Download Invertebrates in Canopy and Ground Organic Matter in a Tropical

Academic Journal of Entomology 7 (1): 32-37, 2014
ISSN 1995-8994
© IDOSI Publications, 2014
DOI: 10.5829/idosi.aje.2014.7.1.81253
Invertebrates in Canopy and Ground Organic Matter in a Tropical Wet
Evergreen Forest of Southern Western Ghats, India
1
T. Mohanraj, 1Albert Rajendran, 2M. Soubadra Devy and 2R. Ganesan
Department of Zoology, St. John’s College, Palayamkottai, Tamil Nadu, India
Ashoka Trust for Research in Ecology and the Environment (ATREE), Bangaluru, India
1
2
Abstract: In a tropical wet evergreen forest of India, in Kalakad Mundanthurai Tiger Reserve of southern
Western Ghats. The density and composition of invertebrates in organic matter found within the various area
of canopy and litter of the forest floor were compared. Berlese funnel trap was used to extract invertebrates from
accumulated epiphytes and litter. The numerically dominant invertebrate groups among epiphytes of the
canopy were ants, beetles, cockroaches, spiders and in the forest floor leaf litter were amphipods and isopods.
Relative abundances of these major taxa were not the same in the canopy and on the forest floor, indicating that
canopy organic matter shares a less dissimilar invertebrate community with that of the forest floor.
Key words: Formicidae
Amphipoda
Ground Litter
INTRODUCTION
Tiger Reserve
energy source for hetetotrophs and as a reservoir for
plant mineral nutrients [7-9]. Because litter fall is a major
pathway of nutrient and energy flux in most forests,
almost all of this research has focused on the abscised
plant material located on the forest floor [10-12].
Epiphytes interact with animals in all of the ways that
promote reproductive success among seed plants
generally.
Insects are the most successful rainforest animals
as demonstrated by their tremendous diversity.
Primary tropical rainforest is vertically divided into at least
five layers: the overstory, the canopy, the understory,
the shrub layer and the forest floor. Each layer has its own
unique plant and animal species interacting with the
ecosystem around them. The overstory refers to the
crowns of emergent trees which soar 20-100 feet above
the rest of the canopy. The canopy is the dense ceiling of
closely spaced trees and their branches, while the
understory is the term for more widely spaced, smaller tree
species and juvenile individuals that form a broken layer
below the canopy. The shrub layer is characterized by
shrubby species and juvenile trees that grow only 5-20
feet off the forest floor. The forest floor is the ground
layer of the forest made up of the trunks of trees,
fungus and low-growing vegetation. These layers are not
always distinct and can vary from forest to forest,
Forest canopies contain a major portion of the
diversity of organisms on Earth and constitute the bulk of
photo synthetically active foliage and biomass in forest
ecosystems. Historically, forest canopies have been
among the most poorly understood regions of our planet.
Initially, people who sought the thrill of climbing and
followed the lure of discovering new species dominated
canopy studies. Many forest canopy ecosystems promote
intensely diverse plant communities such as vascular and
non-vascular epiphytes, hemi-epiphytes and parasites
[1-3]. Canopy-dwelling plants provide largely to overall
forest biodiversity by contributing resources for a diverse
aggregation of arboreal vertebrates, invertebrates and
microbes [4, 5]. Global estimates of 30 million invertebrate
species by Erwin [6] were principally based on early
canopy fogging studies in lowland tropical forests.
These estimates were a key driver in the formulation of
species coexistence and habitat specialization models.
Invertebrates appear to layer vertically at the species
level, though there may be imbricate between forest floor
and canopy at the genus and family level [7]
A major portion of forest nutrient cycling research
has focused on the storage and circulation of dead and
decomposing organic matter, because it is important as an
Corresponding Author: T. Mohanraj, Department of Zoology, St. John's College,
Palayamkottai, Tamil Nadu, India.
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Acad. J. Entomol., 7 (1): 32-37, 2014
but serve as a good model of the vegetative and
mechanical structures of the forest [13]. One important
functional aspect of dead organic matter is the
composition and abundance of the detritivore fauna it
supports. In addition to the pools of nutrients and energy
in their own biomass, detritivores participate in the
regulation of nutrient transfer. Invertebrates are the main
agents of litter fragmentation and mixing of leaf litter with
mineral soil, exposing a greater surface area for microbial
colonization [14-17].
In this study, we quantitatively compared the
composition and abundance of invertebrates that inhabit
canopy and ground litter in a tropical wet evergreen
forest.
within 15cm2 was removed from the substratum carefully
and put in the poly bag. Two such samples were
collected, one closer to main trunk and other at outer limb
(peripheral region). Totally sixty epiphytic load sampling
(from thirty trees) was done in the canopy alone.
Polybags were labeled and tied to assure that insects did
not escape. Litter sampling from the forest floor were
collected under the same tree. Quadrate of 15x15cm was
placed in the forest floor and macro litter with mixture of
soil and fragmented litter were collected in a poly bag.
Litter collection was carried out fewer than thirty tree sites
in the forest floor. Invertebrates from the canopy and
forest floor litter were extracted using Berlese funnel trap,
an extraction technique in which the collected litter
was kept over a funnel with different mesh size of sieves.
The tip of the funnel was inserted inside a sample bottle
with 70% alcohol. The funnel was covered with a
100w incandescent bulb. Invertebrates slowly leave the
drying litter and fall into the alcohol due to the heat
emitted from the bulb. After extracting the invertebrates
the litters were allowed to dry. Invertebrates were sorted
with a dissecting microscope and counted. Invertebrates
were separated into three categories: insects, non
arthropod insects and others. Data were tabulated and,
species richness and similarity indices calculated.
MATERIALS AND METHODS
Study Area: Field research was conducted in the Kalakad
Mundanthurai Tiger Reserve (KMTR), in Western Ghats
(8°33’35”N; 77°22’93”E), from February to May 2008.
These ranges constitute 5% of the total land area of
India but harbour 30% of India’s biological species [18].
KMTR is known for its rich biological diversity lying
in the southernmost part of the ‘Hotspot 25’ [19].
Well-developed root systems occupy the upper 0-15 cm
of soil and substantial amounts of organic matter ate
incorporated into the upper horizons. Relative to the
forest floor, the upper tree canopy experiences more wind
[20], more frequent mist, higher air temperature maxima
and more frequent wetting/drying cycles. Nearly all of the
branch interiors, crotches and trunks of mature trees are
covered with thick epiphyte mats [21].
RESULTS AND DISCUSSION
The numerically dominant family in both canopy and
ground litter were Formicidae, Tenebrionidae,
Staphylinidae, Carabidae, Archinids and Isopods.
Members of these families are no doubt the major agents
of fragmentation of organic matter at the study site.
Formicidae (Fig 2a) is the richest insect family
in the samples. The similarity index value for the
invertebrates both in canopy and forest floor was 42.3 %.
Total invertebrate abundance was higher on the canopy
than in the ground for all sample pairs, with a mean
density 1.7 times greater on the canopy than in the forest
floor. Terrestrial crustaceans (amphipods), the largest
invertebrates in the samples, were readily visible
on the ground, but not seen in the canopy samples.
Arthropod diversity in tropical forests represents a
concentration of biodiversity locally, regionally and
globally. Arthropods carry out many significant
ecosystem processes, notably decomposition, herbivory
and pollination and they also represent a food source for
many vertebrate species. In panama, light traps caught as
many more insects at 20 or 26 meters than at ground level.
This difference held for Coleoptera, Ephemeroptera,
Field Methods: Trees from which samples taken were
chosen to include the largest size class of the most
common tree species in the forest [21]. The thirty samples
were collected from Cullenia exarillata. This tree species
support large accumulations of live epiphytes and
contiguous mats of crown humus on trunks and interior
branches [22]. Climbing of tree was done by Single Rope
Technique (SRT). This single rope technique allowed us
to explore even the restricted areas from which we
collected material to the interior branch regions of the mid
and lower crown (10 to 18 m above ground, to 4 m from
central trunk); the area where epiphyte mats within tree
crowns is located.
A quadrate of 15 x 15cm made with flexi wire was
placed over the epiphytic mat. Then a poly bag was
placed downward to the bark and the litters carefully
collected using scrapers and brushes. The epiphytic mat
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Acad. J. Entomol., 7 (1): 32-37, 2014
Fig. 1: Map showing the study area Kalakad Mundanthurai Tiger Reserve
Fig. 2 a: Abundance and diversity of insect families
found in canopy and ground litter > 3 in
numbers
Fig. 2 b: Abundance and diversity of insect families
found in canopy and ground litter <3 in numbers
than in the tropics [30]. Studies with emergence
traps reveal that these insects originate in the
forest floor or streams, where they feed as larvae.
This input of adult insects from the forest floor may
provide a food source for spiders and other canopy
predators during the winter and early spring and serve to
maintain their populations at high levels throughout the
year [31]. However, the height distributions of insect
abundance, comparable to those reported in tropical
forests [23,24,28,29] have not been measured in temperate
forests.
Probably, tree crowns are accountable to greater
amounts of isolation, wind and more persistent to
wetting and drying cycles than the forest floor [32-35].
Hemiptera, Hymenoptera and Lepidoptera [23]. In lowland
rain forest sites in Brunei, Panama and Papua New Guinea,
Canopy light traps caught more insects of most groups,
including Coleptera, Diptera, Hemiptera, Homoptera and
Hymenoptera, at 30 and 20 m than at ground level [24].
Many abundant tropical insect species appear to be tied
throughout their life cycle to the canopy [25].The high
species diversity of tropical forest arthropods is sustained
in part by the large number of insects in the canopy
[26,27]. The tropical rainforest insects are more abundant
in the canopy than near the forest floor [22, 23, 25, 27-29].
Recent studies suggest that the diversity of arthropods in
the canopies of temperate forests is substantially less
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Acad. J. Entomol., 7 (1): 32-37, 2014
they have not overwhelmingly radiated into or made use
of the canopy, as have the invertebrates. Elucidation of
which factors depress invertebrate density in the
canopy and conversely, which canopy organic matter
characteristics may be caused by depressed invertebrate
density, awit further investigation. We have shown that
canopy-held organic matter, an ecosystem component of
tropical wet evergreen forests, differs from forest floor
organic matter in an important biotic characteristic.
This implies that organic matter in the canopy should be
treated as a separate compartment in ecosystem studies
and cannot be subsumed under studies of organic matter
on the forest floor.
ACKNOWLEDGEMENT
Fig. 3: Abundance and diversity of non insect
arthropods found in canopy and ground litter
*NMT-Near to Main Trunk; FPR-From Peripheral
region; GL-Ground Litter
We thank the Ashoka Trust for Research in Ecology
and the Environment (ATREE), Bangaluru for funding and
logistical support.
Numerous studies have detailed sensitivity of
invertebrates to microclimatic regimes, particularly
moisture, temperature and isolation; many important
detritivore groups tend to drop out with increasing
desiccation. Insects particularly and some of their allies,
have adapted to nearly every physical feature of the
planet and the canopy is no exception. Many beetles have
special feet for walking on leaves; some even have
modified setae on their feet to slow them down upon
landing from rapid flight. Because they are in an
environment with raptorious birds, lizards and frogs,
many insect species have evolved camouflage coloration.
Climate is the main constraint on terrestrial invertebrates.
In the temperate zones, it is the winter cold and dryness;
in the equatorial tropics, it is the dry season for some and
the rainy season for others, with the temperature
far less of an influence than it is in the far north or south.
Many herbivores must contend with plants that produce
toxic chemicals or other defensive systems. All insects
must also deal with other insects that predate, parasitize,
or carry bacteria, fungi, or other insect diseases.
Hammond, Stork and others, in their studies of insects in
the Sulawesi dipterocarp forests and Miller, Basset and
others in New Guinea found much less insect diversity
and richness than Erwin and his teams in the Neotropical
forests. Hammond also found in southwest Asia
that the canopy fauna was not as delimited from the
understory fauna as it is in the Amazon Basin. Terrestrial
crustaceans are very sensitive to moisture conditions [36]
and were abundant in the ground litter samples (Fig 3).
Although canopy vertebrates are important in driving
part of invertebrate evolution in the forest canopy,
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