Abstract:
Large mammalian terrestrial herbivores, such as elephants, have
dramatic effects on the ecosystems they inhabit and at high
population densities their environmental impacts can be devastating.
Pleistocene terrestrial ecosystems included a much greater
diversity of megaherbivores (e.g., mammoths, mastodons, giant
ground sloths) and thus a greater potential for widespread habitat
degradation if population sizes were not limited. Nevertheless,
based on modern observations, it is generally believed that populations
of megaherbivores (>800 kg) are largely immune to the
effects of predation and this perception has been extended into
the Pleistocene. However, as shown here, the species richness of
big carnivores was greater in the Pleistocene and many of them
were significantly larger than their modern counterparts. Fossil
evidence suggests that interspecific competition among carnivores
was relatively intense and reveals that some individuals specialized
in consuming megaherbivores. To estimate the potential impact
of Pleistocene large carnivores, we use both historic and
modern data on predator–prey body mass relationships to predict
size ranges of their typical and maximum prey when hunting as
individuals and in groups. These prey size ranges are then compared
with estimates of juvenile and subadult proboscidean body
sizes derived from extant elephant growth data. Young proboscideans
at their most vulnerable age fall within the predicted prey
size ranges of many of the Pleistocene carnivores. Predation on
juveniles can have a greater impact on megaherbivores because of
their long interbirth intervals, and consequently, we argue that
Pleistocene carnivores had the capacity to, and likely did, limit
megaherbivore population sizes.
