Biology Reference
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frequencies more often used by more species did not show significantly less overlap
as was expected if all species were singing randomly. However, short-term auditory
feedback mechanisms can adjust bird song to reduce interspecific acoustic
interference.
The acoustic character can represent an important trait that drives the survivor-
ship of many animals. The spatial and temporal character of a site can modify the
responses of organisms to the conspecific or heterospecific acoustic cues.
The mechanisms of partitioning may be either spatial or temporal. Spatial
mechanisms require species to move in a way so as to not be masked by other
concurrent species. Temporal strategies present more complex mechanisms: for
instance, a temporal segregation (calling at a specific time of the day, e.g., dawn,
dusk, midday), or a jamming avoidance (inhibition of calling when another species
is calling at the same frequency band).
Evolutionary mechanisms can produce shifts of sounds into highest or lowest
frequencies that are unoccupied by the majority of species, as the case of the cave-
eared torrent frog (
Amolops tormotus
) from China, which produces song below
12 kHz (Feng et al.
2006
).
Sinsch et al. (
2012
) have studied an anuran community inhabiting an agricultural
wetland near Butare, Ruanda. They found that niche segregation was produced
mainly by advertisement call features and that spatial and temporal niche
dimensions contributed secondarily. Significant acoustic resource partitioning has
been found for an average niche overlap (0.30) that was intermediary between a
random overlap (0.51) and the minimum niche overlap (0.11). From this study
appears, interestingly, the wide overlapping of
Ptychaneda
spp., a recent invading
group of frogs.
Playback experiments simulating the invasion of the American bullfrog
(
Lithobates catesbeianus
) on a native species, the white-banded tree frog
(
Hypsiboas albomarginatus
), have been conducted by Both and Grant (
2012
)
who demonstrated the immediate shifting of frequency of native species during
the playback sessions (Fig.
3.11
). This shift was maintained also after the stimulus
associated with a decrease of signal duration. Because of the broad band of the
bullfrog calls, it is expected that the arrival of this species in new areas could
produce severe effects on many other frogs that could be masked. The importance
of frog calls for mating selection is well demonstrated, and an event such as call
masking could produce deleterious effects on the entire frog community.
In some species of anurans, the acoustic niche hypothesis is only partially
verified. For instance, Vasconcelos and Rossa-Feres (
2008
) have found that some
anurans presented different advertisement calls that, combined with the physical
calling sites, create an acoustic partitioning. Similarly Henry and Wells (
2010
) have
found that in the
Crysoperla carnea
group (Insects, Neuroptera) sympatric species
will partition acoustic niche space to reduce mating mistakes. Using an F
1
hybrid
between two very closely related sympatric species,
Chrysoperla plorabunda
and
C. adamsi
, they showed that acoustic discrimination between parents and hybrid is
weaker and the hybrid phenotype overlaps with that of the parents, thus confirming
that the intermediate song phenotype cannot persist.
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