Post on 06-Mar-2015
description
―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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