TROPICAL FOREST FRAGMENTATION: EFFECTS ON THE SPATIAL-TEMPORAL DYNAMICS OF ITS BAT COMMUNITIES

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Optimizing bat bioacoustic surveys in human‐modified Neotropical landscapes

Publication . López-Baucells, Adrià; Yoh, Natalie; Rocha, Ricardo; Bobrowiec, Paulo E. D.; Palmeirim, Jorge M.; Meyer, Christoph F. J.

During the last decades, the use of bioacoustics as a non-invasive and costeffective sampling method has greatly increased worldwide. For bats, acoustic surveys have long been known to complement traditional mist-netting, however, appropriate protocol guidelines are still lacking for tropical regions. Establishing the minimum sampling effort needed to detect ecological changes in bat assemblages (e.g., activity, composition, and richness) is crucial in view of workload and project cost constraints, and because detecting such changes must be reliable enough to support effective conservation management. Using one of the most comprehensive tropical bat acoustic data sets, collected in the Amazon, we assessed the minimum survey effort required to accurately assess the completeness of assemblage inventories and habitat selection in fragmented forest landscapes for aerial insectivorous bats. We evaluated a combination of 20 different temporal sampling schemes, which differed regarding number of hours per night, number of nights per site, and sampling only during the wet or dry season, or both. This was assessed under two different landscape scenarios: in primary forest fragments embedded in a matrix of secondary forest and in the same forest fragments, but after they had been re-isolated through clearing of the secondary forest. We found that the sampling effort required to achieve 90% inventory completeness varied considerably depending on the research aim and the landscape scenario evaluated, averaging ~80 and 10 nights before and after fragment re-isolation, respectively. Recording for more than 4 h per night did not result in a substantial reduction in the required number of sampling nights. Regarding the effects of habitat selection, except for assemblage composition, bat responses in terms of richness, diversity, and activity were similar across all sampling schemes after fragment re-isolation. However, before re-isolation, a minimum of four to six sampling hours per night after dusk and three to five nights of sampling per site were needed to detect significant effects that could otherwise go unnoticed. Based on our results, we propose guidelines that will aid to optimize sampling protocols for bat acoustic surveys in the Neotropics.

2021-05Journal article

Open access

Assessment of the effects of forest fragmentation on aerial insectivorous bats in the Amazonian rainforest

Publication . López-Baucells, Adrià; Meyer, Christoph Friedrich Johannes; Palmeirim, Jorge Manuel Mestre Marques

Land use change and habitat fragmentation are among the most severe threats to biodiversity, especially in the tropics. In the Amazon, the abandonment of formerly deforested areas allowed the expansion of secondary regrowth, a type of habitat where bats are known to provide important ecosystem services. Amongst them, aerial insectivorous bats have been neglected in most Neotropical studies and remain poorly studied. However, the current upsurge in acoustic technology makes them easy targets to be monitored using ultrasound detectors. The aim of this thesis was to reveal the diversity of aerial insectivorous bats and quantify the effects of forest fragmentation on this ensemble within the Biological Dynamics Forest Fragments Project, a whole ecosystem experiment in the Amazon, currently composed of a mosaic of unflooded rainforest with continuous forest, and forest fragments embedded in a matrix of secondary regrowth. As part of this thesis, the first “Field Guide to the Bats of the Amazon” was published. A custom-built classifier was developed which was able to identify a large proportion of files to sonotype level (with > 90% accuracy), leaving the rest (<25%) to be manually classified. I also tested 20 different recording schemes and provided guidelines to optimize protocols for acoustic studies. In forest fragments and their adjoining secondary forests, taxonomic, phylogenetic and functional α diversity became gradually poorer with decreasing fragment size. In terms of β diversity, bat assemblage composition in secondary forests after ~30 years of recovery was still significantly different from that in continuous forest. However, forest edges harboured highly diverse bat assemblages due to the opening of cluttered areas, and the increase of less-sensitive species. Responses towards fragmentation were species-specific and strongly related to their functional traits. The results of this thesis highlight the irreplaceable value of tropical primary forests due to the long time required to recover fragmented ecosystems.

2019-03Doctoral thesis

Open access

Tropical forest fragmentation : effects on the spatio-temporal dynamics of its bat communities

Publication . Rocha, Ricardo; Meyer, Cristoph Friedrich Johannes; Palmeirim, Jorge M., 1957-; Jaimejuan, Maria del Mar Cabeza

Tropical forest ecosystems harbour more than half of the planet’s terrestrial species and are of paramount importance for human well-being. Yet, the persistence of tropical forests and their faunal communities is jeopardised by growing rates of habitat loss, fragmentation and degradation. Bats provide critical ecosystem services to tropical forest and are thus crucial for the maintenance of healthy forest habitats. However, as with many other taxa, they are increasingly threatened by anthropogenic forest modification. The main aim of this thesis was to investigate the spatio-temporal effects of forest fragmentation on tropical forest bats. The study was based at the Biological Dynamics of Forest Fragment Project (BDFFP), a whole-ecosystem experiment implemented in the Central Brazilian Amazon. The BDFFP bat fauna was initially studied in 1996-2002, allowing for a comparative follow-up study capable of unveiling the combined effects of spatial and temporal heterogeneity on tropical bat assemblages in fragmented forest landscapes. The controlled experimental setting provided by the BDFFP was further used to investigate the relative roles of vegetation structure and landscape composition and configuration on bat communities, and the depth of this analysis was extended by the examination of sex-specific responses to both local- and landscape-level attributes. Additionally, the re-isolation of forest fragments in late-2013 enabled a before and after re-isolation comparison, allowing valuable insights into short-term responses to abrupt changes in matrix structure. The regeneration of the secondary forest surrounding the BDFFP fragments buffered some of the pervasive consequences of forest fragmentation, however, more than 30 years after initial deforestation bat communities still exhibited scale-sensitive and sex-specific responses to fragmentation. While results highlight the importance of larger (> 10 ha) forest patches and mature secondary forest (> 20 years) for the conservation of tropical bats, they emphasize the irreplaceable value of vast tracts of primary habitat for the long-term conservation of tropical biodiversity.

2017Doctoral thesis

Open access

Edge effects and vertical stratification of aerial insectivorous bats across the interface of primary-secondary Amazonian rainforest

Publication . Yoh, Natalie; Clarke, James A.; López-Baucells, Adriá; Mas, Maria; Bobrowiec, Paulo E.D.; Rocha, Ricardo; Meyer, Christoph F.J.

Edge effects, abiotic and biotic changes associated with habitat boundaries, are key drivers of community change in fragmented landscapes. Their influence is heavily modulated by matrix composition. With over half of the world’s tropical forests predicted to become forest edge by the end of the century, it is paramount that conservationists gain a better understanding of how tropical biota is impacted by edge gradients. Bats comprise a large fraction of tropical mammalian fauna and are demonstrably sensitive to habitat modification. Yet, knowledge about how bat assemblages are affected by edge effects remains scarce. Capitalizing on a whole-ecosystem manipulation in the Central Amazon, the aims of this study were to i) assess the consequences of edge effects for twelve aerial insectivorous bat species across the interface of primary and secondary forest, and ii) investigate if the activity levels of these species differed between the understory and canopy and if they were modulated by distance from the edge. Acoustic surveys were conducted along four 2-km transects, each traversing equal parts of primary and ca. 30-year-old secondary forest. Five models were used to assess the changes in the relative activity of forest specialists (three species), flexible forest foragers (three species), and edge foragers (six species). Modelling results revealed limited evidence of edge effects, except for forest specialists in the understory. No significant differences in activity were found between the secondary or primary forest but almost all species exhibited pronounced vertical stratification. Previously defined bat guilds appear to hold here as our study highlights that forest bats are more edge-sensitive than edge foraging bats. The absence of pronounced edge effects and the comparable activity levels between primary and old secondary forests indicates that old secondary forest can help ameliorate the consequences of fragmentation on tropical aerial insectivorous bats

2022Journal article

Open access