The Pleistocene extinctions removed a whole functional guild of browsers and grazers. The ecological role of these large animals has been relatively unknown. Modern megaherbivores have a wide range ef effects, including browsing, grazing, seed dispersal.
What drives vegetation dynamics during the Qauternary. At large timescales it is climate, but at fine scales the pattern is less clear. There is vegetation change, but also climate warming and cooling at Pleistocene-Holocene transition.
We do know that during deglaciation, novel vegetation associations were widespread across eastern North America. Plant communities were very different from today - swathes of spruce/ash parklands (no modern analogue). What has driven the formation of these novel associations? Climate change?
Niche theory predicts that novel communities can arise in novel environments. Establishing the order of environment events is challenging. She uses dung fungus Sporomiella as a proxy for megafauna abundance. The analysis combines new pollen analyses from classic no-analogue communities.
Applemean Lake, Indiana. 12 kyr transition from spruce to pine to oak, matches dung fungus decline. Ecosystem novelty is high in the period immediately AFTER the decline in herbivores - allowed deciduous taxa such as ash and ironwood/hophornbeam to thrive. See a spike in charcoal immediately after megafaunal decline (maybe indicator fs loss of herbivory causing build up of biomass and fire fuel)
Now she shows a bunch of data from six sites in the great lakes region. Across all these sites there is ecosystem novelty immediately following the collapse of the megaherbivores.
She then does a massive ordination of fossil and modern pollen assemblages across North America. Axis 1 picks up composition (decid-evergreen) and axis 2 is structure (prairie to forest). Fascinating description of sites jumping from sone stable state to another following megafaunal collapse, with novel and unstable ecosystems in the transition. These sites become ecologically novel, but they are all becoming novel in their own way, and possibly less resilient in their own way. This makes it difficult to predict impacts of extinction or rewilding. Then climate change takes over and ecosystems move to their current states.
Clearly shows widespread impact of megafauna and their loss
When you see evidence for a vegetation driven shift driving herbivore decline, try flipping that in your mind and see if the reverse is true.
What drives vegetation dynamics during the Qauternary. At large timescales it is climate, but at fine scales the pattern is less clear. There is vegetation change, but also climate warming and cooling at Pleistocene-Holocene transition.
We do know that during deglaciation, novel vegetation associations were widespread across eastern North America. Plant communities were very different from today - swathes of spruce/ash parklands (no modern analogue). What has driven the formation of these novel associations? Climate change?
Niche theory predicts that novel communities can arise in novel environments. Establishing the order of environment events is challenging. She uses dung fungus Sporomiella as a proxy for megafauna abundance. The analysis combines new pollen analyses from classic no-analogue communities.
Applemean Lake, Indiana. 12 kyr transition from spruce to pine to oak, matches dung fungus decline. Ecosystem novelty is high in the period immediately AFTER the decline in herbivores - allowed deciduous taxa such as ash and ironwood/hophornbeam to thrive. See a spike in charcoal immediately after megafaunal decline (maybe indicator fs loss of herbivory causing build up of biomass and fire fuel)
Now she shows a bunch of data from six sites in the great lakes region. Across all these sites there is ecosystem novelty immediately following the collapse of the megaherbivores.
She then does a massive ordination of fossil and modern pollen assemblages across North America. Axis 1 picks up composition (decid-evergreen) and axis 2 is structure (prairie to forest). Fascinating description of sites jumping from sone stable state to another following megafaunal collapse, with novel and unstable ecosystems in the transition. These sites become ecologically novel, but they are all becoming novel in their own way, and possibly less resilient in their own way. This makes it difficult to predict impacts of extinction or rewilding. Then climate change takes over and ecosystems move to their current states.
Clearly shows widespread impact of megafauna and their loss
When you see evidence for a vegetation driven shift driving herbivore decline, try flipping that in your mind and see if the reverse is true.