Diet composition of the Common African Toad, Sclerophrys regularis (Anura: Bufonidae), in a human-modified landscape

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Diet composition of the Common African Toad, Sclerophrys regularis (Anura: Bufonidae), in a human-modified landscape
Herpetology Notes, volume 14: 1167-1176 (2021) (published online on 01 September 2021)

 Diet composition of the Common African Toad, Sclerophrys
regularis (Anura: Bufonidae), in a human-modified landscape

       Benjamin Yeboah Ofori1,*, John Bosu Mensah1, Roger Sigismund Anderson2, Jones Kpakpa Quartey3,
                                       and Daniel Korley Attuquayefio1

Abstract. The Common African Toad, Sclerophrys regularis, is widespread and common in West Africa, yet little is known
about its ecology and natural history. Here, we assessed the dietary composition and trophic niche breadth and overlap of
S. regularis in human-modified landscapes in Accra, Ghana, using gut content analysis. Our investigation of 74 individual
toads from farmland and developed urban areas found 935 prey items from six invertebrate classes (Arachnida, Chilopoda,
Diplopoda, Gastropoda, Insecta, and Polychaeta; comprised of at least 18 orders and 31 families). Hymenoptera (family:
Formicidae) and Coleoptera were the most consumed prey items. We found a high degree of dietary niche overlap between
males and females, suggesting no obvious sex-specific preferences in diet. Generally, a positive, but statistically insignificant
correlation existed between snout-vent length of toads and the diversity and quantity of consumed prey items. The broad
dietary niche of S. regularis suggests this toad is a generalist arthropod predator. Our findings highlight basic aspects of the
ecology of S. regularis, which we hope can be used to inform conservation and management strategies for the species.

Key words. Amphibians, Natural history, Predator, Trophic niche, Urbanisation

Introduction                                                      environmental changes (Hof et al., 2011), there remains
                                                                  substantial knowledge gaps in our understanding of the
  Amphibians are among the most species-rich groups
                                                                  ecology and basic biology of many tropical amphibians,
of terrestrial vertebrates, with hundreds of new species
                                                                  particularly in urban landscapes (Hamer and McDonnell,
still being discovered annually (Pincheira-Donoso et
                                                                  2008). This knowledge gap, if not bridged, could hinder
al., 2013). They are important components of tropical
                                                                  the conservation of tropical amphibians.
ecosystems, influencing food webs and energy flow by
                                                                    The dietary niche of amphibians is an important aspect
their feeding behaviour (Le et al., 2018) and by serving
                                                                  of their natural history and determines many of their
as prey for numerous vertebrates (Gibbons et al.,
                                                                  interactions within the environment (Alveal and Diaz-
2006). Yet, amphibians are one of the most threatened
                                                                  Paez, 2021). Amphibian trophic interactions are essential
vertebrate taxa worldwide (Stuart et al., 2004), with over
                                                                  components of food web structure and provides insight
30% of all amphibian species threatened (Baillie et al.,
                                                                  into their population dynamics as well as the selective
2004) in part due to their high susceptibility to habitat
                                                                  pressure they may be exerting on their prey (Layman
modifications, invasive species, overexploitation,
                                                                  et al., 2015). Access to high quality food promotes the
climate change and infectious disease (Stuart et al.,
                                                                  success of amphibians because it can influence their
2004; Cushman, 2006; Pound et al., 2006; Leduc et
                                                                  physiology, body condition, and fitness (Scholz et al.,
al., 2012; Scheele et al., 2019). Despite their ecological
                                                                  2020). Conversely, limited food availability can reduce
importance and high vulnerability to climate and other
                                                                  reproductive success and survival rate, ultimately
                                                                  altering their population dynamics (Scholz et al., 2020).
                                                                  Furthermore, as there can be a direct relationship between
                                                                  habitat condition and prey availability, abundance, and
1
  Department of Animal Biology and Conservation Science,
   University of Ghana, Legon, Ghana.                             distribution, the dietary patterns of amphibians can be
2
  African Regional Postgraduate Programme in Insect Science,      used to inform conservation and management strategies
   University of Ghana, Legon, Ghana.                             (Bastista et al., 2011).
3
  Centre for African Wetlands, University of Ghana, Legon,          The Common African Toad, Sclerophrys regularis
   Ghana.                                                         (Reuss, 1833) (Amphibia: Bufonidae), is a large
*
  Corresponding author. E-mail: byofori@yahoo.com                 sexually dimorphic toad (adult females = 70–130 mm
© 2021 by Herpetology Notes. Open Access by CC BY-NC-ND 4.0.      snout-vent length [SVL] and males = 62–91 mm; Rödel
Diet composition of the Common African Toad, Sclerophrys regularis (Anura: Bufonidae), in a human-modified landscape
1168                                                                                    Benjamin Yeboah Ofori et al.

2000) with rugose skin and a dark olive-brown dorsal         and is a good source of protein in many parts of Nigeria,
surface, a white to beige underside, and a distinguishing    Burkina Faso, and northern Ghana (Akinsanya et al.,
black gular patch for males (Deef, 2019). This species       2020). Yet despite it being widespread and common,
is widely distributed in Sub-Saharan Africa (Iyaji et al.,   there is still much to learn about its basic ecology and
2015; Channing and Rödel, 2019), with its latitudinal        life history. Indeed, there is a paucity of information on
distribution ranging from northern Egypt to north-western    the dietary patterns of S. regularis. To help bridge this
Angola and its longitudinal distribution extending from      knowledge gap, we assessed the trophic niche pattern
Senegal to Ethiopia (IUCN SSC Amphibian Specialist           of S. regularis in human-modified landscape (i.e.,
Group, 2016; Channing and Rödel, 2019). The species          farmland and urban area) in Accra, Ghana. Specifically,
is adapted to a variety of habitats, including forest        we assessed diet composition, trophic niche breadth,
margins, moist and dry savannah, agricultural areas,         and dietary overlap, as well as the relationship between
and other habitats associated with rivers (Deef, 2019)       SVL of toads and diversity of consumed prey items.

Figure 1. Study area on the University of Ghana’s Legon Campus showing the developed urban area (shaded in yellow) and
farmland (shaded in lime green) where Common African Toads, Sclerophrys regularis, were collected.
Diet composition of the Common African Toad in a human-modified landscape                                               1169
Materials and Methods                                            Crops grown in the farm include mango, cashew, maize,
                                                                 and vegetables.
  Study Area. The study was conducted on Legon
                                                                   Data Collection. Using visual encounter surveys,
Campus (5.6508˚N, 0.1869˚W) of the University of
                                                                 samples were collected from farmland (Fig 2A, B) and
Ghana (Fig. 1). The campus has a total area of 1300
                                                                 developed areas on the University of Ghana, Legon
hectares (13 km²) and is located about 13 km north-
east of Accra, the capital city of Ghana (Gbogbo et              Campus (Fig. 2C, D). Prior to sampling, the study
al., 2017). The climate of the area is characterised by          area was surveyed and the breeding sites of toads were
a pronounced gradient of mean annual rainfall ranging            determined using points of male calls. Samples were
from 733–1118 mm distributed over a major (May–                  collected from July to September between the hours of
July) and minor (September–October) rainy season and             22:00 GMT and 08:30 GMT. During the early hours of
a daily mean temperature of about 30 °C (Gbogbo et al.,          the morning, toads were searched for under leaf litter,
2017). The vegetation is generally coastal grasslands,           fallen logs, rocks, and other microhabitats where toads
thickets, and dry forest (Garshong et al., 2013), with           are known to seek refuge. During chorusing nights,
most of the natural vegetation converted into developed          calling males or pairs in amplexus were captured by hand
areas (e.g., buildings, markets, roads, and other man-           following Quiroga et al., (2015) and Oropeza-Sanchez
made infrastructure) and farmland. The only remnant              et al. (2018). The sexes of individuals were determined
of the original vegetation is within the Legon Botanical         using the presence or absence of sub-gular pigmentation
Garden, which is located north of the campus and                 (Vera-Candioti et al., 2019). The SVL of individuals
covers an area of about 2.0 km2. The developed urban             was measured using Digital Vernier callipers (+/- 0.01
area, which covers about 7.3 km2, includes areas                 mm). The toads were sacrificed humanely according
around students’ halls, hostels, chalets, staff bungalows,       to international standards by euthanising them with
academic facilities, central administration blocks,              Xylocaine. They were then dissected and their stomach
library block, bookshops, banking square, restaurants,           contents were emptied into petri dishes containing
and canteens. The farmland is located adjacent to the            70% ethanol. With the help of a dissecting microscope,
botanical garden and covers an area of about 1 km2.              invertebrates in the stomach content were identified to

Figure 2. Typical habitat types in the farmland (A and B) and developed urban areas (C and D- drains behind man-made structures)
where Common African Toads, Sclerophrys regularis, were captured. Photos by John Bosu Mensah.
1170                                                                                    Benjamin Yeboah Ofori et al.

the highest taxonomic level possible (order or family)        respectively (Table 1). Of the non-insect orders,
following the identification keys by Triplehorn and           Polychaetes were the most frequent prey category,
Johnson (2011). Approval for the present study was            occurring in 50% of individuals with gut content,
granted by the University of Ghana College of Basic           followed by Arachnids (25%) and Chilopods (21.4%).
and Applied Sciences Animal Care and Research Ethics          For the class Insecta, the prey category with the highest
Committee (Ref. No. ECBAS 024/18-19).                         frequency of occurrence was Hymenoptera, followed
  Data Analysis. We calculated the Numerical                  by Coleoptera and Orthoptera (Table 1).
Percentage (N%) as (Ni/Nt) x 100, where Ni is the               In the developed urban area, a total of 507 prey
number of prey items in any prey category (i) and Nt is       items, comprising six invertebrate classes (Arachnida,
the total number of all prey categories. The Frequency        Chilopoda, Diplopoda, Gastropoda, Insecta, and
of Occurrence (F%) was estimated as the number of             Polychaeta) from at least 15 orders and 28 families
toad stomachs in which category i prey were found. The        were obtained from the toads’ gut contents. Once again,
trophic niche breadth was estimated using the Shannon-        the class Insecta formed the majority (91.7%) of all the
Wiener index H’ as -∑ [(pi) ×ln (pi)], where ‘pi’represents   prey items, with Hymenoptera (74.0%) and Coleoptera
the proportion of total abundance represented by the ith      (10.1%) being the most numerically abundant (Table
species (any individual member of the prey categories in      2). Formicidae was the most abundant family (74.0%),
the stomach content). A Sorenson’s similarity index was       and the most consumed prey category with 91.1% of
used to assess the dietary niche overlap between sexes.       individuals with prey within their gut contents.
We used Pearson’s correlation coefficient (r) to assess         Comparison between males and females. In general,
the correlation between (1) SVL and prey diversity            there was no significant difference in terms of the
(richness) and (2) SVL and prey category abundance. A         frequency of occurrence of the different prey categories
chi-square test was used to assess the significance of the    between males and females (Table 3). However,
differences in frequency of occurrence and numerical          frequency of occurrence of Coleoptera and Diplopoda
abundance of consumed prey items between males                was significantly higher in females than males from
and females. All analyses were done in the R software         the urban area (χ2 = 6, p = 0.01). Also, the frequency
(Version 4.0.5) and significance was set at an alpha level    of occurrence of Chilopoda was significantly higher
of 0.05.                                                      (χ2 = 6.43, p = 0.01) in females than males from the
                                                              farmland. In terms of the numerical abundance of the
Results                                                       prey items, female toads consumed significantly higher
  Abundance, diversity, composition, and frequency            quantity of the prey categories Chilopoda, Coleoptera,
of occurrence of prey items. A total of 44 individual         Diptera, Hymenopera, Orthoptera, and Polychaeta (4.26
toads (n = 23 females, n = 21 males) and 48 (n = 19           ≤ χ2 ≥ 40.76, p ≤ 0.04; Table 3). The female toads from
females, n = 29 males) were captured from the farmland        the farmland consumed at least 15 prey items, while
and developed urban area, respectively. The proportion        males consumed nine prey items, with all the orders
of individuals with empty stomachs was 34.1% in the           of prey items found in males being present in females.
farmland and 6.3% from the developed urban area. Of           Therefore, females had a slightly higher niche breadth
the individuals with stomach content in the farm land,        (H’ = 1.905) than their male counterpart (H’ = 1.627). In
19 were females and 10 were males, whereas in the             the urban area, females had a higher niche breadth (H’
developed urban area, 16 were females and 29 were             = 1.364) than males (H’ = 0.894), but males consumed
males.                                                        a slightly higher variety of prey items and significantly
  A total of 428 prey items, consisting of six invertebrate   greater quantities of Hymenoptera (χ2 = 116.48, p ≤
classes (Arachnida, Chilopoda, Diplopoda, Gastropoda,         0.0001) and Polychaeta (χ2 = 6.26, p = 0.01; Table 3).
Insecta, and Polychaeta) and belonging to at least            The dietary niche overlap between males and females
16 orders and 31 families, were found in toads from           at both the farmland (Sorenson’s index = 75%) and
farmland. The majority (88.8%) of these were                  developed urban area (Sorenson’s similarity index =
arthropods, of which 82.5% were insects. The most             80%) was high.
abundant prey items were from the order Hymenoptera             Correlation between SVL and diversity and
(39.5%), Coleoptera (15.7%), and Diptera (12.9%).             abundance of prey items. In both developed urban
Formicidae and Stratiomyidae were the most abundant           area and farmland, we found a positive, but statistically
insect families, with 38.6% and 11.4% of prey items,          insignificant correlation between SVL and diversity
Diet composition of the Common African Toad in a human-modified landscape                                                       1171
Table 1. Taxonomic
       Table          composition
             1. Taxonomic           of prey
                           composition       items
                                         of prey     (n (n
                                                 items  = 428)
                                                           = 428)found
                                                                   foundininstomachs  ofCommon
                                                                             stomachs of  CommonAfrican
                                                                                                    African Toads, Sclerophrys regularis,
                                                                                                          Toads,
from the farmland regularis,
       Sclerophrys at the University
                             from theof Ghana’satLegon
                                      farmland             Campusof(nGhana’s
                                                    the University      = Number    of Campus
                                                                                Legon  items, N%
                                                                                               (n ==Number
                                                                                                     Numerical   percentage,
                                                                                                            of items, N% = F = frequency
of occurrence andpercentage,
       Numerical   F% = percentage    frequency
                             F = frequency         of occurrence).
                                             of occurrence  and F% = percentage frequency of occurrence).

        Class              Order                      Family                      n           N%             F           F%
        Arachnida          Araneae                                               10           2.34           7            25
        Chilopoda                                                                14           3.27           6          21.43
        Diplopoda                                                                 3           0.7            3          10.71
        Gastropoda                                                                2           0.47           1           3.57
                           Stylommatophora                                        1           0.23           1           3.57
        Polychaeta                                                               46          10.75          14            50
        Insecta            Blattodea                                              1           0.23           1           3.57
                           Coleoptera                                            10           2.34           3          10.71
                                                      Carabidae                  20           4.67          11          39.29
                                                      Scarabaeidae                9           2.1            3          10.71
                                                      Chrysomelidae               3           0.7            2           7.14
                                                      Curcullionidae              2           0.46           2           7.14
                                                      Curcujidae                  1           0.23           1           3.57
                                                      Coccinellidae               3           0.7            2           7.14
                                                      Phalacridae                19           4.44           3          10.71
                           Dermaptera                                             4           0.93           3          10.71
                                                      Forfinculidae               5           1.17           2           7.14
                           Diptera                                                6           1.4            2           7.14
                                                      Stratiomyidae              49          11.44           5          17.86
                           Hemiptera                  Coreidae                    1           0.23           1           3.57
                           Homoptera                  Acanaloniidae               1           0.23           1           3.57
                           Hymenoptera                Apidae                      1           0.23           1           3.57
                                                      Formicidae                 165         38.55          23          82.14
                                                      Chrysididae                 2           0.46           1           3.57
                                                      Evaniidae                   1           0.23           1           3.57
                           Isoptera                                               2           0.46           1           3.57
                                                      Termitidae                 20           4.67           3          10.71
                           Orthoptera                 Acrididae                   5           1.17           5          17.86
                                                      Gryllidae                  17           3.97          10          35.71
                                                      Gryllotalpidae              1           0.23           1           3.57
                                                      Pygomophidae                4           0.93           3          10.71

of consumed prey items (r ≤ 0.37, p ≥ 0.12- Fig. 3)                    Discussion
and SVL and numerical abundance of consumed prey
                                                                         Most amphibians are generalist and opportunistic
items for both males (n = 29 developed urban area, 10
                                                                       invertebrate feeders (Santana et al., 2019), but certain
farmland) and females (n = 16 developed urban area,
                                                                       species have become specialised on certain prey types
19 farmland). The only exception was that the SVL of
                                                                       (e.g., Smoky Jungle Frog, Leptodactylus pentadactylus;
males from the urban area correlated negatively with the
                                                                       Do Couto et al., 2018). Our data suggest that S. regularis
abundance of consumed prey items (Fig. 3).
                                                                       has a wide taxonomic range of their diet composition,
                                                                       supporting the findings from other studies on toad diets,
                                                                       such as Cane Toads, Rhinella marina (Pamintuan and
                                                                       Starr, 2016), Common Toads, Bufo bufo (Crnobrnja-
1172                                                                                                Benjamin Yeboah Ofori et al.

Table 2. Taxonomic composition of prey items (n = 507) found in stomachs of Common African Toads, Sclerophrys regularis,
from the developed  urban at the
          Table 2. Taxonomic       University
                              composition       of Ghana’s
                                             of prey items (nLegon
                                                              = 507) Campus     (n = Number
                                                                      found in stomachs      of items,
                                                                                        of Common      N% Toads,
                                                                                                    African = Numerical percentage, F =
frequencySclerophrys
          of occurrence  and F%
                      regularis,    = percentage
                                 from              frequency
                                       the developed   urban at of
                                                                theoccurrence).
                                                                    University of Ghana’s Legon Campus (n = Number of items,
          N% = Numerical percentage, F = frequency of occurrence and F% = percentage frequency of occurrence).

           Class                 Order               Family                       n          N%          F         F%
           Arachnida             Araneae                                          6          1.18        4        8.89

                                 Scorpiones                                       1          0.2         1        2.22
           Chilopoda                                                              2          0.39        2        4.44
           Diplopoda                                                              5          0.99        5        11.1
           Gastropoda                                                             1          0.2         1        2.22
           Polychaeta                                                             27         5.33        8        17.8
           Insecta               Blattodea           Blattidae                    2          0.39        2        4.44
                                 Coleoptera                                       1          0.2         1        2.22
                                                     Carabidae                    24         4.73       13        28.9
                                                     Scarabaeidae                 17         3.35        6        13.3
                                                     Chrysomelidae                4          0.79        3        6.67
                                                     Curcujidae                   1          0.2         1        2.22
                                                     Phalacridae                  4          0.79        1        2.22
                                 Dermaptera                                       1          0.2         1        2.22
                                 Diptera                                          1          0.2         1        2.22
                                                     Stratiomyidae                1          0.2         1        2.22
                                                     Drossophilidae               2          0.39        1        2.22
                                                     Anthomyiidae                 3          0.59        1        2.22
                                 Hemiptera           Cydnidae                     4          0.79        2        4.44
                                                     Reduvidae                    1          0.2         1        2.22
                                 Hymenoptera         Formicidae                  375         74         41        91.1
                                 Isoptera            Termitidae                   14         2.76        6        13.3
                                                     Kalotermitidae               1          0.2         1        2.22
                                 Lepidoptera                                      1          0.2         1        2.22
                                 Odonata             Libellulidae                 1          0.2         1        2.22
                                 Orthoptera          Gryllidae                    4          0.79        4        8.89
                                                     Acrididae                    2          0.39        2        4.44
                                                     Pyrogomorphidae              1          0.2         1        2.22

Isailović et al., 2012), and the congeneric species,                  of prey items (Crnobrnja-Isailović et al., 2012).
Guttural Toads, Sclerophrys gutturalis (Baxter-Gilbert                  The most consumed prey items where from the taxa
et al., 2021). Our findings also showed sex-specific                  Hymenoptera (Formicidae) and Coleoptera; similar to
differences, with female toads consuming a wider                      what has been seen in other toad species (e.g., B. bufo;
dietary niche breadth; which could be due to their                    Crnobrnja-Isailović et al., 2012). Given their strong
increased energy requirements, particularly during the                visual response to prey, associated with a sit-and-wait
breeding season when they have higher metabolic rates                 foraging strategy, most toads are often believed to
to support reproductive functions (Quiroga et al., 2015).             consume whatever prey species are readily available
Also, fecundity and egg size in amphibians depend on                  and widely abundant within a landscape (Moser et al.,
the nutritional quality of food (Van Ngo and Ngo, 2014).              2017). Therefore, the high frequency of occurrence and
As such, females may meet their high nutritional quality              numerical abundance of Hymenoptera (Formicidae)
and energetic demands by consuming a broader diversity                and Coleoptera in the diet of the toads would suggest
Diet composition of the Common African Toad in a human-modified landscape                                            1173
Table 3. Differences between males and females Common African Toads, Sclerophrys regularis, in terms of the frequency of
occurrence and numerical abundance of consumed prey items.
       Order               Site                Frequency of occurrence                  Numerical Abundance
                                        Male      Female         χ , p-value
                                                                  2
                                                                                 Male    Female      χ2, p-value
       Arachnida      Developed area     12          6           2.00; 0.16        6        1        3.57; 0.06
                         Farmland        20         25           0.56; 0.46        2        8        3.60; 0.06
       Blattodea      Developed area     3           6           1.00; 0.32        1        1        0.00, 1.00
                         Farmland        0           5                -            0        1             -
       Chilopoda      Developed area     6           0                -            2        0             -
                         Farmland        10         25           6.43; 0.01        1       13       10.29; 0.001
       Coleoptera     Developed area     36         60           6.00; 0.01       19       32        3.314; 0.07
                         Farmland        80         60           2.86; 0.09       16       53      19.84; < 0.0001
       Dermaptera     Developed area     0           6                -            0        1             -
                         Farmland        20         15           0.71; 0.40        4        5        0.11; 0.74
       Diplopoda      Developed area     6          18           6.00; 0.01        2        3        0.20; 0.66
                         Farmland        10         10           0.00; 1.00        1        2        0.33; 0.56
       Diptera        Developed area     6          12           2.00; 0.16        4        3        0.14; 0.71
                         Farmland        20         30           2.00; 0.16        5       49      35.85;
1174                                                                                       Benjamin Yeboah Ofori et al.

Figure 3. Correlation between SVL, diversity and abundance of consumed prey items by male and female common African toads
from the developed area and farmland.

the small size of the prey by consuming large quantities      abundance and diversity (i.e., SVL) and those which
(Novitsky, 2003).                                             do not (i.e., sex) may be due to the high degree of
  The body size (SVL) of S. regularis correlated              variability in our data. Furthermore, the evident overlap
positively with prey diversity and abundance, which           in diet composition between females and males may
suggests that larger individual toads consumed a higher       be attributed to the use of the same microhabitat for
variety and quantity of prey items – albeit this was          foraging and intersexual competition for food resources
not statistically significant. This generally follows the     (Crnobrnja-Isailović et al., 2012).
findings of Almeida et al. (2019) and Le et al. (2020)          Overall, our findings show that these toads capitalise
who attributed this to the relatively larger stomach          on a wide range of prey items, suggesting that S.
capacity that could accommodate large quantities of           regularis is an opportunistic generalist predator. This
prey items compared to smaller individuals. Also, larger      feeding habit may be advantageous in dynamic habitats
individuals tend to be more active and thus encounter and     with constantly changing food availability. Our findings
consume more diverse prey categories (see Mageski et          highlights some of basic aspects of the ecology of
al., 2018). These findings are of interest since we know      common African toads and can be used to inform the
that S. regularis is a sexually dimorphic species (Rödel,     conservation and management of the species in their
2000) and body size was correlated with differences           natural environment as well as in urban and other
in prey diversity and abundance, however we did not           human-dominated landscapes.
detect a significant difference between females and
males. The high level of dietary niche overlap (75% in        Acknowledgements. The authors wish to thank Eudosia Obeng,
farmland and 80% in the developed urban area) observed        Charles Achina, Faustina Adu-Boahene, Patience Darko, and
between females and males and the concordance in the          Caleb Frimpong for their assistance in the field.
distribution of various prey categories between females
and males suggested the absence of sex-biased diet            References
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                                                                         Accepted by Werner Conradie
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