Megafauna history and plant defense traits
The role of large herbivores in explaining broad-scale ecological pattern has often been underestimated [1]. Plants have defenses against large herbivores (e.g., spines, high wood density [2]). And many continents had abundant large herbivores (megafauna) that were extinguished in Pleistocene (except in Africa). In a recent paper [3] we asked, to what extent the past distribution of extinct magafauna explains current geographical distribution of plant defense traits in the Neotropics (South & Central America). We fond that a significant proportion of the variance in the distribution of wood density, leaf size, stem spines, and leaf spines are explained by variable related to past megafauna (richness and body mass).
We defined 3 antiherbiomes in South America, that is, regions with characteristic plant defenses, environmental conditions, and Pleistocene megafauna, as follows: Small-Leaves-Thorny (SLT): thorny and small-leaved plants, in arid, cold and nutrient-rich ecosystems, containing numerous extinct and extant large grazers. Intermediate-Leaves-Woody (ILW): intermediate leaf sizes and levels of chemical defenses, and very high wood density, in moist and hot climates, and extremely nutrient-poor soils; and a high extinct megafauna richness, especially in relation to small browsers and mixed-feeders. Broad-Chemically-defended-Leaves (BCL): very large leaves with chemical defenses, mostly associated with moist climates and intermediate fertility soils, with few but large extinct megafauna species, especially browsers. Similar antiherbiomes can be observed in current Africa. These antiherbiomes represent one of the most striking broad-scale anachronisms in ecology.
We estimated that in South America, savannas occupied about 10 millions of Km2 during the Pleistocene, ca. 63% of them were converted to forests (44% to moist forests, 19% to dry forests) after the megafauna extinction (biome shifts [4]), and ca. 37% remains as savanna (stable). This suggests that South America was a savanna-dominated continent, much more similar to Africa than today, and that a large proportion of South American forests are the result of megafauna extinctions.
Overall our results suggest that past (extinct) large herbivores explain an important proportion of the variability of current plant traits and community assemblies.
Fig. 3. Additional reconstructions of the Pleistocene Brazilian savannas from [5]. Artist: Júlia d’Oliveira
References
[1] Pausas JG & Bond WJ. 2019. Humboldt and the reinvention of nature. J. Ecol. 107: 1031-1037. [doi | jecol blog | jgp blog | pdf]
[2] Dantas V & Pausas JG. 2020. Megafauna biogeography explains plant functional trait variability in the tropics. Glob. Ecol. & Biogeogr. [doi | pdf | data:dryad | blog ]
[3] Dantas V., Pausas J.G. 2022. The legacy of Southern American extinct megafauna on plants and biomes. Nature Comm. 13: 129 [doi | pdf | data & codes] – New!
[4] [2] Pausas JG & Bond WJ. 2020. Alternative biome states in terrestrial ecosystems. Trends Plant Sci. 25: 250-263. [doi | sciencedirect | cell | pdf]
[5] Pansani et al. 2019. Isotopic paleoecology (δ13C, δ18O) of Late Quaternary megafauna from Mato Grosso do Sul and Bahia States, Brazil. Quat Sci Rev, 221, 105864.