Diet Composition of the Common African Toad, Sclerophrys Regularis (Anura: Bufonidae), in a Human-Modified Landscape
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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: [email protected] 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 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