―Insect as Ecosystem Engineer‖

Norhelina Binti Latiff and Johari Bin Jalinas

School of Environmental and Natural Resource Sciences,

Faculty of Science and Technology,

43650 bangi

e—mail: johari_j@ukm.my

Insect as Ecosystem Engineer

Outlines

The definition:

o Ecosystem Engineers

o Autogenic engineer

o Allogenic engineers

o Physical ecosystem engineers

o Extended phenotype engineers

o Accidental engineers

o soil engineering

The Role of Insect Function in Ecosystem

The reason of insect activity that function as Ecosystem Engineer

The Role and Important Function of Insects as Ecosystem Engineer

The Insects as Ecosystem Engineer

o Termites

o Ants

The definition and concept of Ecosystem Engineer

Ecosystem engineers are organisms that directly or indirectly modulate the

availability of resources to other species by causing physical state changes in biotic or

abiotic materials (Cuddington and Hastings 2004; Byers et al. 2006). In so doing they

modify, maintain and create habitats.

Ecosystem engineer can also differentiate into autogenic and allogenic

engineers. Autogenic engineer are organisms that alter environments directly by their

own structure. Allogenic engineers transform other materials, living or non-living,

either mechanically (Cuddington and Hastings 2004).

Physical ecosystem engineers are organisms that physically modify the abiotic

environment (Jones et al. 2006). They can affect biogeochemical processing by

changing the availability of resources for microbes examples carbon and nutrients or

by changing abiotic conditions affecting microbial process rates such as soil moisture

or temperature. Physical ecosystem engineers can therefore create biogeochemical

heterogeneity in soils and sediments (Cuddington and Hastings 2004). They present

via general mechanisms influencing the flows of materials (Jones et al. 2006) for

example by modification of fluid dynamic properties (Cortina et al. 2006), fluid

pumping, and material transport or the transfer of heat such as modification of heat

transfer properties, direct heat transfer, and convective forcing (Jones et al. 2006).

Extended phenotype engineers is defined as organisms creating structures or

effects that directly influence the fitness of individuals, or colonies in the case of the

social insects (ants and termites). Termites and ants can be considered as extended

phenotype engineers because their mounds have direct and positive feedback effects

on the colonies through the maintenance of humidity and protection of the

population from enemies (Jouquet et al 2006).

Extended phenotype engineers concentrate their activities on the building of

biogenic structures in order to maintain optimal conditions for their growth. Termites

and ants are best viewed as extended phenotype engineers.

Extended phenotype engineers have a greater effect on the maintenance of

ecosystem heterogeneity since they concentrate their activities at a few points, as

compared to accidental engineers which may move through the soil and thus

contribute to homogenisation of nutrient distribution throughout the whole

ecosystem Earthworms, termites and ants have been identified as the most important

soil engineers.

Accidental engineers are defined as engineers creating biogenic structures that

have no direct positive effect on themselves. Accidental engineers, such as many

earthworms, create structures that are not directly beneficial to the individuals

through feedback effects. Accidental engineers expend energy in moving through the

soil to be as close as possible to their optimal environment (Jouquet et al 2006).

According to the soil engineering concept, the organisms which have the

ability to move through the soil and to build organo-mineral structures with specific

physical, chemical and microbiological properties are known as ecosystem engineer.

The Role of Insect Function in Ecosystem

In terrestrial ecosystems insects function as herbivores, pollinators, seed dispersers,

predators, parasites, detritivores or ecosystem engineer (Ghazoul and Jeffery 2004;

Brussaard 1998). In biodiversity, insect represent as dominant component in most

terrestrial ecosystems and their role in biodiversity in nutrient cycling as functioning

ecosystem however is been neglected (Ghazoul and Jeffery 2004).

Insects play an important role in the relationship between plants and

ecosystem processes by influencing the physiology, activity and population dynamics

of plants (Brussaard 1998). Ecosystem function is used for processes related to nutrient

cycling at the ecosystem level (Brussaard 1998).

The reason of insect activity that function as Ecosystem Engineer

The reasons of insect built structures are essentially for three reasons: to create a

protected home, foraging food, and for intraspecific communication (Jouquet, Tessier,

and Lepage). The most common functions of this shelter are protection against

extremes temperature and the threat of predation. Architecture may provide ways of

trapping or conserving these to help maintain environmental optima, more

exceptionally it may provide a method of dissipating them if temperatures become

high.

Shelter

Figure 1: A mature mound of the

termite, Macrotemes michaelseni

is showing air passages

connecting the interior of the

nest to spaces lying below the

outer mound wall. (Taken from a

book of Animal Architecture. 2005.

Oxford University Press Inc., New York)

Termites using their architecture to allow air movement controlling nest

temperature the heat at the core of the mound (Black and Okwakol 1997), generated

by termites and their associated fungus gardens (Duringer et al. 2007; Guedegbe et al.

2009), rose up through the colony into an open space in the top of the mound. From

there it was forced into narrow channels carrying the air near to the mound surface to

allow gas exchange by diffusion (Black and Okwakol 1997), and down into a

basement below the hive before it was drawn back into the living space above.

Nest

Ants and termites are particularly important soil engineers. Colonies of these insects

often occur at high densities and introduce cavities into large volumes of substrate.

The infusion of large soil volumes with galleries and tunnels greatly alters soil

structure and chemistry.

Termite and ant nests usually represent sites of concentrated organic matter

and nutrients. Nests may have concentrations of macronutrients 2–3 times higher

than surrounding soil noted that soils outside termite nest zones become relatively

depleted of organic matter and nutrients. Ant nests also have been found to have

higher rates of microbial activity and carbon and nitrogen mineralization than do

surrounding soils. Nest pH often differs from surrounding soil, pH in termite mounds

significantly higher than in surrounding soils. Soil within leaf-cutter ant nests tended

to have higher pH than did soil outside the nest (Schowalter, 2006)

Termites and ants also transport large amounts of soil from lower horizons to

the surface and above for construction of nests, gallery tunnels, and ―carton‖ (the soil

deposited around litter material by termites for protection and to retain moisture

during feeding above ground). Ant and termite nests have particularly important effects

on soil moisture because of the large substrate surface areas and volumes affected.

Protection from environment and natural enemies

Architecture may be used to deal with the control of water availability. At the

extreme dry end the priority is protection from desiccation, at intermediate points

rainfall has various damaging effects, while at the other extreme, water can itself be

used as a protective barrier. Water conservation has been established as one of the

functions of insect larval cases and pupal cocoons. When water vapour turns to rain,

animal architecture must address a new range of problems. Protection against

structural damage to mud and paper architecture is shown in the presence of features

encouraging water run-off.

Figure 2: Termite Nest (Schowalter, 2006)

To a predator, homes contain potential prey in the form of the builders,

frequently their offspring and sometimes also stored or cultivated food. Protection of

homes by means of their architecture essentially takes two forms, avoidance of

detection and prevention of invasion after detection has occurred.

The Role and Important Function of Insects as Ecosystem Engineer

The important function in basic abiotic and biotic processes of ecosystem engineer are

as major bioturbating organism, removing a noticeable amount of soil and making it

more sensitive to climatic factors. Moreover, enhances biodiversity by providing

nesting and roosting habitats to a broad array of organisms and also provides resources

(food) to many other species. Ecosystem engineers add together new habitat niches

from giving new structure to the environment and by doing so acting to promote

organismal diversity.

Ecosystem engineering helps estimate abiotic variability. Environmental

variation may potentially predictable consequence of organismal activities. For

example, organisms are often distributed across physical gradients according to their

physiological tolerances, but occupancy of otherwise intolerable areas can occur

when abiotic stress is restructured by other.

The most important role of ecosystem engineering activities is providing

refugia. Refugia are geographical region that has remained unaltered by a climatic

change affecting surrounding regions and that therefore forms a haven for relict fauna

and flora). These refugia is assist organisms from or increase exposure to abiotic

forcing and predation, all of which can affect species life-history characteristics, such

as reproductive size or age, mobility, mate selection traits, degree of specialization or

competitive ability. Niche constructions have shown how ecosystem engineering

increases the interplay between ecology and evolution by putting these two aspects

on a similar temporal scale.

Engineering can help us understand the mechanisms underlying and

consequences of density dependence. Because ecosystem engineering can create

cycles of habitat degradation and rehabilitation, it can affect population cycles of the

engineer and in turn, the population cycles of organisms responding to the

engineered environmental changes. Engineering may also offer explanations for

overshoots or drops in population levels; the effects of an engineer, especially when

external to the system and not experiencing feedbacks, may directly contribute to

fluctuations, or do so in concert with environmentally stochastic events.

Habitat modification by ecosystem engineers may create patchiness, an aspect

also known to be important in promoting species diversity in ecosystems. The effects

of engineering may be especially important in explaining the higher diversity in

biogeographical transition zones where engineering may cumulatively increase spatial

heterogeneity such that more species can persist in these relatively small areas.

Engineering may also help explain the success of species invasions; engineers may

make novel habitat suitable for themselves, altering the environment for current

species while enhancing conditions for their spread.

Engineering may influence the genetic diversity of populations of both the

engineer and associated species through feedbacks that result in changes in spatial

heterogeneity, habitat area, habitat quality or connectivity between populations. For

example, engineering can affect the extinction and colonization rates of habitat

patches, which is known to influence genetic diversity of fragmented populations in

complex ways. The ecosystem engineering concept helps afford general explanation

for patch conditions, patch formation and maintenance, the abiotically influenced

dynamics of organisms within patches, the population dynamics of the engineers, and

links to the patches they create across the landscape.

Engineering can contribute to theories of species coexistence. When engineers

create different environments and the species can adapt to the new environment, and

then engineering should markedly enhance opportunities for niche differentiation,

diversification and coexistence at the same or multiple trophic levels.

Engineering can affect food webs and our interpretation of trophic interactions

in two basic ways. First, engineering may affect the spatial heterogeneity that is

important in the organization of food webs for example resource distribution patterns.

Second, food webs narrate only part of the story of interactions among species and

their environment as all organisms engages in both trophic and engineering

interactions to some degree.

Ecosystem engineering influence on energy and nutrient flows within and

between ecosystems. Engineering activities act as controls on such flows largely

because the abiotic environment is a master influence on such processes. As a

consequence they often affect biogeochemical process rates and distributions and can

play a major role in the input or export of materials from ecosystems thereby having

effects at larger spatial scales.

The Insects as Ecosystem Engineer

Termites

Fungus-growing species (Termitidae, subfamily Macrotermitinae)

Some large soil invertebrates for examples earthworms, termites and ants have

significant effects on soil structural properties. Fungus-growing termites enrich their

nest structures with clays and can modify the mineralogical properties of silicate

clays. Fungus-growing species (Termitidae, subfamily Macrotermitinae), are often the

dominant invertebrate group in tropical and subtropical habitats. Fungus-growing

termites greatly modify their immediate environment by increasing the clay content

and decreasing the organic matter content and porosity in soil (Jouquet et al 2004)

Soil handling by termite workers can modify the mineralogical properties of

silicate clays, creating expandable clay minerals. The nest structures of fungus-

growing termites are known to be enriched in finer particles, as compared to the

surrounding top soil (Lavelle et al 1997).

Royal Chamber of Termite

Social insects, such as termites, ants, wasps, and bees create amazing structures in

nature. Termites nest are built on an impressive scale, these architectures are

astonishing with their sophisticated functionality, containing purpose built structures

for fungus farming and air conditioning. The interesting part of these insects because

they only require relatively simple mechanisms of communication and control

intended for built the nest. The behavior of each individual termites appear to be

driven by certain factors such as temperature gradients, air flow, the present and

absence of partially complete structures and the concentration of various pheromones

excreted.

Termites, ants and earthworms are considered as soil engineers because of

their effects on soil properties and their influence on the availability of resources for

other organisms, including microorganisms and plants.

Through their building activities, ecosystem engineers have impacts on soil

aggregation and porosity, and hence associated hydraulic properties, and soil organic

matter (SOM) availability for microorganisms (Lavelle et al 1997).

Organisms modifying their environment and controlling energy and matter

flows are likely to modify natural selection pressures which are present in their own

local selective environment, as well as in the selective environments of other

organisms.

Soil engineering activities of termites and ants are due to the construction of

nest structures for the development of their colonies. The social organisation and

architecture of their nest structures allow termites and ants to regulate their

environment to some extent and thus to occupy many different habitats.

Termites are very vulnerable insects that protect their colonies by improving

soil structural stability against water flux or intrusion of soil invertebrate predators, in

particular ants, into the nests.

Soils handled by termites are very cohesive and can resist water disturbance

termite Odontotermes n. pauperans utilises soil selectively, favouring finer particles

and making structures that match their ecological needs: to spend less energy (in term

of saliva enrichment) and to maintain a degree of moisture sufficient for the colony.

Stigmergy is the indirect, environmentally mediated communication that gives

side-effect of activity that requires coordinate. Despite these stigmergic mechanisms

are quite simple, it appears that combining indirect effect with communication are

often subtle and complex, they can enable a colony to coordinate as a whole in order

to construct complicated architectures (Ladley & Bullock, 2005).

Royal chambers are enclosures built around a stationary queen termite who

excretes a pheromone that encourages building activity at a certain level of intensity

that will tend to occur some distance from the queen herself. Cement pheromone

excreted by the first pieces of placed building material tends to attract nearby

termites. The formations of a number of pillars are distributed roughly evenly around

the queen because pillars that is close together. Evenly spaced pillars that are

subsequently joined by low walls which rise until eventually a dome-like royal

chamber with one or more entrances is completed. A third pheromone is deposited by

moving termites and also guides building activity, encouraging the formation of

galleries and covered walkways that protect heavily used thoroughfares. Even wind

may affect the structures built by termites, who are thought to be sensitive to air

currents and able to make decisions based on direct interaction with the wind. In

addition, any wind will disturb pheromone diffusion and may influence the structures

being built as a result (Ladley & Bullock, 2005).

Termites can be roughly grouped into those species that nest within their food,

usually wood, and those that nest elsewhere and must leave their nest in order to

forage for food. Of the latter type, nests may be arboreal or subterranean, centrally

located or dispersed into small, connected units. Most termites shun the open air, and

travel to and from the foraging area by way of subterranean tunnels or covered

galleries. The termites Cubitermes, for example, build mushroom-shaped, mud

mounds with small downward projections from the edge of the roof, and nests of

Procubitermes niapuensis are apparently protected by chevron ridges across tree

trunks above them (Ladley & Bullock, 2005).

Ants

One of the example of shelter as an ecosystem engineer is the structure of ant nest.

Nest building wood ants Formicidae are known for their large colony size and long-

lived nest mounds rich in organic(Tschinkel 2003, 2005). These properties make the

wood ant nests a suitable habitat not only for myrmecophilous invertebrates but also

for an array of decomposer animals and microbes

The behaviour of ants for example choice of prey, nest building materials and

regulation of temperature can actively, modify the structure and function of the

community in the nest mounds, indirectly reflect on ant performance and alter

community or ecosystem level feed back mechanism which in turn also modifies ant

behaviour (Tschinkel 2003, 2005)

Creation of highly favourable conditions for decomposer activity may increase

costs for maintaining the physical structure of the nest mound. Further, the high

energy input by the ants can favour not only the growth of heterotrophic decomposer

microbes, but also the development of microbes to be facultatively pathogenous for

the ants. The maintenance of trophic organisation or a composition of decomposer

species could benefit the ants. For example, the large earthworm biomass in the nest

surface is a potential source of nutrition for the ants (Tschinkel 2005, 2003).

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