Invertebrates are the first animal evolved about 600 million years ago from single-celled microorganism, food eating microorganism. They evolved into countless forms and lead to the enormous diversity of invertebrate's species that are found today. They are organism without backbone, however they have others way to produce structural support of bodies. As examples, leeches have a hydrostatic skeleton supported by sheets of muscles and internal cavity filled with fluid, while insects have a hard outer shell or exoskeleton. Scientist divided them into about 30 different groups (phyla). The phyla include echinoderms (urchins and stars), coelenterates (jellies and anemones), annelids (segmented worms), mollusks (snails and octopuses), and arthropods (insects, spiders, arachnida such as spiders and crustaceans such as crabs) (Saint Louis Zoo, 2011). There are several kinds of phyla can be referred in Figure 1. Some of them are aquatic animal and terrestrial animal, yet this paper will focus on diversity of invertebrates in soil ecosystem only. They participate in tropic level and play vital role in nutrient cycling and decomposition of organic matter. They also interact with others organism and provide many services to the ecosystem. A small decrease in an invertebrate biodiversity may affect ecosystem as they contribute to the succession of above ground and ecosystem. Human activities which give negative effects to the soil invertebrate activities must be controlled. In meanwhile, there are also some practices can be implemented to the site/soil to eager their activities.
Classification of Invertebrates
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An experiment was carried out by several groups of Nottingham students to study the diversity of invertebrates using soil palm sample. The table below indicates the result of my group. There are 9 kinds of animal invertebrates that have been found in the soil sample:
The Invertebrates Found In Soil Palm Sample
Based on the result, all the invertebrates are from phylum of arthropod. The invertebrates are diverse and made up from difference classes and orders. There are 3 kinds of classes which are Insecta, Arachnida and Myriapoda. Class Insecta give the largest percentage (64%), followed by class Myripoda (20%) and the lowest percentage is class Arachnida (16%). None of them comes from the similar order. There are only few organisms were found out. The total number soil invertebrates are 25. This happened because of several unknown factors such as less moisture. The soil sample looks like dry and non-sticky, therefore may proved that the moisture level is low and not really favor the soil invertebrates. However, more experiments should be done to determine the real factors the number of invertebrates are little.
Next, the researchers have classified the diversity of invertebrates according to body width. There are microfauna, mesofauna and macrofauna. Microfauna such as nematodes usually live in water film and have width 0.1mm and below; mesofauna such as mites and springtails live in air spaces and have body width between 0.1mm to 2mm, while macrofauna such as earwigs, centipedes, and millipedes have width from 2mm to 60mm and above. Macrofauna are large enough and have ability create space by burrowing. (http://cwmi.css.cornell.edu, 2011). They exist at any stages of soil which contain appropriate space and nutrients such as in litter, on/between the surface of soil aggregates, on humus and around roots. Invertebrates that graze on bacteria such as mites always concentrate around roots while the litter is always inhibited by collembola and millipedes that break up the litter into smaller chunks (Ingham, 2011). The types of invertebrates are similar in all ground cover types, but the numbers of invertebrates differs significantly. Bare soil show the lowest number of invertebrates due to it is easily exposed to the extreme temperature, drain drop and soil erosion (Kyle and Susan, 2007). Soil invertebrates inhabit a substrate that is more resistant to drought than most terrestrial habitat. Some of them are capable adapted to acidic, however many more organisms thrive in a neutral habitat causing an increase in diversity as pH approaches neutral (Rudd, 2009).
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Soil invertebrates present at several trophic levels of the soil food web as primary, secondary or tertiary consumers. They eat almost everything either live or death organism. They exist in multitude of ways in gaining nutrient. They may present as herbivores, carnivores, scavengers and parasites. As examples, herbivores like caterpillar and nematodes are feeds on plants. Nevertheless, nematodes are complex organisms which appear at several stages of tropic level. Some nematodes feed on the plants and algae (primary consumers); others are grazers that feed on bacteria and fungi (secondary consumers); and some feed on other nematodes (tertiary consumers) (Ingham, 2011). Next, carnivore can be represented by centipedes which feed earthworms by paralyzing their prey with poisoned fang and spider which traps their prey with web. The example of scavengers is millipedes, louse and earwigs which decompose plant matter such as leaf little and dead roots (Dr Alderson, 2011). Most of invertebrates in soil are parasites. Ticks, tapeworms, leeches, mites and roundworms are just a few examples of the parasites. Some parasites live on the external surfaces of the hosts while the others live in the digestive tract or tissues of their hosts (Klappenbach, 2011).
Next, soil invertebrates develop multiple interactions at large scale and contribute to the production of soil ecosystem services in many ways (Figure 3).
The Advantages of Invertebrates Interact with Ecosystem
(Lavellea et.al, 2006)
Firstly, soil invertebrates participate in nutrient cycling as it interact with surface vegetation which supplies them the organic maters or compounds. Scavengers like millipedes and mites will return those elements into a broken down form. These broken forms will be recycling back into the environment, promoting humification and nourishing the plant with the nutrients like nitrogen and carbon. Soil invertebrates are responsible for the mineralization and immobilization of phosphorus and sulphur into the plants. They attribute regulation of leaching nutrients losses and prevent leakage towards low-lying aquifers, streams and oceans (Lavellea et.al, 2006). Soil invertebrates act as buffering system that allows an efficient local recycling of nutrients
Next, invertebrates like ants, termites, earthworms help in formation of soil. They consume small aggregates of mineral particles and organic matter and then generate larger fecal pellets. These fecal pellets are coated with compounds from the gut and become part of soil structure. Charles Darwin has stated that soil invertebrates, earthworm can carry large quantity of soil from the lower strata to the surface and organic matter into deeper soil layers. This organism can form over the top 15 cm of soil within 10-20 years. It helps to hold the soil particle together and maintain it structures too (Clive, 2011).
Invertebrates interact with plants as they support primary production such as genes and protection against pests and diseases for plant health and response to stress. The expert document that the expression in the leaves of three stress-responsive genes (coding for lipoxygenase, phospholipase D and cysteine protease) due to the existence of belowground invertebrate activities. However, they still cannot identity the mechanism involved which affects parasitic nematodes activity and arise beneficial in earthworms. Next, many experiments have shown significant enhancement of plant production in the presence of soil invertebrates such as collembolan, earthworms and combinations of organism termites and ants. Invertebrates capable improve tolerance to stressors or pest such as parasitic nematodes which feed on plant roots. This has been proved since 82% infested plant decrease within the presence of earthworms. Although earthworms do not affect the population size of nematodes, it causes the root biomass not being attacked by such parasite (Manuel et al, 2005).
Besides, the soil invertebrates interact with carbon compound in climate regulation and also with soil for flood and erosion control. The soil invertebrates accumulate over long period of time and form humification. This process results the carbon compounds are sequestered into compact and consequently the carbons can be avoided from rapidly released into atmosphere in the form green house gases. Humification also transforms carbon compounds more resistance to further decomposition and thus slower green house gas released from soil (Lavellea et.al, 2006). Next, flood and erosion control can be regulated by building and maintenance of stable porosity through bioturbation and burrowing. Earthworms burrow, enhance soil aeration and form "tunnel". This "tunnel" can absorb water at a rate 4 to 10 times greater than fields lacking worm (NCAT, 2004).
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Lastly, soil invertebrates do interaction with ecosystem as they are also responsible in production of water supply. Their participation may be in small-scale but are significant. Invertebrates such as millipedes in macrofauna create burrows and structural porosity in soils and thus generate water infiltrations. The variety of pore shapes and size may permit soils to store water within wide range, but the scientist not discovered yet about the amount of water infiltrated and stored (Lavellea et.al, 2006). Invertebrates are necessary to reduce water runoff, recharge groundwater and store large amount of water for dry spells.
Soil invertebrates serve many benefits to plant, animal, and nature. Their present should not be disturbed by human activities because it may influence the presence and activity of organism. Unfortunately, the burgeoning human populations have destroyed the soil physico-chemical environment and the soil's species through activities such as: inputs of chemicals, disposal of waste products in soils and physical modification or removal of soil by cultivation and erosion (Diana, 1994). Those activities may eliminate any invertebrates present on the topsoil and degrade their microenvironment. In addition, the metabolism of microorganisms and arthropods will be altered and this may destroy some layers of the primary food chain too. This happens when harmful chemicals have been passed up to the food chain and ultimately causes mortality or even extinction in the invertebrates.
There are several site/soil management can be practiced to help improving invertebrates number and activities such as enhance nutrient and pest. Organic matter and nutrients in acceptable range can provide more foods to the invertebrates, though they may poison the organism in excess. This is similar to pest which is helpful for invertebrates to resist to pesticide in acceptable range only. Next, people must avoid excess tillage because it can bring advantages or conversely. Some farmers practice tillage because it can control pests, however it also affects decomposition rate of soil invertebrate when excess. The worst is it can reduce organic matter level to below 1% and renders them biologically dead. People also should keep the soil covered to avoid soil erosion that influence the existence of invertebrates at the topsoil especially. It can be done by covered it with plant residue or planting crops. Lastly, diversity cropping is beneficial because it also will increase the diversity of invertebrates. This happen due to differ plant have differ culture practice and thus leads to decrease of disease pressure. All the practices support the invertebrates to survive greater and functions more effectively (USDA, 2011).
In conclusion, there are vast diversity of invertebrates can be found in earth including soil invertebrates. Their size are small which is may be less than 1mm but their interaction with nature bring much benefits to ecosystem. Their existence should not be bothered and people must conserve these species to avoid extinction via soil conservation. Soil conservation can promote better the viability and survivor of soil organisms including soil invertebrates. Loss of invertebrates diversity may affects soil processes and unstable ecosystem too as they are responsible in nutrient cycling, water supply and many more. People can manage the site/soil to improve the population of invertebrates by providing nutrients, pest and others to enhance invertebrate's activities.