Vertical Stratification on Insectivorous Bats Ensembles in Central Amazon
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Vertical stratification on insectivorous bats ensembles in Central Amazon Maria Mas Navarro Master student in Biodiversity September 2014 1 CENTRO DE BIOLOGIA AMBIENTAL (Lisboa) MUSEU DE CIÈNCIES NATURALS DE GRANOLLERS DEPARTAMENT DE BIOLOGIA ANIMAL, UNIVERSTIAT DE BARCELONA Vertical stratification on insectivorous bats ensembles in Central Amazon Maria Mas Navarro Master student in Biodiversity September 2014 Directors: Dr. Christoph Meyer and Dr. Carles Flaquer Tutor UB: Dr. Maria José López Fuster Situdent’s signature Director’s signature Tutor’s signature 2 Table of contents Abstract .......................................................................................................................... 4 Introduction ................................................................................................................... 5 Material and methods ................................................................................................... 8 Study area ................................................................................................................... 8 Acoustic surveys .......................................................................................................... 8 Insect availability ....................................................................................................... 11 Vegetation obstruction ............................................................................................... 11 Statistical analyses .................................................................................................... 11 Results ......................................................................................................................... 12 Discussion ................................................................................................................... 21 Conclusions ................................................................................................................. 24 Acknowledgments ...................................................................................................... 25 References ................................................................................................................... 26 ANNEX ......................................................................................................................... 31 3 Abstract Tropical Amazonian rainforests are under constant anthropogenic pressure. Of all the types of human activities that affect these forests, forest fragmentation probably has the greatest implications for conservation. Due to the pattern of land-use change the landscape can be considered as a mosaic of recovering and mature forests that encompass structurally and ecologically different habitats. Within these forests, two ecosystems are easily distinguishable: the canopy and the understory. Most of the studies of bat ecology and conservation in the Amazon have focused on the understory, which means that there is a remarkable lack of information about higher forest strata. This study aimed to determine the differences in vertical stratification in the activity of aerial insectivorous bat species in primary and secondary forests. Automatic acoustic detectors used to record bat activity in both strata, while insect availability and vegetation obstruction were assessed as variables to explain bat activity. A total of 90,641 bat passes were recorded and classified. Our results showed specific differences in activity between canopy and understory for 8 out of the total of 24 species (Pteronotus sp. and Centronycteris maximiliani being, respectively, the species most strongly associated with the understory and the canopy). Several species showed the same distribution patterns between strata in both the primary and secondary forests, which could possibly be explained by the old age of the regrowth forest in our study area. Insect availability and vegetation obstruction were weakly correlated to only a few species and so bat distribution is hard to explain either food resource availability or by the difficulty of flight inside the forest. Thus, considering those results, to get a complete view of this bat assemblage we strongly recommend that research focuses on sampling aerial insectivorous bats in both strata. Overall, we believe that bat activity patterns in the canopy are similar in both primary and 30-year-old secondary forests. 4 Introduction Tropical Amazon rainforests are the most biodiverse ecosystems in the world and contain a large number of plant and animal species that provide remarkable ecological services (Bradshaw et al., 2009) and natural resources such as wood and minerals (Philips et al., 2008). However, decades of human exploitation of these resources have had detrimental effects on wildlife (Corlett, & Primack, 2008; Hansen et al., 2008). Due to anthropogenic pressure on tropical forests, a widespread process of habitat fragmentation has occurred that affects not only pioneering plants and tree species (Lovejoy, & Bierragaard, 1990; Benétez-Malvido, & Martínez-Ramos, 2003; Laurance et al., 2007) but also communities of various animal groups such as birds, mammals, reptiles and arthropods (Lovejoy et al., 1984; Bierregaard et al., 1992; Watt et al., 1997; Davies et al., 2000; Gascon et al., 2001; Laurance et al., 2001; Peres, 2001; Estrada- Villegas et al., 2010; Laurance et al., 2010) During the regeneration of the matrix surrounding forest fragments, pioneering trees such as Vismia and Cecropia are likely to cover many once deforested areas (Laurance et al., 2001; Laurance et al., 2007). This secondary forest and the non- deforested areas (or primary forest) differ largely in terms of (i) tree biomass, (ii) the presence or otherwise of these two pioneering trees and (iii) tree height (in the secondary forest the canopy height is 20 m, while in the primary forest it is on average 30–35 m, with some trees over 50 m) (Lovejoy, & Bierregaard, 1990; Laurance et al., 2001; Benítez-Malvido, & Martínez-Ramos, 2003; Laurance et al., 2011). It is well known that tropical rainforests usually harbour tall trees and that two physically and biologically distinct areas for aerials foragers tend to exist: canopy and understory (Hecker, & Brigham, 1999, Bernard, 2001). This vertical stratification does not only occur in environmental characteristics but also in plant and animal communities and different functions, such pollination, develop in each of these two strata (Bonaccorso, 1979; Kalko, & Handley, 2001; Pereira et al., 2010). Neotropical bats play key roles in the ecosystems being incolved in important functions such as seed dispersal, flower pollination and the night-flying insect balance (Law, & Lean, 1999; Medellín, & Gaona, 1999; Kalka et al., 2008; Kunz et al., 2011). 5 These interactions are carried out by a number of different bat species. Some species have morphological characteristics that enable them to commute in open or in cluttered areas, and a number of evolutionary adaptations have arisen in terms of the chosen foraging habitat (Henry et al., 2004; Scrimegeour et al., 2013). Bats with short wide wings seem to be more manoeuvrable than long-, slim-winged species whose flight is usually faster (Kalkounis et al., 1999; Hodgkison et al., 2004; Jung, & Kalko, 2010) and who fly mostly along forest edges, trails and in open areas. According to the literature, research on bat vertical stratification in rainforests has mostly been conducted using mist-nets and has been focused mainly on phyllostomid bats that are easier to capture using this technique. Thus, previous studies have no or poor information on aerial insectivorous bats, which are clearly undersampled with mists nets (Kalko, & Handley, 2001; Henry et al., 2004; MacSwiney et al., 2008; Pereira et al., 2010,). Given that aerial insectivorous bats have a greatly evolved echolocation system, mist nets are more easily detectable by them than other species so they can easily avoid them. Studies of bat assemblages in the Neotropics have to date focused on the ground level, which has led to great discrepancies in our knowledge of canopy and understory bat communities (Kalkounis et al., 1999; Bernard, 2001; Kalko, & Handley, 2001; Scrimgeour et al., 2013). The most commonly considered strata – canopy and understory – harbour distinct species and activity levels (Bernard, 2001; Kalko, & Handley, 2001; Pereira et al. 2010). To date, studies have usually depended on mist-netting as the main capture method. Only a few authors assessed vertical stratification employing other sanpling techniques such as stable carbon isotopes or acoustic surveying (Rex et al., 2011; Scrimgeour et al., 2013). In fact, acoustic surveys are a relatively new technique in bat studies in the Neotropics. However, in recent years the use of acoustic methods has improved our knowledge given their ability to sample larger areas and their autonomy (O’Farrell, & Gannon, 1999). Ultrasound detectors are useful to detect and study certain rare species in inaccessible habitats where they may be more common than suggested by the literature (MacSwiney et al., 2008). In successional secondary forest and forest fragments most studies of changes in plant and animal communities have focused on the ground level (Gason et al., 1999; Davies et al., 2000; Laurance et al., 2001), leading to an incomplete and biased picture of the 6 effects of habitat modification on species responses. As Scrimgeour et al. state (2013), a non-detected species is not necessarily absent