Respostas espaço-temporais de mamíferos de médio e grande porte em paisagens modificadas de Cerrado do nordeste do estado de São Paulo
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Data
2019-08-01
Autores
Krepschi, Victor Gasperotto [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O efeito da redução do habitat natural na biodiversidade é idiossincrática a respeito das relações que se estabelecem entre as espécies e as características das paisagens modificadas pelo homem. Nesse contexto, as evidências científicas evidenciam cada vez mais a importância de se utilizar não somente a escala espacial na interpretação das respostas da biodiversidade, mas também a escala temporal. A correlação dos parâmetros biológicos atuais com características do ambiente pretérito mostra que respostas atrasadas das espécies às modificações podem ocorrer após um distúrbio ambiental, o que como consequência, gera interpretação errôneas da relação das espécies com os ambientes da paisagem no presente, o que vem a comprometer as subsequentes tomadas de decisão de viés conservacionista. A fim de compreender como espécies de mamíferos de médio e grande porte neotropicais estão respondendo à paisagens de Cerrado que passaram por redução de habitat ao longo de um intervalo temporal de 48 anos, a presente tese objetivou em seus capítulos: (i) caracterizar a trajetória e a transição das classes de cobertura e uso do solo de três paisagens modificadas pelo homem, (ii) Detectar a existência de respostas atrasadas de sete espécies de mamíferos neotropicais de médio e grande porte em relação ao ambiente nativo dessas três paisagens e (iii) detectar a existência de limiares ecológicos nas respostas de seis espécies de mamíferos neotropicais a ambientes nativo e antrópico. As três paisagens de estudo estão compreendidas na região nordeste do estado de São Paulo e possuem remanescentes de vegetação nativa de Cerrado e de Mata Atlântica sob diferentes graus de proteção ambiental. A partir dos limites das áreas protegidas criou-se uma zona de amortecimento de cinco quilômetros a fim de delimitar a extensão das paisagens a serem estudadas. As classes de cobertura e uso do solo dessas paisagens foi criada a partir de fotointerpretação de imagens aéreas, retroativamente no tempo, nos anos de 2010, 1983 e 1962. Foram determinadas 206 paisagens focais circulares de 200ha nas paisagens de estudo, de forma aleatória e igualmente distribuídas dentro e fora de áreas protegidas, a fim de se calcular a proporção das classes de cobertura e uso do solo em cada paisagem focal. Dessa forma, caracterizaram-se a trajetória de cada classe de cobertura e uso do solo e a transição das classes de vegetação nativa de cada paisagem, entre os períodos e entre as paisagens. Para a amostragem biológica de mamíferos de médio e grande porte foi instalada uma armadilha fotográfica durante 30 dias consecutivos em cada uma dessas paisagens focais para obtenção de registros fotográficos das espécies. Os registros de sete espécies foi individualmente estruturados em históricos de captura de 6 ocasiões de 5 dias, que juntamente com as covariáveis de paisagem específica de cada espécie, foi utilizado para as análises de respostas atrasadas (Capítulo 2) e de limiares ecológicos (Capítulo 3). O método de estimativa de ocupação considerando a detecção imperfeita de espécies, na estrutura de espécie única e estação única foi empregado para essas duas análises. Os principais resultados obtidos foram de que duas das paisagens possuíram predominância de Cerrado aberto (ambiente savânico) na primeira cena temporal da trajetória da paisagem, mostrando que a interpretação encontrada no ano de 2010, a qual indica uma similaridade das áreas em relação ao percentual de cobertura de vegetação nativa, é equivocada. Também demonstrou-se que as principais modificações no ambiente nativo ocorreram entre os anos de 1962 e 1983 em comparação com a magnitude de modificação ocorrida no segundo período, de 1983 a 2010, principalmente em decorrência da expansão agrícola, em parte incentivada por ações governamentais como o programa Pró-álcool. O terceiro resultado mais importante desse capítulo foi a de detectar que o Cerrado aberto foi drasticamente substituído não somente pelas culturas de cana e de reflorestamento comercial de eucalipto e pinus, mas também pela contínua substituição ocasionada adensamento de espécies florestais sobre as espécies da savana, um fenômeno que ocorre ao redor das savanas do mundo conhecido como “savanna enchroachment”, como uma consequência da supressão do fogo no ecossistema savânico do Cerrado. O resultado das análises de respostas atrasadas evidenciou que das sete espécies de mamíferos investigadas, três, o tamanduá-bandeira (Myrmecophaga tridactyla), o lobo-guará (Chrysocyon brachiurus) e o veado-catingueiro (Mazama gouazoubira), estão mais fortemente associadas com o Cerrado aberto existente em 1962 do que com as classes de cobertura do solo da paisagem atual, com exceção do lobo-guará, que também demonstrou uma resposta negativa à proporção atual de cana-de-açúcar nas paisagens. Baseando-se na literatura disponível de respostas atrasadas, estimou-se, de forma conservadora, que um intervalo de tempo entre 40 e 60 anos seria necessário para a primeira espécie de mamífero de grande porte se extinguir das paisagens, o que provavelmente já ocorreu na comunidade de mamíferos neotropicais de médio e grande porte dessa região. Em relação à ocorrência de limiares ecológicos na resposta das espécies à vegetação nativa e à silvicultura, foi encontrado que somente o caititu (Pecary tajacu) apresenta resposta em limiar para a floresta nativa em uma das paisagens, necessitando quantidades superiores a 50% de floresta nativa na paisagem para assegurar que declínios acentuados em sua ocupação não ocorram. Ainda que as paisagens de estudo não retenham essa quantidade de vegetação nativa como um todo (retém em torno de 27% de cobertura de vegetação nativa), o que se sugere é que a presença de um único e grande remanescente de vegetação nativa protegido como Unidade de Conservação Integral em uma das paisagens do estudo esteja exercendo efeito positivo na permanência dessa espécie de mamífero com elevada dependência dos recursos florestais. Essa evidência se contrapõe à proposição do Projeto de Lei no 2362/2019, em tramitação no Senado Brasileiro, de revogar a existência das Reservas Legais no Código Florestal da Constituição Brasileira, essas que compreendem uma quantia fixa de ambientes nativos preservados dentro de terras privadas para assegurar o bom funcionamento e provisão de serviços do ecossistema. Os achados desse estudo indicam que o desaparecimento das savanas nas paisagens de estudo ameaça a permanência de espécies de mamíferos de médio e grande porte, incluindo duas espécies que encontram-se sob estado de ameaça de extinção. A principal medida de conservação sugerida para essas paisagens de estudo e contextos de ocupação humana similares em outras localidades é a de aumentar a proporção de vegetação nativa em paisagens modificadas pelo homem, em especial das fitofisionomias abertas do bioma Cerrado. Contudo, recomenda-se que técnicas de restauração apropriadas para a manutenção do Cerrado savânico sejam adotadas, de forma a evitar que ambientes florestais nativos aumentem em detrimento de ambientes nativos de feição aberta.
The effect of habitat reduction on biodiversity is idiosyncratic regarding the established relationships among species and the traits of human-modified landscapes. In this manner novel scientific evidences point to the importance of considering not only the spatial scale on the interpretation of species responses, but also the temporal scale. The correlation between biological parameters of the present and environmental traits of the past show that species might present delayed responses after a disturbance event, and as consequence, species responses to current landscape traits may be misleading for conservation purposes and environmental management actions. In order to understand how the neotropical medium and large-sized mammals are responding to human-modified landscapes of Cerrado under a 48-years interval of disturbance, the present dissertation aimed in their three chapters: (i) to describe land use and land cover trajectory and native vegetation transition of three human-modified landscapes, (ii) to detect the existence of time-lagged responses among seven neotropical medium and large-sized mammal species to their the natural environment and (iii) to detect the existence of ecological threshold responses of six neotropical medium and large-sized mammal species to natural and human-modified environments. The three studied landscapes are located in the northeastern region of São Paulo State and harbor important protected remnants of Cerrado and Atlantic Rainforest under distinct levels of environmental protection enforcement. From the edges of the protected remnants a 5 km buffer zone was stablished to settle the limits of the landscape under study. Land use and land cover categories were mapped from visual interpretation of aerial images, backwards in time, in three distinct time scenes: 2010, 1983 and 1962. A total of 206 focal landscapes with area of 200ha were randomly created in all three landscapes with a balanced distribution inside and outside of protected areas, aiming the obtaining of the proportion of each class of land cover in each focal landscape. The trajectory of land cover classes and the transition of native vegetation were characterized for each landscape separately to perform comparison within and among landscapes. Medium and large-sized mammal species were surveyed through one camera-trap device placed during 30 days in each focal landscape. The individual history of records of the seven elected species of mammals were arranged in six occasions of five days and joined to the landscape covariates chosen for each species to perform time-lag responses analysis (chapter 2 of this dissertation) and ecological thresholds analysis (Chapter 3). Occupancy estimates modelling accounting for imperfect detection was adopted for both analysis in the in the single species/single framework. The main results of landscape transition showed that two of the three landscapes were mostly covered by the open savannah in 1962 while the third landscape by the wooded savanna, showing that relying in present time native vegetation proportion in the landscape (year of 2010), which by its turn denoted similarity in vegetation composition among the studied landscapes, might be misleading. It was also detected that the main changes in natural environment occurred during 1962 and 1983 period in comparison with the magnitude of change of the second period, between 1983 to 2010, which was partially as a consequence of governmental incentives to agricultural expansion. The third important result of landscape trajectory was noticing that the opened savanna environments were replaced not only but sugar cane and forestry crops, but also encroached by the continuous growth of the wooded savanna species, a phenomena known as “savanna encroachment”, a consequence of fire suppression in the Cerrado ecosystem. The results found for time-lag responses showed that among the seven mammal species analyzed, three species, named the giant anteater (Myrmecophaga tridactyla), the maned wolf (Chrysocyon brachiurus) and the brown brocket deer (Mazama gouazoubira) are still responding to the opened savannah environments of 1962 instead of the current land cover types that substitute them, with the exception of the maned wolf negative response to sugar cane proportion in the landscape. Based on literature data, a conservative estimation points to a 40 to 60 years delay in medium and large-sized mammal response to the first local species extinction take place, what has probably occurred in the community of neotropical medium and large-sized mammals of the studied region. This suggests an uncertain future for the three species presenting delayed responses in the modified landscapes. Regarding the occurrence of ecological threshold responses of the mammal species to native and anthropogenic environments, it was found that collared peccary occupancy presents a steep decline in the threshold cut-value of 50% of native forest in the landscape, even though the landscape where peccary occurs present a mean proportion of 27% of this land cover type. In this sense, it is probable that the presence of the single and large remnant of wooded forest, enforced by law as a Full Protection Conservation Unit, might be exerting a positive effect in the presence of this forest dwelling species, which highly depends on native forest resources. This evidences counteract the recently proposed Law Project (number 2362/2019) processing in the Brazilian Congress, which intend to revoke the category of environmental protection of “Legal Reserves” (a fixed set-aside portion of land of native environment in private lands that assures the maintenance of biodiversity and ecosystem services) from the Brazilian Constitution in favor of agricultural expansion in the country. The evidences of this study indicates that the decrease of the opened savannas in the studied landscapes is a threat to the maintenance of medium and large-sized mammal species. Based in these findings, the most important conservation action suggested to be implemented in the landscapes of this study and other landscapes with similar environmental scenario is to increase the proportion of native vegetation in human-modified landscapes, especially the opened physiognomies of Cerrado. Notwithstanding, it is recommended the adoption of appropriated restoration management technics in order assure the maintenance of the opened Cerrado environments and prevent the savannah encroachment by forests.
The effect of habitat reduction on biodiversity is idiosyncratic regarding the established relationships among species and the traits of human-modified landscapes. In this manner novel scientific evidences point to the importance of considering not only the spatial scale on the interpretation of species responses, but also the temporal scale. The correlation between biological parameters of the present and environmental traits of the past show that species might present delayed responses after a disturbance event, and as consequence, species responses to current landscape traits may be misleading for conservation purposes and environmental management actions. In order to understand how the neotropical medium and large-sized mammals are responding to human-modified landscapes of Cerrado under a 48-years interval of disturbance, the present dissertation aimed in their three chapters: (i) to describe land use and land cover trajectory and native vegetation transition of three human-modified landscapes, (ii) to detect the existence of time-lagged responses among seven neotropical medium and large-sized mammal species to their the natural environment and (iii) to detect the existence of ecological threshold responses of six neotropical medium and large-sized mammal species to natural and human-modified environments. The three studied landscapes are located in the northeastern region of São Paulo State and harbor important protected remnants of Cerrado and Atlantic Rainforest under distinct levels of environmental protection enforcement. From the edges of the protected remnants a 5 km buffer zone was stablished to settle the limits of the landscape under study. Land use and land cover categories were mapped from visual interpretation of aerial images, backwards in time, in three distinct time scenes: 2010, 1983 and 1962. A total of 206 focal landscapes with area of 200ha were randomly created in all three landscapes with a balanced distribution inside and outside of protected areas, aiming the obtaining of the proportion of each class of land cover in each focal landscape. The trajectory of land cover classes and the transition of native vegetation were characterized for each landscape separately to perform comparison within and among landscapes. Medium and large-sized mammal species were surveyed through one camera-trap device placed during 30 days in each focal landscape. The individual history of records of the seven elected species of mammals were arranged in six occasions of five days and joined to the landscape covariates chosen for each species to perform time-lag responses analysis (chapter 2 of this dissertation) and ecological thresholds analysis (Chapter 3). Occupancy estimates modelling accounting for imperfect detection was adopted for both analysis in the in the single species/single framework. The main results of landscape transition showed that two of the three landscapes were mostly covered by the open savannah in 1962 while the third landscape by the wooded savanna, showing that relying in present time native vegetation proportion in the landscape (year of 2010), which by its turn denoted similarity in vegetation composition among the studied landscapes, might be misleading. It was also detected that the main changes in natural environment occurred during 1962 and 1983 period in comparison with the magnitude of change of the second period, between 1983 to 2010, which was partially as a consequence of governmental incentives to agricultural expansion. The third important result of landscape trajectory was noticing that the opened savanna environments were replaced not only but sugar cane and forestry crops, but also encroached by the continuous growth of the wooded savanna species, a phenomena known as “savanna encroachment”, a consequence of fire suppression in the Cerrado ecosystem. The results found for time-lag responses showed that among the seven mammal species analyzed, three species, named the giant anteater (Myrmecophaga tridactyla), the maned wolf (Chrysocyon brachiurus) and the brown brocket deer (Mazama gouazoubira) are still responding to the opened savannah environments of 1962 instead of the current land cover types that substitute them, with the exception of the maned wolf negative response to sugar cane proportion in the landscape. Based on literature data, a conservative estimation points to a 40 to 60 years delay in medium and large-sized mammal response to the first local species extinction take place, what has probably occurred in the community of neotropical medium and large-sized mammals of the studied region. This suggests an uncertain future for the three species presenting delayed responses in the modified landscapes. Regarding the occurrence of ecological threshold responses of the mammal species to native and anthropogenic environments, it was found that collared peccary occupancy presents a steep decline in the threshold cut-value of 50% of native forest in the landscape, even though the landscape where peccary occurs present a mean proportion of 27% of this land cover type. In this sense, it is probable that the presence of the single and large remnant of wooded forest, enforced by law as a Full Protection Conservation Unit, might be exerting a positive effect in the presence of this forest dwelling species, which highly depends on native forest resources. This evidences counteract the recently proposed Law Project (number 2362/2019) processing in the Brazilian Congress, which intend to revoke the category of environmental protection of “Legal Reserves” (a fixed set-aside portion of land of native environment in private lands that assures the maintenance of biodiversity and ecosystem services) from the Brazilian Constitution in favor of agricultural expansion in the country. The evidences of this study indicates that the decrease of the opened savannas in the studied landscapes is a threat to the maintenance of medium and large-sized mammal species. Based in these findings, the most important conservation action suggested to be implemented in the landscapes of this study and other landscapes with similar environmental scenario is to increase the proportion of native vegetation in human-modified landscapes, especially the opened physiognomies of Cerrado. Notwithstanding, it is recommended the adoption of appropriated restoration management technics in order assure the maintenance of the opened Cerrado environments and prevent the savannah encroachment by forests.
Descrição
Palavras-chave
Cerrado, Mamíferos de médio e grande porte, Respostas atrasadas, Débito de extinção, Limiares ecológicos, Savannah, Medium and large-sized mammals, Time-lagged responses, Extinction debt, Ecological thresholds