Effects of anthropogenic disturbances on adult Odonata fauna in Akure, south west Nigeria

Abstract

Background

Human activities such as deforestation, urbanization, industrialization, canalization, and water abstraction, negatively affect biodiversity. This study was carried out to determine the effect of anthropogenic activities on the composition, distribution, and abundance of Odonata of Akure South Local Government Area.

Results

A total of 2376 Odonata individuals (1363 dragonflies and 1013 damselflies) in 6 families (Libellulidae, Ceonagrionidae, Calopterygidae, Platycnemididae, Chlorocyphidae) and Gomphidae, 19 genera and 36 species were recorded in this study. Pseudagrion ‘A’ kersteni (651) is the most frequent species followed closely by Trithemis arteriosa, they were found in all the sites, therefore are generalists. Eight species including Lestinogomphus minutus, Pantala flavescens, Copera sikassoensis, etc., are least represented in the study, they were made up of one individual each. Leo study site has the richest odonate fauna (Simpson dominance: 0.8497, Shannon–Wiener H_: 2.234 and Margalef: 3.021); while, the least was Oda (Simpson dominance: 0.7899 and Shannon Wiener H_: 1.932). The distribution of the species was highest at Oda (evenness E: 0.4931), followed closely by Leo (evenness E: 0.4916); while, Ijapo (evenness E: 0.3852) is the least.

Conclusion

The few stenotopic species and, proliferation of eurytopic species in the study sites proved that the sites are undergoing intense anthropogenic disturbance and conservation efforts must therefore be put in place to prevent the extinction of these species and their restoration in sites they were absent.

Background

The Order Odonata is a well-studied aquatic insect inhabiting freshwater ecosystems although some species have been observed to live in brackish water (Watanabe et al., 2007). Odonata has three suborders—Anisoptera (dragonfly), Zygoptera (damselfly) and Anisozygoptera which has traits that, at first glance, resemble those of the Anisopterans, and its wings also resemble those of the Zygoptera (Bybee et al., 2021). The larvae of this suborder also exhibit characteristics shared by the Zygoptera and Anisoptera. The various Odonata have varying geographic distributions. Some genera and species have a broad distribution; while, others have a narrow distribution (Kadoya et al., 2004). Some species are ubiquitous, such as Palpopleura portia (Drury, 1773) and Orthetrum julia (Kirby, 1900) (Corbet, 1999), and are occasionally observed migrating far from their home. Due to its long lifetime and amphibious tendencies, Odonata is perfect for evaluating environmental changes that occur both above and below the water surface, including short-term changes in conservation biology and long-term changes in biogeography and climatology (Corbet, 1999). In biogeography research, dragonflies and damselflies are useful bioindicators for assessing environmental changes over long- and short-term scales (O’Neill & Paulson, 2001).

With approximately 6500 known and described species worldwide, Odonata are noticeable and characteristic of freshwater environments (Clausnitzer & Dijkstra, 2005). They are extremely important as bioindicators of the ecological integrity of ecosystems (Corbet, 2004) and in biodiversity studies (Adu et al., 2019; Vick, 2003) due to their high diversity, ease of identification, and conspicuousness. A freshwater environment's Odonata species presence or absence may also be a sign of the health of the body of water (Chovanec & Raab, 1997). There is strong evidence that deforestation has caused the extinction of multiple species of dragonflies locally and nationally in countries where the fauna has been thoroughly investigated (Valiente-Banuet et al., 2015). Since the abundance and composition of freshwater odonata assemblages can vary over time at any one location, it is imperative to provide baseline data regarding current patterns of diversity and distribution (Moore, 1991, 2001). Since Akure became the capital of Ondo State in 1976, it had undergone series of developmental changes in the area of physical landscape, city growth and urban sprawl (Balogun et al., 2011). This not only resulted to depletion of natural resources but also environmental problems such as erosion, agro-chemical runoff and deposition of domestic waste and sewage into water bodies (Balogun et al., 2011). This study seeks to determine the effect of anthropogenic activities on the composition, distribution, and abundance of Odonata of Akure South Local Government Area. The aforementioned data will serve as the foundation for evaluating the long-term impacts of pollution and development on freshwater ecosystems in the millennium city, and they may also be utilized as a first step for their conservation.

Methods

Study area

The study site is located within Akure Southwestern Area Akure, in Ondo State Nigeria (Fig. 1). It has a coordinate of latitude 7.25°N and longitude 5.19°E. The climatic conditions attributed to the site are: high temperatures and high humidity with two distinct seasons, namely wet and dry seasons. The wet season lasts for about eight months (March to October) with an annual rainfall of about 1524 mm. Annual temperature ranges between 28 and 31 °C with a mean annual relative humidity of about 80%. The major rivers in the area are; the Ala River, Elegbin River, and Afo River (Akinseye, 2006). The inhabitants of the Ala River predominantly involved in farming and other artisanal activities.

Fig. 1

Map of the Stations Showing the Study Sites in Akure South Local Government Area, Ondo State, Nigeria. A Map of Nigeria showing Ondo State. B Map of Ondo State showing Akure South Local Area. C Map of Akure South Local Government Area showing the stations

Two locations were selected (the Ala River area and the Afo River area) based on the presence of waterbodies and the vegetation architecture. Four stations were also selected in the Ala River area namely: (the Federal University of Technology Area (FUTA), Industrial Layout (I.L), LEO, and Ijapo Estate Akure (Ijapo)) while three stations were also selected at the Afo River area. These are: (The court of Appeal Estate, Akure (COAE), Ayee Community Oda Road, Akure (Ayee), and Ayee Farmland). The physical description of the locations selected is on Tables 1 and 2.

Table 1 Physical Description of the three study sites on the Afo River

Table 2 Physical characteristics of the four study sites on Ala River

Adults’ dragonflies and damselflies was collected once a month for 18 months with the aid of sweep net of 70 cm wide orifices. All the encountered dragonflies and damselflies within 500 m of the water bodies was collected, killed by dipping in acetone for a minute and arranged with the wings at the back to prevent it from rumpled and kept inside a labeled triangular envelop. Those caught in tandem was placed together inside the same envelope. The envelopes with the killed and well-arranged insects was then soaked in acetone for a minimum period of 12 h, depending on the size. Hereafter, the soaked specimens was removed from acetone and then air-dried on a tissue paper. Then, each of the specimens was kept in a transparent small nylon bag (2 × 4 cm), sealed and then placed inside a labeled 3 × 5 cm envelop. The specimen inside envelop was then stored in insect boxes. All odonata species collected, was identified to species level using standard identification manuals (Dijkstra & Clausnitzer, 2014; Vick, 2003). Furthermore, all data collected from the study sites were accumulated and analyzed statistically using both inferential and descriptive statistics. The data collected on physicochemical parameters and odonates were subjected to one-way analysis of variance (at p < 0.05) using SPSS version 20 software package. The species richness of the study sites was determined using diversity indices such as Shannon–Wiener’s index, (H`), Margalef’s index, and Evenness index, (E) with the aid of Paleontologist Statistical Software package (PAST) version 3.0.

Results

A total of 2376 adult odonates (comprising 1363 dragonflies and 1013 damselflies) individuals representing 35 species in 6 families were collected from the study sites. Dragonfly has 1367 individuals from 2 families (Gomphidae and Libellulidae) and 26 species (Table 3); while, damselfly has 1013 individuals from 4 families (Calopterygidae, Ceonagrionidae, Chlorocyphidae, and Platycnemididae) and 9 species (Table 4).

Table 3 Abundance and percentage composition of Anisoptera in the study sites between August 2021 and December 2022

Table 4 Abundance and percentage composition of Zygopteran in the study sites between August 2021 and December 2022

Libellulidae are represented in 25 species; while, Gomphidae is made up of just one species. Also, Ceonagrionidae is made up of 5 species; while, Platycnemididae consists of 2 species; the other is constituted of just one species each.

Libellulidae was the dominant family as it accounted for the highest number of individuals with a percentage composition of 57.32%, followed by Coenagrionidae 38.55%; while, Gomphidae was the least having 0.04% (Fig. 2). All the six families reported in this study were recorded at Ayee Farm land; while, Ijapo (with the highest number of individuals (547)) accounted for five families. However, Ayee, Leo and FUTA have the highest abundance of Libellulidae; while, the least is found in Ayee Farmland. Also, COAE, Ijapo and FUTA have the highest abundance of Coenagrionidae; while, Industrial Layout is the site with the least abundance of Coenagrionidae. (Fig. 3).

Fig. 2

Pie Chart Showing the Percentage Composition of the Families Collected at the Study Sites

Fig. 3

Odonata Family Distribution for each Site in the Study Area

Trithemis arteriosa was the dominant Anisoptera species in the study as it accounted for 465 individuals while Lestinogomphus minutus, Orthetrum chrysostigma, Orthetrum abboti, Acisoma trifidum, Crocothemis erythraea, Pantala flavescens, and Urothemis assignata were the least represented Anisoptera species in the study area. Ijapo accounted for the highest number of Zygopteran species (373); while, the least is found in Industrial Layout, Ilesa Road. Pseudagrion ‘A’ kersteni is the most frequent Zygopteran in the study site while C. sikassoensis is the least frequent.

Trithemis arteriosa and Orthetrum monardi were significantly lower in Ayee Farm Land than all the sites, also, Pseudagrion ‘A’ kersteni and Ceriagrion glabrum in Industrial Layout, Ilesa Road and FUTA, respectively, are significantly lower than those of other sites. Likewise, Trithemis annulata is significantly lower in Court of Appeal Estate than in other sites and was not collected in Ayee Farm Land at all (Table 5).

Table 5 Mean Value of the collected Odonata Species across the Sample Sites

In terms of Species diversity, LEO had highest Shannon wiener value (H’ 2.185) followed by FUTA with (H’ 2.185); while, the least values of Shannon were recorded at both I.L (H’ 2.007) and Ayee farmland (H’ 1.932), respectively (Table 6).

Table 6 Species Diversity of Odonata at Study Sites between August 2021 and December 2022

Discussion

The impact of human activity on the assemblage and composition of Odonata (Dragonflies and Damselflies) at this site is a significant concern. Human anthropogenic activities and the impact of the inhabitants have negatively affected the status of the environment. This, in turn, has led to the gradual loss of typical tropical rainforest features in the study area. Several studies have reported that the reduction of conservation areas has resulted in the extinction of important organisms, including Odonata (Harabiŝ & Dolnŷ, 2012; Jŭnior et al., 2014; Saha & Gaikwad, 2014; Willigalla & Fartmann, 2012). The differences in composition and diversity in some research sites can be caused by differences in environmental conditions such as vegetation, food sources, and physical and chemical factors at each site (Siregar & Bakti, 2016; Saha et al. 2014; Suhonen et al., 2010).

The dominant of the two families (Libellulidae and Coenagrionidae) in this study were found to be in consonant with the previous studies such as Naik et al. (2017) in India; Adu and Ogbogu (2013) carried out in Aponmu forest; Kemabonta et al., (2016) in Lagos state University; Kemabonta et al. in Akwa Ibom state (2019).

A total of 27 species of Anisoptera were recorded at the study sites. The study site is made up of species that can resist pollution and anthropogenic disturbance. The largest number (14) of Anisoptera species was recorded at three sites (Ayee, Leo, and FUTA), these sites were recipients of municipal waste and aquaculture discharge. Enriched water from urbanization waste also provided a food source for the primary prey of odonates, Chironomus sp. (Diptera: Chironomidae), and nutrients for the weeds. The decomposition of organic matter, for example, fallen leaves and also food waste from residential areas increased soft sediments, which was favorable to this dipteran (Hawtin, 1998). In the presence of dense growth of weeds, the population of dragonflies especially tolerant genera such as Pseudagrion, Trithemis, Palpopleura, and Orthetrum surged at these sites (Abdul et al., 2017, Wazhizatul-Afzan et al., 2006; Hornung & Rice, 2003).

Forest species such as Pantala flavescens, Lestinogomphus minutus, Chlorocypha curta, and Allocnemis which are not typical of the study area, were also captured though in limited number in this study; thus, heterogeneity exhibited by odonates in habitat selection, especially when the best desired habitat is not available cannot be down played (Corbet, 1999).

Several studies have also shown that Libellulidae is resistant to urban pollution and development globally and locally (e.g., Manuel Ferreras-Romero et al. 2009); Villalobos-Jimenez et al. (2016); Kemabonta et al. (2016); and also because they are early recolonizer of restored environment (Corbet, 2004). While Gomphidae is resistant to it (Manuel Ferreras-Romero et al. 2009); Gomphidae, Calopterygidae, and Chlorocyphidae were very limited in abundance because they are sensitive to pollution and urban development, the few represented in the studies are found in site located close to secondary forest, i.e., in the farmland and in areas where some conservation efforts such as re-growth of riparian vegetation, dredging, development of open space, garden, etc., had been put in place.

The last number (8) of Anisopteran was recorded at Ayee farm which was located in farmland exposed to only chemical runoff contaminating the water, this site contains fewer species because the stream around the study area has a small volume of water that almost dry off during the dry season; and also because Anisoptera prefers to roam around in the open space while most zygopterans are shade lovers (Corbet et al., 2004). However, the site is the only site where all the families of Odonata collected are represented and evenness and equitability tests indicated that Oda (evenness E: 0.4931) was the site with the best distribution of Odonata species. Also, it is the site with the most unique species of Odonata such as Lestinogomphus minutus, Allocnemis elongata, Chlorocypha curta.

Nine Zygopteran species were recorded in the study area (Fig. 3). Ijapo which is situated in a housing estate with a clean environment and good waste management system, accounted for the highest number of damselfly (373); while, the least is found in Industrial Layout, Ilesa Road. Damselflies are more pollution and development tolerant than dragonflies (Kemabonta et al., 2016 and Fulan et al., 2008); therefore, the presence of more damselfly than dragonflies in Ijapo is an indication of a disturbed and polluted environment and this may be as resulted of anthropogenic and polluted activities outside the estate as Ala River passed through several polluted sites such as FUTA, Leo, Oke Ogba, etc., before getting to Ijapo estate.

Different diversity indices were used to measure diversity and species richness to address the problems or limitations of a single index (Purvis and Hector, 2000). The statistical study utilizing the diversity indices demonstrated that LEO and FUTA had higher values for both the Shannon wiener and Simpson dominance indices, indicating that, they were both higher in terms of species composition, abundance of species collected, and diversity of species. This is thought to be due to the large number of shading trees. This assertion was also supported by Dijkstra and Lempert, (2003) that, the degree of shade tends to be the main indicator for dragonflies when choosing a forest environment. Its status as the most abundant in odonate assemblages may have been influenced by the mild disturbance level in the forest border environment (Seidu et al., 2017). It can just be a result of being out of human reach and far from a residential area (Kemabonta et al., 2019).

Leo, Futa, and Industrial Layout Ilesa Road were the most urbanized and most affected by urban pollution, others were sites located either in the semi-urban or housing estate with reduced pollution. According to Corbet, 1999, Odonata is divided into two behavioral types viz; eurytopic and stenotypic. The eurytopic Odonata includes those that can withstand pollution and urban development such as Libellulidae and Coenagrionidae while stenotopic are the opposite. Also, urban pollution was associated with increased abundance and dominance of Libellulidae and other taxa but decreased abundance of Gomphidae (Manuel Ferreras-Romero et al., 2009) and overall evenness (Henriques-de-Oliveira et al., 2007). Stenotopic species such as L. minutus, Chlorocypha curta, Pantala flavescens, and Allocnemis elongata, were not represented in Leo, FUTA, and Industrial layout Ilesa Road, thus these sites can be said to be most disturbed and polluted of all the sites.

Conclusion

This study revealed the severe nature of the study area's situation because of the detrimental effects that human disturbances and local residents' behaviors have had on the abundance, distribution, and composition of adult Odonata. Additionally, most Odonata species that was gathered belonged to the eurytopic group, which is capable of surviving in a contaminated environment.