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This letter to the editor describes the surge of “photo-friendly” stacks of stones as an emerging tourism-associated threat to rock-dwelling biodiversity.
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Human–Wildlife Interactions 14(1):Early Online, Spring 2020 •
Letter to the Editor
Stone-stacking as a looming threat to
rock-dwelling biodiversity
Ricardo Rocha, CIBIO/InBIO-UP, Research Centre in Biodiversity and Genetic Resources, Uni-
versity of Porto, Rua Padre Armando Quintas, 4485-661 Vairão, Portugal; CEABN-InBIO, Centre for
Applied Ecology “Prof. Baeta Neves,” Institute of Agronomy, University of Lisbon, Tapada da Ajuda,
1349-017 Lisbon, Portugal; and Centre for Ecology, Evolution and Environmental Changes, Faculty
of Sciences, University of Lisbon, 1749-016 Lisbon, Portugal
Paulo A. V. Borges, Centre for Ecology, Evolution and Environmental Changes, Faculty of Sci-
ences, University of Lisbon, 1749-016 Lisbon, Portugal; and Azorean Biodiversity Group (cE3c) and
Universidade dos Açores – Faculty of Agriculture and Environment, Rua Capitão João d’Ávila, São
Pedro, 9700-042 Angra do Heroísmo, Terceira, Açores, Portugal
Pedro Cardoso, Laboratory for Integrative Biodiversity Research (LIBRe), Finnish Museum of
Natural History, University of Helsinki, Helsinki, Finland
Mirza Dikari Kusrini, Faculty of Forestry, IPB University (Institut Pertanian Bogor), Jalan
Ulin, Kampus Darmaga, Bogor 16680, Indonesia
José Luis Martín-Esquivel, National Park of Teide, C. Dr Sixto Perera González, 25.
38300 La Orotava, Canary Islands, Spain
Dília Menezes, Instituto das Florestas e Conservação da Natureza, IP-RAM, 9064-512 Funchal, Portugal
Mário Mota-Ferreira, CIBIO/InBIO-UP, Research Centre in Biodiversity and Genetic Resourc-
es, University of Porto, Rua Padre Armando Quintas, 4485-661 Vairão, Portugal; CEABN-InBIO, Centre
for Applied Ecology “Prof. Baeta Neves,” Institute of Agronomy, University of Lisbon, Tapada da Ajuda,
1349-017 Lisbon, Portugal
Sara F. Nunes, Centre for Ecology, Evolution and Environmental Changes, Faculty of Sciences, Uni-
versity of Lisbon, 1749-016 Lisbon, Portugal; and Global Change and Conservation Faculty of Biological
and Environmental Sciences, University of Helsinki, P.O. Box 65, Viikinkaari 1, 00014, Helsinki, Finland
Inês Órfão, CFCUL – Centro de Filosoa Das Ciências da Universidade de Lisboa; and Centre
for Ecology, Evolution and Environmental Changes, Faculty of Sciences, University of Lisbon, 1749-
016 Lisbon, Portugal
Catarina Serra-Gonçalves, University of Tasmania, Institute for Marine and Antarctic Stud-
ies, School Road, Newnham, Tasmania 7250, Australia
Manuela Sim-Sim, Centre for Ecology, Evolution and Environmental Changes, Faculty of Sci-
ences, University of Lisbon, 1749-016 Lisbon, Portugal; and MUHNAC - Museu Nacional de História
Natural e da Ciência, Universidade de Lisboa, Rua da Escola Politécnica, 58, 1250-102 Lisboa, Portugal
Pedro Sepúlveda, DROTA - Direção Regional do Ordenamento do Território e Ambiente, Rua
Dr. Pestana Júnior, 9064-506 Funchal, Portugal
Dinarte Teixeira, Faculty of Life Sciences, University of Madeira, 9020-105 Funchal, Portugal;
Laboratory for Integrative Biodiversity Research (LIBRe), Finnish Museum of Natural History, Univer-
sity of Helsinki, Helsinki, Finland; and Instituto das Florestas e Conservação da Natureza, IP-RAM,
9064-512 Funchal, Portugal
Anna Traveset, Mediterranean Institute of Advanced Studies, IMEDEA (CSIC-UIB), c/ Miquel
Marqués 21, Esporles- 07190, Mallorca, Balearic Islands, Spain
Key words: habitat disturbance, invertebrate conservation, narrow-range endemics, nature-
based tourism, retreat sites
Nature-based tourism and outdoor recrea-
tion activities are a rapidly growing market
worldwide, and mounting evidence shows
that these can result in positive conservation
outcomes (e.g., Macdonald et al. 2017). Yet,
such activities often take place in areas of high
2Human–Wildlife Interactions 14(1)
conservation value, where even small levels
of human disturbance can cause signicant
impacts (Larm et al. 2018).
Many of the direct and indirect negative
consequences of tourism and recreation, such as
vegetation clearance for infrastructure construc-
tion, spread of invasive species, and trampling
or its pervasive impacts in the behavior of
wildlife, have long troubled conservationists
(Kelly et al. 2003, Li et al. 2017). Here, we
describe the surge of “photo-friendly” stacks of
stones as an emerging tourism-associated threat
to rock-dwelling biodiversity. These structures,
formed by stacked rocks displaced from the
surrounding landscape, have become hugely
popular in many areas worldwide, including
Tenerife and Menorca Islands (Spain) or in Sal
and Boavista Islands (Cape Verde), promoting
soil erosion and modifying habitat structure for
a large array of biota (Figure 1A–C).
These stacks of stones are distinct from
cairns, that have been used for centuries for trail
signaling and still provide useful services for
visitors (acting as orientation signs) and nature
(avoiding unnecessary opening of new trails).
The prolic stone-stacking highlighted here
has no such purpose and is gaining momentum
with the growth of social media and adventure
tourism. Stone stacks can nowadays be found
inside multiple protected natural areas, such
as Teide National Park in Tenerife, where they
are often confused with trail marks, and Ozark
National Scenic Riverways in the United States,
where they pose a threat to fragile riparian
ecosystems. We illustrate the impacts of these
structures by describing the consequences of
stone-stacking in the endemic-rich biodiversity
of the easternmost point of Madeira Island,
Portugal. We use this case in point to argue that,
in areas of conservation concern, authorities
should impose restrictions to this practice
and quickly dismantle stone towers to avoid
a contagious eect that often encourages the
construction of more such structures.
Surface rocks as key
Abiotic (e.g., thermal, hydric, and structural)
conditions associated with rocks are paramount
to many terrestrial and aquatic species that use
these keystone features for physical aachment
(Erman and Erman 1984) or as retreat or
foraging sites (Croak et al. 2010, Penado et al.
2015). Rock size, structure, substrate type and
Figure 1. Stacks of stones in some nature-sensitive areas: (A) Thingvellir National Park, Iceland; (B) Muránska
planina National Park, Slovakia; (C) Madeira Natural Park, Portugal; and (D) information board warning against
stone-stacking (photos courtesy of F. Tavares [A] and R. Rocha [B–C]).
Letter to the Editor • Rocha et al.
depth, and moisture levels inuence species’
occurrence (Goldsbrough et al. 2003) and impact
on the physiological performance and behavior
of rock-dwelling individuals (Goldsbrough
et al. 2004). Additionally, the distribution of
surface rocks can inuence biotic interactions
with conspecics and non-conspecics, such as
competitors, predators, and prey (Penado et al.
2015). This, in turn, can impact population and
community dynamics and even aect species’
long-term persistence (Goldsbrough et al. 2004).
The microhabitat conditions associated with
surface rocks are of particular importance in
areas with low structural complexity, such as
arid landscapes (Penado et al. 2015). In island
ecosystems, many such areas often house
considerable numbers of endemic invertebrates
and other ectotherms, whose behavior and phy-
siological processes are inuenced by the thermal
regimes of rocky retreat sites (Vasconcelos et al.
2012). Removal, displacement, overturning, and
breaking of rocks can aect the thermal prole
of the landscape, exposition to the elements,
and predation levels (Goldingay and Newell
2000), thus inducing signicant impacts to rock-
dwelling organisms.
Stones piles and narrow-range
rock-dwelling species
Ponta de São Lourenço is a 9 x 2-km peninsula
in the Eastern tip of Madeira Island (Figure 2).
It is a popular hiking destination (>150 visitors
per day) and is included in the Natura 2000
Network and in the Madeira Natural Park.
Over the last few years, visitors have formed
considerable numbers of stacks of 5–10 stones
outside marked trails. Until recently, >200 of
these structures were dispersed across an area
of approximately 1 ha, leading to signicant
vegetation damage and soil erosion (Figure 1C).
Despite its xeric conditions, the peninsula
harbors a rich coastal xerophytic bush vegetation,
with >160 vascular plant species (14% of which
are endemic to the Madeira archipelago; see
Borges et al. 2008) and an important community
of bryophytes (approx. 80 species, 15% of
the island’s bryoora), including an endemic
thallose liverwort (Riccia atlantica) found in rock
crevices and classied as critically endangered
by the International Union for Conservation of
Nature (IUCN; Hodges et al. 2019). Surface
rocks are important retreat sites to the unique
native reptile of the island, the Madeira wall
lizard (Teira dugesii). The peninsula hosts a large
diversity of invertebrates and is of particular
interest for the conservation of rock-dwelling
arthropods (e.g., the Madeira archipelago wolf
spider [Hogna insularum]), endemic to arid areas
of the Madeira archipelago. Within the species
heavily dependent on the availability and non-
disturbance of surface rocks, we highlight the
Madeira ower spider (Misumena nigromaculata),
an IUCN Data Decient species with the last
conrmed sighting from 1940 (Cardoso et al.
2017) and the peninsula’s terrestrial mollusks
(Teixeira and Abreu 2003). Regarding the laer,
we know of 35 species that inhabit the peninsula,
including several narrow-range endemics with
areas of occurrence as small as 1 km2 (e.g., São
Lourenço’s snail [Amphorella tornatellina minor]).
The vast majority of these mollusks occupy
small, usually non-overlapping ranges and
use surface rocks as refuge. They are greatly
dependent on rock-associated microhabitats and
thus are highly sensitive to rock displacement.
Stone-stacking in nature-sensitive areas likely
reects more a quest for social media-friendly
photos than any cultural or spiritual beliefs.
These structures can cause signicant negative
impacts in rock-dwelling organisms and, in
turn, jeopardize the long-term persistence of
many narrow-range endemics. We thus urge
visitors to act responsibly and not construct
Figure 2. Location of the Ponta de São Lourenço
peninsula, in the Eastern tip of Madeira Island,
4Human–Wildlife Interactions 14(1)
these structures (“leave no trace” philosophy).
Additionally, we encourage authorities to
promptly dismantle any stacks of stones erected
and to implement educational campaigns about
the importance of surface rocks for rock-dwelling
organisms and the negative consequences of
stone-stacking for biodiversity (e.g., Figure 1D).
We acknowledge the support from ARDITI—
Madeira’s Regional Agency for the Development
of Research, Technology and Innovation (grant
M1420-09-5369-FSE-000002) to R. Rocha. Com-
ments from F. Angelici, HWI associate editor,
provided insight for an earlier version of the leer.
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2004. Fitness benets of retreat-site selec-
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Garcia Criado, L. Patin, A. Nieto, A. Bergamini,
I. Bisang, and E. Baisheva. 2019. A miniature
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Brundin, and A. Angerbjörn. 2018. The role of
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Associate Editor: Francesco M. Angelici
Letter to the Editor • Rocha et al.
Ricardo Rocha has a Ph.D. degree in con-
servation biology from the University of Lisbon and a
master’s degree in conser-
vation science from the
Imperial College London.
His main area of interest
involves the anthropogen-
ic drivers of biodiversity
loss, particularly in tropical
and subtropical forest and
island ecosystems.
Paulo A. V. Borges has a Ph.D. degree
in insect ecology from the University of London
(Imperial College). His
main research interest is
investigating the process-
es aecting patterns of
species diversity, abun-
dance, and distribution
at dierent spatial scales
using Macaronesia as a
model system.
Pedro Cardoso is a curator at the Finnish
Museum of Natural History (arachnids, myriapods,
and terrestrial molluscs)
and adjunct professor in
ecology at the University
of Helsinki. He is also the
founder and former chair
of the IUCN’s Spider &
Scorpion Specialist Group.
His research interests go
from biogeography and
conservation to spider
taxonomy and articial
Mirza Dikari Kusrini works as a
lecturer and researcher at Faculty of Forestry, IPB
University (Institut Perta-
nian Bogor) in Indonesia.
She has a Ph.D. degree
in zoology and tropical
ecology from James Cook
University in Queensland,
Australia, and a Master of
Environmental and Natural
Resources Management
Studies from IPB Uni-
versity. Her main areas
of interest are wildlife
conservation, especially of
amphibians and reptiles in
tropical forest ecosystems,
wildlife trade, human–wildlife conicts, and citizen
José Luis Martín Esquivel has a
Ph.D. degree in biology from the University of La La-
guna (Canary Islands). He
is the head of conserva-
tion in Teide National Park
and an expert in managing
biodiversity and protected
natural areas.
Dília Menezes has a bachelor’s degree in
biology from the University of Madeira. She is a head
of the Division of Manage-
ment and Valorization of
Classied Areas at the
Institute for Forest and
Conservation Nature, Re-
gional Secretariat for the
Environment and Climate
Change of the Regional
Government of Madeira.
Her main areas of interest
are the management and
conservation of Pterodro-
mas, namely P. deserta
and P. madeira.
Mário Mota-Ferreira is a Ph.D.
candidate at the University of Porto. His main area of
interest is the ecology and
conservation of freshwater
ecosystems in human-
dominated landscapes
and the development of
new modeling approaches
for the distribution of
aquatic organisms. He is
also interested in the conservation and ecology of
reptiles in island ecosystems.
Sara F. Nunes has a master’s degree in
conservation biology from the University of Lisbon,
with a thesis dedicated
to the trophic ecology of
insular reptiles, based on
isotopic analyses. Her
research interests include
biological invasions, ecol-
ogy, and conservation of
herpetofauna and insular
Inês Órfão has a Ph.D. degree in ethology
and a master’s degree in ecology and environmental
management from the
University of Lisbon. Her
main research interests
include conservation,
behavioral evolution, and
6Human–Wildlife Interactions 14(1)
Manuela Sim-Sim is a professor of plant
biology at the Faculty of Sciences, University of Lis-
bon. She obtained a Ph.D.
degree in biology (ecology
and biosystematics) from
the University of Lisbon.
Her research interests are
taxonomy, biogeography,
ecology, and conservation
of bryophytes from Portu-
gal and Macaronesia.
Pedro Sepúlveda has a bachelor’s degree
in biology from the University of Madeira. He is a se-
nior technician at the Re-
gional Secretariat for the
Environment and Climate
Change of the Regional
Government of Madeira.
Since June 2019, he acts
as a co-leader of the work-
ing group on marine litter
(ICG-ML) of the OSPAR Convention (Convention
for the Protection of the Marine Environment of the
North-East Atlantic), having coordinated the Regional
Action Plan for Marine Litter of this international con-
vention for about a year.
Dinarte Teixeira has a master’s degree in
ecology from the University of Coimbra, and he is cur-
rently a Ph.D. candidate at
the University of Madeira.
His research interests
range from biogeography
and island ecology to the
taxonomy and conserva-
tion of terrestrial molluscs.
Anna Traveset is a research professor
at the Mediterranean Institute of Advanced Studies
based in the Balearic Is-
lands. Her main research
interest is the ecology and
evolution of plant–animal
interactions and how
these are inuenced by
dierent drivers of global
change. She is involved in
many projects, mostly on islands from both the tropics
and the temperate zone.
Catarina Serra-Gonçalves has a
master’s degree in conservation biology from the
University of Lisbon and is
currently a Ph.D. can-
didate at the University
of Tasmania, where she
is associated with the
Institute of Marine and
Antarctic Studies and
the Centre for Marine
Socioecology. Her main research interests are waste
management, integrating advocacy, governance, and
human behavior.
... L'empilement de galets sur les littoraux français est une pratique touristique qui a pris un essor important sous l'effet des réseaux sociaux ces dernières années. La multiplication de ces empilements sur les littoraux peut réduire considérablement la quantité de microhabitats disponibles pour les plantes et les animaux dans les écosystèmes constitués de galets (Rocha et al. 2020). Les impacts sur la biodiversité de ces structures, en apparence inoffensives, peuvent être donc significatifs dans des écosystèmes présentant une faible complexité structurale. ...
... Plus récemment, la pratique d'empilement de galets dans les espaces naturels s'est développée de manière importante sous l'effet des réseaux sociaux. Sur certains sites, la multiplication de ces empilements peut impacter négativement les microhabitats d'une partie de la faune et de la flore inféodée à cet écosystèmes (Rocha et al. 2020). La Figure 22 ci-dessous résume le fonctionnement global de l'écosystème ainsi que les impacts des principales menaces identifiées. ...
... Cette pratique n'est pas nouvelle mais s'est largement amplifiée en raison de l'effet démultiplicateur des réseaux sociaux. D'apparence peu impactant, ces empilements soulèvent des inquiétudes de la part des acteurs de terrain et de scientifiques (Rocha et al. 2020). En effet, la faune et la flore des cordons de galets et graviers est très liée à la présence de microhabitats. ...
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The Selvagens gecko (Tarentola boettgeri bischoffi Joger, 1984) is a medium sized gecko endemic to the Selvagens archipelago, Madeira, Portugal. The biology of this gecko is poorly known and in this study we present the first evidence regarding its habitat use. In 2010 (spring and autumn) and 2011 (spring), we collected data on the characteristics of the habitat surrounding 168 rocks used by these geckos as retreat sites, as well as on 75 randomly selected rocks. We also recorded body measurements of the individuals caught under each rock. In both seasons retreat site occupancy was found to be related to rock area, with geckos being found mainly under large rocks. Interestingly, we found that in spring heavier males, in better body condition, occupied the largest rocks and larger geckos occupied rocks closer to creek beds. Our results shed some light upon the behavioural ecology of this nocturnally active ecto-therm, that spends the day under a retreat site: i) intraspecific competition may be an ecological factor prevalent in this species, since larger individuals occupy larger rocks, located in a presumably high quality micro-habitat; ii) the possibility of spring territoriality in males, that compete for good quality shelters.
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Many animals spend much of their time within retreat sites underneath loose surface rocks and may be highly selective in terms of the physical characteristics of the sites that they use. If such shelters are eliminated by anthropogenic activities, such as rock removal for landscaping, the only way to restore these nonrenewable habitats may be to replace them with artificial rocks. To construct artificial rock habitats, we need to understand which rock attributes are important for faunal use and develop methods to mimic these important natural retreat site characteristics. Based on our prior understanding of rocky retreat sites used by reptiles in sandstone outcrops of southeastern Australia, we constructed realistic-looking artificial rocks from fiber-reinforced cement and evaluated (1) the degree to which they mimicked natural retreat sites in both thermal regime and three-dimensional crevice structure and (2) their colonization by fauna after deployment in the field. Our results demonstrate that thermal regimes and crevice structures beneath the artificial rocks were similar to those beneath natural rocks. In addition, 100% of the artificial rocks were colonized (by 45 invertebrate, six lizard, and two snake species, including the endangered Broad-headed snake, Hoplocephalus bungaroides) after only 40 weeks. Together, these results suggest that restoring degraded habitats for rock-dwelling species is feasible and can provide a rapid means of enhancing shelter-site availability for such species.
In recent decades, public interest in apex predators has led to the creation and expansion of predator-focused wildlife tourism. As wildlife tourism has become an increasing topic of study for both social and biological scientists, researchers have debated whether these activities serve conservation goals by providing non-con-sumptive values for wildlife. Discussion of predator tourism requires additional recognition of predator-specific biological and ecological characteristics, consideration of human safety concerns, and mitigation of human-wildlife conflict. By reviewing tourism activities centered on both aquatic and terrestrial predators from diverse taxa (sharks, crocodiles, and big cats), we evaluate the potential benefits and conservation challenges associated with predator tourism. Our review suggests that positive conservation outcomes are possible, but not assured given historical, cultural, and ecological complexities. We explore some of the factors which determine whether tourism contributes to conservation outcomes, including (1) effective protection of animals and habitats, (2) avoidance and mitigation of human-wildlife conflict, (3) quality of associated educational interpretation and outreach, (4) collaboration with local stakeholders, and (5) use of generated funds to advance conservation goals. Our findings suggest tourism is most likely to support predator conservation and/or recovery when the industry has both public and political support and under conditions of effective regulation focused on management , monitoring and enforcement by local, national, and international bodies.
Although animals are widely assumed to select habitats in ways that enhance organismal fitness, there are few empirical data to demonstrate this link. We studied flat rock spiders (Hemicloea major, Gnaphosidae) from eastern Australia, where these highly modified (dorsoventrally flattened) spiders live under loose surface rocks on sandstone outcrops. Field surveys showed that the rocks used as diurnal retreat sites by spiders were relatively thin with low canopy cover and a rocky substrate and therefore were likely to experience high temperatures and large thermal fluctuations. Laboratory trials suggest that this nonrandom rock use is a direct response to thermal cues; juvenile spiders selected warmer over cooler retreat sites. To investigate consequences of habitat selection on fitness-related traits, we maintained cohorts of juvenile spiders at cycling-temperature regimes corresponding to those measured in the field under rocks that were fully, partially, or never exposed to direct sunlight (diel thermal ranges of 16.2–37.8C, 15.5–31.2C, and 15.2– 24.3C). Survival rates were high for all groups over the eight-week study, but hotter conditions accelerated growth and development. Our data thus confirm that thermal cues are used in retreat-site selection and that selection of warmer retreat sites will confer fitness benefits to flat rock spiders.