wetland Donatti et al. 2011 - Ecol Lett.!
Seed-dispersal networks Seed dispersal data for different groups Donatti et al. 2011 - Ecol Lett.!
Seed-dispersal networks The Pantanal seed-dispersal network - One of the most complete mammals, birds, reptile, fish Donatti et al. 2011 - Ecol Lett.!
Seed-dispersal networks The Pantanal seed-dispersal network - One of the most complete mammals, birds, reptile, fish How would this network have changed from the Pleistocene to the modern? Donatti et al. 2011 - Ecol Lett.!
Seed-dispersal networks Pleistocene fossil assemblages close to the study site
Seed-dispersal networks Pleistocene fossil assemblages close to the study site We identified megafauna that probably included fruits in their diets
Seed-dispersal networks Identified fruits that fit the megafauna seed-dispersal syndrome Guimarães et al. 2008 - PLoS One!
Seed-dispersal networks We reconstructed networks representing 4 different times periods (i) Pleistocene - megafauna Added megafauna interacting with anachronic fruits
Seed-dispersal networks We reconstructed networks representing 4 different times periods (i) Pleistocene - megafauna (ii) Early Holocene - humans Interactions with fruits currently used by indigenous people
Seed-dispersal networks We reconstructed networks representing 4 different times periods (i) Pleistocene - megafauna (ii) Early Holocene - humans (iii) Colonial period - humans and livestock
Seed-dispersal networks We reconstructed networks representing 4 different times periods (i) Pleistocene - megafauna (ii) Early Holocene - humans (iii) Colonial period - humans and livestock (iv) Modern - extant species and livestock
Seed-dispersal networks We examined the structural properties of each network Network metrics to describe the overlap in interaction patterns: Nestedness and Modularity - Are there modules? - The members of modules are the same across time periods? - Does the role of species in network structure change (connectors vs. peripheral)?
Results Pleistocene - 5 modules Time Period I! [Megafauna]!
Results Early Holocene - 4 modules Mammal-dominated modules are merged Time Period II! [Humans]!
Results Colonial Period - 4 modules Time Period I! [Megafauna]! Mammal-dominated modules separate again Time Period III! [Livestock]!
Results Time Period II! Modern - 5 modules [Humans]! Time Period IV! [Modern]!
Results Large-mammal module now includes species that were functionally small in the Pleistocene Time Period I! [Megafauna]! Time Period III! [Livestock]! Time Period II! [Humans]! Time Period IV! [Modern]!
Results Plant species
Results Plants in the red and yellow modules are now dispersed by species of similar size Plant species
Results Connectivity within modules Connectivity between modules Modern c!value 0.0 0.2 0.4 0.6 0.8 Modern z!value!3!2!1 0 1 2 3 0.0 0.2 0.4 0.6 0.8 Pleistocene c!value!3!2!1 0 1 2 3 Pleistocene z!value
Results The role of mammals in network topology changed Connectivity between Connectivity within modules modules Modern c!value 0.0 0.2 0.4 0.6 0.8 Mammals Modern z!value!3!2!1 0 1 2 3 0.0 0.2 0.4 0.6 0.8 Pleistocene c!value!3!2!1 0 1 2 3 Pleistocene z!value
Conclusions We have limited data to precisely infer effects, but we can recreate ancient systems to understand their properties.
Conclusions Livestock partially recovered network organisation Importance of exotics
Conclusions Species that are now key to network structure would have been less important in the past
Conclusions Possible consequences of the loss of megafauna seed dispersers - Species not directly connected to megafauna might have been impacted - Plants dispersed by small-bodied animals or by abiotic means may have been indirectly favoured - phenomenon occurring in defaunated areas (Wright et al. 2007) Wright et al. 2007 - Biotropica!
Conclusions Possible consequences of the loss of megafauna seed dispersers - Evidence of expansion of grasses and decline in fruiting plants linked to climate change (Whitney et al. 2011): Did megafauna extinction contributed? - Palynological studies may help us evaluate the role of extinction in shaping current plant communities Whitney et al. 2011 - Palaeogeogr, Palaeoclimatol. Palaeoecol."
Acknowledgements
Sensitivity analyses Module composition is robust to: - Assigning other interactions to megafauna beyond those with megafruits - Changes in vegetation - Removal simulations