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BIODIVERSITY
REVIEW
More than marine: revealing the critical
importance of mangrove ecosystems for
terrestrial vertebrates
Stefanie M. Rog*, Rohan H. Clarke and Carly N. Cook
School of Biological Sciences, Monash
University, Clayton, Vic. 3800, Australia
*Correspondence: Stefanie M. Rog, School of
Biological Sciences, Monash University,
Clayton 3800, Vic., Australia.
E-mail: Stefanie.rog@monash.edu
ABSTRACT
Aim Despite mangrove forests spanning marine, freshwater and terrestrial
realms, their function as terrestrial ecosystems has been largely ignored. In the
light of the rapid global decline of mangroves, it is critical to build a more
holistic understanding to plan for effective management of the whole ecosys-
tem. This study examines the importance of mangrove forests for terrestrial
vertebrates.
Location Global mangrove forests.
Methods An extensive review of records of the use of global mangrove forests
by the most poorly studied terrestrial vertebrate groups: mammals, reptiles and
amphibians. We explored the species richness and distribution of these groups,
along with their ecological characteristics. We also explored the relationship
between animal and plant species richness across the distribution of mangrove
forests.
Results Mangroves are used by a remarkable number of terrestrial mammal,
reptile and amphibian species (n=464); five times more than previously
reported. The diversity of species uncovered by this study, almost half of which
are of conservation concern, underscores the value of mangroves as terrestrial
ecosystems. Most species were facultative users of mangroves; however, there
are critical knowledge gaps in how these species interact with these ecosystems.
We found a positive global correlation between animal and mangrove plant
richness.
Main conclusions This study highlights that mangrove forests are considerably
more important for terrestrial animals than generally acknowledged. We pre-
sent the most comprehensive review of the importance of mangrove forests for
terrestrial vertebrates, but also reveal significant knowledge gaps in the ecology
of these ecosystems. Our study uncovers evidence that these habitats may be
increasingly important as refuges for species from anthropocentric disturbance.
Our findings emphasize the importance of moving beyond viewing mangroves
as marine ecosystems, towards recognizing their cross-realm importance. With-
out such a shift, there will be significant limitations in our ability to manage
and conserve these ecosystems.
Keywords
biodiversity patterns, coastal forest, ecosystem function, lagoon, swamp,
transboundary.
INTRODUCTION
Mangrove forests fringe intertidal zones spanning marine,
freshwater and terrestrial realms in tropical, subtropical and
temperate latitudes (30N and 30S; Giri et al., 2011). They
provide a wide range of ecosystem services, including coastal
protection, carbon sequestration and opportunities for bio-
diversity (Macintosh & Ashton, 2002). These services are
DOI: 10.1111/ddi.12514
ª2016 John Wiley & Sons Ltd http://wileyonlinelibrary.com/journal/ddi 1
Diversity and Distributions, (Diversity Distrib.) (2016) 1–10
A Journal of Conservation Biogeography
Diversity and Distributions
being lost because of the decline in mangrove forests, with
major ecological and economic implications for both the
wildlife and people that depend on them (Alongi, 2002).
Globally, 35% of the total area of extant mangroves forests
was lost over a recent 30-year period (Giri et al., 2011) and
currently, 40% of mangrove plant species are listed as
Threatened on the International Union for Conservation of
Nature (IUCN) Red List (Polidoro et al., 2010). A little
known fact is that mangrove forests are declining faster than
inland tropical forests and coral reefs, which are a strong
focus for conservation (Duke et al., 2007). Despite the value
of mangrove forests, aspects of their terrestrial ecology are
poorly understood, limiting the capacity to effectively con-
serve and manage them (Nowak, 2013).
Mangrove forests occur at the interface between land and
sea, and as a consequence, these forests span both aquatic
and terrestrial realms, playing fundamental roles in both
(Beger et al., 2010). Nevertheless, well-justified concerns
about the decline in mangrove systems have focused on their
value as marine environments, largely ignoring their value as
terrestrial ecosystems (e.g. the provision of forest products
for human benefit (Buelow & Sheaves, 2014) and habitat for
terrestrial fauna (Meades et al., 2002)). As mangrove ecosys-
tems are traditionally conceptualized as marine environments
(e.g. providing nursery areas for important commercial fish-
eries (Mumby et al., 2004)), there is a strong bias towards
research on their marine fauna, including polychaetes (Met-
calfe & Glasby, 2008), molluscs (Appadoo & Roomaldawo,
2013), shrimp (Primavera, 1998), crabs (Schories et al.,
2003) and fish (Faunce & Serafy, 2006). This emphasis on
mangroves as marine ecosystems may explain why their value
as terrestrial habitat for vertebrates remains one of the most
poorly studied aspects of this ecosystem (Luther & Green-
berg, 2009; Nowak, 2013).
Previous research on terrestrial vertebrates in mangroves
has largely focused on birds or charismatic fauna, such as
the Sumatran tiger, Panthera tigris sumatra, (Noske, 1996;
Barlow et al., 2011). The assemblage of smaller mammals,
reptiles and amphibians that occupy mangrove forests has,
by contrast, received little attention (but see Nagelkerken
et al., 2008; Luther & Greenberg, 2009; Hogarth, 2015). The
literature also over-represents species that depend on man-
grove forests for all their critical resources (i.e. obligate man-
grove users), resulting in a narrow focus that excludes many
facultative mangrove users (Hansson &
Akesson, 2014). Yet,
facultative users continue to provide important ecosystem
services, such as pollination of mangrove plants (McKenzie
& Rolfe, 1986) and the transfer of nutrients from adjacent
habitats (Reef et al., 2014). In addition, the loss of primary
habitats for these facultative users may mean mangrove for-
ests are increasingly important habitat for these species in
the future (Nowak, 2013; Rodrigues & Martinez, 2014). To
better understand the functioning of mangrove ecosystems, it
is important to understand their relationship with the fauna
that uses them (both obligate and facultative users) in both
the marine and terrestrial realms.
Here, we review existing knowledge of the terrestrial verte-
brates known to use mangroves and document the global
distribution of species richness that can serve as a baseline
for future studies. We explore what is known about the eco-
logical relationships between terrestrial vertebrates and man-
grove forests, identify critical knowledge gaps and provide
recommendations for improved conservation management of
these vital ecosystems.
METHODS
Scope of the review
We sought records of terrestrial mammals, reptiles and
amphibians that use the terrestrial component of mangrove
ecosystems. We defined the terrestrial component of man-
groves as those areas exposed to air at some time during the
tidal cycle (e.g. branches, roots, adjacent mud flats). Semi-
aquatic snakes, water rats and frogs were included as they
routinely occupy terrestrial habitats (Fish & Baudinette,
1999; Gibbons, 2003; Willson et al., 2006), whereas sea tur-
tles were excluded as they exclusively use the aquatic aspects
of mangrove systems (Lutz et al., 2002). While birds are
important inhabitants of mangroves, they were excluded
from this study because they have previously received signifi-
cant attention (e.g. Cawkell, 1964; Buelow & Sheaves, 2014;
Kumar & Kumara, 2014). To ensure that as many records of
terrestrial vertebrates in mangroves were captured, we
include species with only a single record in mangroves. It is
possible that some vagrant species are included in the species
list, so we have indicated how many times the species was
recorded (see Table S1 in Supporting information). Both
obligate and facultative users of mangrove forests were
included to identify the full range of species that exploit their
resources and potentially play a role in ecosystem function.
We defined use of mangroves as when a species was reported
to use any key resource provided by the mangrove forest
(e.g. food, shelter, dispersal route –see ‘Characteristics of
species reported in mangrove forests’ below for more detail).
Search strategy and inclusion criteria
We conducted a comprehensive online search of the litera-
ture published up to the end of June 2016. The publication
databases Web of Science, Trove Thesis Search and Google
Scholar were searched using the following terms: (fauna
AND diversity AND mangrove*); (mangrove*AND mam-
mal*; mangrove*AND biodiversity); (mangrove AND reptile;
mangrove AND amphibian); (mangrove AND monitoring OR
techniques AND fauna OR reptile OR mammal OR amphib-
ian); (mangrove AND survey AND fauna OR reptile OR
mammal OR amphibian OR vertebrate); (mangrove AND ter-
restrial AND vertebrates OR fauna OR mammal OR reptile
OR amphibian). We also searched synonyms for mangrove
habitat (coastal forests, swamp and coastal lagoon) together
with the above search terms. The reference list of each
2Diversity and Distributions, 1–10, ª2016 John Wiley & Sons Ltd
S. M. Rog et al.
relevant publication was scrutinized to identify further rele-
vant literature. All mammal, reptile and amphibian taxa
reported as occurring in mangroves were documented. Tax-
onomy followed the IUCN Red List (IUCN, 2016).
Species records were also obtained from PhD theses and
three open source databases: World Wildlife Fund (WWF,
2016), ARKive (ARKive, 2016) and IUCN Red List (IUCN,
2016). These databases were included because they focus on
global species records, allow for restriction of searches to
mangrove habitat and have provision for peer-review by
experts. Records from guidebooks, local management plans
and additional online sources were excluded because it was
not possible to determine the accuracy and consistency of
the records in those sources.
Characteristics of species reported in mangrove
forests
All literature studies that met the above criteria were read in
full, and records of terrestrial vertebrate species in mangroves
were collated. For each species record, we noted the follow-
ing: (1) countries in which the species was reported to use
mangroves; (2) the total native range; (3) IUCN conservation
status (including ‘not evaluated’); and (4) feeding guild (i.e.
carnivore (including insectivore and piscivore), herbivore,
omnivore). If these characteristics were not mentioned, we
undertook targeted literature searches to ensure the dataset
was comprehensive (e.g. consulting the IUCN Red List data-
base for the total native range (when a species was not evalu-
ated by IUCN, we used Arkive and/or guidebooks to
determine its range) and conservation status and Arkive for
feeding guild).
A species’ dependence on mangrove forests was classified
as obligate, facultative or not reported based on information
in the studies. Obligate users included those species
described as found primarily in mangroves or with a life
history tied to mangrove habitat, whereas facultative users
were those species that occupied both mangrove and adja-
cent terrestrial habitats. Facultative users were further cate-
gorized by their resource use: (1) feeding; (2) breeding; (3)
dispersal route between primary habitats; (4) shelter from
biotic (e.g. predators, competitors) and abiotic stressors
(e.g. temperature extremes; desiccation); (5) use and
increased frequency of use as refugia from human distur-
bance; and vi) novel use of mangroves as a result of human
disturbance.
Species distribution and richness
In many instances, species records were specifically focused
on a subset of countries from within the species’ broader
native range (e.g. snakes in a mangrove patch in Singapore;
Voris (2002)). To estimate the global species richness of ter-
restrial vertebrates, if a species was reported to use man-
groves in part of its range, we inferred that it may do so
wherever its distribution overlapped with mangrove forest.
For example, the Mexican Mouse Possum, Marmosa mexi-
cana, occupies mangrove forest in Mexico (WWF, 2016),
thus, based on the intersection of the species’ range and
extant mangrove forest, we inferred that it also uses man-
groves in Belize, Costa Rica, El Salvador, Guatemala, Hon-
duras, Nicaragua and Panama. With this approach, the alpha
diversity of terrestrial vertebrate species that occupy man-
groves was calculated for each country. As Brazil and Aus-
tralia span >20 degrees of latitude and are substantially
larger than other countries that support mangrove habitat,
outputs are presented at the state level for these two coun-
tries. Species ranges followed Hutchings & Recher (1981);
Uetz (1995) and Wilson & Reeder (2005). Mangrove richness
followed Spalding et al. (2010), and mangrove distribution
followed Giri et al. (2011). Pearson’s correlation coefficient
was calculated to determine whether there was a relationship
between global mangrove plant and terrestrial animal rich-
ness. In an attempt to explain biogeographic patterns of spe-
cies richness, we also calculated the correlation coefficient for
regional groupings of countries (Africa, Asia, Americas, Mid-
dle East and Oceania). While the world can be divided into
regions in many different ways, we followed the United
Nations (2014) macro-geographical global regions as it is a
commonly used source.
RESULTS
We identified 464 terrestrial vertebrate species reported to
occur in mangrove forests: 320 mammals, 118 reptiles and
26 amphibians (including 22 subspecies; Table S1).This is a
fivefold increase in the number of terrestrial vertebrate spe-
cies previously reported to use mangroves (excluding birds),
including representatives of 14 additional families to those in
previous reviews (Kathiresan & Bingham, 2001; Nagelkerken
et al., 2008; Luther & Greenberg, 2009; Hogarth, 2015). Of
the species reported, 34 were reported fewer than five times
or were stated to be rare in mangroves. Of the 391 vertebrate
species whose conservation status has been assessed by the
IUCN, 35% were classified as threatened. Fewer than 41% of
the published species records we found (n=186 of 464)
were derived from or could be directly linked to published
field studies. As such, reports, many of which were reviews,
of the overwhelming majority of species occurring in man-
groves did not reference the field study or observation on
which this species being present in mangrove habitat was
based. Therefore, the origin of these records is uncertain and
separate records may not be independent, suggesting more
field studies on terrestrial vertebrates in mangroves
are important to improve our understanding of these
ecosystems.
Species distribution and alpha diversity
Mammals, reptiles and amphibians were reported to occur in
mangroves in 73 of the 120 countries (60%) in which man-
groves occur (Figure 1b,d), more than doubling previous
Diversity and Distributions, 1–10, ª2016 John Wiley & Sons Ltd 3
Terrestrial vertebrates in mangroves
estimates (Figure 1a). When accounting for the potential
global distribution of these terrestrial vertebrates in man-
grove habitat, this estimate increases to 113 of 120
countries (93%) (Figure 1c), more than trebling previous
reports (Figure 1a). Our findings suggest that the highest
alpha diversity of terrestrial vertebrates in mangroves occurs
Figure 1 Known global number of terrestrial vertebrate species in mangroves: (a) prior to this review, (b) based on this review and (c)
after extrapolating data from this review to intersect with the global distribution of individual vertebrate species with that of (d) the
global distribution and richness of mangroves. Colour categories are scaled to reflect the distribution centred on the median number of
species to aid comparison between maps. Uncoloured countries do not support mangroves.
4Diversity and Distributions, 1–10, ª2016 John Wiley & Sons Ltd
S. M. Rog et al.
within Asia, northern Australia, West Africa and the Cen-
tral American land bridge (Figure 1). In contrast, alpha
diversity is lowest on the east coast of Africa, southern
Australia, New Zealand, the Middle East, Brazil and small
island nations (Figure 1). There were 24 countries that sup-
port extant mangroves where terrestrial vertebrates have yet
to be documented as using this ecosystem as habitat; of
these, 20 were island nations with a total land area of less
than 2535 km
2
(Figure 1b indicated in black).
Relationship between mangrove plant and terrestrial
vertebrate alpha diversity
Globally, there was a positive correlation between terrestrial
vertebrate alpha diversity and mangrove plant richness for
both the recorded and the potential distributions (Table 1;
reported: r=0.55, n=120, P<0.001; extrapolated: r=0.58,
n=120, P≤0.001). When separating the world into macro-
geographical regions, the strength of the relationship varied,
with the strongest correlations in Asia and Oceania for both
the reported data (Asia: r=0.72, P=0.001, n=17; Oceania:
r=0.58, P=0.005, n=22) and extrapolated data (Asia:
r=0.78, P≤0.001, n=17; Oceania: r=0.81, P≤0.001,
n=22). For the Americas, the correlation between mangrove
plant and animal richness was significant only when using the
extrapolated data (r=0.47, P=0.002, n=42). No relation-
ship was found in Africa (reported: r=0.12, P=0.556,
n=27; extrapolated data r=0.13, P=0.528, n=27) and the
Middle East (reported r=-0.24, P=0.941, n=12; extrapo-
lated data r=0.04, P=0.902, n=12).
Use of mangrove forests by terrestrial vertebrates
For the 464 terrestrial vertebrate species reported in man-
groves, 147 (31%) had information about the specific
resources they were using. Species were most often reported
to use mangrove forests as foraging grounds (Figure 2). Ter-
restrial vertebrates were also reported to use mangrove for-
ests as refuges from human disturbance, shelter from
stressors (both biotic and abiotic), to disperse between pri-
mary habitats and for breeding (Figure 2). If species were
reported to use mangrove forests as refuges, most (19) were
considered to be increasing their existing use of mangroves
rather than using mangrove forests as a novel habitat (1).
Most terrestrial vertebrates using mangroves forests are cate-
gorized as carnivorous (52%; Figure 3).
DISCUSSION
Species distribution and richness
We found mangrove forests to be substantially more impor-
tant for terrestrial vertebrates than previously reported, sup-
porting a remarkable richness of terrestrial mammals, reptiles
and amphibians globally. This finding underscores the view
that the emphasis on mangroves as marine ecosystems has
led to the importance of the terrestrial components of man-
grove forests being undervalued (Luther & Greenberg, 2009;
Nowak, 2013).
In addition to extending our knowledge of the global rich-
ness of terrestrial vertebrates in mangrove ecosystems, our
Table 1 Correlation between mangrove plant richness and animal richness in mangrove ecosystems.
Region Asia Oceania Americas Middle East Africa Global
Reported data
Correlation coefficient 0.72 0.58 0.19 0.24 0.12 0.55
Probability 0.001** 0.005** 0.232 0.941 0.556 0.001**
Number of countries 17 22 42 12 27 120
Extrapolated data
Correlation coefficient 0.78 0.81 0.47 0.04 0.13 0.58
Probability <0.001** <0.001** 0.002** 0.902 0.528 0.001**
Number of countries 17 22 42 12 27 120
Figure 2 Mangrove use by facultative terrestrial vertebrates
(n=147). Reported uses are not mutually exclusive.
Obligate users (n=24) are not shown in this figure as by
definition, these species use mangroves for all their
resources.
Diversity and Distributions, 1–10, ª2016 John Wiley & Sons Ltd 5
Terrestrial vertebrates in mangroves
results also reveal a wider range of countries in which these
species use mangroves than previously reported (Figure 1b,
c). There were few places in the world where terrestrial verte-
brates have not been reported to use mangrove forests,
mainly small islands (Figure 1b). The biogeographic patterns
indicate a higher richness of species in the tropics (especially
in Asia) and lower richness in temperate regions, which is
one of the most well-established patterns in macroecology
and biogeography (Koch, 2000). Mammals and amphibians
conform to the pattern of highest diversity in the tropics
(Wiens et al., 2006; Schreier et al., 2009), and our findings
demonstrate this pattern extends to mangrove forests. We
can think of no reason why the key processes that drive bio-
geographic patterns (speciation, extinction and dispersal
(Wiens et al., 2009)) should differ in mangrove ecosystems,
but this could be a focus of further study.
The observed pattern of high animal richness in tropical
mangrove regions was consistent regardless of whether data
were derived from previous reviews, this review or the maxi-
mum possible richness of terrestrial vertebrates based on our
extrapolation (the countries where the known distribution of
a species intersects with the global distribution of mangroves;
Figure 1). Because the extrapolated data assume that species
found in mangroves in one part of their range could also be
found in mangroves across their entire range (Figure 1c),
this may overestimate species occurrences. In particular, spe-
cies may not occupy habitat at the edges of their predicted
distribution, in marginal habitat or areas experiencing
human disturbance or other pressures. The fact that the cor-
relation between floral and faunal richness improved or
remained unchanged with the extrapolation suggests that any
overestimation of richness is unlikely to be significant. Nev-
ertheless, the extrapolated data provide a worst case scenario
about the knowledge gaps associated with the species rich-
ness and distribution of terrestrial vertebrates in mangrove
forests that can help target future research towards areas of
potentially high richness but few records. To be able to make
more detailed predictions and identify important mangrove
areas for terrestrial vertebrates, it is necessary that future
studies report characteristics (e.g. total mangrove area, source
of disturbance, adjacent habitat) about the mangrove region
where a species was observed.
Relationship between mangrove plant and terrestrial
vertebrate alpha diversity
Mangrove plant richness was not always a consistent predic-
tor of animal richness, although correlations suggest that this
relationship is stronger when the data were extrapolated to
the possible extent of recorded species (Figure 1c,d, Table 1).
Further fieldwork may reveal a higher richness of terrestrial
vertebrates in mangrove forests in areas where there is a mis-
match between floral and faunal diversity. Mangrove plant
diversity is an order of magnitude higher in the Indo-West
Pacific (IWP) than it is in the Atlantic, Caribbean and East-
ern Pacific (ACEP) (Ellison et al., 1999), and plant richness
may directly influence richness of other taxa by determining
the variety of food items or habitat structural elements that
create niches for other organisms (Hawkins & Porter, 2003).
A global concordance of plant and animal richness has been
shown for our three species groups (Qian & Ricklefs, 2008).
However, we found some areas of low mangrove plant rich-
ness, such as Mexico and parts of South America, where ver-
tebrate richness was high and similar to that of parts of Asia
where mangrove plant richness is far higher (Figures 1b,c,d).
This suggests that factors other than low mangrove plant
richness, such as the influence of adjacent habitat (e.g.
deserts have lower animal diversity than tropical rain forests
and could affect the number of facultative species using
mangroves) or the availability of prey species to support car-
nivores and omnivores, may also strongly influence animal
richness in some key mangrove ecosystems. The large pro-
portion of species that rely on animal protein instead of
mangrove plant material (Figure 3) provides some support
for the latter hypothesis, but a deeper understanding of the
community ecology of these ecosystems is needed. Temperate
regions in Oceania (e.g. New Zealand and southern Aus-
tralia) showed both low floral and faunal richness in line
with global biogeographic patterns (Wiens et al., 2009).
However, we note that there has been limited survey effort
in temperate areas of these regions where diversity would be
expected to be lower. The weak correlations between animal
and mangrove plant richness in Africa and the Middle East
may be a product of these regions having received little study
(fewer than 10% of the studies we found specifically dis-
cussed these regions), possibly because of political unrest
(Reddy & D
avalos, 2003), as opposed to a genuinely lower
Figure 3 Feeding guild of terrestrial vertebrates in mangroves,
including both facultative and obligate mangrove users
(mammals, n=320; reptiles, n=118; amphibians, n=26).
Insectivores and piscivores are included in the carnivore guild.
6Diversity and Distributions, 1–10, ª2016 John Wiley & Sons Ltd
S. M. Rog et al.
animal richness. The discrepancy between predicted and
observed richness was highest in East Africa, a biodiversity
hotspot (Myers et al., 2000) and with similar mangrove rich-
ness to that of West Africa where a higher animal richness
was observed. One reason for lower than predicted animal
richness in Africa may be the prevalence of threats, such as
hunting pressure for the bushmeat trade, which can be high
in East Africa (Cawthorn & Hoffman, 2015), depleting local
populations to levels that make detection of some species less
likely, especially when combined with lower survey effort in
the region. The variability or lack of research effort across
regions, lack of insight into regional differences and a some-
what inconsistent relationship between mangrove plant rich-
ness and animal richness suggest that additional field studies
are needed to achieve a more complete understanding of the
occurrence of terrestrial vertebrates in mangroves.
Although we present the most comprehensive review of
terrestrial vertebrates in mangroves, and have identified sig-
nificantly more terrestrial vertebrate species using mangrove
forests than previously reported, our findings probably still
underestimate species richness. There was limited direct evi-
dence of species occurrence from published field studies, and
most of the records we found did not report the origin of
the record, suggesting many come from unpublished data.
The small number of field studies carried out in mangroves
could be due to the combination of challenges associated
with accessing these environments and the difficulty of sam-
pling tidal environments due to regular inundation. New
approaches may be needed to facilitate faunal surveys in
mangroves. Our results provide a valuable starting point
from which to target survey effort. Similarly, our findings
highlight the importance of clearly reporting the source of
species records to help identify where research effort is gen-
uinely low.
Use of mangrove forests by terrestrial vertebrates
Understanding habitat use might help explain why biogeo-
graphic patterns differ from predictions associated with floral
richness. Our results highlight that facultative users of man-
groves substantially outnumber specialists, as is predicted by
theory (Wilson & Yoshimura, 1994). This suggests that the
tendency of previous studies to focus on obligate users of
mangrove forests (Nagelkerken et al., 2008; Luther & Green-
berg, 2009) has distorted our understanding of the faunal
species types that use mangroves and contributed to the per-
ception that vertebrate species richness is low in these envi-
ronments. A striking finding from our study is how little is
known about the interaction between terrestrial vertebrate
species and mangroves. For example, the relationships
between seasonality and timing in mangrove use are rarely
studied. We only found 10 records in which seasonality or
tidal phase was reported, including lemurs feeding on man-
grove flowers in the dry season (Gardner, 2016) and varanids
feeding in mangroves during low tide (Kutt, 1997). Under-
standing the resources consumed by facultative users of
mangrove forests, and when these resources are available, is a
particularly important area for future study because habitat
destruction and environmental change is likely to lead to
changes in resource availability (Nowak, 2013).
Our results support the suggestion that at least some ter-
restrial vertebrates are using mangrove forests as a refuge
from anthropocentric disturbance of their primary habitat
(Nowak, 2013; Figure 2). Although the number of species
reported to be using mangrove forests as refuges is low, this
has been reported for many different species groups (e.g.
felids, Barlow et al., 2011; Nowak, 2013; snakes, Nagelkerken
et al., 2008; monkeys, Nowak, 2013) in much of the world
(e.g. Asia, Nowak, 2013; Africa, Nagelkerken et al., 2008;
South America, Rodrigues & Martinez, 2014), suggesting it is
a relatively widespread and possibly underestimated phe-
nomenon. Much of the evidence for the increasing use of
mangroves is anecdotal, with just a few examples in which
empirical data document a novel expansion into mangrove
forests (e.g. Wied’s marmosets, Callithrix kuhlii (Rodrigues &
Martinez, 2014)). Some new records may also reflect a lack
of historical data rather than evidence of a genuine expan-
sion. It is also unclear whether mangrove forests are acting
as population sinks or constitute important habitat for
self-sustaining populations. Understanding this relationship
may help predict the likely future impact of increased use by
current mangrove inhabitants.
Knowledge gaps on vertebrate use of mangroves are partic-
ularly concerning for the many species that are of conserva-
tion significance. Given the high probability that species
classified as ‘Data Deficient’ or ‘Not Assessed’ by the IUCN
Red List are actually of conservation concern (Bland et al.,
2014; 72 species in this review), there is a pressing need to
better understand the importance of mangroves as a resource
for endangered species. Better information about the depen-
dence of terrestrial vertebrates on mangrove forests could
help identify the regions of the world in which mangrove
conservation should be given highest priority.
The high proportion of carnivorous and omnivorous ver-
tebrates in mangrove forests (Figure 3) is likely to be due to
the marked seasonality of other food sources, such as fruit
and nectar (Fernandes, 1999), and the low palatability of
mangrove leaves given their high salt content (Kathiresan &
Bingham, 2001). This finding also accords with the general
prevalence of carnivores among reptiles and amphibians
(Huey, 1982). Given that animal protein appears to be the
most important source of nutrition for terrestrial vertebrates
in mangrove forests, this may account for some of the vari-
ability we found in the relationship between mangrove plant
and animal richness (see Species distribution and richness).
While vertebrate species were most often reported to use
mangrove forests for feeding (Figure 2), for the majority of
species there was no information about how they use man-
groves. We found few primary records of field studies that
documented habitat use by terrestrial vertebrates in man-
groves. Given that most animals spend the majority of their
time feeding, it is not surprising that opportunistic reports
Diversity and Distributions, 1–10, ª2016 John Wiley & Sons Ltd 7
Terrestrial vertebrates in mangroves
of species in mangroves often report individuals to be using
mangroves as feeding grounds. However, we did find evi-
dence that facultative users of mangroves rely on these areas
for critical stages in their life cycles as well, using these areas
to breed (e.g. the Estuarine Crocodile, Crocodylus porosus,
Hutchings & Recher, 1981; and the Sea Krait, Laticauda colu-
brine, Hogarth, 2015). There were also records of species
using mangroves to shelter from heat stress (e.g. bat species
and kangaroos in Australia; Reef et al., 2014) and to disperse
between primary habitats (e.g. the marsh rabbit, Sylvilagus
palustris, in the United States; Kathiresan & Bingham, 2001)
(Figure 2). A better understanding of the dependence of
both obligate and facultative users on mangrove ecosystems
will enable the implications of anthropogenic disturbances
on ecosystem function of these forests to be better
understood.
Importance of terrestrial vertebrates for mangrove
ecosystems
The roles of terrestrial vertebrates in the health of mangrove
ecosystem have been poorly studied, leaving another sub-
stantial gap in our understanding of mangrove ecosystem
functioning. Terrestrial vertebrates can play an important
role in mangrove forests through the provision of essential
ecosystem services, such as pollination of mangroves (Ashraf
& Habjoka, 2013) and nutrient transfer (e.g. Kristensen,
2008; Reef et al., 2014). The ecosystem services provided by
terrestrial vertebrate fauna associated with the health of
mangrove forests should therefore be explored as an impor-
tant precursor to more effective conservation of these
ecosystems.
CONCLUSIONS AND RECOMMENDATIONS
Our data demonstrate that mangrove forests support a con-
siderably higher diversity of terrestrial animals than previ-
ously recognized. In spite of this, the terrestrial components
of mangroves are generally ignored, overlooking a large part
of this transboundary ecosystem. Our findings highlight a
wide range of knowledge gaps in relation to the diversity,
distribution and ecology of species using the terrestrial com-
ponents of these systems. Future research should focus on
undertaking field assessments of terrestrial vertebrates, par-
ticularly in regions where our findings suggest animal rich-
ness is low relative to floral richness (e.g. small islands and
East Africa). Greater attention to reporting the source of
species records could help identify where research effort
should be directed. There is also an urgent need to under-
stand better the ecological relationships between mangroves
and terrestrial vertebrates to plan for effective conservation
of these forests. In particular, it is important to understand
better the role mangrove forests are playing in providing a
refuge for species suffering from the loss of their primary
habitat. This knowledge will help identify regions where pat-
terns of habitat loss and human disturbance may elevate
remaining mangrove forests to an indispensable status, while
also identifying areas where current users of mangroves may
find resources under increasing pressure. In summary, we
recommend a more holistic view of mangrove forests, as
only when this is realized will it be possible to effectively
conserve these vital ecosystems.
ACKNOWLEDGEMENTS
We thank Julie Groce and Guillaume Latombe for helpful
comments on previous versions of the manuscript and
Rebecca Valkan for her assistance with the global maps.
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SUPPORTING INFORMATION
Additional Supporting Information may be found in the
online version of this article:
Table S1 Terrestrial vertebrates reported to occur in man-
groves (mammals, reptiles and amphibians).
Data S1 Supplementary references with Table S1.
BIOSKETCHES
Stefanie M. Rog is a conservation biologist with interests
in management, monitoring, ecology and terrestrial biodiver-
sity.
Rohan Clarke is an ecologist with interests in marine and
terrestrial vertebrates and their conservation management.
Carly N. Cook is a conservation biologist interested in evi-
dence-based conservation and the development of decision
tools that integrate the best available science into conserva-
tion management.
Editor: Robert Cowie
10 Diversity and Distributions, 1–10, ª2016 John Wiley & Sons Ltd
S. M. Rog et al.
