might influence behavior—males of most species broadcast songs from
perches in trees or while in flight in spite of the energetic costs and the
chances of increased predation (Mathevon et al. 1996). Many species of
frogs and insects also call from well above the ground, although species of
frogs that call from ground level across water often do not experience high
levels of call attenuation, perhaps because the water acts as a waveguide
(Venator 1999; Bass and Clark, Chapter 2).
3.3.2. Timing of Signaling
The dawn chorus of birds and evening choruses of insects and frogs are
nearly ubiquitous. Why do these species restrict calling to certain times of
the day, and why to early morning and evening? Meteorological conditions
vary widely over the course of the day, causing variations in signal transmission. In addition, the composition of biotic and abiotic noise in the environment differs at different times of the day. Calling at times when the
meteorological conditions favor sound transmission or when other species
are not calling can increase the active space of a transmitted signal. In environments ranging from desert to tropical forest, early morning and evening
hours usually have the best meteorological conditions for sound transmission (Waser and Waser 1977; Henwood and Fabrick 1979).
3.4. Acoustic Niche Partitioning
In addition to the effects of the physical environment, calling structure
and behavior may be influenced by the other species within a community.
Selection on individual species to match the transmission characteristics
of their calling habitat would lead to convergence among sympatric species.
However, we can easily hear that the calls of each species have distinctive
features. Such differences among sympatric species can reduce the level of
interference among the calls of different species, resulting in a partitioning
of the “acoustic niche.” In addition, when these signals are used for the
recognition of conspecific potential mates over heterospecifics, differences
among calls or calling behavior can be strongly advantageous, preventing
costly mismatings among incompatible individuals.
Some anuran studies provide suggestive evidence for divergence in call
structure or calling behavior among species that call in the same area. Frogs
sometimes maintain different calling sites within a habitat, and these differences in location can reduce the chances of matings among heterospecifics (Duellman 1967; Hödl 1977). Temporal differences in calling
behavior may also reduce interference and promote reproductive isolation
(Duellman 1967). Even so, many species of frogs can often be observed
calling at the same time and in the same place. In these cases, different
species seldom have similar calls; some combinations of temporal or spectral properties of calls will differ among species, allowing for the discrimi238
M.J. Ryan and N.M. Kime
perches in trees or while in flight in spite of the energetic costs and the
chances of increased predation (Mathevon et al. 1996). Many species of
frogs and insects also call from well above the ground, although species of
frogs that call from ground level across water often do not experience high
levels of call attenuation, perhaps because the water acts as a waveguide
(Venator 1999; Bass and Clark, Chapter 2).
3.3.2. Timing of Signaling
The dawn chorus of birds and evening choruses of insects and frogs are
nearly ubiquitous. Why do these species restrict calling to certain times of
the day, and why to early morning and evening? Meteorological conditions
vary widely over the course of the day, causing variations in signal transmission. In addition, the composition of biotic and abiotic noise in the environment differs at different times of the day. Calling at times when the
meteorological conditions favor sound transmission or when other species
are not calling can increase the active space of a transmitted signal. In environments ranging from desert to tropical forest, early morning and evening
hours usually have the best meteorological conditions for sound transmission (Waser and Waser 1977; Henwood and Fabrick 1979).
3.4. Acoustic Niche Partitioning
In addition to the effects of the physical environment, calling structure
and behavior may be influenced by the other species within a community.
Selection on individual species to match the transmission characteristics
of their calling habitat would lead to convergence among sympatric species.
However, we can easily hear that the calls of each species have distinctive
features. Such differences among sympatric species can reduce the level of
interference among the calls of different species, resulting in a partitioning
of the “acoustic niche.” In addition, when these signals are used for the
recognition of conspecific potential mates over heterospecifics, differences
among calls or calling behavior can be strongly advantageous, preventing
costly mismatings among incompatible individuals.
Some anuran studies provide suggestive evidence for divergence in call
structure or calling behavior among species that call in the same area. Frogs
sometimes maintain different calling sites within a habitat, and these differences in location can reduce the chances of matings among heterospecifics (Duellman 1967; Hödl 1977). Temporal differences in calling
behavior may also reduce interference and promote reproductive isolation
(Duellman 1967). Even so, many species of frogs can often be observed
calling at the same time and in the same place. In these cases, different
species seldom have similar calls; some combinations of temporal or spectral properties of calls will differ among species, allowing for the discrimi238
M.J. Ryan and N.M. Kime