Bushmeat biogeochemistry: hunting tropical mammals alters ecosystem phosphorus budgets

Wild meat (or ‘bushmeat’) hunting is nearly ubiquitous across the tropics and is very often unsustainable—driving declines and extirpation of numerous mammal populations. Loss of these animals can alter the transport of nutrients within and between ecosystems. But whether the physical removal of vertebrate carcasses and the nutrients that they store can reduce overall nutrient availability in ecosystems has been little explored. At 32 sites on three continents, we show that annual phosphorus (P) loss via mammal exploitation was low relative to the rate of atmospheric P deposition. But at four sites in Africa and Southeast Asia, removal of P in the skeletons of hunted mammals exceeded the atmospheric input of this nutrient by 10-fold or more. Because P is the growth-limiting nutrient for many tropical terrestrial ecosystems and certain large mammals, the imbalance created by the removal of mammal biomass under very high hunting scenarios could reduce ecosystem carrying capacity if no compensatory P additions occur in the system. This biogeochemical perspective on bushmeat exploitation raises further concerns about harvest sustainability and human food security in areas where hunting rates are high and ecosystem P inputs low.

Global and regional phosphorus budgets in agricultural systems and their implications for phosphorus-use efficiency

The application of phosphorus (P) fertilizer to agricultural soils increased by 3.2 % annually from 2002 to 2010. We quantified in detail the P inputs and outputs of cropland and pasture and the P fluxes through human and livestock consumers of agricultural products on global, regional, and national scales from 2002 to 2010. Globally, half of the total P inputs into agricultural systems accumulated in agricultural soils during this period, with the rest lost to bodies of water through complex flows. Global P accumulation in agricultural soil increased from 2002 to 2010 despite decreases in 2008 and 2009, and the P accumulation occurred primarily in cropland. Despite the global increase in soil P, 32 % of the world's cropland and 43 % of the pasture had soil P deficits. Increasing soil P deficits were found for African cropland vs. increasing P accumulation in eastern Asia. European and North American pasture had a soil P deficit because the continuous removal of biomass P by grazing exceeded P inputs. International trade played a significant role in P redistribution among countries through the flows of P in fertilizer and food among countries. Based on country-scale budgets and trends we propose policy options to potentially mitigate regional P imbalances in agricultural soils, particularly by optimizing the use of phosphate fertilizer and the recycling of waste P. The trend of the increasing consumption of livestock products will require more P inputs to the agricultural system, implying a low P-use efficiency and aggravating P-stock scarcity in the future. The global and regional phosphorus budgets and their PUEs in agricultural systems are publicly available at https://doi.pangaea.de/10.1594/PANGAEA.875296.