Ecological effects of megafauna and rewilding in a neotropical savanna ecosystem

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandling

Herbivores provide key ecosystem functions that can physically shape the landscape and induce changes in biodiversity. However, there has been a severe loss of herbivores, especially large herbivores, since the late Pleistocene. South America experienced one of the most extreme losses of herbivores in the world, with 70 % of species over 10 kg lost in the late quaternary extinction, and further defaunation happening in modern times. A restauration tool, such as rewilding, can promote self-sustaining ecosystems by restoring lost ecosystem functions through species reintroductions in these defaunated areas.
Herbivory is a key ecosystem process that has strong effects on ecosystems, but the animals that provide it have been severely impacted by defaunation in South America. To examine the existence of herbivore-driven top-down control of the vegetation of a South American savanna, in Paper I we established an exclosure experiment for all large herbivores in short (grazing lawns), medium and tall grasslands. We applied linear mixed effects models to study the data we collected in the field. We found that herbivores were decreasing grass height and biomass, and increasing richness in short (grazing lawns) and medium grasslands; but did not have a significant effect in tall grasslands. These results proved that top-down control of the vegetation in this savanna ecosystem exists, but it does not affect tall grasslands. Through the analysis of camera trap images, we attributed this effect on the vegetation to the main grazer in the site, the capybara (Hydrochoerus hydrochaeris).
South America’s history of defaunation has left vacant niche space in its ecosystems that can be occupied by other incoming species. This can be through the invasion of non-native species or the reintroduction of native species. In order to understand the use of the available dietary niche space between resident native, non-native and rewilded herbivores in our field site, we set up a dietary partitioning study. For Paper II I collected dung samples from all large and medium herbivores in the system and we used DNA metabarcoding to find the plant species that they had consumed. We found that non-native species diets overlapped considerably with resident native species and did not expand the dietary niche. Rewilded species diets, on the other hand, moderately overlapped with the rest of herbivores, and thus expanded the dietary breath of the site and could be providing the restoration of some ecological functions.
Defaunation is a global threat to biodiversity that can be partially reversed through rewilding. In Paper III, we present a novel approach for monitoring rewilding progress that focuses on a spatially explicit estimate of progress and ecological integrity within rewilding initiatives. We used high-resolution satellite images and location points for individuals of all four species of rewilded fauna obtained through radio tracking, to create habitat section models for each species. We found that the majority of the site was predicted to be occupied by only one of the rewilded species, and that areas with high ecological integrity increased by 10% through rewilding. Through the results of this analysis, we created a framework to monitor the extent of the habitat occupation by the rewilded species and map which areas are suitable to be selected for future colonization.
UdgivelsesstedAarhus, Denmark
Antal sider100
StatusUdgivet - 28 feb. 2021

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