Njila, H.L*. and Valentine, C.C. 

Department of Science Laboratory Technology, University of Jos, P.M.B. 2084 Jos, Plateau State, Nigeria.

ARTICLE INFORMATION	ABSTRACT
*Corresponding author: Njila, H.L E-mail: njilahl@gmail.com Phone: +2348163365257  Keywords:  Leaf  Litter  Arthropods   Gallery forest  Zoological garden	Arthropods are an important and the most diverse component of terrestrial ecosystems and they occupy a wide variety of functional niches.  Consequently, during the rainy season of September to October 2019, a study on the species composition of leaf litter arthropods in relation to some soil physicochemical parameters was conducted in the Gallery forest of the Jos  Zoological Garden. Arthropods found in leaf litter were gathered using pitfall traps. Standard techniques were used to determine the physic-chemical characteristics of the soil. A total of 965 arthropods were collected,  representing 4 Classes, 12 Orders, 30 Families, 36 Genera, and 39 Species.  There was a significant difference (P<0.05) in the abundance of leaf litter arthropods in comparison to arthropod taxa, with Insecta accounting for  89.01% of the total, followed by Hymenoptera (48.08%), Formicidae (47.56%),  and Camponotus pennsylvanicus (40.41%) as the most abundant taxa. The amount of organic matter, pH, temperature, and soil moisture all have an impact on the diversity and quantity of leaf litter arthropods. The quantity and variety of leaf litter arthropods depend on the availability of food, suitable microhabitats, and favorable soil conditions. Therefore, it is advised that the management of Jos Zoological Garden prohibit all anthropogenic activities.

INTRODUCTION  

Arthropods are essential components of the marine,  freshwater, terrestrial, and avian ecosystems (Rupert et  al. 2004) and play key roles in food chains, population  dynamics, and community structure (Latif et al. 2009).  Arthropod species make up over 80 % of all known living  animal species, with estimates ranging from 1,170,000 to  5 to 10 million (Odegaard, 2000). Cuticle, a non-cellular  substance released by the epidermis, makes up the  exoskeletons of arthropods (Rupert et al. 2004). The  procuticle is the collective name for the exocuticle, which  is made up of chitin and chemically hardened proteins,  and the endocuticle, which is made up of chitin and  unhardened proteins (Schmidt-Rhaesa et al. 1998).

A  flexible cuticle covers the joints between limb segments  and between body segments (Rupert et al. 2004). A  distinguishing characteristic of Ecdysozoa (arthropods,  tardigrades, onychophorans, nematodes, and related taxa) is ecdysis or moulting, which characterizes the  process of shedding the exterior integument, the cuticle  (Schmidt-Rhaesa et al. 1998). Growth, progress toward  an adult body plan, and body part regeneration are all  facilitated by moulting (Drage, 2016). A few species of  crustaceans and insects can reproduce by  parthenogenesis, particularly when the conditions are  right for a “population explosion.”

The majority of  arthropods, however, reproduce sexually, and  parthenogenetic species frequently switch to sexual  reproduction when environmental conditions deteriorate  (Smith, 2014). According to Rupert et al. (2004), most  arthropods lay eggs. Most often, the small nauplius larvae  that hatch from crustaceans have three segments and  pairs of appendages (Rupert et al. 2004).

Arthropods can  act as infectious pathogen carriers or vectors. (Duvallet et al. 2018), yet other arthropod species are crucial to our  survival, giving us access to things like food, clothing,  medicine, and protection from hazardous critters as well  as helping to maintain ecological equilibrium (Myers,  2001). Healthy soil contains leaf litter, dead leaves, twigs,  and pieces of bark that have fallen to the ground. This  dead organic matter offers a wide variety of creatures the  ideal habitat (Lin, 2012). Invertebrates, with arthropods  having the biggest abundance, make up the majority of  the live organisms found in leaf litter.

The need to gather  data on the species composition of leaf litter Arthropods  in conservation areas like the Gallery Forest of Jos  Zoological Garden stems from the fact that sound  information on leaf litter composition must be  incorporated into management practices if ecosystems  are to be managed properly by the next generation. 

MATERIALS AND METHODS 

Study Area 

The investigation was carried out in the Gallery Forest of  Jos Zoological Garden from September to October 2019.  

Techniques for Collection, Identification, and  Quantification of Arthropods 

Twenty pitfall traps were distributed throughout the  Gallery Forest of the Jos Zoological Garden. The sampling  method involved placing traps at intervals of 50 meters  along a transect for a period of 72 hours. Giving all  Arthropods an equal chance to be ensnared is the goal.  After 72 hours, arthropods were harvested.

Arthropods  were collected and stored in 70% alcohol and glycerol  after being freed of plant detritus. Arthropods were  transported to the laboratory for sorting, identifying, and  categorization. A colored atlas and identification keys  from Castner (2000) and Shattuck (2000) were used to  identify, organize, and classify each sample of arthropods  into groups, orders, families, genus, and species. 

Determination of Soil Physicochemical Parameters

The soil temperature was measured by excavating the  ground (approximately 5 cm), inserting a thermometer,  waiting 5 minutes, and then taking the measurement.  Following weighing and the subsequent calculation, 20 g  of soil samples were placed in an ovum at 100°C for 24  hours. The moisture content was then calculated as  follows: 

 % of soil moisture content = ^{��1−��2} 

_��1× 100  

Where w₁-w₂ is loss in weight; w₁ is initial weight  In a 500 ml beaker, 20 g of processed soil samples were  placed. 20ml of distilled water was added to it and stirred;  then allowed to stand for 30min. It was occasionally  stirred with a glass rod. A calibrated pH meter’s electrode  was put into the partially settled slurry, and the meter’s  screen displayed the pH. A modified version of Walkley  and Black’s (1934) approach was used to calculate the soil  organic matter.  

Statistical Analyses 

R Console software was used to analyze the data (version  3.2.2). The relative abundance of leaf litter arthropods  with respect to classes, orders, and families was  compared using Pearson’s Chi-square test. Statistics were  judged to be significant for P-values under 0.05. 

RESULTS 

In total, 965 arthropods were collected and identified,  representing 4 Classes, 12 Orders, 30 Families, 36 Genera,  and 39 Species. (Table 1). The most prominent species of  identified arthropods were Camponotus pennsylvanicus,  Tipula spp.., and Alphitobius spp (Table 1). As shown in  Table 1, the species with the lowest species richness were  Brachycybe spp., Gromphadorhina portentosa, Blatella  lituricollis, Clivina impressefrons, Galerita spp., Podabrus  pruinosis, Episyrphus spp., Triatoma protracta, Triatoma  sanguisuga and Dipogon subintermedius. When compared to class, the number of leaf litter arthropods  varied significantly (χ2= 2134.3, df = 3, P 0.0001) as shown  in Figure 1. As illustrated in Figure 1, the results showed  that the class Insecta was the most numerous, with 859  (89.01%).

According to Figure 2, the Order Hymenoptera  had the most individuals with 464 (48.08%), followed by  the Order Coleoptera with 154 (15.95%), and the Order  Plasmidesmida with just 1 (0.10%). As a result, there was  a significant variation in the number of leaf litter  arthropods according to Orders (χ2= 2705.5, df = 12, P  0.0001).

As indicated in Figure 3, the Formicidae family  had the highest population density with 459 (47.56%)  individuals, while the Andrognalidae, Alaberidae,  Blatellidae, Cantharidae, Pompilila, Syriphidae,  Tenthredinoidea, and Tetrigidae families had the lowest  density with 1 (0.10%) each. As a result, there were  significant differences in the abundance of leaf litter  arthropods according to family (χ2= 6633.6, df = 29, P  0.0001). 

Table 1: Species Checklist of Leaf Litter Arthropods from Gallery Forest of Jos Zoological Garden 

Class	Order	Family	Common Name	Species	Total	Percent (%)
Arachnida	Aranea	Lycosidae	Wolf spider	Lycosidae spp	15	1.55
		Pholcidae	Daddy long legs	Pholcus phalangioides	4	0.41
		Sicariidae	Brown recluse spider	Loxosceles reclusa	80	8.30
Crustacea	Isopoda	Platyarthridae	Pill bug	Armadilllidium vulgare	4	0.41
Diplopoda	Plasmidesmida	Andrognalidae	Feather millipede	Brachycybe spp	1	0.10
	Spirostreptida	Spirostreptidae	Giant African millipede	Archispirostreptus gigas	2	0.21
Insecta	Blateria	Blaberidae	Madagascar hissing  cockroach	Gromphadorhina  portentosa	1	0.10
		Blatellidae	Blatellid cockroach	Blatella lituricollis	1	0.10
	Coleoptera	Carabidae	Ground beetle	Stenolophus ochropezus	9	0.93
			Vivid metallic ground  beetle	Chlaenius scapularis	7	0.73
			Red ground beetle	Clivina impressefrons	1	0.10
			False bombardia beetle	Galerita spp	1	0.10
		Cantharidae	Soldier beetle	Podabrus pruinosis	1	0.10
		Staphylinidae	Devil’s coach horse  beetle	Staphylinus olens	30	3.11
			Rove beetle	Staphylinus aethiops	2	0.21
		Tenebrionidae	Darkling beetle	Alphitobius spp	103	10.67
	Dermaptera	Anisolabididae	Ring legged earwig	Euborelia annulipes	48	4.97
	Diptera	Calliphoridae	Oriental latrine fly	Chrysomya  megacephala	4	0.41
		Drosophilidae	Vinegar fly	Drosophila  melanogaster	6	0.62
		Fannidae	Latrine fly	Fannia scalaris	12	1.24
		Muscidae	House fly	Musca domestica	2	0.21
			Muscid shoot fly	Antherigona reversura	2	0.21
			Unidentified	Unidentified	8	0.83
		Syriphidae	Hover fly	Episyrphus spp	1	0.10
		Tipulidae	Crane fly	Tipula spp	108	11.20
	Hemiptera	Cydnidae	Burrower bug	Pangaeus bilineatus	2	0.21
		Nabidae	Damsel bug	Nabis roseipennis	2	0.21
		Reduviidae	Western bloodsucking  conenose bug	Triatoma protracta	1	0.10
			Eastern bloodsucking  conenose bug	Triatoma sanguisuga	1	0.10
	Hymenoptera	Formicidae	Carpenter ant	Camponotus  pennsylvanicus	390	40.41
			Sugar ant	Camponotus  consobrinus	42	4.40
			Slender twig ant	Tetrasponera allaborans	2	0.21
			Fire ant	Solenopsis geminate	23	2.38
			Mystrium ant	Mystrium rogeri	2	0.21
		Pompilila	Spider wasp	Dipogon subintermedius	1	0.10
		Tenthredinoidea	Saw fly	Tenthredo mesomela	1	0.10
		Vespidae	Paper wasp	Polistes spp	3	0.31
	Lepidoptera	Erebidae	Oak moth	Phoberia atomaris	4	0.41
	Orthoptera	Gryllidae	Field cricket	Gryllus campestris	25	2.60
		Tetrigidae	Black sided pygmy  grasshopper	Tettigidea lateralis	1	0.10
	Unidentified				12	1.24
				Total	965
				Percent (%)		100

Figure 1: Class-specific percentage abundance of leaf litter arthropods 

Figure 2: Order-specific percentage abundance of leaf litter arthropods 

As demonstrated in Table 2, over the four-week study  period, the soil physic-chemical parameters in the Gallery  Forest of the Jos Zoological Garden varied over time. The  physic-chemical parameters that were recorded and their  related abundances are shown in Table 2 in the order that  they were recorded. The first measurement was taken at  the third collection of leaf litter arthropods, the second  

measurement at the seventh collection of leaf litter  arthropods, and the final measurement at the tenth  collection of leaf litter arthropods. When the soil’s physic chemical characteristics were originally measured, they  showed a pH of 7.36 (slightly alkaline), a temperature of  22°C, 2.02% organic matter, and a moisture content of  36.70%. 

The maximum abundance ever observed was 643 leaf litter arthropods, which were gathered under all of these  conditions. The soil physic-chemical parameters revealed  a reduction in the second measurement. It showed that  the soil had a pH of 7.01 (slightly alkaline), was 18°C, had  1.75% organic matter, was 24.10% moist, and had 195  leaf litter arthropods in total.

These conditions led to the  collection of 127 leaf litter arthropods, the lowest abundance ever seen. A total abundance of 965 leaf litter  was produced by the soil’s mean values for pH,  temperature, organic matter, and moisture content,  which are 7.11, 20°C, 1.89%, and 27.10%, respectively. As  indicated in Table 2, the relationship between soil  moisture, soil pH, and the quantity of leaf litter was direct  (soil moisture dropped as soil pH declined). 

Figure 3: Family-specific percentage abundance of leaf litter arthropods 

Table 2: Soil Physicochemical Factors on Abundance of Arthropods in Jos Zoological Garden, Jos.

Mean Soil Physicochemical Factors
Soil pH	Soil  Temperat ure (°C)	Soil  Organic  Matter  Content  (%)	Soil  Moisture  Content  (%)	Leaf litter  Arthropod’s  Abundance
7.36	22.00	2.02	36.70	643
7.01	18.00	1.75	24.10	195
6.91	20.00	1.89	20.55	127
Mean= 7.11	Mean=20. 00	Mean=1. 89	Mean=27 .10	Total=965

DISCUSSION 

Arthropods are essential to the stability and operation of  terrestrial ecosystems (Njila et al. 2022). In this study,  arthropods that live in leaf litter were classified into four  classes, twelve orders, and thirty families. The habitat,  microclimate, and food availability in the leaf litter as well  as the protection from predators and harsh weather  conditions afforded by the leaf litter can be linked to the  36 genera and 39 species that were collected and  identified in this study (Table 1).

According to Njila et al.  (2022) investigation, many arthropods use the leaf litter  layer as a habitat because it provides them with food, a  refuge from the elements, and protection from  predators, all of which increase their population. In this study, the high abundance of Camponotus  pennsylvanicus, Tipula species, and Alphitobius species  (Table 1) was likely caused by these detritivores’  attraction to the fermented byproducts of decomposing  leaf litter as they drank these liquids for the purpose of  feeding, C. pennsylvanicus, Tipula species, and  Alphitobius species congregate at this stage of the  decomposition process when the leaf litter begins to  ferment.

They absorb their liquid meal via their  mouthparts. Since no immature forms were found during  the survey and some Tipula species have been reported  to lay their eggs on fermented material (Njila et al. 2014),  the existence of these insects was attributed to their  affinity to liquid food (Perez and Barrion-dupo, 2013). 

Triatoma protracta, Triatoma sanguisuga, Dipogon  subintermedius, Tenthredo mesomela, and Tettigidea  lateralis were the least common arthropods in this study,  while Galerita species, Podabrus pruinosis, Episyrphus  species, Blatella lituricollis, Clivina impressefrons, and  Gromphadorhina portentosa were the most common  (Table 1). Because they are opportunistic predators, the  presence of these arthropods may only be temporary  (Njila and Hadi, 2015). The torrential rains at the time of  sampling may have contributed to these extremely low  levels. Many arthropods appear to have avoided the leaf  litter due to the recent severe rains.

The arthropods might have looked for areas to reside that were drier or  they might have been washed away by rain. The  variability of the microhabitats and the availability of food in the leaf litter, as well as the canopy provided by trees  covering the leaf litter in the gallery forest of the Jos  Zoological Garden, could be responsible for the  considerable difference in the abundance of leaf litter  arthropods in relation to Class, Order, and Family (Figures  1, 2, and 3) observed in this study.

This result  corroborates the findings of Njila et al. (2022) which  showed that mature forests with a closed canopy are  more likely to host a diversified and rich fauna than  forests in an early successional stage. Insecta and  Hymenoptera were also found to be the most abundant  taxa of ground dwelling arthropods associated with two  habitat types in the Jos Zoological Garden Jos Plateau  state, North central Nigeria (Njila and Hadi, 2015).

This  study’s noticeably high abundance of members of the  family Formicidae is consistent with observations  obtained by Cheli et al. (2010) while studying the  community of ground-dwelling arthropods on Peninsula  Valdes in Patagonia, Argentina. According to Cheli et al.  (2010), the colonial nature of the Formicidae means that  when they are collected in an area, they are typically  captured in relatively large numbers. This supports the  Formicidae’s hegemonic position in a habitat. The Gallery  forest’s soil pH was primarily alkaline (Table 2).

This has a favorable correlation with the abundance and variety  observed. This is in keeping with the findings of Hamilton  (2015) who linked the richness and abundance of  arthropod species to alkaline soils, and with the findings  of Njila et al. (2022), who found that arthropods prefer  alkaline soil to acidic soil in Gallery forest soils. The high  rate of litter decomposition, increased microbial activity,  and water dilution potential with increasing moisture  content were all factors that contributed to the soils’  alkaline nature and supported Leonardo (2006) findings  regarding the decomposition and micro-arthropod  abundance in soil and litter in a Southern Appalachian  wetlands complex.

All of the soil in the Jos Zoological  Garden’s Gallery woodland had low temperatures (Table  2). However, Table 3 shows that the Gallery Forest of the  Jos Zoological Garden has the highest soil temperature  observed and the largest arthropod abundance. This is  likely because, at warmer temperatures, arthropods  reproduce and mature more quickly, which increases  their abundance.

This is in line with Kiritani’s (2006)  assertion that some insects may produce more  generations as a result of increased temperatures likely  stimulating adult reproduction. In general, the weather  during the study period and the shade given by the trees  in the Gallery Forest may be blamed for the low  temperature of the soils. The other significantly lower  temperatures that revealed lower arthropod abundances  may be because of the lower temperatures’ effects on  metabolism and reproduction.

This is corroborated by  research by Block et al. (1990), which showed that as  ambient temperatures drop near the low end of the  arthropod species’ thermal range, each individual’s total  metabolism declines and their ability to move becomes  increasingly constrained. The Gallery woodland of the Jos  Museum Zoological Garden had a low amount of soil  organic matter (Table 2).

The quantity and variety of  arthropods that were collected were adversely affected  by this. Due to excessive rainfall during the study period,  the soil may have been washed away, and the Gallery  Forest of the Jos Zoological Garden’s predominant tree  species may also have contributed to the low proportion  of soil organic matter.

This is consistent with the findings  of Wiwatwitaya and Takeda (2005), who linked seasonal  fluctuations in soil arthropod abundance, and the  findings of Funderburg (2001), who stated that soils that  have grown under forest vegetation typically have  comparatively low levels of organic matter and that there  are at least two explanations for these levels: trees create  a lot smaller root mass per acre than grass plants, and  trees do not die back and decay every year. However, it is  crucial to remember that soil organic matter typically  excludes surface plant litter, or new vegetal waste (Njila  et al. 2022). The Jos Zoological Garden’s Gallery Forest had high soil moisture levels throughout. The highest  level of soil moisture observed had the most leaf litter  arthropods (Table 2).

Thus, there was a correlation  between this and the high number of leaf-litter arthropods. This is consistent with the finding of Sylvain  et al. (2014) that increased soil moisture increased the  abundance of practically all taxa (nematodes and  arthropods) in their study. This is further reinforced by  the research of Njila et al. (2022), who found that places  with high levels of moisture in the leaf litter are regarded  as refuges for desiccation-intolerant species and permit  continued reproduction (abundance) and foraging  activity.

The significant amount of rain that fell during the  sampling period could be blamed for the high soil  moisture content. However, the frequent flooding of the  pitfall traps caused by the continuous rain throughout the  study period limited the collection of arthropods in the  traps, which in turn reduced the number of leaf litter  arthropods that could be gathered. 

CONCLUSION 

Within the Gallery Forest of the Jos Zoological Garden,  there were considerable differences in the species  diversity and richness of leaf litter arthropods. In the  absence of human activities like cattle grazing and the  continuous deforestation there, the Gallery Forest may  host a large variety of leaf litter arthropods. In this study,  it was discovered that carpenter ants (Camponotus  pennsylvanicus) of the Class: Insecta, Order:  Hymenoptera, and Family: Formicidae was the most  predominant taxon.

The majority of the colonies of C.  pennsylvanicus in the forest were discovered in  decomposing wood. As a result, their presence might be considered a key bio-indicator of the forest’s health. The  Jos Zoological Garden’s Gallery Forest was also studied  for its soil physic-chemical parameters, including soil  moisture, temperature, pH, and organic matter. High soil  moisture content and an alkaline soil pH favored the  abundance of leaf litter arthropods, whereas low soil  temperature and low soil organic matter content was  unfavorable to the abundance of leaf litter arthropods as  a direct consequence. 

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