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Ever-increasing human pressures on cave biodiversity have amplified the need for systematic, repeatable, and intensive surveys of cave-dwelling arthropods to formulate evidence-based management decisions. We examined 110 papers (from 1967 to 2018) to: (i) understand how cave-dwelling invertebrates have been sampled; (ii) provide a summary of techniques most commonly applied and appropriateness of these techniques, and; (iii) make recommendations for sampling design improvement. Of the studies reviewed, over half (56) were biological inventories, 43 ecologically focused, seven were techniques papers, and four were conservation studies. Nearly one-half (48) of the papers applied systematic techniques. Few papers (24) provided enough information to repeat the study; of these, only 11 studies included cave maps. Most studies (56) used two or more techniques for sampling cave-dwelling invertebrates. Ten studies conducted ≥10 site visits per cave. The use of quantitative techniques was applied in 43 of the studies assessed. More than one-third (42) included some level of discussion on management. Future studies should employ a systematic study design, describe their methods in sufficient detail as to be repeatable, and apply multiple techniques and site visits. This level of effort and detail is required to obtain the most complete inventories, facilitate monitoring of sensitive cave arthropod populations, and make informed decisions regarding the management of cave habitats. We also identified naming inconsistencies of sampling techniques and provide recommendations towards standardization.
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Abstract: Ever-increasing human pressures on cave biodiversity have amplified the need for
systematic, repeatable, and intensive surveys of cave-dwelling arthropods to formulate
evidence-based management decisions. We examined 110 papers (from 1967 to 2018) to:
(i) understand how cave-dwelling invertebrates have been sampled; (ii) provide a summary
of techniques most commonly applied and appropriateness of these techniques, and; (iii)
make recommendations for sampling design improvement. Of the studies reviewed, over
half (56) were biological inventories, 43 ecologically focused, seven were techniques papers,
and four were conservation studies. Nearly one-half (48) of the papers applied systematic
techniques. Few papers (24) provided enough information to repeat the study; of these,
only 11 studies included cave maps. Most studies (56) used two or more techniques for
sampling cave-dwelling invertebrates. Ten studies conducted ≥10 site visits per cave. The
use of quantitative techniques was applied in 43 of the studies assessed. More than one-
third (42) included some level of discussion on management. Future studies should employ
a systematic study design, describe their methods in sufficient detail as to be repeatable,
and apply multiple techniques and site visits. This level of effort and detail is required to
obtain the most complete inventories, facilitate monitoring of sensitive cave arthropod
populations, and make informed decisions regarding the management of cave habitats. We
also identified naming inconsistencies of sampling techniques and provide recommendations
towards standardization.
systematic sampling, repeatability, conservation, pitfall trapping
Received 8 October 2018; Revised 23 January 2019; Accepted 24 January 2019
Wynne J.J., Howarth F.G., Sommer S. and Dickson B.G., 2019. Fifty years of cave arthropod
sampling: techniques and best practices. International Journal of Speleology, 48 (1), 33-48.
Tampa, FL (USA) ISSN 0392-6672
https://doi.org/10.5038/1827-806X.48.1.2231
Fifty years of cave arthropod sampling: techniques
and best practices
J. Judson Wynne1*, Francis G. Howarth2, Stefan Sommer1, and Brett G. Dickson3
1
Department of Biological Sciences, Merriam-Powell Center for Environmental Research, Northern Arizona University, Box 5640, Flagstaff, Arizona 86011, USA
2Department of Natural Sciences, Bernice P. Bishop Museum, 1525 Bernice St., Honolulu, Hawaii, 96817, USA
3Conservation Science Partners, 11050 Pioneer Trail, Suite 202, Truckee, CA 96161 and Lab of Landscape Ecology and Conservation Biology,
Landscape Conservation Initiative, Northern Arizona University, Box 5694, Flagstaff, Arizona 86011, USA
International Journal of Speleology 48 (1) 33-48 Tampa, FL (USA) January 2019
The author’s rights are protected under a Creative Commons Attribution-
NonCommercial 4.0 International (CC BY-NC 4.0) license.
INTRODUCTION
With mounting anthropogenic threats to cave
ecosystems, it is increasingly important to
systematically and efficiently collect data on cave-
dwelling arthropods, so that informed management
decisions can be made or adjusted on a regular basis.
Cave ecosystems face numerous human impacts
globally including land cover conversion (Culver, 1986;
Trajano, 2000; Howarth et al., 2007; Silva et al., 2015),
mining (Elliott, 2000; Silva et al., 2015; Sugai et al.,
2015), groundwater pollution (Aley, 1976; Notenboom
et al., 1994; Graening & Brown, 2003; Whitten, 2009),
water extraction and water impoundments (Lisowski,
1983; Ubick & Briggs, 2002; Olson, 2005), invasive
species (Elliott, 1992; Reeves, 1999; Taylor et al.,
2003; Howarth et al., 2007; Wynne et al., 2014),
global climate change (Chevaldonné & Lejeune, 2003;
Badino, 2004; Mammola et al., 2018), and recreational
use (Culver, 1986; Howarth & Stone, 1993; Pulido-
Bosch et al., 1997). These threats have significant
implications for conservation because caves are
highly sensitive habitats, often serving as hotspots of
endemism and subterranean biodiversity (Culver et
al., 2000; Culver & Sket, 2000; Eberhard et al., 2005).
Because of their restricted distributions and life
history traits, many populations of troglomorphic
(subterranean-adapted) species are considered highly
sensitive or imperiled and thus high priority targets for
protective management (Culver et al., 2000; Niemiller
& Zigler, 2013; Niemiller et al., 2017). Troglomorphic
species are often endemic to a single cave or region
(Reddell, 1994; Culver et al., 2000; Christman et
al., 2005; Gao et al., 2018) and characterized by
34 Wynne et al.
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
small populations (Mitchell, 1970). Thus, effectively
sampling caves to detect troglobionts should be a
priority of cave biological inventories.
The fauna of most of the world’s caves remain
unknown or, at best, incompletely surveyed
(Howarth, 1983; Whitten, 2009; Gibert & Deharveng,
2002; Deharveng & Bedos, 2000; Encinares & Lit,
2014; Gilgado et al., 2015). In addition, accurate
information on the taxonomy, genetics, distribution,
and environmental requirements of cavernicoles will
be necessary to make rigorous ecological inference,
as well as to develop appropriate recommendations
for monitoring and protecting cave animals (Wynne et
al., 2018).
Numerous researchers (e.g., Weinstein & Slaney,
1995; Howarth et al., 2007; Krejca & Weckerly, 2007;
Zagmajster et al., 2008; Wynne et al., 2018) have
emphasized the difficulties of sampling terrestrial
cavernicolous arthropods, which present challenges
for effectively inventorying, and managing sensitive
cavernicolous arthropod communities. Caves are
highly diverse habitats with constricted, maze-like
interconnected passageways, uneven terrain, loose
rocks and boulders, deep fissures and pits. This
diverse array of habitats often requires technical
climbing and rope work for access. Additionally,
temporal and spatial heterogeneity of cave habitats
(Kane & Poulson, 1976; Chapman, 1983; Pellegrini
& Ferriera, 2013; Trontelj et al., 2013) often requires
considerable pre-planning and on-site evaluations
prior to sampling.
Furthermore, research emphasis should be placed
on identifying and surveying nutrient resource sites
that support troglomorphic animals (Howarth et al.,
2007; Wynne, 2013; Wynne et al., 2018). For example,
Peck & Wynne (2013) showed a cave cricket roost
(Family Rhaphidophoridae), within the type locality
of the troglomorphic leiodid beetle (Ptomaphagus
parashant), provided an important substrate (frass and
decaying carcasses) for the growth of fungi – a primary
food source for this beetle. Additionally, Stone et al.
(2012) and Wynne (2013) underscored the importance
of root curtains as both microhabitats and a nutrient
source for subterranean-adapted animals in Hawai‘i
and New Mexico, respectively. Wynne & Shear (2016),
Wynne et al. (2014), and Benedict (1979) identified
vegetation and moss within entrances and beneath
cave skylights as key habitat for relictual species.
In this study, we (i) examine how cave-dwelling
invertebrates have been sampled (from 1967 to
2018); (ii) provide both a summary of techniques
most commonly applied and their appropriateness,
and; (iii) make recommendations for sampling design
improvement. We also identify naming inconsistencies
of sampling techniques and provide recommendations
towards standardization.
METHODS AND MATERIALS
We reviewed the literature (from 1967 to 2018) by
obtaining articles through a Web of Science search
using combinations of the following search terms
‘cavernicole’, ‘troglobiont,’ ‘troglobite,’ ‘cave arthropod,’
‘cave invertebrate,’ ‘inventory,’ and ‘ecology.’ We
augmented our search using Google Scholar (with the
same search terms), examining titles and abstracts of
all papers published in both the International Journal
of Speleology (1967-2018) and National Speleological
Society Bulletin, now Journal of Cave and Karst Studies
(years 1967-1995 and 1996-2018, respectively), and
working ‘backwards’ into the literature by reviewing
the literature cited of all of the articles considered. As
most of the work in cave biology has been published
in English and to a lesser extend in French, Spanish,
and Portuguese, we assert the papers assembled in
this review are representative of the work conducted
over the past ~50 years.
Papers were selected for inclusion or exclusion
using the following decision rules: (1) papers focused
on inventorying cave-dwelling terrestrial invertebrate
communities and/or investigating an aspect of cave
arthropod community ecology; (2) for studies using
an all taxa approach (i.e., terrestrial and aquatic
invertebrate sampling and vertebrate sampling), only
terrestrial invertebrate techniques were examined;
(3) only multi-taxon inventories were included; single
species or single taxonomic group studies were
excluded; and (4) because reviews and synthesis
papers of specific geographic regions rarely include
sampling methods, these papers were not included.
When possible, we examined the original studies that
included field methods.
We evaluated each article on cave-dwelling
invertebrates using the following questions and criteria.
(1) Were systematic techniques (i.e., techniques
consistently applied throughout a given cave or across
cave study sites) employed (yes, no, or not known)?
(2) Was sufficient information provided to enable
repeatability of data collection and/or the experiment
(yes or no)? (3) To further facilitate repeatability, did
the researchers include cave maps with plotted sample
locations and/or use the information from cave maps
as part of their experimental design (yes or no)? (4)
Did the workers apply multiple sampling techniques
(yes, no, not stated)? If yes, how many? (5) Did the
researchers conduct multiple site visits (yes, no; if
yes, how many?)? (6) Were the data analyzed using
statistical techniques? (7) Finally, did the authors
provide conservation and management implications
for their work (yes or no)? We also summarized the
techniques encountered in the literature, discussed
the functional groups each technique is best suited
for capturing, and provided recommendations for best
practices.
RESULTS
We assessed nearly 300 papers on terrestrial cave-
dwelling arthropods. Of these, 110 articles (Appendix I,
Supplemental Information) met our decision rules
and were included in this review. More than half of
these articles (67) were based upon work conducted
in the Western Hemisphere - United States (36), Latin
America, the Galapagos, and the Caribbean (31; Fig. 1).
Papers reviewed were parsed into four categories
(inventory, ecology, techniques, and conservation).
35Fifty years of cave arthropod sampling
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
Fig. 1. Summary of 110 studies reviewed per geographic
region. Number totals 111, as Wynne et al. (2018) had study
areas in both the United States and Polynesia.
We used these categories to frame how the evaluative
criteria were applied. Slightly over half of the studies
(56) examined were biological inventories, 43
advanced ideas and hypotheses on various aspects
of cave ecology, seven examined the efficacy of
sampling/analytical techniques, and four studies
were conservation focused. For the ecological
studies, 17 examined the distribution and assembly
of communities within caves, 11 investigated the
influence of habitat on arthropod diversity, eight
probed how nutrients affected community structure,
four explored the influence of seasonality on diversity,
and three analyzed the evolution and colonization of
subterranean-adapted arthropods (Fig. 2).
Fig. 2. Pie chart describing the reviewed articles by study type. Numbers
associated with each “pie slice” represent the number of papers per
study type. Subdivisions of ecology (community, habitat, nutrients,
seasonality and evolution) are dipicted in hues of blue. Legend reads left
to right; pie chart reads clockwise starting with the largest slice.
Five studies addressed all seven of our evaluative
criteria. For ecological studies, four (Chapman,
1982; Martín & Oromí, 1986; Ferreira et al., 2000;
Iskali & Zhang, 2015) of 43 papers addressed all of
the criteria. Schneider et al. (2011) met all but one
criterion – the inclusion of cave maps with plotted
sample locations to further enhance repeatability.
An additional four ecological studies (Chapman,
1983; Herrera 1995; Prous et al., 2004; Tobin et al.,
2014) met all criteria with the exception of discussing
conservation implications. One techniques paper
(Wynne et al., 2018) met all evaluative criteria. None
of the conservation studies or biological inventories
met all evaluative criteria. However, one inventory
study (Northup et al., 1994) used a systematic and
repeatable sampling design, applied multiple sampling
techniques, and provided conservation implications.
Systematic sampling
Overall, 48 studies incorporated systematic sampling
into their study design, 50 did not, and 12 studies
did not provide enough information to make this
determination. Of the 43 ecologically focused papers,
26 of these studies applied systematic techniques,
15 did not, and two studies did not provide enough
information to make this determination. For the 56
inventory studies, 15 applied systematic techniques,
while 32 did not; for nine inventory studies, this
could not be determined. Five of seven techniques
studies applied systematic techniques. Two (Borges et
al., 2012; Howarth et al., 2007) of four conservation
papers applied systematic techniques.
Repeatability
Most of the studies (86) did not provide enough
information to replicate the study. The twenty-four
repeatable studies included 15 ecological projects,
five biological inventories, and four techniques papers.
For nearly half of the repeatable studies, maps were
included or referenced; this included seven ecological
studies (Chapman, 1982, 1983; Martín & Oromí, 1986;
Herrera, 1995; Tobin et al., 2014; Iskali & Zhang, 2015;
Lunghi et al., 2014), two techniques papers (Kozel
et al., 2017; Wynne et al., 2018) and two biological
inventories (Lamprinou et al., 2009; Dumnicka et
al., 2015). Additionally, a total of 36 studies (which
included both repeatable and unrepeatable) provided
cave maps with plotted sampling locations or
employed maps to establish sampling intervals. The
combination of both repeatable sampling techniques
and cave maps enables future workers to replicate
those studies with the highest level of accuracy.
Multiple techniques
Multiple sampling techniques were applied in ~51%
of the studies (56 of the 110), while 11 papers did not
provide information on number of techniques used.
Of the 56 studies, 32 applied two techniques, 18 used
three techniques, four employed four techniques, and
two studies applied six techniques (Fig. 3).
Notably, three techniques papers (Weinstein &
Slaney, 1995; Encinares & Lit, 2014; Wynne et
al., 2018) found that applying multiple methods
maximized the completeness of the survey. Weinstein
& Slaney (1995) descriptively compared four sampling
techniques: pitfall trapping (baited and unbaited),
leaf litter traps (wet and dry), timed searches with
interval spacing on transect, and timed direct
intuitive searches in a tropical Australian cave. When
comparing the performance of each technique against
total diversity and abundance values, they found
wet leaf litter traps to be most effective and uniquely
detected two species. Encinares & Lit (2014), when
sampling a tropical Philippine cave by environmental
zone, discovered that a combined wet and dry leaf
36 Wynne et al.
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
Fig. 3. A) Breakdown of studies using multiple techniques (Yes),
one technique (No), and Not known number of techniques. The
‘Not Known’ category was used in the case of three studies where
the authors did not provide an explanation of the methods used.
Of the studies employing multiple techniques, the pie chart (B)
represents the total number of studies per number of techniques
(numbers within each pie slice and color coded in the legend).
Legend reads clockwise starting with largest slice.
litter trap approach was required to maximize the
number of species detected.
Wynne et al. (2018) applied three techniques (live
capture baited pitfall trapping, timed constrained
searches around traps before and after deployment,
and opportunistic searches) across 26 study caves
in the American Southwest and Easter Island, and
applied three additional techniques in selected caves
(bait sampling and timed searches within a 1-m2 grid
established within cave deep zones, timed searches in
nutrient resource sites – moss-fern/ moss gardens in
cave entrances and root curtains in cave deep zones).
They revealed that each method uniquely detected
species, and thus applying multiple techniques (with
multiple site visits) optimized the number of species
detected – in particular, management concern species.
Multiple site visits
Overall, seven studies conducted one site visit, 43
studies applied two or more site visits, eight studies
used a non-standardized approach whereby the
number of site visits varied per cave, and 52 studies
did not disclose the number of site visits. For studies
applying multiple site visits, these were: 15 studies
at two visits, 18 studies between three to eight visits,
nine studies between 10 and 36 visits, and one study
with more than 100 site visits.
For the 43 studies specifically addressing ecological
questions, three studies applied one site visit, 12
conducted two site visits, 10 studies between three
to eight visits, three studies between used 10 and 23
visits, and one study with more than 100 site visits.
Additionally, two studies employed a non-standardized
approach where the number of visits varied across the
caves sampled, while 12 studies did not disclose how
many site visits were conducted.
Quantitative techniques
We found 43 of the 110 studies included some sort
of quantitative analytical framework. Most of the
ecological studies (34 of 43), three of four conservation
papers, six of seven techniques studies applied
quantitative techniques. None of the 56 inventory
papers included quantitative analysis.
Conservation and management
Most studies (68) did not mention conservation
or management. The 42 papers that discussed
conservation were: 16 of 43 ecological studies, all four
conservation papers, five of seven techniques studies,
and 17 of 56 inventory papers. When we examined
this by decade, we found that none of the papers from
1967 through 1979 discussed conservation; however,
for the last two decades, most of the papers (per
decade) addressed conservation issues and impending
human impacts (Fig. 4).
Fig. 4. Frequency in which ‘conservation’ and/ or ‘management’
were mentioned or fully developed by decade for the papers
analyzed. Green bars represent the papers in which these topics
were discussed (Yes), yellow bars indicate the absence of any
discussion on conservation and management (No).
Study design
Cave biologists applied a wide array of techniques
for sampling invertebrate populations. We examined
the most commonly published study designs and
techniques. Based upon our experience, we also
provided information on advantages and disadvantages
of each technique.
Dividing the total length of the cave into sampling
increments occurred in three forms: environmental
zones, predefined intervals, and quadrats. As caves are
strongly zonal habitats, this is often a useful approach
for dividing the cave into more manageable sampling
units. Four principal zones are recognized: two
photic (light and twilight) and two aphotic (transition
and deep; Howarth, 1980). Howarth & Stone (1990)
described a fifth environmental zone, the “bad air”
zone, which is beyond, and technically a subdivision
of, the deep zone. Overall, 25 studies applied a zonal
approach – concentrating on three or more zones, a
variation on this theme, or specifically on the dark
(i.e., deep) zone, which breaks down as follows: 10
of 43 ecological studies, one of four conservation
studies, five of seven techniques studies, and 9 of 56
inventory studies (Table 1). Only two studies (Howarth
37Fifty years of cave arthropod sampling
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
Purpose of study # (%) References
Ecological 9/43 (21%)
Howarth & Stone, 1990; Ashmole et al., 1992; Reeves & McCreadie, 2001;
Dao-Hong, 2006; Silva et al., 2013; Sendra et al., 2014; Iskali & Zhang, 2015;
Araujo & Peixoto, 2015; Růžička et al., 2016
Conservation 1/4 (25%) Borges et al., 2012
Techniques 5/7 (71%) Weinstein & Slaney, 1995; Schneider & Culver, 2004; Krejca & Weckerly, 2007;
Encinares & Lit, 2014; Wynne et al., 2018
Inventory 10/56 (18%)
Barr & Reddell, 1967; Peck & Lewis, 1978; Lewis, 1983; Peck, 1989;
Oromí et al., 1990; Northup & Welbourn, 1997; Buhlmann, 2001;
Wynne & Pleytez, 2005; Serrano & Borges, 2010; Wynne & Voyles, 2014
Table 1. Summary of publications where sampling was conducted by environmental zone.
& Stone, 1990; Borges et al., 2012) applied a study
design examining all four environmental zones. The
remaining studies applied some variation on sampling
by zone.
Interval spacing was applied primarily in four ways:
(1) the cave was sampled at a specific predefined
interval (e.g., sampling at every 5-m); (2) the cave
was subdivided at arbitrary predefined intervals (e.g.,
20-m, 150-m, 225-m, 310-m); (3) a percentage of the
cave’s length was used to define the sampling interval;
or, (4) transects were established along the length
of each cave, and sampled at predefined intervals.
Overall, interval spacing was applied in nine studies.
These consisted of five ecological studies including one
habitat (Prous et al., 2004), two community studies
(Peck, 1976; Novak et al., 2012) and two nutrients
studies (Chapman, 1983; Campbell et al., 2011), as
well as two techniques (Kozel et al., 2017; Wynne et
al., 2018) and two inventory studies (Braack, 1989;
Sharratt et al., 2000).
Seven studies (all ecologically focused) applied a
quadrat approach sampling one cave by: establishing
sampling grids along mud banks to examine
arthropod response to augmented nutrients and
water (Humphreys, 1991); dividing habitat types or
substrates into sampling quadrats (Herrera, 1995;
Zepon & Bichuette, 2017); dividing each study cave
into 3-m quadrats along the length of the cave (Lunghi
et al., 2014); apportioning the cave into five quadrats
(Tobin et al., 2014); establishing sample quadrats/
stations along the length of the study cave (Kur et
al., 2016); and, creating 418 4-m2 grids (surface to
aphotic zone) to examine distribution of arthropods
(Prous et al., 2015).
Sampling techniques
Cave biologists applied an array of methods for
capturing arthropods including direct intuitive
searching, opportunistic collecting, visual searching,
timed and untimed searches, several types of pitfall
trapping, substrate sampling, and using a variety of
baits and leaf litter to attract arthropods (Fig. 5;
Appendix II and III, Supplemental Information;
Table 2). We also provided information on studies
that applied each technique, their methodological
limitations, and functional groups each technique
was most likely to target (Appendix III, Supplemental
Information).
Direct Intuitive Searching (DIS): Direct intuitive searches
(i.e., specifically targeting a microhabitat and/or
environmental zone to address a research question(s)
and/or increase the likelihood of maximizing number
of species detected) were applied in 34 studies. These
microhabitats included flood detritus, penetrating
tree roots hanging from ceilings/walls, guano
deposits, edges of drip pools and ponds, muddy
banks, animal and/or insect carcasses. These areas
were targeted because they were likely to support
high diversity or contained specific functional groups
(e.g., guanophiles). Additionally, researchers applied
this approach to specific environmental cave zones
(typically, the cave deep zone). This method may be
either timed or untimed DIS with defined or undefined
search radius.
Of the 34 studies applying DIS, 16 examined specific
microhabitats, seven studies sampled bat guano
deposits, seven studies searched for subterranean-
adapted arthropods in deep zones, and four studies
used DIS across multiple environmental zones. Eight
studies were timed DIS, while 26 were untimed DIS.
For timed DIS, Ferreira et al., (2000) searched each bat
guano pile encountered within a cave for 30 minutes;
search radius was not defined. Additionally, Wynne et
al. (2018) applied a one-hour DIS in moss-fern/moss
gardens and root curtains without defining a search
radius, and one timed DIS within selected cave deep
zones (10 minutes within an estimated 1-m2 area).
Thirteen of 34 studies employed DIS within
selected habitats as their only technique. Of these,
six were designed to address ecological questions
(Hill, 1981; Trajano, 2000; Silva et al., 2011, 2013;
Zampaulo, 2015; Bento et al., 2016), two studies were
conservation focused (Simões et al., 2014; Silva &
Ferreira, 2015), one was a techniques paper (Gallão
& Bichuette, 2015), and four studies were inventories
(Barr & Reddell, 1967; Holsinger, et al., 1976;
Edington, 1984; Drost & Blinn, 1997).
Visual Searches: Studies applying this technique
explicitly stated “hand collection,” “visible searches,”
“collecting,” and “direct searches;” visual searching
was employed in 29 studies (22 inventory and seven
ecological studies). Overall, hand collecting and/
or using instruments (e.g., aspirators) to facilitate
collection was applied in 13 studies, visual search,
direct search or visual inspection (in none of the cases
was this clearly defined) was applied in six studies,
and some variation on hand collection or visual
search (e.g., “make collections”, “basic collecting”,
“collecting,” etc.) was applied in seven studies, and
visual counting was used in three studies. This
method was combined with other sampling techniques
in four ecological studies and 12 inventory studies.
38 Wynne et al.
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
Group / Method Description Times applied
Hand Sampling
Direct Intuitive Search (DIS)
Surveys targeted to habitats likely to yield highest diversity, which include flood
detritus, edges of pools, streams and flowstone, bat guano and other animal
feces, carrion and/ or cave deep zones; applied in conjunction with a grid/
quadrat system or without defining size of search area; may be timed or untimed;
arthropods collected by hand, aspirator, forceps, or paint brushes.
34
Visual search
Category created due to a lack of information provided; this category is probably
DIS, opportunistic collecting or both; workers described this approach as “visual
searching”, “hand collecting”, “direct searching”, or simply “collecting” with no
additional information provided.
29
Opportunistic collecting Collecting arthropods as encountered while walking through the cave and/or
conducting other tasks. 5
Timed search
Searches were timed and centered around pitfall trapping, leaf litter trap-like
structures (with or without defining search area around traps), or within grids/
quadrats; arthropods were collected via same methods as DIS by examining the
cave floor and/or adjacent wall, and searching beneath rocks and other objects.
16
Untimed search Same as timed searches, but without allocating or reporting a standardized time
spent searching per area. 10
Trapping
Pitfall trapping
A container or tube-like apparatus counter sunk into the cave floor, left in situ
for a specific period of time (typically no more than several days), then traps
and contents are retrieved. The four primary pitfall trap types are baited with or
without a preservative (e.g., alcohol, ethylene, or propylene glycol) and unbaited
with or without a preservative; various baits may be used, refer to text
for more information.
41
Leaf litter
Cleaned (autoclaved recommended), arthropod-free brown leaves from surface
placed upon a wire mesh/ window screen or directly on cave floor, and typically
in damp areas; water delivery systems may be used for xeric areas within caves.
4
Extraction
Substrate sampling
Direct removal of cave sediment, bat guano, leaf litter, and/or flood detritus;
arthropods are subsequently extracted using Berlese/ Tullgren funnels, sorting
and removing by hand, sieving, or a combination thereof.
36
Attractants
Bait
Deployed in specific habitats (typically in cave deep zones to attract troglobionts),
left in situ for a few days, then baits and arthropods selectively removed; baits
typically placed on the cave floor and within cracks and crevices of walls and
ceiling; a variety of baits may be used to attract different feeding guilds, refer to
text for more information.
14
Table 2. Descriptions of the nine primary cave-dwelling arthropod sampling techniques within four methodological groups (hand sampling, trapping,
substrate sampling, and attractants). We recommend standardizing to this terminology and providing more complete descriptions of all techniques
used. Note: Multiple sampling techniques were applied in half the studies reviewed; thus, the “Times Applied” will total more than 110 (i.e., the
number of papers reviewed).
Fig. 5. Total number of times each sampling technique was applied for
the 110 studies reviewed. Because multiple techniques were used for
more than half of the studies reviewed, the contents of this graph total
more than 110. Hand collecting (DIS through Untimed Search in purple
hues), and trapping (pitfall and leaf litter in green hues). Variants of same
color were used to convey similarities across techniques. DIS refers to
'direct intuitive search' (which combined timed and untimed applications).
Visual searching was employed as a single technique
in nine inventory studies and one ecological study.
Additionally, in three cases, arthropods were “visually
counted” (two ecological and one inventory); most of
these studies applied visual counting in combination
with other techniques.
Phrases such as “hand collecting”, “visual searching”,
“direct searching”, or simply “collecting” were used
to describe this technique. This category likely
represents studies applying direct intuitive searches,
opportunistic collecting, or a combination of the two;
unfortunately, there was not sufficient information
provided to confidently make this determination. This
approach is particularly useful for targeting some
predators (in particular, spiders and harvestmen).
Additionally, some negatively phototactic arthropods
will retreat from the observers’ light and may not be
detected.
Opportunistic collecting: Five studies applied what
we considered ‘opportunistic collecting’. With the
exception of two cases (Wynne & Pleytez, 2005; Ferreira
et al., 2000), the remaining studies specifically stated
39Fifty years of cave arthropod sampling
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
arthropods were collected opportunistically (refer to
Reeves et al., 2000; Wynne & Voyles, 2014; Wynne
et al., 2018). This technique involves researchers
walking through the cave, examining rock walls,
floors, and ceilings, and collecting arthropods as they
are encountered (e.g., Wynne et al., 2018).
Timed searches: This adds a systematic component
to visual searches for cave-dwelling arthropods.
Timed searches (TS) may be applied to improve the
thoroughness of trapping or baiting, as well as for
sampling arthropods by cave environmental zone, at
predetermined intervals or within quadrats. When
applied in concert with trapping or baiting, we
recommend further standardizing this approach by
using a fixed grid or radius around the trap or bait.
Timed searches were applied in 16 of the 110 papers
examined. This technique included several variations
viz: coupled TS with pitfall trapping (3 studies);
conducted TS within defined quadrats (5 studies);
applied TS by cave environmental zone (4 studies);
conducted TS at standard intervals (1 study); applied
a total amount of time spent per cave searching
(1 study); and two studies did not provide enough
information to determine how the TS was applied. For
the studies using pitfall trapping, two (Campbell et
al., 2011; Wynne et al., 2018) used fixed radius TS
around the traps prior to deployment and removal,
while Peck (1976) applied an undefined radius, one-
minute search prior to trap deployment and removal.
For 11 studies, timed searches were employed
within study designs using cave environmental zones,
quadrat, or interval sampling approach. Wynne &
Voyles (2014) and Oromí et al. (1990) used TS in the
three primary environmental zones (entrance, twilight,
and “dark”), while Ashmole et al. (1992) applied TS
at selected locations within the twilight and “dark”
zones. Prous et al. (2004) searched for ≥25 minutes
at 2-m intervals. Lunghi et al. (2014), Sharratt et al.
(2000) and Tobin et al. (2014) performed TS using
quadrat sampling at 7.5 minutes, 10 to 25 minutes,
and 30 minutes per quadrat, respectively. Weinstein
and Slaney (1995) employed a TS approach along
five transects, which encompassed the twilight,
transition, and deep zones; their results were
compared to the results of other systematically
applied techniques. Christiansen & Bullion (1978)
applied TS most broadly; whereby they searched
for 30 to 120 minutes along the length of each of their
58 study caves. Both Sendra & Reboleira (2012) and
Sendra et al. (2014) performed one-hour searches
within selected areas, but were not specific about
where these searches occurred.
An added benefit of this technique, when combined
with baited pitfall trapping, is detection of animals
attracted by the bait but not ensnared by the trap.
If consistently applied, it also allows comparisons of
relative population density between caves – at least
for species that are common and whose behavior is
well known (e.g., Wynne et al., 2018).
Untimed searches: Untimed searches (UTS) were
employed in 10 studies and applied in similar
circumstances as timed searches. For five cases,
this protocol was applied in conjunction with either
pitfall or leaf-litter trapping, two studies employed
UTS within a multi-technique sampling frame (not
related to pitfall or leaf litter trapping), and three
studies used UTS as a single technique. For studies
coupling this technique with trapping, three of these
studies used this method both before trap deployment
and prior to trap removal (Poulson & Culver, 1969;
Martín & Oromí, 1986; Wynne & Voyles, 2014),
while two studies (Schneider & Culver, 2004 and
Humphreys, 1991) applied this technique to pitfall
traps and leaf litter traps, respectively, upon trap
removal only. Martín & Oromí (1986) were the only
study to define a search radius (1 to 5-m) around
trapping stations.
The remaining studies used untimed searches within
a quadrat, zonal or zonal sampling design. Krejca &
Weckerly (2007), Dao-Hong (2006) and Prous et al.
(2015) applied UTS as a single technique. Prous et al.
(2015) and Kur et al. (2016) employed this technique
in concert with other sampling methods.
Pitfall trapping: Pitfall trapping (PT) was the most
commonly employed technique (41 of 110 studies;
Fig. 5). Four approaches were used including baited
with or without a preservative (e.g., alcohol, ethylene,
or propylene glycol), and unbaited with or without a
preservative. Traps with preservative result in 100%
take (i.e., kill) of animals that fall into the trap. Traps
without a preservative maintain captured animals alive
until examined by researchers. However, captured
animals may escape, be eaten by other animals, or
die and begin to decompose before retrieval (Weeks
& McIntyre, 1997). Weinstein & Slaney (1995) used
glass jars with a constricted mouth since the curved
neck should limit escape.
Pitfall traps were typically counter-sunk within the
cave sediment and/or rocky substrate to minimize an
exposed lip that might prevent capture of arthropods.
When this was not possible, researchers built ramps
around each trap using local materials (e.g., rocks,
wooden debris, etc.) to provide invertebrates with
easier access to the trap (e.g., Ashmole et al., 1992;
Wynne & Voyles, 2014; Wynne et al., 2018). Campbell
et al. (2011) developed a ramped PT design (trap was
placed on the ground surface with plastic ramps
leading to PT). Růžička et al. (2016) applied a free-
hanging PT design, which attached to the walls of
a vertical deep pit; these traps consisted of a ramp
leading from the wall onto a platform with PT at center.
Of the 41 papers reporting on the use of pitfall
traps, one study used both baited and unbaited
traps (without preservative), 17 studies applied
baited traps without preservative, 13 used bait with
a preservative, three studies applied unbaited traps,
five employed traps with preservative only, and two
studies stated only that traps were used (Fig. 6).
Various types of bait were used including rotten
liver, cheese, banana, and peanut butter (Table 3).
Four studies suspended baits (either cheese or liver)
over a “Turquin” liquid, which served as both an
attractant and preservative. Serrano & Borges (2010)
described Turquin as a mixture of 1000-ml of dark
beer, 5-ml acetic acid, 5-ml formalin, and 10-g of
chloral hydrate. One study used PT with a “variety
40 Wynne et al.
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
Bait type References
Rotten liver Poulson & Culver, 1969; Richards, 1971; Peck, 1976;
Welbourn, 1978; Martín & Oromí, 1986; Ferreira et al., 2000
Cheese
Richards, 1971; Chapman, 1980; Oromí et al., 1990;
Ashmole et al., 1992; Lewis et al., 2003; Schneider & Culver,
2004; Serrano & Borges, 2010; Sendra & Reboleira, 2012;
Sendra et al., 2014
Peanut butter Wynne & Voyles, 2014; Phillips et al., 2016; Wynne et al.,
2018
Mixture of rice, fish, and meat Chapman, 1982
Combination of meat, cheese, tinned fish,
damp biscuits, jam, bird carcasses, human
feces
Chapman, 1980
Ripe banana Weinstein & Slaney, 1992
Beef liver, banana Campbell et al., 2011
Oats, sugar, margarine Reddell & Veni, 1996
Cheese and mushrooms Howarth et al., 2007
Rotten beef with apple and cherry/
maraschino essence Kozel et al., 2017
“Bone” Bertolana et al., 1994
Table 3. Summary of bait types used in pitfall traps.
of attractants” (Araujo & Peixoto, 2015). Two studies
used PT with only a preservative – formalin (Dessen et
al., 1980) and a 50/50 water/ethanol mixture (Iskali
& Zhang, 2015). Two studies (Reeves, 2001; Deleva
& Georgiev, 2015) used ethylene glycol, which served
as both an attractant and preservative. One study
used cheese and ethylene glycol as a bait/ attractant
(Isaia et al., 2011). Wynne & Voyles (2014) used
live capture baited and unbaited PT and Wynne et al.
(2018) used live capture PT; both studies baited with
peanut butter.
Functional groups most often captured in PT
include detritivores and omnivores, as well as some
predators and other functional groups. However,
some cavernicoles, especially many troglomorphic
species, do not enter pitfalls (Kuštor & Novak, 1980;
Bell et al., 2007). Both Barber (1931) and Valentine
(1941) favored baited PT for capturing cavernicolous,
omnivorous, and carrion beetles due to its quick
return rate. Wynne et al. (2018) reported that most
(70% of beetle morphospecies) were detected with
baited traps. Conversely, spiders and volant species
may escape from live capture pitfalls.
Other considerations include anticipating possible
disturbance by rats or other mammals (including
humans), as well as mitigating the potential harmful
effects of this method on the cave resources. Placing
cages around each trap may limit rodent disturbance,
but may also prevent access by targeted animals. To
limit human disturbance, hiding traps or deploying
in cryptic areas may help. Importantly, efforts
must be made to prevent disturbance to other cave
resources (e.g., archaeological, cultural, geologic,
and paleontological) when placing and removing
traps. In some cases, physically disturbing the cave
floor or sediments to install traps may be prohibited.
Additionally, many preservatives applied in the past
(e.g., picric acid, choral hydrate, and formalin) are
now regulated chemicals and considered dangerous to
use in caves. Propylene glycol with the proper mixture
of ethanol to break the surface tension is a preferred
preservative for most invertebrates and is considered
environmentally safe.
Substrate sampling: Substrate sampling involves
collecting samples of sediment (e.g., soil, guano, or
organic material), and then extracting specimens
using a variety of techniques. The most common
extraction methods include using Berlese or Tullgren
funnels, floating in a liquid, and sieving. Thirty-six
studies applied this approach including: 16 studies
examined bat guano; eight studies sampled sediment;
five sampled “organic debris” or “detritus;” two studies
sampled leaf litter; one study examined both sediment
and bat guano; one study sampled oilbird (Steatornis
caripensis Humboldt, 1817) seed beds and bat guano
deposits; and, three studies did not state clearly what
substrate was sampled.
Seventeen studies sampled substrate systematically.
Of note, researchers applied the following methods:
(i) a percentage or specific quantity of sediment
(Welbourn, 1978; Northup et al., 1994; Lamprinou et
Fig. 6. Application of pitfall trapping across the 41 studies
employing this technique. Legend reads left to right; pie
chart reads clockwise starting with largest slice at bottom.
41Fifty years of cave arthropod sampling
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
al., 2009; Dumnicka et al., 2015) or bat guano (Braack,
1989; Pellegrini & Ferriera, 2013; Iskali & Zhang,
2015) was collected; (ii) sediment (Herrera, 1995) or
guano samples (Negrea & Negrea, 1971) were divided
into subsamples by depth; and, (iii) a percentage of
each bat guano pile was sampled (Ferreira & Martins,
1999; Ferreira et al., 2000). The remaining six studies
applied a systematic design, but did not provide the
quantities of materials collected.
Substrate sampling is used primarily for collecting
microarthropods. However, if samples are not
handled properly and processed in a timely manner,
they can become damaged resulting in few to no
animals extracted. Animals most likely to be detected
are guanophiles, edaphobites, detritivores, and their
predators.
Bait sampling: Typically, bait sampling involves
deployment of baits directly onto cave floors, walls,
and ceilings, as well as within cracks and fissures,
and is typically applied to detect subterranean-
limited (i.e., troglomorphic) species. Fourteen studies
reported using baits. These included baits: used
in cave deep zones only in six studies (Peck, 1989;
Buhlmann, 2001; Howarth et al., 2007; Faille et al.,
2015; Kur et al., 2016; Wynne et al., 2018); deployed
along the length of caves in three studies (Peck,
1982; Reeves & McCreadie, 2001; Pape & O’Connor,
2014); employed in select cave zones in one study
(Howarth & Stone, 1990); and, placed at the bottom of
vertical pits in another study (Schneider et al., 2011).
Three studies did not provide specific details on the
placement of baits.
Baits are often chosen based on their potential to
attract specific taxa of interest. A variety of baits have
been used including liver-based cat food (Buhlmann,
2001), chicken liver (Reeves & McCreadie, 2001),
sweet potato (Howarth & Stone, 1990), wooden blocks
(plant species not defined; Pape & O’Connor, 2014),
dung and carrion (type of carrion not identified; Peck
& Peck, 1981; Peck, 1989), liver and “carrion” (type
not defined; Holsinger & Peck, 1971), carrion and
cheese (types not defined; Peck, 1982), cottage cheese
with bread (Kur et al., 2016), commercially-purchased
dead “white lab rats” (Schneider et al., 2011), sweet
potato, native tree branches, chicken liver and fish
entrails (Wynne et al., 2018), cat food, chicken liver,
dung, rotten apples and cheese (Reeves et al., 2000),
sweet potato, blue cheese, mushroom and oatmeal
(Howarth et al., 2007), and moss, rotten wood and
cheese (types not described; Faille et al., 2016). For all
bait types, efforts should be made to remove residues
once sampling is completed.
Leaf litter attractant: Leaf litter was used both as an
attractant and habitat substrate in four studies. The
litter serves as habitat, cover and nutrient source for
fungivores, detritivores, omnivores and their predators.
Three studies (Humphreys, 1991; Weinstein & Slaney,
1995; Encinares & Lit, 2014) placed leaf litter within
a trap structure, while Schneider et al. (2011) placed
leaf litter directly on the cave floor. Humphreys (1991)
used leaf litter traps with a water delivery system to
keep the litter wet and facilitate leaf decomposition;
he examined the effects of nutrient subsidies to caves.
Whereas, Weinstein & Slaney (1995) and Encinares
& Lit (2014) compared the efficacy of using wet and
dry leaf traps. If using a water drip system, checking
and maintaining traps will depend upon the amount
of time water can be actively delivered before the
water runs out. Schneider et al. (2011) reported that
millipedes and collembolans were most abundantly
detected groups in their study.
Leaf litter should be cleaned before deployment in
caves. Encinares & Lit (2014) used a Berlese funnel to
extract arthropods prior to using bamboo. However,
autoclaving leaves would ensure the material does not
harbor harmful and unwanted organisms, such as
Beauveria bassiana (Bals.-Criv.) Vuill. (1912) (Gunde-
Cimerman et al.,1998) and Metarhizium anisopliae
(Metschnikoff, 1879) Sorokin, 1883 (Zhang et al.,
2017), which are entomopathogens; both have broad
host ranges and are widely used for pest control in
surface environments. Insect predators (Howarth &
Moore, 1984) and alien species competitors (Wynne
et al., 2014) may also be introduced. Failure to apply
this cleaning step may also result in captured surface
arthropods being incorrectly classified as cavernicoles.
For reference, Slaney & Weinstein (1996) provided an
illustration of their trap design.
Light trapping & Dry ice: Three studies used
incandescent white light trapping (McClure et al., 1967;
Chapman, 1980; Peck, 1984). Peck (1984) indicated
his light suction trap designed to specifically target
Diptera was unsuccessful. While this technique may
be useful in attracting some arthropods like certain
species of Diptera, Lepidoptera, and Coleoptera, using
full spectrum lighting to attract arthropods hasn’t
resurfaced in the literature (at least based upon our
review) in over 30 years. However, Reeves (2001)
employed both black lights and dry ice for trapping
arthropods, although there was no discussion
specifically stating the efficacy of these techniques.
DISCUSSION
As cavernicolous arthropod inventories and
question-driven research projects are conducted in
the future, we recommend structuring these studies
in a manner that maximizes scientific inference
and provides the information necessary to make
evidence-based management decisions. To this end,
future studies should include the following elements:
systematic experimental design; repeatability (in that
the methods are thoroughly reported); use of multiple
techniques; and use of multiple site visits (Wynne et
al., 2018).
Most of the studies reviewed did not include a
clearly discernable a priori systematic study design.
Culver & Sket (2002) even questioned the utility of
such an approach for both sampling and monitoring
cavernicolous arthropods. Certainly, low population
densities and the heterogeneous nature in which
microhabitats and nutrients are distributed within
caves, as well as the seasonal influx of nutrients
(e.g., bat guano and flood detritus), have presented
researchers with challenges for both optimal sampling
and monitoring. Nonetheless, for cave biology to
42 Wynne et al.
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
progress, systematically applied experimental design
and sampling efforts are necessary both to make results
comparable across caves and to advance hypothesis-
driven studies. For monitoring cave-dwelling arthropod
species of concern, the U.S. Fish and Wildlife Service
has partially addressed the heterogeneity issue by
requiring a suite of environmental conditions be met
and surveys conducted during the most appropriate
season, as well as providing a checklist of suitable
conditions for troglomorphic arthropods (USFWS,
2006). We recommend that sampling also include an
intensive systematic approach to optimally detect the
greatest number of species, as well as potentially detect
more cryptic animals (such as troglobionts; Wynne et
al., 2018).
Only 24 studies were repeatable (i.e., workers
clearly documented their sampling techniques and
experimental design). For cave arthropod studies
to more solidly advance our understanding of cave
communities both temporally and spatially, researchers
should thoroughly document how their field data were
collected. Without this step, meaningful quantitative
comparisons across caves and regions cannot be
made and evidence-based conservation planning and
monitoring of sensitive taxa and/or communities
cannot be assured.
We recognize that optimal sampling methods change
over time as technology and our understanding of
cave ecology advances; therefore, we hope that this
paper will serve to advance future work. We realize
the methods applied must be appropriate to fulfill the
objectives of the particular study. Thus, one set of
protocols will unlikely be suitable for all cave studies.
Furthermore, the complexity of caves often requires
that study designs be modified in the field to address
local cave conditions.
That said, we recommend further standardization
of sampling terminology (refer to Table 2). The most
substantial gray areas in our review were the lack of
clarity on use of the terms: visual searches, direct
searches, opportunistic collecting, and direct intuitive
searches. 'Visual searching' was either 'opportunistic
collecting' or 'direct intuitive searching;' however,
because there was not sufficient information to
explain what the workers meant by ‘visual searching,’
we created the visual search category. Furthermore,
we also found inconsistencies in how direct searches
were described. Thus, when information was lacking,
studies using direct searches were included in
the visual search category. Providing a sufficient
description of the sampling methods applied will be
critical to avoiding confusion in the future.
Clear descriptions of the study design and the
sampling methods can be further enhanced by
including figures of sampling locations plotted
on cave maps for the sake of repeatability. Given
that most journals offer archiving of data as online
supplemental information, this is a methodological
perk available to most researchers, often at no extra
cost. Thus, inclusion of this information will enable
future workers to know the precise locations of past
sampling efforts, and may use this information for
both replicating experiments and establishing future
monitoring strategies for resource management.
However, researchers must adhere to federal and local
agencies and regulations in the countries in which
they work regarding the publication of potentially
sensitive information (e.g., USC, 1988). Research
permits for cave access often include a nondisclosure
clause regarding the dissemination of sensitive data
(e.g., cave names and in some cases, cave maps). When
such guidance is not provided, we recommend using
a decision tree like the one developed by Tulloch et al.
(2018) to examine the risks and benefits associated
with disclosing potentially sensitive information.
Of the papers included in this analysis, 10 studies
conducted 10 or more site visits per cave. We recognize
many biological inventories are designed to visit as
many caves as possible in a short time to establish
a baseline for site specific or regional diversity.
Unfortunately, in most cases it is unlikely enough
site visits were conducted to reasonably characterize
arthropod diversity or community structure. For
example, Wynne et al. (2018) intensively sampled 26
caves (10 caves each in two southwestern U.S. national
monuments and six caves at Rapa Nui National Park,
Easter Island, Chile), where they conducted between
two to six site visits per cave. For each region, they
pooled data across all caves and generated species
accumulation curves – none of the curves for any of
the regions exhibited signs of asymptotic behavior
(Wynne et al., 2018). Thus, while biological inventories
are of critical importance in establishing baseline
information, as well as being helpful as a hypothesis
generating exercise for future work, these data are
typically quite limited in their ability to fully characterize
arthropod communities.
Multiple site visits may be especially critical to
more thoroughly inventory troglomorphic arthropods.
For a cave in Williamson County, Texas, Krejca &
Weckerly (2007) reported that despite intensive
surveys by trained cave biologists an undescribed
pseudoscorpion species was discovered upon the
40th visit to the cave. While not directly applicable to
terrestrial cave-dwelling invertebrates, Sket (1981)
and Culver et al. (2004) reported a new stygobiont
(belonging to a new genus) after over one hundred
site visits to a well studied cave in Slovenia. Granted
it may be impossible for most studies to conduct
40 to 100 site visits per cave, but these examples
underscore the need to conduct multiple site visits to
most thoroughly define cave communities.
When sampling techniques are applied singly,
the study may (a) fail to identify species of potential
management concern (e.g., troglobionts and relict
species), and (b) not be effective for long-term
monitoring to detect changes related to anthropogenic
impacts or stochastic events. Through their work,
Wynne et al. (2018) found that the six techniques
uniquely identified morphospecies; had multiple
techniques not been applied, eight new species of
presumed cave-restricted arthropods on Easter
Island (Wynne et al., 2014), and the range expansions
of two species of two tiphiid wasps in west-central
New Mexico, would not have been detected (Wynne,
2013). In general, numerous studies (e.g., Muma,
43Fifty years of cave arthropod sampling
International Journal of Speleology, 48 (1), 33-48. Tampa, FL (USA) January 2019
1945; Ashmole & Ashmole, 1987; Basset et al., 1996;
Wynne et al., 2018) have shown that applying multiple
techniques resulted in the detection of a greater
number of individuals and species than studies
employing only one technique.
While it is often quite difficult to identify the number
of site visits and the suite of techniques required to
best capture cave arthropod diversity, Wynne et al.
(2018) recommended applying as many sampling
techniques and conducting as many site visits as
possible. Species accumulation curves and species
richness estimators (see Magurran, 2004) are also
recommended tools for both gauging the efficacy of
sampling efforts, and identifying areas requiring
additional inventories. In most cases, Wynne et al.
(2018) reported that species accumulation curves
were more asymptotic (i.e., flatter) for all techniques
combined (they applied a total of six techniques) than
for curves generated using data from single techniques.
Schneider & Culver (2004), who focused their efforts
on troglomorphic arthropods, reported none of their
species accumulation curves neared asymptotic
behavior. Reporting similar non-asymptotic behavior,
Gallão & Bichuette (2015) emphasized that sensitive
subterranean-adapted species may be overlooked
due to limited sampling; this could result in making
incorrect management decisions based upon
incomplete information.
To address the dilemma of incomplete surveys,
Howarth & Ramsay (1989) recommended the use of
‘indicator species’ as a proxy for making management
decisions. Specifically, discovering a cave passage
with suitable environmental conditions associated
with one or more significant cavernicoles may be
sampled to gain inference into whether the cave
warrants protective management or should be more
fully studied.
While most of papers examined (~62%; or 68 of
110) did not discuss conservation and management
implications, we acknowledge recommendations
may have been made directly to resource managers
and thus were not reported in the peer-reviewed
publications we reviewed. Furthermore, conservation
may simply not have been a goal of some studies,
especially for those papers published before the
amendment to the U.S. Endangered Species Act in
1978, which expanded the Act to include invertebrate
species (USC, 1973). Subsequently, our review may
underestimate the contributions made by some of
these studies to conservation. However, with the
rising anthropogenic impacts facing cave ecosystems
globally, we maintain that inclusion of this information
in the published literature is essential to aid in further
developing the field of cave biology and promoting
improved management and policy strategies.
Given the sensitivity of most cave communities
and troglomorphic species to human disturbance,
conservation and management should be at the
forefront of cave biology. Through improvements
in methodological reporting, systematic sampling
designs using multiple techniques, and reliance on
species accumulation curves to guide the number of
site visits required to establish a reasonable baseline,
cave biologists will both strengthen their ability to
make more robust statistical inference and develop
sound management recommendations based upon
the best available data and resultant science.
ACKNOWLEDGEMENTS
We sincerely thank Jeffery Foster and Thomas Sisk
of Northern Arizona University for providing comments
and editorial suggestions. David Culver and Matthew
Niemiller peer-reviewed this paper. Melanie W. Gregory
and Alan Campbell offered fructuous discussions on
color schemes for figures. Their contributions greatly
improved the quality of this manuscript.
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... Immatures of Valenciolenda fadaforesta were located visually and by direct intuitive searching (DIS, sensu Wynne et al. 2019) within an undefined search radius, yet with special emphasis around root patches, in the deep cave zone at the type locality of the species: Murciélagos Cave, in Les Rodanes Municipal Natural Park which is located in Villamarchante, Valencia, Spain. Specimens were collected by hand during three visits to the cave, and immediately transferred to vials containing 70% ethanol (for dates and number of specimens see Table 1). ...
... Immatures of Valenciolenda fadaforesta were located visually and by direct intuitive searching (DIS, sensu Wynne et al. 2019) within an undefined search radius, yet with special emphasis around root patches, in the deep cave zone at the type locality of the species: Murciélagos Cave, in Les Rodanes Municipal Natural Park which is located in Villamarchante, Valencia, Spain. Specimens were collected by hand during three visits to the cave, and immediately transferred to vials containing 70% ethanol (for dates and number of specimens see Table 1). ...
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All nymphal instars of the recently discovered troglobitic planthopper species Valenciolenda fadaforesta Hoch & Sendra, 2021 are described. This represents the first documentation of the complete postembryonic development of any species in the family Kinnaridae. Characters of the external morphology are described and illustrated, and a key to the instars are provided to facilitate discrimination among the different nymphal stages. While V. fadaforesta nymphs share certain synapomorphies with other Fulgoromorpha (except the Tettigometridae), e.g., the cog-wheel structures of the metatrochanters, other characters may be correlated with the subterranean way of life of the species, and thus be autapomorphic, such as the absence of compound eyes in all instars.
... The samplings were carried out by direct intuitive search (DIS) and manual collections with the aid of tweezers, brushes, and entomological nets (Wynne et al., 2019). The specimens observed during collections were accounted for and plotted in a schematic map of the cave according to the methodology proposed by Ferreira (2004), which has been used in previous studies (Souza-Silva et al., 2011a). ...
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... One of the quadrants was positioned near the main cave entrance, in the twilight zone (indirect light incidence), and the other was positioned in the deep cave zone (no light), as far away from the main entrance as possible. The sampling in each of the quadrants was conducted by Direct Intuitive Search (DIS) (Wynne et al. 2019), so that all individuals encountered were captured. For this purpose, tweezers, brushes, and suckers were used. ...
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... The invertebrate sampling was carried out in the transects and quadrats separately using the direct intuitive search -DIS (Wynne et al., 2019;Souza-Silva et al., 2021), and active collection with the aid of forceps and brushes moistened with 70% alcohol. Sampling was conducted, in both transects and quadrats, by a team of two biologists with experience in caving and manual collection of invertebrates. ...
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... 764 uma maior cautela (TOBIN et al., 2013;SCHNEIDER;CULVER, 2004). Como já discutido em outros estudos, para um levantamento de dados mais robusto, recomenda-se utilizar mais de uma técnica de amostragem e preferencialmente mais de um evento amostral (WYNNE et al., 2019). ...
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Two new troglomorphic pseudoscorpion species, Bisetocreagris maomaotou sp. nov. (Family Neobisiidae) and Tyrannochthonius chixingi sp. nov. (Family Chthoniidae) are described from one cave in the tower karst of northern Guangxi Province, China. This cave is located at close proximity to a village and an adjacent urban area. As with many caves in the South China Karst, this feature occurs at an elevation slightly above agriculture and rural activities; thus, we suggest it may be partially buffered from human activities in the lowland areas. We discuss the likelihood of narrow range endemism and provide research and conservation recommendations to guide future management of these two species.
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Aim: Identify the optimal combination of sampling techniques to maximize the detection of diversity of cave-dwelling arthropods. Location: Central-western New Mexico; northwestern Arizona; Rapa Nui, Chile. Methods: From 26 caves across three geographically distinct areas in the Western Hemisphere, arthropods were sampled using opportunistic collecting, timed searches, and baited pitfall trapping in all caves, and direct intuitive searches and bait sampling at select caves. To elucidate the techniques or combination of techniques for maximizing sampling completeness and efficiency, we examined our sampling results using nonmetric multidimensional scaling (NMDS), analysis of similarity (ANOSIM), Wilcoxon signed-rank tests, species richness estimators and species accumulation curves. Results: To maximize the detection of cave-dwelling arthropod species, one must apply multiple sampling techniques and specifically sample unique microhabitats. For example, by sampling cave deep zones and nutrient resource sites, we identified several undescribed cave-adapted and/or cave-restricted taxa in the southwestern United States and eight new species of presumed cave-restricted arthropods on Rapa Nui that would otherwise have been missed. Sampling techniques differed in their detection of both management concern species (e.g., newly discovered cave-adapted/restricted species, range expansions of cave-restricted species and newly confirmed alien species) and specific taxonomic groups. Spiders were detected primarily with visual search techniques (direct intuitive searches, opportunistic collecting and timed searches), while most beetles were detected using pitfall traps. Each sampling technique uniquely identified species of management concern further strengthening the importance of a multi-technique sampling approach. Main conclusions: Multiple sampling techniques were required to best characterize cave arthropod diversity. For techniques applied uniformly across all caves, each technique uniquely detected between ~40% and 67% of the total species observed. Also, sampling cave deep zones and nutrient resource sites was critical for both increasing the number of species detected and maximizing the likelihood of detecting management concern species.