Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 January 2023 | 15(1): 22471–22478
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
https://doi.org/10.11609/jott.7259.15.1.22471-22478
#7259 | Received 08 March 2021 | Final
received 20 December 2022 | Finally accepted 05 January 2023
A
comparison of four sampling techniques for assessing species richness of adult odonates at riverbanks
Apeksha Darshetkar
1, Ankur Patwardhan 2 &
Pankaj Koparde 3
1 230/12/4, Atharva
Apartment, Shukrawar Peth, Pune, Maharashtra 411002,
India.
2 Annasaheb Kulkarni Department of Biodiversity, Abasaheb Garware College, Pune,
Maharashtra 411004 India.
3 Faculty of
Sustainability Studies, Dr. Vishwanath Karad MIT
World Peace University, Pune, Maharashtra 411038, India.
1 adarshetkar25@gmail.com
(corresponding author), 2 ankurpatwardhan@gmail.com, 3 pankaj.koparde@mitwpu.edu.in
Editor: Albert G. Orr,
Griffith University, Nathan, Australia. Date
of publication: 26 January 2023 (online & print)
Citation: Darshetkar,
A., A. Patwardhan & P. Koparde (2023). A comparison of four
sampling techniques for assessing species richness of adult odonates
at riverbanks. Journal of Threatened Taxa 15(1): 22471–22478. https://doi.org/10.11609/jott.7259.15.1.22471-22478
Copyright: © Darshetkar
et al. 2023. Creative Commons Attribution 4.0 International License. JoTT allows
unrestricted use, reproduction, and distribution of this article in any medium
by providing adequate credit to the author(s) and the source of publication.
Funding: The project was funded by the
International Dragonfly Fund, Germany.
Competing interests: The authors
declare no competing interests.
Author details: Apeksha Darshetkar (AD) is a MSc in Biodiversity
from Garware College. She is involved in various environmental education and capacity
building programs working with
multiple organizations. Currently
she works with InSearch Outdoors. Dr. Ankur Patwardhan (AP) is
Head, Dept. of Biodiversity at Garware
College & Chairman, Board of Studies in Biodiversity
at Savitribai Phule Pune University. In honorary capacities, he coordinates
research activities at RANWA, a NGO dedicated to nature conservation in Pune. He is an expert member of the
Monitoring group of CAMPA, MoEF&CC,
GoI. Dr. Pankaj Koparde (PK) is an evolutionary ecologist interested
in understanding patterns
& processes in species distribution.
He works as an Assistant
Professor at MIT-WPU Pune. He is one
of the admins of DragonflySouthAsia and heads Chatur Ullu
Lab, a research group dedicated
to research-based conservation. His research interests
include urban ecology, conservation, citizen science, and biodiversity informatics.
Author contributions: AD collected and analyzed data, and wrote the
initial draft of the
manuscript. PK conceptualized the
study, analyzed data, and helped with
writing and editing the manuscript. AP helped with logistics for the project, provided lab facilities, and edited the
manuscript.
Acknowledgements: This work was
partially supported by the International Dragonfly Fund under a grant awarded
to Dr. Pankaj Koparde and a
BitGiving crowd-funding campaign run by Apeksha Darshetkar. This project
received support from Biodiversity department, Garware
College, Pune.
Abstract: Members of the insect
order Odonata are known as good ecological indicators. Many are sensitive to
habitat modifications and are easily monitored for use in environmental
assessment studies. Rapid assessments rely on efficient sampling techniques. However,
there is limited information available on sampling techniques for adult odonates, and protocols require evaluation. To do this, we
standardized counting methods during sampling of odonates
from August to November 2016 at the Mula River, Pune,
India. We used four counting techniques; full-width belt transect (FWBT),
full-circle point count (FCPC), half-width belt transect (HWBT), and
half-circle point count (HCPC). For HWBT and HCPC areas facing the river were
sampled, and for each technique we took multiple temporal replicates. We
compared species detected per unit time, species detected per unit area, new
species detected per unit time, and new species detected per unit area.
Additionally, we compared species estimates. With HCPC we detected the maximum
number of species and new species per unit area, whereas FWBT returned maximum
coverage of recorded species. We recommend our proposed techniques be
considered in the future across various habitats to decide the most suitable
sampling strategy for the different habitats or situations.
Keywords: Dragonfly, ecological
assessment, point count, species estimates, transect, urban wetland.
Introduction
Odonata depend on
freshwater ecosystems to complete their life cycle, as their larvae are aquatic
(Corbet 1962). This dependency on freshwater ecosystems makes odonates good aquatic and terrestrial bio-indicators
(Corbet 1962; Simaika & Samways 2011, 2012; Stoks & Cordoba-Aguilar 2012; Monteiro-Júnior et al.
2014; Chovanec et al. 2015). Assessment of odonates primarily deals with sampling adults and is highly
recommended (Kutcher & Bried 2014; Valente-Neto et al. 2016), because in many cases collecting and identifying
adults is easier than finding larvae or exuviae,
especially in the case of bio-monitoring projects (Córdoba-Aguilar &
Rocha-Ortega 2019) except for gomphids (da Silva-Méndez et al. 2022).
Identification keys and field guides for adult odonates
are mostly available, while larval identification is more problematic for many
species, as the Indian Odonata literature lacks larval and exuvial
identification keys (Kumar & Khanna 1983). Another aspect is the
availability of comparable data over more extensive spatial coverage. Adult odonate data can be relatively easily obtained for
comparison purposes, making adult sampling more popular than larval or exuvial
or combined sampling.
Odonates play a crucial role as predators in freshwater
ecosystems. They are very useful as ecosystem service providers, especially in
urban wetlands which are the freshwater ecosystems available in human-modified
landscapes (Bolund & Hunhammar
1999; Angold et al. 2006; Suhling
et al. 2015, Córdoba-Aguilar & Rocha-Ortega 2019). Studying such freshwater
ecosystems is vital, as they may provide information about understanding the
pace of urbanization and species losses (McKinney 2008; Johnson et al. 2013,
Córdoba-Aguilar & Rocha-Ortega 2019), aiding conservation management.
Various methods have
been employed to study odonates, such as collecting
individuals with sweep nets, and using lights and malaise traps, line
transects, and point counts (Almeida et al. 2013; Bried
& Ervin 2006; Bried et al. 2012; Patten et al.
2015). Currently, relatively little published literature is available on
standardized methods for sampling adult odonates.
Taking transect surveys on a fixed route is the most popular method
(Córdoba-Aguilar & Rocha-Ortega 2019). Quadrangular or rectangular survey
plots have been used by some ecologists. For ponds and wetlands, sweep-nets
have been used (Oertli 2008). Point counts (PC) have
been used especially across pond ecosystems. Distance sampling methods have
been used in rainforest ecosystems with scattered water resources (Oppel 2006). Random visual scanning method and visual
scanning following a transect have been suggested for counting adult odonates (Sutherland 2006). For sampling adult odonates at rivers and streams, transects along the
riparian zone are suggested (Panzer et al. 2005; Smallshire
& Beynon 2010). Aerial netting is more useful when specimen collection is
the primary aim. For systematic sampling, to come up with diversity indices and
species estimates, non-invasive methods such as transects are expected to be
more useful (Oppel 2006). Presently available
sampling protocols have seldom been critically evaluated to identify the most
efficient protocol that captures a reliable estimate of the species richness in
a habitat.
In the present study,
we tried to standardize a method of counting adult odonates
at the riverbanks of a tropical urban river. We compared four different
sampling techniques to check the best method which provides a complete
assessment of the species richness of the selected urbanized site. This
short-term study provides a baseline for future research on counting adult odonates.
Materials and methods
Sampling Methods
The study area was
the riparian zone of the Mula River, Aundh, Pune,
Maharashtra, India (18.5687 N, 73.8198 E, 551 m). The study site is present in
the city and is much disturbed by humans. They carry out activities like cattle
grazing nearby, and polluting the river by washing their clothes, among other
activities. The study duration was four months from August 2016 to November
2016. We used direct observations for the identification of adult odonates at the site with the aid of binoculars. We
identified species using field guides (Subramanian 2005) and referred to
previously published material from the Pune area (Kulkarni & Subramanian
2013; Koparde 2016). The habitat sampled consisted of
the stream bed and marginal vegetation. We used a transect length of 300 m, as
at the study site it was the length that we could walk continuously without any
breaks in the transect due to water level, mud, garbage, and uneven terrain. We
standardized point count timing to two mins after a pilot survey. During our
pilot sampling, we observed, while walking the transects, odonates
aggregated in high numbers in the area facing the river rather than inland. We
observed a similar pattern while conducting point counts. Therefore, we decided
to add a variant in method, where we maximized the sampling effort at the
riverside. Finally, we used two main sampling methods (belt transect and point
count) with a variant in each (Table 1, Figure 1, Figure 2). We used two
variants of the belt transect method:
1. Full-width belt transect, where we counted the adult individuals of the
species present on the banks inland and at the riverside covering the 300 m
belt transect (Table 1, Figure 1).
2. Half-width belt transect, where we counted the adult individuals of the
species present only at the riverside covering the 300 m belt transect (Table
1, Figure 1).
3. Full-circle point count, where we counted the adult individuals of the
species present in a circle of 5 m radius across a 300 m straight line at each
25 m interval (Table 1, Figure 2).
4. Half-circle point count, where we counted the adult individuals of the
species present in a half circle facing the riverside across a 300 m straight
line at each 25 m interval (Table 1, Figure 2).
Data Analysis
We performed the
analysis in the statistical software PAST (v.3.) (Hammer et al. 2008) and R (R
core team 2014). We compared the cumulative number of species detected per unit
area, cumulative number of species detected per unit time, new species added
per unit area, and new species added per unit time. We used nested analysis of
variance (ANOVA) to compare the four techniques: FWBT, HWBT, FCPC and
HCPC. Additionally, we used box-plots to visualize the differences in the
capture of parameters across the techniques. We calculated species estimates
CHAO1 (Chao 1984; Colwell & Coddington 1994), CHAO2 (Chao 1987; Colwell
& Coddington 1994), Jack1 and Jack2 using Biodiversity Pro v2.0 (McAleece et al. 1997) for each technique and compared it
with the cumulative number of species observed per technique. We kept a
separate list of off-sampling observations to compare with our data and species
estimates.
Results
In total, we recorded
19 odonate species at the site; a complete list of
species detected is given in Supplementary Table 1. We obtained statistically
significant results for comparisons among techniques (Supplementary Table 2
& 3) for species detected per unit area (F = 28.79, P <<0.0001)
(Figure 3A) and new species added per unit area (F = 5.15, P = 0.0012) (Figure
3B), through nested ANOVA (Supplementary Table 3).
The proportion of
species detected and new species added per square meter were highest for HCPC
(Figure 3A, 3B). There was no significant difference across techniques for
species detected and new species added per minute (P > 0.3) (Figure
3C, 3D). We found through species estimate analysis all techniques except FWBT
produced conservative estimates (Table 2).
Discussion
Given equal effort in
terms of replicates, HWBT, FCPC, and HCPC methods produced comparable ranges of
species estimates, whereas the FWBT method had the maximal coverage (89.5% of
19) of the total number of species observed at the site (Table 2). Overall,
belt transects had higher coverage of total species richness (80–90 %) than
point counts (63–74 %), indicating that belt transects are highly
time-efficient techniques, suggesting the reason for their popularity amongst
ecologists. Our comparison of sampling techniques revealed that through the
HCPC technique, we recorded significantly more species per unit area (Figure 3A
& 3B, Supplementary Table 1 & 2). A reason for this is probably the
more intensive search (two minutes) in a smaller area (39.25 m2) per
point count that can be achieved through HCPC compared with other techniques
used. The HCPC method perhaps is the best method for intensive sampling but is
not time-efficient.
This was a short-term
study, but it provided some future research directions. We carried out
standardization of adult odonate sampling technique
only at one field site, however, taking multiple temporal replicates helped in
eliminating sampling errors. Our analysis provided statistically significant
results, but we think this procedure needs to be replicated at several sites
for an extended time period to test if our results are consistent. In addition,
these techniques need to be evaluated at other types of wetlands such as ponds,
lakes, and streams, to come up with standard methods for assessing adult odonates at various habitats. For all the techniques used
in the present study, double-counting seems to be a potential flaw. Individuals
aggregating at a location may also introduce overestimation error, especially
if such sites fall on point count stations. These potential flaws can be fixed
only with capturing and marking individuals or alternatively, by adding several
sampling replicates to reduce the error. Since dragonflies and damselflies have
different flight abilities and habits, it is necessary to adjust strategies and
techniques to sample them (Koparde 2016). A one size
fits all strategy is not suitable to sample both the suborders or habitats.
We draw attention to
the desirability of standardized sampling protocols in species diversity
sampling. Our preliminary analysis indicates that HCPC might be a suitable
method to sample adult odonates at the riverbanks
when time is not a limiting factor, and FWBT when it is.
Table 1. Details of
four sampling techniques evaluated during the study.
|
Technique |
Dimensions &
Details |
Area Sampled |
|
Full-width Belt
Transect (FWBT) |
300 m X 10 m
(length X width) transect covered while walking at the speed of 25 m per two
minutes. |
3,000 m2
in 24 minutes |
|
Half-width Belt
Transect (HWBT) |
300 m X 5 m (length
X width) transect covered while walking at the speed of 25 m per two minutes.
The width of the transect was restricted to the area facing the riverside. |
1,500 m2
in 24 minutes |
|
Full-circle Point
Count (FCPC) |
Point counts with a
radius of 5 m (full circle) placed at an interval of 25 m (such as 0 m, 25 m,
50 m, and so on) across a 300 m straight line. |
78.54 m2
per point X 13 stations = 1,021.02 m2 surveyed in 26 minutes |
|
Half-circle Point
Count (HCPC) |
Point counts with a
radius of 5 m (semi-circle) placed at an interval of 25 m (such as 0 m, 25 m,
50 m, and so on) across a 300 m straight line. The semi-circle was restricted
to cover the area facing riverside. |
39.27 m2
per point X 13 stations = 510.51 m2 surveyed in 26 minutes |
Table 2. Species
estimates across various adult odonate counting
methods. The cumulative number of species observed across all techniques was
19.
|
Estimate |
FWBT (n = 5) |
HWBT (n = 4) |
FCPC (n = 5) |
HCPC (n = 5) |
|
CHAO 1 |
18 |
15 |
12 |
15 |
|
CHAO 2 |
26.7 |
18.13 |
20 |
17.6 |
|
Jack 1 |
23.6 |
18.75 |
15.2 |
18.2 |
|
Jack 2 |
26.45 |
19.92 |
17.15 |
19.25 |
|
Observed |
17 |
15 |
12 |
14 |
|
% coverage of all
the species observed |
89.5 |
80 |
63.2 |
73.7 |
n—number of temporal
replicates | FWBT—Full-width Belt Transect | HWBT—Half-width Belt Transect |
FCPC—Full-circle Point Count | HCPC—Half-circle Point Count.
For figures - - click here for full PDF
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