Diversity of soil arthropods in secondary forest area in Bengkulu

. University sites are generally used as conservation areas in many countries. The secondary forest plays pivotal role in maintaining biodiversity in urban area. One of the creatures that live in secondary forest areas is arthropods. Moreover, there is only limited study about the diversity of soil arthropods in secondary forest of University of Bengkulu (UNIB). This study aimed to calculate the diversity of arthropod species as one of the measurement parameters in biodiversity. The samples were collected from soil and litter taken randomly in the secondary forest area at University of Bengkulu. A total of 5 locations within five replications were placed in the Berlese funnel. The results showed moderate diversity with an index value of 1.18, moderate evenness with an index value of 0.41, and moderate dominance with an index value of 0.56 in the habitat. UNIB secondary forest is being habituated and is still in the category of developing ecosystem. It is estimated that the number of species and populations will increase over time.


Introduction
Conservation is an effort to maintain and protect something regularly to prevent damage and destruction employing preservation.Nature conservation in Indonesia is contained in Law No. 5 of 1990 concerning the conservation of living natural resources and their ecosystems [1].Conservation areas (including forests) function as a food resource, maintain the global climate, a source of oxygen, a source of carbon emissions, a carbon sink, and a place to live for flora and fauna that each region must own.The forest functions as a guard for the stability of the forest soil layer and absorbs carbon stored in plant biomass [2].Arthropods are one of among different taxonomic groups of soil fauna and its normally used to evaluate the ecology because they are representative to the dynamic changes in the environment [3].Soil arthropods play an important role in the ecosystem services such as nutrient cycling and biological controls [4].Therefore, soil arthropods has a great potential as the indicators of environmental changes [5].
University sites are generally used as conservation areas in many countries.The University of Bengkulu (UNIB) has an area as a conservation area.The conservation area is containing various ecosystems, one of which is an area experiencing succession and can be classified as a secondary forest.UNIB secondary forest is inhabited by various kinds of fauna, one of which is arthropods.
One of the essential organisms in the soil ecosystem is the soil arthropods that play a role in the decomposition process [6].Arthropods can be a marker of whether an ecosystem can support life.Many types of arthropods whose existence or population level has been known to be strongly influenced by changes in vegetation as their supporting habitat.These arthropods belong to a group of bodies called bioindicators [7].In recent study, [8] was found that soil secondary forest has higher species richness and diversity index in 10-20 cm depth compare to agricultural field, indicating that secondary forest had typical environment with different composition of soil arthropod community.Moreover, the secondary forest is also considered as a semi-natural habitat and it can maintain the soil arthropods diversity [9] Therefore, the protection of this habitat is crucial to soil arthropods conservation.
However, there is only limited study about diversity and population of arthropods found in the UNIB secondary forest.Consequently, this study aimed to calculate the diversity of arthropod species as one of the measurement parameters in biodiversity and know the status of secondary forest development in supporting the life of arthropods.

Research method
This research was conducted in the secondary forest area of Bengkulu University.The study began by taking leaf litter and soil samples.Leaf litter and soil were taken randomly in the forest behind the LPPM, the forest around the Faculty of Law, the forest of the Department of Fisheries, and the forest around the Department of Soil Science.Furthermore, litter and soil are placed and arranged in a berlese funnel.After two weeks, observations and identification were carried out using Borror [10].Every genus/ordo was counted and recorded and then used for data analysis.

Data analysis
Data analysis was carried out using the diversity index, dominance index, and evenness index.To determine the diversity index (Shanon-Wiener Index) formula is used: with Pi= ni/N explanation : H : diversity index ni : number of individuals in species i N : Total number of individuals Meanwhile, to determine the dominance of an organism, the dominance index is used.The dominance index value can be found using Odum dominance formula [11] :

Results
The results are shown in Table 4.In total, 17 genus/orders were obtained, with a total number of 318 individuals.Acarina and Solenopsis were found in all sampling locations.The same result was stated by the research conducted by Yulianto [12]; Acarina and Hymenoptera (Formicidae) are found in the secondary forest area.The results show there are differences in the number of individuals and the number of types of soil fauna in each ecosystem.Differences in the number of individuals and the number of the kinds of soil fauna can be caused by many environmental factors, including climate (rainfall, humidity, and temperature), soil (aeration, litter, acidity, soil moisture, nutrients, temperature), and vegetation (forest, grasslands, and forest canopy).The biodiversity of soil fauna can be influenced by vegetation cover on land.Vegetation contributes organic matter, the leading food for soil fauna decomposers, especially Acari (Oribatida) and Collembola [13].The activity and population of soil fauna increase with the amount of litter produced.The results found that the arthropods found in all research locations were mites (table 4).This is because the mites are small in size and do not require too many resources, and they have high fecundity so that the mites can multiply in number in a short time.
A habitat consisting of abiotic and biotic elements can be said to be good if it can support all the needs of living things, such as food, drink, breeding places, and shelter.The better it supports life (abiotic and biotic elements sufficient for a habitat), more arthropods can live in that habitat.The biotic and abiotic elements indirectly become the key to the magnitude of the index values of diversity, dominance, and evenness.However, the population is still uneven, which shows that the community is still unstable because humans have not abandoned the location of the secondary forest for a long time.Hence, there is not too much organic matter, and only certain arthropods can become pioneers living in the area.However, the population is still uneven, which shows that the community is still unstable because humans have not abandoned the location of the secondary forest for a long time.Hence, there is not too much organic matter, and only certain arthropods can become pioneers living in the area.
Species diversity describes the high diversity of creatures found in an area.The higher the value of the species diversity index (H), the more species there are in the area.The higher the value of species diversity in a habitat, the higher the community balance will be.The value of the Diversity Index (H') of the sample belongs to the medium group (table 5), meaning that the ecosystem condition is sufficient to support the life of ground surface insects.This is because the location of the sample began to occur in succession so that there are many food sources for soil insects.Insects play an important role in the succession process and maintain the stability of the forest ecosystem.The higher the diversity value of an area, the more stable the community in the area is [14].Low diversity or medium diversity is related to the dominance of a species of creature.The value of the diversity index shows the value of medium diversity, presumably because the condition of the secondary forest is quite good.This can be seen from the condition of the secondary forest, which is entirely covered with forest canopy, and part of the forest floor is covered by litter.The value of diversity in this study indicates that the secondary forest area of UNIB has average productivity and moderate ecosystem conditions, although there are indications of ecological pressure.The dominance index ranges from 0-1.If the value of C = 0 means that no species dominate other species or the community structure is in an unstable condition, but if C = 1 means that there is a species that dominates.The value of the Dominance Index is used to determine whether or not certain species dominate in an ecosystem.The results of the calculation of the dominance index show that there is a moderate level of dominance in the UNIB secondary forest.A low dominance index value indicates that there are no dominant species; on the contrary, the greater the dominance, it indicates that there are certain species [15].
The evenness index value measures the degree of evenness of the abundance of individual species in the community.Evenness describes the balance between one community and another.The species evenness index ranges from 0-1; if 0<E<0.4,then the population is in a state of small evenness and a depressed community.Whereas if 0.4<E<0.6,all species are in fairly exact condition but unstable.Furthermore, if E> 0.6, the population with a high level of evenness indicates that the population is in a stable condition.The evenness index value measures the balance between one community and another.This value is influenced by the number of species contained in one habitat.The calculation of E obtained in the study indicates that the evenness of the population is classified in medium condition but is in an unstable state.Evenness of species is classified as a medium due to competition in utilizing existing resources.This is also influenced by the availability of feed in the habitat it occupies, which is one of the main factors for the presence of the population and the presence or absence of dominance by one species [16].The diversity and evenness index values correlate.The higher the Diversity index (H') than the Uniformity Index (E') getting closer to 0 (zero).The diversity index is indicated by the results obtained.

Conclusion
UNIB secondary forest is being habituated and is still in the category of developing ecosystem.Mite dominance occurs within the UNIB forest habitat.It is estimated that the number of species and populations will increase over time.
We would like to thank students research assistance from the University of Bengkulu for their support during the field work.We also thank to the anonymous reviewer for their constructive review of this manuscript.

Table 1 .
Criteria for the Shannon-Wiener diversity index value.

Table 2 .
Criteria for dominance index.

Table 4 .
Genus/ordo and number of individuals found in the litter.

Table 5 .
Index values and the interpretation.