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Megafauna role in distributing nutrients in ecosystems

From: Ben Creisler

These non-dino papers may be of interest . The role of megafauna in
distributing nutrients through an ecosystem obviously would have
applied to dinosaurian megafauna as well.

Christopher E. Doughty, Adam Wolf & Yadvinder Malhi (2013)
The legacy of the Pleistocene megafauna extinctions on nutrient
availability in Amazonia.
Nature Geoscience (advance online publication)

In the late Pleistocene, 97 genera of large animals went extinct,
concentrated in the Americas and Australia. These extinctions had
significant effects on ecosystem structure, seed dispersal and land
surface albedo. However, the impact of this dramatic extinction on
ecosystem nutrient biogeochemistry, through the lateral transport of
dung and bodies, has never been explored. Here we analyse this process
using a novel mathematical framework that analyses this lateral
transport as a diffusion-like process, and we demonstrate that large
animals play a disproportionately large role in the horizontal
transfer of nutrients across landscapes. For example, we estimate that
the extinction of the Amazonian megafauna decreased the lateral flux
of the limiting nutrient phosphorus by more than 98%, with similar,
though less extreme, decreases in all continents outside of Africa.
This resulted in strong decreases in phosphorus availability in
eastern Amazonia away from fertile floodplains, a decline which may
still be ongoing. The current P limitation in the Amazon basin may be
partially a relic of an ecosystem without the functional connectivity
it once had. We argue that the Pleistocene megafauna extinctions
resulted in large and ongoing disruptions to terrestrial
biogeochemical cycling at continental scales and increased nutrient
heterogeneity globally.


Adam Wolf, Christopher E. Doughty & Yadvinder Malhi (2013)
Lateral Diffusion of Nutrients by Mammalian Herbivores in Terrestrial
PLoS ONE 8(8): e71352

Animals translocate nutrients by consuming nutrients at one point and
excreting them or dying at another location. Such lateral fluxes may
be an important mechanism of nutrient supply in many ecosystems, but
lack quantification and a systematic theoretical framework for their
evaluation. This paper presents a mathematical framework for
quantifying such fluxes in the context of mammalian herbivores. We
develop an expression for lateral diffusion of a nutrient, where the
diffusivity is a biologically determined parameter depending on the
characteristics of mammals occupying the domain, including
size-dependent phenomena such as day range, metabolic demand, food
passage time, and population size. Three findings stand out: (a)
Scaling law-derived estimates of diffusion parameters are comparable
to estimates calculated from estimates of each coefficient gathered
from primary literature. (b) The diffusion term due to transport of
nutrients in dung is orders of magnitude large than the coefficient
representing nutrients in bodymass. (c) The scaling coefficients show
that large herbivores make a disproportionate contribution to lateral
nutrient transfer. We apply the diffusion equation to a case study of
Kruger National Park to estimate the conditions under which
mammal-driven nutrient transport is comparable in magnitude to other
(abiotic) nutrient fluxes (inputs and losses). Finally, a global
analysis of mammalian herbivore transport is presented, using a
comprehensive database of contemporary animal distributions. We show
that continents vary greatly in terms of the importance of
animal-driven nutrient fluxes, and also that perturbations to nutrient
cycles are potentially quite large if threatened large herbivores are
driven to extinction.


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