PERSPECTIVE The silence of biogeographyMark V. Lomolino1*, Bryan C. Pijanowski2 and Amandine Gasc2

1Department of Environmental and Foresty

Biology, College of Environmental Science and

Forestry, Syracuse, NY 13031, USA,2Department of Forestry and Natural

Resources, and Center for Global

Soundscapes, Purdue University, West

Lafayette, IN 47906, USA

*Correspondence: Mark V. Lomolino, College

of Environmental Science and Forestry,

Syracuse, NY 13031, USA.

E-mail: island@esf.edu

ABSTRACT

Modern biogeography now encompasses an impressive diversity of patterns

and phenomena of the geography of nature, providing insights fundamental to

understanding the forces influencing the spatial and temporal dynamics of bio-

logical diversity. However, rather than praise our discipline for its great breadth

of visions, our purpose here is to point out our glaring oversight of a poten-

tially transformative frontier in the geography of nature. A new, emerging area

called soundscape ecology, if guided by the principles of biogeography, holds

the promise of ‘opening the ears’ of our field and providing fresh perspectives

on fundamental problems being addressed by biogeographers.

Keywords

Acoustics, bioacoustics, biogeography, ecology, soundscape ecology, von

Humboldt.

INTRODUCTION

Biogeography is the study of geographical variation in all

biological traits and entities and, from the early classics of

Alexander von Humboldt, Charles Darwin and Alfred Rus-

sel Wallace, biogeographers have explored a marvellous

diversity of the patterns in nature – from local to global

scales. Alexander von Humboldt’s contributions, in particu-

lar the narrative account of his explorations to the Canary

Islands and the New World tropics (1852) and his classic,

comprehensive Essay on the Geography of Plants (von Hum-

boldt & Bonpland, 1807), not only inspired Darwin and

Wallace and generations of others to become naturalists,

but also served as exemplars of holistic approaches to

exploring the geography of nature. The Essay on the Geogra-

phy of Plants included his Tableau Physique which, in addi-

tion to detailing the distributions of plants and animals

along the slopes of Mount Chimborazo (6268 m), describes

elevational variation in air temperature, chemical composi-

tion of the atmosphere, its electrical tension, barometric

pressure, temperature at boiling point, gravity, azureness of

the sky, light intensity, horizontal refractions of the light,

the limits of perpetual snow, geological phenomena, and

cultivation of the soil (i.e. for grazing by domesticated ani-

mals or for crops such as potatoes, barley, wheat, cotton,

corn, sugar or coffee).

Although we can think of no other single work that is as

holistic and eclectic as von Humboldt’s Essay on the Geogra-

phy of Plants and its Tableau Physique, the collective interests

of modern biogeographers have of course expanded to

include an even greater diversity of biotic variables – ranging

from genetic, physiological and morphological traits of indi-

viduals, to the characteristics of entire communities and

regional to continental (whole ocean) scale biotas. Our pur-

pose here, however, is not to praise our modern discipline

for all its insights and breadth of visions, but to point out

our glaring oversight of a potentially transformative frontier

in the geography of nature. The ‘silence of biogeography’

that we allude to in our title refers to the surprising paucity

of studies on the geographical variation of sound. This

neglect of the acoustic character of the environment, at least

in hindsight, is striking given that we, as mammals, are dis-

tinguished by relatively acute hearing and, as humans, by

our highly developed cultural traditions, which are often

based on natural and anthropogenic sounds.

Here, we first provide an account of an exception to the

silence of biogeography, one provided again in von Hum-

boldt’s narrative of his voyages along the Orinoco River of

South America. We then summarize the very limited atten-

tion sound has garnered from modern biogeographers before

describing how we may advance our science in synergy with

an emerging discipline – soundscape ecology. We believe, of

course, that this synergy will be mutualistic. That is, not only

can soundscape ecologists offer tools and methodologies for

objectively describing acoustic features of the natural world,

but it is just as likely that soundscape ecology can gain key

insights by applying the principles and often powerful, infer-

ential approaches of biogeography.

ª 2015 John Wiley & Sons Ltd http://wileyonlinelibrary.com/journal/jbi 1doi:10.1111/jbi.12525

Journal of Biogeography (J. Biogeogr.) (2015)

VON HUMBOLDT’S PARROT AND THE

DISTINCTIVENESS OF PLACE

This account has been described elsewhere (Lomolino, 2010),

but it bears repeating here given its relevance to the geogra-

phy of sound and, in particular, to biogeography’s first and

most fundamental principle – the biological distinctiveness

of place (Buffon’s law; see Lomolino et al., 2010).

At the period of our voyage an old parrot was shown at

Maypures, of which the inhabitants said, and the fact is worthy

of observation, that they did not understand what it said, because

it spoke the language of the [now extinct tribe] Atures.

von Humboldt (1852, p. 620)

von Humboldt meticulously recorded the phonetic

descriptions of the Ature phrases spoken by this old parrot

and, in so doing, preserved at least a few precious features of

the distinctiveness of a lost people and of a place as well.

This lesson speaks to a fundamental theme that is com-

mon to biogeography, anthropology and many related disci-

plines – that evolution (natural or cultural) occurs not just

over time but across space as well, and some of the strongest

evidence for this is preserved in the distinctiveness of place.

Buffon appears to be the first to articulate this for biogeogra-

phers (then simply called ‘naturalists’ or ‘geologists’) during

the 18th century when he described the distinctiveness of

mammals from the New and the Old World tropics (Buffon,

1761). What later became known as Buffon’s law has now

been generalized to describe the distinctiveness of biotas (i.e.

endemic species, genera or families) from different regions,

even those with similar environmental conditions. It is, in

turn, these endemics that can be used to reconstruct the his-

torical development of those regional biotas.

The concept of distinctiveness of place applies to cultural

features, including anthropogenic sounds and sites (Smith &

Pijanowski, 2014), as much as it does to biotic features and

the loss of endemic species. After visiting the area where she

grew up near Oakland, California, Gertrude Stein lamented

that it had lost its defining character:

of rain and wind, of hunting, of cows and dogs and horses, of

chopping wood, of making hay, of dreaming, of lying in a hollow

all warm with the sun shining while the wind was howling . . .

what was the use of my having come from Oakland, it was not

natural to have come from there, yes write about it if I like or

anything if I like but not there, there is no there there.

Stein (1937, p. 289)

The distinctiveness of place and the need to conserve it is

also a theme central to conservation biology. Along with

Aldo Leopold’s (1949) Sand County Almanac, Rachel Car-

son’s (1962) Silent Spring was a watershed wakeup ‘call to

arms’ for the conservationist movement. Here, she warned

us about the devastating effects of pesticides on native spe-

cies of birds and other wildlife. But it is not only that we

experienced a silence in the loss of ivory-billed woodpeckers

(Campephilus principalis), Carolina parakeets (Conuropsis car-

olinensis) and scores of other birds and other vertebrates and

invertebrates whose voices once defined our native land-

scapes, but we are left with, or have created, soundscapes

that are increasingly more homogenized (Schafer, 1993; Kra-

use, 1999; Joo et al., 2011). And this was also anticipated by

Carson who, in her classic book, recounted the lament of a

Wisconsin naturalist who reported that ‘[w]rens, robins, cat-

birds and screech owls have nested each year in our garden.

There are none now. . . . Only pest birds, pigeons, starlings

and English sparrows remain. It is tragic and I can’t bear it’

(Carson 1960, p. 112). These ‘pest birds’ are the same ones

that can be seen and heard in most cities and towns across

the USA, much of Europe, and other developed countries as

well. This homogenization of nature results from anthropo-

genic transformations of natural landscapes, introductions of

a limited collection of commensal species, and extinctions of

the endemics that once distinguished the biota of a particular

place from other places (Lockwood & McKinney, 2001).

Moreover, the impacts of some anthropogenic sounds – or

noise – are well documented for a variety of organisms

across terrestrial and marine habitats (Sun & Narins, 2005;

Codarin et al., 2009; Hu & Cardoso, 2010; Francis et al.,

2011, 2012; Chan & Blumstein, 2012; Melc�on et al., 2012;

McClure et al., 2013).

BIOACOUSTICS AND SOUNDSCAPE ECOLOGY

Biogeographers can draw on two acoustically centric views of

nature – the traditional field of bioacoustics and the emerging

field of soundscape ecology. Bioacoustics (cf. Bradbury & Ve-

hrencamp, 2011) encompasses the topics of animal vocaliza-

tion, signal production, hearing and sound perception,

recording techniques, sound propagation and noise interfer-

ence. Bioacoustics is a subarea of research that can broadly be

defined as animal communication. Research in bioacoustics

has been carried out since the early 1900s (e.g. Yerkes, 1905;

Shepard, 1911, 1912; Lashley, 1913; Greene, 1924; Bierens de

Haan, 1929; Myers, 1929; Burkenroad, 1931) and has focused

on attempts to determine the purpose and methods of com-

munication principally in mammals, birds, fish, reptiles,

amphibians and insects. This research initially grew out of the

fields of psychology and animal behaviour. Much subsequent

work has focused on a variety of aspects of bioacoustics such

as neurobiology (Konishi, 1969; Williams & Nottenbohm,

1985), energetics (e.g. Wells & Taigen, 1986), anatomical fea-

tures of sound production (e.g. Alexander, 1959; Nowicki,

1987; Goller & Daley, 2001), learning (Kroodsma, 1976; Marler

& Peter, 1981; Nelson, 2000), structure of complex songs of ani-

mals (especially marine mammals; Payne & McVay, 1971; Clark

& Clark, 1980; Parks et al., 2013), and acoustic niche separation

(Ficken et al., 1974; Sueur et al., 2008a,b, 2012). Recently, how-

ever, bioacoustics studies have begun to expand into the geogra-

phy of sound, either as the spatial arrangement of animal

sounds or as sound propagation over space as it relates to habi-

tat (e.g. see Lobel, 2002; Laiolo & Tella, 2006; Laiolo, 2008; Vie-

ites et al., 2009).

Just as conservation biologists attempt to conserve ende-

mic species in the face of anthropogenic and natural

Journal of Biogeographyª 2015 John Wiley & Sons Ltd

2

M. V. Lomolino et al.

challenges, soundscape ecologists strive to describe and

archive the acoustic distinctiveness of place (Pijanowski

et al., 2011a,b; Farina, 2014). Soundscape refers to the collec-

tion of sounds – biological, geophysical and anthropogenic –that emanate from and characterize a particular landscape.

Soundscapes, thus, can be distinguished at the simplest level

by the production of particular sounds characterized by spe-

cific frequencies and amplitudes of waves travelling through

air and perceived by organisms (Farina & Morri, 2011; Far-

ina, 2014). In nature, sound qualities are described using a

complex combination of acoustic and musical attributes,

including harmonics, spectral envelope, rise and decay time,

vibrato (frequency modulation), tremolo (amplitude modu-

lation), attack (initial sound), timbre (tonal quality or colour

of a sound) and final sound (Truax, 2001). Finally, these

complex sounds (analogous to distinct musical instruments)

combine over time and space into a natural orchestration of

sounds to form the entire soundscape (Krause, 2012). The

arrangement of all biological sounds are referred to as bio-

phony, while those from the geophysical sources – which

include the movement of fluids (air and wind), and changes

in energy, such as thunder – are geophonies. All sounds pro-

duced by humans have been termed anthrophony, and the

subset of those sounds produced by machines constitutes

technophony (Qi et al., 2008). Soundscape ecologists,

through these various perspectives, study spatial and tempo-

ral variation in complex acoustic environments and the

underlying causal explanations for those patterns, including

the effects of human activities and natural ecological and

evolutionary processes (see also R€omer & Bailey, 1986;

Gogala & Riede, 1995; Pijanowski et al., 2011b).

Soundscape ecologists utilize a variety of technologies to

record and analyse sounds and their patterns of variation

over time and space. We refer readers to Villanueva-Rivera

et al. (2011) and Farina (2014) for summaries of the tools

useful for soundscape analysis, Obrist et al. (2010) for an

overview of bioacoustics approaches in biological inventories,

and Sueur et al. (2014) for a technical review of acoustic

diversity indices that can be applied in the context of sound-

scape studies. These new advances in technology, with the

miniaturization of acoustic sensors and abilities to store and

analyse massive amounts of data, have created opportunities

for integrating data from long-term acoustic recording into

studies of animal communication, climate change and bioge-

ography.

FROM SILENCE TO SYNERGIES

We may assume that biogeographers appreciate the sounds

of nature as much as other natural scientists and, indeed, we

have often used sound to help determine occurrence, relative

densities and behavioural activities of a great variety of spe-

cies (in particular, insects, frogs and toads, bats and birds in

the terrestrial environment, and whales and related species of

mammals in the marine realm). Seldom, however, have we

focused on sound and its geographical variation as a subject

worthy of study in its own right. Reviews of the leading jour-

nals and texts in the field will bear this out. For example, a

review of abstracts from the Journal of Biogeography from

2013 to 2014 (including over 250 papers) reveals that only

three papers specifically use sound, and two of these employ

sound as a surrogate method for species survey. A search of

the issues of this journal from 1996 to 2013 (about 2500

papers spanning 181 issues and over 32,000 pages) finds the

word ‘acoustic’ used in only 33 (1.3%) papers, and only 16

of these use it as a trait of interest. Similarly, a search of the

4th edition of the text Biogeography by Lomolino et al.

(2010) shows that the term ‘acoustic’ is not used at all, and

the term ‘sound’ is used just once (in relation to geographi-

cal variation in ear length). Although our searches were lim-

ited to just these sources, we believe they will be

representative for the body of publications across the disci-

pline of biogeography. On the other hand, we acknowledge

the likelihood that journals in other fields may feature more

frequent focus on the sounds of nature. Our assertion, how-

ever, is that much is to be gained by putting sound into an

explicit geographical context, and on this front biogeogra-

phers have regrettably remained almost silent.

Why then the neglect of the geography of sound? We

believe the simplest and most logical answer is that, up until

relatively recent times, the technologies for objectively

recording and describing sound were either not available or

known to only a small fraction of biogeographers and ecolo-

gists. Fortunately, this is changing, thanks to the efforts of

scientists who are defining and advancing the frontiers of

soundscape ecology and actively seeking collaborations and

synergies with other disciplines, including landscape ecology

and biogeography (see Servick, 2014). Perhaps foremost

among these technological advances is the development of

equipment to automatically record sounds at a broad range

of frequencies (subsonic to ultrasonic, c. 1 Hz to c. 184 kHz,

including those generated by the geophysical, biological and

anthropogenic sources). These acoustic recordings can be

manually or remotely downloaded and transformed in differ-

ent objects easily analysable (i.e. the oscillogram, spectrogram

or mean spectrum), utilizing a variety of specialized software

packages to characterize soundscapes based on the features

of sound described earlier (see primer on acoustic analysis of

soundscapes by Villanueva-Rivera et al., 2011; see also Sueur

et al., 2008a,b; Kasten et al., 2010; Depraetere et al., 2012;

Gasc et al., 2013a,b).

MOVING FORWARD

We see great potential for making fundamental and perhaps

transformative insights by utilizing these technologies and

basic concepts of soundscape ecology to expand the empiri-

cal and conceptual spectra of our research to study sound,

not just as a surrogate indicator of the occurrence and activ-

ity of particular species, but as an important and integral fea-

ture of the natural world. Biogeography can, in turn, provide

the strategic geographical design for studies of soundscapes –

Journal of Biogeographyª 2015 John Wiley & Sons Ltd

3

The silence of biogeography

i.e. strategies for locating acoustic recorders along the princi-

pal geographical gradients including those of latitude, eleva-

tion, depth, area and isolation. In addition, we anticipate

some creative but well-reasoned applications of the biogeog-

raphers’ and macroecologists’ toolkit, including strategies for

processing huge, geo-referenced databases and statistical

approaches for gradients analyses or those for determining

the distinctiveness and similarity among soundscapes.

Central to this work will be the visualization and analysis

of soundscape recordings taken in representative ecosystems

around the world. Accomplishing this will require the use of

some of the soundscape ecologists’ tools, much of which

focuses on the concept of a spectrogram. Spectrograms dis-

play acoustic frequency on the y-axis, time on the x-axis and

the amplitude of sound is shown using a colour ramp. The

spectrogram of Fig. 1 represents a 1-min recording from a

wetland in Indiana at night in May of 2008. The large

amount of activity occurring in the 3–4 kHz range is created

by spring peepers (Pseudacris crucifer). Sounds produced by

other frogs (e.g. green frogs, Rana clamitans, and the Ameri-

can bullfrog, Lithobates catesbeianus) and by a few birds are

also depicted in this spectrogram, along with those of road

noise from a nearby highway.

The requisite for this becoming part of the biogeographer’s

domain, however, is the need to place acoustic variation

within an explicit geographical context. There are several

ways to accomplish this, and ongoing soundscape ecological

studies using automated acoustic sensor recordings are pav-

ing the way for biogeographical inquiry. One of the authors

is leading a large-scale, long-term project entitled, the Van-

ishing Soundscapes Project (http://centerforglobalsound-

scapes.org/vsp.php), where acoustic data for representative

ecosystems around the world are being collected and analy-

sed in the context of the geography of sound (Fig. 2a). Con-

tinuous acoustic recordings for the subarctic, temperate

forests, estuaries, Sonoran Desert, grasslands/steppes, Neo-

tropical forests and the Palaeotropical forests are being used

to assess how these soundscapes vary in three key dimen-

sions: acoustic composition, spatial variability and temporal

dynamics. A variety of metrics (e.g. Farina, 2014; Sueur

et al., 2014) are being employed that quantify soundscape

composition and characterize dynamics. Many soundscape

metrics are based on traditional measures of species diversity

in ecology. For example, indices of acoustic diversity [based

on the Shannon index (Shannon, 1948; Shannon & Weaver,

1949)] and evenness [employing a Gini (1912) coefficient of

evenness] can be estimated by first discretizing a sound file

into 10 or more frequency bands between 1 to 20 kHz, and

then calculating these metrics using the proportion of acous-

tic activity in each band. Figure 2b shows several examples

of the acoustic diversity index (see Villanueva-Rivera et al.,

2011 for details), in this case for four of the biomes that are

part of the Vanishing Soundscapes Project. This index was

calculated for 10-min recordings that started at the top of

the hour for a 24-h period (acoustic data were recorded with

a 44.1 kHz sampling rate). Note that the subarctic boreal

forest (Denali, Alaska), temperate forest (Tippecanoe County,

Indiana), Neotropical forest (La Selva, Costa Rica) and Pal-

aeotropical forest (Kuala Belalong Forest Reserve, Borneo) all

vary in levels of acoustic evenness through time (1 = acoustic

activity occurs in only one frequency band; 0 = acoustic

activity is spread evenly across all frequency bands). The sub-

arctic and the temperate forests exhibit opposite trends, with

the subarctic site having the most even distribution of

sounds across acoustic frequencies during the midday, while

temperate forests have the most evenness at night. The tropi-

cal forests vary less across the day, although inter-hour vari-

ability appears to be greater for Borneo than for Costa Rica.

The examples above represent only a small subset of the

opportunities to conduct near continuous, long-term studies

across large areas and along the principal biogeographical

gradients. One especially powerful approach employed in the

classic biogeographical literature is the use of montane, ele-

vational gradients to study broad-scale biogeographical pat-

terns in conveniently small study areas (e.g. von Humboldt

& Bonpland, 1807; Whittaker & Niering, 1965; see Lomolino

Freq

uenc

y (k

Hz)

0 30 60Time (s)

Band 10

Band 9

Band 8

Band 7

Band 6

Band 5

Band 4

Band 3

Band 2

Band 1

Amplitude(dBFS)

0

-10

-20

-30

-40

-50

-60

-70

10

8

6

4

2

0

Figure 1 A spectrogram illustratingvariation in frequency (pitch; y-axis) and

amplitude (intensity or volume; colour keyon right) during a one-minute recording of

a wetland in Indiana, USA, at night duringMay 2008. Note that this spectrogram is

dominated by the biophonies (soundsgenerated by species) of chorusing frogs

(Band 4) and, to a lesser degree, of toads(Band 2), with harmonics (sounds produced

at multiples of the primary frequency of asound) evident in Bands 5 and 7. Road

noise from a nearby highway is audible inthe very low frequencies (Band 1) (after

Villanueva-Rivera et al., 2011).

Journal of Biogeographyª 2015 John Wiley & Sons Ltd

4

M. V. Lomolino et al.

et al., 2010; fig. 3.21 for von Humboldt’s classic Tableau

Physique of elevational gradients in the Andes). The spectro-

grams from research started in early 2013 by Pijanowski and

his students in the Chiricahua Sky Islands of the Sonoran

Desert (Fig. 2c) show dramatic differences in acoustic pat-

terns between life zones for the same day and time (2 May

2014 at 05:00 h local time). In the morning, sounds from

the oak–pine life zone are dominated by birds that warble,

with acoustic activity spread across a range of frequencies;

those of an oak–chaparral are dominated birds that possess

complex whistles intermixed with distinct simple notes, but

their sounds are limited to a small range of acoustic frequen-

cies. In comparison, the hot desert is relatively silent.

We anticipate many additional, creative means to visualize

spatial variation of acoustic measures at local to global scales,

including integrating maps of acoustic parameters (in shad-

ing or colour) onto three-dimensional relief maps or vegeta-

tion structural maps produced by other remote-sensing

technologies. Soundscape metrics, such as the acoustic diver-

sity index (Villanueva-Rivera et al., 2011), have been used to

correlate acoustic frequency band diversity (top map,

Fig. 2d) with vegetation structural complexity at La Selva

Biological Station (Costa Rica), following MacArthur &

MacArthur’s (1961) classic work on the relationship between

faunal diversity and vegetation structure (MacArthur, 1964).

The Pekin et al. (2012) study accomplished this by compar-

ing long-term acoustic recording data with vegetation struc-

tural complexity metrics calculated from LiDAR (light

detection and ranging) remote-sensing imagery (Fig. 2d,

middle map; see Jung & Pijanowski, 2012), revealing a statis-

tically strong correlation between acoustic diversity and

structural complexity of canopy layers. A map of topography

(Fig. 2d, lower map) helps to visualize key features of this

landscape, such as rivers, wetlands and small hills that

may influence both the vegetative structure and acoustic

composition of this landscape. An alternative, but possibly

(a) (b)Legend Subarctic Boreal Forest Temperate Forest Neotropical Forest Palaeotropical Forest

5 Desert

23

5.0

1680 231680

10

.05

10

5. 01

0. 05

10

(d)

Acoustic Diversity

Layer Count

Elevation (m a.s.l.)

0 200

0

0

10

1.75

No data

1

2

3

4

1

2

3

5

4

4321

5Elevation (metres)(c)

Figure 2 Examples of ongoing soundscape ecology studies that are relevant to biogeography: (a) map of four locations included in the

existing Vanishing Soundscape Project (http://centerforglobalsoundscapes.org/vsp.php) in a variety of representative ecosystems aroundthe world. Point 1: a subarctic boreal forest in Alaska, USA; Point 2: a temperate forest in Indiana, USA; Point 3: a Neotropical forest in

the La Selva Biological Station, Costa Rica; Point 4: a Palaeotropical forest in Borneo; Point 5: a transect across different habitats along anelevational gradient in the Madrean Sky Islands, Arizona, USA; (b) the variation in acoustic evenness across the locations points 1, 2, 3

and 4; (c) a sample spectrograms of three life zones at Point 5 (recordings done simultaneously on the 4 June 2013 at 05:00 h; duration of20 seconds, the frequency range is between 1 and 10 kHz), and (d) a set of maps that show the relationships between an acoustic diversity

index [top, based on the Shannon index (Shannon, 1948; Shannon & Weaver, 1949), interpolated from 2 months of recordings at 24stations], number of vegetation layers in the tropical forest (middle, derived from LiDAR), and elevation (bottom) at La Selva Biological

Station, Costa Rica. Pekin et al.’s (2012) statistical analyses of the relationship between the two top layers revealed a strong correlationbetween vegetative structure (in particular, forest canopy structure and proximity to swamps) and acoustic diversity. The area shown is

approximately 24 km2, covering nearly the entire station. As the acoustic diversity index was interpolated using number of layers as acovariate, the index has no data where the number of layers is 0.0 (see Pekin et al., 2012 for details).

Journal of Biogeographyª 2015 John Wiley & Sons Ltd

5

The silence of biogeography

complementary, means of visualization of the geography of

sounds may include global maps of soundscapes that can be

created using cartograms that purposely distort geographical

units (e.g. countries, continents or ocean basins) to map

soundscapes in proportion to their acoustic diversity (see

Fig. 3 for an example of using the cartogram methodology

based on species diversity).

In short, soundscape ecologists are demonstrating how

acoustic data can supply a wide range of information about

the community structure of vocal organisms at a place, and

this information can be combined with other spatial infor-

mation to describe and explore the correlates of biogeo-

graphical patterns across broader scales of space and time.

We are, however, recommending much more than new field

studies on the geography of sound. Rather, we see much

greater promise and inferential power in field research pro-

grammes that follow von Humboldt’s lead and simulta-

neously record key features of soundscapes with those on the

distributions, densities and activities of species (including

humans), and environmental factors that may influence all

components of biotic communities.

Potential research questions

We conclude with a short list of some of the many potential

research questions that may be addressed by a synergistic

programme of soundscape ecology and biogeography.

1. Geographical clines in soundscapes: does acoustic diversity

(in particular, the diversity of biophonies) increase in a simi-

lar manner along gradients of latitude, elevation and depth

as does species diversity?

2. Distinctiveness of place: does the distinctiveness of sound-

scapes vary in a manner analogous to or parallel with dis-

tinctiveness of biotic communities? For example, is acoustic

distinctiveness of island soundscapes a simple function of

endemicity and distinctiveness of their biotas? Was Janzen

(1967) correct? Or, in the present context, do soundscapes

tend to be more distinct (exhibit higher beta diversity in

acoustic characters) for tropical versus higher latitude sys-

tems?

3. Three dimensional soundscapes: the elevational gradients

referred to above are distinct from altitudinal gradients, as

the former refers to phenomena along the Earth’s surface

and the latter to those within the atmosphere. In another

emerging discipline of natural sciences – aeroecology, Kunz

et al. (2008) emphasize that much of life’s important phe-

nomena occur well above the relatively thin surface film of

the terrestrial environment, i.e. in the aerosphere. In an

entirely analogous fashion, much of the phenomena studied

by marine ecologists and oceanographers occur across a

three-dimensional realm, where simple gradient analyses may

prove inappropriate and insufficient. What patterns in acous-

tic and soundscape character do we predict across these

three-dimensional realms (i.e. the aerosphere and the marine

environment), and should they be analogous to each other

or to those observed for gradients (elevational, latitudinal or

otherwise) along the surface of the Earth?

4. Ecological release and displacement: do the members of

species-poor communities exhibit ecological release to more

fully utilize the available acoustic space and occupy those

features of soundscapes vacated by now absent species [see

Krause (1987) and Forrest (1994) for articulations of their

acoustic niche and acoustic adaptation hypotheses]? On

islands and along gradients where animal species often exhi-

bit clines in body size (e.g. the island and Bergmann’s rules;

see summaries in Lomolino et al., 2010, pp. 593–599,642–647; see also Lomolino et al., 2012, 2013), can we expect

corresponding shifts in the dominant frequencies of sounds

produced by these species (lower frequency, louder sounds

produced by larger individuals)?

5. Historical reconstructions: can we utilize information from

the acoustic character of today’s species and soundscapes,

along with palaeontological and phylogenetic methods, to

reconstruct ancient and now extinct soundscapes? Can par-

ticular acoustic features of biophonies serve as characters to

inform and generate phylogenetic and phylogeographical

Figure 3 Cartograms utilize projections

that purposely exaggerate or otherwisedistort the relative sizes of geographical

units (e.g. countries, continents or oceanbasins) in order to emphasize geographical

variation in a particular characteristic ofthose units (in this case, countries). This

example illustrates geographical variationand concentrations of species diversity of

amphibians among countries across theglobe [after Wake & Vredenburg (2008); see

Gastner & Newman (2004) for anexplanation of cartogram projection

methods].

Journal of Biogeographyª 2015 John Wiley & Sons Ltd

6

M. V. Lomolino et al.

reconstructions? Can we utilize the sounds most particular

to a region (which have been called ‘keynote sounds’ by

Schafer, 1993) to construct maps depicting acoustically

related regions of the world analogous to Alfred Russel Wal-

lace’s classic map of the world’s zoogeographical regions

(Wallace, 1876; see also Holt et al., 2013)?

6. Soundscape diversity and islands: are biophonies on large

islands close to mainland more diverse than those that are

small and more isolated? In other words, does the composi-

tion of biological sounds correspond to those predictive fea-

tures of island theory (see Whittaker & Fern�andez-Palacios,

2007; Lomolino et al., 2010)?

While benefitting from the rich information being gener-

ated on the acoustic nature of the Earth, biogeographers are

perhaps uniquely qualified to reciprocate by contributing to

the nascent development of soundscape ecology. The cacoph-

ony of sounds to be archived from the world’s ecosystems

(natural and anthropogenic) may be likened to Henri Poin-

car�e’s (1905, p. 141) metaphorical heap of stones: ‘The scien-

tist must set in order. Science is built of with facts, as a

house is with stones; but a collection of facts is no more a

science than a heap of stones is a house.’ Well before the

transformative insights of Darwin and Wallace, biogeogra-

phers (then simply referred to as ‘geographers’ or ‘geolo-

gists’) began to provide naturalists with the conceptual

framework and geographical context that served as a blue-

print for understanding the facts and intriguing patterns of

nature. By adding the ‘sounds of nature’ to the long list of

characters we study, and by applying the fundamental princi-

ples of our science along with its ever-advancing battery of

tools for visualizing and analysing patterns across space and

time, we will simultaneously advance the frontiers of bioge-

ography and soundscape ecology.

How vivid is the impression produced by the calm of nature, at

noon, in these burning climates! The beasts of the forests retire

to the thickets; the birds hide themselves beneath the foliage of

the trees, or the crevices of the rocks. Yet, amidst this apparent

silence, when we lend an attentive ear to the most feeble sounds

transmitted through the air, we hear a dull vibration, a continual

murmur, a hum of insects, filling, if we may use the expression,

all the lower strata of the air. . .These are so many voices, pro-

claiming to us that all nature breathes.

von Humboldt (1852, p. 199)

ACKNOWLEDGEMENTS

We thank two anonymous referees for their comments

and suggestions on an earlier version of this manuscript.

We thank Matthew Harris, Benjamin Gottesman and Jar-

rod Doucette for assistance in developing the images of

Fig. 2. Figure 3 was published with permission under

Copyright (2008) National Academy of Sciences, USA.

MaryAm Ghadiri provided comments on an earlier draft.

Data used for illustrations were collected with the financial

support of grants from NSF (CNH) IIS 0705836 and BCS

1114945 and Purdue’s Office of Vice-President for

Research.

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DATA ACCESSIBILITY

Sample recordings of soundscapes, acoustical databases, pub-

lications and descriptions of ongoing research on soundscape

ecology may be found at http://ltm.agriculture.purdue.edu/

soundscapes.htm.

Journal of Biogeographyª 2015 John Wiley & Sons Ltd

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The silence of biogeography

BIOSKETCHES

Mark V. Lomolino is a Professor of Biology, and founding member and past president of the International Biogeography Soci-

ety (http://www.biogeography.org/). His research and teaching focus on the biogeography, community ecology, evolution and

conservation of animals inhabiting islands or island-like ecosystems.

Bryan Pijanowski is a Professor and University Faculty Scholar in the Department of Forestry and Natural Resources, Purdue

University and is the Director of Discovery Park’s Center for Global Soundscapes. His research integrates concepts of soundscape

ecology, landscape ecology and geography. He teaches courses in spatial ecology, geographic information systems and sustainabil-

ity.

Amandine Gasc is a Postdoctoral Research Associate at Purdue University. Her research focuses on bioacoustics and the analy-

sis and monitoring of animal biodiversity using passive acoustic devices.

Editor: Richard Ladle

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M. V. Lomolino et al.