Author(s): Marques, J. Tiago
Date: 2016
Persistent ID: http://hdl.handle.net/10451/25065
Origin: Repositório da Universidade de Lisboa
Project/scholarship: info:eu-repo/grantAgreement/FCT/SFRH/SFRH%2FBD%2F22829%2F2005/PT;
Subject(s): Vegetação ripícola; Heterogeneidade; Florestas tropicais - América do Sul; Morcegos; Amazónia; Teses de doutoramento - 2016; Domínio/Área Científica::Ciências Naturais::Ciências Biológicas
Tese de doutoramento, Biologia (Ecologia), Universidade de Lisboa, Faculdade de Ciências, 2016
Environmental heterogeneity is one of the factors that underpins the species richness of an area. However, this important relationship has only been poorly documented in tropical regions or in low human impact areas due to the scant data. The overall objective of this thesis is to contribute to the understanding of how the spatial components of environmental heterogeneity, both horizontal and vertical, contribute to the high number of ecological niches that explain the high biodiversity of Amazonian rainforests. More specifically, this thesis attempts to unveil the relevance of different types of forests, river bank vegetation and forest vertical component to the ecological structure of the megadiverse bat fauna of Amazonia. First, in Chapter 2 we focused on the horizontal component of environmental heterogeneity. In this paper we studied forest inundation and river banks as determinants of the spatial variation in the availability of fruits for bats in lowland Amazonia. We sampled the bat assemblage composition, fruit availability, and bat diet in terra firme upland forest and in two types of flooded forest - várzea and igapó. We grouped the bat species in two functional groups, the understorey and the canopy feeding guilds. We found that the várzea forests had abundant fruit resources for the canopy bats, while terra firme provided more fruits for the understorey bats. Additionally, river bank vegetation provided more fruit availability for bats, particularly for the canopy feeding guild on the edges of the várzea forests and for the understory feeding guild on the edges of the terra firme forests. In conclusion, both the forest type and the river bank vegetation influence the availability of fruits, although differently for the canopy and understory guilds. The resulting differences in fruit abundance may explain variations in bat assemblages of the different forest types. River banks play a particularly important role in providing food for bats of both guilds. By increasing the niche space, the mosaic of forests may play an important role in supporting such a diverse bat assemblage. The assessment of the contribution of the vertical component of environmental heterogeneity to the structuring of the Amazonian bat assemblage is presented in Chapter 3. Here, we studied the vertical space use of aerial insectivorous bats. Using automatic ultrasound recording stations placed in the canopy, subcanopy and understorey we tested if bat activity and species diversity are vertically stratified, both in the forest interior and near the edges of water bodies. These patterns were tested separately for 21 individual species, and for two functional groups - open space and edge space bats. Our results show that insectivorous bat activity increased by roughly seven fold, and species diversity doubled, from the understorey to the canopy. Both edge space and open space bats were more active in the upper strata, but this tendency was much more accentuated in the latter. Myotis riparius was the only species with greater activity near the understorey. These broad patterns were altered at the edges of water bodies, where vertical stratification was much less marked. The observed patterns are parsimoniously explained by constraints imposed by vegetation clutter that change across strata, which affect bat species differently. Only bats better adapted to closed spaces are usually capable of foraging within the understorey, whereas the majority of species can exploit the free spaces immediately below the canopy; open space bats seem to concentrate their activity above the canopy. Our results underline the need to preserve pristine stratified rainforests. Moreover, the concentration of insectivorous bats at the upper strata of rainforests underlines the need to include canopy level sampling in ecological studies. The study of the pitfalls and optimization of survey methods is one of the important tasks of scientists. In Chapter 4 we addressed this concern and investigated the impact of mist net avoidance in bats and birds. We quantified the day-to-day decline in captures of Amazonian birds and bats with mist nets set at the same location for four consecutive days. We also evaluated how net avoidance influences the efficiency of surveys under different logistic scenarios by subsetting data. Our results demonstrated that net avoidance caused substantial declines in bird and bat captures, although more accentuated in the latter. Most of the decline occurred between the first and second days of netting: 28 % in birds and 47% in bats. Captures of commoner species were more affected and the numbers of species detected also declined. Moving nets daily to minimize the avoidance effect increased captures by 30% in birds and 70% in bats. However, moving the location of nets may cause a reduction in netting time and captures, and we further investigated the implications of that logistic constraint. When moving the nets caused the loss of one netting day it was no longer advantageous to move the nets frequently. In bird surveys that could even decrease the number of individuals captured and species detected.
