Data from: Organic matter and nutrient inputs from large wildlife influence ecosystem function in the Mara River, Africa

Animals can be important vectors for the movement of resources across
ecosystem boundaries. Animals add resources to ecosystems primarily
through egestion, excretion and carcasses, and the stoichiometry and
bioavailability of these inputs likely interacts with characteristics of
the recipient ecosystem to determine their effects on ecosystem function.
We studied the influence of hippopotamus excretion/egestion and wildebeest
carcasses, and their interactions with discharge, in the Mara River,
Kenya. We measured nutrient dissolution and decomposition rates of
wildlife inputs, the influence of inputs on nutrient concentrations and
nutrient limitation in the river and the influence of inputs on biofilm
growth and function in both experimental streams and along a gradient of
inputs in the river. We found that hippopotamus excretion/egestion
increase ammonium and coarse particulate organic matter in the river, and
wildebeest carcasses increase ammonium, soluble reactive phosphorus, and
total phosphorus. Concentrations of dissolved carbon and nutrients in the
water column increased along a gradient of wildlife inputs and during low
discharge, although concentrations of particulate carbon decreased during
low discharge due to deposition on the river bottom. Autotrophs were
nitrogen-limited, and heterotrophs were carbon-limited and nitrogen- and
phosphorus- co-limited, upstream of animal inputs, but there was no
nutrient limitation downstream of inputs. In experimental streams, hippo
and wildebeest inputs together increased biofilm GPP and R. These results
differed in the river, where low concentrations of hippo inputs increased
gross primary production (GPP) and respiration (R) of biofilms, but high
concentrations of hippo inputs in conjunction with wildebeest inputs
decreased GPP. Our research shows that inputs from large wildlife
alleviate nutrient limitation and stimulate ecosystem metabolism in the
Mara River, and that the extent to which these inputs subsidize the
ecosystem is mediated by the quantity and quality of inputs and discharge
of the river ecosystem. Thus, animal inputs provide an important
ecological subsidy to this river, and animal inputs were likely important
in many other rivers prior to the widespread extirpation of large
wildlife.