Appendix
Figure Legends
Figure S1. Call features. Oscillograms (a) and power spectra (b) of the calls of five species of
crickets and katydids used to examine effective acoustic overlap (EAO). Adapted (Diwakar and
Balakrishnan 2006).
Figure S2. Temporal overlap in the five species of crickets and katydids. Box-and-whisker plots
showing distributions of (a) Gross Temporal Overlap (GTO) (b) Fine Temporal Overlap (FTO)
and (c) Effective Temporal Overlap (ETO) values for the 20 species-pair combinations. ETO for
each species-pair was calculated by multiplying all possible combinations of GTO and FTO
since there is no a priori reason to pair specific GTO and FTO values.
Figure S3. Spacing of calling individuals in the field. Box-and-whisker plots showing the
distribution of distances between pairs of heterospecific calling individuals. La = Landreva, Pi =
Pirmeda rosetta, Ph = Phaloria sp., TP = Mecopoda‘Two-Part’, Wh = ‘Whiner.’ Abbreviations
mean the same in all following figures. Numbers indicate sample sizes.
Figure S4. Effect of lowering the hearing threshold on active space overlap. Box-and-whisker
plots of the distributions of acitve space overlap (ASO) values for five species of crickets and
katydids (N = 20 species-pair combinations) in four scenarios: Individuals of all species calling
at equal SPLs (72 dB SPL) with (a) untuned or (c) tuned receivers; individuals calling at mean
species-specific SPLs with (b) untuned or (d) tuned receivers. (e) Distributions of Effective
Acoustic Overlap (EAO) values generated by multiplying all combinations of ETO and ASO
values for species-specific call SPLs and tuned receivers. Receivers were assumed to have a
hearing threshold of 35 dB SPL at their best frequencies.
Figure S5. Effective acoustic overlap in spatially randomized multispecies choruses. Frequency
histogram showing the distribution of Effective Acoustic Overlap (EAO) values for the five
species (N = 9 choruses). (a) P. rosetta, (b) Landreva sp., (c) ‘Whiner’, (d) Mecopoda ‘TwoPart’, (e) Phaloria sp.. White bars: Spatially randomized choruses (100 randomizations per
chorus); Black bars: Observed choruses.
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3
4
5
6
7
Table S1. Call features of the 14 species of crickets and katydids.
Adapted (Diwakar and Balakrishnan 2006).
Bandwidth was measured at 20 dB below peak amplitude .
8
Table S2. Broadcast radii in meters of the five species of crickets and katydids for tuned and
untuned receivers with different hearing thresholds (35 and 40 dB SPL).
Eq_int = Equal calling SPL of 72 dB, SS_int = species-specific call SPLs
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Table S3. Analysis of deviance results for pairwise active space overlap including the effect of
receiver stratification
.
Df
Deviance
Residual
Residual
Df
Deviance
5567
1.66X1011
5.89X1010
5548
1.07X1011
<0.001
10
5547
7.34X1010
<0.001
5546
7.06X1010
<0.001
5545
6.97X10
10
<0.001
5526
4.19X1010
<0.001
9
5507
3.60X10
10
<0.001
5506
3.60X1010
8
5487
3.57X10
10
5486
3.57X1010
0.25
10
0.15
0.99
Null
Speciespair
19
Tuning
1
3.36X10
SPL
1
2.78X109
Stratification
1
8.72X10
8
Speciespair X Tuning
19
2.78X1010
Speciespair X SPL
19
5.97X10
Tuning XSPL
1
1.16X104
P-values
0.96
Speciespair X Stratification
19
2.77X10
Tuning X Stratification
1
7.86X106
SPLX Stratification
1
1.22X10
7
5485
3.57X10
Speciespair X Tuning X SPL
19
2.32X107
5466
3.56X1010
19
2.15X10
8
5447
3.54X10
10
0.009
7
5428
3.54X10
10
0.99
5427
3.54X1010
0.04
Speciespair X Tuning X Stratification
Speciespair X SPL X Stratification
19
4.34X10
Tuning X SPL X Stratification
1
2.79X104
10
<0.001
Table S4. Species composition of ten natural choruses
Methods (Supplementary Information)
Active space overlap
1) Calculation of broadcast radii
We calculated the mean broadcast radius of each species based on its transmission profile for
two different situations: i) when all species call at 72 dB SPL (at 0.5 m from source) and ii) when
each species calls at its own species-specific SPL. In each of these cases, we calculated the
broadcast radius of the callers for two scenarios: a) when the receiver is untuned (same hearing
sensitivity at all frequencies) and b) when the receiver is tuned to the call of its own species
(highest sensitivity to frequencies with maximum energy in its own species’ call).
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Calculation of broadcast radii for untuned receivers: Transmission experiments with the calls of
the five species broadcast at 72 dB SPL (at 0.5 m from source) were carried out in the natural
habitat and attenuation profiles generated as described elsewhere (Jain and Balakrishnan 2012).
SPL measurements for attenuation were made using a Bruel & Kjaer Sound Level Meter (Type
2230) and ½” microphone (Type 4155) with a 500 Hz high-pass filter to approximate an untuned
insect ear (for Mecopoda‘Two-Part’ and P. rosetta, we used our previously published attenuation
curves (Jain and Balakrishnan 2012)). We used 40 (or 35) dB SPL to define the limit of the
broadcast volume based on the known values of hearing thresholds of crickets and katydids
(Kostarakos et al 2008; Schmidt et al 2011; Schmidt and Römer 2011; Hummel et al 2011).
Using the attenuation curve we determined the distance at which the call SPL dropped to the
hearing threshold. This distance was recorded as the broadcast radius of the species when the
sender calls at 72 dB SPL. To calculate the broadcast radius of these species when they call at
species-specific SPLs, we adjusted the starting SPL to equal that of the mean species-specific
SPL. Using the equation of this parallel curve we calculated the broadcast radius as above.
Calculation of broadcast radii for tuned receivers: The three cricket species were assumed to be
narrowly tuned to the carrier frequency (CF) of their own song and to have a hearing threshold of
40 (or 35) dB SPL. The two katydid species were assumed to be broadly tuned with a higher
threshold of 60 dB for all frequencies below 7 kHz and a threshold of 40 (or 35) dB SPL for
higher frequencies, based on the published tuning curve for Mecopoda elongata, a sibling
species of Mecopoda ‘Two-part’ with a very similar call spectrum (Nityananda and Balakrishnan
2006; Hummel et al 2011). For each of the five species we generated four different attenuation
curves, each representing the attenuation profile of an animal’s call as heard by each of the other
four species, by carrying out a separate set of transmission experiments using the setup described
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previously (Jain and Balakrishnan 2012). The calls were broadcast at species-specific SPLs and
the SPL measurements were made using four different filter settings: a 500 Hz high-pass filter to
approximate katydid ear tuning and three sets of measurements taken with a one-third octave
band-pass filter centered at 4, 5 and 6.3 kHz respectively to approximate the tuning curves of
cricket ears of different species (Phaloria sp., Landreva sp. and ‘Whiner’.
To determine the broadcast radius of a given species A (potential masker) as perceived by
the receiver of another species B, we used the attenuation curve of species A generated based on
the SPL measurements made using the frequency filter of species B. Then we used the equation
of the curve to calculate the distance at which the SPL of species A falls to the hearing threshold.
The attenuation curves were then recalculated for a scenario where all species were calling at the
same SPL by adjusting the source SPL to 72 dB. This procedure was repeated to estimate the
broadcast radius of each species as heard by every other species based on its tuning. In this way
we generated four asymmetrical 5 × 5 matrices (Table S2) that contained the broadcast radius of
every species depending on who the listener species was for four different scenarios (Table S2).
2) Simulations for active space overlap in species pairs
In the simplistic case of two intersecting spheres, we created the smallest bounding box whose
volume contained both the spheres completely such that [xmin, ymin, zmin] was the lower left corner
of the bounding box and [xmax, ymax, zmax] was the upper right corner. The simulation then divided
the bounding box into sampling volumes of dimensions of 10 cm3 and checked whether each
sampling volume lay within any of the spheres. If [x, y, z] represents a sampling volume then it
would lie within sphere [C[X ,Y, Z], r] , if the condition below is true:
[x− X ]2+ [ y −Y]2+ [z − Z]2≤ r2
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If dV1 and dV2 are the number of sampling volumes inside sphere 1 and 2 respectively and
dVshared is the number of sampling volumes inside both sphere 1 and sphere 2, then dVshared /
dV1and dVshared /dV2 are the ASO probabilities of sphere 1 masked by sphere 2 and vice versa. In
cases where part of the broadcast sphere was below the ground we adjusted the co-ordinates of
the bounding box such that the lower plane of the box was at ground level (z co-ordinates≥ 0).
This ensured that broadcast volumes below ground were omitted from the calculations. To
incorporate stratification in the simulation, the z co-ordinates (height) of the bounding box were
restricted to a lower and upper bound corresponding to the strata of the caller (Diwakar and
Balakrishnan 2007): 0 – 2 m for Landreva sp. and Mecopoda “Two-part”; 0 – 4 m for Phaloria
sp.; 0 – 8 m for “Whiner” and Pirmeda rosetta.
The algorithm was validated by using a number of test cases. For instance, we ran the
simulations on simulated choruses where the focal animal and the maskers were at the same
height and such that their spheres were well above the ground, and saved the results. We then
lowered the height of the animals to be equal to 0 (simulating a situation where all animals are
calling from the ground) such that the broadcast spheres would be cut by the ground exactly in
the middle rendering them hemispheres. The simulation was validated by comparing the results
of the two runs where the values from the second run were half of that of the first run. Moreover,
we checked for errors resulting from the sampling resolution (d = 0.1) by comparing our results
against the formula for calculating the volume of two intersecting spheres (in the simplistic case
of the callers’ broadcast spheres completely lying above the ground and being sampled by an
unstratified receiver). The simulation results had an error of less than 0.5% with respect to the
theoretical values for spheres of sizes comparable to those in this study.
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3) Simulation for EAO in multispecies choruses
EAO was determined for each calling individual in a spatially reconstructed chorus in three
dimensions taking into account overlap from all heterospecific calling individuals (multiple
neighbours). Here the ASO probability for the focal cricket/katydid will be equivalent to the ratio
of the volume of the focal sphere to the intersecting volumes of the neighboring spheres. The
bounding box, calculated using the same formula as for two-sphere intersection, was restricted to
contain only the focal sphere since we were only interested in the proportion of volume of the
focal sphere shared by other spheres (all maskers). dV1 represented the samples contained in the
focal sphere and dVshared represented the samples that were contained in any of the other spheres
as well as the focal sphere.
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