Echolocation source levels and detection distances of bat assemblages in
biomes of South Africa: A test of the Acoustic Adaptation Hypothesis
Abstract
Echolocating bats use and adapt ultrasound pulses that vary in several
parameters, one of them being the pulse’s source level, which is a
measure of the emitted sound amplitude. This is a vital ecological
parameter as it directly impacts the maximum distance over which bats
can perceive targets in their environment, most importantly their prey.
Different habitats present different sensing challenges for echolocation
systems, and the quality and content of information derived from
echolocation pulses reflect these environmental challenges. As such,
echolocation pulses within or between species may vary from one habitat
to the next due to variable selection pressure, resulting in local
adaptation. Habitat is, therefore, a key component in shaping the
evolution of echolocation. The Acoustic Adaptation Hypothesis (AAH)
proposes that acoustic properties of the environment influence sound
propagation and therefore the evolution of echolocation pulses. Here, we
tested the AAH using multiple microphone arrays to measure the source
levels of echolocation pulses of 14 bat species in bat assemblages
across sites in six biomes in South Africa. Contrary to the AAH, our
results revealed that bats in the same assemblage used different
echolocation pulse source levels, frequencies, and duration resulting in
different detection distances, which differ among bat assemblages
occupying different sites. Furthermore, detection distance was
species-specific and remained similar within species between
assemblages; suggesting that species is a better predictor of detection
distances compared to habitat as indicated by Miniopterus natalensis
across all seven sites. KEYWORDS: adaptation, bat assemblages, detection
distances, microphone arrays, selection pressure, source levels