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Rice fields as alternative habitats for waterbirds : ecological equivalence and mutual cost-benefits for birds and rice growers
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As zonas húmidas naturais, essenciais para aves aquáticas, estão entre os ecossistemas mais ameaçados do planeta. Em paralelo as zonas húmidas artificiais – como os arrozais – têm aumentado a nível global. Os arrozais são fundamentais para a humanidade e constituem um habitat essencial para as aves aquáticas. No entanto, o grau em que estas áreas podem funcionar como habitats alternativos para as aves aquáticas continua a ser amplamente debatido. Além disso, os produtores de arroz frequentemente veem estas aves como pragas, devido ao seu potencial para causar danos às culturas, o que leva à implementação de técnicas de dissuasão para reduzir a presença das aves. Isto resulta num intenso conflito entre humanos e vida selvagem. Neste contexto, o objetivo desta dissertação foi avaliar a adequabilidade dos arrozais como habitats alternativos para as comunidades de aves aquáticas, num cenário de perda global de zonas húmidas naturais. Especificamente, este estudo analisou o papel dos arrozais no suporte das comunidades de aves aquáticas ao longo do ano e investigou de que forma as práticas agrícolas influenciam a abundância e a ecologia alimentar destas aves. Além disso, o trabalho explorou os conflitos entre humanos e vida selvagem nos arrozais, com o objetivo de compreender as preocupações dos agricultores, avaliar o impacto económico destes conflitos e propor estratégias de gestão mais eficazes que conciliem a conservação das aves aquáticas com a produtividade agrícola. Para alcançar os objetivos, o trabalho de campo foi realizado na Lezíria Grande, a maior região produtora de arroz na bacia do rio Tejo e uma das mais importantes de Portugal. Esta área possui uma elevada importância biológica, em particular para as aves aquáticas. Adicionalmente, todos os produtores de arroz desta área consideram as aves aquáticas como pragas e utilizam métodos de dissuasão, criando um cenário de intenso conflito entre humanos e vida selvagem. Estes fatores fizeram da Lezíria Grande um local ideal para a realização deste trabalho. O Capítulo 2 – primeiro capítulo de investigação – teve como objetivo compreender como a estrutura e as funções das comunidades de aves aquáticas nos arrozais se comparam às de outros habitats dentro de uma paisagem agrícola, abrangendo cinco habitats distintos: salinas, lagoas, áreas intertidais, pastagens e arrozais. Durante dois anos, foram realizadas contagens quinzenais de aves aquáticas nestes habitats. Para comparar a composição e estrutura funcional das comunidades de aves aquáticas, utilizou se a técnica de Non-metric multidimensional scaling. Identificaram-se diferenças significativas entre habitats ao longo do ano, impulsionadas por gradientes espaciais (presença de água permanente) e temporais (sazonalidade anual). Os arrozais ocuparam uma posição central dentro destes gradientes, com a composição e estrutura funcional das comunidades de aves aquáticas a sofrerem alterações significativas ao longo do ano, em associação com o ciclo anual de produção do arroz. Este capítulo concluiu que os arrozais desempenham um papel complementar a outros habitats na paisagem, podendo mitigar parcialmente a perda de algumas espécies de aves aquáticas num contexto de declínio global das zonas húmidas naturais.
Natural wetlands – cruciais habitats for waterbirds – are among the most endangered ecosystems worldwide. In parallel, artificial wetlands – such as rice fields – have become increasingly prevalent. Rice fields are vital for humans and offer essential habitat for waterbird. However, the extent to which rice fields can serve as alternative habitats for waterbirds remains widely debated. Furthermore, rice farmers often perceive waterbirds as pests due to their potential to damage crops, leading to the implementation of dissuasion techniques. This results in intense human-wildlife conflict. In this context, the objective of this dissertation was to assess the suitability of rice fields as alternative habitats for waterbird assemblages in light of global wetland loss. Additionally, the study explored human-wildlife conflicts in rice fields and proposed improved management strategies that balance waterbird conservation with agricultural productivity. To achieve these objectives, fieldwork was conducted in Lezíria Grande, the largest rice-growing region in the Tagus River basin and one of the most significant in Portugal. This area was selected due to its high importance for waterbirds. Additionally, all farmers in this area regard waterbirds as pests and use dissuasion techniques leading to human-wildlife conflict. In Chapter 2, the first research chapter of this dissertation, the structure and functions of waterbird communities in rice fields were compared to those in other habitats within an agricultural landscape encompassing five habitats: saltpans, lakes, intertidal areas, pastures, and rice fields. Over two years, waterbird counts were conducted every 15 days in these habitats. Non-metric multidimensional scaling was used to compare the composition and functional structure of the waterbird communities. Differences viii in both metrics were found among habitats throughout the year. These appeared to be driven by spatial (presence of permanent water cover) and temporal gradients (yearly seasonality). Rice fields occupied a central position within the gradients. The composition and functional structure of waterbird communities in rice fields underwent significant changes throughout the year associated with the annual rice production cycle. This chapter concluded that rice fields play a complementary role to other habitats in the landscape, likely acting as a buffer, partially mitigating the loss of some waterbird species amid the global decline of natural wetlands.
Natural wetlands – cruciais habitats for waterbirds – are among the most endangered ecosystems worldwide. In parallel, artificial wetlands – such as rice fields – have become increasingly prevalent. Rice fields are vital for humans and offer essential habitat for waterbird. However, the extent to which rice fields can serve as alternative habitats for waterbirds remains widely debated. Furthermore, rice farmers often perceive waterbirds as pests due to their potential to damage crops, leading to the implementation of dissuasion techniques. This results in intense human-wildlife conflict. In this context, the objective of this dissertation was to assess the suitability of rice fields as alternative habitats for waterbird assemblages in light of global wetland loss. Additionally, the study explored human-wildlife conflicts in rice fields and proposed improved management strategies that balance waterbird conservation with agricultural productivity. To achieve these objectives, fieldwork was conducted in Lezíria Grande, the largest rice-growing region in the Tagus River basin and one of the most significant in Portugal. This area was selected due to its high importance for waterbirds. Additionally, all farmers in this area regard waterbirds as pests and use dissuasion techniques leading to human-wildlife conflict. In Chapter 2, the first research chapter of this dissertation, the structure and functions of waterbird communities in rice fields were compared to those in other habitats within an agricultural landscape encompassing five habitats: saltpans, lakes, intertidal areas, pastures, and rice fields. Over two years, waterbird counts were conducted every 15 days in these habitats. Non-metric multidimensional scaling was used to compare the composition and functional structure of the waterbird communities. Differences viii in both metrics were found among habitats throughout the year. These appeared to be driven by spatial (presence of permanent water cover) and temporal gradients (yearly seasonality). Rice fields occupied a central position within the gradients. The composition and functional structure of waterbird communities in rice fields underwent significant changes throughout the year associated with the annual rice production cycle. This chapter concluded that rice fields play a complementary role to other habitats in the landscape, likely acting as a buffer, partially mitigating the loss of some waterbird species amid the global decline of natural wetlands.
Descrição
Tese de doutoramento em Biologia e Ecologia das Alterações Globais (Ecologia e Biodiversidade Funcional), Universidade de Lisboa, Faculdade de Ciências,2025.
Palavras-chave
functional ecology foraging ecology agricultural management human-wildlife conflicts dissuasion techniques ecologia funcional ecologia alimentar gestão agrícola conflito humanos-vida selvagem técnicas de dissuasão