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Tipping the scales : bats' response to artificial light on a local and national scale
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Com o crescimento da população humana, aumenta também o uso da luz artificial à noite que
se torna uma ameaça emergente à biodiversidade noturna. Os morcegos são particularmente vulneráveis
a esta ameaça e podem ser afetados de maneira distinta em diferentes escalas. Numa escala local,
espécies de voo rápido alimentam-se de insetos atraídos pela luz, enquanto espécies de voo lento evitam
áreas iluminadas. Numa escala mais abrangente, demonstrou-se que ambos os grupos tendencialmente
evitam áreas iluminadas. Assim, procurámos perceber como a atividade, a ocorrência e a composição
das comunidades de morcegos se alteram num gradiente de luz artificial em diferentes escalas, tendo
em conta variáveis ambientais e de vegetação. A amostragem local realizou-se em três áreas florestadas
no centro de Portugal. Para a análise nacional usámos dados do Atlas dos Morcegos de Portugal
Continental. Localmente, a atividade total dos morcegos e do grupo de voo rápido diminuiu com a
distância à luz. Plecotus sp. foi o único do grupo de voo lento a ser afetado pela distância à luz, com
uma diminuição da atividade. No estudo local, a atração parece ocorrer em maior escala que a repulsão.
Evidenciando a escala do efeito de repulsão, a preferência do grupo Plecotus sp. por zonas próximas da
luz está condicionada pela preferência por zonas com menos luminância, revelando um trade-off entre
o risco de predação e a abundância de presas. No estudo nacional, espécies de ambos os grupos
preferiram zonas menos iluminadas, demonstrando a importância da escala em estudos de luz artificial.
Espécies que beneficiam da presença de luz artificial a uma pequena escala mostram um padrão
contrastante em escalas maiores. Com o aumento global de luz artificial à noite, este estudo salientou
que a investigação dos impactos da luz artificial a várias escalas é crucial para a conservação da
biodiversidade noturna.
As the human population grows, so does the use of artificial light at night (ALAN), which is becoming an emerging threat to nocturnal wildlife. Bats, who are particularly vulnerable to this threat, can be affected in distinct ways at different scales. On a local scale, fast-flying bat species hunt insects attracted to light sources while slow-flying species avoid artificially lit areas. Both groups have been shown to avoid artificial light on a larger scale. Therefore, we sought to understand how bat activity, occurrence and assemblage composition change in a gradient of artificial light at different scales, considering other environmental and vegetation variables. Our local sampling took place in three forested areas in central Portugal. We defined linear transects in a gradient of light and sampled bats with ultrasound recorders. We used presence-absence data from the Atlas dos Morcegos de Portugal Continental for the national analysis. On a local scale, bat activity decreased with distance to light. The vast majority of the fast-flying bats showed the same pattern. Plecotus sp. was the only group of slow flying species affected by distance to light, showing decreased activity. Locally, the attraction to light seems to occur on a larger spatial scale than the repulsion. Attesting to the scale of the repulsion effect, Plecotus sp.'s preference for places closer to light sources is conditioned by a preference for low luminance values, which suggests a trade-off between predation risk and high prey abundance. On the national analysis, species from both groups preferred less lit areas, illustrating the importance of scale in ALAN studies. Species who benefit from ALAN at a local scale exhibit a contrasting pattern at a larger scale. In conclusion, with the global increase of ALAN, this study revealed that researching ALANs impacts at several scales is pivotal for the conservation of nocturnal biodiversity.
As the human population grows, so does the use of artificial light at night (ALAN), which is becoming an emerging threat to nocturnal wildlife. Bats, who are particularly vulnerable to this threat, can be affected in distinct ways at different scales. On a local scale, fast-flying bat species hunt insects attracted to light sources while slow-flying species avoid artificially lit areas. Both groups have been shown to avoid artificial light on a larger scale. Therefore, we sought to understand how bat activity, occurrence and assemblage composition change in a gradient of artificial light at different scales, considering other environmental and vegetation variables. Our local sampling took place in three forested areas in central Portugal. We defined linear transects in a gradient of light and sampled bats with ultrasound recorders. We used presence-absence data from the Atlas dos Morcegos de Portugal Continental for the national analysis. On a local scale, bat activity decreased with distance to light. The vast majority of the fast-flying bats showed the same pattern. Plecotus sp. was the only group of slow flying species affected by distance to light, showing decreased activity. Locally, the attraction to light seems to occur on a larger spatial scale than the repulsion. Attesting to the scale of the repulsion effect, Plecotus sp.'s preference for places closer to light sources is conditioned by a preference for low luminance values, which suggests a trade-off between predation risk and high prey abundance. On the national analysis, species from both groups preferred less lit areas, illustrating the importance of scale in ALAN studies. Species who benefit from ALAN at a local scale exhibit a contrasting pattern at a larger scale. In conclusion, with the global increase of ALAN, this study revealed that researching ALANs impacts at several scales is pivotal for the conservation of nocturnal biodiversity.
Descrição
Tese de Mestrado, Biologia da Conservação, 2022, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Atividade de morcegos Composição de comunidades de morcegos Luz artificial à noite Poluição luminosa Teses de mestrado - 2022