Volume 511, 1 April 2015, Pages 288–297
Unravelling trophic subsidies of agroecosystems for biodiversity conservation: Food consumption and nutrient recycling by waterbirds in Mediterranean rice fields
Highlights
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- Waterbirds foraging and roosting in Extremadura´s rice fields recycled more than 1.0 kg·ha-1 of N and 0.2 kg·ha-1 of P during winter.
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- Additionally, 2.3 tons of N and 550 kilograms of P were removed from rice fields and transported to adjacent reservoirs.
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- These should result in a direct benefit for rice farmers by improving nutrient recycling through defecation with respect to artificial fertilization, highlighting the important ecosystem services provided by waterbirds.
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- Our findings may be especially helpful for environmental management decisions regarding rice agroecosystems, which can often serve as important areas for the conservation of migratory waterbirds.
Abstract
Waterbirds
can reallocate a considerable amount of nutrients within agricultural
fields and between agriculture sites and wetlands. However their effects
on biogeochemical cycles have rarely been quantified. We estimated bird
numbers, diet (from stable isotope analysis), food supply, and the food
consumption on rice fields by overwintering waterbirds in one of the
most important areas for rice production in southwestern Europe and a
key area for various migrating and resident waterbird species. Herein,
we modelled the nutrient (N and P) recycling in rice fields, and their
transport to reservoirs. The energy consumption by waterbirds
(96,605 ± 18,311 individuals) on rice fields during winter averaged at
89.9 ± 39.0 kJ·m− 2, with its majority (89.9%) belonging to
foraging on rice seeds. Thus, the birds removed about 26% of rice seeds
leftover after harvest (estimated in 932.5 ± 504.7 seeds·m− 2
in early winter) wherein common cranes and dabbling ducks (four
species) were the most important consumers. Waterbirds foraging and
roosting in the rice fields recycled more than 24.1 (1.0 kg·ha− 1) of N and an additional 5.0 tons (0.2 kg·ha− 1)
of P in the Extremadura's rice fields during winter. Additionally, we
estimated that 2.3 tons of N and 550 kg of P were removed from rice
fields and transported to reservoirs. The seasonal foraging of wildlife
should result in a direct benefit for rice farmers by improving nutrient
recycling through defecation by waterbirds with respect to artificial
fertilisation. Additionally, rice fields located in the cranes' core
wintering areas can provide sufficient food supply to induce habitat
shift from their traditional wintering habitat in ‘dehesas’ to rice
fields, which causes indirect socioeconomic benefit through reduced
acorn consumption by cranes. Our modelling approach may thus be
especially helpful for management decisions regarding rice
agroecosystems in areas which are also important for the conservation of
migratory waterbirds.
Keywords
- Cranes;
- Dabbling ducks;
- Ecosystem services;
- Extremadura;
- Isotopes;
- Management;
- Nitrogen;
- Phosphorous
Copyright © 2014 Elsevier B.V. All rights reserved.
