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Through their interactions with the biosphere, wild herbivorous mammals could influence the climate. But it is difficult to estimate their importance without a model that can estimate their populations and simulate their ecological role.

This is why two climatologists from the LSCE, as part of a collaborative project, have developed a numerical model of mammal populations, which they have supplemented with empirical data.

They were thus able to estimate the global biomass of wild herbivorous mammals:

• 330 megatonnes (Mt) before the advent of the industrial revolution ;
• 180 Mt today, while human activities have led to the decline of many populations.

A decline that varies according to the size of the species

According to their model, the loss of species habitat has reduced the biomass of large herbivores by 60% and that of small herbivores by 30%.

This reversed the distribution between large and small animals, with small herbivores becoming more abundant than large ones.

• The biomass of large herbivores (with a mass greater than 10 kg) has more than halved, falling from 193 Mt to 82 Mt.
• The biomass of small herbivores fell more slowly, from 138 Mt to 98 Mt.

• Outside Africa and the tropics, the decline in large mammals is marked in areas that are now dominated by humans, making the recovery of large species in these regions problematic for lack of space.

  According to Fabio Berzaghi, who led the project at LSCE and now works at World Maritime University(Sweden), "these estimates of herbivore biomass provide a quantitative benchmark for setting conservation and rewilding objectives on large spatial scales. What's more, they are less unfavourable than those published previously. They force us to pay more attention to small, hitherto neglected species, which can help maintain the vitality of the terrestrial ecosystem. What's more, this new numerical model will help us to take account of the role of mammals in global climate models.

  References

  Trait-based mechanistic approach highlights global patterns and losses of herbivore biomass functional diversity

  Total population reports are ill-suited for global biomass estimation of wild animals, PNAS