Defaunation is a massive contemporary phenomenon. Lots of drivers and synergies amongst drivers. He shows a graph of bushmeat extraction per hectare in various tropical countries. In the Brazilian Amazon 16.6-23.5 million animals removed per year (Robinson and Redford, Peres 2000)
The characteristic extinction time (CET) - what is the time required in the future to put 50% of the species in a group into extinction. The timescale is around a few centuries
Map of density of endangered mammal species. Hotspots in tropics, especially SE Asia.
The defaunation gradient. Plots biomass/abundance of animals vs impact of defaunation drivers. Large vulnerable species decline quickly. Medium animals may increase in the short term (loss of predators) but decrease in the long term. Small, fecund, robust species increase in density and biomass over time, In the extreme case we can talk about the phenomenon of RODENTIZATION, or in Spanish, RATIFICACION..
Two cases.
1. The rodentation-defaunation cascade. Increased rodent abundance -> increased predation on small sets -> decline of small seeded species. Large wide life decline -> reduced predation of large seeds -> reduced loss herbivory of large seeded plants. End result is reduction of small seeded trees and increase of large seeded trees.
In Los Tuxtlas, Mexico, understorey ends up dominated by large-seeded Astrocaryum mexicanum palm (Martinez-Ramos et al., in prep). As palm density increases, there is an decrease in sapling density of other species. This leads to impoverishment of future tree diversity.
2. African savanna example. Replicated experimental exclosures at Mpala Research Station, Kenya.. A cascade of effects resulting from experimental defaunation.
Large wildlife removal -> cascade to other consumers -> effects on function and services -> effects on plant-animal interactions
High rodents increase ectoparasites which increase pathogens. The increase in number of rodents increases the density of infected fleas.
Conclusions: The mesofauna of ecosystem are important functional components of the system and relevant for the well-being of humans
Andrew Balmford: situation is more nuanced when we consider introduction of livestock. Deforestation and fire also add to complexity.
John Terborgh: his results from the Peru forests is the opposite. Release of small seeded trees. The rodent community is different
Boo Maisels: the response in Central Africa is also the opposite. Good to compare across sites
The characteristic extinction time (CET) - what is the time required in the future to put 50% of the species in a group into extinction. The timescale is around a few centuries
Map of density of endangered mammal species. Hotspots in tropics, especially SE Asia.
The defaunation gradient. Plots biomass/abundance of animals vs impact of defaunation drivers. Large vulnerable species decline quickly. Medium animals may increase in the short term (loss of predators) but decrease in the long term. Small, fecund, robust species increase in density and biomass over time, In the extreme case we can talk about the phenomenon of RODENTIZATION, or in Spanish, RATIFICACION..
Two cases.
1. The rodentation-defaunation cascade. Increased rodent abundance -> increased predation on small sets -> decline of small seeded species. Large wide life decline -> reduced predation of large seeds -> reduced loss herbivory of large seeded plants. End result is reduction of small seeded trees and increase of large seeded trees.
In Los Tuxtlas, Mexico, understorey ends up dominated by large-seeded Astrocaryum mexicanum palm (Martinez-Ramos et al., in prep). As palm density increases, there is an decrease in sapling density of other species. This leads to impoverishment of future tree diversity.
2. African savanna example. Replicated experimental exclosures at Mpala Research Station, Kenya.. A cascade of effects resulting from experimental defaunation.
Large wildlife removal -> cascade to other consumers -> effects on function and services -> effects on plant-animal interactions
High rodents increase ectoparasites which increase pathogens. The increase in number of rodents increases the density of infected fleas.
Conclusions: The mesofauna of ecosystem are important functional components of the system and relevant for the well-being of humans
Andrew Balmford: situation is more nuanced when we consider introduction of livestock. Deforestation and fire also add to complexity.
John Terborgh: his results from the Peru forests is the opposite. Release of small seeded trees. The rodent community is different
Boo Maisels: the response in Central Africa is also the opposite. Good to compare across sites