herpetofauna of sumak allpa: a baseline assessment of an
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Herpetofauna of Sumak Allpa: A BaselineAssessment of an Unstudied Island HerpetofaunalCommunitySara FreimuthSIT Study Abroad
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Recommended CitationFreimuth, Sara, "Herpetofauna of Sumak Allpa: A Baseline Assessment of an Unstudied Island Herpetofaunal Community" (2018).Independent Study Project (ISP) Collection. 2784.https://digitalcollections.sit.edu/isp_collection/2784
Herpetofauna of Sumak Allpa:
A Baseline Assessment of an Unstudied Island Herpetofaunal Community
Freimuth, Sara
Academic Director: Silva, Xavier, PhD
Project Advisor: Wagner, Martina, MSc
Claremont McKenna College
Organismal Biology and Spanish
South America, Ecuador, Orellana, Sumak Allpa
Submitted in partial fulfillment of the requirements for Ecuador Comparative Ecology and
Conservation, SIT Study Abroad, Spring 2018
Abstract
Sumak Allpa is an island dedicated to the provision and protection of habitat for the
conservation and rehabilitation of primates. As such, the island - a varzea ecosystem located in
the Western Amazon of Ecuador, one of the most biodiverse and also most threatened regions in
the world – consists of protected primary forest that is home not only to a variety of primates, but
also to an even wider variety of other taxa, nearly all of which have gone unstudied on the island.
The present investigation assessed two of those taxa, amphibians and reptiles, in order to
establish a baseline inventory of the island’s herpetofaunal community and provide a preliminary
assessment of its composition, activity, and habitat use as a way to suggest and inform future
investigations for the study and monitoring of the community and its populations. Through 78
hours of visual and acoustic encounter surveys spanned across 16 days, a community of 552
individuals representing 15 species of 5 families of Anura and 11 species of 7 families of
Squamata was observed on the island. Analysis of this community indicated high species
richness and low species diversity and that the majority of species are capable of occupying all of
the island’s habitats, demonstrating preferences for specific habitat characteristics such as leaf
litter microhabitats and high density understory vegetation. An additional analysis of the
population of Adenomera hylaedactyla, a species accounting for 57.4% of all individuals
encountered, also demonstrated these same overall community trends, and this particular
population had an average snout-vent-length (SVL) much smaller than the average SVL reported
for the species overall. Collectively, these findings indicate long-term seasonal monitoring of the
island and future investigation of its individual populations would best inform the conservation
of the island’s herpetofaunal community and fulfill some of the many gaps in the existent
knowledge of Ecuadorian and Neotropical herpetofauna more generally.
Resumen
Sumak Allpa es una isla dedicada a la provisión y protección del hábitat para la
conservación y rehabilitación de primates. Como tal, la isla - un ecosistema de várzea ubicado en
la Amazonía occidental de Ecuador, una de las regiones más biodiversas y más amenazadas del
mundo - consiste en un bosque primario protegido que alberga no solo una variedad de primates,
sino también una variedad aún más amplia de otros taxones, casi todos los cuales no han sido
estudiados en la isla. La presente investigación evaluó dos taxones, anfibios y reptiles, con el fin
de establecer un inventario de línea de base de la comunidad de herpetofauna de la isla y de
proporcionar una evaluación preliminar de su composición, actividad y uso del hábitat como una
forma de sugerir e informar investigaciones futuras para el estudio y monitoreo de la comunidad
y sus poblaciones. A través de 78 horas de encuestas visuales y acústicas durante 16 días, se
observó en la isla una comunidad de 552 individuos que representaban a 15 especies de 5
familias de Anura y 11 especies de 7 familias de Squamata. El análisis de esta comunidad indicó
una alta riqueza de especies y baja diversidad de especies y que la mayoría de las especies son
capaces de ocupar todos los hábitats de la isla, demostrando preferencias por características
específicas del hábitat tales como microhábitats de hojarasca y vegetación de sotobosque de alta
densidad. Un análisis adicional de la población de Adenomera hylaedactyla, una especie que
representa el 57.4% de todas los individuos encontrados, también demostró estas mismas
tendencias generales de la comunidad, y esta población particular tuvo una longitud de rostro-
cloacal promedio (LRC) mucho más pequeña que la LRC promedio declarada para la especie en
general. Colectivamente, estos hallazgos indican un monitoreo estacional a largo plazo de la isla
y la investigación futura de sus poblaciones individuales serían las mejores formas de informar la
conservación de la comunidad herpetofauna de la isla y cubrirían algunas de las brechas en el
conocimiento existente de la herpetofauna ecuatoriana y neotropical en general.
Acknowledgements
A large debt of gratitude is owed to the many people who made this project possible.
First, a special thank you belongs to Diana Serrano, Xavier Silva, and Javier Robayo for their
continued support throughout the ISP process. This project would not have come to fruition
without their constant advice and emotional support. Another special thanks goes to Martina
Wagner for welcoming me to the Amazon, sharing with me a plethora of guides and materials
for the identification of the region’s herpetofauna, introducing me to all of the trails of the island,
and showing me incredible kindness and patience. Further thanks go to Valerio Gualinga for
clearing trails and transects for safer nocturnal surveying and to Hector Vargas for his
hospitality, compassion, and provision of transportation and delicious warm meals. Lastly, many
thanks go to Rachel Meyer and Emily Babb for keeping me sane during my first few days on
Sumak Allpa and to Sophie Cash and Krista Smith-Hanke for their friendship, constant
reassurance, and extraordinary moral support while sharing this experience with me.
Agradecimientos
Se debe una gran deuda de gratitud a las muchas personas que hicieron posible este
proyecto. Primero, un agradecimiento especial les pertenece a Diana Serrano, Xavier Silva y
Javier Robayo por su continuo apoyo durante todo el proceso de ISP. Este proyecto no habría
llegado a buen término sin su constante asesoramiento y apoyo emocional. Otro agradecimiento
especial para Martina Wagner por darme la bienvenida a la Amazonía, compartiendo conmigo
una plétora de guías y materiales para la identificación de la herpetofauna de la región,
presentándome a todos los senderos de la isla y mostrándome una amabilidad y paciencia
increíble. Agradezco a Valerio Gualinga por despejar senderos y transectos para realizar estudios
nocturnos más seguros y a Héctor Vargas por su hospitalidad, compasión y provisión de
transporte y deliciosas comidas calientes. Por último, muchas gracias a Rachel Meyer y Emily
Babb por mantenerme cuerda durante mis primeros días en Sumak Allpa y a Sophie Cash y
Krista Smith-Hanke por su amistad, consuelo constante y extraordinario apoyo moral mientras
compartían esta experiencia conmigo.
Introduction
Global Herpetofauna: Ecological Functions and Population Declines
Although amphibians and reptiles are often considered together in the study of
herpetology, these two vertebrate groups that constitute herpetofauna are actually quite different.
Derived from lineages that have been independent since 300 million years ago, amphibians and
reptiles have quite different life histories with distinct morphological characteristics,
reproductive systems, behavioral traits, and ecological requirements (Zug et al., 2001; Costa et
al., 2016). Consequently, amphibians and reptiles contribute to a diverse range of ecological
functions and herpetofauna constitute abundant and diverse components of many terrestrial and
freshwater ecosystems (Young et al., 2004; Tyler et al., 2007; Pough et al., 2004; Wells, 2007;
Collins & Crump, 2009), particularly in the Neotropics, where they are among the most abundant
and diverse vertebrate taxa (Cortés-Gomez et al., 2016; Stuart et al., 2004).
Despite their plenitude in such a wide range of terrestrial and freshwater ecosystems,
there has been a generally low level of understanding regarding the ecological functions and
services amphibians and reptiles provide (Bickford et al, 2010; Hocking & Babbitt, 2014).
Recent studies, however, cite how in spite of their biological and ecological differences,
amphibians and reptiles often play very similar ecological roles, contributing to nutrient cycling,
bioturbation, seed dispersal, pollination, and energy flow through trophic chains as both predator
and prey species (Cortés-Gomez et al., 2016). Other studies also emphasize their provision of
ecosystem services to humans, specifically, evidencing their regulation of pest outbreaks and
alteration of disease transmission through predation and competition with mosquitoes and
disease-carrying fly species, in addition to their use as food, in cultural practices across the
globe, and in both Western and traditional medicines (Hocking & Babbitt, 2014).
This recent surge in efforts to understand the ecological roles herpetofauna play within
ecosystems, nevertheless, has been prompted by a sense of urgency and out of necessity.
Amphibian and reptile populations in recent decades have experienced rapid declines and
reduction is still ongoing (Gibbons et al., 2000; Lips et al., 2006; Reading et al., 2010; Heatwole
2013). In addition to prompting efforts to better understand the ecological functions of
amphibians and reptiles, these declines also have impelled the investigation of specific threats to
herpetofauna and the establishment of criteria for the evaluation of the degree of threat to species
of amphibians and reptiles (Gibbons et al., 2000; Todd et al., 2010; Stuart et al., 2004; Böhm et
al., 2012).
Among the most significant threats to amphibian and reptilian populations at the global
scale are habitat loss and degradation, introduced invasive species, pollution, disease,
unsustainable use, and climate change (Lips et al., 2006; Gibbons et al., 2000; Todd et al., 2010).
In the Neotropics, these threats are particularly imminent. Not only does this region contain
49.2% of the world’s amphibian species and significant reptile diversity and richness, but also it
has suffered among highest rates of population decline (63.1% for amphibians and about 20% for
reptiles) (Stuart et al., 2004; Böhm et al., 2012).
Herpetofauna of Ecuador
As one of the 17 megadiverse countries in the world that collectively contain 70% of the
animal and plant species on the planet, Ecuador is well represented by a variety of taxa,
particularly amphibians and reptiles (Centro Jambatu, 2011). Home to 615 species of
amphibians, 236 of which are endemic, Ecuador ranks fourth in the world in amphibian species
richness behind Brazil, Colombia, and Peru, respectively (AmphibiaWeb). Given its small
relative size, however, Ecuador ranks first in the world for amphibian species richness per unit
area, and with 464 recorded species of reptiles, it ranks the same in terms of reptilian species
richness per unit area, too (AmphibiaWeb; Reyes-Puig, Almendáriz, & Torres-Carvajal, 2017).
Thus, with such species richness condensed in such a small region and high levels of endemism,
Ecuador is an important area to consider for the investigation herpetofauna in general, but is
especially significant considering the recent trends of Neotropical amphibian and reptile
population declines.
Despite this significance, few studies have been conducted to assess amphibian and
reptilian populations in Ecuador, and very little is known about many of the species that
constitute its richness and diversity. The first quantitative study on amphibian decline in Ecuador
was not published until 2003, and the first comprehensive quantitative study of reptile
conservation in Ecuador was not published until 2017 (Bustamante et al., 2005; Reyes-Puig,
Almendáriz, & Torres-Carvajal, 2017).
The lack of understanding of the status of Ecuador’s amphibian and reptilian diversity is
even further evidenced by how much of it has only been recently discovered. Nearly 10% of all
reptilian species in Ecuador have been reported or described in this century alone (Reyes-Puig,
Almendáriz, & Torres-Carvajal, 2017), and a large number of amphibian species have been
described in the past 5 years alone (e.g. Batallas & Brito, 2014; Reyes-Puig & Yánez-Muñoz,
2012; Brito, Ojala-Barbour, Batallas & Almendáriz, 2016). Assessing these species, especially
their baseline population levels and distributions, is crucial to monitoring these new populations
for their conservation.
Newly described species, however, are not the only understudied populations of
herpetofauna in Ecuador. While amphibian species recently have been assessed more extensively
(Rodrigues et al., 2006), only about 25% of the species of reptiles from continental Ecuador are
listed on the IUCN Red List of Threatened Species and 17% of those listed are Data Deficient
(Reyes-Puig, Almendáriz, & Torres-Carvajal, 2017). Ultimately, one of the biggest deficits in the
conservation of herpetofauna in Ecuador, and the Neotropics accordingly, is simply the lack
baseline knowledge and continued monitoring of its many different species’ populations.
The Ecuadorian Amazon
The Amazon is one of the most biodiverse biomes on the planet, and where Ecuador falls
in western Amazon, in particular, is especially rich in biodiversity and contains some of the
highest levels of amphibian and reptilian species richness in Ecuador (AmphibiaWeb; Reyes-
Puig, Almendáriz, & Torres-Carvajal, 2017). The Ecuadorian Amazon is not only species rich,
however – the region also happens to be rich in untapped oil reserves, many of which are located
in Yasuní National Park, a major protected area within the western Amazon of Ecuador (Bass et
al., 2010). Consequently, the ecosystems of Yasuní and the surrounding areas confront numerous
threats characteristic of the entire Ecuadorian Amazonian region. Most prominent among these
threats is petroleum exploration and exploitation; however, accompanying these projects are
transportation projects that open up the region to numerous other threats, including mining,
illegal logging, oil palm plantations, and rapid resource exploitation and human development
(Bass et al., 2010). Thus, the region’s populations of herpetofauna are at risk for or already are
experiencing consequences of these anthropogenic activities, such as habitat loss and degradation
and pollution, in addition more general threats such as disease and climate change.
Sumak Allpa and the Present Investigation
Sumak Allpa is an island situated in the Ecuadorian Amazon downstream the River Napo
from Coca in the vicinity of Yasuní National Park and the namesake of the non-profit primate
rehabilitation center that was founded in 2006 by Hector Vargas and is housed on the island
(Figure 1). The project concentrates on providing education for the global and local community
on the importance of the protection and conservation of the Amazon and also is centered on the
protection of native primates from anthropogenic destruction through the use of the island as a
sanctuary for primates rescued principally from animal-trafficking in the surrounding area
(Zewdie, 2017). As a result of the island’s use for primate rehabilitation, Sumak Allpa contains
protected primary forest subject to little human activity beyond infrequent, small-scale tourism
that is home not only to primates but also to a wide variety of other taxa that contribute to the
health and maintenance of the ecosystem. Few of these other taxa have been investigated
formally, if at all, and the island’s herpetofauna had never been assessed before the present
investigation.
Figure 1. Satellite imagery of demonstrating where Sumak Allpa is located in Ecuador and how it is
situated downstream from Coca, Puerto Francisco de Orellana, Orellana, Ecuador along the Napo
River.
The conservation scheme of Sumak Allpa provided by its status as a primate
rehabilitation center presents a unique situation for the assessment and continued monitoring of
herpetofauna. While the herpetofaunal community is nearly entirely protected from direct
anthropogenic threats, such as habitat loss and degradation, due the protection of the ecosystem
for primate rehabilitation, the isolation provided by the ecosystem occurring on an island, and the
absence of frequent human use, the herpetofauna on the island still may be threatened by
generalized threats to the surrounding region. For example, while reduced compared to other
sites along the river, Sumak Allpa is still subject to the effects of pollution in both the water and
air as a result of petroleum exploitation in the mainland regions around the island. The island
also is not exempt from climate change and risk of exposure to invasive species and disease.
Thus, Sumak Allpa provides the unique opportunity to study the impacts of such threats using a
small and isolated community of herptofauna.
Being situated in the heart of the northern Ecuadorian Amazon and within the vicinity of
the biodiversity hotspot, Yasuní National Park, the island also contains a small portion of the
Sumak Allpa
amphibian and reptile diversity of this important Neotropical region. Though the populations of
this diversity are small and made up of common and relatively non-threatened species, Sumak
Allpa still carries significance for the conservation of the region’s herpetofauna - some of the
Ecuadorian amphibian and reptile species that have poorly understood ecologies and unassessed
populations by the IUCN are known to exist on the island. Therefore, as small, contained area,
Sumak Allpa serves as an ideal site to study the ecological niches and functions of these species
and fill knowledge gaps to better strategize the conservation of these species throughout their
entire ranges.
Given the unique suitability of Sumak Allpa as a locality for the study of herpetofauna
and lack of prior assessment, the present investigation serves two primary purposes: 1) to
establish a baseline inventory of the island’s herpetofauna for future studies and 2) to provide a
preliminary assessment of the composition, activity, and habitat use of the herpetofaunal
community that can be used to inform future studies and monitoring of the community and
populations of its species.
Materials & Methods
Study Site
Sumak Allpa is an island situated in the Napo River 19 kilometers east of Coca, Puerto
Francisco de Orellana, Orellana, Ecuador at about 315 m above sea level (0°26'24" S 76°49'02"
W). The climate of the island and surrounding area is characterized by high temperatures
averaging between 24°C and 27°C, a high annual rainfall of 3,200 mm, high humidity averaging
between 80 and 94%, and a mild dry season (Bass et al., 2010). The island contains a varzea
ecosystem and experiences various levels of flooding: areas in the northeast are most regularly
flooded and more central areas flood only intermittently, while the southwest areas of the island
remain dry year-round. The island experienced one inundation event during the time of this
study. The forest is recovered from cacao and coffee plantations and now is between 70% and
80% primary forest and 20% and 30% secondary forest (Zewdie, 2017). A small portion of the
southwestern shore of the island has been developed for four cabins and a small dock, and aside
from the seven maintained trails for research and tourism, the rest of the island is permitted to
grow freely and continues to recover (Figure 2).
Figure 2. Satellite image of Sumak Allpa with the seven maintained trails and three
convening transects highlighted and labeled.
Selection of Surveying Techniques
Searches were conducted using a combination of visual encounter surveying and acoustic
encounter surveying, two standard techniques for the inventory and monitoring of herpetofauna
(Heyer, 1994; Eekhout, 2011; Lambert, 1984). Visual encounter surveying (VES) was selected
over other active search techniques, such as quadrat and patch sampling, and passive search
techniques, such as pitfall trapping and PVC pipe refugia sampling, as the principle surveying
method for this study with the consideration of both the present assessment and future studies.
VES has the lowest relative cost and time investment for the inventory and monitoring of
the broadest spectrum of herpetofauna and can still be employed successfully when personnel is
limited (Heyer, 1994). When utilized in short-term studies, such as this, the VES also has
demonstrated significantly higher encounter rates of diurnal amphibians and nocturnal reptiles
than other active search techniques and was comparable to such techniques for the detection of
nocturnal amphibians and diurnal reptiles in the short-term (Doan 2003). VES is even more
effective in combination with other inventory and/or monitoring techniques, to the point where it
may even be able to obtain a complete species inventory when paired with an appropriate
secondary technique (Eekhout, 2011).
Thus, to account for canopy-dwelling and more cryptic calling species, VES was paired
with acoustic encounter surveying (AES), another low-cost, low-personnel, and low-time-
investment monitoring technique (Heyer, 1994). When used together, these methods have been
demonstrated to detect the highest species numbers across families, guilds, and microhabitats
among active and passive search techniques that can be used for short-term surveys (Rödel &
Ernst, 2004). All factors considered, this combination was decidedly the most effective
methodology not only for conducting this short-term baseline assessment but also for
establishing a feasible monitoring scheme for the continued long-term assessment of
herpetofauna on Sumak Allpa.
VES and AES
As much of the island as was accessible and possible was surveyed between April 22 and
May 7, 2018. Using VES and AES, areas of all seven maintained trails and three convening
temporary transects were searched in three, four, and five-hour blocks between the hours of 8:00-
17:15 for what were termed diurnal searches and 19:30- 1:45 for nocturnal searches for a total of
39 hours each of diurnal and nocturnal surveys. Surveys were conducted at an average speed of
2.5 meters per minute. Temperature and relative humidity were recorded at the start and finish of
each survey and averaged to describe conditions at the time of each survey.
Herpetofauna located within 1 meter of the edge of each side of trails and transects were
searched thoroughly from the ground up to 2 meters high. Trails wider than 2 meters were
searched one side at a time. A Black Diamond Spot headlamp was utilized to provide light for all
nocturnal surveys.
Each time an individual was located visually, a photo was taken while it remained at its
perch if possible, and immediately following the individual was captured by hand if possible.
Once captured, a series of 5 photos - top view, ventral view, right side view, front facial view,
and bird’s eye view - was taken of each individual with additional photographs of notable
morphological features taken as necessary. Once photographed, snout-vent-length (SVL) and any
other notable identification features were measured using a digital caliper. Individuals unable to
be handled or successfully captured were photographed to the best extent possible and described
thoroughly in the field immediately after being sighted.
After recording these data and other relevant observations, each individual handled was
released at or near the exact site of capture. All individuals were handled with disposable latex
gloves which were changed after the release of each individual and all equipment to come into
contact with any given organism was sanitized after each use in order to avoid vectoring fungi
and other pathogens between organisms, particularly amphibians.
For these visual encounters, the time of sighting was recorded for each individual, and the
location of each encounter was recorded using the offline smartphone GPS application,
Maps.ME. The perch height of each individual also was measured with measuring tape and
microhabitat, surrounding understory vegetation density, and habitat type of each individual
were noted. Microhabitats were described in the following categories: exposed soil, mud, grass,
leaf litter, leaf, branch, log, and man-made structure. Leaf litter also was further described as wet
or dry and loose or compact. Understory vegetation density was defined as low, medium, or
high.
Habitat types were classified as river edge, high varzea, low varzea, or cabin area. River
edge represented areas within about 20 meters of the edge of the Napo River. High varzea
designated areas unaffected by flooding, while low varzea signified areas subject to any level of
flooding during an inundation event. Cabin area described the man-made clearing of high varzea
and river edge habitat on the southwest shore of the island containing the dock and cabins that is
subject to the most human alteration and highest levels of human activity on the island.
Acoustic encounter surveys were conducted concurrently with VES. When individuals
were heard calling within about 1-2 meters of the trail or transect being searched, they were
recorded for 30-60 seconds using an Olympus VN-721PC Digital Voice Recorder, holding the
recorder as close to the source of the sound as possible. For each of these encounters, time of
call, density of understory vegetation, and habitat type also were documented.
Identification
Given the small size of Sumak Allpa and the lack of knowledge regarding the exact size
and status of populations of herpetofauna on the island, no specimens were collected and
preserved for identification in this study. Species encountered visually were identified instead
entirely based upon the morphological species concept to the most taxonomically specific level
possible using Guía Dinámica de los Anfibios del Ecuador and Guía Dinámica de los Reptiles
del Ecuador from BIOWEB Ecuador, Guía de Campo de Anfibios del Ecuador, Guía de Campo
de Reptiles del Ecuador, Reptiles and Amphibians of the Amazon: An Ecotourist's Guide, the
Frogs of the Yachana Reserve field guide, and additional online resources such as AmphibiaWeb
and BIOWEB Ecuador as necessary. Recorded calls were identified using Frogs of the
Ecuadorian Amazon and online databases with species-specific recordings of calls, such as
AmphibiaWeb and BIOWEB Ecuador.
Community Analysis
The overall herpetofaunal community surveyed was analyzed in a variety of ways. First,
all species encountered were inventoried taxonomically by order, family, and species and by
their IUCN Red List of Threatened Species status. The community was then analyzed first in
terms of the composition of encounters: the proportions of acoustic versus visual and nocturnal
versus diurnal encounters were calculated for each species, and the percentage of overall
encounters of each species was calculated to demonstrate the relative size of each population
within the community.
Sumak Allpa’s herpetofaunal community was then analyzed for its species composition
overall and in terms of various sub-communities. Sub-communities were classified within two
main categories: habitat type, which contained the river edge, high varzea, low varzea, and cabin
area sub-communities, and period of activity, which was categorized as diurnal or nocturnal. The
sample coverage, species richness, and species diversity were estimated for the overall
community and various sub-communities through asymptotic analysis using the software iNext
Online and quantified using Hill numbers. Hill numbers (or the effective number of species) are
parameterized by a diversity order q, which determines the measures’ sensitivity to species
relative abundances (Chao et al., 2015; see A1 in Appendix for formulas). The species richness
(q = 0), Shannon diversity (the exponential of Shannon entropy, q = 1) and Simpson diversity
(the inverse of Simpson concentration, q = 2), all of which are expressed in units of “species
equivalents,” were calculated for the overall community, the 4 defined habitat types, and the
diurnal and nocturnal communities within the overall island community.
The similarity of these two types of sub-communities also was analyzed to determine the
overlap of species and individuals in habitat use and hours of activity. The similarity between
habitat type communities was estimated with SpadeR Online’s Multiple-Community Measures
tool using following measures: Sørensen similarity index, Sørensen pairwise similarity estimates,
and the Bray-Curtis similarity index. The Sørensen similarity index is a classic local species
richness-based similarity measure (Chao et al., 2015) and was utilized to assess the percent of
species overlap in all habitat types (see A2 in Appendix for formula). Sørensen pairwise
similarity estimates are similarity estimates of the same measure but between specific pairs
within the set of local communities compared and were used to evaluate species overlap in
specific pairs of habitat types. The Bray-Curtis similarity index compares absolute abundances
among communities and thus was used to assess the overlap of individuals in habitat types (see
A3 in Appendix formula). The Sørensen similarity index and the Bray-Curtis similarity index
also were used to assess the similarity and overlap of species and individuals in diurnal and
nocturnal communities. For this comparison, these indices were estimated using SpadeR
Online’s Two-Community Measure tool, as the Sørensen similarity index is calculated
differently for comparisons of only two communities (see A4 in Appendix for formula).
The community’s overall microhabitat preference was then analyzed looking at the
overall community usage and species composition of each microhabitat and level of understory
vegetation density.
Population Analysis of Adenomera hylaedactyla
Adenomera hylaedactyla constituted a significant portion of the island’s overall
herpetofaunal community. Thus, in addition to the community analysis of Sumak Allpa, the
population of A. hylaedactyla, specifically, was analyzed in more depth first through the
consideration of population-specific microhabitat preference. The distributions of both acoustic
and visual encounters of the species among levels of understory vegetation and habitat types also
were assessed to determine the population’s preferred habitat conditions for both calling and
general activity. Lastly, the size distribution of individuals within the population was evaluated
using snout-vent-length measurements.
Results
VES and AES Inventory
During the study period, 373 individuals were identified by visual encounter and 179
individuals were identified by acoustic encounter for a total of 552 individuals, representing 15
species from 5 families of the order Anura and 11 species from 7 families of the order Squamata
(Table 1). Of the total of 26 distinct species, 22 were identified taxonomically to species level
and 4 were identified to the genus level as distinct morphospecies. Of the 22 species identified to
species level, 7 were classified as Least Concern on the IUCN Red List of Threatened Species, 5
were as Least Concern but needs updating, indicating their assessment is older than 10 years
(CITE IUCN). None of reptilian species encountered on Sumak Allpa had been evaluated by the
IUCN (Table 1).
Table 1. Families and species encountered during the study period, including their status on the
International Union for Conservation of Nature (IUCN) Red List of Threatened Species (LC = Least
Concern, LC* = Least Concern but needs updating, NE = Not Evaluated, -- = not identified to
species level), and combined number of visual and acoustic encounters. ANURA
FAMILY SPECIES IUCN Status Number of Encounters
BUFONIDAE Rhinella aff. margaritifera LC 1
Rhinella marina LC 2
HYLIDAE
Boana boans NE 8
Dendropsophus parviceps LC* 1
Osteocephalus taurinus LC 1
LEPTODACTYLIDAE
Adenomera andreae LC* 86
Adenomera hylaedactyla LC 317
Adenomera sp. -- 11
Leptodactylus knudseni LC 5
Leptodactylus mystaceus LC 59
Leptodactylus pentadactylus LC 4
MICROHYLIDAE Chiasmocleis bassleri LC* 17
STRABOMANTIDAE
Oreobates quixensis LC* 2
Pristimantis altamazonicus LC* 7
Pristimantis sp. -- 2
SQUAMATA
FAMILY SPECIES IUCN Status #
COLUBRIDAE
Drepanoides anomalus NE 1
Imantodes cenchoa NE 2
Leptodeira annulata NE 1
ELAPIDAE Micrurus lemniscatus helleri NE 1
VIPERIDAE Bothrops atrox NE 1
GEKKONIDAE Thecadactylus solimoensis NE 2
IGUANIDAE
Anolis bombiceps NE 1
Anolis sp. 1 -- 1
Anolis sp. 2 -- 1
SPHAERODACTYLIDAE Pseudogonatodes guianensis NE 15
TEIIDAE Tupinambis cuzcoensis NE 3
TOTAL
FAMILY SPECIES #
12 26 552
0% 50% 100%
Diurnal Nocturnal
Types and Frequency of Encounters
Of the 26 species observed on Sumak Allpa, 19 were encountered only visually, 3 were
encountered only acoustically, and 4 were both seen and heard calling (Figure 3A). Additionally,
18 species were encountered exclusively nocturnally, 5 exclusively diurnally, and 3 were
encountered both nocturnally and diurnally (Figure 3B).
Figure 3. Percentage of (A) acoustic versus visual and (B) diurnal versus nocturnal encounters for
each species observed on Sumak Allpa.
Adenomera hylaedactyla, a principally nocturnal species, was encountered most
frequently in both visual and acoustic surveys, accounting for 57.4% of all encounters (Figure 4).
Adenomera andreae, a principally diurnal species, was the most encountered diurnal species and
second most encountered species overall, accounting for 15.6% of all encounters (Figure 4).
Leptodactylidae was the most encountered family in both VES and AES.
0% 50% 100%
T. cuzcoensis
T. solimoensis
R. marina
R. aff. margaritifera
P. guianensis
Pristimantis sp.
P. altamazonicus
O. taurinus
O. quixensis
M.l. helleri
L. annulata
L. pentadactylus
L. mystaceus
L. knudseni
I.cenchoa
D. anomalus
D. parviceps
C. bassleri
B. atrox
B.boans
Anolis sp. 2
Anolis sp. 1
A.bombiceps
Adenomera sp.
A. hylaedactyla
A. andreae
Spec
ies
Visual Acoustic
Percentage of Type of Encounter
(A) (B)
Figure 4. Percentage of overall encounters of each species surveyed on Sumak Allpa.
Community Composition
The sample coverage of the island overall was a high estimate of 0.982, and each of the
sub-communities were also estimated to be well-surveyed (Figure 5). Low varzea was the best-
sampled habitat type with a sample coverage of 0.975, and the nocturnal community was
estimated to be slightly better sampled than the diurnal community (Figure 5).
Figure 5. Estimated sample coverage for the entire island and the 6 sub-communities of the island,
where 1.00 indicates 100% sample coverage.
The overall community of herpetofauna was characterized by high species richness and
low species diversity (Figure 6). Species richness of the overall community was estimated at
34.98 species equivalents, while the Shannon diversity index estimated 1.60 species equivalents,
or about 2 common species in the overall community, and the Simpson diversity index estimated
0.633 species equivalents, or effectively 1 dominant species in the overall community (Figure 6).
0.9
0.91
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1
Overall River Edge High Varzea Low Varzea Cabin Area Diurnal Nocturnal
Sam
ple
Co
vera
ge E
stim
ate
Sub-Community
A. andreae, 15.6% A. hylaedactyla, 57.4%Adenomera sp., 2.0% A. bombiceps, 0.2%Anolis sp. 1, 0.2% Anolis sp. 2, 0.2%B. boans, 1.4% B. atrox, 0.2%C. bassleri, 3.1% D. parviceps, 0.2%D. anomalus, 0.2% I. cenchoa, 0.4%L. knudseni, 0.9% L. mystaceus, 10.7%L. pentadactylus, 0.7% L. annulata, 0.2%M.l. helleri, 0.2% O. quixensis, 0.4%O. taurinus, 0.2% P. altamazonicus, 1.3%Pristimantis sp., 0.4% P. guianensis, 2.7%R. aff. margaritifera, 0.2% R. marina, 0.4%T. solimoensis, 0.4% T. cuzcoensis, 0.5%
Likewise, each habitat type demonstrated the same trend of much higher species richness
than species diversity. High varzea was estimated to have the highest habitat species richness at
48.89 species equivalents, while the cabin area was the least species rich habitat estimated at
only 5.93 species equivalents (Figure 6). In other words, high varzea habitats are used by the
largest number of species, while the cabin area is occupied by only few species. Meanwhile, all
habitat types had effectively 2 or fewer common species and 1 or fewer dominant ones, as given
by Shannon and Simpson diversity, respectively (Figure 6).
Figure 6. Diversity profile estimates of the overall and sub-communities of herpetofauna on Sumak
Allpa in terms of species richness (q = 0), Shannon diversity (q = 1), and Simpson diversity (q = 2)
(Species Equivalents ± SE).
Diurnal and nocturnal communities also had high species richness relative to species
diversity (Figure 6). The nocturnal community was estimated to be more than twice as rich as the
diurnal community in species with 30.10 species equivalents, yet both communities had roughly
only one common species and about 1 or fewer dominant species.
The Sørensen index, a richness-based similarity measure, for the comparison of all
habitat types was 0.794, indicating that about 79.4% of species on Sumak Allpa can be
encountered in all four of the classified habitat types (Figure 7). The pairwise similarity
estimates indicate the highest levels of overlap in species use of river edge and low varzea and of
high varzea and low varzea, with 31.3% of species estimated to utilize both river edge and low
varzea habitats and 27.9% of species estimated to make use of both high and low varzea habitats
(Figure 7). Meanwhile, the lowest level of species habitat overlap was between high varzea and
the cabin area with an estimated 10.6% of species being encountered in both (Figure 7).
The Bray-Curtis index, a measure for comparing species absolute abundances, estimated
only 48.8% of individuals in the community make use of all four habitat type (Figure 7).
0 10 20 30 40 50 60 70
q = 0
q = 1
q = 2
Species Equivalents
Hill
Ord
er
Nocturnal Diurnal
Cabin Area Low Varzea
High Varzea River Edge
Overall
Figure 7. Estimated similarity of sub-communities based on habitat type (Edge = river edge, HVz =
high varzea, LVz = low varzea, CA = cabin area) given by the classic richness-based Sørensen
similarity index, richness-based Sørensen pairwise similarity estimates, and species absolute
abundance-based Bray-Curtis index (Similarity Estimate ± SE).
There was very little overlap between the diurnal and nocturnal communities on Sumak
Allpa. The richness-based Sørensen similarity index of the communities was 0.177, estimating
that only 17.7% of species on the island could be encountered both diurnally and nocturnally
(Figure 8). The abundance-based Bray-Curtis similarity index was even lower, suggesting that
only about 7.6% of individuals on the island are active during both what were defined as daytime
and nighttime hours for the purposes of this study (Figure 8).
Figure 8. Estimated similarity of diurnal and nocturnal sub-communities given
by the Sørensen similarity index and Bray-Curtis index (Similarity Estimate ±
SE).
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Sørensen index Bray-Curtis index
Sim
ilari
ty E
stim
ate
Similarity Measure
0
0.2
0.4
0.6
0.8
1
Sørensen Edge, HVz Edge, LVz Edge, CA HVz, LVz HVz, CA LVz, CA Bray-Curtis
Sim
ilari
ty E
stim
ate
Similarity Measure
Sørensen index Sørensen pairwise similarity Bray-Curtis index
Microhabitat and Understory Vegetation Density Preference
In visual encounter surveys, 339 individuals representing 12 different species were
encountered in leaf litter, making it the most utilized microhabitat by the island’s community
(Figure 9). More specifically, leaf-litter dwelling individuals exhibited preferences for loose over
compact leaf litter and dry over wet leaf litter (Figure 9). The next most preferred microhabitat
was leaves, upon which 16 individuals of 8 different species were encountered (Figure 9).
Figure 9. Community use of microhabitats by number of visual encounters in terms of species
composition (Soil = exposed soil, MMS = man-made structure, DL = dry loose leaf litter, WL = wet
loose leaf litter, DC = dry compact leaf litter, WC = wet compact leaf litter).
High density understory vegetation was most preferred by the community for both calling
and general dwelling, followed by medium density and low density, respectively (Figure 10).
Figure 10. Community preference for level of understory vegetation density in terms of number of
visual and number of acoustic encounters for each level.
0 20 40 60 80 100 120 140 160 180
DL
WL
DC
WC
Soil
Mud
Grass
Leaf
Branch
Log
MMS
Number of Encounters
Mic
roh
abit
at
A. andreae A. hylaedactyla Adenomera sp.A. bombiceps Anolis sp. 1 Anolis sp. 2B. atrox C. bassleri D. parvicepsD. anomalus I.cenchoa L. mystaceusL. annulata M.l. helleri O. quixensisO. taurinus P. altamazonicus Pristimantis sp.P. guianensis R. aff. margaritifera R. marinaT. solimoensis T. cuzcoensis
0
20
40
60
80
100
120
140
160
180
200
Low Medium High
Nu
mb
er o
f En
cou
nte
rs
Understory Vegetation Density
Visual Acoustic
Additionally, the widest array of species was harbored by high density understory
vegetation with 19 different species encountered, versus 16 in medium density and 6 in low
density (Figure 11). Seven of the species found in high density understory vegetation were found
exclusively in that level of density of understory vegetation.
Figure 11. Community preference for level of understory vegetation density by number of overall
encounters in terms of species composition.
Population Analyses of Adenomera hylaedactyla
Accounting for 57.4% of all visual and acoustic encounters, Adenomera hylaedactyla was
by far the most frequently observed species on the island with the highest relative abundance
(Figure 4). The species is primarily nocturnal; however, of the 317 overall encounters, it was
encountered visually 4 times in the last 30 minutes of what were considered diurnal searches for
the purposes of this study.
The population of A. hylaedactyla followed many of the same trends for the community
overall. Individuals among the population preferred leaf litter habitats - dry over wet leaf litter
and loose over compact leaf litter, in addition to showing overall preference for high density
understory vegetation over medium and low density (Figure 9; Figure 11). In terms visual versus
acoustic encounters, high density understory vegetation was preferred for calling sites, but there
were slightly more visual encounters in medium density than high density understory vegetation
(Figure 12).
The population also showed differences in the number of visual versus acoustic
encounters among habitat types (Figure 13). High varzea was the most preferred habitat for both
calling and general activity, but there were more acoustic encounters than visual encounters in
low varzea areas and more visual than acoustic encounters at the river edge habitat (Figure 13).
Not a single vocalization of the species was recorded in the cabin area, although calls could be
heard from forest areas within the vicinity of it (Figure 13).
0 50 100 150 200 250 300
Low
Medium
High
Number of Encounters
Un
der
sto
ry V
eget
atio
n D
ensi
ty
A. andreae A. hylaedactyla Adenomera sp. A.bombiceps
Anolis sp. 1 Anolis sp. 2 B. atrox B.boans
C. bassleri D. anomalus D. parviceps I.cenchoa
L. annulata L. knudseni L. mystaceus L. pentadactylus
M.l. helleri O. quixensis O. taurinus P. altamazonicus
P. guianensis Pristimantis sp. R. aff. margaritifera R. marina
T. cuzcoensis T. solimoensis
Figure 12. Distribution of Adenomera hylaedactyla visual and acoustic encounters among understory
vegetation densities.
Figure 13. Distribution of Adenomera hylaedactyla visual and acoustic encounters among habitat
types.
The body size of individuals in the population ranged from 5.01 mm to 27.60 mm and on
average was 19.75 mm (Figure 14). The average body size of Adenomera hylaedactyla is 23.5
mm for males and 25.6 mm for females (Angulo et al. 2003; Aichinger 1992), which were the
73rd and 87th percentile, respectively, in the population encountered on Sumak Allpa (Figure 14).
0
20
40
60
80
100
120
Low Medium High
Nu
mb
er o
f En
cou
nte
rs
Understory Vegetation Density
Visual Audio
0
10
20
30
40
50
60
70
80
90
100
River Edge Low Varzea High Varzea Cabin Area
Nu
mb
er o
f En
cou
nte
rs
Habitat Type
Visual Audio
Figure 14. Distribution of body size in terms of snout-vent-length of Adenomera
hylaedactlya individuals encountered on Sumak Allpa.
Discussion
Island Biogeography Theory proposes that the number of species of any island reflects a
balance between the rate at which new species colonize it and the rate at which populations of
established species decline and become extinct posits that the larger and/or closer to the
mainland an island is, the more species it will be able to support (MacArthur & Wilson, 2016).
Thus, a small island close to mainland, such as Sumak Allpa, should in theory be able to support
a medium to high level of species richness but very few individuals within each. Considering the
trends of high species richness and low species diversity in the diversity profile estimates of the
community surveyed in the current study, the herpetofaunal assemblage on Sumak Allpa appears
to be a case in which Island Biogeography Theory holds true.
This conclusion, however, should not be made definitively without the consideration of a
variety of factors. First, although the methodology of combining VES and AES for this study
was effective in detecting a large number of species in a wide range of niches across multiple
taxa, including a number of species that would not have been registered if only a visually-
oriented technique had been applied, there was still bias in the species the methodology
encountered. Because only the understory and visible areas of the forest floor could effectively
searched, aquatic species, fossorial species, and arboreal species dwelling above 2 meters,
especially non-vocalizing species, were heavily biased against in this study. Additionally,
because surveys were conducted on the maintained trails and transects of the island, the study
design also was biased against species particularly sensitive to human use impacts. Furthermore,
as in many active search techniques, species encountered are limited by number of observers and
observer ability, so cryptic species may be detected significantly less, if detected at all, and
species that dwell in open areas or have loud and highly distinguishable calls may be detected
significantly more. Thus, in order to generate a complete species inventory of the island, future
studies should be conducted in areas both on and off trails using multiple observers with
experience in herpetofaunal surveying and also consider the inclusion of additional microhabitat-
specific search techniques to account for species biased against in the methodology of this study.
Though the sample coverage estimates reflected effective and near-complete sampling of
Sumak Allpa’s herpetofaunal community, a variety of observed field conditions and other factors
suggest these estimates may not reflect the true coverage of sampling. The study, for example,
was conducted over a period of only 16 consecutive days all in the same season, and amphibian
and reptile activity can vary temporally, resulting differences in the abundance and number of
species detected in different seasons and even at different times within one season (Menin,
Waldez, & Lima, 2008).
There also was relatively variation in rainfall, temperatures, and percent humidity
throughout the period of study, and all of these factors are known to affect herpetofaunal activity
(Paladino, 1985; Brown & Shine, 2002). Furthermore, by giving rise to cues such as light
intensity, geomagnetism, and gravity, lunar cycles have been associated with the reproductive
phenologies (including mating vocalizations) of a number of anuran and urodele species to
different effects (Grant, Chadwick, & Halliday, 2009). Thus, the full moon occurring in the
middle of the study also may have played a role in the activity and detectability of species on
Sumak Allpa.
Inundation also may have influenced the abundance and number of species detected.
Differences in the number and types of anuran vocalizations heard before and after flooding were
observed informally during surveying; however, inundation occurred too early in the study
period for these differences to be effectively quantified and analyzed. Any number of these
variables could have influenced the high number of Adenomera hylaedactyla and Adenomera
andreae individuals detected and/or the low number of encounters of other species.
Therefore, under the consideration of all of these factors, more long-term future studies
should be conducted throughout different times of year and under a wider array of conditions,
not only to account for the potential impacts of temporality, climate, and lunar cycles on the
composition of the island’s herpetofaunal community but also to investigate how each of these
variables may influence specific populations within it.
These factors and potential limitations aside, a number of important conclusions still can
be made about the composition, activity, and habitat use of the island’s herpetofaunal
community. As previously mentioned, the island supports a high level of species richness
relative to species diversity, and although this trend was consistent across habitat types, species
richness was not the same for each habitat’s community. High varzea, for instance, had much
higher species richness than the river edge, low varzea, and cabin area communities, indicating it
may provide higher resource quality, quantity, and/or accessibility to a wider variety of species
and support a wider variety of niches than other habitats on the island. Additionally, the cabin
area demonstrated the lowest species richness and diversity, suggesting trends opposite to high
varzea in terms of resource and niche availability and also that human activity may severely
inhibit the habitat from supporting large populations and numbers of species.
The similarity indices of communities within these habitats also serve to characterize
much of the habitat use of the island’s herpetofaunal community. The Sørensen index score of
0.794 indicates a high level of overlap in the species utilizing all of the island’s habitats. This
significant overlap not only is indicative of the small size of the island and contiguity of its
habitats but also suggests that a high percentage of the island’s species are habitat generalists.
The pairwise similarity estimates also help characterize the community’s use of specific
habitats. The higher percentages of overlap of river edge with low varzea habitat and high varzea
with low varzea habitat are to be expected, given the river edge and inundated low varzea both
provide access to water, which is necessary for the reproduction of many anuran species, and low
varzea can be very similar to high varzea habitat when it is not inundated.
Furthermore, the richness-based Sørensen similarity index was higher than the
abundance-based Bray-Curtis similarity index, signifying that there is less overlap in habitat use
by specific individuals within populations than there is by overall species. This relationship
possibly suggests that although a species may be able to utilize more than one habitat, not all
individuals in its population necessarily do.
Ultimately, the composition of the herpetofaunal community did vary among habitat
types, but understanding the exact causes of this variation will require further investigation.
Future studies, therefore, should investigate more of the specific shared versus distinguishing
characteristics of each of these habitats in terms of vegetation cover and type, prey and other
resource diversity and availability, microclimate and microhabitat variation, and even
geomorphology, as all of these factors have been evidenced to affect herpetofaunal assemblages
in other Amazonian communities (Doan & Arriaga, 2002; Deichmann, 2009).
The relationships between diurnal and nocturnal communities also provide important
characterizations of the herpetofaunal community composition of Sumak Allpa. The nocturnal
community had more than double the species richness than the diurnal community; however, the
Sørensen similarity index indicated a small percentage of overlap in species between these
communities, and the Bray-Curtis similarity index demonstrated an even smaller percentage of
overlap in individuals. This apparent species richness and lack of overlap signifies the
importance of continuing to monitor herpetofauna during all times of day in order to best
conserve the entire community of herpetofauna on the island. Additionally, the possible
misrepresentation of crepuscular species as nocturnal or diurnal species suggests that future
analysis of communities in terms of periods of activity should be done with more specificity,
blocking surveys during more and different hours of the day to determine more specific hours of
activity for assemblages and specific populations within the overall community.
The trends in microhabitat and understory vegetation density use by the community also
can serve to guide future studies. In terms of microhabitat, leaf litter appeared to be the preferred
by the largest portion of the community, and dry and loose leaf litter was preferred over wet and
compact leaf litter. Given the significance of the microhabitat to so many individuals on the
island and the limitations of using only qualitative descriptions to classify leaf litter, further
analysis of more quantitative leaf litter characteristics with respect to herpetofaunal assemblages
would contribute greatly to the understanding of the herpetofaunal community of Sumak Allpa,
Studying small invertebrate communities inhabiting the leaf litter may also be beneficial to
understanding different herpetofaunal populations and how and why the leaf litter supports them
differently, especially since other Amazonian studies have demonstrated significant differences
in resource utilization and guild structure among leaf-litter dwelling species of frogs and lizards
(Vitt & Caldwell, 1994). Likewise, a further understanding of the relationship between
understory vegetation density and herpetofaunal assemblages would benefit from a more
quantitative analysis of said vegetation, its composition, and potentially associated characteristics
that differentiate it from medium and low density understory vegetation other than visibility by
predators, such as microclimate and prey diversity and availability.
While the population of Adenomera hylaedactyla in the community was analyzed briefly
in this study, there was no conclusive evidence for why it was so much more abundant than all
other species encountered on Sumak Allpa. Though there was evidence that they are able to
occupy all habitat types with all levels of understory vegetation density, this does not explain
their proliferation, as other, less-abundant species also demonstrated these trends. Based off the
observed population trends and observations of other investigations of the species, a variety of
hypotheses may explain the high number of individuals in this population relative to other
species on the island.
The first of these hypotheses is that A. hyladactyla was significantly more influenced than
all other species by one or more of the aforementioned biotic and abiotic factors influencing frog
activity, such as temporality, climate, lunar cycle, and inundation. There also exists the
possibility that they may be able to consume a wider variety of prey or that they may have more
of their type of prey available to them than other species on the island. They also may be
significantly less sensitive than other species to human activity and thus were more likely than
other species to be encountered along the island’s maintained trails. Increased visual detectability
compared to other species, though less likely than the aforementioned hypotheses, is also another
possible explanation for the high frequency of their encounters, and any number of these
hypotheses could be tested simply with any of the aforementioned future study suggestions for
the community by simply changing their scope to the population.
Another hypothesis is that the population of A. hylaedactlya is actually an assemblage of
multiple morphs of the species, subspecies, or even distinct species. A study conducted in the
Peruvian Amazon Basin by Angulo, Cocroft, & Reichile (2003) summarized how the genus
Adenomera has been a difficult group for systematic studies and investigated A. andreae and A.
hylaedactyla, the two most encountered species on Sumak Allpa. The researchers examined
advertisement calls in relation to the frogs’ morphological characteristics and determined
significant enough differences in the morphologies and acoustic parameters of the calls of
associated individuals to indicate potentially four sympatric species derived from A. hylaedactyla
existing at the study site. Given subtle differences in morphological features of Adenomera
hylaedactyla were observed among individuals in Sumak Allpa’s population, a similar study to
that of Angulo, Cocroft, & Reichile (2003) may be merited on the island.
Finally, it also could be proposed that Sumak Allpa has the highest numbers of
individuals of small species and lowest numbers of individuals of large species because it is
experiencing a phenomenon known as excess density compensation. The theory posits that island
assemblages could be partitioned differently (few species or smaller individuals) from mainland
sites without differing in aggregate biomass (Rodda & Dean-Bradley, 2002). Such “excess
density compensation” may be understood as either a lack of interference competition, a lack of
overexploitation, or a release from predation on these islands (Case, Gilpin, & Diamond, 1979;
Wright, 1980).
Lack of interference competition means that this overcompensation of biomass density is
caused by exclusion of more efficient competitors from some portion of the resource spectrum
by inefficient species, allowing species-poor island populations or assemblages to harvest
resources more efficiently and support higher total population densities than species-rich
mainland communities (Wright, 1980).
Resource overexploitation occurs when consumers are so efficient on the mainland that
their resource abundances are reduced to the point that consumer abundances also must decline
until the consumer efficiency declines to the point where resource abundances stop being
reduced enough to also stop reduction of consumer abundances (Wright, 1980). If this
overexploitation occurs on the mainland but not the island, species-poor islands may support
higher resource abundances and higher total population densities of consumers than the species-
rich mainland (Wright, 1980).
Lastly, release from predation indicates that islands containing fewer predators than
corresponding mainland sites would allow for higher prey densities on islands than the mainland
(Wright, 1980).
This final hypothesis is by far the most involved and also probably the least likely,
especially given much of the debate surrounding the concept of excess density compensation in
general, yet there may be merit in investigating it as a potential alternative if the other
hypotheses do not account for the high numbers of A. hylaedactyla and other small-bodied
species on Sumak Allpa.
Ultimately, given its high density and abundance on Sumak Allpa, A. hylaedactyla should
be a priority species for population studies to determine why the island supports so many
individuals compared to other species. Population studies, nevertheless, should not be limited to
this species alone. There is merit in the assessment of all populations of the island, especially
considering the number of outdated IUCN Red List listings of species and unevaluated species
encountered on the island.
Though comprehensive studies of global and national assemblages of herpetofauna are
necessary to generate awareness of the world’s significant amphibian and reptile declines and
call to action the large-scale conservation efforts needed to combat them, these studies ultimately
are informed by the aggregation of small-scale studies monitoring local communities and
populations. Despite the immense species richness and diversity of herpetofauna across Ecuador
and the Neotropics, the study of specific herpetofaunal communities and populations overall is
pretty lacking. Thus, gaining a better understanding of the local interactions, functions,
behaviors, and ecologies of specific species, populations, and communities of herpetofauna in
threatened regions such as the western Amazon and the Neotropics is one of the biggest strides
that needs to be made for the conservation of the immense richness and diversity of these
regions. Thus, especially considering the lack of evaluation and continued monitoring of the
majority of species encountered at Sumak Allpa by the IUCN – the global authority on the status
of the natural world – any investigation filling one of the many knowledge gaps of herpetofauna
on Sumak Allpa is merited, warranted, and valuable work for the conservation of herpetofauna
on the island and in the region overall.
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Appendix
A1. Hill’s number of order q, q ≥ 0:
and
A2. Sørensen similarity index for multiple community measures:
A3. Classic Bray-Curtis similarity index:
A4. Sørensen similarity index for the special case of two communities: